Surface optimized P2-Na2/3Ni1/3Mn2/3O2 cathode material via conductive Al-doped ZnO for boosting sodium storage

Abstract

Layered transition-metal oxides have been potential as high-performance cathode materials for sodium-ion batteries (SIBs), however, suffer from the undesirable side reactions between cathode/electrolyte interface during cycling. One improvement strategy by surface coatings is typically used, but at the compromise of lowering ion transport kinetics and poor rate capability. Herein, we report a surface optimized high-rate P2-Na2/3Ni1/3Mn2/3O2 cathode material for SIBs via a highly conductive Al-doped ZnO (AZO). By tuning the calcination temperatures, the optimized cathode material coated with 1 wt% AZO at 500 °C exhibits decent cycling and rate performances (66.2 mAh g−1 with a capacity retention of 82.6% at 5C after 500 cycles). Electrochemical kinetics analysis demonstrates that the NM@AZO-500 exhibits a high Na+ diffusion coefficient and a low charge-transfer resistance, and in-situ X-ray diffraction (XRD) and ex-situ X-ray photoelectron spectroscopy (XPS) reveal that the AZO coating effectively relieves the lattice stress during cycles and inhibits undesirable side reaction; all of which give rise to the observed enhancement. The result promises an effective surface optimized route for high-performance cathode materials for SIBs by coating highly conductive oxide.