A series of tests were conducted on a single GM pouch (15Ah) cell to measure the heat output at different operating temperatures. A standard CC/CV* protocol from 2.5V to 4.15V at 1C**until the current dropped down to 750mA was used for all tests. A single example of a charge and discharge can be shown in Figure 1 which was conducted at 20°C.
When the battery is cycled at 40°C, the heat generated by the cell and the Joule heating represents 2.37% of the total energy supplied by the battery; at 0°C, it is more than 10.84% of the total energy. The IBC 284 is sensitive to measure low level differences of heat rate generation as well as peak heating which varies widely depending on whether the battery is tested at 0°C, 20°C or 40°C.
The second graph highlights the temperature dependent behavior of the battery. In terms of efficiency, the difference between 0°C and 40°C is lower than what we measure during a discharge; the heat generated is just 417.129mW higher, which increases the efficiency from 94.69% at 0°C to 98.72% at 40°C (Figure 2).
* Constant Current/Constant Voltage
** Charging capacity measured in Amp hours