Changes in double layer capacitance of the positive electrode in Li-O2 battery during discharge: Effect of active material and aprotic electrolyte solvent

Abstract

Changes in the double-layer capacitance of a positive electrode (CDL) are investigated during the discharge of a lithium-oxygen battery (LOB) having various carbon materials (CM), including XC-72, Super P, EC-300 J, and CNT, and electrolytes based on tetraglyme and DMSO, containing 0.1 M LiClO4. It is shown that the initial value of CDL increases proportionally to the external surface area of the carbon material in both the tetraglyme- and DMSO-based electrolyte. The difference between the CDL values in these electrolytes can be explained by the different wetting abilities of the solvents, as well as the ability of the DMSO medium to dissolve the binder (PVDF). During the LOB discharge, a decrease in CDL is observed, which is associated with increasing passivation of the positive electrode with lithium peroxide (Li2O2)). The highest (Li2O2) value (0.5–0.7) is observed for XC-72 and EC-300 J carbon black having the lowest average pore size (9 and 8 nm, respectively) among the studied materials. Nonetheless, no pronounced dependence of (Li2O2) on the nature of a solvent was observed under identical measurement conditions. Along with blocking the surface with lithium peroxide, oxygen transport limitations have a significant impact on the discharge process, which is most pronounced for large-pore CMs (Super P and CNT). Even at a relatively low (Li2O2) (from 0.15 to 0.24), the voltage of such LOBs decreases to 2 V. The results demonstrate that the initial parameter CDL of the active material can be used as a new criterion for pre-selection the electrolyte for LOB.