Abstract: In order to investigate the influence of ambient temperature on the safety performance of square ternary lithium-ion batteries during overcharging, the lithium-ion batteries were overcharged to thermal runaway at a charging multiplication rate of 1.5C, and some representative characteristic values were selected by analyzing the time of thermal runaway of the batteries at different ambient temperatures（30, 40, 50 ℃）, the voltage, surface temperatures at different locations, and the air pressure and gas composition generated by thermal runaway. We investigated the trend and the magnitude of change of these characteristic values （i.e., the sensitivity to the change of ambient temperature） with the change of ambient temperature. The results show that under overcharging conditions, the increase in ambient temperature accelerates the thermal runaway process and exacerbates the risk of thermal runaway. The gas production and exhaust of the side reactions significantly affect the temperature and voltage behaviors of the battery. The higher the ambient temperature, the shorter the time required for thermal runaway. The surface temperatures at most locations of the battery increase with the increase of the ambient temperature. However, the maximum temperature at the center of the battery's surface at the largest side decreases with the increate of ambrent temperature. As the ambient temperature increases, the volume fraction of CO and CO2 increase, while the concentration of CH4 decreases. The sensitivity of different characteristic values to ambient temperature varies. Therefore, according to the characteristics of different characteristic values with the change of ambient temperature, it is necessary to formulate the corresponding safety alarm thresholds in order to better cope with the change of ambient temperature.

Key words: lithium-ion battery, thermal runaway, overcharge, ambient temperature