Electrothermal Analysis of Lithium I

Ahmad Pesaran

Andreas Vlahinos and Desikan Bharathan

National Renewable Energy Laboratory

Golden, CO, USA

ahmad_pesaran@nrel.gov, Tel: 303 275-4441

Tien Duong

U.S. Department of Energy

Washington, D.C., USA

THE 23rd INTERNATIONAL BATTERY SEMINA

March 13 - 16, 2006

Fort Lauderdale, Florida

NREL/PR-540-39503
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Disclaimer and Government License

This work has been authored by Midwest Research Institute (MRI) under Contract No. DE-AC36-99of Energy (the “DOE”). The United States Government (the “Government”) retains and the publishepublication, acknowledges that the Government retains a non-exclusive, paid-up, irrevocable, worldwthe published form of this work, or allow others to do so, for Government purposes.Neither MRI, the DOE, the Government, nor any other agency thereof, nor any of their employees, mimplied, or assumes any liability or responsibility for the accuracy, completeness, or usefulness of a

or process disclosed, or represents that its use would not infringe any privately owned rights. Referecommercial product, process, or service by trade name, trademark, manufacturer, or otherwise does endorsement, recommendation, or favoring by the Government or any agency thereof. The views apresenters expressed herein do not necessarily state or reflect those of MRI, the DOE, the Governm
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Outline

• Introduction• Approach (electrothermal modeling)• Cells Analyzed• Thermal Results

• Thermal Imaging• Summary
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Introduction

• One of the goals of DOE/FreedomCAR 

develop high-power, safe, long-lasting batteries for various hybrid vehicle appincluding the 42V mild hybrids.

• With cost sharing from DOE/FreedomC

State Advanced Battery Consortium (Ucontracted Saft to develop a high-powebattery to meet the FreedomCAR techn42V M-HEV batteries (2003-2005).

• With support from DOE, NREL perform

analysis and testing for understanding improving thermal performance of cells the USABC program.
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Description of Cells a

FreedomCAR/USABC G

USABC/FreedomCAR 42 V 

End-of-Life Perfo

Survival Temperature ( 

oC)

Operating Temperature ( 

oC)

Maximum Cell T (oC) 

Self-Discharge (Wh/Day) 

Minimum Operating Voltage Maximum OCV After 1 Sec. 

Selling Price ($/System at 1

Maximum System Volume (Maximum System Weight (kCalendar Life (Years) 

Cold Cranking at –30 

oC/21V 

Load Profile

Cycle Life, Miles/Profiles (E

Efficiency Load Profile (%) 

Recharge Rate (kW) 

Available Energy (Wh at 3 k

Engine-Off Acce ssory Load Regenerative Power (kW/2 s

Discharge Power (kW/2 sec

Characteristics 

Survival Temperature ( 

oC)

Operating Temperature ( 

oC)

Maximum Cell T (oC) 

Self-Discharge (Wh/Day) 

Minimum Operating Voltage Maximum OCV After 1 Sec. 

Selling Price ($/System at 1

Maximum System Volume (Maximum System Weight (kCalendar Life (Years) 

Cold Cranking at –30 

oC/21V 

Load Profile

Cycle Life, Miles/Profiles (E

Efficiency Load Profile (%) 

Recharge Rate (kW) 

Available Energy (Wh at 3 k

Engine-Off Acce ssory Load Regenerative Power (kW/2 s

Discharge Power (kW/2 sec

Characteristics 

The latest Saft prototype cells meet 

most of the USABC/FreedomCAR performance goals.
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Objectives of This Wo

General• Develop an electrothermal process/mode

thermal performance of real battery cells a

• Use the electrothermal model to evaluate 

to improve battery thermal performance.

This Study• Use electrothermal model to predict the t

of two cell design iterations to identify imperformance. 

– Design A: Saft Li-Ion Cylindrical with terminals 

– Design B: Saft Li-Ion Cylindrical with terminals 
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Motivation for the Therm

Analysis Work

• Temperature greatly affects the performan

thus warranty costs) of batteries.

• Battery thermal control/management is a 

electric vehicles under real driving condition

• Good battery pack thermal management 

and modules that perform well thermally.

• Thermal modeling and simulation could 

batteries with better thermal behavior.

• A 3-D model capturing electrical, as w

behavior of batteries with real geometincluding the non-electrochemical parts, wa
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Analysis Approach 

• Capturing details of a cell including 

non-electrochemical hardware with Finite Element Analysis.

• Estimating resistances of each 

component/part using geometry, materials, and test data.

• Applying voltage drop to calculate 

current density in components.

• Estimating resistive heating (I2R) in 

each component. 

• Applying electrochemical heat of 

reactions in the core (active parts).

• Applying heat transfer boundary 

conditions on cell exterior.

• Predicting temperature distribution in 

the cell from current density and related heat generation distribution.

Temperature Di

Two cells with an interconnect

Example: 6-cell Panasonic NiMH module
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Approximating Core/Winding 

It’s assumed that 

(electrochemically activ

homogenous material w

for resistivity and therm

different properties in 

(orthotropic 

Used finite element analysis to calculate the effective thermal cond

Applied known heat fluxes q to predict ΔT
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Physical Description of Cells 

Captured essential details of Cell Design

• any potential hot spots.

Cell Design ATerminals on each side

Cell De

Terminals 

sam
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List of Assumptions and A

• Captured all geometry and material propertie

– All electrical resistivities from literature except 

electrolyte/separator 

– Used experimental DC resistance of the cell to 

resistivity of the winding

• Air cooling on all exterior surfaces

• Heat transfer film coefficient on all surfaces = 

• Initial battery and air temperature = 35oC

• Target heat generation 12 W (based on heat 

HPPC profile with HP12 LC cells at NREL ca

• Applied a voltage drop across the terminals; 

created based on the electrical resistance of 

• Voltage drop was adjusted so heat dissipatio

be order of 12W.

Delta V = I * R Heat Power = I * Delta 
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Voltage Distribution – Cel

Delta V = 0.22 VCurrent = 56 ACell Resistance = 3.9 m OhmTotal heat gen = 12.3 W
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Temperature Distribution – Ce

Local heat generation based on R*I2

Total heat gen = 12.3 W
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Temperature Distribution in W

Cell Design A
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Results for Cell Design 

(near +ve terminal) 

Temperatur

Current Density Distribution
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Voltage Distribution – Cell D

Delta V = 0.22 VCurrent = 52 ACell Resistance = 4.23 m OhmTotal heat gen = 11.4 W
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Temperature Distribution – Ce

Total heat gen = 11.4 W
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Results for Cell Desig

(near +ve terminal

Temperatu

Current Density Distribution
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Steady-State Results u

“Average” of 110 Amp 

Cell Design A Cell De
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Transient Analysis 

Using P-HEV Heat Rejection Profile from FreedomC

Time 

(s) 

18 10 79 

2 

Cell Design A temperature close to hottest point (-veterminal)
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Hottest spots in Cell Design A after 5 heat 

rejection test profiles

Hottest spots in 

5 heat reject

Cell Design A Exhibits Hotter P

Terminal under the High Curren

Hot spot near –veterminal

Hot spot near +veterminal
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Summary of Electrother

Analysis of Cells

Temperature 

(oC) 

Baseline Cell G

Current 110 Amps 166 Amps 5 cycles of Table 3 110 Amps 

Maximum Hardware 60 93 146 58.1 Maximum 

Winding 43 53 66 42 

Average 

Winding ~ 41 ~ 49 ~ 47 ~ 39 

• The overall resistance of Cell Design B is less t• Under the same current profile, Cell Design B g

and thus performs better thermally.

Cell Design A 
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Thermal Imaging of Li-Ion Ce

the Trends of Electrotherm

Thermal Imaging of a Saft Cell 
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Thermal Imaging Showed Ho

near –ve Terminal for Cell D
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Summary and Observat

• Developed an electrothermal modeling pr

analyzing thermal performance of cells an

• The electrothermal model was used to ev

performance of two Li-Ion cylindrical cells

– The Cell Design A had a less favorable therm

under P-HEV transient heat rejection profile (h

the negative weld).

– The hottest point in Cell Design B was in the p– The winding in Cell Design B was cooler than 

under the same current profile due to its lower 

– The trends of the electrothermal analysis were 

experimental thermal imaging results. 

• The electrothermal analysis is a valuable 

enhancing thermal and thus electrical percycle/calendar life of Li-Ion batteries.
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Acknowledgment

• DOE and FreedomCAR Program 

– Dave Howell

• USABC Technical Guidance

– Bruce Blakemore