In-intercalation and Si-containing protective layer enhance electrochemical performance of NaNi0.5Mn0.5O2 for sodium ion battery

Abstract

Aiming at enhancing the electrochemical performance of cathode material NaNi0.5Mn0.5O2 (NM) for sodium ion battery, a novel Indium-intercalated cathode material NaNi0.5-xMn0.5InxO2 enriched with oxygen vacancies was first synthesized via high-shear co-precipitation method, then, a thin Si-containing protective layer was produced on the surface through the interfacial reaction between oxygen vacancies and tetraethyl orthosilicate. Through performance evaluation and characterizations including in-situ XRD, Ar+ sputtering XPS, STEM-HAADF, etc., the results indicate that the optimal sample Siy@NaNi0.497Mn0.5In0.003O2-y has the superior initial discharge capacity of 125.0 mAh g−1 (0.1 C) and exhibits excellent capacity retention of 98.4% after 100 cycles at 1 C; in particular, Si@In doped sample has larger lattice spacing, higher Na+ diffusion rate as well as better conductivity, comparing with both In-intercalating sample and the pristine NM. DFT calculations illustrate that the element In preferentially substitutes for the site of Mn atom while Si prefers to locate at Ni site close to the In-intercalating place, and Na+ diffusion energy barrier is greatly reduced with the In-intercalation and Si-doping. Such facile strategy to augment the lattice spacing of O3-layer cathode meanwhile produce thin protective layer utilizing the oxygen vacancies on the surface has promising applications to explore new cathode materials with high electrochemical performance for sodium-ion batteries.