Catalyst device for lead-acid battery and lead-acid battery

Abstract

A catalytic device for a lead-acid battery and a lead-acid battery including the catalytic device are disclosed. The device includes a catalyst layer (120) mounted within a cavity (112) of the device, and a porous layer (140) comprising a thermoplastic material is mounted within the cavity to cover a surface of the catalyst layer and configured to prevent thermal runaway of the catalytic device. The porous layer is a planar device larger than the planar size of the catalyst layer. The catalyst layer is mounted within the cavity within a retention mechanism (130) configured to maintain the position of the catalyst layer within the cavity, and at least one surface is covered by the porous layer, ensuring alignment of the catalyst layer and the porous layer during use.

Description

[Technical Field]

[0001] Field The present invention relates to a catalytic device for lead acid batteries, and more particularly to a catalytic device that reduces gas buildup in and electrolyte loss from lead acid batteries, improving battery safety and life span. [Background technology]

[0002] background Lead-acid batteries, especially those for automobiles, generally have an open structure that allows the free flow of electrolyte, such as dilute sulfuric acid. Lead-acid batteries with this structure are equipped with vents to release oxygen and hydrogen gases that are generated during charging. Otherwise, the gas pressure inside the battery may increase, potentially causing deformation and damage to the battery.

[0003] Such gas leakage through the vents leads to a loss of electrolyte, which in turn leads to insufficient battery chemistry and reduced charge and discharge capacity.

[0004] To address these problems, it is known to provide a catalytic device exposed to an enclosure containing the electrolyte to promote the recombination of hydrogen and oxygen gases.

[0005] Japanese Patent Application Laid-Open Publication No. 2017-201594 (Gore Japan Co., Ltd.) discloses a catalyst component for a lead-acid battery, which includes a catalyst layer containing a catalyst that promotes a reaction that generates water or water vapor from oxygen and hydrogen, and a configuration that condenses at least a portion of the water or water vapor and / or returns it to the inside of the battery. This catalyst component can reduce the loss of electrolyte due to gas emission and leakage from the electrolyte, thereby providing a lead-acid battery with a long life.

[0006] U.S. Patent No. 7,326,489 (Philadelphia Scientific) discloses a catalytic device for recombining decomposition gases from an electrolyte. The catalytic material is contained within a container separated from the cell enclosure by a microporous member at the open end of the chamber. The microporous member allows gases to pass through but not liquids. Hydrogen and oxygen pass through the microporous member to the catalyst, where they recombine, and the resulting water vapor can return to the cell through the microporous member.

[0007] CN102800831A and CN202977567U (Zhejiang Narada Power Supply et al.) disclose battery vent plugs each having a housing with a lower portion containing a catalyst material and a porous hydrophobic filter layer separating the catalyst from a battery electrolyte enclosure.

[0008] As mentioned above, typical lead-acid batteries release oxygen and hydrogen gases to the outside through vents during charging, leading to a decrease in the electrolyte within the battery. This decrease in electrolyte ultimately leads to a decrease in charge / discharge capacity. An increase in the concentration of dilute sulfuric acid in the electrolyte can cause corrosion of the positive plate, and a decrease in the electrolyte level can expose the electrode plate, further reducing charge / discharge capacity. An increase in acid concentration can lead to corrosion inside the battery, for example, between the negative plate and the strap.

[0009] Furthermore, a decrease in electrolyte can cause sulfation and short-circuit breakthrough. Sulfation occurs when lead sulfate produced by discharge cannot be fully decomposed into lead dioxide and lead by charging, resulting in the formation of lumpy crystals of lead sulfate. These lumpy crystals are difficult to reduce to metallic lead, reducing battery performance and shortening battery life. These lumpy crystals are also involved in short-circuit breakthrough. The lumpy crystals grow on the electrodes, forming needle-like crystals called "dendrites." If the dendrites continue to grow, they may reach the other electrode and cause a short-circuit. This is a short-circuit breakthrough, which makes it impossible to charge or discharge the battery.

[0010] In recent years, automobiles equipped with start-stop systems have become increasingly popular to improve fuel economy. Lead-acid batteries used in start-stop vehicles power all devices, such as air conditioners and fans, during the stop-start period. Therefore, compared with conventional start-stop lead-acid batteries, lead-acid batteries tend to be undercharged and used at a low state of charge, exacerbating sulfation and short-circuiting.

[0011] The risk of sulfation and short circuiting can be reduced by limiting or preventing electrolyte loss, which is why catalytic devices such as these are increasingly being introduced.

[0012] The recombination of hydrogen and oxygen gases is a highly exothermic reaction (-286 kJ mol -1 ), and if the recombination reaction of H2 + 1 / 2O2 → H2O in the catalyst proceeds too quickly, for example, due to overheating or overcharging of the battery, it can lead to overheating of the catalyst. In general, an increase in catalyst temperature leads to an increase in catalytic activity, which in turn causes a further increase in the reaction rate, potentially leading to thermal runaway. Such thermal runaway can lead to the ignition of gases within the battery, which can then pose a risk of explosion or fire.

[0013] U.S. Patent No. 7,326,489 discloses that catalytic devices can be equipped with a shutdown function. Specifically, a container surrounding the catalytic material melts, physically covering the catalyst and quenching the recombination reaction. A drawback of this disclosed device is that melting of the container material risks compromising the containment of the catalytic material within the container. The exposed catalytic material could then continue to overheat or release debris into the electrolyte, causing a short circuit and potentially dangerous release of electrical energy. Furthermore, for shutdown to occur, sufficient heat must be transferred from the catalytic material to the container to melt it, which takes time and can lead to thermal runaway.

[0014] PCT / JP2018 / 043437 (WL Gore & Associates GK) discloses a catalyst having a porous thermoplastic membrane in contact with the catalyst material. The membrane has a melting point of 160°C or less, allowing the membrane to melt and reduce porosity, thereby slowing or completely quenching the recombination reaction. However, in some applications, such as certain automotive applications, the alignment of the thermoplastic membrane relative to the catalyst (i.e., its position across the catalyst surface) can vary, risking that a portion of the catalyst surface remains exposed to the catalyst enclosure. Summary of the Invention

[0015] Summary of the Invention A first aspect of the present invention relates to a catalytic device for a lead acid battery, said catalytic device comprising: a housing defining a cavity; a catalyst layer mounted within the cavity, the catalyst layer including a catalyst that promotes a reaction from oxygen and hydrogen to produce water or water vapor; and a porous layer comprising a thermoplastic material mounted within the cavity, the porous membrane having a planar size larger than a planar size of the catalyst layer, a surface of the catalyst layer contacting the porous layer and covering at least one surface of the catalyst layer; Including, The catalyst layer is mounted within the cavity in a retaining arrangement configured to maintain the position of the catalyst layer within the cavity, and the at least one surface is covered by the porous layer.

[0016] In use, a porous layer comprising a thermoplastic material (hereinafter referred to as the "porous layer") is disposed between the electrolyte enclosure and the catalyst layer of a lead-acid battery. Hydrogen and oxygen generated within the battery can permeate through the porous layer to reach the catalyst layer and undergo a recombination reaction to produce water vapor. The water vapor permeates into the enclosure and condenses, maintaining the electrolyte level within the battery. When the temperature of the catalyst layer increases above the melting point or glass transition temperature of the thermoplastic material, the porosity of the porous layer decreases, controlling the rate of the recombination reaction and mitigating the temperature of the catalyst layer.

[0017] Due to manufacturing tolerances, it is not possible to completely eliminate relative movement of the catalyst layer and the porous layer relative to each other and the housing. Furthermore, providing some clearance between the housing and these layers can facilitate device fabrication. The retention mechanism maintains the position of the catalyst layer so that the surface of the catalyst layer that contacts the porous layer remains covered within any movement of the catalyst layer or polymer layer within the cavity. Therefore, the possibility of misalignment of the catalyst layer and the porous layer (meaning the portion of the surface of the catalyst layer adjacent to the surface of the porous layer that is not covered by the porous layer) is reduced or eliminated.

[0018] The porous layer, in some embodiments, can undergo some shrinkage when the thermoplastic material is heated above its glass transition temperature or melting point, and the larger area of ​​the porous layer can absorb such shrinkage while the surface of the catalyst layer remains covered. Contact with the catalyst layer can create friction with the porous layer and resist shrinkage.

[0019] A "layer" refers to a structure having parallel or nearly parallel opposing faces, each dimension of which is greater than the thickness of the layer between said faces. A layer can have one or more peripheral surfaces extending around its periphery and between its faces. A layer as disclosed herein is typically planar when installed within a cavity.

[0020] "Cavity" includes a recess or opening sized to receive and hold the catalyst layer and porous layer. The cavity can be of any shape or configuration, but is conveniently circular in cross section.

[0021] The retention mechanism can include one or more retaining formations to prevent or substantially prevent lateral movement of the catalyst layer.

[0022] The retention feature can extend around a periphery of the catalyst layer. One or more retention structures of the retention feature can extend around at least a portion of the catalyst layer.

[0023] The inner profile of the retention mechanism may include one or more of said retention structures.

[0024] The housing can include a retention mechanism, for example, one or more retention structures defined by the housing, the one or more retention structures extending into the cavity.

[0025] The retention mechanism may include a retainer mounted within the cavity in a substantially fixed relationship relative to the housing. One or more retention structures may be defined by the retainer.

[0026] The retention feature may extend around the periphery of the catalyst layer. An inner profile of the retention feature may include one or more of said retention structures.

[0027] For example, the retention feature can include a ring-shaped retainer having a shape roughly similar to the shape of the catalyst layer. The inner profile of the ring can act as a retention structure; i.e., the catalyst layer can fit snugly within the ring.

[0028] A "ring" includes any structure that extends around the periphery of the catalyst layer and can be circular, square, polygonal, etc. The catalyst layer can have a shape that corresponds to the shape of the ring, or can have shapes of different sizes that fit and are held within the ring.

[0029] It will be appreciated that a lateral clearance may be provided between the catalyst layer and the retention feature, for example to allow for manufacturing tolerances or to facilitate assembly, which allows the catalyst layer and porous layer each to have a range of lateral movement within the cavity relative to the housing.

[0030] The extent of lateral movement of the porous layer and the catalyst layer as a whole within the cavity is desirably minimized, for example, in some embodiments, less than 1 mm, less than 0.5 mm, or less than 0.1 mm.

[0031] The porous layer may include a peripheral surface area extending around the entire periphery of the catalyst layer beyond the extent of lateral movement of the porous layer relative to the catalyst layer. For example, if the cavity, catalyst layer, and porous layer are generally circular, the centers of the catalyst layer and the porous layer may be offset axially by up to a first lateral distance. The radius of the porous layer may exceed the radius of the catalyst layer by a distance greater than the first lateral distance. This prevents misalignment of the porous layer and the catalyst layer.

[0032] The peripheral surface area can at least partially cover the retention feature.

[0033] That is, one or more faces of the retention feature may face a peripheral surface region of the porous layer, and the porous layer may extend laterally to cover at least some or all of said faces of the retention feature.

[0034] As disclosed herein, the porous layer, in some embodiments, can be bonded, glued, welded, or otherwise joined to the retention feature, and can at least partially seal to the underlying retention feature during use.

[0035] It will be appreciated that the housing, cavity, porous layer and catalyst layer may each have any suitable shape, with the catalyst layer, porous layer and cavity (and typically the housing as well) conveniently being coaxial and / or circular.

[0036] The catalyst layer can have a catalyst layer thickness, and the retention feature can have a depth (the depth being the distance in a direction between the faces of the catalyst layer when the catalyst layer is installed in the cavity).

[0037] The depth of the retention features may be greater than, equal to, or less than the thickness of the catalyst layer.

[0038] The inventors have found that it is advantageous for the depth of the retention feature to be equal to or less than the thickness of the catalyst layer.

[0039] In some situations, the depth of the retention features is greater than the thickness of the catalyst layer, the depth of the retention features is less than 0.5 mm or less than 0.2 mm greater than the thickness of the catalyst layer.

[0040] In some situations, the depth of the retention features is less than the thickness of the catalyst layer, and the depth of the retention features is at least about 0.2 mm, or less than 0.5 mm, less than the thickness of the catalyst layer.

[0041] Without being bound by theory, it is believed that having a depth of the retention feature equal to or less than the thickness of the catalyst layer can help maintain the porous layer in contact with at least one side of the catalyst layer, thereby allowing the porous layer to more effectively suppress the reaction rate in the catalyst layer when temperatures become excessive during use.

[0042] Thermoplastic materials inherently have a melting point or glass transition temperature, referred to herein as the first temperature. Near or above the first temperature, the thermoplastic material begins to lose its elastic modulus, and the porosity of the porous layer decreases. In effect, as the thermoplastic material begins to deform or melt, the pores of the porous material fuse or close.

[0043] In a preferred embodiment, the retention feature is dimensionally stable up to a second temperature that is greater than the first temperature. In the event of thermal runaway, the retention feature remains dimensionally stable while the porous material moderates or quenches the recombination reaction.

[0044] "Dimensionally stable" means that the retention feature does not melt, deform, or decompose below a second temperature. For example, the retention feature can include a polymeric material having a melting point, glass transition temperature, or decomposition temperature above the first temperature. For the avoidance of doubt, thermal expansion does not constitute a loss of dimensional stability. When the retention feature includes a thermoplastic material and the second temperature is the melting point or glass transition temperature of the thermoplastic material of the retention feature, the second temperature can, in some embodiments, be the same as or substantially the same as the first temperature. For example, the thermoplastic material of the retention feature can be the same thermoplastic material as the porous layer. In such cases, even if the first and second temperatures are the same, the bulk material of the retention structure can maintain sufficient dimensional stability while the porosity of the porous layer decreases. When the first and second temperatures are the same or close, this can aid in adhesion between the porous layer and the retention feature.

[0045] In preferred embodiments, the housing is dimensionally stable up to a third temperature, which may be higher than the first temperature. The second and third temperatures may be the same in some embodiments.

[0046] The porous layer may comprise a porous membrane. The porous layer or membrane may be perforated.

[0047] In some embodiments, the porous layer can comprise an expanded (expanded, swollen, stretched or foamed) thermoplastic polymer film, such as expanded polyethylene, polyurethane, or the like.

[0048] The glass transition temperature or melting point of the thermoplastic polymer material of the porous layer can be 200°C or less, 180°C or less, 160°C or less, or 140°C or less. The glass transition temperature or melting point of the thermoplastic polymer material of the porous layer can be in the range of 50°C to 200°C, or 60°C to 180°C, or 100°C to 180°C, or 100°C to 160°C, or 100°C to 140°C. The glass transition temperature can be in the range of 50°C to 180°C, or 60°C to 160°C, or 80°C to 140°C.

[0049] Those skilled in the art will understand that a thermoplastic material can include one thermoplastic polymer, or in some embodiments, multiple thermoplastic polymers. Furthermore, those skilled in the art will understand that above the glass transition temperature (for amorphous or semi-crystalline polymers) and / or melting point (for crystalline or semi-crystalline thermoplastic polymers), a thermoplastic polymer begins to lose elastic modulus and become dimensionally unstable. Typically, above the glass transition temperature or melting point, the polymer becomes flowable. Furthermore, for a given type of polymeric material, the glass transition temperature or melting point can depend on several factors, such as the average molecular weight or molecular weight range of the polymer and the ratio of monomers present in a copolymer. Therefore, by appropriately selecting the composition of the thermoplastic material, those skilled in the art will be able to select a desired melting point or glass transition temperature for a particular purpose (e.g., the maximum temperature allowed for a particular battery enclosure or catalyst material).

[0050] The catalytic device may include porous layers in contact with both sides of the catalytic layer. The catalytic device may include at least two porous layers, a first porous layer in contact with a first side of the catalytic layer and a second porous layer in contact with a second opposite side of the catalytic layer, each porous layer having a planar size larger than the planar size of the catalytic layer.

[0051] The catalytic device may include at least two porous membranes. Each porous layer may include multiple porous membranes.

[0052] The or each porous layer may be laminated to and in contact with a corresponding face of the catalyst layer.

[0053] "Lamination" or "laminate" refers to a structure formed by applying force between and through the thickness of each layer to bond the layers. Laminated structures are typically formed by the application of pressure, such as with a pinch roller, and heat. Lamination can cause melting or flow between the materials being laminated, or, importantly, can cause a chemical reaction of, for example, adhesive materials present between the layers.

[0054] Each porous layer can be bonded to and in contact with a corresponding surface of the catalyst layer. For example, in some embodiments, an adhesive, such as a contact adhesive, can be used to bond the porous layer and the catalyst layer. The adhesive can be applied discontinuously, for example, in dots, to reduce the risk of blocking the poles of the porous layer or over-covering areas of the surface of the catalyst layer. Bonding can alternatively be achieved by melting or heat welding.

[0055] In some embodiments, alternatively or additionally, some or all of the peripheral regions of at least two porous membranes are bonded to one another, for example, the porous membranes may extend over and around both the retainer and the catalyst layer therein and be bonded to one another.

[0056] In some embodiments, the at least two porous membranes can form an envelope or pouch around the catalyst layer and the retainer.

[0057] The or each porous layer may be laminated or bonded to a retaining structure, for example, a porous layer may be laminated on one or both sides to both the catalyst layer and a retainer around the catalyst layer.

[0058] The catalytic device may include a diffusion-limiting layer configured to regulate the diffusion rate or flow rate of the gas into the catalytic layer.

[0059] The diffusion-limiting layer can be adjacent to the porous layer (in the direction of gas diffusion towards the catalyst layer), or the porous layer can be between the diffusion-limiting layer and the catalyst layer.

[0060] The diffusion-limiting layer may be in contact with the porous layer on the side opposite the side where the porous layer is in contact with the catalyst layer. The diffusion-limiting layer may be laminated or bonded to the porous layer.

[0061] Those skilled in the art will appreciate that during use, gases within a lead-acid battery may diffuse from the electrolyte enclosure of a device according to the present invention to a catalyst layer in fluid communication therewith. Under some operating conditions, such as at elevated temperatures, the pressure within the battery enclosure may exceed ambient pressure. In embodiments of the device that also incorporate a vent to vent such excess pressure from the battery, gas flow from the enclosure may occur, and the catalyst device may be positioned across the gas flow path from the battery enclosure to the external environment.

[0062] The diffusion or flow-restricting effect of the diffusion-restricting layer may be reflected by a relatively high Gurley airflow number, for example, a Gurley airflow number of 50 seconds or greater, or 100 seconds or greater.

[0063] The diffusion-limiting layer may comprise a porous fluoropolymer layer.

[0064] The porous fluoropolymer layer can be hydrophobic.

[0065] The porous fluoropolymer layer may comprise a fluoropolymer membrane, which may be an expanded fluoropolymer membrane such as expanded polytetrafluoroethylene.

[0066] Expanded polymer membranes, such as expanded polyethylene membranes or expanded polytetrafluoroethylene membranes as disclosed herein, comprise a microstructure consisting of fibrils, typically nodes interconnected by fibrils, and pores extending therebetween.

[0067] The porous fluoropolymer layer may have a Gurley number of 100 seconds or more. The porous fluoropolymer layer may have a Gurley number of 200, 300, 400, 700 or 1000 seconds or more.

[0068] The expanded porous polytetrafluoroethylene may have a Gurley number of 100 seconds or more. The porous fluoropolymer layer may have a Gurley number of 200, 300, 400, 700, or 1000 seconds or more.

[0069] The catalytic device may include a porous anti-poisoning layer that is capable of absorbing or decomposing catalyst poisons.

[0070] The poisoning prevention layer may be adjacent to the porous layer (in the direction of gas diffusion to the catalyst layer). The poisoning prevention layer may contact a face of the porous layer and may optionally be laminated or bonded thereto.

[0071] When present, the poisoning prevention layer may be adjacent to, in contact with, laminated to, or bonded to the diffusion-limiting layer. The poisoning prevention layer may be in contact with, and optionally laminated to, or bonded to, the surface of the porous layer.

[0072] That is, the poisoning prevention layer may be located between the porous layer and the diffusion limiting layer, or vice versa.

[0073] Examples of compounds that act as catalyst poisons include dilute sulfuric acid in the electrolyte or sulfides generated from dilute sulfuric acid, such as H2S. Materials such as antimony and arsenic are also present in lead-acid batteries and can act as catalyst poisons. When catalyst poisons come into contact with the catalyst, they reduce its catalytic performance. Materials that can absorb or decompose catalyst poisons include activated carbon, ZnO, and potassium carbonate.

[0074] The poisoning prevention layer can include a membrane. The membrane can be an expanded polymer membrane. The porous poisoning prevention layer or membrane can include a fluoropolymer. The porous poisoning prevention layer or membrane can include polytetrafluoroethylene, such as ePTFE. Woven, nonwoven, or knitted fabrics can also be used.

[0075] The poisoning prevention layer can be hydrophilic. For example, the poisoning prevention layer can include a hydrophilized film, which can more easily adsorb catalyst poisons. One example of the hydrophilization treatment is to use a metal oxide gel. Specifically, a sol of a hydrophilic metal oxide is prepared, and the porous member is immersed in the sol, which subsequently gels the sol. In this way, the inner surfaces of the pores of the porous member can be modified with the hydrophilic oxide gel. For example, the hydrophilization treatment can be performed by coating the surface of the member with a silica material based on the sol-gel method. Alternatively, the hydrophilization treatment can be performed by surface treatment using plasma or the like, as is well known to those skilled in the art.

[0076] The poisoning prevention layer may include a material capable of absorbing or decomposing catalyst poisons inside a porous layer capable of absorbing or decomposing catalyst poisons.

[0077] The term "inside the porous layer (or membrane, as the case may be)" means that a material capable of absorbing or decomposing catalyst poisons may be present or located within the cavities or embedded on the surface or within the pores of the porous layer, similar to, for example, the catalyst in the catalyst layer shown in FIG. 8 and described in more detail below.

[0078] The catalytic device may include an outer hydrophobic porous layer having a Gurley number lower than that of the diffusion-limiting layer, for example, the outer hydrophobic porous layer may have a Gurley number of less than 20 seconds.

[0079] The outer hydrophobic porous layer can inhibit or prevent sulfuric acid mist and / or electrolyte (typically a dilute aqueous sulfuric acid solution) from directly contacting the catalyst layer during use, thereby extending the life of the catalytic device.

[0080] The outer hydrophobic porous layer can comprise a fluoropolymer. The outer hydrophobic porous layer can comprise a membrane. The membrane can be an expanded polymer membrane, such as an expanded fluoropolymer membrane. The membrane can comprise an ePTFE membrane.

[0081] The outer hydrophobic porous layer may be positioned adjacent to the electrolyte enclosure of the battery in use.

[0082] For example, in some circumstances, the cavity has an open end (that, in use, faces towards or is in fluid communication with the electrolyte enclosure), and the outer hydrophobic porous layer is positioned adjacent to, or in some circumstances across, the open end of the cavity.

[0083] The catalyst layer can be porous.

[0084] The catalyst layer may include a hydrophobic porous material. Because hydrogen gas and oxygen gas generated by the cell reaction recombine in the catalyst layer to produce water or water vapor, the environment within or around the catalyst layer tends to be humid. When the catalyst is covered with water or water vapor, hydrogen gas and oxygen gas are less likely to come into contact with the catalyst, and the catalytic reaction (recombination reaction) tends to be less efficient. Providing a catalyst layer with a hydrophobic porous material facilitates the release of water or water vapor generated from the catalyst layer, improving efficiency. In some embodiments, the hydrophobicity may also facilitate the return of water or water vapor to the electrolyte enclosure of the cell during use of the catalytic device.

[0085] The catalyst or a catalyst support carrying the catalyst may be disposed in the cavity or on the pore surface of the catalyst layer (or its hydrophobic porous member). In this case, the catalyst support, particularly the catalyst, is exposed in the cavity of the catalyst layer, thereby allowing hydrogen gas and oxygen gas to come into contact with the catalyst.

[0086] The catalyst layer may alternatively comprise a powder that has been molded, pelletized, or sintered. The catalyst layer may comprise a powder catalyst support that has been molded, pelletized, or sintered. The catalyst layer may comprise a polymer powder mixed with a powder catalyst support, and the mixture is molded, pelletized, or sintered to form the catalyst layer.

[0087] The catalytic layer (or its hydrophobic porous member) is preferably non-reactive with other materials within the cell, such as sulfates. Indeed, other layers of the catalytic device, such as the outer hydrophobic porous layer, the diffusion-limiting layer, and / or the poisoning prevention layer, may further comprise materials or membranes that are preferably non-reactive with other materials within the cell, such as sulfates.

[0088] For example, polypropylene and PTFE can be used, as can woven, nonwoven, knitted fabrics and porous membranes thereof. The catalyst layer can include an expanded polymer membrane.

[0089] The catalyst layer (or hydrophobic porous member) can include porous polytetrafluoroethylene (PTFE), such as ePTFE.

[0090] Polytetrafluoroethylene inherently possesses excellent properties, such as hydrophobicity, chemical resistance, UV resistance, oxidation resistance, and heat resistance, making it suitable as a battery construction material. As known to those skilled in the art, polytetrafluoroethylene can be made porous by stretching a PTFE sheet under controlled expansion ratio and temperature conditions, optionally biaxially stretching, to form a porous ePTFE layer. More specifically, expanded porous polytetrafluoroethylene is composed of nodes (knots) and fibrils (thin fibers). Catalysts or catalyst supports are held within tiny cavities (micropores) defined by the nodes and / or fibrils. Both nodes and fibrils are made of polytetrafluoroethylene, and the difference between them is thought to be due to differences in the aggregation state or crystallization state of polytetrafluoroethylene molecules. It is generally believed that nodes are aggregates of primary particles of polytetrafluoroethylene, while fibrils are made from bundles of crystalline ribbons elongated from the nodes, i.e., primary particles.

[0091] Figure 8 shows a schematic of catalyst particles supported on the surface of a catalytically inert powder support. The catalyst material, including the catalyst and support, is located inside the ePTFE membrane, between the fibrils and nodes. Such materials, like other expanded polymeric materials, can be manufactured by mixing the components in powder form, followed by extrusion (e.g., forming a tape) and expansion under controlled conditions of temperature and expansion ratio to form an expanded membrane.

[0092] The catalyst can be any catalyst that recombines hydrogen and oxygen to produce water, examples of which include Pd, Pt, and Au. The support supporting the catalyst can be any support with a specific surface area sufficient to support the catalyst in the desired dispersed state. The support can be selected from the group consisting of silica, alumina, zeolite, carbon, oxides and carbides of Group IVB, VB, VIB, VIIB, and VIII transition metals, and combinations thereof. Alternatively, the support can be a carbon material. It is undesirable for the support material to undergo chemical reactions other than the desired reaction or for the constituent substances of the support to be eluted upon contact with condensed water. In this regard, carbon materials are chemically stable and are preferred support materials. Examples of carbon materials include carbon black (e.g., oil furnace black, channel black, lamp black, thermal black, and acetylene black), activated carbon, coke, natural graphite, and artificial graphite. These may be used in combination.

[0093] The catalyst layer can further include a substance capable of absorbing or decomposing catalyst poisons, for example, as an alternative to a device that includes a separate anti-poisoning layer. The substance capable of absorbing or decomposing catalyst poisons can be mixed with the catalyst material or a support that includes the catalyst material, and / or can be dispersed within the catalyst layer (e.g., within a porous membrane, as disclosed herein).

[0094] In a further aspect, there is provided a lead-acid battery comprising an electrolyte enclosure and one or more catalytic devices according to the first aspect, the cavity of the or each catalytic device being in fluid communication with the electrolyte enclosure. The cavity of the or each catalytic device may, in use, be located above a nominal level of electrolyte (or may be isolated from the electrolyte). The housing of the or each device may extend into the enclosure. An open end of each cavity may extend into the enclosure.

[0095] A lead-acid battery may include two or more cells or a plurality of cells each having an electrolyte enclosure, each of which may be provided with one or more catalytic devices according to the present invention.

[0096] When multiple cells are present, catalytically generated water or water vapor from the electrolyte in one cell can transfer to other cells. In this case, the amount of electrolyte can vary from cell to cell. At least one catalytic device in each cell can help the hydrogen gas and oxygen gas generated in each cell recombine at the catalyst layer of each cell and help the generated water or water vapor return to the original cell (the cell where the water or water vapor was generated). This is useful for avoiding differences in the amount of electrolyte from cell to cell.

[0097] Unless otherwise indicated, the term "comprising," when applied to a structural feature, material, composition, or method, is used herein to mean including the stated structural feature, material, composition, or method in addition to other structural features, materials, compositions, method steps, etc., or consisting only of said structural feature, material, composition, or method step. [Brief explanation of the drawings]

[0098] BRIEF DESCRIPTION OF THE DRAWINGS Exemplary embodiments will now be described with reference to the following drawings:

[0099] [Figure 1] FIG. 1 is an exploded perspective view of an embodiment of a catalytic device.

[0100] [Figure 2] FIG. 2 is a schematic plan view of the catalytic device of FIG.

[0101] [Figure 3] FIG. 3 is a schematic cross-sectional view of the catalytic device of FIG.

[0102] [Figure 4] FIG. 4 is a schematic cross-sectional view of an alternative catalytic device. [Figure 5] FIG. 5 is a schematic cross-sectional view of an alternative catalytic device. [Figure 6] FIG. 6 is a schematic cross-sectional view of an alternative catalytic device.

[0103] [Figure 7] 7(a)-(e) are schematic plan views of exemplary catalytic devices.

[0104] [Figure 8] FIG. 8 is a diagram of the microstructure of a porous layer having particulate material within the layer.

[0105] [Figure 9] FIG. 9 shows (A) the test enclosure, (B) a schematic of the feed gas supply to the test enclosure, and (C) a schematic cross-sectional view of the catalyst test device.

[0106] [Figure 10] FIG. 10 shows the test data for Examples 1-3. [Figure 11] FIG. 11 shows the test data for Examples 1-3. [Figure 12] FIG. 12 shows the test data for Examples 1-3. DETAILED DESCRIPTION OF THE INVENTION

[0107] Detailed Description of the Embodiments Figure 1 shows an exploded view of a catalytic device 100 for a lead acid battery. Figures 2 and 3 show a schematic plan view and a cross-sectional view of the device 100.

[0108] The catalytic device has a housing 110, typically molded from a plastic material such as polypropylene. The housing defines a cavity 112 (a cylindrical cavity in the illustrated embodiment) having an open end (generally designated 114). In use, the device is configured to be inserted into an aperture in the housing of a cell, with the open end 114 of the cavity 112 facing into the enclosure.

[0109] The catalytic device 100 includes a catalytic layer 120. In the illustrated embodiment, the catalytic layer is subsequently formed from two layers or sub-layers 120a, 120b to form the desired catalytic thickness. The catalytic layer 120 is mounted within the cavity 112 and surrounded by a retaining structure in the form of a ring 130. The ring 130 is also typically formed from a plastic material such as polypropylene.

[0110] A porous layer 140 is mounted within the cavity. The porous layer has an area larger than the area of ​​the upper surface 122 (in the orientation of the drawing) of the catalyst layer 120. The porous layer 140 contacts and covers the upper surface 122. Thus, a peripheral region 144 of the surface 142 adjacent to the catalyst layer 140 partially covers a portion of the end 132 of the ring 130.

[0111] The porous layer 140 comprises a thermoplastic material. A porous polyethylene material, such as an expanded polyethylene film in particular, can be used, where the polyethylene has a melting point lower than the melting point of the polypropylene housing 110 and ring 130.

[0112] Catalyst layer 120 is mounted within ring 130 within cavity 110, and porous layer 140 is also mounted within the cavity so as to contact surface 122 of catalyst layer 120. Ring 130 constrains movement in the lateral direction (i.e., in a direction generally parallel to surfaces 122, 142), so that surface 122 remains covered by porous layer 140 within the range of possible movement.

[0113] This is shown in Figure 2. To facilitate assembly of the device layers and to account for manufacturing tolerances, a small clearance is provided between the inner profile 133 of ring 130 and the outer edge 124 of catalyst layer 120, allowing a maximum lateral displacement L1 between the center of ring 130 and the outer edge 124 of catalyst layer 120 before catalyst layer 126 abuts the ring. Porous layer 140 similarly has a clearance between its center 146 and the center 116 of the housing to allow for a maximum lateral displacement L2 before abutting the inner wall 113 of cavity 112.

[0114] 2, the maximum possible lateral displacement between centers 126, 146 of layers 120, 140 is L1+L2. Advantageously, the radial thickness of ring 130 can be set equal to, or preferably greater than, L1+L2, so as to prevent face 122 of catalyst layer 120 from becoming uncovered by porous layer 140 due to lateral movements (which may occur, for example, during vibrations during use).

[0115] It will be appreciated that the maximum lateral displacement is typically small, in the range of less than 1 mm, less than 0.5 mm or less than 0.1 mm.

[0116] When the porous layer 140 is used and exposed to the electrolyte enclosure of a lead-acid battery, hydrogen and oxygen generated within the battery permeate through the porous layer to the catalyst layer 120 and react in a recombination reaction to produce water vapor, which can be returned to the enclosure. As the temperature of the catalyst layer 120 increases above the melting point or glass transition temperature of the thermoplastic material, the porosity of the porous layer decreases, controlling the rate of the recombination reaction and mitigating the temperature of the catalyst layer. The porous layer 140 has a larger surface area than the catalyst layer 120, and the peripheral region 144 of the porous layer 140 extends sufficiently beyond the surface 122 of the catalyst layer 120 so that portions of the surface 122 are not exposed when the porous layer 140 moves laterally within the cavity 112 and the catalyst layer 120 moves laterally within the retention feature 130. The material selection for the housing 110 and retention mechanism, ring 130 (in the illustrated embodiment, polypropylene) and porous layer 140 (in the illustrated embodiment, polyethylene thermoplastic material) ensures that the housing and retention mechanism remain dimensionally stable and do not shift out of position even when the thermoplastic material of porous layer 140 begins to melt.

[0117] As shown most clearly in the cross-sectional view of FIG. 3, the depth d of the catalyst layer 120 120 is the depth d of ring 130 130 The porous layer 140 covering the catalyst layer 120 is a flexible polyethylene film in the illustrated embodiment, which effectively wraps around and on the periphery of the catalyst layer 120 to mitigate the rate of the recombination reaction.

[0118] In other embodiments (not shown), the depth of the porous layer and the retention features may be substantially the same, or in some cases the depth of the retention features may be greater.

[0119] The catalytic device 100 also includes a diffusion-limiting layer 150, which in the illustrated embodiment is shown in the form of an ePTFE membrane having a Gurley airflow number of about 100 seconds. The diffusion-limiting layer 150a is disposed adjacent the porous layer 140 and is provided between the catalyst layer 120 and the open end 114 of the cavity 112, such that, in use, it is interposed between the electrolyte enclosure and the catalyst layer 120 and controls the diffusion or flow rate of gas from the enclosure to the catalyst layer 120.

[0120] In the illustrated embodiment, an additional diffusion-limiting layer 150b is positioned adjacent to and covers the lower surface 123 (in the orientation shown) of the catalyst layer 120, thereby controlling the diffusion or flow of gas through the catalyst layer 120 and around the ring 130 toward the lower surface 123.

[0121] The catalytic device 100 further includes a porous poisoning prevention layer 160 adjacent to the diffusion-limiting layer 150b. The poisoning prevention layer 160 includes a material capable of absorbing or decomposing catalyst poisons, such as hydrogen sulfide. An example of a suitable poisoning prevention layer 160 is a porous membrane, conveniently an ePTFE membrane, with zinc oxide powder contained within the porous membrane.

[0122] An outer hydrophobic porous layer 170, which in the illustrated embodiment is formed from an ePTFE membrane, is disposed across the open end 114 of the cavity 112 and is sealed or bonded to the housing around the periphery of the cavity 112. The outer hydrophobic porous layer 170 has a relatively lower Gurley airflow number than the diffusion-limiting layers 150a, 150b, conveniently in the range of about 20 Gurley seconds. The outer hydrophobic porous layer 170 prevents liquid electrolyte solution from entering the cavity 112 during use.

[0123] While the various layers are positioned opposite one another in the illustrated embodiment, in alternative embodiments, one or more layers may be laminated or bonded to one another as disclosed herein. Additionally, in some cases, multiple layers of each type may be used, such as two adjacent porous layers. Some embodiments may omit one or more of the layers of device 100. For example, in some cases, an outer layer may function as a diffusion-limiting layer, eliminating the need for a separate diffusion-limiting layer. In some cases, the poisoning prevention layer may be omitted in some applications of a catalytic device as disclosed herein.

[0124] As discussed above, the melting point or glass transition temperature of the thermoplastic material of porous layer 140 can be appropriately selected depending on the amount of gas generated, catalytic performance, etc. in a particular battery application. The melting point can be, for example, in the range of 100°C to 180°C, or approximately 160°C. While porous layer 140 of device 100 comprises polyethylene, in other embodiments, the thermoplastic material can be, for example, polyethylene, polypropylene, polyvinyl chloride, polymethyl methacrylate, polystyrene, or polyvinylidene fluoride with higher or lower melting points. Table 1 shows the melting points and glass transition temperatures of a range of exemplary thermoplastic materials that can be used.

[0125] [Table 1]

[0126] Figure 4 shows a cross-sectional view of an alternative catalytic device 100A. Features in common with device 100 are similarly numbered.

[0127] Device 100A includes a housing 110 defining a cavity 112. Catalytic device 100A has a catalytic layer 120 covered on each side 122, 123 by a porous layer 140 and an adjacent diffusion-limiting layer 150. Also provided is a poisoning prevention layer 160 and an outer porous hydrophobic layer 170. Device 100A further includes a retention feature 130 in the form of a ring 130 within cavity 112.

[0128] 5, a further catalytic device 100B is shown in which a housing 110B has an open end 114B and a closed end 115B. A catalyst layer 120 is mounted in a recess 130B in the closed end 115B of the housing 110B, with an inner wall 133B of the recess limiting lateral movement of the catalyst layer 120, thereby causing the recess 130 to act as a retention mechanism.

[0129] The poisoning prevention layer 160 is adjacent to, but spaced apart from, the diffusion limiting layer 150. The poisoning prevention layer 160 and the porous hydrophobic outer layer 170 extend across the open end 114 of the housing 110B.

[0130] 6, another example of a catalytic device 100C is shown. The catalytic device 100 is similar to the catalytic device 100, except that each porous layer 140a, 140b covers each side 122, 123 of the catalytic layer 120. The porous layers 140a, 140b are bonded (e.g., thermally welded or adhesively bonded) to one another around an outer region 148 of the ring 130, completely surrounding the catalytic layer 120 and the ring 130.

[0131] In other embodiments (not shown), each porous layer may be bonded to a retention feature, such as around the periphery of a retainer, to encapsulate the catalyst layer.

[0132] As shown in the schematic plan view of FIG. 7, various relationships are possible between the shape of the catalyst layer and the retention feature. The outer edge 124 of the catalyst layer 120 can have a shape and size that matches as closely as possible the shape and size of the inner profile 133 of the retention feature 130 (FIGS. 7(a) and 7(e)). Alternatively, a clearance C1 can be provided between the catalyst layer 120 and the retention feature 130 (FIGS. 7(b) and 7(d)), or between the catalyst layer 120 and the inner wall 113 of the cavity 112 (FIG. 7(c)). The inner profile 133 of the retention feature 130 can include multiple retention structures 136 extending from the cavity 112 (FIG. 7(c)), or multiple retention structures 136 extending from the inner profile 133 of the retainer 130 (FIG. 7(d)). The inner profile 133 of the retention feature 130 can have a keyed relationship (FIG. 7(e)). Additionally, although the illustrated examples show the housing and / or retention mechanism having a generally circular symmetry, the invention is not so limited and other shapes and configurations are contemplated.

[0133] experiment A test enclosure 200 (FIG. 9(A)) was provided and connected to a controlled flow of feed gas consisting of a stoichiometric mixture of hydrogen and oxygen feed gases (2:1 molar ratio). The feed gases were provided from respective gas cylinders via mass flow controllers 210, 220 connected to a common supply line 230 extending to the enclosure 200. The catalytic test device 100T was inserted into an aperture in the wall of the test enclosure, with the open end of the cavity in the device housing facing the interior of the enclosure 200.

[0134] An example catalyst testing device 100T was constructed generally similar to the device shown in Figures 1-3, except that the retaining ring 30 shown in the figures was omitted. Each device contained a K-type thermocouple 190 manually placed through a small aperture in the housing, in thermal contact with the ePTFE layer adjacent to the interior wall of the housing, as shown in the schematic diagram in Figure 9(C). The housing, cavity, retaining ring, and all layers of the device were circular in cross section.

[0135] The catalyst material used was alumina-supported palladium (5 wt% Pd / alumina, manufacturer: NECC). The catalyst layer consisted of two 565 μm-thick, loaded PTFE sheets with a composition of Pd / alumina / PTFE = 1.2 / 68.8 / 30 (wt%). Therefore, the total mass of palladium in the catalyst layer was approximately 0.7 mg.

[0136] The porous layers used were expanded polyethylene (ePE) manufactured by Shenzhen Senior Technology Material Co., Ltd., with a melting point of 130°C. Each ePE layer had a thickness of 16 μm, a Gurley number of 200 seconds, and a basis weight (mass per unit area) of 8.9 gm. -2 It was.

[0137] The flow rates of 2H2 / O2 supply gases were controlled at the following flow rates for 5 min each, and the flow rates were increased stepwise according to Table 2.

[0138] The experiments were carried out at ambient temperature in the laboratory, but the temperature was varied from test to test.

[0139] [Table 2]

[0140] The temperature of the catalyst bed was measured throughout.

[0141] In normal use of automotive lead-acid batteries, the gas flow rate vented from the electrolyte enclosure is typically in the range of 2-4 ml / min. Therefore, the test enclosure and feed gas flow rates significantly exceed those typically encountered in lead-acid batteries and are believed to represent an extreme scenario that could lead to thermal runaway of the catalytic device.

[0142] The Gurley value of the porous layer or membrane disclosed herein is evaluated based on JIS P 8117:1998. The Gurley value is the value of the surface area of ​​a porous layer or membrane at a pressure of 1.29 kPa over an area of ​​6.45 cm. 2 100cm through the sample 3The Gurley value is the time (seconds) for air to pass through vertically. It is an index of air permeability. [Example]

[0143] Example 1 A first test device, Device 1, was fabricated in which catalyst layer 120 was positioned in alignment with porous layers covering the inner and outer surfaces of the catalyst layer.

[0144] The device was exposed to a feed gas flow rate according to Table 2 and the temperature was monitored.

[0145] Two examples of Device 1 were tested and the results are shown in FIG.

[0146] The temperature of the catalyst bed in both experiments was the same over time, within experimental error.

[0147] The maximum temperature of the catalyst layer measured by the thermocouple remained below 100 °C in both experiments. This indicates that the porous polyethylene layer served to moderate the rate of the recombination reaction. After approximately 10 minutes, the porosity of the polyethylene layer decreased, preventing the recombination reaction rate and, therefore, the catalyst layer temperature from continuing to increase with increasing feed gas flow rates in steps 3–5 of each experiment. The maximum measured temperature at the contact point between the thermocouple and the catalyst sheet was lower than the melting point of the porous layer, which is understood to reflect the relative thermal conductivity of the catalyst layer. The observed variation in the temperature profile (also visible in Figure 12 below) is due to variations in the relative position of the thermocouple with respect to the catalyst sheet during the manual construction of the test device.

[0148] Example 2 A second test device, Device 2, had the catalyst layer 120 intentionally offset from the porous layer so that a small area of ​​the surface of the catalyst layer was not covered by the porous layer.

[0149] The results of the tests performed on Device 2 are shown in Figure 11 along with the results of the first test Device 1 for comparison.

[0150] In experiments conducted with Test Device 2, ignition of the supply gas within the test enclosure occurred after approximately 9 minutes.

[0151] The ignition indicates that the temperature of the exposed area of ​​the catalyst bed surface reached a high enough temperature to ignite the feed gas. Again, it can be seen that the temperature measured by the thermocouple was lower and did not reflect the hot area of ​​the catalyst bed that caused the ignition.

[0152] Example 3 Two more test devices, Device 4, were constructed generally according to the device of Figure 3, including a polypropylene retaining ring 130 and two ePE layers covering both the catalyst layer and the retaining ring.

[0153] Two additional test devices, Test Device 5, were fabricated in which both polypropylene retaining rings were omitted.

[0154] Tests were performed on all four devices and the results are shown in Figure 12 and Table 3.

[0155] [Table 3]

[0156] Tests performed on Test Device 5 (shown as (3) and (4) in the diagram and table and labeled "without PP ring") resulted in a maximum temperature increase of approximately 150°C, high enough that the polypropylene housing began to deform and risked loss of the catalyst layer and other layers from the device cavity. Note that at the high flow rates used in the test protocol, the thermocouple cooled slightly.

[0157] Experiments performed on test device 4 ("with PP ring" shown as (1) and (2)) show that the polyethylene porous layer melted near the end of step 2, reducing porosity and thereby acting to mitigate the rate of the recombination reaction, but that the presence of the PP ring 130 improved the effectiveness of the shutdown effect of the ePE layer.

[0158] Examples 4 and 5 show the effect of the relative dimensions of the catalyst layer and the polypropylene retaining ring.

[0159] Example 4 Additional test devices similar to Device 4 were constructed. Two additional devices were constructed with reduced catalyst layer area, providing an "edge gap" between the periphery of the catalyst and the polypropylene retaining ring. The catalyst layer and retaining ring were both 0.75 mm thick.

[0160] The results are shown in Table 4 below.

[0161] [Table 4]

[0162] These data show that the maximum recorded rate of temperature rise and maximum recorded temperature of the catalyst layer are correlated with the size of the gap, or clearance, between the catalyst layer and the retainer.

[0163] These results suggest that minimal clearance may be desirable in applications of the devices of the present invention where suppression of catalyst temperature takes priority over the overall rate of the recombination reaction.

[0164] Example 5 An additional test device was fabricated similar to Device 4. The catalyst layer and retaining ring were both 0.75 mm thick.

[0165] Two additional devices were fabricated with increased retaining ring thickness (0.95 mm and 1.20 mm thick rings). The results are shown in Table 5 and show the correlation between increasing retaining ring thickness or depth (relative to catalyst layer thickness / depth) and the maximum catalyst layer temperature rise rate and maximum temperature.

[0166] [Table 5]

[0167] These results suggest that in applications of the devices of the present invention where suppression of catalyst temperature is prioritized over the overall rate of the recombination reaction, it may be desirable to reduce the minimum thickness gap, or indeed the depth of the ring.

[0168] While exemplary embodiments have been described herein, these should not be construed as limiting the modifications and variations possible within the scope of the invention disclosed herein and set forth in the appended claims.

Claims

1. A catalytic device for a lead acid battery, comprising: a housing defining a cavity; a catalyst layer mounted within the cavity, the catalyst layer including a catalyst that promotes a reaction that produces water or water vapor from oxygen and hydrogen; and a porous layer comprising a thermoplastic material mounted within the cavity; Including, the porous membrane has a planar size larger than that of the catalyst layer, a surface of the catalyst layer is in contact with the porous layer, and the porous membrane covers at least one surface of the catalyst layer; The catalyst layer is mounted in the cavity within a retention mechanism configured to maintain the position of the catalyst layer within the cavity, and the at least one surface is covered by the porous layer.

2. The catalytic device of claim 1 , wherein the retention mechanism includes one or more retention structures or retainers mounted within the cavity in a substantially fixed relationship relative to the housing to prevent or substantially prevent lateral movement of the catalyst layer.

3. The catalytic device of claim 2 , wherein the retention mechanism includes a retainer in the form of a ring whose shape generally corresponds to the shape of the catalyst layer.

4. A catalytic device as described in any one of claims 1 to 3, wherein a lateral clearance between the catalytic layer and the retention mechanism allows a certain range of lateral movement of the catalytic layer and the porous layer relative to the housing within the cavity, and the porous layer includes a peripheral surface area extending beyond the range of lateral movement of the porous layer relative to the catalytic layer around the entire periphery of the catalytic layer.

5. The catalytic device according to any one of claims 1 to 4, wherein the catalytic layer has a catalytic layer thickness, the retention feature has a depth, and the depth of the retention feature is equal to or less than the thickness of the catalytic layer.

6. The catalytic device of any one of claims 1 to 5, wherein the thermoplastic material has a melting point or glass transition temperature at a first temperature, and the retention mechanism is dimensionally stable up to a second temperature higher than the first temperature.

7. The catalytic device of any one of claims 1 to 6, wherein the porous layer comprises an expanded thermoplastic polymer membrane.

8. 8. The catalytic device of claim 7, wherein the thermoplastic material of the expanded thermoplastic polymer membrane is polyethylene or polyurethane.

9. The catalytic device according to any one of claims 1 to 8, comprising at least two porous layers, a first porous layer contacting a first surface of the catalytic layer and a second porous layer contacting a second surface opposite the catalytic layer, each porous layer having a planar size larger than the planar size of the catalytic layer.

10. The catalytic device of claim 9 , wherein peripheral regions of the at least two porous membranes are bonded to one another.

11. One or more of the following: a diffusion-limiting layer adapted to adjust the diffusion rate or flow rate of the gas into the catalyst layer; a porous poisoning prevention layer capable of absorbing or decomposing catalyst poisons; outer hydrophobic porous layer, The catalytic device of any one of claims 1 to 10, comprising:

12. One or more of the diffusion-limiting layer, the poisoning prevention layer, or the outer hydrophobic porous layer may be Expanded polymer membrane, an expanded fluoropolymer membrane, or Expanded PTFE membrane The catalytic device of claim 11 , comprising:

13. 13. The catalytic device of claim 12, wherein the catalytic device comprises an anti-poisoning layer, the anti-poisoning layer comprising an expanded polymer membrane and a material capable of absorbing or decomposing catalytic poisons within the membrane.

14. The catalytic device according to any one of claims 11 to 13, wherein the catalytic device comprises both a diffusion-limiting layer and an outer hydrophobic porous layer, the outer hydrophobic porous layer having a Gurley number lower than the Gurley number of the diffusion-limiting layer.

15. The catalytic device according to any one of claims 11 to 14, wherein the catalytic device includes a diffusion-limiting layer, the diffusion-limiting layer having a Gurley permeability of 50 seconds or more or 100 seconds or more.

16. The catalytic device according to any one of claims 1 to 15, wherein the catalytic layer is porous.

17. The catalytic device according to any one of claims 1 to 16, wherein the catalytic layer comprises a hydrophobic porous member and a catalyst or a catalyst carrier supporting the catalyst, the catalyst being disposed within the cavities or on the surfaces of the pores of the catalytic layer.

18. The catalytic device of claim 17 , wherein the hydrophilic porous member comprises ePTFE.

19. A lead-acid battery comprising an electrolyte enclosure and one or more catalytic devices according to any preceding claim, wherein the cavity of the or each catalytic device is in fluid communication with the electrolyte enclosure.

20. 20. A lead acid battery according to claim 19, comprising a plurality of cells, each cell having an electrolyte enclosure, each electrolyte enclosure being provided with one or more catalytic devices according to any one of claims 1 to 18.

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