Superior charge storage performance of WS2 quantum dots in a flexible solid state supercapacitor

Abstract

The fabrication of flexible solid state supercapacitor devices using WS₂ nanocrystals is reported in this paper. The charge storage performance of WS₂ quantum dots (QDs) and nanosheets is compared in a solid state symmetric two electrode system for the first time. A lithium bromide-assisted lithium intercalation and sonication method has been employed to synthesize WS₂ nanosheets and QDs. The formation of defect-rich QDs of size varying from 1 to 3 nm by fragmentation of WS₂ nanosheets is confirmed through different spectroscopic and microscopic techniques. The fabricated solid state devices using WS₂ QDs show a high areal specific capacitance (28 mF cm⁻²) with high energy density (1.49 μW h cm⁻²), at a current density of 0.1 mA cm⁻². The superior performance of the QD-based devices as compared to that of the nanosheets is attributed to the large number of defect states present in the WS₂ QDs. Fabricated solid state devices exhibit good flexibility and superior retention of specific capacitance (80% after 10 000 cycles), indicating WS₂ as a potential candidate for future unconventional energy storage devices.