Thermal runaway characteristics of a LiFePO4-based lithium-ion secondary battery using the laser-irradiation method

Abstract

The establishment of a test method is a prerequisite to ensure the safety of lithium-ion secondary batteries. In context, laser irradiation is a heating technique that causes explosion of the batteries and is deemed as a safety test according to international standards. In this study, we elucidate the characteristics of laser irradiation heating by subjecting a 18650-type battery with LiFePO4 as the cathode material to laser irradiation to cause thermal runaway. Subsequently, we estimated the thermal runaway process and compared the heating method with those of an accelerating rate calorimeter furnace and a ceramic heater. The experimental results revealed that the thermal runaway was activated at the laser-irradiated small area by immediate heating. Initially, the separator shrink occurs, which was followed by an internal short circuit caused by the subsequent heating, and further heating resulted in thermal runaway. The findings of this study indicate that an extremely high power per unit area is generated by laser irradiation heating, and the battery heat generation rate during thermal runaway is equivalent to that obtained by a ceramic heater.