NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Tools for Designing Thermal 

Management of Batteries in 

Electric Drive Vehicles

Ahmad Pesaran, Ph.D.

Matt Keyser, Gi-Heon Kim, Shriram Santhanagopalan, Kandler Smith

National Renewable Energy Laboratory

Golden, Colorado Presented at the

Large Lithium Ion Battery Technology & Application Symposia

Advanced Automotive Battery Conference

Pasadena, CA • February 4-8, 2013

NREL/PR-5400-57747
2

Battery Temperature in xEVs

• Lithium-ion battery (LIB) technology is expected to be the 

energy storage of choice for electric drive vehicles (xEVs) in 

the coming years

• Temperature has a significant impact on life, performance, 

safety, and cost of LIBs

Dictates power capability through 

cold cranking

Also limits the electric driving range

Dictates the size depending 

on the power and energy 

fade rate

Limiting power to 

reduced T increase and 

degradation 

Kandler Smith, NREL Milestone Report, 2008

Desired 

Operating 

Temperature
3

Battery Thermal Management for xEVs

• Higher temperatures degrade LIBs more quickly, while low 

temperatures reduce power and energy capabilities, resulting in 

cost, reliability, safety, range, or drivability implications

• Therefore, battery thermal management is needed for xEVs to:

o Keep the cells in the desired temperature range 

o Minimize cell-to-cell temperature variations

o Prevent the battery from going above or below acceptable limits

o Maximize useful energy from cells and pack

o Use little energy for operation

• However, a battery thermal management systems (BTMS) could:

o Increase complexity

o Add cost

o Reduce reliability 

o Consume energy for operation

o ...
4

Battery Thermal Management System

• Most in the xEV battery community agree that the value that 

a BTMS provides in increasing battery life and improving 

performance outweighs its additional cost and complexity

• However, the BTMS needs to be designed appropriately with 

the right tools

• The National Renewable Energy Laboratory has been a 

leader in battery thermal analysis and characterization for 

aiding industry to design improved BTMSs

• This presentation describes the tools that NREL has used and 

that we believe are needed to design properly sized BTMSs
5

Energy Balance in a Battery

Egen Eloss Ein Eout dt

dE

=  −  +  − 

Energy 

Accumulation 

Rate

Energy 

Generation 

Rate 

Energy 

Loss 

Rate 

Input 

Energy 

Rate 

Output 

Energy 

Rate

Ein +  Egen

 dt

dE

Eloss − 
6

Heat Transfer in a Battery

(Assumption: isothermal ~ very high thermal conductivity)

• Electrochemical reactions 

• Phase changes 

• Mixing effects 

• Joule heating

gen s a s a Ext conduction

s

p Heat hA T T e A T T Q dt

dT mC _

4 4

= − ( − ) − δ ( − ) −

Rate of 

Temp 

Change

Rate of 

Internal Heat 

Generation

Convection 

Heat Rate

Radiation 

Heat Rate

Conduction 

Heat Rate

hA Ts Ta e A Ts Ta QExt _ conduction

4 4 ( − ) + δ ( − ) +

Heatgen

s

p

dt

dT mC

Heat generated ( ) 

in a battery consists of: 

Method of heat rejection/addition for thermal control a

s

T

T = Battery Temp

= Ambient Temp

Heatgen
7

Heat Generation Rate and Specific Heat Impact 

Battery Temperature Rise

0

2

4

6

8

10

12

14

16

0 400 800 1200 1600 2000

Time (seconds)

Temperature Rise (Degree C)

2C Rate (4.45 W/cell) Cp=1019 J/kg/C

C/1Rate (1.33 W/Cell) Cp = 1019 J/kg/C

2C Rate (4.45 W/Cell) Cp = 707 J/kg/C

Slow discharge

Fast discharge

Assuming uniform battery temperature and

the same heat transfer coefficient for three cases
8

n L

t

T h T T e T T C H

n

n k

0.

B

B p,B B

4 4

s s n ( ) ( ) T( )

=

∞ ∞ ∂

∂

= − + − +

∂

∂ − δ ρ

Heat Transfer in a Battery

(Non-isothermal; case and core regions)

Core region

Case or boundary region

Heat k T

t

T C gen p = + ∇ ⋅ ∇

∂

∂

ρ

k :thermal conductivity

Heat flux 

from the 

core

Convection 

from various 

case surfaces

Radiation 

from various 

case surfaces

Heat 

accumulation 

in the case
9

Case + Core Example: T Distribution in a Module 

Air Cooled

Q = 5 W/cell

Tt=0 = 30 o

C

Tair = 25 o

C

hair = 18 W/m2

K

30

35

40

45

50

55

Max. Cell Temperature [oC]

0 10 20 30 40 50 60

Time [min]

Top

Middle

Bottom

Ttop,SS = 54 o

C

Air-cooled

5 W/cell

h = 18 W/Km2

TSS= 54°C

A. Pesaran, A. Vlahinos, S. Burch. Proceedings of the 14th Electric 

Vehicle Symposium, December 1997
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What Information is Needed to Design a BTMS?

• Acceptable temperature range for cell components at all times, i.e., 

active material, binders, separators, electrolyte, etc.

• Acceptable temperature difference within cells and from cell to cell, 

depending on the chemistry and management system 

• Maximum and minimum temperature limits for life specifications, 

performance ratings, and safety considerations

• Thermo-physical properties of cells or components (density, specific 

heat, directional thermal conductivities)

• Heat generation rate under average and aggressive drive profiles and 

loads for the specific electric drive

• Heat rejection rate depending on thermal management strategy

o Fluid heat transfer coefficients or sink conductance

o Cooling fluid flow rate and sink temperature

• Configurations and dimensions of cells and proposed BTMS

• Parasitic power needed to push fluids/cooling through BTMS
11

Tools for Designing BTMS

• Experimental Tools

o Isothermal calorimeters and battery testers 

o Infrared thermal imaging

o Thermal conductivity meters

o Heat transfer characterization setup

o Battery thermal testing loop

• Modeling Tools

o First-order/lumped capacitance thermal and fluid models

o 1-D and 2-D thermal and fluid-flow performance models

o 1-D vehicle integrated thermal-flow models

o 3-D electro-thermal models

o 3-D electrochemical-thermal model

o Computer-aided engineering software
12

Isothermal Battery Calorimeters

• We use a single-ended (one test chamber) conduction 

calorimeter to measure specific heat and heat generation at 

various current rates, temperatures, and states of charge (SOCs)

Sample/Module

Battery Tester

Initially fabricated by Calorimetry Sciences Corporation; later improved by NREL.

A. Pesaran, M. Keyser, D. Russell, J. Crawford, E. Lewis. Presented at the Long Beach Battery Conference, 

January 1998
13

Heat Rate (Watts)

Time (Hours)

NREL’s First Isothermal Battery Calorimeter 

• Heat flux measured between the sample and a heat sink using 

heat flux gauges

• The heat sink is kept at a constant temperature with a precise 

isothermal bath • Max module that could be tested: 21 cm x 20 cm x 32 cm

• Heat rate detection: 0.015 W to 100 W

• Minimum detectable heat effect: 15 J (at 25°C)

• Baseline stability: ±10 mW 

• Temperature range: -30°C to 60°C (±0.001°C)

• Accuracy of better than ±3% 

Calorimeter response 

Total heat generation = 

Area under each curve 

Calorimeter Calorimeter Cavity

Photo Credits: David Parson & Matt Keyser, NREL
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0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

50.0

0.0 20.0 40.0 60.0 80.0 100.0 120.0

Heat Generation (Watts)

RMS Discharge Current (Amps)

Initial Temp = -15 C° Initial Temp = 0 C° Initial Temp = 30 C°

Example Heat Generation Data for CC Discharge

(from max to min allowable capacity-SOC) 

22-Ah Li-Ion Cell
15

Specific Heat (Heat Capacity)

• Can be estimated from constituents of cell/module

• Can be estimated using a calorimeter by measuring heat 

lost/gained (Q) from the battery going from Tinitial to Tfinal

o Heat capacity is calculated by

 

= ∑ • ∑

n

i i

n

Cp ave Cp i m m

1 1

, , ( )/

/( ( )) Cp,ave Q mtotal T initial−Tfinal = •

Cell/Module Taverage 

(°C)

Heat Capacity 

J/kg/°C

NiMH – 18 Ah 33.2 677

Li-Ion 18650 33.1 1,105

Li-Ion Pouch – 4 Ah 18 1,012

VRLA – 16.5 Ah 32 660

Ni Zn – 22 Ah 20 1,167

Thermal Characteristics of Selected EV and HEV Batteries, A. Pesaran, 

M. Keyser. Presented at the 16th Annual Battery Conference; Long 

Beach California, January 2001 
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NREL’s Large Volume Battery Calorimeter

• Single chamber, conduction, isothermal

• Includes several patent-pending 

concepts

• Test chamber submerged 

• Capability to test liquid-cooled batteries

• Safety features in case of events

• Test chamber 6 times larger than the 

NREL module calorimeter

o 2 ft x 2 ft x 4 ft

• Heat Rate: 0.05 W to 4 kW 

• Accuracy of heat meas. ±3%

Test Chamber in Isothermal Bath

Test Chamber

Flux Gauges in Test Chamber

Completed System with Heating/Cooling Unit

Photo Credits: Dennis Schroder & Ahmad Pesaran, NREL
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NREL’s New Isothermal Cell Calorimeter

• Single chamber, conduction, 

isothermal

• Test chamber submerged 

under isothermal bath

• Testing chamber: 15 cm W x

10 cm L x 6 cm H

• Heat detection limit: 1 mW 

and 10 J

• Initial testing shows excellent 

baseline stability and an error 

of less than ±1.6%

• CRADA and license agreement 

signed with NETZSCH to 

commercialize NREL’s battery 

calorimeter design

http://www.nrel.gov/vehiclesandfuels/energystorage/pdfs/50558.pdf

Photo Credits: Dennis Schroder & Dirk Long, NREL
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• Quickly finds thermal signature of the whole 

cell under electrical loads

• Helps understand thermal behavior, creates 

diagnostics, and improves designs

• Could be used as a validation of thermal 

models

• Thermal signature depends on several factors

o Geometry, thermal conductivity of case and core, 

location of terminals, design of interconnects, 

current density, current profile, chemistry, 

environment

• We spray a thin layer of boron nitride on all the 

surfaces of the face that needs to be imaged

• We minimize reflections from other objects by 

placing the cells in a non-reflective 

environment 

• We usually test three cells to see the impact of 

power cable connected to the two end cells

Infrared Thermal Imaging

Thermal image of a 6.5-Ah NiMH module from 

a MY 2002 Prius under 100A CC discharge

Photo Credits: Matt Keyser, NREL
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Examples of Battery Infrared Thermal Imaging

25°C 45°C

http://www.nrel.gov/vehiclesandfuels/energystorage/publications.html

Photo Credits: Matt Keyser & Dirk Long, NREL
20

Thermal Conductivity Estimation & Measurement

Provided by Peter Ralbovsky - Netzsch Instruments

Measurement Techniques

• The core material (electrochemically active 

part) is assumed to consist of a homogenous 

material with average properties for resistivity 

and thermal conductivity, but with different 

properties in different directions 

(orthotropic xyz or rθZ) 

• Usually case and core of a cell 

are considered two different 

regions with different thermal 

conductivity

Can use finite 

element analysis 

to calculate the 

effective thermal 

conductivity in 

each direction

kx = q *∆x /∆T

ky = q *∆y /∆T

or

kz = q *∆z /∆T

kr = q *∆r /∆T
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Measuring Thermal Conductivity of LIB Components

Flash Diffusivity Method: 

• Thermal diffusivity (α) is a measure of how quickly a material can 

change its temperature when heat is applied

• The temperature rise on the rear surface is measured in time using an 

infrared detector K(T ) (T ) c (T ) (T ) = α ⋅ p ⋅ ρ

Provided by Peter Ralbovsky, Netzsch Instruments

• Measurements have shown that generally the thermal conductivity of LIB is much 

lower in-plane than cross-plane

 In plane ~ 0.8 to 1.1 W/m/K Cross plane ~ 28 to 35 W/m/K

Netzsch LFA 447 Unit

Photo Credit: John Ireland, NREL
22

Battery Thermal Testing Loops

• Measuring heat transfer coefficients or conductance

• Hardware in the loop thermal testing 

Temp dist. in a USABC module

Photo Credits: Ahmad Pesaran

Photo Credits: Kandler Smith, NREL
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Battery Thermal Responses

3D

Component

Analysis

System

Analysis

Cell Characteristics

• Shape and size : Prismatic/Cylinder/Oval, etc.

• Materials/Chemistries

• Voltage/current & heat gen data

Module Cooling Strategy • Thermal/Current Paths inside a Cell

• Coolant Type: Air/Liquid

• Direct Contact/Jacket Cooling

• Serial/Parallel Cooling

• Terminal/Side Cooling

• Module Shape/Dimensions

• Coolant Path inside a Module

• Coolant Flow Rate

• Passive with phase change 

• etc.

• Temperature History Cells/Module/Pack

• Temperature Distribution in a Cell 

• Cell-to-Cell Temperature Imbalance in a Module 

• Battery Performance Prediction

• Pressure Prop and Parasitic Power

• etc.

• Vehicle Driving Cycles

• Control Strategy

• Ambient Temperature

• etc.

Operating Conditions

Design Process

Process for Battery Thermal Modeling
24

Lumped Capacitance Thermal Model for 

Vehicle Simulations

• For vehicle simulation, the thermal model needs to be linked to 

the battery model for temperature dependency 

• A 2-node lumped thermal model (case + homogenous core) with 

simple heat convection is developed for ADVISOR vehicle 

simulator
25

Example of 2-D Module Thermal Modeling

Tmax = 44°C

Delta Tcore = 9°C

Case 1. No holes and no air flow between cells

Tmax = 53°C

Delta Tcore = 13°C

Cell core

Plastic 

case

Air

gap

Case 2. With holes and air flow between cells

Photo Credits: David Parsons, NREL
26

Electro-Thermal Analysis Approach 

Current Density

Temperature

• Capture details of a cell including 

non-electrochemical hardware with 

finite element analysis

• Estimate component resistances 

using geometry and materials

• Apply voltage drop to calculate 

current density in components

• Estimate resistive heating (I2R) in 

each component 

• Apply electrochemical heat of 

reactions in the core (active parts)

• Apply heat transfer boundary 

conditions on cell exterior

• Predict temperature distribution in 

the cell from current density and 

related heat generation distribution
27

Example of 3-D Electro-Thermal Modeling

Design A

Terminals on

each side

Design B

Terminals on the 

same side

16 Ah

Power Cell

Temp Dist Design A

Design A

Thermal Response

Design B

Thermal Response

Under 110 A RMS load

• The overall resistance of Cell 

Design B is less than Cell Design A

• Under the same current profile, 

Cell Design B generates less heat 

and thus performs better thermally

Electro-thermal Analysis of Lithium Ion Batteries, Pesaran, A.; Vlahinos, A.; Bharathan, D. Proceedings of 

the 23rd International Battery Seminar, Fort Lauderdale, Florida. March 13-16, 2006.

Photo Credit: Ahmad Pesaran
28

Combined 3D Electrochemical-Thermal Models 

Comparison of two 40-Ah Li-ion 

prismatic cell designs

This cell is cycled more 

uniformly, can 

therefore use less 

active material ($) and 

has longer life.

2 min 5C discharge

working potential working potential

electrochemical

current production

temperature temperature

SOC SOC

electrochemical

current production

High temperature 

promotes faster 

electrochemical reaction

Higher localized reaction 

causes more heat generation

Larger over-potential 

promotes faster discharge 

reaction

Converging current causes 

higher potential drop along 

the collectors

Current Collector (Cu)

Current Collector (Al)

p

Negative

Electrode

Separator

Positive

Electrode
29

Computer-Aided Engineering of Batteries (CAEBAT)

• U.S. Department of Energy is 

supporting development of 

electrochemical-thermal models 

and software design 

• The objective is to shorten time 

and reduce cost for design and 

development of battery systems, 

including the design and analysis 

of BTMSs

• Other software design and analysis 

tools dealing with other physics 

may be incorporated in CAEBAT

Physics of Li-Ion Battery Systems in 

Different Length Scales

Li diffusion in solid phase

Interface physics

Particle deformation & 

fatigue

Structural stability

Charge balance and 

transport

Electrical network in 

composite electrodes

Li transport in electrolyte 

phase

Electronic potential &

current distribution

Heat generation and 

transfer

Electrolyte wetting

Pressure distribution

Atomic Scale

Particle Scale

Electrode Scale Cell Scale

System Scale

System operating 

conditions

Environmental 

conditions

Control strategy

Module Scale

Thermal/electrical

inter-cell 

configuration

Thermal 

management

Safety control Thermodynamic properties

Lattice stability

Material-level kinetic barrier

Transport properties

Thermal-electrochemical response of a pack

Courtesy of Christian Shaffer, EC Power-CAEBAT
30

Summary

• Battery thermal management needed for xEVs

• Battery thermal management system needs to be optimized 

with right tools for lowest cost

• NREL has state-of-the art experimental and analytical tools for 

analysis and design of battery thermal management systems

• Experimental tools, such as the isothermal calorimeter, are 

essential for obtaining data for generating input to design 

tools and eventually verifying the performance of the battery 

thermal management system

• Computer-aided engineering tools for the design of battery 

electrical and thermal management systems are now 

accessible to automotive and battery engineers
31

Acknowledgments

• Support provided by the DOE Vehicle Technologies Program

o Dave Howell, Hybrid and Electric Systems Team Lead

o Brian Cunningham, Energy Storage Technology Manager

• Feedback from CAEBAT Subcontract Technical Leads

o Taeyoung Han (General Motors)

o Steve Hartridge (CD-adapco)

o Christian Shaffer (EC Power)

• Support from NREL Staff 

o John Ireland

o Dirk Long

o Mark Mihalic

o Marissa Rusinek

nrel.gov/vehiclesandfuels/energystorage

Contact Information:

Ahmad Pesaran

ahmad.pesaran@nrel.gov

303-275-4441