Exploring the Inhomogeneous Nature of Li Intercalation and Li Plating on Graphite Anodes—An Experimental Study Combining Inert Gas High‐Resolution Light Microscopy with Colorimetric and Machine Learning‐Based Image Analysis

Li plating significantly contributes to the ageing of lithium‐ion batteries (LIBs). An in‐depth understanding of Li‐ion intercalation kinetics into graphite, still being widely used as anode material, and the subsequent phase formation of Li x C 6 compounds, is necessary to understand kinetic limits and prevent Li plating. Diffraction and colorimetric studies have explored these processes, noting graphite color changes during (de)intercalation. However, these methods fall short of examining graphite intercalation at a microscopic scale, essential for understanding intercalation kinetics and Li plating onset conditions. This study employs a high‐resolution light microscope under inert gas to examine lithiation processes in graphite anodes at the particle level across various C‐rates. Qualitative descriptions and quantitative assessments are achieved through colorimetric analysis based on hue and saturation, complemented by machine learning‐based segmentation. The results show an increased spatial heterogeneity of lithiation stages both between particles and within individual particles, with increasing C‐rate. Notably, up to three stages coexist in one particle, and LiC 6 is present at 50% (SOC) state of charge even when lithiated with 0.2C. At 1C charging, 4% and 32.5% of the surface is covered with Li deposits at 30% and 50% SOC, respectively, with underlying graphite particles showing LiC 6 .