JP4298235B2 - Air secondary battery - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rechargeable 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 is 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 solution. Is the battery used. These are called an air-zinc battery, an air-iron battery, and an air-aluminum battery, respectively, depending on the difference in the negative electrode active material.
[0003]
The feature of the air battery is that it has a high energy density. Since an air battery uses oxygen in the air as a positive electrode active material, it is not necessary to fill the battery with a positive electrode active material. In a normal battery, the negative electrode active material is also used in the space used for filling 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 dissolves 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]
At present, the air batteries generally available on the market are only air-zinc batteries, but they are all coin-type primary batteries and are used for hearing aids and pagers.
In the 1970s, research into the use of air batteries as secondary batteries was made for the purpose of use as a power source for electric vehicles, but it did not come into practical use. The reason why it was difficult to make secondary batteries with air-zinc batteries was
(1) Zinc, which is a negative electrode active material, causes dendritic growth during charging, resulting in a short circuit.
(2) Poor charge / discharge efficiency
(3) The electrolyte solution deteriorates due to absorption of carbon dioxide in the atmosphere.
(4) This is because there were many problems to be solved, such as the carbon material used for the air electrode being oxidized during charging.
[0005]
In order to prevent zinc dendrite of the negative electrode, an electrode exchange type secondary battery called mechanical charging in which the zinc electrode is exchanged for a new one after the discharge has been developed. Furthermore, a method of circulating zinc powder together with an electrolytic solution, reducing discharge products such as zinc hydroxide and zinc oxide outside, and returning them to the inside of the battery has been studied.
On the other hand, no effective improvement method has been developed for the deterioration of the electrolytic solution due to carbon dioxide absorption.
[0006]
Furthermore, a technique called a three-electrode system has been developed for preventing oxidation consumption of the air electrode. This is a method in which the 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.
In addition, methods have been developed to add substances that reduce oxygen overvoltage such as WC and Co to the air electrode, or to add an oxidation-resistant catalyst such as La _0.5 Sr _0.5 CoO _3. It is not a solution that aims to use a fixed type secondary battery.
[0007]
A secondary battery of air-iron battery and air-aluminum battery was also prototyped, but has not been put into practical use for the reason described below.
The air-iron battery does not have the problem of dendrite generation like zinc and has a high energy density, but has a short life and requires regular replacement of the electrolyte.
Since an air-aluminum battery cannot be charged with an aqueous electrolyte, it is basically difficult to make a secondary battery other than mechanical charging.
[0008]
Recently, an air battery that can be charged by using chemically stable activated carbon, carbon nanotubes, or graphite nanofibers as a negative electrode active material has been proposed in JP 2001-313093. Therefore, sufficient energy density cannot be secured as a power source for electric vehicles and hearing aids. Further, since an alkali metal hydroxide aqueous solution is used as the electrolytic solution, 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]
[Problems to be solved by the invention]
In recent years, clean electric energy has been demanded in consideration of the environment. However, it is very preferable not only for an electric vehicle but also for a hearing aid power source that an air battery is used as a secondary battery with a fixed electrode. However, the energy density of the air secondary battery is low, and the electrolytic solution gradually reduces ionic conductivity by absorbing carbon dioxide in the atmosphere. Finally, the voltage drop during charging and discharging increases due to the increase in internal resistance. An air battery exhibiting a practical level of cycle stability has not yet been completed.
[0010]
The present invention provides a high energy density air secondary battery that solves the above-described problems in making a secondary battery of an air battery, is electrode fixed, has excellent cycle stability, and can be charged with a large current density. For the purpose.
[0011]
[Means for Solving the Problems]
The air secondary battery of the present invention includes a group VIII metal oxide having oxygen in the air as a positive electrode active material, combined water or occluded water as a negative electrode active material, or a composite oxide composed of a combination of a group II metal and a group VIII metal, The said subject is solved by using alkaline aqueous solution for electrolyte solution.
[0012]
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 electrolytic solution to become a metal hydroxide.
The reaction formula in the air electrode and the negative electrode at this time is as follows.
Air electrode:
O ₂ + 2H ₂ O + 4e ⁻ → 4OH ⁻ (1)
Negative pole:
2M + 4OH ⁻ → 2M (OH) ₂ + 4e ⁻ (2)
(M is assumed to be 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 with water, H ⁺ is OH generated in the air electrode ^- can be considered to be depolarized reacted with .
[0013]
That is, the reaction formula is as follows.
Air electrode:
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)
(M is assumed to be a divalent metal)
Therefore, in order to convert the air battery into a secondary battery, the negative electrode active material is optimally a material that has H ⁺ occlusion or adsorption and does not cause a chemical reaction with an alkaline aqueous solution.
[0014]
The material satisfying these conditions is a group VIII metal oxide having bound water or occluded water or a composite oxide composed of a combination of a group II metal and a group VIII metal, and includes iron tetroxide, ruthenium dioxide, or a group II metal. As a composite oxide comprising a combination of Group VIII metals, a metal comprising any combination of Sr—Fe, Ca—Fe or Ba—Fe having a Group II metal / Group VIII metal molar ratio of 1/6 to 1/12 An oxide is optimal. Since the reaction area with H ⁺ increases as the specific surface area increases, it is suitable for large current density charging.
[0015]
The air secondary battery of the present invention basically comprises an air electrode having a catalytic action for the redox reaction of O ₂ , a group VIII metal oxide having combined water or occluded water, or a combination of a group II metal and a group VIII metal. After comprising the negative electrode using the composite oxide, the separator separating the air electrode and the negative electrode, and the electrolyte prepared with an alkaline aqueous solution, the battery is first charged.
[0016]
In charging, H ⁺ produced by the decomposition of water is formed on the surface layer or inside of a group VIII metal oxide having negatively polarized bound water or occluded water or a composite oxide crystal composed of a combination of a group II metal and a group VIII metal. Adsorbs or intercalates. At this time, O ₂ is generated from the air electrode and released into the atmosphere.
On the other hand, in discharge, H ⁺ is separated or deintercalated from the surface layer or inside of the oxide crystal, and reacts with OH ⁻ generated at the air electrode to generate water.
[0017]
The reaction formula is as follows when ruthenium dioxide is taken as an example.
Air electrode:
δ / 4O ₂ + δ / 2H ₂ O + δe ⁻ ⇔δOH ⁻ (5)
Negative pole:
_{RuO X- δ (OH) Y +} δ ⇔RuO X (OH) Y + δH + + δe - ·· (6)
(Generally X≈2)
From the reaction formulas (5) and (6), this reaction can be regarded as a decomposition and formation reaction of water using an oxide as a hydrogen storage medium.
[0018]
The group VIII metal oxide, iron trioxide, has a reverse spinel structure and high electronic conductivity, and ruthenium dioxide has a rutile structure but has very high electronic conductivity. When iron trioxide and ruthenium dioxide are charged in an alkaline electrolyte, H ⁺ is adsorbed or intercalated on the surface layer or inside of these oxide crystals in the form of oxonium ions (H ₃ O ⁺ ). At this time, triiron tetroxide and ruthenium dioxide change from weakly alkaline to weakly acidic. However, since triiron tetroxide is stable in the range of pH 9 to pH14 and ruthenium dioxide is stable in the range of pH1 to pH14, Dissolution is suppressed.
[0019]
In order to increase the energy density, it is necessary to increase the amount of H ⁺ adsorbed or intercalated. For this reason, it is important that the oxide crystal has high H ⁺ conductivity. Since ruthenium dioxide has bound water and occluded water, oxonium ions are easily formed in the crystal, and H ⁺ conductivity can be improved.
[0020]
These oxides are preferably prepared by a wet method in which a metal hydrochloric acid solution, a nitric acid solution or a sulfuric acid solution is reacted with an alkaline aqueous solution, and the heating and drying temperature of the reaction product is preferably 300 ° C. or less.
The X-ray diffraction patterns of triiron tetroxide and ruthenium dioxide obtained in this way have a wide peak half-value width, indicating that bound water or occluded water is present in the oxide crystal.
[0021]
There is osmium dioxide as a group VIII metal oxide, but it can be applied to a negative electrode active material because of its relatively high electronic conductivity and large H ⁺ adsorptivity. However, it is a resource-poor metal with a large atomic weight. Therefore, the utility value is poor from the viewpoint of weight reduction and cost reduction of the battery.
On the other hand, as a complex oxide composed of a combination of a Group II metal and a Group VIII metal, the Sr—Fe, Ca—Fe or Ba—Fe based oxide has a Group II metal / Group VIII metal molar ratio of 1/6 to 1 / In the range of 12, the crystal structure approximates that of iron trioxide, and more H ⁺ can be adsorbed or intercalated than iron trioxide.
[0022]
It is considered that the distortion of the crystal lattice due to the addition of the group II metal contributes to an increase in the amount of intercalation of H ⁺ . The X-ray diffraction patterns of these composite oxides are also patterns similar to iron trioxide having a wide peak half width.
When the molar ratio of the Group II metal to the Group VIII metal is greater than 1/6, nickel hydroxide, strontium hydroxide, calcium hydroxide, and barium hydroxide precipitate as the second phase, and the amount of H ⁺ adsorbed or intercalated Reduce the amount.
[0023]
On the other hand, if it is smaller than 1/12, it becomes a substance equivalent to iron trioxide, and no superiority appears in the amount of H ⁺ adsorbed or intercalated.
For the group VIII metal Fe, there are combinations of Be, Mg, and Re, but the ionic radii of Be and Mg are too small, 0.41 and 0.86, so that they have a crystal structure similar to that of iron trioxide. It ’s hard. Re is a radioactive substance and is not suitable for use.
[0024]
When Ru or Os is used in place of Fe of the Group VIII metal, ruthenium dioxide and osmium dioxide itself are substances exhibiting high electronic conductivity and H ⁺ storage, and the complexation with the Group II metal is H ⁺ It is considered that the effect of increasing the energy density is small because the crystal structure is changed so as to suppress adsorption or intercalation.
[0025]
As a method for preparing a composite oxide composed of a Group II metal and a Group VIII metal, a hydrochloric acid solution, a nitric acid solution or a sulfuric acid solution of various metals in accordance with a predetermined composition ratio, as in the preparation method of iron trioxide and ruthenium dioxide. The precipitated product obtained by the reaction between the aqueous solution and the alkaline aqueous solution is dried at 400 ° C. or lower. However, there is no limitation to this method as long as there is another method that does not allow the bound water or the occluded water to be removed.
[0026]
H ⁺ adsorption, desorption or intercalation, deintercalation on the oxide is performed by electrochemical redox reaction, but the reaction rate is extremely fast, following the electric double layer reaction used in capacitors. This is called a pseudo double layer reaction. Therefore, high current density charging is possible, and an air secondary battery having high cycle stability can be manufactured.
[0027]
The air electrode is made of an oxidation-resistant material that is not oxidized and consumed by active O ₂ generated during charging, and has an electrode structure with high gas permeability that can quickly release O ₂ into the atmosphere. By providing oxidation resistance and high gas permeability, the internal resistance during high current density charging can be reduced.
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 rate with the catalyst supported on the carbon, and the oxidative consumption of the carbon can be suppressed. On the other hand, in order to enable high gas permeability, it is necessary to have a porous structure, and water repellency must be imparted in order to prevent leakage of the electrolyte.
[0028]
As an example of the air electrode, there is a sheet in which platinum-supported activated carbon particles are bound with polytetrafluoroethylene. The sheet is held by being pressed against a metal net having excellent acid resistance such as stainless steel.
As a catalyst, in addition to platinum, silver, manganese dioxide, nickel-cobalt composite oxide, phthalocyanine compound, WC, Co, FeWO ₄ , NiS, Co (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, but are not limited thereto.
[0029]
As carbon, carbon black or the like is suitable in addition to activated carbon. However, carbon black has different properties depending on the production method. For example, acetylene black having strong hydrophobicity may be used for the gas supply portion of the air electrode, and carbon black having weak hydrophobicity may be used for the redox reaction portion. If a conductive oxide is used instead of carbon, oxidation consumption can be prevented, but it is difficult to obtain a large specific surface area, and the battery performance is lowered because the specific resistance is larger than that of carbon. Examples of the conductive oxide include SnO ₂ , Fe ₃ O ₄ , RuO ₂ , MoO ₂ , and LaNiO ₃ .
[0030]
An alkaline aqueous solution is used as the electrolytic solution. By using the alkaline aqueous solution, OH ⁻ in the electrolytic solution is increased, and the redox reaction of the air electrode is rapidly performed. As the alkaline aqueous solution, an aqueous solution of an alkali metal hydroxide is generally used. A conventional potassium hydroxide aqueous solution with high ion conductivity is used for the electrolyte of the air battery, and it can be applied to the air battery of the present invention. Therefore, the electrolyte solution absorbs oxygen dioxide in the atmosphere and deteriorates. Weakly acidic electrolytes such as ammonium chloride and zinc chloride other than aqueous potassium hydroxide are not affected by carbon dioxide absorption, but they are inferior in heavy load characteristics, have low output density, and generate chlorine gas during charging. Not suitable for use.
[0031]
In contrast, many aqueous solutions based on alkali metal phosphates or alkali metal borates show alkalinity, but many of them show weak alkalinity compared to alkali metal hydroxides of the same concentration. With carbon partial pressure (101 Pa), deterioration due to carbon dioxide is suppressed.
For example, the reaction formula when an aqueous solution of potassium pyrophosphate, which is one of alkali metal phosphates, is in contact with carbon dioxide is as follows.
[0032]
Potassium pyrophosphate is a salt that is relatively difficult to hydrolyze, and gradually becomes a dipotassium hydrogen phosphate aqueous solution in water.
K ₄ P ₂ O ₇ + H ₂ O → 2K ₂ HPO ₄ (7)
In the dipotassium hydrogen phosphate aqueous solution, the standard free energy change ΔG related to the reaction with carbon dioxide is positive under the atmospheric partial pressure of carbon dioxide (101 Pa), and precipitation of alkali carbonate does not occur. The reaction formula is as follows.
[0033]
2K ₂ HPO ₄ + CO ₂ + H ₂ O ← 2KH ₂ PO ₄ + K ₂ CO ₃ .. (8)
However, in an actual aqueous solution, the ionic state of the alkali metal phosphate and the alkali metal borate is complicated, and formulas (7) and (8) simply show representative reactions.
The potassium pyrophosphate exemplified here is one of the most suitable electrolyte salts because of its high solubility.
[0034]
As an aqueous solution mainly composed of alkali metal phosphate or alkali metal borate, any one of potassium phosphate, sodium phosphate, lithium phosphate, potassium borate, sodium borate, and lithium borate, Alternatively, it is suitable to use a mixed aqueous solution of any one of potassium phosphate, sodium phosphate, lithium phosphate, potassium borate, sodium borate, and lithium borate and potassium hydroxide sodium hydroxide or lithium hydroxide.
[0035]
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 ), tribasic potassium phosphate (K ₃ PO ₄ ), dipotassium hydrogen phosphate (K ₂ HPO ₄ ), potassium dihydrogen phosphate (KH ₂ PO ₄ ), pyrophosphate 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 phosphate 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 (K ₂ B ₆ O ₁₀ ), potassium octaborate (K ₂ B ₈ O ₁₃ ), sodium metaborate (Na ₂₎ B ₂ O _4), sodium tetraborate (Na ₂ B _{4 7),} sodium pentaborate _{(Na 2 B 5 O 8)} , sodium hexaborate acid _{(Na 2 B 8 O 13)} , lithium metaborate _{(Li 2 B 2 O 4)} , lithium tetraborate (Li ₂ B ₄ O ₇ ), lithium pentaborate (LiB ₅ O ₈ ), lithium perborate (Li ₂ B ₂ O ₅ ), and the like, and the presence of other salts are also suggested.
[0036]
Among the above-mentioned salts, dipotassium hydrogen phosphate, disodium hydrogen phosphate, and dilithium hydrogen phosphate are not suitable for the air secondary battery of the present invention because their aqueous solutions exhibit weak acidity.
Among alkali metal phosphates or alkali metal borates, francium phosphate, cesium phosphate, rubidium phosphate, francium borate, cesium borate, and rubidium borate are generally expensive and are used for batteries. It is not useful as an electrolyte salt.
[0037]
The salt concentration is selected so that the salt does not precipitate at least at room temperature. However, if a salt with low solubility is used, the ionic conductivity of the electrolyte is low, so high current density charging cannot be performed, and the use of the battery is greatly limited. .
In order to solve this problem, any one of potassium phosphate, sodium phosphate, lithium phosphate, potassium borate, sodium borate, lithium borate, potassium hydroxide, sodium hydroxide or lithium hydroxide An aqueous solution in which an appropriate amount is mixed is used. Thereby, the ionic conductivity is improved, and further, deterioration due to carbon dioxide absorption is mitigated as compared with the case of using an alkali metal hydroxide, and an electrolytic solution having a high ionic conductivity can be obtained.
[0038]
Generally, potassium hydroxide, sodium hydroxide, or lithium hydroxide is 5 to 50% by mass of the total electrolyte salt, but the ion conductivity and chemical stability differ depending on the type of salt, so the battery is the best. It is necessary to arbitrarily determine the combination and mixing ratio of salts exhibiting excellent characteristics.
[0039]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a configuration diagram of an air secondary battery according to an embodiment of the present invention.
This air secondary 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 collector network 7, and a separator cellophane 10. The negative electrode 2 and the negative electrode container 1 are superposed, and the gap between the positive electrode container 4 and the negative electrode container 1 is sealed with a gasket 3.
[0040]
The negative electrode 2 includes Sr—Fe, Ca—Fe, or Ba—Fe having a bound water or occluded water of triiron tetroxide, ruthenium dioxide, or a group II metal / group VIII metal molar ratio of 1/6 to 1/12. The metal oxide which consists of any combination of these is used.
For triiron tetroxide or ruthenium dioxide, a small amount of hydrochloric acid is usually added to an iron chloride or ruthenium chloride aqueous solution, and then an aqueous solution of an alkali metal hydroxide such as ammonia solution or KOH is added little by little. No. Prepare by filtering with 5B filter paper and drying at 300 ° C. or lower.
[0041]
On the other hand, Sr—Fe, Ca—Fe or Ba—Fe based oxides are composed of iron chloride and strontium chloride, calcium chloride, and barium chloride with a Sr / Fe molar ratio, a Ca / Fe molar ratio, and a Ba / Fe molar ratio of 1 / After weighing at a mass ratio of 6 to 1/12, it is dissolved in water, and in some cases, a small amount of hydrochloric acid is added to make an acidic aqueous solution. To this aqueous solution, an alkali metal hydroxide solution such as an ammonia solution or an aqueous KOH solution was added little by little. Prepare by filtering with 5B filter paper and drying at 400 ° C or lower.
[0042]
Each negative electrode active material was mixed and dispersed with 2 to 15% by mass of carbon black or the like as a conductive auxiliary agent, pressed into a predetermined shape at 4.9 × 10 ⁷ Pa or higher, and then immersed in an electrolyte for 1 hour or longer. Keep the surface wet enough. The electrolytic solution may be impregnated under pressure. In order to maintain the shape, there is no problem with using 2 to 10% by mass of a binder such as polytetrafluoroethylene with respect to the negative electrode active material, but polytetrafluoroethylene is more hydrophilic. The wettability with the electrolyte is improved and the discharge capacity is increased. On the other hand, if the amount of polytetrafluoroethylene used exceeds 10% by mass, a part of the surface of the negative electrode active material is completely covered, so that the discharge capacity decreases.
[0043]
The air electrode 9 has a carbonaceous material obtained by firing in a low-oxygen atmosphere using large sawdust, phenol resin, or the like as a raw material, or after mixing with steam or carbon dioxide, or after mixing with zinc chloride, potassium hydroxide, or the like. A product obtained by supporting a catalyst such as platinum or manganese dioxide on activated carbon activated and prepared at ℃ 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 is not limited thereto. A catalyst such as platinum or manganese dioxide is supported by impregnating activated carbon with a salt such as platinum chloride or manganese sulfate in advance and thermally decomposing it in an inert gas stream such as nitrogen or argon.
[0044]
Activated carbon carrying the catalyst is mixed in a mass ratio of 5-10% polytetrafluoroethylene or the like as a binder in any of fibrous, spherical, and granular forms, and then rolled at 150 ° C. to form a 100 μm sheet. Process. The binder must be an electrically stable material that is corrosion resistant to alkali metal phosphate, alkali metal borate aqueous solution and alkali metal hydroxide aqueous solution, but completely covers the particles. Things that end up cannot be used. Further, the mixing ratio of the binder needs to be as small as possible within the range in which the shape of the sheet is maintained.
[0045]
The activated carbon processed into a sheet shape is pressure-bonded to a current collector network 7 (mesh 150 μm) such as nickel or stainless steel at 4.9 × 10 ⁷ Pa or more to form an air electrode 9.
A porous polytetrafluoroethylene film 6 is brought into close contact with the current collector 7 side of the air electrode 9 to prevent leakage of the electrolyte while controlling the amount of O _{2 taken up} from the atmosphere. Further, in order to uniformly supply O ₂ to the entire air electrode 9, an air diffusion nonwoven fabric 5 made of polypropylene is overlaid on the porous polytetrafluoroethylene film 6.
[0046]
The electrolyte is, for example, potassium pyrophosphate, sodium pyrophosphate or lithium pyrophosphate 5-50% aqueous solution or potassium pyrophosphate, sodium pyrophosphate, lithium pyrophosphate and potassium hydroxide, sodium hydroxide or lithium hydroxide. A 5 to 50% aqueous solution is used in combination. The salt concentration is arbitrarily changed in consideration of improvement in battery characteristics. However, too dilute solutions must be avoided because they reduce ionic conductivity and make high current density charging impossible.
[0047]
In addition, each said structural member can be changed in the range which does not reduce battery performance.
[0048]
【Example】
[Example 1]
In the negative electrode 2, the precipitate obtained by adding a 30% aqueous potassium hydroxide solution to a 30% ferric chloride aqueous solution was subjected to precipitation. The iron trioxide obtained by filtering off with 5B filter paper, washing, and drying at 300 ° C. for 10 hours was used. Iron trioxide: polytetrafluoroethylene powder: carbon black mixed at a mass ratio of 85: 10: 5, rolled 1 mm thick sheet was cut into φ18 mm, and immersed in 40% potassium pyrophosphate aqueous solution for 1 h This was used as negative electrode 2.
[0049]
The air electrode 9 was made of activated carbon activated at 900 ° C. under the introduction of water vapor with coconut shell as a raw material and carrying platinum and manganese dioxide as catalysts. The activated carbon carrying the catalyst had an average particle size of 90 μm and a specific surface area of 1000 m ² / g. After 5% polytetrafluoroethylene was mixed with this activated carbon by mass ratio, it was rolled at 150 ° C. and processed into a sheet shape with a thickness of 100 μm.
[0050]
The activated carbon processed into a sheet shape was cut to φ18 mm, and pressed onto a stainless steel current collector 7 (mesh 150 μm) at 4.9 × 10 ⁷ Pa to form an air electrode 9. A polytetrafluoroethylene film 6 was brought into close contact with the current collector 7 side of the air electrode 9, and a non-woven fabric made of polypropylene was overlaid thereon.
As the electrolytic solution, a 40% potassium pyrophosphate aqueous solution was used.
[0051]
Using the negative electrode 2, the air electrode 9, and the electrolytic solution described above, as shown in FIG. 1, a stainless steel positive electrode container 4 provided with air holes 8, an air diffusion nonwoven fabric 5, a porous polytetrafluoroethylene film 6, The air electrode 9 provided with the current collection network 7, the separator cellophane 10, the negative electrode 2, and the negative electrode container 1 were stacked in this order to constitute an air secondary battery.
The air secondary 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.
[0052]
FIG. 2 shows the cycle change of the discharge capacity. The initial discharge capacity was 14 mAh / cm ³ , and the discharge capacity after 50 cycles maintained 100% of the initial discharge capacity.
[Example 2]
In the negative electrode 2, a precipitate obtained by adding a 30% aqueous potassium hydroxide solution to a 30% aqueous ruthenium chloride solution was obtained as No. 2. The ruthenium dioxide hydrate obtained by filtering off with 5B filter paper, washing, and drying at 300 ° C. for 10 hours was used. A ruthenium dioxide: polytetrafluoroethylene powder: carbon black mixed at a mass ratio of 85: 10: 5, rolled into a 1 mm thick sheet, cut into φ18 mm, and immersed in 40% potassium pyrophosphate aqueous solution for 1 hour Was the negative electrode 2.
[0053]
Otherwise, an air secondary battery was constructed in the same manner as in Example 1, and the cycle stability was similarly examined.
FIG. 2 shows the cycle change of the discharge capacity. The initial discharge capacity was 165 mAh / cm ³ , and the discharge capacity after 50 cycles maintained 100% of the initial discharge capacity.
Example 3
An air secondary battery was constructed in the same manner as in Example 2 except that a 50% aqueous solution of dipotassium hydrogen phosphate was used as the electrolytic solution, and the cycle stability was similarly examined.
[0054]
FIG. 2 shows the cycle change of the discharge capacity. The initial discharge capacity was 110 mAh / cm ³ , and the discharge capacity after 50 cycles maintained 100% of the initial discharge capacity.
Example 4
An air secondary battery was constructed in the same manner as in Example 2 except that a 20% potassium tetraborate aqueous solution was used as the electrolytic solution, and the cycle stability was similarly examined.
[0055]
FIG. 2 shows the cycle change of the discharge capacity. The initial discharge capacity was 120 mAh / cm ³ , and the discharge capacity after 50 cycles maintained 100% of the initial discharge capacity.
Example 5
An air secondary battery was constructed in the same manner as in Example 2 except that a 5% dilithium hydrogen phosphate aqueous solution was used as the electrolytic solution, and the cycle stability was similarly examined.
[0056]
FIG. 2 shows the cycle change of the discharge capacity. The initial discharge capacity was 100 mAh / cm ³ , and the discharge capacity after 50 cycles maintained 100% of the initial discharge capacity.
Example 6
An air secondary battery was constructed in the same manner as in Example 2 except that a mixed aqueous solution of 20% potassium tetraborate and 10% potassium hydroxide was used as the electrolytic solution, and the cycle stability was similarly examined.
[0057]
FIG. 2 shows the cycle change of the discharge capacity. The initial discharge capacity was 160 mAh / cm ³ , and the discharge capacity after 50 cycles maintained 99% of the initial discharge capacity.
Example 7
In the negative electrode 2, the precipitate obtained by adding a 30% aqueous potassium hydroxide solution to a 30% aqueous solution containing strontium chloride and ferric chloride so that the Sr / Fe molar ratio was 1/10 was obtained as No. 2. The composite oxide obtained by filtering off with 5B filter paper, washing, and drying at 400 ° C. for 10 hours was used. Mixed oxide: polytetrafluoroethylene powder: carbon black was mixed so as to have a mass ratio of 85: 10: 5, and a rolled 1 mm thick sheet was cut into φ18 mm and immersed in 40% potassium pyrophosphate aqueous solution for 1 h. This was used as negative electrode 2.
[0058]
Otherwise, an air secondary battery was constructed in the same manner as in Example 1, and the cycle stability was similarly examined.
FIG. 2 shows the cycle change of the discharge capacity. The initial discharge capacity was 50 mAh / cm ³ , and the discharge capacity after 50 cycles maintained 100% of the initial discharge capacity.
Example 8
In the negative electrode 2, the precipitate obtained by adding a 30% aqueous potassium hydroxide solution to a 30% aqueous solution containing calcium chloride and ferric chloride so that the Ca / Fe molar ratio becomes 1/10 is obtained as No. 2. An air secondary battery was constructed in the same manner as in Example 7 except that the composite oxide obtained by filtering with 5B filter paper, washing and drying at 400 ° C. for 10 hours was used, and cycle stability was similarly examined. It was.
[0059]
FIG. 2 shows the cycle change of the discharge capacity. The initial discharge capacity was 40 mAh / cm ³ , and the discharge capacity after 50 cycles maintained 100% of the initial discharge capacity.
Example 9
In the negative electrode 2, a precipitate obtained by adding a 30% aqueous potassium hydroxide solution to a 30% aqueous solution containing barium chloride and ferric chloride so that the Ba / Fe molar ratio becomes 1/10 is obtained as No. 2. An air secondary battery was constructed in the same manner as in Example 7 except that the composite oxide obtained by filtering with 5B filter paper, washing, and drying at 300 ° C. for 10 hours was used, and cycle stability was similarly examined. It was.
[0060]
FIG. 2 shows the cycle change of the discharge capacity. The initial discharge capacity was 48 mAh / cm ³ , and the discharge capacity after 50 cycles maintained 100% of the initial discharge capacity.
[0061]
【The invention's effect】
According to the present invention, it is possible to obtain a high energy density air secondary battery having a fixed electrode type, excellent cycle stability and capable of being charged with a large current density, and not only as an electric vehicle but also as a power supply for a hearing aid to the environment. It becomes possible to supply clean electric 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 the discharge capacity of the air battery in Example 1 to Example 9.
[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 (5)

An air secondary characterized in that oxygen in the air is used as the positive electrode active material, iron tetroxide or ruthenium dioxide having bound water or occluded water is used as the negative electrode active material, and an alkaline aqueous solution is used as the electrolyte. battery. Sr—Fe composite oxide, Ca—Fe composite oxide, or Ba—Fe composite oxide having oxygen in the air as the positive electrode active material and having bound water or occluded water as the negative electrode active material, A composite oxide having a Sr / Fe molar ratio, a Ca / Fe molar ratio, and a Ba / Fe molar ratio of 1/6 to 1/12 is used, and an alkaline aqueous solution is used as an electrolytic solution. Next battery. The alkaline aqueous solution is an aqueous solution mainly containing an alkali metal phosphate or alkali metal borate excluding dipotassium hydrogen phosphate, disodium hydrogen phosphate, and dilithium hydrogen phosphate. The air secondary battery according to 1 or 2 . Use an aqueous solution of potassium phosphate, sodium phosphate, lithium phosphate, potassium borate, sodium borate, or lithium borate as an aqueous solution mainly composed of alkali metal phosphate or alkali metal borate. The air secondary battery according to claim 3 . As an aqueous solution containing an alkali metal phosphate or alkali metal borate as a main component, one of potassium phosphate, sodium phosphate, lithium phosphate, potassium borate, sodium borate, and lithium borate , and hydroxylated 4. The air battery according to claim 3 , wherein a mixed aqueous solution of potassium, sodium hydroxide or lithium hydroxide is used.

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