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22

Li-ion battery cooling

Li-ion battery

Tmax = < 40 C

∆Twithin cell = 5 – 10K

∆Tbetw. cells = 5K

A/C circuit

Cooled air

Refrigerant (direct)

Secondary circuit

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33

Cell structure and cooling paths

Good thermal conductivity:

Along electrodes

In the conductors

In the metallic housing

Low thermal conductivity:

Perpendicular to the electrodes

In cavities Electrode stack comprising:

cathodes, anodes, separators

Housing

Anode conductor

Insulation

Cavities

Cathode conductor

Potential cooling contact points

Heat flows

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44

Cell types

Pouch (“coffee bag”)PrismaticCylindrical

hh

rh d

d

Unfavorable surface/volume ratio

Curved external surface unfavorable for

contact with heat-conducting elements

Aerodynamic when air-cooled

Favorable surface/volume ratio

Level external surface favorable for contact

with heat-conducting elements

Pouch cells: efficient conductor cooling producible

Assessment with regard to cooling:

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55

Cooling concepts for cells

Cell

assembly

in battery+ + + 0 – +

Cooling

effectiveness 0 + + + + +

Package

space

required

in battery

– + + + – + +

a) Air cooling b) Base/head

cooling

c) Cooling plates

between cells

d) Fluid-ducting

cooling plates

e) Conductor

cooling

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66

Cooling systems for batteries

Disadvantages

Package space requirement of entire system

Dependence on vehicle cabin air temperature

Low cooling performance

Inhomogeneous temperature distribution

within battery

Risk of fouling

Potential safety concerns

Advantage

Low complexity

Cabin air cooling

Battery

Ve

hic

le c

ab

in

Refrigerant

circuit

Eva

po

rato

r

Co

nd

en

se

r

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77

Cooling systems for batteriesIndependent air cooling

Advantages

Independent of vehicle cabin air

temperature

High cooling performance

Disadvantages

Package space requirement of entire system

Inhomogeneous temperature distribution

within battery

Risk of fouling

Ba

tte

ry

evapora

tor

Refrigerant

circuit

Co

nd

en

se

r

Battery

Ve

hic

leca

bin

Eva

po

rato

r

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88

Cooling systems for batteriesDirect refrigerant-based cooling

Disadvantages

Battery cooling possible only when A/C circuit

operating

Heating cannot be integrated

Advantages

Bauraum of entire system

Homogeneous temperature distribution

High cooling performance

Battery

Refrigerant

circuit

Compressor Evaporator plate

Co

nd

en

se

r

Eva

po

rato

r

Eva

po

rato

r

pla

te

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Technischer Pressetag Dr. Heckenberger Mai 2009 p0086.ppt

99

Secondary circuit with chiller and heat sink in battery

Disadvantages

Package space and weight of entire system

Cost

Inertia due to high thermal mass

Advantages

Energy efficiency (annual average)

Compact battery module

High cooling performance

Battery heating can be integrated

Co

nd

en

se

r

Ba

tte

ry c

oo

ler

Refrigerant

circuit

Coolant

circuit

Heating

Compressor

ChillerBattery

He

at sin

k

Eva

po

rato

r

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1010

Current examplesDirect refrigerant-based cooling in Mercedes S400 BlueHYBRID

First Li-ion battery to be cooled directly by refrigerant in series

production 2009

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1111

Current examplesDirect refrigerant or coolant-based cooling and conductor cooling

Sponsored by:

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1212

HVAC/battery system test benchBattery, A/C circuit/secondary circuit under real operating conditions

Fan

Movable wall

Mass flow

Flap

Heating

Pre-dryer

Fan

Dryer

Heating

DiaphragmFanFan

Cooling Heating

Mass flow

CompressorCondenser

HVACAuxiliaryunit

Screens

Heating

Dew pointunit

Flap

Diaphragm

Cooling

Cooling

Fan

Evaporator test section Condenser test section

Voltage: 500 V

Current: 300 A

Output: 65 kW

CAN

Driving cycle

Climate profile

Charge/discharge

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1313

Summary

The approach to Li-ion battery cooling depends on the cell type and application.

Behr has over 4 years’ experience in battery cooling and provides a tightly-knit development

process from simulation through validation.

The world’s first direct refrigerant-based cooling system for Li-ion batteries will go into series

production in the Mercedes S400 BlueHYBRID in 2009.

Additional series production orders for battery cooling components have been received.

Behr has successfully developed various battery cooling systems for mild and full hybrids, plug-in

hybrids, and electric vehicles, and supplies the necessary associated components.

Direct refrigerant-based cooling is the compact solution for mild and full hybrids.

We favor secondary circuit cooling for plug-in hybrids and electric vehicles.

This enables valuable electric energy for powering the refrigerant compressor to be saved when

outside temperatures are low.