Experimental research on thermal-electrical behavior and mechanism during external short circuit for LiFePO4 Li-ion battery

External short circuit is a common phenomenon triggering thermal runaway in Li-ion battery. In this research, the electrical and thermal characteristics of the Li-ion battery under different external short circuit current were analyzed combining with the failure characteristics of the electrodes. In addition, the performance of a short-circuited battery was evaluated as well as its potential thermal risks. Results showed that thermal runaway occurrence or not, the temperature rise and temperature rise rate of the battery significant related to the short-circuit current and initial SOC. The battery with 30% initial SOC had the fastest temperature rise rate, whereas higher SOC batteries (80% and 100%) have the maximum temperature rise. According to SEM images of the electrodes, the failure of the short-circuit electrodes was discovered to entail electrolyte consumption, metal deposition, electrode particle breaking, separator closure, and increased internal resistance. The capacity of the battery recovered in the cycle test after the short circuit, which was caused by a decrease in ohmic resistance and the elimination of the polarization effect. When the undamaged batteries in first short circuit process experienced a secondary short circuit, the batteries exhibited a larger voltage drop, faster temperature rise rate and a higher temperature rise than fresh one. It was concluded that although there was no thermal runaway occurred during first short circuit process, it would increase the potential thermal risk in the continuous applications.