Lithium cycling efficiency and conductivity for γ-lactone-based electrolytes

Lithium cycling efficiency on a lithium substrate as well as conductivity were examined for-lactonebased electrolytes incorporating LiClO₄ for use in nonaqueous lithium secondary batteries.-butyrolactone (BL),-valerolactone and-octanoiclactone were used. Conductivity increased with a decrease in viscosity for lactone. Lithium cycling efficiency tended to increase with a decrease in reactivity between lithium and lactone, which would be expected from the oxidation potential for lactone. In order to decrease viscosity, tetrahydrofuran (THF) was mixed with lactone. Conductivity for lactone/THF was higher than those for systems using either lactone or THF alone. For example, 1 M LiClO₄-BL/THF (mixing volume ratio =11) showed conductivity of 13.0 × 10^–3 S cm^–1, approximately 20% higher than that for BL. Lithium cycling efficiency for BL/THF, which exceeded 90%, was also higher than that for BL. Morphology of the deposited lithium in BL/THF was smoother than that in BL and similar to that in THF, as observed with a scanning electron microscope. The reason for the enhancement of the lithium cycling efficiency for BL/THF seems to be the adsorption of THF or THF-Li⁺ around the deposited Li, which has lower reactivity to Li and higher solvation power to Li⁺ than BL.