Battery Thermal Management Systems ‐

BTMS

Charging a battery electric vehicle (BEV)

Principles of a battery

Some batteries

Battery for a vehicle

Battery Type Specific energy J/kg

Specific energy Wh/kg

Energy density Wh/liter

Cell Voltage V

Lead-acid 145 000 41 100 2

Alkaline 400 000 110 320 1.2

Carbon-zinc 130 000 36 92 1.1

NiMH 340 000 95 300 1.2

NiCd 140 000 39 140 1.2

Lithium-ion 460 000 128 230 3.6

Some data for various batteries

Battery Modeling and Simulations

•Estimation of Battery Performance•Battery Design

•Thermal management

Why is thermal management needed?

• To keep the cells at a desired temperature levelToo hot: decreased battery life, decreased performance, risk of fire or explosion

• To minimize the cell‐to‐cell temperature variations• To prevent the battery from going above or below acceptable limits• To maximize the useful energy from cells and pack• To use a small amount of energy for operation

Thermal Runaway

• A condition that is caused by a battery charging current or other process which produces more internal heat than the battery can dissipate

• Early Warnings?increase in charge current at normal operation, increase in cell 

temperature over the ambient temperature

Thermal Runaway of batteries

Importance of temperature

On Battery Temperature

Optimum Temperature Range

Cooling systems in EV/HEV

Battery cooling systemInverter cooling systemMotor cooling system

Electric/hybrid vehicles

Problems in the electric/electronic equipment cooling

Battery: Twork is 50-55 , Tambient is 30-40 , Thus △Tbattery-ambient = 10-25 , It is difficult to cool the battery at a low △T.

Inverter: Heat flux is 150-200 W/cm2, Tjunction is 125 .It is hard to dissipate so high heat flux and keep Tjunction<

125

Motor: Without an appropriate cooling method, the motor performance will decrease greatly.

Thus appropriate thermal management is a significant issue for electric/electronic equipment in EV/HEV.

Example of thermal management

Direct Air Cooling

Direct Liquid cooling

Cold Plate Cooling

Indirect Liquid Cooling

Example of thermal management

Example of battery location in vehicle and thermal management

Using PCM (Phase Change Material) in Battery Thermal Management

Passive thermal management-phase change materials (PCM) as coolantBattery discharge: Battery dissipates the heat to PCM. Solid PCM becomes liquid, and stays solid-liquid state.Battery charge: Battery absorbs some heat from PCM. Liquid PCM becomes solid.

Thus the function temperature of PCM should be higher than the ambient temperature.

But it is lower than the battery working temperature.

PCM is used to surround the array of cells

Battery cooling system

Battery cooling systemPassive thermal management

Passive cooling (PCM) is more useful than the active cooling (air) to keep the battery working temperature under 55 (Sabbah R, 2008)

Active cooling (air): It can not keep the battery working temperature 

under 55 

Passive cooling (PCM): The battery working temperature is kept under 

55

Fig. 5. Cooling performance based on volume averaged cell temperature at 10 A.

Drawback of the thermal management

• Increased  complexity• Added cost• Reduced Reliability• Consumption of energy for operation

Processes needing consideration

• Heat and mass transport• Charge transport• Electrode kinetics• Electrode‐electrolyte interfacial processes

Softwares for Battery Modeling

General Purpose Tools

• MATLAB• COMSOL• ANSYS

Customized tools

•Battery Design Studio

Heat Generation

where the first term is the heat generated by ohmic and other irreversible effects in the cell. The second term represents the heat generated or consumed because of the reversible entropy change due to the electrochemical reactions in the cell.