In Situ Li‐Plating Diagnosis for Fast‐Charging Li‐Ion Batteries Enabled by Relaxation‐Time Detection

Abstract The Li‐plating behavior of Li‐ion batteries under fast‐charging conditions is elusive due to a lack of reliable indicators of the Li‐plating onset. In this work, the relaxation time constant of the charge‐transfer process (τ_CT) is proposed to be promising for the determination of Li‐plating onset. A novel pulse/relaxation test method enables rapid access to the τ_CT of the graphite anode during battery operation, applicable to both half and full batteries. The diagnosis of Li plating at varying temperatures and charging rates enriches the cognition of Li‐plating behaviors. Li plating at low temperatures and high charging rates can be avoided because of the battery voltage limitations. Nevertheless, after the onset, severe Li plating evolves rapidly under harsh charging conditions, while the Li‐plating process under benign charging conditions is accompanied by a simultaneous Li‐intercalation process. The quantitative estimates indicate that Li plating at high temperatures/high charging rates leads to more irreversible capacity losses. This facile method with rational scientific principles can provide inspiration for exploring the safe boundaries of Li‐ion batteries.