Design and assembly of a high stability asymmetric supercapacitor based on pseudocapacitive zinc–nickel sulfide nanosheets and fast ion-transport carbon nanosheets

Abstract

Asymmetric supercapacitors assembled with pseudocapacitive and double-layer capacitive electrodes have a wide potential window, high energy density and long cycle life. Herein, flower-like zinc-nickel sulfide (Zn–Ni–S) nanosheets have been synthesized via a two-step hydrothermal method. Due to the distinctive nanosheet structure with a large number of active sites which enhance the electron transfer and ion diffusion rate, the Zn–Ni–S electrode shows a high specific capacity of 246.7 mA h g⁻¹ at 1 A g⁻¹ and good rate performance. In addition, pitaya mesocarp-based carbon nanosheets (PMCNs) with a large surface area and porous structure have been prepared under a one-step activation and nitrogen doping process, and exhibit a large specific capacitance of 227 F g⁻¹ at 0.5 A g⁻¹. Benefitting from the above, the novel asymmetric supercapacitor based on Zn–Ni–S positive and PMCN negative electrodes exhibits a wide operating voltage of 1.65 V, high specific density of 52.4 W h kg⁻¹ at a specific density of 551.7 W kg⁻¹, and excellent cycling stability with 93.5% capacity retention after 6000 cycles. Thus, the Zn–Ni–S//PMCN asymmetric supercapacitor with outstanding electrochemical behavior is thought to be a promising device for energy storage applications.