Abstract
Layered two-dimensional (2D) materials such as transition metal dichalcogenides (TMDCs) are receiving increased interest for applications in energy storage due to their high specific surface area and versatile electronic structure. In this work, we prepare solvent stabilised dispersions of a variety of few-layer thick TMDC crystals (MoS2, MoSe2, WS2, and TiS2) by ultrasonication. The exfoliated materials were first characterised by a variety of techniques to determine their quality. These dispersions were then used to form supercapacitor electrodes by filtration, without use of any further conductive additives or polymeric binders. These thin layer TMDC electrodes were assembled into symmetrical coin-cell devices for comparative electrochemical testing. It was found that despite being the most widely studied material, MoS2 suffers from inferior charge storage properties compared to the much higher conductivity and lower density TiS2. Impedance spectroscopy was used to investigate the charge storage mechanisms inside the coin cells, which were found to consist of a combination of both rapid, but low magnitude, electric double layer capacitance and much slower, but higher magnitude, ion adsorption pseudocapacitance.
Highlights
Supercapacitors are one of the most promising energy storage technologies for applications in the fields of electric vehicles as well as miniaturization of consumer electronics, due to their high power density, long cycle life, and relatively low cost [1,2,3]
While the materials created by both mechanical peeling and chemical vapor deposition (CVD) are of high quality and large crystal size, these production methods lack scalability and remain high cost
Each of the transition metal dichalcogenides (TMDCs) dispersions were deposited onto a Si/SiO2 (300 nm thickness of oxide) wafer and the solvent removed by heating on a hot plate allowing individual flakes to be identified by optical microscopy and analyzed with Raman spectroscopy
Summary
Supercapacitors are one of the most promising energy storage technologies for applications in the fields of electric vehicles as well as miniaturization of consumer electronics, due to their high power density, long cycle life, and relatively low cost [1,2,3]. The popularity of conductive additives makes understanding the fundamental electrochemical performance of the individual components difficult, as the performance is enhanced through the use of such additives, it is difficult to determine the contribution to the performance from each component This wide degree of variation in the literature makes it difficult to compare similar 2D TMDC materials for use as electrochemical energy storage electrodes and optimise them for future use in applications. In this work we prepare solvent-stabilised dispersions of a variety of 2D layered TMDCs (MoS2, WS2, TiS2, and MoSe2) via ultrasonication These dispersions are used to create supercapacitor electrodes without the use of additives, such as conductive carbon black or polymeric binders. Titanium disulphide (TiS2) displayed the best performance due to a combination of high conductivity, low density, and its intrinsic charge storage ability
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