Solvated Structure of Hybrid Tetraglyme-Aqueous Electrolyte Dissolving High-Concentration LiTFSI-LiFSI for Dual-Ion Battery

The solvated structure of a highly concentrated hybrid tetraglyme (G4)-water electrolyte was studied for an increasing cycle stability and performance of a KS6 used dual-ion battery. Hybrid solvent of G4 and water with a weight ratio of 2 to 8 was able to dissolve 9LiFSI-1LiTFSI supporting salts up to 37 mol kg⁻¹ (37 mol kg⁻¹ G2W8). In spite of such high concentration of supporting salts, reasonable charge and discharge performance of dual-ion battery (discharge capacity of ≈40 mAh g⁻¹ and coulombic efficiency of 90 %) were exhibited over 300 cycles. This was attributed to the decreased hydrogen evolution reaction (HER) potential to −1.05 V vs. Ag/AgCl by addition of G4. From Fourier-transform infrared, nuclear magnetic resonance, and Raman spectroscopies, G4 molecules were more strongly coordinated to Li⁺ to form ion pairs of [Li(G4)_x(H₂O)_y]⁺ complex in hybrid G4-water electrolyte. Co-intercalation of bis(trifluoromethanesulfonyl)imide (TFSI⁻) and bis(fluorosulfonyl)imide (FSI⁻) into graphitic carbon KS6 cathode was confirmed in hybrid aqueous electrolyte.