A new lithium salt with 3-fluoro-1,2-benzenediolato and lithium tetrafluoroborate for lithium battery electrolytes

A new unsymmetrical lithium salt containing F-, C6H3O2F2- [dianion of 3-fluoro-1,2-benzenediol], lithium difluoro(3-fluoro-1,2-benzene-diolato(2-)-o,o')borate (FLDFBDB) is synthesized and characterized. The thermal characteristics of it, and its derivatives, lithium bis[3-fluoro-1, 2-benzenediolato(2-)-o,o]borate (FLBBB), and lithium fluoroborate (LiBF4) are examined by thermogravimetric analysis (TG). The thermal decomposition in air begins at 256 degrees C, 185 degrees C, and 162 degrees C for FLBBB. FLDFBDB and LiBF4, respectively. The order of the stability toward the oxidation of these organoborates is LiBF4 > FLDFBDB > FLBBB. The cyclic voltammetry study shows that the FLDFBDB solution in propylene carbonate (PC) is stable up to 3.9V vs. Li+/Li. It is soluble in common organic solvents. Ionic dissociation properties of FLDFBDB and its derivatives are examined by conductivity measurements in PC, PC+ ethyl methyl carbonate (EMC), PC+ dimethyl ether (DME), PC+ ethylene carbonate (EC)+ DME, PC+ EC+ EMC solutions. The conductivity values of the 0.10 mol dm(-3) FLDFBDB electrolyte in these solutions are higher than those of FLBBB, but lower than those of LiBF4 electrolytes. (C) 2011 Elsevier B.V. All rights reserved.