Experimental and modeling approaches to investigate overcharge-induced thermal runaway behavior for LiFePO4 battery

Intensive electrochemical, thermal, and gas interactive behaviors under overcharge can make it a challenge to accurately investigate the overcharge process. Thus, a special test platform for onboard monitoring of the internal gas pressure, expansion force, voltage and temperature is proposed to investigate the overcharge behavior. The results show that a huge increase in internal pressure and expansion force has occurred during the voltage plateau period and the maximum values can reach 1071 kPa and 6590 N at low temperatures (below 69 °C). A reliable lumped overcharge-induced thermal runaway model by incorporating heat and gas generation reactions is employed to investigate the overcharge and venting gas behavior in depth. The simulation results show that it is the pressure rather than the temperature that triggers the gas venting and ejection. The proposed internal pressure model including gas generation and electrolyte vaporization can reveal the internal pressure change mechanisms. Additionally, the novel gas generation model helps to reveal the internal gas evolution mechanisms. To improve overcharge performance, the model's output can be used to detect venting events and hopefully estimate gas venting events. Alleviating electrolyte reduction is an effective way to improve the overcharge performance, as it dominates the gas generation and internal pressure increase.