Electrochemical profiling method for diagnosis of inhomogeneous reactions in lithium-ion batteries

Lithium-ion batteries are being used in large-scale applications, making safety management a crucial issue. Overcharged areas created by inhomogeneous reactions can potentially induce cell degradation and failure. Despite the safety concerns, few techniques permit simple monitoring of diagnostic signals. Here, we propose electrochemical profiling to diagnose reaction inhomogeneity inside electrodes. Systematic electrochemical measurements are performed using LiNi_0.8Co_0.1Mn_0.1O₂ and graphite electrodes from the electrode-level to the full-cell level. Complementary synchrotron-based X-ray analyses and optical imaging are conducted. The electrode-level inhomogeneous reaction is qualitatively assessed through differential capacity (dQ/dV) curves. An anomalous dQ/dV peak appears when severe reaction inhomogeneity occurs in the negative electrode, correlating to lithium plating reactions. Furthermore, industrial-scale full-cells show a lithium plating-related dQ/dV peak near 4.1 V under conditions that lead to the most severe inhomogeneous reactions. This study proposes a non-destructive, simple, and efficient electrochemical technique that predicts the fading of batteries without requiring postmortem analysis.