Application to lithium batteries of ternary solvent electrolytes with ethylene carbonate - 1,2-dimethoxyethane mixture

The electrolytic conductivity and the lithium cycling efficiency af lithium electrode were examined in ternary solvent electrolytes containing LiClO4 and LiPF6 with ethylene!ene carbonate (EC)-1,2-dimethoxaethane (DME) equimolar binary mixture al 25 degrees C. The solvents applied to EC-DME mixture are dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), I, 3-dimethyl-2-imidazolidinone (DMI) and 1-methyl-2-pyrrolidinone (NMP). The order cif molar conductivities in ternary solvent electrolytes is in disagreement with that of the viscosities in ternary solvent mixtures (bulk). It is thought that the molar conductivities in these electrolytes are mainly influenced by the dielectric constants of mixed solvents. The lithium cycling efficiencies in ternary electrolytes containing LiPF6 became higher than those in ternary electrolytes containing LiClO4. In addition, the efficiencies in ternary solvent electrolytes containing mixed electrolyte of LiPF6 and LiClO4 were higher compared with those in ternary electrolytes containing LiPF6. Especially, the efficiency in LiPF6+LiClO4/EC-DME-DMC electrolyte was about 80% al the 40th cycle. The behavior of electrode/electrolytes interface was investigated by impedance measurements. The lithium cycling efficiency was liable to increase with decrease in the resistance of films formed on electrodes. The formation of films depended on the reductive decomposition of solvents except NMP. The lithium electrodeposition on the Ni (working) electrode surface in binary and ternary solvent electrolytes by cyclic voltammetry was observed by atomic force microscopy (AFM). The lithium cycling efficiency was found to be dependent on the thickness and morphology of films rather than the formation of lithium dendrite al lower cycle numbers.