Operando Quantifying Li Plating Processes in Lithium-Ion Pouch Cells

Lithium-ion batteries require high reliability and extended lifespan for practical grid storage applications, yet Li plating remains a critical hazard inducing rapid capacity fade and safety risks. The transient and heterogeneous nature of Li plating poses a significant challenge to real-time quantitative detection. Herein, we define a critical Li-plating areal capacity (q_Li) derived from dynamic electrochemical impedance spectroscopy (DEIS) and establish an operando strategy to accurately quantify Li plating under diverse charging conditions. Validated by operando solid-state nuclear magnetic resonance (ssNMR)-DEIS combined measurements, incremental capacity analysis, and mass spectrometry titration (MST), this method demonstrates high reliability, exceptional accuracy (R² > 0.97), and general validity across different temperatures (0°C-45°C) and battery capacities (4 to 110 mAh). A transmission line model (TLM) elucidates the physical origin of q_Li: it corresponds to the critical surface coverage (∼10%, model-derived) of lithium nuclei on graphite, marking the transition from nucleation-dominated to growth-controlled deposition. We further demonstrate that regulating temperature can switch the nucleation mode, thereby significantly altering q_Li and the resulting plating characteristics. This study establishes a robust operando quantification platform, enabling early battery warning and adaptive fast charging to suppress excessive Li plating and extend service life in practical cells.