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
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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)
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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
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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
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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
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Cell modeling – pouch cells
terminal tab
separator
equivalent
electrode
equivalent
electrode
X-ray Tomography
of a failed cell
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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
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Cell modeling – cylindrical cells
Comparison of single-layer and multi-layer FEA models
3 layers
approximation
equivalent electrodes1 layer
approximation
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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
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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.
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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
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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
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Model validation – 2C discharge
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
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Model validation – 2C discharge
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
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Cell temperature at 90% DOD 2C discharge - single cold plate, 3-cell module with different busbar
big
busbar
small
busbar
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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
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SAE Paper 2012-01-0119Slide 18
Measured cell temperature with big and small busbars under different discharge rates
big
busbar
small
busbar
Cell Temperature - 4C Discharge
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
4C_Small_Busbar 3C_Small_Busbar 2C_Small_Busbar 4C_Big_Busbar 3C_Big_Busbar 2C_Big_Busbar
3.5
2.4
0.5
B
B
B
B
+
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SAE Paper 2012-01-0119Slide 19
Measured cell temperature with big and small busbars under different discharge rates
Cell Temperature - 4C Discharge
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
4C_Small_Busbar 3C_Small_Busbar 2C_Small_Busbar 4C_Big_Busbar 3C_Big_Busbar 2C_Big_Busbar
big
busbar
small
busbar
1.1
1.3
B
B
B
B
+
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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
(96S2P pack configuration)
T_terminal = 39.7 oC
T_cell, max = 39.0 oC
∆T_cell = 1.8 oC
∆T_cell-coolant = 4.0 oC
Q_gen/cell = 12.7 W
Q_rej/cell = 13.1 W
Dual cold plate, 3C
(96S1P pack configuration)
T_terminal = 53.5 oC
T_cell, max = 49.7 oC
∆T_cell = 7.2 oC
∆T_cell-coolant = 14.7 oC
Q_gen/cell = 50.6 W
Q_rej/cell = 46.4 W
Single cold plate, 3C
(96S1P pack configuration)
T_terminal = 67.1 oC
T_cell, max = 63.1 oC
∆T_cell = 17.5 oC
∆T_cell-coolant = 28.1 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
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Dual cold plate, 3C
(96S1P pack configuration)
T_terminal = 53.5 oC
T_cell, max = 49.7 oC
∆T_cell = 7.2 oC
∆T_cell-coolant = 14.7 oC
Q_gen/cell = 50.6 W
Q_rej/cell = 46.4 W
Single cold plate, 3C
(96S1P pack configuration)
T_terminal = 67.1 oC
T_cell, max = 63.1 oC
∆T_cell = 17.5 oC
∆T_cell-coolant = 28.1 oC
Q_gen/cell = 50.6 W
Q_rej/cell = 24.8 W
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
(96S2P pack configuration)
T_terminal = 39.7 oC
T_cell, max = 39.0 oC
∆T_cell = 1.8 oC
∆T_cell-coolant = 4.0 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
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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
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12-cell module – indirect liquid cooling with dual 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 = 46.9 oC
Max differential cell temperature = 4.9 oC
Cell-coolant temperature difference = 12.9 oC
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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.
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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
Performance• Capacity : 25.3 Ah
• Voltage : 184.8 V
Composition & connection 14 half-module connected in series
Performance• Capacity : 25.3 Ah
• Voltage : 13.2 V
Composition & connection 44 cells connected in 11P4S
Cell
Pack
Half-module
A123 Hymotion™ L5 PCM battery pack for PHEV applications
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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
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Battery module – half module of A123 Hymotiontm L5 PCM battery pack
44 Cells, 4S11P
300K Nodes, 260K Elements
Top View
Bottom View
FE model
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Predicted temperature rise at battery cell wall under 5C discharge rate
Predicted temperature rise vs measured
data at selected thermocouple locations
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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
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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
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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%
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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
Cooling air temperature = 35oC
Heat transfer coefficient = 60 W/m2.C
DOD = 20% 40% 60% 80%
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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
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Warm-up analysis – simple fin structure (no fin insert)
Battery warm-up condition:
Cell initial temperature = -20oC
Warm air temperature = 40oC
Heat transfer coefficient = 60 W/m2.C
1C discharge (cell self heating)
Heating time (sec) = 250 500 750 1000
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Warm-up analysis – influence of air cooling channel design on battery temperatures
Without fin insert
(@820 seconds)
Battery warm-up condition:
Cell initial temperature = -20oC
Cooling air temperature = 40oC
Heat transfer coefficient = 60 W/m2.C
1C discharge (cell self heating)
Temperature distribution when adiabatic edge of the aluminum cooling plate reaches 0oC
With fin insert
(@480 seconds)
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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
Battery warm-up condition:
Cell initial temperature = -20oC
Cooling air temperature = 40oC
Heat transfer coefficient = 60 W/m2.C
1C discharge (cell self heating)
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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
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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
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Warm-up analysis – battery module with finned air channel
Boundary conditions:
Cell capacity = 8 A-hr
Discharge rate = 1C
Heating time = 1000 seconds
Initial temperature = -20 oC
Air temperature = 40 oC
Averaged HTC = 60 W/m2-K
Simulation results:
Time for min cell temperature
to reach 0 oC = 480 sec
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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.
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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