Ethylene Carbonate-Free Electrolytes Based on Ethyl Methyl Carbonate for High-Voltage LiCoO₂/Si-Graphite Lithium-Ion Batteries

Ethylene carbonate-free electrolytes based on ethyl methyl carbonate are initially applied in high-voltage cathode/Si-based anode lithium-ion batteries. Fluoroethylene carbonate and vinylene carbonate are chosen as additives to modify the compatibility between electrolyte and anode. (Ethoxy)pentafluorocyclotriphosphazene is used as a flame retardant to make the electrolyte completely nonflammable and also as a cosolvent in the electrolyte composition. 4.45 V LiCoO₂/Si-graphite pouch cells with the electrolytes containing vinylene carbonate additive have impressive cycle and rate performances at room temperature. The capacity retention of 200 cycles is higher than 80% at 1 C, and the discharge capacity at 2.5 C reaches about 89% of the capacity at 0.5 C. Furthermore, scanning electron microscopy as well as X-ray photoelectron spectroscopy measurements are conducted to explore the morphology and components of the electrode surface.