DIRECT GROWTH OF POLYANILINE NANOTUBES ON CARBON CLOTH FOR FLEXIBLE AND HIGH-PERFORMANCE SUPERCAPACITORS

Abstract

The present disclosure further provides an exemplary energy storage device fabricated from rectangular-tube polyaniline (PANI) that is chemically synthesized by a simple and convenient method. The rectangular-tube PANI, as an active material, is synthesized on a functionalized carbon cloth (FCC) as a substrate, and the obtained composite is immobilized on a stainless steel mesh as a current collector. The present disclosure additionally presents a facile technique for the direct synthesis of PANI nanotubes, with rectangular pores, on chemically activated CC.

Claims

1. A supercapacitor comprising: two or more electrodes, wherein at least one electrode comprises a functionalized carbon electrode; a current collector; and a redox electrolyte.

2. The supercapacitor of claim 1, wherein the functionalized carbon electrode comprises: a carbon substrate comprising carbon cloth, carbon fiber, amorphous carbon, glassy carbon, carbon nanofoam, carbon aerogel, graphene foam or any combination thereof; and a conducting polymer disposed on the carbon substrate, wherein the conducting polymer comprises polyaniline, poly(p-phenylene oxide), poly(p-phenylene sulfide), poly(3,4-ethylenedioxythiophene), polypyrrole, polythiophene, poly(3-alkythiophene), poly(3-methylthiophene), poly(3-hexylthiophene), or any combination thereof.

3. The supercapacitor of claim 2, wherein the conducting polymer has a morphology of one or more nanotubes.

4. The supercapacitor of claim 3, wherein a nanotube has a length of 100 nanometers to 10,000 nanometers.

5. The supercapacitor of claim 3, wherein a nanotube has an outer width of 10 nanometers to 1,000 nanometers.

6. The supercapacitor of claim 3, wherein a nanotube has an inner width of 50 nanometers to 800 nanometers.

7. The supercapacitor of claim 3, wherein a surface of a nanotube contains a nanostructure.

8. The supercapacitor of claim 7, wherein a nanostructure comprises a nanorod, nanochain, nanofiber, nanoflake, nanoflower, nanoparticle, nanoplatelet, nanoribbon, nanoring, nanosheet, or any combination thereof.

9. The supercapacitor of claim 7, wherein a nanostructure has a length of 4 nanometers to 50 nanometers.

10. The supercapacitor of claim 7, wherein a nanostructure has a width of 4 nanometers to 50 nanometers.

11. The supercapacitor of claim 2, wherein the functionalized carbon electrode has an areal capacitance of at least 150 mF/cm.sup.2 to 750 mF/cm.sup.2.

12. The supercapacitor of claim 2, wherein the functionalized carbon electrode has a resistance, which decreases after 1,000 cycles of bending by at most 8%.

13. The supercapacitor of claim 1, wherein the redox electrolyte comprises a quinone.

14. The supercapacitor of claim 1, wherein the supercapacitor has a working potential of 0.1 V to 1.7 V.

15. The supercapacitor of claim 1, wherein the supercapacitor has a gravimetric capacitance which, after 1,000 cycles of charging, decreases by at most 26%.

16. The supercapacitor of claim 1, wherein the supercapacitor has a gravimetric capacitance which is 125 F/g to 20,000 F/g.

17. The supercapacitor of claim 1, wherein the supercapacitor has a gravimetric energy density which is 12 Wh/kg to 3,000 Wh/kg.

18. A method of fabricating a functionalized electrode comprising: a) functionalizing a carbon substrate to form a functionalized carbon substrate; b) preparing the functionalized carbon substrate; c) formulating a polymerization fluid; and d) synthesizing one or more nanotubes on the functionalized carbon substrate.

19. The method of claim 18, wherein the functionalizing of a carbon substrate to form a functionalized carbon substrate comprises: i) forming a functionalization solution; ii) heating the functionalization solution; iii) cooling the functionalization solution; iv) displacing a piece of carbon substrate into the functionalization solution; and v) rinsing a piece of functionalized carbon substrate.

20. The method of claim 19, wherein the heating of the functionalization solution occurs at a temperature of 30° C. to 120° C.

21. The method of claim 19, wherein the heating of the functionalization solution occurs for a period of time of 60 minutes to 240 minutes.

22. The method of claim 18, further comprising a step of annealing the functionalized carbon substrate before the preparing of the functionalized carbon substrate.

23. The method of claim 22, wherein the functionalized carbon substrate is annealed at a temperature of 100° C. to 400° C.

24. The method of claim 22, wherein the functionalized carbon substrate is annealed for a period of time of 0.5 hours to 14 hours.

25. The method of claim 18, wherein the preparing of the functionalized carbon substrate comprises: i) cutting a piece of the functionalized carbon substrate; ii) submerging the piece of functionalized carbon substrate in a solvent solution; iii) sonicating the piece of functionalized carbon substrate in the solvent solution; and iv) drying the piece of functionalized carbon substrate.

26. The method of claim 25, wherein the sonicating occurs for a period of time of 15 minutes to 60 minutes.

27. The method of claim 25, wherein the drying occurs at a temperature of 30° C. to 120° C.

28. The method of claim 25, wherein the drying occurs over a period of time of 3 hours to 12 hours.

29. The method of claim 18, wherein the formulating of a polymerization fluid comprises: i) forming a polymerization solution comprising: a conducting polymer; an acid; a detergent; water; and an oxidizing agent; ii) stirring the polymerization solution to form the polymerization fluid.

30. The method of claim 29, wherein the conducting polymer comprises polyaniline, poly(p-phenylene oxide), poly(p-phenylene sulfide), poly(3,4-ethylenedioxythiophene), polypyrrole, polythiophene, poly(3-alkythiophene), poly(3-methylthiophene), poly(3-hexylthiophene), or any combination thereof.

31. The method of claim 29, wherein the stirring of the polymerization solution occurs for a period of time of 10 minutes to 40 minutes.

32. The method of claim 18, wherein the synthesizing of a nanotube on the functionalized carbon substrate comprises: i) agitating the polymerization fluid; ii) immersing the functionalized carbon substrate in the polymerization fluid; iii) storing the functionalized carbon substrate in the polymerization fluid; iv) removing a functionalized carbon substrate from the polymerization fluid; v) washing the functionalized carbon substrate; and vi) drying the functionalized carbon substrate.

33. The method of claim 32, wherein the storing of the functionalized carbon substrate in the polymerization fluid occurs at a temperature of 10° C. to 50° C.

34. The method of claim 32, wherein the storing of the functionalized carbon substrate in the polymerization fluid occurs for a period of time of at least 8 hours.

35. The method of claim 32, wherein the drying of the functionalized carbon substrate occurs at a temperature of 30° C. to 120° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0122] The novel features of the methods and devices taught herein are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present methods and devices taught herein will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the methods and devices taught herein are utilized, and the accompanying drawings or figures (also “FIG.” and “FIG.s” herein), of which:

[0123] FIG. 1A illustratively depicts electron and ion transfer pathways in a nanofiber morphology of polyaniline, in accordance with some embodiments.

[0124] FIG. 1B illustratively depicts electron and ion transfer pathways in a nanosphere morphology of polyaniline (PANI), in accordance with some embodiments.

[0125] FIG. 1C illustratively depicts electron and ion transfer pathways in a nanotube morphology of polyaniline, in accordance with some embodiments.

[0126] FIG. 2 illustratively depicts an exemplary asymmetric device, in accordance with some embodiments.

[0127] FIG. 3 illustratively depicts an exemplary process of functionalizing carbon cloth, in accordance with some embodiments.

[0128] FIG. 4 illustratively depicts an example of the bonds that change through the connection between PANI and functionalized carbon cloth (FCC), in accordance with some embodiments.

[0129] FIG. 5A displays exemplary field emission scanning electron microscope (FESEM) images of PANI synthesized on carbon cloth (CC) in the presence of sodium dodecyl sulfate (SDS), in accordance with some embodiments.

[0130] FIG. 5B displays exemplary FESEM images of PANI synthesized on CC in the presence of SDS, in accordance with some embodiments.

[0131] FIG. 6A displays an exemplary FESEM image of the surface structure of a CC, in accordance with some embodiments.

[0132] FIG. 6B displays an exemplary FESEM image of a 16-hour polymerized PANI-CC in high magnification, in accordance with some embodiments.

[0133] FIG. 6C displays an exemplary FESEM image of a 16-hour polymerized PANI-CC in low magnification, in accordance with some embodiments.

[0134] FIG. 6D displays an exemplary FESEM image of a 20-hour polymerized PANI-CC, in accordance with some embodiments.

[0135] FIG. 6E displays an exemplary FESEM image of a 24-hour polymerized PANI-CC in low magnification, in accordance with some embodiments.

[0136] FIG. 6F displays an exemplary FESEM image of a 24-hour polymerized PANI-CC in high magnification, in accordance with some embodiments.

[0137] FIG. 6G displays an exemplary FESEM image of a 28-hour polymerized PANI-CC, in accordance with some embodiments.

[0138] FIG. 6H displays an exemplary FESEM image of a 32-hour polymerized PANI-CC, in accordance with some embodiments.

[0139] FIG. 7 displays exemplary cyclic voltammetry (CV) graphs of exemplary CC and PANI-CC devices, in accordance with some embodiments.

[0140] FIG. 8 displays exemplary galvanostatic charge-discharge curves of an exemplary symmetric PANI-CC device, in accordance with some embodiments.

[0141] FIG. 9 displays exemplary CV curves of exemplary PANI-CC symmetric devices with different polymerization times, in accordance with some embodiments.

[0142] FIG. 10 displays exemplary galvanostatic charge-discharge curves of exemplary PANI-CC symmetric devices with different polymerization times, in accordance with some embodiments.

[0143] FIG. 11 displays exemplary powder x-ray diffraction (XRD) patterns of exemplary carbon cloth and functionalized carbon cloth, in accordance with some embodiments.

[0144] FIG. 12 displays exemplary Fourier transform infrared (FTIR) spectroscopy spectrum measurements of exemplary PANI-FCC and PANI-CC electrodes, in accordance with some embodiments.

[0145] FIG. 13A displays exemplary CV curves of an exemplary PANI-FCC symmetric supercapacitor at a scan rate of 100 mV/s, in accordance with some embodiments.

[0146] FIG. 13B displays exemplary charge-discharge (CD) curves of an exemplary PANI-FCC symmetric supercapacitor at a current density of 1 A/g, in accordance with some embodiments.

[0147] FIG. 13C displays an exemplary Nyquist plot of CC, FCC, PANI-CC and PANI-FCC, in accordance with some embodiments.

[0148] FIG. 13D displays an exemplary Bode plot of CC, FCC, PANI-CC and PANI-FCC, in accordance with some embodiments.

[0149] FIG. 13E displays exemplary CV curves of an exemplary PANI-FCC symmetric supercapacitor under scan rates from 20 mV/s to 1000 mV/s, in accordance with some embodiments.

[0150] FIG. 13F displays exemplary CD profiles of an exemplary PANI-FCC symmetric supercapacitor at various current densities ranging from 1 to 50 A/g, in accordance with some embodiments.

[0151] FIG. 13G displays exemplary calculated capacitances as a function of current density of exemplary PANI-FCC and PANI-CC devices, in accordance with some embodiments.

[0152] FIG. 13H displays the exemplary cyclability of an exemplary PANI-FCC device at current densities of 1 to 20 A/g-1 over 5000 cycles, in accordance with some embodiments.

[0153] FIG. 14 displays exemplary CD curves of an exemplary PANI-FCC device at different currents, in accordance with some embodiments.

[0154] FIG. 15A displays exemplary CD curves of an exemplary carbon cloth.

[0155] FIG. 15B displays exemplary Nyquist plots of a PANI-FCC electrodes of various annealing times.

[0156] FIG. 16A displays an exemplary relationship between the resistance and the bending angle of an exemplary PANI-FCC device.

[0157] FIG. 16B displays an exemplary relationship between the resistance and the number of bending cycles of an exemplary PANI-FCC device, in accordance with some embodiments.

[0158] FIG. 16C displays exemplary CV curves of an exemplary bent, flat, and reopened PANI-FCC device, in accordance with some embodiments.

[0159] FIG. 17A displays exemplary CV curves of exemplary three-electrode PANI-FCC and AC-FCC devices at 20 mV/s, in accordance with some embodiments.

[0160] FIG. 17B displays an exemplary CV curve of an exemplary PANI-FCC asymmetric device at 50 mV/s, in accordance with some embodiments.

[0161] FIG. 17C displays exemplary CD curves of an exemplary asymmetric SC at various current densities, in accordance with some embodiments.

[0162] FIG. 17D displays exemplary Ragone plots of exemplary symmetric and asymmetric devices under various current densities, in accordance with some embodiments.

[0163] FIG. 18A displays exemplary CV curves of an exemplary PANI-FCC asymmetric device at different potential windows, in accordance with some embodiments.

[0164] FIG. 18B displays exemplary CV curves of an exemplary PANI-FCC asymmetric device at 50 mV/s and in H.sub.2SO.sub.4 and NQ gel electrolytes, in accordance with some embodiments.

[0165] FIG. 18C displays exemplary Nyquist plot of an exemplary PANI//AC device, in accordance with some embodiments.

[0166] FIG. 18D displays exemplary discharge curves of an exemplary PANI-FCC asymmetric device at different current densities from 2 to 50 A/g, in accordance with some embodiments.

[0167] FIG. 18E displays the calculated capacitance as a function of current density for an exemplary PANI//AC device from 5 to 50 A/g, in accordance with some embodiments.

[0168] FIG. 18F displays an exemplary Ragone plot of exemplary symmetric and asymmetric devices, in accordance with some embodiments.

[0169] FIG. 19A displays exemplary CV curves of exemplary PANI-FCC and AC-FCC electrodes, in accordance with some embodiments.

[0170] FIG. 19B displays exemplary CD curves of exemplary PANI-FCC and AC-FCC electrodes in the presence of NQ at a current density of 10 A/g, in accordance with some embodiments.

[0171] FIG. 19C displays exemplary CD curves of exemplary AC-FCC//PANI-FCC devices in the presence of NQ at different current densities, in accordance with some embodiments.

[0172] FIG. 20A displays exemplary CV curves of an exemplary asymmetric AC-FCC//PANI-FCC device in an NQ gel electrolyte, in accordance with some embodiments.

[0173] FIG. 20B displays exemplary charge and discharge curves of an exemplary asymmetric AC-FCC//PANI-FCC device with and without NQ, in accordance with some embodiments.

[0174] FIG. 20C displays the exemplary relationship between the current density and the specific capacitance of an exemplary AC-FCC//PANI-FCC device in the presence of NQ, in accordance with some embodiments.

[0175] FIG. 20D displays exemplary charge and discharge curves of an exemplary asymmetric AC-FCC//PANI-FCC device under a current density of about 47 A/g, in accordance with some embodiments.

[0176] FIG. 21 displays the exemplary relationship between the power density and the energy density of exemplary symmetric and asymmetric devices, in accordance with some embodiments.

[0177] FIG. 22 displays the gravimetric and volumetric energy densities of the components of an exemplary electrochemical cell, in accordance with some embodiments.

[0178] FIG. 23A illustratively displays an exemplary red LED powered by two exemplary asymmetric devices in series, in accordance with some embodiments.

[0179] FIG. 23B illustratively displays an exemplary a clock powered by two exemplary asymmetric devices in series, in accordance with some embodiments.

DETAILED DESCRIPTION

[0180] The market for flexible electronics such as solar cell arrays, flexible displays, and wearable electronics is rapidly growing and contributing to the design of future electronics, due to their portability, ruggedness, bendability, and rollability. The recent rapid progress in the production of flexible electronic devices over large areas, at the fraction of the cost of traditional semiconductors, has led to the development of various energy storage and power storage devices, including a wide array of flexible semiconductors of varying sizes, shapes, and mechanical properties.

[0181] As such, there are growing demands for flexible, solid-state energy storage devices that are compatible with next-generation printed and flexible electronics. To this effect, the active layer and interfaces between flexible components must be redesigned to replace the rigid components of traditional supercapacitors (SCs). As such, improving the energy density of SCs is necessary and will contribute to the technological advancement of energy storage devices.

[0182] Reducing the size, increasing the flexibility, and achieving a high energy density, integrated with the intrinsic high power density and cyclability of supercapacitors constitutes a major step forward toward more sustainable and efficient energy storage systems.

[0183] Therefore, a current unmet need exists for a battery device that is capable of recharging in seconds, that provides power over long periods of time, can be repeatedly bent without capability loss, and is as miniaturizable as other corresponding electronics components.

[0184] Provided herein are supercapacitor devices and methods for fabrication thereof. The supercapacitor devices may be electrochemical devices. The supercapacitor devices may be configured for high energy and power density. The supercapacitor devices may include an electrode composed of a rectangular-tube PANI that is chemically synthesized on a functionalized carbon cloth (FCC) substrate, and immobilized on a current collector. The supercapacitor devices may be arranged as symmetric, asymmetric, or 3D capacitors devices which contain an electrode immobilized on a current collector. The supercapacitor devices of the disclosure may comprise interconnected devices.

[0185] The present disclosure additionally provides systems and methods for growing polyaniline nanotubes on carbon cloth. The processing may include the manufacture (or synthesis) of functionalized carbon cloth and/or the manufacture (or synthesis) of polyaniline nanotubes and nanostructures. Some embodiments provide methods, devices, and systems for the manufacture (or synthesis) of functionalized carbon cloth and/or for the manufacture (or synthesis) of polyaniline nanotubes and nanostructures and/or for the manufacture (or synthesis) of electrolytes and/or for the manufacture (or synthesis) of supercapacitors. Various aspects of the disclosure described herein may be applied to any of the particular applications set forth below or in any other type of manufacturing, synthesis, or processing setting. Other manufacturing, synthesis, or processing of materials may equally benefit from features described herein. For example, the methods, devices, and systems herein may be advantageously applied to manufacture (or synthesis) of various forms of functionalized carbon. The methods and devices taught herein may be applied as a stand-alone method, device, or system, or as part of an integrated manufacturing or materials (e.g., chemicals) processing system. It shall be understood that different aspects of the methods and devices taught herein may be appreciated individually, collectively, or in combination with each other.

[0186] The present disclosure further provides an exemplary energy storage device fabricated from rectangular-tube polyaniline (PANI) that is chemically synthesized. The rectangular-tube PANI, as an active material, is synthesized on a functionalized carbon cloth (FCC) as a substrate, and the obtained composite is immobilized on a stainless steel mesh as a current collector. The present disclosure additionally presents a technique for the direct synthesis of PANI nanotubes, with rectangular pores, on chemically activated CC.

[0187] The supercapacitors described herein may play an important role in one or more applications or areas, such as, but not limited to, portable electronics (e.g., cellphones, computers, cameras, etc.), medical devices (e.g., life-sustaining and life-enhancing medical devices, including pacemakers, defibrillators, hearing aids, pain management devices, drug pumps), electric vehicles (e.g., batteries with long lifetime are needed to improve the electric vehicle industry), space (e.g., the batteries are used in space to power space systems including rovers, landers, spacesuits, and electronic equipment), military batteries (e.g., the military uses special batteries for powering a large number of electronics and equipment; reduced mass/volume of the batteries described herein are highly preferred), electric aircraft (e.g., an aircraft that runs on electric motors rather than internal combustion engines, with electricity coming from solar cells or batteries), grid scale energy storage (e.g., batteries are used to store electrical energy during times when production, from power plants, exceeds consumption and the stored energy are used at times when consumption exceeds production), renewable energy (e.g., since the sun does not shine at night and the wind does not blow at all times, batteries in off-the-grid power systems are capable of storing excess electricity from renewable energy sources for use during hours after sunset and when the wind is not blowing; high power batteries may harvest energy from solar cells with higher efficiency than current state-of-the-art batteries), power tools (e.g., the batteries described herein may enable fast-charging cordless power tools such as drills, screwdrivers, saws, wrenches, and grinders; current batteries have a long recharging time), or any combination thereof.

Supercapacitors

[0188] Supercapacitors are high-power energy storage devices with a much higher capacitance than normal capacitors. Supercapacitors (SCs) have recently attracted considerable attention as high power density energy storage resources, and have been increasingly employed energy storage resources in portable electronic devices, regenerative braking systems, voltage stabilization devices, hybrid buses, medical devices, and hybrid electric vehicles.

[0189] In some embodiments, supercapacitors or electrochemical capacitors are comprised of two or more electrodes separated by an ion-permeable membrane (separator) and an electrolyte ionically connecting the electrodes, whereas ions in the electrolyte form electric double layers of opposite polarity to the electrode's polarity when the electrodes are polarized by an applied voltage.

[0190] In some embodiments, an electrode in an electrochemical cell comprised of a substrate and an active material referred to as either an anode, whereas electrons leave the active material within cell and oxidation occurs, or a cathode, whereas the electrons enter the active material within cell and reduction occurs. Each electrode may become either the anode or the cathode depending on the direction of current through the cell. In some embodiments, the supercapacitors may be symmetric or asymmetric, wherein the electrodes are identical or dissimilar, respectively. In some embodiments, the supercapacitors are configured with two or more electrodes.

[0191] Supercapacitors store energy via three main mechanisms (i) electric double-layer capacitance (EDLC), (ii) Faradaic capacitance, and (iii) capacitance directly from redox active electrolytes. Via the first two mechanisms, only solid-phase electrode materials contribute to charge storage, while the other cell components, including electrodes and electrolyte, are electrochemically inert. The addition of a redox active species to the electrolyte enhances the cell's capacitance through electrochemical reactions at the electrode/electrolyte interface.

[0192] In some embodiments, the devices herein (e.g., supercapacitors and/or microsupercapacitors) may be configured in different structures. In some embodiments, the devices may be configured in stacked structures (e.g., comprising stacked electrodes), planar structures (e.g., comprising interdigitated electrodes), spirally wound structures, or any combination thereof. In some embodiments, the devices may be configured in a sandwich structure or an interdigitated structure.

Electrodes

[0193] Materials commonly employed in supercapacitor electrodes include transition-metal oxides, conducting polymers, and high-surface carbons. Unfortunately, however, conventional supercapacitors based on these materials may exhibit low energy densities, and are limited by the mass loading of the electrode's active materials.

[0194] In some embodiments, faradaic materials are employed as electrodes because they store charge both on the surface and in the bulk, as opposed to EDLC materials, which only store charge through ion adsorption on the electrode's surface.

[0195] In some embodiments, high-surface-area electrodes are carbonaceous and comprise carbon cloth, carbon fiber, amorphous carbon, glassy carbon, carbon nanofoam, carbon aerogel, or activated carbon (AC).

[0196] In some embodiments, AC refers to carbon that has been treated to increase its surface area. In some embodiments, the crystalline density of AC is about 0.5 g/cm.sup.3.

[0197] The conducting polymer polyaniline serves as an ideal charge storage material due to its low-cost, ease of synthesis, controllable electrical conductivity, large specific capacitance, and environmental stability.

[0198] Among the vast majority of supercapacitive component materials, polyaniline (PANI), and its different morphologies, have been used as an active material because of its intrinsic high oxidation-reduction (redox) active-specific capacitance, flexibility, and ability to convert between multiple redox states accompanied by rapid doping and dedoping of counter ions during charge and discharge processes.

[0199] In some embodiments, polyaniline (PANI) is one example of a semi-flexible rod conducting polymer which is ease to synthesize, is environmentally stable, cheap, and exhibits a high electrical conductivity and specific pseudocapacitance. Additionally, PANI may be readily converted between multiple redox states accompanied by rapid doping and dedoping of counter ions during charge and discharge processes and, as such, electron transfer in PANI is accomplished through a conjugated double bond, passing of an electric current in a coherent wrap. Finally, in some embodiments, PANI exhibits an intrinsic high oxidation-reduction (redox) active-specific capacitance and flexibility. Therefore, developing PANI-based hybrid electrodes has been an attractive topic in the hope of improving its cycling stability.

[0200] Despite being a superior energy storage material, bulk PANI, in some embodiments, suffers from poor mechanical properties and mediocre cycling stability, whereas the large volume changes associated with doping and dedoping of the counter ions destroy the polymer backbone over cycling thus dimishing capacity and limiting the potential commercial applications of PANI pseudocapacitors. As electron transfer in PANI occurs through a conjugated double bond, however, passing an electric current in a coherent wrap may be easier than electron transfer between two independent parts.

[0201] In some embodiments, the structure and geometry of PANI is altered at the nanoscale to relax its internal strain by allowing the small surface features free space to flex. In some embodiments, the PANI is functionalized, wherein new functions, features, capabilities, or properties of a material are added by changing its surface chemistry and morphology.

[0202] In some embodiments, the morphology of a faradaic electrode's materials has a significant impact on the electrochemical performance. Some electrode structures facilitate electron transfer in the active materials and, therefore, increase the conductivity and capacity of their respective devices. Nanostructuring of electrode materials represents an effective strategy towards altering the morphology of, and significantly improving the performance of, supercapacitor electrodes by increasing the interfacial area between the electrode and the electrolyte and by minimizing the ion diffusion pathway within the active materials. In some embodiments, electrode nanostructuring additionally minimizes the ion diffusion pathway within the active material.

[0203] In some embodiments, PANI has a crystalline density of about 1.3 g/cm.sup.3.

[0204] In some embodiments, the chemical and electrochemical properties of an electrode are enhanced through the addition of surface functional groups which increase charge storage capacity via the pseudocapacitive effect. In some embodiments, functionalization alters the features, capabilities, or properties of a material by changing its surface chemistry and morphology. Functionalization synthesizes several forms of surface nanostructures such as nanospheres, nanodiscs, nanowire, nanofibers, nanotubes, nanoplates, and nanoflowers. Among these, nanotube structures with small diameters allow for better accommodation of volume changes, and direct one-dimensional electronic pathway from a substrate, to allow for efficient electron transport and, therefore, provide an increased electrical conductivity and capacity. Furthermore, the combined electrolyte-exposed nanotube external and internal surface areas enable high charge storage capacities, and provide strain relief by increasing the free space available for surface flexing. This approach addresses the stability issues of silicon anodes in lithium ion batteries, which exhibit large volume changes during cycling.

[0205] In designing supercapacitor electrodes, special efforts may be made to provide a high energy density and high power density, including the optimization of the preparation conditions to facilitate ionic and electronic transport within the electrodes, as illustrated in FIGS. 1A-C. As such, the design of high-performance hybrid supercapacitors requires high-energy-high-power hybrid supercapacitor electrodes.

[0206] FIGS. 1A-C schematically illustrate high-energy-high-power hybrid supercapacitor electrode designs, with nanofiber 101, nanosphere, 102 and nanotube morphologies 103, respectively, whereas the electrode with a nanotube morphology of PANI schematically displayed in FIG. 1C is capable of improved facilitation of both the ionic current 102 (IC) and the electronic current (EC), and thus may be capable of forming a supercapacitor with a high energy and a high power.

[0207] In some embodiments, electrodes with nanostructured morphologies exhibit an increased performance, whereas per FIGS. 1A-C, the porous structure of these electrodes increases the exposure area between the active material and the electrolyte, and thus increase the discharge area compared to a solid electrode surface. Particularly, electrodes with nanotube morphologies allow for increased charge storage capacity because both the external and internal surfaces of a nanotube are exposed to an electrolyte.

Substrates

[0208] In some embodiments, carbon cloth (CC) is used as a cell substrate. In some embodiments carbon cloth comprises a woven assembly of multiple carbon fibers. In some embodiments, carbon fiber and graphite fiber are fibers composed mostly of carbon atoms. Additionally, the good electrical conductivity and flexibility of carbon cloth enables devices with low internal resistance (by providing short pathways for electron transport) and mechanical flexibility.

[0209] In some embodiments, CC is an excellent three-dimensional conductive skeleton that supports a high electrolytic-accessible surface area, provides a direct path for electron transfer, improves conductivity of its composites, and relieves the degradation accompanied by volume changes during cycling. Further, CC acts as an ideal substrate for flexible energy storage system because of its mechanical flexibility, porous structure, high electrical conductivity, short electron transport pathway, low internal resistance, high areal loading, and its ability to be easily packaged.

[0210] In some embodiments, the chemical activation of carbon cloth is enhanced through hybridization, by synthesizing conductive polymer nanostructures on the surface of the electrode. In some embodiments, the chemical and electrochemical properties of carbon cloth are modified to enhance the properties of its composite hybrid, whereas the chemical activation of CC, via the addition of functional groups onto the surface, enhances the charge storage capacity via the pseudocapacitive effect. Additionally, the functional groups on the surface of the functionalized carbon cloth allow for a stronger connection to the PANI, thus facilitating the passage of electrons from the polymer to the substrate. In some embodiments, chemical activation of a CC aids in situ polymerization by converting its naturally hydrophobic surface into a hydrophilic surface capable of increased interaction with a, typically aqueous, polymerization or monomer feed solution. In some embodiments, the in situ polymerization of a conductive polymer ensures direct electrical contact with CC, thus eliminating the need for, and the extra weight of, binders and conductive additives.

[0211] An exemplary image of the surface structure of a CC 602 displays, per FIG. 6A, a morphology comprising fibrous structures. The optimal 3D structure of CC enables high areal loading of PANI, which is an important parameter for commercially viable electrodes.

[0212] In some embodiments, carbon cloth has a crystalline density of about 1.6 g/cm.sup.3.

Electrolytes

[0213] The energy storage devices described herein may comprise an electrolyte. Electrolytes herein may include, for example but not limited to, aqueous, organic, and ionic liquid-based electrolytes, which may be in the form of a liquid, solid, or a gel. In some embodiments, an electrolyte is a solution with a uniform dispersion of cations and anions formed from an electrically conductive solute dissolved in a polar solvent.

[0214] Although electrolytes are neutral in charge, applying an electrical potential (voltage) to the solution draws the cations of the solution to the electrode with an abundance of electrons, and the anions to the electrode with an electron deficit. As such, the movement of anions and cations in opposite directions within the solution forms an energy current. Electrolytes described herein may comprise, for example, aqueous, organic, and/or ionic liquid-based electrolytes. The electrolyte may be a liquid, a solid, or a gel. An ionic liquid may be hybridized with another solid component such as, for example, polymer or silica (e.g., fumed silica), to form a gel-like electrolyte (also “ionogel” herein). An aqueous electrolyte may be hybridized with, for example, a polymer, to form a gel-like electrolyte (also “hydrogel” and “hydrogel-polymer” herein). In some cases, a hydrogel electrolyte solidifies during device fabrication, which binds the cell's components together to improve the mechanical and electrical properties of an electrode. An organic electrolyte may be hybridized with, for example, a polymer, to form a gel-like electrolyte. In some embodiments, the electrolyte may also include a lithium salt (e.g., LiPF.sub.6, LiBF.sub.4, or LiClO.sub.4). For example, the electrolyte may include a lithium salt (e.g., LiPF.sub.6, LiBF.sub.4, or LiClO.sub.4) in an organic solution (e.g., ethylene carbonate (EC), dimethyl carbonate (DMC), or diethyl carbonate (DEC). The electrolyte may comprise one or more additional components (e.g., one or more additives) to form an electrolyte composition. In one example, a soft pack polymer LIB electrolyte comprises one or more of EC, ethyl methyl carbonate (EMC), DEC, LiPF.sub.6, and other additives. In another example, a high capacity LIB electrolyte may comprise one or more of EC, DEC, propylene carbonate (PC), LiPF.sub.6, and other additives.

[0215] Quinone electrolyte additives have been employed for their ability to store 2 e.sup.−/2 H.sup.+ per quinone unit to enhance capacities in double-layer supercapacitors. During charge and discharge operations, quinone additives undergo redox processes at the electrodes. In some embodiments, quinone electrolytes are particularly excellent redox-active electrolytes because of their excellent electrochemical reversibility during charge and discharge, small size, high mobility, and an acidic pH compatible with the current family of acid-doped polymers.

Supercapacitor Device Design

[0216] In some embodiments, energy storage devices with ultrahigh energy densities are designed by selecting an electrode material in combination with an electrolyte to attain synergistic interactions among the device's components. Faradaic energy storage materials in current three-electrode devices require aqueous electrolytes for their operation which are limited to about 1.0 V due to the decomposition of water at 1.23 V. Although symmetric devices exhibit a max theoretical voltage window of 1.0 V, asymmetric devices attain the voltage window of aqueous electrolytes by extending their operating voltage beyond the thermodynamic decomposition voltage of water.

[0217] In some embodiments, a supercapacitor device that comprises PANI, which is capable of being converted between multiple redox states, as an electrochemically active material and a 1,4-naphthoquinone (NQ) redox couple electrolyte, forms a tunable double redox shuttle, whereas NQ provides pseudocapacitance through direct redox reactions on the electrode surfaces, catalyzes the regeneration of the oxidized form of PANI, and operates as a redox shuttle for the reversible oxidation/reduction of polyaniline, to considerably enhance the overall performance of the device.

[0218] The 3D nature of polyaniline rectangular tubes supported on a functionalized carbon cloth offers efficient electron and ion transport pathways and provides sufficient space for the addition of NQ, thus forming a second redox system, and thus a tunable redox shuttle in the electrolyte that enhances electron-transfer processes on the surface of the electrode. Further, the addition of NQ not only increases the capacitance of polyaniline electrodes, but also improves the capacitance of EDLC supercapacitor materials, such as activated carbons.

[0219] As such, the use of NQ, through an electrocatalytic mechanism as a redox additive, enables multiple charge transfer processes, provides Faradaic capacitance with direct redox reactions on the electrode surfaces, serves as the basis for a regenerative pathway towards long-term utilization of the electrode active materials, and enables a supercapacitor device with a much higher energy density. In some embodiments, NQ has a crystalline density of about 1.4 g/cm.sup.3.

[0220] FIG. 2 shows the composition of an exemplary supercapacitor 200, whereas the positive electrode 201 and the negative electrode 202 are separated by an ion-and-molecule-permeable membrane 203 that is soaked in an NQ electrolyte comprising sulfuric acid (H.sub.2SO.sub.4) and acetic acid (AcOH).

[0221] In some embodiments, the NQ comprises a polyvinyl alcohol (PVA) gel electrolyte in 1 M H.sub.2SO.sub.4 with 30% acetic acid (AcOH). In some embodiments a polyvinyl alcohol (PVA) gel electrolyte is formed by dissolving 1 g of PVA in 10 mL of deionized water and AcOH, vigorously stirring for 30 minutes, adding a 0.56 mL stoke of H.sub.2SO.sub.4 and adding 1.53 mg of NQ.

[0222] The NQ-promoted regeneration of polyaniline (PANI), which is capable of being reused in multiple redox reactions, plays an important role in a supercapacitor device. FIG. 4 displays the chemical process of converting a functionalized carbon cloth into a PANI functionalized carbon cloth, wherein per FIG. 2 and the equations below, PANI.sub.ox is electrochemically reduced to PANI.sub.red on the electrode surface, and NQ in the electrolyte oxidizes back the reduced form of the PANI via an EC′ regenerative mechanism that may then re-undergo electron transfer reactions on the surface.

##STR00001##

[0223] As such, the Faradaic capacitance of the device increases considerably due to the multiple reuse of the appropriate form (depending on the charge and discharge process) of polyaniline as a starting electroactive material. In addition to its electrocatalytic regenerative mechanism, NQ may undergo redox reactions on the substrate's surfaces. The combinatorial effect of NQ as both a tunable redox shuttle and a redox additive increases the performance of the supercapacitor, since energy is stored both on the polyaniline surfaces using a pseudo-capacitive mechanism and in the electrode-electrolyte interface via the redox reaction. There are several advantages as a result of the electrocatalytic reaction, which provides in situ regeneration of the electrode active materials. First, since Q=mnF, regeneration of the starting active materials increases the value of m, thus providing an additional charge in the cell. Additionally, because catalytic regeneration of the active material attains a higher current without increasing the initial mass of the active materials, reducing the mass of inactive components increases the specific energy and capacitance. Further, because additional mass is not required to increase capacitance, the system's equivalent series resistance (ESR) remains low. Moreover, because the regenerated active materials are firmly immobilized on the substrate surfaces, the ESR of the system does not increase. Also, since current is a function of the surface concentration of the active material (C.sub.AM), the electrocatalytic regeneration of the electrode active material via an EC′ mechanism remarkably increases the C.sub.AM. Finally, the electrocatalytic reaction eliminates the requirement to diffuse the electroactive materials from the bulk of the solution to the electrode surface.

Methods of Fabricating Electrodes

[0224] An exemplary process of fabricating a supercapacitor device 300 comprising fabricating a polyaniline functionalized electrode and packaging the electrode is shown in FIG. 3.

[0225] In exemplary embodiments, a method of fabricating a polyaniline functionalized electrode 305 comprises functionalizing a carbon substrate 301 to form a functionalized carbon substrate 303, preparing the functionalized carbon substrate 303, formulating a polymerization fluid 304, and synthesizing a polyaniline nanotube 306 on the functionalized carbon substrate.

[0226] In exemplary embodiments, the step of functionalizing a carbon substrate 301 to form a functionalized carbon substrate 303 comprises forming a functionalization solution 302, heating the functionalization solution 302, cooling the functionalization solution 302, displacing a piece of the carbon substrate 301 into the functionalization solution 302, and rinsing a piece of functionalized carbon substrate 303.

[0227] In an exemplary embodiment, the functionalization solution 302 comprises nitric acid (HNO.sub.3) and sulfuric acid (H.sub.2SO.sub.4), wherein the volumetric percentage of nitric acid in the functionalization solution 302 is about 15% to about 60%. In an example, the functionalization solution 302 comprises a volumetric percentage of nitric acid of about 33%.

[0228] In an exemplary embodiment, the functionalization solution 302 is heated at a suitable temperature, such as, at about 30° C. to about 120° C. In an example, the functionalization solution 302 is heated at a temperature of about 60° C. In an exemplary embodiment, the carbon substrate 301 is immersed in the functionalization solution 302 for a suitable period of time, such as, about 60 minutes to about 240 minutes. In an example, carbon substrate 301 is immersed in the functionalization solution 302 for a period of time of about 120 minutes.

[0229] In exemplary embodiments, the step of preparing the functionalized carbon substrate 303 comprises cutting a piece of the functionalized carbon substrate 303, submerging the piece of functionalized carbon substrate 303 in a polymerization fluid 304, sonicating the piece of functionalized carbon substrate 303 in the polymerization fluid 304, and drying the piece of functionalized carbon substrate 303.

[0230] In an exemplary embodiment, the functionalized carbon substrate 303 has a suitable geometric surface area, such as about 0.1 cm.sup.2 to about 0.5 cm.sup.2. In an example, the functionalized carbon substrate 303 has a suitable geometric surface area of about 0.25 cm.sup.2.

[0231] In some embodiments, the polyaniline functionalized carbon substrate 305 is then annealed in a furnace, in an air atmosphere, at 200° C. In an exemplary embodiment, the polyaniline functionalized carbon substrate 305 is annealed for a suitable period of time of about 0.5 hours to about 14 hours. In an example, the polyaniline functionalized carbon substrate 305 is annealed for a period of time of about 4 hours.

[0232] In an exemplary embodiment, the polymerization fluid 304 comprises acetone and ethanol. In an exemplary embodiment, the polymerization fluid 304 comprises a suitable volume percentage of acetone, such as, about 25% to about 100%. In an example, the volumetric percentage of acetone in the polymerization fluid 304 is about 50%.

[0233] In an exemplary embodiment, the functionalized carbon substrate 303 is sonicated for a suitable period of time, such as, about 15 minutes to about 60 minutes. In an example, the functionalized carbon substrate 303 is sonicated for a period of time of about 30 minutes.

[0234] In an exemplary embodiment, the functionalized carbon substrate 303 is dried at a suitable temperature, such as, at about 20° C. to about 120° C. In an example, functionalized carbon substrate 303 is dried at a temperature of about 60° C.

[0235] In an exemplary embodiment, the functionalized carbon substrate 303 is dried for a suitable period of time of about 3 hours to about 12 hours. In an example, the functionalized carbon substrate 303 is dried for a period of time of about 6 hours.

[0236] In exemplary embodiments, the step of formulating a polymerization fluid 304 comprises mixing polyaniline, an acid, a detergent, water, and an oxidizing agent; and stirring the polymerization solution 304. In an exemplary embodiment, the acid comprises hydrochloric acid (HCl), the detergent comprises sodium dodecyl sulfate (SDS), and the oxidizing agent comprises ammonium persulfate (APS).

[0237] In an exemplary embodiment, the polymerization fluid 304 comprises a suitable mass of polyaniline of about 20 mg to about 90 mg. In an example, the mass of polyaniline in the polymerization fluid 304 is about 45 mg.

[0238] In an exemplary embodiment, the polymerization fluid 304 comprises a suitable concentration of hydrochloric acid (HCl) of about 0.1 M to about 0.5 M. In an example, the concentration of HCl in the polymerization fluid 304 is about 0.25 M. In an exemplary embodiment, the polymerization fluid 304 comprises a suitable volume of HCl of about 0.1 ml to about 0.6 ml. In an example, the volume of HCl in the polymerization fluid 304 is about 0.3 ml.

[0239] In an exemplary embodiment, the polymerization fluid 304 comprises a suitable mass of SDS of about 1 mg to about 10 mg. In an example, the concentration of SDS in the polymerization fluid 304 is about 5 mg.

[0240] In some embodiments the water comprises deionized water. In an exemplary embodiment, the polymerization fluid 304 comprises a suitable volume of water of about 9 ml to about 40 ml. In an example, the volume of water in the polymerization fluid 304 is about 18 ml.

[0241] In an exemplary embodiment, the polymerization fluid 304 comprises a suitable concentration of APS of about 0.1 M to about 0.5 M. In an example, the concentration of APS in the polymerization fluid 304 is about 0.24 M. In an exemplary embodiment, the polymerization fluid 304 comprises a suitable volume of APS of about 1 ml to about 4 ml. In an example, the concentration of APS in the polymerization fluid 304 is about 2 ml.

[0242] In an exemplary embodiment, the polymerization fluid 304 is stirred for a suitable amount of time of about 10 minutes to about 40 minutes. In an example, the polymerization fluid 304 may be stirred for a period of about 20 minutes.

[0243] In exemplary embodiments, the step of synthesizing a polyaniline nanotube 306 on the functionalized carbon substrate 303 comprises agitating the polymerization fluid 304, immersing the functionalized carbon substrate 303 in the polymerization fluid 304, storing the functionalized carbon substrate 303 in the polymerization fluid 304, removing a polyaniline functionalized carbon substrate 305 from the polymerization fluid 304, washing the polyaniline functionalized carbon substrate 305, and drying the polyaniline functionalized carbon substrate 305.

[0244] In an exemplary embodiment, the polymerization fluid 304 is agitated for a suitable amount of time of about 15 seconds to about 60 seconds. In an example, the polymerization fluid 304 may be agitated for a period of about 30 seconds.

[0245] In an exemplary embodiment, the functionalized carbon substrate 303 is stored in the polymerization fluid 304 at a suitable temperature of about 10° C. to about 50° C. In an example, the functionalized carbon substrate 303 is stored in the polymerization fluid 304 at a temperature of about 25° C.

[0246] In an exemplary embodiment, the functionalized carbon substrate 303 is stored in the polymerization fluid 304 for a suitable polymerization time of about 8 hours to 70 hours. In an example, the functionalized carbon substrate 303 is stored in the polymerization fluid 304 for a polymerization time of about 24 hours.

[0247] In an exemplary embodiment, the polyaniline functionalized carbon substrate 305 is dried at a suitable temperature of about 30° C. to about 120° C. In an example, the polyaniline functionalized carbon substrate 305 is dried at a temperature of about 60° C.

[0248] In some embodiments, the polyaniline functionalized carbon substrate 305 is used directly as SC electrodes without the need for binders or conductive additives typically used in conventional devices.

[0249] Finally, in an exemplary embodiment, the polyaniline functionalized carbon substrate 305 is packaged into a symmetric supercapacitor device 300 whereas a separator, soaked in an electrolyte, is sandwiched between the PANI faces of two polyaniline functionalized carbon substrates 305.

[0250] The PANI functionalized cloths as electrodes, along with a stainless steel current collector and an electrolyte form symmetric (PANI-FCC//PANI-FCC or PANI-CC//PANI-CC) and asymmetric (PANI-FCC//AC) supercapacitor devices.

Characterization and Measurements

[0251] The structure and morphology of the different electrode materials may be examined using field-emission scanning electron microscopy (Philips and JEOL-JSM-6700). The structural changes before and after functionalization of CC in the strong acid mixture may be characterized using an x-ray powder diffraction (Philips X'pert diffractometer with Co Kα radiation [λ=0.178 nanometers] generated at 40 kV and 40 mA with a step size of 0.02° s.sup.−1). A spectrophotometer (Tensor 27 Bruker) may be used for performing Fourier transform infrared (FTIR) spectroscopy.

[0252] The exemplary devices are tested for their electrochemical performance using cyclic voltammetry (CV), galvanostatic charge-discharge (CD) curves, and electrochemical impedance spectroscopy (EIS) experiments. A Biologic potentiostat (SP-300) may be used to acquire cyclic voltammetry and electrochemical impedance spectroscopy data for the different devices. A battery tester (Solartron) equipped with a Cell Test software may be used for the galvanostatic CD studies.

[0253] In some embodiments, the processes described herein employ a magnetic stirrer, which comprises a laboratory device, whereas an emitted rotating magnetic field quickly spins a magnetized stir bar immersed in a liquid for quick, consistent mixing.

[0254] All the chemicals used herein are used directly as purchased, without further purification. Aniline is distilled by water steam before use.

Effect of SDS on Surface Morphology and Performance

[0255] In some embodiments, the anionic surfactant, sodium dodecyl sulfate (SDS), plays an important role as a soft template in doping, in the polymerization process upon the morphology of the synthesized PANI, and with the electrochemical properties and capacitance of the device. The SDS doping of the PANI structure generates a belt-like structure, the rolling up of which takes place subsequently, wherein further polymerization results in the formation of PANI with a rectangular-tube morphology. In some embodiments, the low concentration of HCl triggers PANI polymerization in the medium with low acidity, which slows the reaction processes and may allow for the formation of nanostructures.

[0256] In an example, FIG. 5A shows that the morphology of PANI synthesized on a CC in the presence of SDS, is formed of rectangular nanotubes 502 with PANI nanoparticles on their surfaces, wherein FIG. 5B shows that the morphology of PANI synthesized on the CC in the absence of SDS is comprised of irregular bulky nodules 503. Therefore, the PANI produced in the presence of SDS has rectangular shape with nanostructures on its surface.

[0257] In an exemplary embodiment, the length of a rectangular nanotube 502 synthesized on a CC in the presence of SDS is about 1 micrometers to 200 micrometers. In an example, the length of a rectangular nanotube 502 synthesized on a CC in the presence of SDS is about 1 micrometers.

[0258] In an exemplary embodiment, the outer diameter of a rectangular nanotube 502 synthesized on a CC in the presence of SDS is about 100 nanometers to 1,000 nanometers. In an example, the outer width of a rectangular nanotube 502 synthesized on a CC in the presence of SDS is about 350 nanometers.

[0259] In an exemplary embodiment, the inner diameter of a rectangular nanotube 502 synthesized on a CC in the presence of SDS is about 50 nanometers to 800 nanometers. In an example, the inner width of a rectangular nanotube 502 synthesized on a CC in the presence of SDS is about 250 nanometers.

[0260] In an exemplary embodiment, a nanostructure on the surface of a rectangular nanotube 502 synthesized on a CC in the presence of SDS is a nanorod. In an exemplary embodiment, the nanorod on the surface of the rectangular nanotube 502 has a length of about 4 micrometers to 50 micrometers. In an example, the nanorod on the surface of the rectangular nanotube 502 has a length of about 9 micrometers.

[0261] In an exemplary embodiment, the nanorod on the surface of a rectangular nanotube 502 synthesized on a CC in the presence of SDS has a width of about 20 nanometers to 120 nanometers. In an example, the nanorod on the surface of a rectangular nanotube 502 synthesized on a CC in the presence of SDS has a width of about 50 nanometers.

[0262] The regular hollow nanotube morphology increases electron transfer in the PANI structure synthesized in the presence of SDS. The rectangular hollow nanotube morphology of the synthesized PANI, and the nanoparticle morphology on its surface, enhances the electrochemical performance of an electrode. Per the cyclic voltammograms of the exemplary CC and PANI-CC devices in FIG. 7, the redox peaks at 0.4 V and at 0.2 V represent the reduction and oxidation, respectively, of PANI. The CV curve of PANI-CC displays its pseudocapacitive behavior and confirms the electric double-layer capacitance (EDLC) of CC in the exemplary device, and shows that the pseudocapacitance caused by PANI is dominant. The exemplary CD curves show two plateaus in the CD steps which correspond with the redox peaks of PANI in the exemplary CV curves. It is seen that the exemplary device, containing PANI synthesized in the presence SDS, exhibits a higher capacitance and rate capability per the areas under the exemplary CV curves, and the discharge times in FIGS. 7 and 8, respectively. As such, a PANI-FCC exhibits a significantly high charge/discharge current density and displays obvious redox peaks that are assigned to the redox additive.

Effect of Polymerization Time on Surface Morphology and Performance

[0263] Examples of surface morphologies exhibited by PANI synthesized on CC over different polymerization times (16, 20, 24, 28, and 32 hours) are shown in FIGS. 6A-H. A 16-hour polymerized PANI-CC 601a, per FIG. 6C in low magnification, displays a morphology of hollow rectangularly cross-sectioned PANI nanotubes on the surface of a CC, with outer diameters of about 200-500 nanometers, inner diameters of about 100-400 nm, and lengths of several micrometers. Additionally, the 16-hour polymerized PANI-CC 601a, per FIG. 6B in high magnification, displays a morphology of nanorods disorderly aligned in hierarchical structures on the surfaces of the PANI nanotubes, whose lengths and diameters range from about 100-200 nanometers and about 40-60 nanometers, respectively.

[0264] An image of an exemplary 20-hour polymerized PANI-CC 601b, as shown in FIG. 6D, exhibits a morphology of larger nanotubes, whose surfaces contain a greater size and quantity of nanorods.

[0265] An image of an exemplary 24-hour polymerized PANI-CC 601c, as shown in FIGS. 6E and 6F at low and high magnifications, respectively, exhibits a morphology of poriferous nanotubes, whose surfaces contain a uniform array of nanostructures that are 8-10 nanometers in size.

[0266] An image of an exemplary 28-hour polymerized PANI-CC 601d and a 32-hour polymerized PANI-CC 601e, per FIGS. 6G and 6H, respectively, display that as the polymerization time increases, the nanostructures on the rectangular tubes may aggregate as they grow.

[0267] FIGS. 9 and 10 display example CV and CD curves for the 16, 20, 24, 28, and 32-hour polymerized PANI-CCs in a symmetric PANI-CC device, whereas the exemplary device comprising two 24-hour polymerized PANI-CCs exhibits the highest capacitance, of about 341 F/g, and the greatest discharge time.

[0268] The increased capacitance of an exemplary device comprising a 24-hour polymerized PANI-CC may be due to the fact that its rough surface, with multiple smaller nanostructures whose diameters are between 8 nanometers and 10 nanometers, exhibits a greater surface area and a reduced diffusion length.

Functionalization Characterization

[0269] Exemplary XRD patterns for CC and FCC are displayed in FIG. 11, whereas XRD patterns of pristine CC exhibit two main characteristic diffraction peaks at 20° to 35° and 50° to 55° that are attributed to the (002) and (101) planes of the hexagonal CC structure. It is seen that CC's broad intensity peaks at 20° to 35° C. may greatly reduce due to the destruction of the CC's ordered crystalline structure, and due to the increased bond strength between C═N and COO— groups as their double bond is converted to a single bond during the functionalization process. The initial broad peak may be related to the —OH group of carboxylic acid functional group on the FCC, and the peak shift between the CC and the FCC may be explained by the stretching vibrations of C═C in the quinonoid and benzenoid rings, and the interaction of positive PANI C—N band with the negative carboxylic acid.

[0270] Per FIG. 12, an example of Fourier transform infrared (FTIR) spectrums of CC and PANI-FCC displays a strong and uniform connection between PANI and FCC, and thus provides evidence for a decreased equivalent series resistance and an increased conductance. As shown, after activation of an exemplary CC, a broad peak appears between the range of 3,300 cm.sup.−1 to 3,650 cm.sup.−1, which may indicate the presence of exchangeable protons, typically from carboxylic acid, alcohol, and amine functional groups, on the FCC. The characteristic peaks of PANI may be modified by functionalizing the CC, whereas the bonds at 1,576 cm.sup.−1 and 1,503 cm.sup.−1 corresponding to the stretching vibrations of C═C in the quinonoid and benzenoid rings, respectively, shifted slightly to 1,580 cm.sup.−1 and 1,507 cm.sup.−1. Additionally, the peak at 1,301 cm.sup.−1, associated with C—N stretching vibrations, experienced a large shift to 1,261 cm.sup.−1 revealing a strong interaction of the positive PANI C—N band with the negative carboxylic acid. Finally, the band at 1,240 cm.sup.−1, associated with C—N stretching vibrations of the exemplary device completely disappeared, which may indicate the formation of a covalent connection between the C═N and the COO— groups. Thus, FT-IR spectroscopy provides strong evidence for excellent connections between PANI and the FCC, and a decreased ESR, and thus an increased device conductance, which enables good power density at high rate charge-discharges, and improves the cycle life of a supercapacitor device.

Calculations

[0271] Capacitance is the ability of a body to store an electrical charge. Although any object may be electrically charged and exhibit capacitance, a body with a large capacitance holds more electric charge at a given voltage, than a body with a low capacitance. In some embodiments, capacitance is measured in Farads per gram (F/g).

[0272] The specific capacitance of the devices may be calculated through CD measurements using the following equation where C.sub.sp is the specific capacitance, I is the discharge current density (A), Δt is the discharge duration (s), m is the mass loading (g), and ΔV is the potential range (V).

[00001]$C_{\mathrm{sp}}=\frac{I.Math..Math.\Delta .Math..Math.t}{m.Math..Math.\Delta .Math..Math.V}$

[0273] The specific capacitance of a device with a non-linear CD curve, may be calculated using the following equation where C.sub.sp is the specific capacitance, I is the discharge current density (A), Δt is the discharge duration (s), and V is the potential range (V).

[00002]$C_{\mathrm{sp}}=\frac{2.Math.I.Math.\int \mathrm{Vdt}}{V.Math..Math.2}$

[0274] To achieve the highest working potential range, the mass ratio of the negative electrode to the positive electrode is determined according to the charge balance theory (q.sup.+=q.sup.−). The voltammetric charges (Q) may be calculated based on the following equations where C.sub.single is the specific capacitance (F/g) of each electrode measured in a three-electrode setup (calculated from cyclic voltammograms at a scan rate of 10 mV s-1), ΔV is the potential window (V), and m is the mass of the electrode (g).

Q=C.sub.single×ΔV×m

[0275] To maintain a charge balance between the two electrodes, the mass ratio between the positive (m+) and negative (m−) electrodes needs to follow:

[00003]$\frac{m_{+}}{m_{-}}=\frac{c_{-}\Delta .Math..Math.V_{-}}{c_{+}\Delta .Math..Math.V_{+}}$

[0276] Energy density (ED) may be derived from the galvanostatic discharge curves using the following equation where Csp is specific capacitance (F/g), and ΔV is the potential range (V).

[00004]$\mathrm{ED}=\frac{C_{\mathrm{sp}}.Math.\Delta .Math..Math.V^2}{2}$

[0277] The power density of the electrode is calculated from the following equation where ED is the energy density in Wh/kg, and Δt is the discharge time.

[00005]$\mathrm{PD}=\frac{\mathrm{ED}}{\Delta .Math..Math.t}$

[0278] Areal capacitance is the capacitance of a body per unit area. In some embodiments, areal capacitance is measured in Farads per cubic centimeter (F/cm.sup.2)

[0279] Current density is the electric current per cross section area, defined as a vector whose magnitude is the electric current per cross-sectional area at a given point in space. In some embodiments, current density is measured in Amps per gram (A/g).

[0280] Energy density is a measure of the amount of energy that is stored per unit mass. In some embodiments, energy density is measured in Watt hours per kilogram (Wh/kg).

[0281] Power density is a measure of the amount of power that is stored per unit mass. In some embodiments, power density is measured in kilowatts per kilogram (kW/kg).

Device Performance Characteristics

[0282] Electrochemical performance characteristics of an exemplary PANI-FCC device are shown in FIGS. 13A-H. As seen per the CV graph in FIG. 13A, pristine CC exhibits a small rectangular curve with a very low capacitance. The FCC displays a rectangular CV shape, with a higher EDLC charge storage capability, possibly due to the fact that functionalizing the carbon cloth increases its wettability, and thus facilitates the adsorption and desorption of charge. Additionally, the exemplary PANI-FCC device exhibits a more rectangularly shaped CV, and thus a higher capacitive performance, than the CV curve of the exemplary PANI-CC device, per FIG. 13C. This performance improvement is most likely related to the exemplary PANI-FCC's increased charge storage in its double-layer mechanism, the wettability of the FCC, and the absorption and desorption of charge. Additionally, it is clear that the redox peaks of the PANI that are responsible for the pseudocapacitance of the device are covered by a capacitive portion resulting from FCC, and that the redox peaks of PANI, which are responsible for the pseudocapacitance of the device, are considerably diminished by the electrical double-layer capacitance of the FCC.

[0283] As seen in FIG. 13B, an exemplary PANI-FCC device exhibits a more symmetrically shaped CD curve, and thus a higher capacitive performance, than the PANI-CC, whose CD curve is shown in FIG. 13A. Additionally, FIG. 13B displays that the infrared (IR) drop in the discharge step of the exemplary PANI-FCC device is much smaller than the infrared (IR) drop in the discharge step of the exemplary FCC and CC devices, most likely due to the increased wettability of the carbon substrate and the stronger connection between the PANI and the FCC. As functionalization of the CC may form some carboxylic acid groups with a negative charge, an electrostatic interaction may occur between the carboxylic acid groups and the anilinium ions while the FCC is immersed in the polymerization fluid. Thus, the connection between PANI and the FCC is stronger than the connection between the PANI and the CC, and more PANI is precipitated on FCC. This improvement in the capacity is most likely due to the increased interaction between PANIs and the functional groups present on the FCC substrate.

[0284] Considering the peak current densities, per FIG. 13A, and the exemplary capacitance values in FIG. 13B, the capacitance exhibited by the exemplary PANI-FCC device is about 667 F/g at a 1 A/g current density, whereas the capacitance of the exemplary PANI-CC device is about 341 F/g under the same condition. As acid treatment of the CC imposes negatively charged carboxylic group functionalities on the CC's surfaces, the immersion of the FCC into the polymerization fluid may create an electrostatic interaction between the carboxylic acid groups and the positively charged anilinium ions, which may lead to a stronger conjugation product. As such, the improvement in supercapacitive performance of the exemplary PANI-FCC device may be due to the combined effects of the better interaction between PANI and the functional groups present on the FCC substrate (i.e. the faster electron exchange between PANI and FCC), as well as the redox activity of the functional groups themselves.

[0285] Nyquist and Bode plots are shown in FIGS. 13C and 13D, respectively, for exemplary CC, FCC, PANI-CC, and PANI-FCC devices operated under an open circuit potential. Per FIG. 13C, the exemplary PANI-FCC device displays a lower equivalent series resistance, as evaluated from the x-intercept, than the exemplary PANI-CC, which confirms the low IR drop measurements shown in FIG. 13B. The Bode plot, per FIG. 13D, of the exemplary PANI-CC device also displays a larger phase angle, confirming the lower device resistance, as observed in the Nyquist plot in FIG. 13C.

[0286] Additionally, the scan rate measurements displayed in FIG. 13E from 10 mV/s to 1,000 mV/s, show that the exemplary PANI-FCC device retained a similar CV curve shape at a high scan rate of 200 mV/s, indicating a good rate capability, that is confirmed by the CD plots in FIG. 13F. The large pore volumes which may be filled with a redox active electrolyte allow for charge storage through both adsorption and redox capacitance. As expected, the electrolyte species readily inserted and de-inserted into and out of the electrode surfaces and throughout the pores of the exemplary PANI-FCC device at low scan rates, resulting in the expected rectangular response curve. As the scan rate increases, the interaction between the electrolyte species and the electrode surfaces is theoretically limited by kinetic and mass transport parameters.

[0287] In such a case, a large proportion of the substrate surfaces have little dynamic interaction with the electrolyte, possibly resulting in the non-rectangular and tilted CV curve. The similar CD example plots at different current densities (1-50 A/g), as shown in FIG. 13F serve as an additional indication of the exemplary device's good rate capability.

[0288] The exemplary PANI-FCC device also maintained its electrochemical performance, even when operated at high CD rates. FIG. 13G shows the specific capacitances as a function of the current density of the exemplary PANI-FCC device, compared with the exemplary PANI-CC device. The rate capability of the exemplary symmetric device tested at different current densities from 1 to 50 A/g shows an excellent specific capacitance of 274 F/g at a current density of 50 A/g. The specific capacitance of the exemplary PANI-FCC device (upper curve) at 20 A/g and 50 A/g is as much as about 56% and about 41% of that at 1 A/g, respectively. These results demonstrate the good rate capability of the exemplary PANI-FCC device under high current densities, which is important for practical high rate SC applications.

[0289] The capacitance retention over the long-term charge/discharge cycles is indispensable for practical SC materials. The capacitance of the exemplary PANI-FCC device is measured during CD cycling at a range of current densities (1, 2, 5, 10, and 20 A/g) over 5,000 cycles, per FIG. 13H, whereas the capacitance of the exemplary device in a current density of 1 A/g increases during the first 200 cycles, and whereas the capacitance of the exemplary device decreases during the period from 1,000 to 5,000 cycles. After 200 cycles at a current density of 1 A/g, the specific capacitance of the exemplary device decreases, and at the end of the 1,000th cycle, the exemplary device provides about 91% of its initial specific capacitance of 667 F/g. Finally, the exemplary device exhibits a capacitance retention of about 87% over 5,000 cycles, indicating very good cyclability. The inset in FIG. 13H additionally displays the 1st and 5,000th cycles of the exemplary PANI-FCC electrode at 1 A/g.

[0290] Per FIG. 14, examples of CD curves are shown for an exemplary PANI-FCC device in different currents to calculate its areal capacitance. The areal capacitance of exemplary stack is about 374 mF/cm.sup.2 in 7 mA/cm.sup.2 (equivalent to 1 A/g current).

[0291] After functionalization, an exemplary FCC is annealed in a furnace in an air atmosphere at 200° C. for 1 hour, 4 hours, or 7 hours, the exemplary PANI-(unannealed)FCC device displays a much higher discharge time than the exemplary PANI-(annealed)FCC device. As shown in FIG. 15A, increasing the annealing time increases the discharge time of the exemplary PANI-FCC device, without effecting its capacitance, most likely due to the fact that annealing reduces the number, and thus the pseudocapacitance, of the functional groups present on the CC. Additionally, FIG. 15B depicts that increasing the annealing time decreases the semicircle in the high frequency region, indicating a reduction the charge transfer resistance, most likely due to the fact that as the functional groups on the FCC decrease during annealing, the FCC conductivity increases. As such, annealing the exemplary FCC device reduces the functional pseudocapacitance, increases conductivity, and decreases the exemplary device's resistance. The period of annealing does not seem to affect the capacitance of the exemplary devices.

[0292] The performance of an exemplary device under a constant mechanical stress displays its ability to act as a flexible energy storage device. FIG. 16A shows the resistance of the exemplary PANI-FCC device decreases under mechanical stress from a flat condition at 0° to a bent condition at 180°. Additionally, FIG. 16B displays that the device's resistance, per this example, is maintained within about 4%, as it is bent from its flat to its folded condition over 1,000 cycles. The as-prepared exemplary device exhibits a high flexibility and may be bent 180° without a loss in performance. Additionally, per FIG. 16C, the exemplary PANI-FCC device maintains its rectangularly shaped CV curve and capacitance in its folded condition. This excellent performance durability of the exemplary device may be attributed to the high mechanical flexibility of the electrodes and the strong connections between FCC and PANI, and proves that such a device is suitable for flexible use.

[0293] FIGS. 17A-D display the electrochemical performance of an exemplary asymmetric device comprising a PANI-FCC positive electrode, an activated carbon negative electrode, and a 1 M H.sub.2SO.sub.4 electrolyte. Per the example measurement shown in FIG. 17A, the AC electrode has a predefined voltage potential window of 1.2 V (−0.6 to 0.6 V) which is limited by the water redox range of H.sub.2 evolution. FIGS. 17B and 17C show the CV and CD of the above exemplary device at 50 mV/s and 1 A/g, respectively, whereas the potential window for the asymmetric device is extended to the aqueous electrolyte oxidation wall of 1.3 V, beyond the capabilities of the AC electrode.

[0294] Power density and energy density are the two main parameters used to evaluate a supercapacitor device's performance. FIG. 17D depicts a Ragone plot which compares the energy densities and the power densities of the exemplary PANI-FCC symmetric and asymmetric devices over a range of current densities from 1 A/g to 50 A/g. Per FIG. 17D, the maximum energy density of the exemplary symmetric device is about 59 Wh/Kg, which decreased to about 24 Wh/kg as the power density increased from about 0.4 kW/kg to about 20 kW/kg. The energy and power density of the exemplary asymmetric device increased to about 91 Wh/kg and 33 W/kg, respectively.

[0295] FIGS. 23A and 23B display exemplary device applications, whereas two asymmetric PANI-FCC//AC devices connected in series, successfully powered a 5 mm diameter red LED 2101 indicator for about 47 minutes, and a clock 2102 for 1 h and 17 min, respectively.

[0296] NQ is an effective redox-active electrolyte which is capable of providing additional redox reactions. In one embodiment, the electrochemical performance of an exemplary PANI//AC asymmetric supercapacitor device with a 1 M H.sub.2SO.sub.4+10 millimolar NQ mixed gel electrolyte is shown in FIGS. 18A-F, whereas the addition of NQ extends the measured potential window. The CV curves of the exemplary asymmetric PANI//AC device with an NQ electrolyte at different voltage windows and at 100 mV/s are shown in FIG. 18A, whereas the potential windows are seen to extended to 1.7 V. The relationship between the potential window and the capacitance of the exemplary device is seen in the inset of FIG. 18A, whereas a 1.4 V potential window allows for the highest capacitance. FIG. 18B shows that the implementation of the H.sub.2SO.sub.4+NQ mixed electrolyte in the exemplary device increases the integrated area of cyclic voltammetry compared with H.sub.2SO.sub.4 electrolyte. The Nyquist plots of the PANI//AC devices in the mixed and uniform electrolytes, per FIG. 18C, also proves that the exemplary PANI//AC device in the mixed electrolyte exhibits a lower equivalent series resistance of 2.5Ω than in the uniform electrolyte (3.1Ω) due to the high electrical conductivity of the electrolyte. As the exemplary PANI//AC device in the mixed electrolyte additionally exhibits a smaller semicircle in the high frequency region, per the inset graph than the PANI//AC device in the H.sub.2SO.sub.4 electrolyte, the mixed electrode device exhibits a higher capacitance. Additionally, as the equivalent series resistance of the exemplary PANI//AC device in the H.sub.2SO.sub.4+NQ electrolyte, per the measurements in FIG. 18C, is lower than the calculated equivalent series resistance of the exemplary PANI//AC device without NQ, the lower charge transfer resistance of the NQ may improve the capacitance of the device through increased electron transfer. The appearance of a plateau in the discharge curve of the exemplary mixed electrolyte device, at different current densities per FIG. 18D, confirms the contribution of NQ towards increasing the discharge time to about 2,000 seconds in a current density of 2 A/g. As calculated per the values in FIG. 18D, the addition of 10 millimolar 1,4-naphthoquinon (NQ) into the 1 M H.sub.2SO.sub.4 produces a mixed electrolyte and an exemplary device which exhibits a specific capacity of about 3,200 F/g, in a current density of 1 A/g, and an energy density of about 827 Wh/kg, performing more than 8 times better than the exemplary device in the absence of NQ.

[0297] The inset of FIG. 18D, and FIG. 18E display the CD curve of the exemplary mixed electrode device at a current density of 50 A/g, and the calculated capacitance as a function of current density, respectively, which highlight the high rate capability, and capacity of about 671 F/g. Finally, FIG. 18F shows the Ragone plots of an exemplary device, with and without the presence of NQ in the electrolyte, to highlight the 8 fold positive effect of NQ on energy density.

[0298] The addition of NQ is capable of not only increasing the capacitance of the PANI redox active electrodes, but also improves the capacitance of EDLC materials such as activated carbons. FIG. 19A shows the cyclic voltammogram of an exemplary device comprising an activated carbon electrode in PVA/H.sub.2SO.sub.4 gel redox electrolyte, which demonstrates an outstanding capacitance of about 13,456 F/g. As activated carbon, with its high hydrogen evolution overpotential, may operate at more negative voltages without causing electrolyte decomposition, an exemplary asymmetric supercapacitor exhibits an extended voltage window and a controlled charge storage capacity, via a redox electrolyte that acts on the negative and positive electrodes simultaneously. FIG. 19B shows CD curves of exemplary asymmetric AC-FCC and PANI-FCC electrodes in a 3E cell (triple stacked) configuration at a current density of 10 A/g, the results of which agree with that of CV experiments. FIG. 19C depicts that the exemplary device exhibits a long discharge time of about 2,000 seconds under a current density of 2 A/g. The appearance of a new plateau in the discharge curve may confirm the contribution from NQ towards the capacitance of the exemplary device. The inset to FIG. 19C demonstrates the CD curve of the device at a very high current density (100 A/g), revealing the high rate capability of the AC-FCC//PANI-FCC device in the presence of NQ.

TABLE-US-00001 CAPACI- ENERGY VOLT- ELECTRO- TANCE DENSITY AGE DEVICE LYTE (F/g) (Wh/kg) (V) CC//CC H.sub.2SO.sub.4 8 0.7 0.8 FCC//FCC H.sub.2SO.sub.4 126 11.2 0.8 PANI//PANI H.sub.2SO.sub.4 480 42.6 0.8 0.5 mM 691 61.4 0.8 NQ-in-H.sub.2SO.sub.4 (liquid) 10 mM 710 63.1 0.8 NQ-in-H.sub.2SO.sub.4 (gel) PANI//AC H.sub.2SO.sub.4 276 64.8 1.3 0.5 mM 383 76.6 1.2 NQ-in-H.sub.2SO.sub.4 (liquid) H.sub.2SO.sub.4 314 62.8 1.2 (gel) 10 mM 5,661 @ 1,541 1.4 NQ-in-H.sub.2SO.sub.4 2 A/g (gel) PANI//PANI//PANI 10 mM 10,706 @ — −1 NQ-in-H.sub.2SO.sub.4 10 A/g (gel) AC//AC//AC 10 mM 13,456 @ — −1.1 NQ-in-H.sub.2SO.sub.4 10 A/g (gel)

[0299] FIG. 20A shows the performance of an exemplary asymmetric supercapacitor comprising a PANI-FCC positive electrode and an AC-FCC negative electrode in an acidic polymer hydrogel electrolyte with and without the redox additive. This asymmetric supercapacitor bypasses the inherently low voltage of symmetric polyaniline devices (0.8 V) and extends the operation voltage window to 1.4 V. Furthermore, the integrated area of the cyclic voltammogram is obviously much higher in the presence of the redox additive. The charge and discharge curves in FIG. 20B show a discharge time of about 6,000 seconds under a current density of 1.88 A/g, whereas in the absence of NQ the same device discharges in only 185 seconds. In other words, the specific capacitance of the device in the presence of NQ is about 5,661 F/g (2.3 F/cm.sup.2) under a current density of 1.88 A/g, which is more than 20 times higher than that in the absence of NQ.

[0300] FIG. 20C shows that the device maintains a high specific capacitance even at very high current densities of up to 94 A/g, revealing the high rate capability of the exemplary AC-FCC//PANI-FCC device in the presence of NQ.

[0301] Additionally, the charge/discharge (GCD) cycling of the AC-FCC//PANI-FCC device under a current density of 47 A/g, per FIG. 20D, indicates an 84% capacitance retention over 7,000 cycles.

[0302] FIG. 21 displays an exemplary relationship between the power density and the energy density of exemplary symmetric and asymmetric devices, in accordance with some embodiments. An exemplary redox supercapacitor constructed in accordance with the present disclosure demonstrates an outstanding energy density of 1,541 Wh/kg based on the mass of the active materials only.

Examples

[0303] In one example, an exemplary electrochemical cell has a footprint of about 1 cm.sup.2 and a thickness of about 1 millimeter, thus encompassing a volume of 0.005 cm.sup.3. In this example, the composition of the exemplary electrochemical cell is shown below.

TABLE-US-00002 Mass (g) Density (g/cm.sup.3) Volume (cm.sup.3) CC 0.005 1.55 0.0032 PANI 0.0001 1.33 7.54 × 10.sup.−5 AC 0.0001 0.5 0.0002 NQ 0.000085 1.42 5.99 × 10.sup.−5

[0304] In this example of the electrochemical cell, as the SEM images, per FIG. 5A, display that the PANI nanotubes have a porosity of about 28.4%, the actual PANI volume is calculated to be about 1.05×10.sup.−4 cm.sup.3. Additionally,

[0305] In this example, the exemplary electrochemical cell displays a capacitance, voltage, and energy of about 1.14 F, 1.4 V, and 0.0003 Wh, respectively. Additionally, FIG. 22, displays the gravimetric and volumetric densities of an asymmetric PANI//AC device with an NQ redox electrolyte and carbon cloth, as normalized by the mass and volume of the electrodes (1554 Wh/kg, 1019 Wh/L), by the mass and volume of the electrodes and the redox electrolyte (1091 Wh/kg, 851 Wh/L), and by the mass and volume of the electrodes, the redox electrolyte and the carbon cloth (59 Wh/kg. 87 Wh/L).

Terms and Definitions

[0306] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the device described herein belongs. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. Any reference to “or” herein is intended to encompass “and/or” unless otherwise stated.

[0307] As used herein, and unless otherwise specified, the term AC refers to activated carbon.

[0308] As used herein, and unless otherwise specified, the term CC refers to carbon cloth.

[0309] As used herein, and unless otherwise specified, the term FCC refers to functionalized carbon cloth.

[0310] As used herein, and unless otherwise specified, the term PANI refers to Polyaniline.

[0311] As used herein, and unless otherwise specified, the term PANI-CC refers to a carbon cloth, on which Polyaniline structures have been synthesized.

[0312] As used herein, and unless otherwise specified, the term PANI-FCC refers to a functionalized carbon cloth, on which polyaniline structures have been synthesized.

[0313] As used herein, and unless otherwise specified, the term SDS refers to sodium dodecyl sulfate.

[0314] As used herein, and unless otherwise specified, a CV chart refers to a cyclic voltammogram chart.

[0315] As used herein, and unless otherwise specified, a CD chart refers to a charge-discharge chart.

[0316] While preferable embodiments of the present methods and devices taught herein have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the methods and devices taught herein. It should be understood that various alternatives to the embodiments of the methods and devices taught herein described herein may be employed in practicing the methods and devices taught herein. It is intended that the following claims define the scope of the methods and devices taught herein and that methods and structures within the scope of these claims and their equivalents be covered thereby.

[0317] As used herein, and unless otherwise specified, the term “about” or “approximately” means an acceptable error for a particular value as determined by one of ordinary skill in the art, which depends in part on how the value is measured or determined. In certain embodiments, the term “about” or “approximately” means within 1, 2, 3, or 4 standard deviations. In certain embodiments, the term “about” or “approximately” means within 30%, 25%, 20%, 15%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, or 0.05% of a given value or range.

[0318] In certain embodiments, the term “about” or “approximately” means within 100 nanometers, 90 nanometers, 80 nanometers, 70 nanometers, 60 nanometers, 50 nanometers, 40 nanometers, 30 nanometers, 20 nanometers, 10 nanometers, 9 nanometers, nanometers, 8 nanometers, 7 nanometers, 6 nanometers, 5 nanometers, 4 nanometers, 3 nanometers, 2 nanometers, or 1 nanometers of a given value or range. In certain embodiments, the term “about” or “approximately” means within 100 mF/cm.sup.2, 90 mF/cm.sup.2, 80 mF/cm.sup.2, 70 mF/cm.sup.2, 60 mF/cm.sup.2, 50 mF/cm.sup.2, 40 mF/cm.sup.2, 30 mF/cm.sup.2, 20 mF/cm.sup.2, 10 mF/cm.sup.2, 9 mF/cm.sup.2, mF/cm.sup.2, 8 mF/cm.sup.2, 7 mF/cm.sup.2, 6 mF/cm.sup.2, 5 mF/cm.sup.2, 4 mF/cm.sup.2, 3 mF/cm.sup.2, 2 mF/cm.sup.2, or 1 mF/cm.sup.2 of a given value or range. In certain embodiments, the term “about” or “approximately” means within 5V, 4V, 3V, 2V, 1V, 0.5V, 0.1V, or 0.05V of a given value or range. In certain embodiments, the term “about” or “approximately” means within 100 F/g, 90 F/g, 80 F/g, 70 F/g, 60 F/g, 50 F/g, 40 F/g, 30 F/g, 20 F/g, 10 F/g, 9 F/g, F/g, 8 F/g, 7 F/g, 6 F/g, 5 F/g, 4 F/g, 3 F/g, 2 F/g, or 1 F/g of a given value or range. In certain embodiments, the term “about” or “approximately” means within 100 Wh/kg, 80 Wh/kg, 60 Wh/kg, 40 Wh/kg, 20 Wh/kg, 15 Wh/kg, 10 Wh/kg, 9 Wh/kg, 8 Wh/kg, 7 Wh/kg, 6 Wh/kg, 5 Wh/kg, 4 Wh/kg, 3 Wh/kg, 2 Wh/kg, 1 Wh/kg, 0.5 Wh/kg, 0.1 Wh/kg, or 0.05 Wh/kg of a given value or range. In certain embodiments, the term “about” or “approximately” means within 40° C., 30° C., 20° C., 10° C., 9° C., ° C., 8° C., 7° C., 6° C., 5° C., 4° C., 3° C., 2° C., or 1° C. of a given value or range. In certain embodiments, the term “about” or “approximately” means within 60 minutes, 50 minutes, 40 minutes, 30 minutes, 20 minutes, 10 minutes, 9 minutes, minutes, 8 minutes, 7 minutes, 6 minutes, 5 minutes, 4 minutes, 3 minutes, 2 minutes, or 1 minute of a given value or range. In certain embodiments, the term “about” or “approximately” means within 60 hours, 50 hours, 40 hours, 30 hours, 20 hours, 10 hours, 9 hours, hours, 8 hours, 7 hours, 6 hours, 5 hours, 4 hours, 3 hours, 2 hours, or 1 hour of a given value or range. In certain embodiments, the term “about” or “approximately” means within 40.0 grams, 30.0 grams, 20.0 grams, 10.0 grams, 5.0 grams, 1.0 grams, 0.9 grams, 0.8 grams, 0.7 grams, 0.6 grams, 0.5 grams, 0.4 grams, 0.3 grams, 0.2 grams or 0.1 grams, 0.05 grams, or 0.01 grams of a given value or range. In certain embodiments, the term “about” or “approximately” means within 30.0 A/g, 20.0 A/g, 10.0 A/g, 5.0 A/g, 1.0 A/g, 0.9 A/g, 0.8 A/g, 0.7 A/g, 0.6 A/g, 0.5 A/g, 0.4 A/g, 0.3 A/g, 0.2 A/g, or 0.1 A/g of a given value or range. In certain embodiments, the term “about” or “approximately” means within 20 kW/kg, 15 kW/kg, 10 kW/kg, 9 kW/kg, 8 kW/kg, 7 kW/kg, 6 kW/kg, 5 kW/kg, 4 kW/kg, 3 kW/kg, 2 kW/kg, 1 kW/kg, 0.5 kW/kg, 0.1 kW/kg, or 0.05 kW/kg of a given value or range. In certain embodiments, the term “about” or “approximately” means within 5 L, 4 L, 3 L, 2 L, 1 L, 0.5 L, 0.1 L, or 0.05 L. In certain embodiments, the term “about” or “approximately” means within 30.0 ml, 20.0 ml, 10.0 ml, 5.0 ml, 1.0 ml, 0.9 ml, 0.8 ml, 0.7 ml, 0.6 ml, 0.5 ml, 0.4 ml, 0.3 ml, 0.2 ml, or 0.1 ml of a given value or range. In certain embodiments, the term “about” or “approximately” means within 5 M, 4 M, 3 M, 2 M, 1 M, 0.5 M, 0.1 M, or 0.05 M of a given value or range.