Abstract: To investigate the effects of charging rates and their adjustments on thermal runaway in ternary lithium batteries under overcharging conditions, the batteries were overcharged to thermal runaway at rates of 0.5C, 1.0C, and 1.5C, respectively. Additionally, the charging rate was gradually increased from 0.5C to the point where the battery surface temperature no longer rose, using increments of 0.5C and 0.07C until thermal runaway occurred. Results indicate that overcharging at 0.5C does not lead to thermal runaway in a short time span; however, at 1.0C and 1.5C, thermal runaway occurs, with a shorter time to thermal runaway and greater severity at 1.5C. Compared to the 0.5C increment method, increasing the charging rate by 0.07C significantly raises the critical charging rate, reducing the risk of thermal runaway. During the gradual increase with 0.07C, there is a turning point rate: below this rate, the charging rate correlates linearly with the peak temperature; above it, further increases lead to thermal runaway. Initiating with 0.5C overcharging followed by rate increments results in lower thermal runaway risks compared to direct 1.0C and 1.5C overcharging. Therefore, lower charging rates should be adopted under practical needs, and if rate increases are necessary, gradual increments help mitigate thermal runaway risks.

Key words: lithium battery, thermal runaway, charge multiplier, overheat, overcharge