A new lithium salt with 3-fluoro-1,2-benzenediolato and lithium tetrafluoroborate for lithium battery electrolytes
Abstract A new unsymmetrical lithium salt containing F − , C 6 H 3 O 2 F 2− [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 (LiBF 4 ) are examined by thermogravimetric analysis (TG). The thermal decomposition in air begins at 256 °C, 185 °C, and 162 °C for FLBBB, FLDFBDB and LiBF 4 , respectively. The order of the stability toward the oxidation of these organoborates is LiBF 4  > FLDFBDB > FLBBB. The cyclic voltammetry study shows that the FLDFBDB solution in propylene carbonate (PC) is stable up to 3.9 V 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 LiBF 4 electrolytes.