Research of LiFePO₄/C Energy Storage Batteries' Entropy Coefficient and Discharge Heat Generation Based on the State of Health

The thermal effect of aged battery is quite different from that of a new one. In order to determine the composition of heat generation in the discharge process of the aged battery and provide the basis for monitoring the safety status of the aged battery and the thermal management strategy, we selected aged electric vehicle batteries (LiFePO₄/C) with four states of health(SOH, 83.98%, 73.72%, 64.79%, and 45.68%) to research the heat generation during the discharge stage in the adiabatic environment. Both the discharge resistances of aged batteries in different states of charge(SOC) and SOH were measured. The correlation between SOH and its entropy coefficient was analyzed. Furthermore, the rate of reversible heat generation and irreversible heat generation were calculated, and the components of heat generation were identified. The results show that the minimum resistance of battery appears at 60% SOC, and it becomes higher at 0 and 100% SOC. The entropy coefficient of the aged battery is greatly affected by SOH when it is 45%~100% SOC. When SOH decreases, irreversible heat caused by internal resistance increases to the proportion of the whole heat generation.