Acquiring the safe boundary of battery is beneficial to the safety risk evaluation of power battery and to offer the early warning signs. The method to accurately measure the overcharging capacity was studied, and it was verified through the overcharging test of three types of batteries (ca. 55 Ah) with different energy densities (250, 280, and 300 Wh·kg^-1). Additionally, accelerating rate calorimetry test was conducted to study the self-heating behavior of cells under the adiabatic conditions. The effects of active materials and overcharging current on the safety performance of batteries were given. The safety performance of battery with energy density of 280 Wh·kg^-1 is worse than that of 250 Wh·kg^-1 with the same cathode materials, due to the dominant factor of the 7.6% higher cell capacity. Meanwhile, the LiNi_0.8Co_0.15Al_0.05O₂(LCA) cathode material with higher energy density shows better overcharging performance than the LiNi_0.8Co_0.1Mn_0.1O₂(LCM811) cathode material, which shows that LCA has a preferable thermal stability. Moreover, it is found that increasing the oxidation potential of the electrolyte and increasing the thermal stability of electrode material are the two effective ways to improve the overcharge performance of lithium-ion battery.
Acquiring the safe boundary of battery is beneficial to the safety risk evaluation of power battery and to offer the early warning signs. The method to accurately measure the overcharging capacity was studied, and it was verified through the overcharging test of three types of batteries (ca. 55 Ah) with different energy densities (250, 280, and 300 Wh·kg^-1). Additionally, accelerating rate calorimetry test was conducted to study the self-heating behavior of cells under the adiabatic conditions. The effects of active materials and overcharging current on the safety performance of batteries were given. The safety performance of battery with energy density of 280 Wh·kg^-1 is worse than that of 250 Wh·kg^-1 with the same cathode materials, due to the dominant factor of the 7.6% higher cell capacity. Meanwhile, the LiNi_0.8Co_0.15Al_0.05O₂(LCA) cathode material with higher energy density shows better overcharging performance than the LiNi_0.8Co_0.1Mn_0.1O₂(LCM811) cathode material, which shows that LCA has a preferable thermal stability. Moreover, it is found that increasing the oxidation potential of the electrolyte and increasing the thermal stability of electrode material are the two effective ways to improve the overcharge performance of lithium-ion battery.
 

Battery safety boundary; lithium-ion batteries; NCA cathode; NCM811 cathode; overcharge;