Experimental research on thermal runaway characterization and mechanism induced by the shell insulation failure for LiFePO4 Lithium-ion battery

Insulation failure of energy storage systems can cause overvoltage between electrode and shell of the lithium–ion batteries (LIBs), endangering battery safety. In this research, the electrical and thermal behaviors of LIBs under different application methods of electrode and shell over–voltage were analyzed, combined with the failure characteristics of LIBs. The structural and chemical changes at each electrode were revealed using microscopic and spectroscopy characterizations. Results showed that the LIBs faults include shell breakdown, self–ignition, anode and shell connection, and thermal runaway (TR) under anode–shell overvoltage and cathode–shell overvoltage. The internal insulation structure, the rolling shape, and the application methods of overvoltage influenced LIBs faults. The fault process was divided into five stages: charge polarization, ion conduction, electrolyte decomposition and resistance rise, conduction–fusing, and shell–electrode short circuit. The conduction–fusing stage determined whether the LIBs undergo TR. The duration of each stage of battery faults exhibited a negative correlation with the amplitude of the overvoltage. The amplitude of the overvoltage dictated the duration of the battery's transition from overvoltage to TR. The magnitude of the overcurrent determined the probability of the battery undergoing TR. According to SEM, EDS, and XRD results, shell–anode overvoltage and shell–cathode overvoltage led to the growth of iron dendrites on the anode, while anode–shell overvoltage and cathode–shell overvoltage led to the development of lithium dendrites on the shell, causing side reactions and releasing a large amount of heat, causing the TR of LIBs. The results provided a basis for the insulation designs for LIBs energy storage systems (BESS).