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

Transcription

1 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

2 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 2

3 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) 3

4 Introduction to AVL electro-thermal battery model Inputs Cell specification: Nominal voltage Capacity Cell geometry: Height Diameter or width/thickness Case thickness Cell Characterization Characterizing the battery cells: V R i f ( DOD, Ai, T) f ( DOD, B, T) i Cell level 3D FEA analysis Material data generation Material definition: e.g. electrical conductivity User defined parameters for battery FEA user subroutine files Cell material properties: Thermal conductivity Density Heat capacity Electrical conductivity Cell performance: Charge / discharge curves from suppliers data sheet at different temperatures Parameters: A i a0, a1, a2, a3, a4 B i [ b0, b1, b2, b3, b4] Coupled transient electro-thermal FEA analysis Identify cell temperature distribution under various discharge / charge rates C p 2 r J T t ( k T ) q 4

5 Battery cell modeling process Cell material properties (thermal & electrical conductivities etc) Cell geometry Cell performance User defined parameters for cell characterization 3D FEA Coupled transient electro-thermal analysis User subroutine DOD distribution Current distribution Voltage drops Cell heat generation Cell temperature distribution Thermal boundary conditions 5

6 Electro-thermal analysis of a battery 1) Electrical: Voltage potential Electrical resistance 2 r J Current density 2) Thermal: Heat generation q J 2 R i Coupled Electro- Thermal Analysis Heat transfer model Composite density q = volumetric heat generation J = current density R i = internal resistance C p T t Composite heat capacity ( k T ) q Composite thermal conductivity 6

7 Cell modeling pouch cells terminal tab separator equivalent electrode equivalent electrode X-ray Tomography of a failed cell 7

8 Cell modeling prismatic cells safety valve _ + case equivalent electrodes Analysis conditions: 1) 10C discharge to 80% DOD 2) initial cell temperature = 25 o C 3) T_air = 25 o C, HTC=50 W/m 2 C 8

9 Cell modeling cylindrical cells Comparison of single-layer and multi-layer FEA models 1 layer approximation equivalent electrodes 3 layers approximation 9

10 Cell modeling cylindrical cells Comparison of single-layer and multi-layer FEA models (under the same cell load and thermal boundary condition) 1 layer model 3 layer model Analysis conditions: 1) 10C discharge to 90% DOD 2) initial cell temperature = 25 o C 3) T_air = 25 o C, HTC=10 W/m 2 C 10

11 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. 11

12 Model validation 3-cell module with indirect liquid cooling analysis model basic cooling unit test setup and thermocouples on middle cell, pad side surface - TC14 TC15+ TC1 TC2 TC3 TC4 TC5 TC6 TC7 TC8 TC9 TC10 Cold 25 o C Cooling plate Cell Thermal pad TC11 TC12 TC13 12

13 Temperature [C] Temperature [C] Model validation 2C discharge 40 Test_TC14 35 Test_TC15 30 FEA_TC14 - TC14 TC15 TC1 TC2 TC3 TC4 TC5 TC6 TC7 TC8 TC9 TC10 TC11 TC12 TC13 Cold 25 o C DOD [-] DOD [-] FEA_TC15 Test_TC1 Test_TC2 Test_TC3 Test_TC4 FEA_TC1 FEA_TC2 FEA_TC3 FEA_TC4 13

14 Temperature [C] Temperature [C] Model validation 2C discharge - TC14 TC15 TC1 TC2 TC3 TC4 TC5 TC6 TC7 TC8 TC9 TC10 TC11 TC12 TC13 Cold 25 o C DOD [-] DOD [-] Test_TC5 Test_TC6 Test_TC7 FEA_TC5 FEA_TC6 FEA_TC7 Test_TC8 Test_TC9 Test_TC10 FEA_TC8 FEA_TC9 FEA_TC10 14

15 Temperature [C] Model validation 2C discharge - TC14 TC15 TC1 TC2 TC3 TC4 TC5 TC6 TC7 Cold 25 o C DOD [-] Test_TC11 Test_TC12 Test_TC13 FEA_TC11 FEA_TC12 FEA_TC13 Ave cold plate temp TC8 TC9 TC10 TC11 TC12 TC13 15

16 Cell temperature at 90% DOD 2C discharge - single cold plate, 3-cell module with different busbar big busbar small busbar 16

17 Temperature, C Measured terminal tab temperature with big and small busbars under different discharge rates Cell Temperature - 4C Discharge 4C_Small_Busbar 3C_Small_Busbar 2C_Small_Busbar 4C_Big_Busbar 3C_Big_Busbar 2C_Big_Busbar B B B B DOD [-] big busbar small busbar SAE Paper Slide 17 17

18 Temperature, C Measured cell temperature with big and small busbars under different discharge rates Cell Temperature - 4C Discharge 4C_Small_Busbar 3C_Small_Busbar 2C_Small_Busbar 4C_Big_Busbar 3C_Big_Busbar 2C_Big_Busbar 50 B B 40 B B DOD [-] big busbar small busbar SAE Paper Slide 18 18

19 Temperature, C Measured cell temperature with big and small busbars under different discharge rates Cell Temperature - 4C Discharge 4C_Small_Busbar 3C_Small_Busbar 2C_Small_Busbar 4C_Big_Busbar 3C_Big_Busbar 2C_Big_Busbar B B B B DOD [-] big busbar small busbar SAE Paper Slide 19 19

20 Cell temperature at 90% DOD under same pack load - single and dual cold plates, no busbar Single cold plate, 3C (96S1P pack configuration) T_terminal = 67.1 o C T_cell, max = 63.1 o C T_cell = 17.5 o C T_cell-coolant = 28.1 o C Q_gen/cell = 50.6 W Q_rej/cell = 24.8 W Dual cold plate, 3C (96S1P pack configuration) T_terminal = 53.5 o C T_cell, max = 49.7 o C T_cell = 7.2 o C T_cell-coolant = 14.7 o C Q_gen/cell = 50.6 W Q_rej/cell = 46.4 W B Single cold plate, 1.5C (96S2P pack configuration) B B B B T_terminal = 45.0 o C T_cell, max = 43.8 o C T_cell = 4.6 o C T_cell-coolant = 8.8 o C Q_gen/cell = 12.7 W Q_rej/cell = 9.6 W Dual cold plate, 1.5C (96S2P pack configuration) T_terminal = 39.7 o C T_cell, max = 39.0 o C T_cell = 1.8 o C T_cell-coolant = 4.0 o C Q_gen/cell = 12.7 W Q_rej/cell = 13.1 W cold 35 o C cold 35 o C 20

21 Cell temperature at 90% DOD under same pack load - single and dual cold plates, no busbar Single cold plate, 3C (96S1P pack configuration) T_terminal = 67.1 o C T_cell, max = 63.1 o C T_cell = 17.5 o C T_cell-coolant = 28.1 o C Q_gen/cell = 50.6 W Q_rej/cell = 24.8 W Dual cold plate, 3C (96S1P pack configuration) T_terminal = 53.5 o C T_cell, max = 49.7 o C T_cell = 7.2 o C T_cell-coolant = 14.7 o C Q_gen/cell = 50.6 W Q_rej/cell = 46.4 W Single cold plate, 1.5C (96S2P pack configuration) T_terminal = 45.0 o C T_cell, max = 43.8 o C T_cell = 4.6 o C T_cell-coolant = 8.8 o C Q_gen/cell = 12.7 W Q_rej/cell = 9.6 W Dual cold plate, 1.5C (96S2P pack configuration) T_terminal = 39.7 o C T_cell, max = 39.0 o C T_cell = 1.8 o C T_cell-coolant = 4.0 o C Q_gen/cell = 12.7 W Q_rej/cell = 13.1 W Criteria: Tcell, max < 60.0 o C Tcell < 10.0 o C 21

22 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 o C Coolant temperature = 35 o C Averaged HTC = 800 W/m 2 -K Simulation results: Max cell temperature = 52.3 o C Max differential cell temperature = 7.8 o C Cell-coolant temperature difference = 17.3 o C 22

23 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 o C Coolant temperature = 35 o C Averaged HTC = 800 W/m 2 -K Simulation results: Max cell temperature = 46.9 o C Max differential cell temperature = 4.9 o C Cell-coolant temperature difference = 12.9 o C 23

24 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. 24

25 Model validation battery module with direct air cooling A123 Hymotion L5 PCM battery pack for PHEV applications Cell Pack Half-module Type Performance Performance Composition & connection Performance Composition & connection High-power A Li-ion cylindrical cells (model ANR26650MIA) Capacity : 2.3 Ah Voltage : 3.3 V Capacity : 25.3 Ah Voltage : V 14 half-module connected in series Capacity : 25.3 Ah Voltage : 13.2 V 44 cells connected in 11P4S Pack Cell 25

26 CFD simulation - flow and temperature distributions Velocity [m/s] Temperature [ C] Outlet Inlet Outlet High rise in air temperature 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 26

27 Battery module half module of A123 Hymotion tm L5 PCM battery pack Top View Bottom View FE model 44 Cells, 4S11P 300K Nodes, 260K Elements 27

28 Predicted temperature rise at battery cell wall under 5C discharge rate Predicted temperature rise vs measured data at selected thermocouple locations 28

29 Thermal analysis of battery system with indirect air cooling system description A reference 12 pouch-cell battery module with indirect air cooling 12 Li-ion pouch cell module with indirect air cooling Air flow Cooling fins 19mm 149mm 8Ah Li-ion pouch cell under study 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 0 C Mass 290 g Dimension, T x W x H, mm 8.5 x 140 x 190 Insulated by frame Cooling fin 29

30 Thermal analysis of battery system with indirect air cooling model description Half cooling unit Thermal pad Positive current tab Equivalent electrodes Boundary condition Equivalent Electrodes Adiabatic Insulated by frame Negative current tab Cooling plate Adiabatic Adiabatic Tair & HTC Insulated by frame Insulated by frame Cooling fin Cooling fin inserts Without fin insert With fin insert 30

31 Cooling analysis influence of air cooling channel design on battery temperatures Temperature distribution at DOD = 80% Without fin insert With fin insert Battery operation and cooling condition: Discharge rate = 5C (40A) End of charge DOD = 80% Cell initial temperature = 35 o C Cooling air temperature = 35 o C Heat transfer coefficient = 60 W/m 2. C 31

32 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 = 35 o C Cooling air temperature = 35 o C Heat transfer coefficient = 60 W/m 2. C DOD = 20% 40% 60% 80% 32

33 Temperature, C Cooling analysis battery temperature distribution at 80% DOD under 5C discharge no insert Temperature variation along cooling plate centerline without and with inserts cooling section insulated section No insert With b insert with inserts Tair Distance, mm 33

34 Warm-up analysis simple fin structure (no fin insert) Battery warm-up condition: Cell initial temperature = -20 o C Warm air temperature = 40 o C Heat transfer coefficient = 60 W/m 2. C 1C discharge (cell self heating) Heating time (sec) =

35 Warm-up analysis influence of air cooling channel design on battery temperatures Temperature distribution when adiabatic edge of the aluminum cooling plate reaches 0 o C Without fin insert (@820 seconds) With fin insert (@480 seconds) Battery warm-up condition: Cell initial temperature = -20 o C Cooling air temperature = 40 o C Heat transfer coefficient = 60 W/m 2. C 1C discharge (cell self heating) 35

36 Temperature, C Warm-up analysis battery temperature 820 sec At time the adiabatic edge of the aluminum cooling plate reaches 0 o C Tair Temperature variation along cooling plate centerline 1C discharge, heatup without and with inserts No sec With insert@480 b sec Insulated section Cooling section 480 sec Distance, mm Battery warm-up condition: Cell initial temperature = -20 o C Cooling air temperature = 40 o C Heat transfer coefficient = 60 W/m 2. C 1C discharge (cell self heating) 36

37 Temperature, C Warm-up analysis battery transient temperature adiabatic edge no insert Transient temperature at adiabatic edge of the cooling plate 1C discharge, without and with inserts No insert With insert 5 0 with inserts adiabatic edge sec 820 sec Heating time, second It took 340 seconds less for the adiabatic edge of the aluminum cooling plate with inserts to be heated from -20 o C to 0 o C. 37

38 Heat flux, Watt Warm-up analysis heat flux to cell with cell self heating no insert Heat flux to each cell & cell self heating without and with inserts No insert With insert 10 Q 8 with inserts cell self heating (1C discharge) Q Heating time, second Heat from cell self heating is small compare to external heating. 38

39 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 o C Air temperature = 40 o C Averaged HTC = 60 W/m 2 -K Simulation results: Time for min cell temperature to reach 0 o C = 480 sec 39

40 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. 40

41 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 41