Ionic liquid gel electrolyte with a WS2 electrode for highly stable high-voltage solid-state supercapacitors

Abstract

Inexpensive fabrication with the scalable design of environmentally friendly supercapacitors is highly desirable for portable and wearable electronics. In this context, the role of an electrolyte on two-dimensional (2D) materials such as WS₂ nanosheet-based electrodes is important for the rational design of an efficient, stable, and environmentally friendly supercapacitor. In this paper, high-quality and ultrathin 2D WS₂ nanosheets are synthesized by an easy, fast, and scalable LiI-assisted liquid phase exfoliation method. The synthesized WS₂ nanosheets are then employed as an electrode material in combination with 1-butyl-3-methylimidazolium chloride (BMIC) and polyvinyl alcohol (PVA) gel electrolyte to fabricate a solid-state supercapacitor. The effect of different concentrations of BMIC on the 2D WS₂ nanosheet-based electrodes is investigated in a symmetric supercapacitor. An optimum concentration of BMIC in PVA gel provides the best performance due to the low viscosity and high conductivity of the gel electrolyte, resulting from the H bonding alteration inside the PVA matrix. High voltage supercapacitors with a large electrochemically stable window (up to ±4 V), and higher capacitance (5 F g⁻¹) and specific energy density are fabricated using 0.5 M BMIC in the PVA gel electrolyte. The fabricated solid-state devices show 100% specific capacitance retention up to 8000 cyclic charge–discharge cycles. Electrochemical impedance spectroscopy and Kelvin probe force microscopy are employed to investigate the enhanced performance and stability of 0.5 M BMIC in PVA gel electrolyte in combination with a WS₂-based electrode.