NREL is a national laboratory of the U.S. Department of Energy, Office of Energy 

Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Contract No. DE-AC36-08GO28308

Vehicle Battery Safety 

Roadmap Guidance

Daniel H. Doughty, Ph.D.

Battery Safety Consulting, Inc.

Albuquerque, New Mexico

Technical Monitor:

Ahmad A. Pesaran, Ph.D. 

National Renewable Energy Laboratory

Subcontract Report

NREL/SR-5400-54404

October 2012

NREL is a national laboratory of the U.S. Department of Energy, Office of Energy 

Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

National Renewable Energy Laboratory

15013 Denver West Parkway

Golden, Colorado 80401

303-275-3000 • www.nrel.gov

Contract No. DE-AC36-08GO28308

Vehicle Battery Safety 

Roadmap Guidance

Daniel H. Doughty, Ph.D. 

Battery Safety Consulting, Inc.

Albuquerque, New Mexico

Technical Monitor:

Ahmad A. Pesaran, Ph.D. 

National Renewable Energy Laboratory

Prepared under Subcontract No. LGC-0-40440-01

Subcontract Report

NREL/SR-5400-54404

October 2012
 

 

 

 

 

 

 

 

 

 

This publication received minimal editorial review at NREL. 

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Foreword 

In 2010, the National Renewable Energy Laboratory (NREL) entered into a subcontract 

agreement with Dr. Daniel Doughty, the principal of Battery Safety Consulting Inc. At NREL, 

we perform battery research and development (R&D) in areas of materials, modeling, testing, 

and system analysis, particularly as they relate to the lithium-ion (Li-ion) battery safety modeling 

and testing for electrified vehicles. This work was supported by the U.S. Department of Energy’s 

(DOE) Energy Storage R&D Vehicle Technologies Program in the Office of Energy Efficiency 

and Renewable Energy under DOE/VTP Agreement 16378 of the 1102000 B&R, NREL Task 

Number FC086200. 

The purpose of the subcontract was to investigate the research, development, and other activities 

related to the safety of Li-ion batteries for electric drive vehicles and to provide 

recommendations for developing a DOE roadmap for the safety of Li-ion batteries for electric 

drive vehicles. Dr. Doughty has a long, distinguished career in battery R&D, particularly at 

Sandia National Laboratories (SNL), where he was responsible for the safety and abuse tolerance 

testing of batteries for more than 15 years. Dr. Doughty has chaired the Society of Automotive 

Engineers (SAE) committee that revised and updated SAE Recommended Test Procedure J2464, 

“Electric and Hybrid Electric Vehicle Rechargeable Energy Storage System (RESS) Safety and 

Abuse Testing,” published November 2009. With his strong experience in battery safety and 

involvement with safety committees, Dr. Doughty was in a unique position to perform this work 

by collecting the necessary information, interacting with key players in the community, and 

providing recommendations. 

This document is divided into two sections: (1) the synopsis, which discusses high-level findings 

of the work, and (2) the full report, which provides a comprehensive, in-depth review of the state 

of the art and also discusses interactions with experts, users, researchers, and developers from 

different organizations interested in the safety of vehicle batteries. 

The findings and recommendations in this document will be taken into consideration by the 

Energy Storage R&D Program at the DOE Vehicle Technologies Program for further defining 

the R&D roadmap for developing safer batteries for electric drive vehicles. We appreciate the 

support provided by Dave Howell and Brian Cunningham of DOE’s Vehicle Technologies 

Program. 

Ahmad A. Pesaran, Ph.D. 

Energy Storage Team Lead 

Subcontract Technical Monitor 

National Renewable Energy Laboratory 

15013 Denver West Parkway 

Golden, CO 80401 

ahmad.pesaran@nrel.gov 

iii 
 

 

 

 

 

 

 

Synopsis 

The safety of electrified vehicles with high-capacity energy storage devices creates challenges 

that must be met to ensure commercial acceptance of electric vehicles (EVs) and hybrid electric 

vehicles (HEVs). One of the most important objectives of DOE’s Office of Vehicle 

Technologies is to support the development of Li-ion batteries that are safe and abuse tolerant in 

electric drive vehicles. 

Batteries for EVs and HEVs, which in this document includes plug-in hybrid electric vehicles 

(PHEVs), are different from batteries developed for other applications. The environment that 

vehicle traction batteries experience during their life is more difficult than for applications such 

as portable computers, cell phones, or stationary applications. High-performance vehicular 

traction energy storage systems must be intrinsically tolerant of abusive conditions, including 

overcharge, short circuit, crush, fire exposure, overdischarge, and mechanical shock and 

vibration. 

Battery safety and failure modes of state-of-the-art cells and batteries are reviewed and analyzed. 

Using this information, the roadmap presents recommendations on future investments in three 

areas: 

•	 Improving our understanding of failure modes 

•	 Developing better characterization tools 

•	 Improving the safety of energy storage technologies. 

Mission 

The safety of electrified vehicles with high-capacity energy storage devices creates challenges 

that must be met to ensure commercial acceptance of EVs and HEVs. High-performance 

vehicular traction energy storage systems must be intrinsically tolerant of abusive conditions: 

overcharge, short circuit, crush, fire exposure, overdischarge, and mechanical shock and 

vibration. Fail-safe responses to these conditions must be incorporated into the design at the 

materials and system levels through selection of materials and safety devices that will further 

reduce the probability of single cell failure and preclude propagation of failure to adjacent cells. 

Objectives

One of the most important objectives of DOE’s Office of Vehicle Technologies is to support the 

development of Li-ion batteries that are safe and abuse tolerant in electric drive vehicles. This 

roadmap analyzes battery safety and failure modes of state-of-the-art cells and batteries and 

makes recommendations on future investments that would further DOE’s mission. 

Safety criteria for EV and HEV traction batteries may be viewed from different perspectives, and 

each original equipment manufacturer will have a unique safety approach tailored for its vehicle 

platform. However, two objectives will be fundamental to all efforts: 

• Failure rate of cells that leads to thermal runaway will need to become exceedingly rare. 

ο	 Note that the failure rates have been developed for mass-produced cells such as the 

18650. The influence on failure rates of cell manufacturing techniques (wound versus 

iv 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

prismatic or z-fold design) as well as the effects of cell size/geometry on large format 

cells are largely unknown because of scant manufacturing history/experience. The 

relevancy and scaling of known failure rates are problematic; therefore, measuring 

achievement toward the objective is challenging. 

•	 Propagation of thermal runaway from cell to cell leading to a cascading failure of a 

battery module or pack cannot be allowed to occur. 

Background

Batteries for EVs and HEVs are fundamentally different from batteries developed for other 

applications. In addition to the scale difference—EV batteries store up to three orders of 

magnitude more energy than laptops—the environment that vehicle traction batteries experience 

during their life is more difficult than in other applications, such as portable computers or cell 

phones. The demanding environmental conditions include exposure to wide temperature 

extremes, vibration, high rates of discharge, and high rates of charge. High rates of both 

discharge and charge can occur at extreme temperatures. To increase an all-electric vehicle’s 

driving range, the vehicle traction application will require high voltage, which in turn requires 

long strings of cells, long life, and high energy. Finally, because the focus of this study is on EVs 

and HEVs that are passenger vehicles, fire safety is a primary concern. Batteries with flammable 

electrolytes present challenges when designing the safety of a vehicle’s energy storage device. 

These safety concerns are especially acute for PHEV and EV applications where vehicles may be 

charged in confined garage spaces of private residences and commercial businesses. 

Safety cannot be determined or evaluated by one criterion or parameter. Rather, enhanced safety 

is determined by the implementation of several approaches that work synergistically, such as: 

•	 Reducing the probability of a battery failure event 

•	 Lessening the severity of outcome if an event occurs. 

As this safety approach applies to vehicle batteries, thermal stability is perhaps the most 

important of several parameters that determine safety of Li-ion cells, modules, and battery packs. 

When discussing battery safety, it is important to understand that batteries contain both an 

oxidizer (cathode) and fuel (anode as well as electrolyte) in a sealed container. Combining fuel 

and oxidizer is rarely done due to the potential of explosion (other examples include high 

explosives and rocket propellant), which is why the state of charge (SOC) is a very important 

variable. Lower SOCs reduce the potential of the cathode oxidizing and the anode reducing. 

Under normal operation, the fuel and oxidizer convert the stored energy electrochemically (i.e., 

chemical to electrical energy conversion with minimal heat and negligible gas production). 

However, if electrode materials are allowed to react chemically in an electrochemical cell, the 

fuel and oxidizer convert the chemical energy directly into heat and gas. Once started, this 

chemical reaction will likely proceed to completion because of the intimate contact of fuel and 

oxidizer, becoming a thermal runaway. Once thermal runaway has begun, the ability to quench 

or stop it is nil. 

The energy content of batteries continues to increase as new electrode materials are developed 

with increased capacity and higher voltage operation. With these developments, new high-energy 

v 
 

 

 

 

 

 

 

 

 

cell designs are appearing in the marketplace. Electrode materials represent some of the most 

reactive materials known and operate at high voltage (4.2 V to 4.6 V). 

Different battery chemistries have various failure modes, but several events are common among 

all types of batteries. A typical response of a cell to abusive conditions is generation of heat and 

gas. While they may be linked (i.e., gas and heat are produced by the same chemical reactions), 

there are occasions where heat and gas are produced independently. 

Abuse tests are intended to emulate abnormal conditions or environments or when a battery pack 

is used in a manner outside the design parameters or beyond useful life. Abuse tests can be 

grouped into three major categories: 

1.	 Thermal Abuse (includes thermal stability, simulated fuel fire, elevated temperature 

storage, rapid charge/discharge, and thermal shock cycling) 

2.	 Electrical Abuse (includes overcharge/overvoltage, short circuit, overdischarge/voltage 

reversal, and partial short circuit) 

3.	 Mechanical Abuse (includes controlled crush, penetration, drop, immersion, roll-over 

simulation, vibration, and mechanical shock) 

Heat generation within battery cells (termed “self-generated heat”) underlies many abuse 

responses and can make failures more hazardous. For example, a short circuit will heat up a cell 

because of Joule heating, which depends on the current and resistance of the cell (I2 R). As the 

temperature increases, the cell begins to produce heat by internal chemical reactions (i.e., above 

the temperature where onset of self-heating reactions begin). Overcharge can also generate heat 

within the cell due to other chemical reactions that may trigger thermal runaway. In both of these 

cases, a comprehensive approach is essential to understand cell response and design of thermal 

management of the battery pack that incorporate cell thermal environment, heat capacity, and 

self-heating rate as a function of temperature. 

In addition to safety incidents, which can arise when batteries are abused, spontaneous internal 

failures (called field failures) are observed in battery-powered equipment. Abuse tests in use 

today cannot predict or screen for field failure, as evidenced by the fact that: 

•	 All battery recalls involve cells that have passed Underwriters Laboratories safety tests. 

•	 Battery companies carry out 100% machine vision X-ray inspection. 

•	 All battery manufacturers use high-potentiometer testing designed to find cells with 

internal short circuits. 

Field failures arising from manufacturing defects that cause internal short circuits have very low 

probabilities of occurrence (estimates for 18650-size cells that fail catastrophically are 1 in 10 

million cells to 1 in 40 million cells). While this may be reassuring for manufacturers of portable 

electronics, EV and HEV battery packs may have thousands of cells and up to 1,000 times more 

stored energy, making even this small failure rate unacceptable. The development of an internal 

short circuit test is an important objective and is being explored by several laboratories. 

Experimental simulation of internal short circuit field failure is also an important objective in 

vi 
understanding failure mechanisms and mitigation. Several laboratories are pursuing approaches 

for these purposes and for validation of thermal models of field failure. 

To characterize heat and gas generation that might occur during off-normal conditions, cells and 

packs are exposed to elevated-temperature abusive conditions that resemble conditions that 

might be seen in the field, if only rarely. 

The materials comprising the cell have a profound influence on the safety and abuse tolerance of 

the cell and battery pack. The choice of cathode has a very significant influence on cell safety. 

New, high-energy cathodes are being used in commercial cells or are in development. Lithium 

cobalt oxide (LiCoO2, or LCO) has been the cathode of choice for the majority of consumerlevel Li-ion cells produced today. Although it delivers good capacity, it is the most reactive and 

has poorer thermal stability than other cathodes. Much progress has been made in 

commercializing safer cathodes. A comparison of the thermal stability of cathodes is shown in 

Figure S-1. in)

400

/m

350 LiCoO2 

(C

300 Gen2: LiNi0.8Co0.15Al0.05O2 

250 

200

Normalized Rate 

Gen3: Li1.1(Ni1/3Co1/3Mn1/3)0.9O2 

150 LiMn2O4 

100 LiFePO4 

50 

0 

0 100 200 300 400 

Temperature (C) 

Figure S-1. Self-heating rate of the 18650 full cell as measured by accelerating rate calorimetry 

(ARC). Improving cathode stability results in a higher thermal runaway temperature (increased 

stability) and a reduced peak heating rate.

Source: E. P. Roth, D. H. Doughty, Proceedings of AABC 15-19 May 2006, Baltimore, MD. 

Anode materials are chosen to have a high capacity, high rate capability, and low irreversible

loss on formation cycling and stability with respect to cycling and high-temperature exposure. 

All of these material properties affect the thermal response of the anode under abuse conditions. 

The relative contribution of the anode and cathode material to the full cell response depends on 

the specific reactivity of the active materials and the mass loadings of each (the thermal stability 

of each electrode is important). 

Shutdown separators are intended to stop current flow in a cell above a certain temperature limit. 

An ideal shutdown separator will have a sharp transition to a very high resistance at a relatively 

vii
 

 

 

 

 

 

 

low temperature, an ability to block high voltage, and a wide temperature window of stability. 

Separators generally are classified into three groups: (1) microporous polymer membranes, (2) 

non-woven fabric mats, and (3) inorganic composite membranes. The separators enhance cell 

safety by having properties of high mechanical strength (puncture resistance), high thermal 

stability, and desirable shutdown properties. However, less-than-ideal shutdown separators can 

be the source of internal shorts and cell failure above the shutdown temperature, especially in 

high-voltage, series-connected strings. Non-shutdown separators, even though not offering 

current-limiting protection, can offer a wider range of temperature stability. 

The organic-based electrolytes used in Li-ion batteries have a unique characteristic compared to 

other electrochemical storage systems. Li-ion electrolytes are almost universally based on 

combinations of linear and cyclic alkyl carbonates. These electrolytes make possible the use of 

lithiated graphite (LiC6) as the anodic active component, resulting in the high power and energy 

densities characteristic of the Li-ion chemistries. However, organic electrolytes have high 

volatility and flammability that pose a serious safety issue if the electrolyte is released during an 

abuse event and begins to burn. Under extreme conditions of voltage and temperature, 

electrolytes can react with the active materials of both anode and cathode to release significant 

heat and gas. 

Technology Development Issues

The design of abuse-tolerant energy storage systems begins with specification of relevant abuse 

conditions and the desired responses to those conditions. Development programs sponsored by 

the U.S. Advanced Battery Consortium (USABC) [http://www.uscar.org] include 

characterizations of the candidate technologies in abuse tests. Uniform standards of 

characterization testing in this area have been established. 

Abuse-tolerant subsystems will need to provide robust controls at several levels, up to and 

including the vehicle controller. These controls should include detection and management of the 

SOC, temperature, and electrical faults. Controls at the cell level will likely include devices for 

relief of internal pressure buildup and for external short circuit interruption. This latter approach 

must be compatible with the subsystem’s functional and performance requirements. 

In parallel with lithium battery developers’ efforts to provide abuse-tolerant systems, the DOE 

has two strong battery R&D programs, Batteries for Advanced Transportation Technologies 

(BATT) [http://batt.lbl.gov] and Applied Battery Research (ABR) 

[www1.eere.energy.gov/vehiclesandfuels/technologies/energy_storage/applied_battery.html]. 

These DOE programs fund projects to improve the intrinsic chemical stability of Li-ion 

rechargeable battery chemistries through development of new materials, characterization of 

advanced commercial materials, and development of standard abuse test protocols. 

The programs that are focused on safety and currently funded by DOE and USABC are grouped 

below according to topic of investigation (funding source and principal investigator’s last name 

are included): 

•	 Development of safer electrolytes (including non-flammable electrolytes) 

ο	 Argonne National Laboratory: BATT – Electrolyte Degradation Modeling (Curtiss, 

Amine) [http://www.anl.gov/] 

viii 
 

 

 

 

 

 

 

 

 

 

ο	 Arizona State University: BATT – Thermally Stable Electrolytes (Angell)
 

[http://www.asu.edu/]
 

ο	 Brookhaven National Laboratory: ABR – Thermally Stable Electrolytes (Yang) 

[http://www.bnl.gov] 

ο	 Case Western Reserve University: BATT – Nonflammable Electrolytes (Scherson) 

[https://www.case.edu/] 

ο	 SNL: ABR – Non-Flammable Electrolyte Development (Orendorff)
 

[http://www.sandia.gov]
 

•	 Electrolyte additives 

ο Argonne National Laboratory: ABR – SEI Electrolyte Additives (Zhang, Abraham) 

ο Idaho National Laboratory: ABR – Phosphazene-Based Electrolytes (Gering) 

[http://www.inl.gov]
 

ο University of Rhode Island: BATT – Electrolyte Additives (Lucht)
 

[http://www.uri.edu/]
 

•	 Development of safer cathodes 

ο Argonne National Laboratory: ABR – Gradient Cathodes (Amine) 

•	 Development of safer separators 

ο Celgard: USABC – Separator Development (Ramadass) [http://www.celgard.com/] 

ο Entek: USABC – Separator Development (Pekela) [http://www.entekinternational.com] 

•	 Analysis of electrochemistry materials developed to improve safety 

ο SNL: ABR – Materials Evaluation (Orendorff) 

•	 Overcharge protection 

ο Argonne National Laboratory: ABR – Overcharge Shuttle Development (Amine) 

ο Lawrence Berkeley National Laboratory: ABR – Overcharge/Redox Polymers 

(Richardson) [http://www.lbl.gov/] 

•	 Abuse test method development 

ο NREL: ABR – Internal Short Circuit (Keyser) [http://www.nrel.gov] 

ο SNL: USABC – Internal Short Circuit, Electrolyte Flammability, Abuse Testing 

(Orendorff) 

•	 System safety modeling 

ο NREL: ABR – Chemicals Reaction and Thermal Modeling (Kim, Santhanagopalan) 

ο NREL: Computer-Aided Engineering for Electric Drive Vehicle Batteries – Internal 

Short Circuit Modeling (Kim) 

ix 
 

 

 

 

 

 

 

 

 

 

 

 

Proposed Path Forward

The projects mentioned above have made progress, but more work needs to be done to improve 

the safety of automotive traction batteries. The challenges of large-format energy storage 

applications should be addressed in a systematic manner through R&D. Based on an analysis of 

existing programs, the following three topical areas have the highest impact in addressing the 

gaps to improved safety and removing the sources of concern that could impede commercial 

success of EVs and HEVs. 

1.	 Improve our understanding of failure modes 

A. Failure modes such as an internal short circuit have substantial negative consequences 

and are difficult to characterize. 

i.	 Elucidate the details and provide a better understanding of initiation and 

propagation of internal short circuits. 

ii.	 Develop a standardized test method that would determine cell susceptibility to 

this failure mode. 

B. Propagation of failure from cell to cell, which leads to catastrophic failure, cannot be 

tolerated. 

i.	 Build an easy-to-use, validated cell and battery pack abuse model that realistically 

captures propagation. 

2.	 Develop better characterization tools 

A. Failures often have an incubation period of several hours, but when a “tipping point” 

is reached, a failure happens very fast. 

i.	 Develop diagnostic methods that could alert the Battery Management System 

(BMS) to an incipient failure and trigger early intervention, thus preventing a 

major incident. 

B. Understanding and improving safety of large battery packs is a priority. 

i. Develop models for cell, module, and battery pack safety and abuse tolerance. 

3.	 Improve the safety of energy storage technologies 

A. Since cathodes continue to be a source of failure in Li-ion rechargeable batteries, 

invest in R&D for: 

i.	 Coated cathodes 

ii.	 Novel cathode discovery methods 

iii. Cathode conversion reactions. 

B. Develop non-flammable electrolytes. The flammability of the vented electrolyte is a 

significant unresolved safety issue for Li-ion batteries. 

i.	 Make a concerted effort toward reducing gas generation at elevated temperature 

as well as investigate ionic liquid electrolytes or other non-flammable solvents 

that could permanently solve the electrolyte flammability issue. 

C. Develop methods to prepare a “permanent solid electrolyte interphase (SEI)” 

x 
 

 

 

 

D. Develop new separators (and/or ceramic coatings applied to separator or electrode) as 

they can provide protection from internal short circuits and other abusive events. 

i.	 Answer questions such as “what method of application of a ceramic heat resistant 

layer provides the best safety result?” 

ii.	 Are shutdown separators necessary for high-voltage, series-connected cell
 

strings?
 

E. Better understand the safety performance of batteries containing anodes made with 

silicon or other alloys. Currently the failure modes in Li alloy anodes (e.g., lithium 

dendrite formation on repeated cycling) occurring in these systems are not known. 

Fundamental understanding as well as more test data are needed. 

xi 

Technical Report: Vehicle Battery Safety Roadmap Guidance 

Prepared for: 

National Renewable Energy Laboratory 

15013 Denver West Parkway 

Golden, CO 80401 

Prepared by: 

Daniel H. Doughty, Ph.D. 

President 

Battery Safety Consulting Inc. 

139 Big Horn Ridge Rd. NE 

Albuquerque, NM 87122 USA 

dhdoughty@batterysafety.net

http://www.batterysafety.net

NREL Technical Monitor: Ahmad A. Pesaran, Ph.D. 

Energy Storage Team Lead 

Subcontract Technical Monitor 

ahmad.pesaran@nrel.gov

Prepared under Subcontract No. LGC-0-40440-01 

 

 

 

 

 

 

 

 

 

Executive Summary 

The most important objectives of the U.S. Department of Energy’s Office of Vehicle 

Technologies is to support the development of lithium-ion batteries that are safe and abuse 

tolerant in electric drive vehicles. This roadmap analyzes battery safety and failure modes of the 

state-of-the-art cells and batteries and makes recommendations on future investments that would 

further DOE’s mission. 

Safety criteria for electric vehicle (EV) and hybrid electric vehicle (HEV) (including plug-in 

hybrid electric vehicles) traction batteries will be viewed differently, and each original 

equipment manufacturer will have a unique approach tailored for its vehicle platform. However, 

two objectives will be fundamental to all efforts: 

•	 The failure rate of cells that leads to thermal runaway will need to become exceedingly 

rare (even lower frequency than today’s estimated failure rate of 1 in 5 million cells) 

•	 Propagation of thermal runaway from cell to cell, which leads to a cascading failure of a 

battery module or pack, cannot be allowed to occur. 

Past efforts have traded increased battery safety for lower energy. The goal of this roadmap is to 

identify opportunities where high energy and safety can be simultaneously met—i.e., research 

and development (R&D) priorities that, if achieved, will enable development of cells and 

batteries that can support long-driving range and have sufficient safety to be used in EVs and 

HEVs. 

The following topics are identified as needs that are not being met and for which additional 

funding would have the greatest impact on enabling safe, high-energy vehicle batteries. 

This roadmap provides recommendations in three areas: 

1.	 Improve our understanding of failure modes. 

A. Failure modes such as an internal short circuit have substantial negative consequences 

and are difficult to characterize. We recommend a systematic R&D program that 

would: 

i.	 Elucidate the details and provide a better understanding of initiation and 

propagation of internal short circuit 

ii.	 Develop a standardized test method that would determine cell susceptibility to 

this failure mode. 

B. Propagation of failure from cell to cell that leads to catastrophic failure cannot be 

tolerated. Building an easy-to-use, validated cell and battery pack abuse model that 

realistically captures propagation is essential. 

2.	 Develop better characterization tools. 

A. Failures often have an incubation period of several hours, but when a “tipping point” 

is reached, they happen very fast. Diagnostic methods that could alert the BMS to an 

1 
 

 

 

 

 

 

 

incipient failure and trigger early intervention could pay big dividends by preventing 

major incidents. 

B. Models for cell, module, and battery pack safety should be a priority because they 

will drive understanding and improvements in safety of large battery packs. 

3. Improve the safety of energy storage technologies. 

A. Cathodes continue to be source of failure in Li-ion rechargeable batteries. Three areas 

are recommended for R&D investments: 

i. Coated cathodes 

ii. Novel cathode discovery methods 

iii. Cathode conversion reactions. 

B. Develop non-flammable electrolytes. The flammability of the vented electrolyte and 

the amount of flammable gas ejected from a cell during abusive failure are significant 

unresolved safety issues for Li-ion batteries. The roadmap recommends a concerted 

effort in ionic liquid electrolytes that could permanently solve the electrolyte 

flammability issue. 

C. The stability of the anode/electrolyte interface needs to be durable and tolerant of 

excursions in temperature. SEI stability is a continuing problem. The roadmap 

recommends a concerted effort to prepare a “permanent SEI.” 

D. New separators (and/or ceramic coatings applied to separator or electrode) can 

provide protection from internal short circuit and other abusive events. Many 

questions remain to be answered, such as what method of application of ceramic heatresistant layer provides the best safety result? 

E. Understand the safety performance of batteries containing anodes made with silicon 

or other alloys. 

2 
 

 

Acknowledgements 

D. H. Doughty would like to acknowledge Dr. E. Peter Roth (recently retired from SNL) for his 

contributions to several sections and participation in many helpful discussions, as well as his 

review and edit of the roadmap. 

D. H. Doughty would like to acknowledge the dedicated team at Power Sources Technology 

Group at SNL, who kindly gave permission to include unpublished data and information that 

were used in this report. SNL is a multi-program laboratory managed and operated by Sandia 

Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. 

Department of Energy’s National Nuclear Security Administration under contract DE-AC04­

94AL85000. 

D. H. Doughty would like to acknowledge Dr. Shriram Santhanagopalan, NREL, who 

contributed to the sections on battery modeling. 

D. H. Doughty would like to acknowledge Dr. Ahmad Pesaran, NREL technical monitor, who 

provided insight on the scope of the project. 

D. H. Doughty would like to gratefully acknowledge the support provided by Dave Howell, 

Energy Storage and Hybrid and Electric Systems Team Lead at DOE’s Vehicle Technologies 

Program, for realizing the need for a safety road map and providing funding for this project. 

3 
 

 

 

 

List of Acronyms and Abbreviations
 

ABR 

ARC 

BATT 

BMS 

Cu 

DEC 

DMC 

DOE 

DSC 

EC 

ECS 

EMC 

EV 

Fe 

H2 

HEV 

IEC 

IEEE 

IL 

ISO 

LCO 

Li 

Li4Ti5O12 

LiC6 

LiCoO2 

LiFePO4 

LiMn2O4 

LiNi0.8Co0.15Al0.05O2 

LiPF6 

LTO 

MCMB 

MJ/kg 

NASA 

NiMH 

NMC 

NMP 

NREL 

O2 

PC 

PEO 

PHEV 

R&D 

SAE 

SEI 

Applied Battery Research (DOE program) 

accelerating-rate calorimetry 

Batteries for Advanced Transportation Technologies (DOE program) 

battery management system 

copper 

diethyl carbonate 

dimethyl carbonate 

U.S. Department of Energy 

differential scanning calorimetry 

ethylene carbonate 

The Electrochemical Society 

ethyl methyl carbonate 

electric vehicle 

iron 

hydrogen 

hybrid electric vehicle 

International Electrotechnical Commission 

Institute of Electrical and Electronics Engineers 

ionic liquid 

International Organization for Standardization 

lithium cobalt oxide 

lithium 

lithium titanate 

lithiated graphite 

lithium cobalt oxide 

lithium iron phosphate 

lithium-manganese oxide 

nickel-cobalt-aluminum oxide 

lithium hexafluorophosphate 

lithium titanate 

meso-carbon micro beads 

megajoules per kilogram 

National Aeronautics and Space Administration 

nickel metal hydride 

LiNi1-x-yMnxCoyO2 

N-methyl-2-pyrrolidone 

National Renewable Energy Laboratory 

oxygen 

propylene carbonate 

poly(ethylene oxide) 

plug-in hybrid electric vehicle 

research and development 

SAE International 

solid electrolyte interphase 

4 
 

SNL Sandia National Laboratories 

SOC state of charge 

UL Underwriters Laboratories 

USABC U.S. Advanced Battery Consortium 

VC vinylene carbonate 

VEC vinyl ethylene carbonate 

Wh/kg watt-hour per kilogram 

5 
Table of Contents
 

Executive Summary..................................................................................................................1
 

Acknowledgements ..................................................................................................................3
 

List of Acronyms and Abbreviations.......................................................................................4
 

List of Figures ...........................................................................................................................8
 

List of Tables...........................................................................................................................10
 

1 Introduction .......................................................................................................................11
 

1.1 Characteristics of Battery Failures...............................................................................13
 

1.2 Approach.....................................................................................................................15
 

1.3 Li-ion Rechargeable Batteries .....................................................................................18
 

1.4 Li-Ion Polymer Batteries..............................................................................................20
 

2	 Background .......................................................................................................................23
 

2.1 Cell Design..................................................................................................................23
 

2.2 Battery Safety Events..................................................................................................25
 

3	 Evaluation Techniques for Batteries and Battery Materials...........................................28
 

3.1 Electrochemical Characterization ................................................................................28
 

3.2 Thermal Characterization ............................................................................................28
 

3.3 Differential Scanning Calorimetry ................................................................................28
 

3.4 Accelerating-Rate Calorimetry.....................................................................................29
 

3.5 Thermal Ramp Test ....................................................................................................29
 

3.6 Large-Scale Calorimetry..............................................................................................30
 

4	 Standardized Safety and Abuse Tolerance Test Procedures.........................................31
 

4.1 Pass/Fail Battery Abuse Tests ....................................................................................31
 

4.2 Characterization Battery Abuse Tests .........................................................................31
 

5 Safety Devices...................................................................................................................55
 

6 Typical Failure Modes – Mechanism of Failure...............................................................56
 

6.1 Thermal Abuse............................................................................................................56
 

6.2 Physical Damage ........................................................................................................58
 

6.3 Charge and Discharge Failures...................................................................................58
 

6.4 Short Circuit ................................................................................................................61
 

7	 Discussion of Safety and Abuse Response for Li-ion Rechargeable Battery

Chemistries .......................................................................................................................64
 

7.1 Cathodes in Li-Ion Batteries ........................................................................................64
 

7.2 Anodes in Li-Ion Batteries ...........................................................................................67
 

7.3 Separator Stability.......................................................................................................69
 

7.4 Electrolytes .................................................................................................................70
 

7.5 Gas Generation...........................................................................................................73
 

7.6 Effect of SOC on Thermal Stability..............................................................................76
 

7.7 Effect of Age and Cycling On Thermal Stability ...........................................................78
 

7.8 Effect of Cell Energy on Thermal Stability ...................................................................81
 

6 
8 Review of Approaches to Improve Safety and Recommendations................................85
 

8.1 Issues that Control Abuse Response ..........................................................................85
 

8.2 Cathodes.....................................................................................................................85
 

8.3 Anodes........................................................................................................................91
 

8.4 Separators ..................................................................................................................94
 

8.5 Electrolytes .................................................................................................................98
 

8.6 Improved Diagnostic Tests........................................................................................102
 

8.7 Modeling ...................................................................................................................105
 

8.8 State of Health Monitoring and Failure Prediction......................................................106
 

8.9 Battery Pack and Module Safety ...............................................................................108
 

9 Conclusions and Recommendations.............................................................................111
 

Glossary ................................................................................................................................114
 

Appendix A. Invitation Letter ...............................................................................................115
 

7 
 

 

 

 

 

 

 

 

 

 

 

 

 

List of Figures 

Figure 1. The gravimetric energy densities (Wh/kg) for various types of rechargeable 

batteries compared to gasoline.................................................................................12
 

Figure 2. Managing Li-ion battery safety can be approached by analyzing the triggers of
 

failures and how effectively they can they be managed. ...........................................15
 

Figure 3. Structure of the DOE ABR program............................................................................18
 

Figure 4. Energy density trends for commercial Li-ion cells.......................................................19
 

Figure 5. Illustration of Li-polymer battery.11 ..............................................................................21
 

Figure 6. Schematic diagram of a battery pack, showing relationship of cells, modules, and 

control electronics. ...................................................................................................23
 

Figure 7. Electrode and cell structure of Li-ion rechargeable batteries. .....................................24
 

Figure 8. Cut-away drawing of cylindrical spirally wound Li-ion cell...........................................25
 

Figure 9. Cell self-heating rate during forced thermal ramp test of Li-Ion Gen 2 chemistry: 

anode = MCMB | electrolyte = 1.2 M LiPF6 in EC:PC:DMC | cathode = 

LiNi0.8Co0.05Al0.05O2 | separator = Celgard 2325 trilayer.............................................57
 

Figure 10. Thermal runaway during overcharge due to separator failure following separator 

shutdown..................................................................................................................60
 

Figure 11. Heat output during overcharge for different cathode oxide chemistries, showing a 

marked increase in heat output when final lithium is removed from cathode.............61
 

Figure 12. A 1-mOhm short circuit at room temperature of a Li-ion cell at 100% SOC. .............62
 

Figure 13. Self-heating rate of 18650 full cell measured by ARC...............................................66
 

Figure 14. Expanded view of ARC profiles showing low rate thermal runaway of LiFePO4
 

and LiMn2O4 cells. ....................................................................................................66
 

Figure 15. Onset of self-heating in thermal ramp experiment on Li-ion cells..............................67
 

Figure 16. DSC profiles of anode carbon materials with different morphologies........................68
 

Figure 17. DSC profiles showing contribution of anode, cathode and electrolyte to cell
 

thermal reactions......................................................................................................68
 

Figure 18. Impedance of electrolyte soaked separator materials showing shutdown and the
 

temperature window of stability. ...............................................................................70
 

Figure 19. ARC profiles of GEN2 18650 cells with different solvent electrolyte species. ...........71
 

Figure 20. ARC profiles for GEN3 18650 cells with EC:EMC (3:7) and EC:PC:DMC (1:1:3)
 

electrolyte solvents...................................................................................................71
 

Figure 21. ARC profiles of anode and cathode electrodes in electrolyte compared to full cell
 

response. .................................................................................................................72
 

Figure 22. Comparison of stored electrical energy and energy released from decomposition
 

reactions...................................................................................................................73
 

Figure 23. ARC thermal runaway profile of an 18650 cell (5 mL electrolyte) showing heat
 

and gas generation...................................................................................................74
 

Figure 24. Gas generation of representative electrolyte solutions. ............................................75
 

Figure 25. Gas generation species for EC:EMC 1.2 M LiPF6 electrolyte at 200°C and 

400°C. ......................................................................................................................75
 

Figure 26. ARC runs for Sony 18650 cells versus SOC. ...........................................................77
 

Figure 27. ARC runs for GEN1 cells vs. SOC. ..........................................................................77
 

8 
 

 

 

 

 

 

Figure 28. ARC profiles of Sanyo 18650 cells at increasing SOCs............................................78
 

Figure 29. ARC runs of fresh and aged Sony cells at 100% SOC .............................................80
 

Figure 30. ARC runs of GEN1 cells (100% SOC) aged at 50°C, 8% SOC, at 2%, 6% and 

9% delta SOC...........................................................................................................81
 

Figure 31. Self-heating onset temperature as a function of cell energy and SOC......................83
 

Figure 32. Self-heating rate at 180°C. .......................................................................................83
 

Figure 33. Calculated relationship between oxygen chemical potential at full charge and
 

voltage for many cathodes........................................................................................87
 

Figure 34. ARC profiles of 18650 cells with AlF3-coated and uncoated NMC cathodes.............89
 

Figure 35. DSC measurements of AlF3-coated and uncoated NMC cathodes. ..........................90
 

Figure 36. ARC measurements of full cell and individual 18650 electrodes with AlF3-coated 

NMC cathodes..........................................................................................................90
 

Figure 37. Schematic of alternative designs using electroactive separator for overcharge
 

protection. ................................................................................................................97
 

Figure 38. Rate performance of a protected Li1.05Mn1.95O4–Li cell with the bilayer, parallel
 

cell configuration. .....................................................................................................97
 

Figure 39. StabiLife Salt used as redox shuttle from Air Products ...........................................102
 

Figure 40. Effect of overcharge shuttle compared to normal cell during overcharge................102
 

Figure 41. Sources of variability in internal short circuit test arise because there are four
 

kinds of internal short circuit conditions. .................................................................104
 

Figure 42. Wiring diagram of conventional and “Matrix” design in two battery packs...............109
 

9 
 

 

 

List of Tables 

Table 1. Battery Safety Roadmap Points of Contact .................................................................17
 

Table 2. Comparison of Standard Test Procedures from UN, UL, IEEE, and U.S. Navy ...........34
 

Table 3. Comparison of Standard Test Procedures from SAE, USABC, IEC, and ISO..............40
 

Table 4. Comparison of SAE Standards J2464 and J2929........................................................54
 

Table 5. Characteristics of Some Positive Electrode Materials..................................................65
 

Table 6. Characteristics of Exponent Test Cells Made with Four Different Cathodes ................82
 

Table 7. ARC Test Sample Charge Energy...............................................................................82
 

10 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1 Introduction 

Batteries for electric vehicles (EVs) and hybrid electric vehicles (HEVs), which in this document 

include plug-in hybrid electric vehicles (PHEVs), are different from batteries developed for other 

applications. The environment that vehicle traction batteries experience during their life is more 

difficult than in other applications such as portable computers, cell phones, or stationary 

applications. The demanding environmental conditions include exposure to wide temperature 

extremes, vibration, high rates of discharge, and high rates of charge. The vehicle traction 

application will also require high voltage (which will require long strings of cells), high energy 

(which allows increased all-electric vehicle driving range), and long life. Finally, since the focus 

of this study is on EVs and HEVs that are passenger vehicles, fire safety is a primary concern. 

Batteries with flammable electrolytes present challenges when designing the safety of a vehicle 

energy storage device. These safety concerns are especially acute for PHEV and EV applications 

where vehicles may be charged in confined garage spaces of private residences and commercial 

businesses. 

Safety cannot be determined or evaluated by one criterion or parameter. Rather, safety is 

determined by the implementation of several approaches that work together to enhance safety, 

such as: 

• Reducing the probability of an event 

• Lessening the severity of the outcome if an event occurs. 

As this approach is applied to batteries, thermal stability is perhaps the most important of several 

parameters that determine safety of lithium-ion (Li-ion) cells, modules, and battery packs. 

When discussing battery safety, it is important to understand that batteries contain both the 

oxidizer (cathode) and fuel (anode) in a sealed container. Combining fuel and oxidizer is rarely 

done due to the potential of explosion (other examples include high explosives and rocket 

propellant). Under normal operation, the fuel and oxidizer convert chemical energy to electrical 

energy with minimal heat and negligible gas. If allowed to react chemically in an 

electrochemical cell, the fuel and oxidizer convert the chemical energy directly into heat and gas. 

Once started, this chemical reaction will likely proceed to completion because of the intimate 

contact of fuel and oxidizer, becoming a thermal runaway. Once thermal runaway has begun, the 

ability to quench or stop it is nil. 

The energy content of batteries continues to increase as new electrode materials with larger 

capacity and higher voltage are developed and new designs appear in the marketplace. Electrode 

materials represent some of the most reactive materials known and operate at high voltage (4.2 V 

to 4.6 V). The maximum theoretical voltage that can be obtained from known electrode materials 

is 6.5 V [lithium anode and copper (II) fluoride cathode].1 

The highest specific energy available in today’s commercial Li-ion rechargeable batteries is 

approximately 240 watt-hours per kilogram (Wh/kg), nearly 20% of the energy content of TNT 

1 Linden, D.; Reddy, T. B. (2011). “Basic Concepts.” Reddy, T. B., ed. Linden’s Handbook of Batteries, 4th edition. 

McGraw Hill, 2011, ISBN 978-0-07-162421-3; pp 1.10–1.11. 

11 
 

 

 

 

at 4.61 megajoules per kilogram (MJ/kg) (1,282 Wh/kg).2 Batteries are continuing to increase in 

energy density. Figure 1 compares gravimetric energy (specific energy) of various battery 

chemistries as well as liquid fuel for internal combustion engines. 

Figure 1. The gravimetric energy densities (Wh/kg) for various types of rechargeable batteries 

compared to gasoline.

3 

The theoretical density is based strictly on thermodynamics and is shown as the blue bars while 

the practical achievable density is indicated by the orange bars and numerical values. For 

lithium-air, the practical value is just an estimate. For gasoline, the practical value includes the 

average tank-to-wheel efficiency of cars.3 

[Note: Comparisons of this type need to be regarded with caution, because the battery cell is a 

complete energy storage unit and can deliver electricity without additional equipment. Fuels, 

whether they are delivered to an internal combustion engine or fuel cell, are not complete and 

always require conversion equipment (i.e., the engine or fuel cell stack) as well as an oxidizer.] 

2 Kinney, G. F.; Graham, K. J. (1985) Explosive Shocks In Air, 2nd edition. Springer-Verlag.
 3 Girishkumar, G.; McCloskey, B.; Luntz, A. C.; Swanson, S.; Wilcke, W. (2010). Journal of Physical Chemistry
 

Letters. 2010, 1, pp 2193–2203.
 

12 
 

 

 

 

 

 

 

 

 

1.1 Characteristics of Battery Failures

Safety incidents can arise when batteries are abused (i.e., used in a manner outside design 

parameters or beyond useful life) or from spontaneous internal failures (called “field failures”4

). 

Abuse failures can result during assembly, operation, or maintenance and are a much more likely 

occurrence. 

Field failures usually arise from manufacturing defects and have very low probabilities of 

occurrence. The failure rate has been estimated between 1 in 10 million4 and 1 in 40 million 

cells.

5 Tests in use today cannot predict field failures, as evidenced by the fact that: 

•	 All battery recalls involve cells that have passed Underwriters Laboratories (UL) tests. 

•	 Battery companies carry out 100% machine vision X-ray inspection. 

•	 All battery manufacturers use high-potentiometer testing designed to find cells with 

internal short circuits. 

The most serious consequences occur when the stored energy is rapidly released in an 

unintended manner, producing large quantities of heat and gas. The fact is that, because failures 

will occur, however infrequent, the challenge for cell and battery pack designers is to achieve a 

“graceful failure,” (i.e., a failure that only has minor consequences and avoids a catastrophic 

failure). The goal of graceful failure can be realized by: 

•	 Reducing the severity of response of individual cells to abusive events 

•	 Implementing engineering approaches that keep individual cell failures from propagating 

to adjacent cells, thereby isolating the damage and reducing the risk of injury. 

As we discuss in this roadmap, heat and gas generation are the key parameters that must be 

controlled to improve the safety of Li-ion rechargeable batteries. Heat generation increases 

exponentially with temperature while heat dissipation only increases linearly.6 The response to 

any abuse scenario arises from the dynamics of heat generation and heat dissipation. Below we 

present three possible outcomes of an event that could lead to a safety incident. 

Case #1 – An abuse event that leads to graceful failure at the cell level (the preferred outcome): 

1. ONSET: An abuse event occurs within a cell that leads to an increase in temperature. 

A. Event can be an internal short circuit or an externally driven short circuit, adjacent 

cell heating, or overcharge. 

2.	 ACCELERATION: Decomposition of reactants creates additional heat and gas. Reaction 

zone expands. 

4 Barnett, B. M.; Roth, E. P.; Thomas-Alyea, K. E.; Doughty, D. H. (2006). “Abuse Tolerance versus Field Failure:
 

Two Different Issues for Lithium-Ion Safety.” Prepared for the International Meeting on Lithium Batteries, June
 

2006.
 5 Dahn, J.; Erlich, G. M. (2011). “Lithium Ion Batteries.” Reddy, T. B., ed. Linden’s Handbook of Batteries, 4th 

edition. McGraw Hill, 2011, ISBN 978-0-07-162421-3; pp 26–68.

6 Levy, S. C.; Bro, P. (1994). Battery Hazards and Accident Prevention. Plenum Press, New York, NY.
 

13 
 

 

 

 

 

 

 

 

3.	 NO RUNAWAY: Heat dissipation rate exceeds heat generation rate and cell is cooled, 

preventing thermal runaway. 

Case #2 – An abuse event results in cell explosion but leads to graceful failure at the 

pack/module level (an acceptable outcome): 

1. ONSET: An abuse event occurs within a cell that leads to an increase in temperature. 

A. Event can be internal short circuit or externally driven short circuit, adjacent cell 

heating or overcharge. 

2.	 ACCELERATION: Decomposition of reactants creates additional heat and gas. Reaction 

zone expands. 

3.	 RUNAWAY: Heat dissipation rate is less than heat generation rate, and cell enters 

thermal runaway. 

A. Additional heat and gas are produced. 

B. Decomposition of electrolyte proceeds to completion. 

C. Cell vents violently or explodes. 

Adjacent cells heat up, but are not driven into thermal runaway. Propagation of failure is stopped 

after the initial cell failure. 

Case #3 – An abuse event that leads to catastrophic failure at the pack/module level (an 

unacceptable outcome): 

1. ONSET: An abuse event occurs within a cell that leads to increase in temperature. 

A. Event can be internal short circuit or externally driven short circuit, adjacent cell 

heating, or overcharge. 

2.	 ACCELERATION: Decomposition of reactants creates additional heat and gas. Reaction 

zone expands. 

3.	 RUNAWAY: Heat dissipation rate is less than heat generation rate and cell enters
 

thermal runaway.
 

A. Additional heat and gas are produced. 

B. Decomposition of electrolyte proceeds to completion. 

C. Cell vents violently or explodes. 

4.	 Adjacent cells are driven into thermal runaway and explode. Cascade of cell failures 

consumes the entire battery module/pack. 

Another way to analyze failures is to examine the cause(s) and to evaluate the efficacy of current 

control methods. A TIAX battery safety presentation included a slide that is a useful starting 

point for analysis.7 The analytical approach identifies a trigger for a failure and asks the 

questions: “What is the cause and is it adequately being managed?” The analysis presented at 

7 Stringfellow, R.; Ofer, D.; Sriramulu, S.; Barnett, B. (2010). “Lithium-Ion Battery Safety Field-Failure 

Mechanisms.” Presented at the 218th Meeting of the ECS, Las Vegas, NV, Oct. 12, 2010 (Abstract #582). 

14 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The Electrochemical Society’s (ECS) 218th Meeting in Las Vegas (see Figure 2) highlighted two 

areas that need attention: 

1.	 Internal short circuit 

2.	 Propagation of cell failures in pack or module. 

In our discussion below, we will identify the mechanisms that underlie this sequence of events 

and highlight the methods that will make cells and battery packs more abuse tolerant to minimize 

the possibility of catastrophic failures. 

Trigger Why can this occur ? Is this managed ? 

Overcharge Defective connections, 

failure of charging circuit 

Yes, battery management system 

Yes, cell-level safety devices 

Overheating from external 

sources 

Battery pack placed too 

close to a heat source 

Yes, cell-level safety devices open 

the cell at suitable internal 

pressure 

Cell crushing creating 

massive internal shorts 

Physical abuse of battery 

pack 

Yes, design enclosures are built 

more tolerant to specific abuses 

Internal short-circuits 

(a.k.a., field failures) 

Internal-short caused by 

manufacturing defects No, new technologies needed 

Cascading of thermal 

energy release 

Affected cell can raise the 

temperature of 

surrounding cells 

No, new technologies needed 

Figure 2. Managing Li-ion battery safety can be approached by analyzing the triggers of failures 

and how effectively they can they be managed.7 

1.2 Approach

Information gathered for this roadmap came from several sources. A comprehensive literature 

search was conducted. Published results from existing U.S. Department of Energy (DOE) 

programs—Advanced Battery Research (ABR) (previously named Advanced Technology 

Development) and Batteries for Transportation Technologies (BATT)—were particularly 

valuable because detailed information about cell materials and construction was available. 

Information presented at recent international meetings dealing with battery safety was included. 

These meetings were: 

•	 ECS Symposium B2, Battery Safety and Abuse Tolerance, at the 218th Meeting of the 

ECS in Las Vegas, Nevada, October 10–15, 2010. D. H. Doughty was the lead organizer 

of this symposium. 

•	 Knowledge Foundation’s Battery Safety 2010 and Lithium Mobile Power 2010 in Boston, 

Massachusetts, November 3–5, 2010. 

•	 51st Battery Symposium in Nagoya, Japan, November 9–11, 2010. 

15 
 

 

 

•	 Pacific Power Source Symposium 2011, Hilton Waikoloa Village, Hawaii, January 10– 

15, 2011. 

Finally, input was solicited from many representatives of industry, academia, and national 

laboratories who have experience and expertise in safety and abuse tolerance testing. The list of 

individuals and organizations is presented in Table 1. All points of contact invited to participate 

were sent a list of questions (see Appendix A). Responses were obtained from slightly over half 

of the people on the list. 

16 
 

 

 

 

Table 1. Battery Safety Roadmap Points of Contact 

Battery Safety Roadmap Points of Contact. 

1. Scientists and Battery Research Programs. 

No. 

US National Labs: 1 Argonne National Laboratory Michael Thackeray 

2 Argonne National Laboratory Khalil Amine 

3 Brookhaven National Laboratory Xiao-Qing Yang 

4 Lawrence Berkeley National Lab Venkat Srinivasan 

5 National Renewable Energy Lab Ahmad Pesaran 

6 Oak Ridge National Laboratory Nancy Dudney 

7 Sandia National Laboratories Chris Orendorff 

Universities and individual experts. 

8 Dalhousie University Jeff Dahn 

9 IIT Jai Prakash 

10 SUNY-Binghamton Stan Whittingham 

11 Battery Design Co. Bob Spotnitz 

12 CNRS Dominique Guyomard 

13 Univ. Munster Martin Winter 

14 Broddarp of Nevada Ralph Brodd 

15 Consultant Rick Howard 

2. Commercial Battery Companies and Material Supplier 

US Battery developers and materials suppliers 

16 A123 Tom De Lucia 

17 Ener1 Cyrus Ashtiani 

18 Johnson Controls-SAFT Jim Symanski 

19 Yardney/Lithion Rob Gitzendanner 

20 Amperex Technology Limited Anthony Wong 

21 Celgard John Zhang 

22 Entek Membranes Rick Pekala 

23 Hydro Quebec Karim Zaghib 

24 Quallion Hisashi Tsukamoto 

3. Battery Users – automotive. 

US Industry users (Detroit original equipment manufacturers & other car makers) 

25 General Motors Galen Ressler 

26 General Motors Joe LoGrasso 

27 Ford Ted Miller 

28 Chrysler Ron Elder 

29 Tesla Kurt Kelty 

30 Continental Powertrain Corp. Olaf Bose 

31 Mitsubishi Motors Gerry Wing 

32 

United States Advanced Battery 

Consortium Ahsan Habib (GM) or 

33 

United States Advanced Battery 

Consortium Kent Snyder (Ford) 

4. Battery Users and other. . 

Commercial Companies: US Industry users (Portable Electronics Manufacturers) 

34 Dell Warren Payne 

35 Motorola Jason Howard 

36 Materials Handling Group, Inc. Laurence Dunn 

Government agencies. 

37 Naval Surface Warfare Center Clint Winchester 

38 Naval Surface Warfare Center Julie Banner 

39 ARL Richard Jow 

40 NASA Judy Jeevarajan 

41 NASA Eric Darcy 

42 Department of Transportation Spencer Watson 

43 NHTSA Phil Gorney 

Regulatory Agencies and Test Organizations. 

44 Underwriters Laboratory Lorie Florence 

45 Engineering Laboratory, Inc. Jae-Sik Chung 

46 SGS U.S. Testing Company Inc. Jody Leber 

47 Intertek Rich Byczek 

48 Detroit Testing Laboratory, Inc. Earl L. Smith 

17 
 

 

 

 

 

 

 

 

Much of the research that has been performed in the area of Li-ion abuse tolerance, which is the 

main subject of this Battery Safety Roadmap, has been performed under DOE’s Vehicle 

Technologies Program.

8 The DOE’s Vehicle Technologies Program office works with industry, 

universities, and national laboratories to develop advanced transportation technologies that 

would reduce the nation’s use of imported oil (almost 96% of the U.S. transportation fleet uses 

oil). The Vehicle Technologies Program encompasses multiple activities: hardware development 

with industry [U.S Advanced Battery Consortium (USABC)], short-term research and 

development (R&D) (ABR), and focused fundamental research (BATT). The abuse tolerance 

work that has been performed is part of the ABR program, which encompasses the efforts of 

seven national laboratories and other government agencies. The program covers several 

interrelated areas, many of which impact abuse tolerance of the Li-ion cells (see Figure 3). 

Although this roadmap covers many of these topics, there are many areas of ABR- and BATTsupported research that are not explicitly covered. Please refer to the DOE website, particularly 

the “2010 Annual Progress Report for Energy Storage R&D” 

(http://www1.eere.energy.gov/vehiclesandfuels/resources/vt_es_fy11.html), for a more detailed 

listing of the many applicable areas of research. 

Figure 3. Structure of the DOE ABR program.

8 

1.3 Li-ion Rechargeable Batteries

The demand for high-energy rechargeable batteries has fueled remarkable growth of lithium 

secondary (rechargeable) batteries over the last 20 years. These advances are gradual, resulting 

in increases of specific energy in watt-hours per kilogram of a few percent per year for mature 

technologies, but up to 10% per year for new technologies, such as Li-ion (see Figure 4). Li-ion 

batteries have the advantage of high energy density, high cell voltage, and long shelf life. In 

8 “Vehicle Technologies Program.” http://www1.eere.energy.gov/vehiclesandfuels. Accessed March, 2012. 

18 
 

 

 

 

 

 

 

1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 

addition, they are relatively lightweight compared with lead-acid and nickel metal hydride 

(NiMH) technologies. Projections of higher energy Li-ion cells are impressive. For example, 

Hosoki presented plans for Panasonic to develop 18650-size cells up to 3.4 Ah within the next 

few years.9 He also stated that a silicon-alloy anode with a modified LiNi0.8Co0.15Alx0.05O2 

cathode will produce a 4.0-Ah cell in 2012. He stated that the separator is coated with ceramics 

on only one side (presumably the anode side). 

Energy Trends in Commercial Li Ion Cells 

Energy Density 18650 Cells 

Approximately 10% per year improvement in Energy Density 

150 

200 

250 

300 

350 

400 

450 

500 

550 

600 

650 

700 

750 

800 

Specific Energy (Wh/L)

Sony Data 

Sanyo Data 

Sony Linear Extrapolation 

Year 

Figure 4. Energy density trends for commercial Li-ion cells.

9 

The use of lithium-containing anodes is associated with high energy density, high battery 

voltage, and good shelf life, but also may be associated with safety problems (e.g., fires) that are 

a consequence of the high energy content and flammable electrolyte that often is used in lithium 

systems. These attributes strongly depend on the choice of electrode and electrolyte materials. 

There are many concerns with Li-ion chemistries, such as their sensitivity to overcharging and 

overdischarging, the flammability and toxicity of the materials, and thermal runaway. Because of 

these concerns, a variety of protection mechanisms are frequently employed in Li-ion batteries, 

such as internal cell safety shutdown separators, fuses, external contacts, advanced charging 

algorithms, and monitoring. 

In well-designed and well-engineered battery assemblies with redundant control systems, failures 

are relatively rare. However, with the ever-increasing presence of battery-powered devices, from 

laptops and cellular phones to HEVs, even rare events can attract attention. 

9 Hosoki, K. (2010). “Panasonic’s Advanced Li-ion Batteries.” Presented at Knowledge Foundation’s Lithium 

Mobile Power 2010 Conference, November 4–5, 2010. 

19 
 

 

 

 

 

 

There are common failure modes that occur among all types of batteries. Cells with a flammable 

electrolyte or other flammable materials that could escape when the containment is compromised 

during a crush could present a fire hazard.10 Heat generation and gas generation are the most 

common responses of batteries to abusive conditions.3 While they may be linked (i.e., gas and 

heat may be produced by the same chemical reactions), there are examples where heat and gas 

are produced independently. 

1.4 Li-Ion Polymer Batteries

An alternative to the liquid electrolytes is a solid polymer electrolyte formed by incorporating 

lithium salts into polymer, glassy, or ceramic matrices and forming them into thin films. The 

polymer may serve the function of separator as well as electrolyte, depending on the cell design. 

Unlike Li-ion cylindrical or prismatic cells, which have a rigid metal case, polymer cells have a 

flexible, foil-type (polymer laminate) package but still contain organic solvent. The main 

difference between commercial polymer and Li-ion cells is that in the latter, the rigid case 

presses the electrodes and the separator onto each other, whereas in polymer cells this external 

pressure is not required because the electrode sheets and the separator sheets are laminated onto 

one another (Figure 5). Organic polymers are by far the most common type of separator in Li-ion 

polymer (Li-polymer) batteries. 

The choice of electrode materials in Li-polymer batteries is generally similar to Li-ion batteries 

with liquid electrolytes, except where the electrochemical stability of the polymer used is less 

stable to oxidation (by the cathode) or reduction (by the anode). There are several versions of 

organic polymer electrolytes discussed in this section. Some of the polymers are true solid 

polymers without substantial amounts of additives or plasticizers, and others are gels with a large 

volume of liquid electrolyte (up to 70% by volume). 

10 Roth, E. P.; Crafts, C. C.; Doughty, D. H. (2001). 16th Annual Battery Conference on Applications and Advances 

Proceedings; April 2001, Long Beach, CA; p. 375. 

20 
 

 

Figure 5. Illustration of Li-polymer battery.11 

Initially, high molecular weight polymers such as poly(ethylene oxide) (PEO) and lithium salts 

such as LiClO4 and LiN(CF3SO2)2 (Li imide) were used in Li-ion rechargeable batteries. As 

“true solid polymer electrolytes,” PEO-lithium salt electrolytes have good mechanical properties 

but low conductivities, which are about 10-8 S/cm at 20°C. Therefore, the batteries must be 

heated to 75°C–85°C to get sufficient conductivity. A significant improvement in room 

temperature conductivity (to ~ 10-5 S/cm) has been achieved with the combination of modified 

comb-shaped PEO structures with lithium salts,11 but these types of solid polymer electrolytes 

have poor mechanical properties and their conductivity is still two orders of magnitude lower 

than that of most organic liquid electrolytes. Further improvement in conductivity was obtained 

with the addition of liquid plasticizers, such as polypropylene carbonate.12,13 The amount of 

plasticizer may be as high as 70%, resulting in limited chemical and mechanical stability. 

11 http://www.mpoweruk.com/cell_construction.htm
 12 Abraham, K. M.; Alamgir, M. (1990). Journal of Electrochemical Society, 136 1657.
 

21 
 

 

 

 

 

 

 

 

Because of the restricted high-voltage stability, many of the high-voltage Li-ion battery cathodes 

are not stable with PEO polymer electrolytes. PEO electrolytes will not be discussed in this 

roadmap, even though Bolloré in France has announced plans to commercialize the lithium metal 

polymer battery technology for BlueCar EVs.14 It is the opinion of the roadmap author that the 

PEO-based cells are unsuited for vehicular application. 

Another class of polymer electrolytes, called “gelled“ electrolytes, has been developed by 

trapping liquid solutions of lithium salts in aprotic organic solvents [for example, LiClO4 in 

propylene carbonate (PC)-ethylene carbonate (EC) solvent] into a solid polymer matrix, such as 

poly(vinylidene difluoride)15 and poly(acrylonitrile).16,17 

The “gel” electrolytes are made by adding liquid electrolyte solutions into the polymer porosity 

with an immobilization procedure, such as cross-linking, gellification, and casting. Cross-linking 

may be carried out by ultraviolet, electron-beam, or gamma-ray irradiation. Conductivities as 

high as 10-3 S/cm at 20°C and transference numbers around 0.6 have been obtained. However, 

these plasticized and gelled electrolytes have similar abuse response as liquid electrolyte Li-ion 

batteries. 

Inorganic glasses and ceramics (e.g., NASICON conductive ceramic) can be used, but these 

materials are in the research phase18 with the exception of companies trying to commercialize 

very thin-film, solid state batteries (15 μm or thinner and consequently low-capacity batteries) 

based on lithium phosphorous-oxynitride (LiPON) glass electrolytes initially developed at Oak 

Ridge National Laboratory by John Bates.19 Batteries with glass or ceramic electrolytes will not 

be further discussed in this document because, in the opinion of the roadmap author, the 

likelihood of deployment of this technology for EV and HEV traction applications is remote. 

The safety of polymer electrolyte cells is strongly influenced by the type of polymer electrolyte. 

In general, the trend of increasing safety will be (1) inorganic glass or ceramic electrolytes, (2) 

true solid polymers, and (3) gelled electrolytes. 

In all cases, safety and abuse tolerance are still strongly influenced by the active materials that 

are used. The polymer electrolytes that do not contain solvents and plasticizers will have lower 

gas and heat production and should be more abuse tolerant. Cells made with gelled electrolytes 

should have similar safety performance if the organic liquids are similar or identical to those 

used in liquid electrolyte cells. For this reason, discussion of Li-ion rechargeable battery safety 

and Li-polymer battery safety are combined and treated the same in this roadmap. 

13Koksbang, R.; Gauthier, M.; Belanger, A. (1991) Proc. Symp. Primary and Secondary Lithium Batteries. 

Abraham, K. M.; Salomon, M. eds. The Electrochemical Society, Pennington, N.J.

14 “The LMP Battery.” Bluecar, http://www.bluecar.fr/en/pages-innovation/batterie-lmp.aspx. Accessed March
 

2012.
 15 Gozdz, A. S., et al. U.S. Patent No. 5,456,000, 10 October 1995.
 16 Abraham, K. M. (1993). Applications of Electroactive Polymers, Scrosati, B. ed. Chapman and Hall.
 17 Shen, D. H.; Nagasubramanian, G.; Huang, C. K.; Surampudi, S.; Halpert, G. (1994). 36th Power Sources
 

Conference Proceedings. Cherry Hills, NJ.
 18 “Advanced Lithium Battery Technology.” POLYPLUS. http://www.polyplus.com/
 19 http://www.oakridgemicro.com/
 

22 
 

2 Background 

Cells are assembled into modules and battery packs for most applications. The details of the 

assembly are developed for the intended use. However, many structures are common. Figure 6 

shows the generic relationship between cells, modules, and battery packs. 

Figure 6. Schematic diagram of a battery pack, showing relationship of cells, modules, and control 

electronics.20 

Safety must be addressed in the basic electrochemical cell. Safety-related issues also need to be 

addressed during the battery design and integration into an overall energy storage system. At the 

pack level, additional failure modes are possible. Careful attention to battery pack management 

strategies and good design principles is essential. 

2.1 Cell Design 

A battery is an energy storage device that functions by converting chemical energy into electrical 

energy by reduction and oxidation (redox) chemical reactions. Electrodes are composed of the 

active material, binders, conductive additives, and other materials that are in contact with (and 

often coated on) a current collector. As seen in Figure 7, the electrodes are held apart by a porous 

separator that has good ionic conductivity but poor electronic conductivity (to avoid an internal 

short circuit). 

During discharge, the cathode active material (the oxidizer) is reduced and the anode active 

material (the fuel) is oxidized. The energy released during this reaction is directly proportional to 

the difference in the electromotive force between the two electrode materials. The highest 

20 Diagram from UL 2580, “Standard for Safety for Batteries for Use in Electric Vehicles,”1st Edition, October 13, 

2011. 

23 
 

 

 

 

 

Negative 

Electrolyte/separator

Positive electrode

 

Negative 

Electrolyte/separator

Positive electrode

voltage achievable is between the lithium anode and the copper (II) fluoride cathode, where the 

electromotive force is approximately 6.5 V. The stored energy is also proportional to the capacity 

of the electrode materials, i.e., how many electrons are released during the redox reaction per 

weight and volume of material.21 

Al current collector

Cu current collector

Present Day Elecrochemical Cell 

Structure 

Al current collector

Cu current collector 

Negative 

Electrolyte/separator 

Positive electrode 

Al current collector 

Figure 7. Electrode and cell structure of Li-ion rechargeable batteries.

24 

A schematic cutaway drawing of a cylindrical cell is shown in Figure 8. Because batteries have 

the fuel and oxidizer packaged together in the cell, if the energy embodied in these materials is 

inadvertently released in a way that triggers a rapid chemical reaction leading to thermal 

runaway, there is no way to interrupt the reaction since the fuel and oxidizer are in such intimate 

contact. 

Traditional firefighting techniques that rely on separating the fuel and oxidizer cannot affect the 

outcome of a cell once runaway commences. The course of the reaction is exclusively dictated 

by the material state of change (SOC) and cell design, and it will proceed to completion within 

the cell. In battery packs, there is a risk that the failure of one cell will propagate to adjacent 

cells. Propagation of cell failure has been seen experimentally,

22, 23 as well as in accidents in the 

field. The design goal for battery modules and packs should be to avoid propagation of 

thermal runaway from cell to cell. This is especially true of large battery packs, such as those 

found in EVs and HEVs. 

21 Levy, S. C.; Bro, P. (1994). Battery Hazards and Accident Prevention, Plenum Press, New York, NY.
 22 Govar, C. J.; Fuentevilla, D.; Banner, J.; Winchester, C. (2006). “Safety Lessons Learned from 18650 and D-Cell 

Lithium Ion Rechargeable Batteries in Unmanned Vehicles.” 42nd Power Sources Conference Proceedings, June 12,
 

2006, p 83.

23 Doughty, D. H. (2005). “Li-ion Battery Abuse Tolerance Testing - An Overview.” AABC 2005 Proceedings, 

Honolulu, HI, June 2005.
 

24 
 

 

 

 

 

However, once thermal runaway has commenced 

within a battery pack, the best hope of traditional 

firefighting techniques is to cool the battery pack in 

such a way as to prevent a cascade of failures from cell 

to cell. The failure that is most difficult to guard against 

and typically is the most unpredictable is an internal 

short circuit. Internal short circuits were blamed for the 

well-publicized failures involving fires in laptop 

batteries in 2006. In 2008, HP, Toshiba, and Dell 

recalled over 430,000 laptops with Sony Li-ion 

rechargeable batteries.25 These failures may be caused 

by contaminants such as metal particles inside the cells 

or manufacturing flaws such as burrs on the edge of 

current collector foils. Unlike an external short circuit 

or overcharge, where engineered methods and 

strategies can be effective at interrupting the abuse 

event, internal short circuits are not prevented by these Figure 8. Cut-away drawing of safety devices. cylindrical spirally wound Li-ion cell.

24 

2.2 Battery Safety Events

Safety problems can cause personal 

injury as well as financial loss to the 

battery pack suppliers and device If the energy contained in a battery cell is 

manufacturers. In 2006, several laptop inadvertently released and results in thermal 

Li-ion battery fires did not result in runaway, there is no way to quench the 

injury but did initiate a Sony laptop reaction because the fuel and oxidizer are in 

battery recall that, while not the first of intimate contact. 

its kind, was the largest to date. A failure R&D programs that allow original equipment rate estimated to be 1 in 200,000 

manufacturers to understand the causes of triggered an initial recall of almost six 

million Li these events, implement precautions, and make -ion packs used in laptops 

manufactured these failures exceedingly rare, will directly by Dell and Apple26 that 

was subsequently extended to batteries benefit EV and HEV safety.

used in Sony, Lenovo/IBM, Panasonic, 

Toshiba, Hitachi, Fujitsu, and Sharp 

laptops. The stated cause was contamination within the cell from metal particles created during 

cell manufacturing processes. Under some circumstances, after normal usage these particles can 

pierce the separator, creating an internal short circuit within the cell. Thus, electrical energy 

stored in a single cell was rapidly released, producing heat and gas from an exothermic oxidizing 

reaction. The cell temperature increased by several hundred degrees Celsius in a fraction of a 

24 Colclasure, A. M.; Kee, R J. (2010). Electrochimica Acta 55, Society of Electrochemistry; pp 8960–8973.
 25 “Laptop Fires Prompt Sony Battery Recall — Again.” Wired GADGET LAB,
 

http://www.wired.com/gadgetlab/2008/10/laptop-fires-pr/. Accessed March 2012.
 26 “Lithium-ion Safety Concerns.” Battery University, http://www.batteryuniversity.com/partone-5B.htm. Accessed
 

March 2012.
 

25 
 

 

 

 

 

 

 

 

 

 

 

 

second, and finally triggered thermal runaway. The high temperature of the failed cell heated up 

the neighboring cells, initiating a thermal runaway in other cells in the pack. 

The extent of safety problems in the United States can be roughly estimated by searching the 

U.S. Consumer Product Safety Commission website, http://search.cpsc.gov. A search for 

“Battery Recalls” returned about 2,134 results that span the last 30 years. A search for “Battery 

Failure” gave about 580 results that span the last decade. Many of these recalls and failures were 

due to control circuitry rather than cell failures. 

Typical Consumer Product Safety Commission recalls mention “an internal failure can cause the 

battery to overheat and melt or char the plastic case, posing a burn and fire hazard” as was 

observed in HP and Compaq notebook computer batteries (consistent with an internal short 

circuit). This failure seems similar to the Sony recall in 2006. However, it was based on only 20 

reports of batteries overheating, including two in the United States.27 There was a recent recall of 

a wireless headset with ATL Li-polymer batteries made by GN Netcom due to fire hazard in 

December 2008.28 GN Netcom has received 10 reports of incidents involving overheating, 

including three reports of open flames and property damage to furniture on which the headsets 

were resting. An additional 37 reports of open flames and one report of second-degree burns that 

required medical attention were received from outside the United States. Laptop battery recalls 

seem to be recurring with regularity (e.g., HP laptop batteries were recalled again in May 2010 due 

to fire danger29). 

The number of recalls and failures is small in comparison to production volumes. In 2005, 1.7 

billion Li-ion and Li-polymer cells were made worldwide30 with a projected volume of 2.2 

billion cells per year by 2008. Estimates are that Li-ion rechargeable battery safety incidents 

occur in less than one in a million cells, and probably in less than one in 10 million cells.2 

However, even though the frequency is small based on a percentage basis, it has gained the 

attention of the Consumer Product Safety Commission and other consumer and transportation 

safety regulatory agencies.31,32 

While rare, serious failures do occur in large packaged batteries. In November 2008, perhaps the 

largest single battery-related safety incident occurred to a developmental U.S. Navy electric 

submersible vehicle powered by fourteen 85-kWh Li-ion batteries. The Li-ion battery, a 

replacement for the silver-zinc battery, was both very high energy (>210 Wh/kg) and very large 

(>1 MWh). While under charge, one or more battery sections failed, resulting in a fire that 

consumed several of the battery assemblies and disabled the vehicle. There were no casualties, 

27 “HP Recalls Notebook Computer Batteries Due to Fire Hazard.” (2006). U.S. Consumer Product Safety 

Commission press release, 20 April 2006, http://www.cpsc.gov/CPSCPUB/PREREL/prhtml06/06145.html. 28 “Wireless Headset Batteries Recalled by GN Netcom Due to Fire Hazard.” The Safety Review, December 2008 

edition, p 5. http://www.cpsc.gov/CPSCPUB/PUBS/tsr1208.pdf. 29 “HP Expands Recall of Notebook Computer Batteries Due to Fire Hazard.” (2010). U.S. Consumer Product 

Safety Commission press release, 21 May 2010, http://www.cpsc.gov/cpscpub/prerel/prhtml10/10240.html. 30 Takeshita, H. (2005). “Worldwide Market Update on NiMH, Li-ion and Polymer Batteries for Portable 

Applications and HEVs,” Presented at the 22nd International Battery Seminar & Exhibit, March 14, 2005. 31 “What’s New Basics.” (2008). http://safetravel.dot.gov/whats_new_batteries.html Accessed March 2012. 32 Webster, H. (2004). Flammability Assessment of Bulk-Packed, Nonrechargeable Lithium Primary Batteries in 

Transport Category Aircraft. Office of Aviation Research Report, DOT/FAA/AR-04/26. 

http://www.fire.tc.faa.gov/pdf/04-26.pdf. 

26 
 

 

 

but the repair estimate was $237 million.33 Interestingly, thermal runaway has been documented 

for other chemistries, such as NiMH. In 2005, the CMV Punjab Senator suffered a severe 

explosion and fire in a cargo container containing 16 tons of HR6 NiMH cells.34 This event 

appears to be combination of elevated temperatures and cargo shifting resulting in massive 

shorting. 

33“Prototype mini-sub shelved.” (2009). Honoluluadvertiser.com. 

http://the.honoluluadvertiser.com/article/2009/Jul/25/ln/hawaii907250321.html. Accessed March 2012. 34 “Explosion and fire on board CMV Punjab Senator.” (2007). Casualty and incident report presented to 

International Maritime Organization Sub-Committee on Dangerous Goods, Solid Cargoes and Containers. Report 

DSC 12/6/8, Published 12 July 2007. http://www.emsa.europa.eu/end185d007d003d002d004d005.html 

27 
 

 

 

 

 

3 Evaluation Techniques for Batteries and Battery Materials 

Materials and battery assemblies may be characterized and optimized for safety by various 

means and techniques. The techniques evaluate the response of materials, electrode formulations, 

cell construction, and battery assemblies to a variety of “off-normal” conditions that simulate 

abusive events, such as mechanical, electrical, and thermal abuse. Characterization of cells 

provides baseline information on safety and abuse tolerance of a given cell chemistry. 

Additionally, battery packs have other failure modes, such as inter-cell shorting, inter-cell 

charging, and cell imbalance that can overcharge or over-discharge a cell or group of cells. 

Therefore, module and pack abuse tests are necessary. 

3.1 Electrochemical Characterization 

Electrochemical stability of materials is the basis of safe behavior of the cell and subsequent 

battery assemblies. Cyclic voltammetry can be used to evaluate the electrochemical stability 

window of materials. Thermodynamic stability of materials in intimate contact within the cell is 

desired but not always realized in high-voltage cells. Kinetic stability can be sufficient to design 

a working electrochemical cell. The solid electrolyte interphase (SEI), the passivation layer that 

forms on Li-ion rechargeable battery anode materials, is an example of kinetic stability being 

sufficient for cell operation. Another example is the lithium/oxyhalide catholyte primary battery 

in which the passivation layer forms on the lithium anode surfaces that provide separation 

between the reactive lithium anode and the liquid cathode. The reaction layer of lithium chloride 

crystals protects the lithium metal from continued contact and the self-discharge that would 

result from further chemical reaction. 

3.2 Thermal Characterization 

Thermal characteristics of cells and batteries are one of the most important aspects of safe cell 

and battery design. Individual materials as well as complete battery modules should be 

characterized to understand failure modes in order to develop improved abuse-tolerant cells and 

batteries. Thermal reactions inside the cells are extremely complex chemical interactions 

between the active materials and electrolyte. Characterization should include determination of 

individual reaction mechanisms, enthalpies, and kinetics. The effects of these material properties 

then need to be measured and confirmed at the materials test level as well as at the cell level for 

various form factors and sizes. There are a number of characterization techniques using both 

commercial analytical instruments and custom test fixtures that can be used to determine these 

cell/battery properties and performance. Calorimetric techniques have been very useful for 

obtaining fundamental, quantitative material properties, while laboratory-scale testing has been 

useful to obtain application-level performance. Several of these techniques are discussed below. 

3.3 Differential Scanning Calorimetry

Differential scanning calorimetry (DSC) is used to understand the effects of thermal abuse on 

battery materials. This technique enables the thermal response of individual and selected 

combinations of cell components to be measured over a broad temperature range while scanning 

at a fixed temperature rate. In favorable cases, this information allows identification of the 

components participating in thermal activity. The DSC technique also allows qualitative 

measurement of the effect of the local charge state of the electrodes, which affects the cell 

thermal reactivity that leads to cell thermal runaway as well as cell self-discharge. DSC can be 

used to measure the reaction enthalpy of various active materials with different electrolyte 

28 
 

 

 

 

 

 

 

 

formulations and also determine activation energies for the observed reactions. Measurements 

can be made on materials from disassembled cells as well as laboratory half-cells, enabling 

detailed characterization of individual electrode changes under controlled conditions. DSC 

techniques are limited to a small sample size, but the chemical reactivity studies can be 

effectively applied to study high-temperature stability. For example, Aurbach and coworkers 

have applied DSC and other techniques35 to clarify decomposition reactions and thermal stability 

of Li-ion battery electrolytes in the temperature range of 40°C to 350°C. 

3.4 Accelerating-Rate Calorimetry

Accelerating-rate calorimeter (ARC) tests are conducted on full cells and cell components under 

adiabatic conditions36 that allow precise control of temperature and expose the cell to more 

uniform conditions. Under adiabatic conditions, the cell heating rate is strictly a function of the 

intrinsic heat generating reactions in the cell and the thermal heat capacitance of the cell 

components. The reaction rate typically starts very slowly and increases through a series of 

accelerating stages until a final high-order thermal runaway is reached. The ARC temperature 

chamber tracks this cell temperature profile even up to high rates of heating. A typical 

experiment requires a few days rather than a few hours, as in the case of the heating block. 

Because of the adiabatic environment, the onset of self-heating due to chemical reactions in the 

interior of the cell can be detected with greater sensitivity. The experiment more closely 

simulates a thermal abuse environment that includes moderately high temperatures for relatively 

long periods. 

Gas generation by the cell during the thermal runaway profile is also a critical property of the 

abuse response of the cell. To maintain adiabatic conditions during cell venting, sealed cell 

fixtures are required to confine the vent gases in the ARC chamber with a minimal expansion 

volume. Pressure monitoring during thermal runaway allows determination of the gas volume 

generation profile in conjunction with the thermal runaway profile. This information is essential 

to understanding the cell and cell component reactions during thermal runaway. 

3.5 Thermal Ramp Test

Thermal stability of cells can be studied by linear programmed heating to cell failure, sometimes 

called a thermal ramp experiment.37 In the thermal ramp experiment, cells are heated at a 

programmed heating rate (5°C/min was typical) from room temperature to 250°C or higher, at 

which temperature the cell fails by initiating thermal runaway. The cells are measured under 

open circuit conditions at different states of charge and are open to the atmosphere to allow 

unconstrained cell venting. The flammability of the vent gases and aerosolized electrolyte can be 

determined by placing spark ignition sources in critical locations around the cell fixture. 

The design of the cell holder is crucial to obtaining relevant data. Thermocouples are placed on 

the cell surface and the cell is wrapped with a layer of thermal insulating material so that the cell 

35 Gnanaraj, J. S.; Zinigrad, E.; Asraf, L.; Gottlieb, H. E.; Sprecher, M.; Schmidt, M.; Geissler, W.; Aurbach, D. “A 

Detailed Investigation of the Thermal Reactions of LiPF6 Solution in Organic Carbonates Using ARC and DSC.”
 

Journal of the Electrochemical Society, 150 A1533–A1537 (2003).
 36 Thermal Hazard Technology home page, http://www.thermalhazardtechnology.com/. Accessed March 2012.
 37 Roth, E. P.; Crafts, C. C.; Doughty, D. H.; McBreen, J. (2004). Advanced Technology Development
 

Program for Lithium-Ion Batteries: Thermal Abuse Performance of 18650 Li-Ion Cells. Sandia Report SAND2004­

0584 March 2004.
 

29 
 

 

 

 

is not closely coupled to the thermal heating block. Thermocouples are then placed between the 

insulating layer and the thermal block. The temperature difference between the cell and the 

thermal block is accurately measured and used to calculate self-heating rate (dT/dt in °C/min). 

The analysis of this data allows determination of the onset of self-heating, vent temperature, 

runaway temperature (defined as dT/dt = 10°C/min for small cells, although thermal runaway 

temperature will be lower for large cells since they cannot dissipate heat efficiently) and cell 

disassembly temperature. This method of determining cell self-heating rate data is not as 

sensitive as ARC data, but is more easily performed. However, heating rate data are only 

qualitative after cell venting due to the uncontrolled heat loss by the vent gases. A well-designed 

cell holder can give reproducible data that complement the quantitative ARC data. 

3.6 Large-Scale Calorimetry

The use of DSC and ARC provide for characterization of the electrodes and cells and the 

response to thermal transients. Larger scale calorimetry (e.g., oxygen consumption calorimetry38) 

can characterize the response of a battery to sustained heating with sufficient airflow to permit 

full combustion of all non-electrochemical materials in addition to promoting reactions of the 

electrochemical couple. The result will invariably produce heat release rates in terms of sustained 

kilowatt and megawatt-size fire events that yield significantly more energy through collateral 

combustion than contained electrically. These thermal release rates provide data for fire 

protection system engineering suitable for production facilities, warehouses, and transportation 

systems. 

For any system with a high prevalence of organic construction (plastic cases, separators) or 

organic solvent electrolytes (as in Li-ion cell technologies), the rate of oxygen consumption may 

be directly correlated to the heat released based on a standard of 13.1 MJ/kg oxygen consumed. 

A combination of radiant flux meters provides all necessary data to support large-scale battery 

failure analysis. 

38 “Standard Practice for Full-Scale Oxygen Consumption Calorimetry Fire Tests.” ASTM International, ASTM 

E2067-08, http://www.astm.org/Standards/E2067.htm . Accessed March 2012. 

30 
 

 

 

 

 

 

 

 

4 Standardized Safety and Abuse Tolerance Test Procedures 

Standardization of tests is crucial to comparing safety and abuse response of batteries. For 

example, a change as simple as the charge current can affect the outcome of overcharge tests.39 

There are a number of standardized test procedures that evaluate the safety and abuse tolerance 

of cells and batteries. The test procedures are adapted to the intended applications. 

4.1 Pass/Fail Battery Abuse Tests

Certain test standards classified as “Pass/Fail” type are designed to analyze and approve battery 

use in given environments. Examples of pass/fail tests include: 

•	 United Nations Testing Protocol UN 38.3 “Recommendations on the Transportation of 

Dangerous Goods”40 is the international standard designed to qualify hazardous materials 

(including batteries) for shipment. 

•	 Underwriters Laboratories Standards UL 1642 and UL 2054.

41 These standards are a 

collection of testing protocols that are intended to qualify lithium metal and Li-ion 

rechargeable cells (1642) and batteries (2054) for use in commercial products. UL is also 

developing a pass/fail standard for EVs and HEVs, UL 2580, “Batteries for Use in 

Electric Vehicles,” which likely will be published in mid-2012. 

•	 SAE International (SAE) Standard J2929 “Electric and Hybrid Vehicle Propulsion 

Battery System Safety Standard – Lithium-based Rechargeable Cells” is under 

development at SAE. The standard defines a minimum set of acceptable safety criteria for 

a lithium-based rechargeable battery system to be considered for use in a vehicle 

propulsion application as an energy storage system connected to a high-voltage power 

train. It will likely be published in the first few months of 2012. 

•	 Institute of Electrical and Electronics Engineers (IEEE) Standards #1625-2008 and 

#1725-200642 titled “IEEE Standard for Rechargeable Batteries for Multi-Cell Mobile 

Computing Devices” and “IEEE Standard for Rechargeable Batteries for Cellular 

Telephones,” respectively. 

4.2 Characterization Battery Abuse Tests

Other standards are “characterization” type standards and are designed to evaluate the response 

of batteries to specific “off-normal” conditions that might be expected to occur, although very 

infrequently, during use. Examples are: 

39 Yoshida, T.; Kitoh, K.; Ohtsubo, S.; Shionoya, W.; Katsukawa, H.; Yamaki, J-I. (2007). Electrochemical and 

Solid-State Letters, 10 A60–A64. 

40 http://www.unece.org/trans/danger/danger.html 

41 UL 1642 Standard. “Lithium Batteries.” http://ulstandardsinfonet.ul.com/scopes/scopesnew.asp?fn=1642.html 

42 IEEE Standard #1625-2008, http://standards.ieee.org/findstds/standard/1625-2008.html; IEEE Standard #1725­

2006, http://standards.ieee.org/findstds/standard/1725-2006.html 

31 
 

 

 

 

 

 

 

 

 

 

 

•	 SAE J246443 “EV & HEV Rechargeable Energy Storage System (RESS) Safety and 

Abuse Testing Procedure” evaluates abuse tolerance of cells and battery packs for electric 

vehicles. The hazard severity level observed in the test is input to a risk management 

approach44 that combines probability and severity of occurrence to develop a hazard risk 

number for vehicular applications. 

•	 USABC has published safety and abuse tolerance test procedures 45 that were developed 

at Sandia National Laboratories (SNL) for EVs and HEVs. 

•	 NAVSEA S931046 is a U.S. Navy-published test protocol, “Technical Manual for 

Batteries, Navy Lithium Safety Program Responsibilities and Procedures,” that addresses 

the safety of any type of lithium cell or battery that would be used by Navy and Marine 

Corps activities on any type of vessel or aircraft. The purpose of the manual is broader in 

that abuse testing has the goal to “establish safety guidelines for the selection, design, 

testing, evaluation, use, packaging, storage, transportation, and disposal of lithium 

batteries.” 

•	 IEC47 – The International Electrotechnical Commission has published safety and abuse 

tolerance test for shipping (IEC 62281) and use in portable applications (IEC 62133) and 

is developing a new standard for cells that will be used in vehicles (IEC 62660-02 

“Secondary Batteries for The Propulsion of Electric Road Vehicles”). 

•	 ISO48 – The International Organization for Standardization is developing a new test 

standard for battery systems that will be used in vehicles (ISO/CD 12405-2 “Electrically 

Propelled Road Vehicles — Test Specification for Lithium-ion Traction Battery Packs 

and Systems”). 

•	 EUCAR49 – European Council for Automotive R&D has established performance 

standards, particularly the EUCAR Severity Hazard Levels and Descriptions50 that are 

widely used to characterize the response of test articles to abuse tests. 

•	 VDA51 – The Verband der Automobilindustrie e.V. is a German interest group supporting 

the German automobile industry. VDA published a series of standards and 

43 SAE J2464. (2009). “EV & HEV Rechargeable Energy Storage System (RESS) Safety and Abuse Testing 

Procedure.” Published 11/06/2009 by SAE International and available from www.sae.org
 44 Ashtiani, C. (2008). “Analysis of Battery Safety and Hazards’ Risk Mitigation.” Electrochemical Society 

Transactions, 11 (19), 1 (2008).
 45 “USCAR: USABC Manuals.” USCAR. http://www.uscar.org/guest/article_view.php?articles_id=86. Last
 

accessed March 2012.
 46 “Technical Manual for Batteries, Navy Lithium Safety Program Responsibilities and Procedures.” NAVSEA 

S9310-AQ-SAF-010. http://www.everyspec.com/USN/NAVSEA/NAVSEA_S9310-AQ-SAF-010_4137/
 47 International Electrotechnical Commission (IEC)., http://www.iec.ch/. 48 International Organization for Standardization (ISO). http://www.iso.com/. 49 European Council for Automotive R&D (EUCAR). http://www.eucar.be/. 50 Josefowitz, W., et al. (2005). “Assessment and Testing of Advanced Energy Storage Systems for Propulsion–
 

European Testing Report.” 21st Worldwide Battery, Hybrid and Fuel Cell Electric Vehicle Symposium & Exhibition
 

Proceedings. Monaco, EU. April 2–6, 2005.
 51 Verband der Automobilindustrie (VDA). http://www.vda.de/en/index.html. 

32 
 

 

 

 

 

 

 

 

 

 

 

recommendations. Among those is “Test Specification for Li-ion Battery Systems for 

Hybrid Electric Vehicles,” March 2007. 

•	 JARI52 – The Japan Automobile Research Institute is developing battery safety and 

abuse test standards. 

•	 JIS53– Japanese Industrial Standard JIS C 8714, “Safety Tests for Portable Li-Ion
 

Secondary Cells and Batteries for Use in Portable Electronic Applications.”
 

•	 National Aeronautics and Space Administration (NASA) – When a battery-powered 

system to be used in manned space flight is being designed, NASA recommends 

reference document JSC-20793, “Crewed Space Vehicle Battery Safety Requirements,” 

issued by the NASA Engineering Directorate’s Energy Systems Division.54 Its purpose is 

to define hazard sources, discuss typical system safety measures, and identify issues 

inherent to battery chemistries. As a high-level best-practices design guideline, the 

document does not contain detailed information on test and qualification procedures. 

NASA requires a two-fault tolerance. The document takes this definition in a slightly 

different direction by defining categories of failure for critical equipment. It specifies 

ways in which critical equipment react to the first failure and then to the second failure. 

In this way, equipment can actually cease to function after the first failure as long as it 

does not affect the mission (no damage to equipment, no contingency or emergency 

procedures required). The second failure must be controlled, such that there is no injury 

to personnel and no loss of vehicle or ground facilities. 

Another approach is to incorporate design guidance information in the test standard. An example 

of this is IEEE 1625, which is a 93-page standard that provides recommendations and guidelines 

for cell fabrication and assembly techniques. UL documents often contain a lesser degree of 

design guidance that supplements the test protocols. 

Each standard anticipates use and abuse conditions and develops tests accordingly. Overview 

comparisons between these standards are given in Table 2 and Table 3. It is interesting to note 

that test parameters are sometimes very consistent (e.g., high-altitude simulation requires a 

reduced pressure that is equivalent to 50,000 ft altitude), but others are either completely absent 

or have quite different experimental test conditions. 

52 Japan Automobile Research Institute (JARI). http://www.jari.or.jp/english/.
 53 Japanese Industrial Standards Committee, http://www.jisc.go.jp/eng/index.html. 54 “Design Guidelines Safety Philosophies, Hazard Control, and Safety Verification.” University of Colorado 

Engineering School course notes, http://www.colorado.edu/engineering/ASEN/asen5519/06design-guidelines.htm.
 

33 
 

 

 

 

 

 

 

 

 

 

 

 

Table 2. Comparison of Standard Test Procedures from UN, UL, IEEE, and U.S. Navy

Simplified Comparison Omits Many Test Details. 

Shipping Usage 

Test Title Cell & Pack Testing Cell Testing Cell & Pack Testing 

Portable Electronic Applications Military Applications 

SHIPPING 

UN Manual 

of Tests & 

Criteria 

Canada 

Shipping 

Permit 

SH-6153 

UL 1642 UL 2054 Household and IEEE 1625 IEEE 1725 Japan JIS C8714 "Safety tests for NAVSEA MIL-PRFLithium Commercial Batteries Laptop Cell Phone Portable Li Ion cells and batteries S9310-AQ­ 32052 

Batteries Rech. Rech. for use in portable electronics" SAF-010 

Batteries Batteries 

Altitude T1. 6 hr @ 

0.11 atm 

6 hr @ 

0.11 atm 

6 hr @ 

0.11 atm 

6 hr @ 

0.11 atm 

Hazardous 

Substance 

Monitoring 

Temperature 

Cycling 

(Thermal 

Shock) 

T2. 10 cycles 

of 

6 hr @ 75°C 

& -40°C 

2 cycles of 

6 hr @ 

75°C & ­

40°C 

10 cycles of 6 

hr @ 

70°C & -40°C 

10 cycles of 6 hr @ 

70°C & -40°C 

5 cycles of 

4 hr @ 

75°C & ­

20°C 

Compromise of 

Thermal 

Insulation 

High 

Temperature 

130°C for 10 

min 

130°C for 10 min 130°C for 

10 min 

130°C for 60 

min 

Ramp at 5°C/min to 130°C. Hold for 

10 min. 5 each that were charged at 

the highest temperature and the 

lowest temperature. 

500°C for 60 

min 

Vibration T3. 12 reps 

up to 

8 g peak 

10 to 55 Hz at 

1 Hz/min 

The frequency is to be 

varied at the rate of 1 

hertz per minute between 

10 and 55 hertz and 

return in not less than 90 

nor more than 100 

minutes. The battery is to 

be tested in three 

mutually perpendicular 

directions. 

10 to 55 Hz 

at 1 Hz/min 

10 to 55 Hz at 

1 Hz/min 

Mechanical 

Shock 

T4. 3 ea 

150g shocks 

for cells, 50g 

shocks for 

3 ea 150g 

shocks 

3 ea 125-175g 

shocks 

3 each x 3 axes: 3 ms 

with the min. average 

acceleration is 75 g 

(peak acceleration shall 

3 ea 125­

175g 

shocks 

3 ea 40g 

shocks 

34 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Shipping Usage 

Test Title Cell & Pack Testing Cell Testing Cell & Pack Testing 

Portable Electronic Applications Military Applications 

SHIPPING 

UN Manual 

of Tests & 

Criteria 

Canada 

Shipping 

Permit 

SH-6153 

UL 1642 UL 2054 Household and IEEE 1625 IEEE 1725 Japan JIS C8714 "Safety tests for NAVSEA MIL-PRFLithium Commercial Batteries Laptop Cell Phone Portable Li Ion cells and batteries S9310-AQ­ 32052 

Batteries Rech. Rech. for use in portable electronics" SAF-010 

Batteries Batteries 

modules and 

packs. 

be between 125 and 175 

g) 

External Short 

Circuit 

T5. less than 

100 mΩ at 

55 C 

less than 

100 mΩ at 

55 C 

less than 100 

mΩ at 

20 C & 55 C 

80 ±20 m ohm at both 20 

±5°C and at 55 ±2°C 

less than 

100 mΩ at 

20 C & 55 

C 

less than 50 

mΩ at 55°C 

Circuit resistance = 80 +/- 20 mOhm 

at 55°C for 24 hr. 5 cells each that 

were charged at the highest 

temperature and the lowest 

temperature AND 5 packs each that 

were charged at the highest 

temperature and the lowest 

temperature. 100% SOC. 

less than 20 

mΩ at 

20 C 

at 20 C 

External Short 

Circuit On 

Cycled Cells 

less than 50 

mΩ at 55°C 

less than 20 

mΩ at 

20 C 

Partial Short 

Circuit 

Impact T6. 9.1 kg 

from 61 cm. 

9.1 kg from 61 

cm. 

A 9.10 ±0.46 kg (20 ±1 

pound) weight is to be 

dropped from a height of 

610 ±25 mm (24 ±1 inch) 

onto the sample. 

Overcharge T7. Charge 

to 200% SOC 

to 250% SOC to 150% SOC at room 

temperature. 

to 250% 

SOC 

20 reps to 

125% max 

voltage 

to 400% SOC 

Overcharge 

Protection 

Evaluation 

One cell in a battery is forced 

discharge and current follow is 

measured between cells. 1 battery. 

100% SOC. 

Forced 

Discharge 

(Overdischarge) 

T8. 

Discharge to ­

100% SOC 

to -100% SOC Place one discharged 

cell in a string of charged 

cells, and discharge the 

pack (to -100% SOC). 

to -150% 

SOC 

20 reps to ­

25% SOC 

to -100% 

SOC 

35 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Shipping Usage 

Test Title Cell & Pack Testing Cell Testing Cell & Pack Testing 

Portable Electronic Applications Military Applications 

SHIPPING 

UN Manual 

of Tests & 

Criteria 

Canada 

Shipping 

Permit 

SH-6153 

UL 1642 UL 2054 Household and IEEE 1625 IEEE 1725 Japan JIS C8714 "Safety tests for NAVSEA MIL-PRFLithium Commercial Batteries Laptop Cell Phone Portable Li Ion cells and batteries S9310-AQ­ 32052 

Batteries Rech. Rech. for use in portable electronics" SAF-010 

Batteries Batteries 

Crush 3000 lbs. force 13 kN force Use Force of 13 +/- 1 kN between flat 

surfaces or up to 10% deformation. 

5 cells each that were charged at the 

highest temperature and the lowest 

temperature. 100% SOC. 

Open Flame 

Test (Fuel Fire 

or "Projectile") 

A cell 

contained in a 

wire cage is 

heated from 

below by a 

burner flame ­

No Projectiles 

A cell contained in a wire 

cage is heated from 

below by a burner flame ­

No Projectiles 

A cell 

contained in a 

wire cage is 

heated from 

below by a 

burner flame ­

No Projectiles 

Float Charge 28 days at 

20°C and 

100% SOC 

(float 

charge) 

Cell Balance within 5% 

Cycle Life Meet cell 

performance 

specs. 

High Rate 

Discharge w/o 

Cooling 

Meet cell 

performance 

specs. 

Low 

Temperature 

depends on 

application 

Retention of 

Charge 

94% retention 

- depends on 

application 

Drop Test from 1 meter in an 

orientation so it strikes a 

from 1 

meter 

Height of drop specified by JIS C6950 

or C6065. 5 cells each that were 

36 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

Shipping Usage 

Test Title Cell & Pack Testing Cell Testing Cell & Pack Testing 

Portable Electronic Applications Military Applications 

SHIPPING 

UN Manual 

of Tests & 

Criteria 

Canada 

Shipping 

Permit 

SH-6153 

UL 1642 UL 2054 Household and IEEE 1625 IEEE 1725 Japan JIS C8714 "Safety tests for NAVSEA MIL-PRFLithium Commercial Batteries Laptop Cell Phone Portable Li Ion cells and batteries S9310-AQ­ 32052 

Batteries Rech. Rech. for use in portable electronics" SAF-010 

Batteries Batteries 

concrete surface 

in the position that is 

most likely to produce the 

adverse results 

charged at the highest temp. and the 

lowest temp. 100% SOC. 3 

batteries. 100% SOC. 

Separator 

Shutdown 

>100x 

resistance 

after shutdown 

Separator High 

Temperature 

Stability 

150°C for 10 

min 

High 

Temperature 

Storage 

Nail Penetration 

Internal short 

circuit 

Foreign particle (L-shaped Ni 

02.x0.1x1 mm^3) is inserted into 

charged cell in 2 places – a) between 

pos active and neg active and b) 

between Al foil and neg active 

material. Place cell into pressing jig 

and press at 0.1 mm/s until 50 mV 

drop or 800 N force is achieved. 

Height of drop specified by JIS C6950 

or C6065. 5 cells each that were 

charged at the highest temperature 

and the lowest temperature. 100% 

SOC. 

Roll-Over 

Immersion 

Humidity 

Exposure 

37 
 

 

 

 

 

 

 

 

 

 

 

Shipping Usage 

Test Title Cell & Pack Testing Cell Testing Cell & Pack Testing 

Portable Electronic Applications Military Applications 

SHIPPING 

UN Manual 

of Tests & 

Criteria 

Canada 

Shipping 

Permit 

SH-6153 

UL 1642 UL 2054 Household and IEEE 1625 IEEE 1725 Japan JIS C8714 "Safety tests for NAVSEA MIL-PRFLithium Commercial Batteries Laptop Cell Phone Portable Li Ion cells and batteries S9310-AQ­ 32052 

Batteries Rech. Rech. for use in portable electronics" SAF-010 

Batteries Batteries 

(Dewing) 

Extreme Cold 

Temperature 

Propagation 

Resistance 

Fault Analysis Recommended 

Elec. Safety 

Device 

20 reps to 

125% max 

voltage and ­

25% SOC 

with 

protection in 

place 

Abusive 

Overcharge 

Charge at 2C -rate with 

protective devices in 

place. 

Overdischarge 

Protection 

Evaluation 

250 N Steady 

Force Test 

External enclosures of 

the battery pack are to be 

subjected to a steady 

force of 250 ±10 N (56 ±2 

pounds force) for a 

period of 5 seconds, to 

the top, bottom and sides 

of the battery pack. 

Mold Stress 

Relief Test 

The samples (fully 

discharged) are to 

remain in the oven at 

70°C (158°F) for 7 hours. 

38 
 

 

 

 

 

 

Shipping Usage 

Test Title Cell & Pack Testing Cell Testing Cell & Pack Testing 

Portable Electronic Applications Military Applications 

SHIPPING 

UN Manual 

of Tests & 

Criteria 

Canada 

Shipping 

Permit 

SH-6153 

UL 1642 UL 2054 Household and IEEE 1625 IEEE 1725 Japan JIS C8714 "Safety tests for NAVSEA MIL-PRFLithium Commercial Batteries Laptop Cell Phone Portable Li Ion cells and batteries S9310-AQ­ 32052 

Batteries Rech. Rech. for use in portable electronics" SAF-010 

Batteries Batteries 

Battery Pack 

Component 

Temperature 

Test 

A battery pack 

temperature should be 

<75°C under charge and 

discharge. 

Battery Pack 

Surface 

Temperature 

Test 

During Charge & 

discharge, accessible 

parts should be below 

55°C (metal) or 75°C 

(plastic). 

39 
 

 

 

 

 

 

Table 3. Comparison of Standard Test Procedures from SAE, USABC, IEC, and ISO

Simplified Comparison Omits Many Test Details. 

Usage 

Test Title Cell & Pack Testing 

Automotive Applications 

SAE J2464 2009 

HEV and EV 

Battery Abuse 

Tests 

FreedomCAR 

EESS Abuse 

Test Manual 

(SAND2005­

3123) 

SAE J2929 

Electric and 

Hybrid Vehicle 

Propulsion Battery 

System Safety 

Standard – Libased 

Rechargeable 

Cells 

IEC 62660-2 

Secondary 

lithium-ion cells 

for the 

propulsion of 

electric road 

vehicles – Part 

2: Reliability and 

abuse testing 

ISO/CD 12405 

Electrically 

propelled road 

vehicles — Test 

specification for 

lithium-ion 

traction battery 

packs and 

systems 

UL 2580 

"Batteries for 

Use in Electric 

Vehicles" 

Korea 

MVSS 18-3 

"Driving 

Battery 

Safety 

Test" 

India AIS-048 

"Battery 

Operated 

Vehicles ­

Safety 

Requirements 

of Traction 

Batteries" 

Altitude 

Hazardous 

Substance 

Monitoring 

Analysis of 

electrolyte vapors 

and airborne 

volatiles and 

particulates 

released during 

abuse tests 

Toxic emissions 

through openings 

other than 

exhaust openings 

during testing are 

not allowed or 

limited to ERPG-2 

levels or OSHA 

TWAs. 

Temperature 

Cycling 

(Thermal 

Shock) 

5 cycles between 

70°C & -40°C ­

hold cells for 1 

hour, hold 

modules and 

packs for 6 hours. 

5 cycles between 

@ 80C & -40°C ­

hold cells for 1 

hour, hold 

modules and 

packs for 6 

hours. 

J2464 or UN T2 

testing are 

acceptable. 

30 cycles 

between T(min) 

and T(max). 

Repeat series of 

cycles between 

65 °C and -20 °C 

at various SOC 

for EV and HEV. 

with all thermal 

controls disabled, 

thermally cycle the 

DUT between 

85 °C or Tmax (as 

specified between 

supplier and 

customer) and ­

40 °C 

A fully charged 

electrical energy 

storage assembly 

(MOSOC per 6.1) 

shall be subjected 

to the thermal 

shock test of SAE 

J2464, except 

that the 

temperature 

extremes are 

from 85 ±2°C to 

−40 ±2°C. 

Compromise 

of Thermal 

Insulation 

40 
 

 

 

 

 

 

Test Title 

SAE J2464 2009 FreedomCAR SAE J2929 

HEV and EV EESS Abuse Electric and 

Test Manual 

Tests 

3123) 

Standard – Libased 

Cells 

High Determine ARC test or 

Temperature maximum thermal ramp to 

temperature at 200°C ­

which cell is determine selfstable indefinitely. heating rate 

Vibration See J2380 The r.m.s. UN Test Manual, 

acceleration Test T.3 (12 reps 

value shall be up to 8 g peak) or 

27,8 m/s2. SAE J2380 for full 

system. Subsystem 

testing must be 

followed by vehicle 

vibration test. 

Mechanical 18 ea. 25g shocks Combined with UN Test Manual, 

Shock = XYZ negative & Vibration Test T4; or SAE 

positive directions J2464, Section 

x 3 times. 4.3.1 OR during 

crash vehicle tests 

simulating front, 

rear and side 

impacts, as defined 

in FMVSS 305, 

S6.1, 6.2, 6.3 

Usage 

Cell & Pack Testing 

Automotive Applications 

Battery Abuse 

(SAND2005­

Hybrid Vehicle 

Propulsion Battery 

System Safety 

Rechargeable 

Secondary 

propulsion of 

2: Reliability and 

ISO/CD 12405 

Electrically 

propelled road 

specification for 

traction battery 

packs and 

"Driving 

Battery 

Safety 

"Battery 

Operated 

Safety 

Requirements 

UL 2580 Korea India AIS-048 

"Batteries for MVSS 18-3 

Use in Electric 

Vehicles"
 Vehicles ­

Test" 

of Traction 

Batteries" 

A sample is The battery 

subjected to a module shall be 

vibration subjected to 

endurance test in sinusoidal 

accordance with vibration for at an 

the anticipated acceleration of 3 

end application g in both the axis 

vehicle vibration and a frequency 

profile. In the of 30-150 Hz at a 

absence of this sweep rate of 1 

information, SAE octave per 

J2380 shall be minute. Testing 

used. is to be carried 

out for 2 hours in 

each axis. 

A fully charged The battery shall 

sample is to be be subjected to 

subjected to the the 10 shocks in 

Shock Test in each axis in halfaccordance with sine wave, 30 g 

SAE J2464, with amplitude and 15 

the parameters as ms duration. 

outlined in Table 

24.1 (half sine 

wave, 25 g for 15 

sec). 18 repeats. 

IEC 62660-2 

lithium-ion cells
 

for the
 

electric road
 

vehicles – Part 

abuse testing
 

130°C for 30 min 

Perform the test 

referring to IEC 

60068-2-64 

random vibration. 

500 m/s2 (50g) 6 

msec. 60 ea. = 

XYZ negative & 

positive directions 

x 10 times. HEV 

at 80% SOC and 

EV at 100% SOC 

vehicles — Test 

lithium-ion 

systems 

Perform the test 

according to IEC 

60068-2-64 

random vibration. 

Use test duration 

of 8 h for each 

plane of the DUT. 

The r.m.s. 

acceleration value 

shall be 27,8 m/s2. 

Perform the test 

according to ISO 

16750-3 (500 m/s2 

(50g) 6 msec). 

41 
 

 

 

 

 

 

 

 

 

 

 

Usage 

Test Title Cell & Pack Testing 

Automotive Applications 

SAE J2464 2009 

HEV and EV 

Battery Abuse 

Tests 

FreedomCAR 

EESS Abuse 

Test Manual 

(SAND2005­

3123) 

SAE J2929 

Electric and 

Hybrid Vehicle 

Propulsion Battery 

System Safety 

Standard – Libased 

Rechargeable 

Cells 

IEC 62660-2 

Secondary 

lithium-ion cells 

for the 

propulsion of 

electric road 

vehicles – Part 

2: Reliability and 

abuse testing 

ISO/CD 12405 

Electrically 

propelled road 

vehicles — Test 

specification for 

lithium-ion 

traction battery 

packs and 

systems 

UL 2580 

"Batteries for 

Use in Electric 

Vehicles" 

Korea 

MVSS 18-3 

"Driving 

Battery 

Safety 

Test" 

India AIS-048 

"Battery 

Operated 

Vehicles ­

Safety 

Requirements 

of Traction 

Batteries" 

External Short 

Circuit 

Perform 2 short 

circuit tests: a 

hard short (≤ 5 

mOhm) and 

moderate short at 

a resistance 

comparable to the 

test article 

resistance at 

25 °C ± 5 °C. 

Apply a ‘hard 

short’ of ≤5 mΩ 

in less than one 

second; hold for 

10 minutes at 20 

C 

UN Test Manual, 

Test T.5; or the 

pack hard short 

circuit condition 

defined in SAE 

J2464, Section 

4.5.1. With 

flammable gas 

monitoring. 

≤5 m ohm for 10 

min. at 20 C. The 

sample rate for 

voltage and 

current recording 

shall be ≤ 10 ms 

Use an 

appropriately 

sized conductor of 

≤100 mΩ to apply 

a ‘hard short’ in 

less than one 

second for 10 

minutes 

Total circuit 

resistance less 

than or equal to 

20 mOhm. 

Testing is 

repeated at a load 

that draws a 

maximum current 

no less than 15% 

below the 

operation of the 

short circuit 

protection 

Resistance 

= 50mΩ for 

1 hour or 

when 

current does 

not flow for 

5 minutes. 

SOC 80% 

less than or 

equal to 5 mOhm 

for 10 minutes, or 

for systems with 

less than 0.9 

m/V system 

voltage ± 0.1m 

internal 

resistance, a 

conductor of 

equal or less 

than 1/10 of the 

minimum 

resistance of the 

cell/module shall 

be used. 

External Short 

Circuit On 

Cycled Cells 

Partial Short 

Circuit 

Incorporated into 

External Short 

Circuit. 

Pack response 

to short in cell or 

string. 

Impact 

42
 
 

 

 

 

 

 

 

 

Test Title 

SAE J2464 2009 FreedomCAR SAE J2929 

HEV and EV EESS Abuse Electric and 

Test Manual 

Tests 

3123) 

Standard – Libased 

Cells 

Overcharge Cells should be 32 A to 200% "Single Point 

charged at two SOC Overcharge 

rates: a) 1 C-Rate Protection System 

constant current Failure" to simulate 

and b) at the single point failure 

maximum use of battery system 

current to 200% charge control 

SOC system when the 

battery system 

charge device is no 

longer being 

controlled. With 

flammable gas 

monitoring. 

Overcharge 

Protection 

Evaluation 

Usage 

Cell & Pack Testing 

Automotive Applications 

Battery Abuse 

(SAND2005­

Hybrid Vehicle 

Propulsion Battery 

System Safety 

Rechargeable 

Secondary 

propulsion of 

2: Reliability and 

ISO/CD 12405 

Electrically 

propelled road 

specification for 

traction battery 

packs and 

"Driving 

Battery 

Safety 

"Battery 

Operated 

Safety 

Requirements 

UL 2580 Korea India AIS-048 

"Batteries for MVSS 18-3 

Use in Electric 

Vehicles"
 Vehicles ­

Test" 

of Traction 

Batteries" 

Imbalanced Charge to To 200 % SOC 

Charging Test. 1.5 times by charging at a 

One module at the nominal constant 

approximately voltage with charging current 

50% of its 32 A of 0.1(C10) A 

specified state of constant value for a test 

charge, while all current. duration of ten 

other modules at End hours is 

o% SOC. Charge charging reached. 

according to when SOC 

manufacturer's 150% is 

recommendations reached. 

. 

Charge the test 

sample according 

to manufacturer 

instructions. 

Charge is 

terminated by the 

protective 

circuitry. 

IEC 62660-2 

lithium-ion cells 

for the 

electric road 

vehicles – Part 

abuse testing 

Charge until the 

cell voltage 

reaches 2X 

maximum 

voltage, or 200 % 

SOC 

vehicles — Test 

lithium-ion 

systems 

Continue charging 

until the DUT fails 

or until it reaches 

200% SOC, 

depending on the 

agreement 

between the test 

team and the 

manufacturer. 

The 

recommended 

charge current is 

32 A (but can be 

modified). The 

upper limit for the 

power-supply 

voltage 

determined by 

actual hardware. 

43 
 

 

 

 

Usage 

Test Title Cell & Pack Testing 

Automotive Applications 

SAE J2464 2009 

HEV and EV 

Battery Abuse 

Tests 

FreedomCAR 

EESS Abuse 

Test Manual 

(SAND2005­

3123) 

SAE J2929 

Electric and 

Hybrid Vehicle 

Propulsion Battery 

System Safety 

Standard – Libased 

Rechargeable 

Cells 

IEC 62660-2 

Secondary 

lithium-ion cells 

for the 

propulsion of 

electric road 

vehicles – Part 

2: Reliability and 

abuse testing 

ISO/CD 12405 

Electrically 

propelled road 

vehicles — Test 

specification for 

lithium-ion 

traction battery 

packs and 

systems 

UL 2580 

"Batteries for 

Use in Electric 

Vehicles" 

Korea 

MVSS 18-3 

"Driving 

Battery 

Safety 

Test" 

India AIS-048 

"Battery 

Operated 

Vehicles ­

Safety 

Requirements 

of Traction 

Batteries" 

Forced 

Discharge 

(Overdischarge) 

Cell test to -100% 

SOC and 

additional module 

test. 

C/1 rate for 1.5 

hours (Average 

SOC will be ­

50%), or until 

50% of all 

subassemblies 

(for module- or 

pack-level tests) 

have achieved 

voltage reversal 

for 15 minutes. 

"Single Point Over 

Discharge 

Protection System 

Failure" to simulate 

single point failure 

of battery system 

charge control 

system when the 

battery system 

discharge load is no 

longer being 

controlled. With 

flammable gas 

monitoring. 

reverse charge at 

1 C for 90 min. on 

a discharged cell 

resulting in -150% 

SOC 

C/1 rate for 1.5 

hours (Average 

SOC will be -50%) 

or until 25% of the 

nominal voltage 

level has 

achieved. 

From 0% 

SOC, 

discharge 

the driving 

battery with 

1C for 30 

minutes = ­

150% SOC. 

44
 
 

 

 

 

 

 

 

 

 

Usage 

Test Title Cell & Pack Testing 

Automotive Applications 

SAE J2464 2009 

HEV and EV 

Battery Abuse 

Tests 

FreedomCAR 

EESS Abuse 

Test Manual 

(SAND2005­

3123) 

SAE J2929 

Electric and 

Hybrid Vehicle 

Propulsion Battery 

System Safety 

Standard – Libased 

Rechargeable 

Cells 

IEC 62660-2 

Secondary 

lithium-ion cells 

for the 

propulsion of 

electric road 

vehicles – Part 

2: Reliability and 

abuse testing 

ISO/CD 12405 

Electrically 

propelled road 

vehicles — Test 

specification for 

lithium-ion 

traction battery 

packs and 

systems 

UL 2580 

"Batteries for 

Use in Electric 

Vehicles" 

Korea 

MVSS 18-3 

"Driving 

Battery 

Safety 

Test" 

India AIS-048 

"Battery 

Operated 

Vehicles ­

Safety 

Requirements 

of Traction 

Batteries" 

Crush Crush to 85% of 

the initial 

dimension; hold 

for 5 min. & 

continue the crush 

to 50% . 

to 85% of the 

initial dimension; 

hold for 5 min. & 

continue the 

crush to 50% . 

Option 1: SAE 2464 

except: Crush 

condition shall 

simulate the 

expected battery 

enclosure intrusion 

for each of the 

conditions defined 

in FMVSS 305, 

S6.1, 6.2 & 6.3. 

Option 2: SAE 

J2464 except: crush 

termination at a 

force of 100 kN. 

Option 3: during 

vehicle crash tests 

simulating front, 

rear and side 

impacts, as defined 

in FMVSS 305, 

S6.1, 6.2, 6.3 

Crush to 85% of 

the initial 

dimension or the 

force of 1000 

times the weight 

of cell applied or 

until voltage drop 

of 1/3 of the 

original cell 

voltage occurs. 

Use a sphere or 

hemisphere with 

a 150 mm dia. 

(for a prismatic 

cell) or the round 

bar 150 mm dia. 

(for crush a 

cylindrical cell). 

HEV at 80% SOC 

& EV at 100% 

SOC. 

A sample shall be 

crushed between 

a fixed surface 

and a ribbed test 

platen in 

accordance with 

the test fixture 

described in SAE 

J2464. Crush all 

3 axes. 

Exceptions: max 

force = 100 kN. 

The DUT may be 

installed in a 

protective 

framework 

representative of 

what is provided 

in the vehicle. 

45
 
 

 

 

Battery Abuse 

(SAND2005­

Hybrid Vehicle 

Propulsion Battery 

System Safety 

Rechargeable 

Secondary 

propulsion of 

2: Reliability and 

ISO/CD 12405 

Electrically 

propelled road 

specification for 

traction battery 

packs and 

"Driving 

Battery 

Safety 

"Battery 

Operated 

Safety 

Requirements 

Open Flame 

Test (Fuel Fire 

or "Projectile") 

Test Title 

SAE J2464 2009 

HEV and EV 

Tests 

10 min at 890°C ­

Simulate fuel fire 

Float Charge 

FreedomCAR 

EESS Abuse 

Test Manual 

3123) 

10 min at 890°C 

- Simulate fuel 

fire 

60 days at 40°C, 

60°C and 80C at 

20% SOC, 50% 

SOC and 20% 

SOC, 50% SOC 

and 100% SOC 

(float charge) 

Usage 

Cell & Pack Testing 

Automotive Applications 

IEC 62660-2 

lithium-ion cells 

for the vehicles — Test 

electric road lithium-ion
 

vehicles – Part 

abuse testing systems 

high temperature uniform fire directly 

heat and flame source along the above 

environment until length of the flame. 

the battery system assembly at its Apply heat 

is fully involved in 

the fire. 

bottom surface. 

Within 5 min of 

between 

890°C and 

Procedures ignition, at least 900°C for 2 

described in SAE one thermocouple minutes to 

J2464 (Section shall indicate a the bottom 

4.4.1), ECE R34 minimum of the 

(Annex 5, Sections temperature of driving 

5.3-5.8), SAE 590°C (1094°F). battery. 

J2579 (Appendix The test is SOC 80%. 

C.8), or FMVSS concluded when 

304 (S8.3) are this minimum 

allowed. temperature 

indication of 

590°C (1094°F) 

has been 

maintained for 20 

min. 

SAE J2929 

Electric and 

Standard – Libased 

Cells 

The complete 

battery system is to 

be subjected to a 

UL 2580 

"Batteries for 

Use in Electric 

Vehicles" 

A fully charged 

DUT shall be 

subjected to a 

Korea 

MVSS 18-3 

Test" 

Install the 

driving 

battery 

India AIS-048 

Vehicles ­

of Traction 

Batteries" 

46 
 

 

 

 

 

Usage 

Test Title Cell & Pack Testing 

Automotive Applications 

SAE J2464 2009 

HEV and EV 

Battery Abuse 

Tests 

FreedomCAR 

EESS Abuse 

Test Manual 

(SAND2005­

3123) 

SAE J2929 

Electric and 

Hybrid Vehicle 

Propulsion Battery 

System Safety 

Standard – Libased 

Rechargeable 

Cells 

IEC 62660-2 

Secondary 

lithium-ion cells 

for the 

propulsion of 

electric road 

vehicles – Part 

2: Reliability and 

abuse testing 

ISO/CD 12405 

Electrically 

propelled road 

vehicles — Test 

specification for 

lithium-ion 

traction battery 

packs and 

systems 

UL 2580 

"Batteries for 

Use in Electric 

Vehicles" 

Korea 

MVSS 18-3 

"Driving 

Battery 

Safety 

Test" 

India AIS-048 

"Battery 

Operated 

Vehicles ­

Safety 

Requirements 

of Traction 

Batteries" 

Cell Balance 

Cycle Life 

High Rate 

Discharge w/o 

Cooling 

With active 

thermal controls 

disabled, twenty 

(20) full 

charge/discharge 

cycles at 

maximum 

expected rate with 

no rest period 

With active 

thermal controls 

disabled, twenty 

(20) full 

charge/discharge 

cycles at 3-kW 

constant power 

rate with no rest 

period 

Tested in 

accordance with 

SAE J2464 with 

min/maximum SOC 

defined by 

operational cycles. 

With flammable gas 

monitoring. 

Active thermal 

controls (primary 

and secondary) 

disabled. One full 

charge/discharge 

cycles should be 

performed as 

followed by a rest 

period of 7 hours 

between charge 

and discharge. 

Low 

Temperature 

Retention of 

Charge 

47
 
 

 

 

Battery Abuse 

(SAND2005­

Hybrid Vehicle 

Propulsion Battery 

System Safety 

Rechargeable 

Secondary 

propulsion of 

2: Reliability and 

ISO/CD 12405 

Electrically 

propelled road 

specification for 

traction battery 

packs and 

Korea 

MVSS 18-3 

"Driving 

Battery 

Safety 

Test" 

"Battery 

Operated 

Safety 

Requirements 

Drop Test Drop from 2 

meters on the 

most vulnerable 

location. 

free fall from 

a height of 

4.9 m to a 

concrete 

Test Title 

SAE J2464 2009 

HEV and EV 

Tests 

Apply 20+ volts at 

5 °C above the 

measured 

shutdown 

temperature 

FreedomCAR 

EESS Abuse 

Test Manual 

3123) 

from 10 meters 

See Float 

Charge 

Usage 

Cell & Pack Testing 

Automotive Applications 

IEC 62660-2 

lithium-ion cells 

for the vehicles — Test 

electric road lithium-ion
 

vehicles – Part 

abuse testing systems 

Separator 

Shutdown 

Separator 

High 

Temperature 

Stability 

High 

Temperature 

Storage 

SAE J2929 

Electric and 

Standard – Libased 

Cells 

Minimum of 1 meter 

on most likely 

impact orientation 

at "operational" 

SOC. 

UL 2580 

"Batteries for 

Use in Electric 

Vehicles" 

Sample is to be 

dropped in the 

position most 

likely to produce 

the adverse 

results and in a 

manner and 

height (minimum 

height of 1.0 m) 

most 

representative of 

what would occur 

during 

maintenance and 

handling. 

floor 

Place the 

driving 

battery at 

80°C for 4 

hours. SOC 

80%. 

India AIS-048 

Vehicles ­

of Traction 

Batteries" 

48 
 

 

 

 

Test Title 

Nail 

Penetration 

Internal short 

circuit 

Roll-Over 

Battery Abuse 

FreedomCAR 

EESS Abuse 

Test Manual 

(SAND2005­

3123) 

SAE J2929 

Electric and 

Hybrid Vehicle 

Propulsion Battery 

System Safety 

Standard – Libased 

Rechargeable 

Cells 

IEC 62660-2 

Secondary 

lithium-ion cells 

for the 

propulsion of 

electric road 

vehicles – Part 

2: Reliability and 

abuse testing 

ISO/CD 12405 

Electrically 

propelled road 

vehicles — Test 

specification for 

lithium-ion 

traction battery 

packs and 

systems 

UL 2580 

"Batteries for 

Use in Electric 

Vehicles" 

Korea 

MVSS 18-3 

"Driving 

Battery 

Safety 

Test" 

"Battery 

Operated 

Safety 

Requirements 

8 cm/s and the 

diameter of the 

rod shall be 3 

mm rod (for 

cells) and 20 mm 

rod (for modules 

and packs) . 

One complete 

revolution for 

one minute in a 

continuous, 

slow-roll fashion. 

Then rotate the 

EESS in 90° 

increments for 

one full 

revolution 

At full SOC, the 

sample shall be 

rotated at a 

continuous rate of 

90°/15 s. Testing 

shall subject the 

sample to a 360° 

rotation in 3 

mutually 

perpendicular 

different 

directions. 

SAE J2464 2009 

HEV and EV 

Tests 

8 cm/s or greater 

and rod diameter 

shall be 3 mm rod 

(for cells) and 20 

mm rod (for 

modules and 

packs) . 

Complete 

revolution in 1 

minute. Then 

rotate the RESS 

in 90 degree 

increments for 

one full revolution. 

Usage 

Cell & Pack Testing 

Automotive Applications 

India AIS-048 

Vehicles ­

of Traction 

Batteries" 

8 cm/s nominal 

and rod diameter 

shall be 3 mm 

rod (for cells) and 

20 mm rod (for 

modules and 

packs) . 

Rotate the 

battery module 

one complete 

revolution in one 

direction, for one 

minute in a 

continuous, slowroll fashion, and 

observe leakage. 

Rotate the 

battery module in 

90° increments in 

same direction 

for one full rev. 

Hold the battery 

module for one 

hour at each 

position. 

49 
 

 

 

 

 

Usage 

Test Title Cell & Pack Testing 

Automotive Applications 

SAE J2464 2009 

HEV and EV 

Battery Abuse 

Tests 

FreedomCAR 

EESS Abuse 

Test Manual 

(SAND2005­

3123) 

SAE J2929 

Electric and 

Hybrid Vehicle 

Propulsion Battery 

System Safety 

Standard – Libased 

Rechargeable 

Cells 

IEC 62660-2 

Secondary 

lithium-ion cells 

for the 

propulsion of 

electric road 

vehicles – Part 

2: Reliability and 

abuse testing 

ISO/CD 12405 

Electrically 

propelled road 

vehicles — Test 

specification for 

lithium-ion 

traction battery 

packs and 

systems 

UL 2580 

"Batteries for 

Use in Electric 

Vehicles" 

Korea 

MVSS 18-3 

"Driving 

Battery 

Safety 

Test" 

India AIS-048 

"Battery 

Operated 

Vehicles ­

Safety 

Requirements 

of Traction 

Batteries" 

Immersion In salt water for a 

minimum of 2 

hour. 

In salt water for a 

minimum of 2 

hour. 

Tested in 

accordance with 

SAE J2464. 

With the DUT in 

its normal 

operating 

orientation and 

with 

switches/contacto 

rs in closed 

position, it shall 

be subjected to 

the Immersion 

test of SAE 

J2464. 

completely 

submerse 

the driving 

battery with 

0.6M of salt 

water and 

stabilize it at 

25±5°C for 1 

hour. SOC 

80% 

Humidity 

Exposure 

(Dewing) 

Tested in 

accordance with 

IEC 60068-2-30 

with a severity of 

55°C with 6 cycles, 

utilizing Variant 1 

during the 

temperature 

lowering period. 

Perform the test in 

reference to IEC 

60068-2-30, with a 

severity of 80°C 

with 5 cycles 

Extreme Cold 

Temperature 

50
 
 

 

 

 

 

 

 

 

Battery Abuse 

(SAND2005­

Hybrid Vehicle 

Propulsion Battery 

System Safety 

Rechargeable 

Secondary 

propulsion of 

2: Reliability and 

ISO/CD 12405 

Electrically 

propelled road 

specification for 

traction battery 

packs and 

"Driving 

Battery 

Safety 

"Battery 

Operated 

Safety 

Requirements 

Propagation 

Resistance 

Test Title 

SAE J2929 

Electric and
 

Standard – Libased
 

Cells
 

Perform fault 

analysis of the 

system design that 

single point faults 

will not result in fire, 

explosion or battery 

enclosure rupture. 

Usage 

Cell & Pack Testing 

Automotive Applications 

IEC 62660-2 

lithium-ion cells 

for the vehicles — Test 

electric road lithium-ion
 

vehicles – Part 

abuse testing systems 

Fault Analysis 

Elec. Safety 

Device 

Abusive 

Overcharge 

battery pack? battery pack? 

Cause one cell to Cause one cell 

enter thermal to enter thermal 

runaway and runaway and 

observe the pack. observe the 

Repeat for pack. Repeat for 

different different 

geometric geometric 

locations. locations. 

SAE J2464 2009 

HEV and EV 

Tests 

Does cell failure 

propagate in 

FreedomCAR 

EESS Abuse 

Test Manual 

3123) 

Does cell failure 

propagate in 

UL 2580 

"Batteries for 

Use in Electric 

Vehicles" 

Use J2464 

Propagation Test. 

A representative 

subassembly 

consisting of one 

or more modules 

and surrounding 

representative 

environment is 

allowed, if it can 

be demonstrated 

that there is no 

propagation 

beyond the 

subassembly. 

Required. 

References IEC 

60812, SAE 

J1739, MIL-STD1629A for FMEA; 

IEC 61025 for 

FTA; SAE 

ARP4761 for 

SAP; IEC 61508­

1 for Functional 

Safety. 

Korea India AIS-048 

MVSS 18-3 

Vehicles ­

Test" 

of Traction 

Batteries" 

51 
 

 

Battery Abuse 

(SAND2005­

Hybrid Vehicle 

Propulsion Battery 

System Safety 

Rechargeable 

Secondary 

propulsion of 

2: Reliability and 

ISO/CD 12405 

Electrically 

propelled road 

specification for 

traction battery 

packs and 

"Driving 

Battery 

Safety 

"Battery 

Operated 

Safety 

Requirements 

Overdischarge 

Protection 

Evaluation 

Test Title 

SAE J2464 2009 FreedomCAR SAE J2929 

HEV and EV EESS Abuse Electric and 

Test Manual 

Tests 

3123) 

Standard – Libased 

Cells 

Usage 

Cell & Pack Testing 

Automotive Applications 

IEC 62660-2 

lithium-ion cells 

for the vehicles — Test 

electric road lithium-ion
 

vehicles – Part 

abuse testing systems 

250 N Steady 

Force Test 

Mold Stress
 

Relief Test
 

Battery Pack 

Component 

Temperature 

Test 

UL 2580 

"Batteries for 

Use in Electric 

Vehicles" 

The DUT is to be 

subjected to a 

constant 

discharging 

current that will 

discharge a 

battery at 95% of 

the passive 

protection device 

ratings for the 

pack, or individual 

modules. The test 

will continue until 

the passive 

protection 

device(s, or the 

minimum cell 

voltage/maximum 

temperature 

protection 

device(s) are 

activated. 

Korea India AIS-048 

MVSS 18-3 

Vehicles ­

Test" 

of Traction 

Batteries" 

52 
 

Usage 

Test Title Cell & Pack Testing 

Automotive Applications 

SAE J2464 2009 

HEV and EV 

Battery Abuse 

Tests 

FreedomCAR 

EESS Abuse 

Test Manual 

(SAND2005­

3123) 

SAE J2929 

Electric and 

Hybrid Vehicle 

Propulsion Battery 

System Safety 

Standard – Libased 

Rechargeable 

Cells 

IEC 62660-2 

Secondary 

lithium-ion cells 

for the 

propulsion of 

electric road 

vehicles – Part 

2: Reliability and 

abuse testing 

ISO/CD 12405 

Electrically 

propelled road 

vehicles — Test 

specification for 

lithium-ion 

traction battery 

packs and 

systems 

UL 2580 

"Batteries for 

Use in Electric 

Vehicles" 

Korea 

MVSS 18-3 

"Driving 

Battery 

Safety 

Test" 

India AIS-048 

"Battery 

Operated 

Vehicles ­

Safety 

Requirements 

of Traction 

Batteries" 

Battery Pack 

Surface 

Temperature 

Test 

53
 
 

 

Because of the importance of SAE standards, a more detailed comparison of SAE J2464 and 

J2929 is presented in Table 4. 

Table 4. Comparison of SAE Standards J2464 and J2929 

54
 
 

 

 

 

5 Safety Devices 

Safety devices are incorporated into cells, modules, and battery packs to protect against offnormal conditions. These safety devices mostly work very well, which accounts for the relative 

safety of cells and battery packs in the field. 

To manage the consequences of heat and gas generation, many batteries have the following 

safety features: 

•	 Battery Management System (BMS) controls electrical distribution within a battery 

pack and protects against over- or under-voltage conditions as well as excessive current. 

Moreover, it may have temperature sensors that shut down the pack if the upper or lower 

temperature limits are exceeded. 

•	 Cell Vent or Tear Away Tab allows the safe release of gas if excessive pressure builds 

up within cells. Vents allow predictable pressure relief and are usually activated if the 

internal cell pressure exceeds 10 bar (~150 psid). These features are incorporated to 

prevent injury that could be caused by uncontrolled bursting of a battery container. 

•	 Current Interrupt Device protects against over-current that breaks the internal electrical 

connection when the internal pressure reaches a set value. This pressure rise results from 

internal gas generation caused by thermal or electrical abuse conditions exceeding design 

limits. This safety mechanism is a one-time device that permanently disables the cell. 

•	 Current Limiting Fuses may be used in place of positive temperature coefficient (of 

expansion) devices when a sustained discharge is not preferred. Fusing of this type may 

utilize slow-blow time fuses or fast-acting fuses with little current-time latency. Timedelay and especially fast-acting fuses are external to a cell. However, fusible links may be 

installed in the cell. 

•	 Diodes may be used for primary batteries to prevent inadvertent charging (blocking 

diode) or to steer the discharge current around a weak cell as in a discharge (bypass) 

diode. 

These safety devices work very well, accounting for the relative safety of cells and battery packs 

in the field. (An estimate of failure rates of Li-ion rechargeable battery cells is less than 1 in 106

.) 

55 
 

 

 

 

 

 

 

 

 

 

 

 

6 Typical Failure Modes – Mechanism of Failure 

Different battery chemistries have varying failure modes, but several events are common among 

all types of batteries. A typical response of a cell to abusive conditions is the generation of heat 

and gas.55,56 While they may be linked (i.e., gas and heat are produced by the same chemical 

reactions), there are examples where heat and gas are produced independently. 

6.1 Thermal Abuse 

Heat generation within batteries in response to abusive tests can make failures more hazardous. 

For example, a short circuit will heat up the cell because of Joule heating (I2R) until the cell 

begins to produce heat by internal chemical reactions (i.e., above the temperature where onset of 

self-heating reactions begin). Overcharge can also generate heat within the cell due to other 

oxidative chemical reactions that can trigger thermal runaway. In both these cases, thermal 

management of the battery pack is critical. 

To characterize heat and gas generation that might occur during off-normal conditions, cells and 

packs are exposed to elevated-temperature abuse conditions57 that resemble conditions that might 

be (rarely) seen in the field. In these tests, the response of cells can be characterized as falling 

into three major temperature regimes.58 These regimes are illustrated in Figure 9, which shows 

the temperature rise during thermal ramp of a fully charged Li-ion cell. ARC and thermal ramp 

tests are commonly used. 

Onset of reactions can be interpreted differently depending on the test protocol. Reactivity of the 

anode with the electrolyte can be observed in ARC at temperatures as low as 80°C, but at a very 

low rate. Reactivity is a consequence of SEI decomposition, exposing the reactive anode to the 

self-heating reactions involving the electrolyte.59 

In Figure 9, an external source of heat (that simulates an abuse event) is used to raise the 

temperature of the cell to the Onset Temperature, T(onset). A practical definition of T(onset) is 

typically a self-heating rate of 0.2°C/min. This low heat generation can be accommodated and 

dissipated in the battery packs. However, if this heat is not dissipated, the temperature will 

continue to rise due to sustained exothermic reactions above the onset temperature when the cell 

enters Stage 2 (Acceleration), which is characterized by more rapid and accelerating heat 

release. 

Stage 2 results from increased electrolyte reduction at the anode due to continuing loss of the SEI 

and to onset of electrolyte oxidation at the active cathode surface. These reactions depend highly 

on the active material chemistries and SOC. Venting and release of smoke may occur during 

55 Levy, S. C.; Bro, P. (1994). Battery Hazards and Accident Prevention. Plenum Press, New York, NY; p 113.
 56 Levy, S. C.; Bro, P. (1994). p 43.
 57 Roth, E. P.; Doughty, D. H. (2004). “Thermal abuse performance of high-power 18650 Li-ion cells,” Journal of
 

Power Sources, Vol. 128, April 2004. pp 308-318.
 58 Roth, E. P. (2008). “Abuse Response of 18650 Li-Ion Cells with Different Cathodes Using EC:EMC/LiPF6 and
 

EC:PC:DMC/LiPF6 Electrolytes.” ECS Transactions, Vol. 11 (19); pp 19-41.
 59 MacNeil, D. D.; Larcher, D.; Dahn, J. R. (1999). “Comparison of the Reactivity of Various Carbon Electrode 

Materials with Electrolyte at Elevated Temperature.” Journal of The Electrochemical Society, 146 (10); pp 3596–
 

3602.
 

56 
57 

Stage 2. Additional heating causes the cell to enter Stage 3 (Runaway), in which the high-rate 

cathode and/or anode reactions cause the temperature to rise rapidly (thermal runaway) and 

flame or explosion may follow. Thermal runaway is characterized by a self-heating rate of 

10°C/min or greater. At this self-heating rate, it is highly unlikely that any intervention or 

external cooling mechanism could quench the ensuing thermal runaway. 

Runaway temperature, T(runaway), is a strong function of cell size, cell design, and materials in 

the cell. T(runaway) can vary from 130°C to well over 200°C in Li-ion cells. Cathode materials 

that decompose to release oxygen at high temperatures have especially high reaction rates and 

reaction enthalpies. 

Figure 9. Cell self-heating rate during forced thermal ramp test of Li-Ion Gen 2 chemistry: anode = 

MCMB | electrolyte = 1.2 M LiPF6 in EC:PC:DMC | cathode = LiNi0.8Co0.05Al0.05O2 | separator = 

Celgard 2325 trilayer.60 

Some have argued that adiabatic tests, such as ARC, are not representative of battery failures. 

However, battery packs for EVs are large. For example, the Nissan Leaf battery pack is aircooled and contains 192 stacked laminar battery cells (approximately 34 Ah each) with LiMn2O4

cathodes. The battery and control module together weigh 300 kg (660 lb.). The Tesla Roadster 

contains 6,831 water-cooled 18650-size Li-ion cells. It is not unreasonable to assume that an 

environment that is nearly adiabatic may be created in a large pack in which the cells in the 

 

60 Doughty, D. H. (2005). “Li-ion Battery Abuse Tolerance Testing - An Overview.” AABC 2005 Proceedings, 

Honolulu, HI, June 2005. 

-10

-5

0

5

10

15

20

100 150 200 250

Temperature (C)

Rate (C/min)

Onset

Acceleration

Runaway

Stage 1 Stage 2 Stage 3

Cell self-heating rate (°C/min) 
 

 

 

 

 

 

 

 

 

 

 

central portion are surrounded by other cells at the same temperature. The problem develops if 

there is inadequate thermal transfer to the external environment, either by design or by 

malfunction of the cooling system. If any condition allowed a cell or group of cells to reach 

T(onset) and the heat generated within the pack was not dissipated, the cells would continue to 

heat up due to chemical reactions within the cell. In this case, thermal runaway will ensue. The 

timing of thermal runaway can be delayed by minutes or several hours, since it depends on the 

particulars of construction of the battery pack and the operating environment. Incubation times of 

hours have been observed in accidents investigated by the U.S. Department of Transportation.61 

Events such as these have resulted in the Department of Transportation banning shipment of 

lithium batteries on passenger aircraft.62 Accurate and easy-to-use thermal models of modules 

and packs would be a tremendous benefit in understanding the thermal environment of cells and 

packs under off-normal conditions. 

6.2 Physical Damage 

Physical damage (puncture, crush, vibration, or shock) has the possibility of creating an internal 

short circuit within the cell or creating a short circuit within a battery pack to cause current flow 

in an unintended and unanticipated manner. Internal short circuits are one of the most difficult 

failures to defend against. The potential for current flow in unintended manner should be 

evaluated by experimental tests on all battery packs. 

In general, cells and batteries with higher specific energy (Wh/kg) and energy density (Wh/L) 

will produce a more energetic response when abused by puncture, crush, or shock. Additionally, 

cells with a flammable electrolyte or other flammable materials that could escape when the 

containment is compromised during physical damage have the potential to produce secondary 

fires. 

6.3 Charge and Discharge Failures 

Overcharge and overdischarge (voltage reversal) of rechargeable batteries can occur if the 

control electronics of the charging station or the battery pack control electronics in the BMS 

malfunction or if severe cell imbalance occurs in a battery pack. 

Overcharge and overdischarge of rechargeable cells and batteries can occur due to charger 

failure or cell imbalance within a series/parallel connected battery. During charge, if several cells 

are connected in series and one has a higher SOC than the others do, it will reach full charge 

before the others. If the charger is designed to charge series strings (rather than individual cells), 

as the string reaches full charge, the cell will be overcharged. If overcharge occurs, a cell 

becomes more unstable and creates additional safety problems because it will have poorer 

thermal stability compared to un-abused cells (see Figure 28). Modern sophisticated BMS 

instrumentation can be programmed to detect and avoid this condition. 

Likewise, during discharge of a battery pack, if one cell has a slightly lower beginning voltage or 

lower capacity than the others do, it will reach full discharge before the others. If the string is 

61 Farrington, M. D. (2001). “Safety of lithium batteries in transportation.” Journal of Power Sources, Vol. 96, Issue
 

1, 1 June 2001, pp 260–265.

62 “Batteries can pose fire risk to planes.” USA Today, 07 March 2007.
 

http://www.usatoday.com/tech/news/techpolicy/2007-03-05-batteries-planes_N.htm.
 

58 
 

 

 

 

 

 

 

 

 

 

 

then forced to continue discharging—a situation that can occur if system electronics are not 

sufficiently smart to identify the condition—it will discharge below 0.0 V into a state of 

“overdischarge” or “voltage reversal.”63 This will usually highly degrade the battery’s ability to 

be recharged. Prolonged exposure to this condition (depth of reversal) can lead to safety 

problems, such as evolution of hydrogen and oxygen gases in large amounts sufficient to cause 

cell venting or metal plating on the cathode. In systems where multiple cells are used, a common 

quality-control standard condition is to use cells that have been matched to within ±5% cell 

capacity. 

The ability to withstand overcharge depends strongly on the current level (low charging current 

is more likely to result in benign failure) as well as the chemistry of the battery. Aqueous 

electrolyte systems (e.g., lead-acid, nickel/cadmium, and NiMH) are relatively insensitive to 

overcharge because after 100% SOC is reached, additional current drives the electrolysis of 

water (which produces hydrogen and oxygen) and limits the maximum voltage that the cell 

experiences. Cells with an aqueous electrolyte may contain catalysts to recombine the H2 and O2 

evolved during overcharge to reform water, which will minimize the accumulation of potentially 

explosive gas mixtures. However, this feature is not widely used in commercial lead-acid 

batteries and the prevalence of lead-acid battery explosions during charging is the major 

contributor to more serious injuries attributable to batteries.64 

Li-ion and Li-polymer cells have poor response to overcharge abuse when compared with 

aqueous electrolyte cells because they do not have the protection of water electrolysis as an 

energy sink. In part, this poor response results from the higher energy content, more reactive 

electrode materials, and flammable electrolytes that create the potential for thermal runaway 

during the overcharge event. 

The response of cells and battery packs during overcharge depends on overcharge parameters 

(current, maximum voltage), thermal environment, and cell materials and is a complex function 

of several failure mechanisms.65 Extended overcharge can result in cell heating that initiates 

internal decomposition reactions of the electrodes and electrolyte that lead to thermal runaway. 

In addition, increased cell temperatures can result in melting of the separator material and 

subsequent internal shorting of the cell. This behavior is particularly problematic for shutdown 

separators that result in high-cell impedance at shutdown. For a single cell or a series 

configuration of cells, the charging power supply will apply the full compliance voltage across 

the single cell after separator shutdown occurs. Many separator materials have been observed to 

fail immediately or within a short time after shutdown in this condition, as shown in Figure 10.66 

63 Jeevarajan, J. A. Meeting abstract. - Electrochem. Soc. 1002 321 (2010). Also, “Hazards Associated with High
 

Voltage High Capacity Lithium-ion Batteries.” ECS Transactions (2011) 33(22): 1–6; doi:10.1149/1.3557704.
 64 Levy and Bro, pp 36-38.
 65 Belov, D.; Yang, M. H. (2008). J Solid State Electrochem (2008) 12: 885–894.
 66 Roth, E. P.; Doughty, D. H. AABC Proceedings, 15–19 May 2006, Baltimore, MD.
 

59 
Shutdown Short 

Cell Potential (V) 

20 Runaway 250 

16 

18 Cell Potential Cell Skin 

Temperature 200 

14 

12 150 

10 

8 100 

6 

4 50 

2 

0 0 

60 65 70 75 80 

time (min) 

Cell Skin Temp (C) 

Figure 10. Thermal runaway during overcharge due to separator failure following separator 

shutdown.

67

The thermal response of Li-ion cells during overcharge is largely determined by the cathode 

chemistry. During the charge cycle, lithium is removed from the cathode oxide material. 

Different cathode oxide chemistries have different levels of lithium when fully charged, varying 

from Li0.5CoO2 to Li0.0FePO4 at 100% SOC. Overcharging continues to remove lithium from the 

structure, resulting in permanent crystallographic changes and increased oxidation potentials. 

Measurements of heat flow from the cells and cell skin temperature during overcharging has 

shown that there is a rapid increase in heat generation when all of the lithium has been removed 

from the cathode.67 Figure 11 shows the cell temperature profiles during 1 C-rate overcharge for 

several common cathode materials where it is seen that lower lithium content at 100% SOC 

results in a reduced range of overcharge before increased heat output. Some of the most 

thermally stable cells have the lowest tolerance range for overcharge.

 67 Roth, E. P.; Orendorff, C. (2009). Presentation to Advanced Automotive Battery and EC Capacitor Conference

2009, June 8–12, 2009, Long Beach, California. 

60
 

 

 

 

 

 

LiFePO4 LiMn2O4 Spinel 

x~0 at 100%SOC; x~0.1 at 100%SOC; 

Onset 100%SOC Onset 110%SOC 

Cell Temperature (C)

100 

90 LixNi0.8Co0.15Al0.05O2
 

x=0.36 at 100%SOC;
 

80 Onset 125%SOC
 

70
 

60 

LixNi1/3Co1/3Mn1/3O2 

x~0.48 at 100%SOC; 

Onset 170%SOC 

50
 

40
 

30 LixCoO2 

x~0.5 at 100%SOC 

Onset 150%SOC 

20 

100% 120% 140% 160% 180% 200%
 

% SOC
 

Figure 11. Heat output during overcharge for different cathode oxide chemistries, showing a 

marked increase in heat output when final lithium is removed from cathode.68 

However, an important caution must be added regarding the above overcharge discussion. If the 

stability of the cathode becomes sufficiently good, other problems can become the determining 

factor in cell stability. For example, cells made with lithium iron phosphate (LiFePO4, or LFP) 

cathode materials have the best thermal stability and overcharge stability. LiFePO4 is thermally 

stable up to 250°C and does not evolve oxygen. The lithiated anode is still a significant source of 

energy. At high temperature, the SEI protective layer decomposes, exposing the lithiated carbon 

to the electrolyte. Reduction of the electrolyte can generate sufficient heat to cause a thermal 

runaway reaction with associated gas generation, venting, and possible fire. The electrolyte itself 

breaks down above 160°C, generating sufficient gas volume to cause cell venting.68 

Yamaki and coworkers demonstrated that overcharge response of a lithiated graphite 

(LiC6)/LiMn2O4 cell depended on charge current; at low current, overcharge test results were 

benign, but at high current levels, the cells entered thermal runaway.39 Lithium plating on the 

anode is a possible failure mode during fast charge at low temperature. Lithium plating has the 

potential to create a finely divided lithium powder within the cell that may become electronically 

isolated from the anode. In addition, dendrites of lithium may grow from the anode through the 

separator, possibly resulting in an internal short circuit. This situation, if it arises, creates a safety 

vulnerability that could persist after the overcharge event terminated. 

6.4 Short Circuit 

An external short circuit is the most common type of battery abuse condition. All test protocols 

(for shipping approval as well as use environments) include short circuit tests. A cell is 

connected to a test circuit in which the external resistance either is matched to the unit 

impedance or is set as low as 1 mOhm. The current and cell temperature are monitored as well as 

68 Roth, E.P. (2008). ECS Transactions, 11 (19) 19-41 (2008). 

61 
 

 

the cell response, such as venting and possible self-ignition. An example profile for a Li-ion cell 

is shown in Figure 12. 

0 

20 

40 

60 

80 

100 

120 

140 

0 

200 

400 

600 

800 

1000 

1200 

1400 

1600 

Temperature (C) 

Current (A) 

Current 

Cell Temperature 

0 20 40 60 80 100 

Time (s) 

Figure 12. A 1-mOhm short circuit at room temperature of a Li-ion cell at 100% SOC.69 

The plot shows the response of cells to a short circuit where the external circuit resistance was 

set to 1 mOhm. The cell current shows an initial peak determined by the cell resistance and the 

load. A secondary peak is often observed resulting from a drop in internal resistance with 

increasing temperature. Cells typically can withstand an external short circuit because thermal 

output is small and the cell is in contact with the test fixture. Thermal management will dictate if 

the response of the cells will be benign, as in this test, or exhibit thermal runaway. Large cells 

(i.e., over 10 Ah), cells that can sustain very large short circuit currents, cells that have higher 

internal resistance, and cells with low inherent thermal stability are more prone to exhibiting 

thermal runaway. 

Internal short circuit is a failure mode where a current path develops within the cell. It can be 

caused by several factors, including a foreign object, poor cell design (e.g., lack of sufficient 

separation or insulation of electrodes in the cell), poor manufacturing processes (e.g., burrs on 

cut edge of current collector), or external pressure on the cell walls. 

Internal shorts also may develop because of other abuse conditions that lead to internal gas 

generation and displacement of the internal electrodes so that they can contact each other, 

especially in pouch cells. This deformation mechanism can completely bypass “safe” separators 

designed to resist internal shorting. 

Battery packs and modules have additional failure modes that cannot be examined by cell 

testing. New failure modes arise when the energy in cells is released to adjacent cells. Short 

69 Typical response profile from SNL abuse laboratory. Source: SNL 

62 
 

 

 

 

 

circuit tests can reveal some of these failure modes. For example, a failure was observed in a 

short circuit test of a 12-cell series-connected string of 5-Ah Li-ion rechargeable batteries.70 The 

pack was tested at room temperature in a standard short circuit test. The short circuit current was 

high, over 1,000 A, and as the cells in the series string increased in temperature due to Joule 

heating, the shutdown separator in one cell reached its critical temperature of ~130°C and the 

cell became resistive. It was quickly driven into voltage reversal (forced discharge). The voltage 

across this cell was about -38 V, the potential resulting from the other cells in the 12-cell string. 

Within 1⁄2 minute, the cell burst into flames. Had the cell not become resistive (i.e., fabricated 

without a shutdown separator) or had the current path been interrupted in some other way, the 

failure would not have happened. This failure is an example of combined failure modes—a short 

circuit triggering an overdischarge failure. 

70 Doughty, D. H. (2005). “Li-ion Battery Abuse Tolerance Testing - An Overview.” Advanced Automotive Battery 

Conference Proceedings, June 13–16, 2005, Honolulu, HI. 

63 
 

 

 

 

 

 

 

 

 

 

 

 

7	 Discussion of Safety and Abuse Response for Li-ion 

Rechargeable Battery Chemistries 

Li-ion cells contain more energy because they have more reactive electrode materials. For 

example, the common cathode in today’s Li-ion rechargeable batteries [lithium cobalt oxide 

(LiCoO2, or LCO)] decomposes at elevated temperature to produce oxygen that exothermically 

reacts with organic materials within the cell.71 The safety of a particular battery chemistry is 

directly related to the material choices for the anode, cathode, electrolyte, and separator. The 

performance of Li-ion batteries is most strongly dependent on the selection of the cathode 

material,58 so the major classes of cathodes will be briefly discussed. 

Several representative battery chemistries are discussed below. Each topic covers commercially 

important cell chemistry, briefly describing the relevant aspects of the materials used and the 

safety response. 

The next sections discuss two classes of Li-ion rechargeable batteries—those with carbon anodes 

and liquid electrolytes (Li-ion cells) and those with carbon anodes and polymer electrolytes (Lipolymer cells). Each class has several variations, reflecting the tradeoff of materials choices that 

the manufacturer has made. The choice of cathode materials is probably the most important 

choice that determines the safety, energy density, power, and life of a particular lithium 

rechargeable chemistry. 

Most commercially available Li-ion batteries utilize cathodes made of transition metal oxide, 

such as LiCoO2 anodes made of graphitic carbon (which reversibly binds lithium to form an 

intercalation compound LiC6 during charge) and a non-aqueous electrolyte. A wide range of 

carbonaceous compounds is suitable for use as the anode material, including coke, pure graphite 

and tailored carbon spherical particles, such as meso-carbon micro beads (MCMB). 

All Li-ion cells employ non-aqueous electrolytes with a lithium-containing salts (LiPF6 or other 

salts) dissolved in solvent mixtures of organic liquids, such as EC, PC, diethyl carbonate (DEC), 

or ethyl methyl carbonate (EMC). Numerous options for the choice of salts and/or solvents in 

such batteries are known to exist in the marketplace. Additionally, additives are used to modify 

the reactivity of the anode as well as to reduce the flammability of the electrolyte. 

7.1 Cathodes in Li-Ion Batteries 

The choice of cathode has the strongest influence on cell safety.72 Many cathodes are in 

commercial cells or in development. Table 5 summarizes performance information on the most 

common cathodes in use today. 

LiCoO2 has been the cathode of choice for the majority of consumer-level Li-ion cells produced 

today. Although it delivers good capacity, it is the most reactive and has poorer thermal stability 

than the other cathodes. A calorimetric measurement of cells with different cathodes 

71 Arai, H.; Tsuda, M.; Saito, K.; Hayashi, M.; Sakurai, Y. (2002). Journal of The Electrochemical Society, 149, 

A401–A406.
 72 Maleki, H.; Deng, G.; Anani, A.; Howard, J. (1999). “Thermal Stability Studies of Li-Ion Cells and Components.”
 

Journal of The Electrochemical Society, Vol. 146(9), pp. 3224–3229.
 

64 
 

 

 

 

 

 

 

 

 

 

 

 

demonstrates this point. ARC is a common technique used to measure reactivity of battery 

materials and full cells and is particularly suited to characterize batteries. Self-heating of a cell or 

cell materials at elevated temperature is evidence of chemical instability. The plot of self-heating 

rate versus cell temperature provides a good characterization of chemical instability. A plot of 

self-heating rate versus cell temperature for full Li-ion 18650 cells fabricated with different 

cathodes is shown in Figure 13. Key parameters measured from ARC are onset temperature, 

maximum self-heating rate, and temperature width of the peak thermal runaway. 

Table 5. Characteristics of Some Positive Electrode Materials73 

Material 

Specific capacity 

mAh/g 

Midpoint V vs. 

Li at C/20 Comments 

LiCoO2 155 3.9 Still the most common. Co is expensive 

LiNi1-x-yMnxCoyO2 

(NMC) 140-180 ~3.8 

Capacity depends on upper voltage cutoff. 

Safer and less expensive than LiCoO2 

LiNi0.8Co0.15Alx0.05O2 

(NCA) 200 3.73 High capacity. About as safe as LiCoO2 

LiMn2O4 (Spinel) 100-120 4.05 

Poor high temperature stability (but 

improving with R&D). Safer and less 

expensive than LiCoO2 

LiFePO4 (LFP) 160 3.45 

Synthesis in inert gas leads to process cost. 

Very safe. Low volumetric energy. 

Li[Li1/9Ni1/3Mn5/9]O2 275 3.8 

High specific capacity, R&D scale, low rate 

capability. 

LiNi0.5Mn1.5O2 130 4.6 

Requires an electrolyte that is stable at high 

voltage. 

LiCoO2 cells are clearly less stable than cells with any of the other mixed-metal oxides shown in 

Figure 13 because their onset temperatures are higher and the maximum self-heating rates are 

lower. However, all these materials are unstable at elevated temperature. Work by Dahn and 

coworkers demonstrated that most cathode chemistries decompose and evolve oxygen.74 Data on 

oxygen evolution at elevated temperature have been published for LiCoO2,

75 LiNiO2,76 and 

LiMn2O4.

77 Oxygen production during high-temperature cathode decomposition is correlated 

with exotherms observed in ARC experiments. However, the LiFePO4 cathode material does not 

generate oxygen even when fully decomposed at high temperatures, thus showing the lowest 

heating rate during thermal runaway. Figure 14 shows an expanded view of the thermal runaway 

peaks where it is clearly seen that the lowest heating rates occur for the LiMn2O4 cell (little 

oxygen generation) and the LiFePO4 cell (no oxygen generation). Thermal runaway in these cells 

is dominated by anode/electrolyte reactions resulting from final breakdown of the protective SEI 

layer. 

73 Dahn, J.; Erlich, G. M. (2011). “Lithium Ion Batteries” Reddy, T. B., ed. Linden’s Handbook of Batteries, 4th ed. 

McGraw Hill, ISBN 978-0-07-162421-3; pp 26-8, copy of Table 26.3.

74 Dahn, J. R., et al. (1994). Solid State Ionics, 69(3-4), p. 265-270.
 75 MacNeil, D. D.; Dahn, J. R. (2001). Journal of The Electrochemical Society, 148, A1205.
 76 Arai, H.; Tsuda, M.; Saito, K.; Hayashi, M.; Sakurai, Y. (2002). Journal of The Electrochemical Society, 149,
 

A401.
 77 MacNeil, D. D.; Dahn, J. R. (2001). Journal of The Electrochemical Society, 148, A1211.
 

65 
Normalized Rate (C/min) 400 

350 LiCoO2 

300 Gen2: LiNi0.8Co0.15Al0.05O2 

250 

200 Gen3: Li1.1(Ni1/3Co1/3Mn1/3)0.9O2 

150 LiMn2O4 

100 LiFePO4 

50 

0 

0 100 200 300 400 

Temperature (C) 

Figure 13. Self-heating rate of 18650 full cell measured by ARC.

Improved cathode stability results in higher thermal runaway temperature (increased stability) and 

reduced peak heating rate.69

Normalized Rate (C/min) 1 

2 

3 

4 

5 

Gen2: LiNi0.8Co0.15Al0.05O2 

Gen3: Li1.1(Ni1/3Co1/3Mn1/3)0.9O2 

LiMn2O4 

LiFePO4 

LiCoO2 

0 

0 100 200 300 400 

Temperature (C) 

Figure 14. Expanded view of ARC profiles showing low rate thermal runaway of LiFePO4 and 

LiMn2O4 cells.

69

66
Figure 15 shows the thermal ramp results for the same cell chemistries discussed above. 

Although not as sensitive or as quantitative as ARC, the thermal ramp profiles show the same 

ordering of cell response with reduced oxygen generation. Cathode decomposition onset starts at 

150°C to 250°C. The higher onset temperature of LiMn2O4 and LiFePO4 cells again shows that 

they are more resistant to thermal abuse. Moreover, the reduced peak of self-heating rate of 

LiFePO4-based cells makes them the safest cells Li-ion batteries on the market today. 

100 

90 LiMn2O4 

80 

70 GEN2 

(C/min)

60 LiNi0.8Co0.15Al0.05O2 

50 

Rate 

40 GEN3 

LiFePO4 

30 Li1.1(Ni1/3Co1/3Mn1/3)0.9O2 

20 

10 

0 

0 50 100 150 200 250 300 

Temperature (C) 

Figure 15. Onset of self-heating in thermal ramp experiment on Li-ion cells.

LiFePO4 olivine cathodes show the greatest reduction in self-heating rate and increased onset

temperature for runaway.37

7.2 Anodes in Li-Ion Batteries

Anode materials are chosen to have high capacity, high rate capability, low irreversible loss on 

formation cycling, and stability with respect to cycling and high-temperature exposure. Carbon 

anodes can be based on either natural or synthetic graphite, can have high or low surface area, 

and can have morphologies ranging from amorphous, spherical, or flaky grain structure. All of 

these material properties affect the thermal response of the anode under abuse conditions. As an 

example, DSC curves for three anode materials (100% SOC in electrolyte) are shown in Figure 

16 for anode materials of different morphologies. The anodes are Sony hard carbon, MCMB 

(GEN1), and MAG10 flaky graphite (GEN2). All of the anodes showed a breakdown in the SEI 

layer starting around 120°C but with different rates of reaction at increasing temperature. The 

MAG10 anode material showed the highest level of reaction due to the poor SEI layer that 

formed on the particle edges. 

The relative contribution of the anode and cathode material to the full cell response depends on 

the specific reactivity of the active materials and the mass loadings of each. As an example, 

Figure 17 shows a DSC comparison of the anode, cathode, and electrolyte for a GEN2

(MCMB/LiNi0.8Co0.15Al0.05O2) cell. The anode may have as large (or larger) specific enthalpy of 

reaction, but the reaction is spread out over a wide temperature range. The cathode reactions 

67
occur at higher temperatures and over a much smaller temperature range. This often is the result 

of the high-rate Stage 3 thermal runaway.

Gen2/Gen1/Sony Anodes

100% State of Charge
 

9
 

Gen2 8 (MAG10 Flaky Graphite) 

Heat Flow (mW/mg) 7 

6 

5 

2 

3 

4 

Gen1 (MCMB) 

Sony 

(Hard Carbon) 

1 

0 

0 100 200 300 400 

Temperature (C) 

Figure 16. DSC profiles of anode carbon materials with different morphologies.

58

Gen2: MCMB\LiNi0.8Co0.15Al0.05O2)

25
 Gen2 Cathode 

(1.6 kJ/g) 100% SOC 20 

Heat Flow (W/g) 15 

10 

5 Gen2 Anode 

(2.22 kJ/g) 

-5 

0 

0 100 

EC:EMC Electrolyte 

(0.22 kJ/g) 

200 300 400 

Temperature (C) 

Figure 17. DSC profiles showing contribution of anode, cathode and electrolyte to cell thermal 

reactions.

57

The graphitic anodes used in common technology are only 50 mV or so above the potential of 

lithium. The low potential gives concern about plating of lithium under many aggressive 

charging scenarios or when the local current density is non-uniform. 

68
 

 

 

 

 

 

 

 

The loss of lithium due to side reactions, such as SEI formation, may eventually lead to 

imbalance in the cathode lithiation. The failure mode for Li-ion cells under thermal runaway 

usually initiates with the dissolution of the protective SEI layer at the anode, allowing rapid 

heating and potential thermal runaway. 

7.3 Separator Stability

An ideal shutdown separator will have a sharp transition to a very high resistance at a relatively 

low temperature, robust high-voltage standoff, and a wide temperature window of stability, as 

shown in Figure 18 below. Cell safety is critically dependent on the stability of the separator 

under extreme conditions of temperature and mechanical stress. Separators generally are 

classified into three groups: (1) microporous polymer membranes, (2) non-woven fabric mats, 

and (3) inorganic composite membranes.78 The separators enhance cell safety by having 

properties of high mechanical strength (puncture resistance), high thermal stability, and 

shutdown properties. As discussed earlier, shutdown results when a component of separator 

material (usually polyethylene) melts and restricts ionic conduction through the cell. This feature 

may prevent further heating of the cell at a temperature well below thermal runaway. The 

effectiveness of the shutdown depends on whether the cell temperature does indeed immediately 

begin to decrease. If the temperature continues to drift upwards because of partial electrical 

conduction (partial shutdown), continued exothermic chemical reactions, or outside heating 

sources, thermal effects may diffuse to other parts of the cell or module, triggering a domino 

effect. 

78 Sheng, S.; Zhang, J. (2007). Journal of Power Sources 164 pp. 351–364. 

69 
 

 

 

 

 

Z Total 

1000Hz/50mV 

2.5E+05 

2.0E+05 

1.5E+05 

Entek 

143C/(153C-158C) 

Tonen 

139C/( 190C-204C) 

Celgard 

131C/(165C-167C) 

100 120 140 160 180 200 220 

Temperature (oC) 

Z total 

1.0E+05 

5.0E+04 

0.0E+00 

Figure 18. Impedance of electrolyte soaked separator materials showing shutdown and the 

temperature window of stability.

58 

7.4 Electrolytes

Li-ion batteries have the unique characteristic of using organic-based electrolytes compared to 

other electrochemical storage systems. These electrolytes are almost universally based on 

combinations of linear and cyclic alkyl carbonates. These electrolytes are sufficiently stable 

(kinetic stability results from protective SEI, which limits reactivity with the anode surface) to 

allow the use of lithium and LiC6 as the anodic active component. Liquid electrolytes have good 

conductivity, which results in the high-power cell designs. However, these organic electrolytes 

have high volatility and flammability that pose a serious safety issue for their use in the 

consumer and transportation markets. Under extreme conditions of voltage and temperature, 

these electrolytes can react with the active materials of both anode and cathode to release 

significant heat and gas, as shown in the previous sections. 

The choice of electrolytes is often based on performance criteria such as conductivity, 

temperature range (high and low), and voltage range stability. There are many combinations of 

solvent species, solvent ratios, electrolyte salts, and additives. The choice of electrolyte can also 

have a significant impact on the safety, thermal stability, and abuse tolerance of the cell. Some 

materials that have superior performance properties, such as LiAsF6, cannot be used because of 

its high toxicity.79 Some solvent species, such as PC, are limited in concentration because they 

cause disruption of the anode graphite grains. The choice of electrolyte often is not given full 

consideration to the effect on cell response during an abuse event. For example, the effect of 

electrolytes on the peak thermal runaway reaction in a nickel-cobalt-aluminum 

(LiNi0.8Co0.15Al0.05O2) (GEN2) cell is shown in Figure 19.68 The EC:PC:DMC(1:1:3)/1.2M 

79 Reddy, T. B., ed. Linden’s Handbook of Batteries. 4th edition. McGraw Hill, 2011, ISBN 978-0-07-162421-3, Ch. 

7.3.1. 

70 
LiPF6 electrolyte has significantly reduced the kinetics of the peak runaway reaction while not 

affecting the total enthalpy of the reaction as given by the width of the reaction peak. This effect 

is seen to be even more pronounced for the more stable GEN3 cathode chemistry 

[Li1.1(Ni1/3Co1/3Mn1/3)0.9O2] as shown in Figure 20. 

500 

450 

GDR/Gen2 

EC:EMC 1.2M LiPF6 

400 

350 GDR/Gen2 Baseline 

EC:DEC 1M LiPF6 

300 

250 GDR/Gen2 

200 EC:PC:DMC 1.2M LiPF6 

150 

100 

50 

0 

0 100 200 300 400 500 

Temperature (C) 

Rate (C/min) 

Figure 19. ARC profiles of GEN2 18650 cells with different solvent electrolyte species.

58

350
 

300
 

Rate (C/min) 150 

200 

250 

MCMB/Li1.1(Ni1/3Co1/3Mn1/3)0.9O2 

EC:EMC 1.2M LiPF6 

50 

100 MCMB/Li1.1(Ni1/3Co1/3Mn1/3)0.9O2 

EC:PC:DMC 1.2M LiPF6 

0 

0 100 200 300 400 

Temperature (C) 

Figure 20. ARC profiles for GEN3 18650 cells with EC:EMC (3:7) and EC:PC:DMC (1:1:3) electrolyte 

solvents.

58

71
The energy released by electrolyte reaction with the active materials is strongly dependent on the 

cell chemistry and SOC (see Section 7.6). The most energetic runaway reactions result from 

oxygen released during decomposition of the cathode and subsequent oxidation of the 

electrolyte. As an example, the contributions of the individual cell electrodes to the full cell 

thermal response are shown in Figure 21 for a GEN3 cell. Fully charged electrodes had been 

removed from a cell and resealed in an 18650 can with the electrolyte. For this chemistry, the 

reactions with the electrolyte are comparable over the whole temperature range for both the 

anode and cathode. Cell chemistries with little or no oxygen release (e.g., LiMn2O4 and 

LiFePO4) will have thermal responses determined almost entirely by anode/electrolyte reactions.

50 

45 MCMB/Li1.1(Ni1/3Co1/3Mn1/3O2)0.9 

40 Full Cell EC:PC:DMC/1.2MLiPF6 

35 

30

(C/min) 

25 

20

Rate 

Anode Cathode

10 

15 Electrolyte 

5 

0 

50 100 150 200 250 300 350 400 450 

Temperature (C) 

Figure 21. ARC profiles of anode and cathode electrodes in electrolyte compared to full cell 

58 response. 

The combustion enthalpies for some common solvents are shown below.

80,81

EC: C3H4O3+2

5O2 → 3CO2 + 2H2O ∆H=1161 kJ/M

DEC: C5H10O3 + 6O2 → 5CO2 + 5H2O ∆H=2715 kJ/M

DMC: C3H6O3 + 3O2 → 3CO2 + 3H2O ∆H=1440 kJ/M

EMC: C4H8O3+2

9O2 → 4CO2 + 4H2O ∆H=2000 kJ/M

(Estimated from DEC and DMC)

80 CRC Handbook of Chemistry and Physics. 81 http://webbook.nist.gov/chemistry/name-ser.html

72
 

 

 

 

 

Energy (J/kg)

 

 

The calculated combustion enthalpies based on moles of oxygen are quite similar for all solvents, 

with an average of 460 kJ/mole of O2. However, the amount of oxygen released by even some of 

the most reactive cathodes is not nearly sufficient to cause complete combustion of the 

electrolyte. For example, GEN3 LiNi1-x-yMnxCoyO2 only gives enough oxygen to react with 5%– 

15% of the electrolyte. Thus, the largest source of un-reacted material is the vented electrolyte, 

which can combust externally in air with an energy release several times that of the internal 

reaction enthalpies (as shown in Figure 22). Energy (kJ/kg cell) 

3000 

2500 

2000 

1500 

1000 

500 

0 

Electrical Energy 

Stored in Li-ion 

Battery (per unit of
 

battery)
 

Thermal Energy 

Released on Suitable 

Stimulation (per unit 

of battery) 

Anode reaction with 

electrolyte 

Cathode reaction with 

electrolyte (only above 180C) 

Combustion of 

electrolyte 

(autoignition > 450C) 

Figure 22. Comparison of stored electrical energy and energy released from decomposition 

reactions.

7 

The flammability of the vented electrolyte is a significant unresolved safety issue for Li-ion 

batteries. Accident scenarios involving burning electrolyte have some of the most serious 

consequences, resulting in cascading failure of other cells in the battery pack and involvement of 

adjacent materials and structures. 

7.5 Gas Generation 

Almost all electrochemical couples produce or have the possibility of producing gas. The toxicity 

and flammability of the evolved gas should be studied. Almost all aqueous systems will generate 

hydrogen gas by the decomposition (electrolysis) of water. For non-aqueous systems, the gas 

evolution over time must be addressed by incorporation of adequately designed safety vents on 

the cell to preclude a violent container failure. 

Gas generation will result whenever the cell reaches the solvent decomposition temperature, 

whether from internal or external sources. Mixture of the solvent vapors with the surrounding air 

can result in a highly flammable or explosive composition that only requires an ignition source, 

73 
such as a simple spark, to ignite. Even the safest cathode and anode chemistries will not prevent 

this release of flammable vapors.82

Gas generation in Li-ion cells under abuse conditions has an indirect effect on safety by 

producing sufficient pressure and gas volume to aerosolize the flammable solvents into the 

surrounding environment during cell venting. Figure 23 shows the ARC thermal runaway profile 

of an 18650 cell showing the heat and gas volume generation. The alkyl carbonate-based 

electrolytes, which make up almost all of the Li-ion electrolytes, have been shown to break down 

at temperatures starting around 150°–200°C. Figure 24 shows ARC bomb data for the electrolyte 

only. Venting may occur at lower temperatures strictly due to increased vapor pressure, as seen 

in Figure 23 for a full cell. A high rate of gas generation usually accompanies (or immediately 

follows) the thermal runaway peak. Decomposition of organic solvents may form several gas 

species, some of which are flammable (H2, CO2, CO, and several low molecular weight 

hydrocarbon gases, such as CH4 and C2H6 as shown in Figure 25). 

500 2500 

450 

400 2000 

Rate (C/min) 350 

300 1500 

250 

200 1000 

150 

100 500 

50 

0 0 

0 100 200 300 400 500 

Temperature (C) 

STP vol (ml) 

Figure 23. ARC thermal runaway profile of an 18650 cell (5 mL electrolyte) showing heat and gas 

generation. 

 (Unpublished SNL data)

82 Harrisa, S. J.; Timmons, A.; Pitz, W.J. (2009). Journal of Power Sources 193 (2009) 855–858.

74
 

 

ARC to 200C 

ARC to 400C 0% 

20% 

40% 

60% 

80% 

100% 

H2

CO

CO2

Normalized Composition 

0 

20 

40 

60 

80 

100 

120 

140 

160 

180 

Gas Volume (ml at STP) 

EC:DMC (3:7) 

EC:EMC (3:7) 

EC:DEC (1:1) 500 mg Elec. vol. 

1.2M LiPF6 

0 50 100 150	 200 250 300 350 400 450 500 

Temperature (C) 

Figure 24. Gas generation of representative electrolyte solutions. 

(Unpublished SNL data) 

Temperature Effect for EC:EMC/1.2M LiPF6 Methane Ethylene Ethane Ethyl Fluoride Propylene Propane "C4 species"

n-pentane 

Figure 25. Gas generation species for EC:EMC 1.2 M LiPF6 electrolyte at 200°C and 400°C. 

(Unpublished SNL data) 

75 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

7.6 Effect of SOC on Thermal Stability

SOC is one of the most important factors in determining the response of a cell or pack to abusive 

events, which is why shipping regulations require that Li-ion rechargeable batteries be at a low 

SOC during shipment. While not many careful studies have been published on the effect of SOC 

and age, an SNL publication37 provides quantitative comparison for two Li-ion battery 

chemistries (LiCoO2 and LiNi0.8Co0.2O2). While this summary report relies heavily on 

information published in that reference, information gleaned from other sources shows that most 

Li-ion battery chemistries would follow similar trends. 

Figure 26 shows ARC results for commercial 18650 Sony cells (coke-based anode and LiCoO2 

cathodes) from 0% to 100% SOC. The onset of self-generated heating decreased to lower 

temperatures with increasing SOC, and the magnitude of the heating rate increased more rapidly 

with increasing temperature. Self-generated heating occurred as low as 50°C, but an accelerating 

heating rate was not observed until above 100°C. These thermal reactions are well below the 

cathode/electrolyte reaction range and are believed to result primarily from breakdown of the 

anode SEI layer and subsequent reduction reactions of the lithiated carbon with the electrolyte. 

The higher SOCs result in increased levels of lithiation of the anode that increases these 

reactions. These onset reactions exhibit a much lower heating rate than is seen during full 

thermal runaway, as shown in Figure 13. 

The other cell chemistry examined in this study had an MCMB anode and a LiNi0.8Co0.2O2 

cathode (referred to as a GEN1 cell). Figure 27 shows the ARC profiles with increasing SOC 

showing lower SOCs were more stable. The MCMB carbon anode reactivity shows a weaker 

dependence on SOC compared to the coke-based anodes. Differences in morphology and 

structure of carbon anode material can greatly affect the stability of the SEI and Li intercalation 

kinetics. 

The peak thermal response of a cell also increases rapidly with the degree of charge. Figure 28 

shows the ARC profiles for Sanyo (LiCoO2) cells with increasing SOCs from 3.8V to 4.3V. The 

onset of the high-rate (Stage 3) reactions did not change significantly with SOC, but the peak 

heating rates and the enthalpy of the high rate reactions increased markedly. This peak response 

depends strongly on the type of cathode material used. (Figure 11 showed how heat generation 

increased sharply during overcharge for cathodes at the point of complete lithium removal.) In 

addition, the anode/cathode capacity balance is important for maintaining stability at high SOC. 

Insufficient anode capacity compared to the cathode can result in lithium plating at high SOC 

and subsequently can cause high-rate thermal runaway. 

During overcharge, excessive lithium is extracted from the cathode, and a corresponding 

excessive insertion and/or plating of lithium may occur at the anode. These conditions make both 

electrodes less thermally stable. Figure 28 shows the ARC profiles for Sony cells with increasing 

states of overcharge from 4.1V to 4.5V. There was a marked increase in reaction around 120°C 

with some increase in reaction as low as 70°C. Overcharge resulted in an increase in the lithiated 

anode reaction and apparent reduction in the effectiveness of the SEI layer. 

76 
Figure 26. ARC runs for Sony 18650 cells versus SOC. 58 

Figure 27. ARC runs for GEN1 cells vs. SOC.

37 

77
 
Sanyo Cells 

1000 

700 

800 

900 SanyoCell #809: 4.3V 

SanyoCell: 4.2V 

SanyoCell #778: 4.0V 

SanyoCell #772: 3.8V 4.3V 

600

min) 

4.0V 

500

(C/ Rate 

400 

300 

4.2V 

200 

100 3.8V 

0 

0 100 200 300 400 500 

Temperature (C) 

Figure 28. ARC profiles of Sanyo 18650 cells at increasing SOCs.

(Unpublished SNL data)

Finally, the magnitude of response of a cell to an internal short circuit will be influenced by the

SOC. When a cell is at 100% SOC, an internal short circuit often results in thermal runaway of 

the cell. However, when the cell is at 80% SOC, the maximum temperature will be reduced to 

200°C. At 70% SOC, an internal short circuit can be well tolerated.83

7.7 Effect of Age and Cycling On Thermal Stability

As Li-ion batteries age, they slowly lose capacity by several mechanisms.84 The most important 

mechanism is the buildup of resistive decomposition products in the surfaces of the electrodes. 

The decomposition products have the result of increasing cell impedance, which reduces the 

maximum discharge rate that the cell can sustain and increases the Joule heating during a high

rate of discharge. Although much study has gone into understanding and modeling the lifetime of 

cells with aging, little work has been done on the effects of aging on thermal stability and abuse 

tolerance.

USABC goals, in line with the DOE research program for HEVs, are a calendar life of 15 years

for HEVs and 10 years for EVs.85 A cycle lifetime of up to 1,000 cycles at 80% depth of 

discharge is also required. Little or no safety testing has been performed on cells approaching 

83 Zhang, Z. “Perspectives on Safety and Life for Li-Ion Application in Electric Drive Vehicles (EDV).” Presented

at Pacific Power Source Symposium 2011, Hilton Waikoloa Village, Hawaii, January 10-15, 2011. 84 Vetter, J.; Novák, P.; Wagner, M. R.; Veit, C.; Möller, K.-C.; Besenhard, J. O.; Winter, M.; Wohlfahrt-Mehrens,

M.; Vogler, C.; Hammouche, A. (2005). Journal of Power Sources 147 (2005) pp 269–281 85 http://www.uscar.org/guest/teams/11/Electrochemical-Energy-Storage-Tech-Team

78
 

 

 

 

 

these lifetime limits. There are valid concerns about the stability of the active materials, 

separators, and possible reactions involving new degradation or contamination products. Further 

testing of these aged cells is planned as part of the ABR program. 

This topic was investigated at SNL during the early part of the Advanced Technology 

Development program.37, 86 Decomposition products can passivate the electrode surfaces, making 

them more stable at elevated temperature. These effects of aging on the onset of thermal runaway 

were measured by performing ARC runs of thermally aged cells. 

Figure 29 shows the results for Sony cells that had been aged for 6 months at 25°C, 11 days at 

60°C, and 6 weeks at 70°C. All cells were measured at 100% SOC. The cells showed a loss of 

low-temperature reactivity with increased aging. The data show that aging resulted in loss of the 

low-temperature heat output with increasing time and temperature. The onset temperature of 

sustained heat output increased with increased time/temperature aging. These measurements 

suggest that the anode protection layer is undergoing partial conversion from the metastable 

species to the stable inorganic species even at these low temperatures. The majority of this 

conversion takes place relatively quickly (less than two weeks) even at 60°C, as little further 

change was noticed for the 70°C/6-week cell. After decomposition of the SEI anode protection 

layers (>120°C), the exothermic heating rates are similar regardless of the previous aging 

history. Notably though, the reaction rate immediately following onset was more abrupt with 

increased aging, showing further evidence of a breakdown of a growing SEI layer exposing the 

previously protected lithiated anode particles. Higher temperature measurements were not 

performed during this early phase of the ABR program. 

86 Roth, E. P. (2000). “Thermal Characterization of Li-ion Cells Using Calorimetric Techniques.” 39th Power 

Sources Conference Proceedings, June 12–15, 2000, Cherry Hill, New Jersey. 

79 
Figure 29. ARC runs of fresh and aged Sony cells at 100% SOC 37 

ARC measurements were also performed on GEN1 cells that underwent accelerated cycle aging 

at elevated temperatures of 40°C, 50°C, and 60°C. The cycle consisted of a discharge/charge 

profile resulting in a decrease in SOC of 3%, 6%, or 9% from a baseline of 80% SOC. All cells 

were placed at 100% SOC for ARC measurements up to 160°C. 

The ARC profiles for the cells cycled at 50°C with 3%, 6%, and 9% delta SOC are shown along 

with the unaged baseline cell data shown in Figure 30. The cells aged at 50°C showed increased 

stability as measured by increasing T(onset) temperature, which means that self-sustained 

heating did not occur until above 80°C for the cycled cells. Above 80°C, the heating rates were 

very similar to those for the unaged cell. The dip in the heating rate at 130°C resulted from the 

melting of the separator material. 

80 
 

 

 

 

 

 

Figure 30. ARC runs of GEN1 cells (100% SOC) aged at 50°C, 8% SOC, at 2%, 6% and 9% delta
 

SOC.

37
 

7.8 Effect of Cell Energy on Thermal Stability

As mentioned previously, higher energy cells have a stronger response to abuse events and 

usually have poorer safety performance. A study by Exponent Failure Analysis Associates87 

investigated the thermal stability of cells that contained the same energy but were manufactured 

with four different cathodes. The cathodes studied and the cells that were prepared are 

summarized in Table 6. 

Power and energy characteristics of the tested cells were consistent with expectations for cell 

design and electrode chemistry. 

Cells were charged to predetermined levels prior to ARC testing with the goal of comparing cells 

with identical capacity. All four cells were tested after being charged to a capacity of 1.1 Ah. 

Three cells were tested at 1.5 Ah, two at 2.2 Ah, and one at 2.5 Ah. The cell test matrix is shown 

in Table 7. 

87 White, K.; Horn, Q.; Singh, S.; Spray, R.; Budiansky, N. (2010). “Thermal Stability of Lithium-ion Cells as 

Functions of Chemistry, Design and Energy.” Presented at Lithium Mobile Power 2010, Boston MA, November 4-5, 

2010. 

81 
 

Table 6. Characteristics of Exponent Test Cells Made with Four Different Cathodes87 

Table 7. ARC Test Sample Charge Energy87 

Cell ID 

1100 

mAh 

1500 

mAh 

2200 

mAh 

2500 

mAh 

LFP X 

NCM + LMO X X 

LCO X X X 

LCO X X X X 

The ARC was used to evaluate thermal stability. The experimental measurements used were selfheating onset temperature and self-heating rate at 180°C, important measures of thermal stability 

and cell safety. 

The ARC results are shown in Figure 31 and Figure 32. The self-heating onset temperature is a 

strong function of cell charge energy (i.e., SOC). The onset temperature of high-energy LiCoO2 

at 82% SOC is comparable to LiFePO4 but LiCoO2 has 50% more capacity. The self-heating rate 

at 180°C appears to be dependent on cell energy rather than cell chemistry or cell design. These 

data also suggest an exponential relationship between energy and self-heating rate. 

82 
100 

100 1.5 Ah 98 

98 1.5 Ah NCM

96 1.0 Ah 2.2 Ah LCO 96 2.6 Ah LCO 94

Onset Temperature, o

C

94 1.1 Ah LFP 

92 

90 

88 

86 

84 

82 

Onset Temperature, o

C

92 2.1 Ah 1.5 Ah NCM

90 2.2 Ah LCO 1.1 Ah 

88 2.6 Ah LCO

 1.1 Ah LFP 86 

84 

82 

80 

80 78
 

78
 76 

3.0	 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 

Cell Energy, Wh % State of Charge 

Figure 31. Self-heating onset temperature as a function of cell energy and SOC.

87

12

11
 

 1.5 Ah NCM 10 

Self Heating Rate at 180 oC, oC/min 

 2.2 Ah LCO

9 2.6 Ah LCO

8 1.1 Ah LFP 

7 

6 

5 

4 

3 

2 

1 

3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 

Cell Energy, Wh 

Figure 32. Self-heating rate at 180°C.87

83
 

 

 

The authors at Exponent Failure Analysis Associates raise questions about the validity of 

improved safety claims attributed to cathode substitution that may, in fact, be a result of the low 

energy design. This work poses the question of whether cell energy content determines the safety 

and abuse tolerance response of a cell rather than the current thinking that the materials 

determine the safety and abuse tolerance response. 

This conclusion is controversial, but supports informal discussion with Prof. Gerd Ceder,88 who 

states, “The stability of phosphate cathodes is a result of the lower voltage, not inherent chemical 

stability.” The roadmap recommends that a comprehensive investigation that separates the effect 

of materials and cell capacity and identifies the role(s) of active materials be funded. Further, a 

validated cell abuse model should be developed to help elucidate and understand these effects. 

88 Private communication, Gerd Ceder, January, 12, 2011. 

84 
 

 

 

 

 

 

8	 Review of Approaches to Improve Safety and 

Recommendations 

8.1 Issues that Control Abuse Response

The issues that drive materials developers, cell designers, and battery pack manufactures can be 

summarized by the following topics: 

•	 Oxidative capacity of cathode (O2 generation and surface oxidation potential) 

•	 Stability of anode SEI 

•	 Stability of separator 

•	 Is separator shutdown a good thing in EVs and HEVs? 

•	 Electrolyte flammability and reactivity with electrode materials 

•	 Likelihood of internal short circuit occurring 

•	 Likelihood of single cell failure propagating to adjacent cells. 

The following sections discuss research efforts that are addressing these concerns. 

8.2 Cathodes 

The first of the two cathode issues is the oxidative capability of the cathode. The cathode’s active 

material surface is a source of high-oxidation potential at high SOC and overcharge. The contact 

between the cathode surface and the common organic electrolytes used in Li-ion cells can result 

in increased surface impedance due to: 

•	 The formation of reaction products 

•	 Dissolution of the transition metal active species from the cathode particles 

•	 Irreversible structural changes in the cathode materials. 

These reactions are deleterious and can reduce the rate capability, capacity, and stability of the 

cathode material. These reactions also produce heat at a significant rate, which can lead to 

thermal runaway in the cell. 

The LiFePO4 cathode family has higher oxidative stability than do layered oxides such as 

LiCoO2. However, safety is achieved in cells with significantly reduced energy. LiFePO4 

materials are sufficiently well studied in the commercial and academic sectors. Moreover, the 

low specific energy will limit their usefulness in many traction applications that require high 

energy. Therefore, the author of this roadmap recommends that DOE investments be targeted 

elsewhere for the development of new, high-energy cathode materials. 

High-voltage cathodes are being explored by groups because of the attraction of high energy. 

However, high-potential cathodes in lithium systems have shown evidence of oxidative potential 

and oxygen evolution, which can lead to thermal runaway problems. It has been shown that for 

several cathode systems, there is a linear relation between the logarithm of the equilibrium 

oxygen pressure and the potential, independent of both the chemical compositions and the crystal 

85 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

structures of the phases involved.89 Thus, the worry about oxygen generation at high potential 

can be exacerbated by using high-voltage cathodes. In his publication, Huggins cautions about 

using high-voltage cathodes because of their enhanced oxidative tendency that portends safety 

problems. 

TIAX has developed CAM-7, a stabilized, doped LiNiO2-class cathode material with a unique 

combination of high energy density and high power density that enables significantly longer run 

times in both high-energy and high-power Li-ion applications.90 CAM-7 supports discharge 

capacities exceeding 200 mAh/g without requiring charging beyond the normal Li-ion charge 

voltage of 4.2 V. In addition, CAM-7 supports excellent high-power discharge capacities as 

illustrated by delivery of >130 mAh/g discharge capacity at a rate of 100°C. It has the highest 

capacity at high rates of discharge as any cathode that has been announced recently.91 The 

reported safety of this cathode material looks promising,92 but the impact on industry is still to be 

determined. The TIAX approach, typical of many groups in the United States and elsewhere, is 

to make incremental improvements on today’s mixed oxide cathode materials. Success is to be 

expected, and Li-ion rechargeable battery technology for vehicles will benefit from incremental 

improvement in performance and safety. However, it will not produce a new generation of 

cathodes. A different approach is needed. 

First principles calculation can be a good guide to understanding safety aspects, such as oxygen 

generation at high SOC. Ceder’s group at MIT has developed a methodology that, combined 

with large computing resources and their analysis software, allows the same analysis on a much 

larger scale for intercalation compounds.93 The goal is to identify candidate materials that have 

high-capacity, low-oxidative potential, and are not currently being studied as cathode materials. 

The ability to perform these calculations rapidly on many potential material stoichiometries 

provides a powerful tool. Figure 33 shows a plot of chemical potential of oxygen (which is 

related to oxidative reaction potential and O2 evolution) versus voltage for an extremely wide 

range of hypothetical materials and structures. Early results support the conclusion that, in 

general, the higher voltage cathode creates worse thermal stability. However, new polyanion 

structures potentially achieve a better tradeoff between voltage and thermal stability. Borates and 

silicates seem to offer the best voltage to thermal stability performance. Calculations such as 

these can provide guidance to synthetic programs to discover new cathode materials that can 

have high capacity and improved safety. 

89 Huggins, R. A. (2009). ECS Transactions, 16 (29) 37–47.
 90 Pullen, A.; Ofer, D.; Clatterbuck, D.; Rempel, J.; Oh, B.; Dalton-Castor, S.; Barnett, B.; Sriramulu, S. (2010). “A 

Lithium Nickelate-Based Cathode Material for High-Energy, High-Power Lithium-Ion Batteries” Abstract #1004,
 

218th ECS Meeting, Las Vegas, NV, Oct. 10–15, 2010.
 91 Whittingham, M. S. (2011). “Energy Storage Materials: The Past and the Future.” Pacific Power Source
 

Symposium 2011, January 10–14, 2011. Waikoloa, HI.
 92 Barnett, B. (2010). “TIAX CAM-7 High-Capacity, High-Power Cathode.” Knowledge Foundation Battery Safety
 

2010 Proceedings, Boston, November 3, 2010.
 93 Ong, S. P.; Jain, A.; Hautier, G.; Kang, B.; Ceder, G. (2010). Electrochem. Comm. 12 (2010) 427–430.
 

86 
 

 

 

 

 

 

 

 

 

 

 

 

Figure 33. Calculated relationship between oxygen chemical potential at full charge and voltage 

for many cathodes. 

Source: A. Jain, G. Hautier, S. P. Ong, et al. Physical Review B 2011, 84, 045115 

Cathode conversion reactions are another fertile field for development of high capacity, safe 

cathodes. Several material compositions are potentially available for study, but this discussion 

will highlight only one system being explored by Prof. Glenn Amatucci – nanostructured 

FeF3.

94,95 FeF3 has a theoretical specific capacity of 820 mAh/g and a theoretical specific energy 

of 1,783 mWh/g. These values are several times higher than those of typical lithium battery 

cathode materials. The cathode can be paired with traditional Li-ion anodes as well, but only 

achieves limited cycle life (less than 50 cycles). Materials were cycled in cells that gave 550 

mAh/g (cathode) and over 400 Wh/kg (cell level). Preliminary safety tests of FeF3 are 

encouraging. The thermal stability of FeF3 has also been studied.96 DSC was run on charged and 

discharged FeF3 cathodes, with and without an electrolyte. The DSC results indicated that FeF3 

was stable in the electrolyte after lithiation and delithiation. The only exotherms observed were 

attributed to electrolyte decomposition. Thus, proof-of-principle has been established showing a 

cathode can deliver very high energy without adding to the thermal instability of a cell. This type 

of work should be expanded in future DOE programs. 

94 Cordova, S.; Johnson, Z.; Pereira, N.; Badway, F.; Amatucci, G. G.; Abraham, K.M. (2008). “A Very High 

Specific Energy Rechargeable Lithium Battery Chemistry.” 43rd Power Sources Conference Proceedings, July 7–
 

10, 2008, p. 569.

95 Amatucci, G. G. (2010). “Metal Fluoride Conversion Nanocomposites: An Alternative Road for Lithium-Based
 

Energy Storage.” Li Mobile Power, Boston, MA, November 4–5, 2010.
 96 Zhou, M.; Zhao, L.; Doi, T.; Okada, S.; Yamaki, J.-I. (2010). “Thermal stability of FeF3 as Positive Electrode for
 

Lithium Ion Batteries.” Abstract 3A06, 51st Battery Symposium in Japan Proceedings, November 9–11, 2010,
 

Nagoya, Japan.
 

87 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Significant research has been directed at investigating different coatings for the various cathode 

particles with the goal of reducing oxidative surface reactions.97 It was observed that “when the 

surface of cathode materials, including LiCoO2, LiNiO2, LiMn2O4, and LiMnO2 are coated with 

oxides, such as MgO, Al2O3, SiO2, TiO2, ZnO, SnO2, ZrO2, Li2O ·2B2O3-glass, and other 

materials, the coatings prevent the direct contact with the electrolyte solution, suppress phase 

transition, improve the structural stability, and decrease the disorder of cations in crystal sites.” 

Another proposed advantage of including these oxides is that they can act as scavengers for 

hydrogen fluoride (which results from reactions of the LiPF6 and trace water in the electrolyte 

and can cause corrosive attack of the cathode particles).98 The advantages of these coatings 

depend on several properties such surface coverage, coating thickness, Li-ion diffusivity, and 

long-term mechanical stability after cycling. All of these properties affect the performance of the 

cell but also affect the thermal abuse response. In order to improve the thermal abuse response of 

a cell, these coatings must be stable and maintain their protective properties at high temperatures 

where the kinetics of the cathode/electrolyte reaction greatly increase the exothermic output and 

where the structural stability of many cathode materials begins to degrade. 

Cathode coatings are believed to delay or mitigate these reactions that lead to thermal runaway.99 

DSC results have shown significant heat reduction with application of some of these coatings, 

indicating that, when the surface reactions are minimized by the coating, the oxygen generation 

inside the powders can be reduced. Some of these coatings can also possibly mitigate the cell 

response during overcharge, e.g., AlPO4-coated LiCoO2

100 and LiNi0.8Co0.1Mn0.1O2.101 Recent 

work has investigated coatings for the more recently used NMC “333” [Li(Ni1/3Co1/3Mn1/3)O2] 

cathode. Coatings such as ZrO2,

102 ZrFx,103 and AlF3

98 have shown improved cycling 

performance and lower thermal reactivity. For example, ARC tests were performed at SNL on 

several 18650 cells using AlF3-coated NMC cathodes provided by Argonne National 

Laboratory.104 Figure 34 shows the ARC thermal response profiles for uncoated and AlF3-coated 

cathodes in 18650 cells. All of the coated electrodes showed reduced heating rates and had about 

20°C higher thermal runaway onset temperatures (~260°C). Variations in the peak heating rates 

are believed to result from variations in coating thickness and coverage on the cathode particles 

at these temperatures. 

97 Li, C.; Zhang, H.P.; Fu, L.J.; Liu, H.; Wu, Y.P.; Rahm, E.; Holze, R.; Wu., H.Q. (2006). Electrochimica Acta 51 

3872–3883.
 98 Chen, Z.; Qin, Y.; Amine, K.; Sun, Y.-K. (2007). J. Electrochem. Soc., 154 _3, A168-A172.
 99 Cho, J.; Lee, J-G; Kim, B.; Park, B. (2003). Chem. Mater. 15, 3190–3193.
 100 Cho, J. (2004). Journal of Power Sources 126, 186–189 (2004).
 101 Cho, J.; Kim, H.; Park, B. (2004). J. Electrochem. Soc., 151, 10, A1707–A1711.
 102 Li, J.; Zhang, Q.; Liu, C.; He. X. (2009). Ionics 15, 493–496.
 103 Yun, S.H.; Park, K-S.; Park, Y.J. (2010). Journal of Power Sources 195, 6108–6115.
 104 Orendorff, C. (2011). Advanced Automotive Battery Conference Proceedings, Pasadena, CA, January 25, 2011.
 

88 
 

200 

180 

160 

140

min

NMC (SNL43) 

120

 (C/

100

Normalized Rate -Ah) 

80 AlF3 NMC (SNL35) 

60 

20 

40 AlF3 NMC (SNL33) AlF3 NMC (SNL31) 

0 

150 200 250 300 350 400 450 

Temperature (C) 

Figure 34. ARC profiles of 18650 cells with AlF3-coated and uncoated NMC cathodes. 

(Unpublished SNL data)

Direct measurements of the thermal properties of the coated cathode materials also confirm and 

clarify the role of the cathode in the full cell thermal response. Figure 35 shows DSC 

measurements on coated and uncoated cathode materials; it can be seen that the coating delayed 

the onset of thermal decomposition by at least 20°C as seen in the ARC measurements of the full 

cell.105

Figure 36 shows ARC measurements of the individual 18650 electrodes compared to one of the 

most passivated full cells using the AlF3-coated NMC electrodes. The contributions of the anode 

and cathode to the full cell response can be clearly seen where initial reactions arise at the anode 

followed by the higher-temperature cathode reactions. The coated cathode thermal response has 

now been reduced to a level comparable to that of the anode material. 

105 Data from Argonne National Laboratory obtained as part of the DOE ABR Program.

89
 

 

 

 

 

Figure 35. DSC measurements of AlF3-coated and uncoated NMC cathodes.

105 

3.0 

2.5 

Rate (C/min) 

2.0 

1.5 

1.0 

0.5 

AlF3-NMC 

Full cell 

AlF3- NMC 

cathode only 

AlF3- NMC 

anode only 

150 200 250 300 350 

0.0 

Temperature (C) 

Figure 36. ARC measurements of full cell and individual 18650 electrodes with AlF3-coated NMC 

cathodes. 

(Unpublished SNL data) 

Cathode coatings show good potential to improve cell abuse tolerance and are considered by 

Mike Thackeray as the highest priority in cathode safety topics.106 However, the mechanism-ofaction as well as durability issues have not been solved.107 The potential of cathode surface 

modification techniques is very promising and should be included in the funding priorities of 

future DOE safety and abuse tolerance programs. 

106 Private communication, Mike Thackeray, January 10, 2011. 

107 Private communication, Ratnakumar Bugga, January 10, 2011. 

90 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

8.3 Anodes 

The use of alternate anode materials may also affect cell safety. Materials that operate at higher 

voltage with respect to lithium potential include lithium alloys and various intercalation materials 

of which lithium titanate (Li4Ti5O12, or LTO) is one example108 and Li-metal alloys are 

another.109 The benefits of these anodes are improved thermal stability and the potential for 

competitive performance in high-rate cell designs.110 

8.3.1 LTO Anodes 

Li4Ti5O12 anode has been proposed as a “safe alternative” to graphite electrodes. Manev111 

outlined the advantages of using Li4Ti5O12 anodes: 

• No lithium plating. 

• Lower self-heating with respect to graphite. 

• Heat generation at elevated temperature is less than graphite. 

• Li4Ti5O12 can absorb O2 from the cathode, thus increasing the stability of the cell. 

• Calendar life is estimated to be 20+ years. 

However, from Manev’s Knowledge Foundation presentation in November 2010, we learned 

that the cell-level specific energy is 75 Wh/kg. LiFePO4/Li4Ti5O12 cells have even lower specific 

energy—only 50–60 Wh/kg, as estimated by Hydro Quebec.112 This energy level is only slightly 

more than improved NiMH, a proven technology for vehicle applications. NiMH started at 45 

Wh/kg and is now projected to be 80 Wh/kg within five years.113 The author of this roadmap 

therefore concludes that Li4Ti5O12-based cells will have insufficient energy to have a substantial 

presence in EVs and HEVs. The roadmap does not recommend that additional resources should 

be spent developing this electrochemical couple for traction applications. 

8.3.2 Lithium Alloy Anodes 

It is generally recognized that, while they deliver high capacity, Li-metal anodes paired with Liion cathodes will not have sufficient safety for EV and HEV traction applications. Therefore, 

lithium alloys are gaining commercial and academic interest because of the high-energy 

content.91 Many lithium alloys are being developed that produce Li-ion cells with much higher 

energy than carbon-based anodes. 

Silicon is an attractive anode material for Li-ion batteries because it has a low discharge potential 

and the highest known theoretical charge capacity (4,200 mAh/g).114 Although this is more than 

108 Ohzuku, T.; Ueda, A.; Yamamoto, N. (1995). J. Electrochem. Soc. 142 1431.
 109 Todd, A. D. W.; Mar, R. E.; Dahn, J. R. (2007). J. Electrochem. Soc. 154 A597.
 110 Christensen, J.; Srinivasan, V.; Newman, J. (2006). J. Electrochem. Soc. 153 A560.
 111 Manev, V. (2010). “Large Format Li4Ti5O12 Li-ion Batteries – Performance and Applications.” Li Mobile Power,
 

Boston, MA, Nov. 4–5, 2010.
 112 Zaghib, K. (2011). “Olivine-Polymer Ionic Liquid-Lithium for High Energy Batteries for Green Transportation.”
 

Pacific Power Source Symposium 2011, Jan. 10–14, 2011. Waikoloa, HI.
 113 Fetcenko, M. (2011). “NiMH Advanced Materials for Consumer, Vehicle and Stationary Applications.” Pacific
 

Power Source Symposium 2011, Jan. 10–14, 2011. Waikoloa, HI.
 114 Boukamp, B. A.; Lesh, G. C.; Huggins, R. A. (1981). “All-solid lithium electrodes with mixed-conductor
 

matrix.” J. Electrochem. Soc. 128, 725–729.
 

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ten times higher than existing graphite anodes and much larger than various nitride and oxide 

materials, macro-scale silicon-based anodes have limited applications due to silicon’s large 

volume changes (400%) upon insertion and extraction of lithium, which results in pulverization 

and rapid capacity fading. 

Recently, it has been demonstrated that anodes based on silicon nanowires circumvent these 

issues as they can accommodate large strain without pulverization, provide good electronic 

contact and conduction, and display short lithium insertion distances.115 However, silicon 

nanowire-only anodes possess the following potential drawbacks: 

•	 Reduced Electrical Conductivity: Crystalline silicon nanowires are less conductive than 

carbonaceous materials due to their semiconducting natural properties. Silicon nanowires 

become amorphous with lithium insertion and stay in an amorphous state after the first 

cycle. 

•	 Structural Changes: The electrical conductivity of the silicon nanowires is further 

reduced after lithiation due to dramatic structural changes. The increased resistivity will 

also generate Joule heat, leading to potential safety problems. It will also reduce battery 

capacity at a rapid discharge/charge rate, which is required for high-power applications. 

•	 Less Structure Integrity: The structural change from pristine crystalline silicon nanowires 

to porous amorphous nanostructures could degrade its mechanical robustness, yielding 

potential nanowire fracture and reduced battery capacity. 

•	 Less Area Capacity: Newly grown silicon nanowires have less density compared to 

conventional carbonaceous anodes. 

Groups are working to overcome these and other technical problems, and a recent report from 

Stanford University shows an improved cycle life for an anode that has a three-fold higher 

capacity than graphite.116 However, there is no published work that we could find on the safety 

of batteries made with silicon or other alloys. Because these batteries could be proposed for use 

in traction applications, the DOE should have a program to investigate the safety issues with 

batteries made with high-capacity Li-alloy anodes. 

8.3.3 Additives to Stabilize Anode Surface 

The SEI is a protective film that develops on the anode during the initial formation step of cell 

processing. This film develops from interaction of the electrolyte with the anode surface during 

initial lithiation and occurs at a potential higher than the intercalation potential for the solvated 

lithium ions. This prevents the destructive exfoliation of the graphite that can occur if 

intercalated solvent molecules are reduced within the graphite planes. The composition of this 

SEI layer is quite complex and has been studied for many years.117,118,119,120, 121 The film has been 

115 Chan, C. K.; Peng, H.; Liu, G.; Mcilwrath, K.; Zhang, X. F.; Huggins, R. A.; Cui, Y. (2008). “High performance 

lithium battery anodes using silicon nanowires.” Nature Nanotechnology 3, 31–35.
 116 Cui, Y. (2010). “3X Capacity from Silicon-Nanowire-based Li-ion Batteries.” Presented at Lithium Mobile
 

Power 2010, Boston MA, November 3, 2010.
 117 Peled, E. (1979). J. Electrochem. Soc., 126 12 2047-2051.
 118 Aurbach, D.; Markovsky, B.; Shechter, A.; Ein-E1i, Y.; Cohen, H. (1996). J. Electrochem. Soc., 143 12 3809–
 

3820.
 119 Peled, E.; Golodnitsky, 0.; Ardel, G. (1997). J. Electrochem. Soc., Vol. 144, 8.
 

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seen to be multi-layered and non-uniform and consists of several inorganic and organic 

decomposition products. The composition of these products depends strongly on the composition 

of the electrolyte solvents and salt. Ideally, these films should be relatively thin, have lowporosity to prevent electrolyte contact with the graphite, and have high Li-ion conductivity. They 

should also be mechanically flexible to accommodate expansion of the anode layer during 

intercalation, free of micro cracks, and stable at elevated temperatures.122 

The formation of this layer results in irreversible capacity loss due to the loss of lithium from the 

cathode material. This must be an acceptable loss because this film prevents further reaction 

between the electrolyte and the lithiated anode, which otherwise would continue to consume the 

lithium ions. The SEI forms quickly but continues to develop with time. The layer thickness has 

been shown both experimentally and theoretically to increase with the square root of time.122, 123 

The increasing thickness of the SEI layer can result in increased impedance at the anode and 

reduced rate capability, but it also increases the thermal stability of the protective layer, as shown 

in Figure 29. 

Several electrolyte additives have been proposed and tested to improve the stability of the SEI 

layer, thus reducing irreversible losses, increase lifetime, and improve thermal stability. Two of 

the most common SEI film-forming additives being used in cells today are vinylene carbonate 

(VC) and vinyl ethylene carbonate (VEC). Extensive work has gone into characterizing and 

modeling the effects of these additives. 124, 125, 126, 127, 128 

Work by Aurbach et al.129 showed that VC polymerizes on the lithiated graphite surfaces, 

forming poly alkyl Li-carbonate species that suppress both solvent and salt anion reduction. 

Shima et al.130 have shown increased thermal stability of electrolytes with this additive while Ota 

et al.

121 showed enhanced thermal stability of the VC-derived SEI coating on the exposed anode 

surfaces. It has also been shown that adding a few weight-percent of VEC to PC-based 

electrolytes significantly improves their performance.125 Calculations in this work showed VEC 

underwent direct two-electron reduction more readily than EC and PC and thus should react 

more readily to form the passivating Li2CO3. Lucht et al.126 have investigated electrolyte 

stabilizing additives that reduce species known to attack the SEI layer, namely dimethyl 

acetamide and N-methyl-2-pyrrolidone (NMP). These Lewis-based stabilizing agents have been 

120 Aurbach, D.; Markovsky, B.; Levi, M.D.; Levi, E.; Schechter, A.; Moshkovich, M.; Cohen, Y. (1999). J. Power 

Sources 81–82 95–111.
 121 Aurbach, D.(2000). J. Power Sources 89 _206–218.
 122 Ploehn, H. J.; Ramadass, P.; White, R. E. (2004). J. Electrochem. Soc., 151, A456-A462.
 123 Yoshida, T.; Takahashi, M.; Morikawa, S.; Ihara, C.; Katsukawa, H.; Shiratsuchi, T.; Yamaki, J-I. (2006). J.
 

Electrochem. Soc., 153 _3_ A576-A582.
 124 Ota, H.; Sakata, Y.; Inoue, A.; Yamaguchi, S. (2004). J. Electrochem. Soc., 151 10 A1659-A1669.
 125 Vollmer, J. M.; Curtiss, L. A.; Vissers, D. R.; Amine, K. (2004). J. Electrochem. Soc. 151 1 A178-A183.
 126 M. C. Smart, B. L. Lucht and B. V. Ratnakumar. J. Electrochem. Soc., 155 _8_ A557-A568 (2008)
 127 W. Li, A. Xiao, B. L. Lucht, M. C. Smart, B. V. Ratnakumar. J. Electrochem. Soc., 155 _9_ A648-A657 (2008)
 128 C. Jehoulet, P. Biensan, J. M. Bodet, M. Broussely, C. Moteau, and C. Tessier-Lescourret. “Batteries for Portable
 

Applications and Electric Vehicles,” A. R. Landgrebe and C. F. Holmes, eds, pp. 97–18, p. 974, The 

Electrochemical Society Proceedings Series, Pennington, NJ (1997).
 129 D. Aurbach, K. Gamolsky, B. Markovsky, Y. Gofer, M. Schmidt, U. Heider. Electrochimica Acta 47 1423–1439 

(2002)

130 E.-G. Shima, T.-H. Nama, J.-G. Kima, H.-S. Kim, S.-I. Moon. J. Power Sources 172 901–907 (2007).
 

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found to reversibly bind with phosphorus pentafluoride (PF5), preventing LiPF6 and carbonate 

solvents from decomposition at high temperatures. 

Although these additives have been investigated as to their ability to improve SEI stability for 

improved performance and for moderately elevated temperature stability, little work has been 

performed on their effect on high temperature thermal runaway response in full cells. Although 

SNL and Argonne National Laboratory have produced and measured a number of cells with VC 

and VEC additives, a systematic study with a sufficient number of cells to determine a definitive 

response has not been performed. Continued work on these promising materials is justified 

because they can effectively and economically enable the use of otherwise unstable and reactive 

materials being designed for ever higher potentials and energy. 

8.4 Separators 

8.4.1 Ceramic Composite Separators 

The concern about internal short circuits has resulted in a search for new separators, as well as 

modifications of existing electrode materials. Improvements in safety response have been 

achieved by introducing ceramic particles as either coatings or inclusions in the separator to 

prevent electrical shorting even at temperatures well above the melt temperature. There are two 

basic approaches: 

1.	 Composite separator (polymer and ceramic particles dispersed in the bulk of the polymer) 

2.	 Coating of polymer/ceramic composite on the separator or on one (or both) of the
 

electrodes.
 

Use of ceramic coatings seems to be widespread. The heat resistant layer plays a key role in 

managing safety by preventing contact between the anode layer and the cathode layer at the cell 

level. 

Information on which company is using these approaches is hard to verify because of the 

proprietary nature of development efforts. Information from personal contacts seems to highlight 

the importance of this approach. For example, Dr. Jeon Oh said that, “SK Energy uses Al2O3­

coated separators (both sides) because it allows the cells to pass blunt rod simulated internal 

short circuit test.”131 [It is important to note that SK Energy is the manufacturer of 25-Ah and 

50-Ah cells designed for EV and HEV applications. Dr. Oh claims that their customers require 

ceramic-coated separators for safety.] 

131 Private communication, Jeon Oh, November 10, 2010. 

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Companies that manufacture cells containing heat-resistant separators are believed to be: 

•	 Panasonic – We received information that Panasonic has announced a coating on one 

side of a separator or on a cathode before winding cell. We believe that they are using 

Al2O3. 

•	 LG Chem – LG Chem is using a coated separator (likely both sides). The guess is that 

they are using Al2O3. 

Separator manufacturers who are developing heat-resistant separators are: 

•	 Entek – Entek has a DOE program to produce ceramic-filled ultra-high molecular-weight 

poly(ethylene) porous separator membranes. The studies include Al2O3 and SiO2.

132 

[Notes: Rick Pekala thinks that Al2O3 is too expensive. Most manufacturers use fumed 

Al2O3, which at $20/kg is too expensive for large-scale battery use. SiO2 has potential 

weakness due to hydrogen fluoride attack. Additionally, it carries a lot of water, and the 

separator needs to have extra drying step to avoid introducing water into the battery. 

Entek is making 12-μm ceramic-filled separators.] 

•	 Asahi – Indications are that Asahi is incorporating ceramic-filler in the bulk polyolefin 

shutdown separator. This information is sketchy, and there is no information on the type 

of ceramic. Asahi appears to be the only Japanese manufacturer working on ceramics in 

the polymer bulk. Other companies are coating an inorganic-filled polymer on the surface 

of the separator or cathode. 

•	 Sony – Sony has described the development of a two-sided, coated ceramic separator that 

can reduce the risk of failing a high-current internal short circuit test.133 

•	 Degussa – Degussa has a polyethylene terephthalate-based composite separator marketed 

as Separion. Whether this is a ceramic filler is not certain, but likely Al2O3 or SiO2, or 

some mixture of these (although their patents claim eight different ceramic materials). A 

study was done at ZSW, a German R&D laboratory, on 8-Ah cells with LiMn2O4 

cathodes that contained a normal polyolefin shutdown separator and the Degussa new 

ceramic separator without shutdown properties.134 They demonstrated that the thermal 

runaway produced by overcharge could be avoided with the more stable (ceramic) 

separator. 

•	 Celgard – John Zhang135 said that, “Ceramic-coated shutdown separators are being 

developed by Celgard, but the experienced manufacturers are staying with traditional 

separators.” 

132 R. Waterhouse, R. Pekala, Y. Patil, S. Peddini, J. Emanuel, J. Frenzel, D. Lee, D. Spitz, G. Fraser-Bell.
 

“Development of Separators with Inorganic Fillers for Advanced Lithium Ion Batteries.” Presented at Lithium
 

Mobile Power 2010, Boston MA, November 3, 2010.
 133 A. Kajita et al. “A Novel Separator with Ceramic Layers for Li-ion Batteries.” Abstract 1B26, 51st Battery
 

Symposium, Nov. 9–11, 2010, Nagoya, Japan.
 134 H. Döring, B. Schmid, H. Brazel. Overcharge at 3 C rate and 12 V limit for fresh and cycled Li-Cells with
 

Polyolefin and Separion Separators. Center for Solar Energy and Hydrogen Research, Baden-Württemberg,
 

Germany. Report No. RP-ZSW-05_2005, May 2005.

135 Private communication, John Zhang, January 10, 2011.
 

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There are several fundamental questions that need to answered, such as will a ceramic-coated 

“shutdown separator” actually shut down? Will ceramic coating prevent shrinkage and 

shutdown? Rick Pekala136 says that, with the proper processing, the shutdown can still be 

observed with ceramic-coated polyolefin shutdown separators. It seems that the microstructure at 

the interface and the degree of entanglement between the two polymer structures plays an 

important role. Additional investments from DOE would be valuable in understanding the 

fundamental material interactions and benefits of ceramic coatings in lithium-ion rechargeable 

batteries. 

8.4.2 Electroactive Separators for Overcharge Protection 

Much research has been focused in recent years on development of internal and self-actuating 

overcharge protection mechanisms for Li-ion batteries. Electroactive polymers have the ability to 

switch rapidly between conductive and insulating states and sustain high-current densities. 

Electroactive polymers can provide overcharge protection for rechargeable lithium batteries 

when impregnated into a porous membrane separator. A small amount of the polymer can 

provide self-actuated, reversible protection for cells for a variety of chemistries by providing an 

electrically conductive pathway for the excess electrical charge during overcharge. 

As an electroactive material, the polymer should have an oxidation potential slightly lower than 

the terminating potential of the cathode and considerably lower than the decomposition potential 

of the electrolyte. Electroactive polymers are influenced by factors, such as the loading of the 

polymer, the morphology of the deposited polymer, the porosity of the composite, and the 

availability of doping anions from the electrolyte. 

The most investigated electroactive polymers are thiophene-based polymers137,138,139 and 

phenylamine-based polymers.140,141 Solutions of these polymers are used to impregnate standard 

commercial separators and then dried. Bilayer separators have also been used where different 

electroactive polymers are used for contact with either cathode or anode (see Figure 37).134 The 

layers work in parallel with the active electrodes so as not to introduce excess resistance, 

especially at low temperatures. This configuration allows significantly high current densities 

while maintaining low cell potential during the overcharge (Figure 38). This modified 

configuration may be implemented in larger battery cells, which have uncoated current collector 

areas that are designated for tabs. Improvements still need to be made in current density, stability 

against different electrode materials, and low-temperature performance. 

136 Private communication, Rick Pekala, November 4, 2010.
 137 G. Chen, T. J. Richardson. J. Electrochem. Soc., 157, 6, A735-A740 (2010).
 138 G. Chen, T. J. Richardson. Electrochemical and Solid-State Letters, 7, 2 A23–A26 (2004).
 139 S. L. Li, L. Xia, H. Y. Zhang, X. P. Ai, H. X. Yang, Y. L. Cao. J. Power Sources (2010),
 

doi:10.1016/j.jpowsour.2010.09.111

140 S.L. Li, X.P. Ai, H.X. Yang, Y.L. Cao. J. Power Sources 189 771–774 (2009).
 141 J.K. Feng, X.P. Ai, Y.L. Cao, H.X. Yang. J. Power Sources 161 545–549 (2006).
 

96 
Figure 37. Schematic of alternative designs using electroactive separator for overcharge 

protection.

139 

Figure 38. Rate performance of a protected Li1.05Mn1.95O4–Li cell with the bilayer, parallel cell 

configuration.

139 

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8.5 Electrolytes

As discussed earlier, flammability of the vented electrolyte is a significant unresolved safety 

issue for Li-ion batteries. The energy released by a burning electrolyte is several times larger 

than the energy stored in a battery. Accident scenarios involving burning electrolyte have some 

of the most serious consequences, resulting in cascading failure of other cells in the battery pack 

and involvement of adjacent materials and structures. 

8.5.1 Non-flammable Electrolytes 

Two mechanisms have been suggested to explain the flame retardation: 

•	 A physical char-forming process, which builds up an isolating layer between the
 

condensed and gas phases to retard the combustion process
 

•	 A chemical radical-scavenging process, which terminates the radical chain reactions 

responsible for the combustion reaction in the gas phase. 

Most flame-retarding additives used in liquid electrolytes are based on organic phosphorus 

compounds and their halogenated derivatives, and the radical-scavenging mechanism appears to 

explain experimental results. 

The four main categories of flame retardant additives that have been investigated are phosphates, 

phosphazenes, phosphides, and ethers. The additives that have been evaluated in the literature 

generally fall within one of two main categories, phosphorous-containing compounds, and 

halogen-containing compounds. In the vapor phase, the common mechanism is that phosphorous 

or fluorine radicals, which are provided by the decomposition of the additive, react with 

hydrogen radicals that are part of the flame’s chain-reaction mechanism. Numerous flameretardant additives have been tested in most of the standard Li-ion electrolytes with mixed 

results.142,143,144,145 Often, the amount of additive required to achieve non-flammability 

significantly reduces cell performance. Furthermore, some of the additives are not stable with the 

active electrode materials, especially against reduction at the anode. Non-flammable electrolyte 

additives, such as triphenyl phosphate and dimethyl methyl phosphonate, participate in SEI 

formation and concentration may decrease as cells age.146 Use of flame-retardant additives then 

requires additional additives to stabilize the anode. The long-term effect of these additives on 

cell lifetime and performance is not known. 

One of the major difficulties in evaluating the effectiveness of a flame retardant is a meaningful 

test that is relevant to the case of a venting Li-ion cell. Most tests are based on open flame or 

burning wick-type configurations. These tests are useful for evaluating the relative performance 

of different additives, but do not adequately recreate the conditions of a vented cell that produces 

a fine mist of aerosolized electrolyte and vapors. Flammability needs to be determined with full 

142 K. A. Smith, M. C. Smart, G. K. S. Prakash, B. V. Ratnakumar. ECS Transactions, 16 (35) 33–41 (2009).
 143 K. Xu, M. S. Ding, S. Zhang, J. L. Allen, T. R. Jow. J. Electrochem. Soc., 149 (5) A622–A626 (2002).
 144 X. Wang, C. Yamada, H. Naito, G. Segami, K. Kibe. J. Electrochem. Soc., 153 (1) A135–A139 (2006).
 145 Y. Shigematsu, M. U., and J. Yamaki. J. Electrochem. Soc., 156 (3) A176–A180 (2009).
 146 R. Bugga, “Advanced Lithium-Ion Batteries For NASA Lunar Missions.” Pacific Power Source Symposium
 

2011, Jan. 10-14, 2011. Waikoloa, HI.
 

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cells under controlled thermal conditions with multiple ignition sources to test for different 

fuel/air ratios.79 

8.5.2 Ionic Liquids 

Ionic liquids (ILs) are being investigated because they have the potential to improve abuse 

response, particularly with respect to the flammability of an electrolyte.147 ILs are non-volatile, 

non-flammable, highly conductive, environmentally compatible, and can safely operate in a wide 

temperature range. This unique combination of favorable properties makes ILs very appealing 

materials as stable and safe electrolytes in lithium batteries. 

Batteries filled with such a type of electrolytes do not contain any volatile components; 

therefore, they are not flammable. Room temperature ILs are characterized by negligible vapor 

pressure, which makes them inflammable. In addition, they show a broad electrochemical 

stability window, generally >4 V, which is necessary for the application in Li-ion batteries with 

high-energy cathodes. 

ILs are formed by the combination of a weakly-interacting large cation, such as the imidazole 

type, and a flexible anion, such as N,N-bis(trifluoromethanesulfonyl) imide. A recent review 

article describes substantial progress in the application of ILs to Li-ion rechargeable batteries.148 

The review article includes references to over 70 combinations of ILs and standard Li-ion 

electrolyte and electrode combinations. This area of research is very active, as demonstrated by 

the fact that 78 presentations were on the program at the 218th ECS Meeting in Las Vegas, 

Nevada, in October 2010. 

The stability range of the Li+ conducting electrolyte of above 4 V is necessary in practical 

applications to Li-ion batteries. The electrochemical stability of liquid aprotic quaternary 

ammonium salts, determined usually at glassy carbon or platinum electrodes, is within a wide 

range of 4–6 V. Popular imidazolium salts show stability of ~4 V, while piperidinium and 

pyrrolidinium salts, especially based on imide anions, show stability of ~6 V. Symmetrical 

tetraalkylammonium cations (e.g., tetraethylammonium tetrafluoroborate) have been used for a 

long time as supporting electrolytes in organic solvents due to their good stability. 

Thermal stability of different room temperature ILs may be estimated from DSC experiments. 

Classical solutions in molecular solvents (cyclic carbonates) show a decrease in weight due to 

solvent evaporation at increased temperatures. For example, the solution of LiBF4 in gammabutyrolactone (GBL) + EC shows a decrease in weight at around 90°C to 200°C. The weight loss 

reached 88% at 200°C with the decomposition of the residual of 12% between 200°C and 250°C 

(decomposition of the salt).149 

The substantive issues that must be resolved with ILs are: 

• High viscosity 

• Lack of anode passivation 

147 B. Scrosati , J. Garche. Journal of Power Sources 195 (2010) 2419–2430.
 148 A. Lewandowski, A. Swiderska-Mocek. Journal of Power Sources 194 (2009) 601–609.
 149 H. Nakagawa, S. Izuchi, K. Kuwana, T. Nukuda, Y. Aihara. J. Electrochem. Soc. 150 (2003) A695.
 

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• Low ionic conductivity (leading to low current densities) 

• Poor wettability of electrodes and separators. 

The viscosity of ILs is much higher than that of water (H2O = 0.89 cP at 25°C). Typically ionic 

conductivity is at the level of 30 – 50 cP, but in some cases it is much higher, even several 

hundred centipoise. 

The approach being developed at Hydro Quebec is to use aprotic polymer electrolytes, such as 

polyether, that are compatible with ILs.150 To overcome the viscosity problem, they use vacuum 

impregnation at 60°C to achieve good wetting and good capacity. 

The payoff of developing an IL that would give good performance in a Li-ion rechargeable 

battery is huge. It could largely eliminate the flammable electrolyte issue. 

8.5.3 Overcharge Protection Additives 

Overcharge protection can be achieved by mechanical, electrical, or electrochemical means.151 

One method that has been actively pursued is through the use of additives to the electrolyte that 

are activated at the high-overcharge potentials.152 Overcharge protection additives can generally 

be classified as redox shuttle additives or shutdown additives. The former protects the cell from 

overcharge reversibly, while the latter terminates cell operation permanently. Shutdown additives 

are polymerizable compounds that can be electrochemically polymerized at an overcharged 

cathode. The polymerized coating can reduce the charging current and thus protect the batteries 

from the hazardous overcharge condition. 

For most commercial Li-ion batteries, the upper cut-off potential can be as high as 4.2 V. The 

oxidative decomposition of the electrolyte can occur at about 5 V, which is often seen as a 

voltage plateau during overcharge. To avoid the decomposition of electrolyte, the polymerization 

reaction should take place in the region of 4.2 V – 5.0 V. Biphenyl, cyclohexyl benzene, and 

other substituted aromatic compounds constitute the polymerizable class of shutdown 

additives.153,154 Although these compounds may be useful in consumer-level batteries with few 

cells, they may not provide protection in vehicle-level batteries, which can have more than a 

hundred cells in series. Because a single high-impedance cell would see a significant overpotential from the other cells or the charging system, breakdown of the polymerized film could 

readily occur. 

Redox shuttles involve electrochemical oxidation of a compound at the positive electrode, 

resulting in a radial cation, which diffuses to the negative electrode and gets reduced. The shuttle 

molecules then diffuse back to the positive electrode to restart the process. Thus, redox shuttles 

shunt the excess charge during overcharge and act as a controlled internal “short.” This can 

indefinitely limit the cathode potential near the oxidation potential of the shuttle additive. During 

150 K. Zaghib. “Olivine-Polymer Ionic Liquid-Lithium For High Energy Batteries For Green Transportation.”
 

Pacific Power Source Symposium, Jan. 10-14, 2011. Waikoloa, HI.
 151 P.G. Balakrishnan, R. Ramesh, T. P. Kumar. Journal of Power Sources 155 401–414 (2006)
 152 S. S. Zhang. Journal of Power Sources 162 1379–1394 (2006)
 153 M.Q. Xu, L.D. Xing, W.S. Li, X.X. Zuo, D. Shu, G.L. Li. Journal of Power Sources 184 427–431(2008)
 154 K. Shima, K. Shizuka, M. Ueb, H. Ota, T. Hatozaki, J.-I. Yamaki. Journal of Power Sources 161 1264–1274 

(2006)
 

100 
 

 

 

 

 

 

normal operation, the oxidation potential of the shuttle additives is not reached and the molecules 

remain inert. 

The maximum current that the shuttle additive can carry depends on several factors, including 

the concentration of the shuttle molecules in the electrolyte, the diffusion constant of the shuttle 

molecules, and the number of charges carried by the shuttle molecules.149 

There have been hundreds of compounds investigated for this purpose155,156 and are often aimed 

either at high-voltage cathodes157,158 (e.g., LiCoO2, Mn-spinel, LiNi1-x-yMnxCoyO2, 

LiNi0.8Co0.15Al0.05O2) or lower voltage materials (e.g., LiFePO4).153,159 The limitations on the use 

of shuttle additives often are due to limited charge rate, stability at high potentials, reduction of 

cell performance, and heat generation during shuttle activation.156 One promising shuttle is based 

on electrolyte solutions containing the StabiLife electrolyte salt Li2B12F12.

155 The dodecaborane 

molecular structure is shown in Figure 39. This shuttle has been shown to be effective at 1C 

charging rates for the high-voltage class of cathodes (Figure 40). Effective overcharge shuttles 

may require tailor-made compositions for each type of cell chemistry. 

The roadmap recommends that enough work is being done in industry and in academic 

laboratories in this area. Moreover, because the chemistry may not have broad applicability to all 

types of cathodes and anodes, a “generic overcharge shuttle” may not be achievable. 

155 Z. Chen, Q. Wang, and K. Amine. J. Electrochem. Soc., 153, 12, A2215-A2219 (2006)
 156 C. Buhrmester, J. Chen Lee, M. Junwei, J. Richard, L. Wang, J. R. Dahn. J. Electrochem. Soc., 152 _12_ A2390–
 

A2399 (2005)

157 L. M. Moshurchak, W. M. Lamanna, M. Bulinski, R. L. Wang, R. R. Garsuch, J. Jiang, D. Magnuson, M.
 

Triemert, J. R. Dahn. J. Electrochem. Soc., 156, 4, A309–A312 _(2009)
 158 G. GirishKumar, W. H. Bailey III, B. K. Peterson, W. J. Casteel, Jr. J. Electrochem. Soc., 158, 2, A146–A153 

(2011)

159 J. R. Dahn, Junwei Jiang L. M. Moshurchak, M. D. Fleischauer, C. Buhrmester, L. J. Krausec., J. Electrochem.
 

Soc., 152 6 A1283–A1289 (2005)
 

101 
 

 

 

TEST 

Figure 39. StabiLife Salt used as redox shuttle from Air Products158 

Figure 40. Effect of overcharge shuttle compared to normal cell during overcharge.
 

The cell (MCMB anode and LiCoO2 cathode) was charged at 1C overcharge rate.158
 

8.6 Improved Diagnostic Tests 

8.6.1 Internal Short Circuit 

Internal short hazards have been looked into extensively in the past few years due to the 

inadvertent fires that occurred during transportation, as well as the recalls by major Li-ion cell 

manufacturing companies. Internal shorts arise from two sources: 

•	 Those created by separator flaws or native contamination or foreign object debris 

introduced during manufacturing that manifest themselves during transportation or use. 

102 
 

 

 

 

Commercial 18650 Li-ion cells are manufactured in the millions every month. If the 

quality control is not stringent, there is a higher probability of getting internal cell shorts 

due to the presence of impurities such as metal particles and burrs. Even the best-quality 

manufacturers have had problems. 

•	 Those created due to misuse of the batteries. The proposed origin is the creation of 

dendrites when the cells are subjected to voltages, currents, and temperatures beyond the 

manufacturer’s recommendation (current and voltage anomalies can be caused by fast 

charge or poor cell balance in packs) or due to localized heating or large thermal 

gradients within a battery module. Another factor that could cause this is inadequate cell 

design that causes dry-out of the electrode in certain areas of the cell. 

An internal short hazard is one of the most difficult to reproduce, yet it is the most important to 

solve to improve safety. No one test has gained acceptance by industry or test organizations. 

•	 UL Blunt Nail Crush. This procedure calls for crushing the cell with a blunt nail until 

detection of a 100-mV open circuit voltage drop. 

ο	 PRO: Method does not require a lot of special sample preparation. 

ο	 CON: Short mechanism depends on how the blunt nail interacts with internal 

construction. 

•	 NASA blunt nail method. This method has some similarities to the UL blunt nail crush 

test. 

ο	 Pass/fail depends on vibration tests after blunt nail crush. 

•	 Battery Association of Japan Forced Internal Short-Circuit Test. This procedure requires 

disassembly of a charged cell, insertion of an L-shaped nickel metal particle, cell 

reassembly, and test. 

ο	 PRO: Can control location of internal short circuit 

ο	 CON: Safety concerns. Requires special equipment and cell preparation facilities. 

Difficult to perform. 

•	 Saft – Internal Heater Wire. A heater wire inserted into cell. Application of current 

(external power supply) will melt the separator, and a short circuit ensues. 

ο	 PRO: Can control location of internal short circuit. 

ο	 CON: Heating too diffuse – behaves like internal thermal ramp test. 

•	 SNL – Thermal trigger w/low temperature melting alloy. During winding of cells, low 

melting temperature (~65°C) alloy particles are incorporated. 

ο	 PRO: Can produce internal short circuit in 18650 cells. 

ο	 CON: Elevated temperature is required, and result depends on cell geometry 

(cylindrical versus prismatic). 

It is clear that these tests can cause irreproducible results and are difficult to control. These 

challenges need to be overcome so that the test is tolerant of cell construction variables (i.e., 

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spiral versus planar geometry). An additional problem is that results can be convoluted with 

other factors that influence thermal stability. 

The core difficulty in simulating an internal short circuit is that there are different shorting paths 

within the cell that can cause different short circuit responses. Different current paths are 

demonstrated in Figure 41. 

Figure 41. Sources of variability in internal short circuit test arise because there are four kinds of 

internal short circuit conditions.

85 

The four types of internal short circuit are: 

1. Anode to cathode 

2. Anode to aluminum 

3. Copper to aluminum 

4. Copper to cathode. 

The current that flows through each path depends on the resistance of each element. Moreover, 

the elements in the current path are heated rapidly and the thermal stability of the two electrodes 

varies widely. Current understanding 83 of internal short circuit electrode reactivity comes from 

Saft (France) testing of propagation of each electrode. Thermal conductivity of the carbon anode 

is ~10 W/mK, but the thermal conductivity of the cathode is ~0.5 W/mK. Firing a laser at each of 

the two electrodes in an inert atmosphere glove box shows that the charged anode will burn 

rapidly and consume the entire electrode, but the charged cathode will not propagate the thermal 

runaway. Consequently, shorting to the cathode material will most likely not create a thermal 

runaway event from an internal short circuit failure. Thus, types 1 and 4 have minimal potential 

to cause thermal runaway, whereas types 2 and 3 will cause thermal runaway. This analysis and 

thermal reactivity data led to the application of inorganic barrier coatings on separators and 

anodes (unfortunately termed heat resistant layers [HRL] in the literature). 

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A second element of susceptibility of a cell to thermal runaway from an internal short circuit lies 

in the ability of a cell to dissipate heat. The first-order characteristic is surface-to-volume ratio 

(i.e., high-surface-to-volume ratio will dissipate heat the fastest). Therefore, cell size is an 

important factor. Cell models need to be incorporated into module and battery pack models to 

adequately capture the dynamics of heat dissipation. These models are being developed,

160 but 

the pace needs to increase. 

The take-away message from this analysis is that our understanding of the internal short circuit 

event is superficial and the tests meant to simulate the event are not well developed. A 

systematic R&D program that elucidates the details of internal short circuits as well as heat 

dissipation would support a model of the internal short circuit event that would have substantial 

potential for safety improvement. 

8.7 Modeling 

Battery modeling is well developed, with academic and national laboratory groups very active in 

the area of investigation.161 However, not much attention has been directed at modeling safety 

and abuse tolerance issues. Some of the earliest work developed a thermal model of an 18650 

cylindrical cell.162 Since then, thermal models have been used to analyze temperature gradients 

in cells and battery packs.163 Recently, however, groups at NREL, SNL, TIAX, Battery Design 

LLC and universities have increased their efforts. 

Modeling of internal short circuit events is being developed by Celgard,157 TIAX,

7 and 

NREL.164,165 However, the results do not sufficiently capture the complexity of the internal short 

circuit event. The location of the internal short circuit—not only between which layers within the 

cell as described above, but also the proximity to a tab or other heat-sink—shows important 

effects in the models being developed. Another interesting factor that needs to be captured in any 

model is the effect of cell size on the internal short circuit and abuse tolerance in general. 

Intuitively, small cells seem to be more forgiving and safer in most abusive situations (e.g., 

button cells versus laptop cells). But the tradeoffs are not so clear when different cell geometries 

are considered (i.e., different heat management strategies). 

Validation of these internal short circuit models results poses significant challenges since 

experiments cannot readily control the location of an induced short circuit and often lead to 

results that are not adequately reproducible or that have a satisfactory conclusion. Recent efforts 

160 S. Santhanagopalan, P. Ramadass, J. (Z.) Zhang. Journal of Power Sources 194 (2009) 550–557.
 161 R. Spotnitz. The Electrochemical Society Interface, Winter 2005, p. 39-42.
 162 T. D. Hatchard, D. D. MacNeil, A. Basu, J. R. Dahn. Journal of The Electrochemical Society, 148, A755-A761 

(2001).

163 A. Pesaran, A. Vlahinos, D. Bharathan, G.-H. Kim, and T. Duong. Presented at 21st Electric Vehicle Symposium,
 

Monaco, April 4–7, 2005. 164 G. H. Kim, A. Pesaran, R. Spotnitz. “A Three Dimensional Thermal Abuse Model for Lithium Ion Cells.” J.
 

Power Sources, 170(2), pp. 476-489, 2007 and Gi-Heon Kim., “Li-ion Abuse Model Development,” 2009 Energy
 

Storage Annual Progress Report.

165 S. Santhanagopalan, P. Ramadass, Z. Zhang, “Numerical Experiments on Internal Short Circuit,” Presented at the 

15th International Meeting on Lithium Batteries, Montréal, Canada, June 2010.
 

105 
 

 

 

 

 

 

 

 

 

 

by several national laboratories and the industry have tried to address these concerns,166 but 

significantly more work needs to be done. 

Modeling overcharge, electrolyte decomposition, gas evolution, and lithium deposition are all 

areas that need the development of better models, as well as validation of models that are 

currently used. This effort should be a priority in future DOE R&D programs. 

The other area where models are finding utility is at the battery pack level. The primary need is 

for accurate, validated, easy-to-use thermal models. NREL is well established in developing 

battery thermal models. NREL researchers are applying these techniques to characterize battery 

pack response to abusive environments.167 It is the opinion of the roadmap author that these 

efforts are well funded and should continue to be supported. The only area that might deserve 

attention is if new approaches arise that look promising for solving the problems and are not 

included in the current battery modeling program. 

8.8 State of Health Monitoring and Failure Prediction 

Failures often have a long incubation period, but when a “tipping point” is reached, the failure 

happens very fast. The “tipping point” is usually governed by heat generation and heat 

dissipation from the cell and battery pack to the environment. The internal temperature of a cell 

is difficult to measure, but it is the most crucial measure of whether a cell or module is entering 

the danger zone. By the time the temperature sensor (typically located on the external surface of 

a cell) begins to show a “statistically significant temperature rise,” the rate of temperature rise is 

too large and thermal runaway will ensue. 

Diagnostic methods that could alert the BMS to incipient failures would pay big dividends in 

preventing major incidents.168 The goal is to develop diagnostic techniques that can identify an 

incipient failure and take action early enough to prevent thermal runaway. Diagnostics, artificial 

intelligence, or other data analysis techniques need to be developed to predict failure. 

Quallion is developing a safety prediction technology that employs an embedded microreference electrode with using Li4Ti5O12-coated microelectrode.169 Quallion’s goal is to predict 

failure within a cell before it becomes an issue for the battery pack. The use of a Li4Ti5O12 

coating provides a very stable voltage that can be used to compare actual voltages of both 

electrodes. The Quallion approach is one of many that might be used to give an “early warning” 

alert to the BMS that a failure is about to occur. The cell should be taken “off line” when its 

temperature exceeds 100°C – 130°C. The added time may be important to avoid propagation of 

failure within a module or pack. Dendrite formation should be able to be detected by 

electrochemical impedance spectroscopy. 

166 C. J. Orendorff, E. P. Roth, and T. Lambert. “Lithium-Ion Cell Safety Issues of Separators and Internal Short
 

Circuits.” Meeting abstract, Electrochem. Soc. 1002, 333 (2010).
 167 G-H. Kim, K-J. Lee, L. Chaney, K. Smith, E. Darcy, A. Pesaran. “Numerical Analysis on Multi-physics
 

Behaviors of Lithium-ion Batteries for Internal and External Short.” Meeting abstract, Electrochem. Soc. 1002 331 

(2010); G-H. Kim. “Li ion Abuse Model Development,” 2009 DOE Energy Storage Annual Progress Report; G.H.
 

Kim, A. Pesaran, R. Spotnitz, “A Three Dimensional Thermal Abuse Model for Lithium Ion Cells,” J. Power 

Sources, 170(2), pp. 476-489, 2007.
 168 Private communication, Brian Barnett, May 12, 2010.
 169 Private communication, Hisashi Tsukamoto, January 11, 2011.
 

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Some investigators believe that an internal short circuit is most likely due to dendrite growth 

(from iron or copper dissolution).170 They report data from synchrotron X-ray studies on the 

electrode structural changes of the Li-ion (LiFePO4) cell during cycling. They also used X-ray 

diffraction, transmission electron microscopy, and scanning electron microscopy to investigate 

failures of Li-ion cells. Their early observations are: 

•	 The failure mechanism of LiFePO4 under overdischarge is caused by copper dendrite 

formation. 

•	 The failure mechanism under overcharge is caused by steel can dissolution and iron 

dendrite formation. 

•	 Lithium plating is also observed during overcharge. 

These results are consistent with observations made at Exponent during failure investigations.171 

Entropy measurement as diagnostic tool for cell state of health is being developed by Rachid 

Yazami and Sanyo.172 Entropy is sensitive to phase and structural changes and may be useful in 

predicting degradation and perhaps even incipient failure. The technique requires open circuit 

voltage measurement at range of temperatures, approximately 25°C-40°C. Typically, the cells 

are cooled to get information and avoid self-discharge at higher temperatures. The goal of their 

efforts is to develop a technique in which cells could be tested in situ. Yazami has started a 

company in Singapore to commercialize the idea. 

Other examples of advanced diagnostic procedures being developed for batteries include a 

collaboration between Hydro Quebec and Hitachi High Energy in Tokyo.150 K. Zaghib reported 

the use in-situ scanning electron microscopy to evaluation the effect of cycling of Li-metal 

batteries. 

The techniques mentioned above are only examples of creative approaches being used to 

understand battery aging and failures. Our point is not to necessarily endorse these approaches, 

but to highlight innovative work in this area. Development of improved diagnostic tests should 

be a priority in future DOE R&D programs to allow investigation of cell and battery failures with 

the goal of predicting failure modes, allowing time for intervention, and preventing accidents. 

If electric-powered transportation is to become universally available in all automotive lines, cell 

and pack manufacturing processes and procedures need to be improved. Six-sigma (6σ) process 

control still allows a 3.47 part-per-million failure rate, which is about what the Li-ion 

rechargeable battery failure rate is today. This is not good enough. The approach being pursued 

by Kentucky-Argonne Battery R&D Center is to “build in safety” by better control of 

manufacturing processes. Safety will be accomplished by having a “defect free” manufacturing 

process and “defect free” material used in the cell.173 This roadmap proposes that these efforts 

170 Private communication, Jian Xie, October 13, 2010.
 171 Private communication, Brian Barnett, November 4, 2010.
 172 R. Yazami et al. “Cathode Materials Degradation Mechanism from Thermodynamics and Crystal Structure 

Studies.” Presented at Lithium Mobile Power 2010, Boston MA, November 3, 2010.
 173 R. Brodd, Kentucky-Argonne Battery Manufacturing R&D Center Activities.” Pacific Power Source Symposium
 

2011, January 10–14, 2011. Waikoloa, HI.
 

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are sufficient for now, but DOE should continue to monitor them and look for ways to support 

their effort. 

8.9 Battery Pack and Module Safety

Information on in-vehicle safety is more difficult to obtain because it is often proprietary and 

closely guarded by module and battery pack manufacturers. The following summaries were 

obtained during interviews for this roadmap: 

•	 The best companies have several “layers” of safety. Toyota (“Best HEV Company”) has 

six to seven “defensive lines,” and other companies have one to two defensive lines. 

•	 Researchers in Japan are working on LiNi0.8Co0.15Al0.05O2 and LiCoO2. They must 

believe that these systems have suitable safety. In our experience, the cells with the best 

thermal stability system do not always result in the safest system: 

ο	 Safety also depends on interaction of cells, thermal management, etc. 

ο	 Integrators need to know why and how their cells fail and have design mitigation 

strategies. 

•	 There may be an over-reliance on coated separators or coated electrodes to improve 

safety. Inexperienced companies often have “ridiculous expectations” of separators. 

Some believe that the heat resistant layer will not prevent internal short circuits.174 

•	 Small versus large format cells: which is better? Which is safer? There is a divergence of 

opinion on the topic. The decision needs to be evaluated with respect to module and pack 

design. Electrical interactions and current flow need to be studied, tested, and modeled. 

However, most opinions favor small cells for safety. 

ο	 Toyota is taking a small cell approach to its HEVs. Simple calculation of heat 

released due to an internal short circuit shows a 20-Ah cell cannot avoid runaway 

because local temperatures will exceed 180°C.174 

ο	 For example, if during a short circuit a single cell failure occurs in a five-cell series of 

5-Ah cells, the failed cell will have to dissipate 25 Ah of energy. Overcharge will 

have same effect. Few cells can survive that condition. 

•	 The “tipping points” to thermal runaway are: 

ο	 130°C – 140°C – Anode SEI decomposition and rapid anode/electrolyte reactions 

commence. 

ο	 180°C – O2 generation commences from cobalt- or nickel-containing cathodes with 

subsequent oxidation of the electrolyte. By then, it is too late. 

The wiring design can affect abuse response. Quallion presented a “Matrix” wiring strategy in 

which each parallel string was connected between cells.175 This “balancing line” approach has 

been used by others. It provides additional safety because it avoids high transient voltages that 

could occur in a single string of cells after individual cell failure. Hisashi Tsukamoto showed that 

174 Private communication, John Z. Zhang, January 11, 2011.
 175 H. Tsukamoto. “Quallion Wide Temperature Technology and Hybrid Matrix Battery,” Pacific Power Source 

Symposium 2011, Jan. 10–14, 2011. Waikoloa, HI.
 

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the “Matrix” design in Figure 42 prevented cascade of failure after thermal runaway was induced 

in one cell. 

Figure 42. Wiring diagram of conventional and “Matrix” design in two battery packs.
 

Cell No. 2 was driven into thermal runaway. The failure propagates to the entire battery in the
 

conventional pack, but propagation DID NOT proceed in the “Matrix” pack.176
 

•	 Heat conduction between cells is a crucial parameter to control because it strongly 

influences failure propagation. This effect has been modeled,176 but much more work is 

needed. 

ο	 An example was given of a 3S4P arrangement of 18650 cells. With a 0.5-mm gap, if 

one cell goes into thermal runaway, all cells will go. This is not safe under any 

circumstance. If the separation is increased to 5 mm, propagation does not occur. 

Heat-absorbent materials such as low-molecular-weight polyethylene172 or paraffin,

177 

called phase change materials, can be designed to absorb energy by melting at a 

desired temperature, such as 120°C – 140°C. Battery packs equipped with these 

materials as spacers or liners between cells are more abuse tolerant because the phase 

change material limits temperature rise and increases the uniformity of temperature 

distribution. 

•	 A difficult question to answer is whether or not there is an advantage to using shutdown 

separators in large format cells or packs for HEVs and EVs. The information obtained for 

this report did not lead to a firm conclusion. 

The roadmap recommendations for module and battery pack safety efforts will focus on 

modeling and design tools. These should be generally applicable (i.e., not specific to a certain 

design or cell size), validated, and easy to use. The benefit would be for large original equipment 

176 R. Spotnitz, D. H. Doughty et al. Journal of Power Sources 163 (2007) 1080–1086. 

177 R. Sabbah, R. Kizilel, J.R. Selman, S. Al-Hallaj. Journal of Power Sources 182 (2008) 630–638. 

109 
manufacturers to check their results and for small original equipment manufacturers to receive 

guidance to solve problems that they may not be able to solve in-house. 

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9 Conclusions and Recommendations 

Batteries must have sufficient safety for their targeted application. The safety and abuse 

tolerance of electrochemical cells depends on materials, chemical interactions, the nature of the 

abusive event, as well as battery pack and BMS control engineering. Improved abuse tolerance 

and engineering leading to “graceful failure” is a challenge that encompasses many areas of 

study and specialization. 

It is clear that the safety of Li-ion rechargeable batteries needs to be improved. While the 

activities mentioned in this roadmap are making progress in improving the safety of the traction 

batteries proposed for use in EVs and HEVs, more needs to be done. Past efforts have traded 

increased battery safety for lower energy. 

The goal of this roadmap is to identify opportunities where high energy and safety can be met 

simultaneously. For example, R&D priorities that, if achieved, will enable development of cells 

and batteries that can support long driving range and have sufficient safety to be used in EVs and 

HEVs. 

The following topics are identified as needs that are not being met and on which additional 

funding would have the greatest impact to enable safe, high-energy vehicle batteries. The 

recommendation of the roadmap is that these topics be a priority in future DOE R&D programs. 

[Note: Topics that are not recommended for future investments are not listed here. The 

individual sections in this roadmap provide discussion and reasoning for these decisions.] 

This roadmap provides recommendations in the following three areas: 

1.	 Improve our understanding of failure modes. 

A. Failure modes such as internal short circuits have substantial negative consequences 

and are difficult to characterize. Our understanding of the internal short circuit event 

is superficial, and the tests meant to simulate the event are not well developed. We 

recommend a systematic R&D program that would: 

i.	 Elucidate the details and provide a better understanding of initiation and 

propagation of internal short circuit. 

ii.	 Develop a standardized test method that would determine cell susceptibility to 

this failure mode and provide validation tests to support development of models 

for the internal short circuit event. 

B. Propagation of a failure from cell to cell, leading to catastrophic failure cannot be 

tolerated. Building an easy-to-use, validated cell and battery pack abuse model that 

realistically captures propagation is essential. Standardized test method for 

propagation should be a priority. A propagation model would have a great benefit if it 

could serve as a trusted guide for battery pack manufacturers to avoid propagation of 

failures in all battery packs. 

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2.	 Develop better characterization tools. 

A. Failures often have an incubation period of several hours, but when a “tipping point” 

is reached, the failure happens very fast. Diagnostic methods that could alert the BMS 

to an incipient failure and trigger early intervention would pay big dividends in 

preventing major incidents. Examples are development of diagnostic techniques to: 

i.	 Detect lithium plating on the anode 

ii.	 Identify and predict aging-related failures 

iii. Detect the presence of debris or imperfections within the cell that could lead to an 

internal short circuit. 

B. Models for cell, module, and battery pack safety should be a priority because they 

will drive understanding and improvements in the safety of large battery packs. Large 

original equipment manufacturers will benefit by having an independent check of 

their results, and small original equipment manufacturers will benefit by receiving 

guidance to solve problems that they may not be able to solve in-house. 

i.	 Models should be generally applicable (i.e., not specific to a certain design or cell 

size), validated, and easy to use. 

ii.	 Internal short circuit, overcharge, electrolyte decomposition, gas evolution, and 

lithium deposition are areas that need the development of better models and 

validation 

iii. Failure propagation model mentioned above. 

3.	 Improve the safety of energy storage technologies. 

A. Cathodes continue to be a source of failure in Li-ion rechargeable batteries. New 

cathode materials, which are being designed to achieve high-energy targets, can be 

unstable and reactive. Three areas are recommended for R&D investment: 

i.	 Coated cathodes. The potential of cathode surface modification techniques is very 

promising because it will allow use of high-energy materials and avoid electrolyte 

oxidation. 

ii.	 Novel discovery methods. Calculations of the oxidative stability of layered 

cathodes can provide synthetic R&D programs with guidance to discover new 

cathode materials that can achieve high capacity and improved safety. 

iii. Cathode conversion reactions are a fertile area for research, and a systematic 

investigation to develop high-capacity and safe cathodes should be a priority. 

B. Non-flammable electrolyte development. The flammability of the vented electrolyte 

is one of the most significant unresolved safety issues for Li-ion batteries. From the 

roadmap author’s viewpoint, non-flammable electrolyte additives are unlikely to be a 

permanent solution to the electrolyte flammability problem. Therefore, the author 

recommends a concerted effort in IL electrolytes that could permanently solve the 

electrolyte flammability issue. 

C. Develop methods to prepare a “Permanent SEI.” The breakdown of SEI at 

temperatures ~130°C – 140°C is an important trigger to thermal runaway that needs 

112 
 

 

 

to be eliminated, or at least stabilized to temperatures greater than 200°C. Additives 

to stabilize the anode surface have made improvements, but do not last the life of the 

cell and are compromised at elevated temperatures. 

D. New separators (and/or ceramic coatings applied to a separator or electrode) can 

provide protection from internal short circuits and other abusive events. Many 

questions remain to be answered: 

i.	 What method of application of a ceramic heat resistant layer provides the best 

safety result? 

ii.	 What is the mechanism of the heat-resistant layer that provides abuse tolerance? 

iii. Are there preferred ceramic particles (chemical composition or morphology) for 

the ceramic composite layer? 

iv. Is the durability sufficient? Will the separator layer perform for life of the cell? 

E. Understand the safety performance of batteries containing anodes made with silicon 

or other alloys. Because batteries with alloy anodes could be proposed for use in 

traction applications, the DOE should have a program to investigate the safety issues 

with batteries made with high-capacity Li-alloy anodes. 

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Glossary 

cell	 An assembly of at least one positive electrode, one negative electrode, and 

other necessary electrochemical and structural components. A cell is a 

self-contained energy storage device whose function is to deliver electrical 

energy to an external circuit. 

explosion	 A very fast release of energy sufficient to cause pressure waves and/or 

projectiles that may cause considerable structural and/or bodily damage, 

depending on the size of the test article. The kinetic energy of flying 

debris from the test article may be sufficient to cause damage as well. 

fire or flame	 Ignition and sustained combustion of flammable gas or liquid 

(approximately more than one second). Sparks are not flames. 

GBL Gamma-butyrolactone (C4H6O2) is a solvent used in electrode 

manufacturing processes. It has a boiling point of 206°C. 

I

2 R	 I is the current flowing in the conductor, and R the resistance of the 

conductor. With I specified in amperes and R in ohms, I2 R represents the 

Joule heating as current flows through an object. 

module	 A grouping of interconnected cells in series and/or parallel arrangement 

into a single mechanical and electrical unit. 

NMP	 N-methyl-2-pyrrolidone is a high-boiling (202°C – 204°C) solvent. 

pack	 Interconnected modules, including all ancillary subsystems for mechanical 

support, thermal management, and electronic control. 

PHEV A plug-in hybrid vehicle is a hybrid electric vehicle designed to be 

charged from an electrical grid while stationary. 

redox	 Reduction-oxidation. 

rupture	 The loss of mechanical integrity of the test article container, resulting in 

release of its contents. The kinetic energy of the released material is not 

sufficient to cause physical damage external to the device under test. 

SEI A solid electrolyte interphase or the passivation layer that forms on Li-ion 

rechargeable battery anode materials. 

SOC	 The state of charge is the relative capacity expressed as a percentage of the 

fully charged capacity. 

Thermal runaway	 The uncontrolled increase in the temperature of the device under test 

driven by exothermic processes, such that heat is generated at a rate that 

exceeds the heat dissipation rate. 

Thermal stability The maximum temperature at which battery is stable indefinitely. 

limit 

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Appendix A. Invitation Letter 

The following letter was sent to the people listed in Table 1. 

You are invited to participate in the development of a “Roadmap for Safety and Abuse Testing of 

Lithium-Ion Batteries for HEVs, PHEVs and EVs.” 

One of the goals of the DOE Energy Storage R&D Program at the Office of Vehicle 

Technologies is to foster the development lithium-ion batteries that are safe and abuse tolerant in 

electric drive vehicles. As lithium-ion technology matures, high-energy batteries will be 

produced and more car companies will deliver to consumers electric drive vehicles containing 

lithium-ion batteries. In this environment, the safety issue will become paramount. 

To address this concern, the DOE Office of Vehicle Technologies has initiated the development 

of a roadmap to identify approaches to improve traction battery safety in electric drive vehicles. 

The starting point is to understand the current state of lithium-ion rechargeable battery safety 

technology and highlight industry efforts that will improve safety of lithium-ion batteries in 

vehicular applications. The effort will identify gaps and opportunities as well as highlight 

research topics that should be pursued to achieve the goals. 

Dan Doughty, Battery Safety Consulting Inc., will lead the roadmap effort. The participation of 

your organization is very important to the success of this effort. If you are not able to participate, 

please identify someone in your organization who could participate or serve as a point of contact. 

Questions: 

•	 What are the key problems in lithium-ion rechargeable battery safety and abuse 

tolerance?
 

•	 What are the key developments in lithium-ion rechargeable battery safety and abuse 

tolerance? 

•	 What are research directions in safety and abuse tolerance that your lab is taking? 

•	 What are research directions in safety and abuse tolerance you see in the battery suppliers 

and automotive OEMs? 

•	 What are modeling needs? 

•	 What actions should DOE Office of Vehicle Technologies take to improve safety and 

abuse tolerance of lithium-ion rechargeable batteries in automotive applications? 

115