Quantitative investigation on the overcharge cycling-induced severe degradation of electrochemical and mechanical properties of lithium-ion battery cells

Overcharging is a common type of electrical abuse that significantly threatens the safety properties of lithium-ion batteries particularly in the service conditions of electric vehicles and grid energy storage. This study focuses on investigating the effects of varying degrees of overcharging and cycle numbers on batteries. A range of methods including electrochemical analysis, microstructural morphology observations, and mechanical testing are conducted to quantitatively analyze the property degradation of batteries under overcharge cycling. The findings reveal that higher cut-off voltage leads to battery failure in a short term. Meanwhile, even lower overcharge cut-off voltages result in noticeable capacity fade after multiple cycles. The extensive damage and shedding of cathode particles induced by internal stresses during overcharging severely undermine the modulus and hardness of the cathode materials. Furthermore, the appearance of transition metal deposits and lithium plating on the anode surface is identified as a key factor contributing to capacity loss. Additionally, notable deterioration in the mechanical properties and thermal stability of the separators is emphasized. While slight overcharging may not directly cause severe outcomes such as thermal runaway, the significant degradation of both electrochemical and mechanical properties not only drastically reduces battery lifespan but also introduces non-negligible safety risks.