Magnesium-air battery and method for manufacturing the same

Abstract

A magnesium-air battery 100 comprises: a positive electrode 101 that is constituted by an air electrode; a negative electrode 102 that is formed of magnesium, or a magnesium alloy which contains magnesium and one or more elements selected from the group consisting of iron, calcium and aluminium; and a separator 106 that is disposed between the positive electrode 101 and the negative electrode 102, that provides insulation between the positive electrode 101 and the negative electrode 102, and that absorbs moisture from an electrolyte 103 which is formed of a salt. A silica-containing coating is applied to at least one of the positive electrode 101 and the separator 106.

Description

Technical Field

[0001] The present disclosure relates to a magnesium-air battery and a method for manufacturing the same.

Background Art

[0002] Conventionally, alkaline batteries and manganese batteries have been widely used as disposable primary batteries. In addition, in recent years, with the development of IoT (Internet of Things), the development of scattered sensors existing in all places in nature such as soil and forests has also progressed, and small-sized, high-performance lithium-ion batteries corresponding to various applications such as these sensors as well as conventional mobile devices have become widespread.

[0003] However, conventional disposable batteries are often composed of resources such as lithium, nickel, manganese, or cobalt, and there has been a problem of resource depletion. In addition, since strong alkalis such as aqueous sodium hydroxide solution and harmful organic electrolytes are used as electrolytes, there is a problem of soil contamination at final disposal sites. Furthermore, for example, when used as a power source for sensors embedded in soil, there is a problem that it may have an adverse effect on the surrounding environment depending on the environment where the disposable battery is used.

[0004] Legal systems have been developed in consideration of these environmental impacts and systematized.

[0005] There is a law on chemical substance management in which there are concerns about the impact on human health and the environment via the environment. The law on chemical substance management takes into account the international trends in the management of chemical substances related to environmental conservation, and based on scientific knowledge regarding chemical substances and the situation regarding the manufacture, use, and other handling of chemical substances, while under the understanding of businesses and the public, measures regarding the grasp of the emissions amount, etc. of specific chemical substances into the environment and measures regarding the provision of information regarding the properties and handling of specific chemical substances by businesses are taken, etc., to promote the improvement of the voluntary management of chemical substances by businesses and to prevent obstacles to environmental conservation.

[0006] The following laws are designated for the management of chemical substances: the Chemical Substances Control Law, the Chemical Substances Control Law, the Agricultural Chemicals Control Law, the Air Pollution Control Law, the Water Pollution Control Law, the Soil Contamination Countermeasures Law, the Waste Management Law, the Poisonous and Deleterious Substances Control Law, the Ozone Layer Protection Law, and the Fluorocarbon Recovery and Destruction Law.

[0007] There are concerns about environmental problems that may arise if batteries containing substances specified in these laws are discarded or forgotten without being recycled or otherwise processed.

[0008] As another example, under the classification of the above-mentioned Chemical Substances Control Law, there are substances with high risks such as long-term toxicity and persistence, such as Category 1 and 2 specified chemicals / monitoring chemicals / priority assessment chemicals, while there are also general chemical substances that are not considered to pose such risks. General chemical substances that exist in the market should not be designated as chemical substances that pose environmental concerns under these laws (Non-Patent Literature 1 and Non-Patent Literature 2).

[0009] Zinc is used as a constituent element in the magnesium alloy of the negative electrode of commercially available magnesium-air batteries, or as a negative electrode material in commercially available dry cell batteries. However, zinc is designated as a Class I designated chemical substance under the Act on Promotion of Understanding and Management of Releases of Chemical Substances, for example, in the form of water-soluble compounds (Non-Patent Literature 3 and Non-Patent Literature 4). It is stated that metallic zinc, zinc oxide, etc., dissolve in acidic and basic aqueous solutions.

[0010] To address the aforementioned environmental problems, one type of battery being researched and developed as a next-generation battery is the air battery. In air batteries, oxygen from the air used as the positive electrode active material is supplied from outside the battery, allowing the battery cell to be filled with a metal negative electrode. Metals such as magnesium, aluminum, or zinc can be used for the negative electrode. By using readily available materials, it is possible to construct batteries with low costs and environmental impact. In particular, zinc-air batteries, which use zinc as the negative electrode, have been commercialized as power sources for hearing aids and other devices, and magnesium-air batteries, which use magnesium as the negative electrode, are being researched and developed as primary batteries with low environmental impact (Non-Patent Literature 5 and Non-Patent Literature 6). [Prior art documents] [Non-patent literature]

[0011] [Non-Patent Document 1] Ministry of Economy, Trade and Industry, Chemical Substances Management Division, "Current Status and Challenges of Chemical Substances Management Policy" (P9), [online], October 2012, [Accessed December 25, 2022], Internet <URL: https: / / www.nite.go.jp / data / 000010340.pdf> [Non-Patent Document 2] "Laws and Regulations Related to Chemical Substances" (P4), [online], [Accessed December 25, 2022], Internet <URL: https: / / www.env.go.jp / chemi / communication / taiwa / text / 2s_2008.pdf> [Non-Patent Document 3] "Chemical Substance Emission Identification and Management Promotion Law List of Class 1 Designated Chemical Substances", [online], [searched on December 25, 2022], Internet <URL: https: / / www.meti.go.jp / policy / chemical_management / law / prtr / pdf / sindai1.pdf> [Non-Patent Document 4] "Chemical Substances Release and Management Promotion Act: Water-soluble Zinc Compounds," [online], [Accessed December 25, 2022], Internet <URL: https: / / www.nite.go.jp / chem / chrip / chrip_search / dt / pdf / CI_02_001 / risk / pdf_gaiyou / 001gaiyou.pdf> [Non-Patent Document 5] Yejian Xue et al., “Template-directed fabrication of porous gas diffusion layer for magnesium air batteries”, Journal of Power Sources 297 (2015) 202e207 [Non-Patent Document 6] Naiguang Wang et al., “Discharge behavior of Mg-Al-Pb and Mg-Al-Pb-In alloys as anodes for Mg-air battery”, Electrochimica Acta 149 (2014) 193-205 [Overview of the project] [Problems that the invention aims to solve]

[0012] However, in the air electrode disclosed in Non-Patent Document 5, fluororesin is used as a binder. Since carbon particles alone cannot form and hold a positive electrode, fluororesin is used to form a positive electrode that binds the carbon particles together to form an electric bath and also allows for gas diffusion. In a positive electrode composed of a gas diffusion layer through which air (oxygen) diffuses and a catalyst layer where an oxygen reduction reaction occurs, the gas diffusion layer enables a smooth supply of air and prevents water from entering from the outside air and leakage of the electrolyte into the outside air.

[0013] This fluorine is designated as a hazardous substance under the Soil Contamination Countermeasures Act or the Water Pollution Control Act, etc., as fluorine and fluorine compounds. Furthermore, Non-Patent Literature 6 describes the use of metals containing lead and indium in the negative electrode, a material composition that raises concerns about its impact on the natural environment, such as soil contamination. In addition, chlorine contained in sodium chloride, which is a simple and widely used electrolyte, can become a component of toxic substances such as dioxins and cause furnace corrosion when mixed into general waste incineration facilities, etc.

[0014] A primary battery with a low environmental impact that uses a positive electrode that is a co-continuum with a three-dimensional network structure without using fluororesin as a binder is promising. However, if a positive electrode that does not have a water-repellent effect is used, there is a concern that the battery performance will deteriorate if the amount of electrolyte is large, as the positive electrode will be submerged in the liquid.

[0015] Thus, there is a need for batteries that do not pollute waste treatment facilities or the natural environment, are composed only of low-environmental-impact materials, do not use regulated substances that are a concern for their impact on human health and the environment via the environment as defined by law, and are capable of smoothly supplying air even when the electrolyte is in excess.

[0016] This disclosure is made in view of the above circumstances, and the purpose of this disclosure is to provide a battery that is composed of environmentally friendly materials and can supply air smoothly even when the electrolyte is in excess. [Means for solving the problem]

[0017] A magnesium-air battery according to one aspect of the present disclosure comprises a positive electrode composed of an air electrode, a negative electrode composed of magnesium, or a magnesium alloy containing magnesium and one or more of the group composed of iron, calcium, and aluminum, and a separator disposed between the positive electrode and the negative electrode, insulating between the positive electrode and the negative electrode, and absorbing an electrolyte composed of salt, wherein at least one of the positive electrode and the separator is coated with a silica-containing material.

[0018] A method for manufacturing a magnesium-air battery according to one aspect of the present disclosure comprises the steps of: obtaining a positive electrode composed of an air electrode; coating the positive electrode with a silica-containing material; obtaining a negative electrode composed of magnesium, or a magnesium alloy containing one or more of the group composed of magnesium, iron, calcium, and aluminum; and arranging an electrolyte composed of a salt between the positive electrode and the negative electrode, wherein the air electrode is composed of a cocontinuum which is a three-dimensional network structure consisting of a plurality of nanostructures integrated by non-covalent bonds, and the step of obtaining the positive electrode comprises a production step in which the nanostructure causes a predetermined bacterium to produce a sol or gel in which nanofibers of iron oxide, manganese oxide, and cellulose are dispersed; a freezing step in which the dispersed sol or gel is frozen to obtain a frozen body; and a drying step in which the frozen body is dried in a vacuum to obtain the cocontinuum. [Effects of the Invention]

[0019] According to the present disclosure, it is possible to provide a battery that is composed of materials with low environmental impact and can smoothly supply air even in a state where the electrolyte is excessive.

Brief Description of the Drawings

[0020] [Figure 1] FIG. 1 is a diagram schematically illustrating a magnesium-air battery according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a diagram schematically illustrating the appearance of a magnesium-air battery according to an example. [Figure 3] FIG. 3 is a diagram schematically illustrating a cross-section of a magnesium-air battery according to an example. [Figure 4] FIG. 4 is a diagram illustrating the battery voltage and discharge capacity during discharge in a magnesium-air battery according to an example.

Modes for Carrying Out the Invention

[0021] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the description of the drawings, the same reference numerals are assigned to the same parts and the description thereof is omitted.

[0022] (Magnesium-air battery) Referring to FIG. 1, a magnesium-air battery 100 according to an embodiment of the present disclosure will be described. The magnesium-air battery 100 according to an embodiment of the present disclosure includes a positive electrode 101, a negative electrode 102, an electrolyte 103, a positive electrode current collector 104, a negative electrode current collector 1*05*, a separator 106, and a housing *110*.

[0023] The positive electrode 101 is composed of a gas diffusion type air electrode such as oxygen. The positive electrode 101 is composed of a co-continuous body having a three-dimensional network structure composed of a plurality of nanostructures integrated by non-covalent bonds. A binder, particularly a fluororesin as a binder, is not used for the air electrode.

[0024] *Note: There seems to be a minor error in the original text where "negative electrode current collector 105" and "housing 110" are not properly formatted with asterisks in the provided text. This has been corrected in the translation for better readability.*The negative electrode 102 contains magnesium (Mg). The negative electrode 102 may be composed of magnesium, or a magnesium alloy containing magnesium and one or more elements from the group consisting of iron (Fe), calcium (Ca), and aluminum (Al). However, magnesium alloys containing zinc components, such as AZ31, are excluded.

[0025] The electrolyte 103 is placed between the positive electrode 101 and the negative electrode 102 and is composed of a salt. The electrolyte 103 is an aqueous solution or gel containing magnesium acetate. Preferably, the electrolyte 103 is composed only of an aqueous solution or gel containing a salt such as magnesium acetate. Specifically, the electrolyte 103 may be composed of an aqueous solution of a salt of magnesium acetate, potassium chloride, or sodium chloride, or a mixture of these salts. Since the electrolyte 103 is composed of a salt, it is easy to dispose of, has no concern about impact on the surrounding environment, and is easy to handle. The electrolyte 103 may be either an electrolyte solution or a solid electrolyte. An electrolyte solution refers to the case where the electrolyte 103 is in liquid form. A solid electrolyte refers to the case where the electrolyte 103 is in gel form or solid form. In the case of a solid electrolyte, agar, cellulose, superabsorbent polymer, etc. may be enclosed to provide a water-retaining role. The electrolyte 103 does not need to be initially placed when the magnesium-air battery 100 is not operating as a battery. The electrolyte 103 may be supplied externally, for example, through the separator 106, when the device is operating as a battery.

[0026] The positive electrode current collector 104 can be any known material. For example, the positive electrode current collector 104 may be a carbon sheet, carbon cloth, Fe, or Al plate.

[0027] A known negative electrode current collector 105 can be used. If metal is used for the negative electrode 102, the terminals may be brought out directly from the negative electrode 102 without using the negative electrode current collector 105.

[0028] The separator 106 is placed between the positive electrode 101 and the negative electrode 102, providing insulation between them and absorbing water from the electrolyte 103, which is composed of salt. The separator 106 can be any insulator with water absorption properties. For example, coffee filters, kitchen paper, or paper can be used for the separator 106. Using a sheet of a material that naturally decomposes while maintaining strength, such as a cellulose separator made from plant fibers, for the separator 106 has a low environmental impact. Note that the separator 106 does not need to be installed if insulation between the positive and negative electrodes can be ensured.

[0029] The positive electrode 101 is in contact with the positive electrode current collector 104. When the positive electrode current collector 104 is exposed to the atmosphere, the positive electrode 101 is also exposed to the atmosphere. In addition, the positive electrode 101 is in contact with the electrolyte 103 on a surface other than the surface in contact with the positive electrode current collector 104.

[0030] The negative electrode 102 is in contact with the negative electrode current collector 105. The negative electrode 102 is in contact with the electrolyte 103 on the surface other than the surface in contact with the negative electrode current collector 105.

[0031] In the embodiments described herein, a case in which a positive electrode current collector 104 and a negative electrode current collector 105 are provided will be described, but the invention is not limited to this case. If the strength of the positive electrode 101 and the negative electrode 102 is ensured when connected to an external load, the positive electrode current collector 104 and the negative electrode current collector 105 may be omitted.

[0032] The housing 110 houses the positive electrode 101, the negative electrode 102, and the electrolyte 103. The electrolyte 103 only needs to be housed inside the housing 110 when the magnesium-air battery 100 is in operation. The housing 110 has an air vent that exposes the positive electrode 101 (air electrode) to the atmosphere. The material and shape of the housing 110 are not particularly limited as long as it is possible to keep the battery cells inside and does not contain regulated substances. However, a portion of the positive electrode current collector 104 and a portion of the negative electrode current collector 105 are exposed from the housing 110 for power supply.

[0033] For example, a known laminate film type can be used for the housing 110. When the housing 110 is made from biodegradable materials, it can be made from natural, microbial, or chemically synthesized materials, such as polylactic acid, polycaprolactone, polyhydroxyalkanoate, polyglycolic acid, or modified starch. Chemically synthesized materials such as plant-derived polylactic acid are particularly preferred. Furthermore, a 3D printer can be used as a processing method for the housing 110. The housing 110 can be molded or cut using a 3D printer or the like, and its shape is not limited. In addition to commercially available biodegradable plastics and their films, paper or agar films with a resin coating, such as polyethylene used in milk cartons, can also be used for the housing 110.

[0034] Here, we will describe the positive electrode 101 in detail. The positive electrode 101 can be made of a conductive material commonly used in the positive electrodes of metal-air batteries. A typical example is carbon material, but it is not limited to this. The positive electrode 101 can be manufactured by a known process such as molding carbon powder with a binder. In primary batteries, it is important to generate a large number of reaction sites inside the positive electrode, and it is desirable for the positive electrode 101 to have a high specific surface area.

[0035] In the case of a typical cathode, which is made by molding carbon powder with a binder to form pellets, when the specific surface area is increased, the bonding strength between the carbon powder particles decreases, the structure deteriorates, making it difficult to discharge stably and reducing the discharge capacity.

[0036] Therefore, a cocontinuum with a three-dimensional network structure may be used as the positive electrode 101. By using a cocontinuum with a three-dimensional network structure as the positive electrode 101, it becomes unnecessary to use a binder, and the discharge capacity can be increased.

[0037] A cocontinuum is, for example, a three-dimensional network structure formed by multiple nanostructures being joined together by non-covalent bonds. Cocontinuums are porous and have a monolithic structure. Nanostructures are nanosheets or nanofibers. In a three-dimensional network structure cocontinuum where multiple nanostructures are joined together by non-covalent bonds, the connections between the nanostructures are deformable, resulting in a stretchable structure.

[0038] Nanosheets are compounds containing carbon or iron oxides, or primarily composed of carbon or iron oxides. Nanosheets are composed of at least one of carbon and iron oxides. It is important that nanosheets are electrically conductive. A nanosheet is defined as a sheet-like material with a thickness of 1 nm to 1 μm, where the length and width of the plane are at least 100 times the thickness. For example, graphene is a nanosheet made of carbon. Furthermore, nanosheets may be in the form of rolls or waves, and may be curved or bent; they can take any shape.

[0039] Nanofibers are compounds containing carbon, iron oxide, or cellulose, or primarily composed of carbon, iron oxide, or cellulose. Nanofibers are composed of at least one of carbon, iron oxide, and cellulose. It is important that nanofibers are electrically conductive. Nanofibers are defined as fibrous materials with a diameter of 1 nm to 1 μm and a length of 100 times or more their diameter. Furthermore, nanofibers may be hollow or coiled, and may take any shape. In the case of cellulose, as described later, conductivity is imparted through carbonization.

[0040] In this disclosure, at least one of the positive electrode 101 and the separator 106 is coated with a silica-containing material. Here, the silica-containing material may be coated with a silane coupling agent. The surface of the positive electrode 101, or the cellulose forming the separator 106, is coated with the silica-containing material by a vapor layer method using a silane coupling agent. This allows for a smooth supply of air even when the electrolyte 103 is in excess. Furthermore, the interface between the positive electrode 101 and the electrolyte 103 can prevent water from entering from the outside air and leakage of the electrolyte into the outside air.

[0041] (Manufacturing method) Next, a method for manufacturing the magnesium-air battery 100 will be described. The manufacturing method comprises the steps of obtaining a positive electrode 101 composed of an air electrode, coating the positive electrode 101 with a silica-containing material, obtaining a negative electrode 102 composed of magnesium, or a magnesium alloy containing one or more elements from the group consisting of magnesium, iron, calcium, and aluminum, and placing an electrolyte 103 composed of a salt between the positive electrode 101 and the negative electrode 102. Here, the positive electrode 101 is composed of a cocontinuum which is a three-dimensional network structure made up of multiple nanostructures that are integrated by non-covalent bonds.

[0042] The process for obtaining the positive electrode 101 includes a production step in which the nanostructure causes a predetermined bacterium to produce a sol or gel in which nanofibers of iron oxide, manganese oxide, or cellulose are dispersed; a freezing step in which the dispersed sol or gel is frozen to obtain a frozen body; and a drying step in which the frozen body is dried in a vacuum to obtain the cocontinuum. The cocontinuum that will become the positive electrode 101 may be created by the freezing step in which the sol or gel in which the nanostructure is dispersed is frozen to obtain a frozen body, and the drying step in which the frozen body is dried in a vacuum to obtain the cocontinuum. The positive electrode 101 is constructed from the cocontinuum obtained in the drying step.

[0043] A sol or gel containing dispersed nanofibers made of iron oxide, manganese oxide, silicon, or cellulose may be produced by a predetermined bacterium (sol or gel production step). In this case, the process for obtaining the positive electrode 101 comprises a production step in which the predetermined bacterium produces a sol or gel containing dispersed nanofibers made of cellulose, and a carbonization step in which the sol or gel is heated in an inert gas atmosphere to carbonize it and obtain a cocontinuum. The positive electrode 101 is formed from the cocontinuum obtained in the carbonization step.

[0044] The cocontinuum constituting the positive electrode 101 preferably has an average pore size of 0.1 to 50 μm, and more preferably 0.1 to 2 μm. Here, the average pore size is a value obtained by the mercury intrusion method. In this case, there is no need to use additional materials such as binders as when carbon powder is used, which is advantageous in terms of cost and environmental impact.

[0045] (Electrochemical reaction) Here, the electrochemical reactions at the positive electrode 101 and the negative electrode 102 will be explained using the case of a primary battery using magnesium metal as the negative electrode as an example. In the positive electrode reaction, the reaction shown in "1 / 2O2 + H2O + 2e- → 2OH- (1)" proceeds on the surface of the conductive positive electrode 101 when it comes into contact with oxygen from the air and the electrolyte. On the other hand, in the negative electrode reaction, the reaction "Mg → Mg2 + 2e- (2)" proceeds at the negative electrode 102 which is in contact with the electrolyte 103, and the magnesium constituting the negative electrode 102 releases electrons and dissolves in the electrolyte as magnesium ions.

[0046] These reactions enable discharge. The entire reaction is "Mg + 1 / 2O2 + H2O + 2e- → Mg(OH)2···(3)", in which magnesium hydroxide is produced (deposited). The theoretical electromotive force is approximately 2.7V. Thus, since the reaction shown in equation (1) proceeds on the surface of the positive electrode 101 in a primary battery, it is considered better to generate a large number of reaction sites inside the positive electrode 101.

[0047] The magnesium-air battery 100 according to the embodiments of this disclosure is made of environmentally friendly materials and does not pollute waste treatment facilities or the natural environment. Furthermore, the magnesium-air battery 100 is made only of materials that do not contain regulated substances designated by various laws and regulations. When such a magnesium-air battery 100 is used in disposable devices such as soil moisture sensors, for example, even when it is not collected or disposed of as general waste, it places an extremely low burden on the living environment and the natural environment.

[0048] Furthermore, at least one of the positive electrode 101 and the separator 106 is coated with silica-containing material. This allows for a smooth supply of air even when the electrolyte 103 is in excess. In addition, the interface between the positive electrode 101 and the electrolyte 103 can prevent water from entering from the outside air and leakage of the electrolyte into the outside air.

[0049] Examples 1-1 to 3-6 relating to embodiments of this disclosure will be described below.

[0050] Examples 1-1 to 1-4 show cases in which a cocontinuum, which is a three-dimensional network structure consisting of multiple nanosheets joined together by non-covalent bonds, is used as an air electrode (positive electrode 101).

[0051] As shown in Figures 2 and 3, the magnesium-air battery 100a according to the embodiment comprises a positive electrode 101, a negative electrode 102, an electrolyte 103, a positive electrode current collector 104, a negative electrode current collector 105, a separator 106, a housing 110, a housing lid 111, and a fixing device 112.

[0052] The positive electrode 101, which is an air electrode, was synthesized as follows. In the following explanation, a manufacturing method using graphene as a nanosheet is shown as a representative example, but by changing the graphene to a nanosheet made of other materials, a cocontinuum having a three-dimensional network structure can be prepared.

[0053] First, the method for preparing cathode 101 will be explained. A commercially available carbon nanofiber sol [dispersion medium: water (H2O), 0.4 wt%, manufactured by Sigma-Aldrich] was placed in a test tube, and this test tube was immersed in liquid nitrogen for 30 minutes to completely freeze the carbon nanofiber sol. After the carbon nanofiber sol was completely frozen, the frozen carbon nanofiber sol was taken out into a round-bottom flask, and dried in a freeze-dryer (manufactured by Tokyo Rikakikai Co., Ltd.) under a vacuum of 10 Pa or less to obtain an expandable cocontinuum having a three-dimensional network structure containing carbon nanosheets.

[0054] The obtained cocontinuum was evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM), porosity measurement, tensile testing, and BET (Brunauer Emmett Teller) specific surface area measurement. XRD measurement confirmed that the fabricated cocontinuum was a single-phase carbon (C, PDF card No. 01-075-0444). The PDF card number is the card number in the PDF (Powder Diffraction File) database collected by the International Centre for Diffraction Data (ICDD), and the same applies hereafter. SEM observation and mercury intrusion confirmed that the obtained cocontinuum was a continuous chain of nanosheets (graphene fragments) with an average pore size of 1 μm. Furthermore, BET specific surface area measurement of the cocontinuum using mercury intrusion revealed a specific surface area of ​​510 m². 2 The result was / g. Furthermore, when the porosity of the coconvex material was measured by the mercury intrusion method, it was found to be over 90%. In addition, from the results of tensile tests, it was confirmed that the obtained coconvex material did not exceed the elastic range and returned to its shape before stress application even when a strain of 20% was applied by tensile stress.

[0055] The above cocontinuum was cut into a square shape with sides of 9 mm using a punching blade or laser cutter to obtain a gas-diffusing air electrode (positive electrode 101).

[0056] Examples 2-1 to 2-5 and 3-1 to 3-6 describe the air electrodes. The molded air electrodes were sealed in the same container and maintained at a predetermined temperature and time using the vapor layer method. Methyltrimethoxysilane (manufactured by Tokyo Chemical Industry Co., Ltd.) was used as the reagent, and a silica-containing coating treatment was carried out at 100°C for 1 to 24 hours.

[0057] The positive electrode current collector 104 was made by integrating a 100 μm thick PLA film, which was fabricated by melting and layering PLA (Poly-Lactic Acid) filament using commercially available carbon paper and the FFF (Fused Filament Fabrication) method with a 3D printer, with the two materials by compression molding at 180°C for 10 seconds and 5 kPa. The positive electrode current collector 104 was then shaped into a convex form for connection with an external load. Specifically, the part in contact with the positive electrode 101 was shaped into a square with sides of 10 mm, and the part connecting to the external load was shaped into a rectangle of 2 mm x 10 mm.

[0058] The negative electrode 102 was obtained by cutting a commercially available magnesium metal (100 μm thick) into a square shape with sides of 10 mm using a punching blade or laser cutter.

[0059] The negative electrode current collector 105 was made of the same material as the negative electrode 102, processed to the same shape as the positive electrode current collector.

[0060] For electrolyte 103, a solution of magnesium acetate tetrahydrate dissolved in pure water at a concentration of 1 mol / L was used.

[0061] Separator 106 used a cellulose-based separator intended for batteries.

[0062] The cellulose-based separators for batteries used in Examples 2-1 to 2-8 are described below. A vapor stage method was performed on the molded air electrode, which was sealed in the same container and maintained at a predetermined temperature and time. Methyltrimethoxysilane was used as the reagent, and a silica-containing coating treatment was carried out at 100°C for 1 to 24 hours, similar to the cathode.

[0063] The housing 110 was formed with an internal dimension of 10.1 mm square and an external dimension of 20 mm, with two gaps for positive and negative electrode current collectors for connection to external loads and one gap at the bottom for a separator, in order to accommodate each component.

[0064] The housing cover 111 is the cover of the housing 110. The housing cover 111 secures the positive electrode current collector 104 from above. The housing cover 111 has an air vent 111a for supplying air to the positive electrode current collector 104.

[0065] The fixing device 112 is used to fix the positive electrode 101. The fixing device 112 has a rectangular shape with an inner dimension of 9 mm and an outer dimension of 10 mm, and is formed to accommodate the positive electrode 101 inside.

[0066] The housing 110, housing lid 111, and fasteners 112 were fabricated using the FFF (Fused Filament Fabrication) method with a 3D printer, by melting and layering PLA filaments.

[0067] The assembly of the magnesium-air battery 100a according to the embodiment shown in Figure 2 will be explained.

[0068] First, a negative electrode current collector 105, a negative electrode 102, and a separator 106 are installed inside the housing 110. A portion of the negative electrode current collector 105 is exposed to the outside of the housing 110 through the air gap for the negative electrode current collector, and a portion of the separator 106 is exposed to the outside of the housing 110 through the air gap for the separator located below the housing 110. A fixing device 112 for improving insulation and fixing the positive electrode is installed on the separator 106. The positive electrode 101 is housed inside the fixing device 112, and a positive electrode current collector 104 is installed on top of it. At this time, a portion of the positive electrode current collector 104 is exposed through the air gap for the positive electrode current collector. The battery materials are fixed from above with a housing lid 111, and the housing 110 and housing lid 111 are fixed using heat generated by vibrations from an ultrasonic cutter or the like. By injecting an electrolyte 103 into the externally exposed separator 106, a magnesium-air battery 100a is fabricated.

[0069] The battery performance of the fabricated magnesium-air battery 100a was measured. First, a discharge test was performed. The discharge test of the air battery was performed using a commercially available charge / discharge measurement system (Hokuto Denko Co., Ltd., SD8 charge / discharge system). In the discharge test, the current density per effective area of ​​the air electrode was 0.5 mA / cm². 2 The system was energized, and measurements were taken in a constant temperature chamber at 25°C (under normal living conditions) until the battery voltage dropped from the open-circuit voltage to 0V. The discharge capacity was expressed as the value per unit weight (mAh / g) of the air electrode, which consists of a cocontinuum.

[0070] Figure 4 shows the initial discharge curve when the negative electrode in Example 1-1 is made of magnesium. As shown in Figure 4, when the negative electrode 102 is made of magnesium and a cocontinuum is used as the air electrode, the average discharge voltage is 1.15V and the discharge capacity is 1200mAh / g. The average discharge voltage is defined as the battery voltage at half the battery's discharge capacity. In Example 1, the battery's discharge capacity is 1200mAh / g, and the experimental discharge capacity is 600mAh / g.

[0071] Table 1 shows the results for Examples 1-1 to 1-4, in which only the electrolyte volume was changed. As the electrolyte volume increased, the discharge capacity and average discharge voltage decreased. This is presumed to be because the electrolyte seeped into the positive electrode, reducing the length of the three-phase interface, which is the reaction field at the positive electrode.

[0072] [Table 1]

[0073] Table 2 shows the results for Examples 2-1 to 2-8, which used a stretchable cocontinuum cathode coated with silica. It can be seen that all batteries in Examples 2-1 to 2-4 exhibited average voltage and discharge capacity equal to or greater than Example 1-1, which had a similar electrolyte volume. Furthermore, even in Examples 2-5 to 2-8, where the electrolyte volume was increased, higher battery performance was observed compared to Examples 1-2 and 1-3.

[0074] [Table 2]

[0075] Table 3 shows the results of examples using a stretchable cocontinuum positive electrode coated with silica-containing material for 6 hours, and a separator coated with silica-containing material. It can be seen that all of the batteries from 3-1 to 3-4 show average voltage and discharge capacity values ​​equal to or greater than those of Examples 1-1 and 2-1 with the same amount of electrolyte. Furthermore, even in 3-5 to 3-6, where the amount of electrolyte was increased, the values ​​were equal to or greater than those of Examples 1-2, 1-3, 2-5, and 2-7.

[0076] [Table 3]

[0077] The magnesium-air battery 100 according to this disclosure has an air electrode composed of a cocontinuum which is a three-dimensional network structure consisting of multiple nanostructures that are integrated by non-covalent bonds. A silane coupling agent is applied to the separator 106 and the positive electrode 101 by a vapor layer method, and the cellulose and the positive electrode surface are coated with silica-containing material. By realizing a positive electrode / electrolyte interface that enables a smooth supply of air even when the electrolyte 103 is in excess, and prevents water from entering from the outside air and leakage of the electrolyte into the outside air, a high-performance magnesium-air battery can be manufactured.

[0078] There are batteries made of environmentally harmful materials that do not take into account laws regarding the management of chemical substances, particularly those that pose a risk to human health and the environment via the environment, with the aim of promoting improvements in the voluntary management of conventional chemical substances and preventing environmental damage. In contrast, according to this disclosure, it is possible to provide a magnesium-air battery 100 that does not pollute waste treatment facilities or the natural environment, and is composed only of low-environmental-impact materials, without using regulated substances that pose a risk to human health and the environment via the environment as defined by law.

[0079] According to the embodiments of this disclosure, it is possible to provide a magnesium-air battery 100 that does not pollute waste treatment facilities or the natural environment, and is composed only of environmentally friendly materials without using regulated substances that are of concern for their impact on human health or the environment via the environment. Such a magnesium-air battery 100 can be effectively used as a power source for various applications, including disposable batteries in everyday environments and sensors used in soil.

[0080] This disclosure is not limited to the embodiments described above, and numerous modifications are possible within the scope of its essence. [Explanation of symbols]

[0081] 100 Magnesium-Air Batteries 101 Positive electrode 102 Negative electrode 103 Electrolytes 104 Positive electrode current collector 105 Negative electrode current collector 106 Separator 111 Casing cover 111a Air vent 112 Fixtures

Claims

1. The positive electrode is composed of an air electrode, A negative electrode composed of magnesium, or a magnesium alloy containing magnesium and one or more elements from the group consisting of iron, calcium, and aluminum, A separator is provided, which is positioned between the positive electrode and the negative electrode, insulates between the positive electrode and the negative electrode, and absorbs water from the electrolyte composed of salt. The separator is a magnesium-air battery coated with methyltrimethoxysilane.

2. The aforementioned air electrode is composed of a cocontinuum which is a three-dimensional network structure made up of multiple nanostructures that are joined together by non-covalent bonds. The magnesium-air battery according to claim 1.

3. The methyltrimethoxysilane is coated with a silane coupling agent. The magnesium-air battery according to claim 1.

4. The nanostructure of the air electrode is A compound containing carbon or iron oxide, comprising a nanosheet composed of at least one of carbon and iron oxide, or A compound containing carbon, iron oxide, or cellulose, and a nanofiber composed of at least one of carbon, iron oxide, and cellulose. The magnesium-air battery according to claim 2.

5. The electrolyte is an aqueous solution or gel containing magnesium acetate. The magnesium-air battery according to claim 1.

6. The housing further comprises the positive electrode, negative electrode, and electrolyte, The housing has air holes that expose the air electrode to the atmosphere. The magnesium-air battery according to claim 1.

7. The process of obtaining a positive electrode composed of an air electrode, The process involves coating the separator with methyltrimethoxysilane, A process for obtaining a negative electrode composed of magnesium, or a magnesium alloy containing magnesium and one or more elements from the group consisting of iron, calcium, and aluminum, The process includes placing the separator and an electrolyte composed of a salt between the positive electrode and the negative electrode, The air electrode is composed of a cocontinuum which is a three-dimensional network structure made up of multiple nanostructures that are joined together by non-covalent bonds. The process of obtaining the positive electrode is as follows: The nanostructure is a production process that causes a predetermined bacterium to produce a sol or gel in which nanofibers of iron oxide, manganese oxide, and cellulose are dispersed, A freezing step in which a dispersed sol or gel is frozen to obtain a frozen body, The system includes a drying step in which the frozen material is dried in a vacuum to obtain the cocontinuum. A method for manufacturing magnesium-air batteries.

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