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. Salty: Tetraglyme is used to prepare a hybrid G4‐water electrolyte with high‐concentration supporting salts, which devotes to bond water by hydrogen bonding to form [Li(G4)x(H2O)y]+ to suppress hydrogen evolution reaction. This hybrid G4‐water electrolyte is applied in a dual‐ion battery that delivers an improved reversibility and capability of energy storage for a KS6/AC dual‐ion battery.