JP2023129192A - primary metal battery - Google Patents

Abstract

To provide a primary metal battery from which electric energy can be extracted efficiently and which uses a long-term usable electrode.SOLUTION: A primary metal battery according to the present invention uses a coated metal electrode in which either a conductive film or a semiconducting film each preventing chemical reaction, or both the conductive film and the semiconducting film, are formed on the metal. As a metal electrode, copper, zinc or zinc alloy, aluminum or aluminum alloy, magnesium or magnesium alloy can be used. The conductive film can be a layered compound, a resistor, or metal, and the semiconductive film can be titanium oxide, tungsten oxide, or a photocatalyst.SELECTED DRAWING: Figure 1

Description

The present invention relates to a primary metal battery and its electrodes from which electrical energy can be extracted.

Batteries are widely used as power sources in electronic devices such as mobile phones, notebook computers, and electronic toys. Although manganese batteries, alkaline batteries, and the like are widely used as batteries, zinc batteries, aluminum batteries, magnesium batteries, and the like, which use metal materials for electrodes, are currently being developed. In addition, microbial fuel cells, which can extract electrical energy from the natural world, are attracting attention as natural energy that is compatible with nature and friendly to the environment, although the amount of electrical energy that can be extracted is small.

In the following explanation, the words positive electrode, cathode electrode (or cathode), and negative electrode and anode electrode (or anode) are used interchangeably because the words used are different depending on the industry, but as a primary battery are used with the same meaning.

Zinc batteries use zinc or a zinc alloy for the negative electrode, and are required to have higher capacity and higher voltage, and are also required to be used for longer periods of time.

Patent Document 1 discloses a technique that improves the cycle life and shelf life of a battery. The negative electrode active material of rechargeable zinc-alkaline electrochemical cells is formed from metallic zinc particles coated with tin and/or lead. The remaining zinc electrode components, such as zinc oxide (ZnO), bismuth oxide (Bi ₂ O ₃ ), dispersant, and binder are then added. Due to this. Compared to conventional batteries, hydrogen gas generation is 60-80% less likely, the zinc conductive matrix remains intact, and discharge during storage can be suppressed. This increases the cycle life and shelf life of the battery.

Patent Document 2 discloses a technique for obtaining a battery with high voltage, long life, and low cost even when aluminum is used for the negative electrode of the battery. Aluminum batteries have an electrolyte between the positive and negative electrodes and have clay minerals dispersed in the electrolyte in contact with the negative aluminum electrode, or aluminum batteries have an electrolyte between the positive and negative electrodes. , with a layer of clay mineral in contact with the negative aluminum electrode.

Patent Document 3 discloses a technique that can extend the life of a magnesium battery. Magnesium batteries use magnesium for the negative electrode. The negative electrode has a structure in which a thin film of magnesium negative electrode material is bonded to both sides of a thin aluminum conductive plate. The negative electrode material consists of magnesium to which 1.5-2.5% by weight of calcium is added.

A microbial fuel cell is a system that uses the catabolic ability of microorganisms to produce electricity from organic matter. Sludge is organic matter contained in industrial and domestic wastewater that is deposited along with mud on riverbeds and the ocean floor. When microorganisms decompose the organic matter in the sludge through biomass processing, hydrogen ions and electrons are generated, which can be used as electricity. electrical energy can be recovered directly in the form of In microbial fuel cells, electrons released from microorganisms are transferred to the anode electrode (negative electrode). Electrons move from the anode electrode through an external load to the cathode electrode (positive electrode), where they react with a compound that becomes an oxidizing agent (electron acceptor) and hydrogen ions (H+) that have diffused from the anode side. Therefore, by connecting a load between the anode electrode and the cathode electrode, it functions as an electric circuit.

Patent Document 4 discloses a microbial fuel cell, an electrode for a microbial fuel cell, a manufacturing method thereof, a power production method using microorganisms, and a microorganism used in the power production method, which can improve power production capacity and suppress power generation costs. A method for selective culturing is disclosed. An anode electrode that has a liquid containing an organic substance and an anode electrode, the organic substance is biodegraded by microorganisms in an anaerobic atmosphere, a cathode electrode, and an external circuit that electrically connects the anode electrode and the cathode electrode. The anode electrode includes graphene. The graphene included in the anode electrode is an excellent electron conductive material, so graphene can facilitate electron transfer from microorganisms to the negative electrode, improving power production.

Patent Document 5 discloses a microbial fuel cell electrode capable of generating high output current in a microbial fuel cell, and a microbial fuel cell using the electrode. As an anode electrode for a microbial fuel cell, a nanowire structure is formed on the surface of the electrode base using a conductive polymer to increase the electrode surface area. It has been found that this increases the efficiency of charge transfer from microorganisms to the electrode by 10 to 100 times compared to conventional electrodes for microbial fuel cells.

Japanese Patent Application Publication No. 2012-527733 Japanese Patent Application Publication No. 2018-041670 Japanese Patent Application Publication No. 2017-188483 International Publication 2013/073284 International Publication 2011/025021

Conventional primary metal batteries are composed of a positive electrode (cathode electrode), a negative electrode (anode electrode), and an electrolyte, but when metal is used for the electrodes, there is a problem of corrosion. Furthermore, since electrical energy uses chemical reactions in metals, there is a problem with its lifespan. Furthermore, although carbon felt is used in microbial fuel cells, since the same material is used for the cathode and anode electrodes, the voltage and current are low.

Existing primary metal batteries such as zinc batteries, aluminum batteries, and magnesium batteries utilize chemical reactions, and zinc, aluminum, magnesium, and their alloys dissolve and become smaller due to chemical reactions. For this reason, deterioration of characteristics is unavoidable, and longevity has become a major issue.

Microbial fuel cells have the problem that the amount of electricity that can be extracted is extremely small and the voltage is also lower than that of solar cells, and that it is necessary to further increase the voltage and increase the amount of power production for practical use.

The present invention has been made to solve the above problems, and aims to provide a primary metal battery using electrodes that can efficiently extract electrical energy and can be used for a long period of time.

The present invention aims to extend the life of the electrodes of primary metal batteries by the following means.

(1) The primary metal battery of the present invention is a coated metal in which either a conductive coating or a semiconductive coating, or both a conductive coating and a semiconductive coating are formed on the metal to prevent chemical reactions. It is characterized by the use of electrodes.

(2) In the primary metal battery of the present invention, the metal is preferably zinc or a zinc alloy, aluminum or an aluminum alloy, magnesium or a magnesium alloy.

(3) In the primary metal battery of the present invention, it is preferable that the conductive film is a layered compound, a resistor, or a metal, and the semiconductive film is a semiconductor.

(4) In the primary metal battery of the present invention, the layered compound is preferably graphite, Prussian blue, or a Prussian blue analog. Here, the term "layered compound" is used as a general term for substances having an intercalation function, and includes microporous crystals and porous coordination polymers in which pore structures are fixed in a three-dimensional skeleton.

(5) In the primary metal battery of the present invention, the resistor is preferably iron phthalocyanine, iron oxide, or a conductive passive film.

(6) In the primary metal battery of the present invention, the semiconductor is preferably titanium oxide, tungsten oxide, or a photocatalyst.

(7) In the primary metal battery of the present invention, the conductive coating may contain graphite, carbon nanotubes, carbon black, activated carbon, Ketjen black, fullerene, charcoal fine powder, iron phthalocyanine, iron oxide, or Preferably, an organic conductive polymer is included.

(8) In the primary metal battery of the present invention, it is preferable that the conductive coating is a mixture of a conductive material with a binder or a resin and coated on the metal.

(9) In the primary battery of the present invention, the coated metal electrode is used as a negative electrode, and the positive electrode is a carbon electrode made of carbon-based graphite, activated carbon, carbon graphite, hard carbon, or charcoal, or a carbon electrode with ionization tendency. It is preferred that the metal is a noble metal.

(10) In the primary metal battery of the present invention, it is preferable that the carbon electrode is formed with an iron component film, a titanium oxide film, a tungsten oxide film, or a photocatalytic film formed by coating iron phthalocyanine or iron oxide with a binder or resin. .

(11) In the primary metal battery of the present invention, the electrolyte is preferably water, soil, seawater, an aqueous solution of fertilizer, soil containing organic matter or fertilizer, or a combination thereof.

(12) In the primary metal battery of the present invention, it is preferable that the electrolyte contains sugars produced by plants through photosynthesis and released from their roots.

(13) In the primary metal battery of the present invention, the coated metal electrode is preferably covered with a water-permeable insulating sheet.

(14) In the primary metal battery of the present invention, it is preferable that the insulating sheet is impregnated with the same material as the coating of the coated metal electrode.

(15) The primary metal battery of the present invention is preferably an electrical energy system comprising a storage battery and a control unit that stores electrical energy from the primary metal battery in the storage battery.

(1) The primary metal battery of the present invention utilizes the difference in ionization tendency (oxidation-reduction potential) of the electrodes to apply a voltage to the electrolyte, electrolyze the electrolyte, generate electrons, and extract the electrons from the electrodes. The principle is that it functions as a temporary battery. When metal is used for the electrode, corrosion due to chemical reaction with the electrolyte becomes a problem. For this reason, by using a coated metal electrode in which either a conductive film or a semi-conductive film, or both a conductive film and a semi-conductive film are formed on the metal to prevent chemical reactions, the electrode This prevents dissolution, that is, chemical reaction, and allows for long-term use.

(2) In the primary metal battery of the present invention, zinc or a zinc alloy, aluminum or an aluminum alloy, magnesium or a magnesium alloy can be used as the metal. The redox potential is -0.76V for zinc, -1.68V for aluminum, and -2.34V for magnesium. The generated voltage is determined depending on this redox potential. It is preferable to use zinc, aluminum, magnesium, etc., which have a negative oxidation-reduction potential, for the negative electrode. Each redox potential allows a voltage to be applied to the electrolyte at a difference in the redox cell from other electrodes.

Carbon felt is used as a negative electrode in microbial fuel cells. If this negative electrode is a coated metal electrode according to the present invention, both voltage and current can be significantly increased.

(3) The conductive film is a layered compound, a resistor, or a metal, and the semiconductive film is a semiconductor, and this conductive film can prevent chemical reactions of metals and enable long-term use.

(4) The layered compound of the conductive film is preferably graphite, Prussian blue, or a Prussian blue analog, and must have an intercalation function. Intercalation is a reversible reaction in which another element enters the void space of a molecule or group of molecules. It is preferable that the metal surface of the graphite is coated with zinc, aluminum, magnesium, etc., each having a negative oxidation-reduction potential. The layered compound coating suppresses the chemical reaction of the metal and can replace the charge transfer reaction due to its intercalation function.

(5) The resistor is preferably iron phthalocyanine, iron oxide, or a conductive passive film. This makes it possible to form a low-resistance film and further prevent chemical reactions of the metal.

(6) A semiconductor film can be formed by coating a semiconductor with titanium oxide, tungsten oxide, or a photocatalyst. Titanium oxide, tungsten oxide, or a photocatalyst can be used to electrolyze the electrolyte by applying a voltage generated by the difference in ionization tendency (redox potential) between the negative and positive electrodes, which excites electrons from the valence band to the conduction band. This can increase the generation of electrons, increase the available electrical energy, and prevent chemical reactions of metals.

(7) The conductive coating contains graphite, activated carbon, carbon nanotubes, carbon black, Ketjenblack, fullerene, fine charcoal powder, iron phthalocyanine or iron oxide, or an organic conductive polymer as a conductive material. There is. In particular, Prussian blue and Prussian blue analogs are effective in lowering resistance. These conductive materials have low resistance and allow electrons to pass through them easily.

(8) In the conductive coating, a conductive material is mixed with a binder or a resin to form a coating on the metal. A uniform film is obtained by mixing the conductive material and the binder or resin, stirring the mixture sufficiently to obtain a uniformly dispersed state, and coating the mixture. As a result, the conductive material uniformly and firmly adheres to the metal.

(9) By using the coated metal electrode as the negative electrode and the positive electrode as a carbon electrode made of carbon-based graphite, activated carbon, carbon graphite, hard carbon, or charcoal, or a metal with a noble ionization tendency, It becomes a primary metal battery that functions as a battery.

(10) The carbon electrode has an iron component coating formed by coating iron phthalocyanine or iron oxide with a binder or resin. This can increase the electrical energy that can be obtained.

(11) The electrolyte is water, soil, seawater, an aqueous solution of fertilizer, soil containing organic matter or fertilizer, or a combination thereof. Adding organic matter or fertilizer to the soil has the effect of significantly improving battery performance. In other words, electric energy can be obtained from anywhere on earth using the natural world as an electric field.

(12) The electrolyte may contain sugars produced by plants through photosynthesis and released from their roots. Sugars produced by plants through photosynthesis and released from their roots are continuously released as long as the plant is growing, and can be used as a semi-permanent source of energy.

(13) The coated metal electrode is covered with a water-permeable insulating sheet. By wrapping with a water-permeable insulating sheet, only the charge in the electrolyte can be transferred between the coated metal electrode and the electrolyte. This can prevent the coating formed on the coated metal electrode from peeling off due to scratches or the like. Furthermore, when replacing the coated metal electrode, the coated metal electrode wrapped in the insulating sheet can be removed including any residue, and no residue will remain in the electrolyte, making it easy to replace.

(14) The insulating sheet is impregnated with the same material as the coating of the coated metal electrode. Thereby, the function of the coating can be supplemented.

(15) With the configuration of a primary metal battery, a storage battery, and a control unit that stores electrical energy from the primary metal battery in the storage battery, an electrical energy system can be created, and the electrical energy obtained from the primary metal battery can be efficiently used. can be used.

FIG. 2 is a diagram showing a cross section of a coated metal electrode used in the primary metal battery of the present invention. FIG. 2 is a diagram illustrating the principle of a conventional magnesium air battery. FIG. 1 is a diagram illustrating a primary metal battery according to the present invention. FIG. 2 is a diagram showing a microbial fuel cell in which an anode electrode and a cathode electrode are embedded in soil where plants are growing. FIG. 2 is a diagram illustrating rice field power generation, which is a type of microbial fuel cell in which the electrolyte is composed of a soil region and a water region. An example of a prototype coated metal electrode fabricated as a negative electrode is shown. This is experimental equipment A for confirming the function of coated metal electrodes. FIG. 3 is a diagram showing an experimental device B in which an electrode is embedded in a flowerpot in which flowers are planted to extract electrical energy and turn on illumination.

Batteries include primary batteries and secondary batteries. A primary battery has a cell structure in which a positive electrode and a negative electrode sandwich an electrolyte (chemical substance).In principle, the chemical substance present in the cell undergoes an irreversible chemical reaction with the electrode, so it is non-rechargeable. be. The chemical reaction is a reaction between the electrode and the chemical substance present in the cell, and the electrode is dissolved by the chemical reaction. Power generation ends when all of the electrodes or chemicals are used.

The electromotive force of a primary battery is the difference in ionization tendency between the positive and negative electrodes. The greater the difference in redox potential, which indicates ionization tendency, between the positive electrode and the negative electrode, the greater the electromotive force obtained. Examples of primary batteries include manganese dry batteries and alkaline dry batteries that use manganese dioxide and zinc as electrode materials. The electrolyte for manganese dry batteries is mainly a zinc chloride solution, and the electrolyte for alkaline batteries is a potassium hydroxide solution.

Lithium primary batteries use lithium, which has a strong ionization tendency, as the material for the positive electrode, and manganese dioxide, graphite fluoride, thionyl chloride, etc. as the material for the positive electrode. The mainstream is one that uses inexpensive manganese dioxide and has an output voltage of 3V, but there are also those that use graphite fluoride, thionyl chloride, etc. and have an output voltage of 3.6V.

Magnesium primary batteries are currently in practical use as emergency batteries. Magnesium is used as the negative electrode material, and carbon is used as the positive electrode material. Since a sodium chloride aqueous solution is used as the electrolyte, once magnesium is exposed to the sodium chloride aqueous solution, corrosion occurs. For this reason, aluminum, zinc, etc. are added to magnesium to improve its corrosion resistance, but this is not sufficient, and currently it is limited to emergency use disposable types.

Primary batteries that do not involve chemical reactions of electrode materials include fuel cells and microbial fuel cells. A fuel cell is the opposite of water electrolysis; it creates water using hydrogen and oxygen, and extracts the electricity generated in the process. At the fuel electrode, hydrogen ions (H ⁺ ) and electrons (e ⁻ ) are extracted through a catalytic reaction by supplying hydrogen fuel. The electrolyte is, for example, a phosphoric acid (H ₃ PO ₄ ) aqueous solution, which is a substance that allows ions to pass through but not electrons, so hydrogen ions (H ⁺ ) pass through the electrolyte and move to the air electrode.

Since electrons are blocked by the electrolyte and cannot move, electricity can be generated by extracting them to the outside. At the air electrode, when oxygen in the air is supplied, oxygen (O ₂ ) is separated into two oxygen atoms by a catalytic reaction. Water (H ₂ O) is produced by combining the electrons transferred to the oxygen atoms with the hydrogen ions that have passed through the electrolyte.

Microbial fuel cells utilize the metabolic abilities of microorganisms to convert organic matter into electrical energy. Organic substances that serve as fuel for microbial fuel cells include sugars produced by fermentation of fallen leaves, etc., and sugars produced by photosynthesis of plants and excreted from their roots. The negative electrode (anode) collects electrons generated when organic matter is oxidized and decomposed by microorganisms called amperogens (for example, Shewanella bacteria).

The electrons move to the positive electrode (cathode) via an external circuit, where they are consumed by the reduction reaction of the oxidant, that is, by oxygen in the air, and become water. For this reason, the positive electrode is also called an air cathode. Organic matter such as sewage and sludge can be used as fuel, and it can be applied to power generation as well as environmental purification such as processing organic waste and improving water quality. Carbon felt is mainly used as the electrode material for both the positive and negative electrodes, and the electrical energy that can be extracted is small.

Renewable energy that is a type of primary battery includes solar power generation and wind power generation. Currently, solar power generation is the mainstream, does not generate _CO2 , and is positioned as an important energy source for global warming countermeasures. Since solar power generation uses sunlight as its energy source, it naturally does not generate electricity in areas without sunlight or at night. Wind power generation also uses the wind, so it is an unstable form of energy that is left to the wind, and its installation locations are limited.

Secondary batteries are required to be able to be charged and discharged repeatedly, and it is difficult to repeatedly deposit and dissolve electrode materials in secondary batteries that involve reversible chemical reactions. The mainstream is the charge transfer type, in which charges are transferred between the two. In the charge transfer type, when charging, charge is accumulated in the positive electrode by applying a voltage from the outside, and when in use, the charge accumulated in the positive electrode is transferred to the negative electrode in the electrolyte, and electrons flow to the external circuit. It is.

Examples of secondary batteries include nickel metal hydride batteries and lithium ion batteries. A nickel-metal hydride battery uses nickel hydroxide for the positive electrode and a hydrogen storage alloy for the negative electrode. Hydrogen storage alloys are metals that can store 1000 times their volume of hydrogen. An alkaline solution such as an aqueous potassium hydroxide solution is used as the electrolyte. During charging, hydrogen is stored in the hydrogen storage alloy, and during discharge, the hydrogen stored in the hydrogen storage alloy is released. The voltage of a nickel-metal hydride battery is 1.2V, the same as a nickel-cadmium battery, but it has about twice the electrical capacity.

Lithium ion batteries are a typical secondary battery that utilizes an intercalation phenomenon and are characterized by high voltage and large capacity, and are currently the mainstream. A layered compound with an intercalation function is used for both the positive and negative electrodes, with the positive electrode typically using lithium cobalt oxide and aluminum for the pyroelectric material, and the negative electrode using graphite and copper for the pyroelectric material. This is an example.

Lithium cobalt oxide is also called an oxide composite, and since cobalt is expensive, lithium manganate (LiMn ₂ O ₄ )-based, lithium nickel oxide (LiNiO ₂ )-based, lithium iron phosphate (LiFePO), which can further reduce costs, are used. ₄ ) systems are also used. In order to give high conductivity and safety to the electrolyte (electrolytic solution), we use low viscosity solvents such as dimethyl carbonate, ethyl methyl carbonate, and carbonic acid in addition to cyclic carbonate ester-based high dielectric constant and high boiling point solvents such as ethylene carbonate and propylene carbonate. Lower chain carbonate esters such as diethyl are also used.

The above is an overview of primary batteries and secondary batteries. The main principle of primary batteries is chemical reaction, and the main principle of secondary batteries is charge transfer reaction. These are classified as chemical batteries, but in addition to physical batteries, primary batteries include solar power generation, wind power generation, hydroelectric power generation, etc., and there are also fuel cells that continuously supply electrolyte (fuel).

A primary battery as a chemical battery uses a chemical reaction of metals to generate power, and because the chemical reaction is used to dissolve the metal, it naturally has a limited lifespan. Although secondary batteries can be used repeatedly, they are first charged with external electrical energy. Solar power generation and wind power generation, which are attracting attention as renewable energies that do not emit _CO2 , are unable to provide a stable supply of electricity, and solar power generation is limited to when sunlight is shining, while wind power generation Also only when the wind is blowing. Although fuel cells are capable of continuously supplying electrical energy, the voltage per unit cell is low, and microbial fuel cells in particular have low current capacity.

In order to solve these problems, the primary metal battery of the present invention has been newly devised.

The primary metal battery of the present invention uses the difference in ionization tendency (oxidation-reduction potential) of the materials used for the positive and negative electrodes to generate voltage, and uses this voltage to electrolyze the electrolyte to obtain electrical energy. This is the principle. At this time, a film is formed on the electrode surface in order to suppress the chemical reaction of the electrode. If the materials used for the positive and negative electrodes are metals, the difference in ionization tendency of the metals is used to generate voltage. A coated metal electrode on which a conductive coating that prevents chemical reactions is formed is used as at least one of the positive electrode and the negative electrode. For the positive electrode, a carbon-based material other than metal can be used. In this case, the redox potential of the positive electrode can be considered to be 0V.

Since the metal is coated with a conductive coating that prevents chemical reactions, the metal itself does not come into direct contact with the electrolyte and no chemical reaction occurs. Therefore, there is no generation of metal hydroxides, such as magnesium hydroxide in magnesium batteries, and the coated metal electrode can be used stably over a long period of time.

Zinc or zinc alloy, aluminum or aluminum alloy, magnesium or magnesium alloy, etc. can be used as the metal. The redox potential is -0.76V for zinc, -1.68V for aluminum, and -2.34V for magnesium. The generated voltage is determined depending on this redox potential. It is preferable to use zinc, aluminum, magnesium, etc., which have a negative oxidation-reduction potential, for the negative electrode. Each redox potential allows a voltage to be applied to the electrolyte at a difference in the redox cell from other electrodes. Note that even if the redox potentials are negative, a voltage is generated due to the difference in the redox potentials. For example, if the negative electrode is made of magnesium and the positive electrode is made of zinc, the difference in redox potential is 1.58V.

In microbial fuel cells, carbon felt is used as a positive electrode (cathode). Furthermore, in microbial fuel cells, the same carbon felt is used for the negative electrode (anode), and one side of this carbon felt is in contact with the air and serves as the positive electrode as an air cathode system that takes in oxygen from the air.

When grounding electrodes in rice fields, etc., the negative electrode is buried in the mud of the rice field to create an anaerobic environment, and the positive electrode is placed in an aerobic environment containing oxygen. For this reason, the positive electrode must be installed above the water so that it is in contact with the air, which not only complicates the process, but also reduces the amount of electrical energy that can be extracted. If this negative electrode in a microbial fuel cell is made of a coated metal electrode according to the present invention, both voltage and current can be significantly increased. Furthermore, the primary metal battery of the present invention does not need to be of an air cathode type, the positive electrode may be embedded in anaerobic mud, and it can be easily installed even when obtaining electrical energy from rice fields.

The conductive film is preferably a layered compound, a resistor, or a metal, and the semiconductive film is preferably a semiconductor. Because the conductive film or semiconductive film prevents the electrolyte from coming into direct contact with the metal, can prevent chemical reactions. Therefore, since the metal does not melt, long-term use is possible.

The layered compound of the conductive film is preferably graphite, Prussian blue or a Prussian blue analog, and needs to have an intercalation function. Intercalation is a reversible reaction in which another element enters the void space of a molecule or group of molecules. The invading substance is called an intercalator or intercalant, and due to the intercalation phenomenon, the charge present in the electrolyte (electrolyte) is accumulated on the negative electrode due to the electromotive force due to the difference in ionization tendency, and is transferred to the positive electrode.

Preferably, the resistor is iron phthalocyanine, iron oxide, or a conductive passive film. A resistor applies a voltage (electromotive force) generated by the ionization tendency of a metal, that is, a difference in redox potential, directly to an electrolyte, electrolyzing the electrolyte, and at the same time creating a path through which electrons generated by the potential decomposition flow to the metal. Become. Electrons flow from the negative electrode side to the positive electrode side through the external conductor. Note that the conductive passive film is formed by anodizing. Forming a film with a resistor also has the effect of suppressing the chemical reaction of the metal.

A semiconductor film can be formed by coating the semiconductor with titanium oxide, tungsten oxide, or a photocatalyst. Titanium oxide, tungsten oxide, or a photocatalyst can be applied with a voltage generated by the difference in ionization tendency (oxidation-reduction potential) between the anode electrode and the cathode electrode. As a result, the electrons in the valence band are separated from the holes and excited to the conduction band, and the electrolyte is decomposed by a redox reaction between the holes in the valence band and the electrons in the conductor to generate electrons. Electrons generated at this time flow from the anode side to the cathode side through the external conductor. Therefore, it is possible to electrolyze the electrolyte to increase the generation of electrons, increase the obtainable electrical energy, and further prevent chemical reactions of metals.

The photocatalyst is a material whose main component is titanium oxide or a material whose main component is tungsten oxide. Titanium oxide and tungsten oxide exhibit strong redox functions when irradiated with light, and we have confirmed that they also exhibit the same function when voltage is applied. The photocatalyst mainly composed of titanium oxide or tungsten oxide may contain fine particles of copper, silver, or platinum as a promoter.

The conductive film preferably contains graphite, carbon nanotubes, carbon black, activated carbon, Ketjenblack, fullerene, fine charcoal powder, iron phthalocyanine, iron oxide, or a conductive polymer as a conductive material. . These conductive materials have the effect of lowering the resistance value of the conductive film and facilitating the flow of electrons. In particular, Prussian blue and Prussian blue analogs are effective in lowering resistance.

In addition to iron phthalocyanine or iron oxide, which is a resistor, lead, carbon nanotubes, carbon black, activated carbon, Ketjen black, fullerene, fine charcoal powder, carbon nanotubes, carbon black, activated carbon, Ketjen black, fullerene, fine charcoal powder. Either one or a combination of these may be added.

Titanium oxide, which is a semiconductor, is combined with one or more of graphite, carbon nanotubes, carbon black, activated carbon, Ketjenblack, fullerene, fine charcoal powder, iron phthalocyanine, iron oxide, or an organic conductive polymer. They may be added in combination. For conductive polymers

The conductive film can be formed on metal by coating a conductive material mixed with a binder or resin. By mixing the conductive material and the binder or resin, stirring the mixture sufficiently to obtain a uniformly dispersed state, and coating the mixture, a uniform film can be obtained. As a result, the conductive material uniformly and firmly adheres to the metal.

The layered compound, resistor, or semiconductor used to form the conductive coating is all powder, mixed with a binder or resin, and coated on the metal. Examples of binders include PTFE. Examples of the resin include acrylic resin, epoxy resin, urethane resin, fluororesin, and silicone resin, which are used as paints.

The coated metal electrode 10 is used as a negative electrode, and the positive electrode is a carbon electrode made of carbon-based graphite, activated carbon, carbon graphite, hard carbon, charcoal, or a metal with a noble ionization tendency, so that it can be used as a battery. It becomes a primary metal battery that exhibits the following functions. Metals with noble ionization tendencies include copper, silver, platinum, and gold. The redox potential of copper is 0.34V, the redox potential of silver is 0.78V, the redox potential of platinum is 1.19V, and the redox potential of gold is 1.52V. In addition, since the present invention generates voltage based on the difference in ionization tendency of metals, electric energy can be obtained even if the negative electrode is made of magnesium and the positive electrode is made of zinc, for example.

Although a positive electrode mainly composed of carbon is not a metal and does not have a tendency to ionize, it can be considered to have an oxidation-reduction potential of zero.

In the primary metal battery, the carbon electrode may be formed with an iron component film, a titanium oxide film, a tungsten oxide film, or a photocatalyst film, which is made by coating iron phthalocyanine or iron oxide with a binder or resin. Iron component coating, titanium oxide coating, tungsten oxide, or photocatalyst coating made of graphite, activated carbon, carbon graphite, hard carbon, or charcoal and coated with iron phthalocyanine, iron oxide, or conductive polymer with a binder or resin on the surface. The current capacity increases by forming either one of these. Examples of binders include PTFE. Examples of the resin include acrylic resin, epoxy resin, urethane resin, fluororesin, and silicone resin, which are used as paints.

In primary metal batteries, the electrolyte is preferably water, soil, seawater, an aqueous solution of fertilizer, or a combination thereof. Water, such as river water, contains dissolved minerals and organic matter, which serve as a source of electrical energy. In the wilderness, soil is made up of plant leaves and dead grass that accumulate and ferment to form humus, which is used as fertilizer for plants, and this is also a source of electrical energy. Seawater also contains salt and is suitable as a source of electrical energy. Both chemical and organic fertilizers contain components that serve as electrical energy sources, such as phosphorus, potassium, and calcium. If a primary metal battery is constructed with this configuration, a high-performance primary metal battery using natural materials as an electrolyte can be obtained. Since the electrolyte is water, soil, seawater, an aqueous solution of fertilizer, or a combination thereof, electrical energy can be obtained from anywhere in nature.

Preferably, the electrolyte contains sugars produced by plants through photosynthesis and released from their roots. Plants carry out photosynthesis, which is carried out in chloroplasts present within plant cells, converting light energy into chemical energy and synthesizing organic compounds such as carbohydrates from carbon dioxide and water. Most of the organic compounds are starch, and sucrose and protein are also produced. These are transported to storage organs such as fruits and roots and contribute to plant growth, while the remaining organic compounds are released from the roots. This organic material is decomposed by Shewanella bacteria, which are called power-generating bacteria, and are decomposed into electrons and hydrogen ions.

Electrons are transported from the negative electrode (coated metal electrode) to the positive electrode (carbon electrode) through an external conductor, and react with hydrogen ions to become water. Organic compounds are also electrolyzed by an applied voltage using the ionization tendency of the electrodes, and are decomposed into electrons and hydrogen ions.

At least one of the coated metal electrode and the carbon electrode is preferably covered with a water-permeable insulating sheet. This can prevent the coating formed on the coated metal electrode from peeling off due to scratches or the like. Furthermore, when replacing the coated metal electrode, the coated metal electrode wrapped in the insulating sheet can be removed including any residue, and no residue will remain in the electrolyte, making it easy to replace. In addition, by covering the coated metal electrode with a water-permeable insulating sheet, short circuits between the coated metal electrode and the carbon electrode are prevented, and multiple electrodes can be closely stacked and arranged in contact with each other. The current capacity is increased.

Next, a case where a layered compound is coated on a coated metal electrode will be described.

FIG. 1 is a diagram showing a cross section of a coated metal electrode used in the primary metal battery of the present invention. The coated metal electrode 10 shown in FIG. 1 has a conductive film 14 formed by coating on the surface of a metal 12, and a terminal 16 is provided as an electrode. Various materials having a tendency to ionize can be used as the material of the metal 12. Ionization tendency is a fundamental property unique to metals, and is expressed in the order of standard redox potentials between hydrated ions and simple metals in an aqueous solution.

Examples of metals whose standard redox potential is negative are lithium (redox potential: -3.05V), potassium (redox potential: -2.93V), magnesium (redox potential: -2.36V), and aluminum. (oxidation-reduction potential: -1.68V), titanium (oxidation-reduction potential: -1.63V), zinc (oxidation-reduction potential: -0.76V), iron (redox potential: -0.44V), nickel (oxidation-reduction potential: -0.44V), reduction potential: -0.26V).

Noble metals with a positive redox potential include, for example, copper (redox potential: 0.34V), silver (redox potential: 0.80V), platinum (redox potential: 1.19V), and gold (redox potential: 1.19V). reduction potential: 1.52V).

The conductive film is a layered compound, a resistor, or a metal, and the semiconductive film is a semiconductor. This conductive film prevents chemical reactions of metals and enables long-term use.

The term "layered compound" is used as a general term for substances that have an intercalation function, and includes microporous crystals in which pore structures are fixed in a three-dimensional skeleton and porous coordination polymers. There are two types of layered compounds: layered compounds in which the layer structure is held by van der Ruska, and layered compounds in which the layer structure has a charge, and exchangeable counter ions exist between the layers to compensate for the charge. There are layered compounds whose layered structure is maintained in the working coronka.

Graphite is a typical layered material preserved in Van der Ruska. The graphene sheet layer is a three-dimensional ordered structure formed by regularly arranging the sheets. Carbon atoms within the plane are connected by CC covalent bonds, and van der Waals forces act between the carbon atoms between the planes. This causes charge insertion.

A layered compound in which the layer body has an electric charge, for example, a layered double hydroxide, is a hydroxide layer based on the structure of bluestone, in which a part of the divalent metal ion M ²⁺ is replaced with a trivalent one M ³⁺ Consisting of Therefore, the layers themselves have a positive charge, and to compensate for this, exchangeable anions are present between the layers. Examples of M ²⁺ include Mg, Mn, Fe, Co, Ni, Cu, and Zn, and examples of M ³⁺ include Al, Fe, Cr, Co, and In. Then, layered double hydroxides with various combinations of M ²⁺ and M ³⁺ can be synthesized.

Lithium cobalt oxide used in lithium ion batteries is a type of layered double hydroxide and is also called an oxide composite. Lithium manganate (LiMn ₂ O ₄ ), lithium nickel oxide (LiNiO ₂ ), lithium iron phosphate (LiFePO ₄ ), etc., which can further reduce costs, are also used.

Prussian blue is also a layered compound as a type of porous coordination polymer with an intercalation function. The molecular composition of Prussian blue is mainly iron (Fe ³⁺ /Fe ²⁺ ) and cyano group (CN)-, and has a NaCl-type crystal structure. It contains cations such as potassium (K ⁺ ) and ammonium (NH ₄ ⁺ ).

Cyano groups (CN)- are coordinated in six directions: top, bottom, left, right, front and back of iron ions (Fe ⁺² ), creating a cubic jungle gym structure with metal ions (Fe/Ni/Co, etc.) at the vertices. ．． When the metal ion is Fe, it is Prussian blue. Since the distance between Fe ²⁺ and Fe ³⁺ is as large as 0.5 nm, there is a large void. This large cavity can insert and remove various cations and molecules. Prussian blue analogues are obtained by substituting the metal ions of Prussian blue or the central metal of the ligand, and have the same lattice structure as Prussian blue, but with different lattice constants. Since the distance between Fe ²⁺ and Fe ³⁺ is large, it is suitable as an anode electrode that utilizes inorganic ions such as Na ⁺ , K ⁺ , Ca ⁺ , and Mg ⁺ .

If the layered compound itself does not have conductivity, a conductive material is mixed therein. Examples of the conductive material include carbon materials such as activated carbon, Ketjen black, graphite, and carbon nanotubes, metal materials such as magnesium, copper, and aluminum, and organic conductive materials such as polyphenylene derivatives. Further, a catalyst component for efficiently carrying out the oxygen reduction-oxidation reaction may be included. Catalyst components include metals such as platinum, cobalt, nickel, palladium, and manganese, alloys of these metals, and oxides of these metals.

The layered compound and the conductive material are bound together using a binder. As a binder, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene/hexafluoropropylene copolymer (FEP), tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer (PFA), ethylene - Examples include tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene/chlorotrifluoroethylene copolymer (ECTFE), and polyvinyl fluoride (PVF).

In the primary metal battery according to the present invention, charge is accumulated on the negative electrode (hereinafter referred to as anode electrode) side and current flows in one direction, so that charge is not accumulated on the positive electrode (hereinafter referred to as cathode electrode) side and the cathode electrode The sides do not necessarily need to be coated with a layered compound. Further, if only the oxidation-reduction potential on the anode side is used, an electromotive force can be generated without using metal on the cathode side.

For this reason, the cathode electrode is preferably coated with a carbon-based layered compound using, for example, copper with a positive redox potential, but it is not necessarily necessary to use a metal such as copper, and it is not necessary to use a layered compound. It's okay. That is, as a cathode electrode, a carbon-based material may be coated on metal, or may be used alone.

There are various carbon-based materials, but graphite is a layered compound. Graphite, also called graphite, is an elemental mineral consisting of carbon, with hexagonal, hexagonal plate-shaped crystals. The structure is a layered material shaped like a tortoise shell, with carbons connected in the plane of each layer by strong covalent bonds, but bonds between layers (interplanes) are weak by van der Waals forces. In addition to layered compounds, there are amorphous carbons that do not have a proper crystal structure, such as carbon fiber, charcoal, and activated carbon, and these amorphous carbons can also be used. Since it has a cylindrical hollow space inside, it can contain various molecules.

Carbon nanotubes can also be used. Carbon nanotubes have a structure similar to that of graphite rolled up into a cylindrical shape. In the closed state, both ends are closed with a structure similar to a fullerene hemisphere, and it always has six five-membered rings. Due to the small number of five-membered rings, it is difficult to dissolve in organic solvents. Because the tube has a cylinder-like structure, various substances can be taken into it by burning off the cap.

Additionally, Ketjenbrak is also available. Compositionally speaking, Ketjen black is composed of carbon like carbon black for rubber, carbon fiber, and graphite, and is composed of crystallites called a pseudographite structure. Crystallites consist of fused benzene rings with π electrons, and these π electrons can move freely on the carbon black. Because π electrons move on the conductive circuit formed by the aggregate or agglomerate, the material to which Ketjenblack is added exhibits conductivity. Ketjenblack is characterized by high specific surface area and high porosity, and the formation of conductive circuits due to increased particle density is dominant, resulting in high conductivity.

Further, iron phthalocyanine or iron oxide may be used. Iron phthalocyanine is an iron-based organometallic complex and has catalytic activity. Iron oxide means iron oxide of iron, and ferric oxide (Fe ₂ O ₃ ) is particularly suitable.

Next, the primary metal battery of the present invention will be explained by comparing it with a conventional magnesium battery.

FIG. 2 is a diagram explaining the principle of a conventional magnesium-air battery. Magnesium air batteries are already commercially available as emergency power sources. The magnesium air battery 20 uses a magnesium alloy (hereinafter simply referred to as magnesium) as an anode electrode 22 and carbon as a cathode electrode 26. Note that the anode electrode 22 is a negative electrode, the cathode electrode 26 is a positive electrode, and the anode electrode 26 is a negative electrode. The cathode electrode 22 is exposed to the atmosphere on the side opposite to the side in contact with the electrolyte 30 in the container, so that oxygen in the air can be used for the reaction. For this reason, it is sometimes called an air cathode. The electrolyte 30 is, for example, an aqueous solution of sodium chloride. Salt water is used as the electrolyte. By using salt water, the amount of electricity acquired is significantly increased.

Here, we will explain how to use the terms cathode electrode and positive electrode, and anode electrode and negative electrode. Generally, in the case of batteries, they are distinguished by potential, and the one with a higher potential is called a positive electrode or anode, and the one with a lower potential is called a negative electrode or cathode. In English, the side where negative charges (anions) gather from a solution is called an anode, and the side where positive charges (cations) gather is called a cathode. In the case of corrosion or electrolysis, the side where positive ions (positive charge) move from the metal (electrode) to the solution is called the anode, and the side where the positive ions move is called the cathode. It was named by Faraday and is derived from the Greek words ``anodos'', which means upward, and ``cathode'', which means downward.

For this reason, in explaining the examples below, we will use the term cathode, which is more faithful to the phenomenon, in a general term, the cathode electrode in a physical object that becomes a cathode, the anode in a general term, and the anode electrode in a physical object that becomes an anode. I will use the term in the sense of something specific.

The basic chemical reaction of a magnesium battery is as follows.
The reaction at the cathode is
O ₂ +2H ₂ O+4e ^- → 4OH ^-
and the reaction at the anode is
2Mg → 2Mg ²⁺ +4e ^-
It is. The overall reaction was
2Mg+O ₂ +2H ₂ O → 2Mg(OH) ₂
becomes.

The anode electrode is magnesium, which dissolves through a chemical reaction to produce magnesium hydroxide (Mg(OH) ₂ ). Due to dissolution, the magnesium electrode decreases and eventually disappears, reaching the end of its life. Naturally, as the number of magnesium electrodes decreases, the current capacity also decreases. In order to extend the service life, it is necessary to increase the thickness of the magnesium plate.

FIG. 3 is a diagram illustrating a primary metal battery using a coated metal electrode according to the present invention. FIG. 3(A) is a diagram showing the configuration of a primary metal battery 36 using a coated metal electrode 144, and FIG. 3(B) is a model diagram of the primary metal battery 36 using a coated metal electrode. An interlayer compound is used for the metal conductive coating. The configuration of the primary metal battery 36 using coated metal electrodes is such that the anode electrode 22 is a magnesium plate coated with graphite, Prussian blue, or a Prussian blue analog, and the cathode electrode 26 is a copper plate coated with graphite. ing. A mesh copper plate is used as the copper plate to serve as an air cathode. Both the anode electrode 22 and the cathode electrode 26 are coated metal electrodes in which a metal plate is coated with a layered compound.

The anode electrode 22 uses a magnesium plate, and the cathode electrode 26 uses a copper mesh. The redox potential of magnesium is -2.34V, and the redox potential of copper is +0.34V. The difference in redox potential is 2.68V, which becomes an electromotive force. This electromotive force decomposes organic matter in the electrolyte, and electrons generated at this time flow from the anode electrode 22 to the cathode electrode through an external conductor (not shown). This is the principle of a primary metal battery.

Although the cathode electrode 26 is illustrated as an air cathode type in which it is in contact with air, it does not necessarily have to be an air cathode type, and may simply be placed in the electrolytic solution 30 like the cathode electrode 26.

The electrolyte (electrolytic solution) 30 is, for example, an aqueous solution (saline solution) of sodium chloride (NaCl). Sodium chloride and water are electrolyzed by electromotive force due to the difference in redox potential, and electrons and positives are generated in the electrolytic solution. H ⁺ (hydrogen ion) and Na ⁺ are present as ions. These cations become intercalators (also called intercalants) 38 and enter the layered compound to generate an intercalation reaction.

The cations serving as the intercalator 38 may be inorganic ions such as Mg ⁺ (magnesium ion), K ⁺ (potassium ion), Ca ⁺ (calcium ion), and S ⁺ (sulfide ion). Since pure magnesium is highly soluble in water, an aqueous solution of pure magnesium dissolved in water can be used as an electrolyte. Furthermore, Mg ⁺ , K ⁺ , Ca ⁺ , S ^{+ ,} etc. are also components of fertilizers used to grow plants; for example, chemical fertilizers and phosphoric acid fertilizers contain K ⁺ . Magnesium lime contains Mg ⁺ and Ca ⁺ . Furthermore, fermented chicken manure is an organic fertilizer that contains K ⁺ ingredients. Therefore, the electrolyte may be an aqueous solution of fertilizer.

In the primary metal battery 36 using the coated metal electrode 10, the electromotive force is generated by the difference in ionization tendency between the magnesium used in the anode electrode 22 and the copper used in the cathode electrode 26, and the cations in the electrolyte become intercalators. 38 to generate an intercalation reaction on the anode electrode 22 side, and when the battery is used, the intercalator 38 is released and flows from the anode electrode 22 to the cathode electrode 26 via an external circuit.

The use of intercalation reactions in primary metal batteries is a new principle that has never existed before, and detailed study is a future issue. In principle, the chemical reaction can be changed to a charge transfer reaction, so there is no dissolution of the electrode and the lifespan can be extended. Therefore, for example, if the present invention is applied to an emergency magnesium-air battery and the magnesium electrode is replaced with the coated metal electrode 10 of the present invention, the battery can be used at all times by replacing the sodium chloride aqueous solution (salt water).

Furthermore, if the electrolyte is supplied continuously or periodically, like a fuel cell supplies hydrogen, it becomes possible to continuously generate electricity. For periodic supply, for example, the electrolyte may be exposed to the atmosphere and evaporated content may be replenished. Furthermore, if applied to microbial fuel cells, it is possible to increase voltage and current capacity.

If a resistor is used for the conductive film 14, it must have low resistance, and iron phthalocyanine, iron oxide, or a conductive passive film may be used. Iron phthalocyanine also has a catalytic function. Regarding the conductive passive film, for example, the conductive anodic oxide film disclosed in Patent No. 4367838 (Hori Metal Surface Treatment Co., Ltd., Okayama Prefecture) can be used to form a conductive passive film on magnesium or a magnesium alloy. The conductive passive film is prepared by immersing magnesium or a magnesium alloy in an electrolytic solution containing 0.1 to 1 mol/L of phosphate radicals, 0.2 to 5 mol/L of ammonia or ammonium ions, and having a pH of 8 to 14. , can be manufactured by anodizing the surface thereof.

When using a semiconductor for the conductive film, titanium oxide (TiO ₂ ), tungsten oxide (WO ₃ ), or a photocatalyst can be used. Titanium oxide is also called titanium dioxide. Titanium oxide is used as a raw material for photocatalysts. When titanium oxide is irradiated with ultraviolet light, electrons in the valence band are excited to the conduction band, causing a redox reaction with the holes left in the valence band. Even if it is not ultraviolet rays, the application of voltage excites electrons in the electronic band to the conduction band, so the voltage can be applied using the difference in redox potential of the metals used in the anode and cathode electrodes as an electromotive force. can do.

FIG. 4 is a diagram showing a microbial fuel cell in which an anode electrode and a cathode electrode are embedded in soil where plants are growing. In the microbial fuel cell 40, fertilizer such as chemical fertilizer is mixed into the soil 42. An anode electrode 22 and a cathode electrode 26 are embedded in this soil 42 to extract electrical energy. The anode electrode 22 is formed by coating a metal with a base ionization tendency, such as magnesium or aluminum, with a layered compound such as graphite, Prussian blue, or a Prussian blue analog.

The anode electrode 22 may be formed by coating a metal with a low ionization tendency, such as magnesium or aluminum, with iron phthalocyanine or iron oxide as a resistor using PTFE, urethane resin, or the like. Furthermore, titanium oxide as a semiconductor may be coated with PTFE, urethane resin, or the like. As the titanium oxide, anatase type titanium oxide is used.

The cathode electrode 26 is made of a noble metal with a tendency to ionize, such as copper, coated with a layered compound such as graphite. The cathode electrode 26 may be made of charcoal, graphite, carbon graphite felt, hard carbon, carbon fiber sheet, etc., instead of using a noble metal with a tendency to ionize, such as copper. Further, the cathode electrode 26 may be made of charcoal, graphite, carbon graphite, or hard carbon, and may have an iron component film coated with iron phthalocyanine or iron oxide with a binder or resin on its surface.

In the soil 42, sugar (C ₆ H ₁₂ O ₆ ) produced by the plants 44 through photosynthesis of the sun is discharged from the roots 46, and hydrogen ions (H ⁺ ) and electrons (e ^- ) and becomes a source of electrical energy. Furthermore, organic matter, fertilizer, etc. present in the soil 42 are electrolyzed by electromotive force due to the difference in ionization tendency between the electrodes, and become an electrical energy source.

In general, a microbial fuel cell is a system that uses the catabolic metabolic ability of microorganisms to produce electricity from organic matter, and is also a sustainable power generation system because it can use biomass such as sludge and garbage as fuel. Since the microorganism itself functions as a biocatalyst that extracts electrons from organic matter, it also has the advantage of being low cost.

Microorganisms present in soil include highly thermophilic sulfur-dependent archaea, which use hydrogen as an electron emission source and sulfur to accept electrons, and these bacteria produce hydrogen sulfide. In addition, there are methane bacteria that use carbon dioxide as an electron acceptor, sulfate-reducing bacteria that use sulfate as an electron acceptor, acetogenic bacteria that use carbonate as an electron acceptor, and catabolic iron that uses iron as an electron acceptor. Reducing bacteria are present.

Among microorganisms, there are bacteria called amperogenes, which have the property of emitting electrons to the outside during the process of decomposing organic matter. Current-producing bacteria are these dissimilatory iron-reducing bacteria.Dissimilatory iron-reducing bacteria reduce trivalent iron to divalent iron by directly touching amorphous iron oxide, and produce nano-sized magnetic particles. to produce.

Examples of catabolic iron-reducing bacteria include Geobacter and Schwanella. These bacteria hate oxygen in the air and live in environments with little oxygen, such as underground, the ocean floor, and the bottom of swamps. When these current-generating bacteria are given water together with organic matter, the current-generating bacteria decomposes the organic matter and releases hydrogen ions and electrons. When the emitted electrons are passed to the anode electrode and flowed to the cathode side, a current flows, and hydrogen ions react with oxygen on the cathode side to form water. Therefore, if organic matter and water are continuously fed to microorganisms, it becomes possible to generate electricity sustainably.

Plant photosynthesis can be used to continuously provide soil with organic matter. Plants perform photosynthesis using sunlight in their chloroplasts, and synthesize organic substances such as sucrose (C ₆ H ₁₂ O ₆ ) and starch from water sucked up from roots through ducts and carbon dioxide from the air. Oxygen produced in the process of decomposing water is released into the air. Some of the organic matter produced through photosynthesis is released into the soil through plant roots. Therefore, it is possible to continuously supply organic matter as an energy source.

Conventional microbial fuel cells generate electricity by using only electrons (e ^- ) generated by current-producing bacteria as an electrical energy source, but by applying it to the primary metal battery of the present invention, the ionization tendency between the electrodes can be reduced. Organic matter and fertilizers are electrolyzed by the electromotive force caused by the difference in energy, and become an electrical energy source, significantly increasing the amount of power obtained. Therefore, by incorporating fertilizer into the soil, the ingredients of the fertilizer can also be used as electrical energy, dramatically increasing power generation capacity.

Fertilizers can be broadly divided into two types: "organic fertilizers" and "chemical fertilizers," and either of them may be used. Chemical fertilizers belong to the category of chemical fertilizers and are made from ingredients extracted from minerals such as ores. Organic fertilizers are fertilizers made from vegetable or animal organic matter (compounds containing carbon other than carbon dioxide itself) such as oil cake, fish meal, and chicken manure. Furthermore, fertilizers are classified into nitrogen fertilizers, phosphoric acid fertilizers, potash fertilizers, silicate fertilizers, lime fertilizers, compound fertilizers, etc. according to their components, and are divided into alkaline fertilizers and acidic fertilizers according to their chemical properties.

Fertilizer is a nutritional substance applied to soil, thereby maintaining and increasing the productivity of the soil and promoting plant growth. The three major elements of fertilizer are nitrogen, phosphoric acid, and potassium. Furthermore, in addition to nine elements including magnesium, calcium, sulfur, oxygen, and hydrogen, trace elements such as manganese, zinc, iron, and boron are required.

The reason why electrical energy increases with fertilizer is that the nine elements and trace components are electrolyzed by the electromotive force caused by the difference in ionization tendency between the electrodes, become ions, generate electrons, and move through the electrolyte.

Furthermore, fertilizers are effective in increasing plant growth and electrical energy. For this reason, it is compatible with the natural ecosystem and becomes a natural energy that truly coexists with the natural world. Other natural energy sources, such as solar power generation, destroy nature by fixing it with concrete to install solar panels. The landscape of the completed solar power generation system is incompatible with nature and will completely change the landscape. The same is true for wind power generation, which causes destruction of nature and also has low noise issues. All of them are expensive to dispose of, and there are problems with disposal.

Fertilizer-based electrolytes can be created by mixing fertilizers into soil. Soil is composed of solid (solid phase), liquid (liquid phase), and gas (vapor phase), and these three are called the three phases of soil, and the distribution ratio of these three phases is called the three-phase distribution of soil. The three-phase distribution of soil is one of the important factors for plant growth, influencing factors such as the difficulty of plant root elongation and the quality of the supply of water, oxygen, and nutrients to the roots.

The interstices in the soil are occupied by gas and liquid phases. The distribution ratios of these three phases vary depending on the type of soil and the type of use. In the case of field soil, a three-phase distribution in which the solid phase accounts for 30 to 40% and the liquid phase accounts for 40 to 30% is said to be optimal for plant growth. Soil structure is classified into two types: unit structure and aggregate structure. A unit structure is a state in which soil particles are arranged singly. The aggregate structure is a state in which individual particles gather to form aggregates, and these aggregates are lined up.

The aggregate structure has both large and small pores. Large pores improve drainage, while small pores improve water retention. Generally, soil with a granular structure has more voids (pores) in the soil, and a certain amount of voids is suitable for plant growth, including drainage, water retention, ventilation, and root elongation.

Soil contains nutrients such as nitrogen, phosphoric acid, and potash (potassium) that are essential for plant growth, as well as trace elements such as iron, manganese, copper, zinc, and boron. The role of fertilizer is to replenish the soil with elements that are easily deficient, especially nitrogen, phosphoric acid, and potassium.

Soil is composed of solid (solid phase), liquid (liquid phase), and gas (vapor phase).The liquid phase is moisture and the gas phase is mainly air, so even if the anode electrode is embedded in the soil, it will not absorb hydrogen. Ions (H ⁺ ) react with oxygen in the air in the gas phase, and can function as a battery. In addition, the water in the liquid phase provides conductivity and enables the movement of electrons to the anode electrode. Therefore, electrical energy can be extracted even if the anode and cathode electrodes are buried in soil.

The electrolyte containing fertilizer may be an aqueous solution in which fertilizer is dissolved in water. In this case, the fertilizer components are used to extract electrical energy using electrodes. As mentioned above, the ingredients of fertilizer include nine elements: nitrogen, phosphoric acid, potassium, magnesium, calcium, sulfur, oxygen, and hydrogen.

Among these nine elements, potassium, magnesium, calcium and sulfur can be cited as electrical energy sources. These components are ionized in an aqueous solution and play a role in electrical conduction between the anode electrode and the cathode electrode. This causes the movement of electrons, which becomes electrical energy. Therefore, it is preferable that the fertilizer contains any one or more of potassium, magnesium, calcium, and sulfur.

Plants absorb carbon dioxide from the atmosphere and release oxygen through photosynthesis. Photosynthesis uses carbon dioxide to produce sugar (organic compounds), but since more sugar is produced than is consumed within the plant, the excess sugar is excreted from the roots. In addition, fallen leaves and dead branches are present in the soil, contributing to an increase in organic matter. Exudates and secretions from plant roots also contribute to electrical energy.

These organic substances are decomposed by a current-generating bacterium called Shewanella bacteria present in the soil, and hydrogen ions (H ⁺ ) and electrons (e ⁻ ) are generated. At the anode electrode, electrons (e ⁻ ) and oxygen flowing from the cathode electrode through an external circuit react with hydrogen ions (H ⁺ ) to become water (H ₂ O). This chemical reaction is the basic principle, and is converted into electrical energy by generating a flow of electrons (e ⁻ ).

Add fertilizer to soil nutrients, thereby promoting plant growth. Plants photosynthesize using sunlight, absorb carbon dioxide (CO ₂ ) from the atmosphere, and produce sugars within their bodies to grow themselves. The sugars produced are not all consumed within the plant; the excess sugars are released from the roots. Sugars released from the roots are broken down into hydrogen ions and electrons by current-generating bacteria, which react with oxygen to become an electrical energy source. It is a natural energy that coexists with nature and is compatible with nature's sustainable ecological circulation cycle.

FIG. 5 is a diagram illustrating rice field power generation, which is a type of microbial fuel cell in which the electrolyte is composed of a soil region and a water region. The rice field power generation 50 is a microbial fuel cell using a rice field, and the electrolyte is composed of a water region 54 and a soil region 52. Rice 56 is planted, and the rice 56 discharges sugar (C ₆ H ₁₂ O ₆ ) from its roots 46 through photosynthesis of the sun. The discharged sugar (C ₆ H ₁₂ O ₆ ) is decomposed into hydrogen ions (H ⁺ ) and electrons (e ⁻ ) by current-producing bacteria such as Shewanella bacteria, and an electromotive force is generated due to the difference in ionization tendency between the electrodes. The sugar content (C ₆ H ₁₂ O ₆ ) discharged by is electrolyzed and becomes an electrical energy source. Rice 56 continuously produces sugar through photosynthesis and excretes it from its roots 46, making continuous power generation possible.

Conventionally, the same carbon felt has been used for both the anode electrode 22 and the cathode electrode 26. The cathode electrode 26 is placed in contact with air in order to take in oxygen from the air and cause a chemical reaction. For this reason, it is also called an air cathode. At the cathode electrode 28, hydrogen ions (H ⁺ ) generated by decomposing sugar by current-producing bacteria combine with oxygen in the air to generate water. At this time, electrons (e ^- ) are required, and since the electrons (e ^- ) are drawn from the anode electrode 22 via the external circuit, a current flows through the external circuit and can be extracted as electrical energy.

By using the coated metal electrode 10 for the anode electrode 22 of this rice field power generation 50, electrical energy can be significantly increased. As the metal 12, magnesium, a magnesium alloy, or aluminum can be used. The layered compound 14 that coats the metal 12 can be Prussian blue or a Prussian blue analog. Alternatively, it may be a resistor or a semiconductor. In rice field power generation using this coated metal electrode 10, electrical energy can be extracted efficiently without chemical reactions. For example, if magnesium is used as the metal 12 and Prussian blue is used as the layered compound 14, An output voltage of around 1.8V can be obtained. When aluminum is used as the metal 12, the output voltage is around 0.8V. In conventional rice field power generation, the output voltage is about 0.5V, which can be significantly improved.

When installing the electrode in soil or the like, the coating of the layered compound 14 of the coated metal electrode 10 may be damaged during handling, but it is preferable to cover it with a water-permeable sheet. By wrapping the entire electrode-coated metal electrode 10, the coating can be protected, and at the same time, the coated metal electrode 10 wrapped in the water-permeable sheet can be completely removed together with the residue when replaced. Therefore, replacement becomes easy.

FIG. 6 shows an example of a coated metal electrode and a cathode electrode that were prototyped as an anode electrode. FIG. 6(A) is a prototype example of a coated metal electrode 22 in which a magnesium plate is coated with Prussian blue. FIG. 6(B) is a prototype example of a coated metal electrode 22 in which a magnesium plate coated with Prussian blue is covered with a water-permeable sheet. FIG. 6(C) is a prototype example of the cathode electrode 26.

The magnesium plate used is AZ31 with a thickness of 0.5 mm. Prussian blue is used as a layered compound, mixed with urethane resin as a binder, and diluted with thinner. Activated carbon was used as the conductive material, and was mixed in a diluted Prussian blue solution at 20 to 30%. This diluted solution was applied to a magnesium plate and dried at room temperature. The Prussian blue-coated magnesium plate is entirely wrapped in a water-permeable sheet, and the water-permeable sheet has the function of a protective cover and an insulating function.

FIG. 7 is an experimental apparatus A for confirming the function of the coated metal electrode. The primary metal battery 10 uses a three-layer coated metal electrode in which a separator 62 is sandwiched between an anode electrode 22 and a cathode electrode 26. An insulating water-absorbing sheet is used as the separator 62 to suck up the aqueous solution of the electrolytic solution 30 by capillary action and supply it to the battery section composed of the anode electrode 22 and the cathode electrode 26. As the electrolytic solution 30, an aqueous solution of chemical fertilizer (nitrogen phosphate potassium) is used and is placed in a container 32.

The anode electrode 22 is a magnesium plate (AZ31) with a thickness of 0.5 mm coated with a mixture of activated carbon, urethane resin, and Prussian blue, and wrapped in a water-permeable sheet. This is the electrode in FIG. 6(B) shown in Example 1. The cathode electrode 26 was prepared by mixing Ketjen black and polyvinylidene fluoride (PVDF) on a copper mesh plate with a thickness of 0.3 mm, and heating and baking the mixture using platinum as a catalyst. The anode electrode 22 and the cathode electrode 26 have a length of 7.4 cm, a width of 2.5 cm, and an area of 18.5 cm ² .

Under these conditions, open circuit voltage and short circuit current were measured. As a result, an open circuit voltage of 1.8 V and a short circuit current of 48.7 mA were obtained. The current density is 2.6 mA/ ^cm2 . If the cathode electrode 26 is also provided on the opposite side of the anode electrode 22 with the separator 62 in between, the current density will be doubled to 5.2 mA/cm ² . In this case, the energy density simply multiplied by the open circuit voltage and the short circuit current is 9.6 mW/cm ² .

Furthermore, when cathode electrodes are provided on both sides of anode electrode 22 with separators 62 in between, the thickness is approximately 3 mm, and when the electrodes with a height of 15 cm are installed vertically, the energy density is 481 mW/cm ² . Become. When installing, even if three electrodes are installed per 1 cm, the energy density in the installation area is 441 mW/cm ² .

The energy density was calculated as (maximum extractable short-circuit current density) x (maximum extractable open-circuit voltage), but the maximum extractable power is not (maximum extractable short-circuit current density) x (maximum extractable open-circuit voltage). This is due to the effects of the series resistance and parallel resistance (shunt resistance) inside the microbial fuel cell, and the ratio of maximum generated power to (maximum extractable short-circuit current density) x (maximum extractable open circuit voltage) is called the form factor. It is.

The energy density of solar cells is said to be 13 to 15 mW/cm ² . This is the maximum energy density of solar cells. The power that falls from directly above when sunlight is at its midpoint is approximately 1 kW per ^square meter of ground, and the conversion efficiency of solar cells is currently 13 to 15% of the light received. Naturally, the energy density decreases in the morning and evening, on cloudy days, and on rainy days, and no power is generated at night. Therefore, even if the form factor is taken into account, electrical energy that significantly exceeds that from solar cells can be obtained.

FIG. 8 is a diagram showing an experimental device B that embeds electrodes in a flowerpot containing flowers to extract electrical energy and turn on illumination. In experimental apparatus B66, the anode electrode 22 is a coated metal electrode with a cover, which is a magnesium plate coated with Prussian blue and wrapped in a water-permeable sheet. Commercially available water-absorbing sheets and root-prevention sheets can be used as water-permeable sheets. The cathode electrode 26 is a charcoal electrode made of charcoal wrapped with stainless steel wire. These two electrodes are embedded in the soil of a flower pot. Flowers are grown while supplying an aqueous solution of chemical fertilizer to the flower pots.

Electrical energy extracted from electrodes embedded in the flowerpot is input to a control circuit and stored in a nickel-metal hydride battery. The control circuit is connected to the illumination and turns on the illumination. The illumination lighting is controlled by a control circuit, and several lighting modes can be controlled, including continuous lighting and on/off flashing.

A voltage of 1.5 to 1.8 V was obtained from the electrode embedded in the flower pot, and a short circuit current of 5 to 10 mA was obtained. Naturally, the current that can be extracted depends on the soil condition, and is particularly influenced by the moisture content. The nickel-metal hydride battery used had a rating of 1.2V and 1900mAh, and the illumination could be turned on for about two days when fully charged. The nickel-metal hydride battery is constantly charged, and depending on the soil conditions, it can be lit for even longer periods of time. The voltage of the nickel-metal hydride battery was 836 mV when the brightness of the illumination decreased and the light became faint, but it took about half a day to charge it to the rated voltage.

Although the embodiments of the present invention have been described above, the present invention includes appropriate modifications without impairing its objects and advantages, and is not limited by the above-described embodiments.

10 Coated metal electrode 12 Metal 14 Conductive coating 16 Terminal 20 Conventional magnesium air battery 22 Anode electrode 24 Anode terminal 26 Cathode electrode 28 Cathode terminal 30 Electrolyte 32 Container 36 Primary metal battery using coated metal electrode 38 Intercalator 40 Microbial fuel Battery 42 Soil 44 Plant 46 Root 50 Rice field power generation 52 Soil area 54 Water area 56 Rice 58 Prototype electrode 60 Experimental device A
62 Separator 66 Experimental apparatus B

Claims (15)

Using a coated metal electrode in which either a conductive film or a semi-conductive film, or both a conductive film and a semi-conductive film, are formed on the metal to prevent chemical reactions;
A primary metal battery characterized by: the metal is zinc or a zinc alloy, aluminum or an aluminum alloy, magnesium or a magnesium alloy;
The primary metal battery according to claim 1, characterized in that: The conductive film is a layered compound, a resistor, or a metal, and the semiconductive film is a semiconductor;
The primary metal battery according to claim 1, characterized in that: the layered compound is graphite, Prussian blue or a Prussian blue analog;
The primary metal battery according to claim 3, characterized in that: The resistor is iron phthalocyanine, iron oxide or a conductive passive film;
The primary metal battery according to claim 3, characterized in that: the semiconductor is titanium oxide, tungsten oxide or a photocatalyst;
The primary metal battery according to claim 3, characterized in that: The conductive film contains graphite, carbon nanotubes, carbon black, activated carbon, Ketjen black, fullerene, charcoal fine powder, iron phthalocyanine or iron oxide, or an organic conductive polymer as a conductive material. ,
The primary metal battery according to claim 3, characterized in that: The conductive coating is formed by mixing the conductive material with a binder or a resin to form a coating on the metal;
The primary metal battery according to claim 7, characterized in that: The coated metal electrode is used as a negative electrode, and the positive electrode is a carbon electrode made of carbon-based graphite, activated carbon, carbon graphite, hard carbon, or charcoal, or a metal with a noble ionization tendency;
The primary metal battery according to claim 1, characterized in that: The carbon electrode has an iron component film formed by coating iron phthalocyanine or iron oxide with a binder or resin;
The primary metal battery according to claim 9, characterized in that: The electrolyte is water, soil, seawater, an aqueous solution of fertilizer, soil containing organic matter or fertilizer, or a combination thereof;
The primary metal battery according to claim 9, characterized in that: The electrolyte contains sugars produced by plants through photosynthesis and released from their roots;
The primary metal battery according to claim 11, characterized in that: the coated metal electrode is covered with a water-permeable insulating sheet;
The primary metal battery according to claim 9, characterized in that: the insulating sheet is impregnated with the same material as the coating of the coated metal electrode;
The primary metal battery according to claim 13, characterized in that: The primary metal battery according to any one of claims 1 to 14,
An electrical energy system comprising a storage battery and a control unit that stores electrical energy from the primary battery in the storage battery.