Consolidating cationic and anionic redox by all-in-one approach for air-stable layered sodium-ion oxide cathodes

The practical application of layered O3-phase oxide cathodes is impeded seriously by its irreversible phase transitions, structural collapse, and inadequate air stability. An all-in-one strategy is developed by introducing Li/Ti lattice doping and engineered Na vacancies in NiMnCu-based cathodes, exemplified by Na_0.95Ni_0.3Mn_0.5Cu_0.1Li_0.05Ti_0.05O₂ (NMCLT). This approach leverages Ti-O covalency from Ti dopants to stabilize phase transitions, while the high ionicity of Li-O bonds strengthen the interactions between transition metal and oxygen. Interstitial Na vacancies significantly facilitate rapid ionic diffusion. Consequently, NMCLT cathode exhibits a reversible capacity of 157.0 mAh g^-1 with initial coulombic efficiency of 95 % at 0.1C and superior rate capability as well as exceptional cycling stability. Moreover, robust wide-temperature operational performance is recorded in the range from -15 °C to 40 °C. Notably, aged NMCLT after exposure to air for seven days retains 96 % of its original capacity. In situ and ex situ characterizations reveal that NMCLT undergoes a rapid and reversible phase transition from O3 to P3 without irreversible P3-O3’’ occurrence under high voltage, maintaining high microstructural integrity without succumbing to structural degradation caused by accumulated internal stress. This all-in-one approach inaugurates an innovative trajectory for the practical O3-type layered sodium-ion oxide cathodes.