リチウムイオン電池正極粒子内の格子歪みの可視化と定量化：EBSDイメージングによる解析

Lattice strain critically affects electrochemical performance and durability of battery electrode materials. Here we report an electron-backscatter-diffraction-based imaging method to quantify lattice strain evolution and its spatial heterogeneity in two technologically important layered oxide cathodes (i.e. positive electrodes). Quantitative analysis is achieved by examining numerical distribution of the crystal misorientation data from thousands of positive electrode particles, which follows a positively skewed distribution. We reveal pronounced lattice strain heterogeneities both within individual grains and across different particles. These strain variations self-heal during relithiation but intensify with deeper delithiation and repeated cycling. The increased strain impedes Li-ion bulk diffusion, thereby limiting the maximum accessible capacity, especially at high current densities. Three-dimensional pole-figure analysis further identifies layer bending and layer twisting as the two major lattice distortion modes in the electrochemically cycled positive electrode particles. The accumulation of the unrecoverable layer bending governs the kinetically controlled capacity loss in the layered oxide positive electrodes.