Inner Lithium Fluoride (LiF)-Rich Solid Electrolyte Interphase Enabled by a Smaller Solvation Sheath for Fast-Charging Lithium Batteries

Fast-charging lithium-ion batteries (LIBs) have been severely hampered by the slow development of their electrolytes. Herein, we demonstrate that the size effect of solvent sheath would pose a great effect on the fast-charging performance of LIBs. Three similar ethers, including diethyl ether (DEE), dipropyl ether (DPE), and dibutyl ether (DBE), were mixed with 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) and lithium bis(fluorosulfonyl)imide (1 M) to form an electrolyte for fast-charging LIBs, respectively. The results showed that it is more difficult to form ternary graphite intercalation compounds (GICs) in the electrolyte with a larger solvation sheath. The DEE electrolyte can form stable GICs and generate an inner LiF-rich solid electrolyte interphase (SEI), lowering the diffusion barrier of Li+. Therefore, the graphite anode powered by the DEE electrolyte can maintain a capacity of 190 mAh g-1 at 4 C after 500 cycles. This kind of size effect of solvation sheath is also applicable to lithium metal batteries.