Beyond Qualitative Diagnosis of Li Plating in Li-ion Batteries: A Critical-State Metric from Electrochemical Impedance Spectroscopy

Lithium-ion batteries (LIBs)​ deployed in smart grid applications​ require extended cycle life and predictable safety performance​ through advanced battery management systems. Li plating, a major cause of capacity fade and thermal runaway, poses a critical challenge owing to its transient, heterogeneous nature and the lack of operando quantitative detection tools. To address this gap, we establish an operando quantitative framework​ for real-time monitoring​ of Li plating on graphite anodes. The proposed critical Li-plating areal capacity (q _Li ), derived from dynamic electrochemical impedance spectroscopy (DEIS) enables precise calculation​ of Li deposition kinetics under various charging protocols. Multi-modal validation​ through operando solid-state nuclear magnetic resonance (ssNMR)-DEIS combined measurements, incremental capacity analysis (ICA), and mass spectrometry titration (MST)​ demonstrates​ the method’s robustness​ with high accuracy (R ²  > 0.97)​ across diverse charging conditions and battery configurations. Furthermore, accelerated aging under coupled conditions identifies critical thresholds: mild Li plating not only accelerates capacity fade, but also drives Li plating-boundary migration beyond the critical q _Li , thereafter causing capacity plunge. This work advances both methodological frameworks—by establishing the first operando quantification platform for Li plating—and battery safety management strategies, offering safety alerting and adaptive charging protocols to keep plating below q _Li and thereby extend cycle life.