Facile synthesis of mesoporous Ni(x)Co(9−x)S(8) hollow spheres for high-performance supercapacitors and aqueous Ni/Co–Zn batteries

Porous micro/nanostructure electrode materials have always contributed to outstanding electrochemical energy storage performances. Co(9)S(8) is an ideal model electrode material with high theoretical specific capacity due to its intrinsic two crystallographic sites of cobalt ions. In order to improve the conductivity and specific capacitance of Co(9)S(8), nickel ions were introduced to tune the electronic structure of Co(9)S(8). The morphology design of the mesoporous hollow sphere structure guarantees cycle stability and ion diffusion. In this work, Ni(x)Co(9−x)S(8) mesoporous hollow spheres were synthesized via a facile partial ion-exchange of Co(9)S(8) mesoporous hollow spheres without using a template, boosting the capacitance to 1300 F g(−1) at the current density of 1 A g(−1). Compared with the pure Co(9)S(8) and Ni-Co(9)S(8)-30%, Ni-Co(9)S(8)-60% exhibited the best supercapacitor performance, which was ascribed to the maximum Ni ion doping with morphology and structure retention, enhanced conductivity and stabilization of Co(3+) in the structure. Therefore, Ni/Co–Zn batteries were fabricated by using a Zn plate as the anode and Ni-Co(9)S(8)-60% as the cathode, which deliver a high energy density of 256.5 W h kg(−1) at the power density of 1.69 kW kg(−1). Furthermore, the Ni/Co–Zn batteries exhibit a stable cycling after 3000 repeated cycles with capacitance retention of 69% at 4 A g(−1). This encouranging result might provide a new perspective to optimize Co(9)S(8)-based electrodes with superior supercapacitor and Ni/Co–Zn battery performances.