NbSe2@PPy nanosheets as anode materials for flexible all-solid-state asymmetric supercapacitors

Abstract

High-performance all-solid-state supercapacitors call for stable high capacitive anode materials, yet the selection of materials, currently, is limited to carbon and few inorganic materials. NbSe₂, as one of the metallic transition metal dichalcogenides (TMD), has recently been explored as candidates due to its inherent metallicity, layered structure, and versatile tunability of electronic properties. However, the poor structure stability and fast degraded electrochemical properties still impede their practical application. Therefore, sandwich-structure NbSe₂@PPy nanosheets have been synthesized by coating conductive polymer polypyrrole (PPy) on the surface of NbSe₂ nanosheets which were prepared by a facile molecular assembly method. NbSe₂@PPy nanosheets show a specific capacitance of 394 F g⁻¹ as an active anode material and retain 97.0% of its initial capacitance after 10 000 charge/discharge cycles, with largely improved performance compared with NbSe₂ and PPy. This superior capacitor performance can be attributed to the 2D–2D tight combination between NbSe₂ and PPy that facilitates structure stability, electron transport, as well as the effective prevention of surface oxidation of NbSe₂. Furthermore, an optimized flexible asymmetric all-solid-state supercapacitor based on NbSe₂@PPy nanosheets without a metallic current collector has been assembled and delivers a high energy density of up to 11.9 mW h cm⁻³ at a power density of 29.6 mW cm⁻³. This work demonstrates the potential application of NbSe₂/PPy as anodes and opens a new venue for high-performance flexible supercapacitors based on metallic TMD materials.