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


 Hybrid water-acetonitrile (AN) electrolytes with concentrated bis(trifluoromethanesulfonyl) imide (LiTFSI) and Lithium bis(fluorosulfonyl) imide (LiFSI) (LiTFSI-LiFSI=3:1, molar ratio) supporting salts are studied for high potential and large capacity rechargeable dual-ion battery. Hybrid water-acetonitrile electrolyte (WA) shows a wide electrochemical stability window from 3.1 V in 20m W electrolyte to 3.6 V in 20m W1A3 (water: AN=1:3, molar ratio) electrolyte, particularly, high oxidation potential, which can be assigned to the strong ionic solvated cluster formed between AN, water and LiTFSI-LiFSI supporting salts. The dual-ion battery is assembled using graphitic carbon (KS6) and activated carbon (AC) as cathode and anode, respectively, and 20m LiTFSI-LiFSI in hybrid AN-water as electrolyte. It was found that 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 within a voltage range of 0-3.25 V, and average coulombic efficiency of 85% was 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 solvated structure is the main reason for increased dual-ion battery performance.