Application of lithium organoborate with salicylic ligand to lithium battery electrolyte

The thermal characteristics of lithium bis[salicylato(2-)]borate (LBSB) and its novel derivatives synthesized by us, such as lithium bis[3-methylsalic ylato(2-)]borate (3-MLBSB), lithium bis[3,5-dichlorosalicylato(2-)]borate ( DCLBSB), and lithium bis[3,5,6-trichlorosalicylato(2-)]borate (TCLBSB) were examined by thermogravimetric analysis (TG). The thermal decomposition in air begins at 260, 290, 310, and 320 degreesC for TCLBSB, LBSB, DCLBSB, and 3-MLBSB, respectively. The thermal stabilities of 3-MLBSB and DCLBSB are n early equal to those of LiN(CF3SO2)(2) and LiN(C2F5SO2)(2). The order of th e stability toward oxidation of these organoborates is TCLBSB approximate t o DCLBSB > LBSB > 3-MLBSB, which differs from the thermal stability. Ionic dissociation properties of LBSB and its derivatives were examined by conduc tivity measurements in ethylene carbonate-1,2-dimethoxyethane (EC-DME) equi molar binary dilute solutions. The conductivities of the 0.1 mol dm(-3) DCL BSB and TCLBSB electrolytes become higher than those in the LBSB and 3-MLBS B electrolytes. It means that DCLBSB and TCLBSB have high dissociating abil ities in EC-DME mixture. The 0.5 mol dm(-3) LBSB/EC-DME equimolar binary so lution exhibits the highest lithium electrode cycling efficiency of more th an 85% in the higher range of cycle numbers. This is a good electrolyte for rechargeable batteries. (C) 2001 The Electrochemical Society.