Mixture of monoglyme-based solvent and lithium Bis (trifluoromethanesulfonyl)amide as electrolyte for lithium ion battery using silicon electrode

The electrochemical property of a silicon electrode in a half-cell was investigated using the mixture of monoglyme-based solvents and lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) with 2:1 stoichiometry. The solvents used in this study are monoglyme (G1), 1,2-diethoxyethane (DEE), 1,2-dibutoxyethane (DBE), and 1,2-dimethoxypropane (P-G1). When Li (DEE)(2) or Li(P-G1)(2) was used, the cell retained ca. 20% capacity at a rate of 3 C, while the other samples showed almost no capacity under the same conditions. Raman spectroscopy measurement revealed that Li+ exists as two forms in the mixture, that is, a solvent shared ion pair (SSIP) [Li+ center dot center dot center dot solvent center dot center dot center dot TFSA(-)] and a contact ion pair (CIP) [Li+ center dot center dot center dot TFSA(-)]According to the spectroscopic analysis, SSIP is the dominant species for Li (DEE)(2) and Li(P-G1)(2), and CIP for Li (G1)(2) and Li (DBE)(2). The order of the rate property was Li(P-G1)(2) similar to Li (DEE)(2) > Li (DBE)(2)similar to Li (G1)(2), which is almost consistent with the stability of free energy levels of Li+ in the respective monoglymes against CIP Li+ center dot center dot center dot TFSA(-) evaluated from the Raman spectra.