image: (a) Solubility of H2O-ILs and KOTf-H2O -ILs (EMIMNTf2, EMIMOTf, EMIMBF4, and EMIMPF6). (b) Schematic illustration of the possible change in potassium-ion primary solvation shell. (c) Ternary phase diagrams of KOTf-H2O-EMIMNTf2 mixtures at room temperature. (d) ESW for various electrolytes measured at a scan rate of 5 mV s−1 versus Ag wire. (e) Raman spectra of different electrolytes compared with pure water and IL. (f) MD snapshots of KOTf-H2O-(EMIMNTf2)0.1 electrolyte. (g) PDF (g(r)) and corresponding coordinate number (n(r)) of KOTf-H2O-(EMIMNTf2)0.1 electrolyte.
Credit: ©Science China Press
Conventional aqueous supercapacitors face limitations in extreme temperatures due to water evaporation. To address this, a team from Shandong University designed a hybrid electrolyte by blending potassium trifluoromethanesulfonate (KOTf) with the ionic liquid EMIMNTf₂. This combination reshapes the solvation structure around potassium ions, reducing free water activity and suppressing harmful side reactions.
Through solubility tests and molecular dynamics simulations, the team identified EMIMNTf₂ as the optimal additive. The resulting electrolyte exhibits a 3.37 V electrochemical stability window and operates reliably from 0 to 100°C. At 60°C, supercapacitors retained 81.8% capacity after 10,000 cycles, outperforming existing WIS-based devices. This work bridges the gap between high voltage and thermal stability, also enhances safety, critical for real-world deployment. The study, published in Science Bulletin, highlights the potential of ionic liquids to revolutionize next-generation energy storage systems.