Hierarchical hollow structured NixCo3−xO4 particles for high-performance hybrid supercapacitors with ultralong cyclic stability

Abstract

Hybrid supercapacitors (HSCs), inheriting the high power density of electrical double-layer capacitors (EDLCs) and the high energy density of pseudocapacitors, have broad application prospects in the field of large-scale energy storage and rapid charge–discharge. Mixed transition metal oxides are considered to be excellent candidate electrodes due to their multiple oxidation states, which can provide more active sites. Herein, a facile strategy for the fabrication of Ni_xCo_3−xO₄ hierarchical hollow particles (NC-HHPs), involving solution growth and subsequent thermal annealing, is developed. Benefiting from the higher pseudocapacitor proportions provided by the numerous active sites, excellent electrical conductivity, and unique hierarchical structure with high porosity, the as-synthesized NC-HHPs show outstanding electrochemical properties of 115.7 mA h g⁻¹ after 40 000 cycles at 10 A g⁻¹. Furthermore, a HSC is assembled by using NC-HHP as the positive electrode and active carbon as the negative electrode (NC-HHP//AC). As a result, a high energy density of 68.1 W h kg⁻¹ with a power density of 881 W kg⁻¹ and an ultralong cycle life of 161 F g⁻¹ for 50 000 cycles at 10 A g⁻¹ are obtained. The presented strategy could be applied to develop high energy density electrode materials with ultralong cyclic stability in energy conversion and storage fields.