Holey Carbon Allotropes

In traditional batteries with liquid electrolytes, e.g., lithium-ion, each battery cell must be individually sealed, packaged, and electrically connected to other cells in the pack. The cells in solid-state batteries on the other hand may be stacked on top of one another with only a separation layer in between, called a bipolar plate. These bipolar plates or membranes if thin enough must be electrochemically inert to the electrode and electrolyte materials while providing electrical connectivity between the individual cells. Here, NASA has combined advances in the preparation of carbon nanomaterials and solid-state batteries to create extremely lightweight bipolar plates and membranes. These bipolar membranes will enable high energy density solid-state batteries unachievable with typical bipolar plate materials like stainless steel, aluminum, aluminum-copper, or conductive ceramics. The carbon bipolar membranes may be fabricated in multiple ways including but not limited to directly compressing carbon powders onto an electrode-electrolyte stack or separately making a film of the carbon material and dry pressing the film between other battery layers. The new bipolar membranes have been demonstrated in high energy density solid-state batteries in coin and pouch cells. The carbon bipolar membranes are at technology readiness level TRL-4 (Component and or breadboard validation in laboratory environment)and are available for patent licensing.

The electrodes are soaked in electrolyte, separated by a separator membrane and packaged into a cell assembly to form an electrochemical double layer supercapacitor. Its capacitance can be enhanced by a redox capacitance contribution through additional metal oxide to the porous structure of vertical graphene or coating the vertical graphene with an electrically conducting polymer. Vertical graphene offers high surface area and porosity and does not necessarily have to be grown in a single layer and can consist of two to ten layers. A variety of collector metals can be used, such as silicon, nickel, titanium, copper, germanium, tungsten, tantalum, molybdenum, & stainless steel. Supercapacitors are superior to batteries in that they can provide high power density (in units of kw/kg) and the ability to charge and discharge in a matter of seconds. Aside from its excellent power density, a supercapacitor also has a longer life cycle and can undergo many more charging sequences in its lifespan than batteries. This long life cycle means that supercapacitors last for longer periods of times, which alleviates environmental concerns associated with the disposal of batteries.

Fabrication of the biocapsule is accomplished by the use of a perforated mold, which allows CNTs in suspension or solution to be deposited by vacuum filtration. Other methods of creating a pressure differential between the outside of the mold and the inside of the mold can be used to drive the CNT deposition process. The mesh builds up gradually, over the course of minutes, so the thickness of the mesh can be controlled by the time of deposition. The fabrication procedure results in a mesh that is held together entirely by entanglement and non-covalent interaction between the CNTs. Filtration of CNTs onto the surface of a mold as the method of biocapsule fabrication is superior to other methods of fabrication that require assembly from multiple pieces of buckypaper, since these methods require seams in order to create a closed container. Seams result in weakness of the biocapsule and can result in leakage of the transplanted cells outside the container, which defeats the immune-shielding function of the biocapsule. The perforated mold/filtration method makes biocapsule manufacture more efficient, and makes possible a wider range of shapes of the biocapsule, to facilitate transplantation into a wider range of sites in the body. The perforated mold/filtration method also allows small beads to be incorporated into the wall of the biocapsule. Small beads, functionalized with bioactive materials, may be used to maintain the health or enhance the function of the cells inside the biocapsule, or may be used to enhance biocompatibility. The pores of the biocapsule permit gas exchange (oxygen, carbon dioxide), as well as free diffusion of metabolites, proteins and other cell products, which keep the cells healthy, and may provide useful therapeutics. Tissue or tissue fragments, and micro or nanoscale medical devices can also be placed inside the biocapsule to facilitate their implantation into the body.

Various aerospace and terrestrial applications require lightweight materials with very high mechanical properties. Carbon nanotubes and graphene sheets have been found to be such materials. In addition, they have been found to have excellent electrical and thermal transport properties. However, retaining the excellent nanoscale properties, particularly mechanical and thermal transport, in bulk materials has proven to be challenging. In order for the nanotubes to be used in applications, they must be spun into yarn(s), sheet(s), and other macroscopic forms introducing relatively weak tube-to-tube and inter-bundle bonds. Also, the nanotubes tend to be entangled, and they therefore do not all contribute in load bearing. Weak coupling at tube and bundle interfaces also leads to mechanical and thermal transport that are much lower than would be expected from the nanoscale carbon nanotube or graphene properties. This invention is for consolidated carbon nanotube or graphene yarns and woven sheets via the formation of a carbon binder formed from the dehydration of sucrose. The resulting materials are lightweight and possess a high specific modulus and/or strength on the macro-scale. Sucrose is relatively inexpensive and readily available, leading to a cost-effective route for achieving bulk nanotube/graphene based multifunctional material formats.

The HGM or composite HGM developed is a novel nanocarbon-based architecture that (1) is prepared from dry processing from commercially available starting materials or readily prepared composites thereof; (2) exhibits micropores and mesopores due to the holey graphene sheets and their stacking; (3) exhibits micron- and macro-sized pores in the article. The method can produce a range of high-fidelity hole size, shape, and distribution on the graphene or composite articles. The disclosed laser-based method is easily scaled-up and automatable. The result is a novel ultra-lightweight graphene-based mesh structure with high electrical conductivity, thermal conductivity, high surface area, high through-thickness unimpeded ion transport, mechanical robustness. The HGM-based composites utilize HGM as a novel framework, matrix, or substrate for secondary components that are active for energy storage, catalysis, sensing, optical, filtration, and biological applications.