Aligned ZnO nanorod@Ni–Co layered double hydroxide composite nanosheet arrays with a core–shell structure as high-performance supercapacitor electrode materials

Abstract

Electrode materials are important components of supercapacitors and have a significant influence on the electrochemical properties. Herein, a hierarchical core–shell structure of ZnO nanorods (NRs) wrapped with feather-like ultrathin Ni–Co layered double hydroxide composite nanosheet arrays (ZnO NR@Ni–Co LDH CNSAs) was directly fabricated and established on a soft carbon cloth substrate through two facile hydrothermal processes. ZnO NR@Ni–Co LDH CNSAs, which were used as the positive electrode material, exhibited extremely high specific capacitance. The electrode materials integrating the good conductivity of ZnO NRs and the high coulombic efficiency of the ultrathin Ni–Co LDH nanosheets exhibited an excellent supercapacitive performance. The specific capacitance could reach 2683.8 F g⁻¹ when the current density was 1 A g⁻¹. Even at 10 A g⁻¹, the specific capacitance could reach 1986 F g⁻¹. In particular, ZnO NRs were employed as the conductive materials to take advantage of their beneficial electron transport. Furthermore, the interface between Ni–Co LDH CNSAs increased the diffusion rate of the ions due to its buffering function. ZnO NR@Ni–Co LDH CNSAs as the positive electrode material and commercial activated carbon as the negative electrode material established an asymmetric supercapacitor, which demonstrated excellent cycling stability and retained 91.7% of the specific capacitance after 5000 cycles. Moreover, the ASC device exhibited a maximum energy density of 40.04 W h kg⁻¹ at a power density of 1118 W kg⁻¹. The electrode material designed in this paper can be considered as a candidate for positive electrode materials in order to obtain a high-performance storage device with high energy density and high power density.