Correlation of the electronic structure and Li-ion mobility with modulus and hardness in LiNi0.6Co0.2Mn0.2O2 cathodes by combined near edge X-ray absorption finestructure spectroscopy, atomic force microscopy, and nanoindentation

The electrochemical performance of cathode materials in Li-ion batteries is reflected in macroscopic observables such as the capacity, the voltage, and the state of charge (SOC). However, the physical origin of performance parameters are atomistic processes that scale up to a macroscopic picture. Thus, revealing the function and failure of electrochemical devices requires a multiscale (and -time) approach using spectroscopic and microscopic techniques. In this work, we combine near-edge X-ray absorption fine structure spectroscopy (NEXAFS) to determine the chemical binding state of transition metals in LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622), electrochemical strain microscopy to understand the Li-ion mobility in such materials, and nanoindentation to relate the mechanical properties exhibited by the material to the chemical state and ion mobility. Strikingly, a clear correlation between the chemical binding, the mechanical properties, and the Li-ion mobility is found. Thereby, the significant relation of chemo-mechanical properties of NCM622 on a local and global scale is clearly demonstrated.