The snowball effect in electrochemical degradation and safety evolution of lithium-ion batteries during long-term cycling

Lifespan and safety are the most critical issues for the application of lithium-ion batteries (LIBs). During long-term service, the degradation mechanisms and safety evolution of LIBs remain unclear, posing significant obstacles to battery design and management. This study analyzes the electrochemical degradation mechanisms of LIBs under normal temperature cycling (NTC) and high-temperature cycling (HTC) conditions, linking these mechanisms to the evolution of battery safety. The findings reveal that during NTC, there is a “snowball effect” in performance degradation and safety evolution, leading to sudden death of battery and posing serious safety risks. The degradation pattern of LIBs during NTC and HTC is consistently dominated by the increase of internal resistance and the loss of lithium inventory (LLI). In the aging process, electrolyte consumption and the growth of the solid electrolyte interface (SEI) cause localized lithium plating on the anode, resulting in accelerated capacity decay. However, in batteries subjected to NTC, rapid accumulation of localized lithium plating can trigger a snowball effect, causing electrode deformation, internal short-circuit (ISC) and separator melting. These interacting catastrophic events form a vicious cycle, ultimately leading to battery sudden death and pose significant safety hazards. Additionally, thermal safety analysis reveals the correlation between thermal safety parameters and state of health (SOH), quantifying the thermal safety degradation caused by sudden death. Sudden death directly alters the evolution pattern of battery safety, leading to a severe decline in battery safety. These findings offer new insights into potential safety hazards associated with long-term use of LIBs.