Largely improved cycling stability of CoV2O6 supercapacitor electrode synthesized by deep eutectic solvent

Abstract

Transition metal oxides composed of cobalt-based and vanadate configurations are widely used in supercapacitor electrodes due to the abundant nature of the various elements and their outstanding electrochemical performance. However, redox and ion intercalation mechanisms are involved between the electrodes and electrolyte, which inevitably lead to large differences in capacity retention and long-term cycling ability of synthetic electrodes by different preparation methods. In this work, the CoV2O6 electrode with a capacity of 194.0 C g−1 and a capacitance retention of 122.2 % after performing 100,000 cycles was synthesized by using deep eutectic solvent. In addition, the underlying mechanism of its excellent cycling stability was systematically studied. It was demonstrated that the continuous growth of particles on the electrode surface could lead to the formation of a stable polyhedron structure. More specifically, the generation of the CoOOH phase with strong reversibility on the electrode surface is considered the key to attaining the long cycling life of the CoV2O6 electrode. A hybrid supercapacitor (CoV2O6//AC HSC) was assembled for the evaluation of practical applications. It delivers a specific capacity of 119.3 C g−1 as well as a rate capability with 92.3 % capacity retention and good cycling durability, and the energy density of the HSC can reach up to a high energy density of 20.6 W h kg−1 at 373.4 W kg−1. A new cobalt vanadate electrode synthesis method was proposed here to examine the changes in the specific capacity and capacitance retention after performing ultra-long cycles, which provide a solid experimental basis for the development of supercapacitors for practical applications.