Effect of surface characteristics of carbon host on electrochemical performance of nonaqueous Li–O₂ batteries

Carbon-based air cathodes are considered the ideal choice for Li–O₂ batteries. However, the parasitic reaction on the carbon surface remains a critical hurdle to progress toward practical Li–O₂ batteries. To address this issue, an in-depth understanding of the effect of surface chemistry is needed as it is a key factor determining the electrochemical performance of Li–O₂ batteries. In this study, to elucidate the relationship between the surface characteristics of carbon and the electrochemical performance of a Li–O₂ battery, we prepared a series of porous carbon nanoweb electrodes with systematically controlled surface properties. We then closely investigated the effect of the surface chemistry of carbon on the electrochemical performance of the Li–O₂ battery. The key factors greatly contributing to the performance were determined to be the degree of graphitization and the density of oxygen functional groups on the carbon surface. These factors have a strong effect on the initial reaction route for Li₂O₂ formation, naturally resulting in large differences in the electrochemical properties such as the capacity, cyclability, efficiency, and Li₂O₂ yield. We define the relationship between the surface properties and key performance factors, and suggest the ideal conditions for a carbon electrode for Li–O₂ batteries. Our demonstration will help guide the future design of ideal carbon-based air cathodes for practical Li–O₂ batteries.