High Voltage and Capacity Dual-Ion Battery Using Acetonitrile-Aqueous Hybrid Electrolyte with Concentrated LiFSI-LiTFSI

Water-acetonitrile (AN) hybrid electrolyte with high concentration of bis(trifluoromethanesulfonyl) imide (LiTFSI) and Lithium bis(fluorosulfonyl) imide (LiFSI) (LiTFSI-LiFSI=3:1, molar ratio) supporting salts are studied for the high potential and large capacity rechargeable dual-ion battery. Water-acetonitrile hybrid electrolyte (WA) shows a wide electrochemical stability window of 3.1 V in 20 m aqueous electrolyte and 3.6 V in 20 m 9LiFSI-1LiTFSI in water: AN=1:3 molar ratio electrolyte. In particular, high oxidation potential, which can be assigned to the strong solvated ionic cluster formed between AN, water and LiTFSI-LiFSI supporting salts. The dual-ion battery is assembled using the graphitic carbon (KS6) and the activated carbon (AC) as cathode and anode, respectively, and 20 m LiTFSI-LiFSI in hybrid AN-water as electrolyte. It is found that the reasonably large capacity, coulombic efficiency and cycle stability were achieved. The KS6/AC cell shows 86 mAh g −1 at the initial cycle and 50 mAh g −1 at 100th cycle in a voltage range of 0–3.25 V, and the average coulombic efficiency of 85% is sustained over 200 cycles. The solvated structure of water to Li + is strengthened by addition of AN from ATR-IR and NMR spectrums analysis and this change in the solvated structure is the main reason for the increased performance of the aqueous dual-ion battery.