kim yeow, ho teng, marina thelliez and eugene tan avl …€¦ · cell level 3d fea analysis user...

3D Thermal Analysis of Li-Ion Battery Cells with Various Geometries and Cooling Conditions Using Abaqus

Kim Yeow, Ho Teng, Marina Thelliez and Eugene Tan

AVL Powertrain Engineering, Inc

22012 SIMULIA Community Conference

Contents

Objectives

Introduction to AVL Electro-thermal modeling of Li-ion battery cells

Development of battery cell models for different cell geometries

Development of battery cooling models with different cooling methods

Validation of the battery model with test data

Simulations of thermal behavior of battery cells for different applications

Summary


Objectives

Develop a 3D electro-thermal model for characterization of thermal behavior

of Li-ion battery cells with various geometries

Use the battery cooling model developed to evaluate

Thermal behavior of Li-ion cells in battery systems for HEV/PHEV/EV

applications

Effectiveness and performance of various battery cooling methods

Liquid cooling

Air cooling

How the cell temperatures are influence by

busbar designs

different cooling strategies (single vs dual cold plates)

battery pack configurations (96S1P vs 96S2P)


Inputs

Cell geometry:

• Height

• Diameter or width/thickness

• Case thickness

Cell material properties:

• Thermal conductivity

• Density

• Heat capacity

• Electrical conductivity

Cell performance:

• Charge / discharge curves from

suppliers’ data sheet at different

temperatures

Cell Characterization

Material data

generation

Cell level 3D FEA analysis

User defined

parameters for

battery

Material definition:

e.g. electrical

conductivity

Coupled transient electro-thermal FEA

analysis

FEA user

subroutine files

Cell specification:

• Nominal voltage

• CapacityCharacterizing the battery

cells:

),,( TBDODfR ii

),,( TADODfV i

Parameters:

4,3,2,1,0 aaaaaAi

]4,3,2,1,0[ bbbbbBi Identify cell temperature distribution

under various discharge / charge

rates

Jr 2

qTkt

TC

p

)(

Introduction to AVL electro-thermal battery model


Cell geometry

Cell material properties

(thermal & electrical

conductivities etc)

Cell performance

User defined parameters for

cell characterization

User subroutine

Thermal boundary conditions

3D FEA

Coupled transient electro-thermal analysis

• DOD distribution

• Current distribution

• Voltage drops

• Cell heat generation

• Cell temperature distribution

Battery cell modeling process


Electro-thermal analysis of a battery

1) Electrical:

2) Thermal:Heat generation

q J2 Ri

q = volumetric heat generation

J = current density

Ri = internal resistance

Heat transfer model

Composite thermal conductivity

qTkt

TC

p

)(

Composite heat capacity

Composite density

Coupled Electro-

Thermal Analysis

Current densityJr 2

Voltage potential

Electrical resistance


Cell modeling – pouch cells

terminal tab

separator

equivalent

electrode

equivalent

electrode

X-ray Tomography

of a failed cell


Cell modeling – prismatic cells

+

_safety valve

case equivalent electrodes

Analysis conditions:

1) 10C discharge to 80% DOD

2) initial cell temperature = 25oC

3) T_air = 25oC, HTC=50 W/m2 C


Cell modeling – cylindrical cells

Comparison of single-layer and multi-layer FEA models

3 layers

approximation

equivalent electrodes1 layer

approximation


Cell modeling – cylindrical cells

Comparison of single-layer and multi-layer FEA models

(under the same cell load and thermal boundary condition)

3 layer model1 layer model

Analysis conditions:

1) 10C discharge to 90% DOD

2) initial cell temperature = 25oC

3) T_air = 25oC, HTC=10 W/m2 C


Brief summary - modeling of battery cells with different geometries

Pouch cells

Temperature difference across the cell thickness is small.

Temperature difference across the cell surface can be large for high current applications.

Maximum cell temperatures generally located around the positive cell terminal.

Prismatic cells

Temperature difference across its thickness can be large and must be considered.

The large thermal mass for this type of cells may mitigate the cell temperature rise.

Cylindrical cells

Temperature difference across its thickness in the radial direction can be large and must be

considered.

Without external heating through the terminal tabs, max cell temperature occurs in core areas

of the cell.

Maximum cell temperature and the differential temperature in the radial direction vary with

concentric layers in the model.

Modeling cylindrical cell with a single homogeneous layer appears to be conservative.


Model validation – 3-cell module with indirect liquid cooling

Cold plate

@ 25oCTC1 TC2 TC3 TC4

TC5 TC6 TC7

TC8 TC9 TC10

TC11 TC12 TC13

+- TC14 TC15

test setup and thermocouples

on middle cell, pad side surface

analysis model basic cooling unit

Cooling plate Cell Thermal pad


Model validation – 2C discharge

TC1 TC2 TC3 TC4

TC5 TC6 TC7

TC8 TC9 TC10

TC11 TC12 TC13

+- TC14 TC15

Cold plate

@ 25oC

20

25

30

35

40

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

DOD [-]

Tem

pera

ture

[C

]

Test_TC14

Test_TC15

FEA_TC14

FEA_TC15

24

26

28

30

32

34

36

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

DOD [-]

Tem

pera

ture

[C

]

Test_TC1

Test_TC2

Test_TC3

Test_TC4

FEA_TC1

FEA_TC2

FEA_TC3

FEA_TC4



Cold plate

@ 25oC

TC1 TC2 TC3 TC4

TC5 TC6 TC7

TC8 TC9 TC10

TC11 TC12 TC13

+- TC14 TC15

24

26

28

30

32

34

36

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

DOD [-]

Tem

pera

ture

[C

]

Test_TC5

Test_TC6

Test_TC7

FEA_TC5

FEA_TC6

FEA_TC7

24

26

28

30

32

34

36

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

DOD [-]

Tem

pera

ture

[C

]

Test_TC8

Test_TC9

Test_TC10

FEA_TC8

FEA_TC9

FEA_TC10



TC1 TC2 TC3 TC4

TC5 TC6 TC7

TC8 TC9 TC10

TC11 TC12 TC13

+- TC14 TC15

Cold plate

@ 25oC

24

26

28

30

32

34

36

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

DOD [-]

Tem

pera

ture

[C

]

Test_TC11

Test_TC12

Test_TC13

FEA_TC11

FEA_TC12

FEA_TC13

Ave cold

plate temp


Cell temperature at 90% DOD 2C discharge - single cold plate, 3-cell module with different busbar

big

busbar

small

busbar


SAE Paper 2012-01-0119Slide 17

Measured terminal tab temperature with big and small busbars under different discharge rates

Cell Temperature - 4C Discharge

20

25

30

35

40

45

50

55

60

65

70

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

DOD [-]

Tem

pera

ture

, C

4C_Small_Busbar 3C_Small_Busbar 2C_Small_Busbar 4C_Big_Busbar 3C_Big_Busbar 2C_Big_Busbar

9.6

6.2

big

busbar

small

busbar

B

B

B

B

+

2.3



Measured cell temperature with big and small busbars under different discharge rates

big

busbar

small

busbar


20

25

30

35

40

45

50

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

DOD [-]

Tem

pera

ture

, C


3.5

2.4

0.5

B

B

B

B

+



Measured cell temperature with big and small busbars under different discharge rates


20

25

30

35

40

45

50

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

DOD [-]

Tem

pera

ture

, C


big

busbar

small

busbar

1.1

1.3

B

B

B

B

+


Single cold plate, 1.5C

(96S2P pack configuration)

T_terminal = 45.0 oC

T_cell, max = 43.8 oC

∆T_cell = 4.6 oC

∆T_cell-coolant = 8.8 oC

Q_gen/cell = 12.7 W

Q_rej/cell = 9.6 W

Dual cold plate, 1.5C




∆T_cell = 1.8 oC


Q_gen/cell = 12.7 W

Q_rej/cell = 13.1 W

Dual cold plate, 3C




∆T_cell = 7.2 oC


Q_gen/cell = 50.6 W

Q_rej/cell = 46.4 W

Single cold plate, 3C




∆T_cell = 17.5 oC


Q_gen/cell = 50.6 W

Q_rej/cell = 24.8 W

B

B

B

B

B

Cell temperature at 90% DOD under same pack load -single and dual cold plates, no busbar

cold plate

@ 35 oC

cold plates

@ 35 oC


Dual cold plate, 3C




∆T_cell = 7.2 oC


Q_gen/cell = 50.6 W

Q_rej/cell = 46.4 W

Single cold plate, 3C




∆T_cell = 17.5 oC


Q_gen/cell = 50.6 W

Q_rej/cell = 24.8 W

Single cold plate, 1.5C




∆T_cell = 4.6 oC


Q_gen/cell = 12.7 W

Q_rej/cell = 9.6 W

Dual cold plate, 1.5C




∆T_cell = 1.8 oC


Q_gen/cell = 12.7 W

Q_rej/cell = 13.1 W

Criteria:

Tcell, max < 60.0 oC

∆Tcell < 10.0 oC

Cell temperature at 90% DOD under same pack load -single and dual cold plates, no busbar


12-cell module – indirect liquid cooling with single cold plate

Boundary conditions:

Cell capacity = 60 A-hr

Discharge rate = 3C

Depth of discharge = 90%

Initial temperature = 35 oC

Coolant temperature = 35 oC

Averaged HTC = 800 W/m2-K

Simulation results:

Max cell temperature = 52.3 oC

Max differential cell temperature = 7.8 oC

Cell-coolant temperature difference = 17.3 oC


12-cell module – indirect liquid cooling with dual cold plate



Discharge rate = 3C

Depth of discharge = 90%

Initial temperature = 35 oC

Coolant temperature = 35 oC


Simulation results:

Max cell temperature = 46.9 oC

Max differential cell temperature = 4.9 oC

Cell-coolant temperature difference = 12.9 oC


Brief summary - modeling of battery module with indirect liquid cooling

The following design features were found to influence the cell terminal tab

temperatures, maximum cell temperature, and maximum cell differential temperatures:

Busbar design

The busbar thermal mass can have significant influence on the cell terminal tab and the

maximum cell temperatures. It should be taken into account in the cell thermal testing.

Cooling system design

Dual cold plate provides cooling to cell terminals and busbars, resulting in much lower

terminal and cell temperatures compare to single cold plate cooling under the same pack

load and configuration.

Pack configuration

Under the same pack load, a 96S1P with dual cold plate cooling can be thermally

equivalent to a 96S2P with single cold plate cooling. Trade-off studies should be done in

early concept stage.


Model validation – battery module with direct air cooling

Pack

Cell

TypeHigh-power A123 26650 Li-ion cylindrical

cells (model ANR26650MIA)

Performance• Capacity : 2.3 Ah

• Voltage : 3.3 V


• Voltage : 184.8 V

Composition & connection 14 half-module connected in series


• Voltage : 13.2 V

Composition & connection 44 cells connected in 11P4S

Cell

Pack

Half-module

A123 Hymotion™ L5 PCM battery pack for PHEV applications


CFD simulation - flow and temperature distributions

Velocity [m/s]

Air flows mainly through paths in the

middle and two sides of the half

module, indicating that the cooling for

the cells is basically from one side

Outlet

Inlet

Outlet

Temperature [°C]

High rise in air

temperature


Battery module – half module of A123 Hymotiontm L5 PCM battery pack

44 Cells, 4S11P

300K Nodes, 260K Elements

Top View

Bottom View

FE model


Predicted temperature rise at battery cell wall under 5C discharge rate

Predicted temperature rise vs measured

data at selected thermocouple locations


Thermal analysis of battery system with indirect air cooling – system description

Cell Specification

Normal capacity 8 Ah

Normal voltage 3.6 V

Internal resistance < 1.5 mΩ

Max discharge rate 25C

Operating temperature -15 to 50 0C

Mass 290 g

Dimension, T x W x H, mm 8.5 x 140 x 190

Cooling finsAir flow

19mm

Cooling finInsulated by frame

149mm

12 Li-ion pouch cell module

with indirect air cooling

A reference 12 pouch-cell battery

module with indirect air cooling

8Ah Li-ion pouch cell under study


Thermal analysis of battery system with indirect air cooling – model description

Equivalent

Electrodes

Tair & HTC

Insulated by frame

Adiabatic Adiabatic

Adiabatic

Without fin insert

Cooling fin

Insulated by frame

Thermal pad

Negative

current tab

Positive

current tab

Equivalent

electrodes

Cooling plate

Half cooling unit

Cooling fin inserts

Insulated by frame

With fin insert

Boundary condition


Cooling analysis – influence of air cooling channel design on battery temperatures

Without fin insert With fin insert

Battery operation and cooling condition:

Discharge rate = 5C (40A)

End of charge DOD = 80%

Cell initial temperature = 35oC

Cooling air temperature = 35oC

Heat transfer coefficient = 60 W/m2.C

Temperature distribution at DOD = 80%


Cooling analysis – indirect air cooling with simple fin structure (no fin insert) at 80% DOD under 5C discharge

Battery operation and cooling condition:

Discharge rate = 5C (40A)

End of charge DOD = 80%

Cell initial temperature = 35oC



DOD = 20% 40% 60% 80%


Cooling analysis – battery temperature distribution at 80% DOD under 5C discharge

Temperature variation along cooling plate centerline

without and with inserts

34

36

38

40

42

44

46

48

50

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

Distance, mm

Te

mp

era

ture

, C

insulated

section

cooling

section

bNo insert

With insert

Tair

with inserts

no insert


Warm-up analysis – simple fin structure (no fin insert)

Battery warm-up condition:

Cell initial temperature = -20oC

Warm air temperature = 40oC


1C discharge (cell self heating)

Heating time (sec) = 250 500 750 1000


Warm-up analysis – influence of air cooling channel design on battery temperatures

Without fin insert

(@820 seconds)






Temperature distribution when adiabatic edge of the aluminum cooling plate reaches 0oC

With fin insert

(@480 seconds)


Warm-up analysis – battery temperature distribution

Temperature variation along cooling plate centerline

1C discharge, heatup without and with inserts

0

5

10

15

20

25

30

35

40

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

Distance, mm

Te

mp

era

ture

, C

@ 820 sec

@ 480 sec

bNo insert @820 sec

With insert@480 sec

Insulated

section

Cooling

section

At time the adiabatic edge of the aluminum cooling plate reaches 0oC

Tair







It took 340 seconds less for the adiabatic edge of the aluminum cooling

plate with inserts to be heated from -20oC to 0

oC.

Warm-up analysis – battery transient temperature

Transient temperature at adiabatic edge of the cooling plate

1C discharge, without and with inserts

-25

-20

-15

-10

-5

0

5

10

15

20

0 100 200 300 400 500 600 700 800 900 1000

Heating time, second

Te

mp

era

ture

, C

480 sec 820 sec

No insert

With insert

No insert

With insert

with inserts

no insert

adiabatic

edge

adiabatic

edge


Heat from cell self heating is small compare to external heating.

Warm-up analysis – heat flux to cell with cell self heating

Heat flux to each cell & cell self heating

without and with inserts

0

2

4

6

8

10

12

14

0 100 200 300 400 500 600 700 800 900 1000

Heating time, second

He

at

flu

x, W

att

cell self heating

(1C discharge)

No insert

With insert

with inserts

no insert

Q

Q


Warm-up analysis – battery module with finned air channel



Discharge rate = 1C

Heating time = 1000 seconds

Initial temperature = -20 oC

Air temperature = 40 oC


Simulation results:

Time for min cell temperature

to reach 0 oC = 480 sec


Brief summary - modeling of battery module with direct and indirect air cooling

Battery module with direct air cooling

Correlated reasonably well with the available test data.

The air temperature rise in the module has significant influence on the cell-to-cell

temperature difference in the module.

The coolest cells are located at the air entrance and the hottest cells are located at the air

exit.

Battery module with indirect air cooling

Battery temperature distribution is governed by the heat transfer condition of the cooling

plate.

Highest cell temperature are not located at area around the terminal tabs.

Air cooling channel design has significant impact on the battery temperature.

Air cooling channel with structure similar to that in compact heat exchangers can greatly

improve effectiveness of heat transfer between air and the cooling plates, which greatly

influence the battery cooling and warm-up.

For battery system warm-up, heat generated from within the cell is small compare to the

external heat source.


Summary

AVL battery model reasonably characterizes thermal behavior of Li-ion

battery systems:

With various geometries

Cylindrical cells

Pouch cells

Prismatic cells

With different cooling methods

Air cooling

Direct cooling

Indirect cooling

Liquid cooling

Direct cooling (not presented due to customer information)

Indirect cooling

For cooling and warm-up transient processes

kim yeow, ho teng, marina thelliez and eugene tan avl …€¦ · cell level 3d fea analysis user...

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