An Ether-Based Ionic Gel Electrolyte with High Ionic Conductivity and Thermal Stability Screened Based on Density Functional Theory as EDLCs

As an electrolyte material for electric double-layer capacitors (EDLCs), ionic gel electrolytes (IGEs) exhibit excellent electrochemical performance and superior safety characteristics. According to the density functional theory (DFT), 1-(2-ethoxyethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([C2OC2mim][TFSI]) was screened out using TURBOMOLE software. A series of IGEs incorporating varying proportions of [C2OC2mim][TFSI] were prepared. By optimizing the proportion of ionic liquids (IL), IGE-2 sample (The gel electrolyte with a ratio of PVDF-HFP to ether-functionalized ionic liquid of 1:2 is denoted as IGE-2) with the best electrochemical and mechanical properties was obtained. IGE-2 exhibited a broad electrochemical stability window (ESW = 5.3 V) and high ionic conductivity (σ = 15.46 mS/cm) at room temperature. This high ionic conductivity can be primarily attributed to the relatively high self-diffusion coefficients of the individual components within IGE-2. The electrochemical performance of the supercapacitor assembled using IGE-2 was evaluated through an electrochemical workstation. At a current density of 1 A/g, the specific capacitance achieved 257 F/g, and the coulombic efficiency was 97.5%. The tensile properties of IGE-2 were evaluated using a universal tensile testing machine. The maximum tensile stress was 1.10 MPa, and the maximum elongation at break was as high as 216%. The impact of introducing ether-based functional groups on the electrochemical and mechanical properties of ionic gels was thoroughly investigated through the analysis of electrostatic potential (ESP) and molecular dynamics simulations (MD). Therefore, the incorporation of ether-based IL into ionic gels not only significantly enhances the ionic conductivity of the gel electrolyte but also improves its electrochemical and mechanical properties.