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 KCo_0.5Ni_0.5PO₄ 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 KCo_1−xNi_xPO₄ electrodes. The KCo_0.5Ni_0.5PO₄ 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 KNi_0.5Co_0.5PO₄ 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 KCo_0.5Ni_0.5PO₄ a potential positive electrode for the development of high-performing HSCs.