An All-Fluorinated Ester Electrolyte for Stable High-Voltage Li Metal Batteries Capable of Ultra-Low-Temperature Operation

Improving the energy output of batteries at sub-zero temperatures is crucial to the long-term application of advanced electronics in extreme environments. This can generally be accomplished by employing high-voltage cathodes, applying Li metal anodes, and improving the electrolyte chemistry to provide facile kinetics at ultralow temperature. However, systems capable of all three of these have seldom been studied. Herein, we demonstrate the design of such a system through solvent fluorination, applying a 1 M LiPF6 in a methyl 3,3,3-trifluoropionate (MTFP)/fluoro-ethylene carbonate (FEC) (9:1) electrolyte that simultaneously provided high-voltage cathode and Li metal anode reversibility at room temperature. This performance was attributed to the production of fluorine-rich interphases formed in the MTFP-based system, which was investigated by X-ray photoelectron spectroscopy (XPS). Furthermore, the all-fluorinated electrolyte provided 161, 149, and 133 mAh g(-1) when discharged at -40, -50, and -60 degrees C, respectively, far exceeding the performance of the commercial electrolyte. This work provides new design principles for high-voltage batteries capable of ultra-low-temperature operation.