Dynamic overcharge investigations of lithium ion batteries with different state of health

Overcharge and even further thermal runaway of lithium ion batteries may occur when there are inconsistencies between batteries, charging devices or battery management system fails. In this work, the thermal behavior and heat accumulation of commercial lithium ion batteries with different states of health (SOH) are studied for aging batteries when they are subjected to overcharging. The results show that the thermal runaway is triggered by the melting of separator which leads to internal short circuit, and this triggering factor does not change with SOH. Through the changes of temperature, voltage and duration before the thermal runaway, the safety decreases after aging, which is mainly due to the loss of lithium ions and the change of negative capacity after the battery is overcharged at a high rate. The contribution rate of heat generated by side reaction to thermal runaway is almost not affected by SOH. In addition, overcharge experiments of batteries with 80% SOH are carried out under different current rates. The results provide a method for warning the risk of thermal runaway. When the voltage reaches an inflection point, safety measures should be taken within 3 min.