Construction of a high-performance flexible hybrid capacitor at extreme working temperature (−20 °C)

Abstract

Designing electrode materials with special core–shell structures is of great significance in improving the performance of supercapacitors. In this work, we fabricated several types of ZnCo₂S₄@Ni(OH)₂ composite electrodes through a multistep hydrothermal strategy. ZnCo₂S₄ nanowire clusters grow uniformly on a nickel foam substrate. They were covered with Ni(OH)₂ nanosheets to form a core–shell structure. A three-dimensional structured composite exposes many active sites and shortens the ion transport path. The as-obtained electrode material presents a specific capacity of 1262.1 C g⁻¹ at 1 A g⁻¹. Moreover, it maintains 81% of the initial capacity after 20 000 cycles at 10 A g⁻¹. ZnCo₂S₄@Ni(OH)₂//AC delivers an energy density of 127.5 Wh kg⁻¹ when the power density reaches 2700 W kg⁻¹. The devices possess exceptional mechanical stability after repeated folding from 0° to 180°. In addition, it maintains an initial capacitance of 68% after 2500 cycles at 3 A g⁻¹ even when the operating temperature decreases to −20 °C.