Tailoring interphase structure to enable high-rate, durable sodium-ion battery cathode

Na-based layered transition metal oxides with O3-type structure have been considered to be promising cathodes for Na-ion batteries. However, the intrinsically limited Na-ion conductivity induced by the O-type Na-coordinate environment compromises their rate and cycle capability, hindering their practical application. Here, we report an interphase-structure tailoring strategy that improves the electrochemical properties of O3-type layered cathodes achieved through surface coating and doping processes. Specifically, a Zr-doped interphase structure is designed in the model compound NaNi_1/3Mn_1/3Fe_1/3O₂ using the ionic conductor Na₃Zr₂Si₂PO₁₂ as the surface coating material and Zr-dopant provider. We discover that the modified NaNi_1/3Mn_1/3Fe_1/3O₂ cathode shows a stable Na-storage structure as well as an enhanced rate/cycle capability. Combined with theoretical calculations, it is suggested that the superior electrochemical performances originate from the Zr-doped interphase structure, which has an enlarged Na layer spacing that forms favorable Na-ion diffusion channels. This work highlights a general material interface optimization method which opens a new perspective for fabricating high-performance electrodes for Na-ion batteries and beyond.