Holey Graphene Mesh from Solvent-Free Manufacturing and Composites Thereof

This invention is for scalable methods that allows preparation of bulk quantities of holey nanocarbons with holes ranging from a few to over 100 nm in diameter. The first method uses metal particles as a catalyst (silver, copper, e.g.) and offers a wider range of hole diameter. The second method is free of catalysts altogether and offers more rapid processing in a single step with minimal product work-up requirements and does not require solvents, catalysts, flammable gases, additional chemical agents, or electrolysis. The process requires only commercially available materials and standard laboratory equipment; and, it is scalable. Properties that can be controlled include: surface area, pore volume, mechanical properties, electrical conductivity, and thermal conductivity.

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.

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.

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 technology portfolio spans several methods for dispersion and processing of CNTs in polymer resins and composites. CNT/resin systems with high dispersion and long-term stability are provided by three general approaches. One method relies on mechanical dispersion by sonication simultaneous with partial polymerization to increase the resin viscosity to maintain dispersion and enable further polymer processing of the CNT blend into films and other articles. Another approach relies on what is termed donor acceptor bonding, which essentially is a dipole bond created on the CNT/resin interface to maintain dispersion and stability of the CNT/resin blend. This dispersion method also provides advantages in mechanical properties of processed composites due to the interface characteristics. A range of polymer types can be used, including polymethyl methacrylate, polyimide, polyethylene, and others. An additional dry blending approach provides advantages for a variety of thermoplastic and thermoset systems. Use of ball mill mixing achieves effective blending and dispersion of the CNT, even at high loadings. Further processing steps using injection molding or similar melt processing methods have yielded CNT/ polymer composites with a range of useful electronic, optical, and mechanical properties.