Abstract
Spinel-type high entropy oxides (HEOs) have emerged as promising next-generation lithium-ion battery anodes owing to exceptional electrochemical performance. However, suppressing irreversible phase transformations caused by high-entropy to low-entropy state transitions during discharge-charge has remained challenging. The core issue stems from an insufficient understanding of phase evolution pathways and the key thermodynamic/kinetic driving forces, which is due to current methodological limitations in analyzing highly disordered structures. Further complicating this challenge is the elusive impact of nanosized effects on both thermodynamic and kinetic processes. This study addresses these challenges through three synergistic approaches: 1) investigating phase evolution mechanisms across different particle sizes to delineate nanosized effects; 2) resolving complex local structures by pair distribution function analyses and (7)Li magic-angle spinning nuclear magnetic resonance spectroscopy; 3) elucidating influences of high entropy on phase evolution via DFT calculations. Comprehensive results reveal a complex phase evolution process governed by the thermodynamic-kinetic interplay. The incomplete phase transformations of the rock-salt-like intermediate phase during discharge, which are attributable to high entropy-mediated kinetic sluggish diffusion, account for the transition from high-entropy to low-entropy states. By shortening the solid-state diffusion lengths, the kinetic limitations can be overcome, as demonstrated by nanosized spinel-type HEOs achieving reversible phase transformations during discharge-charge.