WO2024150394A1

WO2024150394A1 - Magnesium-air battery and manufacturing method therefor

Info

Publication number: WO2024150394A1
Application number: PCT/JP2023/000730
Authority: WO
Inventors: 博章田口; 政彦林; 正也野原; 匠大久保; 周平阪本; 淳荒武
Original assignee: 日本電信電話株式会社
Priority date: 2023-01-13
Filing date: 2023-01-13
Publication date: 2024-07-18

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

Magnesium air battery and its manufacturing method

This disclosure relates to a magnesium-air battery and a method for manufacturing the same.

Traditionally, alkaline batteries and manganese batteries have been widely used as disposable primary batteries. Furthermore, with the recent development of the IoT (Internet of Things), the development of scattered sensors that can be found all over nature, such as in soil and forests, has progressed, and small, high-performance lithium-ion batteries that can be used for a variety of purposes, including these sensors as well as conventional mobile devices, are becoming widespread.

However, conventional disposable batteries are often made from resources such as lithium, nickel, manganese, or cobalt, which poses the problem of resource depletion. In addition, strong alkalis such as sodium hydroxide aqueous solution or harmful organic electrolytes are used as electrolytes, which poses the problem of soil contamination at final disposal sites. Furthermore, depending on the environment in which disposable batteries are used, such as when used as a power source for sensors that are embedded in the soil, there is the problem that they may have a negative impact on the surrounding environment.

Systematic legislation is being developed that takes these environmental impacts into consideration.

There are laws governing the management of chemical substances that are of concern for their impact on human health and the environment via the environment. The purpose of these laws is to promote improvements in the voluntary management of chemical substances by businesses and prevent impediments to environmental conservation by taking into consideration trends in international cooperation regarding the management of chemical substances related to environmental conservation, scientific knowledge about chemical substances, and the circumstances surrounding the manufacture, use, and other handling of chemical substances, with the understanding of businesses and the public, and by taking measures to grasp the amount of specific chemical substances emitted into the environment, etc., and measures for businesses to provide information on the properties and handling of specific chemical substances.

The laws governing chemical substance management include the Chemical Substances Control Law, the Chemical Substances Management Law, the Agricultural Chemicals Control Law, the Air Pollution Prevention Law, the Water Pollution Prevention Law, the Soil Contamination Countermeasures Law, the Waste Disposal Law, the Poisonous and Hazardous Substances Control Law, the Ozone Layer Protection Law, and the Fluorocarbons Recovery and Destruction Law.

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

As another example, the classification of substances under the Chemical Substances Control Law includes Type 1 and Type 2 Specified Chemicals, Monitoring Chemicals, and Priority Assessment Chemicals, which are substances with high risks such as long-term toxicity and persistence, while there are also general chemicals, which are general chemicals for which the risks are less of a concern. General chemicals present in the city should not be designated as chemicals that pose environmental concerns under these laws (Non-Patent Documents 1 and 2).

Zinc is used as a constituent element in the magnesium alloy of the negative electrode of commercially available magnesium-air batteries, or as the negative electrode material of commercially available dry batteries. However, zinc is designated as a Class 1 designated chemical substance in the Act on Reporting, etc. of Releases of Chemical Substances and Promotion of Their Management (Non-Patent Documents 3 and 4). It is described that zinc metal, zinc oxide, etc. dissolve in acidic and basic aqueous solutions.

In order to solve the above environmental problems, the research and development of next-generation batteries is being promoted, and one of these is the air battery. In air batteries, oxygen in the air used as the positive electrode active material is supplied from outside the battery, so the inside of the battery cell can be filled with a metal anode. Metals such as magnesium, aluminum, or zinc can be used for the anode. By using abundant materials, it is possible to construct a battery that is both low cost and has a low environmental impact. In particular, zinc-air batteries that use zinc for the anode have been commercialized as a power source for hearing aids, and magnesium-air batteries that use magnesium for the anode are being researched and developed as primary batteries with a low environmental impact (Non-Patent Documents 5 and 6).

However, in the air electrode disclosed in Non-Patent Document 5, a fluororesin is used as a binder. Carbon particles alone cannot form and hold a positive electrode, so a fluororesin is used to bind the carbon particles together to form an electric bus and a positive electrode that can also diffuse gas. In the positive electrode, which is composed of a gas diffusion layer through which air (oxygen) diffuses and a catalyst layer where the reduction reaction of oxygen occurs, the fluororesin allows for a smooth supply of air and plays a role in preventing the intrusion of water from the outside air and the leakage of electrolyte into the outside air.

Fluorine and fluorine compounds are designated as hazardous substances under the Soil Contamination Countermeasures Act and the Water Pollution Prevention Act. In addition, in Non-Patent Document 6, metals containing lead and indium are used for the negative electrode, which is a material composition that raises concerns about its impact on the natural environment, such as soil contamination. The chlorine contained in sodium chloride, which is simply and widely used as an electrolyte, can cause corrosion inside the furnace and become a component of toxic substances such as dioxins when mixed into general waste incineration facilities, etc.

A primary battery with low environmental impact that uses a positive electrode that is a bicontinuous body 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 a large amount of electrolyte will cause the positive electrode to become submerged in the liquid, resulting in a decrease in battery performance.

As such, there is a demand for batteries that do not use regulated substances stipulated by law that are of concern for their impact on human health and the environment, that are made only of materials with a low environmental impact, that do not pollute waste disposal facilities or the natural environment, and that can smoothly supply air even when there is an excess of electrolyte.

This disclosure has been made in light of the above circumstances, and the purpose of this disclosure is to provide a battery that is made of materials that have a low environmental impact and that can smoothly supply air even when there is an excess of electrolyte.

The magnesium-air battery of one embodiment of the present disclosure comprises a positive electrode composed of an air electrode, a negative electrode composed of magnesium or a magnesium alloy containing one or more of the group consisting of magnesium and iron, calcium, and aluminum, and a separator disposed between the positive electrode and the negative electrode, providing insulation between the positive electrode and the negative electrode and absorbing an electrolyte composed of salt, and at least one of the positive electrode and the separator is coated with a silica-containing material.

The manufacturing method of a magnesium-air battery according to one embodiment of the present disclosure includes the steps of obtaining a positive electrode made of an air electrode, coating the positive electrode with a silica-containing material, obtaining a negative electrode made of magnesium or a magnesium alloy containing at least one of the group consisting of magnesium and iron, calcium, and aluminum, and disposing an electrolyte made of a salt between the positive electrode and the negative electrode, and the air electrode is composed of a co-continuum having a three-dimensional network structure made of a plurality of nanostructures integrated together by non-covalent bonds, and the step of obtaining the positive electrode includes the steps of causing a specific bacterium to produce a sol or gel in which nanofibers of any one of iron oxide, manganese oxide, and cellulose are dispersed, freezing the dispersed sol or gel to obtain a frozen body, and drying the frozen body in a vacuum to obtain the co-continuum.

According to the present disclosure, it is possible to provide a battery that is made of materials with low environmental impact and that can smoothly supply air even when there is an excess of electrolyte.

FIG. 1 is a diagram illustrating a magnesium-air battery according to an embodiment of the present disclosure. FIG. 2 is a diagram for explaining the appearance of the magnesium-air battery according to the embodiment. FIG. 3 is a schematic diagram illustrating a cross section of a magnesium-air battery according to an embodiment of the present invention. FIG. 4 is a diagram illustrating the battery voltage and discharge capacity during discharge in the magnesium-air battery according to the embodiment.

Below, an embodiment of the present disclosure will be described with reference to the drawings. In the description of the drawings, the same parts are given the same reference numerals and the description will be omitted.

(Magnesium air battery)
A magnesium-air battery 100 according to an embodiment of the present disclosure will be described with reference to Fig. 1. The magnesium-air battery 100 according to the 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 105, a separator 106, and a housing 110.

The positive electrode 101 is composed of a gas diffusion type air electrode for oxygen, etc. The positive electrode 101 is composed of a bicontinuum with a three-dimensional network structure made up of multiple nanostructures that are integrated by non-covalent bonds. No binder, especially no fluororesin, is used in the air electrode.

The negative electrode 102 contains magnesium (Mg). The negative electrode 102 may be made of magnesium or a magnesium alloy containing one or more of the group consisting of magnesium and iron (Fe), calcium (Ca), aluminum (Al), etc. However, magnesium alloys containing zinc components such as AZ31 are excluded.

The electrolyte 103 is disposed 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. The electrolyte 103 is preferably composed only of an aqueous solution or gel containing a salt such as magnesium acetate. Specifically, the electrolyte 103 may be composed of, for example, an aqueous solution of any of magnesium acetate, potassium chloride, and sodium chloride, or a mixture of these salts. Since the electrolyte 103 is composed of salt, it is easy to dispose of, has no concerns about the impact on the surrounding environment, and is easy to handle. The electrolyte 103 may be either an electrolytic solution or a solid electrolyte. The electrolytic solution refers to the electrolyte 103 in a liquid form. The solid electrolyte refers to the electrolyte 103 in a gel form or a solid form. The solid electrolyte may be enclosed with agar, cellulose, water-absorbing polymer, etc. to have a role of retaining water. The electrolyte 103 does not have to be initially disposed when the magnesium-air battery 100 is not operating as a battery. When operating as a battery, the electrolyte 103 may be supplied, for example, from the outside through the separator 106.

A known material can be used for the positive electrode collector 104. For example, a carbon sheet, carbon cloth, Fe, or Al plate can be used for the positive electrode collector 104.

A known negative electrode current collector 105 can be used. If a metal is used for the negative electrode 102, a terminal may be taken out directly from the negative electrode 102 without using the negative electrode current collector 105.

The separator 106 is disposed between the positive electrode 101 and the negative electrode 102, provides insulation between the positive electrode 101 and the negative electrode 102, and absorbs the electrolyte 103 composed of salt. The separator 106 may be any insulator that has 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 decomposes naturally while maintaining its strength, such as a cellulose-based separator made from plant fibers, for the separator 106 reduces the environmental impact. Note that the separator 106 does not need to be installed if insulation between the positive and negative electrodes can be guaranteed.

The positive electrode 101 is in contact with the positive electrode collector 104. When the positive electrode 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 collector 104.

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 a surface other than the surface in contact with the negative electrode current collector 105.

In the embodiment of the present disclosure, a case in which a positive electrode current collector 104 and a negative electrode current collector 105 are provided will be described, but this is not limited to the above. If the strength of the positive electrode 101 and the negative electrode 102 is guaranteed when connected to an external load, the positive electrode current collector 104 and the negative electrode current collector 105 can be omitted.

The housing 110 contains the positive electrode 101, the negative electrode 102, and the electrolyte 103. The electrolyte 103 may be contained inside the housing 110 when the magnesium-air battery 100 is in operation. The housing 110 has an air hole that exposes the positive electrode 101 (air electrode) to the atmosphere. There are no particular limitations on the material or shape of the housing 110, so long as it is capable of maintaining a battery cell inside and is made of a material that 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 in order to supply power.

The housing 110 can be, for example, a known laminate film type. When the housing 110 is made of a naturally degradable material, it may be made of any of natural, microbial, and chemically synthesized materials, such as polylactic acid, polycaprolactone, polyhydroxyalkanoate, polyglycolic acid, and modified starch. In particular, chemically synthesized materials such as plant-derived polylactic acid are preferable. A 3D printer is used as a processing means for the housing 110. The housing 110 can be molded or cut using a 3D printer or the like, and the shape is not limited. In addition to commercially available biodegradable plastics and their films, the housing 110 can also be made of paper coated with a resin such as polyethylene used in milk cartons, or agar film.

The positive electrode 101 will now be described in detail. The positive electrode 101 can be made of a conductive material that is used in the positive electrodes of common, well-known metal-air batteries. A typical example is a carbon material, but it is not limited to this. The positive electrode 101 can be made by a known process, such as forming carbon powder with a binder. In a primary battery, 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.

In the case of typical positive electrodes, which are made by molding carbon powder with a binder and forming it into pellets, when the specific surface area is increased, the bonding strength between the carbon powder particles decreases and the structure deteriorates, making it difficult to discharge stably and reducing the discharge capacity.

Therefore, a bicontinuum having a three-dimensional network structure may be used as the positive electrode 101. By using a bicontinuum having a three-dimensional network structure for the positive electrode 101, it is not necessary to use a binder, and the discharge capacity can be increased.

In a cocontinuum, for example, multiple nanostructures are integrated together through non-covalent bonds to form a three-dimensional network structure. The cocontinuum is a porous body that has an integrated structure. The nanostructure is a nanosheet or nanofiber. In a cocontinuum of a three-dimensional network structure in which multiple nanostructures are integrated together through non-covalent bonds, the bonds between the nanostructures are deformable, giving the structure flexibility.

　A nanosheet is a compound that contains carbon or iron oxide, and is mainly composed of carbon or iron oxide. A nanosheet is composed of at least one of carbon and iron oxide. It is important that the nanosheet is conductive. A nanosheet is defined as a sheet-like material with a thickness of 1 nm to 1 um, and with a planar length and width of 100 times or more the thickness. For example, graphene is an example of a carbon nanosheet. A nanosheet may be rolled or wavy, curved or bent, or of any other shape.

Nanofibers are compounds that contain carbon, iron oxide, or cellulose, and are 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 also have electrical conductivity. Nanofibers are defined as fibrous materials with a diameter of 1 nm to 1 μm and a length of 100 times or more the diameter. Nanofibers may be hollow or coiled, and may have any shape. As for cellulose, it is made electrically conductive by carbonization, as described later.

In the present 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 gas layer method using a silane coupling agent. This allows for a smooth supply of air even when the electrolyte 103 is in an excess state. Furthermore, the interface between the positive electrode 101 and the electrolyte 103 can play a role in preventing the intrusion of water from the outside air and the leakage of the electrolyte into the outside air.

(Production method)
Next, a manufacturing method of the magnesium-air battery 100 will be described. The manufacturing method includes a step of obtaining a positive electrode 101 composed of an air electrode, a step of coating the positive electrode 101 with a silica-containing material, a step of obtaining a negative electrode 102 composed of magnesium or a magnesium alloy containing at least one of a group consisting of magnesium and iron, calcium, and aluminum, and a step of disposing 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 bicontinuum having a three-dimensional network structure composed of a plurality of nanostructures integrated by non-covalent bonds.

The process for obtaining the positive electrode 101 includes a production step of causing a specific bacterium with nanostructures to produce a sol or gel in which nanofibers of either iron oxide, manganese oxide, or cellulose are dispersed, a freezing step of freezing the dispersed sol or gel to obtain a frozen body, and a drying step of drying the frozen body in a vacuum to obtain the co-continuum. The co-continuum that serves as the positive electrode 101 may be created by the freezing step of freezing the sol or gel in which the nanostructures are dispersed to obtain a frozen body and the drying step of drying the frozen body in a vacuum to obtain a co-continuum. The positive electrode 101 is composed of the co-continuum obtained in the drying step.

If the sol or gel has dispersed nanofibers made of any of iron oxide, manganese oxide, silicon, and cellulose, it may be produced by a specific bacterium (sol or gel production process). In this case, the process of obtaining the positive electrode 101 includes a production process of producing a sol or gel with dispersed cellulose nanofibers by a specific bacterium, and a carbonization process of heating and carbonizing the sol or gel in an inert gas atmosphere to obtain a co-continuum. The positive electrode 101 is composed of the co-continuum obtained in the carbonization process.

The co-continuum constituting the positive electrode 101 preferably has an average pore size of, for example, 0.1 to 50 μm, and more preferably 0.1 to 2 μm. Here, the average pore size is a value determined by mercury intrusion porosimetry. In this case, there is no need to use additional materials such as binders as in the case of using carbon powder, which is advantageous in terms of cost and also in terms of the environment.

(Electrochemical reaction)
Here, the electrochemical reactions at the positive electrode 101 and the negative electrode 102 will be described taking as an example a primary battery using magnesium metal for the negative electrode. The positive electrode reaction proceeds as shown in "1/2O2 + H2O + 2e- → 2OH- ... (1)" when oxygen in the air and the electrolyte come into contact with the surface of the conductive positive electrode 101. Meanwhile, the negative electrode reaction proceeds as shown in "Mg → Mg2+ + 2e- ... (2)" at the negative electrode 102 in contact with the electrolyte 103, and the magnesium constituting the negative electrode 102 releases electrons and dissolves into the electrolyte as magnesium ions.

These reactions make it possible to discharge the battery. The overall reaction is "Mg + 1/2O2 + H2O + 2e- → Mg(OH)2 ... (3)", which is the reaction that produces (precipitates) magnesium hydroxide. The theoretical electromotive force is approximately 2.7 V. Thus, in a primary battery, the reaction shown in formula (1) proceeds on the surface of the positive electrode 101, so it is considered better to produce a large number of reaction sites inside the positive electrode 101.

The magnesium-air battery 100 according to the embodiment of the present disclosure is made of materials with low environmental impact 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 specified by various laws and regulations. Such a magnesium-air battery 100 places an extremely low burden on the living environment and the natural environment, even when used in a disposable device such as a soil moisture sensor, and when it is not collected or is discarded as general waste.

Furthermore, at least one of the positive electrode 101 and the separator 106 is coated with a silica-containing material. 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 serve to prevent the intrusion of water from the outside air and the leakage of the electrolyte into the outside air.

　We will explain examples 1-1 to 3-6 related to the embodiment of this disclosure.

Examples 1-1 to 1-4 are examples in which a bicontinuum having a three-dimensional network structure made up of multiple nanosheets bound together by non-covalent bonds is used as an air electrode (positive electrode 101).

As shown in Figures 2 and 3, the magnesium air battery 100a according to the embodiment includes 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 cover 111, and a fastener 112.

The cathode (air electrode) 101 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 of another material, it is possible to prepare a bicontinuum having a three-dimensional network structure.

First, a method for producing the positive electrode 101 will be described. A commercially available carbon nanofiber sol [dispersion medium: water (H ₂ O), 0.4 wt %, manufactured by Sigma-Aldrich] was placed in a test tube, and the test tube was immersed in liquid nitrogen for 30 minutes to completely freeze the carbon nanofiber sol. After completely freezing the carbon nanofiber sol, the frozen carbon nanofiber sol was taken out into an eggplant flask, and this was dried in a vacuum of 10 Pa or less using a freeze dryer (manufactured by Tokyo Rikakikai Co., Ltd.), to obtain an elastic bicontinuum having a three-dimensional network structure containing carbon nanosheets.

The obtained co-continuum was evaluated by X-ray diffraction (XRD) measurement, scanning electron microscope (SEM) observation, porosity measurement, tensile test, and BET (Brunauer Emmett Teller) specific surface area measurement. The prepared co-continuum was confirmed to be a single phase of carbon (C, PDF card No. 01-075-0444) by XRD measurement. The PDF card No. is the card number of the PDF (Powder Diffraction File), a database collected by the International Centre for Diffraction Data (ICDD), and the same applies below. In addition, by SEM observation and mercury intrusion porosimetry, it was confirmed that the obtained co-continuum was a co-continuum with an average pore size of 1 μm in which nanosheets (graphene pieces) were continuously connected. In addition, the BET specific surface area of the co-continuum was measured by mercury intrusion porosimetry, and it was found to be 510 m ² /g. The porosity of the co-continuum was measured by mercury intrusion porosimetry and found to be over 90%. Furthermore, the results of a tensile test confirmed that the co-continuum did not exceed its elastic region and restored its shape before the application of stress even when a 20% strain was applied due to tensile stress.

The above-mentioned co-continuum was cut into a square shape with a side length of 9 mm using a punching blade or a laser cutter, etc., to obtain a gas diffusion type air electrode (positive electrode 101).

The air electrodes of Examples 2-1 to 2-5 and 3-1 to 3-6 are explained below. The molded air electrodes were sealed in the same container and subjected to the gas phase method, in which they were maintained at a specified temperature for a specified time. The reagent used was methyltrimethoxysilane (Tokyo Chemical Industry Co., Ltd.), and the coating process was carried out with silica-containing silica at 100°C for 1 to 24 hours.

The positive electrode current collector 104 was made by compressing commercially available carbon paper and a PLA film of about 100 μm, which was made by melting and laminating PLA (Poly-Lactic Acid) filaments using the FFF (Fused Filament Fabrication) method with a 3D printer, at 180°C for 10 seconds at 5 kPa to integrate them. The positive electrode current collector 104 was processed into a convex shape for connection to an external load. Specifically, the part that contacts the positive electrode 101 was processed into a square shape with one side measuring 10 mm, and the part that connects to the external load was processed into a rectangle measuring 2 mm x 10 mm.

The negative electrode 102 was obtained by cutting commercially available magnesium metal (thickness 100 μm) into a square shape with each side measuring 10 mm using a punching blade or laser cutter.

The negative electrode current collector 105 is made of the same material as the negative electrode 102, but is processed into the same shape as the positive electrode current collector.

The electrolyte 103 was a solution of magnesium acetate tetrahydrate dissolved in pure water at a concentration of 1 mol/L.

Separator 106 is a cellulose-based separator for batteries.

The cellulose-based separator for batteries used in Examples 2-1 to 2-8 will be described. The molded air electrode was sealed in the same container and subjected to the gas layer method, which involved maintaining the electrode at a specified temperature for a specified period of time. The reagent used was methyltrimethoxysilane, and the coating process was carried out with a silica-containing solvent at 100°C for 1 to 24 hours, just like the positive electrode.

The housing 110 is designed to accommodate each component, with inner dimensions of 10.1 mm square and outer dimensions of 20 mm, with two gaps for the positive and negative electrode collectors for connection to an external load, and one gap at the bottom for the separator to be exposed.

The housing lid 111 is a lid for the housing 110. The housing lid 111 fixes the positive electrode collector 104 from above. The housing lid 111 has an air hole 111a for supplying air to the positive electrode collector 104.

The fixture 112 is used to fix the positive electrode 101. The fixture 112 has a rectangular shape with inner dimensions of 9 mm and outer dimensions of 10 mm, and is formed so that the positive electrode 101 can be accommodated inside.

The housing 110, housing lid 111, and fixture 112 were produced by melting and stacking PLA filament using the FFF (Fused Filament Fabrication) method with a 3D printer.

The assembly of the magnesium-air battery 100a according to the embodiment shown in Figure 2 will now be described.

First, the negative electrode collector 105, the negative electrode 102, and the separator 106 are placed in the housing 110. A part of the negative electrode collector 105 is exposed to the outside of the housing 110 from the gap for the negative electrode collector in the housing 110, and a part of the separator 106 is exposed to the outside of the housing 110 from the gap for the separator provided at the bottom of the housing 110. A fixing device 112 for improving insulation and fixing the positive electrode is placed on the separator 106. The positive electrode 101 is stored inside the fixing device 112, and the positive electrode collector 104 is placed on top of it. At this time, a part of the positive electrode collector 104 is exposed from the gap for the positive electrode collector. The battery material is fixed from above with the housing lid 111, and the housing 110 and the housing lid 111 are fixed using heat generated by vibrations from an ultrasonic cutter or the like. The magnesium-air battery 100a was produced by injecting the electrolyte 103 into the separator 106 exposed to the outside.

The battery performance of the prepared 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 (SD8 charge/discharge system, manufactured by Hokuto Denko Corporation). In the discharge test, a current density of 0.5 mA/ ^cm2 was applied per effective area of the air electrode, and measurements were performed in a thermostatic chamber at 25°C (atmosphere: normal living environment) until the battery voltage decreased from the open circuit voltage to 0V. The discharge capacity was expressed as a value (mAh/g) per weight of the air electrode made of a bicontinuum.

The initial discharge curve when the negative electrode is made of magnesium in Example 1-1 is shown in Figure 4. As shown in Figure 4, when the negative electrode 102 is made of magnesium and the co-continuum is used as the air electrode, the average discharge voltage is 1.15 V and the discharge capacity is 1200 mAh/g. The average discharge voltage is the battery voltage when the discharge capacity is 1/2 of the battery's discharge capacity. In Example 1, the battery discharge capacity is 1200 mAh/g and the discharge capacity in the experiment is 600 mAh/g.

Table 1 shows the results of Examples 1-1 to 1-4, in which only the amount of electrolyte was changed. As the amount of electrolyte increased, the discharge capacity and average discharge voltage decreased. This is presumably because the electrolyte seeped into the positive electrode, reducing the length of the three-phase interface, which is the reaction site at the positive electrode.

Table 2 shows the results of Examples 2-1 to 2-8, which used a positive electrode made of an elastic bicontinuum that had been coated with silica-containing electrolyte. It can be seen that all of the batteries 2-1 to 2-4 exhibit average voltages and discharge capacities equal to or greater than those of Example 1-1, which had the same amount of electrolyte. It can also be seen that batteries 2-5 to 2-8, which had an increased amount of electrolyte, had higher battery performance than Examples 1-2 and 1-3.

Table 3 shows the results of examples using an elastic bicontinuous positive electrode coated with a silica-containing electrolyte for 6 hours and a separator coated with a silica-containing electrolyte. It can be seen that all of the batteries 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, which have the same amount of electrolyte. Also, batteries 3-5 to 3-6, which have an increased amount of electrolyte, show values equal to or greater than those of Examples 1-2, 1-3, 2-5, and 2-7.

The magnesium-air battery 100 according to the present disclosure has an air electrode made of a co-continuum with 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 gas layer method, and the cellulose and positive electrode surface are coated with silica-containing material. By realizing a positive electrode/electrolyte interface that allows for a smooth supply of air even when there is an excess of electrolyte 103 and prevents water from entering from the outside air and electrolyte from leaking into the outside air, a high-performance magnesium-air battery can be produced.

　There are batteries made of environmentally hazardous materials that do not take into consideration laws governing chemical substance management, particularly those that are of concern for their impact on human health and the environment via the environment, with the aim of promoting improvements in conventional voluntary management of chemical substances and preventing impediments to environmental conservation. In contrast, according to the present disclosure, it is possible to provide a magnesium-air battery 100 that does not pollute waste treatment facilities or the natural environment and is made only of materials with low environmental impact, without using any regulated substances stipulated by laws and regulations that are of concern for their impact on human health and the environment via the environment.

According to the embodiment of the present disclosure, it is possible to provide a magnesium-air battery 100 that does not pollute waste treatment facilities or the natural environment and is made only of materials with low environmental impact, without using regulated substances that are of concern for their impact on human health and the environment via the environment. Such a magnesium-air battery 100 can be effectively used as a variety of power sources, including disposable batteries in everyday environments and sensors used in soil.

Note that this disclosure is not limited to the above-described embodiments, and many variations are possible within the scope of the gist of the disclosure.

REFERENCE SIGNS LIST 100 Magnesium-air battery 101 Positive electrode 102 Negative electrode 103 Electrolyte 104 Positive electrode current collector 105 Negative electrode current collector 106 Separator 111 Housing cover 111a Air hole 112 Fixing device

Claims

a positive electrode composed of an air electrode;
a negative electrode made of magnesium or a magnesium alloy containing at least one of the group consisting of magnesium and iron, calcium, and aluminum;
a separator disposed between the positive electrode and the negative electrode, providing insulation between the positive electrode and the negative electrode and absorbing an electrolyte composed of a salt;
At least one of the positive electrode and the separator is coated with a silica-containing material.
The magnesium-air battery according to claim 1 , wherein the air electrode is composed of a bicontinuous body having a three-dimensional network structure composed of a plurality of nanostructures bound together by non-covalent bonds.
The magnesium-air battery according to claim 1 , wherein the silica-containing material is coated with a silane coupling agent.
The nanostructure of the air electrode is
A nanosheet made of at least one of carbon and iron oxide, which is a compound containing carbon or iron oxide; or
The magnesium-air battery according to claim 2, wherein the compound is a compound containing carbon, iron oxide, or cellulose, and the compound is a nanofiber composed of at least one of carbon, iron oxide, and cellulose.
The magnesium-air battery according to claim 1 , wherein the electrolyte is an aqueous solution or gel containing magnesium acetate.
Further comprising a housing for housing the positive electrode, the negative electrode, and an electrolyte;
The magnesium-air battery according to claim 1 , wherein the housing has an air hole for exposing the air electrode to the atmosphere.
obtaining a positive electrode composed of an air electrode;
coating the positive electrode with a silica-containing coating;
obtaining a negative electrode made of magnesium or a magnesium alloy containing at least one of the group consisting of magnesium and iron, calcium, and aluminum;
A step of disposing an electrolyte composed of a salt between the positive electrode and the negative electrode,
The air electrode is composed of a bicontinuous three-dimensional network structure composed of a plurality of nanostructures that are integrated by non-covalent bonds;
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 any one of iron oxide, manganese oxide, and cellulose are dispersed;
a freezing step of freezing the dispersed sol or gel to obtain a frozen body;
The method for manufacturing a magnesium-air battery includes a drying step of drying the frozen body in a vacuum to obtain the co-continuum.