High-Performance P2-Na _0.70 Mn _0.80 Co _0.15 Zr _0.05 O ₂ Cathode for Sodium-Ion Batteries

Roomerature sodium-ion batteries (NIBs) using a manganese-based layered cathode have been considered promising candidates for grid-scale energy storage applications. However, manganese-based materials suffer from serious Jahn-Teller distortion, phase transition, and unstable interface, resulting in severe structure degradation, sluggish sodium diffusion kinetics, and poor cycle, respectively. Herein, we demonstrate a Zr-doped Na _0.70 Mn _0.80 Co _0.15 Zr _0.05 O ₂ material with much improved specific capacity and rate capability compared with Zr-free Na _0.70 Mn _0.85 Co _0.15 O ₂ when used as cathode materials for NIBs. The material delivers a reversible capacity of 173 mA h g ^-1 at 0.1 C rate, corresponding to approximately 72% of the theoretical capacity (239 mA h g ^-1 ) based on a single-electron redox process, and a capacity retention of 88% after 50 cycles was obtained. Additionally, a homogenous solid-state interphase (SEI) film was revealed directly by high-resolution transmission electron microscopy in Zr-doped material after battery cycling. Electrochemical impedance spectroscopy proves that the formation of SEI films provides the Zr-doped material with special chemical/electrochemical stability. These results here give clear evidence of the utility of Zr-doping to improve the surface and environmental stability, sodium diffusion kinetics, and electrochemical performance of P2-type layered structure, promising advanced sodium-ion batteries with higher energy density, higher surface stability, and longer cycle life compared with the commonly used magnesiumdoping method in electrode materials.