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-methylsalicylato(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°C for TCLBSB, LBSB, DCLBSB, and 3-MLBSB, respectively. The thermal stabilities of 3-MLBSB and DCLBSB are nearly equal to those of LiN ( CF 3 SO 2 ) 2 and LiN ( C 2 F 5 SO 2 ) 2 . The order of the stability toward oxidation of these organoborates is TCLBSB ≈ DCLBSB > LBSB > 3 ­ MLBSB , which differs from the thermal stability. Ionic dissociation properties of LBSB and its derivatives were examined by conductivity measurements in ethylene carbonate-1,2-dimethoxyethane (EC-DME) equimolar binary dilute solutions. The conductivities of the 0.1 mol dm −3 DCLBSB and TCLBSB electrolytes become higher than those in the LBSB and 3-MLBSB electrolytes. It means that DCLBSB and TCLBSB have high dissociating abilities in EC-DME mixture. The 0.5 mol dm −3 LBSB/EC-DME equimolar binary solution exhibits the highest lithium electrode cycling efficiency of more than 85% in the higher range of cycle numbers. This is a good electrolyte for rechargeable batteries.