Two unsymmetrical lithium organoborates with mixed-ligand of croconato and oxalicdiolato or benzenediolato for lithium battery electrolytes

Two new unsymmetrical lithium salts, lithium (oxalicdiolato croconato)borate (LOCB) and lithium (1,2-benzene-diolato(2-)-o,o' croconato)borate (LBDCB), are synthesized and characterized. The thermal characteristics of them, and their derivative, lithium bis(croconato)borate (LBCB), are examined by thermogravimetric analysis (TG). The thermal decomposition in air begins at 186 degrees C, 250 degrees C, and 265 degrees C for LBDCB. LBCB and LOCB, respectively. The order of the stability toward the oxidation of these organoborates is LBCB > LOCB > LBDCB. The cyclic voltammetry study shows that the LOCB and LBDCB solutions in propylene carbonate (PC) are stable up to 5.1 and 3.7 V versus Li+/Li. They are soluble in common organic solvents. Ionic dissociation properties of them 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) LOCB and LBDCB electrolytes in these solutions are lower than those of LBCB electrolytes. (C) 2012 Elsevier B.V. All rights reserved.