Phase engineering of nickel-based sulfides toward robust sodium-ion batteries.

Nickel-based sulfides are considered promising materials for sodium-ion batteries (SIBs) anodes due to their abundant resources and attractive theoretical capacity. However, their application is limited by slow diffusion kinetics and severe volume changes during cycling. Herein, we demonstrate a facile strategy for the synthesis of nitrogen-doped reduced graphene oxide (N-rGO) wrapped NiS nanocrystals composites (NiS-N-rGO-700 °C) through the cubic NiS precursor under high temperature (700 ℃). Benefitting from the variation in crystal phase structure and robust coupling effect between the NiS nanocrystals and N-rGO matrix, the NiS-N-rGO-700 °C exhibits enhanced conductivity, fast ion diffusion kinetics and outstanding structural stability. As a result, the NiS-N-rGO-700 °C delivers excellent rate capability (345.17 mAh g at a high current density of 5 A g) and long-term cyclic stability over 400 cycles at 2 A g with a high reversible capacity of 377 mAh g when evaluated as anodes for SIBs. This study open a promising avenue to realize advanced metal sulfide materials with desirable electrochemical activity and stability for energy storage applications.