Constructing metallic zinc–cobalt sulfide hierarchical core–shell nanosheet arrays derived from 2D metal–organic-frameworks for flexible asymmetric supercapacitors with ultrahigh specific capacitance and performance

Abstract

Low capacitance and sluggish kinetics of positive and negative electrode materials are two main obstacles that restrict the electrochemical performance of flexible asymmetric supercapacitors (ASCs). In this work, an effective metal–organic framework (MOF)-derived approach is proposed to construct high-performance positive and negative electrode materials with a core–shell heterostructure. The binary MOF arrays are converted to zinc–cobalt sulfide nanosheet scaffolds with excellent conductivity and a ductile structure, which can offer an electrically and ionically conductive 3D continuous network for the growth of active materials. Based on this platform, the originally built Ni(OH)₂@ZnCoS-NSs are validated to be a highly capacitive positive electrode (8.1 F cm⁻² at 3 mA cm⁻², i.e., 2730 F g⁻¹), matching well with the similarly constructed VN@ZnCoS-NS negative electrode (1.35 F cm⁻² at 3 mA cm⁻²). Benefiting from the rationally engineered electrodes, the assembled ASC device can exhibit ultrahigh energy density (75 W h kg⁻¹ at a power density of 0.4 kW kg⁻¹), stable electrochemical stability (82% capacitance retention even after 10 000 cycles), and excellent flexibility (92% capacitance retention after bending 4000 times). This study demonstrates an attractive strategy for the rational design of high-performance heterostructure electrodes by exploiting the compositional and structural versatility of 2D MOF arrays.