Cobalt-Nickel Sulfide Hierarchical Hollow Microspheres to Boost Electrochemical Activity for Supercapacitors

Abstract

Cobalt-nickel bimetallic sulfides are promising candidates for supercapacitors due to their high theoretical specific capacity, good electrical conductivity and fast redox kinetics. Nevertheless, they confront challenges such as poor cycling stability, volume expansion, and complicated synthesis methods. To address these issues, in this work, a MOF-assisted synthesis strategy is developed to achieve the one-pot formation cobalt-nickel sulfide hollow microspheres. The 2D nanosheet-constructed hierarchical hollow configuration promotes rapid electron/ion transfer, provides more active sites and effectively mitigates volume expansion during cycling. The optimized Co₁Ni₄S exhibits high electrochemical performance, such as a specific capacity of 277.2 mAh/g (2217 F·g⁻¹) at 1 A·g⁻¹, remarkable cycling stability with ~100% retention after 5,000 cycles, and favorable rate capability with 84.8% retention at 20 A·g⁻¹. Furthermore, an aqueous asymmetric supercapacitor (ASC) assembled with the Co₁Ni₄S and active carbon (AC) derived from lotus pollen achieves an energy density of 86.9 Wh·kg^-1 at 800.1 W·kg^-1, along with significant cycling stability (97.1% retentions over 30,000 cycles). These superior results showcase a simple one-step method for developing superior-performing electrode materials applicable to advanced supercapacitors.