Element doping-driven band regulation toward stable 4.5 V sodium-ion layered oxides

Abstract

P2-type layered oxide cathode materials have garnered significant attention as promising candidates for sodium-ion batteries due to their high specific capacity, competitive energy density, robust structural stability, and straightforward synthesis. However, their practical deployment at high operating voltages is largely hindered by issues such as severe phase transitions and irreversible oxygen release. In this study, we introduce a simple and cost-efficient single-element doping approach to modulate the electronic and structural properties of the cathode. Doping effectively shifts the oxygen p-band center, modifies the local coordination environment of transition metals, enhances TM–O bonding, and stabilizes the octahedral framework. This synergistic mechanism suppresses Jahn–Teller distortions and improves the reversibility of anionic redox reactions. Consequently, the structural and interfacial integrity of the cathode is maintained over prolonged cycling, while additional charge compensation alleviates capacity degradation. As a result, the capacity retention is markedly enhanced from 23.4% to 69.3% after 300 cycles. The proposed doping strategy, combined with the elucidation of the mechanism and the structure–activity relationship of doping, provides valuable insights for the rational design and optimization of high-voltage layered oxide cathodes for sodium-ion batteries.