期刊
ENERGY & ENVIRONMENTAL SCIENCE
卷 7, 期 1, 页码 416-426出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/c3ee42351d
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资金
- OE BATT program [DE-AC02-05-CH11231]
- U.S. Department of Energy
- U.S. Army Research Laboratory [DE-IA01-11EE003413]
Highly concentrated electrolytes containing carbonate solvents with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) have been investigated to determine the influence of eliminating bulk solvent (i.e., uncoordinated to a Li+ cation) on electrolyte properties. The phase behavior of ethylene carbonate (EC)-LiTFSI mixtures indicates that two crystalline solvates form-(EC)(3):LiTFSI and (EC)(1):LiTFSI. Crystal structures for these were determined to obtain insight into the ion and solvent coordination. Between these compositions, however, a crystallinity gap exists. A Raman spectroscopic analysis of the EC solvent bands for the 3-1 and 2-1 EC-LiTFSI liquid electrolytes indicates that similar to 86 and 95%, respectively, of the solvent is coordinated to the Li+ cations. This extensive coordination results in significantly improved anodic oxidation and thermal stabilities as compared with more dilute (i.e., 1 M) electrolytes. Further, while dilute EC-LiTFSI electrolytes extensively corrode the Al current collector at high potential, the concentrated electrolytes do not. A new mechanism for electrolyte corrosion of Al in Li-ion batteries is proposed to explain this. Although the ionic conductivity of concentrated EC-LiTFSI electrolytes is somewhat low relative to the current state-of-the-art electrolyte formulations used in commercial Li-ion batteries, using an EC-diethyl carbonate (DEC) mixed solvent instead of pure EC markedly improves the conductivity.
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