Dry Pressing Neat Active Materials into Ultrahigh Mass Loading Sandwich Cathodes Enabled by Holey Graphene Scaffold

High areal performance from high cathode mass loading is an essential requirement to bring battery chemistries beyond the lithium (Li) ion, such as lithium-sulfur (Li-S) or lithium-selenium (Li-Se), toward practical applications. These conversion chemistry cathodes have been typically prepared by using conventional slurry-based techniques widely used for Li ion battery electrodes, requiring the use of solvent and binder and multiple steps such as mixing, casting, drying, and collecting and proper disposing of organic solvents. To increase active material mass loading, the processing steps become even more time-consuming when multiple casting-drying cycles are needed. Here we report an extremely facile procedure to prepare ultrahigh mass loading (>15 mg/cm2) with high active material content (>70%) conversion chemistry cathodes in a single step directly from neat active material, such as sulfur (S), selenium (Se), or selenium sulfide (SeS2), without the need of solvent or binder. This is achieved by the use of holey graphene (hG), a unique lightweight material that can be dry pressed by itself or as a host into neat or composite electrode forms. In the electrode preparation, hG, the neat active material, and hG are sequentially added to the pressing die, resulting in a sandwich architecture containing a neat active material layer with conveniently tunable ultrahigh mass loading. The sandwich electrodes exhibit excellent overall electrochemical performance with great active material utilization. Mechanistically, when Se is used as the example active material, the neat Se layer becomes electrochemically redistributed throughout the entire cathode thickness after the first cycle. The sandwich cathode not only does not crack or fail but also spontaneously densifies for stable and prolonged cycling. The sandwich electrode architecture is also compatible with the use of a fluorinated electrolyte solvent to significantly reduce polyselenide solubility and shuttling for improved cycling performance. Such sandwich electrodes from the hG-enabled, one-step, dry-press method offer an attractive fast fabrication option in bulk production of ultrahigh mass loading cathodes for practical applications.