A high-entropy engineering on sustainable anionic redox Mn-based cathode with retardant stress for high-rate sodium-ion batteries

Manganese-based (Mn-based) layered oxides have emerged as competitive cathode materials for sodium-ion batteries (SIBs), primarily due to their high energy density, cost-effectiveness, and potential for mass production. However, these materials often suffer from irreversible oxygen redox reactions, significant phase transitions, and microcrack formation, which lead to considerable internal stress and degradation of electrochemical performance. This study introduces a high-entropy engineering strategy for P2-type Mn-based layered oxide cathodes (HE-NMCO), wherein a multi-ingredient cocktail effect strengthens the lattice framework by modulating the local environmental chemistry. This innovative approach fosters sustainable reversible oxygen activity, mitigates stress concentrations at grain boundaries, and accelerates Na⁺ transport kinetics. The resulting robust lattice framework with optimized elemental interactions significantly improves structural integrity and reduces the formation of intragranular fractures. Consequently, HE-NMCO demonstrates remarkable cycling stability, retaining 93.5% capacity after 100 deep (de)sodiation cycles, alongside an enhanced rate capability of 134.1 mAh g-1 at 5C. Notably, comparative studies through multimodal characterization techniques highlight HE-NMCO's superior reversibility in oxygen anion redox (OAR) reactions over extensive cycling, contrasting sharply with conventional NMCO cathode. This work elucidates the potential for advancing high energy and power density Mn-based cathodes for SIBs through local species diversity.