Crystal structure and physical properties of lithium difluoro(oxalato)borate (LiDFOB or LiBF2Ox)

The structural characterization and properties of lithium difluoro(oxalato)borate (LiDFOB) are reported. LiDFOB was synthesized as previously described in the literature via direct reaction of boron trifluoride diethyl etherate with lithium oxalate. The crystal structure of the salt was determined from single crystal X-ray diffraction yielding a highly symmetric orthorhombic structure (Cmcm, a = 6.2623(8) Å, b = 11.4366(14) Å, c = 6.3002(7) Å, V = 451.22(9) Å3, Z = 4 at 110 K). Single crystal X-ray diffraction of a dihydrate of LiDFOB yielded a monoclinic structure (P21/c, a = 9.5580(3) Å, b = 12.7162(4) Å, c = 5.4387(2) Å, V = 634.63(4) Å3, Z = 4 at 110 K). Along with the crystal structures, additional structural information and the properties of LiDFOB (via 11B and 19F NMR, DSC, TGA and Raman spectroscopy) have been compared with those of LiBF4 and LiBOB to better understand the differences between these lithium battery electrolyte salts.