Understanding the Effect of Local Short-Range Ordering on Lithium Diffusion in Li_1.3Nb_0.3Mn_0.4O₂ Single-Crystal Cathode

We report the observation of persistent chemical gradient on rock-salt Li1.3Nb0.3Mn0.4O2 single crystals transforming through a second-order reaction and reveal the dominating effect of local chemistry on Li diffusion within the percolated network. By using advanced 2D and 3D nanoscale X-ray spectro-microscopy on well-formed crystal samples, our study visualizes the mesoscale chemical distribution as a function of the state of charge at the subparticle level. We further reveal the presence of thermodynamically favorable short-range ordering of Nb-cation-only (Nb6) and Nb-cation-enriched (MnNb5) configurations, which promote non-equilibrium diffusion pathways and the expansive chemical heterogeneity observed on LixNb0.3Mn0.4O2 particles. The present study utilizes large single crystals to eliminate the influence of kinetic factors such as particle-size distribution, crystal facet, grain boundary, and strain, allowing us to clearly demonstrate the strong correlation between a material's structural defects and chemical propagation and its crucial impact on electrode performance and stability.