Thermal runaway behaviors in 18,650 LiFePO₄ batteries under high C-rate charge/discharge operations

The thermal behaviors of the LiFePO₄ battery are examined to understand how C-rate and convective heat transfer rate ( h ) influence thermal stability. A heat generation model, including side reaction heat, is utilized for numerical simulations. Temperature behaviors and the onset of thermal runaway are studied under different C-rates and convective heat transfer coefficients. The thermal stability is categorized into three levels to assess battery safety. When thermal runaway occurs, the onset time and peak temperature are analyzed to evaluate stability. The contributions from each heat source are also measured. Side reactions start above 8C during charging and above 10C during discharging, while thermal runaway happens above 10C and 12C for charging and discharging, respectively. Higher C-rates and lower convective heat transfer coefficients reduce thermal safety. Furthermore, electro-thermal heat is the main heat source before thermal runaway, whereas the heat from reaction between the cathode and electrolyte dominates afterward until the maximum temperature is reached.