Electrochemical capacitor

An electroactive material for charge storage and transport in an electrochemical capacitor. The material is formed of a plurality of nanocomponents including nanoparticles, in turn formed of conductive carbon-based clusters bound together by a conductive carbon-based cluster binder including nanoclusters and nanocluster binders, all having high densities of mobile charge carriers (electrons, electronic acceptors, ionic species). A terminal is electrically coupled to the nanoparticles for charge transport.

TECHNICAL FIELD

The present invention relates to electrodes and electrochemical devices having electrodes that undergo electrochemical reactions and particularly to nanomaterial electrodes and devices.

BACKGROUND OF THE INVENTION

Nanomaterials are materials that include components with nanometer dimensions, for example, where at least one dimension is less than 100 nanometers. Examples of such materials are allotropes of carbon such as nanotubes or other carbon fullerenes and components of carbon char. Carbon black was an early use of nanomaterials in tire manufacturing. Other nanomaterials include inorganic materials such as metal sulfides, metal oxides and organic materials. Because of the small dimensions, nanomaterials often exhibit unique electrical and electrochemical properties and unique energy transport properties. These properties are most pronounced when high surface areas are present and when charge transport mechanisms exist in the nanomaterials.

Some nanomaterials are manufactured using rigorous processing steps that are expensive and commercially unattractive. Some nanomaterials occur naturally or incidentally in commercial processing steps. Naturally or incidentally occurring nanomaterials tend to be highly irregular in size and composition because the environment in which they are produced is not adequately controlled for the production of nanomaterials. Processing methods that produce nanomaterials include among others, liquid-phase steps, gas-phase steps, grinding steps, size-reduction steps and pyrolysis steps.

Pyrolysis is the heating of materials in the absence of oxygen to break down complex matter into simpler molecules and components. When carbon based materials are pyrolyzed, the process of carbonization can occur leading to an ordered state of semi-graphitic material. When carbon based materials are pyrolyzed in uncontrolled conditions, a large amount of randomly ordered carbon material results. When both carbon and inorganic materials are present, pyrolysis under controlled conditions can lead to highly useful and unique results. An example of a use of pyrolysis is for the break down of used tires (typically from automobiles, trucks and other vehicles). The pyrolysis of tires results in, among other things, a carbon/inorganic residue called char.

The composition of char from tire pyrolysis is determined by the materials that are used to manufacture tires. The principal materials used to manufacture tires include rubber (natural and synthetic), carbon black (to give strength and abrasion resistance), sulfur (to cross-link the rubber molecules in a heating process known as vulcanization), accelerator metal oxides (to speed up vulcanization), activation inorganic oxides (principally zinc oxide, to assist the vulcanization), antioxidant oxides (to prevent sidewall cracking), a textile fabric (to reinforce the carcass of the tire) and steel belts for strength. The carbon black has a number of carbon structures including graphitic spheroids with nanometer dimensions, semi graphitic particles and other forms of ordered carbon structures.

In summary, the manufacture of tires initially mixes the materials to form a “green” tire where the carbons and oxides form a homogenous mixture. The “green” tire is transformed into a finished tire by the curing process (vulcanization) where heat and pressure are applied to the “green” tire for a prescribed “cure” time. The carbon materials used in “green” tires are typically as indicated in TABLE 1:

When tires are discarded, they are collected for pyrolysis processing to reclaim useful components of the tires. In general, tire pyrolysis involves the thermal degradation of the tires in the absence of oxygen. Tire pyrolysis has been used to convert tires into value-added products such as pyrolytic gas (pyro-gas), oils, char and steel. Pyrolysis is performed with low emissions and other steps that do not have an adverse impact on the environment. The basic pyrolysis process involves the heating of tires in the absence of oxygen. To enhance value, the oils and char typically under go additional processes to provide improved products.

In electrochemical capacitors, electrical charge is stored on the surface of an electrically conductive electrode material. The capacitance arises by separation of electrons at the electrode surface and ionic charges in the electrolyte solution. Because the charge separation arises over only a distance of 0.1 to 10 nanometers, large specific capacitances can be achieved on the order of 10-20 microfarads per square centimeter of electrode material. The larger the surface area of the electrode material, the greater the charge that can be stored. Since the capacitance, or the amount of charge that an electrochemical capacitor can hold, is directly related to the surface area of the electrodes, electrodes made from conductive materials with high surface areas are preferred. Devices incorporating such electrodes are referred to as double layer capacitors or supercapacitors.

Electrochemical capacitors are charge-storage devices that are capable of delivering high power densities and that are capable of being cycled (charged and discharged) millions of times, hence demonstrating a significant advantage over conventional batteries. Electrochemical capacitors have energy and power capabilities that lie between the capabilities of a battery and of a conventional capacitor (electrolytic, thin film and others).

There is substantial demand for a rechargeable energy source that can provide high power and energy densities, can be charged quickly, has a high cycle life is environmentally benign and cost effective. Double layer capacitors, especially when used in conjunction with batteries, are rechargeable charge storage devices that fulfill this need.

In prior art capacitors, the production of activated carbon is an energy intensive process that first includes heating of a precursor material (natural or synthetic) to form a carbon powder or carbon fiber, in many cases requiring temperatures up to 3000° C. Next, to form activated carbon, the material is heated to about 800° C. in an atmosphere of steam or carbon dioxide, or electrochemical reaction in a strongly oxidizing solutions (such as Hummers reagent) to produce a carbon with high surface area to provide high energy density and high power density. Overall, the yield for activated carbons is generally not better than 25% based on weight of the precursor material.

A single cell double-layer capacitor consists of two electrodes which store electrical charge (called the active materials), separated by an ion permeable but electrically insulating membrane. Each electrode is also in contact with a current collector which provides for electrical contact outside of the cell. The electrodes and membrane are infused with an electrolyte and enclosed in an inert housing which provides a sealed environment and also enough compression to reduce contact resistance between the different layers. Multiple cells may be used in series to increase the allowable potential (voltage), and also in parallel to increase the capacitance.

Applying an electrical potential across the electrodes causes charge to build up in the electrochemical double layer that exists at the electrode/electrolyte interface for each electrode. This process continues until a state of equilibrium is reached, so that the potential of the electrodes is at the charging potential and the current is reduced to that required to maintain the charge.

Because carbon is relatively chemically inert, has a high electrical conductivity, is environmentally benign, and is relatively inexpensive, some forms of carbon are excellent materials for fabricating electrodes. However, many forms of carbon are not suitable for electrodes. The desired properties of the electrochemical capacitor electrodes include the following high surface area, electrically conductive, low cost, readily available source of material and long-term stability under operating conditions.

Advances are being made in electrochemical capacitor technology research using nanomaterials. While capacitors of many types are known, there is a need for improved electrodes based on nanomaterials and for new electrochemical capacitors using the new nanomaterials.

SUMMARY

The present invention is an electroactive material for charge storage and transport in an electrochemical capacitor. The material is formed of a plurality of nanocomponents including nanoparticles, in turn formed of conductive carbon-based clusters bound together by a conductive carbon-based cluster binder including zinc sulfide nanoclusters and nanocluster binders, all having high densities of mobile charge carriers (electrons, electronic acceptors, ionic species). A terminal is electrically coupled to the nanoparticles for charge transport.

The material and each of the nanocomponents play key roles in the process of charge transport including supplying electrons and electron acceptor sites. The charge transport occurs by the electron travel through the highly conductive and relatively short path of the binders with proximity to the nanoclusters. The small sizes of the particles provide large surface areas. In general, particle sizes of less than about 100 nanometers are preferred in order to have large surface areas which provide ready access of the electrolyte to the nanocomponents of the particles. The combination of the high density of available electrons in all the nanocomponents of the particles with the short distances among all the nanocomponents of the particles and the large surface areas of the nanocomponents greatly enhances the energy and power densities achieved.

Because of the short nanodistances of the particles, the density of clusters producing electrons tends to be high resulting in high energy densities. Because of the short nanodistances of the particles, the intercalation rate is fast resulting in high power densities, for example, greater than 1000 watts/kilogram. In a further embodiment, a second electroactive material is provided for charge transport. The second material is formed of a second plurality of nanocomponents including second nanoparticles, in turn formed of conductive carbon-based clusters bound together by a conductive carbon-based cluster binder including nanoclusters and nanocluster binders, all having high densities of mobile charge carriers (electrons, electronic acceptors, ionic species). A second terminal is electrically coupled to the nanoparticles for charge transport.

In a further embodiment, the second plurality of particles are substantially the same as the first plurality of particles including zinc sulfide nanoclusters.

In a further embodiment, the second plurality of particles are substantially different from the first plurality of particles including zinc sulfide nanoclusters.

In a further embodiment, the zinc sulfide nanoclusters are charge receptors and wherein charge transport uses electrolyte ions.

In a further embodiment, the second plurality of particles are separated from the first plurality of particles by an ion permeable membrane.

In a further embodiment, the carbon nanosphere cores have diameters of less than approximately 100 nanometers.

The electroactive material of claim2wherein the composite layer has a wall thickness of less than approximately 1200 nanometers.

In a further embodiment, a substantial number of the clusters have diameters of less than approximately 1200 nanometers.

The foregoing and other objects, features and advantages of the invention will be apparent from the following detailed description in conjunction with the drawings.

DETAILED DESCRIPTION

The electrode materials used in electrochemical capacitors serve multiple concurrent functions by acting both as a battery and an electrochemical capacitor with tunable power and energy capabilities. The cost of the carbon-based electrode materials is substantially reduced through use of materials derived from tire pyrolysis. These nanosized carbon-based materials are preferred materials for the electrodes in electrochemical capacitors due to their large surface areas and high charge densities. The large surface areas and high charge densities are accessible to the charge carrying electrolyte ions. Highly accessible surface areas and high charge densities are important for high energy density and high power density.

The char obtained from the pyrolysis of tires is an inexpensive source of nanomaterials that, with further control and added processing, are potentially useful in many fields including Photo Catalysts, Contact Catalysts, Capacitors, Batteries, Sorbents (Adsorbents and Absorbents) and Photo Voltaic Materials. The ability to use nanomaterials derived from char in useful applications is dependent on controlling the parameters of the tire pyrolysis process and the processing of char for particular applications.

One particular application of processed char is for electrodes that are used in batteries, electrochemical capacitors and other devices. In general, electrodes undergo reactions that take place in a solution at the interface of an electron conductor (electrode) and an ionic conductor (electrolyte). Electrons transfer between the electrode and the electrolyte or species in solution. Typical electrolytes include aqueous, organic, inorganic and polymeric.

The electron transfer can occur at an electrode through the release of chemical energy to create an internal voltage or through the application of an external voltage. Electrochemical reactions transfer electrons between atoms or molecules. These reactions can be separated in space and time and devices with such reactions are often connected to external electric circuits. The creation of internal voltages at electrodes is useful in electrochemical capacitors.

One example of batch pyrolysis uses a furnace/retort, a three stage condensing system, a water scrubber, and a flare. An oil tank collects the condensed oil at the end of each test. The furnace uses two burners. The operating temperature of the furnace is set at 1,750° F. with a control range of plus/minus 30 to 40° F. When the control temperature is reached, one burner is shut off continuing with a small upward drift in temperature. When the temperature drifts down, the burner restarts automatically. Both burners are on for the first 90 minutes. Burner cycle time after the start of the run is a few seconds; near the end of the run, one burner is off for period as long as three minutes with a like interval of being on. Exhaust gas temperature remains relatively stable between 1,250 and 1380° F. Pyro gas generation starts after 105 minutes of operation at a temperature of 650° F., reached a high of 700° F., and dropped to 375° F. at the end of the thermal cycle.

The control of the temperatures and the control of the heating and cooling rates during pyrolysis are critical for producing the nanocomponents having the nano structures of the present invention.

The thermal operation is monitored using the back pressure in the retort, the cooling water temperature, and visually watching the flare. A run lasts approximately 16 hours. At the end of the run, the furnace back pressure is almost atmospheric, the cooling water delta temperature is almost zero, and the flare is out. During this operational period, the ambient air temperature ranged from about 20 to 45° F. The retort is opened approximately 8 hours after the thermal cycle is shut down. The estimated temperature of the char is less than 350° F. Prior to opening the retort, the retort is purged with nitrogen for a brief period of time. After the lid is opened, a very small quantity of vapor comes from the remaining char and tire wire. Cooling water flow (rate and temperature) is monitored as a check of the process gas generation rate and the condensing duty for both the condensable and non-condensable fraction of the process gas produced. When the inlet and outlet temperatures of the cooling water measures about the same, the operation is complete. The operating pressure of the retort ranges from two to eight millibars above atmospheric, which is sufficient to transport the gas through the condensing system to the flare. For the example described, the tire charge was 3,400 pounds in eight bales. The eight bales averaged 15 tires, with an average weight of 28 pounds per tire. The output yield of char was approximately 25% or more of the tire input.

After pyrolysis of tires, the composition of char, for one typical example, includes carbon as previously indicated in TABLE 1 and includes inorganic materials, such as metal sulfides and metal oxides, as indicated in the following TABLE 2:

The combination of TABLE 1 materials and TABLE 2 materials as produced by the pyrolysis process form nanomaterial composites useful in many fields including Photo Catalysts, Contact Catalysts, Capacitors, Batteries, Sorbents (Adsorbents and Absorbents) and Photo Voltaic Materials.

The TABLE 2 materials are “heavy metal free” in that even if trace amounts of heavy metals were produced as a result of tire pyrolysis, the trace amounts are so small that no environmental hazard is presented.

InFIG. 1, the material5includes nanomaterial in the form of particles21derived from char in the manner previously described. Typically, the char is processed for size reduction, sorting, classification and other attributes to form the char particles21.

InFIG. 2, a schematic representation of a particle21is shown that is typical of the particles21in the material5ofFIG. 1. In embodiments where the material5is used in an electrode, the particles21ofFIG. 1typically have at least one dimension, P, in a range from approximately 10 nm to approximately 10,000 nm. InFIG. 2, the particle21includes a plurality of clusters30that are held together by a cluster binder22. The material of the cluster binder22primarily contains components of TABLE 1 and TABLE 2.

In the particle21, a number of the clusters30are externally located around the periphery of the particle21and a number of the clusters30, designated as clusters30′, are located internally away from the periphery of particle21. The internally located clusters30′ are loosely encased by the cluster binder material22. The selection of particle sizes in a range from approximately 50 nm to approximately 1000 nm tends to optimize the number of active and externally located clusters30and thereby enhances the electrochemical operations of the electrodes. The internally located clusters30′ are efficiently coupled electrically and through intercalation.

InFIG. 3, a schematic representation is shown of a cluster30-1that is typical of one embodiment of clusters30ofFIG. 2. The cluster30-1has a graphitic carbon nanosphere cores33encased by a composite layer34. The carbon nanosphere core33is generally spherical in shape (a nanosphere) and has a core diameter, DC1, in a range from approximately 10 nanometers to approximately 1000 nanometers. The composite layer34has a wall thickness, WT1, in a range from approximately 0.2 nanometers to approximately 300 nanometers. The overall diameter of the cluster30-1(DC1+WT1) in a range from approximately 10 nanometers to approximately 1300 nanometers.

InFIG. 3, the size and shape of the carbon nanosphere cores33are limited primarily by the size and the shape of the cores used in the mixture forming the “green” tires as indicated in TABLE 1. The melting point of graphite is approximately in the range from 1900° C. to 2800° C. Since both the vulcanization and the pyrolysis processes operate at much lower temperatures, the carbon nanosphere cores33in finished tires and in tire char remain essentially undisturbed from their original size and shape.

InFIG. 3, the composite layers34surrounds and incases the carbon nanosphere cores33. The sizes and the shapes of the composite layers34are determined in part by the sizes and the shapes of the carbon nanosphere cores33and additionally by the processing of the tire char. The processing of the char is done so as to achieve the 0.2 nanometers to approximately 300 nanometers for the wall thickness, WT1, and so as to achieve the overall diameter, (DC1+WT1), of the clusters30-1in a range from approximately 10 nanometers to approximately 1300 nanometers.

InFIG. 3, the composite layer34is carbon and contains a mixture of metal oxides and metal sulfides of TABLE 2 and other materials as described in TABLE 1, surrounding and bound to the carbon nanosphere core33. Specifically, the composite layer34includes zinc sulfide nanoclusters32embedded in and forming part of the composite layer34. A number of the nanoclusters32are externally located, that is, located around the periphery of the cluster30-1and a number of the nanoclusters32, designated as nanoclusters32′, are located internally away from the periphery of the composite layer34. The composition of the composite layer34typically has zinc sulfide (ZnS) in a range, for example, of 2% to 20% by weight, and carbon and other components of TABLE 2.

InFIG. 4, a schematic representation is shown of a cluster30-2that is typical of one embodiment of clusters30ofFIG. 2. The cluster30-2has a carbon nanosphere core43encased by a composite layer44. The carbon nanosphere core43is generally spherical in shape (a nanosphere) and has a core diameter, DC2, in a range from approximately 10 nanometers to approximately 1000 nanometers. The composite layer44has a wall thickness, WT2, in a range from approximately 0.2 nanometers to approximately 300 nanometers. The overall diameter of the cluster30-2(DC2+WT2) in a range from approximately 10 nanometers to approximately 1300 nanometers.

InFIG. 4, the size and shape of the carbon nanosphere cores43are limited primarily by the size and the shape of the cores used in the mixture forming the “green” tires as indicated in TABLE 1. The melting point of graphite is approximately in the range from 1900° C. to 2800° C. Since both the vulcanization and the pyrolysis processes operate at much lower temperatures, the carbon nanosphere cores43in finished tires and in tire char remain essentially undisturbed from their original size and shape.

InFIG. 4, the composite layers44surrounds and incases the carbon nanosphere cores43. The sizes and the shapes of the composite layers44are determined in part by the sizes and the shapes of the carbon nanosphere cores43and additionally by the processing of the tire char. The processing of the char is done so as to achieve the 0.25 nanometers to approximately 80 nanometers for the wall thickness, WT2, and so as to achieve the overall diameter, (DC2+WT2), of the clusters30-2in a range from approximately 5 nanometers to approximately 100 nanometers.

InFIG. 4, the composite layer44is a mixture of metal oxides and metal sulfides of TABLE 2 and other materials as described in TABLE 1, surrounding and bound to the carbon nanosphere core43. Specifically, the composite layer44includes zinc sulfide nanoclusters42embedded in and forming part of the composite layer44. A number of the nanoclusters42are externally located, that is, located around the periphery of the cluster30-2and a number of the nanoclusters42, designated as nanoclusters42′, are located internally away from the periphery of the composite layer44. The composition of the composite layer44typically has zinc sulfide (ZnS) in a range from approximately 2% to approximately 20% by weight, carbon in a range from approximately 60% to approximately 70% by weight, with the balance of the composite layer44principally being a mixture of metal oxides and metal sulfides of TABLE 2 and other materials as described in TABLE 1.

FIG. 5depicts an electroactive material215having nanoparticles and having a terminal565electrically coupled to the particles for charge transport. The terminal565functions as an electrode for allowing charge transport to and from the particles forming the nanomaterial215.

FIG. 6depicts a device including first and second electroactive materials21-16and21-26of theFIG. 5type, each having nanoparticles and having terminals56-16and56-26electrically coupled to the particles of the first and second electroactive materials21-16and21-26, respectively, for charge transport.

FIG. 7depicts a device including a first electroactive material electroactive material21-17of theFIG. 5type and having terminals56-17and including a second electroactive material21-27, different from the first electroactive material, having nanoparticles and having a terminal56-27electrically coupled to the particles for charge transport.

FIG. 8depicts a device a device including first and second electroactive materials21-18and21-28of theFIG. 5type, each having nanoparticles and having terminals56-18and56-28electrically coupled to the particles of the first and second electroactive materials21-18and21-28, respectively, for charge transport and including a third electroactive material21-38, like the first electroactive material and having nanoparticles and having a terminal56-38electrically coupled to the particles for charge transport.

InFIG. 9, a schematic representation of an electrochemical capacitor50is shown having one electrode (anode)52and another electrode (cathode)54. The anode52is formed of particles21as described in connection withFIG. 1,FIG. 2andFIG. 3and includes cluster30and specifically cluster30-1having zinc sulfide nanoclusters32. The cathode54is formed of particles21as described in connection withFIG. 1,FIG. 2andFIG. 3and includes cluster30and specifically cluster30-2having zinc sulfide nanoclusters32.

InFIG. 9, the electrode (anode)52and electrode (cathode)54are immersed in a solution58which in one example is 38% potassium hydroxide, KOH, in water. A separator53is provided between the anode52and the cathode54. The separator53is a membrane which pre-vents any carbon transfer or contact between the anode52and the cathode54while permitting the transport of electrolyte ions. The anode52contacts a metal or other good-conducting material51to enable electron flow at terminal56. The cathode54contacts a metal or other good-conducting terminal connector55to enable electron flow at contact57. The capacitor elements51,52,53,54and55are schematically shown with exaggerated spacing for clarity in the description and ease of viewing the drawing.

InFIG. 10, a schematic representation of capacitor50ofFIG. 9is shown having the addition of spacers560and570. The spacer560is between the anode52and the membrane separator53. The spacer570is between the cathode54and the membrane separator53. The spacers560and570help establish the thickness of the capacitor50and also provide hermetic seals that constrain the electrolyte58. The capacitor elements51,52,53,54,55,560and570are schematically shown with exaggerated spacing for clarity in the description and ease of viewing the drawing.

InFIG. 11, a schematic representation of capacitor50ofFIG. 6is shown without expanded spacing.

InFIG. 12, the capacitor50shown inFIG. 9,FIG. 10andFIG. 11is shown with greater details of the nanoscale structure of the materials and of the charge transport.

InFIG. 12, the capacitor50includes a first electroactive electrode52-1including a material5-1formed of plurality of particles21-1. Each includes a plurality of clusters, of which cluster30-1is typical. Each cluster includes a carbon nanosphere core33, a composite layer34surrounding and bound to the carbon nanosphere core33. The composite layer34includes zinc sulfide nanoclusters32embedded in the composite layer34, and a binding composite31binding the plurality of nanoclusters32. A first terminal5612-1electrically couples to the first plurality of particles21-1for charge transport.

A second electroactive electrode electroactive electrode52-2including a material5-2formed of plurality of particles21-2. Each includes a plurality of clusters, of which cluster30-2is typical. Each cluster includes a carbon nanosphere core33, a composite layer34surrounding and bound to the carbon nanosphere core33. The composite layer34includes zinc sulfide nanoclusters32embedded in the composite layer34, and a binding composite41binding the plurality of nanoclusters32. A second terminal5612-2electrically couples to the first plurality of particles21-2for charge transport.

A separator53is provided between the first electrode52-1and the second electrode52-2. An electrolyte58contacts the first electrode52-1and the second electrode52-2for transporting electrical charges between the first electrode52-1and the second electrode52-2using electrolyte ions.

In general inFIG. 12, the electroactive electrodes52-1and52-2undergo reactions that take place in an electrolyte solution58, for example KOH, at the interfaces of the electroactive electrodes52-1and52-2using electrolyte ions. Electrons transfer between the electroactive electrodes52-1and52-2and the electrolyte solution58or dissociated species of the electrolyte, nK1+and nOH1−.

When terminals5612-1and5612-2are connected to an external circuit (not shown), the electrolyte solution58reacts with the material5-1and particularly the particles21-1, clusters30-1. For each cluster30-1, the electrolyte solution58reacts with the nanoclusters32and couples directly with the composite layer34, the nanocluster binder31and the carbon nanosphere core33. The electrolyte is in one example potassium hydroxide, KOH.

The process of electron production involves the species nOH1−from solution contacting a cluster such as cluster30-1. For each cluster the species nOH1−balances the charges imposed on the nanoclusters32, nanocluster binder31and the carbon nanosphere core33to form the ionic double layer. The reaction of the species nOH1−is efficient when the electrolyte solution58is in contact with the surface located nanoclusters clusters32and nanocluster binder31and hence where the diffusion path of the species nOH1−is short, typically 10 nanometers or less. Because the diffusion path of the species nOH1−is short, the diffusion rate is fast.

Additionally, the internal nanoclusters32′, the internal nanocluster binder31and the carbon nanosphere core33are efficiently coupled for electron production by reaction with the species nOH1−through intercalation and close proximity of the internal nanoclusters32′, the internal nanocluster binder31and the carbon nanosphere core33. Again, the intercalation distance is short, typically 80 nanometers or less and hence the intercalation rate is fast.

The process of electron recombination involves the ion nOH1from solution contacting a cluster such as cluster30-2. For each cluster30-2, the ion nOH1−reacts with nanoclusters32and with nanocluster binder41and with the carbon nanosphere core33. The reaction of the ion nOH1−is efficient when the electrolyte solution58is in contact with the surface located nanoclusters clusters32, zinc sulfide clusters and nanocluster binder31. Because the diffusion path of the species the ion nOH1−is short, typically 10 nanometers or less, the diffusion rate is fast.

For recharging operation, the process is the reverse of electron production. The recharging operation involves the species nOH1−from solution contacting a cluster such as cluster30-2. For each cluster the species nOH1−reacts with nanoclusters32, with nanocluster binder31and with the carbon nanosphere core33. The reaction of the species nOH1−is efficient when the electrolyte solution58is in contact with the surface located nanoclusters clusters32and nanocluster binder31and hence where the diffusion path of the species nOH1−is short, typically 10 nanometers or less. Because the diffusion path of the species nOH1−is short, the diffusion rate is fast.

Additionally, the internal nanoclusters32′, the internal nanocluster binder31and the carbon nanosphere core33are efficiently coupled for electron production by reaction with the species nOH1−through intercalation and close proximity of the internal nanoclusters32′, the internal nanocluster binder31and the carbon nanosphere core33. Again, the intercalation distance is short, typically 80 nanometers or less and hence the intercalation rate is fast.

At the cathode, the species, the species nK1+has interacted with ZnS.

The process of electron recombination involves the ion nK1+from solution contacting a cluster such as cluster30-1. For each cluster30-1, the ion nK1+reacts with nanoclusters32, and with nanocluster binder31and with the carbon nanosphere core33. The reaction of the ion nK1+is efficient when the electrolyte solution58is in contact with the surface located nanoclusters clusters32, zinc sulfide clusters and nanocluster binder31. Because the diffusion path of the species the ion nK1+is short, typically 10 nanometers or less, the diffusion rate is fast.

The nanomaterial5is formed of a plurality of nanocomponents including nanoparticles21, in turn formed of conductive carbon-based clusters30bound together by a conductive carbon-based cluster binder22including zinc sulfide nanoclusters32and nanocluster binders, all having high densities of mobile charge carriers (electrons, electronic acceptors, ionic species).

The nanomaterial5, and each of the nanocomponents, plays a key role in the process of charge transport including supplying electrons (at the anode52-1and52-2). The charge transport occurs by the electron travel through the highly conductive and relatively short path of the binders22and31with proximity to the nanoclusters32. The small sizes of the particles21provide large surface areas. In general, particle sizes of less than about 100 nanometers are preferred in order to have large surface areas which provide ready access of the electrolyte58to all the nanocomponents of the particles21. The combination of the high density of available electrons in all the nanocomponents of the particles21with the short distances among all the nanocomponents of the particles21and the large surface areas of the nanocomponents greatly enhances the energy and power densities achieved.

Because of the short nanodistances of the particles of the present invention, the density of clusters producing electrons tends to be high resulting in high energy densities greater than 100 watt-hours/kilogram. Because of the short nanodistances of the particles of the present invention, the intercalation rate is fast resulting in high power densities, for example, greater than 2000 watts/kilogram.

This efficiency of the production of electrons with the nanostructure elements of the present invention is distinguished from the inefficiency in conventional batteries where the electrodes are formed with materials having larger-sized particles and where the intercalation distance is long, typically 800 nanometers or more and the intercalation rate is slow.

The electron transfer can occur at an electrode through the release of chemical energy to create an internal voltage or through the application of an external voltage.

FIG. 13depicts an electron-microscope scan of a particle21including composites having zinc sulfide nanoclusters. The particle21has a dimension P that is typically less than 100 nanometers, approximately 1×10−7meters. The electron-microscope scan ofFIG. 13was produced with 60,000× magnification using a Transmission Electron Microscope with a scan time of approximately one minute. A slide was prepared by dissolving 1 milligram of material into 20 milliliters of methanol in a scintillation vial, sonicating for 5 minutes and placing a 70 micro liter aliquot drop onto a TEM copper grid for imaging. The grid is then covered and placed in an environmental chamber to evaporate the methanol. The example ofFIG. 13is typical of many samples.

InFIG. 13, a plurality of zinc-sulfide clusters30-1are shown, including among others clusters30-11,30-12,30-13,30-14, . . . ,30-112. By way of example, the cluster30-11includes a carbon nanosphere core33, surrounded by a composite layer34, having a large number of nanoclusters32(only two of which are labeled but includes many more as a function of the zinc sulfide packing density) held together by a nanocluster binder311. Each of the others clusters30-11,30-12,30-13,30-14, . . . ,30-112has similar structures.

InFIG. 13, the plurality of zinc-sulfide nanoclusters30-11,30-12,30-13,30-14, . . . ,30-112are arrayed in a structure that couples the nanoclusters30-1for energy transfer (electrical, thermal, photon, mechanical and other). It is evident inFIG. 13that nanoclusters30-11,30-12,30-13,30-14, . . . ,30-112are linked together to form a serial chain whereby the composite layer34of one cluster are in close proximity to the composite layer34of one or more adjacent nanoclusters. With such close proximity of composite layers34, energy transfer is readily facilitated from adjacent to adjacent nanoclusters. It is highly desirable to have linking of nanostructures to provide the enhanced performance that derives from efficient electrical coupling and charge transport. The linking is achieved by close proximity binding of the clusters with conductive composite binders. The linking is further enhanced by the structure of the nanoclusters based upon carbon nanocores encased in a conductive carbon-based nanocluster binder. This linking is achieved as a result of the control of char formation in tire pyrolysis. This linking in the present invention is superior to nanotube technology where the linking is not in-situ provided, but must be added at great expense and with high difficulty.

FIG. 13is a planar view of a thin plane of nanomaterial representing a monolayer of material, but it should be noted that the close proximity of the composite layers34occurs in three dimensions of a volume of material.

The close proximity of composite layers34and the resultant high energy transfer characteristics of the nanomaterials are determined as a function of the processing times, temperatures and pressures during pyrolysis of tires.

FIG. 14depicts an enlarged view of a portion of the electron-microscope scan of the cluster30-19adjacent to and in close proximity to the cluster30-18ofFIG. 13. The composite layers348and349of clusters30-18and30-19are in close proximity. The cluster30-19includes, by way of example, nanoclusters329-1,329-2and329-3. The nanoclusters329-1,329-2and329-3are bound together in the composite layer349by the nanocluster binder319. The zinc sulfide properties of the nanoclusters329-1,329-2and329-3are identified by in-situ x-ray backscattering images observed during the scan. The other materials present (not shown inFIG. 14) include many of the materials of TABLE 2 in varying concentrations that are generally less than the concentration of zinc sulfide. The concentration of pyrolitic carbon is typically greater than the concentration of zinc sulfide. The pyrolitic carbon in the composite34facilitates the ion formation and charge transport. The other materials of TABLE 2 may also play a contributing role to the operation.

FIG. 15depicts an electron-microscope scan showing further details of the nanocluster ofFIG. 14.

FIG. 16depicts an electron-microscope scan showing even further details of the nanocluster ofFIG. 15. The nanocluster329-3is much larger than the nanocluster329-4and demonstrates that the zinc sulfide nanocluster have widely varying size distributions.

The manufacturing process for forming electrochemical capacitors from tire char, in one embodiment, is as follows. The carbon char from pyrolyzed tires is ground or otherwise formed into a fine powder with a particle size distribution that includes a substantial number of small particles, that is, particles measuring less than 100 nanometers. The resultant fine powder is mixed with an electrolyte solution consisting of approximately 38% NaOH in distilled water at a ratio of 4 g fine powder (carbon) to 3.5 g of electrolyte. This carbon/electrolyte mixture is then ground (if done by hand using a mortar and pestle) for approximately 10 minutes or until the electrode material has a smooth consistency. The ground electrode material can be stored for weeks or more in a sealed container.

Capacitors are assembled by rolling out the electrode material in a thin layer onto a current collector which, for example, is 316 stainless steel foil supported by a rigid member such as plate glass. A separator is placed atop the thin layer of electrode material. The separator consists of an ion permeable, electrically insulating membrane (Pall Rai membrane) which is pre-saturated with electrolyte solution by soaking in the electrolyte solution for longer than 30 minutes. Another layer of electrode material is placed atop the insulating membrane to form a symmetrical electrode, followed by a collector plate. The capacitor layers are then compressed, for example using clips, sealed with epoxy and allowed to cure at 50° C. for an hour. After the epoxy has cured, the binder clips are removed. The resulting electrochemical capacitors are tested.

The capacitors are tested by first charging to 0.75V until the current required to maintain this charge level falls below 1 milliamp. The capacitors are then cycled through charge/discharge cycles whereby the charging current is reversed until the potential at the collector reaches 0V. Then the current is switched to charge the capacitors back to their previous potential. The time required to discharge and recharge the cell is recorded as is the current used and the total voltage change. These values along with the carbon mass in each electrode are used to calculate the energy stored in the cell.