Multidimensional characterization of graphite anode degradation in used lithium-ion batteries under real-life conditions

The degradation of graphite anodes in lithium-ion batteries remains a critical barrier to extending cycle life and enabling efficient recycling. This study employs a multi-technique approach combining XRD, FTIR, SEM-EDS, ICP-MS, and XPS to investigate degradation mechanisms in graphite anodes recovered from commercial spent mobile phone batteries. While unused reference anodes show no significant degradation, spent anodes exhibit surface cracks, porous networks, heterogeneous SEI growth, and pronounced oxygen/fluorine accumulation. FTIR and XRD confirm increased LiF and Li2CO3 formation, indicating electrolyte decomposition and structural breakdown. ICP-MS reveals transition metal migration (Co, Ni, Mn) and current collector corrosion (Cu, Al), which correlate with degradation severity. Surface-sensitive XPS analysis further resolves a progressive degradation pathway: from limited SEI formation in low-degradation samples, through concurrent corrosion and metal crossover in medium-degradation samples, to extensive LiF-rich SEI accumulation in the most degraded samples. These findings are consistent with a self-accelerating chain-reaction mechanism wherein electrolyte decomposition, metal migration, and corrosion synergistically accelerate capacity fade. This study proposes a mechanistic framework for understanding heterogeneous degradation in real-world spent batteries and offers a practical, multi-technique diagnostic tool for recycling and second-life applications.