Metal-air battery and manufacturing method

Abstract

The metal-air battery (100) has a first housing portion (111) and a second housing portion (112), which together form a battery housing (110). The metal-air battery includes a metal-based anode (120) and a layered air cathode (130) and an electrolyte. The first housing portion (111) has at least one vent opening (114). A layered air diffuser (140) is disposed between the first housing portion (111) and the air cathode (130). A layered separator (150) is disposed between the air cathode (130) and the metal-based anode (120). According to the present invention, the laminar air diffuser (140) is breathable and has a first side facing the air cathode (130) and a second side facing away from the air cathode (130), and the laminar air diffuser (140) has a hydrophobic coating on at least one of the sides.

Description

[Technical Field]

[0001] This invention relates to a metal-air battery, a method for manufacturing a layered air diffuser, and the use of a layered air diffuser for manufacturing a metal-air battery. [Background technology]

[0002] Metal-air batteries typically contain a metal-based anode and an air cathode as electrochemically active components, which are spatially separated from each other by a separator but simultaneously connected via an ion-conducting electrolyte. The separator is usually impregnated with the electrolyte. During discharge, oxygen is reduced in the air cathode, and electrons are taken up in the process. Hydroxide ions are formed and move to the anode via the electrolyte. There, the metal base of the anode is oxidized, releasing electrons. The resulting metal ions react with the hydroxide ions.

[0003] Both primary and secondary metal-air batteries exist. Primary metal-air batteries are not rechargeable. Secondary metal-air batteries are recharged by applying a voltage between the anode and the air cathode, causing the electrochemical reaction described to proceed in reverse. Oxygen is released during this process. The best-known example of a metal-air battery is the zinc-air battery, which is used in the form of a button cell, particularly as an energy storage cell in hearing aids.

[0004] Metal-air batteries have a very high energy density because the oxygen requirements in the air cathode can be met by atmospheric oxygen from the surrounding environment. Therefore, it is necessary to supply atmospheric oxygen to the air cathode during the discharge process. Conversely, it is necessary to remove the oxygen generated in the air cathode during the charging process of a secondary metal-air battery. For these reasons, metal-air batteries generally have a housing with corresponding inlet and outlet openings. Generally, holes are formed in the housing as inlet and outlet openings, for example, by punching them out.

[0005] Typically, a gas diffusion electrode is used as the air cathode in a metal-air battery. A gas diffusion electrode is an electrode in which substances involved in electrochemical reactions (generally a catalyst, electrolyte, and atmospheric oxygen) exist side by side in solid, liquid, and gaseous forms and can come into contact with each other. The catalyst catalyzes the reduction of atmospheric oxygen and, if necessary, also catalyzes the oxidation of hydroxide ions during battery charging.

[0006] Plastic-bonded gas diffusion electrodes are often used as air cathodes in metal-air batteries, particularly in the form of button batteries. Such gas diffusion electrodes are described, for example, in German Patent Application Publication No. 3722019 A1. In such electrodes, a plastic binder (e.g., polytetrafluoroethylene, abbreviated as PTFE) forms a porous matrix in which particles of electrochemically active material (e.g., particles of noble metals such as platinum or palladium, or manganese oxide particles) are embedded. These electrochemically active materials catalyze the aforementioned conversion of atmospheric oxygen. Such electrodes are manufactured by rolling a dry mixture of the binder and catalyst to form a foil. This dry mixture can, for example, be rolled to obtain a mesh or expanded metal grid of silver, nickel, or silver-plated nickel. The metal mesh or expanded metal forms a conductive structure within the electrode and functions as a conductor.

[0007] When oxygen is reduced in such an air cathode, the electrons released during the process can be discharged through the aforementioned conductive structure. The conductive structure preferably comes into direct contact with a portion of the housing that functions as a electrode of the battery.

[0008] The aforementioned oxygen inlet or outlet is generally formed at the bottom of the housing of a metal-air battery, especially in the case of a button cell. To allow oxygen to come into as direct contact as possible with the air cathode through the opening, the air cathode in such a battery is usually positioned flat on the bottom of the housing so as to cover the opening. This often involves a layered air diffuser between the air cathode and the bottom of the housing, which may be made of, for example, porous filter paper.

[0009] British Patent No. 2109622B describes a zinc-air battery in the form of a button cell. A PTFE film is provided beneath the air cathode, and together with the air cathode, they form a laminate. A porous air diffusion disc made of filter paper is provided between this laminate and the bottom of the housing having a ventilation opening, thereby dispersing the incoming air across the surface and achieving a dispersed approach of air to the cathode.

[0010] A zinc-air battery with a similar structure is known from International Publication No. 01 / 93366 A1. Here too, the air cathode is formed as a laminate with a PTFE film. An air dispersion layer is provided between the gas-permeable PTFE film of the laminate and the bottom of the housing which has an air inlet opening.

[0011] In many cases, a problem associated with metal-air batteries is that leakage can occur from the battery's ventilation openings, particularly during or after discharge under high humidity conditions. This is because the hygroscopic electrolyte absorbs gaseous water from the surrounding air. The higher the humidity, the more water the electrolyte absorbs. Due to this water absorption, the internal pressure of the metal-air battery increases to the point where the hydrophobic PTFE film of the air-cathode stack can no longer adequately repel the aqueous electrolyte. As a result, the electrolyte is pushed out of the film. As soon as the electrolyte passes through the PTFE film in the direction of the ventilation openings at the bottom of the housing, the porous air dispersion layer, such as air dispersion paper, absorbs the electrolyte, causing leakage from the battery's ventilation openings.

[0012] International Publication No. 2006 / 098718 A1 describes a metal-air cell in which a PTFE film is provided between an air cathode laminate having a hydrophobic film and an air dispersion layer made of a porous material, such as paper.

[0013] International Publication No. 2008 / 051508 A2 deals with a metal-air battery equipped with an air cathode having a laminated PTFE film. An air dispersion layer is provided between the bottom of the housing and the air cathode laminate, which can be formed from porous paper or fibers. In another embodiment, the air dispersion layer may be a breathable and hydrophobic PTFE film. [Overview of the Initiative] [Problems that the invention aims to solve]

[0014] The conventional methods mentioned above do not satisfactorily solve the leakage problems that can occur in metal-air batteries. Therefore, the present invention sets forth the objective of providing a metal-air battery that reliably prevents electrolyte leakage while ensuring optimal function of the metal-air battery. Furthermore, a cost-effective solution suitable for mass production of metal-air batteries in an economical manner should be provided. [Means for solving the problem]

[0015] To solve this problem, the present invention proposes a metal-air battery having the features of claim 1. Furthermore, the problem is solved by a method for manufacturing a layered air diffuser and its use for manufacturing a metal-air battery. Preferred embodiments of the metal-air battery, the method for manufacturing a layered air diffuser, and its use for manufacturing a metal-air battery will also become apparent from the dependent claims.

[0016] The metal-air battery according to the present invention is characterized by the following features a. to e.: a. A metal-air battery has a first housing portion and a second housing portion, which together form the battery housing; b. A metal-air battery comprises a metal-based anode, a layered air cathode, and an electrolyte; c. The first housing portion has at least one ventilation opening; d. A layered air diffuser is placed between the first housing portion and the air cathode; e. A layered separator is arranged between the air cathode and the anode based on metal. The battery is characterized in particular by the following features f. and g.: f. The layered air diffuser is configured to be breathable and has a first side facing the air cathode and a second side facing away from the air cathode; g. The layered air diffuser has a hydrophobic coating on at least one of the sides.

[0017] On the one hand, a layered air diffuser having a breathable property and thus enabling optimal dispersion of the air entering onto the surface of the metal-air battery surface, and on the other hand, having a hydrophobic coating that prevents the passage of the electrolyte, makes it possible to provide a metal-air battery that can reliably prevent battery leakage or at least delay it for a long time even under extreme conditions. The hydrophobic coating is designed to supply sufficient atmospheric oxygen to the battery and ensure sufficient breathability so that optimal functionality is maintained. The hydrophobic coating reliably prevents the air diffuser from starting to saturate with the electrolyte by wicking action and drawing the electrolyte towards the ventilation openings. The hydrophobic coating of the air diffuser keeps the electrolyte away from the ventilation openings of the housing, and the battery either does not leak at all or leaks only at a very slow stage from the ventilation openings compared to conventional metal-air batteries under extreme conditions. Therefore, when a metal-air battery according to the present invention is used, for example, in a hearing aid, damage to the device due to electrolyte leakage can be avoided.

[0018] In addition to a covered air diffuser, the metal-air battery according to the present invention can, in principle, be configured in the same way as a conventional metal-air battery. In particular, the metal-air battery according to the present invention may have a conventional metal-containing anode, a conventional air cathode, and a conventional separator arranged between the anode and the air cathode. For example, the gas diffusion electrode described first is suitable as the air cathode of the metal-air battery according to the present invention. Suitable electrolytes for the metal-air battery according to the present invention are, for example, conventional aqueous electrolyte solutions, particularly alkaline aqueous solutions. Suitable separators include, for example, nonwoven fabric impregnated with an electrolyte, or porous plastic film impregnated with an electrolyte.

[0019] Similar to conventional metal-air batteries, at least one ventilation opening provided in the housing of the metal-air battery according to the present invention ensures that air oxygen can reliably enter the battery housing of the metal-air battery. Depending on the size and dimensions of the ventilation opening, one opening may be sufficient. However, several ventilation openings, for example 2 to 10 openings, or particularly preferably 2 to 5 openings, can also be provided.

[0020] Compared to conventional metal-air batteries that have an air diffusion layer in the form of porous filter paper or similar material, or simply a PTFE film as a hydrophobic material, the hydrophobic coating of the air diffuser ensures optimal dispersion of air entering the surface of the metal-air battery, thereby reliably preventing electrolyte leakage.

[0021] The covered air diffuser according to the present invention does not necessarily need to be directly connected to the housing and / or air cathode. However, the layered air diffuser can also be fixed inside the battery housing. For example, the layered air diffuser can be fixed to the bottom of the housing cup by, for example, one or more dots of adhesive. Preferably, the layered air diffuser is connected to the bottom of the cup with an adhesive dot near the center.

[0022] In a first particularly preferred embodiment of the present invention, the hydrophobic coating is a polytetrafluoroethylene (PTFE) coating. Particularly suitable for the purposes of the present invention is a variant of semicrystalline fluorine-carbon PTFE formed in a non-branched, linear manner. PTFE is hydrophobic and therefore water-repellent. Furthermore, it is highly resistant to various chemicals, making it very suitable for use in energy storage cells.

[0023] In a particularly preferred method, the metal-air battery according to the present invention is characterized by at least one of the further features a. and b. below: a. Hydrophobic coatings are based on coatings using polytetrafluoroethylene dispersions, particularly aqueous dispersions; b. The hydrophobic coating is based on a coating using a dispersion of polytetrafluoroethylene, particularly a dispersion in an aqueous dispersant, and especially a dispersion in water, wherein the solid content of polytetrafluoroethylene in the dispersion is in the range of 5 to 75% by weight, preferably 15 to 60% by weight, and particularly preferably 30 ± 2% by weight.

[0024] The hydrophobic coating is preferably a particulate coating. In a particularly preferred method, the coating contains PTFE particles having an average size (d50) in the range of 0.04 to 1 μm. A particularly preferred size range for the d50 value is 0.10 to 0.30 μm. In particular, the proportion of PTFE particles in the dispersion having a size of <0.04 μm is less than 10%. Furthermore, it is preferable that the proportion of PTFE particles in the dispersion having a size of >1 μm is less than 10%.

[0025] In particular, the corresponding dispersion of polytetrafluoroethylene in water can be easily prepared and processed. In principle, other dispersants are also possible. However, water is especially preferred as a dispersant because it is available at low cost and can generally be used without further safety measures. For example, a starting dispersion having PTFE with a solid content of 60% can be used as a starting point for preparing a suitable dispersion. This starting dispersion can be mixed with water and used for coating.

[0026] The higher the weight percentage of polytetrafluoroethylene in the dispersion, the more hydrophobic the coating becomes, and the more effectively electrolyte leakage can be prevented. However, the weight percentage of polytetrafluoroethylene in the dispersion is particularly preferably 75% by weight or less, because coatings using dispersions with higher percentage values ​​can significantly reduce the air permeability of the air diffuser, and therefore the air dispersion characteristics of the air diffuser may no longer be optimal. Particularly preferably, the weight percentage of polytetrafluoroethylene is in the range of 5 to 75% by weight. The range of 15 to 60% by weight is particularly preferred. In a particularly preferred embodiment, the concentration or weight fraction of polytetrafluoroethylene in the dispersant is 30 ± 2% by weight. These percentage values ​​refer to the solid content of polytetrafluoroethylene in the dispersion used for coating.

[0027] In principle, other materials can also be used for the hydrophobic coating. For example, polyether ketone (PEK) or hydrophobic polyether sulfone are suitable as hydrophobic coating materials. For example, polyether ether ketone (PEEK) is particularly suitable. In another particularly preferred embodiment of the present invention, the hydrophobic coating is an alkyl ketene dimer coating.

[0028] Alkyl ketene dimers generally have the following general structural formula: [ka] It is based on a four-membered ring system of 2-oxetanone.

[0029] Residue R is a hydrocarbon group that may be the same or different in each case. Preferably, these are unbranched or branched alkyl or alkenyl groups having 6 to 24 carbon atoms. Furthermore, residue R may be a cycloalkyl group having at least 6 carbon atoms, or an aryl group having at least 6 carbon atoms, or an aralkyl group having at least 7 carbon atoms, or an alkaryl group having at least 7 carbon atoms, or a mixture thereof. Suitable alkylketene dimers are available, for example, under the trade name AQUAPEL® (e.g., Solenis LLC, USA). For example, AQUAPEL® 201 is particularly suitable for the purposes of the present invention.

[0030] Coatings using at least one alkyl ketene dimer provide very good water repellency. At the same time, one particular advantage of alkyl ketene dimer coatings is that, especially when the solid content in the dispersion is within the preferred range further mentioned below, the coating generally has little to no adverse effect on the air permeability of layered air diffusers. In this respect, alkyl ketene dimer coatings can be superior to polytetrafluoroethylene coatings. Further advantages of alkyl ketene dimer coatings over polytetrafluoroethylene coatings are that alkyl ketene dimers are easier to handle and, moreover, more environmentally friendly because they do not contain fluorine.

[0031] In one particularly preferred method, the hydrophobic coating is based on a coating using a dispersion of at least one alkyl ketene dimer, which is in particular an aqueous dispersion. Alkyl ketene dimers are generally insoluble in water, and the coating is preferably provided as an aqueous dispersion. Since alkyl ketene dimers typically have melting points in the range of about 45°C, mixtures of alkyl ketene dimers in water above about 50°C exist as emulsions, i.e., as a two-phase system with droplets in a liquid medium, and below about 40°C they exist as dispersions, i.e., as a two-phase system with solid particles in a liquid medium. Such dispersions having a temperature of <40°C for coating are particularly preferred for the purposes of the present invention.

[0032] It is preferable that the solid content of at least one alkyl ketene dimer in the dispersant is in the range of 0.01 to 8.0% by weight. Particularly preferable is a solid content in the range of 0.05 to 5.0% by weight, and especially preferably 0.08 to 3.0% by weight. A solid content in the coating dispersion in the range of 0.7 to 0.9% by weight is particularly preferable because, surprisingly, very high hydrophobicity is already achieved at such a low value, while at the same time, air permeability does not decrease and the weight per unit area does not increase. With such a solid content, the inventors were able to achieve particularly good results, obtaining very good water barrier properties along with very good air permeability of the coated air diffuser. Good results were also obtained with a solid content of 0.16% by weight. Preferably, the particle size of the alkyl ketene dimer in the coating dispersion is in the range of less than 1 μm on average, preferably less than 0.5 μm, for example, about 0.3 μm on average.

[0033] The pH of the coating dispersion is preferably in the range of less than pH 7, and particularly preferably less than pH 4. The coating dispersion may further contain stabilizers such as cationic starch or other substances. Examples of stabilizers include water-soluble alkylglycidyl ether-modified poly(aminoamides), particularly as described in European Patent No. 2691572 B1. Furthermore, the coating dispersion may contain other additives such as biocides.

[0034] In one particularly preferred method, the metal-air battery according to the present invention is characterized by the following further feature a: a. The layered air diffuser includes a permeable matrix formed from a hydrophilic material.

[0035] In a particularly preferred embodiment, the metal-air battery according to the present invention has at least one of the following further features a. to d. with respect to the breathable matrix: a. The breathable matrix is ​​a nonwoven fabric; b. The breathable matrix is ​​formed from a fiber mixture, preferably containing polyvinyl alcohol fibers in a proportion of at least 50% by weight; c. The breathable matrix is ​​20-30 g / m² in its uncoated state. 2 Within the range of 24-26 g / m², preferably 24-26 g / m² 2 Having a weight per unit area within the range; d. The breathable matrix, in its uncovered state, has a thickness of 20,000 to 40,000 cm². 3 / cm 2 Within a range of minutes, preferably 25,000 to 35,000 cm 3 / cm 2 Within a range of minutes, particularly preferably 29,000 to 30,000 cm 3 / cm 2 • Has a degree of ventilation within a range of minutes. In one particularly preferred method, features a. and b., or a., b., and c., or a., b., c., and d. are each realized in combination with one another. A particularly suitable porosity of the nonwoven fabric (before coating) is, for example, in the range of 70-90%, preferably in the range of about 80%.

[0036] The mixed fiber may be, for example, a mixture of polyvinyl alcohol fibers and rayon fibers. The proportion of polyvinyl alcohol fibers may be, for example, in the range of 50 to 80%, preferably 60 to 70%. The proportion of rayon fibers may be, for example, in the range of 20 to 50%, preferably 30 to 40%. In one particularly preferred embodiment, the mixed fiber consists of 65% polyvinyl alcohol fibers and 35% rayon fibers.

[0037] In principle, any fiber that is easily processable in terms of manufacturing technology, resistant to the alkaline electrolyte of metal-air batteries, and does not have adverse effects on battery chemistry, for example, is suitable for the production of fiber mixtures.

[0038] The average length of individual fibers may be in the range of 1 mm to 10 mm, for example, in the range of 3 to 5 mm, with 4 mm being particularly preferred.

[0039] Generally, nonwoven fabrics are characterized by being formed from fibers of a limited length that, in principle, can be connected in various ways but are not formed by weaving or knitting. Therefore, paper should also be understood as a fibrous web.

[0040] For the purposes of the present invention, it is particularly preferable that the permeable matrix be formed from a mixed fiber that is more hydrophilic than a nonwoven fabric made of PTFE. For this purpose, it is preferable that this includes fibers of a polymer that is more hydrophilic than PTFE, such as polyvinyl alcohol or a polyvinyl alcohol derivative. It is preferable that these fibers constitute at least 50%. The required hydrophobicity is imparted to the nonwoven fabric by coating it with a PTFE dispersion or an alkyl ketene dimer coating.

[0041] It is particularly preferred if the non-woven fabric contains a large proportion of polyvinyl alcohol fibers. The non-woven fabric that can be produced in this way is particularly suitable for the production of the layered air diffuser according to the invention, because particularly good results can be achieved with regard to stability, air permeability, and the prevention of leakage of the resulting battery, and with regard to the optimal dispersion of air in the battery for coatings using PTFE dispersions or alkyl ketene dimers.

[0042] A weight per unit area of the breathable matrix in the range from 25 g / m 2 is particularly suitable for the purposes of the present invention, because if the material of the breathable matrix of the air diffuser has such a thickness, very good results have been obtained with regard to the properties of the resulting metal-air battery. The same applies to the air permeability of the matrix in the range from 29,000 to 30,000 cm / cm 32 ·min, and particularly good results have been obtained for metal-air batteries manufactured using this.

[0043] In one particularly preferred method, the layered air diffuser according to the invention has coatings on both sides. In one particularly simple and practical method, such a coating of the air diffuser can be achieved by an immersion method in which the breathable matrix of the air diffuser is immersed in a corresponding dispersion having PTFE or alkyl ketene dimer. Subsequently, drying, for example drying at room temperature, can be carried out. This process can be fully automated and is therefore also suitable for mass production in the manufacture of metal-air batteries. Advantageously, a larger portion of the sheet-like material of the breathable matrix is coated in the immersion process. Next, the mold required for the air diffuser can be manufactured, for example, by a stamping process.

[0044] In principle, the hydrophobic coating can be provided on only one side of the layered air diffuser. In these embodiments, it is advantageous when the side with the hydrophobic coating is positioned in the direction of the air cathode. In this embodiment, electrolyte leakage is particularly reliably prevented because the side of the layered air diffuser with the hydrophobic coating is the side that is primarily in contact with the electrolyte.

[0045] In a particularly preferred embodiment of the metal-air battery according to the present invention, the battery always has the following further features with respect to a layered air diffuser: a. The layered air diffuser has a polytetrafluoroethylene coating and a density of 40-160 g / m². 2 Within the range of 45-100 g / m², preferably 45-100 g / m². 2 Within the range, more preferably 60-70 g / m² 2 Having a weight per unit area within the range; or b. The layered air diffuser (140) has a coating using at least one alkyl ketene dimer, with a coating of 10-50 g / m². 2 Within the range of preferably 20-30 g / m² 2 It has a weight per unit area within the range.

[0046] Particularly favorable results were obtained for coated air diffusers at 65±2 g / m². 2 The properties of a metal-air battery fitted with a PTFE-coated air diffuser having a weight per unit area within the range of 29,000 cm / cm² are obtained. 32 When the permeability is within the range of minutes, a hydrophobic coating, preferably prepared using a 30% by weight dispersion of PTFE in water, does not adversely affect the permeability. That is, the permeability is very high despite the hydrophobic coating. In one particularly preferred method, the permeability of a PTFE-coated air diffuser is 21,000 to 23,000 cm⁻¹. 3 / cm 2It is within the range of minutes. On the other hand, hydrophobic coatings mean that there will be no leakage of metal-air cells through layered air diffusers. If the weight per unit area of ​​the layered air diffuser is very large, which can be achieved by coatings with higher percentage values ​​of PTFE dispersions, the air permeability of the air diffuser may be adversely affected, and therefore all functions of the metal-air cell to which it is installed can no longer be guaranteed.

[0047] For air diffusers coated with alkyl ketene dimers, a preferred weight per unit area is 20-30 g / m². 2 Within this range, for example, aqueous dispersions of alkyl ketene dimer containing 0.8 or 7.6% by weight are preferably used for coating. The resulting hydrophobicity is very high, and at the same time, no adverse effect on air permeability is detected. In one particularly preferred method, the air permeability of an air diffuser coated with alkyl ketene dimer is 21,000 to 23,000 cm⁻¹. 3 / cm 2 It is within the minutes range.

[0048] In a more preferred embodiment of the metal-air battery according to the present invention, at least one of the further features a. and / or b. below can be obtained: a. A metal-air cell includes at least one additional layer between the air cathode and a layered air diffuser; b. At least one additional layer is a hydrophobic membrane, preferably a membrane made of polytetrafluoroethylene. In a particularly preferred method, features a. and b. described immediately above are realized by a combination of each other.

[0049] The additional layer between the air cathode and the layered air diffuser may be a PTFE film that forms an assembly, such as a laminate, with the layered air cathode by, for example, lamination or another bonding process. In another embodiment, the PTFE film may be located not in close contact with the air cathode and the air diffuser.

[0050] In addition, in a further preferred embodiment, a further layer, in particular a further PTFE film, can be provided between the air cathode assembly (laminated) and the air diffuser. This method can, for example, achieve a pore gradient that improves the supply of air to the air cathode. At the same time, a particularly high degree of leak safety of the metal-air cell can be achieved, which can be particularly advantageous under very high humidity conditions. The further PTFE film can be positioned, for example, not in close proximity between the air cathode or air cathode laminate and the layered air diffuser. In another embodiment, the further layer, i.e., the further PTFE film, can also be firmly attached to the air cathode assembly (e.g., by lamination or another bonding process), thereby attaching two PTFE films to the air cathode.

[0051] The air cathode of the metal-air battery according to the present invention, which is equivalent to the air cathode in conventional metal-air batteries, preferably comprises at least one noble metal, particularly platinum and / or palladium and / or manganese oxide, with manganese oxide being particularly preferred as the electrochemically active material.

[0052] Preferably, the layered air cathode of the metal-air battery according to the present invention is formed of a porous matrix of plastic (plastic binder), particularly PTFE, and particles of an electrochemically active material. Furthermore, a conductive material, such as carbon black, may be included. During manufacturing, these materials can be supplied as a dry mixture and formed into layers by a rolling process. Preferably, the air cathode further includes a metal mesh of, for example, silver, nickel, or silver-plated nickel. Alternatively, a metal mesh, expanded metal, metallized nonwoven fabric, or similar conductors can be used to form a metal conductor structure. During the manufacturing process, a dry mixture containing the plastic binder and catalyst particles, and optionally carbon black, can be rolled onto this structure. Circular or similar shapes can be punched out from this sheet-like structure and used as air cathodes in the housing of the manufactured metal-air battery.

[0053] The air cathode may be in the form of a cathode disk having a circumferential cathode disk end. This cathode disk can be placed within the housing of the metal-air battery such that the end of the cathode disk is adjacent to the inside of the housing region along the circumferential contact zone. In this connection, conveniently, a metal arrester structure of the air cathode, i.e., a silver mesh, for example, protrudes from the cathode disk at the cathode disk end. In these respects, a conductive connection of the metal-air battery to the housing is realized, and the polarity of the housing is determined by the resulting connection of the air cathode.

[0054] The metal-based anode of the metal-air battery according to the present invention can also be designed in the same manner as conventional metal-air batteries. Preferably, the metal-based anode contains metal powder, particularly metallic zinc and / or aluminum and / or magnesium powder, as an electrochemically active material. In this case, zinc or a zinc alloy is particularly preferred, and in a particularly preferred embodiment of the metal-air battery according to the present invention, this results in a zinc-air battery. However, in principle, another oxidizable metal such as aluminum and / or magnesium can be used instead of zinc.

[0055] When manufacturing a metal-air battery according to the present invention, the metal-based anode material can be introduced into the housing, for example, in the form of a paste.

[0056] With respect to the housing, the metal-air battery according to the present invention preferably features at least one of the further features a. to e immediately below: a. The first housing portion, hereafter referred to as the battery cup, is cup-shaped and has a cup-shaped base; b. The second housing section, referred to as the battery cover below, is cup-shaped. c. The first housing portion and / or the second housing portion consist of a metallic material, particularly steel, preferably nickel-plated steel, and / or sheet metal, and / or trimetal, preferably a trimetal having nickel, steel, and copper; d. At least one electrical insulating seal is provided between the first housing portion and the second housing portion; e. At least one ventilation opening has an opening diameter in the range of 10 to 500 μm. Preferably, features a, b, and c described above, and especially preferably a, b, c, and d, are realized in combination with each other. Furthermore, in these embodiments, feature e is also preferably realized.

[0057] In a more preferred embodiment, two or more vent openings can be provided in the housing of the metal-air battery according to the present invention. In this case, the vent openings can be particularly advantageously distributed on the surface of the bottom of the battery cup so that atmospheric oxygen can enter in a uniform distribution. However, since the layered air diffuser according to the present invention allows for particularly good and uniform distribution of air oxygen entering through the bottom of the cup, it is generally sufficient to provide only one vent opening.

[0058] In a particularly preferred embodiment of the metal-air battery according to the present invention, the battery is a button cell, that is, a cylindrical battery having a circular or elliptical base and a height smaller than the diameter of the base. However, the metal-air battery according to the present invention may have a different shape. In particular, in the button cell embodiment, the housing of the metal-air battery includes the battery cup and the battery cover, and conveniently a seal. The battery cup and the battery cover form the battery poles.

[0059] In addition to the bottom region, the battery cup preferably has an annular shell and preferably a circumferential end separating the bottom region from the annular shell. The end may be sharp or rounded. The battery cover preferably has a similar structure. Generally, it also has a bottom region and an annular shell. However, instead of a circumferential end, it may preferably have a shoulder-type transition region.

[0060] Each of the battery cup and its region has an inner side facing the internal space of the battery housing and an outer side facing the opposite side. The same applies to each of the battery cover and its region. Preferably, both the battery cup and the battery cover have a circumferential cut that forms the opening end of the battery cup and the battery cover. In a preferred embodiment, the cut of the battery cover can be folded over at the end, thereby having a double opening end. The opening end defines the respective shell region, defines the opening, and allows access to the interior of the battery cup and battery cover through it.

[0061] In a preferred embodiment, the bottom regions of the battery cup and battery cover are flat and have a circular or elliptical shape. Preferably the same applies to the opening defined by the opening end. Particularly preferred, the flat bottom regions of the battery cup and battery cover are arranged parallel to each other within the housing.

[0062] The annular shell regions of the battery cup and battery cover are preferably circular or elliptical in shape. Generally, the annular shell region, or at least the axial portion of the annular shell region, is oriented perpendicular to, or at least substantially perpendicular to, the associated bottom region. The height of the shell region is preferably constant in the circumferential direction in each case.

[0063] In the case of a battery cup, it is preferable that the shell region meets the bottom region at a 90° angle. In this case, the edge of the battery cup preferably forms a sharp boundary between the bottom of the battery cup and the shell region. Unlike the case of a battery cover, in a preferred embodiment, the bottom region of the battery cover also forms a 90° angle with the annular shell region of the battery cover or at least one axial portion of the shell region, but it is preferable that these regions do not come into direct contact. The resulting gap is preferably occupied by a shoulder-type transition region.

[0064] The battery cover is generally first inserted into the battery cup, which has a cut or open end. A seal separates the battery cup and the battery cover from each other. This ensures that the two housing parts are electrically insulated from each other. This also provides an external seal to the housing, preventing electrolyte leakage in the boundary area between the battery cup and the battery cover.

[0065] The housing, consisting of a battery cup and a battery cover, preferably has a basic cylindrical shape. Generally, the bottom region of the battery cup forms the flat bottom side of the housing, while the bottom region of the battery cover forms the flat top side of the housing. On the sides, the housing is bounded by the shell region of the battery cup.

[0066] In a preferred embodiment, the housing is closed by a crimp. For this purpose, the end portion of the shell region of the battery cup, including the open end that forms the boundary of the shell region, is pressed radially inward, resulting in a reduction of the cross-section of the opening defined by the open end. In a preferred embodiment, the crimped open end is on the transition region of the battery cover or on a seal attached to this region. The battery cup and battery cover are generally joined by interlocking crimps.

[0067] As mentioned above, both the battery cup and the battery cover are preferably manufactured from a metal material, for example by a deep drawing process. Suitable materials include, for example, nickel-plated deep-drawn sheets, or clad composite materials (so-called trimetals) having one layer of nickel, one layer of copper, and an intermediate layer of steel or stainless steel.

[0068] The seal is preferably a film seal, such as the one described in German Patent Application Publication No. 19647593 A1. A thermoplastic film seal is preferred. Suitable materials include polyamide or polyetheretherketone. However, the seal may also be a conventional injection-molded seal, for example, also made of polyamide.

[0069] In one preferred design of the metal-air battery according to the present invention, the bottom region of the battery cup is substantially flat. The bottom of the cup may also have a small step, for example, in the range of 0.02 to 0.09 mm. In the bottom region where ventilation openings are provided, a layered air diffuser having a hydrophobic coating is arranged inside the battery. The air diffuser is followed by an air cathode, which may optionally be formed as a laminate with a PTFE film or another hydrophobic film, and if a film side of the air cathode is present, this faces the air diffuser. If necessary, another hydrophobic layer, in particular another PTFE film, may be provided between the air cathode laminate and the layered air diffuser. This is followed by a layered separator, which may be in the form of a separator disc, and which is located on the air cathode. The separator disc, like the air cathode which can be designed as a cathode disc, is generally aligned parallel to the bottom region of the battery cup. On the separator, a metal-based anode is present, for example, in the form of a paste. Towards the top, the housing is closed by a battery cover adjacent to the anode.

[0070] In particular, disc-shaped air cathodes and separators can first be cut or punched out from, for example, ribbon-shaped foil during manufacturing, and then sequentially inserted and / or pressed into the battery cup, preferably onto the bottom region of the battery cup, where a layered air diffuser has been previously inserted. Generally, the air cathode, separator, and air diffuser, all of which are disc-shaped, are constructed as circular discs of approximately the same diameter. These are then arranged flat on top of each other within the internal space of the metal-air battery housing.

[0071] A typical embodiment of the metal-air battery according to the present invention in the form of a button cell is characterized by a substantially cylindrical design with a battery height ranging from approximately 3.30 mm (PR70 design in accordance with the International Electrotechnical Commission, IEC 60082-2) to 5.40 mm (PR44 design in accordance with IEC) and a battery diameter of approximately 5.65 mm (PR70 design in accordance with IEC) and 11.60 mm (PR44 design in accordance with IEC).

[0072] The present invention further includes a method for manufacturing a layered air diffuser provided for a metal-air battery as described above. The method for manufacturing a layered air diffuser is characterized by the following steps a. to c.: a. Provide a breathable matrix; b. Provide a hydrophobic coating to the permeable matrix; here, c. Dispersions of polytetrafluoroethylene, particularly in aqueous dispersants, for example, a dispersion of polytetrafluoroethylene in water, or a solution or dispersion of at least one alkyl ketene dimer, are used for hydrophobic coatings.

[0073] For further details of this method, in particular, regarding the characteristics of the permeable matrix and hydrophobic coating, and the relevant advantages over conventional air diffusers, please refer to the above description.

[0074] In a particularly preferred embodiment of the method of the present invention, the method is characterized by either the following further feature a. or b.: a. The polytetrafluoroethylene dispersion has a solid content of polytetrafluoroethylene in the dispersant that is in the range of 5 to 75% by weight, preferably 15 to 60% by weight, and more preferably 30 ± 2% by weight; b. The dispersion of at least one alkyl ketene dimer has a solid content of alkyl ketene dimer in the dispersant that is in the range of 0.1 to 8.0% by weight, preferably 0.5 to 3.0% by weight, and more preferably 0.5 to 1.0% by weight.

[0075] In a particularly preferred embodiment, the coating is achieved by immersion. On the one hand, the immersion process has the advantage that coating can be performed very easily, reliably, and with little effort using this method. On the other hand, this results in highly consistent and reproducible results without requiring significant equipment costs. During the immersion process, both sides of a relatively large portion of the permeable matrix can be coated in a single operation. Then, the required shape for the air diffuser can be achieved, for example, by cutting or punching.

[0076] To perform the immersion process, a breathable matrix, such as a fibrous nonwoven fabric, can be immersed in a PTFE dispersion or an alkyl ketene dimer dispersion for several seconds (e.g., 1 to 10 seconds). Preferably, drying is then performed, which can be done, for example, at room temperature or ambient conditions.

[0077] The present invention further includes the use of a layered air diffuser having a permeable matrix with a hydrophobic coating for manufacturing a metal-air battery. In particular, the battery manufactured is a metal-air battery as described above. Further details relating to this use, or to a method for manufacturing a metal-air battery using the layered air diffuser according to the present invention, can also be obtained from the above description.

[0078] In particular, this method provides a housing portion for a metal-air battery. A layered air diffuser, an optional additional layer, an air cathode, a separator which can be impregnated with an electrolyte, and a metal-based anode are inserted into the housing portion, the housing is closed, and insulation and / or sealing are performed if necessary. This suitable method of manufacture is well known to those skilled in the art.

[0079] Further features and advantages of the present invention will become apparent from the drawings and the following description of preferred embodiments associated therewith. Here, each of the individual features can be realized separately or in combination with each other. [Brief explanation of the drawing]

[0080] [Figure 1] This is a schematic cross-sectional view of one embodiment of a metal-air battery according to the present invention. [Modes for carrying out the invention]

[0081] Figure 1 shows a cross-section of a metal-air button cell 100, which basically has a design well known in the prior art. A layered air diffuser 140 having a hydrophobic coating according to the present invention is attached to this metal-air cell 100.

[0082] The metal-air battery 100 includes a metal housing 110 which comprises a battery cup 111 (first housing portion), a battery cover 112 (second housing portion), and a seal 113. The battery cup 111 has, for example, a circular bottom region 111a and an annular shell region 111b. At the end, the shell region 111b is bounded by a cut 111c which forms the open end of the battery cup 111.

[0083] The battery cover 112 has, for example, a circular bottom region 112a and an annular shell region 112b. The bottom region 112a and the shell region 112b of the battery cover 112 are connected by a circumferential transition region 112d. At the end, the shell region 112b is bounded by a cut 112c that forms the open end of the battery cover 112.

[0084] First, the cut 112c of the battery cover 112 is inserted into the battery cup 111. The seal 113 separates the battery cup 111 and the battery cover 112 from each other. This ensures electrical insulation between the two housing parts (battery cup 111 and battery cover 112). This also seals the housing 110 and prevents electrolyte leakage.

[0085] The battery cup 111 and the battery cover 112 are connected to each other by a crimp to form a closed housing 110, which is formed in the area of ​​the end portion 111d of the shell region 111b of the battery cup 111 by pressing the end portion 111d radially inward after the battery cover 112 is inserted.

[0086] A ventilation opening 114 is provided in the central part of the bottom region 111a of the battery cup 111. Air oxygen can enter the internal space of the metal-air battery through the ventilation opening 114. Above the ventilation opening 114 is a layered air diffuser 140, which is hydrophobic coated on at least one side. A layered air cathode 130 is adjacent to the air diffuser 140, and one or two additional layers, particularly PTFE films 131 and 132, can be provided between the air diffuser 140 and the air cathode 130. The PTFE film 131 closest to the air cathode 130 can form a laminate with the air cathode 130. A layered separator 150 is placed above the air cathode 130, thereby separating the air cathode 130 from the metal-based anode 120 located on top of the separator 150.

[0087] The metal-based anode is preferably zinc paste. The anode 120 is in direct contact with the battery cover 112. Thus, the battery cover 112 forms the negative electrode of the metal-air battery 100. The separator 150 is impregnated with, for example, an alkaline electrolyte, thereby allowing hydroxide ions to move from the air cathode 130 to the anode 120. The air cathode 130 is provided with a metal conductor structure, which is not shown in detail here, and is electrically connected to the battery cup 111. Thus, the battery cup 111 forms the positive terminal of the metal-air battery 100.

[0088] A central aspect of the present invention is a hydrophobic coating for a layered air diffuser 140. In this context, the air diffuser 140 preferably consists of a permeable matrix made of a hydrophilic material in particular. In this regard, a nonwoven fabric formed from a fiber mixture is particularly preferred, the fiber mixture mainly containing polyvinyl alcohol fibers, and particularly having a ratio of 50% by weight or more of polyvinyl alcohol fibers. This permeable matrix is ​​preferably coated with a dispersion of polytetrafluoroethylene (PTFE), or more preferably with a dispersion of at least one alkyl ketene dimer (AKD) in water. The solid content of the polytetrafluoroethylene dispersion is preferably in the range of 5 to 75% by weight, particularly preferably about 30% by weight. The solid content of the alkyl ketene dimer dispersion is preferably in the range of 0.01 to 8% by weight, more preferably in the range of 0.01 to 3% by weight, more preferably in the range of 0.01 to 1% by weight, more preferably in the range of 0.01 to 0.8% by weight, and most preferably in the range of 0.05 to 0.8% by weight. The hydrophobic coating of the breathable matrix ensures the reliable retention of the electrolyte inside the metal-air battery, even in high-humidity environments, while simultaneously achieving good dispersion of atmospheric oxygen entering through the ventilation openings 114 across the entire surface of the metal-air battery 100.

[0089] The following nonwoven fabric was used as the breathable matrix (Schweitzer-Mauduit International Inc., USA, nonwoven fabric type PA 125 S): Weight 24.8g / m 2 Thickness (at 100kPa): 88μm Tensile strength: 2,100 cN / 15 mm Wicking agent KOH 50mm / 10mn Absorption 145g / m² 2 Shrinkage 0% MD 0%CD Air permeability: 29.360 cm / cm 32 • Minutes (1 kPa) R. Index 0.75 These measurements for the fleece fabric refer to measurements taken at a temperature of 23°C and 50% humidity.

[0090] PTFE coating Nonwoven fabrics were coated with PTFE dispersions of various concentrations using an immersion process. The weight per unit area and Gurley's air permeability were measured and compared with uncoated nonwoven fabrics and PTFE films. Dispersions with various PTFE concentrations were prepared using an aqueous starting dispersion with a 60% PTFE solid content. These initial dispersions were mixed with water. In this way, mixtures with approximately 6 wt% PTFE (10% PTFE starting dispersion + 90% water), approximately 15 wt% PTFE (25% PTFE starting dispersion + 75% water), approximately 30 wt% PTFE (50% PTFE starting dispersion + 50% water), and approximately 60 wt% PTFE (100% PTFE starting dispersion) were obtained. These blends were used to coat fiber webs in an immersion process. In the immersion process, fiber webs were immersed in each PTFE dispersion for 1 to 10 seconds and then dried at room temperature.

[0091] The Gurley method for measuring air permeability records the time it takes for each medium, i.e., air, to pass through the test material under defined conditions. The longer this time, the lower the air permeability of the test material. However, if the air permeability of the test material is very high, the flow through the material is too fast (not measurable), and therefore the time cannot be measured.

[0092] The results are summarized in Table 1 below. [Table 1]

[0093] These results suggest that nonwoven fibers coated with PTFE dispersion have a weight of 67 g / m² per unit area. 2 It can be seen that it exhibits very high breathability. The fiber fleece is undiluted PTFE dispersion (60% by weight PTFE, weight per unit area 144 g / m²). 2 When coated with PTFE, it has been shown to reduce air permeability, which is already significantly lower compared to coatings using 30 wt% PTFE dispersion. In contrast, pure PTFE films exhibit even more significantly lower air permeability.

[0094] Table 2 below shows experimental results using various metal-air batteries, each having an air diffuser with a different coating according to the present invention. For each type of air diffuser, three individual batteries (batteries #1, #2, and #3) were observed for several days under high humidity conditions (90% relative humidity at 30°C) to check whether electrolyte leakage was detected after discharge (x - electrolyte leakage present; 0 - electrolyte leakage not present). [Table 2]

[0095] These results indicate that using an air diffuser coated with 30 wt% PTFE dispersion reliably prevented electrolyte leakage for 7 days in all individual batteries of this type tested. Air diffusers with a 15 wt% PTFE dispersion coating have already shown favorable effects with respect to electrolyte leakage, and this favorable effect was observed to some extent even when the air diffuser was coated with 6 wt% PTFE dispersion. Therefore, approximately 30 wt% PTFE dispersion is particularly preferred for air diffuser coatings, especially for reliable protection against leakage in metal-air batteries.

[0096] AKD coating Similarly, nonwoven fabrics (type PA 125-35 S and type PA 125 from Schweitzer-Mauduit International Inc., USA) were coated with an alky-ketene dimer (AKD). Unlike type PA 125, type PA 125-35 S uses a wetting agent. Aqueous dispersions containing 0.8% by weight and 7.6% by weight of AKD were used for coating. The AKD material used was AQUAPEL® 201 (Solenis LLC, USA).

[0097] Hydrophobicity was measured using the droplet method. Here, one drop of water (2 μl) was placed on the fleece fabric. Time was then stopped after the fleece fabric absorbed the water. Therefore, a longer measurement time indicates higher hydrophobicity. If the water droplet was not absorbed after 15 minutes, the test was stopped (result > 15 minutes / 2 μl).

[0098] Table 3 below summarizes the material properties of AKD-coated fiber webs. [Table 3]

[0099] For both fiber webs examined (PA 125-35 S and PA 125), very good hydrophobic values ​​(>15 min / 2 μl) were obtained with coatings containing both 0.8% and 7.6% AKD. The measurable thickness of the nonwoven fabric was not significantly affected by the coating and was in the range of 80–100 μm in all cases. The weight per unit area of ​​the nonwoven fabric did not change when coated with 0.8% AKD. A slight increase in weight per unit area was observed with the coating containing 7.6% AKD. Air permeability was very good in all cases, and there was no measurable effect from the AKD coating.

[0100] Further tests were conducted at lower AKD concentrations. A clear increase in hydrophobicity was already observed at a 0.08% AKD concentration compared to uncoated fleece fibers. Further significant increases in hydrophobicity were observed at 0.16% and 0.8% AKD (actually 0.76% AKD). No further significant improvements in hydrophobicity were observed at AKD concentrations above 0.8%.

[0101] Table 4 below shows the test results using various metal-air batteries, each having an air diffuser coated with various amounts of AKD according to the present invention (uncoated nonwoven fabric (PA 125-35 S); nonwoven fabric coated with 0.8% AKD (PA 125-35 S); nonwoven fabric coated with 7.6% AKD (PA 125-35 S)). Percentage values ​​are based on the weight percentage of the coating dispersion. For each type of air diffuser, four individual batteries (battery numbers 1, 2, 3, and 4) were observed for a total of 7 days under high humidity conditions to determine whether electrolyte leakage was detected immediately after discharge, or 1, 3, or 7 days after deep discharge (x - electrolyte leakage present; 0 - electrolyte leakage absent). [Table 4]

[0102] These results indicate that electrolyte leakage after deep discharge occurs more frequently and rapidly when using uncoated fiber fleece as an air diffuser than when using AKD-coated fiber fleece. Regarding electrolyte leakage, the results with a 0.8% AKD coating were comparable to those with a 7.6% AKD coating. The 0.8% AKD coating is particularly advantageous for air diffusers due to its lower material consumption and easier handling of lower concentrations of dispersion.

Claims

1. A metal-air battery (100): a. The metal-air battery has a first housing portion (111) and a second housing portion (112), which together form a battery housing (110); and b. The metal-air battery comprises a metal-based anode (120), a layered air cathode (130), and an electrolyte; and c. The first housing portion (111) has at least one ventilation opening (114); and d. A layered air diffuser (140) is positioned between the first housing portion (111) and the air cathode (130); and e. A layered separator (150) is placed between the air cathode (130) and the metal-based anode (120); It has the following characteristics: f. The layered air diffuser (140) is configured to be permeable and has a first side facing the air cathode (130) and a second side facing away from the air cathode (130); g. The layered air diffuser (140) has a hydrophobic coating on at least one of its sides; and h. The layered air diffuser (140) includes a permeable matrix formed of a hydrophilic material; A metal-air battery characterized by the following features.

2. a. The hydrophobic coating is a polytetrafluoroethylene coating. The metal-air battery according to claim 1, having the further feature of the above.

3. a. The hydrophobic coating is an alkyl ketene dimer coating. The metal-air battery according to claim 1, having the further feature of the above.

4. a. The hydrophobic coating is based on a coating using a polytetrafluoroethylene dispersion; b. The hydrophobic coating is based on a coating using a polytetrafluoroethylene dispersion in a polytetrafluoroethylene dispersion, wherein the solid content of polytetrafluoroethylene in the dispersion is 5 to 75% by weight; c. The hydrophobic coating is based on a coating using a solution or dispersion of at least one alkyl ketene dimer; d. The hydrophobic coating is based on a coating using a dispersion of at least one alkyl ketene dimer, wherein the solid content of the at least one alkyl ketene dimer in the dispersion is in the range of 0.01 to 8.0% by weight. A metal-air battery according to claim 2 or 3, having at least one of the following further features.

5. a. The breathable matrix is ​​a nonwoven fabric; b. The breathable matrix is ​​formed from a fiber mixture; c. The permeable matrix has a density of 20-30 g / m² in its uncoated state. ２ Having a weight per unit area within the range; d. The permeable matrix, in its uncovered state, has a thickness of 20,000 to 40,000 cm². ３ / cm ２ - Having a degree of ventilation within a range of minutes, The metal-air battery according to claim 1, having at least one of the following further features.

6. a. The layered air diffuser (140) has a coating on both sides. A metal-air battery according to any one of claims 1 to 5, having the further feature of the above.

7. a. The layered air diffuser (140) has a polytetrafluoroethylene coating and has a density of 40 to 160 g / m². ２ Having a weight per unit area within the range; b. The layered air diffuser (140) has a coating using at least one alkyl ketene dimer, with a density of 10 to 50 g / m². ２ Having a weight per unit area within the range, A metal-air battery according to any one of claims 1 to 6, having any one of the further features described above.

8. a. The metal-air cell (100) includes at least one additional layer (131, 132) between the air cathode (130) and the layered air diffuser (140); b. The at least one additional layer (131, 132) is a hydrophobic film. A metal-air battery according to any one of claims 1 to 7, having at least one of the following further features.

9. a. The metal-air battery (100) is a zinc-air battery; b. The metal-air battery (100) is a button cell. A metal-air battery according to any one of claims 1 to 8, having at least one of the following further features.

10. A method for manufacturing a layered air diffuser (140) for a metal-air battery according to any one of claims 1 to 9: a. A breathable matrix is ​​provided; and b. The permeable matrix is ​​provided with a hydrophobic coating; This method includes the following steps: c. A method wherein a dispersion of polytetrafluoroethylene, or a solution or dispersion of at least one alkyl ketene dimer, is used for the hydrophobic coating.

11. a. The dispersion of polytetrafluoroethylene has a solid content of polytetrafluoroethylene in the dispersion of 5 to 75% by weight; b. The dispersion of at least one alkyl ketene dimer has a solid content of alkyl ketene dimer in the dispersion in the range of 0.01 to 8.0% by weight. The method according to claim 10, having any of the further features of the above.

12. a. The coating is provided by an immersion process. The method according to claim 10 or claim 11, which has the further feature of the above.

Images