Improved electrochemical properties of vanadium substituted Na0·67Fe0·5Mn0·5O2 cathode material for sodium-ion batteries

Abstract Layered transition metal oxide Na0·67Fe0·5Mn0·5O2 is considered as a promising cathode material of sodium-ion batteries because of its naturally elemental abundance and high energy density. However, low rate capability and poor structural reversibility of Na0·67Fe0·5Mn0·5O2 greatly hinder its large scale application. In this study, V-substituted Na0·67Fe0·5Mn0·5O2 cathode material with improved electrochemical performance is successfully synthesized via a sol-gel method. The effects of V-substitution on chemical composition, crystal structure and morphology of Na0·67Fe0·5Mn0·5O2 are studied in detail. Furthermore, modification mechanisms on the improved electrochemical performance by V-substitution are investigated. The results demonstrate that the rate capability and cycle stability of Na0·67Fe0·5Mn0·5O2 cathode material is significantly elevated by V-substitution. And the enhanced electrochemical properties are mainly attributed to the improved Na+ diffusion rate and structural reversibility. This study suggests that introducing V ions into the lattice of Na0·67Fe0·5Mn0·5O2 crystals is a favorable strategy to improve its electrochemical properties.