Unraveling the Positive Roles of Point Defects on Carbon Surfaces in Nonaqueous Lithium–Oxygen Batteries

Abstract

Carbon has been widely used to form cathodes for nonaqueous lithium–oxygen (Li–O2) batteries due to its high specific surface area, high electrical conductivity, and cost-effectiveness. The mechanistic understanding of carbon materials, particularly the effect of carbon surface properties on the battery’s performance, however, is limited. In this work, we perform first-principles calculations to study the roles of point defects on carbon surfaces. Five representative defective structures, including SV (single vacancy), DV5-8-5 (two pentagons and one octagon), DV555-777 (three pentagons and three heptagons), DV5555-6-7777 (four pentagons, one hexagon, and four heptagons), and SW (Stone–Wales) defects, are considered. On the basis of the adsorption energies of O2 and Li, the different Li4O4 growing pathways on these structures are identified, and free energy diagrams are then obtained. It is found that the presence of DV5555-6-7777 and SW defects is beneficial to nonaqueous Li–O2 batteries because (i) DV5555-6-7777 and SW defects exhibit zero-band-gap semiconductor behaviors, ensuring excellent electrical conductivity; (ii) DV5555-6-7777 and SW defects lead to a high discharge voltage but low charge voltage; (iii) DV5555-6-7777 and SW defects are stable during battery cycling and do not promote the formation of side product Li2CO3; and (iv) by using DMSO as a sample, DV5555-6-7777 and SW defects are not supposed to decompose electrolytes. Hence, carbon materials containing DV5555-6-7777 and SW defects are desired for nonaqueous Li–O2 batteries.