Synthesis of bimetallic nickel cobalt selenide particles for high-performance hybrid supercapacitors

Supercapacitors are known as promising excellent electrochemical energy storage devices because of their attractive features, including quick charge and discharge, high power density, low cost and high security. In this work, a series of litchi-like Ni-Co selenide particles were synthesized via a simple solvothermal method, and the Ni-Co compositions were carefully optimized to tune the charge storage performance, charge storage kinetics, and conductivity for battery-like supercapacitors. Interestingly, the optimal sample Ni_0.95Co_2.05Se₄ exhibits a high capacity of 1038.75 F g^-1 at 1 A g^-1 and superior rate performance (retains 97.8% of the original capacity at 4 A g^-1). Moreover, an asymmetric supercapacitor device was assembled based on the Ni_0.95Co_2.05Se₄ cathode and activated carbon anode. The device of Ni_0.95Co_2.05Se₄//active carbon (AC) reveals a peak energy density of 37.22 W h kg^-1, and the corresponding peak power density reaches 800.90 W kg^-1. This work provides a facile and effective way to synthesize transition metal selenides as high-performance supercapacitor electrode materials.