Patent Publication Number: US-9431181-B2

Title: Energy storage devices including silicon and graphite

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is:
         a continuation of U.S. non-provisional patent application Ser. No. 13/868,957 filed Apr. 23, 2013;   a continuation of U.S. non-provisional patent application Ser. No. 13/779,409 filed Feb. 27, 2013;   a continuation-in-part of U.S. non-provisional patent application Ser. No. 13/725,969 filed Dec. 21, 2012 which claimed priority to U.S. provisional patent applications 61/578,545 filed Dec. 21, 2011, 61/603,833 filed Feb. 27, 2012 and 61/615,179 filed Mar. 23, 2012, and which in turn is a continuation-in-part of U.S. non-provisional patent application Ser. No. 12/392,525 filed Feb. 25, 2009 now U.S. Pat. No. 8,420,258;   a continuation-in-part of U.S. non-provisional patent application Ser. No. 12/904,113 filed Oct. 13, 2010 which in turn claims benefit and priority to U.S. provisional patent application 61/254,090 filed Oct. 22, 2009;   and claims benefit and priority to U.S. provisional patent applications:
           61/667,876 filed Jul. 3, 2012,   61/677,317 filed Jul. 30, 2012, and   61/752,437 filed Jan. 14, 2013.   
               

     This application is related to U.S. non-provisional patent application Ser. Nos. 13/779,571, 13/779,472 and 13/779,522 filed Feb. 27, 2013. The disclosures of all the above provisional and non-provisional patent applications are hereby incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The invention is in the field of energy storage devices, including but not limited to batteries, capacitors and fuel cells. 
     2. Related Art 
     Rechargeable lithium ion batteries are key electrical energy storage devices for power supply in portable electronics, power tools, and future electric vehicles. Improving the specific energy capacity, charging/discharging speed, and cycling lifetime is critical for their broader applications. 
     In current commercial Li-ion batteries, graphite or other carbonaceous materials are used as the anodes which have a theoretical capacity limit at 372 mAh/g by forming fully intercalated LiC 6  compound. In contrast, silicon has a much higher theoretical specific capacity of 4,200 mAh/g by forming fully lithiated alloy Li 4.4 Si. However, the large volume expansion of lithiated Si by up to ˜300% causes great structural stress that in the past inevitably lead to fractures and mechanical failure, which significantly limited the lifetime of Si anodes. 
     SUMMARY 
     In some embodiments, a power storage device includes a hybrid core-shell NW (nano-wire) architecture in a high-performance Li-ion anode by incorporating an array of vertically aligned carbon nanofibers (VACNFs) coaxially coated with a layer of amorphous silicon. The vertically aligned CNFs include multiwalled carbon nanotubes (MWCNTs), which are optionally grown on a Cu substrate using a DC-biased plasma chemical vapor deposition (PECVD) process. The carbon nanofibers (CNFs) grown by this method can have a unique interior morphology distinguishing them from the hollow structure of common MWCNTs and conventional solid carbon nanofibers. One of the distinguishing characteristics is that these CNFs optionally consist of a series of bamboo-like nodes across the mostly hollow central channel. This microstructure can be attributed to a stack of conical graphitic cups discussed further elsewhere herein. In larger length scale, these PECVD-grown CNFs are typically uniformly aligned normal to the substrate surface and are well separated from each other. They may be without any entanglement or with minimal entanglement, and thus form a brush-like structure referred to as a VACNF array. The diameter of individual CNFs can be selected to provide desired mechanical strength so that the VACNF array is robust and can retain its integrity through Si deposition and wet electrochemical tests. 
     Various embodiments of the invention include types of support filaments other than VACNFs. These support filaments can include, for example, nanowires, carbon sheets or other structures described herein. Other embodiments do not include any support filaments and use a binder instead. 
     Various embodiments of the invention include an energy storage system comprising a conductive substrate; a plurality of vertically aligned carbon nanofibers grown on the substrate, the carbon nanofibers including a plurality multi-walled carbon nanotubes; and an electrolyte including one or more charge carriers. 
     Various embodiments of the invention include an energy storage system comprising a conductive substrate; a plurality of vertically aligned carbon nanofibers grown on the substrate; and a layer of intercalation material disposed on the plurality of vertically aligned carbon nanofibers and configured to have a lithium ion storage capacity of between approximately 1,500 and 4,000 mAh per gram of intercalation material. 
     Various embodiments of the invention include an energy storage system comprising a conductive substrate; a plurality of vertically aligned carbon nanofibers grown on the substrate; and a layer of intercalation material disposed on the plurality of vertically aligned carbon nanofibers and configured such that an ion storage capacity of the intercalation material is approximately the same at charging rates of 1C and 3C. 
     Various embodiments of the invention include a method of producing an energy storage device, the method comprising providing a substrate; growing carbon nanofibers on the substrate, the carbon nonofibers having a stacked-cone structure; and applying intercalation material to the carbon nanofibers, the intercalation material being configured for intercalation of charge carriers. 
     Various embodiments of the invention include an energy storage system comprising: an electrolyte including one or more charge carriers; a conductive substrate; a plurality of vertically aligned support filaments attached to the substrate; intercalation material disposed on each of the support filaments and configured to reversibly adsorb members of the charge carriers within a bulk of the intercalation material; and a binder disposed on the intercalation material and including a plurality of nanoparticles, each of the nanoparticles being configured to provide surface effect dominant sites configured to adsorb members of the charge carriers via faradaic interactions on surfaces of the nanoparticles. 
     Various embodiments of the invention include an energy storage system comprising: an electrolyte including one or more charge carriers; a conductive substrate; a plurality of support filaments attached to the substrate; intercalation material disposed on each of the support filaments and configured to reversibly adsorb members of the charge carriers within a bulk of the intercalation material; and a binder disposed on the intercalation material and including a plurality of surface effect dominant sites configured to catalyze intercalation of the charge carriers into the intercalation material. 
     Various embodiments of the invention include an energy storage system comprising: an electrolyte including one or more charge carriers; a conductive substrate; intercalation material configured to reversibly adsorb members of the charge carriers within a bulk of the intercalation material; and a binder disposed on the intercalation material and including a plurality of nanoparticles, each of the nanoparticles being configured to provide surface effect dominant sites configured to donate electrons to members of the charge carriers via faradaic interactions on surfaces of the nanoparticles. 
     Various embodiments of the invention include an energy storage system comprising: a cathode; and an anode separated from the cathode by an electrolyte including one or more charge carriers, the anode comprising, an intercalation material configured to intercalate the charge carriers and to donate electrons to the charge carriers at a first reaction potential, a plurality of nanoparticles including surface effect dominant sites configured to donate electrons to the charge carriers at a second reaction potential, a absolute difference between the first reaction potential and the second reaction potential being less than 2.4V. 
     Various embodiments of the invention include a system comprising: means for establishing a potential gradient at an anode of a charge storage device, the anode including an electrolyte, a plurality of surface effect dominant sites, an intercalation material and a substrate; means for receiving a charge carrier of the electrolyte at one of the surface effect dominant sites; means for receiving an electron at the charge carrier from one of the surface effect dominant sites; and means for receiving a charge carrier at the intercalation material. 
     Various embodiments of the invention include a method of producing an energy storage device, the method comprising: providing a conductive substrate; growing support filaments on the substrate; applying intercalation material to the support nanofibers, the intercalation material being configured for intercalation of charge carriers; and applying a plurality of surface effect dominant sites in close proximity to the intercalation material. 
     Various embodiments of the invention include a method of producing an anode, the method comprising: providing a conductive substrate; mixing a binding material, surface effect dominant sites and intercalation material, the surface effect dominant sites being configured to accept electrons from charge carriers at a first reaction potential and the intercalation material being configured to accept the charge carriers or electrons from the charge carriers at a second reaction potential; and applying the binding material, surface effect dominant sites and intercalation material to the substrate. 
     Various embodiments of the invention include a method of producing an energy storage device, the method comprising: providing a conductive substrate; providing support filaments; applying intercalation material to the support filaments, the intercalation material being configured for intercalation of charge carriers; and adding surface effect dominant sites to the support filaments. 
     Various embodiments of the invention include a method of charging a charge storage device, the method comprising establishing a potential between a cathode and an anode of the charge storage device, the charge storage device including an electrolyte; receiving a first charge carrier of the electrolyte at a surface effect dominant site of the anode; transferring an electron of the anode to the first charge carrier; receiving a second charge carrier of the electrolyte at an intercalation material of the anode; and transferring an electron from the intercalation material to the second charge carrier. 
     Various embodiments of the invention include a method of charging a charge storage device, the method comprising: establishing a potential gradient at an anode of the charge storage device, the anode including an electrolyte, a plurality of nanoparticles having surface effect dominant sites, an intercalation material and a substrate; receiving a first charge carrier of the electrolyte at one of the surface effect dominant sites; transferring an electron to the first charge carrier from the one of the surface effect dominant sites; receiving a second charge carrier at the intercalation material of the anode; and transferring an electron from the intercalation material to the second charge carrier. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  illustrate a CNF array comprising a plurality of CNF grown on a substrate, according to various embodiments of the invention. 
         FIGS. 2A-2C  illustrate a plurality of vertically aligned CNFs in different states, according to various embodiments of the invention. 
         FIGS. 3A-3C  illustrate details of a CNF, according to various embodiments of the invention. 
         FIG. 4  illustrates a schematic of the stacked-cone structure of a CNF, according to various embodiments of the invention. 
         FIGS. 5A-5C  illustrate an electrochemical characterization of ˜3 μm long CNFs, according to various embodiments of the invention. 
         FIGS. 6A-6C  illustrates scanning electron microscopy images of 3 μm long CNFs, according to various embodiments of the invention. 
         FIGS. 7A-7C  illustrate results obtained using CNFs including a Si layer as Li-ion battery anodes, according to various embodiments of the invention. 
         FIG. 8  illustrates how the capacity of a CNF array varies with charging rate, according to various embodiment of the invention. 
         FIG. 9  illustrates Raman spectra of CNF arrays, according to various embodiments of the invention. 
         FIGS. 10A-10C  shows the variation of Li +  insertion-extraction capacities and the coulombic efficiency over 15 charge-discharge cycles, according to various embodiments of the invention. 
         FIGS. 11A-11C  show scanning electron microscopy images of freshly prepared CNF arrays, according to various embodiments of the invention. 
         FIG. 11D  shows a cross-section of a nanofiber/silicon complex including more than one CNF. 
         FIG. 12  illustrates a carbon nano-fiber array including fibers of 10 um in length, according to various embodiments of the invention. 
         FIG. 13  illustrates methods of producing CNF arrays, according to various embodiments of the invention. 
         FIG. 14A  illustrates a CNF including a power enhancement material, according to various embodiments of the invention. 
         FIG. 14B  illustrates detail of the power enhancement material illustrated in  FIG. 14A , according to various embodiments of the invention. 
         FIG. 14C  illustrates alternative detail of the power enhancement material illustrated in  FIG. 14A , according to various embodiments of the invention. 
         FIG. 15  illustrates an electrode surface including a power enhancement material and non-aligned CNFs coated by intercalation material, according to various embodiments of the invention. 
         FIG. 16  illustrates an electrode surface including power enhancement material, non-aligned CNFs and free intercalation material, according to various embodiments of the invention. 
         FIG. 17  illustrates an electrode surface including intercalation material and power enhancement material, without CNFs, according to various embodiments of the invention. 
         FIG. 18  illustrates an electrode surface including surface effect dominant sites disposed in close proximity to CNFs, according to various embodiments of the invention. 
         FIGS. 19 and 20  illustrate electrode surfaces including surface effect dominant sites disposed in close proximity to free intercalation material, according to various embodiments of the invention. 
         FIG. 21  illustrates methods of assembling an electrode surface, according to various embodiments of the invention. 
         FIG. 22  illustrates methods of operating a charge storage device, according to various embodiments of the invention. 
         FIG. 23A  illustrates a cross section of an electrode, according to various embodiments of the invention. 
         FIG. 23B  is a cross section illustrating details of a seed layer of  FIG. 23A  according to various embodiments of the invention. 
         FIG. 23C  is a cross section of a portion of the electrode extension of  FIG. 23A  illustrating an under-layer between a support filament and an intercalation layer, and an over-layer that encapsulates the intercalation layer, according to various embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments of the invention include a rechargeable (secondary) battery including an improved electrode. The electrode of the invention is optionally included within a part of a cathode and/or an anode of a secondary battery/cell  100  to create an improved battery. The electrode typically includes an electrode extension grown on or attached to a substrate using a seed layer. The electrode extension is configured to increase the surface area of the electrode and includes a support filament and an intercalation layer. In various embodiments, the support filament material includes a carbon nano-tube (CNT), a carbon nano-fiber (CNF), a nano-wire NW (a wire having a diameter less than approximately five micrometer), metal, semiconductor, insulator, silicon, and/or the like. The CNT, CNF, and/or NW may be single walled or multi walled. The support filament may provide an electrical path to the substrate and a mechanical base for the intercalation layer. The intercalation layer provides a region for absorption and/or donation of ions from the electrolyte. As used herein, an intercalation layer can be used at both an anode and a cathode. In various embodiments, the intercalation layer includes a donor/acceptor material (DAM) configured for donating and/or accepting the ions from the electrolyte. This ion donating and/or accepting may include both adsorbing and absorbing processes. The intercalation layer may expand in volume by at least 5, 10, 15, 50, 100, 200 or 400 percent on the absorption of ions. 
     In various embodiments, the DAM includes silicon, graphite, Sn, Sn—C, inter-metallics, phosphides, nitrides, 3d metal oxides, or LiCoPO 4 , LiMnPO 4 , LiMn 2 O 4 , LiCoO 2 , LiNiO 2 , MnO 2 , vanadium oxides V 2 O 5  and LiV 3 O 8 , polyanionic materials such as Li(1-x)VOPO 4 , Li(x)FePO 4 ), LiMnO 2 , Li 2 FePO 4 F, doped LiMn 2 O 4 , and/or the like. The DAM is deposited or grown on the support filament. In some embodiments, the support filament is provided with additional strength (e.g., tensile, compression, shear, and/or the like) for supporting the DAM particularly during expansion and/or contraction of the DAM in the intercalation layer. In some embodiments, the DAM covers part but not all of the support filament. For example, portion of the support filament may remain uncoated. The uncoated portion can provide for flexibility and freedom of movement, for example between the electrode extension and the substrate. In some circumstances this reduces the likelihood of separation of the support filament from the seed layer during expansion and/or contraction of the DAM in the intercalation layer. 
     The electrode extension increase intercalation volume and surface area, thereby improving energy density of the electrode over a layer of material deposited on a flat surface. The electrode extensions may serve as a flexible interface between the substrate and intercalation layer, thereby allowing a large degree of expansion in volume (e.g., 2×, 4×, 6×, etc.) of the intercalation layer, while at the same time reducing a risk of the material separating from the substrate. The electrode extension can also reduce diffusion distances of the ions in the bulk of the intercalation material, therefore improving power density of the electrode. 
       FIGS. 1A and 1B  illustrate a CNF Array  100  comprising a plurality of CNF  110  grown on a conductive Substrate  105 , according to various embodiments of the invention. In  FIG. 1A  the CNF Array  100  is shown in the Li extracted (discharged) state and in  FIG. 1B  the CNF Array  100  is shown in the Li inserted (charged) state. The CNF  110  in these and other embodiments discussed herein are optionally vertically aligned. The CNF  110  are 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 can have a unique morphology that includes a stack of conical graphitic structures similar to stacked cups or cones or a spiral. This creates a very fine structure that facilitates lithium intercalation. This structure is referred to here as the “stacked-cone” structure elsewhere herein. In larger length scale, these CNFs  110  are typically uniformly aligned normal to the substrate surface and are well separated from each other. The diameter of individual CNFs can be selected to provide desired mechanical strength so that the CNF Array  100  is robust and can retain its integrity through Si deposition and wet electrochemical cycles. A seed layer is optionally employed for growing CNFs  110  on Substrate  105 . In use the CNF Array  100  is placed in contact with an Electrolyte  125  including one or more charge carriers, such as a lithium ion. The CNFs  110  are configured such that some of Electrolyte  125  is disposed between CNFs  110  and/or can ready Substrate  105  via gaps between CNFs  110 . 
     The diameter of individual CNFs  110  illustrated in  FIGS. 1A and 1B  are nominally between 100 and 200 nm, although diameters between 75 and 300 nm, or other ranges are possible. CNFs  110  are optionally tapered along their length. The CNFs  110  produced using the techniques discussed herein have excellent electrical conductivity (σ=˜2.5×10 5  S/m) along the axis and do form firm Ohmic contact with Substrate  105 . The open space between the CNFs  110  enables a Silicon Layer  115  to be deposited onto each CNFs to form a gradually thinned coaxial shell with a mass at a Tip  120  of the CNF  110 . This design enables the whole Silicon Layer  115  to be electrically connected through the CNF  110  and to remain fully active during charge-discharge cycling. The expansion that occurs on alloying of lithium with Silicon Layer  115  can be easily accommodated in the radial direction, e.g. perpendicular to the long dimension of the CNFs  110 . The charge and discharge capacity and cycling stability of non-Si-coated CNFs  110  and Si-coated CNFs  110  can be compared. The addition of Silicon Layer  115  provided a remarkable Li +  insertion (charge) capacity up to 3938 mAh/g Si  at the C/2 rate and retained 1944 mAh/g Si  after 110 cycles. This charge/discharge rate and the corresponding capacity are significantly higher than previous architectures using Si nanowires or hybrid Si—C nanostructures.  FIGS. 1A and 1B  are perspective views. 
     In various embodiments, from 0.01 up to 0.5, 1.0, 1.5, 2.5, 3.0, 4.0, 10, 20, 25 μm (or more) nominal Si thickness can be deposited onto 3 μm long CNFs  110  to form CNF Arrays  100  such as those illustrated in  FIGS. 1A and 1B . Likewise, in various embodiments, from 0.01 up 0.5, 1.0, 1.5, 2.5, 3.0, 4.0, 10, 20, 25 μm (or more) nominal Si thickness can be deposited onto 10 μm long CNFs  110  to form CNF Arrays  100 . In some embodiments, the nominal thickness of Si is between 0.01 μm and the mean distance between CNFs  110 . 
     Using CNF Arrays  100 , Li ion storage with up to ˜4,000 mAh/g mass-specific capacity at C/2 rate is achieved. This capacity is significantly higher than those obtained with Si nanowires alone or other Si-nanostructured carbon hybrids at the same power rate. The improved performance is attributed to the fully activated Si shell due to effective charge collection by CNFs  110  and short Li +  path length in this hybrid architecture. Good cycling stability has been demonstrated in over 110 cycles. In various embodiments the storage capacity of Li ion storage of CNF Arrays  100  is approximately 750, 1500, 2000, 2500, 3000, 3500 or 4000 mAh per gram of Si, or within any range between these values. As used herein, the term “nominal thickness” (of e.g., Si) is the amount of Si that would produce a flat layer of Si, of the said thickness, on Substrate  105 . For example, a nominal thickness of Si of 1.0 μm is an amount of Si that would result in a 1.0 μm thick layer of Si if deposited directly on Substrate  105 . Nominal thickness is reported because it can easily be measured by weight using methods know in the art. A nominal thickness of 1.0 μm will result in a smaller thickness of Si Layer  115  on CNFs  110  because the Si is distributed over the greater area of the CNFs  110  surfaces. 
       FIGS. 2A-2C  illustrate CNF Array  100  having an average fiber length of approximately 3 μm, according to various embodiments of the invention.  FIGS. 2A-2C  are scanning electron microscopy (SEM) images.  FIG. 2A  shows a plurality of vertically aligned CNFs  110  without Silicon Layer  115 .  FIG. 2B  shows a plurality of vertically aligned CNFs  110  including Silicon Layer  115 .  FIG. 2C  shows a plurality of vertically aligned CNFs  110  in the extracted (discharged) state after experiencing  100  lithium charge-discharge cycles. The CNFs  110  are firmly attached to a Cu Substrate  105  with essentially uniform vertical alignment and a random distribution on the surface of the substrate. The samples used in this study have an average areal density of 1.11×10 9  CNFs/cm 2  (counted from top-view SEM images), corresponding to an average nearest-neighbor distance of ˜330 nm. The average length of the CNFs  110  in  FIG. 2  is ˜3.0 μm with &gt;90% of CNFs in the range of 2.5 to 3.5 μm in length. The diameter spreads from ˜80 nm to 240 nm with an average of ˜147 nm. An inverse teardrop shaped Ni catalyst at Tip  120  presents at the tip of each CNF  110  capping the hollow channel at the center of the CNF, which promoted the tip growth of CNF  110  during the PECVD process. The size of the Ni catalyst nanoparticles defined the diameter of each CNFs  110 . Longer CNFs  110 , up to 10 were also employed in some studies to be discussed in later sections. 
     In various embodiments the average nearest neighbor distance can vary between 200-450 nm, 275-385 nm, 300-360 nm, or the like. Further, the average length of the CNFs  110  can be between approximately 2-20, 20-40, 40-60, 60-80, 80-100, 100-120, 120-250 (μm), or more. Standard carbon nanofibers as long as a millimeter long are known in the art. In various embodiments, the average diameter can vary between approximately 50-125, 100-200, 125-175 (nm), or other ranges. 
     An amorphous Si Layer  115  was deposited onto the CNF Array  100  by magnetron sputtering. The open structure of brush-like CNF Arrays  100  made it possible for Si to reach deep down into the array and produce conformal structures between the CNFs  110 . As a result, it formed a thick Si coating at the CNF tip followed by a gradually thinned coaxial Si shell around the lower portion of the CNF, presenting an interesting tapered core-shell structure similar to a cotton swab. The amount of Si deposition is characterized by the nominal thickness of Si films on a flat surface using a quartz crystal microbalance (QCM) during sputtering. The Li +  insertion/extraction capacities were normalized to the total Si mass derived from the nominal thickness. At 0.50 μm nominal thickness, the Si-coated CNFs  110  were well-separated from each other, forming an open core-shell CNF array structure (shown in  FIG. 2B ). This structure allowed electrolyte to freely accessing the entire surface of the Si Layer  115 . In the embodiment illustrated the average tip diameter was ˜457 nm in comparison with the ˜147 nm average diameter of the CNFs  110  prior to application of the Si Layer  115 . The average radial Si thickness at the Tip  120  was estimated to be ˜155 nm. This was apparently much smaller than the 0.50 μm nominal Si thickness since most Si spread along the full length of CNFs. Other radial Si thicknesses in the range of 10-1000, 20-500, 50-250, 100-200 (nm) or different ranges are found in alternative embodiments. As discussed elsewhere herein, the stacked-cone of CNFs  110  provides additional fine structure to the Si Layer  115 . The stacked-cone structure is optionally the result of a spiral growth pattern that produces the stacked-cone structure when viewed in cross-section. 
     The transmission electron microscopy (TEM) images in  FIGS. 3A-3C  further illustrate the structural details of Si-coated CNFs  110 . A Si Layer  115  of ˜390 nm Si was produced directly above the Tip  120  of a ˜210 nm diameter CNF  110 . The largest portion of the cotton-swab-shaped Si Layer  115  was ˜430 nm in diameter which appeared near the very end of the Tip  120 . The coaxial Si Layer  115  around the CNF  110  showed a feather-like texture with modulated contrast, clearly different from the uniform Si deposits above the tip (see  FIG. 3A ). This is likely a result of the stacked-cone microstructure of the PECVD-grown CNFs  110 . It is known from the literature that such CNFs  110  include unevenly stacked cup-like graphitic structures along the CNF  110  center axis. The use of such variations in the diameter of CNFs  110  was previously disclosed in commonly owned U.S. patent application Ser. No. 12/904,113 filed Oct. 13, 2010. The stacked-cone structure consists of more than ten cup-like graphitic layers that can be clearly seen in  FIG. 3B  as indicated by the dashed lines. The resolution and contrast of  FIGS. 3B and 3C  are limited since the electron beam needs to penetrate through hundreds of nanometer thick CNF or Si—CNF hybrid, but the structural characteristics are consistent with the high-resolution TEM studies using smaller CNFs in literature. This unique structure generated clusters of broken graphitic edges along the CNF sidewall which cause varied nucleation rates during Si deposition and thus modulate the density of the Si Layer  115  on the CNF  110  sidewall. The modulated density results in the ultra-high surface area Si structures indicated by a (100 nm square) Box  310  in  FIG. 3A . The feather like Si structures of Si Layer  115  provide an excellent Li ion interface that results in very high Li capacity and also fast electron transfer to CNF  110 . In  FIG. 3A  the dark area at Tip  120  is Nickel catalyst for growth of the CNFs. Other catalysts can also be used. 
       FIGS. 3B and 3C  are images recorded before ( 3 B) and after ( 3 C) lithium intercalation/extraction cycles. The sample in  3 C was in the delithiated (discharged) state when it was taken out of an electrochemical cell. The dashed lines in  FIG. 3B  are visual guidance of the stacked-cone graphic layers inside the CNFs  110 . The long dashed lines in  FIG. 3C  represent the sidewall surface of the CNF  110 . 
     As discussed elsewhere herein, the stacked-cone structure of CNFs  110  is drastically different from commonly used carbon nanotubes (CNTs) or graphite. The stacked-cone structure results in improved Li +  insertion, even without the addition of Si Layer  115 , relative to standard carbon nanotubes or nanowires. For example, the stacked-cone graphitic structure of CNFs  110  allows Li +  intercalation into the graphitic layers through the sidewall of CNFs  110  (rather than merely at the ends). The Li +  transport path across the wall of each of CNFs  110  is very short (with D ˜290 nm in some embodiments), quite different from the long path from the open ends in commonly used seamless carbon nanotubes (CNTs).  FIG. 4  illustrates a schematic of the stacked-cone 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, graphitic cone angle θ=10°, and the graphitic cone length D=t w /sin θ=290 nm. 
       FIGS. 5A-5C  illustrate an electrochemical characterization of ˜3 μm long CNFs  110 . This characterization illustrates the phenomenon described in relation to  FIG. 4 .  FIG. 5A  shows cyclic voltammograms (CV) from 1.5 V to 0.001 V versus a Li/Li +  reference electrode at 0.1, 0.5 and 1.0 mV/s scan rates. A lithium disk was used as the counter electrode. Data were taken from the second cycle and normalized to the exposed geometric surface area.  FIG. 5B  shows the galvanostatic charge-discharge profiles at C/0.5, C1 and C/2 power rates, corresponding to current densities of 647, 323 and 162 mA/g (normalized to estimated carbon mass) or 71.0, 35.5 and 17.8 μA/cm2 (normalized to the geometric surface area), respectively.  FIG. 5C  shows intercalation and extraction capacities (to left vertical axis) and Coulombic efficiency (to right vertical axis) versus the cycle number at C/1 charge-discharge rate. (The C/1 discharge rate=1 hour, C/2 discharge rate=120 min, 2C=C/0.5=30 min, etc.) 
     A freshly assembled half-cell typically showed the open circuit potential (OCP) of the uncoated CNFs  110  anode was ˜2.50 to 3.00 V vs. Li/Li +  reference electrode. The CVs measured between 0.001 V and 1.50 V show that Li +  intercalation starts as the electropotential is below 1.20 V. The first cycle from OCP to 0.001 V involved the formation of a necessary protective layer, i.e. the solid electrolyte interphase (SEI), by the decomposition of solvent, salts, and impurities and thus presented a large cathodic current. Subsequent CVs showed smaller but more stable currents. The cathodic current associated with Li +  intercalation rose slowly as the electrode potential was swept to negative until a sharp cathodic peak appeared at 0.18 V. As the electrode potential was reversed to positive after reaching the low limit at 0.001 V, lithium extraction was observed in the whole range up to 1.50 V, indicated by the continuous anodic current and a broad peak at 1.06 V. 
     The CV features of CNF arrays  100  were somewhat different from those of staged intercalation into graphite and slow Li +  diffusion into the hollow channel of CNTs. Li-ion insertion into CNFs  110  is likely through intercalation between graphitic layers from the sidewall due to its unique structure. The TEM image in  FIG. 3C  indicates that the graphitic stacks in the stacked-cones inside the CNF  110  are somewhat disrupted during Li +  intercalation-extraction cycles, likely due to the large volume change that occurs on Li +  intercalation. Some debris and nanoparticles are observed as white objects inside CNFs  110  as well as at the exterior surface. 
     The galvanostatic charge-discharge profiles in  FIG. 5B  showed that the Li+ storage capacity decreased as the power rate was increased from C/2 to C/0.5 (C/0.5 is also referred to as “2C”). To make it easier to compare the rates (particularly for those higher than C/1), we use the fractional notation C/0.5 herein instead of “2C” that is more popularly used in the literature. The Li +  intercalation and extraction capacities were normalized to the estimated mass of the CNFs  110  (1.1×10 4  g/cm 2 ) that was calculated based on a hollow vertically aligned CNF structure with the following average parameters: length (3.0 μm), density (1.1×10 9  CNFs per cm 2 ), outer diameter (147 nm), and hollow inner diameter (49 nm, ˜⅓ of the outer diameter). The density of the solid graphitic wall of the CNFs  110  was assumed to be the same as graphite (2.2 g/cm 3 ). At the normal C/2 rate, the intercalation capacity was 430 mA h g −1  and the extraction capacity is 390 mA h g −1 , both of which are slightly higher than the theoretical value of 372 mA h g −1  for graphite, which may be attributed to SEI formation and the irreversible Li +  insertion into the hollow compartments inside the CNFs  110 . The extraction capacities were found to be more than 90% of the intercalation values at all power rates and both the intercalation and extraction capacities decreased by ˜9% as the power rate increased from C/2 to C/1 and by ˜20% from C/1 to C/0.5, comparable to graphite anodes. 
     Upon charge-discharge cycling, the intercalation capacity was found to slightly drop from 410 mA h g −1  to 370 mA h g −1  after 20 cycles at the C/1 rate, while the extraction capacity was maintained between 375 and 355 mA h g −1 . The overall coulombic efficiency (i.e. the ratio of extraction capacity to intercalation capacity) was ˜94%, except in the first two cycles due to SEI formation on the CNF  110  surface. The SEI film is known to form readily on carbonaceous anodes during the initial cycles which allows lithium ion diffusion but is electrically insulating, leading to 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 serves as a sheath to increase the mechanical strength of the CNFs  110 , preventing them from collapsing into microbundles by the cohesive capillary force of a solvent as observed in the study with other polymer coatings. 
       FIGS. 6A-6C  illustrates scanning electron microscopy images of 3 μm long CNFs  110 , according to various embodiments of the invention.  FIG. 6A  shows CNFs  110  in delithiated (discharged) state after intercalation/extraction cycles.  FIG. 6B  shows CNFs  110  including Si Layer  115  after 100 cycles in the delithiated state.  FIG. 6C  shows CNFs  110  including Si Layer  115  after 100 cycles in the lithiated state. These images are 45 degree perspective views. 
       FIGS. 7A-7C  illustrate results obtained using CNFs  110  including a Si Layer  115  as Li-ion battery anodes. These results were obtained using a nominal Si thickness of 0.50 μm.  FIG. 7A  shows cyclic voltammograms between 1.5 V and 0.05 V versus Li/Li +  at 0.10, 0.50 and 1.0 mV s −1  scan rates. The measurements were made after the sample going through 150 charge-discharge cycles and the data of the second cycle at each scan rate are shown.  FIG. 7B  shows galvanostatic charge-discharge profiles at C/0.5, C/1 and C/2 power rates with the sample at 120 cycles. All profiles were taken from the second cycle at each rate.  FIG. 7C  shows insertion and extraction capacities (to the left vertical axis) and coulombic efficiency (to the right vertical axis) of two CNF Arrays  100  (used as electrodes) versus the charge-discharge cycle number. The first CNF Array  100  was first conditioned with one cycle at the C/10 rate, one cycle at the C/5 rate, and two cycles at the C/2 rate. It was then tested at the C/2 insertion rate and C/5 extraction rate for the rest of the 96 cycles. The filled and open squares represent the insertion and extraction capacities, respectively. The second electrode was first conditioned with two cycles each at C/10, C/5, C/2, C/1, C/0.5 and C/0.2 rates. It was subsequently tested at the C/1 rate for the next 88 cycles. The columbic efficiencies of both electrodes are represented by filled (1st electrode) and open (2nd electrode) diamonds, which mostly overlap at 99%. 
     The CVs in  FIG. 7A  present very similar features to those of Si nano-wires. Compared to uncoated CNF Array  110 , both the cathodic wave for Li +  insertion and the anodic wave for Li +  extraction shift to lower values (below ˜0.5 and 0.7 V, respectively). The peak current density increases by 10 to 30 times after application of Si Layer  115  and is directly proportional to the scan rate. Clearly, alloy-forming Li +  insertion into Si is much faster than intercalation into uncoated CNFs, which was limited by the slow diffusion of Li +  between graphitic layers. The cathodic peak at ˜0.28 V was not observed in previous studies on pure Si nanowires. The three anodic peaks representing the transformation of the Li—Si alloy into amorphous Si are similar to those with Si nanowires despite shifting to lower potentials by 100 to 200 mV. 
     The galvanostatic charge-discharge profiles of a CNF Array including Si Layer  115 , shown in  FIG. 7B  included two remarkable features: (1) a high Li +  insertion (charge) and extraction (discharge) capacity of ˜3000 mA h (g Si ) −1  was obtained at the C/2 rate even after 120 cycles; and (2) the Li +  capacity was nearly the same at the C/2, C/1, and C/0.5 power rates. In other words, the capacity of CNF Array  100  to operate as an electrode did not decline when charging rates were increased from C/2 to C/1 and C/0.5. Over these charging rates the capacity was nearly independent of charging rate, in various embodiments. The total Li +  storage capacity of CNF Arrays  100  including Si Layer  115  was about 10 times greater than CNF Arrays  100  that lacked Si Layer  115 . This occurred even though the low potential limit for the charging cycle was increased from 0.001 V to 0.050 V. As a result, the amount of Li +  intercalation into the CNF core appears to have been negligible. The specific capacity was calculated by dividing only the mass of Si that was calculated from the measured nominal thickness and a bulk density of 2.33 g cm −3 . This method was chosen as an appropriate metric to compare the specific capacity of the Si Layer  115  to the theoretical value of bulk Si. For the 3.0 μm long CNFs  110  deposited with a Si Layer  115  of 0.456 μm nominal thickness, the real mass density of Si Layer  115  was ˜1.06×10 −4  g cm −2 , comparable to that of CNFs  110  (˜1.1×10 −4  g cm −2 ). The corresponding coulombic efficiency in  FIG. 7B  is greater than 99% at all three power rates, much higher than that of the CNFs  110  without Si Layer  115 . 
       FIG. 8  illustrates how the capacity of CNF Array  100  varies with charging rate, according to various embodiments of the invention. Data is shown for several numbers of cycles.  FIG. 8  shows average specific discharge capacity for a group of cycles with identical current rates versus the charge rate (C-rate) required to achieve full capacity in set hours (C/h e.g., full Capacity/hours). Vertical Lines are focused on C/4, 1C, 3C and 8C. The CNF Array  100  was first conditioned with two cycles each at C/8, C/4, C/2, C/1, C/0.8, C/0.4, and C/0.16 rates symmetrically, and subsequently tested at a C/1 symmetric rate for the next 88 cycles. This was repeated from cycle  101  to cycle  200 . Starting at cycle  201 , the electrode was cycled for five cycles at each of 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 rates symmetrically and subsequently tested at a C/1 symmetric rate for the next 45 cycles. This was repeated from cycle  301  to cycle  400  and from cycle  401  to cycle  500 . The change in capacity is small (&lt;16%) while the C-rate is varied by 32 fold. The electrode after 100 cycles showed increased capacity when the C-rate is changed from 3C to 8C. Thus, faster charge rates resulted in improved capacity. High capacity (&gt;2,700 mAh/g) was obtained at both high and lower rates (C/4 and 8C). Capacity at rates above 3C increase as C-rate increased. The drop in specific capacity with the number of cycles is due to known, correctable, factors. 
     Both the CVs and charge-discharge measurements indicated that the Li +  insertion into Si Layer  115  was fast and highly reversible, which are features desired for high-performance Li-ion battery anodes. This was further demonstrated (See  FIG. 7C ) with two long cycling tests on two identical samples at different testing conditions: (1) slow asymmetric tests with the C/2 rate for insertion and the C/5 rate for extraction; and (2) the fast symmetric test at the C/1 rate for both insertion and extraction. Both sets of data showed &gt;98% coulombic efficiency over the long cycling except for the initial conditioning cycles (4 cycles in the former and 12 cycles in the latter at varied low rates). In the slow asymmetric tests, the insertion capacity only dropped by 8.3% from 3643 mA h g −1  at the 5th cycle to 3341 mA h g −1  at the 100th cycle. Even at the C/1 charge-discharge rate, the insertion capacity only drops by 11% from 3096 mA h g −1  at the 13 th  cycle to 2752 mA h g −1  at the 100 th  cycle. The difference in the Li +  capacity between these two sets of data was mostly attributable to the initial conditioning parameters and small sample-to-sample variations. This was indicated by the similar values of insertion-extraction capacity during the first few conditioning cycles in  FIG. 7C  at C/10 and C/5 rates. The faster rates (C/0.5 for 9th and 10th cycles and C/0.2 for 11th and 12 th  cycles in sample #2) were found to be harmful and caused an irreversible drop in the capacity. However, the electrode became stabilized after longer cycling. As shown in  FIG. 7B , the charge-discharge profiles are almost identical at C/2, C/1, and C/0.5 rates, which were measured with sample #1 after going through 120 cycles. This is over a charging rate variation of four times. 
     The specific capacity of the Si Layer  115  in the range of 3000 to 3650 mA h g −1  is consistent with the highest values of amorphous Si anodes summarized in literature. It is remarkable that the entire Si shell in the CNF Array  110  was active for Li+ insertion and remained nearly 90% of the capacity over 120 cycles, which to our knowledge has not been achieved before except with flat ultrathin (&lt;50 nm) Si films. The specific capacity disclosed herein is significantly higher than those reported using other nanostructured Si materials at similar power rates, including ˜2500 mA h g −1  at the C/2 rate and ˜2200 mA h g −1  at the C/1 rate with Si NWs, and ˜800 mA h g −1  at the C/1 rate with randomly oriented carbon nanofiber-Si core-shell NWs. Clearly, the coaxial core-shell NW structure on well-separated CNFs  110 , such as included in various embodiments of the invention, provides an enhanced charge-discharge rate, nearly full Li +  storage capacity of Si, and a long cycle life, relative to the prior art. 
     As shown in  FIG. 7C , an anomalously high insertion capacity (˜4500 mA h g −1 ) was always observed in the initial cycles, which was 20-30% higher than the latter cycles. In contrast, the extraction values were relatively stable over all cycles. The extra insertion capacity can be attributed to the combination of three irreversible reactions: (1) the formation of a thin SEI (surface electrolyte interphase) layer (of tens of nanometers); (2) reactions of Li with SiO x , presented on the Si surface (SiO x +2xLi→Si+xLi 2 O); and (3) the conversion of the starting crystalline Si coating with a higher theoretical capacity (˜4200 mA h g −1 ) into amorphous Si with lower capacity (&lt;3800 mA h g −1 ). The TEM image ( FIG. 3C ) and SEM image ( FIG. 6B ) showed that a non-uniform SEI can be deposited on the surface of Si Layer  115  after the charge-discharge cycles. This elastic SEI film can help secure Si Layer  115  on the CNF  110  surfaces as CNF Array  110  goes through the large volume expansion-contraction cycles that occur during the charge-discharge cycles. The dramatic difference between the SEM images in  FIGS. 6B and 6C  indicates the large expansion of Si Layer  115  in the lithiated (charged) state relative to the non-lithiated state. (Although some of the expansion may be due to oxidation of Li by air as the electrochemical cell was dissembled for imaging.) Note that the production of SEI during initial charge-discharge cycles causes the differences seen in Si Layer  115  between  FIGS. 3A and 3B . In  FIG. 3B  the Si has interacted with electrolyte to produce SEI that fills the gaps between the feather-like structures. The interaction can include mixing, chemical reactions, charge coupling, encapsulation, and/or the like. The Si Layer  115 , therefore, looks more uniform in  FIG. 3B . However, the Si Layer  115  now comprises interleaved layers of Si (the feather-like structures) and SEI. Each of these interleaved layers can be on the order of a few 10s of nanometers. The SEI layer can be an ion permeable material that is a product of interaction between the electrolyte and Si Layer  115  (or other electrode material). 
     The crystalline and amorphous structure of the Si shell was revealed by Raman spectroscopy. As shown in  FIG. 9 , the pristine CNF Array  100  including Si Layer  115  showed multiple broad bands overlapped in the range of 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 sharp peak disappeared while the broad bands merged into a single peak at 470 cm −1 . The bare CNFs  110  did not show any feature in this range. The crystalline Si peak downshifted by ˜40 cm −1  from that measured with a single-crystalline Si(100) wafer and by ˜20 to 30 cm −1  from other micro-crystalline Si materials. This shift was likely due to the much smaller crystal size and large disorders. The original Si Layer  115  likely consisted of nanocrystals embedded in an amorphous matrix associated with the feather-like TEM image in  FIG. 3A . After initial cycles, the Si nanocrystals were converted into amorphous Si, consistent with the TEM images after the cycling test (see  FIGS. 3B and 3C ). However, the Si Layer  115  apparently did not slide along the CNF, in contrast to the large longitudinal expansion (by up to 100%) in pure Si NWs. Si Layer  115  was, thus, securely attached to CNFs  110  for over 120 cycles. The volume change of the Si shell during Li +  insertion was dominated by radial expansion, while the CNF-Si interface remained intact. 
     Various embodiments of the 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 , e.g., the mean distance between CNFs  110  within CNF Array  100 . This space allows Si Layer  115  to expand radially when charging and, thus in some embodiments provides stability. Because an optimum electrode structure depends on both the length of CNFs  110  and the thickness of Si Layer  115 , it is sometimes desirable to use longer CNFs  110  and thicker Si Layers  115  in order to obtain higher total Li +  storage capacity. Longer CNFs  110  do correlate with greater storage capacity.  FIGS. 10A-10C  shows the variation of Li +  insertion-extraction capacities and the coulombic efficiency over 15 charge-discharge cycles with three 10 μm long CNF  110  samples deposited with Si Layer  115  at a nominal thickness of 0.50, 1.5 and 4.0 μm, respectively. After conditioning at the C/10 rate for the first cycle and the C/5 rate for the second cycle, asymmetric rates (C/2 for insertion and C/5 for extraction) were used in subsequent cycles similar to the measurements of sample #1 in  FIG. 7C . This protocol provided nearly 100% coulombic efficiency and minimum degradation over the cycles. The nominal thickness was measured in situ with a quartz crystal microbalance during sputtering. 
     The specific capacities as high as 3597 mA h g −1  and 3416 mA h g −1  were obtained with 0.50 and 1.5 μm thick Si Layer  115 , respectively, very similar to that with 0.50 μm thick Si Layer  115  on 3.0 μm long CNFs  110  (see  FIG. 7C ). The capacity remained nearly constant over 15 cycles. However, the electrode with 4.0 μm nominal Si thickness showed a significantly lower specific capacity at only 2221 mA h g −1 . This indicates that, with expansion, the Si Layers  115  from adjacent CNFs  110  began to contact into each other, limiting them from further expansion and limiting diffusion of Li between CNFs  110 . As a result, only a fraction of the silicon coating was active in lithium insertion. 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  110  comprising 10 μm long CNFs  110  gave nearly the same amount of Li +  storage capacity (3597 mA h g −1 , see  FIG. 6 a   ) as that of 3 μm long CNFs  110  (3643 mA h g −1 , see  FIG. 7C ), even though the carbon mass is more than 3 times higher. This is very strong evidence that the contribution of CNFs  110  is negligible in calculating Li +  storage. It is likely that very little Li +  ions were intercalated into CNFs  110  in the Si-coated sample, this contributes to the stability of the structure during multiple charge-discharge cycles. 
     The variation of the specific Li +  storage capacity in the three samples correlated well with their structures revealed by the SEM images illustrated in  FIGS. 11A-11C .  FIGS. 11A-11C  show scanning electron microscopy images of freshly prepared CNF Arrays  100  (on ˜10 μm long CNFs  110 ). The 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 were measured in-situ using a quartz crystal microbalance during deposition. All images are 45° perspective views. At 0.50 μm nominal Si thickness, the average tip diameter was found to be ˜388 nm on the 10 μm long CNFs, much smaller than the ˜457 nm average diameter on the 3.0 μm long CNFs  110 . The Si Layer  115  was thinner but more uniformly spread along the 10 μm long CNFs  110 . 
     It is noted that growing 10 μm CNFs  110  took 120 min, about six times as long as growing the 3 μm CNFs  110 . Some nickel catalysts were slowly etched by NH 3  during the long PECVD process, resulting in continuous reduction in the Ni nanoparticle size and leading to the tapered Tip  120  (as shown in  FIG. 12 ). The CNF  110  length variation also increased with long CNFs  110 . These factors collectively reduced the shadow effects of the Tip  120 . As a result, even at 1.5 μm nominal Si thickness, the CNFs  110  coated with 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 that of 0.50 μm Si on 3.0 μm CNF Arrays  110  ( FIG. 2B ). But as the nominal Si thickness was increased to 4.0 μm, the Si Layers  115  clearly merged with each other and filled up most of the space between the CNFs  110  (see  FIG. 10C ). This reduced the free space needed to accommodate the volumetric expansion of the Si Layer  1151 . As a result, the specific Li +  storage capacity significantly dropped. 
       FIGS. 11A and 11B  each include roughly the same number of CNFs  110 , however, in  FIG. 11B  has substantially fewer visible Tips  120 . This is because Si Layer  115  can form a nanofiber/silicon complex that includes a single CNF  110  (a cross-section of which is shown in  FIG. 1A ). Or, Si Layer  115  can form a nanofiber/silicon complex that includes two, three or more CNF  110  under a single cover of silicon. This occurs when two or more CNFs  110  come together during the Si Layer  115  deposition process. A nanofiber/silicon complex is a structure that includes a continuous Si Layer  115  that envelops one or more CNF  110 . A cross-section of a nanofiber/silicon complex that includes two CNF  110  is illustrated in  FIG. 11D . In various embodiments at least 1%, 5% or 10% of nanofiber/silicon complexes include more than one CNF  110 . 
     In various embodiments, instances of CNF Arrays  100  having 0.50 and 1.5 μm nominal Si thicknesses have comparable mass-specific capacities of 3208±343 and 3212±234 mA h g −1 , respectively. The samples with a 4.0 μm nominal Si thickness give much lower capacity at 2072±298 mA h g −1 . The thinner Si coatings are fully activated and provide the maximum Li insertion capacity that amorphous Si could afford. On the other hand, the area-specific capacity increases proportionally with the Si thickness from 0.373±0.040 mA h cm −2  at 0.50 μm Si to 1.12±0.08 mA h cm −2  at 1.5 μm Si thickness, but drops off from the linear curve to give 1.93±0.28 mA h cm −2  at 4.0 μm nominal Si thickness. Clearly, at this thickness, only a fraction 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 mean distance between CNFs  110 . The electrochemical results are consistent with the structure shown in SEM image in  FIG. 11C , which shows that space between CNFs  110  is essentially filled. 
     In various embodiments of the invention, the structure of CNF Array  100  includes an Si Layer of approximately 200 to 300 nm radial thickness on CNFs  110  having a length of approximately 30-40, 40-75, 75-125 microns (or more or combinations thereof) and diameters on the order of ˜50 nm. In some embodiments, these CNF Array  100  are grown on conductive foils having a thickness within 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  100  to form CNF Arrays  100 . This is accomplished while maintain the open vertical core-shell nanowire structure with individual CNFs  110  well separated from each other such that Li ions can penetrate the CNF Arrays  100  between the CNFs  110 . This unique hybrid architecture allowed the Si Layers  115  to freely expand/contract in the radial direction during Li+ insertion and extraction. High-performance Li storage with a mass-specific capacity of 3000 to 3650 mA h g −1  was obtained even at the C/1 rate. The capacity matched the maximum value that would be expected from a similar mass of amorphous Si, indicating that the Si Layer  115  was fully active. This 3D nanostructured architecture enables effective electrical connection with bulk quantities of Si material while maintaining a short Li+ insertion-extraction path. As a result, high capacity near the theoretical limit is possible for over 120 charge-discharge cycle. There was little change in capacity as the rate was increased 20 times from C/10 to C/0.5 (or 2C). The high capacity at significantly improved charging and power rates and the extraordinary cycle stability make this novel structure a choice anode material for high-performance Li-ion batteries. The same core-shell concept may 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 , or the like. 
       FIG. 13  illustrates methods of producing the CNF Arrays  100  disclosed herein. In a Provide Substrate Step  1310  a Substrate  105  suitable for growth of CNFs  110  is provided. 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 an optional Provide Nucleation Sites Step  1320  nucleation cites for the growth of CNFs  110  are provided on Substrate  105 . A variety of nucleation materials, such as Ni particles, are known in the art. The nucleation cites are optionally provided at a density so as to produce mean distances between CNFs  110 , such as those taught elsewhere herein. Provide Nucleation Sites Step  1320  is optional in embodiments in which nucleation is not required for growth of CNFs  110 , or similar structures. 
     In a Grow CNFs Step  1330  CNFs  110  are grown on Substrate  105 . The CNFs  110  are optionally grown to produce the stacked-cone structure taught elsewhere herein, or a similarly variable structure. The CNFs  110  can be grown to any of the lengths taught elsewhere herein. Growth is optionally accomplished using PECVD processes such as those taught or cited in “A high-performance lithium-ion battery anode based on the core-shell heterostructure of silicon-coated vertically aligned carbon nanofibers” Klankowski et al. J. Mater. Chem. A, 2013, 1, 1055. 
     In an Apply Si Layer Step  1340  an intercalation material such as Si Layer  115  is applied to the grown CNFs  110 . The applied material may have any of the nominal thicknesses taught elsewhere herein so as to produce a Si Layer  115  thickness of tens or hundreds of nanometers. The thickness of the intercalation material may vary. For example, a region of the intercalation material may include less than 75, 50, 25, 10 or 5 percent (by weight per unit area of support filament  110 ) of the intercalation material relative to other areas of CNFs  110 . In various embodiments, the intercalation layer covers between 90 and 99%, 75 and 90%, 25 and 75%, and less than 25% of CNFs  110 . 
     In an optional Apply PEM Step  1345  a power enhancement material (PEM) is added to the CNF Array  100 . The PEM typically includes a binder and surface effect dominant sites, as discussed in further detail elsewhere herein. In an optional Condition Step  1350  the CNF Array  100  produced using Steps  1310 - 1340  is conditioned using one or more lithium intercalation cycles. 
       FIG. 14A  illustrates a CNF  110  including a Power Enhancement Material  1320 , according to various embodiments of the invention. The Power Enhancement Material  1320  is applied as a layer over the intercalation material, e.g. over Silicon Layer  115 .  FIG. 14B  illustrates detail of the Power Enhancement Material  1320  illustrated in  FIG. 14B , according to various embodiments of the invention. Power Enhancement Material  1320  includes Surface Effect Dominant Sites  1430  and an optional Binder  1440 . Silicon Layer  115  is but one example of intercalation material. Where Silicon Layer  115  is used as an example herein, it should be understood that other types of intercalation material can be substituted 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 large number of CNF  110  within a CNF Array  100 . 
     In some embodiments, Surface Effect Dominant Sites  1430  include surfaces of a nanoparticle configured to adsorb charge carriers in a faradaic interaction, e.g., to undergo redox reactions with charge carriers. They are referred to as “surface effect dominant” because typically, for these nanoparticles, the faradaic interaction between the charge carriers and the nanoparticle surfaces dominate bulk faradaic interactions. Thus, the charge carriers are much more likely to react at the surface relative to the bulk of the nanoparticles. For example, a lithium ion would more likely adsorb onto the surface of the nanoparticle rather than being absorbed into the bulk of the nanoparticle. These nanoparticle are sometimes referred to as surface redox particles. The faradaic interaction results in a pseudo capacitor that can store a significant amount of loosely bound charge and thus provide a significant power density. In pseudo capacitance an electron is exchanged (e.g., donated). In this case between the charge carrier to the nanoparticle. While some potentials would result in some intercalation of charge carrier into the nanoparticle, this does not constitute the bulk of the interaction at Surface Effect Dominant Sites  1430  and can degrade some types of nanoparticles. A faradaic interaction is an interaction in which a charge is transferred (e.g., donated) as a result of an electrochemical interaction. 
     The nanoparticles that include Surface Effect Dominant Sites  1430  can be comprised of transition metal oxides, such as 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. They may also be comprised of metal nitrides, carbon, activated carbon, graphene, graphite, titanate (Li 4 Ti 5 O 12 ), crystalline silicon, tin, germanium, metal hydrides, iron phosphates, polyaniline, mesophase carbon, and/or the like. It is appreciated that mixtures of the above and/or other materials having desired faradaic properties may be included in the Surface Effect Dominant Sites  1430 . In various embodiments, these nanoparticles can be less than 1, 2, 3, 5, 8, 13, 21 or 34 nanometers in diameter. The lower limit of the nanoparticle size is a function of the size of the molecules of constituent materials. A nanoparticle includes at least a few molecules. A smaller size provides for a greater surface to bulk ratio of possible adsorption sites. However, a particle comprising only a couple of molecules has reduced stability. The nanoparticles are optionally multi-layered. For example, they can comprise a TiO 2  layer (or any of the other nanoparticle materials discussed herein) on a transition metal, Co, Ni, Mn, Ta, Ru, Rb, Ti, Sn, V 2 O 2 , FeO, Cu or Fe core or a graphene/graphite layer on a core of some other material. In some embodiments, different core materials affect the reaction potentials of the surface material. The amount of Surface Effect Dominant Sites  1430  is optionally selected depending on desired power and energy densities. For example, a greater power density may be achieved by have a larger number of Surface Effect Dominant Sites  1430  per quantity of intercalation material, or a greater amount of energy density may be achieved by having a larger amount of intercalation material per number of Surface Effect Dominant Sites  1430 . It is an advantage of some embodiments of the invention that both historically high energy and power density can be achieved simultaneously. 
     By adsorbing charge carriers on the surface of the nanoparticle the charge carriers can provide a power density such as previously only achieved with capacitors. This is because the release of the charge is not dependent on diffusion of charge carriers though an intercalation material. Further, by placing the Surface Effect Dominant Sites  1430  in close proximity to the intercalation material, charge carriers can move from the intercalation material to the Surface Effect Dominant Sites  1430  (or directly to the electrolyte). This results in energy densities that are equal to or greater than conventional batteries. Both the energy densities of batteries and the power densities of capacitors are achieved in the same device. Note that during discharge charge carriers within the intercalation material can migrate to the Surface Effect Dominate Sites  1430  and thus recharge these sites. 
     In some embodiments, Surface Effect Dominant Sites  1430  are disposed on larger particles. For example, the particle size may be greater than 1, 10, 25, 100 or 250 microns, (but generally less than 1 millimeter). Activated carbon, graphite and graphene are materials that can be included in particles of these sizes. For example, activated carbon can be included in Power Enhancement Material  1320  while having a pore size of Surface Effect Dominant Sites  1430  similar to the nanoparticle diameters taught above. For the purposes of this disclosure, a nanoparticle is a particle with an average diameter of less than 1 μm. 
     Optional Binder  1440  is configured to keep the Surface Effect Dominant Sites  1430  in proximity to the intercalation material. In some embodiments, the distribution of Surface Effect Dominant Sites  1430  is uniform throughout Binder  1440 . For example, nanoparticles including the Surface Effect Dominant Sites  1430  may be mixed with Binder  1440  before Binder  1440  is applied to the intercalation material to produce a relatively uniform distribution. Alternatively, the nanoparticles may be applied to the surface of the intercalation material prior to application of Binder  1440 . This can result in a greater concentration of Surface Effect Dominant Sites  1430  (within Binder  1440 ) proximate to the intercalation material as compared to areas of Binder  1440  that are distal to the intercalation material. Binder  1440  is optional in embodiments in which Surface Effect Dominant Sites  1430  or the associated nanoparticles are directly attached to the intercalation material, e.g., attached to Silicon Layer  115 . 
     Binder  1440  is permeable (e.g., porous) to charge carriers of the electrolyte. Examples of suitable materials for Binder  1440  include polyvinyl-idene fluoride (PVDF), styrene butadiene rubber, poly (acrylic acid) (PAA), carbo-xymethyl-cellulose (CMC), and/or the like. Other binders may be used that meet the permeability requirements. Binder  1440  optionally includes materials that increase its conductivity. For example, Binder  1440  may include conductive polymer, graphite, graphene, metal nanoparticles, carbon nano-tubes, carbon nano fibers, metal nano-wires, Super-P (conductive carbon black), and/or the like. The materials are preferably at concentrations high enough to make Binder  1440  conductive, e.g., a percolation threshold. 
     The addition of Surface Effect Dominant Sites  1430  in close proximity to the intercalation material (e.g., Silicon Layer  115 ) does not necessarily require the use of vertically aligned CNF  110 , or any support filaments. For example,  FIG. 15  illustrates an electrode surface including Power Enhancement Material  1320  and non-aligned CNFs  110  coated by intercalation material, according to various embodiments of the invention. In these embodiments, the CNFs  110  are not directly attached to Substrate  110 , but are held in close proximity to Substrate  110  by Binder  1440 . While CNF  110  are used herein as an example of support filaments, it should be understood that other types of support filaments discussed herein can be used to supplement or replace the carbon nanofibers of CNF  110  in any of the examples. 
     The embodiments illustrated by  FIG. 15  can be produced, for example, by first growing unattached CNFs  110 . These are then coated with Silicon Layer  115  (or some other intercalation material) such that the intercalation material is generally in contact with the CNFs  110  as a coating layer. The coated CNFs  110  are then mixed with Surface Effect Dominant Sites  1430  and Binder  1440 . Finally, the resulting mixture is deposited on Substrate  105 . 
       FIG. 16  illustrates an electrode surface including Power Enhancement Material  1320 , non-aligned CNFs  110  and free Intercalation Material  1610 , according to various embodiments of the invention. In these embodiments, the Intercalation Material  1610  is not necessarily disposed around the CNF  110  as a coating. The Intercalation Material  1610  is free in the sense that it is not restricted to the surface of CNFs  110 , however it is still held in proximity to Substrate  105  by Binder  1440 . 
     The embodiments illustrated in  FIG. 16  can be produced, for example, by mixing Binder  1440 , Surface Effect Dominant Sites  1430 , Intercalation Material  1610  and CNF  110  together (in any order). The mixture is then applied to Substrate  105 . In these embodiments, CNFs  110  may or may not be attached to Substrate  105  by means other than Binder  1440 . Intercalation Material  1610  may and/or may not be in contact with CNF  110  or Substrate  105 . Likewise, Surface Effect Dominant Sites  1430  are optionally in contact with Substrate  105 , CNF  110 , and/or Intercalation Material  1610 . Intercalation Material  1610  optionally includes particles, suspensions, clusters, and/or droplets of intercalation material with sizes of at least 0.1, 0.6, 1, 1.5, 2, 3, 5, 7, 9, 10, 13, 15, 18, 21 or 29 μm or any range there between. Other sizes are possible in alternative embodiments. 
       FIG. 17  illustrates an electrode surface including Binder  1440 , Surface Effect Dominant Sites  1430  and Intercalation Material  1610 , without support filaments, according to various embodiments of the invention. In these embodiments Surface Effect Dominant Sites  1430  and Intercalation Material  1610  are held in proximity to Substrate  11005  by Binder  1440 . 
       FIG. 18  illustrates an electrode surface similar to that illustrated in  FIG. 15 . However, in the embodiments illustrated by  FIG. 18  Surface Effect Dominant Sites  1430  are concentrated in close proximity to Intercalation Material  1610 . For example, in some embodiments at least 2%, 10%, 25%, 50%, 75% or 85% of Surface Effect Dominant Sites  1430  are on particles in contact with Intercalation Material  1610 . Increased concentration of Surface Effect Dominant Sites  1430  proximate to Intercalation Material  1610  can be achieved using methods described elsewhere herein. This results in a greater concentration of Surface Effect Dominant Sites  1430  at the surface of Intercalation Material  1610  relative to other volumes within Binder  1440 . 
       FIGS. 14C, 19 and 20  illustrate an electrode surface similar to that illustrated in  FIGS. 14B, 16 and 17  respectively. However, in the embodiments illustrated by these figures, Surface Effect Dominant Sites  1430  are disposed in close proximity to free intercalation material, according to various embodiments of the invention. As in the embodiments illustrated by  FIG. 18 , in some embodiments at least 2%, 10%, 25%, 50%, 75% or 85% of Surface Effect Dominant Sites  1430  are in contact with Intercalation Material  1610 . In some embodiments a higher concentration of nanoparticles including Surface Effect Dominant Sites  1430  are disposed within 5 nanometers of Intercalation Material  1610  surfaces than between 10 and 15 nanometers of these surfaces. Increased concentration of Surface Effect Dominant Sites  1430  proximate to Intercalation Material  1610  can be achieved by selecting appropriate Zeta potentials of the nanoparticles and Intercalation Material  1610  in solution so that the nanoparticles form an electrostatic double layer at the surface of Intercalation Material  1610 . The Zeta potential is the electric potential in the interfacial double layer at the location of the surface versus a point in the bulk liquid away from the surface. The Zeta potential is optionally greater than 25 mV (absolute). In other embodiments, the nanoparticles are applied to the surfaces of Intercalation Material  1610  prior to the application of Binder  1440 . 
     Intercalation Material  1610 , as illustrated in  FIGS. 16-20 , can include any single one or combination of the materials discussed herein with respect to Silicon Layer  115  (including or excluding silicon). Likewise, CNFs  110 , as illustrated in  FIGS. 16-20 , can include any single one or combination of the various types fibers discussed here (including or excluding carbon nanofibers). For example, these CNFs  110  may include branched fibers, multi-walled fibers, wires, aerogel, graphite, carbon, graphene, boron-nitride nanotubes, etc. The number of Surface Effect Dominant Sites  1430  and CNF  110  shown in these figures and other figures herein is for illustrative purposes only. For example, in practice the number of Surface Effect Dominant Sites  1430  can be much greater. Likewise, the amount and size of Intercalation Material  1610  and Silicon Layer  115  shown is for illustrative purposes. Alternative embodiments may include greater or lesser amounts and greater or lesser sizes. Likewise, the depth of PEM  1420  and the length of CNF  110  can vary from that shown in the figures. 
     In various embodiments, the amount of nanoparticles including Surface Effect Dominant Sites  1430  may be selected to so as 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 (or any range there between) times a monolayer of the nanoparticles on the surface of Intercalation Material  1610  or Silicon Layer  115  (as measured in a discharged state). As used herein, a 0.1 monolayer indicates 10% and a 10× monolayer is 10 monolayers. In various embodiments, the amount of nanoparticles including Surface Effect Dominant Sites  1430  may be selected to result in at least 1, 5, 10, 20, 50, 100, 250 or 500 nanometer layer (or any combination there between) of nanoparticles on the surface of Intercalation Material  1610  (as measured in a discharged state). Other coverage densities as measured in monolayers or depth are possible. As the coverage of the nanoparticles (that include Surface Effect Dominant Sites  1430 ) approaches 1.0 monolayer the nanoparticles can form a layer between the Intercalation Material  1610  and charge carriers of the electrolyte that migrate through Binder  1440 . For example in some embodiments the electrolyte includes lithium as a charge carrier. The lithium can migrate through Binder  1440  and undergo a faradaic reaction with Surface Effect Dominant Sites  1430  in which an electron is donated to the lithium from one of Surface Effect Dominant Sites  1430 . This electron has been transferred (e.g., donated) from Substrate  105  to the nanoparticle via Intercalation Material  1610 . Because the nanoparticles form a barrier, at this stage in a charging process, only a limited amount of charge carrier reaches Intercalation Material  1610 . Charging is dominated by reactions at the Surface Effect Dominant Sites  1430 . In some embodiments, charging can be rapid because intercalation of the charge carrier into Intercalation Material  1610  is not necessary before the faradaic reaction with the charge carrier occurs. The presence of Surface Effect Dominant Sites  1430  greatly increases the surface area where the initial faradaic reaction can occur prior to intercalation. Surface Effect Dominant Sites  1430  catalyze the intercalation of charge carrier into Intercalation Material  1610 . The charge carrier can be intercalated in the form as received at Surface Effect Dominant Sites  1430  or intercalated in an alternate form such as a metal oxide. If intercalated as a metal oxide, the oxygen of the oxide may be recycled back to the Surface Effect Dominant Site  1430  following the intercalation. 
     In some embodiments, because the nanoparticles form an imperfect barrier some charge carriers still reach Intercalation Material  1610  at this stage of charging (e.g., an initial stage of charging a power storage device including the electrodes discussed herein). Because the Intercalation Material  1610  of some embodiments, such as silicon, expands when charge carrier intercalation occurs the surface area Intercalation Material  1610  also increases. This reduces the surface coverage of nanoparticles on the surface of Intercalation Material  1610  and reduces the effectiveness of the nanoparticles in forming a barrier to charge carriers. Thus, as charging progresses, greater numbers of charge carriers per unit time can reach Intercalation Material  1610 . This is optionally continued until charging is dominated by reactions within the Intercalation Material  1610 . The reduction in surface coverage may also increase the average fraction of Surface Effect Dominant Sites  1430  on each nanoparticle that are exposed to the electrolyte. As used herein the phrase “surface coverage” is used to represent a density of a species on a surface and may be measured as a number of monolayers (or fraction thereof), as a thickness, or as a concentration, etc. 
     In some embodiments, the power storage at Surface Effect Dominant Sites  1430  occurs at potentials at which faradaic surface reactions occur but intercalation of charge carriers into the nanoparticles that include the Surface Effect Dominant Sites  1430  does not occur. This prevents degradation of the nanoparticles by repeated intercalation and de-intercalation of charge carrier and allows for a longer cycle lifetime. At the same electrode it is desirable to store power within Intercalation Material  1610  via faradaic reactions that occur at a higher potentials, optionally including potentials that would cause intercalation of charge carriers into the nanoparticles having Surface Effect Dominant Sites  1430 . This can occur in some embodiments of the invention because there is a potential drop between Substrate  105  and the Electrolyte  125 . 
     In one specific example, in which lithium is the charge carrier, the Surface Effect Dominant Sites  1430  are on TiO 2  nanoparticles and Intercalation Material  1610  is predominantly silicon. The particular voltages in other embodiments will be understood to be dependent on the chemical species included in Surface Effect Dominant Sites  1430  and Intercalation Material  1610 , and the reactions occurring during charging, etc. In various embodiments the potential difference between Surface Effect Dominant Sites  1430  and 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 there between. As used herein the term “potential” is used to refer to an absolute value (e.g., |x|) of an electrostatic potential. 
       FIG. 21  illustrates methods of assembling an electrode surface, according to various embodiments of the invention. The assembled electrode surface may be used, for example, as an anode in a battery, capacitor or hybrid device. The methods illustrated in  FIG. 21  are optionally used to produce the various electrodes discussed elsewhere herein. 
     In a Provide Substrate Step  2110  a conductive substrate is provided. Provide Substrate Step  2110  is similar to Provide Substrate Step  1310 . In Provide Substrate Step  2110 , Substrate  105  optionally suitable for growth of CNFs  110  or other support filaments is provided. As discussed herein, Substrate  105  may include a variety of materials, for example Cu, Au, Sn, etc. Substrate  105  optionally includes nucleation sites as described elsewhere herein. 
     In an optional Provide CNF Step  2120 , CNF  110  (or any of the other support filaments described herein) are provided. Provide CNF Step  2120  is optional in embodiments in which electrodes that lack support filaments, such as those illustrated by  FIGS. 17 and 20 , are produced. In some embodiments the CNF  110  are provided by growing CNF  110  on Substrate  105 . In some embodiments, CNF  110  are provided by adding CNF  110  to a mixture, that is later applied to Substrate  105 . In some embodiments CNF  110  are produced separate from Substrate  105  and later attached to Substrate  105 . 
     In a Provide Intercalation Material Step  2130 , Intercalation Material  1610  is provided. In some embodiments, Intercalation Material  1610  is first applied to CNF  110 . In various embodiments, Intercalation Material  1610  is applied as a colloidal suspension, using vapor deposition, in a solvent, as a paste, or the like. 
     In a Provide Surface Effect Dominant Sites (SEDS) Step  2140 , Surface Effect Dominant Sites  1430  are 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. Surface Effect Dominant Sites  1430  can be provided as a suspension in Binder  1140 , or in a solvent, using sputter deposition, using electro deposition, using evaporation, as a spray or the like. In some embodiments a Zeta potential of Intercalation Material  1610  is selected such that Surface Effect Dominant Sites  1430  are concentrated at surfaces of Intercalation Material  1610 . 
     In an Apply Step  2150  Intercalation Material  1610 , Surface Effect Dominant Sites  1430  and optionally CNFs  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 CNFs  110  (perhaps already attached to Substrate  105 ) and then Surface Effect Dominant Sites  1430  can be then applied on top of the Intercalation Material  1610 . Alternatively, free CNF  110 , Intercalation Material  1610  may be first mixed, then Surface Effect Dominant Sites  1430  and Binder  1140  either alone or in combination are added. Based on the teachings herein, one of ordinary skill in the art will understand that in different embodiments, these components can be mixed or added in any order or combination. Further, the components can be mixed prior to or after being applied to Substrate  105 . The Steps  2110 - 2150  can be performed in any order. Apply Step  2150  is optionally followed by Condition Step  1350 . 
     In some embodiments the method illustrated in  FIG. 21  includes mixing Intercalation Material  1610  and Surface Effect Dominant Sites  1430  in a suspension in a solvent with a sufficient amount of dispersion. The dispersion is optionally applied to CNFs  110 . The solvent of the dispersion is then evaporated from the mixture resulting in a powder or coating on the CNFs  110 . Binder  1440  can be added to the suspension before or after application to the CNFs  110 . In some embodiments, the application of Surface Effect Dominant Sites  1430  occurs at the final stage of Intercalation Material  1610  deposition by changing the materials being sputtered onto Substrate  105 . In these embodiments, for example, TiO2 can be added to the sputtering mix after almost all the Intercalation Material  1610  is deposited. This produces a sputtered layer of TiO 2  as Surface Effect Dominant Sites  1430  on top of Intercalation Material  1610 . 
       FIG. 22  illustrates methods of operating a charge storage device, according to various embodiments of the invention. This method may be used, for example, when charging the charge storage device. In some embodiments the method includes attaching a charging device to both an anode and cathode of the charge storage device via wires. This charging storage device places potentials at the anode and cathode resulting in a potential gradient there between. The potential gradient drives electrons into the anode. The steps illustrated in  FIG. 22  optionally occur contemporaneously, e.g., they can occur at the same or at overlapping times with respect to each other. 
     In an Establish Potential Step  2210  a potential is established at the charge storage device. This potential may be between an anode and a cathode of the charge device. Such a potential will result in a potential gradient between Substrate  105  and Electrolyte  125  within the charge storage device. The potential gradient can produce a potential difference between locations of Surface Effect Dominant Sites  1430  and 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 there between. 
     In a Receive Lithium Step  2220  a charge carrier, of which Lithium is but one possible example, is received at one of Surface Effect Dominant Sites  1430 . This charge carrier is optionally received through Binder  1440 . 
     In a Transfer Electron Step  2230  an electron is transferred (e.g., donated) from Surface Effect Dominant Site  1430  to the charge carrier received in Receive Lithium Step  2220 . This transfer may comprise sharing of the electron between the Surface Effect Dominant Site  1430  and the charge carrier. The electron is transferred in a faradaic reaction and is typically conducted from Substrate  105 . The transfer occurs while the charge carrier is at the surface of the Surface Effect Dominant Site  1430  and occurs at the potential of that location. A reaction potential of the electron transfer is, for example, dependent on the reaction potential of the charge carrier and the reaction potential of the Surface Effect Dominant Site  1430 . The reaction potential can 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 an appreciable rate. The reaction potential of a reaction can be illustrated by, for example, peaks in a cyclic voltammogram. In another example, the potentials required for the reactions Li +  +e − →Li or 2Li +  +MO+2e − →Li 2 O+M (where M is any of the transition metals discussed herein) to occur in an electrochemical cell are the reaction potentials of these reactions. The reaction potential can be highly dependent on the environment in which the reaction occurs. For example, the second reaction above may have a lower reaction potential in the presence of a TiO 2  nanoparticle having a diameter in the range of 2-10 nm. Likewise, the reaction potential can be influenced by the energy required for intercalation or by the close proximity of Surface Effect Dominant Sites  1430  and Intercalation Material  1610 . 
     In an Intercalate Lithium Step  2240  a charge carrier, of which Lithium is but one possible example, is intercalated within Intercalation Material  1610 . This step may include migration of the charge carrier into the bulk interior of Intercalation Material  1610 . The charge carrier can be received at Intercalation Material  1610  as the same chemical species as received at the Surface Effect Dominant Sites  1430  in Receive Lithium Step  2220 , or alternatively in as a chemical species produced at the Surface Effect Dominant Sites  1430 . For example, the charge carrier can be received at the Intercalation Material  1610  as an oxide (e.g., Li 2 O, etc.) of the chemical species received at Surface Effect Dominant Sites  1430 . 
     In a Transfer Electron Step  2250  an electron is transferred from Intercalation Material  1610  to the charge carrier of Intercalate Lithium Step  2240 . The electron is transferred in a faradaic reaction and is typically conducted from Substrate  105 . The transfer occurs while the charge carrier is within Intercalation Material  1610  and occurs at the potential of that location. A reaction potential of the electron transfer may be dependent on the reaction potential of the charge carrier and the reaction potential of the Intercalation Material  1610 . The potential of this conduction band can be influenced by both the Intercalation Material  1610  and nearby Surface Effect Dominant Sites  1430 . Surface Dominant Sites  1430  can catalyze transfer of lithium from Electrolyte  125  to Intercalation Material  1610 . As discussed elsewhere herein, this transfer can occur via an intermediate oxide such as Li 2 O. The work function of this electron transfer can be different than the work function of the electron transfer in Transfer Electron 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 there between. In some embodiments it is thermodynamically more favorable for lithium to be intercalated into Intercalation Material  1610  than into the bulk of nanoparticles that include the Surface Effect Dominant Sites  1430 . However, the presence of the Surface Effect Dominant Sites  1430  can catalyze intercalation of a charge carrier into Intercalation Material  1610 . 
     If the charge carrier is converted to an oxide in Transfer Electron Step  2230  then, in some embodiments, Transfer Electron Step  2250  include transfer of an oxygen back from Intercalation Material  1610  back to Surface Effect Dominant Sites  1430 . This oxygen received at Intercalation Material  1610  as the oxide of the charge carrier, and is released from the charge carrier during intercalation. After being transferred back to Surface Effect Dominant Sites  1430 , this oxygen can then be used in further occurrences of Transfer Electron Step  2230 , i.e., the oxygen is recycled. 
     While the description of  FIG. 22  above assumes that the charge carrier received in Receive Lithium Step  2220  and the charge carrier Intercalate Lithium Step  2240  are two different individual charge carriers (that could be of the same type), in various embodiments steps  2220 ,  2230  and  2240  can be performed in by the same individual charge carriers. For example, in some embodiments, Receive Lithium Step  2220  includes receiving a charge carrier at one of Surface Effect Dominant Sites  1430 . Transfer Electron Step  2230  then includes a reaction in which the charge carrier reacts with the Surface Effect Dominant Site  1430  to produce an intermediate compound. In some embodiment this reaction includes 2Li +  +_MO+2e − →Li 2 O+M (Where M is any of the transition metals discussed herein and Li 2 O is the resulting intermediate compound). In Intercalate Lithium Step  2240  the intermediate compound (e.g., Li 2 O) is intercalated into Intercalation Material  1610 , or one (or both) of the Li in the intermediate compound are transferred from the O of Li 2 O to an atom of the Intercalation material (e.g., Li x Si). This transfer may result in regeneration of the MO that was split in Transfer Electron Step  2230 . Note that in this example the same individual Li atom was involved in each of the Steps  2220 - 2230  and  2240 . Transfer Electron Step  2250  is not required in these embodiments of the methods illustrated by  FIG. 22 . It is possible that in some embodiments both reaction sequences that include an intermediate such as Li 2 O and reaction sequences that do not include an intermediate occur during a single charging cycle. 
       FIG. 23A  illustrates a cross section of an electrode  2300 . One or more of electrode  2300  may be used in a rechargeable battery in accordance with various embodiments of the invention. The electrode  2300  includes a substrate  2310 , an optional seed layer  2315 , and an electrode extension  2320 . The electrode extension  2320  includes a support filament  2330  and an intercalation layer  2340 . The seed layer  2315  may be used to initiate growth of the support filament  2330  and to facilitate connection of the electrode extension  2320  to the substrate  2310 . In alternative embodiments the electrode extension  2320  is coupled directly to the substrate  2310 . The support filament  2330  supports the intercalation layer  2340  and provides an electrical path between the intercalation layer  2340  and the substrate  2310 . The intercalation layer  2340  includes DAM and provides a surface/volume for intercalation of ions. The electrode  2300  typically includes multiple electrode extensions  2320 . 
     The support filament  2330  is less than roughly 500 nanometers in diameter. (Averaged along its length.) More specifically, the diameter of support filament  2330  may vary between 1-10 nanometers, 10-50 nanometers and 100-500 nanometers. 
     In various embodiments, the substrate  2310  includes a porous material, metal, a semiconductor, and/or an insulator. For example, the substrate  2310  may include a low oxygen content copper. The substrate  2310  may be fabricated in a variety of shapes. For example, the substrate  2310  may be planar (single sided and double sided), cylindrical, finned, and/or the like. In some embodiments, the shape Substrate  2310  is selected so as to maximize available surface area. In various embodiments, the thickness of the substrate  2310  ranges from 1 micron to 100 microns; from 100 micros to a millimeter; from one millimeter to 3 millimeters, or larger, depending on the particular application of the secondary battery/cell  100 . 
     The optional seed layer  2315  serves one or more of a number of functions and may include several sub-layers. For example, the seed layer  2315  may comprise an initial layer  2350 , an intermediate layer, and/or a final layer  2360 . The seed layer  2315  may be configured to control a diameter of the support filament  2330  by controlling an area in which initial growth of the support filament  2330  occurs. The relative and/or absolute thicknesses of the initial layer  2350 , an intermediate layer, and/or a final layer  2360  can be selected to control the area of initial growth of the support filament  2330  and thus the support filament diameter  310 . The support filament diameter  310  is alternatively controlled use a reverse-micelle process wherein the diameter  310  of the initiation sites is determined by an appropriate size or amount of seed material used in the reverse-micelle process. Those skilled in the art of CNT/CNF/NW growth will appreciate that other methods are also available to control the diameter of the support filament  2330 . In some embodiments, the seed layer  2315  may control adhesion of the support filament  2330  to the substrate. The spacing between adjacent support filaments  2330  and/or the diameter of the support filaments may limit the possible thickness of the DAM in the intercalation layer  2340 , and vice-versa. 
     The seed layer  2315  may control a density of initiation points and/or an areal density of growth initiation points for the support filament  2330 . The density of initiation points determines the density of support filament  2330  attachment points. The density of attachment points may by between 10 6 /cm 2  to 10 11  cm 2 , generally 10 7 /cm 2  to 10 10 /cm 2 . The initiation density may be expressed as a number of support filament initiation sites per unit area, e.g., number/cm 2 . The areal density is the density of support filament  2330  tips that are distal from seed layer  2315  and substrate  2310 . The areal density can be greater than the density of attachment points because the support filaments  2330  may be branched, as discussed further elsewhere herein. The areal density may be expressed as a number of support filament tips per unit area, e.g., number/cm′. 
     In some embodiments, the seed layer  2315  is a single material deposited on the substrate  2310  in a single layer. Alternatively, the seed layer  2315  includes multiple (2, 3 or more) sub-layers of differing materials, e.g., initial layer  2350 , intermediate layer, and/or final layer  2360 . Each of the sub-layers of the seed layer  2315  may be configured to perform various functions. For example, one of the sub-layers may include a barrier layer configured to prevent migration of atoms between layers; include an adhesion layer configured to bind two layers together; a protection layer configured to protect underlying or overlying layers from chemical/physical degradation; a conduction layer configured to provide conductivity; a stress/strain layer configured to act as a mechanical buffer between two layers; a binding/release layer configured to bind/release the final seed material to/from the underlying substrate; a layer configured to inhibit the growth of CNT/CNF/NW, and/or a seed layer to initiate CNT/CNF or NW growth. Persons having ordinary skill in the art of thin film growth and deposition will recognize that there other utilities a thin film layered structure of seed layer  2315  can serve. 
       FIG. 23B  is a cross section illustrating details of the seed layer  2315  of  FIG. 23A , according to various embodiments of the invention. The seed layer  2315  illustrated in  FIG. 23B  includes a stack of sub-layers comprising different materials. As described elsewhere herein, the sub-layers include, for example, an initial layer  2350 , an intermediate layer  2355  and a final layer  2360 . The initial layer  2350  is coupled to the substrate and forms a base for the intermediate layer  2355 . The intermediate layer  2355  is deposited on the initial layer  2350  and configured to form a base for the final layer  2360 . The final layer  2360  is deposited on the intermediate layer  2355  and is configured to provide sites for attachment and initiation of growth of the support filament  2330 . Alternatively, the final layer  2360  is configured to inhibit the growth of CNT/CNF/NW. 
     In various embodiments, the final layer  2360  includes molybdenum, iron, cobalt, nickel and/or the like. Various materials in the final layer  2360  may initiate or inhibit growth and/or provide for attachment of the including CNT, CNF, and/or NW. The intermediate layer  2355  may include, for example, iron, cobalt, nickel, titanium, titanium nitride, aluminum, and/or the like. The initial layer  2350  may include, for example, platinum, tungsten, titanium, chromium, and/or the like. It will be appreciated that alternative materials may be included in the sub-layers of Seed Layer  2315 . 
     In various embodiments, the support filament  2330  includes NW, CNF, and/or CNT. The support filament  2330  provides a mechanical base for deposition and growth of the intercalation layer  2340 . The support filament  2330  may also provide strength (e.g., tensile strength, compression strength, shear strength, and/or the like) to the DAM of the intercalation layer  2340 . The additional strength reduces or prevents damage to the intercalation layer  2340  during expansion and/or contraction of the DAM. In various embodiments, the material of the support filament  2330  includes CNT, CNF, NW, metal, semiconductor, insulator, and/or the like. The CNT may include a single wall or multiple walls. In some embodiments, the CNT/CNF of the support filament  2330  is configured to act as a DAM. 
     In some embodiments, the intercalation layer  2340  does coat some but not all of the length of the support filament  2330 . As a result, a portion of the support filament  2330  forms an uncoated trunk  2335 . The trunk  2335  is configured to provide a region for flex and motion of the support filament  2330 . This flex can reduce mechanical stress resulting from expansion and contraction of the intercalation layer  2340 . If not reduced, this stress can cause breakage and/or separation of the support filament  2330  from the seed layer  2315 . The length of the trunk  2335  may range from several angstroms to several microns. In some embodiments the length of the trunk  2335  is selected such that the intercalation layer  2340  does not reach or only just reaches the seed layer  2315  when fully expanded. In various embodiments the length of the trunk is at least 0.1, 0.25, 0.3, 0.5, or 1.0 micrometers. In some embodiments, the length of the trunk  2335  is substantially greater than a micron. The trunk  2335  is typically located proximate to the end of support filament  2330  closest to the seed layer  2315 . However, uncoated trunk  2335  may be provided at other or alternative parts of support filament  2330 . For example, uncoated trunk  2335  may be provided proximate to branches within support filament  2330 . 
     In some embodiments, trunk  2335  is a region that has reduced coating of intercalation layer  2340  relative to other parts of electrode extension  2320 , rather than a region having no coat at all. For example, trunk  2335  may have a coating of intercalation layer  2340  whose thickness is less than 10, 25 or 50% of the thickness of the intercalation layer  2340  found in other regions of electrode extension  2320 . 
       FIG. 23C  is a cross section of a portion of the electrode extension  2320  of  FIG. 23A  including an optional under-layer  2390  between the support filament  2330  and the intercalation layer  2340 , and an optional over-layer  2395  that encapsulates the intercalation layer  2340 . In some embodiments, the under-layer  2390  is configured to provide a seed layer for vapor-liquid-solid (VLS) growth of the intercalation layer  2340 . Alternatively, the under-layer  2390  includes a thin layer (less than one micrometer) of a metal or a series of metals (e.g., gold, silver, copper, and/or the like) or a salt (e.g., LiF). Other materials may be used to form an under-layer  2390  depending on the desired effect. 
     The over-layer  2395  may be grown/deposited on the intercalation layer  2340 . The over-layer  2395  may partially or fully encapsulate the intercalation layer  2340 . The materials that comprise the over-layer  2395  include, for example, metals such as gold, silver, copper, and/or the like. The over-layer  2395  can also include a diamond-like coating (DLC), or an insulator, such as SiO 2 , a binder, a polymer, or the like. The thickness of the over-layer  2395  is typically less than one micrometer in the case of metals, semiconductors or insulators. In various embodiments, the thickness of the over-layer  2395  may be as large as a micrometer for a binder or larger for polymers. 
     The DAM may be grown/deposited on the support filament  2330  using a various methods. These methods include, for example, evaporation, sputtering, PECVD (Plasma-Enhanced Chemical Vapor Deposition), low-pressure chemical vapor deposition (LPCVD), VLS (Vapor Liquid Solid synthesis), electroplating, electro-less deposition, “field-free” chemical vapor deposition (CVD), metal-organic CVD, molecular beam epitaxy (MBE), and/or the like. In some embodiments, the DAM distribution over the surface of the support filament is uniform. Alternatively, the DAM distribution is not uniform over the length of the support filament  2330 . For example, the trunk  450  height may vary from 0% to 99% of the height of the CNT/CNF/NW. In some embodiments, the DAM proximate to the substrate  2310  has a smaller thickness relative to the distal end of the support filament  2330 . As such, the thickness of the DAM may increase, along support filament  2330 , with distance from the substrate  2310 . 
     The expansion of the DAM is dependent on the materials included in the DAM. For example, in the case of silicon the expansion may be as much 400% For Sn (tin) the expansion may be roughly 233%. Cathodes expansion occurs on insertion of the electrode into electrolyte, and when the battery is driven to overdisharge. The thickness of a DAM can range from several nanometers to several tens of microns. For example, in various embodiments, the thickness (unexpanded) is between 1-10 nanometers, 10-1000 nanometers, 1 micrometer to 50 microns. Larger thicknesses are optionally used on a cathode relative to an anode. 
     A number of methods may be employed to achieve a desired length for the trunk  2335 . Examples of such methods include controlling the aspect ratio of the support filaments  2330  during growth, directional deposition, electro-deposition, electro-less deposition at the bottom layer to isolate the trunk, sputter and light etch of a masking layer to open the support filament  2330  to intercalation layer  2340  growth/deposition, pre-coupling layer isolation (i.e. mask seed locations) prior to growth of the support filament  2330 , modifying growth parameters of the support filament  2330  to achieve an advantageous aspect ratio (such as a tree like structure), or performing a deposition and directional etch back to free the support filament  2330  from coverage by the DAM. 
     Several embodiments are specifically illustrated and/or described herein. However, it will be appreciated that modifications and variations are covered by the above teachings and within the scope of the appended claims without departing from the spirit and intended scope thereof. For example, while the examples discussed herein have been focused on CNFs having a stacked-cone structure the teachings may be adapted to other materials having similar or alternative structures. Likewise, while a Cu substrate and Li charge carriers are discussed herein other substrates and charge carriers will be apparent to one of ordinary skill 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 could be used as intercalation material. Additionally, aerogels, nano-wires, TiO 2  (titanium oxide), metal wires, carbon wires, or boron nitride nano-fibers can be used in place of the carbon nano-fibers discussed herein. The relative concentrations of Binder  1440 , Surface Effect Dominant Sites  1430 , Intercalation Material  1610  and CNF  110  and other elements in the figures can vary significantly from that illustrated. 
     The electrodes taught herein may be included in a wide variety of energy storage devices including capacitors, batteries and hybrids thereof. These energy storage devices can be used in, for example, lighting systems, portable electronics, load balancing devices, communication devices, backup power supplies, vehicles and computing devices. The concepts taught herein can be, in many cases, applied to cathodes as well as anodes. 
     The embodiments discussed herein are illustrative of the present invention. As these embodiments of the present invention are described with reference to illustrations, various modifications or adaptations of the methods and or specific structures described may become apparent to those skilled in the art. All such modifications, adaptations, or variations that rely upon the teachings of the present invention, and through which these teachings have advanced the art, are considered to be within the spirit and scope of the present invention. Hence, these descriptions and drawings should not be considered in a limiting sense, as it is understood that the present invention is in no way limited to only the embodiments illustrated.