Cauliflower-like CoNi₂S₄ microspheres derived from bimetallic hydroxides as highly active electrode material for asymmetric supercapacitors

Transitional bimetallic sulfides are highly attractive electrode materials for supercapacitors because of their remarkable electrochemical activity. However, designing and preparing efficient transitional bimetallic sulfides with super specific capacitance, high energy density, and good cycling stability by simple methods are still facing great challenges. Herein, a cauliflower-like spinel-type CoNi₂S₄ microsphere structure is synthesized by a facile solvothermal method using layered cobalt nickel hydroxides (CoNi-LDH) precursor as raw material and thioacetamide as sulfurizing reagent. The as-prepared CoNi₂S₄ electrode exhibits an exceptional specific capacitance high up to 2384 F g⁻¹ at 1 A g⁻¹, significantly higher than that of cobalt nickel hydroxide precursor (1358 F g⁻¹), which can be due to the higher electrical conductivity of CoNi₂S₄ than the precursor, the sulfur element which has lower electronegativity than the oxygen element, leading to rapider reversible redox processes, and the unique cauliflower-like micromorphology with rough surface. The constructed CoNi₂S₄//PC asymmetric supercapacitor exhibits excellent electrochemical performance with an extremely high energy density of 71.97 Wh kg⁻¹ at the power density of 375 W kg⁻¹, a remarkable capacity retention rate of 88.43% after 5000 cycles at 5 A g⁻¹, and an impressive coulombic efficiency of 99.8%. The outstanding electrochemical properties suggest that CoNi₂S₄ would be a promising candidate for supercapacitors.