Hierarchical nanosheet-nanowire heterostructures of NiCo-LDH@NiCo2S4 for high-performance asymmetric supercapacitors

Partial sulfidation yields NiCo-LDH@NiCo 2 S 4 sheet-wire heterostructures. • Sheet-wire structure enables 3400 F g −1 specific capacitance at 1 A g −1 . • Sheet-wire morphology boosts active sites and ion diffusion kinetics. • DFT shows higher Fermi level electron density, aiding charge transfer. • Kinetics show coexisting capacitive and diffusion-controlled processes. Developing electrode materials with enhanced specific capacitance and exploring their structural-property relationships are essential for optimizing the overall performance of supercapacitors. In this study, a novel binder-free electrode material comprised of NiCo-LDH and NiCo 2 S 4 was successfully synthesized on a nickel foam substrate through a hydrothermal method combined with a high-temperature gas-phase sulfidation process. After partial sulfidation treatment, NiCo-LDH@NiCo 2 S 4 composite presents a special structure composed of the nanosheet-like NiCo-LDH and the nanowire-like NiCo 2 S 4 assemblies. It has a significant specific capacitance of 3400 F g −1 at 1 A g −1 , the specific capacitance retention remained at 44.7% even at a high current density of 10 A g −1 . Additionally, a NiCo-LDH@NiCo 2 S 4 //AC asymmetric supercapacitor (ASC) device was constructed using the NiCo-LDH@NiCo 2 S 4 as the positive electrode, activated carbon (AC) as the negative electrode and 1 M KOH as the electrolyte. This device achieved an energy density of 82.6 Wh kg −1 at a power density of 700 W kg −1 and retains 90.1% capacitance after 10,000 cycles at a current density of 10 A g −1 . More importantly, DFT calculations reveal that NiCo-LDH@NiCo 2 S 4 facilitates charge transfer and increases specific capacitance. This work presents a viable strategy for the design of electrode materials, facilitating the development of high-performance supercapacitors. A novel binder-free electrode material was synthesized on nickel foam using a hydrothermal and sulfidation method. This material is composed of NiCo-LDH and NiCo 2 S 4 , exhibiting a unique nanosheet layered structure assembled from nanowires. Due to the synergistic effect of NiCo-LDH and NiCo 2 S 4 , and the assistance of the conductive nickel foam substrate, the NiCo-LDH@NiCo 2 S 4 composite material demonstrates excellent electrochemical performance. Compared with other asymmetric supercapacitor (ASC) devices, the NiCo-LDH@NiCo 2 S 4 //AC ASC device exhibits higher energy density and power density. Download: Download high-res image (158KB) Download: Download full-size image