POROUS SILICON MEMBRANE MATERIAL, MANUFACTURE THEREOF AND ELECTRONIC DEVICES INCORPORATING THE SAME
20230411642 ยท 2023-12-21
Assignee
Inventors
- Ryan G. Redford (Irvine, CA, US)
- Daniel Carothers (Lucas, TX, US)
- Janet M. Roveda (Tucson, AZ, US)
- Joley D. Michaelson (Tucson, AZ, US)
Cpc classification
H01M8/188
ELECTRICITY
International classification
H01M8/18
ELECTRICITY
Abstract
A redox flow battery includes positive and negative electrodes respectfully located in half-cells separated by a porous silicon wafer separator formed by MEMS Technology. The first half cell and the second half cell each preferably include a plurality of dividers or barriers configured to create flow channels which introduce turbulence ensuring the electrolytes are changing or mixing at surfaces of the electrodes and the membrane. Also disclosed is a solar energy generation and storage system which includes a photovoltaic cell and an electrochemical energy storage battery which share a common electrode. Also disclosed is a membrane-less redox flow electrical energy storage battery, having a cathode electrode, an anode electrode formed of a porous silicon substrate in which surfaces of the pores of the porous silicon substrate are coated at least in part with a metal silicide, and an electrolyte.
Claims
1. A redox flow battery, comprising: a single cell including an anode and cathode, wherein the anode and the cathode are positioned on opposite sides of the single cell; a single electrolyte reservoir connected to the single cell by at least one inlet tube and at least one outlet tube, such that an electrolyte is configured to flow from the single electrolyte reservoir through the at least one inlet tube into the single cell and then back to the single electrolyte reservoir through the at least one outlet tube; and a porous separator element positioned directly adjacent to an interior side of the cathode within the single cell; wherein the porous separator element includes at least one porous silicon wafer.
2. The redox flow battery of claim 1, wherein a surface of a plurality of pores of the at least one porous silicon wafer is coated with at least one metal silicide.
3. The redox flow battery of claim 2, wherein the at least one metal silicide includes a titanium silicide, a tungsten silicide, a nickel silicide, a cobalt silicide, a platinum silicide, and/or a palladium silicide.
4. The redox flow battery of claim 1, wherein each of a plurality of pores of the at least one porous silicon wafer has a depth to cross-section aspect ratio less or equal to 50:1.
5. The redox flow battery of claim 1, wherein the single cell does not include an ion-selective membrane between the anode and the cathode.
6. The redox flow battery of claim 1, wherein the redox flow battery shares the anode and/or the cathode with at least one other redox flow battery in a redox flow battery stack.
7. The redox flow battery of claim 1, wherein the anode is thicker than the cathode.
8. The redox flow battery of claim 1, wherein the electrolyte is a zinc-bromide electrolyte, an iron-chloride electrolyte, an iron-chromium electrolyte, a zinc-nickel electrolyte, a zinc-iodide electrolyte, or a zinc-iron electrolyte.
9. A redox flow battery, comprising: a single cell including an anode and cathode, wherein the anode and the cathode are positioned on opposite sides of the single cell; a single electrolyte reservoir connected to the single cell by at least one inlet tube and at least one outlet tube, such that an electrolyte is configured to flow from the single electrolyte reservoir through the at least one inlet tube into the single cell and then back to the single electrolyte reservoir through the at least one outlet tube; and a porous separator element positioned directly adjacent to an interior side of the cathode within the single cell; wherein the single cell does not include an ion-selective membrane between the anode and the cathode.
10. The redox flow battery of claim 9, wherein a surface of a plurality of pores of the porous separator element is coated with at least one metal silicide.
11. The redox flow battery of claim 10, wherein the at least one metal silicide includes a titanium silicide, a tungsten silicide, a nickel silicide, a cobalt silicide, a platinum silicide, and/or a palladium silicide.
12. The redox flow battery of claim 9, wherein each of a plurality of pores of the porous separator element has a depth to cross-section aspect ratio less or equal to 50:1.
13. The redox flow battery of claim 9, wherein the redox flow battery shares the anode and/or the cathode with at least one other redox flow battery in a redox flow battery stack.
14. The redox flow battery of claim 9, wherein a direction of flow of electrolyte within the single cell is substantially orthogonal to a central axis between the anode and the cathode.
15. The redox flow battery of claim 9, wherein the electrolyte is a zinc-bromide electrolyte, an iron-chloride electrolyte, an iron-chromium electrolyte, a zinc-nickel electrolyte, a zinc-iodide electrolyte, or a zinc-iron electrolyte.
16. The redox flow battery of claim 9, wherein each of a plurality of pores of the porous separator element are substantially cylindrical through holes.
17. A redox flow battery, comprising: a single cell including an anode and cathode, wherein the anode and the cathode are positioned on opposite sides of the single cell; a single electrolyte reservoir connected to the single cell by at least one inlet tube and at least one outlet tube, such that an electrolyte is configured to flow from the single electrolyte reservoir through the at least one inlet tube into the single cell and then back to the single electrolyte reservoir through the at least one outlet tube; and a porous separator element positioned directly adjacent to an interior side of the cathode within the single cell; wherein a surface of a plurality of pores of the porous separator element is coated with at least one metal silicide; and wherein each of the plurality of pores of the porous separator element has a depth to cross-section aspect ratio less or equal to 50:1.
18. The redox flow battery of claim 17, wherein the at least one metal silicide includes a titanium silicide, a tungsten silicide, a nickel silicide, a cobalt silicide, a platinum silicide, and/or a palladium silicide.
19. The redox flow battery of claim 17, wherein the single cell does not include an ion-selective membrane between the anode and the cathode.
20. The redox flow battery of claim 17, wherein the redox flow battery shares the anode and/or the cathode with at least one other redox flow battery in a redox flow battery stack.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
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DETAILED DESCRIPTION
[0080] The present invention is generally directed to a novel porous silicon material for use in redox flow batteries, and more specifically to membrane-less flow batteries including a silicon wafer separator.
[0081] In one embodiment, the present invention is directed to a redox flow battery, including a single cell including an anode and cathode, wherein the anode and the cathode are positioned on opposite sides of the single cell, a single electrolyte reservoir connected to the single cell by at least one inlet tube and at least one outlet tube, such that an electrolyte is configured to flow from the single electrolyte reservoir through the at least one inlet tube into the single cell and then back to the single electrolyte reservoir through the at least one outlet tube, and a porous separator element positioned directly adjacent to an interior side of the cathode within the single cell, wherein the porous separator element includes at least one porous silicon wafer.
[0082] In another embodiment, the present invention directed to a redox flow battery, including a single cell including an anode and cathode, wherein the anode and the cathode are positioned on opposite sides of the single cell, a single electrolyte reservoir connected to the single cell by at least one inlet tube and at least one outlet tube, such that an electrolyte is configured to flow from the single electrolyte reservoir through the at least one inlet tube into the single cell and then back to the single electrolyte reservoir through the at least one outlet tube, and a porous separator element positioned directly adjacent to an interior side of the cathode within the single cell, wherein the single cell does not include an ion-selective membrane between the anode and the cathode.
[0083] In yet another embodiment, the present invention is directed to a redox flow battery, including a single cell including an anode and cathode, wherein the anode and the cathode are positioned on opposite sides of the single cell, a single electrolyte reservoir connected to the single cell by at least one inlet tube and at least one outlet tube, such that an electrolyte is configured to flow from the single electrolyte reservoir through the at least one inlet tube into the single cell and then back to the single electrolyte reservoir through the at least one outlet tube, and a porous separator element positioned directly adjacent to an interior side of the cathode within the single cell, wherein a surface of a plurality of pores of the porous separator element is coated with at least one metal silicide, and wherein each of the plurality of pores of the porous separator element has a depth to cross-section aspect ratio less or equal to 50:1.
[0084] Referring now to the drawings in general, the illustrations are for the purpose of describing one or more preferred embodiments of the invention and are not intended to limit the invention thereto.
[0085] The present disclosure relates to novel porous silicon material, the manufacture thereof and the use thereof. The disclosure has utility in connection with manufacture of porous silicon material for use as a membrane in redox flow energy storage batteries, and to solar photovoltaic (PV) cells having integrated electrical energy storage batteries, and will be described in connection with such utility, although other utilities are contemplated.
[0086] Redox flow electrical energy batteries exhibit high energy conversion efficiency, flexible design, high energy storage capacity, flexible location, deep discharge, high safety, environmental friendliness and low maintenance cost compared with other types of energy storage systems and are being adopted for various uses including renewable energy storage for wind energy, solar energy and tidal energy installations, emergency power supply systems, standby power supply systems, and load leveling for conventional power supply systems.
[0087] A membrane/separator, being one of the key elements of a redox flow battery, is employed to prevent cross mixing of the positive and negative electrolytes, and for completing the current circuit by transferring protons. Proton conductivity, chemical stability and ion selectivity of the membrane directly affect the electrochemical performance and useful lifetime of a redox flow battery. Therefore, the membrane should possess several properties, including low active species permeability (high ion selectivity), low membrane area resistance (high ion conductivity), high physicochemical stability and low cost. The membranes most commonly used in redox flow batteries are formed of perfluorosulfonic acid polymers such as DUPONT NAFION owing to their high proton conductivity and chemical stability. However, NAFION membranes are expensive, and exhibit relatively low ion selectivity when used in redox flow batteries, which limits commercialization of redox flow batteries. Thus, there exists a need for better membranes with high ion selectivity, high physicochemical stability, and low cost.
[0088] The terms top and bottom and left and right are employed in a relative, and not an absolute sense to facilitate description and to describe relative locations of elements. The terms are used interchangeably.
[0089] The present disclosure in one aspect provides a method for forming novel porous silicon wafer material and the use thereof as membranes in batteries such as redox flow batteries, and other electronic devices. More particularly, the present disclosure provides a method for forming novel porous silicon wafers for use as membrane separators for redox flow batteries using MEMS (microelectromechanical systems) technology. In accordance with the present disclosure, a silicon wafer is selectively masked using resist deposition and photolithography techniques and selected portions of the wafer are subjected to electrochemical etching to form pores or channels extending through the silicon wafer. Preferably, the channels or pores are substantially cylindrical in shape, and have a relatively high, (e.g., 50:1) depth to cross section dimension aspect ratios.
[0090] In one embodiment, pore size, membrane selectivity and ion conductivity are tuned by inorganic doping of the silicon wafer to enhance metal ion rejection and proton conductivity, for when the membrane is used as a separation barrier in a redox flow battery.
[0091] The disclosure also provides redox flow batteries in which the novel porous silicon wafers are used as membrane materials.
[0092] More particularly, the present disclosure also provides a redox flow battery comprising a separator membrane element formed of a porous silicon wafer.
[0093] In one embodiment, pores of the porous silicon wafer are substantially cylindrical through holes. Preferably, the cylindrical through holes have a depth to cross section dimension aspect ratio of 50:1.
[0094] In another embodiment surfaces of pores of the porous silicon wafer are treated to enhance surface ion conductivity. For example, in one embodiment, the surfaces of the pores are oxidized, or the surfaces are modified by deposition of a metal.
[0095] In yet another embodiment, the porous silicon wafer is doped to enhance metal ion rejection and proton conductivity.
[0096] The present disclosure also provides a redox flow battery comprising an electrical assembly comprising positive and negative electrodes respectfully located in half-cells separated by a separator, wherein the separator comprises a porous silicon wafer, and including an electrolyte in the half cells.
[0097] In one embodiment of the battery, pores of the porous silicon wafer preferably have a depth to cross section dimension aspect ratio of 50:1.
[0098] In one embodiment of the battery the electrolyte is selected from the group consisting of iron-ligand electrolyte, an iron-chloride electrolyte, and iron-chromium electrolyte, a vanadium-based electrolyte, a zinc-based electrolyte, a sulfuric acid-based electrolyte, a hydrochloric acid electrolyte, a zinc-bromide electrolyte, a zinc-iodide electrolyte, a zinc-cerium electrolyte, a zinc-nickel electrolyte, and a zinc-iron electrolyte such as zinc-ferricyanide.
[0099] In a preferred embodiment of the battery surfaces of the pores are treated to enhance surface ion conductivity. For example, the surfaces of the pores are oxidized, or the surfaces are modified by deposition of a metal.
[0100] In another embodiment of the battery, the porous silicon wafer is doped to enhance metal ion rejection and proton conductivity.
[0101] In still yet another aspect of the disclosure, the redox flow battery system further comprises positive and negative current collectors respectfully located in the half-cells. In a particularly preferred embodiment of the disclosure the paired half-cells are arranged in a stack, and at least one of adjacent half-cells in the stack share a common electrode.
[0102] In yet another embodiment of the disclosure the separator member comprises a shaped porous silicon wafer having a porous middle section of a first thickness, and solid silicon end sections of a second thickness greater than the middle section.
[0103] In still yet another embodiment of the disclosure the redox flow battery system further comprises an electrolyte in the half-cells. Preferably the electrolyte is selected from the group consisting of an iron-ligand electrolyte, an iron-chloride electrolyte, and iron-chromium electrolyte, a vanadium-based electrolyte, a sulfuric acid-based electrolyte, a hydrochloric acid electrolyte, a zinc-bromide electrolyte, a zinc-iodide electrolyte, a zinc-cerium electrolyte, a zinc-nickel electrolyte, and a zinc-iron electrolyte, such as zinc-ferricyanide.
[0104] The present disclosure also provides a method of forming a separator for use in a redox flow battery, comprising providing a silicon wafer; and etching through holes extending through at least a portion of the wafers, wherein the through holes preferably have a depth to cross section dimension aspect ratio of 50:1.
[0105] In one embodiment of the method surf aces of the pores are treated to enhance surface ion conductivity. For example, the surfaces of the pores are oxidized, or the surfaces are modified by deposition of a metal.
[0106] In yet another embodiment of the method the silicon wafer is doped to enhance metal ion rejection and proton conductivity.
[0107] In yet another aspect the present disclosure integrates energy storage battery elements with photovoltaic cell elements whereby to permit direct charging of the battery, thereby eliminating the need for complex electrical distribution and conditioning circuits employed with conventional photovoltaic cells. More particularly, redox flow cell battery elements are integrated with a photovoltaic cell. In accordance with a preferred embodiment of this aspect of the present disclosure, the redox flow battery incorporates a porous silicon membrane formed using MEMS technology. However, the disclosure is not limited to the use of redox flow batteries incorporating porous silicon membranes, and other redox flow battery systems are also advantageously able to be used.
[0108] More particularly, the present disclosure in one aspect provides a solar energy generation and storage system comprising a photovoltaic cell and an electrochemical energy storage battery, wherein the photovoltaic cell and the electrochemical storage battery share a common electrode.
[0109] In one preferred aspect, the electrochemical energy storage battery comprises a redox flow battery. In such embodiment, the redox flow battery preferably incorporates a porous silicon membrane or a membrane of a perfluorosulfonic acid polymer. In one embodiment, the photovoltaic cell comprises a silicon solar cell or a gallium arsenide cell; a monocrystalline silicon solar energy cell; a monocrystalline silicon body of P-type conductivity which has been treated to provide a zone of N-type conductivity or a monocrystalline silicon body of N-type conductivity which has been treated to provide a zone of P-type conductivity; a polycrystalline silicon cell; a thin-film solar cell, preferably formed of a semi-conductor material selected from the group consisting of amorphous thin-film silicon, cadmium telluride and copper indium gallium diselenide; or, a multi junction solar cell, preferably comprising a top cell formed of, e.g., indium gallium phosphide, a middle cell formed of, e.g., indium gallium arsenide, and a bottom cell formed of, e.g., germanium.
[0110] In yet another aspect, the process disclosure provides a process and apparatus for providing a superior uniformly etched silicon wafer for use in a redox flow battery as above described, and in forming an integrated energy storage battery and photovoltaic cell as above described.
[0111] More particularly, in accordance with one embodiment of our disclosure, a thin interface metal layer is deposited on one side, i.e., the back side of a silicon wafer. The silicon wafer metal layer assembly is loaded into an etching fixture, an electrical charge applied to the metal layer deposited on the back side surface of the wafer, and an etchant flowed across the front, i.e., exposed side surface of the wafer. The charge is applied between metal layer on the back side surface of the wafer and the etchant. Also provided are etching fixtures and a system for etching silicon wafers.
[0112] The present disclosure also provides improvement over redox flow electrical energy battery constructions of the prior art by providing a plurality of dividers or barriers that divide and/or direct the electrolyte flow in the half cells to add turbulence to the flowing electrolyte and increase mixing of the electrolyte adjacent the electrode surfaces.
[0113] In one aspect the disclosure provides redox flow electrical energy storage battery comprising a first half cell and a second half cell separated by a porous membrane; an anode and an analyte electrolyte flowing through the first half cell; and a cathode electrode and a catholyte electrolyte flowing through the second half cell; wherein the first half cell and the second half cell each include a plurality of dividers or barriers which dividers or barriers are configured to create flow channels running essentially the length of the half cells and which to introduce turbulence insuring that the electrolytes are changing or mixing at surf aces of the electrodes and the membrane.
[0114] In one preferred aspect the dividers or barriers are configured essentially parallel to one another. In another aspect the dividers or barriers are configured as interdigitized fingers. In yet another aspect, the battery comprises a plurality of half cells arranged parallel to one another. In still yet another aspect, the battery comprises a plurality of half cells arranged in series, with an outlet of a first half cell being connected to an inlet of an adjacent second half cell.
[0115] The present disclosure also provides improvements over conventional dual electrode redox flow electrical energy storage battery systems by providing a membrane-less redox flow battery system. The membrane-less flow battery in accordance with the present disclosure includes a high surface area porous silicon electrode. More particularly, in accordance with the present disclosure, silicon substrate material is subjected to an electrochemical etching to form interconnected nano structures or through holes or pores through the silicon substrate material. Surfaces of the porous silicon substrate material are then treated to enhance surface ion conductivity by deposition of a metal, preferably, titanium metal to form titanium silicide on surfaces of the pores of the silicon substrate material. In one embodiment, the titanium metal is deposited on the porous silicon substrate material using various deposition techniques including but not limited to chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), thermal CVD, electroplating, electroless plating, and/or solution deposition techniques, which are given as exemplary, and the metal-coating on the porous silicon substrate material is converted to the corresponding metal silicide by heating. Tungsten, nickel, cobalt, platinum, and palladium metals also are able to be deposited on the porous silicon substrate material to form the corresponding metal silicide coated electrodes. Another possibility is to deposit amorphous carbon from CH3.
[0116] The resulting substrate is a porous silicon substrate which includes a metallurgically bonded surface layer of metal silicide on the walls of the porous structure, which advantageously are able to be used as an electrode in a membrane-free redox flow energy storage battery as will be described below.
[0117] The present disclosure also provides an electrode for use in a redox flow electrical energy storage battery, wherein the electrode comprises a substrate formed of porous silicon in which surface areas of the pores are coated at least in part with a metal silicide. In one embodiment, the silicon substrate comprises monocrystalline silicon, polycrystalline silicon, or amorphous silicon, the pores preferably have a depth to cross section dimension aspect ratio of 50:1, and the metal silicide preferably is selected from the group consisting of titanium silicide and tungsten silicide, although other metal silicides are also able to be used as noted above.
[0118] The system of the present invention contemplates both redox flow batteries having membranes and having no membranes. With regard to the membrane-less embodiments of the present invention, one of ordinary skill in the art will understand that the term separator or porous separator does not refer to an equivalent element to a membrane that splits the battery into two half cells, with electrolyte flowing on both sides of the separator. Instead, the porous separator lines an interior face of the cathode and provides ion selectivity (e.g., via coating or other surface treatment of the pores of the separator) to restrict flow access to the cathode for improved performance. In this case, all electrolyte flows on one side of the separator, while the other side of the separator directly abuts the cathode. The membrane-less embodiment of the present invention is therefore distinct from, for example, U.S. Pat. No. 9,627,670, both because '670 describes a traditional battery, not a redox flow battery, and because the '670 patent describes a membrane-based system divided into two half cells. Other patents may discuss the use of porous plates or elements in redox flow batteries, such as U.S. Patent Pub. No. 2022/0158214, but these only discuss the use of such elements as membrane separators between two half cells of the battery, not in the context of elements in a membrane-less system.
[0119] Modes for carrying out the present disclosure will be described in detail below, with reference to the drawings.
First Embodiment
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[0121] Referring to
[0122] Next, in step 102, the front side mask 14a is patterned with a photoresist 16 which is spun and patterned on the front side of the wafer, and a polymer material 18 is spun onto the back side of the wafer. Pattern 16 defines the hard mask etch which will in turn be used for a deep anisotropic etch. Alignment elements (not shown) for a subsequent backside etch are also formed at this step 102.
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[0124] As shown in
[0125] After the back side pad structures are patterned at step 108, a dry etch (plasma) is used in step 110 to etch the dielectrics while controlling the edge shape. This is shown in
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[0128] The next step 116 is to etch the silicon to thin it locally to create regions 26 for defining thinner silicon regions for formation of the porous silicon material in a subsequent step 118 as will be described below. This step preferably is conducted using a simple open bath etch, although a tool etch is able to be used.
[0129] The thinned or contoured silicon wafer from step 116, is then subjected to an electrochemical etching by applying uniform electrical field across the wafer while immersing the wafer in an etchant such a Dimethylformamide (DMF)/Dimethylsulfoxide (DMSO)/HF etchant in an electrochemical immersion cell, in an electrochemical etching step 118, to form through holes or pores 28 through the thinned section 26 as shown in
[0130] The resulting pores have a high aspect ratio of length to cross-sectional diameter typically a depth to cross section dimension aspect ratio of 50:1. The resulting structure, shown in
Second Embodiment
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[0132] However, referring to
[0133] As shown in
[0134] After porous silicon formation, step 222, the front side is protected by spinning a photoresist 46 on it in step 224 (see
Third Embodiment
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[0136] The porous silicon wafers as produced above are assembled into a redox flow battery as will be described below.
[0137] Battery Formation
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[0139] In some embodiments, multiple redox flow cells are electrically coupled (e.g., stacked) either in series to achieve higher voltage or in parallel in order to achieve higher current to form stack 801. The stacked cells are collectively referred to as a battery stack and flow cell battery refer to a single cell or battery stack. As shown in
[0140] When filled with electrolyte, half-cell 310 of redox flow cell 800 contains anolyte 826 and the other half-cell 808 contains catholyte 824, the anolyte and catholyte being collectively referred to as electrolytes. Reactant electrolytes are able to be stored in separate reservoirs and dispensed into half-cells 808 and 810 via conduits coupled to cell inlet/outlet (I/O) pipes 812, 814 and 816, 818 respectively. In some embodiments, an external pumping system is used to transport the electrolytes to and from the redox flow cell. Electrolyte 824 flows into half-cell 808 through inlet pipe 812 and out through outlet pipe 814, while electrolyte 826 flows into half-cell 810 through inlet pipe 816 and out of half-cell 810 through outlet pipe 818.
[0141] At least one electrode 802 and 804 in each half-cell 808 and 810 provides a surface on which the redox reaction takes place and from which charge is transferred. Suitable materials for preparing electrodes 802 and 804 generally include those known to persons of ordinary skill in the art. Redox flow cell 800 operates by changing the oxidation state of its constituents during charging or discharging. The two half-cells 808 and 810 are connected in series by the conductive electrolytes, one for anodic reaction and the other for cathodic reaction. In operation (e.g., during charge or discharge), electrolytes 826 and 824 are flowed through half-cells 308 and 810 through inlet/outlet pipes 812, 814 and 816, 818 respectively as the redox reaction takes place.
[0142] Positive ions or negative ions pass through permeable membrane 806, which separates the two half-cells 808 and 810, as the redox flow cell system 800 charges or discharges. Reactant electrolytes are flowed through half-cells 808 and 810, as necessary, in a controlled manner to supply electrical power or be charged by load/source 820.
[0143] A feature and advantage of the present disclosure derives from the size and aspect ratio of the pores or through holes of the membrane. Within the pores, which are treated as an array of regular cylindrical ion channels, the ionic current is described as:
I.sub.ion=(KA+K.sup.p)E
[0144] where E is the tangential electric field parallel to the channel walls, K is the bulk conductivity, K.sup. is the surface conductivity, A is the round pore channel cross sectional area and p is the cross-sectional perimeter. The ionic current has a bulk convective component which is proportional to ion mobility and electrolyte concentration n. In specific embodiments, the length of the pore will be 50 times or more greater than the diameter of the pores. As such, the second term in the above equation will dominate in most cases as applied. The resulting material is able to be modified for use in redox flow batteries to enhance the surface ion conductivity to allow optimization of the ion current. The ability to also tune the geometry of the porous silicon channels allow control of the separation of electrolytes or other fluids while providing a path for ions to flow in the presence of an electric field. By comparison to standard flow battery configurations the separation of electrodes is reduced from millimeters to microns. The surfaces of these channels are also able to be modified to enhance the transport of specific cation or anion species, and control the separation of fluids having a wide range of viscosities. These modifications include everything from the oxidation of the surface to create deep silicon dioxide surfaces, or through various vapor-based deposition methods to add a metal layer, e.g., tungsten, nickel, platinum, or palladium, which are given as exemplary, to modify the ion mobility.
[0145] By comparison to prior art approaches, such as membranes formed of NAFION, the high porosity of porous silicon wafer and very large surface-to-volume ratio ensures high proton/ion conductivity, comparable with or in excess of that of polymer membranes employing the standard NAFION materials, and at a fraction of the cost.
[0146] The ability to control the transport behavior of ions is another important capability as it allows the shaped porous silicon wafer to be employed in a wide range of applications, from fuel cell and flow battery to chemical synthesis and separation.
[0147] As noted supra, our process also allows for functionalization of the membrane. In one embodiment, the fluid interfaces on each side of the membrane are coated with catalytic materials to enhance and control the interaction with the electrolyte chemistry. In one embodiment, metal deposition technologies are used to form electrodes at the interfaces of the porous silicon material, further reducing separation and increasing field density, and in the case of fuel cells and flow batteries enhancing the overall efficiency of the ion transport (e.g., stronger field; reduced ion travel length.)
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TABLE-US-00001 TABLE I Positive/ Negative/ Discharge Anode/Redox Cathode/Plating Energy Density Description electrode reaction electrode reaction (Watt*hour/liter) Iron-ligand 2Fe.sup.2+ Fe.sup.3+ + 2e.sup. Fe.sup.2+ + 2e.sup. Fe.sup.0 3/30 chemistry (+0.77 V) (0.44 V) redox flow batteries
[0150] In some embodiments, multiple redox flow cells are electrically coupled (e.g., stacked) either in series (
[0151] When filled with electrolyte, half-cells 1304A, 1306A, 1308A contain anolyte 1326 and the other half-cells 1304B, 1306B, 1308B contain catholyte 1324, the anolyte and catholyte being collectively referred to as electrolytes. In one embodiment, reactant electrolytes are stored in separate reservoirs 1342, 1344 and flowed into half-cells 1304A/B, 1306A/B, 1308A/B via conduits 1330, 1332 coupled to half-cell inlet/outlets, respectively. In some embodiments, an external pumping system is used to transport the electrolytes to and from the redox flow cells. Electrolyte 1324 flows into and out of half-cells 1308A/B/C through conduits 1330, while electrolyte 1326 flows into and out of half-cells 1304B, 1306B, 1308B through conduit 1332.
[0152] At least one current collector or electrode 1302 and 1304 in each half-cell 1304A, 1306A, 1308A and 1304B, 1306B, 1308B provides a surface on which the redox reaction takes place and from which charge is transferred. Suitable materials for forming electrodes 1302 and 1304 generally include those known to persons of ordinary skill in the art. Redox flow battery 1300 operates by changing the oxidation state of its constituents during charging or discharging. The two half-cells 1304A, 1306A, 1308A and 1304B, 1306B, 1308B are connected in series by the conductive electrolytes, one for anodic reaction and the other for cathodic reaction. In operation (e.g., during charge or discharge), electrolytes 1326 and 1324 are flowed through half-cells 1304A, 1306A, 1308A and 1304B, 1306B, 1308B through conduits 1330, 1332 to the inlets/outlets of the half-cells 1304A, 1306A, 1308A, as the redox reaction takes place.
[0153] Positive ions or negative ions pass through thinned or porous sections 1104 of the contoured wafers 1110A/B/C, which separates the two half-cells 1304A, 1306A, 1308A and 1304B, 1306B, 1308B, as the redox flow cell battery 1300 charges or discharges. Reactant electrolytes are flowed through half-cells 1304A/B, 1306A/B, 1308A/B, as necessary, in a controlled manner to supply electrical power or be charged by load/source 1320.
[0154] Referring to
[0155] In existing zinc-based flow batteries, the uniformity of the electric field across the electrolyte is limited by technical challenges associated with solid metal electrode integration and design, control of their separation, and electrode shape. Further complicating operations and operational effectiveness is the fact that the plating uniformity is impacted by the chemical stoichiometry which will vary with interactions within the flowing fluid. Here the rate of plating and generation of secondary chemistry is non-uniform due to the varying chemical distribution resulting from the variations in laminar flow effects across the electrodes, relative to the input and output fluid ports. With the present disclosure, well controlled channels control the flow of the electrolyte relative to the electrodes. This use of non-linear flow channels in the battery allows for disruption of the laminar flow. This ensures constant mixing of electrolyte and uniform plating of the Anode, while the porous patterned Cathode allows for field shaping and increases surface area for efficient electron exchange.
[0156] Conventional zinc bromide batteries employ Activated Titanium Electrodes which employ a metallic coating to enhance initiation of the plating cycle and which limit the battery's operation and require electrode refurbishment. There are, however, a number of limitations associated with existing conventional zinc-based flow batteries that are avoided in the present disclosure. A schematic of a zinc-based battery operation in accordance with the present disclosure is shown in
[0157] Batteries made in accordance with the present disclosure preferably employ Titanium Silicide electrodes which will provide improved surface activation energy supporting enhanced chemical disassociation and plating efficiency. This change in materials allows the present disclosure to employ a single flow loop system and to eliminate the need for an ion exchange membrane. The use of a single loop reduces the volume of electrolyte required for the target energy storage level and the number of tanks and pumps required for managing the electrolyte. This is illustrated in
[0158] The present disclosure also provides for the integration of energy storage elements with photovoltaic cell elements whereby to permit direct charging of the battery, thereby eliminating the need for complex electrical distribution and conditioning circuits employed with conventional photovoltaic cells.
[0159] A conventional photovoltaic cell 10 is illustrated in
[0160] More particularly, the upper zone 2014 of the semiconductor silicon body 2012 is doped with, for example, phosphorous so that it has a slight excess of electrons, while the remainder lower zone of the semiconductor silicon body 2012 is doped with boron so that it has slightly too few electrodes. The upper zone 2014 is called the N-type or negative type silicon, while the lower zone is called the P-type zone or positive type silicon. The zone where the N-type and the P-type silicon contact one another, is called the P-N junction 2014. When the photovoltaic cell 2010 is illuminated by solar radiation, excess electrons from the P-type silicon zone are fused with holes in the P-type silicon zone wherein excess holes of the P-type silicon zone try to fuse with the excess electrons of the N-type silicon zone. This results in a flow of electrons which are removed from electrodes 2020 and 2024 by wires 2026 and 2028 to an external load 2030 which includes distribution and conditioning circuits.
[0161]
[0162] The upper zone 2104 of semiconductor body 2102 is doped with, for example, phosphorous so that it has a slight excess of electrons, while the remainder lower zone of the semiconductor silicon body 2102 is doped with boron so that is has slightly too few electrodes.
[0163] As so described to this point photovoltaic cell 2100 of
[0164] In contrast to
[0165] In contrast to
[0166] In contrast to
[0167] In contrast to
[0168] Various changes are able to be made without departing from the spirit and scope of the disclosure. For example, various other III-V group compound semiconductor materials such as GaAs, InGaAs, InP, InAs, GaN, GaP, GaSb, InSb and InGaAsN are able to be used in forming the photovoltaic cells in connection with the above disclosure. Still other changes are possible.
[0169] As will be appreciated, by integrating photovoltaic cells and redox flow cell battery element, the disclosure permits direct solar charging of electrolytes, and thus storage of energy without the use of complex electrical distribution and conditioning circuits and without suffering their inherent loss. Also, the present disclosure permits handling of energy carrying electrolyte fluid in the fluid transport of energy from a point of generation at a photovoltaic cell directly to a point of use.
[0170] Referring to
[0171] Rather than employing spring loading plate electrodes, a wire tongue or the like are provided against the wafer. Also, for in bath electrodes, noble metals such as platinum or gold are the best choice as they are inert. However, other materials such as stainless steel, brass, tungsten, or aluminum are able to be used if the electrochemical cell is designed to prevent the electrical contact from exposure to the etching electrolyte (i.e., etchant). Still other changes are possible.
[0172] Referring to
[0173] There results a porous silicon wafer having substantially uniform size pores extending therethrough, substantially uniformly covering the surface of the wafer.
[0174] Referring to
[0175] The present disclosure provides several important advantages. For one, the wafer holders allow the wafer to be held in a manner which controls its exposure to the electrolyte. This allows the wafer contact electrode to make dry contact to the wafer such that aluminum or other metal electrodes not compatible with the electrolyte are able to be used, greatly reducing associated costs and complexity. The immersed fixture (
[0176] Chamber 3300 also includes inlets and outlets (not shown) for connection to sources of etching electrolytes, wash fluid, etc. through conduits and valves and pumps as described below in
[0177] Referring to
[0181] Following these pre-treatments, silicon wafers are electrochemically etched as described above, the metal layer is stripped from the back side of the wafer, and the wafer is washed and ready to use to produce porous Si structures.
[0182] Referring to
[0183] In order to increase mixing of the electrolyte as it is flowed through the half cells 4042 and 4044, a plurality of dividers or barriers 4066A, 4066B are formed in half cells 4042 and 4044 creating flow channels 4066A configured essentially parallel to one another running essentially the length of the half cells 4042 and 4044. Dividers or barriers 4066A introduce turbulence ensuring that the electrolyte fluids are always changing or mixing at the surfaces of the electrodes 4052 and 4054 and the membrane 4046.
[0184] Referring to
[0185] Referring to
[0186] The resulting pores have a high aspect ratio of length to cross-sectional diameter typically a depth to cross section dimension aspect ratio of 50:1. The resulting structure, shown in
[0187]
[0188]
[0189] Porous silicon wafers as produced above are assembled into a lithium-ion battery as is described below.
[0190]
[0191] Referring to
[0192] A feature an advantage of the present disclosure is that the anode is able to be made physically larger, i.e., thicker than the cathode. The increased thickness porous structure of the anode allows protons more time to move into the electrode matrix. Also, less electrolyte is required for similar energy storage. And, since the protons move more slowly into the anode, this permits a faster charge and discharge rate without a danger of fractures or pulverization of the electrode.
[0193] Changes are able to be made in the above disclosure without departing from the spirit and scope thereof. For example, while the porous electrode production has been described as being formed from monocrystalline silicon wafers, monocrystalline silicon ribbon advantageously are employed for forming the anode. Referring to
[0194] Referring to
[0195] Still other changes are possible. For example, rather than using monocrystalline silicon chips or monocrystalline silicon ribbon, the silicon is able to be polysilicon silicon or amorphous silicon. Also, while tungsten and titanium have been described as the preferred metals for forming the metal silicide coated electrodes, other conventionally used in forming include silver (Ag), aluminum (Al), gold (Au), palladium (Pd), platinum (Pt), Zn, Cd, Hg, B, Ga, In, Th, C, Si, Ge, Sn, Pb, As, Sb, Bi, Se and Te. Also, while the use of iron-ligand and iron-chloride electrolytes has been disclosed, other redox electrolytes such as, but not limited to vanadium-based electrolytes, such as vanadium-chloride based electrolytes, zinc-based electrolytes such as zinc-bromide and zinc iodide-based electrolytes, sulfuric acid-based electrolytes, and iron-chromium electrolytes are also able to be used. Still other changes are possible.
[0196] Certain modifications and improvements will occur to those skilled in the art upon a reading of the foregoing description. The above-mentioned examples are provided to serve the purpose of clarifying the aspects of the invention and it will be apparent to one skilled in the art that they do not serve to limit the scope of the invention. All modifications and improvements have been deleted herein for the sake of conciseness and readability but are properly within the scope of the present invention.