Strain and Kinetics Synergy in Octahedral High-Entropy Cathodes Enables Ultra-Durable Sodium-Ion Batteries.

High-entropy oxides represent a paradigm shift in sodium-ion battery cathodes by utilizing entropy-driven structural stabilization to address the intrinsic challenges of lattice strain and sluggish ion kinetics. However, conventional high-entropy oxides face challenges in synthesis complexity and insufficient mechanistic insights into strain-kinetics coupling. Here, a high-entropy O3-type layered oxide, NaNiCoFeMnZnCuTiO (NNCFMZCT), is proposed featuring seven transition metals in a single crystallographic site, to synergistically optimize Na⁺ diffusion and structural resilience. Density functional theory calculations reveal that configurational disorder mitigates anisotropic lattice contraction during O/P phase transitions, while X-ray photoelectron spectroscopy and in situ X-ray diffraction confirm stable TMO₆ octahedra and suppressed irreversible phase transitions. The NNCFMZCT cathode delivers a high reversible capacity (>130 mAh g at 10 mA g), exceptional cycling stability (82.9% retention over 300 cycles at 500 mA g), and superior rate capability (>110 mAh g at 1000 mA g) within 2.0-4.0 V. When paired with commercial hard carbon in ampere-hour-level cylindrical cells, the full cell achieves 84% capacity retention after 200 cycles. This work demonstrates scalable viability for grid storage by establishing a universal strain-kinetics coupling strategy, which advances the rational design of entropy-stabilized cathodes for sustainable energy systems.