High-Mass-Loading Ni–Co–S Electrodes with Unfading Electrochemical Performance for Supercapacitors

Abstract

Although nanostructured Ni/Co sulfides have shown compelling evidence and outstanding characteristics when applied for energy storage, their practical applications still face a challenge due to the sluggish electronic and ionic transport at practical levels of mass loading. Herein, we report a Ni–Co–S material with a unique structure of hollow nanospheres covered by interconnected nanosheets synthesized through an electrodeposition method. By systematically investigating the effects of Ni and Co ions on the materials growth and capacitance contribution, we found that the optimal Ni–Co–S electrode simultaneously achieves a high mass loading (8.84 mg/cm2) and a nearly constant specific capacitance (640 F/g), exhibiting excellent rate capability, superior electrical conductivity, and outstanding cyclability (84% retention of capacitance). The asymmetric supercapacitor assembled with the optimal Ni–Co–S cathode and an active carbon anode delivers a high energy density. These achievements provide a promising route toward practical applications at practical levels of mass loading.