Thermal Testing

The thermal characteristics of a battery cell or pack are as important as the electrical characteristics as they can limit performance and increase ageing.

Cooling Curve

A way of establishing the rate at which you can extract heat from an object to a cooling system is to measure the cooling curve.

Side vs Base Cooled Prismatic Cell

To quantify the impact of surface cooling orientation, we performed a controlled experiment on a 314Ah LFP prismatic cell, testing two distinct configurations. In the first, the cooling plate was applied to the base edge of the cell, whilst in the second the cooling plate was on the side edge. Each test was conducted over five hours to evaluate the thermal performance measured. The cooling plate was set to -30°C and the test was performed at 23°C ambient temperature.

Room Temperature

The IEC battery standards [1] describe room temperature as 25°C +/-2K.

Specific Heat Capacity

We all often use specific heat capacity values from literature. This is ok initially, but errors in this will lead to errors in models.

specific heat capacity measurement schematic

Measuring Specific Heat Capacity

A quick method to measure/estimate Specific heat which can be done in any lab setting is by using a well insulated (adiabatic) box.

Thermal Conductivity

Whatever way we cool a battery cell we will create temperature gradients in the cell.

thermal conduction

Thermal Conduction in a Cell

We have a material of length, d and cross-sectional area, A that is hot, T2 at one end and cold, T1 at the other end. Knowing the thermal conductivity, k of the material we can calculate the heat, Q.

References

  1. IEC 62660-1, Edition 2.0 2018-12
  2. See our summary of IEC 62660-1, which sets the thermal-performance test methods (including the cooling-curve and thermal-cycling procedures) that this page’s techniques feed into.

Related Reading

See also: Performance Testing