Kyohei Usami

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.

Chelate complexes with boron as lithium salts for lithium battery electrolytes

Abstract The electrolytic conductivity and charge–discharge characteristics of lithium electrodes are examined in propylene carbonate (PC)- and ethylene carbonate (EC)-based binary solvent electrolytes containing lithium bis[1,2-benzenediolato(2-)-O,O′]borate (LBBB), lithium bis[2,3-naphthalenediolato(2-)-O,O′]borate (LBNB) and lithium bis[2,2′-biphenyldiolato(2-)-O,O′]borate (LBBPB). The LBBPB exhibits high thermal and electrochemical stability compared with LBBB and LBNB. Conductivities in PC-THF and EC-THF binary solvent electrolytes at X THF (mole fraction of tetrahydrofuran, THF)=0.5 containing 0.5 M LBBB and LBNB are nearly equal to that in 0.5 M LiCF 3 SO 3 electrolyte as a typical lithium battery electrolyte. The conductivity in 0.3 M LBBPB/PC-DME (DME: 1,2-dimethoxyethane) electrolyte is fairly low compared with that in other electrolytes. The energy density with the LBNB electrolyte is higher than that with LBBB or LBBPB electrolyte. In general, lithium cycling efficiencies in THF-based LBBB and LBNB electrolytes become higher than those in DME-based electrolytes. The 0.5 M LBNB/PC-THF electrolyte is a moderately rechargeable lithium battery electrolyte. The 0.3 M LBBPB/PC-DME equimolar solvent electrolyte displays the highest cycling efficiency, viz., >70%, at a high range of cycle number.

Application to lithium battery electrolyte of lithium chelate compound with boron

Abstract The electrolytic conductivities and charge–discharge characteristics of lithium electrode are examined in propylene carbonate (PC)- and ethylene carbonate (EC) tetrahydrofurans, such as 2-methyltetrahydrofuran (2-MeTHF) and 2,5-dimethyltetrahydrofuran (2,5-DMeTHF), binary solvent electrolytes containing lithium bis[1,2-benzenediolato(2-)- O , O ′]borate (LBBB), lithium bis[2,3-naphthalenediolato(2-)- O , O ′]borate (LBNB), lithium bis[2,2′-biphenyldiolato(2-)- O , O ′]borate (LBBPB) and lithium bis[salicylato(2-)]borate (LBSB). The order of specific conductivities in PC- and EC-based equimolar binary solutions containing these organoborates is LBBB≥LBNB>LBSB>LBBPB. The conductivity in LBNB electrolyte with higher viscosity than that in LBSB electrolyte becomes high. The PC–2-MeTHF and PC–2,5-DMeTHF equimolar binary solutions containing LBSB and a mixed electrolyte (LBBPB+LiPF 6 ) show very high cycling efficiencies more than 90% at a higher range of cycle number. The EC–THF and EC–2-MeTHF equimolar binary solutions are moderate electrolytes with about 80% cycling efficiencies. It is found by using scanning electron microscope (SEM) that the films formed on the electrode in PC–2-MeTHF and PC–2,5-DMeTHF electrolytes with higher cycling efficiencies have a homogeneous surface with uniform grain size.