Quantitative Measurement of Li‐Ion Concentration in NCM811 Cathodes via Optimized Electrochemical Strain Microscopy

Inter-particle state-of-charge (SOC) heterogeneity governs electrochemical degradation in Ni-rich layered oxide cathodes, yet quantifying the underlying nanoscale lithium distribution remains inaccessible to bulk-averaging characterization techniques and impractical for destructive nanoscale probes. Here, a practical process for nanoscale Li-ion quantification in NCM811 cathodes is established by optimizing the measurement conditions of electrochemical strain microscopy (ESM). Through rational probe selection to suppress electrostatic artifacts and contact potential difference drift sensitivity combined with a markedly reduced acquisition time, a quantitative calibration framework directly correlating pixel-averaged ESM amplitude with ICP-MS-derived bulk Li concentration is constructed. Classification among three SOCs exceeds 90% accuracy with as few as four images per sample. This work establishes multi-particle ESM imaging as a statistically robust and non-destructive platform for nanoscale Li-ion quantification in NCM811 cathodes, with broad applicability across mixed ionic-electronic conductors in which local Vegard strain arises from ion redistribution.