Innovative solvent-free compound-direct synthesis of defect-rich ultra-thin NiS nanosheets for high-performance supercapacitors

Defect engineering in NiS nanosheets is an effective method to improve their surface properties and electronic structure for promoting electrochemical properties. However, a tunable, simple, and safe strategy for the introduction of abundant defect sites with a high activity into NiS with a special microstructure is worth developing. Herein, a novel hierarchical micro-flower-like NiS using graphene-like ultra-thin nanosheets with abundant defects as the building blocks was facilely synthesized by an innovative solvent-free compound-direct reaction strategy, which employed cost-efficient NaCl as the friction agent and dispersant to ensure adequate contact between sulfur ions and nickel ions and regulate the growth direction of NiS. Graphene-like ultra-thin NiS nanosheets effectively shorten the transport distance of ions and electrons. Defect engineering in NiS nanosheets provides more adsorption and storage sites for ions and high-activity sites for electrode materials, as well as adjusts the local electronic structure so as to effectively promote ion diffusion and charge transfer. The high performance of the as-obtained N-NiS electrode is illustrated by fabricating an asymmetric supercapacitor, which exhibits a specific capacitance of 351.5 F g-1 and energy density of 71.0 W h kg-1 at a power density of 229.3 W kg-1. The solvent-free compound-direct reaction strategy demonstrated in this study provides a new direction for the synthesis of high-performance nanomaterials for electrochemical energy storage applications.