期刊
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
卷 7, 期 18, 页码 3554-3559出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpclett.6b01664
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资金
- National Natural Science Foundation of China [21373213]
- Chinese Academy of Sciences
- Ministry of Science and Technology
- NSF [CHE-1503865]
- Welch foundation [C-1752]
- Packard Fellowship
- Sloan Fellowship
- PKU
- DSM-Energie CEA Program
- [ANR-2011 PRGE002-04 ALIBABA]
- Division Of Chemistry
- Direct For Mathematical & Physical Scien [1503865] Funding Source: National Science Foundation
Rechargeable lithium ion batteries are an attractive alternative power source for a wide variety of applications. To optimize their performances, a complete description of the solvation properties of the ion in the electrolyte is crucial. A comprehensive understanding at the nanoscale of the solvation structure of lithium ions in nonaqueous carbonate electrolytes is, however, still unclear. We have measured by femtosecond vibrational spectroscopy the orientational correlation time of the CO stretching mode of Li+-bound and Li+ unbound ethylene carbonate molecules, in LiBF4, LiPF6, and LiClO4 ethylene carbonate solutions with different concentrations. Surprisingly, we have found that the coordination number of ethylene carbonate in the first solvation shell of Li+ is only two, in all solutions with concentrations higher than 0.5 M. Density functional theory calculations indicate that the presence of anions in the first coordination shell modifies the generally accepted tetrahedral structure of the complex, allowing only two EC molecules to coordinate to Li+ directly. Our results demonstrate for the first time, to the best of our knowledge, the anion influence on the overall structure of the first solvation shell of the Li+ ion. The formation of such a cation/solvent/anion complex provides a rational explanation for the ionic conductivity drop of lithium/carbonate electrolyte solutions at high concentrations.
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