From apparent recovery to lithium compensation: Rethinking lithium-ion battery capacity recovery

Capacity recovery is frequently observed in lithium-ion battery aging studies, yet the underlying mechanisms are often conflated in the literature, complicating accurate health diagnostics. This review proposes a classification framework for interpreting such capacity rebounds. The primary classification boundary is whether external lithium is introduced and, if so, whether its contribution remains electrochemically available during subsequent baseline cycling. Without external lithium input, a measured gain is classified as apparent recovery when it reflects capacity re-expression or renewed access to lithium already present in the cell. With external lithium input, the measured gain is classified as cyclable lithium inventory compensation only when the added lithium remains electrochemically available during later charge-discharge reactions. A subsequent safety screen classifies rebounds accompanied by lithium plating, gas generation, local instability, or internal short circuits as risk-related responses. By separating temporary capacity re-expression, retained lithium compensation, and risk-related rebound, this hierarchical framework provides a unified basis for battery health diagnosis, aging interpretation, remaining-useful-life assessment, and safety evaluation.