Heterogeneous NiS/NiO multi-shelled hollow microspheres with enhanced electrochemical performances for hybrid-type asymmetric supercapacitors

Abstract

Heterogeneous structures with binary chemical compositions could achieve unique chemical properties by modification of the components and interface engineering. Meanwhile, hollow microspheres with complex interiors have been extensively studied in energy storage and conversion systems due to their possibility of adjusting the electrochemical performances. In this work, we report the reliable preparation of heterogeneous (NiO)_x(NiS)_1−x (0 ≤ x ≤ 1) multi-shelled hollow microspheres derived from carbon sphere@nickel precursor templates. The structural evolution of the multiple shells is carefully studied. Moreover, the effect of sulfurization extent of the (NiO)_x(NiS)_1−x compounds on the electrochemical performance is also explored. As electrode materials for supercapacitors, the heterogeneous (NiO)_0.1(NiS)_0.9 multi-shelled hollow microspheres exhibit the best electrochemical performances among a series of nickel oxide/sulfide compounds. The (NiO)_0.1(NiS)_0.9 sample can deliver a high specific capacitance of 1063 F g⁻¹ at 2 A g⁻¹. Even at a high current density of 50 A g⁻¹, the electrode can still retain a high specific capacitance of 486 F g⁻¹ after 10 000 cycles. Furthermore, a (NiO)_0.1(NiS)_0.9‖active carbon asymmetric supercapacitor (ASC) exhibits a specific capacitance of 58.5 F g⁻¹ at 2 A g⁻¹ in 2 M KOH solution. The superior electrochemical performances can be attributed to the careful composition regulation and the stable multi-shelled structure.