Electronic-Structure Tuning of Honeycomb Layered Oxide Cathodes for Superior Performance

Abstract

Recently honeycomb-ordered Na₃M₂XO₆ (M = Ni, Cu, Co; X = Sb, Bi etc.) layered oxide cathode materials have attracted significant interest because of their excellent voltage platform and high energy density. Despite their excellent prospects, they still suffer from insufficient rate capability and poor structure stability. Herein, we find that the specific capacity, electronic conductivity and structural stability of honeycomb-ordered Na₃Ni₂SbO₆ cathode material can be well promoted through partial Ru substitution. By combining the experimental analyses and theoretical calculations, we reveal that the partial substitution of Sb(V) with low valence Ru(IV) generated a strong Ru-O covalency reduces the bandgap, leading to a decreased redox potential and enhanced electrochemical kinetics. Meanwhile, the formed honeycomb RuNi₆-ring superstructure with structural distortion can adapt large strain fluctuation during cycling and eventually enhance the electrochemical cyclability. Such a proposed strategy provides valuable insights into further developments of the high-performance honeycomb layered oxides cathodes.

Keywords: Honeycomb layered oxides, Ru substitution, Electronic-structure tuning, Electrochemical kinetics, Structural integrity