Constructing LiMn6 superlattice covalent framework to enable reversible anionic redox toward layer‐structured oxide for sodium batteries

Abstract

High-voltage anionic redox reactions offer an effective approach to enhancing the energy density for layer-structured oxides. However, such reactions are often accompanied by complex structural rearrangements and oxygen release, posing significant challenges to structural stability. A superstructure-regulating strategy is employed to construct LiMn6 ribbon ordering in O3-type Na[Li0.1Ni0.2Mn0.6Cu0.05Ti0.05]O2, aiming to address these issues and achieve high energy density alongside long-term cycling performance. Combined theoretical and experimental investigations it reveals that the incorporation of Li enhances electron localization around neighboring oxygen atoms, thereby modulating anionic redox activity. Moreover, the ordered LiMn6 framework facilitates directional hybridization between Mn 3d eg, and O 2p orbitals, forming a highly covalent network that effectively suppresses P-to-O type phase transitions and transition metal migration, thereby enhancing structural stability under high-voltage operation. The modified material delivers a highly reversible capacity of 207.98 mAh g−1 and exhibits excellent capacity retention of 80.43% after 125 cycles within a wide voltage range of 1.5–4.5 V. Furthermore, a full cell assembled with hard carbon as the anode demonstrates a capacity retention of 76.6% after 300 cycles. This work provides a new perspective on the superstructural design of high-performance O3-type cathodes for advanced sodium-ion batteries.