Revealing position-dependent degradation mechanisms in LiFePO₄/graphite batteries under high-temperature over-discharge condition

Elucidating the degradation pathway of lithium-ion batteries is essential for improving its cycling and safety performance. However, in most cases, battery degradation pathway is evaluated by the overall battery behavior yet neglecting regional reaction heterogeneities within the battery. To address this, the present work investigates the position-dependent degradation phenomena by dividing the LiFePO₄/graphite pouch batteries into central region and outer edge under high-temperature over-discharge condition. The results indicate that the central region of battery experiences more severe degradation demonstrated by more drastic side reactions, thicker interphase layer accumulation and accelerated lithium inventory loss. The nonuniform chemical and structural degradations originate from local uneven reaction kinetics caused by coupled electrochemical and thermal gradients. These findings could help establish a direct correlation between spatial degradation heterogeneity and integrated battery performance fading. It also offers mechanistic understandings into how localized chemical environment difference influence macroscopic degradation of battery. The proposed regional degradation perspective could also provide insights for rational battery architecture design of high-capacity lithium-ion batteries.