Ether-Based Ionic Gel Electrolytes with High Ionic Conductivity and High Thermal Stability for Energy Storage Device Applications

Abstract

The current ionic gel electrolyte (IGE) materials cannot simultaneously achieve high ionic conductivity and high thermal stability. The regulatory mechanism of the ether functional groups on the interaction between ions still needs further investigation. Based on the above research status, this work relied on the σ-profile curve of the conductor-like screening model for real solvents (COSMO-RS) to compare the interface characteristics of different ionic liquids (IL). N-methyl-N-methoxyethyl pyrrolidine bis(trifluoromethanesulfonyl)imide salt ([C1OC2Pyr][TFSI]) was screened as the ionic conductive source. Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) was chosen as the polymer substrate. A series of IGEs were successfully prepared by adjusting the mass ratio of the IL to the substrate material. IGE-3 sample (with an IL to PVDF-HFP mass ratio of 1:3) exhibited excellent comprehensive performance. This ionic gel presented a continuous, uniform, and loose network structure without obvious agglomeration. The thermal stability temperature was up to 380 oC, the electrochemical stability window reached 5.3 V, and the ionic conductivity was 4.25 × 10–3 S·cm–1. IGE-3 was assembled into a supercapacitor (cell-3). The coulombic efficiency of the device reached 97.9% at 1 A·g–1. Based on density functional theory (DFT) calculations, the intermolecular interactions of IL systems with or without ether functional group modifications were obtained using TURBOMOLE software. Therefore, the IGE prepared in this work combines the excellent electrochemical properties of IL with high thermal stability, making it a core electrolyte material with great application potential.