Interface engineering with fluorine-doped amorphous carbon thin film coating on graphite anodes compatible with non-flammable sulfone-based electrolyte

To achieve full commercialization of Li-ion batteries, fire safety issues, which primarily start and accelerate from the electrode/electrolyte interface, should be resolved. Therefore, ionic liquids containing sulfone-based Li salts and solvents have been demonstrated to exhibit higher flame-retardancy than carbonate-based electrolytes. However, these sulfone-based electrolytes (sulfone EL) still face the challenges of sluggish Li-ion diffusivity of the electrolyte itself and poor compatibility especially with graphite anodes, lowering the specific capacity and high rate capability of the anodes. Herein, interface engineering was achieved by introducing a fluorine-doped amorphous carbon thin film coating (sub-20 nm) between graphite and sulfone EL, thereby simultaneously enhancing the ultrafast rate capability and flame-retardancy. The semi-ionic C–F abundant surface chemistry of graphite (F–C/Gra) not only induces robust solid electrolyte interface (SEI) formation with a LiF-rich composition and moderate thickness, but it also promotes fast-rated electron transfer into the graphite interior, which differs from bare graphite in sulfone EL. Surprisingly, this robust SEI formation on F–C/Gra was achieved at an elevated temperature (60 °C), enhancing Li-ion transport kinetics and allowing graphite-based anodes to achieve ultrafast longevity (discharge capacity of 152.6 mAh/g after 300 cycles at 1000 mA/g, 60 °C) even under harsh conditions.