Sustained cycling of metallic lithium negative electrodes is possible without dendrite failure in the convection battery due to the ability to effectively lower concentrations within the separator region during charge by flowing electrolyte through the negative electrode first, where lithium ions are consumed, prior to entering the separator. Consumption of lithium ions prior to entering the separator region results in a lowered concentration and reduced electrochemical potential. Additionally, convective flow reduces overall concentration gradients therefore lowering concentration overpotentials. At these lowered concentrations, dendrite formation is not thermodynamically favored as shown through the relationship between concentration, electrochemical potential and Gibbs free energy. This work presents theory, experimental validation, and autopsy (visual) verification of how the pumping of electrolyte between counter-electrodes eliminates dendrite short-circuit through the separator. Experimental validation included establishing a control using lithium particles as the negative electrode. The control consistently failed due to dendrite-based short circuit when operated without the flow of electrolyte. For the same experimental system operated with flow, the battery operated for 10 cycles (limit of study), exhibiting characteristic capacity fade at these rates. Imagery confirmed that dendrite crystals were not forming in the separator when operated during flow and that crystals did form without flow.

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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.

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Solvents and binders are typical requirements in conventional lithium ion battery electrode fabrication to enable intimate material mixing, mechanical robustness, and reproducibility. However, for high energy density conversion chemistry cathodes such as sulfur (S) and selenium (Se), the time-consuming solvent-based methods are proven unreliable to achieve high mass loading cathodes with sufficient quality. Here, we report a facile solvent-free and binder-free method to prepare high mass loading composite Se cathodes that is enabled by the use of holey graphene (hG) as a lightweight conductive scaffold. Holey graphene is a derivative of graphene and can be dry-pressed into robust discs by itself. It can also serve as a matrix to host materials such as Se for composite disc preparation in a mix-and-press process free of solvent and binder. The method allows the preparation of ultrahigh Se content cathodes (up to 90 wt% Se) and ultrahigh Se mass loading (up to 15.6 mg cm−2 in this work). These cathodes exhibit excellent Se utilization, high areal capacity (up to 9 mAh cm−2), and good rate performance. The dry-press approach also allows for the preparation of a layered composite cathode architecture, where a thin hG layer is inserted between the composite and the current collector to improve the electrical contact. A solvent-free approach is also used to prepare hG-based hybrids with metal sulfides to be incorporated into a composite cathode to help entrap soluble polyselenide intermediates. The hybrid material is compatible with the solvent-free mix-and-press electrode fabrication approach and shows promise in improving the Se retention. While further improvements are still required, this work demonstrates the outstanding potential of using this facile, solvent-free approach enabled by hG for fabrication of high-performance, high mass loading conversion chemistry cathodes.