JP2004063345A - Air battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make an air battery as an electrode fixed-type secondary battery having superior charging and discharging cycle stability. <P>SOLUTION: This air battery uses oxygen in the air in a positive electrode active material, an active carbon, a carbon nano-tube or a graphite nano-fiber having a specific surface area of 800m<SP>2</SP>/g or more is used in a negative electrode 2, and an aqueous solution mainly composed of alkali metal phosphate or alkali metal borate is used in the electrolyte. The adsorption and releasing of H<SP>+</SP>occurs on a surface of the negative electrode 2 in charging and discharging, here, the charge is accumulated and released to an electric double layer formed on an interface of a surface of the negative electrode 2 and the electrolyte. In discharging, H<SB>2</SB>O is produced by the reaction of OH<SP>-</SP>supplied from the air pole 9 and the H<SP>+</SP>supplied from the negative electrode. Further the charging is performed by utilizing the decomposition reaction of the water. The negative electrode active material is chemically stable, so that the electrolyte is hardly deteriorated by carbon dioxide, and the secondary battery having superior cycle stability can be provided. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a chargeable air battery.
[0002]
[Prior art]
An air battery generally refers to a battery using oxygen in the air as a positive electrode active material and a metal as a negative electrode active material, and the air electrode for taking oxygen in the air into the battery has a catalytic action. A porous carbon material, a porous metal material, or a composite material of both are used. The negative electrode active material is zinc, iron or aluminum, and the electrolyte is about 30% potassium hydroxide aqueous solution, ammonium chloride solution or zinc chloride. The battery in which the solution is used. These are called air-zinc batteries, air-iron batteries, and air-aluminum batteries, respectively, depending on the difference in the negative electrode active material.
[0003]
A feature of the air battery is that it has a high energy density. An air battery uses oxygen in the air as the positive electrode active material, so there is no need to fill the battery with the positive electrode active material.In a normal battery, the negative electrode active space is also used in the space used to fill the positive electrode active material. The reason is that the substance can be filled. In the discharge of the air battery, O ₂ in the air is dissolved in the electrolyte as OH ^{− by} the catalytic action of the air electrode and reacts with the negative electrode active material to generate an electromotive force.
[0004]
Currently, the only commercially available air batteries are air-zinc batteries, but all are coin-type primary batteries, which are used for hearing aids and pagers.
In the 1970's, research on the conversion of an air battery to a secondary battery was conducted for the purpose of use as a power source for electric vehicles, but was not practical. The reason that it was difficult to make a secondary battery with an air-zinc battery is that
(1) A short circuit occurs because zinc as the negative electrode active material causes dendrite growth during charging.
(2) poor charge / discharge efficiency,
(3) the electrolyte is deteriorated by absorption of carbon dioxide in the atmosphere;
(4) There are many problems to be solved, such as the carbon material used for the air electrode being oxidized and consumed.
[0005]
Regarding the prevention of zinc dendrite on the negative electrode, an electrode-exchange-type secondary battery called mechanical charging in which the zinc electrode is replaced with a new one after the discharge is completed has been developed. Further, a method of circulating zinc powder together with an electrolytic solution to externally reduce zinc hydroxide or zinc oxide as a discharge product and returning the zinc oxide and zinc oxide to the inside of the battery has also been studied.
On the other hand, no effective improvement method has been developed for the deterioration due to carbon dioxide absorption of the electrolytic solution.
[0006]
Further, with respect to the prevention of oxidative consumption of the air electrode, a technique called a three-electrode method has been developed. This method is a method in which an energization circuit is automatically switched so that a porous carbon material is used for discharging and a non-oxidizing porous metal material is used for charging.
Also, a method of adding a substance that reduces oxygen overvoltage such as WC or Co to the air electrode, or a method of adding an oxidation-resistant catalyst such as La _0.5 Sr _0.5 CoO ₃ has been developed. In any case, this is not a solution aiming at a secondary battery with a fixed electrode.
[0007]
In addition, secondary batteries such as an air-iron battery and an air-aluminum battery were also prototyped, but have not been put into practical use for the reasons described below.
An air-iron battery does not have the problem of dendrite generation unlike zinc and has a large energy density, but has a short life and requires periodic replacement of an electrolyte.
Since an air-aluminum battery cannot be charged with an aqueous electrolyte solution, it is basically difficult to make a secondary battery other than mechanical charging.
[0008]
Recently, in Japanese Patent Application Laid-Open No. 2001-313093, an air battery that can be charged by using chemically stable activated carbon, carbon nanotube, or graphite nanofiber has been proposed. However, an alkaline metal hydroxide aqueous solution is used as an electrolyte. Therefore, there is a disadvantage that long-term cycle stability cannot be obtained due to deterioration due to absorption of carbon dioxide in the atmosphere.
[0009]
The deterioration due to carbon dioxide absorption is caused by the fact that alkali metal ions combine with carbon dioxide in an aqueous solution to precipitate alkali metal carbonate.
[0010]
[Problems to be solved by the invention]
In recent years, clean electric energy has been demanded for environmental considerations. However, it is very preferable that the air battery is a secondary battery with a fixed electrode, not only for an electric vehicle but also for a hearing aid. If high-current-density charging is possible, the application will be further expanded.However, the electrolyte of the air battery gradually absorbs carbon dioxide in the atmosphere, causing a gradual decrease in ionic conductivity and ultimately an internal resistance. As a result, the voltage drop at the time of charging and discharging increases, and an air cell exhibiting a practical level of cycle stability has not yet been completed.
[0011]
An object of the present invention is to solve the above-mentioned problems in converting an air battery into a secondary battery, and to provide an air battery that has a fixed electrode, has excellent cycle stability, and can be charged with a large current density. .
[0012]
[Means for Solving the Problems]
The air battery of the present invention comprises oxygen in the air as a positive electrode active material, activated carbon having a specific surface area of 800 m ² / g or more as a negative electrode active material, carbon nanotubes or graphite nanofibers, and an alkali metal phosphate or an alkali metal as an electrolyte. The above problem has been solved by using an aqueous solution containing a borate as a main component.
[0013]
In the discharge of a conventional air battery, O ₂ in the atmosphere is reduced to OH ⁻ at the air electrode, and OH ⁻ reacts with the metal of the negative electrode in the electrolyte to form a metal hydroxide.
The reaction formula at the air electrode and the negative electrode at this time is as follows.
Cathode:
O ₂ + 2H ₂ O + 4e ⁻ → 4OH ⁻ (1)
Negative pole:
2M + 4OH ⁻ → 2M (OH) ₂ + 4e ⁻ (2)
(Assuming M is a divalent metal)
With respect to the above reaction formula, placing the viewpoint to the negative electrode, H ⁺ is generated when the negative electrode metal is oxidized in water, H ⁺ is OH generated in the air electrode ^- can be considered to be depolarized reacted with .
[0014]
That is, the reaction formula is as follows.
Cathode:
O ₂ + 2H ₂ O + 4H ⁺ + 4e ⁻ → 4OH ⁻ + 4H ⁺ → 4H ₂ O (3)
Negative pole:
2M + 4H ₂ O → 2M (OH) ₂ + 4H ⁺ + 4e ⁻ (4)
(Assuming M is a divalent metal)
Therefore, in order to make the air battery a secondary battery, the material for the negative electrode active material that has H ⁺ storage properties or adsorptivity and that does not cause a chemical reaction with the alkaline aqueous solution is optimal.
[0015]
Materials satisfying these conditions are activated carbon, carbon nanotubes, and graphite nanofibers. These materials must have a specific surface area of 800 m ² / g or more. If the specific surface area is less than 800 m ² / g, the amount of H ⁺ adsorbed is too small, and a practical discharge capacity cannot be obtained. Generally, the larger the specific surface area, the better.
[0016]
The air battery according to the present invention is basically composed of an air electrode having a catalytic action on a redox reaction of O ₂ , an active carbon having a specific surface area of 800 m ² / g or more, a negative electrode using carbon nanotube or graphite nanofiber, and an air electrode. After being composed of a separator for separating the negative electrode and an electrolytic solution prepared with an aqueous solution mainly containing an alkali metal phosphate or an alkali metal borate, charging is performed first.
[0017]
During charging, H ⁺ generated by the decomposition of water is adsorbed on the surface of negatively polarized activated carbon, carbon nanotubes or graphite nanofibers, and the electric double layer formed at the solid-liquid interface between the surface of the carbon material and the electrolytic solution is charged. Stored. At this time, O ₂ is generated from the air electrode and released into the atmosphere. On the other hand, in the discharge, H ⁺ is released from the surface of the carbon material and reacts with OH ⁻ generated at the air electrode to generate water. At this time, the charges stored in the electric double layer are released.
[0018]
This reaction is a decomposition and generation reaction of water as shown in the following reaction formula.
_{^{H + + OH - ⇔H 2 O}} ···· (5)
Activated carbon is activated by reacting carbonaceous material with water vapor, carbon dioxide or zinc chloride, potassium hydroxide, etc., and has a structure in which micropores have been developed.The specific surface area, pore distribution, Since the surface properties greatly change, a material having a quality that improves the battery performance is appropriately selected. Generally, activated carbon prepared from a phenol resin has a high specific surface area. The shape may be any of fibrous, spherical, and granular. Upon charging, H ⁺ is adsorbed in the micropores, and charges are accumulated in the electric double layer.
[0019]
Carbon nanotubes are produced by vapor-phase growth using hydrocarbon as a raw material, arc discharge using carbon electrodes, or vacuum heating of SiC, etc. ing. The single-layer (single-layer) tube has a diameter of about 1.2 nm, and the specific surface area is theoretically 3000 m ² / g or more. Upon charging, H ⁺ is adsorbed on the inner surface or outer surface of the tube, and charges are accumulated in the electric double layer.
[0020]
Graphite nanofibers are fibrous carbons having a diameter of about 100 nm generated when ethylene or the like is thermally decomposed on a metal catalyst, and have a structure in which the a-plane or b-plane of graphite crystals is extremely exposed on the fiber surface. H ⁺ is adsorbed between graphite crystal layers, and charges are accumulated in the electric double layer.
Activated carbon, carbon nanotubes or carbon nanofibers do not undergo a chemical change when H ⁺ is adsorbed and released. Therefore, it is a negative electrode active material which can be charged at a large current density and is important for producing a battery having high cycle stability.
[0021]
The air electrode must be made of an oxidation-resistant material that is not oxidized and consumed by active O ₂ generated during charging, and must have an electrode structure with high gas permeability that can quickly release O ₂ into the atmosphere. It is. An electrode material suitable for this condition is carbon carrying a catalyst. The four-electron reduction represented by the reaction formula (1) proceeds at a high speed with the catalyst supported on carbon, and the oxidation and consumption of carbon can be prevented. On the other hand, in order to enable high gas permeability, it is necessary to have a porous structure, and at this time, water repellency must be imparted to prevent leakage of the electrolyte.
[0022]
As an example of the air electrode, there is a sheet in which activated carbon particles carrying platinum are bound with polytetrafluoroethylene. In order to hold the sheet, it is used by being pressed against a metal net having excellent oxidation resistance such as stainless steel.
As the catalyst, other platinum, silver, manganese dioxide, nickel - cobalt composite oxide, phthalocyanine _{compounds, WC, Co, FeWO 4,} NiS, Co (OH) 2, Ni (OH) 2, La 0.5 Sr _0.5 CoO ₃ , Pr _0.2 Ca _0.8 Mn _0.1 Fe _0.9 O ₃ , La _0.8 Rb _0.2 MnO _{3 and the} like are known, and these can be used alone or in combination. However, it is not limited to these.
[0023]
As the carbon, carbon black or the like is suitable other than activated carbon. However, carbon black has different properties depending on the manufacturing method. For example, acetylene black having high hydrophobicity is preferably used for a gas supply portion of an air electrode, and carbon black having low hydrophobicity is preferably used for a redox reaction portion.
If a conductive oxide is used in place of carbon, oxidative consumption can be prevented, but a large specific surface area is difficult to obtain, and the battery performance is reduced because the specific resistance is larger than carbon. Examples of the conductive oxide include SnO ₂ , Fe ₃ O ₄ , RuO ₂ , MnO ₂ , and LaNiO ₃ .
[0024]
As the electrolyte, an aqueous solution containing an alkali metal phosphate or an alkali metal borate as a main component is used. Potassium phosphate, sodium phosphate, lithium phosphate, potassium borate, sodium borate, and lithium borate are used. Of any of the following, or a mixture of potassium phosphate, sodium phosphate, lithium phosphate, potassium borate, sodium borate, and lithium borate with potassium hydroxide, lithium hydroxide, or lithium hydroxide Suitably, an aqueous solution is used.
[0025]
The following salts are generally known as potassium phosphate, sodium phosphate, lithium phosphate, potassium borate, sodium borate and lithium borate.
Potassium pyrophosphate (K ₄ P ₂ O ₇ ), potassium tertiary phosphate (K ₃ PO ₄ ), dipotassium hydrogen phosphate (K ₂ HPO ₄ ), potassium dihydrogen phosphate (KH ₂ PO ₄ ), pyrophosphoric acid Sodium (Na ₄ P ₂ O ₇ ), tribasic sodium phosphate (Na ₃ PO ₄ ), disodium hydrogen phosphate (Na ₂ HPO ₄ ), sodium dihydrogen phosphate (NaH ₂ PO ₄ ), tertiary phosphoric acid Lithium (Li ₃ PO ₄ ), dilithium hydrogen phosphate (Li ₂ HPO ₄ ), lithium dihydrogen phosphate (LiH ₂ PO ₄ ), potassium metaborate (K ₂ B ₂ O ₄ ), potassium tetraborate (K ₂ B ₄ O _7), potassium pentaborate _{(KB 5 O} 8), potassium hexaborate acid _{(K 2 B 6 O 10)} , potassium eight borate _{(K 2 B 8 O 13)} , sodium metaborate (Na ₂ B ₂ O ₄ ), sodium tetraborate (Na ₂ B ₄ O ₇ ), sodium pentaborate (NaB ₅ O ₈ ), sodium hexaborate (Na ₂ B ₆ O ₁₀ ), octaborate Sodium (Na ₂ B ₈ O ₁₃ ), sodium diborate (Na ₄ B ₂ O ₅ ), lithium metaborate (Li ₂ B ₂ O ₄ ), lithium tetraborate (Li ₂ B ₄ O ₇ ), pentaborate Examples thereof include lithium acid (LiB ₅ O ₈ ) and lithium perborate (Li ₂ B ₂ O ₅ ), and the presence of a salt other than these is also suggested.
[0026]
Among the above salts, dipotassium hydrogen phosphate, disodium hydrogen phosphate, and dilithium hydrogen phosphate are not suitable for the air battery of the present invention because their aqueous solutions show weak acidity. Also, among alkali metal phosphates or alkali metal borates, francium phosphate, cesium phosphate, rubidium phosphate, francium borate, cesium borate, rubidium borate are generally expensive, and are used for batteries. It is not useful as an electrolyte.
[0027]
As a conventional air battery electrolyte, a potassium hydroxide aqueous solution having a high ionic conductivity is generally used, and it is naturally applicable to the air battery of the present invention. Since the period is long, the electrolyte absorbs oxygen dioxide in the atmosphere and deteriorates. Weakly acidic electrolytes other than aqueous potassium hydroxide, such as ammonium chloride and zinc chloride, are characterized by being free from carbon dioxide absorption, but cannot be used because they have low output density and generate chlorine gas during charging.
[0028]
In contrast, many alkali metal phosphates or alkali metal borates have an aqueous solution that is alkaline due to hydrolysis, but many of them show weak alkalinity as compared with an alkali metal hydroxide aqueous solution of the same concentration. At carbon dioxide partial pressure (101 Pa), deterioration due to carbon dioxide is suppressed.
For example, the reaction formula when potassium pyrophosphate is used is as follows.
[0029]
Potassium pyrophosphate is a salt that is relatively difficult to hydrolyze, and gradually becomes an aqueous solution of dipotassium hydrogen phosphate in water.
K ₄ P ₂ O ₇ + H ₂ O → 2K ₂ HPO ₄ (6)
In the aqueous solution of dipotassium hydrogen phosphate, the standard free energy change ΔG for the reaction with carbon dioxide becomes positive under the partial pressure of carbon dioxide in the atmosphere (101 Pa), and the precipitation of alkali carbonate does not occur.
[0030]
2K ₂ HPO ₄ + CO ₂ + H ₂ O ← ₂ KH ₂ PO ₄ + K ₂ CO ₃ (7)
However, in an actual aqueous solution, the ionic state of the alkali metal phosphate and the alkali metal borate is complicated, and the equations (6) and (7) are simplified representations of typical reactions.
The potassium pyrophosphate exemplified here has high solubility and is one of the most suitable electrolyte salts.
[0031]
For the salt concentration, select a concentration at which no salt precipitates at least at room temperature. However, if a salt with low solubility is used, the ionic conductivity of the electrolyte is low, so that high current density charging cannot be performed, and the application of the battery is greatly limited. .
Therefore, an aqueous solution in which potassium hydroxide, sodium hydroxide, or lithium hydroxide is appropriately mixed with any of potassium phosphate, sodium phosphate, lithium phosphate, potassium borate, sodium borate, and lithium borate is used. . By using this aqueous solution, the ionic conductivity is improved, and deterioration due to carbon dioxide absorption is alleviated as compared with the case where an alkali metal hydroxide is used, so that an electrolytic solution having high ionic conductivity can be obtained. Generally, potassium hydroxide, sodium hydroxide or lithium hydroxide is used in an amount of 5 to 50% by mass of the total electrolyte salt, but the ionic conductivity and the chemical stability vary depending on the type of the salt. It is necessary to arbitrarily determine the combination and mixing ratio of the salt exhibiting the characteristics.
[0032]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a configuration diagram of an air battery according to an embodiment of the present invention.
This air battery includes a stainless steel positive electrode container 4 provided with air holes 8, an air diffusion nonwoven fabric 5, a porous polytetrafluoroethylene film 6, an air electrode 9 provided with a current collecting network 7, a cellophane 10 for a separator, and a negative electrode. 2. The negative electrode container 1 is overlapped, and the space between the positive electrode container 4 and the negative electrode container 1 is sealed with a gasket 3.
[0033]
Activated carbon, carbon nanotube or graphite nanofiber having a specific surface area of 800 m ² / g or more is used for the negative electrode 2. Each material is press-molded into a predetermined shape at 4.9 × 10 ⁷ Pa or more, and then immersed in an electrolytic solution for 1 h or more to sufficiently wet the surface. The electrolytic solution may be impregnated under pressure. Although there is no problem with using a binder such as polytetrafluoroethylene to maintain the shape, a binder that completely covers the surface of the carbon material cannot be used because it causes a decrease in discharge capacity. However, in the case of an activated carbon woven cloth, it is cut into a predetermined size, and is immersed in an electrolytic solution and used as it is.
[0034]
The air electrode 9 is formed by mixing carbonaceous material obtained by firing wood, sawdust, phenol resin, or the like in a low oxygen atmosphere under the introduction of steam or carbon dioxide, or after mixing with zinc chloride, potassium hydroxide, etc. Activated carbon prepared by activating at ~ 1000 ° C and carrying a catalyst such as platinum or manganese dioxide is optimal. The particle size is suitably 100 μm or less, and the specific surface area is suitably 200 to 1000 m ² / g, but not limited thereto. A catalyst such as platinum and manganese dioxide is supported by impregnating activated carbon with a salt such as platinum chloride or manganese sulfate in advance and thermally decomposing in an inert gas stream such as nitrogen or argon.
[0035]
Activated carbon supporting a catalyst is prepared by mixing 5 to 10% by mass ratio of polytetrafluoroethylene or the like as a binder in any of fibrous, spherical, and granular forms, and then rolling at 150 ° C. to form a 100 μm sheet. Process. The binder must be corrosion resistant to alkali phosphate, alkali borate and alkali metal hydroxide solutions, and must be an electrochemically stable material, but will completely cover the particles. Can not be used. Further, it is necessary that the mixing ratio of the binder be as small as possible within a range where the shape of the sheet is maintained. The activated carbon formed into a sheet shape is pressed into a current collecting network 7 (aperture 150 μm) of nickel, stainless steel, or the like at 4.9 × 10 ⁷ Pa or more to form an air electrode 9.
[0036]
A porous polytetrafluoroethylene film 6 is adhered to the current collecting network 7 side of the air electrode 9 to prevent electrolyte leakage while controlling the amount of O _{2 taken in} from the atmosphere. Further, in order to uniformly supply O ₂ to the whole air electrode, a nonwoven fabric 5 for air diffusion made of polypropylene is superposed on the porous polytetrafluoroethylene film 6.
The electrolytic solution is, for example, a 5 to 50% aqueous solution of potassium pyrophosphate, sodium pyrophosphate or lithium pyrophosphate, or any one of potassium pyrophosphate, sodium pyrophosphate, and lithium pyrophosphate and potassium hydroxide, sodium hydroxide, or lithium hydroxide. Use a 5 to 50% aqueous solution. The salt concentration is arbitrarily changed in consideration of improvement in battery characteristics. However, very dilute solutions must be avoided because they reduce ionic conductivity and make high current density charging impossible.
[0037]
In addition, each of the above-mentioned components can be changed within a range that does not lower the battery performance.
[0038]
【Example】
[Example 1]
For the negative electrode 2, a sheet of φ18 mm × 0.4 mm thick was cut out from an activated carbon woven fabric having a specific surface area of 1500 m ² / g prepared using a phenol resin as a raw material, and immersed in a 40% aqueous potassium pyrophosphate solution for 1 hour. One used.
[0039]
The air electrode 9 was activated carbon activated at 900 ° C. by introducing water vapor from coconut husk as a raw material, and used a catalyst carrying platinum and manganese dioxide as a catalyst. The activated carbon supporting the catalyst had an average particle size of 90 μm and a specific surface area of 1000 m ² / g. After mixing 5% by mass of polytetrafluoroethylene with this activated carbon, it was rolled at 150 ° C. and processed into a sheet having a thickness of 100 μm.
[0040]
The activated carbon processed into a sheet shape was cut into φ18 mm, and pressed into a stainless steel current collector 7 (mesh opening 150 μm) at 4.9 × 10 ⁷ Pa to form an air electrode 9. A polytetrafluoroethylene film 6 was adhered to the current collecting network 7 side of the air electrode 9, and a nonwoven fabric made of polypropylene was laminated thereon.
As the electrolytic solution, an aqueous solution of potassium pyrophosphate was used.
[0041]
Using the above negative electrode 2, air electrode 9, and electrolytic solution, a non-woven fabric for air diffusion 5, a porous polytetrafluoroethylene film 6, a stainless steel positive electrode container 4 provided with air holes 8 as shown in FIG. The air electrode 9 provided with the current collecting network 7, the cellophane for separator 10, the negative electrode 2, and the negative electrode container 1 were stacked in this order to form an air battery.
The air battery was repeatedly charged and discharged at a charging current of 10 mA and a discharging current of 1 mA in the range of 0 to 1.45 V, and the cycle stability was examined.
[0042]
FIG. 2 shows the cycle change of the discharge capacity. The initial discharge capacity was 10 mAh / cm ³ , and the discharge capacity after 50 cycles maintained 100% of the initial discharge capacity.
[Example 2]
Except that the specific surface area of the activated carbon nonwoven fabric used for the negative electrode was 800 m ² / g, an air battery was constructed in the same manner as in Example 1, and the cycle stability was examined in the same manner.
[0043]
FIG. 2 shows the cycle change of the discharge capacity. The initial discharge capacity was 4 mAh / cm ³ , and the discharge capacity after 50 cycles maintained 100% of the initial discharge capacity.
[Example 3]
An air battery was constructed in the same manner as in Example 1 except that a 50% aqueous solution of dipotassium hydrogen phosphate was used as the electrolytic solution, and the cycle stability was examined in the same manner.
[0044]
FIG. 2 shows the cycle change of the discharge capacity. The initial discharge capacity was 9 mAh / cm ³ , and the discharge capacity after 50 cycles maintained 100% of the initial discharge capacity.
[Example 4]
An air battery was constructed in the same manner as in Example 1 except that a 20% aqueous solution of potassium tetraborate was used as the electrolytic solution, and the cycle stability was examined in the same manner.
[0045]
FIG. 2 shows the cycle change of the discharge capacity. The initial discharge capacity was 8 mAh / cm ³ , and the discharge capacity after 50 cycles maintained 100% of the initial discharge capacity.
[Example 5]
An air battery was constructed in the same manner as in Example 1, except that a 5% aqueous solution of dilithium hydrogen phosphate was used as the electrolytic solution, and the cycle stability was examined in the same manner.
[0046]
FIG. 2 shows the cycle change of the discharge capacity. The initial discharge capacity was 5 mAh / cm ³ , and the discharge capacity after 50 cycles maintained 100% of the initial discharge capacity.
[Example 6]
An air battery was constructed in the same manner as in Example 1 except that a mixed aqueous solution of 20% potassium tetraborate and 10% potassium hydroxide was used as the electrolytic solution, and cycle stability was examined in the same manner.
[0047]
FIG. 2 shows the cycle change of the discharge capacity. The initial discharge capacity was 10 mAh / cm ³ , and the discharge capacity after 50 cycles maintained 99% of the initial discharge capacity.
[0048]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, an air battery can be made into a secondary battery which is a fixed electrode, is excellent in cycle stability, and can be charged with a large current, and is environmentally friendly as a power source for not only electric vehicles but also hearing aids. It is possible to supply a great amount of electrical energy.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an air battery according to an embodiment of the present invention.
FIG. 2 is a diagram showing a cycle change of a discharge capacity of an air battery in Examples 1 to 6.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Negative electrode container 2 Negative electrode 3 Gasket 4 Positive electrode container 5 Non-woven fabric for air diffusion 6 Porous polytetrafluoroethylene film 7 Current collection network 8 Air hole 9 Air electrode 10 Cellophane for separator

Claims (3)

Oxygen in the air is used as a positive electrode active material, activated carbon, carbon nanotube or graphite nanofiber having a specific surface area of 800 m ² / g or more is used as a negative electrode active material, and an alkali metal phosphate or an alkali metal borate is used as an electrolyte. An air battery using an aqueous solution containing an acid salt as a main component. As an aqueous solution mainly containing an alkali metal phosphate or an alkali metal borate, an aqueous solution of any of potassium phosphate, sodium phosphate, lithium phosphate, potassium borate, sodium borate, and lithium borate is used. The air battery according to claim 1, wherein: As an aqueous solution containing an alkali metal phosphate or an alkali metal borate as a main component, any one of potassium phosphate, sodium phosphate, lithium phosphate, potassium borate, sodium borate, and lithium borate, The air battery according to claim 1, wherein a mixed aqueous solution of potassium, sodium hydroxide or lithium hydroxide is used.

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