A sandwich-like CoNiLDH@rGO@CoNi2S4 electrode enabling high mass loading and high areal capacitance for solid-state supercapacitors

Abstract

In this work, a sandwich heterostructure CoNiLDH-rGO-CoNi₂S₄ nanosheet array is prepared by electrochemical deposition and hydrothermal synthesis using nickel foam (NF) as the conductive current collector, which is then applied to asymmetric supercapacitors (ASCs). Furthermore, the open-pore framework integrated by cross-linked CoNiLDH and CoNi₂S₄ nanosheets gives rise to a honeycomb-like hierarchical nanostructure. Due to the maximum synergistic effect of the ultrathin CoNiLDH inner-layer, conductive rGO interlayers and CoNi₂S₄ outer-layer, the electrode exhibits fast electron/ion transport, high efficiency and excellent electrochemical performance. The CoNiLDH-rGO-CoNi₂S₄ electrode allows a high mass loading of 7 mg cm⁻², while maintaining a high specific capacitance of 2101 F g⁻¹ (14.708 F cm⁻²) at 1 A g⁻¹ (7 mA cm⁻²). Its aqueous asymmetric device delivers a mass specific capacitance of 101.3 F g⁻¹ at 1 A g⁻¹. Additionally, an LED can be lit up for more than 1 h when two ASCs are connected in series. The all-solid-state ASC device also gives a high energy density of 1.12 W h cm⁻³ at a power density of 32.25 W cm⁻³. This work proposes a method to obtain high areal capacitive performance and volumetric energy density of thick electrodes by designing nanostructures with efficient synergistic effects.