Electrolyte engineering via ether solvent fluorination for developing stable non-aqueous lithium metal batteries

Fluorination of solvents, useful for non-aqueous lithium-based batteries, improves the electrochemical stability but decreases the ionic conductivity. Here, the authors report a targeted functionalization of an ether solvent to balance the electrolyte ionic conductivity and oxidative stability. Fluorination of ether solvents is an effective strategy to improve the electrochemical stability of non-aqueous electrolyte solutions in lithium metal batteries. However, excessive fluorination detrimentally impacts the ionic conductivity of the electrolyte, thus limiting the battery performance. Here, to maximize the electrolyte ionic conductivity and electrochemical stability, we introduce the targeted trifluoromethylation of 1,2-dimethoxyethane to produce 1,1,1-trifluoro-2,3-dimethoxypropane (TFDMP). TFDMP is used as a solvent to prepare a 2 M non-aqueous electrolyte solution comprising bis(fluorosulfonyl)imide salt. This electrolyte solution shows an ionic conductivity of 7.4 mS cm(-1) at 25 degrees C, an oxidation stability up to 4.8 V and an efficient suppression of Al corrosion. When tested in a coin cell configuration at 25 degrees C using a 20 mu m Li metal negative electrode, a high mass loading LiNi0.8Co0.1Mn0.1O2-based positive electrode (20 mg cm(-2)) with a negative/positive (N/P) capacity ratio of 1, discharge capacity retentions (calculated excluding the initial formation cycles) of 81% after 200 cycles at 0.1 A g(-1) and 88% after 142 cycles at 0.2 A g(-1) are achieved.