Varying Thermal Runaway Mechanism Caused By Fast Charging for High Energy Pouch Batteries

Abstract

Increasing charging rate is usually considered as safety issue inducements for lithium-ion batteries, especially for high energy batteries with thick electrodes. However, the interaction mechanism between charging rate and safety behavior still needs to be further explored.In this work, thermal runaway process of commercial NMC532/graphite pouch cells are compared after undergoing increasing charging rates, and decreasing trends of self-heating temperature, onset temperature and maximum temperature are observed, which poses potential danger for battery applications after fast charging. Through the ARC test of corresponding card cells and DSC test of active materials, it was found that the full cell’s characteristic temperature of thermal runaway evolution and active energy of the self- heating process under high charging rate are similar to the reaction between anode and electrolyte, while those under low charging rate are similar to the reaction between cathode and anode. Moreover, the thermal runaway behavior at middle charging rate is influenced by both reactions simultaneously. Under condition where reaction between anode and electrolyte is the dominant factor of thermal runaway process, the lithium plating which discovered on the graphite surface, is found to trigger the strongly exothermic reaction around 110℃ and heat the cell to thermal runaway. It was concluded that the thermal runaway mechanism changes from cathode and anode reactions to anode and electrolyte reactions after batteries are fast charged.This work will help researchers understand more about the principle of thermal runaway process under different charging rates, and develop more reasonable charging profiles for high energy batteries avoiding deteriorated battery’s safety performance. Figure 1