JP2022166341A - Charge transfer type primary battery - Google Patents

Abstract

To provide a primary battery using electrodes capable of efficiently extracting electrical energy and usable over a long period of time.SOLUTION: The primary battery of the present invention uses a coated electrode, in which a film including a layered compound is formed on a metal for at least one of a positive electrode (cathode electrode) and a negative electrode (anode electrode). The layered compound is used here as a generic term for materials with an intercalation function and includes microporous crystals and porous coordination polymers with a fixed pore structure in a three-dimensional framework. The layered compounds preferably include graphite and Prussian blue or Prussian blue analogs.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a primary battery electrode from which electrical energy can be extracted.

Batteries are widely used as power sources in electronic devices such as mobile phones, laptop computers, and electronic toys. Manganese batteries, alkaline batteries, and the like are widely used as batteries, and zinc batteries, aluminum batteries, magnesium batteries, and the like using metal materials as electrodes are currently being developed. Microbial fuel cells, which can extract electric 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 electric energy that can be extracted is small.

In the following description, the terms positive electrode and cathode electrode (or cathode), and negative electrode and anode electrode (or anode) are mixed because the terms used as standard are different depending on the industry. are used interchangeably. In addition, since the direction of current in a secondary battery is reversed during charging and during discharging, even if the cathode electrode and the anode electrode are the same electrode, their meanings may be reversed.

A zinc battery uses zinc or a zinc alloy for the negative electrode, and is required to have a high capacity and a high voltage, but is also required to be used for a longer period of time.

Patent Literature 1 discloses a technique for improving the cycle life and shelf life of a battery. The negative electrode active material for rechargeable zinc-alkaline electrochemical cells is formed from metallic zinc particles coated with tin and/or lead. Thereafter, the remaining zinc electrode components, such as zinc oxide (ZnO), bismuth oxide ₍ Bi2O3) _, dispersant and binder are added. By this. Compared to conventional batteries, generation of hydrogen gas is 60 to 80% less likely to occur, the zinc conductive matrix is preserved in its original state, and discharge during storage can be suppressed. This improves the cycle life and shelf life of the battery.

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

Patent Literature 3 discloses a technique capable of extending the life of a magnesium battery. Magnesium batteries use magnesium for the negative electrode. The negative electrode has a configuration in which thin film magnesium negative electrode material is bonded to both surfaces of a thin aluminum conductive plate. The anode material consists of magnesium doped with 1.5-2.5% by weight of calcium.

A microbial fuel cell is a system that uses the catabolic ability of microorganisms to produce electricity from organic matter. Sludge consists of organic substances contained in industrial and domestic wastewater, etc., which are deposited together with mud on the bottom of rivers and seas. Biomass treatment, in which the organic substances in sludge are decomposed by microorganisms, generates hydrogen ions and electrons, generating electricity. Electric energy can be recovered directly in the form of In a microbial fuel cell, electrons emitted from microorganisms are transferred to an 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 serves as an oxidant (electron acceptor) and hydrogen ions (H+) diffused from the anode side. Therefore, it functions as an electric circuit by connecting a load between the anode electrode and the cathode electrode.

In Patent Document 4, a microbial fuel cell capable of improving power productivity and suppressing power generation costs, an electrode for a microbial fuel cell, a method for producing the same, a method for producing power using microorganisms, and a microorganism used in the method for producing power A method for the selective culturing of is disclosed. An anode electrode having a liquid containing an organic substance and an anode electrode, wherein the organic substance is biodegraded by microorganisms in an anaerobic atmosphere, a cathode electrode, and an external circuit electrically connecting the anode electrode and the cathode electrode. and the anode electrode comprises graphene. Graphene provided in the anode electrode is an excellent electron-conducting material, so graphene can facilitate electron transfer from microorganisms to the negative electrode, which can improve power production.

Patent Document 5 discloses a microbial fuel cell electrode capable of generating a high output current in a microbial fuel cell and a microbial fuel cell using the same. As an anode electrode for a microbial fuel cell, a nanowire structure is formed on the surface of the electrode substrate with a conductive polymer to increase the surface area of the electrode. As a result, the efficiency of charge transfer from microorganisms to electrodes is found to be increased by 10 to 100 times compared to conventional electrodes for microbial fuel cells.

JP 2012-527733 A JP 2018-041670 A JP 2017-188483 A WO2013/073284 WO2011/025021

Conventional primary batteries such as zinc batteries, aluminum batteries, and magnesium batteries utilize chemical reactions, and zinc, aluminum, magnesium, and alloys thereof dissolve and become smaller due to chemical reactions. For this reason, the deterioration of characteristics is inevitable, and life is a major issue.

Microbial fuel cells have the problem that the amount of power that can be extracted is remarkably small, and the voltage is also lower than that of solar cells.

SUMMARY OF THE INVENTION An object of the present invention is to provide a primary battery using an electrode that can efficiently extract electric energy and can be used for a long period of time.

The present invention attempts to extend the life of the electrode by the following means.

(1) In the primary battery of the present invention, a coated electrode in which a film containing a layered compound is formed on a metal is used as at least one of the positive electrode (cathode electrode) and the negative electrode (anode electrode). Characterized by Here, the layered compound is used as a general term for substances having an intercalation function, and includes microporous crystals and porous coordination polymers in which a pore structure is fixed in a three-dimensional skeleton.

(2) In the primary battery described in (1) of the present invention, the metal is preferably copper, zinc or a zinc alloy, aluminum or an aluminum alloy, magnesium or a magnesium alloy.

(3) In the primary battery according to (1) of the present invention, the layered compound is preferably graphite, Prussian blue, or a Prussian blue analogue.

(4) In the primary battery according to (1) of the present invention, it is preferable that the film contains a conductive material.

(5) In the primary battery described in (1) of the present invention, the conductive material is one or a mixture of one or more of fine powder of graphite, carbon nanotube, carbon black, activated carbon, ketjen black, fullerene, and charcoal. , is preferred.

(6) In the primary battery described in (1) of the present invention, it is preferable that the layered compound, the conductive material, and the binder are mixed and coated on the metal.

(7) In the primary battery described in (6) of the present invention, the coated electrode is preferably wrapped with a water-permeable polymer film.

(8) The primary battery according to (1) of the present invention preferably comprises a carbon electrode made of carbon, an electrolyte containing plant-derived organic matter or fertilizer, and a coated electrode.

(9) In the primary battery described in (8) of the present invention, it is preferable that the electrolyte is mixed with fertilizer in the soil.

(10) In the primary battery described in (8) of the present invention, the electrolyte is preferably an aqueous solution of fertilizer.

(11) In the primary battery described in (8) of the present invention, the electrolyte preferably comprises a soil region and a water region.

(1) A primary battery is composed of a positive electrode (cathode electrode), a negative electrode (anode electrode), and an electrolyte. When metal is used for the electrodes, there is a problem of corrosion. Furthermore, since electrical energy uses chemical reactions of metals, there is also the problem of life span. Further, although carbon felt is used in the microbial fuel cell, the same material is used for the cathode electrode and the anode electrode, so the voltage and current are reduced.

In the present invention, since the film containing the layered compound is formed on the metal electrode, the electric energy can be changed from chemical reaction to charge transfer reaction utilizing intercalation phenomenon. Therefore, the problem of service life can be solved because the chemical reaction of the metal does not occur and the metal does not dissolve. Also, since the layered compound is not a metal, there is no problem of corrosion. Furthermore, since the intercalation phenomenon is used, it is possible to increase the current capacity. Since the voltage depends on the ionization tendency, that is, the oxidation-reduction potential of the metal, the higher the ionization tendency, the higher the voltage.

Carbon felt is used as the anode electrode in microbial fuel cells. If this anode electrode is used by forming a film containing a layered compound on a metal having a negative oxidation-reduction potential, it is possible to greatly increase both voltage and current.

(2) The metal is preferably copper, zinc or a zinc alloy, aluminum or an aluminum alloy, magnesium or a magnesium alloy. The redox potentials are +0.34V for copper, -0.76V for zinc, -1.68V for aluminum and -2.34V for magnesium. The generated voltage is determined depending on this oxidation-reduction potential. It is preferable to use copper, which has a positive redox potential, for the positive electrode, and zinc, aluminum, magnesium, etc., which have a negative redox potential, for the negative electrode.

(3) The layered compound is preferably graphite, Prussian blue, or a Prussian blue analogue, and must have an intercalation function. Intercalation is a reversible reaction in which other elements enter the voids of a molecule or group of molecules. Graphite is preferably coated with copper having a positive redox potential, and Prussian blue or a Prussian blue analog is preferably coated with zinc, aluminum, magnesium or the like with a negative redox potential on the metal surface. Layered compound coatings can suppress metal chemical reactions and replace charge transfer reactions with intercalation functions.

(4) The film formed on the surface of the metal preferably contains a conductive material. In particular, Prussian blue and Prussian blue analogues have no electrical conductivity, so it is necessary to contain a conductive material. The conductive material allows electrons to move, so that current can be extracted.

(5) The conductive material is preferably one or a mixture of one or more fine powders of graphite, carbon nanotube, carbon black, activated carbon, ketjen black, fullerene, and charcoal. These conductive materials are carbon-based, have low resistance, and easily pass electrons.

(6) The film is preferably a mixture of a layered compound and a conductive material and coated on a metal. Prior to coating, the layered compound, the conductive material and the binder are mixed and thoroughly stirred to form a uniformly dispersed state, which is then coated to form a uniform coating.

(7) By wrapping the coated electrode with a water-permeable polymer film, only charge transfer in the electrolyte can be performed between the coated electrode and the electrolyte. Moreover, when replacing the coated electrode, the coated electrode wrapped with the polymer film can be removed including the residue, and the electrolyte can be easily replaced without leaving any residue.

(8) The battery can be composed of a carbon electrode made of carbon, or an electrolyte containing fertilizer, and a coated electrode. Incorporating organic matter or fertilizer into the electrolyte is effective in greatly improving the performance of the microbial fuel cell.

(9) The electrolyte is preferably mixed with fertilizer in the soil. Plant-derived organic matter is soil that has fallen leaves piled up on the ground and fermented to become leaf mulch, and plant-derived organic matter is present. This organic matter is decomposed by electrogenic bacteria such as schwanellakin to generate hydrogen ions and electrons. Furthermore, the addition of fertilizer components such as potassium and magnesium has the effect of increasing the amount of charge that moves and increasing the power that can be obtained.

(10) The electrolyte may be an aqueous solution of fertilizer, and has the effect of being able to acquire electrical energy from potassium and magnesium, which are components of the fertilizer.

(11) The electrolyte may be composed of a soil region and a water region, enabling the acquisition of electrical energy in, for example, paddy fields and wetlands.

FIG. 2 is a diagram showing a cross section of a coated electrode used in a charge transfer primary battery; It is a figure explaining the principle of a magnesium air battery. It is a figure explaining the charge transfer type|mold primary battery by this invention. FIG. 2 is a diagram showing a microbial fuel cell in which plants are planted in soil and an anode electrode and a cathode electrode are embedded; 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 trial production of a coated electrode produced as an anode electrode is shown. Experimental device A for confirming the function of the coating electrode. Fig. 10 is a diagram showing an experimental device B in which electrodes are embedded in a flower pot in which flowers are planted, and electrical energy is extracted to turn on illumination.

Batteries include primary batteries and secondary batteries. A primary battery has a cell structure in which an electrolyte (chemical substance) is sandwiched between a cathode (positive electrode) and an anode (negative electrode). Therefore, it is non-rechargeable. The chemical reaction is the reaction between the electrode and the chemicals present in the cell, and the electrode dissolves due to the chemical reaction. Power generation ends when all of the electrodes or chemicals are used.

The electromotive force of a primary cell is the difference between the ionization tendencies of the cathode and anode. A larger electromotive force can be obtained as the difference between the oxidation-reduction potential, which indicates the ionization tendency, between the cathode and the anode is larger. Examples of primary batteries include manganese dry batteries using manganese dioxide and zinc as electrode materials, and alkaline dry batteries. The electrolyte of manganese dry batteries is mainly zinc chloride solution, and the electrolyte of alkaline dry batteries is potassium hydroxide solution.

Lithium primary batteries use lithium, which has a high ionization tendency, as an anode electrode material, and manganese dioxide, graphite fluoride, thionyl chloride, or the like as a cathode electrode material. Most of them use inexpensive manganese dioxide and have 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 anode electrode material, and carbon is used as the cathode electrode material. Since an aqueous sodium chloride solution is used as the electrolyte, corrosion occurs once the magnesium is exposed to the aqueous sodium chloride solution. For this reason, the corrosion resistance is improved by adding aluminum, zinc, etc. to magnesium, but it is not sufficient, and at present, it is limited to a single-use type for emergency use.

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

Electrons cannot move because they are blocked by the electrolyte, so electricity can be generated by taking them out. At the air electrode, by supplying oxygen in the air, oxygen (O ² ) is separated into two oxygen atoms by a catalytic reaction. Water (H ₂ O) is produced by combining the electrons that have moved to the oxygen atoms with the hydrogen ions that have passed through the electrolyte.

Microbial fuel cells use the metabolic ability of microorganisms to convert organic matter into electrical energy. The organic substances that serve as fuel for the microbial fuel cell are fermented fallen leaves and the like, and sugars produced by photosynthesis of plants and discharged from the roots. At the negative electrode (anode), electrons generated when organic matter is oxidatively decomposed by microorganisms called galvanogenic bacteria (for example, Shewanella bacteria) are recovered.

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, oxygen in the air to become water. For this reason, the positive electrode is also called an air cathode. Organic substances such as sewage and sludge can be used as fuel, and at the same time as power generation, it can also be applied to environmental purification such as treatment of organic waste and improvement of 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, which is a type of primary battery, includes solar power generation, wind power generation, and the like. At present, photovoltaic power generation is the mainstream, does not generate _CO2 , and is positioned as an important energy for global warming countermeasures. Since solar power generation uses sunlight as an energy source, it naturally does not generate electricity in places where sunlight does not hit or at night. Wind power generation also uses the wind, so it is an unstable energy that depends on the wind, and the installation location is limited.

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

Examples of secondary batteries include nickel-metal hydride batteries and lithium-ion batteries. A nickel-metal hydride battery is a battery that uses nickel hydroxide for the positive electrode and a hydrogen absorbing alloy for the negative electrode. A hydrogen storage alloy is a metal that can store hydrogen up to 1000 times its volume. An alkaline solution such as an aqueous potassium hydroxide solution is used as the electrolyte. During charging, hydrogen is accumulated in the hydrogen-absorbing alloy, and during discharging, hydrogen accumulated in the hydrogen-absorbing alloy is released. Nickel metal hydride batteries have a voltage of 1.2 V, which is the same as nickel cadmium batteries, but have about twice the electric capacity.

Lithium ion batteries are typical secondary batteries characterized by high voltage and large capacity utilizing the intercalation phenomenon, and occupy the current mainstream. A layered compound with an intercalation function is used for both the positive electrode and the negative electrode. Typically, the positive electrode uses lithium cobalt oxide and the pyroelectric material is aluminum, while the negative electrode uses graphite and the pyroelectric material is copper. This is a typical example.

Lithium cobalt oxide is also called an oxide compound, and since cobalt is expensive, lithium manganate (LiMn ₂ O ₄ ) based, lithium nickel oxide (LiNiO ₂ ) based, lithium iron phosphate (LiFePO ₄ ) system is also used. In order to give high conductivity and safety to the electrolyte (electrolytic solution), cyclic carbonate-based high dielectric constant and high boiling point solvents such as ethylene carbonate and propylene carbonate are mixed with low viscosity solvents such as dimethyl carbonate, ethyl methyl carbonate, and carbonate. Lower chain carbonates such as diethyl are also used.

The primary battery and the secondary battery have been overviewed above. The main principle of the primary battery is a chemical reaction, and the secondary battery is based on a charge transfer reaction. These are classified as chemical batteries, but primary batteries include physical batteries, solar power generation, wind power generation, hydraulic power generation, etc., and fuel cells that continuously supply electrolyte (fuel).

A primary battery, which is a chemical battery, uses the difference in ionization tendency of metal electrodes to generate electromotive force, but the current is generated by dissolving the metal using a chemical reaction, so there is a natural limit to the life of the battery. A secondary battery can be used repeatedly, but is initially charged with electric energy from the outside. Solar power generation and wind power generation, which are attracting attention as renewable energies that do not emit _CO2 , cannot supply electricity stably. only when the wind is blowing. Fuel cells can supply continuous electrical energy, but the voltage in a unit cell is low, and the current capacity of microbial fuel cells in particular is low.

In order to solve these problems, a charge transfer type primary battery was newly devised.

A charge transfer primary battery utilizes the difference in the ionization tendency of metals for the electromotive force. A layered compound having an intercalation function is coated on the metal electrode. Intercalation is a reversible reaction in which other elements enter the voids of a molecule or group of molecules. The intruding substance is called an intercalator or an intercalant, and the charge present in the electrolyte (electrolytic solution) is accumulated in the anode (negative electrode) by the electromotive force due to the difference in ionization tendency due to the intercalation phenomenon.

When the battery is in use (discharging), the charge accumulated in the anode as an intercalator, possibly including the charge in the electrolyte, moves to the cathode (positive electrode) side, and electrons flow to the cathode side through an external circuit. , reacts with oxygen in the air or dissolved oxygen in electrolytes.

When the charge in the electrolyte is used up, it no longer emits electric energy, and can be used repeatedly by replacing the electrolyte with a new electrolyte. Also, if it is used while supplying an electrolyte like a fuel cell, continuous use becomes possible. Assuming that the detailed structure of the charge transfer primary battery will be described later, first, the coated electrode coated with the layered compound will be described.

FIG. 1 is a cross-sectional view of a coated electrode used in a charge transfer primary battery. The coated electrode 10 of FIG. 1 forms a layered compound film on the metal 12 by coating. Various materials can be considered for the material of the metal 12 in order to utilize the ionization tendency.

Ionization tendency is a unique fundamental property of metals and is expressed in order of standard redox potentials between hydrated ions and elemental metals in aqueous solutions.

Metals with a negative standard redox potential include, for example, lithium (standard redox potential: -3.05 V), potassium (standard redox potential: -2.93 V), magnesium (standard redox potential: -2.36 V ), aluminum (standard redox potential: -1.68 V), titanium (standard redox potential: -1.63 V), zinc (standard redox potential: -0.76 V), iron (standard redox potential: -0 .44 V), nickel (standard oxidation-reduction potential: -0.26 V), and the like.

Metals with a positive standard redox potential include, for example, copper (standard redox potential: 0.34 V), silver (standard redox potential: 0.80 V), platinum (standard redox potential: 1.19 V), gold (standard oxidation-reduction potential: 1.52 V).

A layered compound is used as a general term for substances having an intercalation function, and includes microporous crystals and porous coordination polymers in which a pore structure is fixed in a three-dimensional skeleton. The layered compound has a layered compound whose layer structure is held by van der Luska, and the layered body has an electric charge, and exchangeable counter ions exist between the layers to compensate for the charge. There are layered compounds in which the layered structure is preserved by the working kulonka.

Layered Compounds Retained by Van der Luska A representative layered substance is graphite. A graphene sheet layer is a three-dimensional ordered structure that is regularly arranged. In-plane carbon atoms are linked by C—C covalent bonds, and van der Waals forces act between the carbon atoms between the planes. This becomes a factor of charge insertion.

A layered compound having an electric charge, for example, a layered double hydroxide, is based on the structure of ^bruceite , and a hydroxide layer in which a part of the divalent metal ion M2 ⁺ is replaced with a trivalent metal ion M3+. consists of The layers themselves therefore have a positive charge and there are exchangeable anions between the layers to compensate. 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. Layered double hydroxides of 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 compound. Lithium manganate (LiMn ₂ O ₄ ), lithium nickelate (LiNiO ₂ ), lithium iron phosphate (LiFePO ₄ ), and the like, which are more economical, are also used.

Prussian blue is also a layered compound as a kind of porous coordination polymer having an intercalation function. The molecular composition of Prussian blue is mainly composed of iron (Fe ³⁺ /Fe ²⁺ ) and cyano groups (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 6 directions of iron ions (Fe ⁺² ) up, down, left, right, front and back, forming a cubic jungle gym structure with metal ions (Fe/Ni/Co, etc.) as vertices. . Prussian blue is obtained when the metal ion is Fe. Since the distance between Fe ²⁺ and Fe ³⁺ is as large as 0.5 nm, it has large voids. This large cavity can de-insert various cations and molecules. Prussian blue analogues are obtained by substituting the central metal of the metal ion or ligand of Prussian blue, and have the same lattice structure as Prussian blue, but different lattice constants. Since the distance between Fe ²⁺ and Fe ³⁺ is large, it is suitable as an anode electrode using 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 conductive materials 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. Moreover, a catalyst component for efficiently performing the reduction-oxidation reaction of oxygen may be contained. 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 with a binder. Binders include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene・Tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene/chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), etc.

In a charge transfer primary battery, charge is accumulated on the anode side and current flows in one direction. Therefore, no charge is accumulated on the cathode side, and the cathode side does not necessarily need to be coated with a layered compound. If only the oxidation-reduction potential on the anode side is used, an electromotive force is generated even if no metal is used on the cathode side.

For this reason, the cathode electrode is preferably coated with a carbon-based layered compound using, for example, copper having a positive oxidation-reduction potential, but it is not always necessary to use a metal such as copper, and it is not necessary to use a layered compound. may That is, as the cathode electrode, a metal may be coated with a carbon-based material, or it may be used alone.

Among various carbon-based materials, there is graphite as a layered compound. Graphite, also known as graphite, is an elemental mineral composed of carbon, with a hexagonal system and hexagonal plate-like crystals. The structure is a tortoise shell-like layered substance, in which carbon atoms are connected by strong covalent bonds in the planes of each layer, but weak Van der Waals forces are formed between layers (between planes). Besides layered compounds, there are amorphous carbons such as carbon fiber, charcoal, and activated carbon that do not have a proper crystal structure, and this amorphous carbon can also be used. Since it has a cylindrical hollow space inside, it can contain various molecules.

Carbon nanotubes can also be used. A carbon nanotube has a structure that looks like a uniform flat graphite rolled into a cylindrical shape. In the closed state, both ends are closed with a structure like a hemisphere of fullerene, and always have six five-membered rings each. Since the number of 5-membered rings is small, it is difficult to dissolve in organic solvents. Since the tube has a cylinder-like structure, it is possible to take in various substances by burning off the cap.

In addition, Ketjen Black is also available. Ketjenblack is composed of carbon, like carbon black for rubber, carbon fiber, and graphite, and is composed of crystallites called a pseudo-graphite structure. The crystallites consist of condensed benzene rings with π electrons that can move freely on the carbon black. Because π electrons move on conductive circuits formed by aggregates and agglomerates, materials to which Ketjenblack is added exhibit conductivity. Ketjenblack is characterized by its high specific surface area and high porosity, and the formation of conductive circuits due to an increase in particle density is dominant, resulting in high conductivity.

Next, a charge transfer type primary battery using a coated electrode will be described. First, a magnesium battery will be described in comparison with conventional batteries.

FIG. 2 is a diagram explaining the principle of a magnesium air battery. Magnesium-air batteries are already on the market as emergency power sources. The magnesium-air battery 20 uses a magnesium alloy (hereinafter simply referred to as magnesium) as the anode electrode 22 and carbon as the cathode electrode 26 . 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 the oxygen in the air can be used for the reaction. Therefore, it is sometimes called an air cathode. The electrolyte is, for example, water or an aqueous solution of sodium chloride.

The reaction at the cathode is
O ₂ +2H ₂ O+4e ⁻ → 4OH ⁻
and the reaction at the anode is
2Mg → 2Mg ²⁺ +4e ^-
and the overall reaction is
2Mg+ _O2 +2H2O → _2Mg (OH) ₂
becomes.

The anode electrode is magnesium, which is dissolved by a chemical reaction to produce magnesium hydroxide (Mg(OH) ₂ ). Due to dissolution, the magnesium electrode decreases and eventually runs out and reaches the end of its life. Naturally, as the magnesium electrode decreases, so does the ampacity. In order to prolong the life, it is necessary to increase the thickness of the magnesium plate.

FIG. 3 is a diagram illustrating a charge transfer primary battery according to the present invention. FIG. 3A is a diagram showing the configuration of the charge transfer primary battery 40, and FIG. 3B is a model diagram of the charge transfer primary battery 36. As shown in FIG. The structure of the charge transfer primary battery 36 uses, for the anode electrode 22, a magnesium plate coated with, for example, Prussian blue or a Prussian blue analogue, and the cathode electrode 26 uses a copper plate coated with graphite. A mesh-like copper plate is used as the copper plate for use as an air cathode. Both the anode electrode 22 and the cathode electrode 26 are coated electrodes obtained by coating a layered compound on a metal plate.

The electrolyte (electrolytic solution) is, for example, an aqueous solution of sodium chloride (NaCl), and H ⁺ (hydrogen ion) and Na ⁺ are present as cations in the electrolytic solution. These cations act as intercalators (also called intercalants) and enter the layered compound to generate an intercalation reaction.

The cations serving as intercalators may be inorganic ions such as Mg ⁺ (magnesium ion), K ⁺ (potassium ion), Ca ⁺ (calcium ion), S ⁺ (sulfide ion). Since pure magnesium dissolves well in water, an aqueous solution of pure magnesium dissolved in water can be used as the electrolyte. Mg ⁺ , K ⁺ , Ca ⁺ , S ⁺ and the like are also components of fertilizers for growing plants. For example, K ⁺ is contained in chemical fertilizers and phosphorous fertilizers. Magnesium lime contains Mg ⁺ and Ca ⁺ . Further organic fertilizers include fermented poultry manure, which contains K ⁺ components. Therefore, the electrolyte may be an aqueous solution of fertilizer.

In the charge transfer primary battery 20, the electromotive force is the difference in ionization tendency between magnesium used in the anode and copper used in the cathode. The intercalator is released and flows from the anode electrode 22 to the cathode electrode 26 through an external circuit to produce a reaction and during use of the battery.

Utilizing an intercalation reaction in a primary battery is a new idea that has not existed in the past, and it is true that there are many unclear points about the detailed principle, and the principle has not been completely explained. However, since the chemical reaction is changed to the charge transfer reaction, there is no dissolution of the electrode and the life can be extended. For this reason, for example, if it is applied to an emergency magnesium-air battery and the magnesium electrode is replaced with the coated electrode 10 of the present invention, the battery can always be used by replacing the sodium chloride aqueous solution (salt water).

Also, if the electrolytic solution is supplied continuously or periodically like the fuel cell supplies hydrogen, power can be continuously generated. In the periodic supply, for example, the electrolytic solution may be exposed to the atmosphere to replenish the evaporated amount. Furthermore, if applied to a microbial fuel cell, it is possible to increase the voltage and current capacity.

FIG. 4 is a diagram showing a microbial fuel cell in which plants are planted in soil and an anode electrode and a cathode electrode are embedded. In the microbial fuel cell 40, soil 42 is mixed with fertilizer such as chemical fertilizer. The anode electrode 22 and the cathode electrode 26 are embedded in this soil 42 to take out electrical energy. The anode electrode 22 is formed by coating a layered compound such as Prussian blue or a Prussian blue analog on a metal having a low ionization tendency, such as magnesium or aluminum. The cathode electrode 26 is formed by coating a metal such as copper having a noble ionization tendency with a layered compound such as graphite. The cathode electrode 26 may be made of charcoal, graphite electrode, carbon graphite felt, carbon fiber sheet, etc., without using a metal such as copper that has a noble ionization tendency.

In soil 42, sugar (C ₆ H ₁₂ O ₆ ) produced by plants 44 by photosynthesis of the sun is discharged from roots 46, and hydrogen ions (H ⁺ ) and electrons (e ⁻ ) and become a source of electrical energy. In addition, organic substances, fertilizers, and the like existing in the soil 42 serve as electric energy sources.

In general, microbial fuel cells are systems that produce electric power from organic matter using the catabolic ability of microorganisms, and are also sustainable power generation systems because biomass such as sludge and garbage can be used as fuel. Since the microorganism itself functions as a biocatalyst that extracts electrons from organic matter, it also has the advantage of low cost.

Microorganisms in soil include highly thermophilic sulfur-dependent archaea that use hydrogen as an electron source and sulfur to accept electrons, and this bacterium produces hydrogen sulfide. Furthermore, methanogenic 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 dissimilatory iron bacteria that use iron as an electron acceptor Reducing bacteria are present.

Among microorganisms, there is a bacterium called an electroproducing bacterium that has the property of releasing electrons to the outside during the process of decomposing organic matter. Current-producing bacteria are dissimilatory iron-reducing bacteria, and dissimilatory iron-reducing bacteria reduce trivalent iron to divalent iron by directly contacting amorphous iron oxide, and form nano-sized magnetic particles. to produce.

Dissimilatory iron-reducing bacteria include Geobacter and Shewanella. These fungi do not like oxygen in the air, and live in environments with little oxygen, such as the ground, the bottom of the sea, and the bottom of a swamp. When water is given to the elec- trogen-producing bacteria together with the organic matter, the elec- trogen-producing bacterium decomposes the organic matter and releases hydrogen ions and electrons. If the emitted electrons are transferred to the anode electrode and flowed to the cathode electrode side, an electric current flows, and hydrogen ions react with oxygen on the cathode electrode side to form water. Therefore, if organic matter and water are continuously given to microorganisms, it will be possible to generate electricity continuously.

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

By adding fertilizer to the soil, the components of the fertilizer can also be used as electrical energy, resulting in a dramatic increase in power generation capacity. Conventional microbial fuel cells obtain electrical energy mainly from organic matter, but by including fertilizer, the components of the fertilizer are added, leading to a dramatic increase in power generation capacity.

Fertilizers are roughly classified into two types, "organic fertilizers" and "chemical fertilizers", but either of them may be used. Chemical fertilizers belong to the classification 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 carbonic acid itself) such as oil cake, fishmeal, and poultry manure. Fertilizers are classified into nitrogen fertilizers, phosphate fertilizers, potash fertilizers, silicic acid fertilizers, lime fertilizers, compound fertilizers, etc. according to their components, and are classified into alkaline fertilizers and acid fertilizers according to their chemical properties.

Fertilizers are nutrients applied to soil to maintain and increase soil productivity and promote plant growth. The three major elements of fertilizer are nitrogen, phosphoric acid and potash (potassium). In addition, nine elements including magnesium, calcium, sulfur, oxygen and hydrogen, as well as trace elements such as manganese, zinc, iron and boron are required.

The reason why the electric energy is increased by the fertilizer is that the nine elements and trace elements become ions and move in the electrolyte.

In addition, fertilizers are effective in increasing plant growth and electrical energy. For this reason, it is suitable for the ecosystem of the natural world, and it is truly a natural energy that 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 completely changes the landscape. Similarly, wind power generation also has problems of destruction of nature and low noise. In either case, disposal costs are high, and there is also the problem of disposal.

Electrolytes using fertilizer can be realized by mixing fertilizer into the soil. Soil consists of solid (solid phase), liquid (liquid phase) and gas (gas phase). The three-phase distribution of soil affects factors such as the difficulty of plant root elongation and the availability of water, oxygen and nutrients to the roots, and is one of the important factors for plant growth.

Soil voids are occupied by gas and liquid phases. The distribution ratio of these three phases varies and varies depending on the type of soil and the form of use. In the case of upland soil, a three-phase distribution of 30 to 40% solid phase and 40 to 30% liquid phase is considered optimal for plant growth. The structure of soil is classified into two types, unit structure and aggregate structure. A unit structure is a state in which soil particles are arranged in a single line. Aggregated grain structure is a state in which individual particles gather to form aggregated grains, and these aggregated grains are lined up.

The aggregate structure has both large and small pores. Large pores are associated with good drainage and small pores are associated with water retention. In general, soil with an aggregated structure has more gaps (pores) in the soil, and more gaps are suitable for plant growth, such as drainage, water retention, aeration, and root elongation.

Soil contains nutrients essential for plant growth such as nitrogen, phosphoric acid and potash (potassium), as well as trace elements such as iron, manganese, copper, zinc and boron. The role of fertilizers is to replenish components that tend to be lacking in the soil, especially nitrogen, phosphoric acid, and potassium.

Soil consists of a solid (solid phase), a liquid (liquid phase) and a gas (gas phase). The liquid phase is water and the gas phase is mainly air. The ions (H ⁺ ) react with the oxygen in the air in the gas phase, and the function as a battery can be achieved. In addition, the water in the liquid phase imparts electrical conductivity, allowing electrons to move to the anode electrode. Therefore, electric energy can be taken out even if the anode electrode and the cathode electrode are buried in the soil.

The fertilizer-containing electrolyte may be an aqueous solution in which the fertilizer is dissolved in water. In this case, the components of fertilizer are used to extract electric energy with electrodes. As mentioned above, fertilizers have nine elements, namely nitrogen, phosphoric acid, potash (potassium), magnesium, calcium, sulfur, oxygen and hydrogen.

Among these nine elements, potassium, magnesium, calcium and sulfur are listed as electrical energy sources. These components ionize in an aqueous solution and are responsible for electrical conduction between the anode electrode and the cathode electrode. This causes the movement of electrons, resulting in electrical energy. Therefore, the fertilizer preferably contains at least one of potassium, magnesium, calcium and sulfur.

Plants absorb carbon dioxide in the atmosphere and release oxygen through photosynthesis. Photosynthesis uses carbon dioxide to produce sugar, but since sugar is produced in excess of the amount consumed in the plant body, 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, secretions, etc. from plant roots also contribute to electrical energy. These organic substances are decomposed by current-producing fungi called Shewanella bacteria present in the soil to generate hydrogen ions (H ⁺ ) and electrons (e ⁻ ). At the anode electrode, electrons (e ⁻ ) and oxygen flowing from the cathode electrode through the external circuit react with hydrogen ions (H ⁺ ) to form water (H ₂ O). This chemical reaction is the basic principle, which is converted into electrical energy by creating a flow of electrons (e ⁻ ).

Fertilizers add nutrients to the soil, thereby promoting plant growth. Plants photosynthesise with sunlight to absorb carbon dioxide (CO ₂ ) in the atmosphere, produce sugars in the plant body, and grow themselves. Not all of the sugars produced are consumed within the plant body, but surplus sugars are released from the roots. Saccharides released from the roots are decomposed into hydrogen ions and electrons by electrogenic bacteria, which react with oxygen to become an electrical energy source. It is truly a natural energy that coexists with nature and is compatible with nature's sustainable ecosystem circulation cycle.

FIG. 5 is a diagram for explaining 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 paddy fields, and the electrolyte is composed of a water region 54 and a soil region 52 . A rice plant 56 is planted, and the rice plant 56 excretes sugar (C ₆ H ₁₂ O ₆ ) from the root 46 by photosynthesis of the sun. The excreted sugar (C ₆ H ₁₂ O ₆ ) is decomposed into hydrogen ions (H ⁺ ) and electrons (e ⁻ ) by current-producing bacteria such as Shewanella, and serves as an electric energy source. The rice plant 56 continuously produces sugar by photosynthesis and discharges it from the root 46, so that continuous power generation is possible.

Conventionally, the same carbon felt is used for both the anode electrode 22 and the cathode electrode 26 . The cathode electrode 26 is arranged so as to be in contact with the air in order to take in oxygen in 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 decomposition of sugar by current-producing bacteria combine with oxygen in the air to generate water. At this time, electrons (e ⁻ ) are required, and electrons (e ⁻ ) are attracted from the anode electrode 22 via the external circuit, so that current flows through the external circuit and can be extracted as electrical energy.

By using the coated electrode 10 for the anode electrode 22 of this rice field power generation 50, electric energy can be greatly increased. Magnesium or aluminum can be used as the metal 12 . The layered compound 14 that coats the metal 12 can be Prussian blue or a Prussian blue analogue. In rice field power generation using this coated electrode 10, electric energy can be efficiently extracted without a chemical reaction. An output voltage of around .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 0.5 V, which can be greatly improved.

When the electrode is installed in soil or the like, the film of the layered compound 14 of the coating electrode 10 may be damaged during handling, but it is preferable to cover it with a water-permeable sheet. By wrapping the entire coating electrode 10, the film can be protected, and at the time of replacement, the entire coating electrode 10 wrapped in the water-permeable sheet can be removed together with the residue. Therefore, replacement is facilitated.

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

The magnesium plate uses 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 with a diluted solution of Prussian blue 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 functions as a protective cover.

FIG. 7 shows an experimental device A for confirming the function of the coating electrode. The charge transfer primary battery has a three-layer structure in which a separator 62 is sandwiched between the anode electrode 22 and the cathode electrode 26 . An insulating water-absorbing sheet is used for the separator 62 , and the aqueous solution of the electrolyte 30 is sucked up by capillary action and supplied to the battery section composed of the anode electrode 22 and the cathode electrode 26 . As the electrolyte 30 , an aqueous solution of chemical fertilizer (potassium nitrogen phosphate) is used and placed in a container 32 .

The anode electrode 22 is formed by coating a magnesium plate (AZ31) having a thickness of 0.5 mm with a mixture of activated carbon, urethane resin and Prussian blue, and wrapping it with a water-permeable sheet. 6(B) shown in Example 1. FIG. The cathode electrode 26 was prepared by mixing Ketjenblack and polyvinylidene fluoride (PVDF) on a copper mesh plate having a thickness of 0.3 mm and heating and calcining the mixture using platinum as a catalyst. The anode electrode 22 and cathode electrode 26 are 7.4 cm long and 2.5 cm wide with an area of 18.5 cm ² .

The open-circuit voltage and short-circuit current were measured under these conditions. 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/cm ² . When the cathode electrode 26 is provided on the opposite side of the anode electrode 22 with the separator 62 interposed therebetween, the current density doubles to 5.2 mA/cm ² . In this case, the energy density obtained by simply multiplying the open-circuit voltage and the short-circuit current is 9.6 mW/cm ² .

In addition, when the cathode electrode is provided on both sides of the anode electrode 22 with the separator 62 interposed therebetween, the thickness is about ³ mm. Become. Even if three electrodes per cm are installed, 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 available short-circuit current density) x (maximum available open-circuit voltage) is called the form factor. is

The energy density of solar cells is said to be 13-15 mW/cm ² . This is the maximum energy density of a solar cell. The power that falls from directly above at the time of the sun's mid-century is about 1 kW in an area of 1 m ² above the ground, and the conversion efficiency of solar cells is currently 13 to 15% of the received light. Naturally, the energy density decreases in the morning and evening, cloudy days, and rainy days, and no power is generated at night. Therefore, even if the form factor is taken into account, it is possible to obtain electric energy that greatly exceeds the electric energy from the solar cell.

FIG. 8 is a diagram showing an experimental device B in which electrodes are embedded in a flowerpot in which flowers are planted, and electrical energy is extracted to turn on the illumination. In the experimental apparatus B66, the anode electrode is a covered coated electrode in which a magnesium plate is coated with Prussian blue and wrapped with a water-permeable sheet. The cathode electrode is a charcoal electrode in which charcoal is wound with a stainless steel wire. These two electrodes are embedded in the soil of the flowerpot. Flowers are grown while supplying an aqueous solution of chemical fertilizer to the flowerpot.

Electric energy extracted from the electrodes embedded in the flower pot is input to the control circuit and stored in the nickel metal hydride battery. The control circuit is connected to the illumination and turns on the illumination. The lighting of the illumination is controlled by a control circuit, and several lighting modes such as continuous lighting and on/off flashing can be controlled.

A voltage of 1.5 to 1.8 V and a short-circuit current of 5 to 10 mA were obtained from the electrode embedded in the flower pot. Naturally, the electric current that can be taken out depends on the condition of the soil, and the water content has a particularly large effect. A nickel-metal hydride battery with a rating of 1.2 V and 1900 mAh was used, and illumination lighting in a fully charged state could be performed for about two days. The nickel-metal hydride battery is constantly charged, and depending on the condition of the soil, it can be lit for a longer period of time. The voltage of the nickel metal hydride battery was 836 mV when the brightness of the illumination decreased and the light became dim, but it took about half a day to charge the battery to the rated voltage.

Although the embodiments of the present invention have been described above, the present invention includes appropriate modifications that do not impair its objects and advantages, and is not limited by the above-described embodiments.

REFERENCE SIGNS LIST 10 coated electrode 12 metal 14 layered compound 16 terminal 20 conventional magnesium air battery 22 anode electrode 24 anode terminal 26 cathode electrode 28 cathode terminal 30 electrolyte 32 container 36 charge transfer primary cell 38 intercalator 40 microbial fuel cell 42 soil 44 plant 46 Root 50 Rice field power generation 52 Soil region 54 Water region 56 Rice 58 Prototype electrode 60 Experimental device A
62 Separator 66 Experimental device B

Claims (11)

A coated electrode in which a film containing a layered compound is formed on a metal is used as at least one of the positive electrode and the negative electrode;
A primary battery characterized by: the metal is copper, zinc or a zinc alloy, aluminum or an aluminum alloy, magnesium or a magnesium alloy;
The primary battery according to claim 1, characterized by: the layered compound is graphite, Prussian blue or a Prussian blue analog;
The primary battery according to claim 1, characterized by: The coating contains a conductive material;
The primary battery according to claim 1, characterized by: The conductive material is graphite, carbon nanotube, carbon black, activated carbon, ketjen black, fullerene, fine powder of charcoal,
The primary battery according to claim 3, characterized by: The layered compound and the conductive material are mixed with a binder and coated on the metal in the coating;
The primary battery according to any one of claims 1 to 4, characterized by: The coated electrode is wrapped with a water-permeable polymer film;
The primary battery according to claim 6, characterized by: a carbon electrode made of carbon;
an electrolyte containing organic matter or fertilizer;
the coating electrode;
consist of
The primary battery according to claim 1, characterized by: The electrolyte is mixed with fertilizer in the soil;
The primary battery according to claim 8, characterized by: The electrolyte is an aqueous solution of fertilizer;
The primary battery according to claim 8, characterized by: the electrolyte being composed of a soil region and a water region;
The primary battery according to claim 8, characterized by:

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