Experimental study on expansion force characteristics of LiFePO4 battery under overcharge cycles

Addressing early stage of overcharge cycling through reliable detection methods is crucial to enhancing battery reliability and lifespan. This study examines the characteristics of expansion force evolution in lithium iron phosphate (LiFePO₄) batteries during overcharge cycles under different cut-off voltages, with a view to elucidating the impact of cut-off voltage on expansion force. The results demonstrate that the expansion force and its derivative increase with the number of cycles and cut-off voltages, with the expansion during discharge being more significant than during the charging process. Furthermore, a correlation between irreversible expansion force and capacity loss has been identified, with post-mortem analysis and theoretical studies shedding light on the underlying mechanisms of expansion force evolution during overcharge cycles. Based on these findings, an early warning method based on expansion force is proposed, which can also assess the severity of failure by analyzing the expansion force derivative. This work reveals characterization of the expansion force evolution of batteries under overcharge cycling, and provides a reliable approach for the early warning strategy of slight failure due to overcharge cycling, helping to prevent the escalation of accidents.