An Overview of

Battery Simulation

Robert Spotnitz, Battery Design LLC

Overview

A. Battery History

B. Battery Market and Technology

C. Battery Modeling

2

What is a battery?

• A battery or “galvanic cell” converts chemical energy to electrochemical energy using at least one of reactant stored in a cell.

• A fuel cell converts chemical energy to electrochemical energy using reactants stored externally.

• A capacitor stores and releases electrical energy using double-layer charge separation or a pseudo-capacitive effect such as surface adsorption, reaction or bulk intercalation. Volta’s pile

Ag/Zn (1800) 3

4

Terminology

OH-

Zn

ZnO

e-

Ag 2

O

2Ag

e-

Battery consists of one or more cells Cell consists of a pair of electrodes and an ion conductor Electrode consists of active material, current collector, and tab Positive electrode is called “cathode” Negative electrode is called “anode” Package, separator, insulators, etc.

ionic conductor

e- e-

eOHZnOOHZn 22 2 OHAgeOHOAg 22222

ZnOAgZnOAg 22

1959: Alkaline 1991: Li Ion

1958: Organic Li primary

1947: O2 Recomb. Ni/Cd

5

1980s: NiMH

1866: Dry cell 1860: Pb Acid 1800: Volta invents battery

1962: Newman and Tobias, Porous Electrode Theory

1994: Doyle, Fuller, Newman, DUAL model Li Ion

2005: Garcia et al., microstructural model

1905: Nernst Equation: G=-nFE 1887: Peukert’s Law: Iptd=constant 1834: Faraday’s law of electrolysis

1930: Butler-Volmer Eqn

RTRTii cao

expexp

Battery Market

Only a few chemistries dominate market

Rechargeable

- Pb Acid

- Lithium Ion

Primary or single discharge

- Alkaline

@ $60/battery ~$8 Billions

North American Lead Acid SLI Battery Forecast

7

C. Pillot, Batteries 2009, Avicenne

Worldwide Rechargeable Battery Sales Excluding Lead Acid

8

Lithium Ion

NiCd

NiMH

Lithium-ion dominates market for portable electronics.

by application

Li-Ion Cell World Market Size & Forecast ($Billions)

S. Inagaki, Yano Research Institute, SAE Intl. Vehicle Battery Summit, Shangahi 2011

Consumer

Industrial Automotive

Other

35

30

25

20

15

10

5

conversion used $1 = 100 Yen Consumer - phones, computers, cameras, etc. Other - power tools, e-bikes, medical, aerospace Industrial - smart-grid, residential, UPS Automotive - passenger vehicles excluding bus, railroad

Huge growth in lithium-ion market is forecast for vehicles

9

Battery Requirements: Consumer Products

• Consumer electronics – high volumetric

energy density – low cost – 1 year life – Safety

• Power tools – high power density – low cost – 2-3 year life – safety

10

Largest market and growing.

• Trends

– longer calendar life

– higher energy density

Battery Requirements: Hybrid Electric Vehicles

• High Power (> 1 kW/kg)

• Low cost

• 8+ year life

• Abuse tolerance

Typical is ~1 kWh systems capable of providing ~25 kW

11

Nickel metal hydride batteries dominate but lithium-ion is projected to win out by providing smaller, lower cost packs

Battery Requirements: Battery Electric Vehicles

• High gravimetric energy density (>100 Wh/kg)

• Very low cost

• 8+ year life

• Abuse tolerance

Typical is 24 kWh systems capable of providing ~50 kW

12

Lithium-ion is currently only viable chemistry with sufficient energy density for this application.

Battery Requirements: Grid Regulation

• High power, fast response (seconds)

• Cost? Life? Abuse?

13

Market is potentially larger than automotive, but large uncertainty as to economic feasibility.

Lead Acid (Valve Regulated) - Actives and Separator 2

432.3 10

45%

cmacm

Sep ~95% porous, ~1.3 mm thick

Charged

Discharged

D. Pavlov, V. Iliev, J. Power Src / 7 (1981) 153.

J. H. Yan et al. , J. Power Src. 133 (2004) 135-140.

Negative ~ 2 mm thick

Positive ~ 2 mm thick

25

32.3 10

40%

cmacm

Lead-acid electrochemistry is very complex.

Pb + H2SO4 PbSO4 + 2e + 2H+ PbO2 + 2e +2H+ + 2H2SO4 PbSO4 + 2H2O

Li-ion Cell Cross-Section

Z. G. Li et al. J. Electrochem. Soc., 150 (9) A1171 (2003)

15 Lithium ion battery operation is relatively simple.

LiC6 Li+ + e + C6

Li+ + e + Mn2O4 LiMn2O4

Typical Lead-Acid Battery

DOE-HDBK-1084-95

September 1995 16

Spirally-Wound Cells

17

Tesla Powertrain Technology

K. Kelty, 26th Intl. Battery Sem., Ft. Lauderdale, Fl, 2009

Small Cells 18650

18

Mitsubishi iMiEV Battery

22 modules (4 cells/module)

19

• 2011 World Markets for Batteries – Primary

• estimated at ~$4 Billions for alkaline and ~$1.5 billions for others

– Rechargeable • lead acid ~$20 Billions

• lithium ion ~$12 Billions

• nickel metal hydride ~$1.5 Billions

• Automotive market is growing rapidly and is amenable to design

• Opportunities for – design tools for batteries

– prediction of life and abuse tolerance

Summary

20

Overview

A. Battery History

B. Battery Market

C. Battery Modeling

21

Battery Modeling

• Concept of Electroactive Species

• Concept of Exchange Current Density

• Battery Equations and Modeling Approaches

22

+

1

Nernst Equation

2 2

3

ln21

Fe

Feo

c

cRTGF

23

Can compute voltage based on chemistry.

+

1

2

Nernst Equation

2

3

ln21

Fe

Feo

c

cRTGF

24

Can compute voltage based on chemistry.

RTcki

FeeFe

c

Feoff21

,

23

exp3

RTcki

eFeFe

a

Feobb21

,

32

exp2

1

2

+

25

bfnet iii

Butler-Volmer Equation

Can compute reaction rates.

1

2

RTcki

FeeFe

c

Feoff21

,

23

exp3

RTcki

eFeFe

a

Feobb21

,

32

exp2

+

bfnet iii

Butler-Volmer Equation

26

Can compute reaction rates.

2,1 PbO

2

Pb,1

2

OHPbSOPbSOHPbO 24422 222

Lead Acid Battery

27

2,1 PbO

2

Pb,1

2

OHPbSOPbOSOHPb 24242 222

28

2,1 PbO

2

Pb,1

2 cD

t

c

STkt

Tcp

x

T

xE

XXI2

1*

Eulerian strain

v

t

j

Poisson

1

2

11

'

i

LawsOhm i1

RTk

RTckj

ePbSOSOPb

caPb

a

SOaPb21

,21

,

4

2

4

expexp

2

24

RTck

RTkj

SOOHPbSOeSOHPbO

cSOHcPbO

aaPbO

212

,21

,

2

424422

expexp

222

4222

j

j

atF

RTi o ln2122

i2

29

Macro-Homogeneous Modeling

Negative Electrode

Positive Electrode

Separator L

r

22 Lr

J. Newman, C. Tobias, “Theoretical Analysis of Current Distribution in Porous Electrodes,” J. Echem. Soc., 109,1183 (1962)

Phenomena included in macro-homogeneous battery models (partial) • multi-component electrolytes • precipitation • side reactions • particle size distribution • mixtures of active materials • expansion/contraction of

particles • convection • current distribution along

collectors • local heat generation • stress generation

30

Unit Cell

Full Cell

Module/Pack

Vehicle

Hierarchy of Battery Simulation

31

Hierarchy enables higher level models to be built on lower level models.

STAR-CCM+

CBD

Macro-homogeneous models

Some questions answered: • What limits performance?

– diffusion, kinetics, ohmic

• What is optimal grid design? • How thick/porous should

electrode/separator be? • What is optimal electrolyte

concentration? • How much heat does the cell

generate?

Need to calibrate model against actual cell - tortuosities - kinetics - paste conductivity - contact resistances

Some outstanding questions: • What is optimal mix of binder,

conductivity aid, active material? – what is porosity, conductivity of a

blend?

• What are kinetic parameters?

• What is contact resistance between paste and grid?

• What are physical properties such as diffusion coefficients?

• How does battery fade over time?

• Microstructural modeling

• Atomistic modeling

32

CD-adapco’s Microstructural Model

This approach provides the most realistic model of a battery and is attracting interest of battery researchers worldwide. This tool is useful for calibrating conventional macro-homogeneous models and designing microstructures.

33

Boris Kaludercic Christian Walchshofer Milovan Perić Gaëtan Damblanc Steve Hartridge Robert Spotnitz

Summary

• Physical processes involved in battery include – electrochemistry – phase change – shape change – current and potential distributions in multiple phases – diffusion and migration – convective fluid flow (gas and liquid) – heat transfer

• To-date, most successful approach is based on volume averaging (macro-homogenous)

• Microstructural modeling promise to address major questions in battery design

34

BACKUP

35

Battery Design Tools

Battery Design Process

Expert

Analysis

Build

Pack

Test

Pack

Reqmts

Met?

Reqmts

Done

yes

no

design

pack

Build

Pack

Test

Pack

design

pack

Reqmts

Met?

Analyze

no

yes

In software

Assess

Reqmts

37

Battery Testing Small consumer cells

• typically ~1-10 Wh/cell ($0.25-2.5), 1-90 Wh/pack ($0.25-22.5)

• typically 300 cycles, if 4 hours/cycle, then ~1.7 months/test

• 9 – 12 month warranty

• abuse testing required for shipping (UN, DOT)

Large automotive

• typically ~10-500 Wh/cell ($0.25-, 1-10 kWh/module, 1-60 kWh/pack

• typically >1000 deep cycles, if 4 hours/cycle, then 5.5 months/test

• 8-10 year warranty

• abuse testing required for shipping (UN, DOT)

38

Battery Test Equipment Small cell testing ~$200/channel example: 96 channel Series 4000

Large cell/pack testing ~$50K/channel example: 2 channel ABC-150

39

Motivation for Simulation

Methodology for system

design

• Cooling system

• Vehicle

Reduce development

time/cost

• Case studies in software to eliminate testing

Improve design

• Explore larger parameter space for pack, module, cell

40

Unit Cell

Full Cell

Module/Pack

Vehicle

Hierarchy of Battery Simulation

41

Hierarchy enables higher level models to be built on lower level models.

Software Tools for Battery Design

• BDS and STAR-CCM+ BSM

• Comsol Multiphysics

• Fluent, Matlab, others (EC Power, Fortran codes, Excel spreadsheets)

42

From cell to system design

• Button cell

• Formulations

• Test results

Materials Developer (cathode, anode,

separator, electrolyte, etc.)

• Model selection

• Electrodes, incl. tabbing

• Separator

• Cylindrical, prismatic, pouch

Cell Designer • Performance estimation

• Model selection

• Series/Parallel cells

• Cooling

End User, Module and/or Pack Developer, End

TBM file, prg, out

TBM file

Battery Design Studio

Star CCM+

CD-adapco is the only provider of an integrated solution for cell, module, battery, and system design.

43

BDS Cell Design Process

Physical Cell Description

• Coin, cylindrical pouch, prismatic

• Gives size, weight, equilibrium voltage, capacity, bill of materials, etc.

Fit Model Parameters

• circuit, physics

• Allows simulation of performance

Use and/or Distribute

Text Battery Model (TBM)

44

Air Temperature Animation

Air Flow

Maximum Temperatures

Courtesy of Bob Reynolds, CD-adapco

45

EV Battery (15S-3P) Example – Air Cooling

Cooling Media Temperature distribution

Battery SOC Distribution

Battery Temperature Distribution

Coupled Flow/thermal & electrochemical solution

Courtesy of G. Damblanc, CD-adapco

46

47

48

Conclusion

• CD-adapco is clear leader in battery simulation.

• ANSYS is working in this area, but it is not clear what product they are developing.

• COMSOL is preferred product for model development in academia, and has some traction in industry (example Ford).

• There are a number of other companies offering products.

49

Future Development: Life Prediction

LIFE PREDICTION A Grand Challenge for Battery Modeling

• How many years of service a battery will provide is a critical concern for large-scale applications of batteries such as electric vehicles and grid energy storage.

• Problem is considered as comprised of calendar life and cycle life components.

• The key stress factors are known to be – temperature, – state of charge, – depth of discharge, – discharge/charge rates.

51

Calendar Fade due to Film Growth

SEI (P)

Graphite

L

Li+

Film at Solid Electrolyte Interface (SEI) grows due to reduction of solvent

PeLiS 22

Solvent (S)

S e- e-

e- e-

e- e-

e- e-

e- e-

e- e-

e- e-

Ploehn et al. “Solvent diffusion model for aging of Lithium-Ion battery cells”, J.

Electrochem. Soc., 151 (3), A456 – A462 (2004).

tRT

EDtL

L

tL

R

R

ao

S

o

o

SEI

SEI

exp2

,

Model predicts capacity loss and impedance growth as function of time and temperature

52

Cycle Fade using Analogy to Wöhler Fatigue M. W. Verbrugge and Y.-T. Cheng, J. Electrochem. Soc., 156 (11) A927-A937 (2009).

Approach predicts capacity loss and impedance growth as function of cycle #, charge/discharge rate

53

Commodity Pricing

• 18650 size lithium-ion cell ~$2 or $0.25/Wh

• Lead acid car battery (12V, ~50 Ah) ~$60-90 or ~$0.1-0.15/Wh

Note: Unlike lead-acid, lithium-ion requires electronics for safety.

54

In practice lithium-ion is typically >3X cost of lead acid.

Rechargeable Battery Producers and Customers

Lithium-ion Producers

Samsung, Panasonic/Sanyo, LG, GS Yuasa, Hitachi, NEC, Toshiba, SK, Sony, Lishen, BYD, A123, JCI, Saft, others

Pb Acid Producers

JCI, Exide, Panasonic, Trojan, many others

Customers

• Consumer electronics – Apple, Panasonic, Sony, LG,

Samsung, Lenovo, Dell, HP, HTC, RIM, Motorola, etc.

• Automotive – Toyota, Honda, GM, Ford,

Nissan, BMW, Daimler, VW, Audi, etc.

– Sears, Walmart, etc.

• Industrial – UPS – Sony, Panasonic, etc. – Tools – Black & Decker,

Bosch, Ryobi, etc. – E-bikes-Honda, Yamaha,

Accell, etc.

• Military – all branches 55

Major lithium-ion producers tend to be large vertically integrated companies.