Effects of quinoneimine dyes on lithium cycling efficiency for LiClO4-propylene carbonate

Additive effects of quinoneimine dyes (QIDs) on Li cycling efficiency (E _ff) were examined in 1 M LiClO₄-propylene carbonate (PC). TheE _ff values were measured galvanostatically on a Pt working electrode. TheE _ff values for solutions with QID addition were higher than those for PC alone and theE _k values depended on cycling current density and on the amounts of QID added. For example, 1 M LiClO₄-PC with added methylene blue (MB) (10^–3 M addition) showedE _ff values exceeding 90% at 0.5mA cm^–2, 0.6 C cm^–2, while theE _ff values for PC alone were approximately 65%. From observation with a scanning electron microscope the morphology for the deposited Li in solution with MB added was found to be smoother than that in PC alone. TheE _ff values for solutions with QID added tended to increase with an increase in the reduction potential for QID vs Li-Li₊. The enhancement of the Li cycling efficiency by QID addition seems to be caused by Li₊ ion-conductive film formation on the deposited Li surface, resulting from the reaction between QID and the deposited Li, that suppresses the reaction between PC and the deposited Li. This film formation was strongly suggested by the measurement of the resistance on the Li surface.