Abstract: Addressing the issues of lithium dendrite growth, unstable electrode/electrolyte interface, and poor oxidation stability in ethylene glycol dimethyl ether (DME) electrolyte in lithium metal batteries. This work uses trimethoxy (3,3,3-trifluoropropyl) silane (TFS) as the electrolyte solvent and combines with lithium difluorosulfonylimide (LiFSI) salt to design a novel fluorinated siloxane electrolyte. The lithium solvation structure of the electrolyte were analyzed by using density functional theory (DFT) calculations and molecular dynamics simulations (MD). The electrochemical performance of the cells in fluorinated siloxane electrolyte and DME electrolyte were compared and analyzed through charge discharge tests, cycle performance tests, and rate performance tests. The lithium deposition morphology and electrode interface composition were analyzed by using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). As a results, the Si-O bond in TFS has a higher bond energy than the C-O bond in DME electrolyte, which can enhance the oxidation stability of the electrolyte and match high-voltage cathode materials. In addition, TFS solvent exhibits relatively weak binding ability with Li+, this unique lithium solvation structure is conducive to inducing FSI- anions to preferentially decompose on the surface of lithium metal anode and form rich-LiF SEI films, effectively inhibiting lithium dendrite growth, stabilizing the electrode interface, and improving the cycle life of lithium metal batteries. In TFS electrolyte, the Li||Cu cell can be stably cycled for 300 cycles at a current density of 1.0 mA/cm2, The Li||LFP full cell showed no significant capacity degradation after 400 cycles at 2.0 C, and the Li||NCM811 full cell maintained a discharge specific capacity retention rate of 83% after 300 cycles at a 1.0 C, demonstrating excellent cycling stability.

Key words: Lithium metal battery, Fluorosiloxane solvent, Electrochemical performance, Cycling stability