APPLICATION TO LITHIUM BATTERIES OF TERNARY SOLVENT ELECTROLYTES WITHETHYLENE CARBONATE - 1,2-DIMETHOXYETHANE MIXTURE

The electrolytic conductivity and the lithium cycling efficiency af li thium electrode were examined in ternary solvent electrolytes containi ng LiClO4 and LiPF6 with ethylene!ene carbonate (EC)-1,2-dimethoxaetha ne (DME) equimolar binary mixture al 25 degrees C. The solvents applie d to EC-DME mixture are dimethyl carbonate (DMC), ethyl methyl carbona te (EMC), diethyl carbonate (DEC), I, 3-dimethyl-2-imidazolidinone (DM I) and 1-methyl-2-pyrrolidinone (NMP). The order cif molar conductivit ies in ternary solvent electrolytes is in disagreement with that of th e viscosities in ternary solvent mixtures (bulk). It is thought that t he molar conductivities in these electrolytes are mainly influenced by the dielectric constants of mixed solvents. The lithium cycling effic iencies in ternary electrolytes containing LiPF6 became higher than th ose in ternary electrolytes containing LiClO4. In addition, the effici encies in ternary solvent electrolytes containing mixed electrolyte of LiPF6 and LiClO4 were higher compared with those in ternary electroly tes containing LiPF6. Especially, the efficiency in LiPF6+LiClO4/EC-DM E-DMC electrolyte was about 80% al the 40th cycle. The behavior of ele ctrode/electrolytes interface was investigated by impedance measuremen ts. The lithium cycling efficiency was liable to increase with decreas e in the resistance of films formed on electrodes. The formation of fi lms depended on the reductive decomposition of solvents except NMP. Th e lithium electrodeposition on the Ni (working) electrode surface in b inary and ternary solvent electrolytes by cyclic voltammetry was obser ved by atomic force microscopy (AFM). The lithium cycling efficiency w as found to be dependent on the thickness and morphology of films rath er than the formation of lithium dendrite al lower cycle numbers.