Nonflammable Electrolyte Based on Fluoroethylene Carbonate for High-Voltage LiCoO2/Si–Graphite Lithium-Ion Batteries

An electrolyte for high-voltage LiCoO2/Si–graphite pouch cells is proposed in this work, which is composed of LiPF6 salt and fluoroethylene carbonate solvent as well as tris(trimethylsilyl) phosphate and (ethoxy)pentafluorocyclotriphosphazene additives. Tris(trimethylsilyl) phosphate additive plays a role in improving the interfacial properties of electrodes, and (ethoxy)pentafluorocyclotriphosphazene additive makes this electrolyte nonflammable. Its conductivity is as high as 5.48 mS cm–1 at 25 °C. This safe electrolyte also enables the high-voltage LiCoO2/Si–graphite pouch cells to obtain the ideal electrochemical performances. At room temperature, the capacity retention reaches 81.7% after 200 cycles at 1C, and the discharge capacity at 3C still retains about 77% of the capacity at 1C. Furthermore, the interfacial properties of electrodes are analyzed by scanning electron microscopy and X-ray photoelectron spectroscopy measurements.