Enabling High Reversibility of Both Cationic and Anionic Redox in Layered Oxide Cathodes via NiMn6 Superlattice Topology for Sodium-Ion Batteries

Abstract

High-voltage oxygen anionic redox provides a transformative opportunity to achieve high energy density of batteries. However, it is challenging to guarantee the reversibility of both cationic and anionic redox for layered transition metal (TM) oxide cathode materials due to the high oxygen-redox reactivity and the complex structural rearrangements. Herein, a honeycomb-layered Na_0.78Ni_0.12Li_0.18Mn_0.7O₂ (NNLMO) cathode material with the NiMn₆ and LiMn₆ dual-topology superlattice is proposed for sodium-ion batteries. The theoretical and experimental studies demonstrate that the Ni²⁺ electronic configuration serves as a redox buffer to tune the cationic and anionic redox activity by enlarging the energy gap between O 2p and Mn 3d orbitals, while the NiMn₆ topology renders the LiMn₆ topology delocalized in the TM layers to reinforce the superstructure stability through suppressing the intralayer Mn migration and O₂ formation. As a result, NNLMO delivers a highly reversible capacity of 224 mAh g⁻¹ with the mitigated voltage hysteresis and exhibits remarkable capacity retention of 92.2% over 50 cycles within the wide voltage range of 1.5–4.5 V. The findings suggest a new insight into the topological superstructure design of high-energy oxide cathode materials for sustainable batteries.