Abstract:
Various methods and apparatus relating to three-dimensional battery structures and methods of manufacturing them are disclosed and claimed. In certain embodiments, a three-dimensional battery comprises a battery enclosure, and a first structural layer within the battery enclosure, where the first structural layer has a first surface, and a first plurality of conductive protrusions extend from the first surface. A first plurality of electrodes is located within the battery enclosure, where the first plurality of electrodes includes a plurality of cathodes and a plurality of anodes, and wherein the first plurality of electrodes includes a second plurality of electrodes selected from the first plurality of electrodes, each of the second plurality of electrodes being in contact with the outer surface of one of said first plurality of conductive protrusions. Some embodiments relate to processes of manufacturing energy storage devices with or without the use of a backbone structure or layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. section 119(e) to: (i) U.S. Provisional Application No. 60/884,836, entitled “Electrodes For Three Dimensional Lithium Batteries And Methods Of Manufacturing Thereof,” filed on Jan. 12, 2007; (ii) U.S. Provisional Application No. 60/884,828, entitled “Three-Dimensional Batteries and Methods of Manufacturing Using Backbone Structure,” filed on Jan. 12, 2007; and (iii) U.S. Provisional Application No. 60/884,846, entitled “Three-Dimensional Lithium Battery Separator Architectures,” filed on Jan. 12, 2007; all of which are hereby incorporated by reference herein in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field of the Invention 
         [0003]    Implementations consistent with the principles of the invention generally relate to the field of battery technology, more specifically to three-dimensional energy storage systems and devices, such as batteries and capacitors, and methods of manufacturing thereof. 
         [0004]    2. Background 
         [0005]    Existing energy storage devices, such as batteries, fuel cells, and electrochemical capacitors, typically have two-dimensional laminar architectures (e.g., planar or spiral-wound laminates) with a surface area of each laminate being roughly equal to its geometrical footprint (ignoring porosity and surface roughness). 
         [0006]      FIG. 1  shows a cross sectional view of an existing energy storage device, such as a lithium-ion battery. The battery  15  includes a cathode current collector  10 , on top of which a cathode  11  is assembled. This layer is covered by a separator  12 , over which an assembly of an anode current collector  13  and an anode  14  are placed. This stack is sometimes covered with another separator layer (not shown) above the anode current collector  13 , and is rolled and stuffed into a can to assemble the battery  15 . During a charging process, lithium leaves the cathode  11  and travels through the separator  12  as a lithium ion into the anode  14 . Depending on the anode  14  used, the lithium ion either intercalates (e.g., sits in a matrix of an anode material without forming an alloy) or forms an alloy. During a discharge process, the lithium leaves the anode  14 , travels through the separator  12  and passes through to the cathode  11 . 
         [0007]    Three-dimensional batteries have been proposed in the literature as ways to improve battery capacity and active material utilization. It has been proposed that a three-dimensional architecture may be used to provide higher surface area and higher energy as compared to a two dimensional, laminar battery architecture. There is a benefit to making a three-dimensional energy storage device due to the increased amount of energy that may be obtained out of a small geometric area. 
         [0008]    The following references may further help to illustrate the state of the art, and are therefore incorporated by reference as non-essential subject matter herein: Long et. al., “Three-Dimensional Battery Architectures,”  Chemical Reviews,  (2004), 104, 4463-4492; Chang Liu, FOUNDATIONS OF MEMS, Chapter 10, pages 1-55 (2006); Kanamura et. al., “Electrophoretic Fabrication of LiCoO 2  Positive Electrodes for Rechargeable Lithium Batteries,”  Journal of Power Sources,  97-98 (2001) 294-297; Caballero et al., “LiNi 0.5 Mn 1.5 O 4  thick-film electrodes prepared by electrophoretic deposition for use in high voltage lithium-ion batteries,”  Journal of Power Sources,  156 (2006) 583-590; Wang and Cao, “Li + -intercalation Electrochemical/Electrochromic Properties Of Vanadium Pentoxide Films By Sol Electrophoretic Deposition,”  Electrochimica Acta,  51, (2006), 4865-4872; Nishizawa et al., “Template Synthesis of Polypyrrole-Coated Spinel LiMn 2 O 4  Nanotubules and Their Properties as Cathode Active Materials for Lithium Batteries,”  Journal of the Electrochemical Society,  1923-1927, (1997); Shembel et. al., “Thin Layer Electrolytic Molybdenum Oxysulfides For Lithium Secondary Batteries With Liquid And Polymer Electrolytes,” 5 th    Advanced Batteries and Accumulators, ABA -2004, Lithium Polymer Electrolytes; and Kobrin et. al., “Molecular Vapor Deposition—An Improved Vapor-Phase Deposition Technique of Molecular Coatings for MEMS Devices,”  SEMI Technical Symposium: Innovations in Semiconductor Manufacturing  ( STS: ISM ),  SEMICON West  2004, 2004  Semiconductor Equipment and Materials International.    
         [0009]    It would be desirable to make three-dimensional electrochemical energy devices that may provide significantly higher energy and power density, while addressing the above issues or other limitations in the art. 
       SUMMARY OF THE INVENTION 
       [0010]    Various methods and apparatus relating to three-dimensional battery structures and methods of manufacturing them are disclosed and claimed. In certain embodiments, a three-dimensional battery comprises a battery enclosure, and a first structural layer within the battery enclosure, where the first structural layer has a first surface, and a first plurality of conductive protrusions extend from the first surface. A first plurality of electrodes is located within the battery enclosure, where the first plurality of electrodes includes a plurality of cathodes and a plurality of anodes, and wherein the first plurality of electrodes includes a second plurality of electrodes selected from the first plurality of electrodes, each of the second plurality of electrodes being in contact with the outer surface of one of said first plurality of conductive protrusions. 
         [0011]    Other aspects and advantages of the present invention may be seen upon review of the figures, the detailed description, and the claims that follow. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Some embodiments of the invention are described with reference to the following figures. 
           [0013]      FIG. 1  is a generic cross-section of an existing two-dimensional energy storage device such as a lithium ion battery. 
           [0014]      FIG. 2  is a schematic illustration of a backbone structure according to an embodiment of the invention. 
           [0015]      FIGS. 3A-3D  are schematic illustrations of some shapes into which backbone structures may be assembled according to certain embodiments of the invention. 
           [0016]      FIGS. 4A-4E  depict a schematic representation of a process for manufacturing a backbone structure using a subtractive reactive ion etch process, according to an embodiment of the invention. 
           [0017]      FIGS. 5A-5D  depict a schematic representation of a process for manufacturing a backbone structure using a subtractive electrochemical etch process, according to an embodiment of the invention. 
           [0018]      FIGS. 6A-6C  depict a schematic representation of a process for manufacturing a backbone structure using a subtractive stamping process, according to an embodiment of the invention. 
           [0019]      FIGS. 7A-7D  depict a schematic representation of a process for manufacturing a backbone structure using an additive electrochemical deposition, electroless deposition, or electrophoretic deposition process, according to an embodiment of the invention. 
           [0020]      FIGS. 8A-8E  depict a schematic representation of a process for manufacturing a backbone structure using an additive extrusion process, according to an embodiment of the invention. 
           [0021]      FIGS. 9A-9C  depict a schematic representation of a process for manufacturing a backbone structure using a sequential deposition and assembly process, according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Certain embodiments of the invention relate to the design of a three-dimensional lithium-ion battery. Existing energy storage devices, such as batteries, fuel cells, and electrochemical capacitors, typically have two-dimensional laminar architectures (e.g., planar or spiral-wound laminates) with a surface area of each laminate being roughly equal to its geometrical footprint (ignoring porosity and surface roughness). A three-dimensional energy storage device can be one in which an anode, a cathode, and/or a separator are non-laminar in nature. For example, if electrodes protrude sufficiently from a backplane to form a non-laminar active battery component, then the surface area for such a non-laminar component may be greater than twice the geometrical footprint of its backplane. In some instances, given mutually orthogonal X,Y,Z directions, a separation between two constant-Z backplanes should be at least greater than a spacing between electrodes in an X-Y plane, divided by the square root of two. 
         [0023]    Some embodiments of the invention relate to the use of a backbone structure for the manufacture of three-dimensional energy storage devices, such as batteries, capacitors, and fuel cells. The backbone structure may be used for the purpose of providing mechanical stability, electrical connectivity, and increased surface area per unit geometrical area. By way of example, the backbone structure may be made in the shape of pillars by wire-bonding aluminum on a flat substrate, which may be subsequently coated with a cathode or anode material for the purpose of assembling a battery. Examples of backbone formation using various materials, shapes, and methodologies are presented herein, among other embodiments. 
         [0024]    Three-dimensional energy storage devices may produce higher energy storage and retrieval per unit geometrical area than conventional devices. Three-dimensional energy storage devices may also provide a higher rate of energy retrieval than two-dimensional energy storage devices for a specific amount of energy stored, such as by minimizing or reducing transport distances for electron and ion transfer between an anode and a cathode. These devices may be more suitable for miniaturization and for applications where a geometrical area available for a device is limited and/or where energy density requirement is higher than what may be achieved with a laminar device. 
         [0025]    Some embodiments of the invention include a mechanically stable, electrically conductive backbone structure that ends up being a part of the final assembled energy storage device. A backbone material typically does not take an active part in electrochemical reactions of the energy storage device, and may enhance mechanical and electrical robustness. 
         [0026]    The backbone material may also act as a high surface area substrate for manufacturing the high surface area electrochemical device. Mechanical robustness may increase the lifetime of the device, since active materials that constitute the device are typically porous electrodes with relatively lower mechanical stability. Electrical conductivity may enhance or maintain a power density of the device (e.g., by decreasing resistivity) while also equalizing current distribution between electroactive species. 
         [0027]    A backbone structure may be made in any shape that provides higher surface area relative to geometrical area, such as pillars, posts, plates, waves, circles, diamonds, spirals, staircase structures, and so forth. The backbone structure may be made out of any material that may be shaped, such as metals, semiconductors, organics, ceramics, and glasses. The backbone structure may serve to provide: (i) rigidity to active electrodes in an energy storage device, such as anodes and cathodes in a lithium ion battery; (ii) electrical connectivity to tall three-dimensional structures; and (iii) increased surface area per unit geometrical area. Desirable materials include semiconductor materials such as silicon and germanium. Carbon-based organic materials may also be used to form backbone structures for three-dimensional shaping. Metals, such as aluminum, copper, nickel, cobalt, titanium, and tungsten, may also be used for backbone structures. 
         [0028]    In some embodiments, a backbone structure is made out of a metal, semiconductor, organic material, ceramic, or glass using a subtractive formation technique. These materials may be processed by reactively etching a substrate using a selective etch mask and a plasma etch process. Alternatively, or in conjunction, electrochemical etching, stamping, or electrical discharge machining may be used to selectively remove material preferentially in areas where these materials are not desired. 
         [0029]    In other embodiments, a backbone structure is made out of a metal, semiconductor, organic, ceramic, or glass using an additive formation technique. These materials may be processed by making a sacrificial mold using a technique such as conventional lithography, and depositing a backbone material using techniques such as electrochemical deposition, electroless deposition, electrophoretic deposition, vacuum assisted filling, stencil assisted filling, and so forth. In certain cases, the backbone structure may be assembled directly using a wirebonding process. In other cases, the backbone structure may be made on a flat plate using conventional lithography and deposition techniques, and subsequently assembled by “pick and place” and soldering or gluing techniques. 
         [0030]    In other embodiments, a backbone material may be shaped using printing techniques, such as three-dimensional printing and inkjet printing, to form a backbone structure using single or multiple layers of printing to obtain a desired shape and thickness. Alternatively, or in conjunction, the backbone material may be assembled in the form of layered sheets, with sacrificial layers deposited in between. After stacking of the sheets is substantially complete, a resulting structure is cut into pieces of a desired height, assembled together, and the sacrificial material is released to provide the backbone structure. 
         [0031]    In the case of an electrically conductive backbone structure, an active material may be directly assembled on top of and around the backbone structure by various techniques, such as electrochemical deposition, electroless deposition, co-deposition in an organic or inorganic matrix, electrophoretic deposition, mechanical filling and compacting, and vacuum assisted flow deposition. 
         [0032]    In case of an electrically non-conductive backbone structure, a conducting layer may be deposited by various techniques, such as electrochemical or electroless deposition, vapor assisted vacuum deposition such as Atomic Layer Deposition (ALD) and Chemical Vapor Deposition (CVD), sputter deposition, evaporation, and electrophoretic deposition. This conductive layer may be subsequently removed in order to remove an electrical connection between an anode and a cathode. This removal may be accomplished using techniques such as sputter etching, ion milling, and liftoff. In addition, techniques such as chemical dissolution may be used with standard techniques such as lithography to protect areas that do not need to be removed. 
         [0033]      FIG. 2  illustrates an exemplary concept of a backbone structure  20  used in the formation of a three-dimensional battery.  FIG. 2  shows a cross-sectional schematic of two positive electrodes  21  and a negative electrode  23 . In this embodiment, the backbone structure  20  includes a non-conductive base  24  of a common material on which a conductive material  22  has been deposited and removed in the areas where it is not needed in order to separate the electrodes  21  and  23 . It is apparent from comparing  FIG. 2  and  FIG. 1  that a surface area for the electrodes  21  and  23  in  FIG. 2  is relatively higher as compared to the surface area for the electrodes shown in  FIG. 1 , calculating this area as a product of a length L and a thickness T of the electrodes  21  and  23 . It should be noted that the thickness, and therefore related properties such as conductivity, of various features (such as electrodes and backbone structure protrusions) according to certain embodiments may be varied locally (e.g., from electrode to electrode or from protrusion to protrusion) based on current-carrying requirements or other relevant performance specifications. 
         [0034]    Some examples of three-dimensional architectures that are capable of use with certain embodiments of the present invention, and that have cathodes and anodes protruding from the same backplane, are shown in  FIGS. 3A-3D .  FIG. 3A  shows a three-dimensional assembly with cathodes and anodes in the shape of pillars,  FIG. 3B  shows a three-dimensional assembly with cathodes and anodes in the shape of plates,  FIG. 3C  shows a three-dimensional assembly with cathodes and anodes in the shape of concentric circles, and  FIG. 3D  shows a three-dimensional assembly with cathodes and anodes in the shape of waves. Other configurations, such as honeycomb structures and spirals might also be used with certain embodiments of the present invention. In  FIGS. 3A-3D , cathodes  30  and anodes  31  protrude from the same backplane and are alternating in a periodic fashion. However, in other embodiments the cathodes  30  may protrude from a different backplane than anodes  31 . 
         [0035]      FIGS. 4A-4E  depict a schematic representation of an overall process flow for manufacturing a backbone structure using a subtractive reactive ion etch process according to certain embodiments. The process involves using a substrate  40  that may be shaped using a directional plasma source to form a volatile gaseous by-product, thereby facilitating its removal. A non-limiting example of the substrate  40  is one formed of silicon, which may be single-crystal or polycrystalline in nature. A masking layer  41  is deposited on top of the substrate  40  by methods such as vacuum deposition, thermal oxidation, surface coating, and wet chemical deposition. In the case of silicon as the substrate  40 , a thermally grown silicon dioxide layer of a particular thickness may serve as the masking layer  41 . This layer  41  may be subsequently patterned by standard patterning techniques such as lithography in order to provide a pattern suitable for further processing to create the backbone structure. In some embodiments of the invention, the masking layer  41  may be covered with a second masking layer  42  that is used to pattern the first masking layer  41  (see  FIGS. 4A-4B ). In this case, the first masking layer  41  is patterned by using the second masking layer  42  as a stencil (see  FIG. 4C ). For the silicon/silicon dioxide case, a standard photoresist may be used as the second masking layer  42 . The second masking layer  42  may be patterned with standard optical lithography techniques. The second masking layer  42  may be selectively removed using selective wet or dry methods, leaving behind the patterned first masking layer  41  (see  FIG. 4D ). This combination of the substrate  40  and the patterned first masking layer  41  is subjected to a directional plasma  43  in a controlled environment in order to transfer the image of the first masking layer  41  onto the substrate  40  (see  FIG. 4D ). This reactive etch process in the presence of a directional plasma source may provide excellent anisotropic etching of the substrate  40  while etching the masking layer  41  itself at a very low rate. After the reactive etch of the substrate  40  is substantially complete, the masking layer  41  may be removed to leave the patterned substrate  40  behind, thereby forming the backbone structure (see  FIG. 4E ). 
         [0036]    The following example further explains concepts described with reference to  FIGS. 4A-4E . Single-crystal or polycrystalline silicon may be used as the substrate  40  that may be etched directionally in the presence of a plasma. The first masking layer  41  may be a thermally grown silicon dioxide layer of a particular thickness. A standard photoresist, such as AZ4620™ and AZP4620™ (commercially available from Clariant Corporation), may be used as the second masking layer  42 . This layer  42  may be spin coated on top of the silicon dioxide layer, and subsequently patterned with standard optical lithography techniques. The areas of the photoresist that are exposed to light may be developed away using a developer solution, such as AZ400K™ (commercially available from Clariant Corporation). This patterned structure is dipped in a solution of HF, NH 3 F, and water (Buffered Oxide Etch), wherein exposed silicon dioxide surfaces are dissolved. The remaining photoresist may be selectively removed by using a compatible organic solvent, such as N-methyl-2-Pyrrolidone, leaving behind the patterned silicon dioxide layer. This combination of the silicon and patterned silicon dioxide may be subjected to a directional fluoride plasma source in order to etch an image of the silicon dioxide layer onto the substrate  40 . The directionality of the plasma  43  is controlled by a bias voltage between an anode and a cathode in a conventional plasma reactive ion etcher. A difference in rate between etch of silicon and silicon dioxide causes a pattern to be transferred to the substrate  40  without much etching in a lateral direction. After the reactive etch of silicon is substantially complete, the masking layer  41  may be removed by immersion in the Buffered Oxide Etch solution to leave the patterned substrate  40  behind. In some cases, a stop layer can be added to the bottom of the substrate  40  to facilitate complete etching and isolation of the cathode and anode backbone structures. 
         [0037]    In some embodiments, the patterned substrate  40  is electrically conductive, in which case the resulting backbone structure is ready for further processing of active materials. In certain other embodiments, the backbone structure is electrically non-conductive. In this case, further processing by deposition of a conductive layer may be performed by various methods. 
         [0038]      FIGS. 5A-5D  depict a schematic representation of a process for manufacturing a backbone structure using a subtractive electrochemical etch process according to certain embodiments. In these particular embodiments, a substrate  50  is patterned using a electrically insulating masking layer  51  that is deposited on top of the substrate  50  by methods such as vacuum deposition, thermal oxidation, surface coating, and wet chemical deposition. This layer  51  is subsequently patterned by standard patterning techniques such as lithography in order to provide a pattern suitable for further processing to create the backbone structure. In some embodiments of the invention, the masking layer  51  is covered with a second masking layer  52  that is used to pattern the first masking layer  51  (see  FIGS. 5A-5B ). In this case, the first masking layer  51  is patterned by using the second masking layer  52  as a stencil. The second masking layer  52  is selectively removed using selective wet or dry methods, leaving behind the patterned first masking layer  51  (see  FIG. 5B ). The combination of the substrate  50  and the first masking layer  51  is placed in an electrochemical cell  53  that has a counter electrode  54  and a nozzle  55  that delivers a solution used to electrochemically remove a material in areas that are exposed to the solution (see  FIG. 5C ). In certain embodiments, the whole workpiece may be dipped into the solution that may dissolve the material that is in contact with the solution. However, the illustrated process may be more isotropic in nature, and typically an amount of material removed in the depth direction D may be substantially the same as the amount of material removed in each side of the width direction W. A dip-tank solution may be used for making features in which gaps G in the resulting backbone structure are significantly narrower than the width W. A DC power source  56  may be used to apply a potential that is sufficient to remove the material in contact with the solution. The process is substantially complete when essentially the desired amount of material is removed, which may be controlled based on the rate of etching that has been previously determined. In certain other cases, a current may be monitored, and a drop in the current may correspond to an end-point of the electrochemical reaction. After the reaction is substantially complete, the workpiece is removed, and the masking layer  51  may be removed to leave the patterned substrate  50  behind, thereby forming the backbone structure. 
         [0039]    The following example further explains concepts described with reference to  FIGS. 5A-5D . One example of the substrate  50  for electrochemical patterning is a copper sheet. A sheet of the desired thickness may be used as the substrate  50 , and may be patterned using the electrically insulating masking layer  51  (e.g., AZ4620™ or AZP4620™ photoresist) that is deposited on top of the substrate  50  by spin coating. This layer  51  may be exposed to light in the presence of a photomask that blocks light to areas in which the resist should be left behind. The workpiece may be placed in a solution that selectively removes the exposed areas. The combination of the substrate  50  and the first masking layer  51  is placed in the electrochemical cell  53  that has the counter electrode  54  (e.g., platinum) and the nozzle  55  that delivers the electrochemical etch solution used to electrochemically remove the metal in areas that are exposed to the solution. A combination of 10 wt % sulfuric acid and 1 wt % hydrogen peroxide may be delivered through the nozzle  55  to the workpiece. The DC power source  56  may be used to apply an anodic potential to the substrate  50 , which removes copper in areas where the solution comes in contact with the copper anode and the platinum cathode at the same time, thereby forming a local electrochemical cell. After the reaction is substantially complete, the workpiece may be removed, and the masking layer  51  may be removed with N-methyl-2-pyrrolidone to leave the patterned substrate  50  behind. 
         [0040]      FIGS. 6A-6C  depict a schematic representation of a process for manufacturing a backbone structure using a subtractive stamping process according to certain embodiments. A mandrel  60  is pre-fabricated with patterns that are inverted from a desired backbone pattern, and the mandrel  60  is coated with a thin release layer  61  that may be used to facilitate removal of the mandrel  60  after processing. The release layer  61  may be, for example, an organic material that may be vapor-deposited uniformly into three-dimensional features. This material may have additional properties of having either poor adhesion or the ability to be selectively etched without etching the mandrel  60  or a backbone material. For example, a stainless steel mandrel coated with a thin layer of copper deposited by chemical vapor deposition may act as an adequate stamping device for a process where a material that is used as a mold is thermally curable photoresist (see  FIG. 6A ). The combination of the mandrel  60  and the release layer  61  is contacted with a sheet of moldable material  62  that is on top of a substrate  63 . Pressure is applied in order to transfer the pattern to the moldable material  62  (see  FIG. 6B ). This combination is hardened by curing into place the moldable material  62  using temperature or other means, such as light, in case the substrate  63  is transparent. The release layer  61  is removed by suitable means while separating the mandrel  60  and the resulting backbone structure that includes the molded material and the substrate  64  (see  FIG. 6C ). 
         [0041]    In certain other embodiments of the invention, additive processes may be used to process a backbone structure of an energy storage device.  FIGS. 7A-7D  depict a schematic representation of a process for manufacturing the backbone structure using an additive electrochemical deposition process according to certain embodiments. This process may be referred to as a LIGA process in the art, which in German stands for “lithography, galvano-forming and molding (Abformung).” In this process, a conductive or non-conductive substrate  70  is used. In case of a non-conducting substrate, a conducting layer  71  is deposited. Photoresist  72  is coated on top of this substrate  70 , and is patterned by standard lithography techniques using a photomask  73  to leave behind the photoresist  72  in areas where a backbone material is not to be deposited (see  FIGS. 7A and 7B ). The workpiece is placed in an electroplating bath with a potential enough to reduce metallic ions present in solution to form a metal  74  (see  FIG. 7C ). The metallic ions are reduced at a conductive surface and are not deposited where the photoresist  72  is present. When the process is substantially complete, the workpiece including components  70 ,  72 , and  74  is removed from a plating cell, and the photoresist  72  is removed to leave the backbone structure (including components  70  and  74 ) behind (see  FIG. 7D ). 
         [0042]    The following example further explains concepts described with reference to  FIGS. 7A-7D . In this process, a silicon wafer may be used as the semi-conductive substrate  70 . Copper may be deposited using sputter deposition to create the conductive layer  71  on top of the silicon. A positive or negative tone photoresist  72  (e.g., AZ4620™ or AZP4620™) may be coated on top of this substrate  70  and patterned by standard lithography techniques to leave behind the photoresist  72  in areas where a backbone material is not to be deposited. This workpiece may be placed in a nickel electroplating bath including 1 M nickel sulfate, 0.2 M nickel chloride, 25 g/l boric acid, and 1 g/l sodium saccharin, along with a platinum counter electrode and a potential enough to reduce nickel ions present in the solution to Ni metal  74 . The metal ions are reduced at a conductive surface and are not deposited where the photoresist  72  is present. When the process is substantially complete, the workpiece including the silicon wafer  70 , photoresist  72 , and nickel metal  74  may be removed. Subsequently, the photoresist  72  may be removed using N-methyl-2-pyrrolidone to leave the backbone structure including components  70  and  74  behind. The remaining copper metal in the area where the photoresist  72  was present may be removed by a chemical etch involving 2% sulfuric acid and 1% hydrogen peroxide. 
         [0043]      FIGS. 8A-8E  depict a schematic representation of a process for manufacturing a backbone structure using an additive extrusion process according to certain embodiments. A mandrel  80  is pre-fabricated with patterns that are inverted from a desired backbone pattern, and the mandrel  80  is coated with a thin release layer  81  that may be used to facilitate removal of the mandrel  80  after processing (see  FIG. 8A ). This mandrel  80  also has openings either at the edges or on top of each opening  85  in order to facilitate the addition of a material that may be made into a mold. The release layer  81  may be, for example, an organic material that may be vapor-deposited uniformly into three-dimensional features. This material may have additional properties of having either poor adhesion or the ability to be selectively etched without etching the mandrel  80  or a backbone material. For example, a stainless steel mandrel coated with a thin layer of copper deposited by chemical vapor deposition may act as an adequate stamping device for a process where a material that is used as the moldable material  82  is a thermally curable photoresist. The combination of the mandrel  80  and the release layer  81  is contacted with a substrate  83  (see  FIG. 8B ). The moldable material  82  is extruded into the openings  85  and filled (see  FIG. 8C ). Any residual material within the openings  85  is cleaned out at this time (see  FIG. 8D ). This combination is hardened by curing into place the moldable material  82  using temperature or other means, such as light, in case the substrate  83  is transparent. The release layer  81  is removed by suitable means while separating the mandrel  80  and the resulting backbone structure that includes the molded material  82  and the substrate  83  (see  FIG. 8E ). Depending on the requirements of each particular implementation, release layer  81  may not be necessary (e.g., if the mandrel/mold  80  itself satisfies the required characteristics that would otherwise be satisfied by a release layer). In certain embodiments, the mandrel/mold  80  may be released by dissolution. 
         [0044]      FIGS. 9A-9C  depict a schematic representation of an exemplary process for manufacturing a backbone structure using a sequential deposition and assembly process according to certain embodiments. In this process, alternating layers of backbone material and a sacrificial material are assembled. An example of a set of materials that may be assembled together are sheets of polyethylene terephthalate (PET)  90  interspersed with copper foils  91 . The resulting stack thus includes PET/copper/PET/copper/PET (see  FIG. 9A ). The layers are diced to a thickness substantially corresponding to a height of a backbone structure H, spirally wound within their axes, and assembled onto a substrate  92  using epoxy glue (see  FIG. 9B ). A sacrificial PET layer is removed by selectively etching it away in a selective chemical etch solution containing sodium hypochlorite (NaOCl). This leaves behind two spirally wound copper substrates, one for cathode backbone and another for anode backbone with gaps in the middle which will house active materials and separators for an electrochemical energy device (see  FIG. 9C ). 
         [0045]    Once a backbone structure is available, materials that are involved in electrochemical reactions, also called active materials, may be loaded onto the backbone structure. This may be done by several different methods. An anode backbone and a cathode backbone may be separate from each other, but each electrode may be electrically conductive by itself. This lends to electrochemical deposition techniques and electrophoretic deposition techniques as viable options for adding the active materials. For example, in the case of a lithium-ion battery, a cathode material, such as LiCoO 2 , LiNi 0.5 Mn 1.5 O 4 , Li(Ni x Co y Al z )O 2 , LiFePO 4 , or Li 2 MnO 4  may be electrophoretically deposited onto a conductive substrate. Electrophoretic deposition may also be performed for V 2 O 5  films. Cathode materials may also be co-deposited along with a polypyrrole matrix. In addition, certain cathode materials for lithium-ion batteries may be electrochemically deposited, such as molybdenum oxysulfides. In certain embodiments, cathode formation comprises electrophoretic deposition of LiCoO 2  until a layer thickness between 1 micron and 300 microns is formed. In certain embodiments, the layer thickness is between 5 microns and 200 microns, and in certain embodiments, the layer thickness is between 10 microns and 150 microns. With regards to anode materials, electrochemical deposition may be used for plateable anode materials, such as tin, electrophoretic deposition may be used to assemble graphite, and an electrophoretic resist deposition followed by pyrolysis may form a carbon anode. Other suitable anode materials may include titanates, silicon, and aluminum. Similar layer thicknesses apply to anode formation as described above. Suitable separator materials may include polyethylenes, polypropylenes, TiO 2 , SiO 2 , Al 2 O 3 , and the like. 
         [0046]    While some embodiments have been described with reference to energy storage devices, it should be recognized that the backbone structures described herein may be useful in various other types of devices to provide increased surface area per unit geometrical area (or per unit weight or volume). These other types of devices may involve various types of processes during their operation, such as heat transfer, chemical reactions, and diffusion. 
         [0047]    While the invention has been described with reference to the specific embodiments thereof, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention as defined by the appended claims. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, method, operation or operations, to the objective, spirit, and scope of the invention. All such modifications are intended to be within the scope of the claims appended hereto. In particular, while the methods disclosed herein have been described with reference to particular operations performed in a particular order, it will be understood that these operations may be combined, sub-divided, or re-ordered to form an equivalent method without departing from the teachings of the invention. Accordingly, unless specifically indicated herein, the order and grouping of the operations is not a limitation of the invention.