Aging effect delays overcharge-induced thermal runaway of lithium-ion batteries

This research focuses on the effect of overcharging on aged batteries, and the experiments aim to show the thermal runaway (TR) behavior of batteries with different degrees of aging. In order to clarify the typical behavioral characteristics of overcharge-induced battery thermal runaway, commercial 18,650 type LiMn2O4 (LMO)/graphite batteries with different capacity retention rates (CRRs) were applied for overcharge testing operation. The changes of external characteristics, such as surface temperature, voltage and fire explosion phenomena of aged batteries during the whole process of thermal runaway under overcharge conditions were investigated. The results showed that the battery TR trigger time was negatively correlated with the CRR. The batteries having CRR of 86.7%, 80.8%, and 75.2% took 28.2%, 32.5%, and 52.0% longer than fresh battery to reach the TR triggering temperature. Besides, they took 54.1%, 91.8% and 115.1% longer than fresh battery to reach the lithium plating time point. The deposition of manganese oxide on the cathode surface and the phenomenon of lithium plating on the anode surface together lead to the reduction of reversible lithium. With the deepening of aging, the amount of reversible lithium inside the battery decreases, which is the main reason why the TR trigger time is delayed.