Background:
Graphene has recently received significant attention due to its many attractive properties, including: chemical and electrochemical stability; electrical conductivity; and theoretical surface area twice as Carbon nanotubes (CNT) and about 5 times of activated carbon. Producing CNT has remained quite expensive despite several decades of research and development. In contrast, graphene can be prepared by a number of diverse routes, ranging from Carbon Vapor deposition to mechanical cleaving of graphite. In particular, thermochemical exfoliation of graphite powder has rapidly become a cost-effective method for large-scale production of graphene and graphene oxide nanosheets.
Graphene oxide nanosheets or graphene nanosheets with various functional groups, such as carboxylic acid and phenolic hydroxyl groups, attached to the edges or basal plane. Graphene oxide can be reduced to graphene. Aqueous dispersions of graphene oxide nanosheets are colloidally stable, a state generally attributed to electrostatic interactions resulting from the ionization of these functional groups. Due to the presence of oxidized functional groups, graphene oxide nanosheets are surface active. Graphene oxide can be easily reduced by thermal reduction, chemical reduction, or flash reduction to obtain reduced graphene oxide, a material that is comparable to graphene. In the majority of current research and practical applications, the processing of graphene oxide nanosheets is based on filtration of graphene oxide dispersion through a membrane filter. Concerns raised by such filtration-based methods include:(1) stacking of graphene oxide nanosheets renders a portion of the surface area inaccessible, thereby adversely affecting the electrochemical or electrical properties (e.g., capacitance) of the graphene oxide devices;(2) re-stacking of graphene oxide nanosheets during application, such as, for example, in supercapacitors where irreversible loss of capacity during cycling occurs, and is likely due to re-stacking of nanosheets during charging and discharging operation; and(3) Environmental, safety and health (ESH) concerns associated with both the processing and the application of graphene oxide, since the material is cytotoxic in its nanoscale form.
Summary:
In the present invention, granules comprising graphene nanosheets have substantially greater surface area and longer ion pathways than non-corrugated granules of comparable size. In some embodiments, the granules include a structural modifier that modifies the morphology of the granules, and increases the degree and complexity of the corrugations. The granules include reduced graphene oxide. In some embodiments, the granules are primarily reduced graphene oxide. In some embodiments, the granules are components of electrodes for capacitors.
In the present invention, an aqueous dispersion of graphene oxide nanosheets is spray-dried to form granules of graphene oxide. In some embodiments, the aqueous suspension also includes structural modifiers that modify the morphology of the granules. In some embodiments, the structural modifier is a salt having volatile components. The graphene oxide granules are reduced to modify their electrical properties. The reduced graphene oxide granules are combined with a binder to form an electrode.
Benefits:
- Less expensive method for manufacturing of granules of graphene oxide useful for fabricating electrical components.
Applications:
- Enhances the conductivity of electrical components
- Reduction in prices of graphene coated devices
Full Patent: Granules of graphene oxide by spray drying