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

Abstract

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.

Holey Graphene–Enabled Solvent-Free Preparation of Ultrahigh Mass Loading Selenium Cathodes for High Areal Capacity Lithium–Selenium Batteries

“…Compared to Li-S batteries with similarly prepared hG/S cathodes (Lin et al, 2019), the observed capacity loss for Li-Se batteries was much more severe with much lower percentages of capacity retention. Similar capacity loss was also previously observed for ultrahigh Se mass loading electrodes with a layered architectural configuration (Plaza-Rivera et al, 2020). Nevertheless, data of subsequent cycles 51-100 from the same cells of Figure 4D are shown in Supplementary Figure S2.…”

“…The dual discharge voltage plateaus were also observed at higher current densities. At the same J A , the charge reaction exhibited a single plateau at ∼2.2 V, suggesting that the intermediate steps in the reverse battery reaction were much less distinct, commonly observed in the charge reactions of Li-S and Li-Se batteries in general (Eftekhari, 2017;Lin et al, 2019;Plaza-Rivera et al, 2020).…”

Li-Ion Permeability of Holey Graphene in Solid State Batteries: A Particle Dynamics Study

“…Holey graphene (hG), also known as graphene nanomesh, is a structural derivative of graphene, formed by producing nanometer-sized holes (i.e., nanopores) using a variety of techniques − such as electron or ion-beam bombardment, nanolithography, templated growth, liquid-phase oxidation, chemical activation, gaseous-phase etching, or guided etching with catalytic or reactive nanoparticles. Significant progress has been made recently by taking advantage of the unique dry compressibility of hG for high mass loading, high areal capacity electrodes in a variety of energy-storage applications, including supercapacitors, Li-ion batteries, , Li–S/selenium (Se) batteries, , and Li-oxygen (O 2 ) batteries. , These electrodes for liquid electrolyte batteries were all prepared under solvent-free and binder-free conditions in straightforward dry-pressing processes enabled by hG. The role for hG is not only as a conductive additive but also as a dry-pressable matrix and a scaffold/binder.…”

Achieving High-Performance Li–S Batteries via Polysulfide Adjoining Interface Engineering

“…25 Meanwhile, electrolyte design is another applicable approach, and it has been signified as a simple 28 However, a high proportion of inert species, i.e., cosolvent, in the electrolyte increases the cell polarization and lowers the capacity. 29 Even if an inert cosolvent can prevent the elution of LiPSs at low Sloading levels, techniques to investigate the behavior at high Sloading levels, where high amounts of LiPSs are generated, are lacking. 26 Therefore, to address the challenges arising due to the generation of high amounts of LiPSs and the resulting electrolyte viscosity in Li−S batteries with high S-loading levels, an electrolyte design that can stabilize the electrode and electrolyte interface is in high demand.…”

“…For example, Gu et al incorporated 1,3-(1,1,2,2-tetrafluoroethoxy)­propane (FDE), wherein LiPSs had poor solubility, in a DOL/DME ratio of 4:1 to suppress LiPS dissolution and improve cell performance . However, a high proportion of inert species, i.e., cosolvent, in the electrolyte increases the cell polarization and lowers the capacity . Even if an inert cosolvent can prevent the elution of LiPSs at low S-loading levels, techniques to investigate the behavior at high S-loading levels, where high amounts of LiPSs are generated, are lacking .…”