CN116420249A

CN116420249A - Improved energy generation or energy storage system

Info

Publication number: CN116420249A
Application number: CN202180066937.7A
Authority: CN
Inventors: 赖安·雷德福德; 丹尼尔·卡罗瑟斯
Original assignee: Dan NierKaluosesi; Lai AnLeidefude
Current assignee: Dan NierKaluosesi; Lai AnLeidefude
Priority date: 2020-09-29
Filing date: 2021-09-28
Publication date: 2023-07-11
Also published as: KR20230107556A; WO2022072371A1; EP4222796A1; JP2023543365A

Abstract

A Proton Exchange Membrane Fuel Cell (PEMFC) is disclosed that includes a porous membrane element formed from a porous silicon wafer, wherein the pores are at least partially coated with a noble metal. Alternatively, the porous silicon wafer may be sandwiched between sheets of paper, carbon or graphite impregnated with noble metals. The separator is formed using MEMS technology. Also disclosed is a lithium ion battery having: a cathode electrode; an anode electrode formed of a porous silicon substrate, wherein surfaces of pores of the porous silicon substrate are at least partially coated with a metal silicide; a separator element disposed between the cathode and the anode; and (3) an electrolyte.

Description

Improved energy generation or energy storage system

Technical Field

In one aspect, the present disclosure relates to proton exchange membrane fuel cells and methods of forming fuel cells, and more particularly to proton exchange membrane fuel cells including novel membranes formed from porous silicon materials, and methods of forming novel porous silicon membranes for proton exchange membrane fuel cells. In another aspect, the present disclosure is directed to a lithium ion rechargeable battery having an anode electrode formed from a porous silicon substrate at least partially coated with a metal silicide.

Background

Fuel cells, particularly Proton Exchange Membrane Fuel Cells (PEMFCs), are attractive due to their high theoretical efficiency and pollution-free nature of the reaction byproducts.

Furthermore, PEMFCs provide a large power range, which makes them suitable for stable applications, such as high power devices for generating electricity, and for electric vehicles, or any other devices (generator sets, portable electronic devices, etc.) that require autonomous power sources.

Typically, PEMFCs operate by oxidizing a fuel (e.g., hydrogen or methanol) at an anode, and by proton exchange from the anode to the cathode by means of a proton exchange membrane. Electrons generated by the oxidation reaction are transferred back to the cathode through an external circuit, where the chemical energy is converted into electrical energy and heat.

PEMFCs have many advantages, such as insensitivity to carbon dioxide; a relatively low operating temperature that allows for quick start; flexibility in use and thermal management; the electrode corrosion problem is reduced; and no electrolyte leakage.

However, PEMFCs also have drawbacks such as high sensitivity to carbon monoxide; relatively low operating temperatures (below 100 ℃) and therefore not effective use of the heat generated; and expensive noble metal catalysts (typically based on platinum).

Useful membranes for PEMFCs must be impermeable to gas, have good mechanical properties and high proton conductivity. In addition, they should be thin, typically having a thickness of a few microns. Finally, the membrane should be made of electrochemically and chemically stable materials.

Currently, membranes of PEMFCs are formed from perfluorosulfonate ionomers (PFSA), such as dupont

And Solvay specialty polymers +.>

In such perfluorosulfonate ionomers, the proton conductivity of the membrane is defined by-SO ₃ The H group (sulfonic acid function) is ensured.

However, such membranes have drawbacks due to their permeability to methanol and hydrogen. Furthermore, their mechanical properties are reduced beyond their optimum operating temperature (80 ℃). This is particularly limiting in the automotive field, for example. In fact, for this type of application, PEMFC operating with a gas between-30 and 120 ℃ and slightly humid (relative humidity between 0 and 50%) is required.

The performance of PEMFCs is also associated with other problems, including:

the presence of carbon monoxide (CO) generally leads to catalyst poisoning. When hydrogen (fuel) is obtained by reforming, it generally contains a trace amount of carbon monoxide. The presence of CO reduces the efficiency of the platinum-based catalyst that adsorbs it. Thus degrading the performance of the PEMFC. On the other hand, adsorption of CO on platinum-based catalysts is favourable at low temperatures, but is affected at high temperatures by the negative entropy of the adsorption reaction. Thus, the tolerance to CO increases with temperature. The performance degradation of PEMFC due to CO poisoning can thus be significantly reduced at high temperatures (about 140 ℃).

The thermal management of the PEMFC is more complex at low temperature, since 40% to 50% of the energy of a typical PEMFC is generated in the form of heat. Therefore, when the battery is operated at a low temperature, a large amount of energy must be dissipated. In contrast, when the battery is operated at a temperature in the range of 120 ℃ to 140 ℃, the heat generated by the battery can maintain the system temperature and requires a smaller cooling system. This is particularly important for automotive applications. Furthermore, for temperatures above 100 ℃, the generated heat may also be used for other purposes (e.g. heating in cogeneration mode).

Humidification of the membrane is essential at low temperatures, since conventional PFSA-type membranes require constant hydration. The additives necessary for humidification complicate the system and reduce the reliability of the system. Humidification is necessary because the proton conductivity of the membrane increases with the amount of water contained in the polymer matrix, which itself increases with the amount of water outside the membrane (relative humidity). The implementation and management of such humidification is more complex and requires more energy as the temperature increases.

There is a need to develop a PEMFC membrane that can be used with gases having low moisture content (< 50% relative humidity) at low as well as high temperatures.

Furthermore, the demand for high-capacity rechargeable batteries is strong and increasing every year. Many applications, such as aerospace, medical devices, portable electronics, and automotive applications, require high weight and/or volumetric capacity batteries. Lithium ion electrode technology has important applications in this field. However, lithium ion batteries employing graphite electrodes have heretofore been limited to theoretical specific energy densities of only 372 mAh/g.

Silicon is an attractive active electrode for lithium ion battery materials due to its high electrochemical capacity. Silicon has a theoretical capacity of about 4200mAh/g, which corresponds to Li _4.4 And Si phase. However, silicon is not widely used in commercial rechargeable lithium ion batteries. One reason is that silicon exhibits significant volume changes during charge and discharge cycles. For example, silicon may expand up to 400% when charged to its theoretical capacity. Volume changes of this magnitude can cause significant stresses in the active material structure, leading to breakage and shattering, loss of electrical and mechanical connections within the electrode, and capacity fade.

Conventional rechargeable lithium ion battery electrodes typically include a polymeric binder to hold the active material on a carbon or graphite substrate. However, most polymeric binders are not elastic enough to accommodate the large expansion of some high capacity materials. As a result, the active material particles tend to separate from each other and from the current collector. In general, there is a need for improved application of high capacity active materials in rechargeable lithium ion battery electrodes to minimize the above-described drawbacks.

Us patent nos. 8,257,866 and 8,450,012 propose to solve the problem of elasticity and expansion of prior art rechargeable lithium ion battery electrode materials by providing an electrochemically active electrode material comprising a high surface area template comprising a metal silicide and a high capacity active material layer deposited on the template. Templates are reported to serve as mechanical supports for the active material and/or electrical conductors between the active material and, for example, the substrate. According to the inventors of the '866 and' 012 patents, even a thin active material layer may provide sufficient active material loading and corresponding electrode capacity per unit surface area due to the high surface area of the template. Thus, the thickness of the active material layer can theoretically be kept small enough to be below its fracture threshold to maintain its structural integrity during battery cycling. The thickness and/or composition of the active layer may also be specifically designed to reduce swelling near the substrate interface and maintain the interface connection.

Disclosure of Invention

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

More specifically, the present disclosure provides a novel porous silicon wafer substrate material and a method for forming the novel porous silicon wafer substrate material and its use as a membrane in PEMFCs. More specifically, the present disclosure provides a method of forming a novel porous silicon wafer used as a membrane separator of a PEMFC using MEMS (micro electro mechanical system) technology. In accordance with the present disclosure, a silicon wafer is selectively masked using resist deposition and photolithographic techniques, and selected portions of the wafer are electrochemically etched to form holes or channels extending through the silicon wafer. Preferably, the channels or holes are substantially cylindrical in shape and have a relatively high (e.g., >25:1, preferably 35:1, more preferably 50:1) aspect ratio of length to cross-sectional diameter.

In one embodiment, the pore size, membrane selectivity and ionic conductivity are "tuned" by inorganic doping of the silicon wafer to allow only positively charged ions to pass through the membrane to the cathode when the membrane is used as a separation barrier in a PEMFC.

The present disclosure also provides PEMFCs in which a novel porous silicon wafer is used as a membrane material. More specifically, the present disclosure provides a PEMFC that includes a separation 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 holes have a length to width aspect ratio of >25:1, preferably 35:1, more preferably 50:1.

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

The present disclosure also provides a PEMFC including an electrical assembly including cathode (positive) and anode (negative) electrodes respectively located in a fuel cell, and including a proton exchange membrane formed of a porous silicon wafer, the proton exchange membrane being sandwiched between two porous sheets coated with a noble metal catalyst.

In a particular embodiment of the PEMFC, the catalyst includes a noble metal, preferably platinum.

In addition, in the case of lithium ion rechargeable batteries, to overcome the above and other problems in the prior art, we provide a high surface area porous silicon substrate material for forming the anode electrode of rechargeable lithium ion batteries. More specifically, in accordance with the present disclosure, a silicon substrate material is subjected to electrochemical etching to form interconnected nanostructures or vias or holes through the silicon substrate material. Thereafter, an electrochemically active material, such as a metal silicide, is formed on the surfaces of the pores of the silicon substrate material, such as by depositing a suitable metal (e.g., titanium or tungsten or cobalt) 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, as examples given, the metal coating on the porous silicon substrate material being converted to the corresponding metal silicide by heating.

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 is advantageously useful as an electrode in a rechargeable lithium ion battery.

While the efficiency per charge volume of the resulting porous substrate material may be slightly lower than conventional carbon or graphite-based electrodes used in, for example, rechargeable lithium ion batteries, the porous structure provides several significant advantages. In one aspect, the porous structure allows more time for protons to move through the electrode matrix. As a result, expansion during the charging cycle is significantly reduced. Therefore, dendrites or fractures are less likely to form on the substrate during the charging cycle. Thus, the charge and discharge rate can be increased without the risk of breakage or explosion. In addition, when used as an anode, the anode can be made much larger than the cathode, further improving overall performance.

The present invention also provides a lithium ion battery comprising: a cathode electrode; an anode electrode formed of a porous silicon substrate, wherein surfaces of pores of the porous silicon substrate are 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. Preferably, the aspect ratio of the length to the diameter of the hole>25:1, preferably 35:1, more preferably 50:1, and the electrolyte comprises a conventional lithium salt electrolyte, such as LiPF, in an organic solvent, such as vinylene carbonate, 1, 3-propane sultone, 2-propylmethane sulfate, phenylcyclohexane, tert-pentylene or adiponitrile, as given by way of example ₆ Or LiBF ₄ 。

In one embodiment, the metal silicide coating is selected from the group consisting of TiSi given as an example ₂ 、CoSi ₂ And WSi ₂ A group of groups.

The present disclosure also provides an electrode for a lithium ion battery, wherein the anode electrode comprises a substrate formed of porous silicon, wherein a surface area of the pores is at least partially coated with a metal silicide. The silicon substrate may comprise monocrystalline silicon, polycrystalline silicon, or amorphous silicon, and the aspect ratio of the length to the diameter of the hole is>25:1, preferably 35:1, more preferably 50:1, metal silicide is preferredSelected from TiSi given by way of example ₂ 、CoSi ₂ And WSi ₂ A group of groups.

Drawings

Further features and advantages of the present disclosure will become apparent from the following detailed description, wherein like numerals represent like parts, and wherein:

fig. 1 is a schematic flow chart showing the formation of a porous silicon wafer used as a membrane in a PEMFC according to a first embodiment of the present disclosure;

FIGS. 2 (a) -2 (h) are cross-sectional views of a silicon wafer showing various stages of the process of FIG. 1;

fig. 3 is a view similar to fig. 1, showing the formation of a porous silicon wafer used as a porous membrane in a PEMFC according to a second embodiment of the present disclosure;

fig. 4 (a) -4 (k) are cross-sectional views showing a silicon wafer at various stages of the process of fig. 3;

fig. 5 (a) -5 (d) are schematic cross-sectional views showing the formation of a porous silicon wafer manufactured according to another embodiment of the present disclosure;

fig. 6 is a schematic diagram of a PEMFC according to the present disclosure;

FIG. 7 is a schematic block diagram of an electrode material production process according to one embodiment of the present disclosure;

fig. 8A and 8B are cross-sectional views of an electrode material at different stages of production according to the present disclosure;

FIG. 9 is a schematic block diagram of a process for producing an electrode material according to another embodiment of the present disclosure;

FIG. 10 is a schematic block diagram of yet another process for producing an electrode material according to the present disclosure;

FIG. 11 is a cross-sectional view of a rechargeable battery made in accordance with the present disclosure;

FIG. 12 is a schematic block diagram of yet another process for producing an electrode material according to the present disclosure;

fig. 13 is a cross-sectional view of a rechargeable battery according to the present disclosure; and

fig. 14 is a perspective view of a battery made in accordance with the present disclosure.

Detailed Description

The terms "upper" and "lower" and "left" and "right" are used in a relative rather than absolute sense to facilitate the description, as well as to describe the relative positions of elements. These terms may be used interchangeably.

The manner in which the present disclosure is performed will be described in detail below with reference to the accompanying drawings.

First embodiment

Fig. 1 and 2 (a) -2 (h) are schematic diagrams and cross-sectional views showing a manufacturing step of a porous silicon wafer according to a first embodiment of the present disclosure. In the drawings, the cross-sectional dimensions of the holes are exaggerated in the horizontal direction of the drawings for clarity.

Referring to fig. 1 and 2 (a) -2 (h), starting with a silicon wafer 10, as shown in fig. 2 (a), dielectric material is deposited in step 100 to form a hard mask on the front and back sides of the wafer 10. In this case, each side of the wafer will first deposit 50nm of SiO ₂ Layers 12a, 12b, then 300nm SiN _x Layers 14a, 14b.

Next, in step 102, the front side mask 14a is patterned with the photoresist 16, the photoresist 16 is spin-coated and patterned on the front side of the wafer, and the polymer material 18 is spin-coated onto the back side of the wafer. Pattern 16 defines a hard mask etch that will in turn be used for deep anisotropic etching. Alignment elements (not shown) for subsequent backside etching are also formed in this step 102.

Fig. 2 (c) shows a cross-section of the wafer after pad hard mask etching (step 104). Dry etching (plasma) is used here to control the edge of the hard mask to ensure uniform edge erosion during KOH etching.

As shown in fig. 2 (d), the front side of the wafer has been spin coated with polymer 20 in step 106 to protect the pattern on the front side, while the pad structures on the back side are patterned at 22 in step 108. Alternatively, a backside hard mask may be deposited after front side patterning. The back pattern 22 is aligned with marks (not shown) formed on the front side of the wafer to ensure their alignment.

After patterning the backside pad structure in step 108, dry etching (plasma) is used to etch the dielectric in step 110 while controlling the edge shape. This is shown in fig. 2 (e).

Fig. 2 (e) shows a nitride (PAD) etch of the back PAD structure aligned with the front pattern. This step is followed by a resist strip and wafer cleaning step 112 in preparation for wet etching of the features.

Fig. 2 (f) shows the wafer configuration after resist stripping and prior to KOH or other anisotropic etching in step 114. We prefer to use wet etching so that both faces can be etched simultaneously to ensure the same etch depth on both faces. However, plasma etching may be used to etch each face independently. An open area 24 defined by etching of the dielectric is shown on each side of the wafer.

The next step 116 is to etch the silicon to locally thin it, resulting in regions 26 defining thinner silicon regions for forming porous silicon material (described below) in a subsequent step 118. Although tool etching may be used, this step is preferably performed using a simple open bath etch. Fig. 2 (g) shows the wafer after anisotropic wet etching 116.

Subsequently in an electrochemical etching step 118, the thinned or contoured silicon wafer from step 116 is subjected to electrochemical etching by applying a uniform electric field across the wafer while immersing the wafer in an etchant such as Dimethylformamide (DMF)/Dimethylsulfoxide (DMSO)/HF etchant in an electrochemical immersion tank, thereby forming a via or hole 28 through thinned portion 26 as shown in fig. 2 (h). Following the teachings of Santos et al (Electrochemically Engineered Nanoporous Material, springer Series in Materials Science, 220 (2015), chapter 1), the contents of which are incorporated herein by reference, the growth of well-defined cylindrical micro-holes or vias can be controlled by controlling the etching conditions, i.e., etching current density, etchant concentration, temperature, silicon doping, etc.

The resulting holes have a high aspect ratio of length to cross-sectional diameter, typically an aspect ratio of length to diameter >25:1, preferably 35:1, more preferably 50:1. The resulting structure as shown in fig. 2 (h) comprises a porous silicon wafer 30 having substantially cylindrical through holes or pores 28, the through holes or pores 28 having a length of, for example, 180 μm and a diameter of 1.6 μm, i.e. an aspect ratio of 112.5:1, which is very effective for use as a membrane in a PEMFC as will be described below. The surface of the resulting porous silicon wafer 30 may then be coated with noble metal in step 120, and the resulting porous wafer 30 coated with noble metal may be added as a membrane to a PEMFC, as described below.

Second embodiment

Fig. 3-4 illustrate a second embodiment of the present disclosure. The process steps 200-216 of fig. 3 and the cross-sectional views of fig. 4 (a) -4 (g) are identical to the process steps 100-116 of fig. 1 and the cross-sectional views 2 (a) -2 (g) described above.

However, referring to fig. 4 (h), after the profile etching step 216 is completed, we place a thin metal layer 40 on the back side of the formed wafer, for example by sputtering, in step 218, and then perform a photoresist step 220 on the front side of the formed wafer. The metal layer 40 on the back side of the wafer promotes improved electrical contact with the wafer, while the resist 42 applied in the photolithography step 220 limits the formation of porous silicon to the thinned regions 26 of silicon in a subsequent etching step described below.

As shown in fig. 4 (i), electrochemical etching (step 222) is used to form porous silicon 44 in areas not protected by resist 42.

After the porous silicon is formed (step 222), the front side is protected by spin-coating the photoresist 46 on the front side in step 224 (see fig. 4 (j)), and the thin metal 40 is removed from the front side using a wet etch (step 226). The front side resist 46 is then stripped in a resist stripping step 228. Fig. 4 (k) shows the configuration after metal etching and photoresist stripping. The holes may then be coated with a noble metal at step 230. Optionally, additional processes such as atomic layer deposition may be used to coat the surface or pore size of the pores with noble metal prior to the stripping step 228. The resulting porous silicon wafer can then be added as a membrane in a PEMFC, as described below.

Third embodiment

Fig. 5-6 illustrate a third embodiment of the present disclosure. The process starts withA silicon wafer 400, one side of which is covered with a resist layer 402, and the other side is covered with a protective metal layer 404 formed of, for example, a noble metal such as platinum (see step fig. 5 (a)). The resist layer 402 is patterned at step 502 and etched to expose a selected surface 406 of one side of the wafer 400 at step 504 (fig. 5 (b)). In step 506, when the wafer is immersed in a solution containing, for example, HF and H ₂ O ₂ By applying a uniform electric field between the metal layer 404 and the substrate wafer 400, thereby producing substantially uniform holes 408 through the exposed portions of the substrate 400 to the metal layer 404 (fig. 5 (c)). As before, the growth of well-defined cylindrical microwells with two holes can be controlled again following the teachings of Santos et al by controlling the etching conditions, i.e., etching current density, etching concentration, temperature, silicon doping, etc. Alternatively, the formation of micro-holes or vias may be controlled by covering selected portions of the silicon wafer with a nanoporous anodized aluminum mask. Self-ordered nanoporous anodic alumina is basically an alumina-based nanoporous matrix characterized by a densely woven array of hexagonally arranged cells, with cylindrical nanopores growing at their centers perpendicular to the underlying aluminum substrate. Nanoporous anodized aluminum can again be produced by electrochemical anodization of aluminum following the teachings of Santos et al, the teachings of which are incorporated herein by reference. The resist layer 402 and the protective metal layer 404 may then be removed in step 508, leaving a porous silicon wafer with a portion 405 having substantially cylindrical through holes or pores 408 (fig. 5), which may then be coated with a noble metal catalyst coating, the resulting porous silicon substrate may be added as a film in a PEMFC, as described below.

The noble metal catalyst may be platinum black, platinum on carbon, and/or other composite noble metal materials such as silver, gold, rhodium, iridium, palladium, ruthenium, and osmium.

Referring now to fig. 6, the pemfc is assembled as follows:

the porous silicon film formed as above may be incorporated into the PEMFC module 700 schematically shown in fig. 6. The PEMFC module 700 includes the porous silicon membrane 702 formed as above sandwiched between the anode or negative electrode 704 and the cathode or positive electrode 706. The anode/membrane/cathode sandwich is in turn sandwiched between a hydrogen flow channel or plate assembly 708 on the anode side and an oxidant (oxygen or air) flow channel or plate assembly 710 on the cathode side. The assembly is held together in a housing (not shown) that includes fittings for flowing oxygen, hydrogen and oxides, a sump and drain (not shown) for draining water formed by the reaction of hydrogen and oxides, and a circuit 712 that includes

electrodes

714, 716 coupled across a payload/source 718.

In operation, (1) gaseous hydrogen fuel is directed to the anode side of the fuel cell by hydrogen flow assembly 708, while oxygen (oxygen or air) is directed to the cathode side of the cell by oxygen flow assembly 710. (2) At the anode 704, the platinum catalyst splits hydrogen into positive hydrogen ions (protons) and negatively charged electrons. (3) The porous silicon membrane 702 only allows positively charged ions to pass through it to the cathode. The negatively charged electrons travel along an external circuit 712 to the cathode 706, generating an electrical current. (4) At the cathode 706, the electrons and positively charged hydrogen ions combine with oxygen to form water, which then collects at the bottom of the cell and is removed.

Various changes may be made to the above disclosure. For example, as described above, the noble metal catalyst may be directly coated on the pores of the porous silicon substrate film, or the porous silicon substrate film may be sandwiched between porous paper or carbon or graphite sheets impregnated with noble metal. In addition, other hydrogen fuel sources, such as methanol and chemical hydrides, may be used.

Referring now to fig. 7-14, an improved lithium ion rechargeable battery is formed in accordance with the present disclosure as follows.

Referring specifically to fig. 7, starting with a thin single crystal silicon wafer 10, typically 50-200 mils thick, in an electrochemical etching step 1012, the wafer 1010 is electrochemically etched by: a uniform electric field is applied across the wafer while the wafer is immersed in an etchant such as Dimethylformamide (DMF)/Dimethylsulfoxide (DMSO)/HF etchant in an electrochemical immersion tank, thereby forming micron-sized through-holes or vias 1016 through the wafer, as shown in fig. 8A. Following the teachings of Santos et al (Electrochemically Engineered Nanoporous Material, springer Series in Materials Science, 220 (2015), chapter 1), the contents of which are incorporated herein by reference, the growth of well-defined cylindrical micro-holes or vias can be controlled by controlling the etching conditions, i.e., etching current density, etchant concentration, temperature, silicon doping, etc.

The resulting holes have a high aspect ratio of length to cross-sectional diameter, typically an aspect ratio of length to diameter >25:1, preferably 35:1, more preferably 50:1. As shown in fig. 8A, the resulting structure comprises a porous silicon wafer 1018 having a substantially cylindrical through-hole or aperture 1016, the through-hole or aperture 1016 having a length of, for example, 180 μm and a diameter of 1.6 μm, i.e., an aspect ratio of 112.5:1, which is very effective for use as an electrode in a lithium ion battery, as will be described below. The walls of the resulting porous silicon wafer 1018 are then coated with a metal, such as titanium, tungsten or cobalt, in step 1020, and the metal-coated porous silicon wafer is then heat treated in a heating step 1022 to convert the deposited metal to the corresponding metal silicide 1025 in the heat treatment step 1022. A porous silicon-based plate material 1024 is obtained in which the wall surfaces of the pores of the material are coated with a thin layer 1026 of metal silicide material (fig. 8A).

Fig. 9 illustrates an alternative embodiment of the present disclosure. The process begins with a silicon wafer 1030 with a thin metal layer 1032 being applied to the silicon wafer 1030 in step 1034, for example by sputtering on the back side of the wafer 1030. The metal layer 1032 on the back side of the wafer promotes improved electrical contact with the wafer. Electrochemical etching (step 1036) is used to form holes 1037 through the silicon wafer 1030. After the porous silicon is formed, a wet etch is used (step 1038) to remove the thin metal 1032 from the back side. A porous silicon wafer similar to the porous silicon substrate shown in fig. 8A is then coated with a metal in step 1040, which is converted to a silicide in a heating step 1042 similar to the first embodiment. A porous silicon substrate was obtained in which the surface of the wall surface of the hole was coated with a metal silicide similar to that of the porous silicon substrate shown in fig. 8B.

Fig. 10 shows a third embodiment of the present disclosure. The process starts with a silicon wafer 1050, which is covered on one side in step 1052, for example by a method such asA protective metal layer 1054 formed of noble metal of platinum. Then, in step 1056, when the wafer is immersed in a solution containing etchants (e.g., HF and H ₂ O ₂ ) To apply a uniform electric field across the metal layer 1054 and the substrate wafer 1050, thereby electrochemically etching the silicon wafer 1050, thereby creating substantially uniform holes 1058 through the exposed portions of the silicon wafer substrate 1050 to the metal layer 1054. As previously mentioned, again following the teachings of Santos et al, the growth of well-defined cylindrical micro-holes or vias can be controlled by controlling the etching conditions, i.e., etching current density, etching concentration, temperature, silicon doping, etc. Alternatively, the formation of micro-holes or vias may be controlled by covering selected portions of the silicon wafer with a nanoporous anodized aluminum mask. Self-ordered nanoporous anodic alumina is basically an alumina-based nanoporous matrix characterized by a densely woven array of hexagonally arranged cells, with cylindrical nanopores growing at their centers perpendicular to the underlying aluminum substrate. The nanoporous anodized aluminum can be produced by electrochemical anodization of aluminum, again following the teachings of Santos et al, the teachings of which are incorporated herein by reference. The protective metal layer 1054 may then be removed in step 1058, leaving a porous silicon wafer with substantially cylindrical through holes or pores with an aspect ratio of length to diameter>25:1, preferably 35:1, more preferably 50:1, i.e., similar to the porous silicon substrate shown in fig. 8A. The porous silicon substrate is then coated with a metal in step 1058, and the porous silicon substrate is heated in step 1060 to convert the metal to a metal silicide, thereby producing a porous silicon substrate in which the wall surfaces of the pores are coated with a metal silicide similar to that of fig. 8B.

As will be described below, the porous silicon wafer produced as above is assembled into a lithium ion battery.

Fig. 11 shows a lithium ion battery 1060 in accordance with the present disclosure. The battery 1060 includes a housing 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. The anode 1064 and cathode 1066 are connected to

external tabs

1070, 1072, respectively. A lithium-containing electrolyte 1074 (e.g., lithium cobalt oxide) is contained within the battery 1060.

Both the anode and cathode allow lithium ions to move into and out of their structure through a process called intercalation (intercalation) or deintercalation (deintercalation), respectively. At the time of discharge, positive lithium ions move from the negative electrode (anode) to the positive electrode (cathode) forming a lithium compound through the electrolyte, while electrons flow through an external circuit in the same direction. When the battery is charged, the situation is reversed, with lithium ions and electrons moving back to the negative electrode in a higher net energy state.

One feature and advantage of the present disclosure is that the anode can be made physically larger than the cathode, i.e., thicker than the cathode. The porous structure of the anode with increased thickness allows more time for protons to migrate into the electrode matrix. In addition, similar energy storage requires less lithium electrolyte. Moreover, since protons enter the anode more slowly, faster charge and discharge rates can be achieved without the risk of electrode breakage or pulverization.

Variations may be made in the foregoing disclosure without departing from the spirit or the scope thereof. For example, while anode production has been described as being formed from a single crystal silicon wafer, single crystal silicon ribbons may be advantageously used to form the anode. Referring to fig. 12, the use of a silicon ribbon 1080 allows for a continuous process in which the ribbon is run through an electrochemical etching bath 1082 to form holes through the ribbon, then through a metal coating station 1084, and then through a heat treatment station 1086 to form metal silicide on the hole wall surfaces. The resulting porous silicon metal silicide-coated tape can then be used to form lithium ion batteries using standard roll-to-roll manufacturing techniques. For example, referring to fig. 13, a silicide coated porous silicon anode electrode 1084 may be assembled with a cathode electrode 86 in a stack between separator sheets 1088. The

electrodes

1084, 1086 and separator 88 are wound together into a jelly roll and then inserted into the housing 1090 with the positive and

negative tabs

1092, 1094 extending from the jelly roll. The tabs may then be welded to the exposed portions of the

electrodes

1084, 1086, with the housing 1090 filled with electrolyte, and the housing 1090 sealed. A high capacity lithium ion rechargeable battery is obtained in which the anode material comprises a porous silicon ribbon coated with a porous metal silicide that is capable of repeated charge and discharge without adverse effects.

Other variations are also possible. For example, the silicon may be polysilicon or amorphous silicon, rather than using monocrystalline silicon pieces or strips of monocrystalline silicon. Further, while tungsten, cobalt, and titanium have been described as preferred metals for forming metal silicides, other metals commonly used for forming metal silicides, including 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, may also be advantageously used. In addition, although LiPF ₆ And LiBf ₄ Other electrolytes that have been described as useful electrolytes, but commonly used in lithium ion batteries, include, but are not limited to, lithium cobalt oxide (LiCoO) ₂ )。

Claims

1. A Proton Exchange Membrane Fuel Cell (PEMFC) includes a separation membrane element formed from a porous silicon wafer.

2. PEMFC according to claim 1, wherein the pores of the porous silicon wafer are substantially cylindrical through-holes, and/or wherein the length to diameter aspect ratio of the cylindrical through-holes is >25:1, preferably 35:1, more preferably 50:1.

3. PEMFC according to claim 1, wherein the surface of the pores of the porous silicon wafer is at least partially coated with a noble metal, preferably noble metal selected from the group consisting of silver, gold, platinum, rhodium, iridium, palladium, ruthenium and osmium, and/or wherein the porous silicon wafer is sandwiched between sheets of paper, carbon or graphite impregnated with noble metal, preferably noble metal selected from the group consisting of silver, gold, platinum, rhodium, iridium, palladium, ruthenium and osmium.

4. A Proton Exchange Membrane Fuel Cell (PEMFC) comprising:

an electrical assembly comprising a positive electrode and a negative electrode separated by a porous membrane, wherein the porous membrane comprises a porous silicon wafer.

5. PEMFC according to claim 4, wherein the pores of the porous silicon wafer are substantially cylindrical through-holes and/or their aspect ratio of length to diameter is >25:1, preferably 35:1, more preferably 50:1.

6. PEMFC according to claim 4, wherein the pores of the porous membrane are at least partially coated with a noble metal catalyst, preferably noble metals selected from the group consisting of silver, gold, platinum, rhodium, iridium, palladium, ruthenium and osmium, and/or wherein the porous silicon wafer is sandwiched between sheets of paper, carbon or graphite impregnated with noble metals, preferably noble metals selected from the group consisting of silver, gold, platinum, rhodium, iridium, palladium, ruthenium and osmium.

7. A method of forming a membrane for a Proton Exchange Membrane Fuel Cell (PEMFC), comprising:

providing a silicon wafer;

etching a via extending through at least a portion of the wafer, wherein the aspect ratio of the length to the diameter of the via is >25:1, preferably 35:1, more preferably 50:1; and

the surface of the pores is at least partially coated with a noble metal, preferably selected from the group consisting of silver, gold, platinum, rhodium, iridium, palladium, ruthenium and osmium, or an etched silicon wafer is sandwiched between paper, carbon or graphite sheets impregnated with noble metal.

8. A lithium ion battery, comprising:

a cathode electrode;

an anode electrode formed of a porous silicon substrate, wherein surfaces of pores of the porous silicon substrate are at least partially coated with a metal silicide;

a separator member disposed between the cathode and the anode; and

and (3) an electrolyte.

9. The lithium ion battery of claim 8, wherein the silicon substrate comprises monocrystalline silicon, polycrystalline silicon or amorphous silicon, and/or wherein the metal silicide coating is preferably selected from the group consisting of TiSi ₂ 、CoSi ₂ And WSi ₂ A group of groups.

10. The lithium ion battery of claim 8, wherein the aspect ratio of length to diameter of the pores is >25:1, preferably 35:1, more preferably 50:1.

11. The lithium ion battery of claim 8 wherein the electrolyte is selected from the group consisting of LiPF ₆ 、LiBF ₄ And LiCoO ₂ A group of groups.

12. An electrode for a lithium ion battery, wherein the anode electrode comprises a substrate formed of porous silicon, wherein a surface area of the pores is at least partially coated with a metal silicide.

13. The electrode of claim 12, wherein the silicon substrate comprises monocrystalline silicon, polycrystalline silicon, or amorphous silicon.

14. The electrode according to claim 12, wherein the aspect ratio of length to diameter of the aperture is >25:1, preferably 35:1, more preferably 50:1.

15. The electrode of claim 12 wherein the metal silicide is selected from the group consisting of TiSi ₂ 、CoSi ₂ And WSi ₂ A group of groups.