Unveiling the Three Stages of Li Plating and Dynamic Evolution Processes in Pouch C/LiFePO4 Batteries

Abstract Li plating is widely known as the key factor leading to degradation and safety issues in lithium‐ion batteries (LIBs). Herein, the feasibility of monitoring the onset and progression of Li plating is proposed and justified in the graphite/LiFePO 4 pouch cell by an operando impedance‐thickness combinational technique. First, as a proof‐of‐concept, the real‐time thickness/impedance variations of LIBs during charging at low temperature (≈0 °C) are obtained and dissected. Three distinct stages corresponding to different Li plating patterns are observed with the critical changing points of charge‐transfer resistance, which match well with the counterpoints in the differential thickness/capacity curves. Post‐mortem analysis by Mass Titration and Scanning Microscopy also indicate that these stages are Li intercalation, Li nucleation & nuclei growth, and Li dendrite growth, respectively. Thereafter, different cycling protocols are proposed and carried out to test the as‐mentioned Li plating processes by this novel technique. The results disclose that the extensive deposition of metallic Li significantly intensifies the loss of Li inventory, leading to cell aging or even a “capacity plunge”, and depict a safer boundary plot about preventing the occurrence of “Li plating” region. This work provides new insights on Li plating behavior and battery safety control under harsh operational conditions.