Patent Publication Number: US-2011059362-A1

Title: Methods for forming foamed electrode structures

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 61/239,910, filed Sep. 4, 2009, which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to forming electrodes, and more particularly to processing techniques for creating electrode structures containing an electronically conductive foam and an electronically conductive substrate. 
     BACKGROUND OF THE INVENTION 
     Electrodes are used to supply and remove electrons from some medium, and are typically manufactured from metals or metal alloys. Electrochemical cells use electrodes to facilitate electron transport and transfer during electrochemical interactions. Batteries, or electrochemical storage devices, may use electrodes in both galvanic and electrolytic capacities, corresponding to discharging or charging processes, respectively. Electrochemical reactions generally occur at or near the interfaces of an electrolyte and the electrodes, which may extend to an external circuit through which electric power can be applied or extracted. 
     Electrodes are typically placed in contact with current collectors in order to draw and/or supply electrical power. In order to reduce system losses, there must be sufficient electrical contact at the interface between the electrode and the current collector. The quality of this interface may depend on the processing steps used to manufacture the electrode and the current collector, and the assembly steps used to place the two components in electrical contact. 
     Numerous processing steps, which include both mechanical and chemical interactions, are typically required to manufacture the electrodes and current collectors that accomplish the aforementioned assembly. These numerous processing steps, often using multiple subassemblies, may increase cost, increase infrastructure requirements, and introduce opportunities for manufacturing errors to occur. Accordingly, it would be desirable to reduce and/or consolidate the processing steps required to manufacture electrode structures. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, provided are techniques, compositions, and arrangements for forming electrode structures that include one or more electronically conductive foams in contact with one or more electronically conductive substrates. In some embodiments the present invention provides techniques for forming electronically conductive foams directly on an electronically conductive substrate. In some approaches, forming electronically conductive foams directly on an electronically conductive substrate may reduce, consolidate, or both, the process steps for forming electrode structures. 
     In some embodiments, a precursor material may be placed in contact with an electronically conductive substrate (e.g., metal), where an interface may exist between a surface of the substrate and the precursor material. The precursor material may be a polymer foam, polymer slurry, dried polymer slurry, any other suitable precursor material or any suitable combination thereof. In some embodiments, the precursor material in contact with the substrate may be further processed (e.g., dried, cured) while in contact with the substrate. For example, a plating or coating process may be applied to the subassembly of the precursor material and substrate in contact with one another. The plating or coating process may include coating all or part of the precursor material and substrate with an electronically conductive material (e.g., metal) to form an electronically conductive network throughout the volume of the precursor material. The plated precursor material, as well as one or more components of the plated precursor material, may be substantially removed (e.g., pyrolyzed), thereby leaving an electronically conductive foam in contact with the substrate. In some embodiments, active materials may be included in the precursor material, or the active materials may be introduced to the electronically conductive foam, or both. In some embodiments, the electronically conductive foam may be sintered at elevated temperature. The substrate and foam may be of any suitable shape, including flat plate, curved plate, dome, or any other suitable shape or combination thereof. 
     In some embodiments, a plurality of first particles may be combined with a plurality of second particles and a liquid agent to form a slurry. The slurry may include at least one electronically conductive component and at least one electronically nonconductive component including, but not limited to, one or more of polymer particles, binders, liquid agents, any other suitable electronically nonconductive material or any suitable combination thereof. At least one contiguous layer of the slurry may be formed on a surface of an electronically conductive substrate. The layers may be uniform or non-uniform in thickness and may be contiguous or non-contiguous on the surface of the substrate. In some embodiments, more than one contiguous layer may be formed on a surface of the substrate. 
     Substantially all (i.e., all or almost all) of the liquid agent may be removed from the at least one contiguous layer of the slurry to leave a solid composite material, where the solid composite material may remain in contact with the surface of the substrate. For example, the liquid agent may be removed by drying, heating, any other suitable removal process, or any combination thereof. Substantially all of the plurality of first particles may be removed from the composite material (e.g., pyrolyzed), where the remaining plurality of second particles may form a corresponding electronically conductive foam in contact with the substrate. 
     In some embodiments, a composite material may be placed in contact with an electronically conductive substrate. The composite material may include at least one electronically conductive component and at least one electronically nonconductive component including, but not limited to, one or more of a polymer foam, dried polymer slurry, any other suitable electronically nonconductive material or any suitable combination thereof. The composite material may be a composite slurry including two or more types of particles. For example, the composite material may be a slurry including a liquid agent (e.g., organic solvent), electronically conductive particles (e.g., metal) and electronically nonconductive particles (e.g., polymer). In some embodiments, the composite slurry may be further processed (e.g., dried, cured) while in contact with the substrate. The electronically nonconductive components, or any other components, may be substantially removed (e.g., pyrolyzed) from the dried composite slurry, thereby leaving an electronically conductive foam in contact with the substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic cross-sectional view of an illustrative structure of a bi-polar electrode-unit (BPU) in accordance with some embodiments of the present invention; 
         FIG. 2  shows a schematic cross-sectional view of an illustrative structure of a stack of BPUs of  FIG. 1  in accordance with some embodiments of the present invention; 
         FIG. 3  shows a schematic cross-sectional view of an illustrative structure of a mono-polar electrode-unit (MPU) in accordance with some embodiments of the present invention; 
         FIG. 4  shows a schematic cross-sectional view of an illustrative structure of a device containing two MPUs of  FIG. 3  in accordance with some embodiments of the present invention; 
         FIG. 5  shows a cubic section of an illustrative solid-phase foam in accordance with some embodiments of the present invention; 
         FIG. 6  shows an illustrative electrode structure with a cutaway section in accordance with some embodiments of the present invention; 
         FIG. 7  shows an illustrative flow diagram for creating an electrode structure in accordance with some embodiments of the present invention; 
         FIG. 8  shows an illustrative flow diagram for creating an electrode structure in accordance with some embodiments of the present invention; 
         FIG. 9  shows an illustrative flow diagram for creating an electrode structure in accordance with some embodiments of the present invention; 
         FIG. 10  shows an illustrative flow diagram for creating an electrode structure in accordance with some embodiments of the present invention; 
         FIG. 11  shows an illustrative side elevation view of a precursor material in contact with a substrate in accordance with some embodiments of the present invention; 
         FIG. 12  shows an illustrative top plan view of the elements of  FIG. 11 , taken from line XII-XII, in accordance with some embodiments of the present invention; 
         FIG. 13  shows an illustrative partial cross-sectional view of an interface between a precursor material and a substrate in accordance with some embodiments of the present invention; 
         FIG. 14  shows an illustrative partial cross-sectional view of the interface of  FIG. 13 , coated with an electronically conductive material in accordance with some embodiments of the present invention; 
         FIG. 15  shows an illustrative partial cross-sectional view of the interface of  FIG. 14  in accordance with some embodiments of the present invention; 
         FIG. 16  shows an illustrative side elevation view of a composite material in contact with a substrate in accordance with some embodiments of the present invention; 
         FIG. 17  shows an illustrative top plan view of the elements of  FIG. 16 , taken from line XVII-XVII, in accordance with some embodiments of the present invention; 
         FIG. 18  shows an illustrative partial cross-sectional view of an interface between a composite material and a substrate in accordance with some embodiments of the present invention; 
         FIG. 19  shows an illustrative partial cross-sectional view of an interface between an electronically conductive foam and a substrate in accordance with some embodiments of the present invention; 
         FIG. 20  shows an illustrative partial cross-sectional view of an interface between a composite material and a substrate in accordance with some embodiments of the present invention; and 
         FIG. 21  shows an illustrative partial cross-sectional view of an interface between an electronically conductive foam and a substrate in accordance with some embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides methods, compositions, and arrangements for forming electrode structures that include one or more electronically conductive foams in contact with one or more electronically conductive substrates. The present invention provides methods, compositions, and arrangements for forming electronically conductive foams directly on an electronically conductive substrate. The electrode structures and assemblies of the present invention may be applied to energy storage devices such as, for example, batteries, capacitors or any other energy storage device which may store or provide electrical energy or current, or any combination thereof. For example, the electrode structures and assemblies of the present invention may be implemented in a mono-polar electrode unit (MPU) or a bi-polar electrode unit (BPU), and may be applied to one or more surfaces of the MPU or BPU. It will be understood that while the present invention is described herein in the context of stacked energy storage devices, the concepts discussed are applicable to any intercellular electrode configuration including, but not limited to, parallel plate, prismatic, folded, wound and/or bipolar configurations, any other suitable configurations or any combinations thereof. 
     In some embodiments, electrodes may contain porous structures or conductive foams to increase interface area, which may improve transport of compounds such as molecules (e.g., water) or ions (e.g., hydroxyl ions), or both. Electrochemical reactions may occur at or near interfaces between an active material, an electrolyte and an electronically conducting component. Increased interface area may allow increased charge or discharge rates for electrochemical devices. In some embodiments, the disclosed techniques, compositions, and arrangements may provide electrodes having porous structures or conductive foams in contact with suitable substrates. 
     The present disclosure includes methods, compositions, and arrangements for forming electronically conductive electrodes in contact with electronically conductive substrates. The electrode may be formed, for example, by coating a porous precursor material with electronically conductive material, or removing one or more components of a solid composite material, or both. In some embodiments, electronically conductive networks or foams may be formed directly on one or more surfaces of a substrate. 
     The invention will now be described in the context of  FIGS. 1-21 , which show illustrative embodiments. 
       FIG. 1  shows a schematic cross-sectional view of an illustrative structure of BPU  100  in accordance with some embodiments of the present invention. Exemplary BPU  100  may include a positive active material electrode layer  104 , an electronically conductive, impermeable substrate  106 , and a negative active material electrode layer  108 . Positive electrode layer  104  and negative electrode layer  108  are provided on opposite sides of substrate  106 . 
       FIG. 2  shows a schematic cross-sectional view of an illustrative structure of stack  200  of BPUs  100  of  FIG. 1  in accordance with some embodiments of the present invention. Multiple BPUs  202  may be arranged into stack configuration  200 . Within stack  200 , electrolyte layer  210  is provided between two adjacent BPUs, such that positive electrode layer  204  of one BPU is opposed to negative electrode layer  208  of an adjacent BPU, with electrolyte layer  210  positioned between the BPUs. A separator may be provided in one or more electrolyte layers  210  to electrically separate opposing positive and negative electrode layers. The separator allows ionic transfer between the adjacent electrode units for recombination, but may substantially prevent electronic transfer between the adjacent electrode units. As defined herein, a “cell” or “cell segment”  222  refers to the components included in substrate  206  and positive electrode layer  204  of a first BPU  202 , negative electrode layer  208  and substrate  206  of a second BPU  202  adjacent to the first BPU  202 , and electrolyte layer  210  between the first and second BPUs  202 . Each impermeable substrate  206  of each cell segment  222  may be shared by applicable adjacent cell segment  222 . 
       FIG. 3  shows a schematic cross-sectional view of an illustrative structure of MPU  300  in accordance with some embodiments of the present invention. Exemplary MPU  300  may include active material electrode layer  304  and electronically conductive, impermeable substrate  306 . Active material layer  304  may be any suitable positive or negative active material. 
       FIG. 4  shows a schematic cross-sectional view of an illustrative structure of a device containing two MPUs of  FIG. 3  in accordance with some embodiments of the present invention. Two MPUs  300  having a positive and negative active material, respectively, may be stacked to form electrochemical device  400 . Electrolyte layer  410  may be provided between two MPUs  300 , such that positive electrode layer  404  of one MPU  300  is opposed to negative electrode layer  408  of the other MPU  300 , with electrolyte layer  410  positioned between the MPUs. A separator may be provided electrolyte layers  410  to electrically separate opposing positive and negative electrode layers. Although not shown, in some embodiments two MPUs having positive and negative active material, respectively, may be added to stack  200 , along with suitable layers of electrolyte, to form a bi-polar battery. Bi-polar batteries and battery stacks are discussed in more detail in Ogg et al. U.S. patent application Ser. No. 11/417,489, Ogg et al. U.S. patent application Ser. No. 12/069,793, and West et al. U.S. patent application Ser. No. 12/258,854, all of which are hereby incorporated by reference herein in their entireties. 
     The substrates used to form electrode units (e.g., substrate  106 ,  206 ,  406 ,  416 ) may be formed of any suitable electronically conductive and impermeable or substantially impermeable material, including, but not limited to, a non-perforated metal foil, aluminum foil, stainless steel foil, cladding material including nickel and aluminum, cladding material including copper and aluminum, nickel plated steel, nickel plated copper, nickel plated aluminum, gold, silver, any other suitable electronically conductive and impermeable material or any suitable combinations thereof. In some embodiments, substrates may be formed of one or more suitable metals or combination of metals (e.g., alloys, solid solutions, plated metals). Each substrate may be made of two or more sheets of metal foils adhered to one another, in certain embodiments. The substrate of each BPU may typically be between 0.025 and 5 millimeters thick, while the substrate of each MPU may be between 0.025 and 30 millimeters thick and act as terminals or sub-terminals to the ESD, for example. Metalized foam, for example, may be combined with any suitable substrate material in a flat metal film or foil, for example, such that resistance between active materials of a cell segment may be reduced by expanding the conductive matrix throughout the electrode. 
     The positive electrode layers provided on these substrates to form the electrode units of the invention (e.g., positive electrode layers  104 ,  204  and  404 ) may be formed of any suitable active material, including, but not limited to, nickel hydroxide (Ni(OH) 2 ), zinc (Zn), any other suitable material, or combinations thereof, for example. The positive active material may be sintered and impregnated, coated with an aqueous binder and pressed, coated with an organic binder and pressed, or contained by any other suitable technique for containing the positive active material with other supporting chemicals in a conductive matrix. The positive electrode layer of the electrode unit may have particles, including, but not limited to, metal hydride (MH), palladium (Pd), silver (Ag), any other suitable material, or combinations thereof, infused in its matrix to reduce swelling, for example. This may increase cycle life, improve recombination, and reduce pressure within the cell segment, for example. These particles, such as MH, may also be in a bonding of the active material paste, such as Ni(OH) 2 , to improve the electrical conductivity within the electrode and to support recombination. 
     The negative electrode layers provided on these substrates to form the electrode units of the invention (e.g., negative electrode layers  108 ,  208 , and  408 ) may be formed of any suitable active material, including, but not limited to, MH, cadmium (Cd), manganese (Mn), Ag, any other suitable material, or combinations thereof, for example. The negative active material may be sintered, coated with an aqueous binder and pressed, coated with an organic binder and pressed, or contained by any other suitable technique for containing the negative active material with other supporting chemicals in a conductive matrix, for example. The negative electrode side may have chemicals including, but not limited to, Ni, Zn, Al, any other suitable material, or combinations thereof, infused within the negative electrode material matrix to stabilize the structure, reduce oxidation, and extend cycle life, for example. 
     Various suitable binders, including, but not limited to, organic carboxymethylcellulose (CMC), Creyton rubber, PTFE (Teflon), any other suitable material or any suitable combinations thereof, for example, may be mixed with or otherwise introduced to the active material to maintain contact between the active material and a substrate, solid-phase foam, any other suitable component, or any suitable combination thereof. Any suitable binders may be included in slurries or any other mixtures to increase adherence, cohesion or other suitable property or combination thereof. 
     The separator of each electrolyte layer of an ESD may be formed of any suitable material that electrically isolates its two adjacent electrode units while allowing ionic transfer between those electrode units. The separator may contain cellulose super absorbers to improve filling and act as an electrolyte reservoir to increase cycle life, wherein the separator may be made of a polyabsorb diaper material, for example. The separator may, thereby, release previously absorbed electrolyte when charge is applied to the ESD. In certain embodiments, the separator may be of a lower density and thicker than normal cells so that the inter-electrode spacing (IES) may start higher than normal and be continually reduced to maintain the capacity (or C-rate) of the ESD over its life as well as to extend the life of the ESD. 
     The separator may be a relatively thin material bonded to the surface of the active material on the electrode units to reduce shorting and improve recombination. This separator material may be sprayed on, coated on, pressed on, or combinations thereof, for example. The separator may have a recombination agent attached thereto. This agent may be infused within the structure of the separator (e.g., this may be done by physically trapping the agent in a wet process using a polyvinyl alcohol (PVA or PVOH) to bind the agent to the separator fibers, or the agent may be put therein by electro-deposition), or it may be layered on the surface by vapor deposition, for example. The separator may be made of any suitable material such as, for example, polypropylene, polyethylene, any other suitable material or any combinations thereof. The separator may include an agent that effectively supports recombination, including, but not limited to, lead (Pb), Ag, platinum (Pt), Pd, any other suitable material, or any suitable combinations thereof, for example. In some embodiments, an agent may be substantially insulated from (e.g., not contact) any electronically conductive component or material. For example, in some arrangements the agent may be positioned between sheets of the separator material such that the agent does not contact electronically conductive electrodes or substrates. While the separator may present a resistance if the substrates of a cell move toward each other, a separator may not be provided in certain embodiments of the invention that may utilize substrates stiff enough not to deflect. 
     The electrolyte of each electrolyte layer of an ESD may be formed of any suitable chemical compound that may ionize when dissolved or molten to produce an electrically conductive medium. The electrolyte may be a standard electrolyte of any suitable ESD, including, but not limited to, NiMH, for example. The electrolyte may contain additional chemicals, including, but not limited to, lithium hydroxide (LiOH), sodium hydroxide (NaOH), calcium hydroxide (CaOH), potassium hydroxide (KOH), any other suitable material, or combinations thereof, for example. The electrolyte may also contain additives to improve recombination, including, but not limited to, Ag(OH) 2 , for example. The electrolyte may also contain rubidium hydroxide (RbOH), for example, to improve low temperature performance. The electrolyte may be frozen within the separator and then thawed after the ESD is completely assembled. This may allow for particularly viscous electrolytes to be inserted into the electrode unit stack of the ESD before the gaskets have formed substantially fluid tight seals with the electrode units adjacent thereto. 
     Electrodes may contain an electronically conductive network or component. The electronically conductive network or component may reduce ohmic resistance and may allow increased interface area for electrochemical interactions. For example, in stack  400  shown in  FIG. 4 , the interface between electrolyte  410  and either positive electrode layer  404  or negative electrode layer  408  appears to be a planar, two dimensional surface. While a planar interface may be employed in some embodiments of energy storage devices, the electrode may also have porous structure. The porous structure may increase the interface area between electrode and electrolyte, which may increase the achievable charge or discharge rate. Active materials may be mixed with or applied to the conductive component or network to extend the interface over a greater surface area. Electrochemical interactions may occur at the interface between an active material, an electrolyte, and an electronically conductive material. 
     The electronically conductive substrate may be impermeable, preventing leakage or short circuiting. In some arrangements, one or more porous electrodes may be maintained in contact with an electronically conductive, non-porous substrate, as shown in  FIGS. 1-4 . This arrangement may allow for electronic transfer among an external circuit and the electrode. 
     As defined herein, “foam” shall mean solid-phase porous structures, or solid-phase networks having pores. Foams may contain voids that may be filled with gas or vacuum, or may be partially or entirely filled with gas, liquid, paste, particles, any other suitable material or any combination thereof. Porosity describes the fraction of foam volume occupied by voids. Foams may contain more than one solid component and may include composites of different materials. Open cell foams refer to foams in which the pores are interconnected. Open cell foams may allow for molecular transport of reactants, products, electrolytes, ions or other compounds throughout the foam and between the foam and the surrounding environment. Closed cell foams include pores that are sealed off from one another, effectively preventing transport of compounds throughout the foam. In the following discussion, the term foam will be understood to refer to open cell foams. 
       FIG. 5  shows a cubic section of illustrative foam  500  in accordance with some embodiments of the present invention. Solid phase component  502  may have a plurality of pores  504  interspersed throughout, thereby imparting porosity. Foam  500  may include a plurality of pores  506  having a relatively smaller spatial scale than pores  504 . Pores  506  may be characteristic of electronically conductive particles used to create foam  500 . Pores  504  may form a substantially interconnected network throughout the foam which may allow transport processes to occur. Pores  504  may have any suitable shape or size distribution. Pores  504  may have shape and size characteristics, for example, of a precursor material (e.g., polymer particles). The porosity of foam  500  may have any suitable value between 0 and 1, with larger porosity being associated with values nearer to 1. Larger values of porosity may correspond to larger values of surface area of the foam. In some embodiments, foam  500  may include one or more electronically conductive components (e.g., metals), one or more active materials (e.g., Ni(OH) 2 ), one or more binders, any other suitable materials or any combination thereof. 
       FIG. 6  shows an illustrative electrode structure  600  with a cutaway section in accordance with some embodiments of the present invention. Electrode structure  600  may include foam  602  and substrate  606 . Foam  602  and substrate  606  may share interface  610  as a plane of contact. Interface  610  represents the plane or path in space where at least two components, materials or any suitable combination thereof may meet in contact. The term “interface” as used herein shall refer to the substantially planar area of contact between a slurry and a substrate, a solid foam and a substrate, any two suitable components, any suitable component and a non-solid phase, or any other plane of contact between two distinct materials or components. Although shown as a planar disk geometry, electrode structure  600  may have any suitable shape, curvature (e.g., dome shaped), thickness (of either layer), relative size (among substrate and foam), relative thickness (among substrate and foam), any other property or any suitable combination thereof. Foam  602  and substrate  606  may have any suitable three dimensional shape, having a cross section that may be substantially circular, square, rectangular, triangular, hexagonal, elliptical, and any other suitable cross section, or combinations of shapes thereof. For example, in some embodiments, foam  602  may be a parallelepiped with square cross section and substrate  606  may be cylindrical. Foam  602  may include one or more electronically conductive components (e.g., metals), one or more active materials (e.g., Ni(OH) 2 ), one or more binders, any other suitable materials or any combination thereof. In some embodiments, active materials may be introduced to foam  602  following assembly or creation of structure  600 . 
     Some exemplary techniques for creating electronically conductive foams in contact with electronically conductive substrates will be discussed in the context of illustrative  FIGS. 7-10  in accordance with some embodiments of the present invention. 
       FIG. 7  shows illustrative flow diagram  700  for creating an electrode structure in accordance with some embodiments of the present invention. Process step  702  may include preparing a precursor material such as, for example, a polymer foam. In some embodiments, process step  702  may include making the polymer foam by use of, for example, blowing agents. It will be understood that any suitable technique or combination of techniques may be used to make a polymer foam. Process step  702  may include cleaning the polymer foam, etching the polymer foam, adjusting the size or shape of the polymer foam (e.g., cutting, grinding, splitting, drilling, machining), treating the polymer to accept an electrical charge, electrically charging the polymer, any other suitable preparation technique or combinations thereof. The polymer foam may be made of carbon based polymers including but not limited to polyurethane, polyethylene, polypropylene, polyvinyl chloride, polystyrene, nylon, polyester, acrylic, polycarbonate, any other suitable polymer or combination thereof, and any suitable additives. The polymer material may substantially maintain its shape characteristic of solid materials. The polymer material may undergo pyrolysis or carbonization at elevated temperature. 
     The polymer foam may be plated or otherwise coated with an electronically conductive material at process step  704 . The conductive coating may be any suitable type of metal (e.g., nickel), any other suitable electronically conductive material or any suitable combination thereof. Process step  804  may include electroplating, electro-less plating, chemical vapor deposition (CVD), physical vapor deposition (PVD), any other suitable plating or coating technique or any suitable combination thereof. In some embodiments, performance of processes  702  and  704  may result in a composite foam with an electronically conductive component or coating material. In some embodiments, active electrode materials may be added to the composite foam during process  704 . 
     The polymer precursor may be removed, as shown by process  706  in  FIG. 7 , following coating process  704 . Process  706  may include increasing the temperature of the coated foam while maintaining the foam in a reducing (e.g., forming gas, hydrogen, humidified hydrogen, diluted hydrogen) or substantially inert (e.g., diatomic nitrogen, argon, helium) environment. Increased temperature in the absence of substantial oxygen or oxygen containing compounds may induce thermal decomposition of organic material (e.g., pyrolysis, carbonization) of the polymer component. The polymer component may decompose into lighter compounds and vaporize, desorb, or otherwise leave the remaining components of the solid foam and enter the gas phase. The polymer may also decompose into solid, carbon-rich compounds or residues which may remain in the solid foam. Process  706  may include processes that cause some portion or substantially all of the polymer component to decompose, carbonize, enter the gas phase, or any combination thereof. Process  706  may remove substantially all of the polymer component and associated decomposition products. In some embodiments, process step  706  may include increasing the temperature to over 300 degrees Celsius in any suitable environment. Process step  706  may also include sintering or otherwise processing the remaining electronically conductive foam at the same or different elevated temperature, for example, to increase conductivity, connectivity, durability, other suitable property or any combination thereof, of the foam. 
     At step  708  shown in  FIG. 7 , an electronically conductive, impermeable substrate may be prepared. In some embodiments, the substrate may be larger than the metal foam in some dimension such as, for example, a bi-polar or mono-polar plate. In some embodiments, the substrate may be relatively smaller than the foam in some dimension such as, for example, embodiments where the substrate may be one or more tabs. The substrate may be formed of any suitable electronically conductive and impermeable material. The substrate may be a flat plate of any shape (e.g., disk), curved plate of any shape (e.g., dome), a thin foil, or any other suitable shape having any suitable cross-section. The substrate may include one or more components (e.g., composites). Process step  708  may include preparation steps such as cleaning the substrate, adjusting the surface finish of the substrate (e.g., polishing, roughening), etching the substrate, adjusting the size or shape of the substrate (e.g., cutting, grinding, splitting, drilling, machining), any other suitable preparation steps or any suitable combination thereof. 
     At process step  710  shown in  FIG. 7 , the electronically conductive substrate and the electronically conductive foam may be affixed together. The substrate and foam may be placed in contact, forming an interface between the foam and one or more surfaces of the substrate. In some embodiments, more than one foam may be placed in contact with a particular substrate or tab at process step  710 . In some embodiments, more than one substrate or tab may be placed in contact with a particular foam at process step  710 . The substrate and foam may be maintained in contact by mechanical clamping, bonding, spot welding, maintaining orientation by placing substrate and foam in a vertical manner such that gravity causes a nonzero normal force between the components, any other suitable adherence technique or any combination thereof. Process step  710  may include bonding, sintering, soldering, welding, any other suitable technique or any combination thereof to create a durable adherence between the one or more substrates and the one or more foams. Following process step  810 , the electrode structure may be ready for assembly in a device (e.g., ESD), addition of active materials, sintering, any other further processing steps or suitable combination thereof. 
       FIG. 8  shows illustrative flow diagram  800  for creating an electrode structure in accordance with some embodiments of the present invention. Process step  802  may include preparing a composite material which includes one or more components. The composite material may include components such as polymer particles, polymer foam, binders, electronically conductive particles (e.g., metal particles), carbon particles, active materials, coated materials, liquid (e.g., water, organic solvent), any other suitable components or any suitable combinations thereof. The composite material may be in the form of a slurry, paste, solid foam, solid particles, coated solid components (e.g., coated polymer foam), any other suitable form or combination thereof. Process step  802  may include mixing, blending, stirring, sonicating (i.e., applying sound waves to agitate particles), ball milling, grinding, sizing (e.g., sieving), drying, coating (e.g., electroplating, electro-less plating, CVD, PVD), sintering, any other suitable process to prepare the composite material or any suitable combination thereof. 
     At process step  804  shown in  FIG. 8 , the composite material may be placed in contact with one or more substrates. The composite material may be placed in one or more contiguous layers on one or more surfaces of the substrate. For example, composite material may be applied to both opposing surfaces of a flat substrate as separate layers (e.g., BPU). In some embodiments, different composite materials (e.g., different composition) may be placed in contact with a single substrate (e.g., BPU). In some embodiments, process step  804  may include applying a slurry composite material to the substrate, for example by doctor-blading, spin coating, screen printing, any other suitable slurry application technique or any suitable combination thereof. In some embodiments, process step  804  may include placing and maintaining a solid composite material in contact with the substrate including techniques such as, for example, mechanically clamping of a solid composite material to the substrate, bonding of a solid composite material to the substrate, pressing of a solid composite material to the substrate, maintaining orientation by placing one component on another in a vertical manner such that gravity causes a nonzero normal force between the components, any other suitable adherence technique or any suitable combination thereof. 
     At process step  806  shown in  FIG. 8 , one or more electronically nonconductive components of the composite material in contact with the substrate may be removed. Process step  806  may include increasing the temperature of the composite material and the substrate while maintaining the composite material and substrate in a reducing (e.g., forming gas, hydrogen, humidified hydrogen, diluted hydrogen) or substantially inert (e.g., diatomic nitrogen, argon, helium) environment. Process step  806  may also include chemical leaching, dissolving, any other suitable low-temperature (e.g., less than 100 degrees centigrade) technique or combination thereof. In some examples, process step  806  may correspond to process step  706  shown in  FIG. 7 . The resulting structure following process step  806  may include a porous electronically conducting solid in contact with a non-porous electronically conducting substrate. In some embodiments, the resulting structure following process step  806  may include active materials, binders, any other suitable materials or components, or any suitable combination thereof. Following process step  806 , the electrode structure may be ready for assembly in a device such as an ESD, addition of active materials, coating with an electronically conductive material, sintering, any other further processing or assembly steps or any suitable combinations thereof. 
       FIG. 9  shows illustrative flow diagram  900  for creating an electrode structure in accordance with some embodiments of the present invention. At process step  902  shown in  FIG. 9 , a precursor material, such as, for example, a polymer foam or a polymer slurry, may be prepared. The precursor material may be solid, liquid, or any suitable combination (e.g., slurry, colloid, suspension). In some embodiments, the precursor may be polymer slurry and may include polymer particles, one or more liquid agents (e.g., organic solvent, water, alcohol), one or more binders, active materials, carbon (e.g., graphite), any other suitable materials or any suitable combination thereof. The polymer particles may have any suitable shape or size distribution. The polymer particles may include any suitable type of polymer or combination of polymers. Process step  902  may include mixing, blending, stirring, sonicating, ball milling, grinding, sizing (e.g., sieving), drying, any other suitable preparation steps or any suitable combination thereof. In some embodiments, the precursor may be a polymer foam, created from any type of suitable polymer or combination thereof. In some embodiments, process step  902  may include cleaning the polymer foam, etching the polymer foam, adjusting the size or shape of the polymer foam (e.g., cutting, grinding, splitting, drilling, machining), treating the polymer to accept an electrical charge, electrically charging the polymer, any other suitable preparation technique or combinations thereof. 
     At process step  904  shown in  FIG. 9 , the precursor material of process step  902  may be applied to one or more surfaces of a suitable substrate. In some embodiments, process step  904  may include applying a slurry by doctor-blading, spin coating, screen printing, any other suitable slurry application technique or any suitable combination thereof. In some embodiments one or more molds of any suitable shape may be used to maintain the slurry of process step  902  in a particular shape. For example, a cylindrical mold in contact with the substrate may be used to maintain the slurry of process step  902  in a cylindrical shape while preventing the slurry of process step  902  from flowing or otherwise deforming. In some embodiments, the mold may be removed at any suitable process step following application of the slurry to the substrate. In some embodiments, process step  904  may include mechanically clamping or bonding a solid precursor material such as, for example, a polymer foam to the substrate. Any suitable adherence technique may be used to maintain contact between the solid precursor material and the substrate. 
     At process step  906  shown in  FIG. 9 , the precursor material in contact with the substrate may be further processed. In some embodiments, a precursor slurry may be dried (e.g., some fraction or all of one or more liquid components may be removed). Drying process  906  may impart rigidity to the residual components (e.g., remaining slurry components). In some embodiments, drying process  906  may allow for the residual components to maintain shape such that the mold, if used, may be removed. In some embodiments, drying process  906  may impart porosity to the collection of residual components. In some embodiments, drying process  906  may include heating, immersing the substrate and slurry in a prescribed gaseous environment (e.g., heated argon), any other suitable drying process or combination thereof. In some embodiments, process step  906  may include any suitable processing steps for preparing the precursor material for coating with an electronically conductive material. Process step  906  may be skipped in some embodiments, such as, for example, embodiments in which the precursor material is a solid. 
     At process step  908  shown in  FIG. 9 , the processed precursor materials in contact with the substrate may be coated with a suitable material. Coating process  908  may include electroplating, electro-less plating, CVD, PVD, any other suitable plating or coating technique or any suitable combination thereof. In some embodiments, active materials may be added to the porous structure as part of (e.g., before or after) coating process  908 . The resulting structure following process step  908  may include a porous electronically conducting network (or foam) and a precursor material component in contact with an impermeable electronically conducting substrate. 
     At process step  910  shown in  FIG. 9 , one or more components of the precursor material in contact with the substrate may be removed. Process step  910  may include increasing the temperature of the composite material and the substrate while maintaining the composite material and substrate in a reducing (e.g., forming gas, hydrogen, humidified hydrogen, diluted hydrogen) or substantially inert (e.g., diatomic nitrogen, argon, helium) environment. Process step  910  may also include chemical leaching, dissolving, any other suitable low-temperature (e.g., less than 100 degrees centigrade) technique or combination thereof. In some examples, process step  910  may correspond to process step  706  shown in  FIG. 7 . The resulting structure following process step  910  may include a porous electronically conducting network or foam in contact with an impermeable electronically conducting substrate. In some embodiments, the resulting structure following process step  910  may include active materials, binders, any other suitable materials or components, or any suitable combination thereof. Following process step  910 , the electrode structure may be ready for assembly in a device (e.g., ESD), addition of active materials, sintering, any other further processing steps or suitable combination thereof. 
       FIG. 10  shows illustrative flow diagram  1000  for creating an electrode structure in accordance with some embodiments of the present invention. At process step  1002  shown in  FIG. 10 , a slurry may be prepared including electronically conducting particles (e.g., metal particles) and any suitable combination of polymer particles (of any suitable size or shape), one or more liquid agents (e.g., organic solvent, water, alcohol), active materials, binders, carbon (e.g., graphite), or any other suitable materials. The one or more electronically nonconductive components may have any suitable shape or size distribution. In some embodiments, the electronically conducting particles and the electronically nonconductive particles may not necessarily be of the same size and shape. The electronically nonconductive particles may include any suitable type of polymer or combination of polymers. Process step  1002  may include mixing, blending, stirring, sonicating, ball milling, grinding, sizing (e.g., sieving), drying, any other suitable preparation process or any suitable combination thereof. 
     At process step  1004  shown in  FIG. 10 , the slurry of process step  1002  may be applied to one or more surfaces of a suitable substrate. Process step  1004  may include doctor-blading, spin coating, screen printing, any other suitable slurry application technique or any suitable combination thereof. In some embodiments one or more molds of any suitable shape may be used to maintain the slurry of process step  1002  in a particular shape on the substrate. For example, a rectangular prism mold in contact with the substrate may be used to maintain the slurry of process step  1002  in a rectangular prism shape while preventing the slurry of process step  1002  from flowing or otherwise deforming. 
     At process step  1006  shown in  FIG. 10 , the slurry of process step  1002  in contact with the substrate of process step  1004  may be dried (e.g., some fraction or all of one or more liquid components is removed). Drying process  1006  may impart rigidity to the residual components such as, for example, remaining slurry components. In some embodiments, drying process  1006  may allow for the residual components to maintain shape such that the mold, if used, may be removed. In some embodiments, drying process  906  may impart porosity to the collection of residual components. In some embodiments, drying process  906  may include heating, immersing the substrate of process step  1004  and slurry of process step  1002  in a prescribed gaseous environment (e.g., heated argon), any other suitable drying process or combination thereof. 
     At process step  1008  shown in  FIG. 10 , the electronically nonconductive component of the dried slurry residual components in contact with the substrate may be removed. Process step  1008  may include increasing the temperature of the residual components and the substrate of process step  1006  while maintaining the residual components and substrate in a reducing (e.g., forming gas, hydrogen, humidified hydrogen, diluted hydrogen) or substantially inert (e.g., diatomic nitrogen, argon, helium) environment. Process step  1008  may also include chemical leaching, dissolving, any other suitable low-temperature (e.g., less than 100 degrees centigrade) technique or combination thereof. In some examples, process step  1008  may correspond to process step  706  shown in  FIG. 7 . The resulting structure following process step  1008  may include an electronically conducting foam in contact with an impermeable electronically conducting substrate. In some embodiments, the resulting structure following process step  1008  may include active materials, binders, any other suitable materials or components, or any suitable combination thereof. Following process step  1008 , the electrode structure may be ready for assembly in a device (e.g., ESD), addition of active materials, sintering, coating with an electronically conductive material, any other further processing steps or suitable combination thereof. 
     It will be understood that the steps of flow diagrams  700 - 1000  are illustrative. Any of the steps of flow diagrams  700 - 1000  may be modified, omitted, rearranged, combined with other steps of flow diagrams  700 - 1000 , or supplemented with additional steps, without departing from the scope of the present invention. 
     An illustrative process for making an electrode structure in accordance with some embodiments of the present invention will be discussed further in the context of  FIGS. 11-15 . 
       FIG. 11  shows an illustrative side elevation view of precursor material  1102  in contact with substrate  1106  in accordance with some embodiments of the present invention. Shown in  FIG. 12  is an illustrative top plan view of the elements of  FIG. 11 , taken from line XII-XII of  FIG. 11  in accordance with some embodiments of the present invention. Precursor material  1102  is shown in contact with substrate  1106  at interface  1110 . Substrate  1106  and precursor material  1102  may have any suitable shape, cross-section shape, curvature, thickness (of either layer  1106  or  1102 ), relative size (among substrate and precursor material), relative thickness (among substrate and precursor material), any other property or any suitable combinations thereof. Precursor material  1102  may be any suitable material for forming an electrode structure, and may include polymer foams, composite materials (e.g., the composite material discussed in flow diagram  800  of  FIG. 8 ), dried polymer slurries (e.g., the dried slurry discussed in process step  906  of  FIG. 9 ), binders, any other suitable materials or any suitable combinations thereof. 
       FIG. 13  shows an illustrative partial cross-sectional view of interface region  1300  between precursor material  1302  and substrate  1306  in accordance with some embodiments of the present invention. Interface region  1300  shown in  FIG. 13  may correspond to or represent a schematic close-up view of interface  1110  shown in  FIG. 11 . In some embodiments, precursor material  1302  may include solid component  1304  and pore network  1308 . Pore network  1308  may include pores of any suitable size and/or shape. Although shown illustratively in  FIG. 13  as being made of particles having circular cross-section, precursor material  1302  may have any suitable cross-section profile that includes a solid phase and a pore network (e.g., any suitable porous solid). It will be understood that an illustrative, schematic two dimensional section representation of a three dimensional porous solid, such as that shown by  FIG. 13 , may not show some connectivity of the solid (or pores) but that connectivity may nonetheless exist. 
       FIG. 14  shows an illustrative partial cross-sectional view of interface region  1400  between precursor material  1302  and substrate  1306  of  FIG. 13 , coated with electronically conductive material  1412  in accordance with some embodiments of the present invention. Interface region  1400  shows the interface between precursor material  1302  and substrate  1306  of  FIG. 13  following a coating process (e.g., process step  908  of  FIG. 9 ) of interface region  1300 . Coating material  1412  may be applied to some or all of the surfaces of precursor material  1302 , forming coated precursor material  1402 . In some embodiments, the coating process may also include coating substrate  1306  with coating material  1410 . In some embodiments, coating material  1410  and coating material  1412  may be in contact, for example, allowing electronic conduction. Coated precursor material  1402  may include pore network  1408 , which may impart porosity. Pore network  1408  may correspond substantially with pore network  1308  prior to the coating process. 
       FIG. 15  shows an illustrative partial cross-sectional view of interface region  1500  between electronically conductive network  1502  and substrate  1306  of  FIG. 14  in accordance with some embodiments of the present invention. Interface region  1500  includes an illustrative interface between precursor material  1402  and substrate  1306  of  FIG. 14  following removal of one or more components of coated precursor material  1402 , such as, for example, described by process step  910  of  FIG. 9 . In some embodiments, electronically conductive network  1502  may substantially correspond to coating  1412 . In some embodiments, electronically conductive network  1502  may include pore network  1508  which may arise from pore network  1408 . In some embodiments, pore network  1514  may arise from removal of one or more suitable components of coated precursor material  1402 . Pore network  1514  may have properties (e.g., pore size, interconnectivity) that differ from pore network  1508 . In some embodiments, pore network  1508  and pore network  1514  may form a single pore network following removal of one or more components of coated precursor material  1402 . Although  FIG. 15  shows complete removal of precursor material  1302 , it will be understood that one or more components of precursor material  1302  may not be removed. It will also be understood that electronically conductive network  1502  may include one or more components, either electronically conducting or otherwise, remaining from precursor material  1302 . The electrode structure containing interface region  1500  may be plated or otherwise coated with an electronically conductive material. The electrode structure containing interface region  1500  may be sintered during or after removal of one or more suitable components of coated precursor material  1402 . 
     An illustrative process for making an electrode structure in accordance with some embodiments of the present invention will be discussed further in the context of  FIGS. 16-21 . 
       FIG. 16  shows an illustrative side elevation view of composite material  1602  in contact with substrate  1606  in accordance with some embodiments of the present invention. Shown in  FIG. 17  is an illustrative top plan view of the elements of  FIG. 16 , taken from line XVII-XVII of  FIG. 16  in accordance with some embodiments of the present invention. Composite material  1602  is shown in contact with substrate  1606  at interface  1610 . Substrate  1606  and composite material  1602  may have any suitable shape, cross-section shape, curvature, thickness (of either layer  1606  and  1602 ), relative size (among substrate and composite material), relative thickness (among substrate and composite material), any other property or any suitable combinations thereof. In some embodiments, composite material  1602  may include the dried slurry discussed above in process step  1006  of  FIG. 10 . Composite material  1602  may be any suitable material for forming an electrode structure and may include an electronically conductive material, and one or more of a polymer foam, electronically nonconductive particles (e.g., polymer particles), composite material (e.g., the composite material discussed in process step  802  of  FIG. 8 ), binder, any other suitable material, or any suitable combination thereof. 
       FIG. 18  shows an illustrative partial cross-sectional view of interface region  1800  between composite material  1802  and substrate  1806  in accordance with some embodiments of the present invention. Interface region  1800  shown in  FIG. 18  may correspond to or represent a schematic close-up view of interface  1610  shown in  FIG. 16 . In some embodiments, composite material  1802  may include solid components  1808  and  1810 , of which one or both may be electronically conductive, and pore network  1812 . Pore network  1812  may include pores of any suitable size and/or shape. Although shown illustratively in  FIG. 18  as being made of particles having circular cross-section, composite material  1802  may have any suitable cross-section profile including a solid phase and a pore network (e.g., any suitable porous solid). Composite material  1802  may include any number of components greater than one, in any suitable combination. It will be understood that an illustrative, schematic two dimensional section representation of a three dimensional porous solid, such as that shown by  FIG. 18 , may not show some connectivity of the solid (or pores) but that connectivity may nonetheless exist. 
       FIG. 19  shows an illustrative partial cross-sectional view of interface region  1900  between electronically conductive foam  1902  and substrate  1806  in accordance with some embodiments of the present invention. In some embodiments, interface region  1900  shows an interface between composite material  1802  and substrate  1806  of  FIG. 18  following removal of one or more components of composite material  1802 , such as, for example, described by process step  806  of  FIG. 8  or step  1008  of  FIG. 10 . In some embodiments, electronically conductive network  1902  may correspond to one or more components of composite material  1802 . In some embodiments, electronically conductive network  1902  may include pore network  1912 . In some embodiments, pore network  1912  may arise in part from removal of one or more components of composite material  1802 . It will be understood that one or more components of composite material  1802  may not be removed. It will also be understood that electronically conductive network  1902  may include one or more components, either electronically conducting or otherwise, remaining from composite material  1802 . In some embodiments, the electrode structure containing interface region  1900  may be sintered during or after removal of one or more suitable components of composite material  1802 . 
       FIG. 20  shows an illustrative partial cross-sectional view of interface region  2000  between composite material  2002  and substrate  2006  in accordance with some embodiments of the present invention. Interface region  2000  shown in  FIG. 20  may correspond to or represent a schematic close-up view of interface  1610  shown in  FIG. 16 . In some embodiments, composite material  2002  may include solid components  2008  and  2010 , of which one or both may be electronically conductive, and pore network  2012 . Solid components  2008  and  2010  may have any suitable size distributions and/or shape distributions. In some embodiments, solid components  2008  and  2010  may have different size distributions and/or shape distributions. Pore network  2012  may include pores of any suitable size and/or shape. Although shown illustratively in  FIG. 20  as being made of particles having circular cross-section, composite material  2002  may have any suitable cross-section profile including a solid phase and a pore network (e.g., any suitable porous solid). Composite material  2002  may include any number of components greater than one, in any suitable combination. It will be understood that an illustrative, schematic two dimensional section representation of a three dimensional porous solid, such as that shown by  FIG. 20 , may not show some connectivity of the solid (or pores) but that connectivity may nonetheless exist. 
       FIG. 21  shows an illustrative partial cross-sectional view of interface region  2100  between electronically conductive foam  2102  and substrate  2006  in accordance with some embodiments of the present invention. Interface region  2100  shows an illustrative interface between composite material  2002  and substrate  2006  of  FIG. 21  following removal of one or more components of composite material  2002 , such as, for example, described by process step  806  of  FIG. 8  or step  1008  of  FIG. 10 . In some embodiments, electronically conductive foam  2102  may correspond to one or more components of composite material  2002 . In some embodiments, electronically conductive foam  2102  may include pore network  2112  and pore network  2114 . In some embodiments, pore network  2112  may correspond to pore network  2012 . In some embodiments, pore network  2114  may arise in part from removal of one or more components of composite material  2002 . In some embodiments, pore network  2112  and  2114  may form a single pore network. It will be understood that one or more components of composite material  2002  may not be removed. It will also be understood that electronically conductive foam  2102  may include one or more components, either electronically conducting or otherwise, remaining from composite material  2002 . 
     It will be understood that the foregoing is only illustrative of the principles of the invention, and that various modifications may be made by those skilled in the art without departing from the scope and spirit of the invention. It will also be understood that various directional and orientational terms such as “horizontal” and “vertical,” “top” and “bottom” and “side,” “length” and “width” and “height” and “thickness,” “inner” and “outer,” “internal” and “external,” and the like are used herein only for convenience, and that no fixed or absolute directional or orientational limitations are intended by the use of these words. For example, the devices of this invention, as well as their individual components, may have any desired orientation. If reoriented, different directional or orientational terms may need to be used in their description, but that will not alter their fundamental nature as within the scope and spirit of this invention. Those skilled in the art will appreciate that the invention may be practiced by other than the described embodiments, which are presented for purposes of illustration rather than of limitation, and the invention is limited only by the claims that follow.