Role of Mixed Solvation and Ion Pairing in the Solution Structure of Lithium Ion Battery Electrolytes

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• 作者：Daniel M. Seo ; Stefanie Reininger ; Mary Kutcher ; Kaitlin Redmond ; William B. Euler ; Brett L. Lucht
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：June 25, 2015
• 年：2015
• 卷：119
• 期：25
• 页码：14038-14046
• 全文大小：536K
• ISSN：1932-7455

文摘

The solution structures of organic carbonate solvents (ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and diethyl carbonate (DEC)) as electrolyte solutions of LiPF₆ were investigated with FTIR and NMR spectroscopy and DFT computational methods. Both coordinated and uncoordinated solvents are observed by IR spectroscopy, allowing the determination of solvent coordination numbers, which a range from 2 to 5. The predominant species in solution changes as a function of LiPF₆ concentration. At low salt concentrations (<1.2 M), the predominant species is a solvent-separated ion pair, whereas at high salt concentrations (>2.0 M) the predominant species in solution is the contact ion pair. In mixed solvent systems (PC鈥揇MC, PC鈥揇EC, EC鈥揇MC, or EC鈥揇EC), the mixed solvated cations are observed in the presence of high concentrations of uncoordinated cyclic carbonate despite the much larger dielectric constant of the cyclic carbonates than dielectric constant of linear carbonate.