High-Performance\nP2-Na_0.70Mn_0.80Co_0.15Zr_0.05O₂ Cathode for Sodium-Ion\nBatteries

Abstract

Room-temperature\nsodium-ion batteries (NIBs) using a manganese-based\nlayered cathode have been considered promising candidates for grid-scale\nenergy storage applications. However, manganese-based materials suffer\nfrom serious Jahn–Teller distortion, phase transition, and\nunstable interface, resulting in severe structure degradation, sluggish\nsodium diffusion kinetics, and poor cycle, respectively. Herein, we\ndemonstrate a Zr-doped Na_0.70Mn_0.80Co_0.15Zr_0.05O₂ material with much improved specific\ncapacity and rate capability compared with Zr-free Na_0.70Mn_0.85Co_0.15O₂ when used as cathode\nmaterials for NIBs. The material delivers a reversible capacity of\n173 mA h g^–1 at 0.1 C rate, corresponding to approximately\n72% of the theoretical capacity (239 mA h g^–1) based\non a single-electron redox process, and a capacity retention of 88%\nafter 50 cycles was obtained. Additionally, a homogenous solid-state\ninterphase (SEI) film was revealed directly by high-resolution transmission\nelectron microscopy in Zr-doped material after battery cycling. Electrochemical\nimpedance spectroscopy proves that the formation of SEI films provides\nthe Zr-doped material with special chemical/electrochemical stability.\nThese results here give clear evidence of the utility of Zr-doping\nto improve the surface and environmental stability, sodium diffusion\nkinetics, and electrochemical performance of P2-type layered structure,\npromising advanced sodium-ion batteries with higher energy density,\nhigher surface stability, and longer cycle life compared with the\ncommonly used magnesiumdoping method in electrode materials.