Crystal Modulation of Mn‐Based Layered Oxide toward Long‐Enduring Anionic Redox with Fast Kinetics for Sodium‐Ion Batteries

Abstract

Mn-based layered oxide cathodes for sodium-ion batteries with anionic redox reactions hold great potential for energy storage applications due to their ultra-high capacity and cost effectiveness. However, achieving high capacity requires overcoming challenges such as oxygen-redox failure, sluggish kinetics, and structural degradation. Herein, we employ an innovative crystal modulation strategy, using Mn-based Na_0.72Li_0.24Mn_0.76O₂ as a representative cathode material, which shows that the highly exposed {010} active facets enable an enhanced rate capability (119.6 mAh g^-1 at 10 C) with fast kinetics. Meanwhile, the reinforced Mn-O bond inhibits excessive oxidation of lattice oxygen and O-O cohesion loss, stabilizing and maintaining a long-enduring reversible oxygen-redox activity (100 % high capacity retention after 100 cycles at 0.5 C and 84.28 % retention after 300 cycles at 5 C). Time-resolved operando two-dimensional X-ray diffraction reveals the robust structural stability, zero-strain behavior, and suppressed phase transition with ultra-low volume variation during cycling at different rates (0.1 C: 1.75 %, 1 C: 0.31 %, 5 C: 0.04 %). Additionally, the full cell coupled with hard carbon achieves a high energy density of approximately 211 Wh kg^-1 with superior performance. This work highlights the significance of crystal modulation and presents a universal approach in developing Mn-based oxide cathodes with stable anionic redox for high-performance sodium-ion batteries.