Coral-Inspired Hierarchical Structure Promotes a Win-Win on Mass Loading and Rate Capability: A Nickel-Cobalt-Zinc-Sulfide@Nickel-Cobalt Layered Double Hydroxide Electrode for a High-Performance Hybrid Supercapacitor

A hierarchical structure, defined as structural features occurring on different levels of scale, is widely used in the rational design of composite electrodes for its superiorities in abundant electrochemical active sites and functional differentiation for various components. Herein, we in situ prepare a nickel-cobalt layered double hydroxide (NiCo-LDH) nanosheet network on ultrathin nickel-cobalt-zinc-sulfide (NiCoZnSx) microplate arrays to construct a special, coral-inspired hierarchical structure. In this structure, NiCoZnSx microplate arrays not only provide plenty of rooms for nanosheet growth but also improve the ion diffusion, charge transfer, and structural stability of the composite electrode. The NiCo-LDH nanosheet network paved through the microplate surface offers a high specific surface area and capacitance. The composite electrode delivers a high specific capacitance of 8.1 F cm-2 (1928 F g-1) at a loading mass of 4.2 mg cm-2, outstanding rate capability (63% capacitance retention, 50 mA cm-2), and cycling stability (80% capacitance retention, 10 000 cycles). Furthermore, the hybrid asymmetric supercapacitor assembled by the composite electrode and active carbon exhibits a maximal power density of 80.3 mW cm-2 at an energy density of 270 mu Wh cm-2 with good rate capability and cycling stability. This work reveals the significance and practical potential of rational design in the electrode's hierarchical structure for a high-performance supercapacitor.