Multi-stage degradation mechanisms of lithium iron phosphate batteries under alternating salt spray and cycling conditions

With the expanding use of lithium-ion batteries (LIBs) in marine energy storage and electric ships, increasing attention has been paid to their reliability under corrosive environments such as salt spray. To address the lack of realistic aging protocols for LIBs in marine environments, this study establishes a cyclic salt spray–electrochemical aging framework that more accurately mimics operational corrosion stress. A clear two-stage degradation mechanism is identified, with early-stage lithium inventory loss (LLI) transitioning into a combined LLI and loss of active material (LAM) regime. Electrochemical diagnosis, combined with detailed analyses of electrode morphology, crystalline structure, and interfacial chemistry, is systematically conducted at each aging stage to elucidate the underlying degradation mechanisms. Half-cell measurements further quantify electrode-specific contributions to capacity fade, revealing that the graphite anode plays a dominant role in late-stage degradation. Unlike conventional aging studies, this work integrates corrosion stress with functional cycling to uncover degradation behavior under realistic conditions. This study deepens the understanding of battery aging mechanisms in marine environments and lays a foundation for predictive modeling and long-term reliability optimization under harsh conditions.