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

Layered transition metal oxide Na 0·67 Fe 0·5 Mn 0·5 O 2 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 Na 0·67 Fe 0·5 Mn 0·5 O 2 greatly hinder its large scale application. In this study, V-substituted Na 0·67 Fe 0·5 Mn 0·5 O 2 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 Na 0·67 Fe 0·5 Mn 0·5 O 2 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 Na 0·67 Fe 0·5 Mn 0·5 O 2 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 Na 0·67 Fe 0·5 Mn 0·5 O 2 crystals is a favorable strategy to improve its electrochemical properties.