Patent Description:
The present invention relates to increasing the conductivity of battery cathodes and anodes to enhance battery performance. More specifically, the present invention relates to methods and systems for enhancing the performance of batteries by lowering the electrical resistance both across and particularly through the active films, thus increasing conductivity to increase discharge and charge rates, and ultimately to increase both power and energy density.

Among many other technologies, the preferred method to store electrical energy is in a battery. A battery is simply a device in which the anode (negatively charged or reducing electrode) may be loaded with electrons through an electrochemical galvanic process, and a cathode (positively charged or oxidizing electrode), where the electrochemical galvanic reaction is reversed and the stored electron is discharged to a circuit, thus providing an electrical current. Batteries where these reactions are singularly non-reversible are called primary batteries, which are non-rechargeable. Batteries where these reactions can be reversed multiple times are called secondary batteries, or rechargeable. Though the examples described in this disclosure are secondary in nature, those skilled in the art will understand that the concepts herein described may apply to both primary and secondary systems.

Battery design and choice of materials are a function of the galvanic potential between the materials and their ability to provide a designed voltage potential to drive a current to a circuit to supply electrical power.

An important part of the design of a battery is the method by which the electrical current is collected and distributed. While the examples described herein apply to a lithium-ion rechargeable battery, the concepts disclosed herein (methods and materials that significantly improve current collection) apply to all batteries, as all batteries generally use a current collector. For the purposes of this disclosure, all battery systems containing lithium will be identified as lithium-ion batteries. The choice of materials used to improve the current collection by methods described herein must be compatible with the electrochemical galvanic reactions of said battery, such that the selected materials do not become an active corrosion product of the battery.

For purposes of this disclosure, the exemplary embodiments described herein involve a lithium-ion secondary battery, specifically a lithium iron phosphate or a lithium nickel manganese cobalt oxide cathode and a carbon powder anode. However, one reasonably skilled in the art will understand that the concepts taught herein may apply to any battery where the materials, methods and techniques described would provide the described improvements.

There are many factors that influence battery performance, such as ion transport through both the anode and the cathode and across the separation barrier, chemistry kinetics, SEI (solid electrolyte interphase) formation, and so forth. A significant factor is the ability to transport the electrons through the system, that being a number of resistors in series; starting with the anode current collector foil, the anode foil/active mass interface, the anode active mass, to the electrolyte (in this case, the lithium accepting an electron at the anode when charging), transport of that electron and lithium across the barrier to the cathode, separation of the electron from the lithium in the cathode, transport of the electron through the cathode active mass, then to the active mass/foil interface, then moving the electron out of the foil and to the device it services.

In the lithium-ion battery system considered by example herein, current collection in the anode is inherently facilitated because the carbon powder that is used to capture and store the lithium ion during the charge cycle, is already moderately conductive. Its conductivity is often further enhanced by the addition of a finely divided carbon powder. Still, the anode film must be made thin (e.g., <NUM> to <NUM> microns thick) and must be applied to a copper or nickel foil current collector. Furthermore, its inherent volume resistivity is such that the rate by which it is charged is limited, in part, by its ability to run current both through the active mass and through the carbon/foil interface and polymer binder (another limiting factor is the ability to transport, accept and store lithium ions). The relationship of the voltage, current and resistance is defined by Ohms law. If the anode is more conductive, the electrical resistance is lowered, thus reducing the required applied voltage to run a given current, or conversely, to run a higher current at a given voltage. This reduction in resistance also results in reducing the resistive heating losses. Likewise, increased conductivity will permit thicker anodic film to be employed, thus increasing capacity.

Current collection in the cathode, however, is a different story, as many cathodic active materials are either non-conductors or poor conductors. In the exemplary embodiments described herein, the lithium iron phosphate (hereafter LFP) and the lithium nickel manganese cobalt oxide (hereafter NMC) are non-conductive insulators. However, typically, these materials are combined with small amounts of a polymer binder and a conductive sub-micron carbon and then spread thinly onto an aluminum foil substrate. For a given battery design, the cathode film is about twice the thickness of the anode film. In order that an adequate level of conductivity through the thickness of the non-conductive LFP or NMC is provided, a few percent of a moderately-conductive, finely divided carbon powder (such as Super P by name) is added to the mix. Still to put this into perspective, the volume resistivity of the cathode film is about one to two orders of magnitude less than the volume resistivity of the anode.

This vast difference in conductivity results in cathode resistance being the most prohibitive limiting factor for battery discharge rate or capacity. For instance, to get a higher discharge rate (power cell) the cathode must be made thinner so that the electron is more proximate to the current collecting foil. However, making the film thinner reduces the capacity of the battery. Conversely, the capacity of the battery may be increased by increasing the thickness of the cathode film, but then the discharge rate is commensurately reduced. Thus, one may design for power, or design for capacity, but not for both. If the cathode may be made significantly more conductive, then significant increases in capacity or power or a combination of both may be achieved.

The same design concepts also apply to the tradeoffs among thickness, capacity, and rate in the anode. Furthermore, any measure which increases the conductivity of the anode or the cathode will result in a lower resistance, or impedance, across the entire battery system, increasing the voltage or amperage, and also increasing either rate or capacity or both. An increase in conductivity also results in less joule heating. A decrease in Joule heating is a very important factor for two reasons. First, the reduction in Joule heating results in this energy being manifest in greater capacity. Second, reduce heating results in a cooler and safer battery.

Despite many recent advances in the ability of the battery industry to transport, store and chemically exchange lithium and its ion and electron, and advances in cathodic and anodic chemistry, the industry has not seen any significant advances in the electrical conductivity of the anode or cathode films for several decades. <NPL> discloses that the electrical conductivity of cathodes may be enhanced by incorporating pure nickel fibers having a length of <NUM>-<NUM> into the cathode matrix. <CIT> discloses that short fibers coated with metal may be used in an electrode to enhance conductivity. <NPL> and <NPL> disclose methods of producing nickel coated carbon fibers.

Accordingly, a need exists for more efficient electrodes, electrodes that improve efficiency, discharge time, recharge rate, power density and energy density significantly without sacrificing weight or size. Such electrodes are disclosed herein.

The present disclosure describes developments responsive to the present state of the art, and in particular, a response to the problems and needs in the art that have not yet been fully solved by currently available electrodes. The electrodes of the present disclosure are easily implemented and provide significant advances in both power density and energy density. The exemplary electrodes may be used in batteries in a full range of sizes and weights for use in small electronic devices such as cell phones and laptop computers to electric vehicles such as golf carts and automobiles, to very large-scale centralized batteries for renewable energy storage, for example.

Improvements in conductivity in both the anode and the cathode are desirable and beneficial. The larger benefit comes from the ability to improve the conductivity of the cathode. Whereas the anode is moderately conductive, typically about <NUM> ohm-cm in volume resistivity; the cathode has a volume resistivity of about <NUM> to <NUM> ohm-cm. Due to the poor conductivity of cathodic films, the discharge energy capacity of the battery is limited by the inability of the cathode film to conduct electrons through its thickness to the aluminum foil current collector. Conversely, if more power is desired, then the film must be made thinner in order to facilitate faster electron transport to the foil, thus sacrificing capacity. Given a constant thickness, a more conductive cathodic film will result in a faster discharge rate. Alternatively, a film with less resistivity can be laid down thicker at an equal resistance, thus increasing capacity at the same power rate. Thus, the energy density may be increased approximately by the ratio of the thicknesses.

A significant improvement in the conductivity of either the anode or the cathode leads to lower resistivity, not only across or through the respective cathodic or anodic film, but also generally across the entire battery cell. As a result, a lower resistance leads to higher voltage to move a given current or move a higher current at a given voltage. This, in turn, leads to faster charging or discharging, or the ability to move an electron at greater ease through thicker films, thus increasing capacity. There will also be a decrease in Joule heating, with a corresponding reduction in temperature and in energy loss. A decrease in operating temperature also results in a more efficient and safer battery.

This disclosure describes various exemplary methods by which electrical conductivity of the cathode and/or the anode may be improved. The magnitude of the improvement may be by a fractional margin (e.g., such as <NUM>% or <NUM>%), or an integral margin, such as doubling, or tripling or better. This disclosure also describes improvements in the operation of a complete lithium-ion cell.

Also described in this disclosure are exemplary conductive additives for the anode and the cathode, and their respective effects on the performance of these members. Further, a battery cell fabricated from these materials is described. Although optimal performance is yet to be achieved, this disclosure clearly demonstrates the efficacy of these exemplary materials.

Furthermore, there may be evidence suggesting that the morphological changes wrought by adding some of these exemplary materials may facilitate ion transport. It is also postulated that the non-carbon surfaces of the highly conductive anode additives may inhibit SEI growth. However, at this point both of these concepts are postulated and are not claimed or exemplified herein.

The following exemplary materials were evaluated for increasing conductivity performance. It should be understood, this disclosure is not limited to only these exemplary materials and methods. Those skilled in the art, armed with the disclosures herein will understand that the exemplary materials described exemplify the broader concepts.

The addition of metal-coated fibers to either the anode or the cathode improves conductivity in both films. The metal may be any metal, and the fiber may be any fiber, so long as the chemical, physical and mechanical properties of the fiber and metal coating are compatible with each other and compatible with the respective properties of the selected anode or cathode. Minimization of fiber diameter, maximization of length, optimization of length vs dispersibility vs. efficacious concentration, minimization of density, and maximization of conductivity of the fiber are just a few of the highly interrelated properties to be considered.

Metal-coated fibers have been items of commerce for many decades. Many metals (nickel, silver, aluminum, gold, iron, copper, chromium, cobalt, molybdenum, to name a few) have been deposited onto a wide variety of fibers (carbon, surface-modified carbon, silicon carbide, silicate, borosilicate, alumina, basalt, quartz, aramid, acrylic, rayon, nylon, cotton, silk, to name a few). A smaller fiber diameter is better, as this increases the available length and specific surface area of fibers in a given unit weight and the available conductive surface area per unit weight for electronic interconnectivity.

Deposition processes for coating the fiber include vacuum processes (PVD, sputtering, evaporation, etc.), wet chemistry processes (electroplating, electroless plating) and Chemical Vapor Deposition (CVD). Though the general conductivity concepts taught in this disclosure are somewhat agnostic to the deposition method, some of these methods provide for better coating uniformity and control.

Other parameters have significance. For example, the choice of fiber (substrate) and the choice of metal (coating) must also be compatible with the chemistry of the battery system. The galvanic corrosion potential of the metal-coating with respect to the chosen ionic electrolyte must be greater than the operating voltage of the battery, for if it is less, it will prematurely galvanically corrode, as will be discussed below regarding Example <NUM>. Additionally, the volume resistivity of the coated fiber must be less than that of the active film. The wider this improvement is, the greater the increase in performance. The length of the fiber also has importance. Fibers may be cut to very precise and consistent lengths, ranging from <NUM> to <NUM>. In addition, fibers also may be cut precisely to traditional lengths of several mm.

Dispersion efforts show that the precision consistency of fiber length greatly reduces the loading of fiber required for a desired conductivity, thereby reducing viscosity and dispersion issues. However, at concentrations high enough to achieve the desired conductivity, fibers that are above <NUM> in length may become entangled and may not disperse well. At the other end of the length spectrum, fibers that are <NUM> in length disperse very well, but their shorter aspect ratio mandates that higher loading is required for a desired conductivity. This added material loading adds weight and cost, but more importantly, displaces active battery materials, thereby commensurately reducing the available capacity.

The use of <NUM> fibers or fibers of about <NUM> are particularly suitable for dispersion, and that length may be adjusted upward or downward from <NUM> depending on other factors such as diameter or to facilitate dispersion. Although fibers, produced by any known means, may vary in length within the <NUM> to <NUM> range mentioned above, it is preferred to use precision-chopped fibers, wherein precision-chopped fibers means that the fibers are uniformly ± <NUM>% of the selected length (e.g., for <NUM> fibers, all fibers are between <NUM> and <NUM>). At that length, fibers may be dispersed in the active anode and cathode materials up to about <NUM>% by weight. But in practice, dispersions above <NUM>% are difficult to achieve, and dispersions above about <NUM>% to <NUM>% do not contribute to conductivity commensurate with their added weight, cost, or displacement of active material.

Listed below are various examples of metal-coated fiber additive candidates with descriptions of their relative efficacy as additives:.

Many types of aluminum-coated fiber may be contemplated. Aluminum is coated onto fibers and fabrics usually through a vacuum process or melt process. Applications for these products are usually optical in nature, such as a reflector (optical fibers or mylar balloons) or as a reflector of heat (gloves for high temperature processes). These have been items of commerce for decades. However, these fibers are large in diameter (usually over <NUM> microns) and have a density of about <NUM>/cc. Though they could be a viable candidate, their large diameter and moderate density results in a linear yield that is less than desirable.

Aluminum-coated carbon fiber - As the carbide of aluminum is easily formed, an aluminum-coated carbon fiber is not a viable option.

Aluminum coating over nickel coating on carbon fiber - If a barrier is placed between the carbon and aluminum, such as a nickel film or coating, the aluminum may be deposited as a thin film over the nickel. This is shown in a successful example below. However, after about a week of cycling, the nickel begins to react with the lithium and the battery fails.

Aluminum-coating onto other fibers. Any fiber that will not form a carbide during or after deposition or is already a carbide at least at its surface is a candidate for aluminum deposition. The aluminum deposition is deposited by chemical vapor deposition from any aluminum bearing organometallic compound. Examples of aluminum-coated fibers that have been demonstrated include fibers of silicon carbide, silicate, alumina, aluminum borosilicate, basalt, quartz, aramid, and so forth. Each of these fibers have been demonstrated to readily accept a thin aluminum film, but this list is by no means exhaustive. Hence the fiber (substrate) of an aluminum-coated fiber may be selected from the group including carbon, pan ox, silica, quartz, silicates, alumina, aluminosilicates, borosilicates, glass, minerals, carbides, nitrides, borides, polymers, cellulose, inorganic fibers, and organic fibers.

Surface modification of carbon fiber. The surface of a carbon fiber may be modified to a silicon carbide, after which the aluminum readily coats onto the silicon carbide surface. This fiber provides the smallest diameter and lowest density approach.

Other metal-coated fibers (not forming part of the present invention) - Such metal-coated fibers have been demonstrated as useful, such as copper-coated carbon fibers.

Powders and filamentary branching metals - In the cases where nickel is active employed for the conductivity, such as in the lithium-ion anode or the LFP cathode, certain types of nickel powders may act to provide further electrical paths between the metal-coated fibers or act to provide multiple conductive paths through the active mass/polymer/foil current collector interface. The synergistic effects of adding other conductive solid shapes, such as platelets or spheres, are known to increase the interconnectivity between the metal-coated fibers. In one particularly advantageous method, nickel powder of a highly filamentary and branched structure, where the main branches of the structure are generally above a micron in diameter, with some branching (such as Inco type <NUM> powder) may be used. A filamentary branching metal known as "nanostrands" generally has branches below a micron in diameter and exhibits very extensive branching ("nanostrands" are available from Conductive Composites Company of Heber City, Utah).

By using a combination of additives such as metal-coated fiber and a filamentary branching structure such as a branching nickel powder or nanostrands, the metal-coated fiber and the high-aspect ratio, conductive filamentary structures work together to create a comprehensive network of electron transport pathways. The physical nature of metal-coated fibers and the high-aspect ratio, conductive filamentary structure(s) facilitate the creation of an inter-fiber electron transport network for moving electrons between the anode and the current collector interface. The metal-coated fibers act much like logs being elongated linear electron transport conduits and the conductive filamentary structures act much like tumbleweeds that electrically interconnect the logs.

When such a combination of additives is used on the anode, anode conductivity is further enhanced. Whereas the carbon powder of the anode is already somewhat conductive, the spaces between the filamentary network of the conductive filamentary branching structure is about the same dimension and geometry as the carbon powder particle size. Consequently, the filamentary branching structures somewhat three-dimensionally wrap themselves around the carbon particles, like a spider web or a net (hereinafter referred to as a "nanonet"). This "nanonet" phenomenon leads to a much greater level of electrical interconnectivity between the carbon particles, the filamentary branching structures, the metal-coated fibers, and the current collecting foil. This effect is more pronounced for the nanostrands, due to their smaller diameter and larger degree of branching.

The amount of metal coating on the fiber is an important parameter in modifying conductivity, as will be demonstrated in the examples provided below in the Detailed Description.

These and other features of the exemplary embodiments of the present invention will become more fully apparent from the drawings, examples, and the following description, or may be learned by the practice of the invention as set forth hereinafter. Viewed from a first aspect the present invention provides a battery cathode with enhanced electrical conductivity as defined in claim <NUM>.

Exemplary embodiments of the present invention are described more fully hereinafter with reference to the accompanying drawings, in which multiple exemplary embodiments of the invention are shown. Like numbers used herein refer to like elements throughout. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be operative, enabling, and complete. Accordingly, the arrangements disclosed are meant to be illustrative only and not limiting the scope of the invention, which is to be given the full breadth of the appended claims.

Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. Unless otherwise expressly defined herein, such terms are intended to be given their broad ordinary and customary meaning not inconsistent with that applicable in the relevant industry and without restriction to any specific embodiment hereinafter described. As used herein, the article "a" is intended to include one or more items. Where only one item is intended, the term "one", "single", or similar language is used. When used herein to join a list of items, the term "or" denotes at least one of the items but does not exclude a plurality of items of the list. Additionally, the terms "operator", "user", and "individual" may be used interchangeably herein unless otherwise made clear from the context of the description.

The drawings are schematic depictions of various components and embodiments and are not drawn to scale. Schematic depictions are being used in this application to assist in the understanding of relative relationships between the components. Understanding that these drawings depict only typical exemplary embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail with reference to the accompanying drawings in which:.

The exemplary embodiments of the present disclosure will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. It will be readily understood that the components of the exemplary embodiments of the present invention, as generally described and illustrated in the figures and examples herein, could be arranged and designed in a wide variety of different arrangements. Thus, the following more detailed description of the exemplary embodiments, as represented in the figures and examples, is not intended to limit the scope of the invention, as claimed, but is merely representative of exemplary embodiments of the disclosure.

This detailed description, with reference to the drawings, describes a representative rechargeable lithium-ion battery <NUM> as known in the prior art that operates with a standard cathode <NUM> made of a base cathode material <NUM> and a standard anode <NUM> made of a base anode material <NUM>. The exemplary embodiments of the present invention comprise modified electrodes with increased conductive that separately or together may be components of an enhanced battery.

Turning to <FIG>, a representative rechargeable lithium-ion battery <NUM> as known in the prior art is depicted schematically. The lithium-ion battery <NUM> comprises the standard cathode <NUM> made of the base cathode material <NUM>, the standard anode <NUM> made of the base anode material <NUM>, an electrolyte <NUM>, a separation barrier <NUM>, an anode current collector foil <NUM>, and a cathode current collector foil <NUM> encased within a battery housing <NUM>. The base cathode material <NUM> may be any of many cathode compounds known to be of use in batteries; however, for the purposes of this description, the battery <NUM> is a lithium-ion battery <NUM> and exemplary base cathode materials <NUM> may include lithium iron phosphate (LFP) and the lithium nickel manganese cobalt oxide (NMC) and any other cathode material used in lithium-ion batteries. The base anode material <NUM> may be any of the anode materials known to be of use in batteries; however, for the purposes of this description, the battery <NUM> is a lithium-ion battery <NUM> and exemplary base anode materials <NUM> may include carbon power, graphite powder, and any other cathode material used in lithium-ion batteries. Such compounds also contain a small amount of a polymer used as a binder. Also, the most used electrolyte <NUM> in lithium-ion batteries <NUM> is lithium salt, such as LiPF6 in an organic solution. The key role of the electrolyte <NUM> is transporting positive lithium ions between the cathode <NUM> and anode <NUM>.

The battery <NUM> operates to transport electrons through the system of components. In <FIG>, in the discharging mode the electron transport starts with the anode current collector foil <NUM>, then through the anode foil/active mass interface to the anode active mass (in this case, the standard anode <NUM>). The discharging direction of electron flow (shown by schematic flow path <NUM>) is shown generally at Arrow A from negative to positive. Positively charged lithium ions <NUM> travel within the electrolyte <NUM> (in this case, the lithium accepting an electron at the standard anode <NUM> when charging), that electron and lithium (of the lithium ions <NUM>) pass across the separation barrier <NUM> (as shown by Dashed Arrows B) to the standard cathode <NUM>. Separation of the electron from the lithium (of the lithium ions <NUM>) occurs in the standard cathode <NUM>. The electron is transported through the cathode active mass (standard cathode <NUM>) to the active mass/foil interface then moves the electrons out of the cathode current collector foil <NUM> to the device it services.

<FIG> shows the battery <NUM> of <FIG> during charging. The charging direction of electron flow (shown by schematic flow path <NUM>) is reversed as shown generally at Arrow C from positive to negative. Positively charged lithium ions <NUM> travel within the electrolyte <NUM> from the standard cathode <NUM> passing across the separation barrier <NUM> (as shown by Dashed Arrows D) to the standard anode <NUM>.

Significant improvement in the conductivity of either the anode or the cathode or both leads to lower resistivity, not only across or through the respective cathodic or anodic film, but also generally across the entire battery cell. As a result, a lower resistance leads to higher voltage to move a given current or move a higher current at a given voltage. This, in turn, leads to faster charging or discharging, or the ability to move an electron at greater ease through thicker films, thus increasing capacity. There will also be a decrease in Joule heating, with a corresponding reduction in temperature and in energy loss. A decrease in operating temperature also results in a more efficient and safer battery.

Described in this disclosure are exemplary conductive additives <NUM> (see <FIG>, <FIG>, <FIG>) for the anode <NUM> and the cathode <NUM> that significantly improve conductivity enhancing the performance of these components <NUM>, <NUM> and the battery <NUM> within which they are used. By dispersing some of these exemplary additives <NUM> within the base cathode material <NUM> and/or the base anode material <NUM>, the resultant, enhanced cathode <NUM> and/or enhanced anode 44exhibit increased conductivity and ion transport within the battery system is facilitated. It is also postulated that the non-carbon surfaces of the highly conductive anode additives may inhibit SEI growth.

<FIG> is a representative depiction of a portion of an exemplary embodiment of a cathode <NUM> as generally known in the prior art showing a base cathode material <NUM> from which the cathode <NUM> is made. As noted above, the base cathode material <NUM> may be any of many cathode compounds known to be of use in batteries.

An exemplary embodiment of an enhanced cathode <NUM> showing metal-coated fibers <NUM> dispersed throughout the base cathode material <NUM> is depicted in <FIG>. The depiction of <FIG> is not drawn to scale, nor does it suggest any specific level of loading. Rather, the depiction is merely intended to give context to the dispersion of metal-coated fibers <NUM> within the base cathode material <NUM>.

<FIG>, a magnification compared to <FIG>, depicts an alternative exemplary embodiment of the enhanced cathode <NUM> showing metal-coated fibers <NUM> and high aspect ratio conductors <NUM>, for example, conductive filamentary structures <NUM> dispersed throughout the base cathode material <NUM>. Such high aspect ratio conductors <NUM> are smaller than the metal coated fibers <NUM> in at least one material physical aspect, such as diameter, weight, or volume and may also exhibit branching. The electrical conductivity between the conductive metal-coated fibers <NUM> is further enhanced by the addition of such high aspect ratio conductors <NUM>. Again, the depiction of <FIG> is not drawn to scale, nor does it suggest any specific level of loading. Rather, the depiction is merely intended to give context to the dispersion of metal-coated fibers <NUM> within the base cathode material <NUM>.

<FIG> is a representative depiction of a portion of an example anode <NUM> as generally known in the prior art showing a base anode material <NUM> from which the anode <NUM> is made. As noted above, the base anode material <NUM> may be any of the anode materials known to be of use in batteries.

An example (provided for illustrative purposes only and not forming part of the present invention) enhanced anode <NUM> showing metal-coated fibers <NUM> dispersed throughout the base anode material <NUM> is depicted in <FIG>. The depiction of <FIG> is not drawn to scale, nor does it suggest any specific level of loading. Rather, the depiction is merely intended to give context to the dispersion of metal-coated fibers <NUM> within the base anode material <NUM>.

<FIG>, a magnification compared to <FIG>, depicts another example (provided for illustrative purposes only and not forming part of the present invention) of an enhanced anode <NUM> showing metal-coated fibers <NUM> and high aspect ratio conductors <NUM>, for example, conductive filamentary structures <NUM> dispersed throughout the base anode material <NUM>. Such high aspect ratio conductors <NUM> are smaller than the metal coated fibers <NUM> in at least one material physical aspect, such as diameter, weight, or volume and may also exhibit branching. The electrical conductivity between the conductive metal-coated fibers <NUM> is further enhanced by the addition of such high aspect ratio conductors <NUM>.

Following are a few representative examples that demonstrate the concepts and advancements disclosed herein:.

Example #<NUM> - Nickel-coated carbon fiber in a cathode. A nickel-coated carbon fiber (<NUM> microns diameter, with <NUM>% nickel coating, or <NUM> micron thick, precision chopped to <NUM>) provided excellent conductivity in the cathode. Adding <NUM>% by weight of the described fiber moved the through thickness resistance of a <NUM> microns film from <NUM> ohms (no fiber) down to <NUM> ohms (<NUM>% fiber). However, the lithium-ion coin cells made from these films would not cycle. It was discovered that the cell corroded at <NUM> volts, before reaching the <NUM> volts operating condition. This is because the half-cell potential of nickel and lithium is <NUM> volts. However, this did demonstrate that the conductivity could be greatly improved and suggested that the nickel-coated fiber should work in systems that remain below about three and a half volts (see anode examples below).

Note that the fiber loaded film is <NUM>% thicker than the standard film but exhibits the same resistance and same voltage as its thinner parent. Thus, the capacity of the fiber-loaded film was increased by <NUM>%. The implication is a higher capacity at the same rate (resistance driven), or a higher rate at equal capacity.

Example #<NUM> - Aluminum-coated fibers precision chopped to <NUM>. These coated fibers were dispersed into a standard cathode mix at <NUM>% by weight (always reserving a portion of the mix for a control). This was repeated several times, the largest variable being a batch to batch or fiber type variation in the aluminum-coated fiber conductivity.

Films were extruded onto aluminum foil with a doctor blade, the height of the blade being adjusted to achieve a consistent film thickness and weight, depending on the desired thickness and the solvent-to-solids ratio of the mix. After drying, the uncalendared films were tested for volume resistivity per ASTM Method D2739. The table below reports several of these comparative batches.

With sample set D, the samples were calendared and measured for composite Volume Resistivity (CVR) and interface resistivity (IR).

Example # <NUM> - Higher fiber loading in cathode. A standard cathode mixture was loaded with <NUM>%, <NUM>%, <NUM>% and <NUM>% of <NUM> precision chopped, nickel-coated fiber having a <NUM>% nickel coating (<NUM> thickness). Attempts to mix above <NUM>% resulted in poor dispersion. However, the following table illustrated the improvement in through thickness volume resistivity when films of equal thickness were pulled from these mixtures.

Volume resistivity of cathode films modified with precision-chopped nickel-coated carbon fiber at <NUM>% nickel and <NUM> length.

Example #<NUM> - Effect of percent nickel coating on the fiber. In the same experiment as Example #<NUM>, one sample was made with <NUM>% nickel coating on the fiber, resulting in four times the weight and thickness of nickel on the fiber (carbon fiber) (base weight is <NUM> gm/meter, while the <NUM>% is <NUM> gm/meter, and the <NUM>% is <NUM> gm/meter). The density of the <NUM>% nickel-coated fiber is <NUM> gm/cc, while the density of the <NUM>% nickel-coated fiber is <NUM> gm/cc. For this example, the objective was to add a volume consistent with that representative of the <NUM>% nickel-coated fiber loading. The loading weight range for <NUM>% nickel-coated fiber may range up to <NUM>%, but for this example <NUM>% by weight was chosen, which is equivalent to the fiber volume loading of <NUM>% of the <NUM>% nickel-coated fiber. At this loading, the dispersion went well and the film pulled well. But the through thickness volume resistivity of this film was an outstanding <NUM> ohm-cm, almost double that the best loading of the <NUM>% nickel-coated fiber. This higher conductivity and nickel loading will result in greatly improved performance, but furthermore, will have improved current capability, making it more appropriate for power cells.

Examples <NUM>, <NUM> and <NUM> are provided for illustrative purposes only and do not form part of the present invention.

Illustrative Example #<NUM> - Anode with copper-coated carbon fibers. Because the current collector of the anode is copper foil, copper may be a viable candidate for anode improvement. In this example, up to <NUM>% of a copper-coated carbon fiber was added to the anode. The copper coating is <NUM>% by weight on an AS4 fiber. The copper coated carbon fiber was obtained from Technical Fiber Products of Schenectady, New York, and precision chopped to <NUM> length. The resistivity of the resulting anode was reduced from <NUM> ohms to <NUM> ohms, or a <NUM>% improvement in the conductivity. As a result, the voltage of the anode was reduced from <NUM> ohm down to <NUM> ohm. This lower voltage implies a higher capacity at a given charge rate, or alternatively, a higher charge rate.

Illustrative Example #<NUM> - Anode with precision-chopped, nickel-coated carbon fiber (NiPCF). Nickel is also a viable element for inclusion into the anode. Precision-chopped, nickel-coated carbon fibers were obtained from The Conductive Group, Heber City, Utah. The nickel coating was <NUM>% by weight, or <NUM> microns thickness, on an AS4 carbon fiber. Remembering that the anode is already composed of conductive graphite powder, the addition of the NiPCF alone either at <NUM>% by weight or even <NUM>% by weight, did little to significantly improve the conductivity (either the CVR or the IR) of the anode film. Some samples showed no statistically significant improvement, while some others showed perhaps about a <NUM>% improvement. These improvements are considered marginal.

Illustrative Example #<NUM> - Anode with filamentary branching structures. Nickel powders produced by chemical vapor decomposition may be produced in two distinct geometrical classes; either spherical (type <NUM> powders) or filamentary (type <NUM> powders). Type <NUM> powders are of little use in increasing conductivity until loadings are exceptionally high, due to the need for the particles to come in close contact to each other. However, the filamentary powders become conductive at lower loadings due to the higher aspect ratio, and in part due to filamentary powders generally exhibiting some degree of branching. These powders in larger diameter format (generally above one micron in diameter of the main branch) are available through Vale or Novamet, notably as Type <NUM> powder (and its derivatives). Nanostrands are a filamentary branching metal having a smaller diameter with more extensive branching. Nanostrands are available from The Conductive Group, Heber City, Utah.

The type <NUM> powder alone did little to increase the conductivity of the system. However, the nanostrands did show a significant increase in the conductivity of the anode mix.

Of interest are the combinations of the NiPCF fibers with the filamentary branching structures, forming a so called "logs and tumbleweeds" network.

The following table compares the CVR and IR of standard anode films to that of <NUM>% NiPCF, <NUM>% type <NUM>, <NUM>% nanostrands, and <NUM>%+<NUM>% NiPCF/<NUM> and <NUM>%+<NUM>% NiPCF/nanostrands:.

It is noted that the CVR of individual additives seem to not be very effective, but the combinations do move the CVR somewhat. They all have some effect on the IR, some very significant. This is likely because none of the additives individually are much more conductive than the carbon powder. But the "logs and tumbleweeds" provides a more complex electron transport opportunity. The IR, the interfacial resistance, suggests that the combinations of additives multiple paths directly to the underling foil across the ever-present polymer binder barrier. Calendaring likely provides additional physical impression of the conductors into the foil.

It has been observed that the filamentary branching structures (tumbleweeds) not only provide a multiplicity of high aspect ratio paths to the nickel-coated fibers (logs), but they also tend to lay on, or tend to touch the carbon particles in multiple places (each such touching hereinafter being referred to as a "touch point"). With the more open and branched nanostrands, they tend to wrap themselves around and envelop the carbon particles, like a spider web or net, creating a nanonet and exhibiting a multiplicity of touch points. It is this fashion of multiple touching and nanonetting that adds significantly more conduction opportunities. It becomes a "logs and tumbleweeds and nanonet" model and is structured uniquely in its ability to collect current at higher rates, higher amperages, and lower voltages.

The NiPCF/nanostrands sample was chosen to be the anode, and along with the cathode described near the end of Example <NUM>, were used to fabricate an experimental pouch cell battery.

Illustrative Example #<NUM> - Modified anode with standard cathode. This example is provided for illustrative purposes only and does not form part of the present invention. A control pouch cell was fabricated using a standard cathode and a standard anode. A second pouch cell was constructed using a standard cathode and a nickel-coated fiber modified anode. The standard anode had a CVR and IR values of <NUM> and <NUM> ohm, respectively. The modified anode had a CVR and IR of <NUM> and <NUM>, respectively. Thus, the CVR and IR of the modified anode were improved by <NUM> x and <NUM> x, respectively. As a result of the improved conductivity, the capacity at various discharge rates is shown in the following table:
<IMG>.

It is believed that this is due to the conductivity network of the previously described logs and tumbleweeds and nanonets, such structures more efficiently collect and transport the electrons. It has also been observed that the logs and tumbleweeds create a more open structure. Hence, it is likely that easier and more pathways for lithium-ion transport are being created.

Example #<NUM> - Modified cathode with standard anode. For this example, pouch cells were constructed with standard anodes and lithium iron phosphate cathodes. The control cell used a standard lithium iron phosphate cathode, while the second cell used a cathode with <NUM>% (wt%) loading of the <NUM>% nickel-coated carbon fiber, precision chopped to <NUM> in length, given the results of Example #<NUM>, this is a rather conservative loading.

The following table lists the discharge voltage and capacity of these cells at various discharge rates.

Claim 1:
A battery cathode [<NUM>] with enhanced electrical conductivity for use in a battery [<NUM>] having an electrolyte [<NUM>] with an electromotive potential, the battery cathode comprising:
an active base cathode material [<NUM>] having an operating voltage and comprising lithium iron phosphate; and
at least one additive dispersed within the active base cathode material [<NUM>] creating a dispersed mixture, the at least one additive comprising:
a first additive comprising a plurality of nickel-CVD coated fibers [<NUM>] having a diameter of from <NUM> microns to <NUM> microns, a nickel-coating thickness between <NUM> micron and <NUM> microns; and a fiber length of from <NUM> to <NUM>, the nickel-CVD coated fibers [<NUM>] comprising nickel having an electromotive potential, the selection of the nickel for the nickel coating and thickness for the nickel coating affects the electrical conductivity and the electromotive reactivity; the fiber diameter and fiber length of the nickel-CVD coated fibers [<NUM>] affects the aspect ratio, the surface area, and the dispersibility of the nickel-CVD coated fibers [<NUM>] within the active base cathode material [<NUM>], the dispersed mixture imparts improved electrical and mechanical properties to the battery cathode [<NUM>]; and
the first additive is dispersed into the active base cathode material [<NUM>] in a loading weight of up to <NUM>% of the active base battery cathode material [<NUM>];
wherein because the nickel coating may react corrosively to the electrolyte [<NUM>] at a reaction voltage, the operating voltage of the base cathode material [<NUM>] remains less than the reaction voltage of the nickel coating to the electrolyte [<NUM>].