An Ordered Ni₆ -Ring Superstructure Enables a Highly Stable Sodium Oxide Cathode.

Abstract

Sodium-based layered oxides are among the leading cathode candidates for sodium-ion batteries, toward potential grid energy storage, having large specific capacity, good ionic conductivity, and feasible synthesis. Despite their excellent prospects, the performance of layered intercalation materials is affected by both a phase transition induced by the gliding of the transition metal slabs and air-exposure degradation within the Na layers. Here, this problem is significantly mitigated by selecting two ions with very different MO bond energies to construct a highly ordered Ni₆ -ring superstructure within the transition metal layers in a model compound (NaNi_2/3 Sb_1/3 O₂ ). By virtue of substitution of 1/3 nickel with antimony in NaNiO₂ , the existence of these ordered Ni₆ -rings with super-exchange interaction to form a symmetric atomic configuration and degenerate electronic orbital in layered oxides can not only largely enhance their air stability and thermal stability, but also increase the redox potential and simplify the phase-transition process during battery cycling. The findings reveal that the ordered Ni₆ -ring superstructure is beneficial for constructing highly stable layered cathodes and calls for new paradigms for better design of layered materials.