WO2013148210A1

WO2013148210A1 - Aligned nano-scale structured carbon-oxide nanoparticle composites as electrodes in energy storage devices

Info

Publication number: WO2013148210A1
Application number: PCT/US2013/031013
Authority: WO
Inventors: George Gruner
Original assignee: University of California Berkeley; University of California San Diego UCSD
Current assignee: University of California Berkeley; University of California San Diego UCSD
Priority date: 2012-03-26
Filing date: 2013-03-13
Publication date: 2013-10-03
Anticipated expiration: 2014-09-26

Description

ALIGNED NANO-SCALE STRUCTURED CARBON-OXIDE

NANOPARTICLE COMPOSITES AS ELECTRODES IN ENERGY STORAGE DEVICES CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a nonprovisional of U.S. provisional patent

application serial number 61/615,402 filed on March 26, 2012, incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

INCORPORATION-BY-REFERENCE OF MATERIAL

SUBMITTED ON A COMPACT DISC

Not Applicable

NOTICE OF MATERIAL SUBJECT TO COPYRIGHT PROTECTION

[0004] A portion of the material in this patent document is subject to

copyright protection under the copyright laws of the United States and of other countries. The owner of the copyright rights has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the United States Patent and Trademark Office publicly available file or records, but otherwise reserves all copyright rights whatsoever. The copyright owner does not hereby waive any of its rights to have this patent document maintained in secrecy, including without limitation its rights pursuant to 37 C.F.R. § 1 .14. BACKGROUND OF THE INVENTION

[0005] 1 . Field of the Invention

[0006] This invention pertains generally to electrode architectures in energy storage devices, and more particularly to an electrode comprising aligned nano-scale structured carbon composites.

[0007] 2. Description of Related Art

[0008] Novel electrode architectures used in batteries and supercapacitors are important ingredients of increased performance of these devices.

Different approaches to this issue have been proposed. Composites that incorporate nano-scale materials are hoped to provide high electrical conductivity needed for power delivery.

[0009] However, these devices to date fail to provide a performance that meets the energy storage capacity required for a large class of applications.

[0010] Therefore, there is a need for new geometries, and compositions, capable of providing high energy and power density.

BRIEF SUMMARY OF THE INVENTION

[0011] A nano-scale structured carbon electrode apparatus is described with aligned nano-scale carbon structures. The apparatus is particularly well-suited for use within energy storage devices, such as batteries and supercapacitors.

[0012] Further aspects of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

[0013] The invention will be more fully understood by reference to the

following drawings which are for illustrative purposes only:

[0014] FIG. 1 is a side view schematic diagram of an aligned nano-scale structured carbon-oxide nanoparticle composite electrode according to an embodiment of the present invention, shown attached to a current collector.

[0015] FIG. 2 is a top view schematic diagram of the aligned nano-scale structured carbon-oxide nanoparticle composite electrode shown in FIG. 1 . [0016] FIG. 3 is a side view schematic diagram of a supercapacitor device, or battery device, according to an embodiment of the invention, shown incorporating the inventive electrode of FIG. 1 and FIG. 2.

[0017] FIG. 4 is a side view schematic diagram of an aligned nano-scale structured carbon - oxide nanoparticle - nanostructured carbon ternary composite electrode according to an embodiment of the invention.

[0018] FIG. 5 is a graph representing x-ray diffraction (XRD) counts in

relation to position, for a ΤΊΟ2 / nano-scale structured carbon composite, with the circle indicating peaks associated with the nano-scale structured carbons.

[0019] FIG. 6 is a graph of weight change with respect to temperature for the ΤΊΟ2 / carbon composite according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0020] Introduction.

[0021] The inventive electrode structure utilizes nano-scale structured

carbon and nanoparticles in a specific configuration. Before proceeding, the following defines a number of the relevant terms utilized herein.

[0022] The specification speaks of nano-scale structured carbon, which may comprise any of a number of nanoscale carbon structures, such as carbon nanotubes, and graphene.

[0023] Nanoparticles are nano-scale materials having at least one

dimension in the structure at or less than approximately 100 nm.

Nanoparticles may have a variety of shapes, including round, wire shaped, or sheets, either singular or multiple. Examples of shapes of nanoparticles include, but are not limited to, nanoparticles, nanowires, nanobelts, nanotubes, nanosheets, and combinations of nanoparticle shapes.

[0024] The use of nanoparticle oxides is addressed as the most common material interspersed between the carbon nanostructures within the present invention. It should be appreciated, for example, that various orders of oxides can be utilized according to the invention. The examples describe the use of binary oxides (e.g., xxO₂) and ternary oxides (e.g., xxO₃), as well as quinarry oxides. It will be appreciated that various orders (e.g., binary, trinary, quaternary, quinarry, and so forth), and shapes of oxide particles may be utilized without departing from the teachings of the present invention.

[0025] FIG. 1 illustrates an example embodiment 10 of a nano-scale carbon electrode structure, showing nano-scale oxide particles 12 interspersed between nano-scale structured carbon 14, attached to a conductive layer (e.g., metallic layer such as a metallic foil) 16. It will be noted that the majority of elements of the nano-scale structured carbon 14 are aligned nearly (e.g., approximately) perpendicularly to the conductive layer. These nanoparticles are preferably grown upon the carbon nanostructures. It should be appreciated that oxides are most commonly used for the application, however, one of ordinary skill in the art will recognize that other compounds with large electrochemical activity, such as sulphides, selenides, and so forth are also suitable for the application; a typical example being chalcogenides.

[0026] FIG. 2 illustrates a top view of the oxide particles 12 dispersed

between the aligned nano-scale carbon structures 14 that extend from conductive layer 16.

[0027] FIG. 3 illustrates an example embodiment of a charge storage

device, which is exemplified here as a supercapacitor. A first electrode 10 is shown with oxide nanoparticles 12 interspersed between nano-scale structured carbons 14 shown in aligned extension from conductive layer 16, as described in FIG. 1 . A second electrode 30 is a counterpart to the first electrode. This second electrode may be fabricated in any desired manner, including known electrode materials and processes, and includes at least a conductive layer. In one preferred embodiment, the second electrode comprises a non-structured carbonaceous material 32, over a conductive layer 34. Alternatively, the second electrode may comprise a similar plurality of nano-scale carbon structures containing different oxides. An electrolyte 36 is disposed between the first and second electrodes.

[0028] It will be appreciated that depending on the choice of electrode and electrolyte chemistry, FIG. 3 also describes a battery structure. It will be appreciated that the carbonaceous material 32 refers to a material that undergoes a chemical reaction, such as the release of Li ions - upon the application of a voltage. Additional materials, including different oxides, such as T1O2 and MnO2, other nanostructured carbon materials, such as graphene, can also be included for the purpose of enhancing

electrochemical activity, expanding the voltage range of the device and optimizing the interface between the vertically aligned nanotubes and the 1 st and 2nd electrode materials.

[0029] FIG. 4 illustrates an example embodiment 70 of an electrode formed including an additional nano-scale material. This example shows the addition of activated carbon 72 to the oxide nanoparticles 74 upon nano- scale structured carbon 76 over the conductive base layer 78. Including this third component leads to additional electrochemical activity and more optimal porosity, and operates as a material that establishes electrical contact between the nanotubes and oxide nanoparticles.

[0030] Vertically Aligned Nano-scale Structured Carbons.

[0031] One of ordinary skill in the art will appreciate that the plurality of vertically aligned nano-scale structured carbon can be fabricated in a number of ways. According to one example, these vertically aligned nano- scale carbon structures are fabricated by depositing metal catalysts onto a metallic surface, followed by a growth process at elevated temperatures using a gas of molecules having carbon constituents. It will be appreciated that both the density and length of the structures can be controlled by the growth conditions utilized, allowing structures (e.g., tubes) up to several hundreds of microns to be grown.

[0032] Direct Growth of Oxide Nanoparticles onto Aligned Nanotubes.

[0033] A wide range of nanoparticles have been grown onto individual

nano-scale structured carbon, or on a random array, or a film of nanotubes. Similarly, oxides can be grown on other carbon nanostructure forms. In the current invention oxide growth was also performed on graphene.

[0034] TiO₂ Direct Growth on Nanotube Surface. [0035] It is recognized that oxide nanoparticles (e.g., ΤΊΟ2) can be grown onto nano-scale structured carbon according to a number of alternate processes. For example, oxide nanoparticle growth can be initiated at nucleation sites provided by each of the plurality of nano-scale carbon structures.

[0036] The direct growth of ΤΊΟ2 on the surface of nano-scale structured carbon involves introducing the carbon nanostructures at the earliest possible stage of synthesis of the ΤΊΟ2 nanoparticles, where the nano-scale structure surface operates as a nucleation point for the ΤΊΟ2. Nano-scale structured carbon is therefore successfully dispersed in anhydrous ethanol through ultrasonication in a sonic bath for four hours. Following this, the TiCU initiator was added slowly (e.g., drop wise). The process was continued, with the exception of redispersing the nanotube / T1O2

nanocomposite with shaking rather than sonication. This was performed toward limiting the amount of disruption to the nano-scale structured carbon / T1O2 interface. The resulting product was a milky grey dispersion in the ethanol. It was decided again to carry out transmission electron

microscope (TEM) imaging to obtain a clearer picture of the interaction between the nanotubes and the T1O2. Following X-ray diffraction (XRD), thermogravimetric analysis was carried out to further evaluate the nature of the composite. Upon analyzing the resulting nanotube / T1O2

nanocomposite dispersion by TEM, a large concentration of T1O2

nanoparticles were found in close proximity to the nano-scale carbon structures.

[0037] FIG. 5 illustrates the results of XRD analysis, showing characteristic peaks of T1O2, with an additional peak, marked by the dashed circle, which indicates carbon.

[0038] Finally, the sample was analyzed using thermogravimetric analysis, wherein a considerable decrease in mass of the sample was detected once the temperature had reached 400 °C. This decrease in mass indicates decomposition of the nano-scale structured carbons.

[0039] FIG. 6 illustrates the results of the thermogravimetric analysis. It will be seen that the long broad curve in the figure is indicative of the removal of carboxylic acid groups on the surface of the nano-scale structured carbon. The remaining mass of 70 % can be attributed to TiO₂ as it typically does not decompose until over 2000 °C. The same method can be utilized for dispersing nanoparticle oxides in prefabricated aligned carbon nanostructures.

[0040] According to another example, a quinarry oxide V₂O₅ has also been grown on a plurality of nano-scale carbon structures using precursors, resulting in a random network of nanostructure / V₂O₅ architecture.

[0041] Several additional factors have to be considered in order to arrive at an architecture that leads to high electrochemical activity. Use of nanoscale TiO₂ leads to enhanced redox reaction, a reaction advantageous for high electrochemical capacitance with long cycling lifetime. This length scale should be compatible with the average distance between the vertically aligned nano-scale carbon structures. The optimal configuration is achieved when D approximates d, whereby D is the diameter of the TiO₂ nanoparticle and d is the average distance between the nano-scale carbon structures. With a typical diameter D of approximately 5 nm of the TiO₂ and a typical nano-scale structured carbon diameter of 2 nm, the density of the nanotubes is smaller than the density for vertically aligned carbon nanostructures typically used for supercapacitor electrodes.

[0042] Deposition of Oxide Nanoparticles from a Slurry or Dispersion.

[0043] Another method for constructing the inventive electrode includes using a slurry (or similarly a paste) of oxide nanoparticles that is pressed against the vertically aligned nano-scale structured carbon. Appropriate heat treatment removes the solvent and dispersants, leaving the oxide nanoparticles in direct contact with the carbon nanostructure. The method is made particularly effective, when in addition to the oxide nanoparticles, another nano-scale material that facilitates electrical contact between the nanoparticles and nanotubes are also included in the slurry. A typical example for this additionally nano-scale material is activated carbon, as was seen in FIG. 4. [0044] Including nanoparticle activated carbon as the third component can have beneficial affects is different ways. First, activated carbon can enhance the electrical interconnect between the oxide and the carbon nanostructures. Second, the presence of activated carbon can reduce the amount of electrolyte needed. The following method is an example of preparing the composite electrodes using the dispersed ΤΊΟ₂ nanoparticles combined with activated carbon. By way of example and not limitation, activated carbon is mixed with polyvinylidene fluoride (PVDF) binder (10 % weight) in N-methyl-2-pyrrolidone solvent. The mixture is sonicated in an ultrasonic bath for a period of 1 hour. T1O₂ nanoparticles dispersed in ethanol are added to the mixture and this is again sonicated for 1 hour. This mixture is placed in a fan oven at 120 °C to evaporate the ethanol. Once all ethanol has been removed, the remaining slurry is sonicated again for a further hour to ensure homogeneity. The slurry is drop cast onto the film of vertically grown carbon nanostructures, or the thick slurry is pressed onto the film in order to achieve penetration of the T1O₂ / activated carbon onto the films. The electrode / current collector is placed into an oven at 120 °C for 2 hours to evaporate the solvent and create a robust electrode. Following this process, the electrodes are removed from the oven and stored in an inert environment until measurement / use.

[0045] Devices Utilizing the Inventive Electrode.

[0046] The composite material described in the above sections can be

utilized as an electrode which is particularly well-suited for use in energy storage devices. Both supercapacitors and battery devices can be fabricated using the teaching of the present invention in combination with methods and configurations well known in the literature.

[0047] From the discussion above it will be appreciated that the invention can be embodied in various ways, including the following:

[0048] 1 . An electrode, comprising: a plurality of nano-scale structured

carbons; a conductive surface from which said nano-scale structured carbons extend; wherein said nano-scale structured carbons extend in approximately perpendicular alignment from said conductive surface; and a plurality of oxide nanoparticles, or other nanoparticle compound with large electrochemical activity, dispersed upon said nano-scale structured carbons.

[0049] 2. The electrode of any of the previous embodiments, wherein said conductive surface comprises a metallic foil.

[0050] 3. The electrode of any of the previous embodiments, wherein said electrode is a component of a charge storage device.

[0051] 4. The electrode of any of the previous embodiments, wherein said electrode comprises an electrode in a supercapacitor or a battery.

[0052] 5. The electrode of any of the previous embodiments, further

comprising non-structured carbonaceous nanoparticles dispersed upon said nano-scale structured carbon.

[0053] 6. The electrode of any of the previous embodiments, wherein said non-structured carbonaceous nanoparticles comprise activated carbon nanoparticles.

[0054] 7. The electrode of any of the previous embodiments, wherein said oxide nanoparticles comprise T1O₂ or V₂O₅ nanoparticles.

[0055] 8. The electrode of any of the previous embodiments, wherein said nanoparticle compound with large electrochemical activity is selected from the group of compounds consisting essentially of sulphides, selenides, and chalcogenides.

[0056] 9. A supercapacitor comprising: (a) a first electrode; and (b) a

second electrode, comprising at least a conductive surface, said second electrode being a counter electrode to said first electrode; (c) wherein said first electrode comprises: (i) a plurality of nano-scale carbon structures attached to a conductive surface; (ii) wherein the majority of said nano- scale carbon structures are attached to the conductive surface, and aligned perpendicular to the conductive surface, and (iii) oxide nanoparticles, or other nanoparticle compound with large electrochemical activity, dispersed within said plurality of nano-scale carbon structures; and (d) an electrolyte disposed between said first electrode and said second electrode.

[0057] 10. The supercapacitor of any of the previous embodiments, wherein said conductive surfaces comprise current collectors.

[0058] 1 1 . The supercapacitor of any of the previous embodiments, further comprising non-structured carbonaceous nanoparticles which are also dispersed within said plurality of nano-scale carbon structures.

[0059] 12. The supercapacitor of any of the previous embodiments, wherein said oxide nanoparticles comprise T1O2 or V₂O₅ nanoparticles.

[0060] 13. The supercapacitor of any of the previous embodiments, wherein said nanoparticle compounds with large electrochemical activity are selected from the group of compounds consisting essentially of sulphides, selenides and chalcogenides.

[0061] 14. A method fabricating an electrode for an energy storage device, the method comprising: (a) fabricating a plurality of nano-scale carbon structures extending approximately perpendicularly from a conductive surface from which said plurality of nano-scale carbon structures extend; and (b) dispersing a plurality of oxide nanoparticles, or other nanoparticle compound with large electrochemical activity, between the extending portions of the nano-scale carbon structures.

[0062] 15. The method of any of the previous embodiments, further

comprising dispersing carbonaceous nanoparticles between the extending portions of said plurality of nano-scale carbon structures.

[0063] 16. The method of any of the previous embodiments, wherein said dispersing of the oxide nanoparticles, or other nanoparticle compound with large electrochemical activity, is performed in response to growing said oxide nanoparticles, or other nanoparticle compound with large

electrochemical activity, directly onto an array of pre-fabricated vertically aligned nano-scale carbon structures.

[0064] 17. The method of any of the previous embodiments, wherein said dispersing of the oxide nanoparticles, or other nanoparticle compound with large electrochemical activity, is performed in response to pressing a slurry containing oxide nanoparticles, or other nanoparticle compound with large electrochemical activity, into said plurality of nano-scale carbon structures.

[0065] 18. The method of any of the previous embodiments, further comprising incubating said slurry containing to remove solvents and dispersants, leaving the said oxide nanoparticles, or other nanoparticle compound with large electrochemical activity, in direct contact with said plurality of nano-scale carbon structures.

[0066] 19. The method of any of the previous embodiments, wherein said slurry containing oxide nanoparticles, or other nanoparticle compound with large electrochemical activity, further incorporates a carbonaceous nanoparticle material.

[0067] 20. The method of any of the previous embodiments, further

comprising: incubating said slurry containing oxide nanoparticles, or other nanoparticle compound with large electrochemical activity, and

carbonaceous nanoparticle material to remove solvents and dispersants, leaving said oxide nanoparticles, or other nanoparticle compound with large electrochemical activity, in direct contact with said plurality of nano-scale carbon structures; and wherein the inclusion of said carbonaceous nanoparticle facilitates electrical contact between said oxide nanoparticles, or other nanoparticle compound with large electrochemical activity, and said plurality of nano-scale carbon structures, while reducing an amount of electrolyte needed between the electrode fabricated in said method and a counterpart electrode.

[0068] Although the description above contains many details, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Therefore, it will be appreciated that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean "one and only one" unless explicitly so stated, but rather "one or more." All structural, chemical, and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. 1 12, sixth paragraph, unless the element is expressly recited using the phrase "means for."

Claims

CLAIMS What is claimed is:

1 . An electrode, comprising:

a plurality of nano-scale structured carbons;

a conductive surface from which said nano-scale structured carbons extend;

wherein said nano-scale structured carbons extend in approximately perpendicular alignment from said conductive surface; and

a plurality of oxide nanoparticles, or other nanoparticle compound with large electrochemical activity, dispersed upon said nano-scale structured carbons.

2. The electrode recited in claim 1 , wherein said conductive surface comprises a metallic foil.

3. The electrode recited in claim 1 , wherein said electrode is a component of a charge storage device.

4. The electrode recited in claim 1 , wherein said electrode comprises an electrode in a supercapacitor or a battery.

5. The electrode recited in claim 1 , further comprising non-structured carbonaceous nanoparticles dispersed upon said nano-scale structured carbon.

6. The electrode recited in claim 5, wherein said non-structured carbonaceous nanoparticles comprise activated carbon nanoparticles.

7. The electrode recited in claim 1 , wherein said oxide nanoparticles comprise T1O2 or V₂O₅ nanoparticles.

8. The electrode recited in claim 1 , wherein said nanoparticle compound with large electrochemical activity is selected from the group of compounds consisting essentially of sulphides, selenides, and chalcogenides.

9. A supercapacitor comprising:

(a) a first electrode; and

(b) a second electrode, comprising at least a conductive surface, said second electrode being a counter electrode to said first electrode;

(c) wherein said first electrode comprises:

(i) a plurality of nano-scale carbon structures attached to a conductive surface;

(ii) wherein the majority of said nano-scale carbon structures are attached to the conductive surface, and aligned substantially perpendicular to the conductive surface, and

(iii) oxide nanoparticles, or other nanoparticle compound with large electrochemical activity, dispersed within said plurality of nano-scale carbon structures; and

(d) an electrolyte disposed between said first electrode and said second electrode.

10. The supercapacitor recited in claim 9, wherein said conductive surfaces comprise current collectors.

1 1 . The supercapacitor recited in claim 9, further comprising non- structured carbonaceous nanoparticles which are also dispersed within said plurality of nano-scale carbon structures.

12. The supercapacitor recited in claim 9, wherein said oxide

nanoparticles comprise T1O2 or V₂O₅ nanoparticles.

13. The supercapacitor recited in claim 9, wherein said nanoparticle compounds with large electrochemical activity are selected from the group of compounds consisting essentially of sulphides, selenides and chalcogenides.

14. A method of fabricating an electrode for an energy storage device, the method comprising:

(a) fabricating a plurality of nano-scale carbon structures extending approximately perpendicular from a conductive surface from which said plurality of nano-scale carbon structures extend; and

(b) dispersing a plurality of oxide nanoparticles, or other nanoparticle compound with large electrochemical activity, between the extending portions of the nano-scale carbon structures.

15. The method recited in claim 14, further comprising dispersing carbonaceous nanoparticles between the extending portions of said plurality of nano-scale carbon structures.

16. The method recited in claim 14, wherein said dispersing of the oxide nanoparticles, or other nanoparticle compound with large electrochemical activity, is performed in response to growing said oxide nanoparticles, or other

nanoparticle compound with large electrochemical activity, directly onto an array of pre-fabricated vertically aligned nano-scale carbon structures.

17. The method recited in claim 14, wherein said dispersing of the oxide nanoparticles, or other nanoparticle compound with large electrochemical activity, is performed in response to pressing a slurry containing oxide nanoparticles, or other nanoparticle compound with large electrochemical activity, into said plurality of nano-scale carbon structures.

18. The method recited in claim 17, further comprising incubating said slurry to remove solvents and dispersants, leaving the said oxide nanoparticles, or other nanoparticle compound with large electrochemical activity, in direct contact with said plurality of nano-scale carbon structures.

19. The method recited in claim 17, wherein said slurry containing oxide nanoparticles, or other nanoparticle compound with large electrochemical activity, further incorporates a carbonaceous nanoparticle material.

20. The method recited in claim 19, further comprising:

incubating said slurry containing oxide nanoparticles, or other nanoparticle compound with large electrochemical activity, and carbonaceous nanoparticle material to remove solvents and dispersants, leaving said oxide nanoparticles, or other nanoparticle compound with large electrochemical activity, in direct contact with said plurality of nano-scale carbon structures;

wherein the inclusion of said carbonaceous nanoparticle facilitates electrical contact between said oxide nanoparticles, or other nanoparticle compound with large electrochemical activity, and said plurality of nano-scale carbon structures, while reducing an amount of electrolyte needed between the electrode fabricated in said method and a counterpart electrode.