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

A new unsymmetrical lithium salt containing F-, C6O2F42- [dianion of tetrafluoro-1,2-benzenediol], lithium difluoro[tetrafluoro-1,2-benzenediolato(2-)-O,O']borate (4FLDFBDB) is synthesized and characterized. The thermal characteristics of it, and its derivatives, lithium difluoro[3-fluoro-1,2-benzene-diolato(2-)-O,O']borate (FLDFBDB), and lithium difluoro[1,2-benzene-diolato(2-)-O,O']borate (LDFBDB) are examined by thermogravimetric analysis (TG). The thermal decomposition in air begins at 170 degrees C, 185 degrees C. and 230 degrees C for 4FLDFBDB, FLDFBDB, and LDFBDB respectively. The order of the stability toward oxidation of these organoborates is 4FLDFBDB > FLDFBDB > LDFBDB. The cyclic voltammetry study shows that the 4FLDFBDB solution in propylene carbonate (PC) is stable up to 4.2 V versus Li+/Li. They are soluble in common organic solvents. Ionic dissociation properties of 4FLDFBDB and its derivatives are examined by conductivity measurements in PC, PC + ethyl methyl carbonate (EMC), PC + dimethyl ether (DME). PC+ ethylene carbonate (EC) + EMC. The conductivity values of the 0.10 mol dm(-3) 4FLDFBDB electrolyte in these solutions are higher than those of FLDFBDB and LDFBDB electrolytes. (C) 2011 Elsevier B.V. All rights reserved.