KR20230107556A - Improved energy generation or energy storage systems - Google Patents

Abstract

A proton exchange membrane fuel cell (PEMFC) is disclosed that includes a porous membrane element formed from a porous silicon wafer, the porosity of which is at least partially coated with a noble metal. Alternatively, porous silicon wafers may be sandwiched between graphite sheets impregnated with paper, carbon or precious metals. The separator is constructed using MEMS technology. In addition, a cathode electrode; an anode electrode formed of a porous silicon substrate, wherein the surface of the pores of the porous silicon substrate is at least partially coated with a metal silicide; a separator element disposed between the cathode and the anode; and a lithium ion battery having an electrolyte.

Description

Improved energy generation or energy storage systems

In one aspect, the present disclosure relates to a proton exchange membrane fuel cell (PEMFC) and a method of forming the fuel cell, and more particularly, to a proton exchange membrane including a new membrane formed of a porous silicon material. Methods of forming new porous silicon membranes for use in fuel cells and proton exchange membrane fuel cells. In another aspect, the present disclosure relates to a lithium ion rechargeable battery having a positive electrode formed of a porous silicon substrate at least partially coated with a metal silicide.

Fuel cells, especially proton exchange membrane fuel cells (PEMFCs), are attractive due to their high theoretical efficiency and non-polluting nature of reaction by-products.

In addition, PEMFCs have a wide power range, so they can be used in stationary applications such as high-power installations for electricity generation, as well as electric vehicles or other devices that require an autonomous power source (e.g., electricity generation devices). , portable electronic devices, etc.).

In general, PEMFCs work by oxidizing a fuel (such as hydrogen or methanol) at the anode and moving protons from the anode to the cathode through a proton exchange membrane. Electrons generated by the oxidation reaction are transferred back to the cathode through an external circuit, whereby chemical energy is converted into electrical energy and heat.

PEMFCs have many advantages, such as low sensitivity to carbon dioxide, fast start-up with relatively low operating temperature, flexibility in use and thermal management, reduced electrode corrosion problems, and low electrolyte leakage.

However, PEMFCs also have disadvantages, such as high sensitivity to carbon monoxide, inability to effectively use the generated heat due to relatively low operating temperatures (less than 100 °C), and expensive noble metal catalysts (usually based on platinum).

A membrane useful for a PEMFC must be impermeable to gases and must have good mechanical properties and high proton conductivity. In addition, films useful for PEMFCs must be thin, typically several microns in thickness. Finally, the membrane must be made of a material that is electrically and chemically stable.

Currently, membranes for PEMFCs are formed from perfluorosulfonate type ionomers (PFSA) such as Dupont's Nafion® and Solvay Specialty Polymers' Aquivion® Aquivion®. do. In this perfluorosulfonate-type ionomer, proton conductivity of the membrane is ensured by -SO3H groups (sulfonic acid function).

However, these membranes have disadvantages due to their permeability to methanol and hydrogen. In addition, the mechanical properties of the membrane deteriorate when the optimal operating temperature (80 °C.) is exceeded. For example, this disadvantage is particularly limiting in the automotive field. In practice, this type of application requires a PEMFC to operate at -30 to 120°C in the presence of slightly moist gas (0 to 50% relative humidity).

The performance of PEMFCs is also related to other issues such as:

The presence of carbon monoxide (CO) generally causes poisoning of the catalyst. Hydrogen obtained by reforming hydrogen (fuel) generally contains trace amounts of carbon monoxide. The presence of CO lowers the efficiency of platinum-based catalysts to adsorb CO. Therefore, the performance of the PEMFC is degraded. On the other hand, CO adsorption on platinum-based catalysts is favored at low temperatures but is affected at high temperatures due to the negative entropy of the adsorption reaction. Thus, resistance to CO increases with temperature. Therefore, the performance degradation of PEMFCs due to CO poisoning can be significantly attenuated at high temperatures (approximately 140 °C).

Considering that typical PEMFCs generate 40-50% of their energy in the form of heat, the thermal management of PEMFCs is more complex at low temperatures. Therefore, when a cell is operated at a low temperature, a large amount of energy must be consumed. Conversely, when the cell operates at temperatures ranging from 120 to 140 °C, the heat generated by the cell makes it possible to maintain the system temperature and requires a smaller cooling system. This is particularly important for applications in the automotive industry. Also, at temperatures above 100 °C, the heat generated can be used for other purposes, such as heating in cogeneration mode.

Since conventional PFSA-type membranes need to continuously supply moisture, humidification of the membrane is essential at low temperatures. Additives required for humidification reduce reliability and complicate the system. Humidification is necessary given that the proton conductivity of a membrane increases with the amount of water contained in the polymer matrix and with the amount of water outside the membrane (relative humidity). Such humidification is more complex to achieve and maintain, and requires more energy at higher temperatures.

Therefore, there is a need to develop a PEMFC membrane that can be used not only at high temperatures but also at low temperatures using gases with low moisture content (relative humidity less than 50%).

In addition, demand for high-capacity secondary batteries is strong and increasing every year. Many applications, such as aerospace, medical devices, portable electronics, and automotive applications, require high gravimetric and/or volumetric capacity batteries. Lithium ion electrode technology finds important applications in this field. However, to date, lithium ion batteries employing graphite electrodes have a theoretical specific energy density of only 372 mAh/g.

Silicon is an attractive active electrode for use in lithium-ion battery materials due to its high electrochemical capacity. Silicon has a theoretical capacity of about 4200 mAh/g, which corresponds to Li _4.4 Si phase. However, silicon is not widely used in commercial rechargeable lithium ion batteries. One reason is that silicon changes greatly in volume during charge and discharge cycles. For example, silicon can swell up to 400% when charged to its theoretical capacity. Volume changes of this magnitude can cause significant stress in the active material structure, resulting in fracture and pulverization, loss of electrical and mechanical connections within the electrodes, and capacity degradation.

Conventional lithium ion secondary battery electrodes generally include a polymer binder used to fix an active material to a carbon or graphite substrate.

However, most polymeric binders are not elastic enough to accommodate the large expansion of some high volume materials. As a result, the active material particles tend to separate from each other and from the current collector. Overall, there is a need to improve and apply a high-capacity active material that minimizes the above-described disadvantages to a lithium ion secondary battery electrode.

U.S. Patent Nos. 8,257,866 and 8,450,012 provide an electrochemically active electrode material comprising a high surface area template containing a metal silicide and a high capacity active material layer deposited on the template, thereby improving the conventional lithium ion secondary battery electrode material. We propose to solve the elasticity and swelling problem. It is known that the template serves as a mechanical support for the active material and/or as an electrical conductor between the active material and the substrate. According to the inventors of the '866 and '012 patents, the high surface area of the template allows even a thin active material layer to provide sufficient active material loading and electrode capacitance per surface area. Thus, in theory, the thickness of the active material layer can be kept small enough below the fracture threshold to maintain structural integrity during battery cycling. The thickness and/or composition of the active layer may also be specifically profiled to reduce swelling near the substrate interface and preserve interface connectivity.

In one aspect, the present disclosure provides a PEMFC membrane that can be used over a wide temperature range and over a wide relative humidity range.

More specifically, the present disclosure provides new porous silicon wafer substrate materials and methods of forming the new porous silicon wafer substrate materials and methods of using the new porous silicon wafer substrate materials as PEMFC films. More specifically, the present disclosure provides a method of forming a new porous silicon wafer for use as a PEMFC membrane separator using microelectromechanical system (MEMES) technology. In accordance with the present disclosure, a silicon wafer is selectively masked using resist deposition and photolithography techniques, and a selected portion of the wafer is subjected to an electrochemical process to form a pore or channel extending through the silicon wafer. Etching is performed. The channels or pores are substantially cylindrical and exhibit a relatively high length to cross section diameter aspect ratio (eg, 25:1, preferably 35:1, more preferably 50:1 or greater). it is desirable to have

In one embodiment, the pore size, membrane selectivity, and ionic conductivity of the silicon wafer can be determined by inorganic doping ( It is "adjusted" by inorganic doping.

The present disclosure also provides a PEMFC in which a novel porous silicon wafer is used as a membrane material. More specifically, the present disclosure provides a PEMFC including a separator membrane element formed of a porous silicon wafer.

In one embodiment, the pores of the porous silicon wafer are substantially cylindrical through holes. Preferably, the cylindrical through hole has a length to diameter aspect ratio of 25:1, preferably 35:1, more preferably 50:1 or greater.

In another embodiment, the porous surface of the porous silicon wafer is treated to enhance surface ionic conductivity. For example, the surface of the pores can be modified by deposition of a noble metal catalyst, preferably platinum.

The present disclosure also includes an electrical assembly comprising a cathode (anode) and an anode (cathode) electrode, each located in a fuel cell, sandwiched between two noble metal catalyst coated porous sheets. Provided is a PEMFC including a proton exchange membrane formed of a porous silicon wafer.

In one embodiment of the PEMFC, the catalyst comprises a noble metal, preferably platinum.

In addition, in the case of a lithium ion secondary battery, in order to overcome the problems of the prior art as described above, a high surface area porous silicon substrate material for forming an anode electrode for a lithium ion secondary battery is provided. More specifically, according to the present disclosure, the silicon substrate material is subjected to electrochemical etching to form interconnected nanostructures or through holes or pores through the silicon substrate material. Thereafter, an electrochemically active material such as a metal silicide is formed on the pore surface of the silicon substrate material by depositing a suitable metal such as titanium or tungsten or cobalt on the porous silicon substrate material, for example by chemical vapor deposition. (chemical vapor deposition, CVD), plasma-enhanced chemical vapor deposition (PECVD), thermal CVD, electroplating, electroless plating and/or solution deposition A metal coating on a porous silicon substrate material is converted by heating to a corresponding metal silicide.

The resulting substrate is a porous silicon substrate comprising a metallurgically bonded surface layer of metal silicide on the walls of the porous structure, which can advantageously be used as an electrode in a lithium ion secondary battery.

Although the resulting porous substrate material may be slightly less efficient per charge than conventional carbon- or graphite-based electrodes used in lithium-ion secondary batteries, the porous structure offers several important advantages. First, the porous structure allows protons to travel more time through the electrode matrix. As a result, expansion during the charging cycle is significantly reduced. Thus, the substrate is less likely to form dendrites or fractures during the charging cycle. Also, when used as an anode, the overall performance can be further improved by making the anode much larger than the cathode.

The present disclosure also includes a cathode electrode; an anode electrode formed of a porous silicon substrate in which a surface of pores of the porous silicon substrate is at least partially coated with a metal silicide; a separator element disposed between the cathode and the anode; and an electrolyte. The silicon substrate may include monocrystalline silicon, polycrystalline silicon or amorphous silicon. It is preferred that the pores have a length-to-diameter aspect ratio of at least 25:1, preferably 35:1, more preferably 50:1, and the electrolyte may be vinylene carbonate, 1,3-propane, given by way of example. In organic solvents such as sultone (1,3-propane sultone), 2-propylmethanesulfate, cyclohexylbenzene, t-amylbenzene or adiponitride These include conventional lithium salt electrolytes such as lithium hexafluorophosphate (LiPF ₆ ) or lithium tetrafluoroborate (LiBF ₄ ).

In one embodiment, the metal silicide coating is selected from the group consisting of illustratively given titanium silicide (TiSi2), cobalt silicide (CoSi2) and tungsten silicide (WSi2).

Further, the present disclosure provides an electrode for a lithium ion battery, wherein the anode electrode includes a substrate formed of porous silicon in which a surface region of pores is at least partially coated with a metal silicide. The silicon substrate may include monocrystalline silicon, polycrystalline silicon, or amorphous silicon, wherein the pores have a length-to-diameter aspect ratio of 25:1, preferably 35:1, more preferably 50:1 or greater, and metal silicides are exemplary. It is preferably selected from the group consisting of titanium silicide (TiSi2), cobalt silicide (CoSi2) and tungsten silicide (WSi2) given by

1 is a schematic flow diagram illustrating the formation of a porous silicon wafer useful as a film in a PEMFC according to one embodiment of the present disclosure.
2A to 2H are cross-sectional views showing a silicon wafer at various stages of the process of FIG. 1 .
FIG. 3 is a perspective view showing formation of a porous silicon wafer useful as a porous film in a PEMFC according to a second embodiment of the present disclosure, similar to FIG. 1 .
4A-4K are cross-sectional views showing a silicon wafer at various stages of the process of FIG. 3 .
5A to 5D are schematic cross-sectional views illustrating the formation of a porous silicon wafer produced according to another embodiment of the present disclosure.
6 is a schematic diagram of a PEMFC according to the present disclosure.
7 is a schematic block diagram illustrating a process of producing an electrode material according to an embodiment of the present disclosure.
8A and 8B are cross-sectional views of electrode material at various production stages according to the present disclosure.
9 is a schematic block diagram of a process for producing an electrode material according to another embodiment of the present disclosure.
10 is a schematic block diagram of another process for making an electrode material according to the present disclosure.
11 is a cross-sectional view of a secondary battery made according to the present disclosure.
12 is a schematic block diagram of another process for producing an electrode material according to the present disclosure.
13 is a cross-sectional view of a secondary battery support according to the present disclosure.
14 is a perspective view of a battery made in accordance with the present disclosure.

Additional features and advantages of the present disclosure will become apparent from the detailed description that follows, wherein like numbers indicate like parts, and wherein the terms 'top' and 'bottom', 'left' and 'right' are used to facilitate explanation. and is used in a relative sense rather than an absolute sense to describe the relative position of elements. The terms may be used interchangeably.

A mode for carrying out the present disclosure will be described in detail below with reference to the drawings.

first embodiment

1 and 2a to 2h are schematic and cross-sectional views illustrating manufacturing steps of a porous silicon wafer according to an embodiment of the present disclosure. In the drawings, the cross-sectional dimensions of the pores in the horizontal direction of the drawings are shown enlarged for clarity.

1 and 2A to 2H, as shown in FIG. 2A, starting from a silicon wafer 10, a dielectric material is applied to form a hard mask on the front and rear surfaces of the wafer 10. deposited in step 100 for In this case, 50nm layers 12a and 12b of SiO2 are first deposited on each side of the wafer, and then SiNx of 300nm layers 14a and 14b is deposited.

Next, in step 102, the front mask 14a is patterned with a photoresist 16 that is rotated and patterned on the front side of the wafer, and a polymer material 18 is applied to the front surface of the wafer. rotated on the back Pattern 16 defines a hard mask etch used for a deep anisotropic etch. Alignment elements (not shown) for the subsequent backside etch are also formed in this step 102 .

2C shows a cross-section of the wafer after pad hardmask etch (step 104). Here a dry etch (plasma) is used to control the edges of the hardmask to ensure uniform edge erosion during the KOH etch.

As shown in FIG. 2D, the front side of the wafer is rotated with polymer 20 to protect the pattern on the front side in step 106 while the pad structure on the back side is patterned on 22 in step 108. Alternatively, the back hard mask may be deposited after patterning the front side. The rear surface pattern 22 is aligned with the marks formed on the front surface of the wafer to ensure that the marks formed on the front surface of the wafer (not shown) are aligned.

After patterning the backside pad structure at step 108, at step 110 a dry etch (plasma) is used to etch the dielectric with controlled edge shape. This is shown in Figure 2e.

Figure 2e shows a nitride (PAD) etch of a back pad structure aligned to a front surface pattern. Following this step, a resist strip and wafer cleaning step 112 prepares the wet etch of the features.

Figure 2f shows the configuration of the wafer after resist stripping and before potassium hydroxide (KOH) or other anisotropic etch at step 114. We prefer to use a wet etch so that both sides can be etched simultaneously to ensure equal etch depth on both sides. However, a plasma etch can be used to etch each side independently. An open area 24 delineated by etching of the dielectric is shown on each side of the wafer.

A next step 116, in a subsequent step 118 described below, is to locally etch the silicon to create a region 26 to define a thinner silicon region for the formation of a porous silicon material. This step may be performed using a tool etch, but is preferably performed using a simple open bath etch. 2G shows the wafer after an anisotropic wet etch 116.

The silicon wafer thinned or contoured in step 116 is then subjected to electrochemical etching in step 118 to form through holes or pores 28 through the thinned section 26 as shown in FIG. 2H. A uniform electric field across the entire wafer while immersing the wafer in an etchant such as dimethylformamide (DMF)/dimethylsulfoxide (DMSO)/HF etchant in an electrochemical immersion cell is applied and electrochemically etched. The growth of well-defined cylindrical micropores or through-holes can be controlled by controlling the etching conditions, i.e., etching current density, etchant concentration, temperature, silicon doping, etc., as described in Santos et al., Electrochemically Engineered Nanoporous Material, Springer. Series in Materials Science 220 (2015), chapter 1 incorporated herein by reference.

The resulting pores have a high length to cross section diameter aspect ratio, typically a length to diameter aspect ratio of at least 25:1, preferably 35:1, more preferably 50:1 or greater. The resulting structure shown in FIG. 2H is, for example, a porous silicon wafer 30 having substantially cylindrical through holes or pores 28 that are 180 μm long and 1.6 μm in diameter, i.e., with an aspect ratio of 112.5:1. , which is very effective for use as a membrane in a PEMFC described below. The surface of the resulting porous silicon wafer 30 may then be coated with a noble metal in step 120, and the resulting noble metal coated porous wafer 30 may be incorporated into the film of the PEMFC as will be described below. .

second embodiment

3 and 4 show a second embodiment of the present disclosure. The cross-sectional views of process steps 200 to 216 of FIG. 3 and FIGS. 4A to 4G are the same as the cross-sectional views of process steps 100 to 116 and FIGS. 2A to 2G of FIG. 1 described above.

However, with reference to FIG. 4H, once the contour etching step 216 is complete, the front surface of the contour wafer is photolithographed resist step 220 followed by sputtering in step 218. Place a thin metal layer 40 on the back side. The metal layer 40 on the back side of the wafer improves electrical contact to the wafer, while the resist 42 applied in the photolithography step 220 forms a thinned region of silicon 26 in the next etching step described below. ) to limit the formation of porous silicon.

As shown in FIG. 4I , an electrochemical etch (step 222 ) is used to form porous silicon 44 in areas not protected by resist 42 .

After porous silicon formation (step 222), the front surface is protected by spinning photoresist 46 in step 224 (see FIG. 4j), and a wet etch (step 226) is used to remove thin metal 40 from the back surface. The front side resist 46 is then stripped in a resist stripping step 228. Figure 4K shows the configuration after metal etch and photoresist strip. Then in step 230 the pores may be coated with a noble metal. Optionally, an additional process such as atomic layer deposition may be used to coat the surface or pore diameter of the pore with a noble metal prior to the stripping step 228 . The resulting porous silicon wafer can be incorporated into the membrane of a PEMFC as described below.

third embodiment

5 and 6 show a third embodiment of the present disclosure. The process begins by covering one side of a silicon wafer 400 with a resist layer 402 and covering the opposite side with a sacrificial metal layer 404 formed of a noble metal, for example platinum ( See Figure 5a step). The resist layer 402 is patterned in step 502 and etched in step 504 to expose selected surfaces 406 on one side of the wafer 400 (FIG. 5B). The resist covered and patterned wafer is then immersed in step 506 in an electrochemical cell comprising HF and an etchant such as hydrogen peroxide (H2O2) to metal layer 404 and substrate wafer 400. The electrochemical etching is performed by applying a uniform electric field across the substrate 400 to create substantially uniform pores 408 in the metal layer 404 through the exposed portions of the substrate 400 (FIG. 5C). As before, the growth of well-defined cylindrical micropores with two pores can be controlled by controlling the etching conditions, i.e., etching current density, etching concentration, temperature, silicon doping, etc., again in the teachings of Santos et al. Follow Alternatively, microporous or through-hole formation can be controlled by covering selected portions of the silicon wafer with a nanoporous anodic alumina mask. Self-ordered nano porous anodic alumina is an alumina-based nanoporous matrix characterized by a dense array of basically hexagonally arranged cells, at the center of which is a cylindrical nanopore. Grow perpendicular to the underlying aluminum substrate. Nanoporous anodic alumina can be produced by electrochemical anodization of aluminum, also according to the teachings of Santos et al., the teachings of which are incorporated herein by reference. The resist layer 402 and the sacrificial metal layer 404 can be removed in step 508 leaving a porous silicon wafer having sections 405 with substantially cylindrical through holes or pores 408 (FIG. 5); It can then be coated with a noble metal catalyst coating, so that the porous silicon substrate can be incorporated as the membrane of a PEMFC as will be described below.

Noble metal catalysts are platinum black, platinum-on-carbon and/or other complex noble metal materials such as silver, gold, rhodium, iridium, palladium, ruthenium. (ruthenium) and osmium).

Referring now to Figure 6, the PEMFC is assembled as follows:

The porous silicon film thus formed may be incorporated into a PEMFC module 700 as schematically shown in FIG. 6 . The PEMFC module 700 includes a porous silicon film 702 formed as above, sandwiched between an anode or cathode 704 and a cathode or anode 706. The anode/membrane/cathode sandwich, in turn, consists of an anode-side hydrogen gas flow channel or plate assembly 708 and a cathode-side flow channel or plate assembly 710 of an oxidizing agent (oxygen or air) is sandwiched between The assembly is coupled across a fitting to flow oxyhydrogen gas and oxides, a sump and drain (not shown) to discharge water formed by the reaction of hydrogen gas and oxides, and payload/source 718. Electrodes 714 and 716 are secured together in a case (not shown) containing an electrical circuit 712 .

In operation, gaseous hydrogen fuel is delivered to the anode side of the fuel cell through a hydrogen gas flow assembly 708 and oxygen gas (oxygen or air) is delivered to the oxidant gas flow assembly 710 ) to the cathode side of the cell. At anode 704, a platinum catalyst splits hydrogen into positive hydrogen ions (protons) and negatively charged electrons. The porous silicon film 702 allows only positively charged ions to pass through to the cathode. At the cathode 706, electrons and positively charged hydrogen ions combine with oxygen to form water, which then collects at the bottom of the cell and is removed.

The above disclosure is subject to various changes. For example, as mentioned above, the noble metal catalyst may be directly coated into the pores of the porous silicon substrate film, or the porous silicon substrate film may be sandwiched between porous paper or noble metal impregnated carbon or graphite sheets. Other hydrogen fuel sources such as methanol and chemical hydrogen compounds can also be used.

Referring now to FIGS. 7 to 14 , an improved lithium ion secondary battery according to the present disclosure is formed as follows.

Referring in particular to FIG. 7 , starting from a thin monocrystalline silicon wafer 10, typically 50 to 200 millimeters thick, the wafer 1010 is subjected to dimethyl formamide (DMF) in an electrochemical immersion cell in an electrochemical etching step 1012. /Dimethyl sulfoxide (DMSO)/hydrogen fluoride (HF) etchant, etc. while immersing the wafer in an etchant while applying a uniform electric field across the wafer to perform electrochemical etching, as shown in FIG. (micron) size through holes or pores 1016 are formed. The growth of well-defined cylindrical micropores or through-holes can be controlled by controlling the etching conditions, i.e., etching current density, etchant concentration, temperature, silicon doping, etc., as described in Santos et al., Electrochemically Engineered Nanoporous Material, Springer. Series in Materials Science 220 (2015), chapter 1 incorporated herein by reference. The growth of well-defined cylindrical micropores or through-holes can be controlled by controlling the etching conditions, i.e., etching current density, etchant concentration, temperature, silicon doping, etc., as described in Santos et al., Electrochemically Engineered Nanoporous Material, Springer. Series in Materials Science 220 (2015), chapter 1 incorporated herein by reference.

The resulting pores have a high length to cross section diameter aspect ratio, typically a length to diameter aspect ratio of at least 25:1, preferably 35:1, more preferably 50:1 or greater. The resulting structure, shown in FIG. 8A , is a substantially cylindrical through-hole or, for example, 180 μm long and 1.6 μm diameter, i.e. aspect ratio of 112.5:1, highly effective for use as an electrode in a lithium ion battery. It includes a porous silicon wafer 1018 having pores 1016 and is very effective for use as an electrode in a lithium ion battery as will be described below. Thereafter, the wall of the resulting porous silicon wafer 1018 is coated with a metal such as titanium, tungsten or cobalt in step 1020, and the metal-coated porous silicon wafer is heat-treated in step 1022 to convert the deposited metal to the corresponding metal silicide. Heat treatment is performed in heat treatment step 1022 to convert to (1025). The result is a porous silicon substrate material 1024 in which the walls of the pores of the material are coated with a thin layer of metal silicide material 1026 (FIG. 8A).

9 shows an alternative embodiment of the present disclosure. The process begins with a silicon wafer 1030, and a thin metal layer 1032 is applied to the back side of the wafer 1030, for example by sputtering in step 1034. A metal layer 1032 on the back side of the wafer improves electrical contact with the wafer. An electrochemical etch (step 1036) is used to form pores 1037 through the silicon wafer 1030. After porous silicon formation, wet etching (step 1038) is used to remove the thin metal 1032 from the back side. Then, a porous silicon wafer similar to the porous silicon substrate shown in FIG. 8A is coated with a metal in step 1040, and the metal is converted to a silicide in a heating step 1042 similar to the first embodiment. The result is a porous silicon substrate in which the wall surfaces of the pores are coated with a metal silicide similar to the porous silicon substrate shown in Figure 8B.

10 is a diagram showing a third embodiment of the present disclosure. The process begins by covering one side of the silicon wafer 1050 in step 1052 with a sacrificial metal layer 1054 formed of a noble metal, for example platinum. The silicon wafer 1050 then forms a metal layer 1054 and a substrate wafer ( 1056 ) when the wafer is immersed in an electrochemical cell comprising an etchant such as hydrogen fluoride (HF) and hydrogen peroxide (H ₂ O ₂ ). Electrochemical etching is performed by applying a uniform electric field across 1050 , thereby creating substantially uniform pores 1058 in metal layer 1054 through exposed portions of silicon wafer substrate 1050 . As before, the growth of well-defined cylindrical micropores or through-holes can be controlled by controlling the etching conditions (etching current density, etch concentration, temperature, silicon doping, etc.), again following the teachings of santos et al. Alternatively, microporous or through-hole formation can be controlled by covering selected portions of the silicon wafer with a nanoporous anodic alumina mask. Self-ordered nano porous anodic alumina is an alumina-based nanoporous matrix characterized by a dense array of basically hexagonally arranged cells, at the center of which is a cylindrical nanopore. Grow perpendicular to the underlying aluminum substrate. The sacrificial metal layer 54 is then a porous silicon substrate having substantially cylindrical through holes or pores having a length-to-diameter aspect ratio of 25:1, preferably 35:1, more preferably 50:1 or greater, i.e., the porous silicon substrate shown in FIG. 8A. can be removed in step 58 leaving a porous silicon wafer similar to The porous silicon substrate is then coated with a metal in step 1058 and heated in step 1060 to convert the metal to a metal silicide, resulting in a porous silicon substrate with the walls of the pores coated with a metal silicide similar to FIG. 8B. .

The porous silicon wafer produced above is assembled into a lithium ion battery as described below.

11 shows a lithium ion battery 1060 according to the present disclosure. The battery 1060 includes a case 1062, an anode 1064 formed of a metal silicide coated porous silicon substrate formed as described above, and a cathode 66 formed of, for example, graphite, separated by a membrane or separator 1068. do.

Anode 1064 and cathode 1066 are connected to external taps 1070 and 1072, respectively. A lithium-containing electrolyte 1074, for example lithium cobalt oxide, is included in battery 1060. Both the anode and cathode allow lithium ions to move into and out of the structure through a process called intercalation (intercalation) or extraction (deintercalation), respectively. During discharge, positive ions move from the negative electrode (anode) to the positive electrode (cathode) to form a lithium compound through the electrolyte, and the electrode flows through an external circuit in the same direction to form a lithium compound. When the cell is charging, the opposite occurs, with lithium ions and the electrode moving back to the negative electrode, which has a higher energy share.

An advantage of the present disclosure is that the anode can be made physically larger, ie thicker, than the cathode. The porous structure with increased thickness of the anode allows more time for protons to migrate into the electrode matrix. Also, the amount of lithium electrolyte required for similar energy storage is small. In addition, since protons move more slowly to the anode, faster charge and discharge rates can be achieved without risk of breakage or crushing of the electrode. Changes may be made without departing from the spirit and scope of the above disclosure. For example, although anode production has been described as being formed from monocrystalline silicon wafers, a monocrystalline silicon ribbon may advantageously be used to form the anode. Referring to FIG. 12, if a silicon ribbon 1080 is used, the ribbon passes through an electrochemical etching bath 1082 to form pores through the ribbon, and then a metal coating station 1084 is applied thereto. A continuous process is allowed to form a metal silicide on the surface of the pore wall by passing through and thereto a heat treating station 1086. The resulting porous silicon metal silicide coated ribbon can be used to form lithium ion batteries using standard roll manufacturing techniques. For example, referring to FIG. 13 , a silicide-coated porous silicon ribbon anode electrode 1084 may be assembled in a stack with a cathode electrode 86 between separator sheets 1088. Electrodes 1084, 1086 and separator sheet 88 are wound together into a jelly roll, then positive tab 1092 and negative tab 1094 are extended from the jelly roll case (1090) is inserted. The tabs may then be welded to the exposed portions of electrodes 1084 and 1086, electrolyte filled case 1090 and sealed case 1090. As a result, a high-capacity lithium-ion secondary battery including a porous metal silicide coated with a porous silicon ribbon in which an anode material can be repeatedly charged and discharged without side effects is created.

Other changes are also possible. For example, polycrystalline or amorphous silicon can be used instead of monocrystalline silicon chips or monocrystalline silicon ribbons. Additionally, while tungsten, cobalt, and titanium have been described as preferred metals for forming metal silicides, 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, other metals commonly used to form metal silicides can be preferably used. Additionally, although lithium hexafluorophosphate (LiPF ₆ ) and lithium tetrafluoroborate (LiBF ₄ ) have been described as useful electrolytes, other electrolytes are also commonly used in lithium ion batteries, including but not limited to lithium cobalt oxide (LiCoO 2 ). do.

Claims (15)

In a proton exchange membrane fuel cell,
A separator membrane element formed of a porous silicon wafer
A proton exchange membrane fuel cell comprising a.
According to claim 1,
The pores of the porous silicon wafer are
is a substantially cylindrical through hole, and/or
The cylindrical through hole,
having a length to diameter aspect ratio of at least one of 25:1, 35:1, and 50:1;
Proton Exchange Membrane Fuel Cell.
According to claim 1,
The surface of the pores of the porous silicon wafer,
at least partially coated with a noble metal selected from the group consisting of silver, gold, platinum, rhodium, iridium, palladium, ruthenium, and osmium; and /or
The porous silicon wafer,
sandwiched between sheets of paper, carbon or graphite impregnated with a precious metal selected from the group consisting of silver, gold, platinum, rhodium, iridium, palladium, ruthenium, and osmium,
Proton Exchange Membrane Fuel Cell.
As a proton exchange membrane fuel cell,
An electrical assembly comprising an anode and a cathode separated by a porous membrane;
The porous membrane,
porous silicon wafer
A proton exchange membrane fuel cell comprising a.
According to claim 4,
The pores of the porous silicon wafer are
a substantially cylindrical through hole, and/or having a length to diameter aspect ratio of at least one of 25:1, 35:1, and 50:1;
Proton Exchange Membrane Fuel Cell.
According to claim 4,
The pores of the porous membrane are
at least partially coated with a noble metal catalyst selected from the group consisting of silver, gold, platinum, rhodium, iridium, palladium, ruthenium, and osmium, and/or
The porous silicon wafer,
sandwiched between sheets of paper, carbon or graphite impregnated with a noble metal selected from the group consisting of silver, gold, platinum, rhodium, iridium, palladium, ruthenium, and osmium,
Proton Exchange Membrane Fuel Cell.
A method for forming a membrane for a fuel cell,
providing a silicon wafer;
etching a through hole through at least a portion of the wafer, the through hole having a length to diameter aspect ratio of at least one of 25:1, 35:1, and 50:1; and
coating the surface of the hole at least partially with a noble metal or sandwiching an etched silicon wafer between sheets of paper, carbon or graphite impregnated with the noble metal;
including,
A method for forming a membrane for a proton exchange membrane fuel cell.
As a lithium ion battery,
a cathode electrode;
an anode electrode formed of a porous silicon substrate;
a separator element disposed between the cathode and the anode; and
electrolyte
including,
The surface of the pores of the porous silicon substrate,
At least partially coated with a metal silicide,
lithium ion battery
According to claim 8,
The silicon substrate,
contains monocrystalline silicon, polycrystalline silicon, or amorphous silicon; and/or
The metal silicide coating,
a metal silicide coating selected from the group consisting of titanium silicide (TiSi ₂ ), cobalt silicide (CoSi ₂ ) and tungsten silicide (WSi ₂ );
lithium ion battery.
According to claim 8,
The pores are
having a length to diameter aspect ratio of at least one of 25:1, 35:1, and 50:1;
lithium ion battery.
According to claim 8,
The electrolyte is
It is selected from the group consisting of lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ) and lithium cobalt oxide (LiCoO ₂ ),
lithium ion battery.
In the electrode for a lithium ion battery,
the anode electrode is
A substrate formed of porous silicon in which the surfaces of the pores are at least partially coated with a metal silicide.
Electrode for a lithium ion battery comprising a
According to claim 12,
The silicon substrate,
Monocrystalline silicon, polycrystalline silicon, or amorphous silicon
including,
Electrodes for lithium ion batteries.
According to claim 12,
The pores are
having a length to diameter aspect ratio of at least one of 25:1, 35:1, and 50:1;
Electrodes for lithium ion batteries.
According to claim 12,
The metal silicide is
A metal silicide selected from the group consisting of titanium silicide (TiSi ₂ ), cobalt silicide (CoSi ₂ ) and tungsten silicide (WSi ₂ ),
Electrodes for lithium ion batteries.

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