(Invited) Ultrahigh Areal Capacity Holey Graphene Air Cathodes for Li-O_2 and Li-CO_2 Batteries

摘要

Advanced lithium (Li) batteries using gaseous cathode reactants such as oxygen (O_2) and carbon dioxide (CO_2) are attractive energy storage platforms because the gases are obtained externally and thus not accounted for in the total battery weight when fully charged. The discharge products at the cathode, typically Li_2O_2 for Li-O_2 batteries and Li_2CO_3 for Li-CO_2 batteries, are insoluble in the electrolyte. Therefore, in order for such batteries to function properly, an "air cathode", which is a conductive scaffold within the battery cell, is required as a physical location for cathode electrochemical reactions to occur. Prior research has identified many carbon nanomaterials such as carbon nanotubes and graphene as viable choices for air cathode scaffold, while various metallic and metal-free catalytic systems integrated onto carbon-based air cathodes have been developed to improve the sluggish discharge and charge reactions. For future practical applications, the air cathode must exhibit a usable capacity per unit electrode area, or areal capacity, a critical parameter that has been largely overlooked so far in this field. In order to achieve high areal capacity, the air cathode must exhibit a sufficient amount of accessible void volume per unit electrode area while maintaining the conductive scaffold integrity during the entire electrochemical process.