Ta‐Driven Suppression of Transition Metal Interdiffusion and Particle Coarsening in Concentration Gradient Ni‐Rich Cathodes for Li‐Ion Batteries

This work presents a comprehensive investigation into the synthesis of Ni‐rich layered oxide cathodes (LiNi _x Mn _y Co _z O ₂ , x+y+z = 1, x = 0.9, NMC9) with concentration‐gradient (CG) structures. A modified co‐precipitation method is employed to systematically investigate key synthesis parameters, supported by a mathematical model predicting transition metal (TM) distribution within agglomerates. The preservation of the CG structures during high‐temperature lithiation is addressed through Ta ₂ O ₅ modification, which effectively inhibited both the TM interdiffusion and particle coarsening. The combination of powder X‐ray diffraction (PXRD) and advanced transmission electron microscopy (TEM) techniques revealed that the Ta‐rich phase epitaxially extends the crystal structure of the primary particles, forming a thick (≈5 nm) Ta‐rich surface layer. Density functional theory calculations confirm that Ta segregation is thermodynamically favorable, simultaneously inhibiting Ni migration and grain boundary mobility. Consequently, the Ta‐modification successfully preserves both the CG structure and the elongated primary crystallites, ultimately resulting in improved capacity retention (capacity fade per cycle of 0.07 ± 0.01% vs 0.12 ± 0.02% for homogeneous NMC9).