Architecture Transformations of Ultrahigh Areal Capacity Air Cathodes for Lithium‐Oxygen Batteries

Abstract

AbstractLithium‐oxygen (Li−O2) batteries have the highest known theoretical energy density but are still not practical for use in most applications. A key aspect that has been largely overlooked in the field is how to improve the reversible areal capacity of the air cathode to a competitive level (>5–10 mAh cm−2). For carbon‐based air cathodes, increase of areal capacity requires a corresponding increase of carbon mass loading. As a result, the electrode thickness also increases which impedes the mass transport of Li ions and O2 needed for battery reactions. It is therefore imperative to investigate not only the air cathode composition, but also its dimensional architecture, for the effective function of high areal capacity Li−O2 batteries. Herein, we present the use of several representative additives of carbon‐based nanomaterials, including carbon black, two different diameters of multi‐walled carbon nanotubes, and graphene materials from two sources, into a high mass loading (10 mg cm−2), ultrathick (∼100 μm) air cathode architectural platform matrix based on dry‐compressed holey graphene. The performances of these all‐carbon composite air cathodes differ from that of the neat holey graphene, but not by a simple addition or subtraction effect. In addition, the additive effects to full discharge and curtailed cycling experiments are significantly different. The presented results strongly suggest that the architectural volume expandability is critical for the full discharge properties. However, the cycling performance depends more upon the resilience of the air cathode architecture (“breathability”), which does not necessarily correlate with its expandability.