Thermal runaway features of prismatic NCM battery undergone high-rate charging/discharging: Mechanism investigation and safety evaluation

The effects of charge/discharge rates (1, 2, 3C) on the structural stability and thermal runaway (TR) features of NCM batteries are investigated. Ex-situ techniques have revealed that high-rate charging/discharging significantly damages the structural stability of cathode and anode. As a result, TR behavior of batteries worsens with the increasing of charge/discharge rates and SOC, reflected by the earlier opening of safety valve and shorter TR onset time. The valve opening time is reduced from 1119 to 870 s, when the current rate changes from 1 to 3C. Meanwhile, TR consequences become more severe, verifying by the increased TR peak temperature. According to Arrhenius equation, the markedly reduced activation energy values are discerned for the batteries undergone high-rate cycling. Subsequently, a comprehensive thermal safety evaluation scoring system is proposed. As demonstrated, the batteries undergone high-rate charging/discharging exhibit greater TR hazards and risks. The above findings systematically elucidate the intrinsic mechanisms underlying the elevated risk of TR in batteries under high-rate cycling conditions. This work contributes to a deeper understanding of TR characteristics and risks of NCM batteries and provides valuable insights into battery safety protection measures.