Studies of Li Anodes in the Electrolyte System 2Me-THF/THF/Me-Furan/LiAsF₆

The correlation between Li cycling efficiency, Li morphology Li surface chemistry, and the properties of the Li-solution interphase was investigated in the THF, 2Me-THF, 2Me-Furan (MF), LiAsF6 electrolyte system. Surface sensitive FTIR, EDAX-x-ray microanalysis, SEM, and impedance spectroscopy were used in conjunction with standard electrochemical techniques. Using THF as a cosolvent to 2Me-THF decreases the detrimental impact of contaminants such as water as it is more reactive toward lithium than 2Me-THE The presence of MF (a few percent) influences the Li surface chemistry since its reduction to surface compounds with alkoxy groups suppresses solvent and salt reduction. However, its effect on Li morphology and cycling efficiency is marginal. It is concluded that the main positive impact of this additive reported in the literature is due to the stabilizing effect of the ethers by its possible reaction with trace Lewis acid contaminants in the solutions. The superiority of LiAsF6 as an electrolyte for these solutions is attributed to the precipitation of elementary arsenic and arsenic compounds (e.g., Li3As, LixAsFy) on lithium, which modifies Li deposition to become uniform and smooth.