Battery Pack Design. Thermal design

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mvkf25vt18 Battery Pack Design Mechanical and electrical layout, Thermal modeling, Battery management Avo Reinap, IEA/LU BPD:TH Thermal design CELL PACK SYSTEM Electricity Chemistry Geometry

1 mvkf25vt18 Battery Pack Design Mechanical and electrical layout, Thermal modeling, Battery management Avo Reinap, IEA/LU BPD:TH Thermal design CELL PACK SYSTEM Electricity Chemistry Geometry Properties Heat Thermal interface Cooling integration Methods, models, calculation examples for thermal design Practical realisation examples from some car manufacturers Avo R MVKF25-vt18 Battery Pack Design 39

Thermal modelling Models 1D, 2D, 3D analytic or numeric Computation time vs accuracy, Single cell, a module of cells, battery back Specification of equivalent cell volume with specific losses,

and performance, Source Link Sink Avo R MVKF25-vt18 Battery Pack Design 40 Thermal integration Direct cooling where it is most needed in order to minimize heat transport through the solids that

2 Thermal modelling Models 1D, 2D, 3D analytic or numeric Computation time vs accuracy, Single cell, a module of cells, battery back Specification of equivalent cell volume with specific losses, Assembling, heat transport and temperature distribution Mechanical assembly and thermal accessibility, thermal contacts Integration of active cooling circuits Realisation, estimation of coolant flow and performance, Source Link Sink Avo R MVKF25-vt18 Battery Pack Design 40 Thermal integration Direct cooling where it is most needed in order to minimize heat transport through the solids that causes interior temperature rise and uneven temperature distribution Consider the effects of thermal cycling and expansion Experiences from other electric drive components Avo R MVKF25-vt18 Battery Pack Design 41

Time, Scale and Model Thermal design simplifies

battery pack (Duty) Battery thermal management Keep

it Simple is the rule of the day Prototype

(SW) components and parts (Ansys or Comsol fluids

3 Time, Scale and Model Thermal design simplifies control and BMS Cells (EL+Chemi) modules (Heat) battery pack (Duty) Battery thermal management Keep temperature & use little energy for operation Keep it Simple is the rule of the day Prototype development and prototyping supported buy models CAD (SW) components and parts (Ansys or Comsol fluids and solids) system (Simulink/Matlab) Avo R MVKF25-vt18 Battery Pack Design 43

4 Thermal model Ccell d dt Q cell C P cell c P fluid, out cell h surf R cell Rcell P cell fluid, in 1 C cell surf Rlink fluid representing physical reality (?) Main focus on only on reasonable cell surface temperature surf as cell is remains unknown (?) surf = fluid + R*P Thermal resistances: simplifications vs idealisation Practical realization for fluid dynamics Thermography for rapid thermal assessment Avo R MVKF25-vt18 Battery Pack Design 44 Cooling integration Cooling mechanisms Cooling flow determination Cooling duct and system design Avo R MVKF25-vt18 Battery Pack Design 45

5 Model library Impedance based equivalent circuit models, dynamic experiment based Physics and chemistry-based models relay on model parameterisation and properties Energy or power-flow models are typically used on a system level Empirical models black box models suitable for control not design Avo R MVKF25-vt18 Battery Pack Design 46 Avo R MVKF25-vt18 Battery Pack Design 47

Cell library Selected cell examples: cylindrical, prismatic, pouch This information is

Manufacturer configuration Geometry Voltage Capacity Specific power Weight [mm] [V] [Ah]

5 3.6 28 2300 7 Kokam Pouch 462x327x15.8 3.

there is need of 84 series connected 3.6V cells First draft of 148x26.

of 7 cells First draft of ø18 mm 4 parallel cylindrical cell arrangement with cooling

6 Cell library Selected cell examples: cylindrical, prismatic, pouch This information is used for virtual packing and rough estimation on temperature rise and distribution Manufacturer configuration Geometry Voltage Capacity Specific power Weight [mm] [V] [Ah] [W/kg] [g] Panasonic Cylindrical Ø18.5x Hitatchi Prismatic 148x91x Kokam Pouch 462x327x Avo R MVKF25-vt18 Battery Pack Design 48 Cell virtual packing For 300V there is need of 84 series connected 3.6V cells First draft of 148x26.5 mm prismatic cell arrangement where 5 mm distance is left between the rows and groups of 7 cells First draft of ø18 mm 4 parallel cylindrical cell arrangement with cooling channel in between the cells Not only visualization but a parameterized model with coupling to finite element analysis (FEA) Avo R MVKF25-vt18 Battery Pack Design 49

Electric connection of cells Series-parallel connections Connection-bars and cables are

resistance connections Avo R MVKF25-vt18 Battery Pack Design 50 Estimation of thermal

cond cond ins f Equivalent thermal conductivity of a coil is given by the filling factor

medium between the conductor foils jelly-roll:12% Al+Cu λ>0w/mk, 6% eparator λ<0.

7 Electric connection of cells Series-parallel connections Connection-bars and cables are part of heat generation but also distribution Nickel plate + spot welding = healthy low resistance connections Avo R MVKF25-vt18 Battery Pack Design 50 Estimation of thermal conductivity cond ins eff k 1 k L eff ins L k f cond f L cond 1 k L k 1 k ins f f ins f cond cond ins f Equivalent thermal conductivity of a coil is given by the filling factor of the conductor foil (copper in this example) and the thermal conductivity of the medium between the conductor foils jelly-roll:12% Al+Cu λ>0w/mk, 6% eparator λ<0.35w/mk, rest λ~1w/mk Across coil or roll λ~1w/mk, along λ>>1w/mk Avo R MVKF25-vt18 Battery Pack Design 51

Using 2D FE for sketching FEMM electromagnetism, heat transfer, electric currents Easy to

region, Connecting the endpoints with either line segments or arc segments to complete the

conditions on the outer edges of the geometry.

between cells Cross-flow through battery module Narrow spacing expectedly no cooling Large

8 Using 2D FE for sketching FEMM electromagnetism, heat transfer, electric currents Easy to use, library of Matlab functions Drawing the endpoints of the lines and arc segments for a region, Connecting the endpoints with either line segments or arc segments to complete the region, Defining material properties and mesh sizing for each region, Specifying boundary conditions on the outer edges of the geometry. Avo R MVKF25-vt18 Battery Pack Design 52 Battery pack with cylindrical cells Empty space between cells Cross-flow through battery module Narrow spacing expectedly no cooling Large spacing for sake of better cooling is often considered impractical CFD vs fast design approaches Avo R MVKF25-vt18 Battery Pack Design 53

(MOR) simulation compared to thermographic

singular value decomposition (SVD) Direct

9 Battery back with prismatic cells Temperature homogenization analysis Analysis of thermal runaway Avo R MVKF25-vt18 Battery Pack Design 54 Battery pack with pouch cells Coupled electro-thermal FE+model order reduction (MOR) simulation compared to thermographic images A reduced order model (ROM) based on singular value decomposition (SVD) Direct air-cooled Li-ion pouch battery cell in order to improve the understanding (modelling) and practical realization of battery module Avo R MVKF25-vt18 Battery Pack Design 55

10 Vehicular application Avo R MVKF25-vt18 Battery Pack Design 56 Avo R MVKF25-vt18 Battery Pack Design 57

Chevy 104kW kwh GM Volt and Spark EV use

between the cells with the liquid coolant

The Volt cooling scheme is very effective

frames Avo R MVKF25-vt18 Battery Pack Design

11 Chevy 104kW kwh GM Volt and Spark EV use thin prismatic shaped cooling plates in between the cells with the liquid coolant circulating thru the plate. The Volt cooling scheme is very effective from a cooling point of view but it is complicated. The cells are encased in multiple plastic frames Avo R MVKF25-vt18 Battery Pack Design 58 Tesla S 285kW 70kWh Tesla snakes a flattened cooling tube thru their cylindrical cells resulting in a very simple cooling scheme with very few points for leakage. Avo R MVKF25-vt18 Battery Pack Design 59

12 BWM i3 125kW 21-33kWh The BMW i3 cools the bottom of the battery case with refrigerant eliminating the liquid coolant entirely. New energy dense lithium ion cells (50% more) Avo R MVKF25-vt18 Battery Pack Design Integration example by BMW Avo R MVKF25-vt18 Battery Pack Design 61

13 Integration example by Tesla kwh, 352V, 14 modules, 6216 cells in groups of 74=6x14 85kWh, 402V, 16 modules, 7104 cells Avo R MVKF25-vt18 Battery Pack Design 62 Integration example by Tesla Avo R MVKF25-vt18 Battery Pack Design 63

14 Accommodation of cylindrical cells Avo R MVKF25-vt18 Battery Pack Design 64 Cool-plate and coolant Single stage heat transfer insufficient ha vs UA Avo R MVKF25-vt18 Battery Pack Design 65

15 Coolant Air H 2 C0 2 H 2 0 Tr Oil, degc c, kj/kgk , kg/m λ,mw/mk , upas Avo R MVKF25-vt18 BTMS Battery Pack Design 66 Conjugate heat transfer The character of flow is described by Reinolds number, Re 1 vdh Q A the heat transfer is expressed by Nusselt number h qdh Nu Dh k k in wall D h bulk in and the coolant is described by Prandtl number c p Pr k The hydraulic diameter is related to the geometric layout of the cooling channel area D h 4 perimeter P cool cq P ha out heat cool win d cool d cond Avo R MVKF25-vt18 Battery Pack Design 67 L h L

50 B. Sundén, Introduction to Heat transfer 2 Heat transfer mapping Cooling power, p=c p Q( out - in ) [W] 0 2 180 0 Nusselts number, Nu=f(Re,Pr) [-] 1 2 180 140 Heat transfer coefficient, h=nu k/d30

80 180 0 300 400 500 0 700 800 900 0 40 140 Cooling power, p=c 0 flow rate, Q [L/min] 1 p Q( out - in ) [W] 26 1 250 0 80 180 0 300 400 500 0 700 800 900 0 40 140 flow rate, Q [L/min] 1 25 1 0 80 0 0

16 50 B. Sundén, Introduction to Heat transfer 2 Heat transfer mapping Cooling power, p=c p Q( out - in ) [W] Nusselts number, Nu=f(Re,Pr) [-] Heat transfer coefficient, h=nu k/d30 0 h [W/(m 2 K)] Temperature across boundary, P cool /(ha cool ) [C] Pressure drop, dp 28[Pa] Ideal cooling supply power, 27 dpq [-] Cooling power, p=c 0 flow rate, Q [L/min] 1 p Q( out - in ) [W] flow rate, Q [L/min] flow rate, Q [L/min] flow rate, Q [L/min] flow rate, Q [L/min] flow rate, Q [L/min] flow rate, Q [L/min] flow rate, Q [L/min] outlet temperature, out [C] outlet temperature, out [C] outlet temperature, out [C] outlet temperature, out [C] outlet temperature, out [C] outlet temperature, out [C] outlet temperature, out [C] wall temperature, out [C] Reynolds number, Re=2d h Q/(A) [-] outlet temperature, out [C] Driving parameters for cooling P=f( out,q) at in Flow (Re) and coolant (Pr) characterization cooling power, p=c p Q( out - in ) [W] Heat transfer correlations (Nu) and coefficient h Wall and winding temperature Pressure across cooling channel Power for supply Expected cooling power P=f( w,q) at in flow rate, Q [L/min] Avo R MVKF25-vt18 Battery Pack Design c=3500j/kgk, =900kg/m Thermal analysis of cell assembly Hitachi 3.6v 35Ah 0.8mΩ@10A 155x27x118 incl terminals 810g Geometric data Defined by German standard DIN Heat transfer inside the cell From cell to module and pack Cell = Jelly-roll (heater) + carrier (assembly) Heating power Worst case P=I 2 R o =50W Avo R MVKF25-vt18 Battery Pack Design 69

Thermal accessibility of a cell Available thermal connection areas Large long sides 2x134cm 2 but low thermal conductivity

Avo R MVKF25-vt18 Battery Pack Design 70 H.

Cell dimensions are known, jelly-roll geometry only guessed DIN SPEC 91252:11 Lundgren et al 16 Heat conductivity defined

17 Thermal accessibility of a cell Available thermal connection areas Large long sides 2x134cm 2 but low thermal conductivity Sides, lateral sides 2x24cm 2 and Bottom side 39cm 2 Bottom and short sides have expectedly better inherit thermal contact Avo R MVKF25-vt18 Battery Pack Design 70 H. Lundgren et al, Thermal Management of Large-Format Prismatic Lithium-Ion Battery in PHEV Application Inside a battery cell Cell dimensions are known, jelly-roll geometry only guessed DIN SPEC 91252:11 Lundgren et al 16 Heat conductivity defined in-plane and cross-plane for whole cell unit and jelly roll (including heat capacity) Important part for thermal models are termination and equivalent jelly-roll Avo R MVKF25-vt18 Battery Pack Design 71

18 H. Lundgren et al, Thermal Management of Large-Format Prismatic Lithium-Ion Battery in PHEV Application Surface temperature response Thermal vs electric power extraction and comparison Thermal conductivity Through-foil 0.95W/mK Along foil 30.8 W/mK Avo R MVKF25-vt18 Battery Pack Design D FE over cross-sections Q v =140W/dm 3, surf =30 o C 30 Temperature, [C] λ cell = W/mK Case 2 Q base [W] Q lateral [W] max [ o C] λ cell =1 W/mK Avo R MVKF25-vt18 Battery Pack Design 73

fluid = wall = surf =30 o C surf =30 o C

both in plane directions Lateral clamp or

19 Observations A Battery cell P=50 W heating, 1/R={ } K/W, ={ } K Heat conductor Ideal 1/R=0 K/W, =0 K Cooling plate Ideal fluid = wall = surf =30 o C surf =30 o C wall =30 o C fluid =30 o cell = surf +Δ C Source Link Sink 50 W per cell Avo R MVKF25-vt18 Battery Pack Design 74 Realization A Mechanical assembly in cross plane direction Thermal enhancement both in plane directions Lateral clamp or forcing plate Battery to base contact.. Avo R MVKF25-vt18 Battery Pack Design 75

1 Cell clamped into heat conductor Q v =140W/dm 3, surf =30 o

06 0.05 0.04 0.03 0.02 0.01 0-0.08-0.06-0.04-0.02 0 0.02 0.04

08 length, [m] 54 Case 2 Q base [W] Q lateral [W] max [ o C] 1

27 23 72 Avo R MVKF25-vt18 Battery Pack Design 76 1 30

02 36 Cell linked to cool-plate 42 48 2 54 Q v =140W/dm 3,

14 53 2-h 1 35 15 68 3-0.1-0.08-0.06-0.04-0.02 0 0.02 0.04 08 0.

20 1 Cell clamped into heat conductor Q v =140W/dm 3, surf =30 o C Temperature, [C] height, [m] length, [m] 54 Case 2 Q base [W] Q lateral [W] max [ o C] μm gap gap =3 o C μm gap gap =21 o C Avo R MVKF25-vt18 Battery Pack Design Temperature, [C] height, [m] Cell linked to cool-plate Q v =140W/dm 3, fluid =25 o C Case Q base [W] Q lateral [W] max [ o C] h length, [m] h 1 =0W/Km 2 wall wall =15 o C h 2 =0W/Km 2 wall wall =95 o C 3-h Avo R MVKF25-vt18 Battery Pack Design 77

scale (usually presented in between -30 o C)

MVKF25-vt18 Battery Pack Design 78 Summary

load is lower Heat conductor Insufficient

w l =95 o C cell = surf +Δb surf = wall +Δc

21 Transient heating 5 minutes between the frames (FEMM transient HT) Hot side of the scale (usually presented in between -30 o C) One dominating heat capacitance only Avo R MVKF25-vt18 Battery Pack Design 78 Summary Battery cell b={ } 50W actual load is lower Heat conductor Insufficient thermal contact 0.1 mm air 50W Cooling plate Insufficient heat transfer h 2 =0W/Km 2 wall w l =95 o C cell = surf +Δb surf = wall +Δc wall = fluid +Δw fluid =30 o C Source Link Sink 50 W per cell Avo R MVKF25-vt18 Battery Pack Design 79

22 Evaluation of direct forced cooling Cooling channel arrangements Thermography of heat transients 300 A DC L/min Location of hot-spots turns of the layer edges where the cross section is less than 10 mm 2 Edge layer 1 is closest to air-gap Avo R MVKF25-vt18 Battery Pack Design 80

Battery Pack Design MVKF25-vt17

Battery Pack Design MVKF25-vt17 Mechanical and electrical layout, Thermal modeling, Battery management 25-27/4 Avo Reinap, IEA/LU Goals Design and dimensioning of battery pack based on suitable models