Effect of Ni Incorporation in KCoPO4 on the Charge Storage Capacity of KCo1−xNixPO4 (0 ≤ x ≤ 0.5) Electrodes for the Fabrication of High-Performing Hybrid Supercapacitors

Abstract

Fulfilling the increasing energy demands of the world through renewable energy sources requires the utilization of a highly efficient large-scale electrochemical energy storage device. A hybrid supercapacitor (HSC) that consists of a battery-type electrode coupled with a counter-capacitive electrode, while in principle offering supercapacitor-like power, cyclability, and higher energy density, can be a potential device for large-scale energy storage to cater to the energy needs through renewable energy sources. The KCo0.5Ni0.5PO4 electrode demonstrated notably enhanced electrochemical performance, attributed to the synergistic interaction of Co2+ and Ni2+ ions in a phosphate framework. The incorporation of redox-mediated diffusive charge storage through the incorporation of Ni2+ on the Co2+ site resulted in a large-scale charge storage capacity, coupled with capacitive-type surface charge storage on the KCo1−xNixPO4 electrodes. The KCo0.5Ni0.5PO4 delivers 173 mAh/g (capacitance: 1038 F/g) at a current density of 0.5 A/g in an aqueous 2 M KOH electrolyte, accompanied by cyclic stability up to 5000 cycles. HSC mode consists of activated carbon as the negative electrode along with KNi0.5Co0.5PO4 as the positive electrode, displaying high energy density and power density of 183.7 Wh/kg and 7952 W/kg, respectively, in 2 M aqueous KOH electrolyte. The superior performance in HSC mode makes KCo0.5Ni0.5PO4 a potential positive electrode for the development of high-performing HSCs. © 2025 John Wiley & Sons Ltd.