Heat Generation and Degradation Mechanism of Lithium-Ion Batteries during High-Temperature Aging

High-temperature aging has a serious impact on the safety and performance of lithium-ion batteries. This work comprehensively investigates the evolution of heat generation characteristics upon discharging and electrochemical performance and the degradation mechanism during high-temperature aging. Post-mortem characterization analysis revealed that lithium plating is the main degradation mechanism. The occurrence of side reactions leads to cell capacity fading and electrochemical performance degradation. The DC resistance and AC impedance increase significantly, and the severe internal polarization makes the incremental capacity curve shift to lower voltage. In the early aging stage, the cell degrades slightly, and the temperature rise rate has not changed significantly upon discharging. The cell capacity plays a leading role, whose degradation makes the temperature rise decrease. With the aging deepening, the severe cell degradation makes the temperature rise rate increase significantly. Even if the capacity fading, the temperature rise still increases significantly compared to the fresh state. Furthermore, irreversible heat and reversible heat increase significantly with the aging deepening and current rate increasing.