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The thermal characteristics of lithium bis͓salicylato͑2-͔͒borate ͑LBSB͒ and its novel derivatives synthesized by us, such as lithium bis͓3-methylsalicylato͑2-͔͒borate ͑3-MLBSB͒, lithium bis͓3,5-dichlorosalicylato͑2-͔͒borate ͑DCLBSB͒, and lithium bis͓3,5,6-trichlorosalicylato͑2-͔͒borate ͑TCLBSB͒ were examined by thermogravimetric analysis ͑TG͒. 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 LiN͑CF 3 SO 2 ͒ 2 and LiN͑C 2 F 5 SO 2 ͒ 2 . The order of the stability toward oxidation of these organoborates is TCLBSB Ϸ DCLBSB Ͼ LBSB Ͼ 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-DME͒ equimolar binary dilute solutions. The conductivities of the 0.1 mol dm Ϫ3 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 Ϫ3 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.Many workers have attempted to develop improved electrolytes for lithium batteries with high energy density and good rechargeability as power sources for many portable instruments and electric vehicles in order to protect the natural environment and resources. Recently, Barthel et al. 1-5 reported a new class of electrochemically and thermally stable lithium salts with a chelate-type anion of boron, such as lithium bis͓1,2-benzenediolato͑2-͒-O,OЈ͔borate ͑LBBB͒, lithium bis͓2,3-naphthalenediolato͑2-͒-O,OЈ͔borate ͑LBNB͒, lithium bis͓2,2Ј-biphenyldiolato͑2-͒-O,OЈ͔borate ͑LBBPB͒, and lithium bis͓salicylato͑2-͔͒borate ͑LBSB͒ as shown in Fig. 1. In previous papers, 6-8 we reported the thermal characteristics of LBBB, LBNB, and LBBPB and the electrolytic behavior in propylene carbonate ͑PC͒-1,2-dimethoxyethane ͑DME͒, ethylene carbonate ͑EC͒-DME, PC-tetrahydrofuran ͑THF͒, and EC-THF binary solvent electrolytes containing LBBB, LBNB, and LBBPB.In this paper, the thermal characteristics of LBSB and its novel derivatives synthesized by us, such as lithium bis͓3-methylsalicylato͑2-͔͒borate ͑3-MLBSB͒, lithium bis͓3,5-dichlorosalicylato͑2-͔͒borate ͑DCLBSB͒, and lithium bis͓3,5,6-trichlorosalicylato͑2-͔͒borate ͑TCLBSB͒ as shown in Fig. 2, were examined. In addition, the electrolytic behavior and chargedischarge characteristics of a lithium electrode in EC-DME binary solvent electrolytes containing LBSB, 3-MLBSB, DCLBSB, and TCLBSB were studied and compared with those in the LiPF 6 electrolyte, which is a common salt for lithium batteries. ExperimentalMaterials.-The LBSB raw salt was easily obtained using lithium carbonate as the starting material instead of lithium hydroxide monohydrate of Bar...

A chelate complex with boron, lithium bis[2,3-naphthalenediolato(2-)-O,O']borate was used in lithium battery electrolytes for LiN 2 O 5 prototype cells. This lithium salt remains a safe and thermally stable compound up to 320°C without melting. A high specific conductivity (4.63 mS cm-1 ) is exhibited in spite of its high viscosity (1.732 cP) in a 0.5 mol dm-3 electrolyte/ethylene carbonate-1,2-dimethoxyethane (mol ratio 2:3) binary solvent mixture at 25°C. Based on the discharge characteristics of a Li/VN 2 O prototype cell, this lithium salt electrolyte resulted in high energy density (460 Wh kg-') at a cutoff potential of 2.5 V vs. Li/Li +.

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