Construction of Single-Phase Nickel Disulfide Microflowers as High-Performance Electrodes for Hybrid Supercapacitors

Developing supercapacitors with simultaneous superior power and energy density for energy-storage devices remains a challenge. In this work, single-phase NiS₂ microflowers were synthesized through a hydrothermal process coupled with subsequent sulfidation. The obtained NiS₂ microflowers perfectly inherited the flowerlike structure of the precursor, which was composed of nanosheets with firmly integrated nanoparticles. With the benefit of the single-phase crystal structure, suppressed surface oxidation, relatively high apparent conductivity, and unique nano/microstructure, the NiS₂ microflowers presented outstanding electrochemical performance in the LiOH electrolyte. Specifically, the NiS₂ microflowers exhibited high specific capacities of 813 C g^-1 at 1 A g^-1 and 580 C g^-1 at 20 A g^-1 and retained 93% of its initial capacity after 10,000-time cycling test. Moreover, an optimized NiS₂//activated carbon (AC) hybrid supercapacitor fabricated with NiS₂ microflowers as the positive electrode and AC as the negative electrode operated stably at a large voltage window of 1.8 V. It further delivered a considerable energy density of 39.8 W h kg^-1 at 900 W kg^-1. Impressively, the intriguing nano/microstructure further endowed the almost unabated capacitance after continuous cycling of 10,000 times. This study will definitely promote the design and preparation of high-performance nickel-based sulfides for hybrid supercapacitors.