Lithium cycling efficiency and conductivity for high dielectric solvent/low viscosity solvent mixed systems

Abstract

Lithium cycling efficiency on a lithium substrate (Li-on-Li cycling) and conductivity for various mixed solvent systems of high dielectric solvent (HDS) and low viscosity solvent (LVS) were examined for secondary lithium batteries. For the HDS, sulfolane, dimethylsulfoxide, γ-lactones, propylene carbonate (PC) and ethylene carbonate (EC) were used. For the LVS, tetrahydrofuran (THF), 2-methyl-THF, 1,2-dialkoxyethanes and 1,3-dioxolane (DOL) were used. For the solute, LiAsF 6, LiBF 4, LiCF 3CO 3 and LiClO 4 were used. Lithium cycling efficiencies newly measured on a Li substrate ( E a ) for EC/LVS or PC/LVS were ca 5% or 15% higher than those previously obtained by simple cycling of Li on a Pt substrate, while the order of Li cycling efficiencies to LVS change is similar in both cases, except for EC/DOL or PC/DOL. The reasons seem to be that the Li-on-Li cycling minimizes the influence of electrochemical Li/Pt alloying and partial solvent oxidation during the cycle on Li cycling efficiency. The E a values in HDS/LVS mixed systems incorporating LiAsF 6 or LiClO 4 tended to increase with a decrease in the reactivity to Li, of not only LVS but also HDS. EC/THF systems incorporating LiAsF 6 or LiClO 4 showed high E a values of ca 95% even by Li-on-Li cycling, the value being higher than those (ca 92%) for LiBF 4 or LiCF 3SO 3 systems. In addition, for all the HDS/LVS mixed systems examined in this work, conductivities were higher than those for HDS or LVS single solvent systems. In regard to both conductivity and Li cycling efficiency, HDS/LVS mixed systems are considered to be effective in various lithium battery applications.