Solvate Structures and Computational/Spectroscopic Characterization of Lithium Difluoro(oxalato)borate (LiDFOB) Electrolytes

Lithium difluoro­(oxalato)­borate (LiDFOB) is a relatively new salt designed for battery electrolyte usage. Limited information is currently available, however, regarding the ionic interactions of this salt (i.e., solvate formation) when it is dissolved in aprotic solvents. Vibrational spectroscopy is a particularly useful tool for identifying these interactions, but only if the vibrational bands can be correctly linked to specific forms of anion coordination. Single crystal structures of LiDFOB solvates have therefore been used to both explore the DFOB^–...Li⁺ cation coordination interactions and serve as unambiguous models for the assignment of the Raman vibrational bands. The solvate crystal structures determined include (monoglyme)₂:LiDFOB, (1,2-diethoxyethane)_3/2:LiDFOB, (acetonitrile)₃:LiDFOB, (acetonitrile)₁:LiDFOB, (dimethyl carbonate)_3/2:LiDFOB, (succinonitrile)₁:LiDFOB, (adiponitrile)₁:LiDFOB, (PMDETA)₁:LiDFOB, (CRYPT-222)_2/3:LiDFOB, and (propylene carbonate)₁:LiDFOB. DFT calculations have been incorporated to provide additional insight into the origin (i.e., vibrational modes) of the Raman vibrational bands to aid in the interpretation of the experimental analysis

Solvate Structures and Computational/Spectroscopic Characterization of LiBF₄ Electrolytes

Crystal structures have been determined for both LiBF₄ and HBF₄ solvates: (acetonitrile)₂:LiBF₄, (ethylene glycol diethyl ether)₁:LiBF₄, (diethylene glycol diethyl ether)₁:LiBF₄, (tetrahydrofuran)₁:LiBF₄, (methyl methoxyacetate)₁:LiBF₄, (succinonitrile)₁:LiBF₄, (<i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>″,<i>N</i>″-pentamethyldiethylenetriamine)₁:HBF₄, (<i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethylethylenediamine)_3/2:HBF₄, and (phenanthroline)₂:HBF₄. These, as well as other known LiBF₄ solvate structures, have been characterized by Raman vibrational spectroscopy to unambiguously assign the anion Raman band positions to specific forms of BF₄^–···Li⁺ cation coordination. In addition, complementary DFT calculations of BF₄^–···Li⁺ cation complexes have provided additional insight into the challenges associated with accurately interpreting the anion interactions from experimental Raman spectra. This information provides a crucial tool for the characterization of the ionic association interactions within electrolytes