Overcharging beha1vior and multi-signal early warning of the LiNi0.6Co0.2Mn0.2O2 lithium-ion pouch cells

Overcharging of lithium-ion batteries (LIBs) leads to irreversible degradation, failure, and severe thermal runaway (TR). This study systematically investigates the TR behavior of commercial Li (Ni_0.6Co_0.2Mn_0.2) O₂//graphite pouch cells under overcharging conditions at different C-rates (0.5, 0.75, and 1C). Based on the evolution of key parameters, the overcharging process could be divided into four stages, and the electrical and thermal behaviors of each stage are studied. Incremental capacity and differential voltage analysis reveals that overcharging disrupts the lithium-ion transport channels, leading to electrode material degradation and side reactions, which in turn increases the risk of TR. This deduction is confirmed through microscopic and spectroscopic characterizations. Post-mortem analysis reveals that overcharging causes the collapse of the layered cathode structure, the formation of large amounts of lithium deposits on the anode surface, and a reduction in the graphitization degree. To enhance the safety of LIBs, a multi-level early warning strategy is proposed according to the changes in multiple signals, such as maximum temperature difference, crest voltage, and the detection of gas. This study through comprehensive analyses, links electrode degradation to TR risk and innovatively proposes a multi-level early warning strategy with clear thresholds based on the evolution of multiple signals during the overcharging process, alleviating the limitations of existing single signal studies. It provides a theoretical foundation for the life management and safety surveillance of lithium-ion batteries under overcharge conditions.