Thermal behaviors study of LiFePO4 cell by electrochemical-calorimetric method

Measurement and analysis of the heat effects by electrochemical calorimetry play an important role in lithium-ion cell safety. In order to disclose thermal behaviors of LiFePO4 used in lithium-ion cell, an eight-channel micro-calorimeter combined with battery test system were employed in this study. The results show that the specific capacity and the amount of heat were strongly affected by operating temperature and charge–discharge rate. The specific capacity and the amount of heat are linear with the current and temperature. With the increase of current and temperature, the specific capacity decreased and the amount of heat increased. At low rate (0.1 C, 0.2 C), the cell has a smaller polarization and a better reversibility, both reversible and irreversible heat contribute to the overall heat production, while irreversible heat dominates the overall heat production when the cell cycles at high rate (0.5 C, 1.0 C). From the comparison of thermal behavior at target temperature (30 °C, 40 °C, 50 °C), a pronounced exothermic thermal behavior was observed during charge–discharge process in the high current region (0.5 C, 1.0 C) at elevated temperature. These suggest that appropriate current and temperature for battery should be choose in order to avoid safety problem, which initiated by internal heat accumulation of battery, and experimental thermo-electrochemical data for LiFePO4 cell should be included in thermal modeling.