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 °C, 185 °C, and 230 °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.

► A new lithium salt, lithium difluoro[tetrafluoro-1,2-benzenediolato(2-)-O,O′]borate (4FLDFBDB), has been synthesized.
► The salt, 4FLDFBDB, is thermally stable and soluble in many of the common organic solvents used in batteries.
► The conductivities and electrochemical oxidation potential of 4FLDFBDB solutions are higher than those of FLDFBDB solutions.
► A strong correlation between the adiabatic ionization potential and the electrochemical stability is established.