KR20200122426A - Hybrid energy storage devices including support filaments - Google Patents

Abstract

The present invention relates to a novel hybrid lithium-ion anode material 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, the highly conductive and mechanically stable CNF core optionally supports a coaxially coated amorphous Si shell with a much higher theoretical specific capacity by forming a fully lithiated alloy. The addition of surface effect dominant sites close to the intercalation medium forms a hybrid device that includes the advantages of both batteries and capacitors.

Description

Hybrid energy storage devices including support filaments {HYBRID ENERGY STORAGE DEVICES INCLUDING SUPPORT FILAMENTS}

<Cross-reference to related applications>

This application has been filed on February 27, 2013 in a partial continuation application of US Regular Patent Application No. 13/779,409; It is a partial serial application of U.S. Regular Patent Application No. 13/725,969 filed on December 21, 2012, and U.S. Provisional Patent Application No. 61/667,876 (filed on July 3, 2012), 61/677,317 (2012 Filed on July 30), 61/806,819 (filed on March 29, 2013), and 61/752,437 (filed on January 14, 2013), claiming and claiming priority.

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

The contents of all the above provisional patent applications and regular patent applications are incorporated herein by reference.

<Field of invention>

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 power supply in portable electronics, power tools, and future electric vehicles. Improving the specific energy capacity, charge/discharge rate, and cycling life is important for wider applications of the rechargeable lithium ion batteries.

In current commercial Li-ion batteries, graphite or other carbonaceous materials are used as anodes, and the anodes are theoretically 372 mAh/g by forming a fully intercalated LiC ₆ compound. Has a capacity limit of. In contrast, silicon has a much higher theoretical specific capacity of 4,200 mAh/g, by forming a fully lithiated alloy Li _4.4 Si. However, the large volume expansion of the lithiated Si by up to ~300-400% causes a large structural stress that inevitably leads to fractures and mechanical failure in the prior art, which is the lifespan of the prior art Si anodes. Is quite limited.

In some embodiments, the power storage device is a hybrid core-shell of high-performance Li-ion anode by introducing an array of vertically aligned carbon nanofibers (VACNF) coaxially coated with a layer of amorphous silicon. Includes NW (nano-wire) architecture. Vertically aligned CNFs include multi-walled carbon nanotubes (MWCNT), which are optionally grown on a Cu substrate using a DC-biased plasma chemical vapor deposition (PECVD) process. Carbon nanofibers (CNF) grown by this method may have a unique internal morphology that distinguishes them from the hollow structure of common solid carbon nanofibers and common MWCNTs. One of the distinguishing features is that these CNFs arbitrarily consist of a series of bamboo-like nodes over most of the hollow central channel. This microstructure can be attributed to the stack of conical graphitic cups discussed further elsewhere herein. At a larger length scale, these PECVD-grown CNFs are typically uniformly aligned perpendicular to the substrate surface and well separated from each other. They may have no entanglement or may have minimal entanglement, thus forming a brush-like structure referred to as a VACNF array. The diameter of the individual CNFs can be chosen to provide the desired mechanical strength so that the VACNF array is robust and maintains its integrity throughout Si deposition and wet electrochemical tests.

Various embodiments of the present invention include certain types of support filaments different from VACNF. Such support filaments may include, for example, nanowires, carbon sheets, or other structures described herein. Other embodiments do not include any support 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 including a plurality of multi-walled carbon nanotubes; And an energy storage system 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 a substrate; And an intercalation material layer disposed on a plurality of vertically aligned carbon nanofibers and configured to have a lithium ion storage capacity of approximately 1,500 to 4,000 mAh per gram of intercalation material. Including the system.

Various embodiments of the present invention include a conductive substrate; A plurality of vertically aligned carbon nanofibers grown on a substrate; And an energy storage system comprising an intercalation material layer disposed on the plurality of vertically aligned carbon nanofibers and configured such that the ion storage capacity of the intercalation material is approximately the same at charge rates 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, and having a stacked-cone structure in which carbon nanofibers are stacked; And applying an intercalation material to the carbon nanofibers, wherein the intercalation material is configured for intercalation of charge carriers.

Various embodiments of the present invention include an electrolyte comprising one or more charge carriers; A 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 the charge carrier within most intercalation materials; And a surface effect dominant site disposed on the intercalation material and comprising a plurality of nanoparticles, wherein each of the nanoparticles adsorbs a member of the charge carrier through a faradaic interaction on the surface of the nanoparticle. an energy storage system comprising a binder configured to provide an effect dominant site.

In various embodiments of the present invention, an electrolyte comprising one or more charge carriers; A conductive substrate; A plurality of support filaments attached to the substrate; An intercalation material disposed on each support filament and configured to reversibly adsorb a member of the charge carrier within most intercalation materials; And a binder disposed on the intercalation material and comprising a plurality of surface effect dominant sites configured to facilitate intercalation of the charge carrier to the intercalation material.

Various embodiments of the present invention include an electrolyte comprising one or more charge carriers; A conductive substrate; An intercalation material configured to reversibly adsorb a member of the charge carrier in most intercalation materials; And a binder disposed on the intercalation material and comprising a plurality of nanoparticles, each of the nanoparticles providing a surface effect dominant site configured to donate electrons to a member of the charge carrier through Faraday interactions on the surface of the nanoparticles. Includes an energy storage system that includes.

Various embodiments of the present invention include a cathode; And an anode separated from the cathode by an electrolyte comprising at least one charge carrier, an intercalation material configured to intercalate charge carriers and donate electrons to the charge carrier at a first reaction potential, a charge carrier at a second reaction potential. An energy storage system comprising a plurality of nanoparticles comprising a surface effect dominant site configured to donate electrons to the anode, wherein the absolute difference between the first reaction potential and the second reaction potential is less than 2.4V.

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

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

Various embodiments of the present invention provide a conductive substrate; The bonding material, the surface effect dominant site and the intercalation material are mixed, wherein the surface effect dominant site is configured to accept electrons from the charge carrier at a first reaction potential, and the intercalation material accepts a charge carrier or electron at a second reaction potential Configured to receive from the charge carrier; And applying a bonding material, a surface effect dominating site, and an intercalation material to the substrate.

Various embodiments of the present invention provide a conductive substrate; Providing a support filament; Applying an intercalation material to the support filament, wherein the intercalation material is configured for intercalation of charge carriers; And adding a surface effect dominant site to the support filament.

Various embodiments of the present invention include establishing a potential between a cathode and an anode of the electrical charge storage device, wherein the electrical charge storage device comprises an electrolyte; Receiving a first charge carrier of the electrolyte at the surface effect dominant site of the anode; Transferring electrons of the anode to a first charge carrier; Receiving a second charge carrier of the electrolyte in the intercalation material of the anode; And transferring electrons from the intercalation material to the second charge carrier.

Various embodiments of the present invention include setting a charge gradient at an anode of an electrical charge storage device, wherein the anode comprises an electrolyte, a plurality of nanoparticles having a surface effect dominant site, an intercalation material, and a substrate; Receiving a first charge carrier of the electrolyte at one of the surface effect dominant sites; Transferring electrons from one of the surface effect dominant sites to the first charge carrier; Receiving a second charge carrier in the intercalation 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 the conductive substrate; And an intercalation material configured to form a shell over at least a portion of the carbon nanofibers, wherein the carbon nanofibers include 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 the 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-like structures along the length of the carbon nanofibers, such as a battery or electrode. Include.

Various embodiments of the present invention include a conductive substrate; Carbon nanofibers or other supporting filaments connected to the 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 disposed in a feather-like structure along the length of the carbon nanofibers.

Various embodiments of the present invention include a conductive substrate; Carbon nanofibers connected to the 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 such that expansion of the intercalation material does not delaminate the intercalation material from the carbon nanofibers. Includes an energy storage system.

Various embodiments of the present invention provide a conductive substrate; Adding carbon nanofibers each including a plurality of exposed nanoscale edges along the length of the carbon nanofibers to the conductive substrate; And a method of manufacturing an energy storage device comprising applying an intercalation material configured for intercalation of charge carriers to carbon nanofibers.

Various embodiments of the present invention provide a conductive substrate; Adding carbon nanofibers each including a plurality of cup-like structures along the length of the carbon nanofibers to the conductive substrate; And a method of manufacturing an energy storage device comprising applying an intercalation material configured for intercalation of charge carriers to carbon nanofibers.

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

1A and 1B illustrate a CNF array comprising a plurality of CNFs grown on a substrate, according to various embodiments of the present invention.
2A-2C illustrate a plurality of vertically aligned CNFs in different states, according to various embodiments of the present invention.
3A-3C illustrate details of CNF, according to various embodiments of the present invention.
4 illustrates a schematic diagram of a stacked-conical structure of CNF, according to various embodiments of the present invention.
5A-5C illustrate electrochemical characterization of ~3 μm long CNFs according to various embodiments of the present invention.
6A-6C illustrate scanning electron microscopy images of 3 μm long CNFs, according to various embodiments of the present invention.
7A-7C illustrate the results achieved using CNFs comprising a Si layer as Li-ion battery anodes, according to various embodiments of the present invention.
8 illustrates how the capacity of a CNF array varies with charging rate, according to various embodiments of the present invention.
9 illustrates Raman spectra of CNF arrays, according to various embodiments of the present invention.
10A-10C illustrate the variation in coulombic efficiency and Li ⁺ insertion-extraction capacities over 15 charge-discharge cycles, according to various embodiments of the present invention.
11A-11C show scanning electron microscopy images of freshly prepared CNF arrays, according to various embodiments of the present invention.
11D shows a cross-sectional view of a nanofiber/silicone composite comprising more than one number of CNFs.
12 illustrates a carbon nano-fiber array comprising fibers of 10 μm in length, according to various embodiments of the present invention.
13 illustrates methods of making CNF arrays and/or CNFs, according to various embodiments of the present invention.
14A illustrates a CNF comprising a power enhancement material, according to various embodiments of the present invention.
14B illustrates details of the power enhancement material illustrated in FIG. 14A, according to various embodiments of the present invention.
14C illustrates another detail of the power enhancement material illustrated in FIG. 14A, according to various embodiments of the present invention.
15 illustrates an electrode surface comprising a power enhancing material and non-aligned CNF coated with an intercalation material, according to various embodiments of the present invention.
16 illustrates an electrode surface comprising a power enhancement material, a non-aligned CNF and a free intercalation material, according to various embodiments of the present invention.
17 illustrates an electrode surface comprising an intercalation material and a power enhancement material without CNF, according to various embodiments of the present invention.
18 illustrates an electrode surface comprising a surface effect dominant site disposed in close proximity to the CNF, according to various embodiments of the present invention.
19 and 20 illustrate an electrode surface comprising a surface effect dominating site disposed in close proximity to a free intercalation material, according to various embodiments of the present invention.
21 illustrates a method of assembling an electrode surface, according to various embodiments of the present invention.
22 illustrates a method of operating an electrical charge storage device, according to various embodiments of the present invention.

1A and 1B illustrate a CNF array 100 comprising a plurality of CNFs 110 grown on a conductive substrate 105, according to various embodiments of the present invention. FIG. 1A shows the CNF array 100 in a state where Li is extracted (discharged), and FIG. 1B shows the CNF array 100 in a state where Li is inserted (charged). The CNFs 110 of this and other embodiments discussed herein are optionally vertically aligned. CNF 110 is grown on a substrate 105 of Cu using a DC-biased plasma chemical vapor deposition (PECVD) process. As discussed above, the CNFs 110 grown by this method may have a unique morphology comprising stacked cups or stacks of cones or spiral-like conical graphite structures. This creates a very fine structure that facilitates lithium intercalation. Herein, this structure is referred to elsewhere herein as a “stacked-cone” structure. At a larger length scale, these CNFs 110 are typically uniformly aligned perpendicular 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 maintains 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 may be solid or liquid, or a combination of solid and liquid, and is also placed in contact with an electrolyte 125 comprising one or more charge carriers such as lithium ions. The CNFs 110 are configured such that some of the electrolyte 125 is disposed between the CNFs 110 and/or the substrate 105 can be prepared through the gaps between the CNFs 110.

Diameters or other ranges of 75-300 nm are possible, but the diameter of the individual CNFs 110 illustrated in FIGS. 1A and 1B is nominally 100-200 nm. The CNFs 110 are arbitrarily tapered along their length. The CNFs 110 generated using the techniques discussed herein have excellent electrical conductivity (σ = ~2.5×10 ⁵ S/m) along the axis, and have a solid ohmic contact with the substrate 105. To form. The open space between the CNFs 110 is to form a gradually thinned coaxial shell according to mass at the tip 120 of the CNF 110 It allows the silicon layer 115 to be deposited onto the respective CNFs. This design allows the entire silicon layer 115 to be electrically connected across the CNF 110 and remain fully active during charge-discharge cycling. The expansion generated when lithium is alloyed with the silicon layer 115 can be easily accommodated in, for example, a radial direction perpendicular to the long dimension of the CNFs 110. The cycling stability, and charge and discharge capacity of the non-Si-coated CNFs 110 and the Si-coated CNFs 110 can be compared. The addition of the silicon layer 115 provided significant Li ⁺ intercalation (charging) capacity up to 3938 mAh/g _Si at a C/2 charge rate, and 1944 mAh/g _Si was retained after 110 cycles. This charge/discharge rate and corresponding capacity are significantly higher than previous architectures using Si nanowires or hybrid Si-C nanostructures. 1A and 1B are perspective views.

In various embodiments, a nominal Si thickness from 0.01 to 0.5, 1.0, 1.5, 2.5, 3.0, 4.0, 10, 20, 25 μm (or more) is CNF, such as those illustrated in FIGS. 1A and 1B. To form the arrays 100, it may be deposited onto the 3 μm long CNFs 110. 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 μm (or more) to form the CNF arrays 100 It may be deposited on 10 μm long CNFs 110. In some embodiments, the nominal thickness of Si is 0.01 μm to the average distance between the CNFs 110.

Using CNF arrays 100, Li ion storage with a mass-specific capacity of up to 4,000 mAh/g at a C/2 charge rate is achieved. This capacity is significantly higher than those 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. Good cycling stability has been demonstrated over 110 cycles. In various embodiments, the storage capacity of the Li ion storage of the CNF arrays 100 is approximately 750, 1500, 2000, 2500, 3000, 3500 or 4000 mAh per gram of Si, or any between these values. Within range. The term "nominal thickness" (eg, of Si), as used herein, is the amount of Si that forms, on the substrate 105, a flat layer of Si of that thickness. For example, a nominal thickness of Si of 1.0 μm is the amount of Si that, if deposited directly on the substrate 105, will result in a 1.0 μm thick layer of Si. 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 μm will result in a smaller thickness Si layer 115 on the CNFs 110 because Si is distributed over a larger area of the CNFs 110 surfaces.

2A-2C illustrate a CNF array 100 having an average fiber length of approximately 3 μm, according to various embodiments of the present invention. 2A-2C are scanning electron microscope (SEM) images. 2A shows a plurality of vertically aligned CNFs 110 without a silicon layer 115. 2B shows a plurality of vertically aligned CNFs 110 including a silicon layer 115. 2C shows a plurality of vertically aligned CNFs 110 in an extracted (discharged) state after experiencing 100 lithium charge-discharge cycles. 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. The samples used in this study were 1.11×10 ⁹ CNF/cm (counted from the top view of SEM images), corresponding to an average nearest-neighbor distance of ~330 nm. ^It has an average areal density of ² . The average length of the CNFs 110 of FIG. 2 is -3.0 μm for >90% of the CNFs in the range of 2.5 to 3.5 μm in length. The diameter is spread from -80 nm to 240 nm, with an average of -147 nm. An inverse teardrop shaped Ni catalyst of the tip 120 is provided at the tip of each CNF 110 capping the central hollow channel of the CNF, which is used during the PECVD process. ) Promoted the cutting edge growth. The size of the Ni catalyst nanoparticles defined the diameter of each of the CNFs 110. Longer CNFs 110, up to 10 μm, have also been used in some studies that will be discussed in the following sections.

In various embodiments, the average nearest distance may vary from 200 to 450 nm, 275 to 385 nm, 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 (μm), or more. Standard carbon nanofibers as long as millimeters long are known in the art. In various embodiments, the average diameter can vary from approximately 50 to 125, 100 to 200, 125 to 175 (nm), or other ranges.

An amorphous Si layer 115 was deposited onto the CNF array 100 by magnetron sputtering. The open structure of the brushed CNF arrays 100 enables Si to reach deep down into the array to form conformal structures between the CNFs 110. As a result, it formed a thick Si coating on the CNF tip, followed by a progressively thinning coaxial Si shell around the bottom of the CNF, which is an interesting tapered core-shell similar to a cotton swab. Shows the structure. The amount of Si deposition is characterized by the nominal thickness of the Si films on a flat surface, using a quartz crystal microbalance (QCM) during sputtering. Li ⁺ insertion/extraction capacities were normalized to the total Si mass derived from the nominal thickness. At a nominal thickness of 0.50 μm, the Si-coated CNFs 110 are well-separated from each other, forming an open core-shell CNF array structure (shown in FIG. 2B). This structure allowed the electrolyte to freely access the entire surface of the Si layer 115. In the illustrated embodiment, compared to the -147 nm average diameter of the CNFs 110 before application of the Si layer 115, the average tip diameter was -457 nm. The average radial Si thickness of the tip 120 was estimated to be ~155 nm. This was apparently much smaller than the nominal Si thickness of 0.50 μm, because most of the Si spreads 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 different ranges are identified in alternative embodiments. As discussed elsewhere herein, the stacked-cone of CNFs 110 provides an additional microstructure to Si layer 115. The stacked-conical structure is the result of a spiral growth pattern that optionally forms a stacked-conical structure when viewed in cross section.

The transmission electron microscopy (TEM) images of FIGS. 3A-3C further illustrate structural details of Si-coated CNFs 110. A Si layer 115 of -390 nm Si was formed just above the tip 120 of the -210 nm diameter CNF 110. The largest portion of the swab-shaped Si layer 115 was ˜430 nm in diameter, which appeared near the very end of the tip 120. A coaxial Si layer 115 around the CNF 110, showing a feather-like texture with a modulated contrast, clearly different from uniform Si, is deposited over the tip (see Fig. 3A). . This is likely the result of the stacked-conical microstructure of PECVD-grown CNFs 110. It is known from the literature that these CNFs 110 include cup-like graphite structures that are not uniformly stacked along the CNF 110 central axis. The use of these variations in the diameter of CNFs 110 was previously disclosed in U.S. Patent Application Serial No. 12/904,113, filed Oct. 13, 2010, owned by the applicant.

The stacked-conical structure along the length of each CNF consists of 1 to 5, 5 to 15 or more than 10 cup-shaped graphite layers that can be clearly identified in Fig. 3b, as indicated by the dotted lines. Done. At the edge of each stacked-cone, the side edges of some of the graphite layers are exposed. Lithium may penetrate between the graphite layers at the exposed edges. At the molecular level, the cup-like structure comprises a cone of graphene and/or a graphite sheet capable of interacting with lithium. While the cup edge is a nanoscale edge and can have the properties of a graphene edge, the same properties can be found between graphene layers as between graphene sheets. The cup edges are provided on vertically aligned carbon nanofibers through which lithium ions can move. The novel microstructure of VACNF creates a stack of exposed graphite edges, such as cup edges, along the length of the CNF sidewalls. The nanoscale edges are similar to those typically found on graphene/graphite sheets and ribbons. The exposed cup edge results in an altered silicon nucleation rate, resulting in a modulated silicon shell texture. The exposed edge also forms an excellent interface between the VACNF core and the Si shell, facilitating rapid electron transfer in the hybrid structure. The two different structures of the Si shell can be controlled by changing the growth process of VACNF. The region of VACNF containing the cup structure results in a feathered Si shell, and the region of VACNF not containing the cup structure has a Si structure similar to the structure observed at the tip of VACNF. The VACNF is arbitrarily configured to have one or more regions along the length of the VACNF and also without a cup stack structure at the tip. In an alternative embodiment, the carbon nanofibers also include exposed graphite/graphene or cup laminate structures with graphite edges, but not vertically aligned and/or even attached directly to the substrate. Unless the use of “cup stacked” graphite microstructures is discussed elsewhere herein, another method of creating exposed nanoscale edges of graphite sheets involves unraveling carbon nanotubes using an acid. The exposed nanoscale edges created in this way are expected to also provide advantages in the control and/or fixation of the Si shell and may be included in some embodiments. For example, the edge of a graphite nanoscale ribbon can be used to influence the growth of the Si shell around the ribbon.

The term “nanofiber” as used herein is intended to include structures having at least two dimensions of nanoscale (less than 1 micron). This includes, for example, wires, tubes and ribbons, which may or may not be nanoscale in thickness and width but nanoscale in length. The term nanofiber is intended to exclude graphene sheets, which can be nanoscale in thickness but are both nanoscale in length and width. In various embodiments the support filaments discussed herein are nanofibers.

Since the electron beam needs to penetrate hundreds of nanometer-thick CNFs or Si-CNF hybrids, the resolution and contrast in Figs. 3b and 3c are limited, but structural features are high-resolution TEM studies using smaller CNFs in the literature. Matches with This unique structure resulted in clusters of broken graphite edges along the CNF sidewall that resulted in altered nucleation layers during Si deposition and thus a modulated density of Si layer 115 on the CNF 110 sidewall. The modulated density results in ultra-high surface area Si structures indicated by the (100 nm square) box 310 of FIG. 3A. The feathered Si structures of Si layer 115 provide an excellent Li ion interface resulting in very high Li capacity and also high speed electron transfer to CNF 110. In Figure 3A, the dark area of the tip 120 is the nickel catalyst for the growth of CNFs. Other catalysts can also be used.

3B and 3C are images recorded before (FIG. 3B) and after (FIG. 3C) lithium intercalation/extraction cycles. The sample in Fig. 3C was in a delithiated (discharged) state when taken out of the electrochemical cell. The dotted lines in FIG. 3B are visual guidance of the stacked-conical graphite layers inside the CNFs 110. Long dotted lines in FIG. 3C represent the sidewall surface of the CNF 110.

As discussed elsewhere herein, the stacked-conical structure of CNFs 110 is completely different from commonly used carbon nanotubes (CNTs) or graphite. The stacked-conical structure results in improved Li ⁺ insertion compared to standard carbon nanotubes or nanowires, even without the addition of a Si layer 115. For example, the stacked-conical graphite structure of the CNFs 110 allows Li ⁺ intercalation to the graphite layers through the sidewall of the CNFs 110 (rather than just at the ends). The Li ⁺ transport path across the wall of each of the CNFs 110 is very short (in some embodiments, with D ~ 290 nm), and of the commonly used seamless carbon nanotubes (CNTs). It is quite different from the long path from the open ends. 4 illustrates a schematic diagram of a stacked-conical structure of CNFs 110. 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 /sinθ = 290 Is nm.

5A-5C illustrate the electrochemical characterization of ˜3 μm long CNFs 110. This characterization illustrates the phenomenon described in connection with FIG. 4. 5A shows 1.5 V to 0.001 V versus Li/Li ⁺ cyclic voltammograms (CV) from the reference electrode at 0.1, 0.5, and 1.0 mV/s scan rates. Shows. Lithium disks were used as counter electrodes. Data were taken from the second cycle and normalized to the exposed geometric surface area. Figure 5b corresponds to current densities of 647, 323, and 162 mA/g (normalized for the estimated carbon mass) or 71.0, 35.5, and 17.8 μm/cm ² (normalized for geometric surface area), respectively. , Galvanostatic charge-discharge profiles at C/0.5, C1, and C/2 power rates. 5C shows the intercalation and extraction capacities (relative to the left vertical axis) and the number of cycles in the coulombic efficiency (versus) C/1 charge-discharge rate (relative to 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 the anode of the uncoated CNFs 110 being -2.50 to 3.00 V vs. (vs.) Li/Li ⁺ reference electrode. Seemed to be. CVs measured from 0.001 V to 1.50 V show that the Li ⁺ intercalation starts when the electrical potential is less than 1.20 V. The first cycle of 0.001 V from OCP was accompanied by the formation of the required protective layer, i.e. solid electrolyte interphase (SEI), by the decomposition of solvents, salts and impurities, and thus a large cathode current Is shown. Subsequent CVs showed smaller but more stable currents. The cathode current associated with the Li ⁺ intercalation rose slowly as the electrode potential swept negatively until a sharp cathode peak appeared at 0.18 V. Since the electrode potential was positively inverted after reaching the lower limit at 0.001 V, lithium extraction, indicated by a continuous anode current and a broad peak at 1.06 V, was observed over the entire range up to 1.50 V.

The CV features of CNF arrays 100 were somewhat different from those of slow Li ⁺ diffusion into the hollow channel of CNTs and staged intercalation into graphite. Li-ion intercalation into the CNFs 110 is likely through intercalation between graphite layers from the sidewall due to its inherent structure. The TEM image of FIG. 3C shows that the graphite stacks of stacked-cones inside the CNF 110 are somewhat disturbed during the Li ⁺ intercalation-extraction cycles, which is a large volume change occurring on Li ⁺ intercalation. It may be due to. Some debris and nanoparticles are observed as white objects inside the CNFs 110 as well as on the outer surface. This indicates penetration into the CNF through the sidewall.

The constant current charge-discharge profiles of FIG. 5B showed that the Li+ storage capacity decreased as the power rate increased from C/2 to C/0.5 (C/0.5 is also referred to as “2C”). In order to make it easier to compare power factors (especially for those higher than C/1), the present inventors use fractional notation C/0.5 herein instead of "2C", which is more commonly used in the literature. Use. Li ⁺ intercalation and extraction capacities were calculated for the estimated mass (1.1 × 10 ⁴ g/cm ² ) of CNFs 110, which were calculated based on the hollow vertically aligned CNF structure, using the following average parameters. Normalized, 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 wall of the CNFs 110 was assumed to be the same as the graphite (2.2 g/cm ³ ). At the normal C/2 power rate, the intercalation capacity was 430 mA hg ^-1 , the extraction capacity was 390 mA hg ^-1 , and both the intercalation capacity and the extraction capacity were the theoretical values for graphite 372 mA hg. Slightly higher than ^-1 , which may be due to the irreversible Li ⁺ insertion and SEI formation into the hollow compartments inside the CNFs 110. The extraction capacities were found to exceed 90% of the intercalation values at all power rates, and both the intercalation and extraction capacities, compared to the graphite anodes, have power rates ranging from C/2 to C/1. It decreased by ~9% as it increased to and by ~20% as it increased 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 ^- It was confirmed that it was maintained at ¹ . Excluding the first two cycles due to SEI formation on the CNF (110) surface, the overall Coulomb efficiency (ie, ratio of extraction capacity to intercalation capacity) was -94%. It is known that the SEI film is readily formed on the 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 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, such that the cohesive capillary force of the solvent as observed in studies with other polymer coatings. Protects the CNFs 110 from collapsing into microbundles by.

6A-6C illustrate scanning electron microscopy images of 3 μm long CNFs 110, according to various embodiments of the present invention. 6A shows CNFs 110 in a delithiated (discharged) state after intercalation/extraction cycles. 6B shows the CNFs 110 including the Si layer 115 after 100 cycles in the delithiated state. 6C shows CNFs 110 including Si layer 115 after 100 cycles in the lithiated state. These images are 45° perspective views.

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 μm. 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 were made after the sample went through 150 charge-discharge cycles, and data of the second cycle at each scan rate is shown. 7B shows constant current charge-discharge profiles at C/0.5, C/1, and C/2 power rates, using a sample 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 Coulomb efficiency (versus for the right vertical axis) versus the number of charge-discharge cycles of two CNF arrays 100 (used as electrodes). Shows. The first CNF array 100 uses one cycle at C/10 power rate, one cycle at C/5 power rate, and first using two cycles at C/2 power rate. It was conditioned. It was then tested at C/2 insertion rate and C/5 extraction rate for the remainder of 96 cycles. The filled and open squares represent the insertion and extraction volumes, 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 rates. After that, it was tested at the C/1 power rate for the next 88 cycles. The coulombic efficiencies of both electrodes are represented by filled (first electrode) and open (second electrode) diamonds, which mostly overlap at 99%.

The CVs of FIG. 7A show features very similar to the CVs of Si nano-wires. Compared to the uncoated CNF array 100, both the cathode wave for Li ⁺ insertion and the anodic wave for Li ⁺ extraction are lower values (less than ~0.5 and 0.7 V, respectively) Is moved to. The peak current density increases 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 ⁺ insertion into Si is much faster than the intercalation into uncoated CNFs, which was limited by the slow diffusion of Li ⁺ between 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 alloy to amorphous Si are similar to those using Si nanowires, despite the shift to lower potentials by 100 to 200 mV.

The constant current charge-discharge profiles of the CNF array including the Si layer 115 shown in FIG. 7B show two salient features: (1) -3000 mA h (g _Si ) ^-1 high Li ⁺ insertion (charge). And extraction (discharge) capacity was achieved even after 120 cycles at the C/2 rate; And (2) Li ⁺ capacity was almost the same at C/2, C/1, and C/0.5 power rates. That is, the capacity of the CNF array 100 acting as an electrode did not decrease when the charging rate was increased from C/2 to C/1 and C/0.5. In various embodiments, across these filling rates, capacity was largely independent of filling rates. The total Li ⁺ storage capacity of the CNF arrays 100 including the Si layer 115 was about 10 times greater than that of the CNF arrays 100 without the Si layer 115. This occurred even though the lower potential limit for the charging cycle was increased from 0.001 V to 0.050 V. As a result, the amount of Li ⁺ intercalation to the CNF core appears to be negligible. The specific capacity was calculated by dividing only the mass of Si which was calculated from the measured nominal thickness and a bulk density of 2.33 g cm ^-3 . 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. For 3.0 μm long CNFs 110 on which a 0.456 μm nominal thickness Si layer 115 was deposited, compared to the actual mass density of the CNFs 110 (~1.1 × 10 ^-4 g cm ^-2 ), Si The actual mass density of layer 115 was -1.06 x 10 ^-4 g cm ^-2 . The corresponding Coulomb efficiency in FIG. 7B is greater than 99% at all three power rates, and much higher than the Coulomb efficiency of CNFs 110 without Si layer 115.

8 illustrates how the capacity of the CNF array 100 varies with the charging rate, according to various embodiments of the present invention. Data is plotted for several cycles. Figure 8 is the same current rates (versus) charge rate (C-rate) required to achieve the full capacity (C/h, for example, full Capacity/hours) at set times. Shows the average specific discharge capacity for a group of cycles with. Vertical lines were focused on C/4, 1C, 3C, and 8C. The CNF array 100 is symmetrically first using two cycles at C/8, C/4, C/2, C/1, C/0.8, C/0.4, and C/0.16 power rates, respectively. Conditioned and then tested at a C/1 symmetric power rate for the next 88 cycles. This was repeated from Cycle 101 to Cycle 200. Starting in cycle 201, the electrodes are symmetrically C/4, C/3, C/2, C/1, C/0.75, C/0.66, C/0.50, C/0.33, C/0.25, C/0.20 , And C/0.15 power rates were cycled for 5 cycles, respectively, and then tested at C/1 symmetric power rates for the next 45 cycles. This was repeated from Cycle 301 to Cycle 400 and from Cycle 401 to Cycle 500. The change in dose is small (<16%), but the C-rate changes by 32 fold. When the C-rate was changed from 3C to 8C, the electrode after 100 cycles showed increased capacity. Thus, faster charging rates resulted in improved capacity. High capacity (>2,700 mAh/g) was achieved at both high and lower charging rates (C/4 and 8C). As the C-rate increases, the capacity increases at charge rates above 3C. The drop in specific capacity with the number of cycles is due to known, correctable factors.

Both CVs and charge-discharge measurements indicated that the Li ⁺ insertion into the Si layer 115 was fast and very reversible, which are desired features for high performance Li-ion battery anodes. These include different testing conditions: (1) slow asymmetry tests with a C/2 rate for insertion and a C/5 rate for extraction; And (2) two long cycling tests on two identical samples in a rapid symmetry test at the C/1 rate for both insertion and extraction (see Fig. 7c). All of the sets of data showed a coulomb efficiency of >98% over long cycling, except for the initial conditioning cycles (former 4 cycles and the latter 12 cycles changed to lower charge rates). In the slow asymmetry tests, the insertion capacity dropped by only 8.3% from 3643 mA hg ^-1 in the 5th cycle to 3341 mA hg ^-1 in the 100th cycle. Even at the C/1 charge-discharge rate, the insertion capacity only drops by 11% from 3096 mA hg ^-1 in the 13th cycle to 2752 mA hg ^-1 in the 100th cycle. The difference in Li ⁺ capacity between these two data sets may have been largely due to initial conditioning parameters and small sample-to-sample variations. This was indicated by similar values of the insertion-extraction capacity during the first few conditioning cycles of FIG. 7C at C/10 and C/5 rates. Faster fill rates (C/0.5 for the 9th and 10th cycles of Sample #2 and C/0.2 for the 11th and 12th cycles) were found to be detrimental and would result in an irreversible drop in capacity. . However, the electrode stabilized after longer cycling. As shown in Fig. 7B, the charge-discharge profiles are approximately the same at C/2, C/1, and C/0.5 charge rates, which were measured using Sample #1 after 120 cycles. This ends with 4 charging rate fluctuations.

The specific capacity of the Si layer 115 in the range of 3000 to 3650 mA hg ⁻¹ is consistent with the highest values of the amorphous Si anodes summarized in the literature. It is noteworthy that the entire Si shell of the CNF array 100 was active against Li+ intercalation and that nearly 90% of the capacity was retained over 120 cycles, which in our knowledge is flat ultrathin (<50 nm). ) Not previously achieved except for Si films. Disclosed herein, specific capacity is, C / 2 rate at ~ 2500 mA hg ^-1 and the C / 1 ratio of the ~ 2200 mA hg ^-1, and the randomly oriented carbon nanofibers using the Si NW -Si core - shell It is significantly higher than the specific capacities that were reported using other nanostructured Si materials at similar power rates, including ~800 mA hg ⁻¹ at the C/1 rate using NWs. Obviously, the coaxial core-shell NW structure on well-separated CNFs 110, such as those included in the various embodiments of the present invention, has an improved charge-discharge rate compared to the prior art, almost the total Li ⁺ storage capacity of Si And long cycle life.

As shown in FIG. 7C, an unusually high insertion capacity (~4500 mA hg ⁻¹ ) was always observed in the initial cycles, which was 20 to 30% higher than the later cycles. In contrast, extraction values were relatively stable over the entire cycle. The extra intercalation capacity consists of three irreversible reactions: (1) formation of a thin (ten nanometers) surface electrolyte interphase (SEI) layer; (2) reactions of Li with SiO _x provided on the Si surface (SiO _x + 2xLi → Si + xLi ₂ O); And (3) due to the combination of conversion of the starting crystalline Si coating with a higher theoretical capacity (~4200 mA hg ^-1 ) to amorphous Si with a lower capacity (<3800 mA hg ^-1 ). I can. The TEM image (FIG. 3C) and SEM image (FIG. 6B) showed that non-uniform SEI can be deposited on the surface of the Si layer 115 after charge-discharge cycles. This resilient SEI film fixes the Si layer 115 on the CNF 110 surfaces when the CNF array 100 undergoes large volume expansion-contraction cycles occurring during charge-discharge cycles. Can help. The impressive difference between the SEM images of FIGS. 6B and 6C shows a large expansion of the Si layer 115 in the non-lithiated and comparatively lithiated (charged) states. (However, since the electrochemical cell was dissembled during imaging, some of the expansion may be due to oxidation of Li by air). It is noted 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 Figure 3b, Si interacted with the electrolyte to create SEI filling the gaps between the feathery structures. Interactions may include mixing, chemical reactions, charge coupling, encapsulation and/or the like. Therefore, the Si layer 115 looks more uniform in FIG. 3B. However, Si layer 115 now includes interleaved layers of SEI and Si (feather-like structures). Each of these interleaved layers may be on the order of tens of nanometers. The SEI layer may be an ion permeable material that is the product of an interaction between the electrolyte and the Si layer 115 (or other electrode material).

The crystalline and amorphous structures of the Si shell were revealed by Raman spectroscopy. As shown in Fig. 9, a pristine CNF array 100 comprising a Si layer 115 has a plurality of overlapped broad bands ranging from 350 to 550 cm ^-1 corresponding to amorphous Si. ), and a much higher sharp band at 480 cm ^-1 corresponding to nanocrystalline Si. After charge-discharge tests, the broadbands merged into a single peak at 470 cm ^-1 , but the clear peak disappeared. Bare CNFs 110 did not show any feature in this range. The crystalline Si peak was downshifted by -40 cm ^-1 from that measured using a single-crystalline Si (100) wafer and by -20 to 30 cm ^-1 from other micro-crystalline Si materials. This shift may have been due to the much smaller crystal size and large disorders. The original Si layer 115 may have been made of nanocrystals embedded in an amorphous matrix associated with the feathery TEM image of FIG. 3A. After the initial cycles, the Si nanocrystals were converted to amorphous Si, which is consistent with the TEM images after the cycling test (see FIGS. 3B and 3C). However, the Si layer 115 clearly did not slide along the length of the CNF, as opposed to the large longitudinal expansion (up to 100%) of pure Si NWs. This indicates that, in some embodiments, the expansion of silicon is primarily radial rather than length for carbon nanofibers. In some embodiments, swelling occurs between the feathery structures of Si. For example, one feather may expand in the upward and downward directions of the nearest neighboring feathers, thereby filling the gap between the feathers. In any case, the expansion occurs in such a way that the 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 over 120 cycles. The CNF-Si interface was kept 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 thickness. One factor that can be controlled when CNFs 110 are generated is the open space between each CNF 110, for example, the average distance between CNFs 110 in the CNF array 100 . This space allows the Si layer 115 to expand radially upon filling, thus providing stability in some embodiments. Since the optimal electrode structure depends on both the length of the CNFs 110 and the thickness of the Si layer 115, longer CNFs 110 and thicker Si layers to achieve a higher total Li ⁺ storage capacity. It is sometimes desirable to use 115. Longer CNFs 110 correlate with greater storage capacity. 10A-10C show Coulomb efficiency and Li+ over 15 charge-discharge cycles using three 10 μm long CNF 110 samples deposited with a Si layer 115 at nominal thicknesses of 0.50, 1.5, and 4.0 μm, respectively. The variation of the insertion-extraction doses is shown. After conditioning at the C/10 fill rate for the first cycle and the C/5 rate for the second cycle, the asymmetric fill rates (C/2 for insertion and C/5 for extraction) are obtained in sample #1 of FIG. 7C. It was used in subsequent cycles similar to the measurements of. This protocol provided minimal degradation and nearly 100% Coulomb efficiency over cycles. The nominal thickness was measured in situ using a quartz crystal microbalance (QCM) during sputtering.

Specific specific capacities as high as 3597 mA hg ^-1 and 3416 mA hg ^-1 are very similar to those using a 0.50 μm thick Si layer 115 (see FIG. 7C) on 3.0 μm long CNFs 110, respectively, 0.50 and This was achieved using a 1.5 μm thick Si layer 115. The capacity remained almost constant over 15 cycles. However, an electrode with a nominal Si thickness of 4.0 μm showed significantly lower specific capacity at only 2221 mA hg ⁻¹ . This indicates that upon expansion, the Si layers 115 from adjacent CNFs 110 start 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 intercalation. The cycle stability was correspondingly worse than the samples with thinner Si layers 115.

The same amount of Si (500 nm nominal thickness) on CNF arrays 100 comprising 10 μm long CNFs 110, 3 μm long CNFs 110, although the carbon mass is more than 3 times higher. Li ⁺ storage capacity (3597 mA hg ^-1 , see FIG. 6A) of about the same amount as that of (3643 mA hg ^-1 , see FIG. 7C) was provided. This is very strong evidence that the contribution of the CNFs 110 is negligible in calculating the Li ⁺ storage. Very few Li ⁺ ions in the Si-coated sample may have been intercalated into CNFs 110, which contributes 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. 11A to 11C show scanning electron microscopy images of newly prepared CNF arrays 100 (on ˜10 μm long CNFs 110). Si layer 115 was generated using a nominal Si thickness of (a) 0.50 µm, (b) 1.5 µm, and (c) 4.0 µm, which was in-situ using a quartz crystal microbalance (QCM) during deposition. in-situ) was measured. All images are 45° perspective views. At 0.50 μm 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 diffused more evenly along the 10 μm long CNFs 110.

It is noted that growing of the 10 μm CNFs 110 took 120 minutes, which is about 6 times that of the growing of the 3 μm CNFs 110. Some Ni catalysts are slowly etched by NH ₃ during a long PECVD process, resulting in a continuous reduction in Ni nanoparticle size, resulting in a tapered tip 120 (as shown in FIG. 12). CNF 110 length variation was also increased using long CNFs 110. These factors collectively reduced the shading effects of the tip 120. As a result, even at 1.5 μm nominal Si thickness, the CNFs 110 coated with the Si layer 115 are well separated from each other. The SEM image of 1.5 μm Si on 10 μm CNF arrays 100 (FIG. 11B) is very similar to the SEM image of 0.50 μm Si on 3.0 μm CNF arrays 100 (FIG. 2B ). However, since the nominal Si thickness has been increased to 4.0 μm, the Si layers 115 are apparently merged with each other and fill up to most of the space between the CNFs 110 (see Fig. 10C). This has reduced the free space required to accommodate the volumetric expansion of the Si layer 115. As a result, the specific Li ⁺ storage capacity dropped considerably.

11A and 11B each contain approximately the same number of CNFs 110, but substantially fewer visible tips 120 in FIG. 11B. This is because the Si layer 115 can form a nanofiber/silicon composite including a single CNF 110 (the cross section is shown in FIG. 1A). Alternatively, the Si layer 115 may form a nanofiber/silicon composite including 2, 3, 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/silicon composite including two CNFs 110 is illustrated in FIG. 11D. In various embodiments, at least 1%, 5%, or 10% of the nanofiber/silicon composites comprise more than one number of CNFs (110).

In various embodiments, for CNF arrays 100 with 0.50 and 1.5 μm nominal Si thicknesses, they have comparable mass-specific capacities of 3208±343 and 3212±234 mA hg ⁻¹ , respectively. Samples with a 4.0 μm nominal Si thickness gave a much lower capacity at 2072±298 mA hg ⁻¹ . The thinner Si coatings are fully activated and provide the maximum Li insertion capacity that amorphous Si can provide. 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 However, it is dropped off from the linear curve to give 1.93±0.28 mA h cm ^-2 at 4.0 μm nominal Si thickness. At a nominal silicon thickness of 4.0 micrometers, only a portion of the extra silicon in the thick Si coating is actively involved in Li storage. The thickness of 4.0 μm is greater than the average distance between the 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 is approximately 30 to 40, 40 to 75, 75 to 125 microns (or more or combinations thereof) in length and approximately 50 It includes a Si layer of approximately 200 to 300 nm radial thickness on CNFs 110 with diameters of nm. In some embodiments, these CNF arrays 100 are grown on conductive foils having a thickness in the ranges of ˜10 microns, ˜10-20 microns, ˜10-50 microns, or more. In various embodiments, Si (equivalent to 1.5 μm nominal thickness on a flat surface) is deposited onto 10 μm long CNFs 110 to form CNF arrays 100. This is, while maintaining an open vertical core-shell nanowire structure having individual CNFs 110 well separated from each other so that Li ions can pass through the CNF arrays 100 between the CNFs 110 Is achieved. 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 mA hg ^-1 was even achieved at the C/1 rate. The capacity matches the maximum value that would have been expected from a similar mass of amorphous Si, indicating that the Si layer 115 was fully activated. This 3D nanostructured architecture allows efficient electrical connections with large amounts of Si materials while maintaining a short Li+ intercalation-extraction path. As a result, high capacities close to the theoretical limit are possible during charge-discharge cycles in excess of 120. When the filling rate was increased 20 times from C/10 to C/0.5 (or 2C), there was little change in capacity. The high capacity and surprising cycle stability at significantly improved charge and power rates make this new structure a choice anode material 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, etc.

13 illustrates methods for generating CNF arrays 100 and/or CNFs 110 disclosed herein. In a substrate providing step 1310, a substrate 105 is provided. The substrate 105 is optionally suitable for the growth of CNFs 110. The substrate 105 may include a variety of materials, for example Cu. Substrate 105 is optionally a conductive foil having a thickness described elsewhere herein. In a step 1320 of providing optional nucleation sites, nucleation sites for growth of CNFs 110 are provided on the substrate 105. Various nucleating materials, such as Ni particles, are known in the art. The nucleation sites are optionally provided at a density to produce average distances between CNFs 110, such as those taught elsewhere herein. In the step 1320 of providing nucleation sites, nucleation is not required for the growth of the CNFs 110 or similar structures, or after growing elsewhere, the CNFs 110 are transferred to the substrate 105 using a binder. Optional in attaching embodiments.

In the CNFs growing step 1330, the CNFs 110 are grown on the substrate 105 or separated from the substrate 105 in some embodiments. The CNFs 110 are optionally, to create the stacked-conical structure taught elsewhere herein, to create a structure with exposed graphite edges along its length, or similarly to create a variable structure. To be grown. CNFs 110 may be grown to any of the lengths taught elsewhere herein. Growth was randomly carried out by Klankowski et al. "A high-performance lithium-ion battery anode based on the core-shell heterostructure of silicon-coated vertically aligned carbon nanofibers" J. Mater. Chem. A, 2013, 1 , 1055 is achieved using PECVD processes such as those cited or taught.

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 can have any of the nominal thicknesses taught elsewhere herein to create a thickness of the Si layer 115 of tens or hundreds of nanometers. In some embodiments, the Si layer application step 1340 includes growing the intercalation material along the length of the CNF 110 into a structure independent of the exposed edge. For example, if the CNFs 110 comprise the cup-like structure discussed herein, the Si layer application step 1340 includes growing the feather-like structure illustrated in the figure, eg, FIG. 3A.

In an optional PEM application step 1345, a power enhancement material (PEM) is added to the CNF array 100 or CNFs 110. In some embodiments, the PEM application step 1345 occurs prior to attaching the CNFs 110 to the substrate 105. PEM typically includes a binder and a surface effect dominating site, as discussed in further detail elsewhere herein. In an optional conditioning step 1350, the CNF array 100 formed using steps 131-1340 is conditioned using one or more lithium intercalation cycles.

14A illustrates CNF 110 including power enhancement material 1320, according to various embodiments of the present invention. Power enhancement material 1320 is applied as a layer over the intercalation material, for example over silicon layer 115. 14B illustrates details of the power enhancement material 1320 illustrated in FIG. 14B, in accordance with various embodiments of the present invention. The power enhancement material 1320 includes a surface effect dominant site 1430 and an optional binder 1440. The silicon layer 115 is an example of an intercalation material. When the silicon layer 115 is used as an example herein, it will be understood that other types of intercalation materials may be substituted with or combined with silicon. Such 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 number of CNFs 110 in the CNF array 100.

In some embodiments, the surface effect dominant site 1430 comprises a surface of nanoparticles configured to adsorb charge carriers in a Faraday interaction, for example to undergo a redox reaction with the charge carrier. These are referred to as “surface effect governing” because, typically for such nanoparticles, the Faraday interactions between the charge carrier and the nanoparticle surface dominate the bulk Faraday interactions. Accordingly, the charge carrier is very likely to react on the surface for most nanoparticles. For example, lithium ions will be more likely to adsorb on the surface of nanoparticles than will be absorbed by most nanoparticles. These nanoparticles are sometimes referred to as surface redox particles. The Faraday interaction results in a similar capacitor that can store a significant amount of loosely coupled charge and thus provide a significant power density. In pseudo-capacitance, electrons are exchanged (eg donated). In this case, there is an exchange between the charge carrier and the nanoparticle. Although some potentials cause some intercalation of charge carriers to the nanoparticles, this does not constitute most of the interaction at the surface effect dominant site 1430 and can degrade some types of nanoparticles. Faraday interactions are interactions in which electric charges are transferred (eg, donated) as a result of electrochemical interactions.

The nanoparticles including the surface effect dominant site 1430 are transition metal oxides, 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 are also metal nitrides, carbon, activated carbon, graphene, graphite, titanate (Li ₄ Ti ₅ O ₁₂ ), crystalline silicon, tin, germanium, metal hydride, iron phosphate, polyaniline, mesophase carbon, and/or etc. It may include. It is appreciated that mixtures of these and/or other materials having the desired Faraday properties may be included in the surface effect dominant 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 size of the molecules of the constituent material. Nanoparticles contain at least several molecules. Smaller sizes provide a larger surface to the bulk ratio of possible adsorption sites. However, particles containing only a pair of molecules reduce stability. The nanoparticles are arbitrarily formed in multiple layers. For example, these may be a transition metal, Co, Ni, Mn, Ta, Ru, Rb, Ti, Sn, V ₂ O ₂ , FeO, Cu, or a layer of TiO ₂ on the Fe core (or any other Nanoparticle material), or a graphene/graphite layer on the core of some other material. In some embodiments, different core materials affect the reaction potential of the surface material. The amount of surface effect dominant sites 1430 is arbitrarily selected according to the desired power and energy density. For example, a greater power density can be achieved by having a greater number of surface effect dominant sites 1430 per amount of intercalation material, or a greater amount of energy density may be achieved by This can be achieved by having a greater amount of intercalation material per number. In fact, it is an advantage of some embodiments of the present invention that both high energy and power density can be achieved simultaneously.

By adsorbing the charge carrier on the surface of the nanoparticle, the charge carrier can only provide the same power density as previously achieved with a capacitor. This is because the discharge of charge does not follow the diffusion of charge carriers through the intercalation material. In addition, by placing the surface effect dominant site 1430 in close proximity to the intercalation material, the charge carrier can move from the intercalation material to the surface effect dominant site 1430 (or directly to the electrolyte). This results in an energy density equal to or greater than that of conventional batteries. 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 dominant sites 1430 and thus recharge these sites.

In some embodiments, the surface effect dominant sites 1430 are disposed on larger particles. For example, the particle size can be greater than 1, 10, 25, 100 or 250 microns (but is 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 enhancing material 1320 while having a pore size of the surface effect dominating site 1430 similar to the nanoparticle diameter taught above. For the purposes of the present invention, nanoparticles are particles with an average diameter of less than 1 μm.

The optional binder 1440 is configured to hold the surface effect dominant site 1430 proximate the intercalation material. In some embodiments, the distribution of surface effect dominating sites 1430 is uniform throughout binder 1440. For example, nanoparticles including the surface effect dominant sites 1430 may be mixed with the binder 1440 before the binder 1440 is applied to the intercalation material to form a relatively uniform distribution. Alternatively, nanoparticles may be applied to the surface of the intercalation material prior to application of the binder 1440. This may result in a greater concentration of the surface effect dominant sites 1430 (in the binder 1440) close to the intercalation material compared to the region of the binder 1440 distal to the intercalation material. The binder 1440 is optional in embodiments in which the surface effect dominant sites 1430 or related nanoparticles are attached directly to the intercalation material, for example to the silicon layer 115.

The binder 1440 is permeable (eg, 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 that meet the permeability requirements can be used. Binder 1440 optionally includes a material that increases its conductivity. For example, the binder 1440 may include a conductive polymer, graphite, graphene, metal nanoparticles, carbon nanotubes, carbon nanofibers, metal nanowires, Super-P (conductive carbon black), and/or the like. have. The material is preferably present in a concentration high enough to make the binder 1440 conductive, for example a percolation threshold.

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

The embodiment illustrated by FIG. 15 can be formed, for example, by first growing the unattached CNF 110. Thereafter, these are 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 dominant site 1430 and the binder 1440. Finally, the resulting mixture is deposited on the substrate 105.

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

The specific example illustrated in FIG. 16 may be formed by mixing the binder 1440, the surface effect dominant site 1430, the intercalation material 1610, and the CNF 110 together (in any order), for example. . 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 means other than the binder 1440. The intercalation material 1610 may or may not be in contact with the CNF 110 or the substrate 105. Likewise, the surface effect dominant site 1430 is optionally in contact with the substrate 105, CNF 110, and/or intercalation material 1610. The intercalation material 1610 optionally has a size of at least 0.1, 0.6, 1, 1.5, 2, 3,5, 7, 9, 10, 13, 15, 18, 21 or 29 μm or a range therebetween. Particles, suspensions, clusters, and/or droplets of intercalation material having. Other sizes are possible in alternative embodiments.

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

18 illustrates an electrode surface similar to that illustrated in FIG. 15. However, in the embodiment illustrated by FIG. 18, the surface effect dominant sites 1430 are concentrated in close proximity to the intercalation material 1610. For example, at least 2%, 10%, 25%, 50%, 75% or 85% of the surface effect dominant sites 1430 are present on the particles in contact with the intercalation material 1610. An increased concentration of surface effect dominant sites 1430 proximate intercalation material 1610 may be achieved using methods described elsewhere herein. This causes a greater concentration of surface effect dominating sites 1430 on the surface of intercalation material 1610 compared to other volumes in binder 1440.

14C, 19 and 20 illustrate electrode surfaces similar to those illustrated in FIGS. 14B, 16 and 17, respectively. However, in the embodiment illustrated by this figure, the surface effect dominant site 1430 is disposed very close to the free intercalation material, according to various embodiments of the present invention. As in the embodiment illustrated by FIG. 18, in some embodiments, at least 2%, 10%, 25%, 50%, 75% or 85% of the surface effect dominant sites 1430 are intercalated material 1610 ). In some embodiments, a higher concentration of nanoparticles comprising the surface effect dominant sites 1430 is disposed within the surface of the intercalation material 1610 at 5 nanometers than such a surface at 10 to 15 nanometers. The increased concentration of the surface effect dominant site 1430 close to the intercalation material 1610 results in nanoparticles and intercalation in solution such that the nanoparticles form an electrostatic bilayer on the surface of the intercalation material 1610. This can be achieved by selecting the appropriate zeta potential of the material 1610. Zeta potential is the electrical potential in the interfacial bilayer at the location of the surface versus the electrical potential at the point in the bulk solution spaced from the surface. The zeta potential is arbitrarily greater than 25 mV (absolute). In another embodiment, nanoparticles are applied to the surface of intercalation material 1610 prior to application of binder 1440.

Intercalation material 1610 as illustrated in FIGS. 16-20 may comprise any single material or combination of materials discussed herein for silicon layer 115 (including or excluding silicon). . Likewise, CNF 110 may include any single fiber or combination of the various types of fibers discussed herein (including or excluding carbon nanofibers), as illustrated in Figures 16-20. have. For example, the CNF 110 may include branched fibers, multi-wall fibers, wires, airgels, graphite, carbon, graphene, boron-nitride nanotubes, and the like. The number of surface effect dominant sites 1430 and CNF 110 shown in this figure and other figures herein is for illustrative purposes only. For example, in practice, the number of surface effect dominant sites 1430 may be greater. Likewise, the amounts and sizes of intercalation material 1610 and silicon layer 115 shown are for illustrative purposes. Alternative embodiments may include larger or smaller 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 figure.

In various embodiments, the amount of nanoparticles comprising the surface effect dominant site 1430 (when measured in a discharged state) is a single number of nanoparticles on the surface of the intercalation material 1610 or silicon layer 115. It can be chosen 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 in between) of the layers. As used herein, 0.1 monolayer is to specify 10%, and 10x monolayer is 10 monolayer. In various embodiments, the amount of nanoparticles comprising the surface effect dominant site 1430 is at least 1, 5, 10, or more of the nanoparticles on the surface of the intercalation material 1610 (when measured in a discharged state). It may be chosen to result in a 20, 50, 100, 250 or 500 nanometer layer (or any combination therebetween). Other coverage densities or depths are possible when measuring in a single layer. As the coverage of the nanoparticles (including the surface effect dominant site 1430) approaches 1.0 monolayer, the nanoparticles are intercalated between the charge carrier of the electrolyte and the intercalation material 1610 moving through the binder 1440. Layers can be formed. For example, in some embodiments, the electrolyte includes lithium as a charge carrier. Lithium can move through the binder 1440 and cause a Faraday reaction with the surface effect dominant sites 1430, where electrons are donated to lithium from one of the surface effect dominant sites 1430. These electrons are transferred from the substrate 105 to the nanoparticles through the intercalation material 1610 (eg, donated). Because the nanoparticles form a barrier, at this stage in the charging process, only a limited amount of charge carriers reach the intercalation material 1610. Filling is dominated by a reaction at the surface effect dominating site 1430. In some embodiments, charging may be fast because intercalation of the charge carrier to the intercalation material 1610 is not necessary before the Faraday reaction with the charge carrier occurs. The presence of the surface effect dominant site 1430 greatly increases the surface area in which the initial Faraday reaction can occur prior to intercalation. The surface effect dominant site 1430 promotes intercalation of charge carriers to the intercalation material 1610. The charge carriers may be intercalated in the form upon reception at the surface effect dominant site 1430 or may be intercalated in an alternative form such as metal oxide. When intercalated as a metal oxide, the oxygen in the oxide can be recycled back to the surface effect dominant site 1430 after intercalation.

In some embodiments, because the nanoparticles form an imperfect barrier, some charge carriers are still intercalating material in this charging step (e.g., the initial step of charging the power storage device comprising the electrode discussed herein). Reach (1610). As the intercalation material 1610 of some embodiments, for example silicon, expands when charge carrier intercalation occurs in the surface region, the intercalation material 1610 also increases. 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. Accordingly, as charging proceeds, a greater number of charge carriers per unit time may reach the intercalation material 1610. This optionally continues until filling is dominated by a reaction within intercalation material 1610. Reducing the surface coverage can also increase the average fraction of surface effect dominating sites 1430 on each nanoparticle exposed to the electrolyte. As used herein, the phrase “surface coverage” is used to indicate the density of species on a surface and can be measured as the number (or fraction thereof) of a single layer, as a thickness, or as a concentration or the like.

In some embodiments, power storage at the surface effect dominant site 1430 occurs at the potential at which the Faraday surface reaction occurs, but no intercalation of the charge carriers to the nanoparticles comprising the surface effect dominant site 1430 occurs. . This prevents decomposition of the nanoparticles by repeated intercalation and de-intercalation of the charge carrier, and enables a longer cycle life. In the same electrode, in the intercalation material 1610 via a Faraday reaction occurring at a higher potential, optionally involving a potential that causes intercalation of the charge carrier to the nanoparticles with the surface effect dominant site 1430. It may be desirable to store power. This may occur in some embodiments of the invention because there is a potential drop between the substrate 105 and the electrolyte 125.

In one specific example, where lithium is the charge carrier, the surface effect dominant site 1430 is on TiO ₂ and the intercalation material 1610 is primarily silicon. In other embodiments, it will be appreciated that the specific voltage will depend on the chemical species included in the surface effect dominant site 1430 and intercalation material 1610, and the reactions that occur during charging, and the like. In various embodiments, the potential difference between the surface effect dominant 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 2.4V, Or any range between them. As used herein, the term “potential” is used to refer to the absolute value of an electrostatic potential (eg, |x|).

21 illustrates a method of assembling an electrode surface, according to various embodiments of the present invention. The assembled electrode surface can be used, for example, as an anode in batteries, capacitors or hybrid devices. 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, a substrate 105 optionally suitable for the growth of CNF 110 or other supporting filaments is provided. As discussed herein, the substrate 105 may comprise a variety of materials, such as Cu, Au, Sn, and the like. Substrate 105 optionally includes nucleation sites as described elsewhere herein.

In an optional CNF providing step 2120, CNF 110 (or any other support filament described herein) is provided. The CNF providing step 2120 is optional in embodiments in which an electrode without supporting filaments, for example those illustrated by FIGS. 17 and 20, is 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 is then attached to the substrate 105.

In an intercalation material providing step 2130, an intercalation material 1610 is provided. In some embodiments, intercalation material 1610 is first applied to 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 the step 2140 of providing a surface effect dominant site (SEDS), a surface effect dominant site 1430 is provided. As discussed elsewhere herein, the surface effect dominant sites 1430 may be disposed on nanoparticles, or larger structures, such as graphite, graphene, or activated carbon. The surface effect dominating site 1430 may be provided as a suspension in the binder 1140, or as a spray using sputter deposition, electro deposition, evaporation, or the like in a solvent. In some embodiments, the zeta potential of the intercalation material 1610 is selected such that the surface effect dominant sites 1430 are concentrated at the surface of the intercalation material 1610.

In an application step 2150, intercalation material 1610, surface effect dominant site 1430 and optionally CNF 110 are applied to substrate 105. These materials can be applied in a wide variety of orders and combinations. For example, intercalation material 1610 can be applied to CNF 110 (probably already attached to substrate 105), after which surface effect dominant site 1430 is Can be applied on top. Alternatively, the free CNF 110 and the intercalation material 1610 may be mixed first, and then any one of the surface effect dominating 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 understand that in other embodiments, these components may be mixed or added in any order or combination. Also, 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 conditioning step 1350 is optionally followed.

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

22 illustrates a method of operating an electrical charge storage device, according to various embodiments of the present invention. This method can be used, for example, when charging an electrical charge storage device. In some embodiments, such a method includes attaching the charging device to both the anode and cathode of the electrical charge storage device via a wire. These electrical charge storage devices generate electric potentials at the anode and cathode, causing a potential gradient between them. The potential gradient induces electrons to the anode. The steps illustrated in FIG. 22 may occur arbitrarily concurrently, for example they may occur concurrently with each other or at overlapping times.

In the potential setting step 2210, a potential is set in the electrical charge storage device. This potential can arise between the anode and cathode of the electrical charge device. This potential will cause a potential gradient between the substrate 105 and the electrolyte 125 in the electrical charge storage device. The potential gradient may create a potential difference between the position of the surface effect dominant site 1430 and the intercalation material 1610. In various embodiments, this 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 in between.

In the lithium receiving step 2220, the charge carrier, which is lithium, but only one possible example, is received at one of the surface effect dominant sites 1430. These charge carriers are optionally received through the binder 1440.

In the electron transfer step 2230, electrons are transferred (eg, donated) from the surface effect dominant site 1430 to the charge carrier received in the lithium receiving step 2220. This transfer may include the sharing of electrons between the surface effect dominant site 1430 and the charge carrier. Electrons are transferred in the Faraday reaction and are typically conducted from the substrate 105. The transfer occurs while the charge carrier is on the surface of the surface effect dominant site 1430 and occurs at the potential at that location. The reaction potential of electron transfer depends, for example, on the reaction potential of the charge carrier and the reaction potential of the surface effect dominant site 1430. The reaction potential may be dependent on both the surface effect dominant site 1430 and the nearby intercalation material 1610. As used herein, the term “reaction potential” is used to refer to the potential at which a reaction occurs at a remarkable rate. The reaction potential of a reaction can be illustrated, for example, by a peak in a cyclic voltamogram. 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 can be very 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 may be affected by the energy required for intercalation, or by the proximity of the surface effect dominant site 1430 and intercalation material 1610.

In the lithium intercalation step 2240, the charge carrier, where lithium is just one possible example, is intercalated in the intercalation material 1610. This step may include transfer of charge carriers into the bulk of intercalation material 1610. The charge carrier is in the intercalation material 1610 as the same chemical species as received at the surface effect dominant site 1430 in the lithium accepting step 2220, or alternatively as a chemical species formed at the surface effect dominant site 1430. Can be accommodated. For example, the charge carrier may be received in the intercalation material 1610 as an oxide of a chemical species (eg, Li ₂ O, etc.) received at the surface effect dominant site 1430.

In the electron transfer step 2250, electrons are transferred from the intercalation material 1610 to the charge carrier of the lithium intercalation step 2240. Electrons are transferred 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 a potential at that location. The reaction potential of 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 affected by both the intercalation material 1610 and the adjacent surface effect dominant site 1430. The surface dominant site 1430 may facilitate the transfer of lithium from the electrolyte 125 to the intercalation material 1610. As discussed elsewhere herein, this shift can occur through an intermediate oxide such as Li ₂ O. The work function of the electron movement may be different from the work function of the electron movement in the electron movement 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 2.4V, or any combination therebetween. In some embodiments, it is thermodynamically more desirable for lithium to be intercalated in intercalation material 1610 than in most nanoparticles comprising surface effect dominant sites 1430. However, the presence of the surface effect dominant site 1430 may catalyze the intercalation of charge carriers to the intercalation material 1610.

When the charge carrier is converted to oxide in the electron transfer step 2230, in some embodiments, the electron transfer step 2250 transfers oxygen back to the surface effect dominant site 1430 in the intercalation material 1610. Includes. This oxygen is received as an oxide of the charge carrier in the intercalation material 1610 and is released from the charge carrier during intercalation. After being moved back to the surface effect dominant site 1430, this oxygen can be used in further generations of the electron transfer step 2230, ie the oxygen is recycled.

Although the description of FIG. 22 assumes that the charge carrier received in the lithium receiving step 2220 and the charge carrier in the lithium intercalation step 2240 are two different individual charge carriers (which may be of the same type), various In an embodiment, steps 2220, 2230 and 2240 may be performed by the same individual charge carrier. For example, in some embodiments, lithium receiving step 2220 includes receiving a charge carrier at one of the surface effect dominant sites 1430. The electron transfer step 2230 includes a reaction in which the charge carrier subsequently reacts with the surface effect dominant site 1430 to form an intermediate compound. In some embodiments, this reaction ^{2Li + + MO + 2e - →} Li 2 O + M ( where, M is any of transition metals discussed herein, Li ₂ O is obtained intermediate compound Im) a. In the lithium intercalation step 2240, the intermediate compound (e.g., Li ₂ O) is intercalated with the intercalation material 1610, or one (or both) of Li in the intermediate compound is Li ₂ From O to O are transferred to the atoms of the intercalation material (eg Li _x Si). This movement may result in regeneration of the MO divided in the electron movement step 2230. It is noted that in this example, the same individual Li atoms are included in each of steps 2220-2230 and 2240. The electron transfer step 2250 is not required in this embodiment of the method illustrated by FIG. 22. In some embodiments, it is possible that both a reaction sequence comprising an intermediate such as Li ₂ O and a reaction sequence not including an intermediate occurs during a single charging cycle.

Several 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, although the examples discussed herein have focused on CNFs having a stacked-conical structure, the above teachings may be adapted to other materials having similar or different structures. Likewise, while Cu substrate and Li charge carriers have been discussed herein, other substrates and charge carriers will be apparent to those skilled in the art. Silicon layer 115 is optionally formed of 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. Additionally, aerosol, nano-wire, TiO ₂ (titanium oxide), metal wire, carbon wire, or boron nitride nano-fibers may be used in place of the carbon nano-fibers discussed herein. In the figure, the relative concentrations of the binder 1440, the surface effect dominant site 1430, the intercalation material 1610 and the CNF 110, and other elements may deviate greatly from those illustrated.

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

Details of VACNF growth and silicon deposition, microscopy and spectroscopic characterization, and electrochemical cell assembly and charge-discharge testing can be found in U.S. Provisional Application 61/667,876, filed July 3, 2012.

The embodiments discussed herein are illustrative of the invention. Since 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. Any such modifications, adaptations, or changes that rely on the teachings of the present invention and which improve the art through these teachings are considered to be within the spirit and scope of the present invention. Therefore, as it is to be understood that the invention is not limited in any way to the illustrated embodiments, these descriptions and drawings should not be considered in a limiting sense.

Claims (16)

As an electrode,
A conductive substrate; And
Intercalation material layer
Including, the intercalation material layer,
Intercalation material; And
A plurality of nanoparticles-The plurality of nanoparticles are selected to reversibly adsorb one or more charge carriers, the plurality of nanoparticles are distributed in the intercalation material layer, and at least some of the plurality of nanoparticles are It is attached to the surface of the intercalation material, wherein the plurality of nanoparticles include multilayer nanoparticles, and the multilayer nanoparticles include a core layer including a transition metal,
The intercalation material layer further comprises a plurality of support structures, the support structures comprising a plurality of separated carbon nanotubes disposed adjacent to the conductive substrate and detached from the conductive substrate. The electrode of claim 1, wherein some of the plurality of nanoparticles are suspended in the intercalation material layer. The electrode of claim 1, wherein the conductive substrate also comprises one or more of Cu, Au, and Sn. The electrode of claim 1, wherein the intercalation material is connected to a plurality of support structures. The electrode of claim 1, wherein each of the plurality of support structures comprises at least one of graphite and a carbonaceous material. The electrode of claim 1, wherein the plurality of support structures comprises a plurality of carbon nanotubes attached to a conductive substrate. The electrode of claim 1, wherein the plurality of support structures also comprises a plurality of carbon particles. The electrode of claim 1, wherein the one or more charge carriers comprise lithium ions. The method of claim 1,
The electrode, wherein the plurality of nanoparticles are selected to donate electrons to one or more charge carriers on the surface of each of the plurality of nanoparticles through Faraday interactions. The method of claim 1, wherein the plurality of nanoparticles are 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, Activated carbon, graphene, graphite, titanate (Li ₄ Ti ₅ O ₁₂ ), crystalline silicon, tin, germanium, metal hydride, iron phosphate, polyaniline, an electrode comprising at least one of mesophase carbon. The electrode of claim 1, wherein each of the multilayer nanoparticles also comprises an outer nanoparticle layer. The method of claim 11, wherein the core layer of each of the multilayer nanoparticles is among graphene, graphite, Si, Co, Ni, Mn, Ta, Ru, Rb, Ti, Sn, V ₂ O ₂ , FeO, Cu, and Fe. An electrode comprising at least one. The method of claim 11,
An electrode, wherein the outer nanoparticle layer of each of the multilayer nanoparticles also comprises at least TiO ₂ . The electrode of claim 1, wherein the intercalation material layer comprises at least one of Si, Ag, Al, Bi, C, Se, Sb, Sn and Zn. As an electrode,
A conductive substrate;
A plurality of support structures held in the vicinity of the conductive substrate;
Intercalation material;
A plurality of multilayer nanoparticles dispersed with a plurality of support structures-the multilayer nanoparticles promote intercalation of charge carriers to the intercalation material or adsorb charge carriers through Faraday interactions. Providing surface effect dominant sites such that the multilayer nanoparticles comprise a core layer comprising a transition metal; And
The electrode, wherein the plurality of support structures comprises a plurality of separated carbon nanotubes disposed adjacent to the conductive substrate but detached from the conductive substrate. The electrode of claim 15, wherein the plurality of nanoparticles have an average diameter of less than 1 μm.

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