KR20150058143A - Hybrid energy storage devices including support filaments - Google Patents

Abstract

The present invention relates to novel hybrid lithium-ion anode materials based on Si shells coaxially coated on carbon nanofibers (CNF). The unique cup-stacking graphite microstructure makes CNF an efficient Li ⁺ intercalation medium. Highly reversible Li ⁺ intercalation and extraction were observed at high power rates. More importantly, highly conductive and mechanically stable CNF cores optionally support coaxially coated amorphous Si shells with much higher theoretical specific capacities by forming fully lithiumated alloys. Adding a surface effect dominating site near the intercalation medium forms a hybrid device that includes the advantages of both the battery and the capacitor.

Description

[0001] HYBRID ENERGY STORAGE DEVICES INCLUDING SUPPORT FILAMENTS [0002]

<Mutual Reference to Related Applications - Reference>

This application is a continuation-in-part of U.S. Provisional Patent Application No. 13 / 779,409, filed February 27, 2013; This is a continuation of part of U.S. Provisional Patent Application No. 13 / 725,969 filed on December 21, 2012, which is a continuation-in-part of U.S. Provisional Patent Application 61 / 667,876 (filed July 3, 2012), 61/677, (Filed on July 30, 2013), 61 / 806,819 (filed on March 29, 2013), and 61 / 752,437 (filed on January 14, 2013).

This application is also related to U.S. Patent Application Nos. 13 / 779,472, 13 / 779,522, and 13 / 779,571, all filed on March 26, 2013.

The contents of all such patent applications and formal patent applications are incorporated herein by reference.

[0001]

The present invention relates to the field of energy storage devices including, but not limited to, batteries, capacitors, and fuel cells.

Rechargeable lithium-ion batteries are important electrical energy storage devices for powering portable electronic devices, power tools, and future electric vehicles. Improving the specific energy capacity, charge / discharge rate, and cycling life is important for the wider applications of these rechargeable lithium ion batteries.

In current commercial Li- ion battery, the graphite or other carbon-containing material (carbonaceous material) have been used as the anode, the anode may, completely intercalation (intercalate) with LiC ₆ theoretical 372 mAh / g by forming the compound Lt; / RTI &gt; In contrast, the silicon, and has a fully lithiated a (lithiated) Li alloy to form a _{4 .4} Si, the theoretical specific capacity of a much higher of 4,200 mAh / g (specific capacity) . However, the large volume expansion of the lithiated Si by as much as ~ 300-400% causes a large structural stress which conventionally leads to fractures and mechanical failure inevitably, which leads to the lifetime of the prior art Si anodes .

In some embodiments, the power storage device includes a hybrid core-shell of a high performance Li-ion anode by introducing an array of vertically aligned carbon nanofibers (VACNF) coaxially coated with an amorphous silicon layer NW (nano-wire) architecture. Vertically aligned CNFs include multi-wall carbon nanotubes (MWCNTs), which are optionally grown on a Cu substrate using a DC-Biased Plasma Chemical Vapor Deposition (PECVD) process. Carbon nanofibers (CNFs) grown by this method can have a unique internal morphology that differentiates them from conventional solid carbon nanofibers and the hollow structure of common MWCNTs. One distinguishing feature is that these CNFs are arbitrarily made up of a series of bamboo-like nodes across most hollow center channels. This microstructure can be attributed to the stack of conical graphitic cups discussed further elsewhere herein. On a larger length scale, these PECVD-grown CNFs are normally uniformly aligned vertically to the substrate surface and are well separated from each other. They may have no entanglement or have minimal entanglement and thus form a brush-like structure referred to as a VACNF array. The diameter of the individual CNFs can be selected to provide the desired mechanical strength so that the VACNF arrays are robust and can maintain their integrity over Si deposition and wet electrochemical tests.

Various embodiments of the present invention include certain types of support filaments that differ from VACNF. Such supporting filaments may include, for example, nanowires, carbon sheets, or other structures described herein. Other embodiments do not include any supporting filaments and instead use a binder.

Various embodiments of the present invention include a conductive substrate; A plurality of vertically aligned carbon nanofibers grown on a substrate, the carbon nanotubes comprising a plurality of multi-walled carbon nanotubes; And an electrolyte comprising an electrolyte comprising one or more charge carriers.

Various embodiments of the present invention include a conductive substrate; A plurality of vertically aligned carbon nanofibers grown on the substrate; And an energy storage layer disposed on the plurality of vertically aligned carbon nanofibers and comprising an intercalation material layer configured to have a lithium ion storage capacity of from about 1,500 to 4,000 mAh per gram of intercalation material, System.

Various embodiments of the present invention include a conductive substrate; A plurality of vertically aligned carbon nanofibers grown on the substrate; And an energy storage system disposed on the plurality of vertically aligned carbon nanofibers and including an intercalation material layer configured such that the ion storage capacity of the intercalation material is approximately the same at a charge rate of 1C and 3C.

Various embodiments of the present invention provide a method of manufacturing an energy storage device, comprising: providing a substrate; Growing carbon nanofibers on a substrate, the carbon nanofibers having a stacked-cone structure in which carbon nanofibers are stacked; And applying the intercalation material to the carbon nanofibers, wherein the intercalation material is configured for intercalation of the charge carriers.

Various embodiments of the invention include an electrolyte comprising at least one charge carrier; Conductive substrate; A plurality of vertically aligned support filaments attached to the substrate; An intercalation material disposed on each support filament and configured to reversibly adsorb a member of a charge carrier within most of the intercalation material; And a surface effect control surface disposed on the intercalation material and configured to adsorb a member of the charge carrier through a faradic interaction on the surface of the nanoparticles, each nanoparticle comprising a plurality of nanoparticles, an energy storage system comprising a binder configured to provide an effect dominant site.

In various embodiments of the present invention, an electrolyte comprising at least one charge carrier; Conductive substrate; A plurality of support filaments attached to a substrate; An intercalation material disposed on each support filament and configured to reversibly adsorb a member of a charge carrier within most of the intercalation material; And an energy storage system disposed on the intercalation material and comprising a binder comprising a plurality of surface effect control sites configured to promote intercalation of the charge carrier to the intercalation material.

Various embodiments of the invention include an electrolyte comprising at least one charge carrier; Conductive substrate; An intercalation material configured to reversibly adsorb a member of a charge carrier within most of the intercalation material; And a binder disposed on the intercalation material and configured to provide a surface effect dominating site comprising a plurality of nanoparticles, each nanoparticle configured to donate electrons to a member of a charge carrier through Faraday interaction on the surface of the nanoparticles And an energy storage system including

Various embodiments of the present invention include a cathode; An intercalation material configured to intercalate the charge carrier and donate electrons to the charge carrier at a first reaction potential as an anode separated from the cathode by an electrolyte comprising at least one charge carrier; Wherein the absolute difference between the first reaction potential and the second reaction potential comprises an anode having an anode of less than 2.4 volts.

Various embodiments of the present invention provide a device for setting a potential gradient in an anode of a charge storage device, comprising: means comprising an anode comprising an electrolyte, a plurality of surface effect dominating sites, an intercalation material and a substrate; Means for receiving a charge carrier of the electrolyte in one of the surface effect dominating sites; Means for receiving electrons from a charge carrier from one of the surface effect dominating sites; And means for receiving a charge carrier in the intercalation material.

Various embodiments of the present invention provide a method comprising: providing a conductive substrate; Growing a supporting filament on a substrate; Applying an intercalation material to the support nanofibers, wherein the intercalation material is configured for intercalation of the charge carriers; And applying the plurality of surface effect dominating sites in close proximity to the intercalation material.

Various embodiments of the present invention provide a method comprising: providing a conductive substrate; A surface effect dominating site is configured to receive electrons from a charge carrier at a first reaction potential and wherein the intercalation material is configured to accept a charge carrier or electron at a second reaction potential, Configured to receive from a charge carrier; And applying the bonding material, the surface effect dominating site and the intercalation material to the substrate.

Various embodiments of the present invention provide a method comprising: providing a conductive substrate; Providing a supporting filament; Applying an intercalation material to the supporting filament, wherein the intercalation material is configured for intercalation of the charge carrier; And adding the surface effect dominating site to the supporting filament.

Various embodiments of the present invention provide a method comprising: establishing a potential between a cathode and an anode of a charge storage device, wherein the charge storage device comprises an electrolyte; Receiving a first charge carrier of the electrolyte at the surface effect dominating site of the anode; Moving electrons of the anode to the first charge carrier; Receiving a second charge carrier of the electrolyte in the intercalating material of the anode; And transferring electrons from the intercalation material to the second charge carrier.

Various embodiments of the invention include the steps of setting a charge gradient in the anode of a charge storage device, wherein the anode comprises an electrolyte, a plurality of nanoparticles having surface effect dominating sites, an intercalation material, and a substrate; Accepting a first charge carrier of the electrolyte at one of the surface effect dominating sites; Transferring electrons from one of the surface effect dominating sites to the first charge carrier; Receiving a second charge carrier in the intercalating material of the anode; And transferring electrons from the intercalation material to the second charge carrier.

Various embodiments of the present invention include a conductive substrate; Carbon nanofibers or other supporting filaments connected to a conductive substrate; And an intercalation material configured to form a shell over at least a portion of the carbon nanofibers, wherein the carbon nanofibers comprise a plurality of exposed nanoscale edges along the length of the carbon nanofibers .

Various embodiments of the present invention include a conductive substrate; Carbon nanofibers or other supporting filaments connected to a conductive substrate; And an intercalation material configured to form a shell over at least a portion of the carbon nanofibers, wherein the carbon nanofibers comprise a plurality of cup-shaped structures along the length of the carbon nanofibers, such as a battery or an electrode .

Various embodiments of the present invention include a conductive substrate; Carbon nanofibers or other supporting filaments connected to a conductive substrate; And an intercalation material configured to form a shell over at least a portion of the carbon nanofibers, wherein the intercalation material is arranged in a feathered structure along the length of the carbon nanofibers.

Various embodiments of the present invention include a conductive substrate; Carbon nanofibers connected to a conductive substrate; And an intercalation material configured to form a shell over at least a portion of the carbon nanofibers, wherein the intercalation material is configured so that the expansion of the intercalation material does not delaminate the intercalation material from the carbon nanofibers Energy storage systems.

Various embodiments of the present invention provide a conductive substrate; Adding carbon nanofibers, each containing a plurality of exposed nanoscale edges along the length of the carbon nanofibers, to the conductive substrate; And applying an intercalation material configured for intercalation of the charge carriers to the carbon nanofibers.

Various embodiments of the present invention provide a conductive substrate; Adding carbon nanofibers, each containing a plurality of cup-shaped structures, along the length of the carbon nanofibers to the conductive substrate; And applying an intercalation material configured for intercalation of the charge carriers to the carbon nanofibers.

Various embodiments of the present invention provide a conductive substrate; Adding carbon nanofibers to the conductive substrate; And applying an intercalation material configured for intercalation of the charge carriers and arranged in a feather-like structure along the length of the carbon nanofibers to the carbon nanofibers.

Figures 1A and 1B illustrate a CNF array comprising a plurality of CNFs grown on a substrate, in accordance with various embodiments of the present invention.
Figures 2A-2C illustrate a plurality of vertically aligned CNFs of different states, in accordance with various embodiments of the present invention.
Figures 3A-3C illustrate the details of CNF, in accordance with various embodiments of the present invention.
Figure 4 illustrates a schematic diagram of a stacked-cone structure of CNF, in accordance with various embodiments of the present invention.
Figures 5A-5C illustrate electrochemical characterization of ~ 3 mu m long CNF's, according to various embodiments of the present invention.
Figures 6A-6C illustrate scanning electron microscopy images of 3 mu m long CNFs according to various embodiments of the present invention.
Figures 7A-7C illustrate the results achieved using CNFs comprising a Si layer as Li-ion battery anodes, in accordance with various embodiments of the present invention.
Figure 8 illustrates how the capacity of a CNF array varies with charge rate, in accordance with various embodiments of the present invention.
Figure 9 illustrates Raman spectra of CNF arrays, in accordance with various embodiments of the present invention.
Figures 10A-10C illustrate the variation of coulombic efficiency and Li ⁺ insertion-extraction capacities over 15 charge-discharge cycles, in accordance with various embodiments of the present invention.
11A-C illustrate SEM images of freshly prepared CNF arrays, in accordance with various embodiments of the present invention.
Figure 11d shows a cross-sectional view of a nanofiber / silicone composite comprising more than one CNF.
Figure 12 illustrates a carbon nanofiber array comprising fibers 10 mu m in length, according to various embodiments of the present invention.
Figure 13 illustrates methods of fabricating CNF arrays and / or CNFs, in accordance with various embodiments of the present invention.
Figure 14A illustrates a CNF comprising a power enhancing material, in accordance with various embodiments of the present invention.
Figure 14B illustrates details of the power enhancing material illustrated in Figure 14A, in accordance with various embodiments of the present invention.
Figure 14C illustrates another detail of the power enhancing material illustrated in Figure 14A, in accordance with various embodiments of the present invention.
Figure 15 illustrates an electrode surface comprising non-aligned CNF and power enhancing material coated by an intercalation material, in accordance with various embodiments of the present invention.
Figure 16 illustrates an electrode surface comprising a power enhancing material, a non-aligned CNF and a free intercalation material, according to various embodiments of the present invention.
Figure 17 illustrates an electrode surface comprising CNF free, intercalating material and power enhancing material, according to various embodiments of the present invention.
Figure 18 illustrates an electrode surface comprising a surface effect control site disposed in close proximity to CNF, according to various embodiments of the present invention.
Figures 19 and 20 illustrate electrode surfaces including surface effect dominated sites disposed in close proximity to free intercalation material, in accordance with various embodiments of the present invention.
Figure 21 illustrates a method of assembling electrode surfaces, in accordance with various embodiments of the present invention.
Figure 22 illustrates a method of operating a charge storage device, in accordance with various embodiments of the present invention.

1A and 1B illustrate a CNF array 100 including a plurality of CNFs 110 grown on a conductive substrate 105, in accordance with various embodiments of the present invention. FIG. 1A shows a CNF array 100 in a Li-extracted (discharged) state, and FIG. 1B shows a CNF array 100 in a Li-inserted (charged) state. The CNFs 110 of these and other embodiments discussed herein are arbitrarily aligned vertically. The CNF 110 is grown on the substrate 105 of Cu using a DC-biased plasma chemical vapor deposition (PECVD) process. As discussed above, the CNFs 110 grown by this method can have a unique morphology comprising a stack of cone-shaped graphite structures similar to stacked cups or cones or spirals. This results in a very fine structure that facilitates lithium intercalation. Here, this structure is referred to as a "stacked-cone" structure in other parts of the present application. On a larger length scale, these CNFs 110 are typically uniformly aligned vertically to the substrate surface and well separated from each other. The diameter of the individual CNFs can be selected to provide the desired mechanical strength so that the CNF array 100 is robust and can maintain its integrity through Si deposition and wet electrochemical cycles. A seed layer is optionally used to grow the CNFs 110 on the substrate 105. In use, the CNF array 100 can be a solid or a liquid, or a combination of solid and liquid, and is disposed in contact with an electrolyte 125 comprising one or more charge carriers, such as lithium ions. The CNFs 110 are configured such that a portion of the electrolyte 125 is disposed between the CNFs 110 and / or can prepare the substrate 105 through gaps between the CNFs 110.

Diameters of 75 to 300 nm or other ranges are possible, but the diameter of the individual CNFs 110 illustrated in FIGS. 1A and 1B is nominally 100 to 200 nm. The CNFs 110 are optionally tapered along their length. The CNFs 110 produced using the techniques discussed herein have excellent electrical conductivity along the axis (sigma = - 2.5 x 10 ⁵ S / m) and have a robust ohmic contact with the substrate 105, . The open space between the CNFs 110 is used to form a gradually thinned coaxial shell that gradually tapers in accordance with the mass at the tip 120 of the CNF 110 Enabling the silicon layer 115 to be deposited onto the respective CNFs. This design enables the entire silicon layer 115 to be electrically connected across the CNF 110 and to remain fully active during charge-discharge cycling. The expansion that occurs when alloying lithium with the silicon layer 115 can be readily accommodated in a radial direction perpendicular to, for example, the long dimension of the CNFs 110. The cycling stability of the non-Si-coated CNFs 110 and the Si-coated CNFs 110, and the charge and discharge capacities can be compared. The addition of the silicon layer 115 provided a significant Li ⁺ insertion (charge) capacity at C / 2 loading to 3938 mAh / g _Si , and 1944 mAh / g _Si was maintained after 110 cycles. This charge / discharge rate and corresponding capacity is significantly higher than previous architectures using Si nanowires or hybrid Si-C nanostructures. Figures 1A and 1B are perspective views.

In various embodiments, nominal Si thicknesses from 0.01 to 0.5, 1.0, 1.5, 2.5, 3.0, 4.0, 10, 20, 25 microns (or more) Lt; / RTI &gt; may be deposited onto 3 mu m long CNFs 110 to form the arrays 100. Likewise, in various embodiments, a nominal Si thickness of from 0.01 to 0.5, 1.0, 1.5, 2.5, 3.0, 4.0, 10, 20, 25 microns (or greater) can be used to form the CNF arrays 100 Lt; RTI ID = 0.0 &gt; 110 &lt; / RTI &gt; In some embodiments, the nominal thickness of Si is an average distance between 0.01 μm and CNFs 110.

Using the CNF arrays 100, Li ion storage with a mass-specific capacity from C / 2 charge rate to ~ 4,000 mAh / g is achieved. This capacity is significantly higher than that achieved using only Si nanowires or other Si-nanostructured carbon hybrids at the same power rate. The improved performance is due to the fully activated Si shell due to the short Li ⁺ path length of this hybrid architecture and efficient charge collection by the CNFs 110. Excellent cycling stability has been demonstrated over 110 cycles. In various embodiments, the storage capacity of the Li ion storage of the CNF arrays 100 may be about 750, 1500, 2000, 2500, 3000, 3500, or 4000 mAh per gram of Si, Lt; / RTI &gt; As used herein, the term "nominal thickness" (e.g., of Si) is the amount of Si that forms a flat layer of Si on the substrate 105. For example, the nominal thickness of Si of 1.0 [mu] m is the amount of Si that will result in a 1.0 [mu] m thick layer of Si when deposited directly on the substrate 105. [ The nominal thickness is reported because the nominal thickness can be easily measured by weight using methods known in the art. A nominal thickness of 1.0 占 퐉 will result in a smaller Si layer 115 on the CNFs 110 because Si is distributed over a larger area of the CNFs 110 surfaces.

Figures 2A-2C illustrate a CNF array 100 having an average fiber length of approximately 3 mu m, according to various embodiments of the present invention. 2A to 2C are scanning electron microscope (SEM) images. 2A shows a plurality of vertically aligned CNFs 110 having no silicon layer 115. FIG. FIG. 2B shows a plurality of vertically aligned CNFs 110 including a silicon layer 115. 2C shows a plurality of vertically aligned CNFs 110 that are extracted (discharged) after experiencing a 100 lithium charge-discharge cycle. The CNFs 110 are firmly attached to the Cu substrate 105 with an essentially uniform vertical alignment and random distribution on the surface of the substrate. Samples used in these studies were 1.11 x 10 ⁹ CNF / cm (counted from the top view of SEM images), corresponding to an average nearest-neighbor distance of ~ 330 nm ² &lt; / RTI &gt; average area density. The average length of the CNFs 110 in Fig. 2 is ~ 3.0 占 퐉 at> 90% of the CNFs in the range of 2.5 to 3.5 占 퐉 in length. The diameter spreads from ~ 80 nm to 240 nm, on average, to ~ 147 nm. The inverse teardrop shaped Ni catalyst of tip 120 is provided at the tip of each CNF 110 capping the hollow channel at the center of the CNF, ). The size of the Ni catalyst nanoparticles defined the diameter of each CNF 110. Longer CNFs 110 up to 10 [mu] m were also used in some studies to be discussed in the sections that follow.

In various embodiments, the average nearest distance may vary from 200 to 450 nm, from 275 to 385 nm, from 300 to 360 nm, and the like. In addition, the average length of the CNFs 110 may be approximately 2 to 20, 20 to 40, 40 to 60, 60 to 80, 80 to 100, 100 to 120, 120 to 250 (mu m), or more. Standard carbon nanofibers as long as millimeters long are known in the art. In various embodiments, the average diameter can vary from about 50 to 125, 100 to 200, 125 to 175 (nm), or other ranges.

An amorphous Si layer 115 was deposited on the CNF array 100 by magnetron sputtering. The open structure of the brush-like CNF arrays 100 has enabled Si to reach deep down into the array to form conformal structures between the CNFs 110. Consequently, it forms a thick Si coating on the CNF tip followed by a coaxial Si shell that gradually thinens around the bottom of the CNF, which is similar to a cotton swab, with an interesting tapered core-shell Structure. The amount of Si deposition is characterized by the nominal thickness of Si films on a flat surface, using quartz crystal microbalance (QCM) during sputtering. The Li ⁺ intercalation / extraction capacities were normalized to the total Si mass derived from the nominal thickness. At a nominal thickness of 0.50 m, the Si-coated CNFs 110 are well-separated from each other to form an open core-shell CNF array structure (shown in Figure 2b). This structure allowed the electrolyte to freely approach the entire surface of the Si layer 115. In the illustrated embodiment, the average tip diameter was ~ 457 nm, as compared to the ~ 147 nm average diameter of the CNFs 110 before application of the Si layer 115. The average radial Si thickness of peak 120 was estimated to be ~ 155 nm. This was obviously much smaller than the nominal Si thickness of 0.50 micrometers because most of the Si spread along the entire length of the CNFs. Other radial Si thicknesses in the range of 10 to 1000, 20 to 500, 50 to 250, 100 to 200 (nm) or in different ranges are identified in alternative embodiments. As discussed elsewhere herein, the stacked-cone of CNFs 110 provides an additional microstructure to the Si layer 115. [ The stacked-cone structure is optionally the result of a spiral growth pattern that forms a stacked-cone structure when viewed in cross-section.

The transmission electron microscopy (TEM) images of FIGS. 3A-3C further illustrate the structural details of the Si-coated CNFs 110. FIG. A Si layer 115 of ~ 390 nm Si was formed directly over the tip 120 of the ~ 210 nm diameter CNF 110. [ The largest portion of the swab Si layer 115 had a diameter of ~ 430 nm, which appeared near the very end of the apex 120. A coaxial Si layer 115 about the CNF 110 is deposited on the tip, showing a feather-like texture with modulated contrast that is distinctly different from the uniform Si (see Figure 3a) . This is likely to be the result of the stacked-cone microstructure of the PECVD-grown CNFs 110. It is known from the literature that these CNFs 110 include cup-like graphite structures that are unevenly stacked along the CNF 110 central axis. The use of these deviations in the diameter of the CNFs 110 has previously been disclosed in U.S. Patent Application Serial No. 12 / 904,113, filed October 13, 2010, owned by the Applicant.

The stacked-cone structure along the length of each CNF is formed by cup-like graphite layers of from 1 to 5, 5 to 15 or more than 10, which can be clearly identified in Figure 3b, as indicated by the dashed lines . The side edges of some of the graphite layers are exposed at the edge of each stacked-cone. At the exposed edges, lithium may penetrate between the graphite layers. In the molecular unit, the cup-shaped structure comprises graphene cone and / or graphite sheet which can interact with lithium. While the cup edge is a nanoscale edge and can have properties of graphene edges, properties such as those between graphene sheets can be found between graphite layers. The cup edge is provided to vertically aligned carbon nanofibers through which lithium ions can migrate. The new microstructure of VACNF creates a stack of exposed graphite edges, for example cup edges, along the length of the CNF sidewalls. The nanoscale edges are similar to the edges typically found on graphene / graphite sheets and ribbons. The exposed cup edge results in a modified silicon nucleation rate, thus producing a modulated silicon shell texture. The exposed edges also form a good interface between the VACNF core and the Si shell to facilitate rapid electron transfer in the hybrid structure. The two different structures of the Si shell can be controlled by altering the growth process of the VACNF. The region of the VACNF including the cup structure results in a feathered Si shell and the region of the VACNF not including the cup structure has a Si structure similar to that observed at the tip of the VACNF. VACNF is optionally configured to have one or more regions along the length of the VACNF and also at the apex without a cup stack. In an alternative embodiment, the carbon nanofibers also include a cup laminate structure with exposed graphite / graphene or graphite edges, but are not aligned and / or even directly attached to the substrate. Other methods of producing exposed nanoscale edges of graphite sheets include loosening carbon nanotubes using acids, unless the use of "cup-laminated" graphite microstructures is discussed elsewhere herein. The exposed nanoscale edges produced in this way are expected to also provide benefits in the control and / or fixation of the Si shell and may be included in some embodiments. For example, the edges of graphite nanoscale ribbons can be used to affect the growth of Si shells around the ribbon.

As used herein, the term "nanofibers" is intended to include structures having at least two dimensions on a nanoscale (less than one micrometer). This includes, for example, wires, tubes and ribbons, which may or may not be nanoscale in thickness and width but of length nanoscale. The term nanofiber is intended to exclude graphene sheets, both of which may be nanoscale in thickness, but are both nanoscale in length and width. In various embodiments, the supporting filaments discussed herein are nanofibers.

Although the resolution and contrast of FIGS. 3b and 3c are limited because the electron beam needs to penetrate hundreds of nanometer thick CNF or Si-CNF hybrids, the structural features are limited by the high resolution TEM studies using smaller CNFs in the literature . This unique structure generated clusters of broken graphite edges along the CNF sidewalls resulting in modulated density of the nucleation layers changed during Si deposition and thus the Si layer 115 on the CNF 110 sidewalls. The modulated density results in ultra-high surface area Si structures displayed by the (100 nm square) box 310 of FIG. 3A. The feathered Si structures of the Si layer 115 provide a very high Li capacity and also excellent Li ion interface resulting in fast electron transfer to the CNF 110. In Figure 3a, the dark areas of tip 120 are nickel catalysts for growth of CNFs. Other catalysts may also be used.

Figures 3b and 3c are images before (Figure 3b) and after (Figure 3c) lithium intercalation / extraction cycles. The sample of Figure 3c was in a delithiated (discharged) state when it was taken out of the electrochemical cell. The dashed lines in FIG. 3B are visual guidance of the laminated-cone graphite layers within the CNFs 110. The long dashed lines in Figure 3c represent the sidewall surface of the CNF 110. [

As discussed elsewhere herein, the stacked-cone structures of the CNFs 110 are thoroughly different from commonly used carbon nanotubes (CNTs) or graphite. The stacked-cone structure results in improved Li ⁺ implantation compared to standard carbon nanotubes or nanowires, even without the addition of Si layer 115. For example, the stacked-cone graphite structure of the CNFs 110 allows Li ⁺ intercalation into the graphite layers through the sidewalls of the CNFs 110 (rather than only at the ends). The Li ⁺ transport path across the walls of each of the CNFs 110 is very short (in some embodiments, has D ~ 290 nm), and of the commonly used seamless carbon nanotubes (CNTs) Lt; RTI ID = 0.0 &gt; open ends. &Lt; / RTI &gt; 4 illustrates a schematic diagram of a stacked-cone structure of CNFs 110. As shown in FIG. In this particular embodiment, the average values of the parameters are: CNF radius r _CNF = 74 nm, CNF wall thickness t _W = ~ 50 nm, graphite cone angle θ = 10 °, and graphite cone length D = t _W / Nm.

Figures 5A-5C illustrate electrochemical characterization of CNFs 110 ~ 3 mu m long. This characterization illustrates the phenomenon described in connection with FIG. 5A shows cyclic voltammograms (CV) from a 1.5 V to 0.001 V versus Li / Li ⁺ reference electrode at 0.1, 0.5, and 1.0 mV / s scan rate Respectively. A lithium disk was used as a counter electrode. Data was taken from the second cycle and normalized to the exposed geometric surface area. FIG. 5B is a graph of current density versus current densities of 64.7, 323, and 162 mA / g (normalized for the estimated carbon mass) or 71.0, 35.5, and 17.8 μm / cm ² (normalized for the geometric surface area) , Galvanostatic charge-discharge profiles at C / 0.5, C1, and C / 2 power ratios. Figure 5c shows the intercalation and extraction capacities (for the left vertical axis) and the number of cycles at the Coulomb efficiency versus C / 1 charge-discharge rate (for the right vertical axis). (C / 1 discharge rate = 1 hour, C / 2 discharge rate = 120 minutes (min), 2C = C / 0.5 = 30 minutes, etc.).

The newly assembled half-cell typically has an open circuit potential (OCP) of uncoated CNFs 110 anode of ~ 2.50 to 3.00 V vs. (vs.) Li / Li ⁺ reference electrode . CVs measured at 0.001 V to 1.50 V show that Li ⁺ intercalation starts when the electric potential is less than 1.20 V. The first cycle of 0.001 V from OCP involved the formation of the required protective layer, i.e. the solid electrolyte interphase (SEI), by decomposition of solvents, salts and impurities, Respectively. Subsequent CVs showed smaller but more stable currents. The cathode current associated with Li ⁺ intercalation slowly rose as the electrode potential swept negatively until a sharp cathode peak appeared at 0.18 V. [ Since the electrode potential was reversed positively after reaching the lower limit at 0.001 V, lithium extraction, indicated by continuous anode current and broad peak at 1.06 V, was observed over the full range up to 1.50 V.

The CV features of CNF arrays 100 were somewhat different from those of staged intercalation to graphite and slow Li ⁺ diffusion of CNTs into hollow channels. Li-ion implantation into the CNFs 110 is likely to be through intercalation between the graphite layers from the sidewalls due to their inherent structure. The TEM image of Figure 3c shows that graphite stacks of stacked-cones inside the CNF 110 are somewhat hindered during Li ⁺ intercalation-extraction cycles, which results in a large volume change that occurs on Li ⁺ intercalation There is a possibility. Some debris and nanoparticles are observed as white objects inside the CNFs 110 as well as on the outer surface. This represents penetration into the CNF through the sidewalls.

The constant current charge-discharge profiles of Figure 5b showed that the Li + storage capacity was reduced as the power rate increased from C / 2 to C / 0.5 (C / 0.5 also referred to as "2C &quot;). In order to make it even easier to compare the power ratios (especially for those higher than C / 1), the present inventors have used fractional notation C / 0.5 in place of "2C" . Li ⁺ intercalation and extraction capacities were calculated for the estimated mass of CNFs 110 (1.1 × 10 ⁴ g / cm ² ) which had been calculated based on the hollow vertically aligned CNF structure, using the following average parameters: The average parameters are: length (3.0 μm), density (1.1 × 10 ⁹ CNF per cm ² ), outer diameter (147 nm), and hollow inner diameter (49 nm, ~ 1/3 of the outer diameter) . The density of the solid graphite walls of the CNFs 110 was assumed to be the same as graphite (2.2 g / cm ³ ). At the normal C / 2 power ratio, the intercalation capacity was 430 mA hg ^-1 and the extraction capacity was 390 mA hg ^-1 . Both the above intercalation capacity and extraction capacity were theoretical values of 372 mAhg ^-1 , which may be due to irreversible Li ⁺ intercalation and SEI formation into hollow compartments within the CNFs 110. Extraction capacities were found to exceed 90% of the intercalation values at all power ratios, and both intercalation and extraction capacitances showed that the power ratio increased from C / 2 to C / 1 To ~ 9% as increasing from C / 1 to C / 0.5, and ~ 20% as increasing from C / 1 to C / 0.5.

Charge-discharge cycling according to, intercalation capacity is C / 1 In the power ratio after 20 cycles of 410 mA hg ^-1 but rather drops (drop) with 370 mA hg ^-1 from, extraction capacity is 375 to 355 mA hg ^{- 1. &} Lt; / RTI &gt; The overall Coulomb efficiency (i.e., the ratio of the extraction capacity to the intercalation capacity), excluding the first two cycles, was ~94% due to SEI formation on the CNF 110 surface. The SEI film is known to be readily formed on carbon-containing anodes during initial cycles, which allows lithium ion diffusion but is electrically insulated resulting in an increase in series resistance. The TEM image (FIG. 3C) and the SEM image (FIG. 6A) show that a non-uniform thin film was deposited on the CNF (110) surface during charge-discharge cycles. In some embodiments, the SEI functions as a sheath to increase the mechanical strength of the CNFs 110, resulting in a cohesive capillary force of the solvent as observed in the study with other polymer coatings. Which protects the CNFs 110 from collapsing into microbundles by the microfibers.

Figures 6A-6C illustrate SEM images of 3 mu m long CNFs 110, according to various embodiments of the present invention. FIG. 6A shows the CNFs 110 in the de-lithiated (discharged) state after the intercalation / extraction cycles. FIG. 6B shows CNFs 110 that include the Si layer 115 after 100 cycles in the de-lithiated state. FIG. 6C shows CNFs 110 comprising Si layer 115 after 100 cycles in the lithiated state. These images are 45 ° perspective views.

Figures 7A-7C illustrate the results achieved using CNFs 110 comprising a Si layer 115 as Li-ion battery anodes. These results were achieved using a nominal Si thickness of 0.50 m. FIG. 7A shows cyclic voltammograms of 1.5 V to 0.05 V versus Li / Li ⁺ at 0.10, 0.50, and 1.0 mV s ^-1 scan rates. Measurements are taken after the sample has gone through 150 charge-discharge cycles, and data for the second cycle at each scan rate is shown. Figure 7b shows constant current charge-discharge profiles at C / 0.5, C / 1, and C / 2 power ratios using samples at 120 cycles. All profiles were taken from the second cycle at each power rate. Figure 7c shows the intercalation and extraction capacities (for the left vertical axis) and the number of versus charge-discharge cycles (for the right vertical axis) of the two CNF arrays 100 (used as electrodes) Respectively. The first CNF array 100 uses one cycle at a C / 5 power rate and one cycle at a C / 2 power rate using one cycle at a C / 10 power rate Conditioned. It was then tested for C / 2 insertion rate and C / 5 extraction rate for the rest of the 96 cycles. The filled and open squares represent the insertion and extraction capacities, respectively. The second electrode was first conditioned using each of the two cycles at C / 10, C / 5, C / 2, C / 1, C / 0.5, and C / 0.2 power ratios. It was then tested at the C / 1 power rate for the next 88 cycles. The coulombic efficiencies on both sides of the electrodes are represented by filled (first electrode) and open (second electrode) diamonds, which mostly overlap at 99%.

The CVs in Figure 7a represent features that are very similar to the CVs of Si nanowires. (Less than about 0.5 and less than 0.7 V, respectively) for both the cathodic wave for Li ⁺ insertion and the anodic wave for Li ⁺ extraction, as compared to uncoated CNF array 100, . The peak current density is increased by 10 to 30 times after application of the Si layer 115 and is directly proportional to the scan speed. Obviously, the alloy-forming Li ⁺ insert into Si is much faster than the intercalation into uncoated CNFs, which was limited by the slow diffusion of Li ⁺ between the graphite layers. The cathode peak at ~ 0.28 V was not observed in previous studies on pure Si nanowires. The three anode peaks representing the conversion of Li-Si alloys to amorphous Si are similar to those using Si nanowires, despite the shift to lower potentials of 100-200 volts.

The constant current charge-discharge profiles of the CNF array, including the Si layer 115 shown in Figure 7b, are characterized by two remarkable features: (1) ~ 3000 mAh (g _Si ) ^-1 high Li ⁺ And extraction (discharge) capacity were achieved even at C / 2 rates and even after 120 cycles; And (2) Li ⁺ capacity was approximately the same at C / 2, C / 1, and C / 0.5 power ratios. That is, the capacity of the CNF array 100 operating as an electrode did not decrease when the charge rate was increased from C / 2 to C / 1 and C / 0.5. In various embodiments, over these fill rates, the capacity was largely independent of the fill rate. The total Li ⁺ storage capacity of the CNF arrays 100 including the Si layer 115 was about 10 times greater than the CNF arrays 100 without the Si layer 115. [ This occurred even though the low potential limit for the charge cycle was increased from 0.001 V to 0.050 V. As a result, the amount of Li ⁺ intercalation into the CNF core seems to have been negligible. The specific capacity was calculated by dividing the mass of Si which was calculated from the bulk density of 2.33 g cm ^-3 and the measured nominal thickness. This method was chosen as a suitable metric to compare the specific capacity of the Si layer 115 to the theoretical value of bulk Si. As compared to the actual mass density (~1.1 x ^10-4 g cm- ² ) of the CNFs 110, for 3.0 um long CNFs 110 deposited with a Si layer 115 of 0.456 um nominal thickness, Si The actual mass density of layer 115 was ~ 1.06 × 10 ^-4 g cm ^-2 . 7B is greater than 99% at all three power ratios and much higher than the coulomb efficiency of CNFs 110 without Si layer 115. [

Figure 8 illustrates how the capacity of the CNF array 100 varies with charge rate, in accordance with various embodiments of the present invention. The data is shown for several cycles. 8 shows the same current rates vs. versus charge rate (C-rate) required to achieve the total capacity at set times (C / h, for example, full Capacity / hours) &Lt; / RTI > for each group of cycles having the average specific discharge capacity. Vertical lines were focused on C / 4, 1C, 3C, and 8C. The CNF array 100 is symmetrically arranged in a first cycle using two cycles at C / 8, C / 4, C / 2, C / Conditioned and then tested at the C / 1 symmetry power rate for the next 88 cycles. This was repeated from cycle 101 to cycle 200. Beginning with cycle 201, the electrodes are symmetrically arranged in the order C / 4, C / 3, C / 2, C / 1, C / 0.75, C / 0.66, C / 0.50, C / , And C / 0.15 power ratios, respectively, and then tested at C / 1 symmetric power ratios for the next 45 cycles. This was repeated from cycle 301 to cycle 400 and from cycle 401 to cycle 500. The change in capacity is small (<16%), but the C-rate is changed by 32 folds. When the C-rate varied from 3C to 8C, the electrode after 100 cycles showed an increased capacity. Thus, a faster charge rate resulted in improved capacity. High capacity (> 2,700 mAh / g) was achieved on both high and low charge rates (C / 4 and 8C). As the C-rate is increased, the capacity is increased at charge rates above 3C. The non-capacity drop with the number of cycles is due to known, correctable factors.

Both CVs and charge-discharge measurements indicated that Li ⁺ implantation into the Si layer 115 was rapid and highly reversible, which is a desired feature for high performance Li-ion battery anodes. This results in different testing conditions: (1) slow asymmetric tests using C / 2 rate for insertion and C / 5 rate for extraction; And (2) two long cycling tests for two identical samples in a rapid symmetry test at a C / 1 ratio for both the insert and the extract (see FIG. 7C). All of the sets of data showed> 98% coulombic efficiency over long cycling except for the initial conditioning cycles (former 4 cycles and latter 12 cycles being changed to lower charge rates). In slow asymmetric tests, the insertion capacity dropped from 3643 mA hg ^-1 in the fifth cycle to 3341 mA hg ^-1 in the 100th cycle only by 8.3%. Even at a C / 1 charge-discharge rate, the insertion capacity drops only by 11% from 3096 mA hg ^-1 in the thirteenth cycle to 2752 mA hg ^-1 in the 100th cycle. The difference in Li ⁺ capacitances between these two data sets may mostly be due to the initial conditioning parameters and small sample-to-sample variations. This was indicated by similar values of insertion-extraction capacity during the first few fractional conditioning cycles of FIG. 7C at C / 10 and C / 5 rates. Faster charge rates (C / 0.5 for the ninth and tenth cycles of sample # 2 and C / 0.2 for the 11th and 12th cycles) were found to be detrimental and resulted in an irreversible drop in capacity . However, the electrode stabilized after longer cycling. As shown in FIG. 7B, the charge-discharge profiles were approximately the same at C / 2, C / 1, and C / 0.5 charge rates, which was measured using Sample # 1 after 120 cycles. This ends with four charge rate variations.

The specific capacity of the Si layer 115 in the range of 3000 to 3650 mA hg < ^-1 &gt; is consistent with the highest values of the amorphous Si anodes summarized in the literature. It is noted that the entire Si shell of the CNF array 100 was active for Li + insertion and maintained almost 90% of its capacity over 120 cycles, which, by the knowledge of the present inventors, is flat ultrathin (&lt; ) Si films. &Lt; / RTI &gt; The specific capacities disclosed herein were: ~ 2500 mA hg- ¹ at C / 2 rate with Si NWs and ~ 2200 mA hg- ¹ at C / 1 rate, and randomly oriented carbon nanofiber- Are much higher than those reported using other nanostructured Si materials at similar power rates, including ~ 800 mAhg &lt; ^-1 &gt; at a C / 1 ratio using NWs. Clearly, the coaxial core-shell NW structure on the well-isolated CNFs 110, such as those included in various embodiments of the present invention, has improved charge-discharge rates, substantially total Li ⁺ storage capacity of Si, And long cycle life.

As shown in Fig. 7C, an exceptionally high insertion capacity (~ 4500 mA hg ^-1 ) was always observed in the initial cycles, which was 20-30% higher than later cycles. On the other hand, the extraction values were relatively stable over the entire cycles. The extra insertion capacity includes three irreversible reactions: (1) the formation of a thin surface electrolyte interphase (SEI) layer (tens of nanometers); (2) reactions of Li with SiO _x provided on the Si surface (SiO _x + 2xLi? Si + xLi ₂ O); And (3) the conversion of a starting crystalline Si coating with a higher theoretical capacity (~ 4200 mA hg ^-1 ) to amorphous Si with lower capacity (<3800 mA hg ^-1 ) . The TEM image (FIG. 3C) and the SEM image (FIG. 6B) showed that a non-uniform SEI could be deposited on the surface of the Si layer 115 after charge-discharge cycles. This elastic SEI film can be used to secure the Si layer 115 to the CNF 110 surfaces when the CNF array 100 undergoes large volume expansion-contraction cycles that occur during charge- Can help. The impressive difference between the SEM images of FIGS. 6B and 6C shows the large expansion of the lithiated (filled) Si layer 115 compared to the non-lithiated state. (However, since the electrochemical cell was disseminated during imaging, some of the expansion may be due to oxidation of Li by air). Note that the generation of SEI during the initial charge-discharge cycles results in the differences shown in the Si layer 115 between FIGS. 3A and 3B. In Fig. 3B, Si interacted with the electrolyte to create an SEI filling the gaps between the feather-like structures. Interactions can include blending, chemical actions, charge coupling, encapsulation, and / or the like. Therefore, the Si layer 115 appears more uniform in Figure 3B. However, the Si layer 115 now includes interleaved layers of SEI and Si (feather-like structures). Each of these interleaved layers may be approximately tens of nanometers. The SEI layer can be an ion-permeable material that is the product of the interaction between the electrolyte and the Si layer 115 (or other electrode material).

The crystalline and amorphous structures of the Si shells were revealed by Raman spectroscopy. 9, a pristine CNF array 100 comprising a Si layer 115 is formed by a plurality of overlapping broad band spans of 350-550 cm &lt; ^-1 &gt; corresponding to amorphous Si, ), And a much higher sharp band at 480 cm &lt; ^-1 &gt; corresponding to nanocrystalline Si. After the charge-discharge tests, the broadband was merge to a single peak at 470 cm ^-1 , but the clear peak disappeared. The bare CNFs 110 did not show any features in this range. The crystalline Si peaks were down-shifted by ~ 40 cm ^-1 from those measured using single-crystalline Si (100) wafers and ~ 20-30 cm ^-1 from other micro-crystalline Si materials. These shifts may be due to much smaller crystal sizes and large disorders. The original Si layer 115 may be comprised of nanocrystals embedded in an amorphous matrix associated with the feather-type TEM image of Figure 3A. After the initial cycles, the Si nanocrystals were converted to amorphous Si, which is consistent with TEM images after the cycling test (see Figures 3b and 3c). However, the Si layer 115 apparently did not slide along the length of the CNF, in contrast to the large longitudinal expansion (up to 100%) of the pure Si NWs. This, in some embodiments, indicates that the expansion of the silicon is primarily radial rather than length relative to the carbon nanofibers. In some embodiments, the expansion occurs between the feathered structures of Si. For example, one feather may be inflated above and below the nearest neighbor feathers, thereby filling the gap between the feathers. In any case, the expansion occurs in such a way that the interlayer delamination of the silicon is significantly reduced compared to the prior art. Thus, the Si layer 115 was firmly fixed to the CNFs 110 for more than 120 cycles. The CNF-Si interface remained intact, but the volume change of the Si shell during Li ⁺ insertion was dominated by radial expansion.

Various embodiments of the present invention include CNFs 110 having different lengths and silicon shell thicknesses. One factor that can be controlled when CNFs 110 are generated is the average distance between CNFs 110 in the open space between each CNF 110, e.g., CNF array 100 . This space allows the Si layer 115 to expand radially upon charging and thus provides stability in some embodiments. Optimal since the electrode structure is dependent on both thickness sides of the length and the Si layer 115 of the CNF 110, the higher the total Li ⁺ the longer CNF to achieve a storage 110 and a thicker Si layers Lt; / RTI &gt; (115). &Lt; / RTI &gt; The longer CNFs 110 are correlated with the larger storage capacity. Figures 10a-10c illustrate Coulomb efficiency and Li + over 15 charge-discharge cycles using three 10 mu m long CNF (110) samples with a Si layer 115 deposited at nominal thicknesses of 0.50, 1.5, Lt; RTI ID = 0.0 &gt; insert-extraction capacities. After conditioning at C / 10 charge rate for the first cycle and C / 5 rate for the second cycle, asymmetric charge rates (C / 2 for insertion and C / 5 for extraction) &Lt; / RTI &gt; were used in subsequent cycles. This protocol provided minimal degradation and nearly 100% coulombic efficiency over cycles. Nominal thickness was measured in situ using quartz crystal microbalance (QCM) during sputtering.

The capacities as high as 3597 mA hg ^-1 and 3416 mA hg ^-1 are very similar to those using the 0.50 탆 thick Si layer 115 (see Fig. 7C) on 3.0 탆 long CNFs 110, A 1.5 탆 thick Si layer 115 was used. The capacity remained nearly constant over 15 cycles. However, an electrode with a 4.0 탆 nominal Si thickness showed a significantly lower specific capacitance at only 2221 mA hg ^-1 . This indicates that upon expansion, the Si layers 115 from adjacent CNFs 110 begin to contact each other, limiting them from further expansion and limiting the diffusion of Li between the CNFs 110. As a result, only a fraction of the silicon coating was activated in lithium insertion. Cycle stability is correspondingly worse than samples with thinner Si layers 115.

The same amount of Si (500 nm nominal thickness) on CNF arrays 100 containing 10 탆 length CNFs 110 has a 3 탆 length CNFs 110, even though the carbon mass is higher than 3 times, (3597 mA hg ^-1 , see Fig. 6A) in an amount almost equal to that of the Li ⁺ storage tank (3643 mA hg ^-1 , see Fig. 7C). This is a very strong evidence that the contribution of CNFs 110 is negligible in calculating Li ⁺ storage. In the Si-coated sample, very few Li ⁺ ions may have been intercalated into the CNFs 110, contributing to the stability of the structure during multiple charge-discharge cycles.

Variations in the well of the correlated three samples with their structure Li ⁺ storage capacity ratio (specific Li ⁺ storage capacity) is revealed by the SEM image illustrated in Figure 11a to Figure 11c. Figs. 11A-11C show scanning electron microscope images of newly prepared CNF arrays 100 (on CNFs 110 of ~ 10 mu m length). Si layer 115 was generated using a nominal Si thickness of (a) 0.50 m, (b) 1.5 m, and (c) 4.0 m which was used for in-situ in-situ. All images are 45 ° perspective views. At 0.50 탆 nominal Si thickness, the average tip diameter was found to be ~ 388 nm on 10 μm long CNFs, much smaller than the ~457 nm average diameter on 3.0 μm long CNFs 110. The Si layer 115 was thinner but more uniformly diffused along the 10 [mu] m long CNFs 110.

It is noted that the growth of 10 占 퐉 CNFs 110 took about 120 minutes, which is about six times that of the 3 占 퐉 CNFs 110 growing. Some Ni catalysts are etched slowly by NH ₃ during the long PECVD process, resulting in a continuous reduction of the Ni nanoparticle size and result in a tapered tip 120 (as shown in FIG. 12). The CNF 110 length variation was also increased using long CNFs 110. Collectively, these factors have reduced the shadowing effects of peak 120. As a result, even at 1.5 탆 nominal Si thickness, the CNFs 110 coated with the Si layer 115 are well separated from each other. The SEM image (Fig. 11B) of 1.5 탆 Si on 10 urn CNF arrays 100 is very similar to the SEM image (Fig. 2B) of 0.50 탆 Si on 3.0 urn CNF arrays 100. However, because the nominal Si thickness is increased to 4.0 占 퐉, the Si layers 115 are apparently merged with each other and filled to the greatest extent of the space between the CNFs 110 (see Fig. 10c). This reduced the free space required to accommodate the volumetric expansion of the Si layer 115. [ As a result, the Li + storage capacity (specific Li ⁺ storage capacity) was significantly lowered.

11A and 11B each include substantially the same number of CNFs 110, but with substantially less visible peaks 120 in FIG. 11B. This is because the Si layer 115 can form a nanofiber / silicon composite comprising a single CNF 110 (the cross section of which is shown in FIG. 1A). Alternatively, the Si layer 115 may form a nanofiber / silicon composite comprising two, three, or more CNFs 110 under a single silicon cover. This occurs when two or more CNFs 110 are combined during the Si layer 115 deposition process. The nanofiber / silicon composite is a structure comprising a continuous Si layer 115 enveloping one or more CNFs 110. A cross section of a nanofiber / silicone composite comprising two CNFs 110 is illustrated in FIG. In various embodiments, at least 1%, 5%, or 10% of the nanofiber / silicone composites comprise more than one CNF (110).

In various embodiments, the CNF arrays 100 with 0.50 and 1.5 탆 nominal Si thicknesses have comparable mass-specific capacities of 3208 343 and 3212 234 mAhg ^-1 , respectively. Samples with 4.0 μm nominal Si thickness provide much lower capacity at 2072 ± 298 mA hg ^-1 . Thinner Si coatings are fully activated and provide the maximum Li insertion capacity at which amorphous Si can be provided. On the other hand, the region-specific capacity (area-specific capacity) is, by 1.12 ± 0.08mA cm ^-2 h increases in proportion to the thickness of the Si in the Si thickness 1.5 ㎛ from 0.373 ± 0.040 mA h cm ^-2 at 0.50 ㎛ Si , But drop off from the linear curve to provide 1.93 ± 0.28 mAh cm ^-2 at 4.0 μm nominal Si thickness. At a nominal silicon thickness of 4.0 micrometers, only a fraction of the extra silicon of the thick Si coating is actively involved in Li storage. The thickness of 4.0 [mu] m is greater than the average distance between CNFs 110. [ The electrochemical results are consistent with the structure shown in the SEM image of FIG. 11C, which shows that the space between the CNFs 110 is essentially filled.

In various embodiments of the present invention, the structure of the CNF array 100 has a length of approximately 30 to 40, 40 to 75, 75 to 125 microns (or more, or combinations thereof) On the CNFs 110 having diameters of about 200 to about 300 nm. In some embodiments, these CNF arrays 100 are grown on conductive foils having a thickness in the range of ~ 10 microns, ~ 10 to 20 microns, ~ 10 to 50 microns, or more. In various embodiments, Si (equivalent to a 1.5 um nominal thickness on a flat surface) is deposited onto CNFs 110 of length 10 mu m to form CNF arrays 100. This maintains an open vertical core-shell nanowire structure with individual CNFs 110 well separated from one another so that Li ions can penetrate the CNF arrays 100 between the CNFs 110 . This unique hybrid architecture allowed the Si layers 115 to expand / contract freely in the radial direction during Li + insertion and extraction. High performance Li storage with a mass-specific capacity of 3000 to 3650 mAhg &lt; ^-1 &gt; was achieved even at C / 1 ratios. The capacity is matched with the maximum value expected from amorphous Si of similar mass, indicating that the Si layer 115 is fully activated. This 3D nano-structured architecture enables efficient electrical connections with large quantities of Si material while maintaining a short Li + insertion-extraction path. As a result, a high capacity close to the theoretical limit is possible during more than 120 charge-discharge cycles. When the filling rate was increased by 20 times from C / 10 to C / 0.5 (or 2C), there was little change in capacity. High capacity and remarkable cycle stability at significantly improved charge and power rates make this novel structure a choice of anode materials for high performance Li-ion batteries. The same core-shell concept can be applied to cathode materials by replacing the Si shell with TiO ₂ , LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , Li ₂ O, Li ₂ O ₂ and the like.

FIG. 13 illustrates methods for generating the CNF arrays 100 and / or CNFs 110 disclosed herein. In the substrate providing step 1310, a substrate 105 is provided. The substrate 105 is optionally suitable for growth of CNFs 110. The substrate 105 may comprise a variety of materials, for example, Cu. The substrate 105 is optionally a conductive foil having a thickness as described elsewhere herein. In the optional nucleation sites provision step 1320, nucleation sites for the growth of the CNFs 110 are provided on the substrate 105. A variety of nucleation materials, such as Ni particles, are known in the art. The nucleation sites are optionally provided at a density to produce average distances between the CNFs 110, such as those taught elsewhere herein. The nucleation sites providing step 1320 may be performed by using CNFs 110 on the substrate 105 using a binder after nucleation is not required or growth elsewhere for growth of CNFs 110 or similar structures Lt; / RTI &gt;

CNFs In the growth step 1330, the CNFs 110 are grown on, or in some embodiments separated from, the substrate 105. The CNFs 110 may optionally be fabricated to create a structure with exposed graphite edges along its length, to create a stacked-cone structure taught elsewhere herein, or similarly to create a variable structure . CNFs 110 may be grown to any of the lengths taught in other parts of the disclosure. Growth may be randomly generated by the method of Klankowski et al., "A high-performance lithium-ion battery based on the core-shell heterostructure of silicon-coated vertically aligned carbon nanofibers" J. Mater. Chem. A, 2013, 1 , 1055, which are incorporated herein by reference.

In the Si layer application step 1340, an intercalation material, such as Si layer 115, is applied to the grown CNFs 110. In some embodiments, the Si layer application step 1340 occurs prior to attaching the CNFs 110 to the substrate 105. The applied material may have any of the nominal thicknesses taught elsewhere herein to produce a Si layer 115 thickness of tens or hundreds of nanometers. In some embodiments, the Si layer application step 1340 includes growing the intercalation material in a structure that is independent of the exposed edges along the length of the CNF 110. For example, where the CNFs 110 comprise a cup-shaped structure as discussed herein, the Si layer application step 1340 includes the growth of the figure, for example the feathered structure illustrated in FIG. 3A.

In the optional PEM application step 1345, a power enhancement material (PEM) is added to CNF array 100 or CNFs 110. [ In some embodiments, the PEM application step 1345 occurs before attaching the CNFs 110 to the substrate 105. PEMs typically include binders and surface effect control sites, as discussed in further detail elsewhere herein. In the optional condition step 1350, the CNF array 100 formed using steps 1310-1340 is conditioned using one or more lithium intercalation cycles.

14A illustrates CNF 110 including power enhancing material 1320, in accordance with various embodiments of the present invention. The power enhancing material 1320 is applied as a layer on the intercalation material, for example, over the silicon layer 115. [ FIG. 14B illustrates details of the power enhancing material 1320 illustrated in FIG. 14B, in accordance with various embodiments of the present invention. The power enhancing material 1320 includes a surface effect dominating site 1430 and an optional binder 1440. The silicon layer 115 is an example of an intercalation material. It will be appreciated that when the silicon layer 115 is used herein as an example, other types of intercalation material may be substituted or combined with silicon. These alternative or additional intercalation materials include Ag, Al, Bi, C, Se, Sb, Sn, and Zn. The CNF 110 illustrated in FIG. 14 is typically one of a plurality of CNFs 110 in the CNF array 100.

In some embodiments, the surface effect dominating site 1430 comprises a surface of a nanoparticle configured to adsorb a charge carrier in a Faraday interaction, for example, to perform a redox reaction with a charge carrier. These are referred to as "surface effect dominance" because for such nanoparticles, the Faraday interaction between the charge carrier and the nanoparticle surface dominates the bulk Faraday interaction. Thus, the charge carriers are much more likely to react at the surface to most nanoparticles. For example, lithium ions are more likely to adsorb on the surface of nanoparticles than to be absorbed by most nanoparticles. These nanoparticles are sometimes referred to as surface redox particles. Faraday interactions result in a pseudo capacitor that can store a significant amount of loosely coupled charge and thus provide significant power density. In quasi-capacitances, the electrons are exchanged (e. G., Donated). In this case, it is exchanged between the charge carrier and the nanoparticles. Some dislocations cause some intercalation of the charge carriers to the nanoparticles, but this does not constitute most of the interaction at the surface effect dominating site 1430 and can break down some types of nanoparticles. A Faraday interaction is an interaction in which charge is transferred (e. G., Donated) as a result of an electrochemical interaction.

Nanoparticles containing surface effect dominant site 1430 is a transition metal oxide, for example TiO _2, Va ₂ O _5, MnO, MnO _2, NiO, tantalum oxide, ruthenium oxide, rubidium oxide, tin oxide, cobalt oxide, Nickel oxide, copper oxide, iron oxide, and / or the like. These may also be selected from metal nitrides, carbon, activated carbon, graphene, graphite, titanate (Li ₄ Ti ₅ O ₁₂ ), crystalline silicon, tin, germanium, metal hydrides, iron phosphates, polyanilines, . &Lt; / RTI &gt; It is recognized that a mixture of such materials and / or other materials having the desired Faraday properties may be included in the surface effect dominating site 1430. In various embodiments, such nanoparticles may have a diameter of less than 1, 2, 3, 5, 8, 13, 21 or 34 nanometers. The lower limit of the nanoparticle size depends on the molecular size of the constituent material. Nanoparticles contain at least several molecules. Smaller sizes provide a larger surface for bulk ratios of possible adsorption sites. However, particles containing only a single pair of molecules reduce stability. The nanoparticles are optionally formed in multiple layers. For example, these are the transition metal, Co, Ni, Mn, Ta, Ru, Rb, Ti, Sn, V ₂ O _2, FeO, Cu or Fe core onto a TiO ₂ layer (or any other discussed herein Nanoparticle material), or a graphene / graphite layer on the core of some other material. In some embodiments, the different core materials affect the reaction potential of the surface material. The amount of surface effect dominating site 1430 is arbitrarily selected according to the desired power and energy density. For example, a larger power density may be achieved by having a greater number of surface effect dominating sites 1430 per amount of intercalation material, or a greater amount of energy density may be achieved by having a larger Can be achieved by having a larger amount of intercalation material per number. It is an advantage of some embodiments of the present invention that both realistically high energy and power density can be achieved simultaneously.

By adsorbing the charge carrier on the surface of the nanoparticle, the charge carrier can provide the same power density as previously achieved with the capacitor. This is because the discharge of charge is not due to the diffusion of the charge carrier through the intercalation material. Also, by placing the surface effect dominating site 1430 in close proximity to the intercalation material, the charge carrier can move from the intercalation material to the surface effect dominating site 1430 (or directly to the electrolyte). This causes an energy density equal to or greater than a conventional battery. Both the energy density of the battery and the power density of the capacitor are achieved in the same device. It is noted that during discharge, the charge carriers in the intercalation material can migrate to the surface effect dominating site 1430 and thus recharge these sites.

In some embodiments, surface effect dominating site 1430 is disposed on larger particles. For example, the particle size can be greater than 1, 10, 25, 100 or 250 microns (but generally less than 1 millimeter). Activated carbon, graphite, and graphene are materials that can be included in particles of this size. For example, the activated carbon may be included in the power enhancement material 1320 with a pore size of the surface effect control site 1430 similar to the nanoparticle diameter taught above. For purposes of the present invention, nanoparticles are particles having an average diameter of less than 1 占 퐉.

Optional binder 1440 is configured to maintain surface effect dominating site 1430 close to the intercalation material. In some embodiments, the distribution of surface effect dominating sites 1430 is uniform throughout the binder 1440. For example, the nanoparticles comprising the surface effect control site 1430 can be mixed with the binder 1440 before the binder 1440 is applied to the intercalation material to form a relatively uniform distribution. Alternatively, the nanoparticles may be applied to the surface of the intercalation material prior to application of the binder 1440. This can cause a greater concentration of surface effect dominating site 1430 (in binder 1440) close to the intercalation material as compared to the area of the binder 1440 on the circle for the intercalation material. Binder 1440 is optional in embodiments where surface effect dominating site 1430 or associated nanoparticles are attached directly to the intercalation material, e.g., silicon layer 115. [

The binder 1440 is transparent (e.g., porous) to the charge carrier of the electrolyte. Examples of suitable materials for the binder 1440 include polyvinylidene fluoride (PVDF), styrene butadiene rubber, poly (acrylic acid) (PAA), carboxymethyl-cellulose (CMC), and / or the like. Other binders meeting the permeability requirements may be used. Binder 1440 optionally includes a material that increases its conductivity. For example, the binder 1440 may comprise a conductive polymer, graphite, graphene, metal nanoparticles, carbon nanotubes, carbon nanofibers, metal nanowires, Super-P (conductive carbon black), and / have. The material is preferably present at a sufficiently high concentration, e. G., A percolation threshold, to render the binder 1440 conductive.

The addition of surface effect control site 1430 in close proximity to the intercalation material (e.g., silicon layer 115) does not necessarily require the use of vertically aligned CNF 110, or any supporting filament . For example, Figure 15 illustrates an electrode surface comprising a non-aligned CNF 110 and a power enhancing material 1320 coated by an intercalation material, according to various embodiments of the present invention. In this embodiment, the CNF 110 is not directly attached to the substrate 110 but is held in close proximity to the substrate 110 by the binder 1440. In some embodiments, the CNF 110, including for example the cup-shaped structure illustrated in FIG. 3B, is used in a non-attached configuration, as illustrated in FIG. In this embodiment, the cup-shaped structure helps to prevent delamination of the silicon from the underlying CNF 110 still. Although CNF 110 is used herein as an example of a supporting filament, other types of supporting filaments discussed herein may be used to supplement or replace CNF 110 carbon nanofibers in certain embodiments.

The embodiment illustrated by Fig. 15 can be formed, for example, by growing CNF 110 that is not attached first. These are then coated with a silicon layer 115 (or some other intercalation material) such that the intercalation material is generally in contact with the CNF 110 as a coating layer. The coated CNF 110 is then mixed with the surface effect control site 1430 and the binder 1440. Finally, the resulting mixture is deposited on a substrate 105.

Figure 16 illustrates an electrode surface comprising a power enhancing material 1320, a non-aligned CNF 110 and a free-intercalation material 1610, according to various embodiments of the present invention. In this embodiment, the intercalation material 1610 does not necessarily have to be disposed around the CNF 110 as a coating. The intercalation material 1610 is free in terms of being not limited to the surface of the CNF 110, but is held close to the substrate 105 by the binder 1440.

The embodiment illustrated in FIG. 16 may be formed by, for example, mixing (in any order) the binder 1440, the surface effect dominating site 1430, the intercalation material 1610 and the CNF 110 together . The mixture is then applied to the substrate 105. In this embodiment, the CNF 110 may or may not be attached to the substrate 105 by a means other than the binder 1440. The intercalation material 1610 may or may not be in contact with CNF 110 or substrate 105. Likewise, surface effect dominating site 1430 is optionally in contact with substrate 105, CNF 110, and / or intercalation material 1610. The intercalation material 1610 may optionally have a size ranging from at least 0.1, 0.6, 1, 1.5, 2, 3,5, 7, 9, 10, 13, 15, 18, 21, Particles, suspensions, clusters, and / or drips of the intercalating material having the particles. Other sizes are possible in alternative embodiments.

Figure 17 illustrates an electrode surface comprising a binder 1440, a surface effect dominating site 1430, and an intercalation material 1610, without including support filaments, according to various embodiments of the present invention. In this embodiment, the surface effect dominating site 1430 and the intercalation material 1610 are held close to the substrate 11005 by a binder 1440.

Fig. 18 illustrates an electrode surface similar to that illustrated in Fig. However, in the embodiment illustrated by FIG. 18, the surface effect dominating site 1430 is concentrated in close proximity to the intercalation material 1610. For example, at least 2%, 10%, 25%, 50%, 75%, or 85% of the surface effect dominating site 1430 is on the particles contacted with the intercalation material 1610. The increased concentration of surface effect dominating site 1430 proximate to the intercalation material 1610 can be achieved using the methods described elsewhere herein. This causes a greater concentration of surface effect dominating site 1430 on the surface of the intercalation material 1610 compared to other volumes in the binder 1440.

Figures 14c, 19 and 20 illustrate electrode surfaces similar to those illustrated in Figures 14b, 16 and 17, respectively. However, in the embodiment illustrated by these figures, the surface effect dominating site 1430 is disposed very close to the free-intercalation material, in accordance with various embodiments of the present invention. At least 2%, 10%, 25%, 50%, 75%, or 85% of the surface effect dominating site 1430 is an intercalation material 1610 . In some embodiments, higher concentrations of nanoparticles, including surface effect dominating sites 1430, are disposed within the surface of the intercalation material 1610 of 5 nanometers above this surface of 10 to 15 nanometers. The increased concentration of surface effect dominating site 1430 proximate to the intercalation material 1610 is sufficient to allow the nanoparticles to form an electrostatic double layer on the surface of the intercalation material 1610, Can be achieved by selecting the appropriate zeta potential of the material 1610. The zeta potential is the electrical potential at the interface in the interface bilayers at the location of the surface versus the electrical potential at the point in the bulk solution away from the surface. The zeta potential is arbitrarily greater than 25 mV (absolute). In another embodiment, the nanoparticles are applied to the surface of the intercalation material 1610 prior to application of the binder 1440.

The intercalation material 1610 as illustrated in Figs. 16-20 may include any single material or combination of materials discussed herein for the silicon layer 115 (with or without silicon) . Likewise, the CNF 110 may comprise any single fiber of various types of fibers (with or without carbon nanofibers) discussed herein or a combination thereof, as illustrated in Figs. 16-20. have. For example, such CNF 110 may include branched fibers, multiwall fibers, wires, aerogels, graphite, carbon, graphene, boron-nitride nanotubes, and the like. The number of surface effect dominating sites 1430 and CNFs 110 shown in these figures and other figures herein is for illustrative purposes only. For example, in practice, the number of surface effect dominating sites 1430 may be greater. Likewise, the amount and size of the illustrated interlacer material 1610 and silicon layer 115 are for illustrative purposes. Alternative embodiments may include more or less amounts, and larger or smaller sizes. Likewise, the depth of the PEM 1420 and the length of the CNF 110 may deviate from those shown in the figures.

In various embodiments, the amount of nanoparticles comprising surface-effect dominated sites 1430 can be determined by measuring the concentration of nanoparticles on the surface of the intercalation material 1610 or silicon layer 115 (as measured in a discharged state) Can be selected to result in at least 0.1, 0.5, 0.7, 0.9, 1.1, 1.3, 1.5, 2, 3, 5, 10, 25, 50 or 100 times (or any range therebetween) of the layer. The 0.1 monolayer used herein specifies 10% and the 10x monolayer is 10 monolayers. In various embodiments, the amount of nanoparticles comprising the surface-effect dominating site 1430 is at least 1, 5, 10, or even 10 times greater than the nanoparticles on the surface of the intercalation material 1610 (as measured in a discharged state) 20, 50, 100, 250, or 500 nanometer layers (or any combination therebetween). Different coverage densities or depths are possible when measuring in a single layer. As nanoparticles (including surface-effect dominating sites 1430) approach the 1.0 monolayer, the nanoparticles are transferred between the charge carriers of the electrolyte moving through the binder 1440 and the intercalation material 1610 Layer can be formed. For example, in some embodiments, the electrolyte comprises lithium as a charge carrier. Lithium can migrate through the binder 1440 and cause a Faraday reaction with the surface effect dominating site 1430 where the electrons are donated from one of the surface effect dominating sites 1430 to lithium. These electrons are transferred (e.g., donated) to the nanoparticles through the intercalation material 1610 at the substrate 105. At this stage in the filling process, only a limited amount of charge carriers reach the intercalation material 1610 because the nanoparticles form a barrier. The charge is governed by the reaction at the surface effect dominating site 1430. In some embodiments, the filling can be fast because intercalation of the charge carrier to the intercalation material 1610 is not necessary before a Faraday reaction with the charge carrier takes place. The presence of the surface effect dominating site 1430 greatly increases the surface area where the initial Faraday reaction can occur prior to the intercalation. Surface effect dominating site 1430 facilitates intercalation of charge carriers to intercalation material 1610. The charge carriers may be intercalated into a form of acceptance at the surface effect dominating site 1430 or may be intercalated into an alternative form such as a metal oxide. When intercalated as a metal oxide, the oxygen of the oxide can be recycled back to the surface effect dominating site 1430 after the intercalation.

In some embodiments, because the nanoparticles form an imperfect barrier, some charge carriers still remain in the charge stage (e.g., the initial stage of charging the power storage device, including the electrodes discussed herein) (1610). The intercalation material 1610 also increases because some embodiments of the intercalation material 1610, e.g., silicon, expands when charge carrier intercalation occurs in the surface region. This reduces the surface coverage of the nanoparticles on the surface of the intercalation material 1610 and reduces the effectiveness of the nanoparticles in forming a barrier to the charge carrier. Thereby, as the charging progresses, a greater number of charge carriers per unit time can reach the intercalation material 1610. This continues until the charge is arbitrarily governed by the reaction in the intercalation material 1610. Reducing the surface coverage can also increase the average fraction of surface effect dominated sites 1430 on each nanoparticle exposed to the electrolyte. As used herein, the phrase "surface coverage" is used to denote the density of species on a surface and can be measured as the number of single layers (or fraction thereof), thickness, or concentration.

In some embodiments, power storage at the surface effect dominating site 1430 occurs at a potential where the Faraday surface reaction occurs, but no intercalation of the charge carriers to the nanoparticles including the surface effect dominating site 1430 occurs . This prevents degradation of the nanoparticles by repeated intercalation and de-intercalation of the charge carriers and allows for longer cycle life. At the same electrode, within the intercalation material 1610 through a Faraday reaction that takes place at a higher potential, optionally involving dislocations that cause intercalation of the charge carriers to the nanoparticles with surface effect dominating sites 1430 It may be desirable to store power. This may occur in some embodiments of the present invention because there is a potential drop between the substrate 105 and the electrolyte 125.

In one particular example, where lithium is a charge carrier, the surface effect dominating site 1430 is on TiO ₂ and the intercalation material 1610 is primarily silicon. It will be appreciated that in other embodiments, the particular voltage is dependent on the surface effect control site 1430 and the chemical species included in the intercalation material 1610, and the reactions that occur during charging, and so on. In various embodiments, the potential difference between the surface effect dominating site 1430 and the substrate 105 is at least 0.001, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1.0, 1.3, 1.7, 2.0, 2.2, Or any range therebetween. As used herein, the term " dislocation "is used to refer to the absolute value of the electrostatic potential (e.g., | x |).

Figure 21 illustrates a method of assembling electrode surfaces, in accordance with various embodiments of the present invention. The assembled electrode surface may be used as an anode, for example, in a battery, a capacitor or a hybrid device. The method illustrated in FIG. 21 is optionally used to form the various electrodes discussed elsewhere herein.

In the substrate providing step 2110, a conductive substrate is provided. The substrate providing step 2110 is similar to the substrate providing step 1310. [ In the substrate providing step 2110, an optional substrate 105 is optionally provided for the growth of the CNF 110 or other supporting filament. As discussed herein, the substrate 105 may comprise a variety of materials, such as Cu, Au, Sn, and the like. The substrate 105 optionally includes a nucleation site as described elsewhere herein.

In the optional CNF providing step 2120, the CNF 110 (or any other supporting filament described herein) is provided. The CNF providing step 2120 is optional in embodiments in which the support filament-free electrodes, for example those illustrated by Figures 17 and 20, are formed. In some embodiments, CNF 110 is provided by growing CNF 110 on substrate 105. In some embodiments, CNF 110 is provided by adding CNF 110 to the mixture, which is then applied to substrate 105. In some embodiments, the CNF 110 is formed separately from the substrate 105, and then attached to the substrate 105.

In an intercalation material providing step 2130, an intercalation material 1610 is provided. In some embodiments, the intercalation material 1610 is first applied to the CNF 110. In various embodiments, the intercalation material 1610 is applied as a colloidal suspension, using vapor deposition, in a solvent, as a paste, or the like.

In a surface effect dominating site (SEDS) providing step 2140, a surface effect dominating site 1430 is provided. As discussed elsewhere herein, the surface effect dominating site 1430 may be disposed on nanoparticles, or larger structures, such as graphite, graphene, or activated carbon. Surface effect dominating site 1430 may be provided as a suspension in binder 1140 or in a solvent, such as by spraying using sputter deposition, electro-deposition, evaporation, or the like. In some embodiments, the zeta potential of the intercalation material 1610 is selected such that the surface effect control site 1430 is concentrated at the surface of the intercalation material 1610.

In application step 2150, the intercalation material 1610, the surface effect dominating site 1430 and optionally the CNF 110 are applied to the substrate 105. Such materials can be applied in a wide variety of orders and combinations. For example, the intercalation material 1610 may be applied to the CNF 110 (possibly already attached to the substrate 105), and then the surface effect dominating site 1430 may be applied to the intercalation material 1610 It can be applied on the top. Alternatively, the free CNF 110, the intercalation material 1610 may be mixed first, and then either the surface effect control site 1430 and the binder 1140 may be added alone or in combination have. Based on the teachings herein, one of ordinary skill in the art will appreciate that in other embodiments, such components may be mixed or added in any order or combination. In addition, these components may be mixed before or after application to the substrate 105. Steps 2110-2150 may be performed in any order. After the applying step 2150, a condition step 1350 is optionally followed.

In some embodiments, the method illustrated in Figure 21 involves mixing the intercalation material 1610 and the surface effect control site 1430 in a suspension or solvent having a sufficient amount of dispersion. The dispersion is optionally applied to CNF (110). The solvent of the dispersion is then evaporated from the mixture to form a powder or coating on the CNF (110). Binder 1440 may be added to the suspension before or after application to the CNF 110. [ In some embodiments, application of the surface effect dominating site 1430 occurs at the end of the deposition of the intercalation material 1610 by replacing the material sputtered on the substrate 105. In this embodiment, for example, TiO ₂ may be added to the sputtering mix after almost all of the intercalation material 1610 has been deposited. This forms a sputtered layer of TiO ₂ on top of the intercalation material 1610 as surface effect dominating site 1430.

Figure 22 illustrates a method of operating a charge storage device, in accordance with various embodiments of the present invention. This method can be used, for example, when charging a charge storage device. In some embodiments, the method includes attaching the charging device to both the anode and the cathode of the charge storage device via a wire. These charge storage devices generate potentials at the anode and the cathode, causing a potential gradient between them. A potential gradient induces electrons to the anode. The steps illustrated in Figure 22 occur randomly at the same time, for example, they can occur at the same time or at the same time with respect to each other.

In the potential setting step 2210, the potential is set in the charge storage device. This potential can occur between the anode and the cathode of the charge device. This potential will cause a potential gradient between the substrate 105 and the electrolyte 125 in the charge storage device. The potential gradient can create a potential difference between the surface effect dominating site 1430 and the location of the intercalation material 1610. In various embodiments, the potential difference is at least 0.001, 0.1, 0.3, 0.4, 0.5, 0.8, 1.0, 1.3, 1.7, 2.0, or 2.4 V, or any range therebetween.

In the lithium receiving step 2220, a charge carrier, which is lithium but only one possible example, is accommodated in one of the surface effect dominating sites 1430. This charge carrier is optionally received through a binder 1440.

In the electron transfer step 2230, electrons are transferred (e.g., donated) to the charge carriers contained in the lithium acceptance step 2220 at the surface effect dominating site 1430. This transfer may involve sharing electrons between the surface effect dominating site 1430 and the charge carrier. The electrons are moved in the Faraday reaction and are typically conducted from the substrate 105. Movement occurs while the charge carrier is on the surface of the surface effect dominating site 1430 and occurs at the potential of such location. The reaction potential of the electron transfer depends on, for example, the reaction potential of the charge carrier and the reaction potential of the surface effect control site 1430. The reaction potential may be dependent on both the surface effect dominating site 1430 and the neighboring intercalation material 1610. The term "reaction potential &quot;, as used herein, is used to refer to the potential at which the reaction occurs at a remarkable rate. The reaction potential of the reaction can be illustrated, for example, by a peak in the cyclic voltammogram. In another example, the reaction Li + + e in an electrochemical cell ^- → Li or ^{2Li + + MO + 2e - →} Li 2 O + M ( where, M is any of transition metals being discussed herein), the potential required to produce a Is the reaction potential of this reaction. The reaction potential may be highly dependent on the environment in which the reaction takes place. For example, the second reaction may have a lower reaction potential in the presence of TiO ₂ nanoparticles having a diameter in the range of 2 to 10 nm. Likewise, the reaction potential can be influenced by the energy required for the intercalation, or the adjacency of the surface effect dominating site 1430 and the intercalation material 1610.

In the lithium intercalation step 2240, a charge carrier, in which lithium is only one possible example, is intercalated in the intercalation material 1610. This step may include movement of the charge carrier into the bulk of the intercalation material 1610. [ The charge carriers may be introduced into the intercalation material 1610 as a species species formed in the surface effect dominating site 1430 as the same chemical species that is received in the surface effect dominating site 1430 in the lithium receiving step 2220, Lt; / RTI &gt; For example, a charge carrier may be accommodated in the intercalation material 1610 as an oxide of a species (e.g., Li ₂ O, etc.) that is received at the surface effect dominating site 1430.

In electron transfer step 2250, electrons are transferred from the intercalation material 1610 to the charge carrier of the lithium intercalation step 2240. The electrons are moved in the Faraday reaction and are typically conducted from the substrate 105. Movement occurs while the charge carrier is in the intercalation material 1610 and occurs at the potential of such a location. The reaction potential of the electron transfer may depend on the reaction potential of the charge carrier and the reaction potential of the intercalation material 1610. [ The potential of this conduction band can be influenced by both the intercalation material 1610 and the adjacent surface effect dominating site 1430. Surface-dominated sites 1430 can facilitate the transfer of lithium from electrolyte 125 to intercalation material 1610. [ As discussed elsewhere herein, this migration can occur via a middle oxide such as Li ₂ O. This work function of electron transfer may differ from the work function of electron transfer in electron transfer step 2230. [ For example, in various embodiments, the work function is at least 0.001, 0.1, 0.3, 0.4, 0.5, 0.8, 1.0, 1.3, 1.7, 2.0 or 2.4 V, or any combination thereof. In some embodiments, it is thermodynamically more desirable for lithium to be intercalated into the intercalation material 1610 than from most of the nanoparticles, including the surface effect dominating site 1430. [ However, the presence of the surface effect dominating site 1430 can catalyze the intercalation of the charge carrier to the intercalation material 1610.

In some embodiments, when the charge carrier is converted to an oxide in the electron transfer step 2230, the electron transfer step 2250 moves the oxygen from the intercalation material 1610 back to the surface effect dominating site 1430 . This oxygen is received as an oxide of the charge carrier in the intercalation material 1610 and is released from the charge carrier during the intercalation. After being moved back to surface effect dominating site 1430, this oxygen can be used in further generation of electron transfer step 2230, i.e., oxygen is recycled.

Although the description of Figure 22 assumes that the charge carriers received in the lithium receiving step 2220 and the charge carriers in the lithium intercalation step 2240 are two different individual charge carriers (which may be of the same type) In embodiments, steps 2220, 2230, and 2240 may be performed by the same individual charge carriers. For example, in some embodiments, the lithium accepting step 2220 includes receiving a charge carrier in one of the surface effect dominating sites 1430. Electron transfer step 2230 then involves a charge carrier reacting with surface effect dominating site 1430 to form an intermediate compound. In some embodiments, this reaction includes 2Li ⁺ + MO + 2e ^- → Li ₂ O + M, where M is any transition metal discussed herein and Li ₂ O is the resulting intermediate compound. In the lithium intercalation step 2240, the intermediate compound (e.g., Li ₂ O) is intercalated into the intercalation material 1610, or one of the Li in the intermediate compound (or both) is Li ₂ Lt _; RTI ID = _0.0 &gt; Si) _{&lt; /} RTI &gt; of the intercalation material (e. Such movement may result in the regeneration of the MOs partitioned in the electron movement step 2230. [ In this example, it is noted that the same individual Li atoms are included in each of steps 2220-2230 and 2240. Electron transfer step 2250 is not required in this embodiment of the method illustrated by FIG. In some embodiments, it is possible that both the reaction sequence comprising an intermediate such as Li ₂ O and the reaction sequence without an intermediate occur during a single charge cycle.

Various embodiments are specifically illustrated and / or described herein. However, it will be understood that modifications and variations are covered by the above teachings and are within the scope of the appended claims, without departing from the spirit and intended scope of the appended claims. For example, while the examples discussed herein focus on CNFs having stacked-cone structures, the teachings may be adapted to other materials having similar or different structures. Likewise, although Cu substrates and Li charge carriers are discussed herein, other substrates and charge carriers will be apparent to those skilled in the art. The silicon layer 115 is optionally formed with intercalation materials in addition to or as an alternative to silicon. For example, tin, germanium, carbon, graphite, graphene, silicon, other materials discussed herein or combinations thereof may be used as the intercalation material. In addition, aerosols, nano-wires, TiO ₂ (titanium oxide), metal wires, carbon wires, or boron nitride nano-fibers can be used in place of the carbon nanofibers discussed herein. The relative concentrations of binder 1440, surface effect dominating site 1430, intercalation material 1610 and CNF 110, and other elements in the figure may deviate significantly from those illustrated.

The electrodes taught herein may be included in a wide variety of energy storage devices, including capacitors, batteries, and hybrids thereof. These energy storage devices will be used in, for example, lighting systems, portable electronic devices, load balancing devices, communication devices, standby power supplies, vehicles, and computing devices. The concepts taught herein can in many cases be applied to the cathode and also to the anode.

Details of VACNF growth and silicon deposition, microscopy and spectroscopic characterization, and electrochemical cell assemblies and charge-discharge tests can be found in U.S. Provisional Application No. 61 / 667,876, filed July 3, 2012.

The embodiments discussed herein are illustrative of the present invention. As these embodiments of the invention have been described in connection with the drawings, various modifications or adaptations of the described methods and / or specific structures may become apparent to those skilled in the art. It is contemplated that all such modifications, adaptations, or variations that rely on the teachings of the present invention and that are amenable to those techniques through these teachings are within the spirit and scope of the present invention. Therefore, it is to be understood that these descriptions and drawings are not to be considered in a limiting sense, since it is understood that the invention is not limited in any way to the illustrated embodiments.

Claims (38)

Conductive substrate;
Carbon nanofibers connected to a conductive substrate, comprising a plurality of exposed nanoscale edges along the length of the carbon nanofibers; And
An intercalation material configured to form a shell over at least a portion of the carbon nanofibers
&Lt; / RTI &gt; 32. A system or method according to any one of claims 1 and 29 to 31, wherein each exposed nanoscale edge comprises an edge of a plurality of graphite sheets. 32. A system or method according to any one of claims 1, 2 and 29 to 31, wherein each exposed nanoscale edge is configured to control the growth of the intercalation material. 31. A system according to any one of claims 1 to 3 and 29 to 31, wherein each exposed nanoscale edge is configured to provide a path of travel for a charge carrier inside the carbon nanofibers or Way. 32. A system or method according to any one of claims 1 to 4 and 29 to 31, wherein each exposed nanoscale edge comprises a plurality of graphene edges. Conductive substrate;
A carbon nanofiber connected to the conductive substrate, the carbon nanofiber including a plurality of cup-shaped structures along the length of the carbon nanofibers; And
An intercalation material configured to form a shell over at least a portion of the carbon nanofibers
&Lt; / RTI &gt; 32. A system or method according to any one of claims 1 to 6 and 29 to 31, wherein each cup-shaped structure comprises a wall having a plurality of graphite sheets. The system or method according to any one of claims 1 to 7 and 29 to 31, wherein each cup-shaped structure is configured to control the growth of the intercalation material. Conductive substrate;
Carbon nanofibers connected to a conductive substrate; And
An intercalation material arranged to form a shell over at least a portion of the carbon nanofibers and arranged in a feather-like configuration along the length of the carbon nanofibers
&Lt; / RTI &gt; Conductive substrate;
Carbon nanofibers connected to a conductive substrate; And
An intercalation material configured to form a shell over at least a portion of the carbon nanofibers and an expansion of the intercalation material not to delaminate the intercalation material from the carbon nanofibers;
&Lt; / RTI &gt; The system or method according to any one of claims 1 to 10 and 29 to 31, wherein the expansion is radial to carbon nanofibers. 31. A system or method according to any one of claims 1 to 11 and 29 to 31 wherein expansion occurs between portions of the intercalation material disposed on the carbon nanofibers. 13. The system or method according to any one of claims 1 to 12, further comprising an electrolyte in contact with the intercalating material and comprising a charge carrier. The system or method according to any one of claims 13 and 29 to 31, wherein the electrolyte is a solid electrolyte. 32. A system or method according to any one of claims 13, 14 and 29 to 31, wherein the charge carrier comprises lithium. The system or method according to any one of claims 1 to 15 and 29 to 31, wherein the carbon nanofibers are one of a plurality of vertically aligned carbon nanofibers attached to a substrate. 32. The system or method according to any one of claims 1 to 16 and 29 to 31, wherein the conductive substrate, the carbon nanofibers, and the intercalation material are configured to act as an anode. 18. The system or method of claim 17, further comprising a cathode in contact with the electrolyte. 19. The system or method according to any one of claims 1 to 18, wherein the carbon nanofibers are directly attached to the conductive substrate. 32. The system or method according to any one of claims 1 to 19 and 28 to 30, wherein the intercalation layer comprises silicon. 31. The system or method according to any one of claims 1 to 20 and 29 to 31 wherein the carbon nanofibers are configured to grow the intercalation material structure at the exposed edges of the carbon nanofibers. 32. The system or method according to any one of claims 1 to 20 and 29 to 31, wherein the carbon nanofibers are indirectly attached to the conductive substrate using a binder. 32. The system or method according to any one of claims 1 to 22 and 29 to 31, wherein the cup-shaped structure comprises a spiral having a cup-shaped cross-section. 24. The method of any one of claims 1 to 23, wherein the carbon nanofibers and the intercalation material have a Li ⁺ insertion capacity of 2752 to 3650 mAhg &lt; ^-1 &gt; and a retention capacity of greater than 85% insertion capacity during 100 charge / &Lt; / RTI &gt; 31. The system or method according to any one of claims 1 to 24 and 29 to 31 wherein the intercalation material is disposed in a layer having a nominal thickness of 0.1 to 4.0 占 퐉. 32. The system or method according to any one of claims 1 to 25 and 29 to 31, wherein the carbon nanofibers have a length of 3 to 200 mu m. 27. The method according to any one of claims 1 to 26, further comprising a plurality of nanoparticles attached to the intercalation material, wherein each nanoparticle adsorbs the charge carrier through a Faraday interaction on the surface of the nanoparticle Wherein the surface effect dominating site is configured to provide a surface effect dominant site that is configured to &lt; RTI ID = 0.0 &gt; 31. The method of any one of claims 1 to 27 and 29 to 31, wherein the conductive substrate, the carbon nanofibers, and the intercalation material have an increase in Li ⁺ insertion capacity as the filling rate increases from 2C to 8C Gt; and / or &lt; / RTI &gt; Providing a conductive substrate;
Adding carbon nanofibers, each containing a plurality of exposed nanoscale edges along the length of the carbon nanofibers, to a conductive substrate;
Application of intercalation materials configured for intercalation of charge carriers to carbon nanofibers
&Lt; / RTI &gt; Providing a conductive substrate;
Adding carbon nanofibers, each containing a plurality of cup-shaped structures, along the length of the carbon nanofibers to the conductive substrate;
Application of intercalation materials configured for intercalation of charge carriers to carbon nanofibers
&Lt; / RTI &gt; Providing a conductive substrate;
Adding carbon nanofibers to the conductive substrate;
Application of intercalation materials constructed for intercalation of charge carriers and arranged in a feather-like structure along the length of carbon nanofibers to carbon nanofibers
&Lt; / RTI &gt; 32. A method according to any one of claims 29 to 31, further comprising adding an electrolyte that contacts the intercalating material and comprises a charge carrier. 33. The method according to any one of claims 29 to 32, wherein the carbon nanofibers are vertically aligned carbon nanofibers attached to the substrate. 34. The method of any one of claims 29 to 33, wherein the conductive substrate, the carbon nanofibers, and the intercalation material are configured to act as an anode. 35. A method according to any one of claims 29 to 34, further comprising a cathode in contact with the electrolyte. The method according to any one of claims 29 to 35, wherein the carbon nanofibers are directly attached to the conductive substrate. 37. The method of any one of claims 29 to 36, further comprising attaching a plurality of nanoparticles to the intercalation material, wherein each nanoparticle has a charge carrier through Faraday interaction on the surface of the nanoparticle Wherein the surface effect control site is configured to provide a surface effect dominated site configured to adsorb. 29. The system or method according to any one of claims 1 to 28, wherein the intercalation material comprises a first silicon structure along with the carbon nanofibers and a second silicon structure along the length of the carbon nanofibers.

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