Patent Application
20130143087
Not applicable.
Not applicable.
The present invention generally relates to carbon nanostructures in electrodes, and, more specifically, in core/shell electrode structures.
Energy storage devices are widely used in every aspects of our economy. By way of nonlimiting examples, low-capacity batteries are used as the power supply for small electronic devices, such as cellular telephones, notebook computers, and camcorders, while the high-capacity batteries are used as the power supply for driving motors in hybrid electric vehicles and the like. Recently, grid scale energy storage for renewable energy sources also needs large quantity of energy be stored and delivered quickly. As the devices used in conjunction with electrochemical energy storage devices become more complex with greater electrical demand, the energy storage device characteristics must improve.
Energy storage devices can be characterized by their cycling lifetime and their charge-discharge rates. These characteristics are primarily influenced by the positive and negative electrodes of the energy storage device. Generally, an electrode of an energy storage device includes an active material and a current collector. The active material undergoes a chemical reaction, e.g., reduction or oxidation of ions, during charging and discharging while the current collector transmits electrons between the active material and its respective terminal. Further, an electrolyte that mediates transfer of ions, e.g., lithium ions, between the positive electrode and the negative electrode.
The composition and configuration of the active material and the current collector affect the characteristics of the electrode. Charge and discharge rates of energy storage devices depend on, among other things, the electrical resistance and ion diffusion rate of the electrodes. Many high capacity electrode materials, such as LiFePO4, V2O5, have high resistance and low ion diffusion rates. Nanoparticles of the electrode material have been incorporated into the electrode to mitigate the problem. The electrodes are usually prepared by mixing nanoparticles and traditional conductive additives. Nanoparticles act to decrease the ion diffusion path thereby increasing the ion diffusion rate. To ensure the nanoparticles are in good contact with conductive additives, the amount of the additive must be high, which inevitably reduces the specific capacity of the electrode.
As electrodes proceed with the progress of the charging and discharging cycles, the electrodes expand and contract during the absorption and desorption of the ions. The expansion and contraction result in reduction in or loss of contacts between the active material and its current collector. These adverse effects result in a significantly shortened cycling lifetime. To overcome the problems associated with such mechanical degradation, several approaches have been proposed, including using nano-scaled particles as active material. However, most of prior art composite electrodes have deficiencies like less than satisfactory reversible capacity, poor cycling stability, high irreversible capacity, and ineffectiveness in reducing the internal stress or strain during the charge/discharge cycles such as lithium ion insertion and extraction cycles.
In view of the foregoing, electrode structures with higher charge-discharge rates and increased cycling lifetime would be of substantial beneficial in the art. The present invention satisfies this need and provides related advantages as well.
In general, embodiments disclosed herein relate to carbon nanostructures in core/shell electrode structures for use in energy storage devices.
In certain embodiments, an energy storage device has at least one electrode that includes a plurality carbon nanostructure (CNS)-infused fibers in contact with an active material and an electrolyte.
In certain embodiments, an energy storage device has a plurality of positive electrodes, a plurality of negative electrodes, and an electrolyte. At least one of the positive electrodes and/or at least one of the negative electrodes includes a CNS-infused fiber in contact with an active material.
In certain embodiments, an electrode has a CNS-infused fiber in contact with an active material.
In certain embodiments, a method of producing a core/shell electrode structure includes providing a CNS-infused fiber and applying an active material to the CNS-infused fiber so as to create a plurality of contact points between the active material and the CNS-infused fiber.
The foregoing has outlined rather broadly the features of the present disclosure in order that the detailed description that follows can be better understood. Additional features and advantages of the disclosure will be described hereinafter, which form the subject of the claims.
For a more complete understanding of the present disclosure, and the advantages thereof, reference is now made to the following descriptions to be taken in conjunction with the accompanying drawings describing specific embodiments of the disclosure, wherein:
The present disclosure is directed, in part, to carbon nanostructures in core/shell electrode structures for energy storage devices.
As used herein, the terms “electrochemical energy storage device” or “energy storage device” refers to a chargeable and dischargeable power storage unit. Nonlimiting examples of electrical storage devices include capacitors, ultracapacitors, supercapacitors, pseudocapacitors, batteries, low-capacity secondary batteries, high-capacity secondary batteries, ultracapacitor-battery hybrids, pseudocapacitor-battery hybrids, and energy storage cells.
As used herein, the term “carbon nanostructures” (CNS, plural CNSs) refers to a structure that is less than about 100 nm in at least one dimension and substantially made of carbon. Carbon nanostructures can include graphene, fullerenes, carbon nanotubes, bamboo-like carbon nanotubes, carbon nanohorns, carbon nanofibers, carbon quantum dots, and the like. Further, CNSs can be present as an entangled and/or interlinked network of CNSs. Interlinked networks can contain CNSs that branch in a dendrimeric fashion from other CNSs. Interlinked networks can also contain bridges between CNSs, by way of nonlimiting example, a carbon nanotube can have a least a portion of a sidewall shared with another carbon nanotube.
As used herein, the term “graphene” will refer to a single- or few-layer (e.g., less than 10 layer) two-dimensional carbon sheet having predominantly sp2 hybridized carbons. In the embodiments described herein, use of the term graphene should not be construed to be limited to any particular form of graphene unless otherwise noted.
As used herein, the term “carbon nanotube” will refer to any of a number of cylindrically-shaped allotropes of carbon of the fullerene family including single-walled carbon nanotubes (SWNTs), double-walled carbon nanotubes (DWNTs), and multi-walled carbon nanotubes (MWNTs). Carbon nanotubes can be capped by a fullerene-like structure or open-ended. Carbon nanotubes can include those that encapsulate other materials.
As used herein, the term “substrate” is intended to include any material upon which CNSs can be synthesized and can include, but is not limited to, a carbon fiber, a graphite fiber, a cellulosic fiber, a glass fiber, a metal fiber (e.g., steel, aluminum, etc.), a metallic fiber, a ceramic fiber, a metallic-ceramic fiber, a polymer fiber (e.g., nylon, polyethylene, aramid, etc.), or any substrate comprising a combination thereof. The substrate can include fibers or filaments arranged, for example, in a fiber tow (typically having about 1000 to about 12,000 fibers) as well as planar substrates such as fabrics, tapes, or other fiber broadgoods (e.g., veils, mats, and the like), and materials upon which CNSs can be synthesized.
As used herein, the term “infused” means chemically or physically bonded and “infusion” means the process of bonding. The particular manner in which a CNS is “infused” to a substrate is referred to as a “bonding motif”
Core/shell electrode structures generally comprise CNS-infused fiber in contact with an active material. Contact can involve a coating, particles intercalated in the CNS of the CNS-infused fibers, particles on the CNS of the CNS-infused fibers, or any combination thereof, nonlimiting examples of which are shown in
Examples and production methods of CNS-infused fibers can be found in U.S. Patent Application Publication Numbers 2010/0159240 entitled “CNT-Infused Metal Fiber Materials and Process Thereof,” 2010/0178825 entitled “CNT-Infused Carbon Fiber Materials and Process Thereof,” and 2011/0171469 entitled “CNT-Infused Aramid Fiber Materials and Process Thereof” and U.S. patent application Ser. No. 12/611,103 entitled “CNT-Infused Ceramic Fiber Materials and Process Thereof,” the entire disclosures of which are herein incorporated by reference. In some embodiments, CNSs of the CNS-infused fibers are aligned radially from the fiber longitudinal axis. It should be noted that the term “radially” does not imply a 90° deviation from the longitudinal axis of the fiber for all CNSs, rather an orientation the extends outward from the fiber rather than aligned with the longitudinal axis of the fiber.
The properties of the CNSs can impact the properties of the bicontinuous current collectors. In some embodiments, CNS can extend from the fiber surface about 100 nm or greater, about 500 nm or greater, about 1 micron or greater, about 5 microns or greater, or about 50 microns or greater. One skilled in the art, with the benefit of this disclosure, would understand that CNSs that extend farther from the fiber surface can be beneficial with an upper limit being in excess of about 100 microns. In some embodiments, CNSs can include CNTs. While smaller diameter CNTs are preferable, diameters in excess of about 100 nm are acceptable.
The amount of CNS-infused to the fiber can also impact the properties of the bicontinuous current collectors. In some embodiments, the density of CNSs on the fiber surface, or percent of fiber surface covered (in direct contact) with CNSs, can range from about 1% to about 95%. In some embodiments, the CNS-infused fiber can have CNS in an amount ranging from about 1% to about 80% by weight of CNS to fiber.
Fibers suitable for infusion can include, but not be limited to, carbon fibers, glass fibers, metal fibers, ceramic fibers, polymer (e.g., aramid) fibers, ceramic on glass, or any combination thereof. Examples of a carbon fiber material include, but are not limited to, a carbon filament, a carbon fiber yarn, a carbon fiber tow, a carbon tape, a carbon fiber-braid, a woven carbon fabric, a non-woven carbon fiber mat, a carbon fiber ply, and other 3D woven structures.
In some aspects of the disclosure, a number of primary fiber material structures can be organized into fabric or sheet-like structures. These include, for example, woven carbon fabrics, non-woven carbon fiber mat and carbon fiber ply, and tapes. Such higher ordered structures can be assembled from parent tows, yarns, filaments or the like, with or without CNSs already infused in the parent fiber.
Positive electrode active materials can include, but not be limited to, pure elements (sulfur), organic compounds and/or inorganic compounds like transition metal oxides, complex oxides of lithium and transition metals, metal sulfite, phosphate, sulfate or any combination thereof. Suitable organic compounds can include, but not be limited to, polyaniline, polypyrrole, polyacene, disulfide system compound, polysulfide system compound, N-fluoropyridinium salt, or any combination thereof. Suitable transition metal oxides can include, but not be limited to, oxides of Li, Fe, Co, Ni, Ru and Mn (e.g., MnOx, V2O5, V6O13, V2O5, RuOx, TiO2); or any combination thereof. Suitable complex oxides of lithium and transition metals can include, but not be limited to, lithium nickelate, lithium cobaltate, lithium manganate, LiCoO2 LiNiO2, LiMnO3, LiMn2O3, LiMnO2, LiV3O8, LiFe3O4, Cu2V2O7, LiNi1-xMxO2 (where, M=Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x=0.01 to 0.3), LiMn2-xMxO2 (where, M=Co, Ni, Fe, Cr, Zn, or Ta, and x=0.01 to 0.1), Li2Mn3MO8 (where, M=Fe, Co, Ni, Cu, or Zn), LiFePO4, AgxNiYO (wherein X/Y is smaller than 1 and not smaller than 0.25), or any combination thereof. Suitable metal sulfides can include, but not be limited to, TiIS2, FeS, MoS2, Li2S, or any combination thereof.
Negative electrode active materials can include, but not be limited to, pure elements with minimal impurities (e.g., carbons, silicon, and germanium), carbon mixtures, conductive polymers oxides, sulfates, or any combination thereof. Suitable carbons can include, but not be limited to, graphite and coke. Suitable carbon mixtures can include, but not be limited to, carbons mixed with metals, metallic salts, oxides, or any combination thereof. Suitable conductive polymers can include, but not be limited to, polyacetylene. Suitable oxides and sulfates can include, but not be limited to, oxides and sulfates of silicon, tin, zinc, manganese, iron, nickel, vanadium, antimony, lead, germanium, and/or lithium (e.g., SnO, SiSnO3, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, LiNiVO4, LiCoVO4, LiNiO2, Li0.95NiOz, LiNi0.9Co0.1Oz, LiNi0.98V0.02Oz, LiNi0.9Fe0.1Oz, LiNi0.95Mn0.05Oz, LiNi0.97Ti0.03Oz, LiNi0.97Cu0.030Oz, LiMn2O4, Li0.95Mn2Oz, LiMn1.8Co0.1Oz, LiMn0.9Fe0.1Oz, LiMn0.97Ti0.03Oz, and LiMn0.97Cu0.03Oz, wherein z is from 1.7 to 2.3); lithium transition metal nitride; calcined carbonaceous materials; spinel compounds (e.g., TiS2, LiTiS2, WO2, and LixFe(Fe2O4) wherein x is from 0.7 to 1.3); lithium compounds of Fe2O3; Nb2O5; iron oxides (e.g., FeO, Fe2O3, and Fe3O4); cobalt oxides (e.g., CoO, Co2O3, and Co3O4); and the like; or any combination thereof.
Forming contact between the CNS-infused fibers and active material can include coating CNS-infused fibers with active materials. As used herein, the term “coating,” and the like, does not imply any particular degree of coating. In particular, the terms “coat” or “coating” do not imply 100% coverage by the coating. In some embodiments, coatings can be greater than about 1 nm. One skilled in the art, with the benefit of this disclosure, would understand that the coating thickness can be to any operable upper limit which depends on the active material and the characteristics of the CNS-infused fibers. Further, one skilled in the art would understand that while excessively thick coatings may be operable, they may reduce the benefits of the core/shell electrode structures discussed herein. In some embodiments, coatings can be of thicknesses ranging from about 1 nm to about 10 microns, about 1 nm to about 1 micron, about 10 nm to about 1 micron, or about 1 nm to about 100 nm.
Forming contact between the CNS-infused fibers and active material can include particles on the CNSs and/or intercalated within the CNS network. Particles of active materials can be of any shape including, but not limited to, spherical and/or ovular, substantially spherical and/or ovular, discus and/or platelet, flake, ligamental, acicular, fibrous, polygonal (such as cubic), randomly shaped (such as the shape of crushed rocks), faceted (such as the shape of crystals), or any hybrid thereof. Particles can have a size with at least one dimension ranging from about 1 nm to about 100 microns, 1 nm to about 10 microns, about 1 nm to about 1 micron, about 10 nm to about 1 micron, or about 1 nm to about 100 nm. Particles can be a mixture of particles having different compositions, sizes, shapes, microstructures, crystal structures, or any combination thereof.
Contact between CNS-infused fibers and active materials (coatings and/or particles) can be achieved by dip coating, painting, washing, spraying, aerosolizing, sputtering, chemical reaction based deposition, electrochemical depositing, chemical vapor deposition, physical vapor deposition or any combination thereof. In some embodiments, coatings may be applied during production of the CNS-infused fibers. In some embodiments, coatings may be applied in post-production methods. In some embodiments, active materials can be applied in the form of particles, as a fluid, in a suspension, as precursors in a suspension, or any combination thereof. It should be noted that the term “suspension” includes solutions.
In some embodiments, the active materials may have a high surface area in contact with the electrolyte. In some embodiments, the surface area can range from about 0.1 m2/g to about 500 m2/g, about 1 m2/g to about 500 m2/g, about 10 m2/g to about 500 m2/g, or about 10 m2/g to about 250 m2/g.
Active materials can have several spatial arrangements relative to the CNS-infused fiber, e.g., periodically along the longitudinal axis of the fiber, more than one active material in alternating coatings along the axis of the fiber, more than one coating on the CNS-infused fiber (including multiple coatings on only portions of the CNS-infused fiber), at the ends of the CNSs distal to the fiber, intercalated between CNSs, intercalated between CNSs through to the surface of the fiber, or any combination thereof.
In some embodiments, CNSs may be functionalized to enhance contact between the active material and the CNSs. Some embodiments can involve covalent functionalization and/or non-covalent functionalization, e.g., pi-stacking, physisorption, ionic association, van der Waals association, and the like. Suitable functional groups may include, but not be limited to, moieties comprising amines (1°, 2°, or 3°), amides, carboxylic acids, aldehydes, ketones, ethers, esters, peroxides, silyls, organosilanes, hydrocarbons, aromatic hydrocarbons, or any combination thereof; polymers; chelating agents like ethylenediamine tetraacetate, diethylenetriaminepentaacetic acid, triglycollamic acid, and a structure comprising a pyrrole ring; or any combination thereof. One skilled in the art would understand that functionalization can decrease the conductivity of CNSs, and therefore, the degree of functionalization should provide the necessary enhancement in contact between the CNSs and the active material while maintaining necessary conductivity of the CNSs.
While the core/shell electrode structures describe herein can be used to form standard electrodes configurations, e.g., rods and discs, the core/shell electrode structures are advantageously flexible while being mechanically strong which provides for electrodes with woven or nonwoven fabric configurations, wound configurations, tape configurations, and the like. Electrode configurations can be individual core/shell electrode structures; a plurality of core/shell electrode structures that are aligned, wound, woven, braided, matted, and the like, or any combination thereof; or individual or a plurality of core/shell electrode structures in conjunction known electrodes.
In some embodiments, core/shell electrodes comprising CNS-infused fiber in contact with an active material can be included in an energy storage device. Generally, an energy storage device can include positive electrodes, negative electrodes, and electrolytes therebetween. Energy storage devices can further include a positive terminal connected to the positive electrodes and a negative terminal connected to the negative electrodes. Energy storage devices can further include a separator in the electrolyte to assist in the flow of ions between the positive electrodes and the negative electrodes.
Electrolytes may be in the form of solids, liquids (aqueous and/or nonaqueous), pastes, and the like. Suitable electrolytes can comprise salts like borate salts lithium salts, sodium salts, magnesium salts, iron salts, and bismuth salts (e.g., LiClO4, LiBF4, LiPF6, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2), LiCF3CO2, LiAsF6, LiSbF6, LiB10Cl10, Li(1,2-dimethoxyethane)2ClO4, lower fatty acid lithium salts, LiAlO4, LiAlCl4, LiCl, LiBr, LiI, chloroboran lithium, lithium tetraphenylborate, BiSO4HSO4); solid electrolytes containing lithium compounds like Li3PO4, Li4SiO4, and Li2SO4; polyethylene oxide added to any of the foregoing salts; organic solid electrolytes like polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohols, polyvinylidene fluoride, and polymers containing ionic dissociation groups; any derivative thereof; and the like; or any combination thereof. By way of nonlimiting examples, nonaqueous liquids may be an electrolyte in an aprotic organic solvent including, but not limited to, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, methyl propionate, ethyl propionate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, phosphoric triesters, trimethoxymethane, dioxolane derivatives, sulfolane, 3-methyl-2-oxazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethyl ether, 1,3-propanesultone, ionic liquids (e.g. methylimidazolium tetrafluoroborate), any aprotic derivative thereof, and any mixture thereof.
Separators can have a pore diameter of about 0.01 to about 10 microns and a thickness of about 5 microns to about 300 microns. Separators can be sheets or non-woven fabrics made of an olefin polymer, such as polypropylene, cellulose and modified cellulose, polyimides, glass fibers or polyethylene, or any combination thereof, which has chemical resistance and hydrophobicity. When a solid electrolyte, such as a polymer, is employed, the solid electrolyte can also serve as both the separator and the electrolyte, which may include, but not be limited to, poly(ethylene oxide), poly(vinylidene fluoride), NAFION® (a sulfonated tetrafluoroethylene based fluoropolymer-copolymer, available from DuPont), sulfonated and phosphonated polymers, or any combination thereof.
In some embodiments, energy storage devices can include core/shell electrodes according to any structure described herein as at least some of the negative electrodes, at least some of the positive electrodes, or any combination thereof. When not included as all electrodes of the energy storage device, any other electrode structure and/or configuration known to one skilled in the art may be used in conjunction with the core/shell electrodes according to any structure and/or configuration described herein. By way of nonlimiting example, other electrode structures can include fabrics, sheets, meshes, fibers, wires, and the like of active materials with thicknesses and/or diameters of about 1 nm to about 10 mm.
Energy storage devices can have any architecture of positive electrodes, negative electrodes, and electrolyte known to one skilled in the arts. By way of nonlimiting example, energy storage devices can have electrodes in a stacked architecture, a rolled architecture, an intermingled fiber architecture, any hybrid thereof, or any combination thereof. Further, energy storage devices can include electrodes in a unipolar and/or bipolar configuration.
By way of nonlimiting example,
By way of nonlimiting example,
An intermingled fiber architecture generally includes a plurality of elongated electrodes with an intermingling between the positive and negative electrodes. Intermingled fiber architectures can include, but not be limited to, wound electrodes, interwoven electrodes (either with a desired pattern or randomly), interlaced electrodes, alternating electrodes, and the like. In some embodiments, all or some of the positive electrodes can be core/shell electrode structures. In some embodiments, all or some of the negative electrodes can be core/shell electrode structures.
By way of nonlimiting example,
In some embodiments, energy storage devices according to any embodiments disclosed herein can be a component of another device and/or operably connected to another device including, but not limited to, sensors, small electronic devices, cellular telephones, notebook computers, cameras, camcorders, audio players, hybrid electric vehicles, electric grids, and the like. In some embodiments, energy storage devices according to any embodiments disclosed herein can be operably connected energy production and/or harvesting devices including, but not limited to, photovoltaics, wind turbines, fuel cells, flow batteries, and the like.
It should be noted that while some embodiments of the present application are directed toward energy storage devices that are rechargeable and dischargeable for several cycles, the electrodes, electrode configurations, energy storage device architectures, and the like may be adapted to primary storage devices like one-time use batteries.
In some embodiments, an energy storage device can include at least one electrode that comprise a plurality CNS-infused fibers in contact with an active material and an electrolyte.
In some embodiments, an energy storage device can include a plurality of positive electrodes, a plurality of negative electrodes, and an electrolyte. At least one of the positive electrodes and/or at least one of the negative electrodes can include a CNS-infused fiber in contact with an active material.
In some embodiments, an electrode can include a CNS-infused fiber in contact with an active material.
In some embodiments, a method of producing a core/shell electrode structure can include applying an active material to a CNS-infused fiber so as to create a plurality of contact points between the active material and the CNS-infused fiber.
It is understood that modifications which do not substantially affect the activity of the various embodiments of this invention are also included within the definition of the invention provided herein. Accordingly, the following Examples are intended to illustrate but not limit the present invention.
Example 1 investigated the deposition of polypyrrole on a CNS-infused carbon fiber. A CNS-infused carbon fiber was continuously fed into a deposition bath containing 0.05 M pyrrole with KCl as the supporting electrolyte. As the CNS-infused fiber was passed through the deposition bath, a positive potential was applied to the tow against a counter electrode thereby causing the pyrrole to polymerize on the surface of the CNSs. After the deposition bath, the CNS-infused fiber was rinsed to remove excess pyrrole and salt, then dried, and finally would onto a collecting spool.
It is to be understood that the above-described embodiments are merely illustrative of the present invention and that many variations of the above-described embodiments can be devised by those skilled in the art without departing from the scope of the invention. For example, in this Specification, numerous specific details are provided in order to provide a thorough description and understanding of the illustrative embodiments of the present invention. Those skilled in the art will recognize, however, that the invention can be practiced without one or more of those details, or with other processes, materials, components, etc.
Furthermore, in some instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the illustrative embodiments. It is understood that the various embodiments shown in the Figures are illustrative, and are not necessarily drawn to scale. Reference throughout the specification to “one embodiment” or “an embodiment” or “some embodiments” means that a particular feature, structure, material, or characteristic described in connection with the embodiment(s) is included in at least one embodiment of the present invention, but not necessarily all embodiments. Consequently, the appearances of the phrase “in one embodiment,” “in an embodiment,” or “in some embodiments” in various places throughout the Specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments. It is therefore intended that such variations be included within the scope of the following claims and their equivalents.
