CoNi₂ S₄ Electrode with High Mass-Loading for High-Energy-Density Supercapacitor: Role of S-Containing Anions...

Anion exchange is recognized as an effective method to regulate the composition, electronic conductivity, and electrochemical behavior of the transition metal-based compounds. In this work, anion exchange is adopted as a rational post-treatment route to facilitate the capacitive activity of CoNi₂ S₄ nanoparticle arrays grown on carbon cloth (CC) with high mass-loading. As soaked in saturated Na₂ S solution, the CoNi₂ S₄ /CC electrode showed an increased capacity from 483 C g^-1 to 841 C g^-1 at 10 mA cm^-2 with excellent rate performance and stable cycling performance, which was superior to the CoNi₂ S₄ /CC electrode activated by NaBH₄ reduction. Anion exchange was beneficial for enhancing the crystallinity, retaining the adhesion of nanoarrays, and realizing low resistance nature in a mild route. The as-assembled CoNi₂ S₄ /CC//activated CC hybrid supercapacitor delivered a high areal capacitance of 1.28 F cm^-2 at 5 mA cm^-2 , and achieved an energy density of 0.58 mWh cm^-2 at a power density of 4.5 mW cm^-2 with excellent cycle stability with 90.6 % capacity retention after 10000 cycles.