Experimental investigation on thermal runaway propagation in the lithium ion battery modules under charging condition

• Further insight to characterize TR of LIBs under charging is presented. • The heat transfer of each part between cells are analyzed in detail. • Acceleration of TR propagation under charging conditions in LIB cells is evidenced. Thermal runaway (TR) is the most critical safety issue of lithium ion battery (LIB), and more uncertain hazard factors may be introduced under working state. In this study, TR propagation in LIB modules during charging was investigated firstly. A shorter TR propagation time is observed with increasing charging rate, and the average TR propagation time at 3C charging rate is only 12.1% of that at 0.5C. Besides, the TR propagation exhibited an obvious acceleration effect and the TR onset temperature decreased with TR propagation at high charging rates, the lowest TR onset temperature is only 127.4 ℃. Redistributed current led to rapid heat generation of the remaining cells, and the side reaction heat gradually replaced the heat absorbed from surroundings and became the main source of heat accumulation. Coupled with the heat generation of charging, the TR propagation accelerated. In addition, the heat conduction through air accounts for 67% of the total heat transfer, so reducing the thermal conductivity between cells can be considered as a means of mitigating TR propagation. This study delivers an underlying analysis of TR propagation during charging, and which is expected to contribute references for the safety of LIB application.