JP2023055467A - Positive electrode for storage battery and bismuth-zinc storage battery - Google Patents

Abstract

To provide a method for sufficiently preventing oxygen evolution in a positive electrode for a storage battery.SOLUTION: A positive electrode used in a storage battery is a positive electrode for a storage battery, containing an active material containing 50% by mass or more of bismuth.SELECTED DRAWING: Figure 1

Description

The present invention relates to positive electrodes for storage batteries and bismuth-zinc storage batteries. More specifically, a positive electrode for a storage battery particularly used in a bismuth-zinc storage battery, a bismuth-zinc storage battery constructed using the same, a bipolar electrode, a laminate thereof, and a bipolar type storage battery constructed using a bipolar electrode or a laminate thereof Regarding.

In recent years, the importance of batteries has rapidly increased in many industries, from small portable devices to large applications such as automobiles. For example, zinc negative electrodes using zinc species as the negative electrode active material have been studied for a long time with the spread of batteries. Widely used in the world.
A bismuth-zinc primary battery has also been proposed (see, for example, Patent Document 1).

Furthermore, a zinc storage battery has been developed as a rechargeable water-based storage battery that does not spread fire, and an alkaline storage battery using a nickel positive electrode is being studied (see Patent Documents 2 and 3, for example).

Also, a bipolar nickel-metal hydride battery has been developed as a long-life and safe battery (see, for example, Patent Document 4), and is already used in hybrid vehicles and the like.

Japanese Patent Publication No. 2009-543313 Japanese Patent Publication No. 2008-539559 JP 2017-182996 A JP 2018-28982 A

When a nickel positive electrode is used, a water electrolysis reaction (oxygen generation reaction) occurs at the end of charging. If an oxygen-producing reaction occurs in the positive electrode, there is a risk that the amount of charge will be inconsistent between the positive electrode and the negative electrode, or that the generated oxygen will cause the electrolyte to leak. In a conventional alkaline storage battery using a nickel positive electrode, it was necessary to take measures such as providing a mechanism for absorbing the generated oxygen or limiting the amount of charge so as not to generate oxygen.
A bipolar electrode using nickel as a positive electrode active material also has the problem of generating oxygen.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for sufficiently preventing oxygen generation in a positive electrode for a storage battery.

The present inventors have studied various methods for sufficiently preventing oxygen generation in the positive electrode for storage batteries, and found that bismuth, which is a sufficiently base potential (about 0.7 V) than the oxygen generation potential for zinc (about 1.8 V) It was found that the electrolysis reaction of water can be sufficiently suppressed by using a positive electrode for a storage battery in which is the main component of the active material. In addition, the inventors of the present invention have found that the positive electrode for a storage battery has a very flat potential curve during charging, and the amount of change in voltage (voltage between the terminals, which is the voltage between the positive electrode and the negative electrode) due to temperature changes etc. is sufficiently small, and the voltage rises sharply when the charging reaction of bismuth is completed. It has been found that charging can be easily stopped before charging. Furthermore, the present inventors found that oxygen generation can be sufficiently prevented in a bipolar electrode by using bismuth species as the positive electrode active material, and conceived that the above problems can be solved successfully. have arrived at the present invention.

That is, the present invention is a positive electrode for use in a storage battery, characterized in that the positive electrode contains an active material containing 50% by mass or more of bismuth.
The present invention is also a bipolar electrode characterized by comprising a cathode active material containing bismuth species.

ADVANTAGE OF THE INVENTION According to the positive electrode or bipolar electrode for storage batteries of this invention, oxygen generation at the time of charge can be fully prevented, and charge can be stopped stably.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which illustrates the structure of the bismuth zinc storage battery comprised using the positive electrode for storage batteries of this invention. 4 is a graph showing initial discharge capacity in one embodiment of the bismuth-zinc storage battery of the present invention. 1 is a graph showing terminal voltage versus charge/discharge capacity in an embodiment of a bismuth-zinc storage battery of the present invention. 1 is a graph showing terminal voltage versus charge/discharge capacity in an embodiment of a bismuth-zinc storage battery of the present invention. FIG. 3 is a schematic diagram illustrating the configuration of a laminate of bipolar electrodes according to the present invention. FIG. 4 is a schematic diagram showing a case where a short circuit occurs in the laminate of the present invention; 1 is a schematic diagram illustrating the configuration of a bipolar electrode of the present invention; FIG. FIG. 3 is a schematic diagram illustrating the configuration of a laminate of bipolar electrodes according to the present invention. 4 is a graph showing discharge voltage versus discharge capacity in one embodiment of the bipolar storage battery of the present invention. 1 is a schematic diagram illustrating the configuration of a bipolar electrode of the present invention; FIG. FIG. 3 is a schematic diagram illustrating the configuration of a laminate of bipolar electrodes according to the present invention. 4 is a graph showing discharge voltage versus discharge capacity in one embodiment of the bipolar storage battery of the present invention.

The present invention will be described in detail below.
A combination of two or more of the individual aspects of the present invention described below is also an aspect of the present invention.

(Positive electrode for storage battery)
The positive electrode for a storage battery of the present invention contains an active material containing 50% by mass or more of bismuth. In other words, the positive electrode for a storage battery of the present invention contains, as an active material, a compound containing 50% by mass or more of bismuth. The mass ratio of bismuth in the active material refers to the mass ratio of the bismuth element in the compound that is the active material, and this is 50% by mass or more. Also called For example, bismuth oxide (Bi ₂ O ₃ ), which is the active material, has a molecular weight of 465.96 (208.98×2+16.00×3), and the mass ratio of bismuth in the active material is 89.7% by mass ({ (208.98*2)/465.96}*100). In addition, the simple substance of bismuth, which is the active material, has a bismuth mass ratio of 100% by mass in the active material, and is also an active material having a bismuth mass ratio of 50% by mass or more.
The mass ratio of bismuth in the active material is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. Moreover, the upper limit of the mass ratio of bismuth in the active material is not particularly limited, and may be 100% by mass.
The mass ratio of the active material in which the mass ratio of bismuth is specified as described above is preferably 50% by mass or more with respect to the total amount of the active material contained in the positive electrode for a storage battery of the present invention. The upper limit of the mass ratio of the active material is not particularly limited, and may be 100% by mass.

Moreover, it is preferable that the mass ratio of bismuth to the total amount of active materials contained in the positive electrode for a storage battery of the present invention is 50% by mass or more.
One preferred embodiment of the positive electrode for storage battery of the present invention is a positive electrode for storage battery in which the mass ratio of bismuth to the total amount of active materials contained in the positive electrode for storage battery is 50% by mass or more.
If the active material also functions as a conductive aid, it is included in the active material instead of the conductive aid.
The mass ratio of bismuth is more preferably 60% by mass or more, more preferably 80% by mass or more, relative to the total amount of the active materials.
The mass ratio of bismuth is preferably 100% by mass or less, more preferably 99% by mass or less, relative to the total amount of the active materials.
In this specification, the mass ratio of bismuth to the total amount of the active material is measured by fluorescent X-ray analysis of the active material.

Examples of the active material include bismuth alone, bismuth oxide, and composite metal oxides containing a bismuth element and at least one other metal element. The active material may further contain an active material containing no bismuth element, but the content of the active material containing no bismuth element in the active material is preferably 10% by mass or less, % or less, and even more preferably 0.1 mass % or less. Moreover, it is particularly preferable that the active material does not substantially contain an active material that does not contain a bismuth element.

The active material preferably has an average particle size of 1 nm to 50 μm. It is more preferably 10 nm to 10 μm, still more preferably 30 nm to 5 μm, and particularly preferably 100 nm to 1 μm.
The average particle size is an average particle size in a volume-based particle size distribution obtained by particle size distribution measurement using a dynamic light scattering method.
As the particle size distribution measuring device by the dynamic light scattering method, a concentrated particle size analyzer FPAR-1000AS manufactured by Otsuka Electronics Co., Ltd. is used. A measurement sample is obtained by diluting the measurement target with a dispersion medium (ion-exchanged water containing 0.2% sodium hexametaphosphate).

The mass ratio of the active material is 10 to 99% by mass with respect to 100% by mass of the total solid content of the active material, water retention component, polymer, and conductive aid contained in the positive electrode for storage battery. is preferred. The mass ratio of the active material is more preferably 20 to 97 mass %, still more preferably 30 to 95 mass %, and particularly preferably 40 to 93 mass %.
When the positive electrode for a storage battery of the present invention does not contain any one or more of the water retention component, the polymer, and the conductive aid, the total content is the content excluding the components not included.

The positive electrode for a storage battery of the present invention preferably further contains a water-retaining component.
The water-retaining component is a component that retains water necessary for electrode reaction in the vicinity of the active material. It is preferably composed of a material that allows moisture to be taken in and out as necessary.
For example, the electrochemical reaction of bismuth is as shown in the following formula (1), and when water is consumed during the charging reaction of a positive electrode for a storage battery or a bipolar electrode, the water retaining component retains this water and supplies it to the charging reaction. It is something that can be done.
Bi ₂ O ₃ +3H ₂ O+6e ⁻ ⇔ 2Bi+6OH ⁻ (1)
Clay minerals such as silicic acid, silica gel, and zeolite; natural fibers such as cotton and hemp; water-retaining polymers such as polyamide, polyimide, polyvinyl alcohol, and polyacrylic acid (salts); sugars; ² /g or more carbon materials, etc., and one or more of these can be used.
Since the positive electrode for storage battery of the present invention further contains a water-retaining component, it becomes unnecessary to additionally dispose a water-retaining polymer film on the positive electrode side for storage battery of the separator in order to supply water to the charging reaction in the positive electrode for storage battery. It is also possible to sufficiently shorten the distance between the electrodes and reduce the internal resistance of the storage battery.

Above all, the water-retaining component in the positive electrode for storage battery of the present invention is preferably a carbon material having a specific surface area of 100 m ² /g or more. In the conventional nickel positive electrode containing nickel as the main component of the active material, the oxidative decomposition of the carbon material could not be sufficiently suppressed. By including it as a component, oxidative decomposition of the carbon material can be sufficiently suppressed.
The carbon material having a specific surface area of 100 m ² /g or more is not particularly limited, but preferred examples include activated carbon, carbon black, and carbon treated to be hydrophilic by introducing an oxygen-containing functional group. It is one of the preferred embodiments of the present invention.
When activated carbon or other carbon material having a specific surface area of 100 m ² /g or more is introduced into the positive electrode for a storage battery, it is possible to secure water retention and obtain an electric double layer capacity by the charge-discharge reaction of the carbon material. The output performance of the storage battery can be improved by temporarily storing in this electric double layer a high input/output current that cannot keep up with the reaction of bismuth in the battery.
It is also one of preferred embodiments of the present invention that the water-retaining component is a water-retaining component other than the above-described carbon material having a specific surface area of 100 m ² /g or more. When the electric double layer capacity cannot be obtained, the voltage rises more rapidly when the charging reaction of bismuth is completed. Therefore, it is possible to further prevent the charge amount from fluctuating at each charge depending on the timing of stopping charging. can.
Among carbon materials that are water-retaining components, those having a graphite structure also work as conductive carbon.

The water-retaining component (preferably carbon material) preferably has a specific surface area of 200 m ² /g or more, more preferably 300 m ² /g or more, and even more preferably 400 m ² /g or more.
Although the upper limit of the specific surface area is not particularly limited, it is usually 2600 m ² /g or less, preferably 1000 m ² /g or less.
The specific surface area is measured by the nitrogen adsorption BET method with a specific surface area measuring device.

The mass ratio of the water retention component is 0.1 to 80% by mass with respect to 100% by mass of the total solid content of each solid content of the active material, water retention component, polymer, and conductive aid contained in the positive electrode for storage battery. Preferably. The mass ratio of the water-retaining component is more preferably 0.3 to 70% by mass, still more preferably 0.5 to 60% by mass, and particularly preferably 1 to 50% by mass.
In addition, in this specification, the above water-retaining component refers to a substance other than the active material.

The positive electrode for storage battery of the present invention preferably further contains a polymer.
Examples of the above polymers include hydrocarbon moiety-containing polymers such as polyethylene and polypropylene; aromatic group-containing polymers such as polystyrene; ether group-containing polymers such as alkylene glycol; halogen-containing polymers such as polyvinyl chloride, polyvinylidene fluoride, and polytetrafluoroethylene. Polymer; Epoxy resin; Sulfonate-containing polymer; Quaternary ammonium salt or quaternary phosphonium salt-containing polymer; Ion-exchange polymer used for cation/anion exchange membranes; carbamate group site-containing polymer; carbamide group site-containing polymer; epoxy group site-containing polymer; heterocyclic and/or ionized heterocyclic site-containing polymer; One or more of these can be used. These polymers act as a binder for the active material of the positive electrode for storage batteries, and can prevent the occurrence of cracks.

Among others, the polymer is preferably a conjugated diene polymer.
Examples of the conjugated diene-based polymer include styrene-butadiene-based polymer (SBR), carboxy-modified styrene-butadiene-based polymer, polybutadiene-based polymer, carboxy-modified polybutadiene-based polymer, polyisoprene-based polymer, carboxy-modified polyisoprene-based polymer, acrylonitrile-butadiene. One or two or more of carboxy-modified acrylonitrile-butadiene-based polymers and the like can be suitably used. Among these, styrene-butadiene-based polymers and carboxy-modified styrene-butadiene-based polymers are preferred, and carboxy-modified styrene-butadiene-based polymers are particularly preferred.

The conjugated diene-based polymer includes monomer units derived from an aliphatic conjugated diene-based monomer, monomer units derived from an aromatic vinyl monomer, and monomer units derived from an unsaturated monomer having a carboxy group and/or a carboxylate group that is a salt thereof. , may have monomer units derived from other unsaturated monomers.
In 100% by mass of the conjugated diene-based polymer, the mass ratio of monomer units derived from other unsaturated monomers is preferably 30% by mass or less, more preferably 5% by mass or less, and 0.1% by mass. More preferably:

Polymers are radical polymerization, radical (alternating) copolymerization, anionic polymerization, anionic (alternating) copolymerization, cationic polymerization, cationic (alternating) copolymerization, graft polymerization, graft (alternating) copolymerization from monomers corresponding to their constituent units. , living polymerization, living (alternating) copolymerization, dispersion polymerization, emulsion polymerization, suspension polymerization, ring-opening polymerization, cyclization polymerization, polymerization by irradiation with light, ultraviolet rays or electron beams, metathesis polymerization, electrolytic polymerization, etc. . When these polymers have functional groups, they may have them on the main chain and/or side chains, and may exist as bonding sites with the cross-linking agent. One type of these polymers may be used, or two or more types may be used.
The polymer may be crosslinked.

The polymer preferably has a weight average molecular weight of 200 to 7,000,000. The weight average molecular weight of the polymer is more preferably 1,000 to 2,000,000, still more preferably 5,000 to 800,000.
The weight average molecular weight can be measured as a polystyrene-equivalent weight average molecular weight by gel permeation chromatography (GPC) under the following conditions.
Apparatus: HCL-8220GPC manufactured by Tosoh Corporation
Column: TSKgel Super AWM-H
Eluent (LiBr.H ₂ O, NMP with phosphoric acid): 0.01 mol/L

The mass ratio of the polymer is 0.1 to 30% by mass with respect to 100% by mass of the total solid content of each solid content of the active material, water retention component, polymer, and conductive aid contained in the positive electrode for storage battery. is preferred. The mass ratio of the polymer is more preferably 0.3 to 15% by mass, still more preferably 0.5 to 10% by mass, and particularly preferably 0.5 to 5% by mass.
In addition, in this specification, the above-mentioned polymer refers to anything other than the active material and the water-retaining component.

The positive electrode for a storage battery of the present invention preferably further contains a conductive aid.
Examples of conductive aids include conductive carbon, conductive ceramics, metals and metal compounds such as copper, brass, nickel, silver, indium, lead, tin, cobalt, etc. One or more of these can be used. Since the positive electrode for storage battery of the present invention contains a conductive agent, the conductive performance of the positive electrode for storage battery is improved, and the active material contained in the positive electrode for storage battery is effectively used to further increase the capacity of the storage battery.
Among them, it is preferable that the conductive aid is conductive carbon and/or cobalt species.
The above-mentioned conductive carbon is a carbon material that can impart conductivity by mixing the carbon material, and the sheet resistance of the carbon layer formed by coating the carbon material alone on an insulating substrate is 10 ⁶ . A carbon material with a resistance of Ωcm or less.
Examples of the conductive carbon include graphite such as natural graphite and artificial graphite, glassy carbon, graphitizable carbon, non-graphitizable carbon, graphene, nanographene, graphene nanoribbon, carbon black, graphitized carbon black, Ketjenblack, Vapor-grown carbon fiber, pitch-based carbon fiber, mesocarbon microbeads, metal-coated carbon, carbon-coated metal, fibrous carbon, multi-/single-wall carbon nanotube, carbon nanohorn, vulcan, acetylene black, SiC-coated carbon, Examples include carbon surface-treated by dispersion, emulsification, suspension, microsuspension polymerization, microcapsule carbon, and the like, and one or more of these can be used.
Among them, natural graphite, graphite such as artificial graphite, graphitizable carbon, non-graphitizable carbon, graphene, carbon black, graphitized carbon black, Ketjen black, vapor growth carbon fiber, pitch-based carbon fiber, mesocarbon microbeads , fibrous carbon, multi-/single-wall carbon nanotubes, vulcan, and acetylene black.

Examples of the cobalt species include cobalt alone (metallic cobalt) and cobalt-containing compounds such as cobalt oxide and cobalt hydroxide, and one or more of these can be used.

Some metals that function as conductive aids also function as active materials. In addition, conductive carbon also acts as a water retention component when the specific surface area is 100 m ² /g or more.
In this specification, the conductive aid refers to anything other than the active material, water-retaining component, and polymer described above.

The mass ratio of the conductive aid is 0.1 to 30% by mass with respect to 100% by mass of the total solid content of the active material, polymer, water retention component, and conductive aid contained in the positive electrode for storage battery. is preferably The mass ratio of the conductive aid is more preferably 0.3 to 20% by mass, still more preferably 0.5 to 15% by mass, and particularly preferably 1 to 10% by mass.

The positive electrode for a storage battery of the present invention may contain the active material described above, and if necessary, an active material layer containing a polymer, a water-retaining component, a conductive aid, and other components, and a current collector. When the positive electrode for a storage battery of the present invention includes the active material layer and a current collector, even if the current collector is impregnated with the active material or the like, and at least a part of the active material layer is impregnated with the current collector. good.

Examples of the current collector include (electrolytic) copper foil, copper mesh (expanded metal), foamed copper, punched copper, copper alloys such as brass, brass foil, brass mesh (expanded metal), foamed brass, punched brass, and nickel foil. , corrosion-resistant nickel, nickel mesh (expanded metal), punching nickel, metallic zinc, corrosion-resistant metallic zinc, zinc foil, zinc mesh (expanded metal), (punched) steel plate, nonwoven fabric with conductivity; Ni Zn Sn Pb・Hg, Bi, In, Tl, brass, etc. added (electrolytic) copper foil ・Copper mesh (expanded metal) ・Foamed copper ・Punched copper ・Copper alloys such as brass ・Brass foil ・Brass mesh (expanded metal) ・Foam Brass, punched brass, nickel foil, corrosion-resistant nickel, nickel mesh (expanded metal), punched nickel, metallic zinc, corrosion-resistant metallic zinc, zinc foil, zinc mesh (expanded metal), (punched) steel plate, nonwoven fabric; Ni, Zn, Sn・(Electrolytic) copper foil plated with Pb, Hg, Bi, In, Tl, brass, etc. ・Copper mesh (expanded metal) ・Foamed copper ・Punched copper ・Copper alloys such as brass ・Brass foil ・Brass mesh (expanded metal) ), foamed brass, perforated brass, nickel foil, corrosion-resistant nickel, nickel mesh (expanded metal), punched nickel, metallic zinc, corrosion-resistant metallic zinc, zinc foil, zinc mesh (expanded metal), (punched) steel plate, non-woven fabric; silver; Examples include materials used as current collectors and containers in storage batteries.

The positive electrode for a storage battery of the present invention can be obtained by, for example, adding an active material, a water-retaining component, a conductive aid, a polymer, a solvent, etc. to form a slurry, applying the slurry to a current collector, and drying it. It can also be press-molded into pellets.
The positive electrode for a storage battery of the present invention can be used for various types of storage batteries using a bismuth positive electrode, but it is preferably used for a bismuth-zinc storage battery.

(bismuth-zinc storage battery)
The present invention also provides a bismuth-zinc storage battery comprising the positive electrode for a storage battery of the present invention, a negative electrode containing a zinc species, and a separator. In addition, below, the positive electrode for storage batteries of this invention is only called a positive electrode.

<Negative Electrode Containing Zinc Species>
The negative electrode contains a zinc species as an active material, and usually contains zinc alone.
The negative electrode preferably further contains a zinc-containing compound other than simple zinc as an active material. Thereby, the life performance of the bismuth-zinc storage battery can be further improved.
The zinc-containing compound may be any compound that can be used as a negative electrode active material.・Zinc sulfide ・Tetrahydroxy zinc alkali metal salt ・Tetrahydroxy zinc alkaline earth metal salt ・Zinc halogen compound ・Zinc carboxylate compound ・Zinc alloy ・Zinc solid solution ・Zinc borate ・Zinc phosphate ・Zinc hydrogen phosphate ・Silicate Zinc containing at least one element selected from the group consisting of elements belonging to Groups 1 to 17 of the periodic table represented by zinc, zinc aluminate, carbonate compounds, hydrogen carbonate compounds, nitrate compounds, sulfate compounds, etc. (alloy) compounds, organic zinc compounds, zinc compound salts, etc., and one or more of these can be used.
Among the zinc-containing compounds, zinc oxide is preferred.

In the negative electrode, the active material layer may be formed by laminating a layer composed of zinc alone and a layer composed of a zinc-containing compound. Here, it is preferable that the layer composed of zinc alone is arranged on the current collector side of the negative electrode, and the layer composed of the zinc-containing compound is arranged on the separator side. Among them, it is more preferable that the layer composed of simple zinc is in contact with the current collector of the negative electrode, and the layer composed of the zinc-containing compound is in contact with the separator.

The mass ratio of zinc alone and the zinc-containing compound in the negative electrode is preferably 1:99 to 100:0, more preferably 2:98 to 80:20, and 3:97 to 50:50. is more preferred, 5:95 to 35:65 is even more preferred, and 8:92 to 25:75 is particularly preferred.

It is preferable that the zinc simple substance has an average particle size of 10 nm to 500 μm. It is more preferably 100 nm to 400 μm, still more preferably 500 nm to 200 μm, and particularly preferably 1 μm to 100 μm.
The zinc-containing compound preferably has an average particle size of 1 nm to 50 μm. It is more preferably 10 nm to 10 μm, still more preferably 30 nm to 5 μm, and particularly preferably 100 nm to 1 μm.
The method for measuring the average particle size of the elemental zinc and the zinc-containing compound is the same as the method for measuring the average particle size of the active material contained in the positive electrode for storage battery.

The negative electrode may further contain a polymer. This can prevent cracks in the negative electrode. As the polymer, the same water-retaining polymer and other polymers as those in the positive electrode can be used. For example, at least one selected from the group consisting of halogen atoms, carboxylic acid (salt) groups, hydroxyl groups, and ether groups. Polymers containing seeds are also preferred.

The mass ratio of the zinc species is preferably 50 to 99.9 mass % with respect to the total 100 mass % of the zinc species and polymer (solid content) contained in the negative electrode. When the ratio of the active material is within such a range, the negative electrode has a more sufficient battery capacity. The proportion of the zinc species is more preferably 55-99.5% by weight, more preferably 60-99% by weight.
The negative electrode may contain other components such as a conductive aid together with the zinc species and the polymer. The negative electrode may include, for example, an active material layer containing the zinc species, polymer, and other components such as a conductive aid, and a current collector. As the current collector, the same current collector as described above in the positive electrode for storage battery of the present invention can be used. When the negative electrode includes an active material layer and a current collector, the current collector may be impregnated with the active material, and at least a part of the active material layer may be impregnated with the current collector.
In the bipolar electrode described later, the positive electrode active material (layer) and the negative electrode active material (layer) usually share a current collector, and the positive electrode active material (layer) is on one side of the current collector. A negative electrode active material (layer) is disposed on the surface opposite to the surface.

<Separator>
The separator is a member that secures ionic conductivity between the positive electrode and the negative electrode while isolating the positive electrode and the negative electrode described above. Among them, a separator capable of preventing a short circuit due to dendrite derived from the negative electrode is preferable.
For example, the separator in the bismuth-zinc storage battery of the present invention preferably contains a polymer and inorganic particles, in other words, it contains a composite membrane (also referred to as an organic-inorganic composite membrane or anion-conductive membrane) containing a polymer and inorganic particles. is one of the preferred embodiments of the present invention. More preferably, it is a composite membrane containing a certain proportion or more of the polymer and the inorganic particles and containing less than a certain proportion of the binder component.

The composite film containing the polymer and inorganic particles has excellent durability due to its configuration, and in particular, when used as a separator in the bismuth-zinc storage battery of the present invention, which includes a zinc negative electrode that undergoes morphological changes during charging and discharging. , when using the bismuth-zinc storage battery of the present invention, the polymer will limit the substantial amount of electrolyte in the composite membrane, and free active material-derived ions in the composite membrane (e.g., zincate ions ) Since the concentration is low, the growth of dendrites generated in the process of the dissolution and deposition reaction of the active material component (for example, zinc component) can be further suppressed, and the life of the bismuth-zinc storage battery can be extended. . In addition, since the composite film contains inorganic particles, the surface of the inorganic particles serves as an ion-conducting path. It is possible to sufficiently prevent the part from being buried, and to make the ionic conductivity of the composite membrane sufficiently high. By making the ionic conductivity inside the bismuth-zinc storage battery sufficiently high and providing a storage battery with low internal resistance, the bismuth-zinc storage battery can be appropriately driven, contributing to longer life. When the polymer is in the form of particles rather than fibrous particles having a small specific surface area, the above performance can be exhibited more remarkably. Similarly, the particle shape of the inorganic particles can make the ionic conductivity of the composite membrane very excellent.

The polymer/(inorganic particles and binder component) volume ratio is preferably more than 20/80, more preferably 25/75 or more, and even more preferably 37/63 or more. The volume ratio of the polymer/(inorganic particles and binder component) is preferably less than 80/20, more preferably 70/30 or less.
The inorganic particles/(polymer and binder component) volume ratio is preferably more than 20/80, more preferably 30/70 or more. The inorganic particles/(polymer and binder component) volume ratio is preferably less than 80/20, more preferably 75/25 or less, and even more preferably 63/37 or less.
The binder component/(polymer and inorganic particles) volume ratio is preferably less than 30/70, more preferably 20/80 or less, and even more preferably 10/90 or less. The binder component is an optional component, and the lower limit of the volume ratio of the binder component/(polymer and inorganic particles) is preferably 0/100, more preferably 0.1/99.9. , and more preferably 1/99.

In the following, the polymer, the inorganic particles, the optional binder component, etc. contained in the composite film will be described in order.

〔polymer〕
The polymer usually refers to a component having a glass transition temperature of 60° C. or higher.
In this specification, the glass transition temperature is obtained by applying a material such as a polymer to a glass plate and drying it at 120 ° C. for 1 hour. ).

As the polymer, conventionally known various polymers can be used, and they may be either thermoplastic or thermosetting. Among them, halogen-containing ethylene-based polymers and/or polysulfone-based polymers are preferred.

The halogen-containing ethylene-based polymer has a structure in which at least some of the hydrogen atoms in polyethylene are substituted with halogen atoms, and among others, a fluorine-containing structure in which at least some of the hydrogen atoms in polyethylene are substituted with fluorine atoms. It is preferably an atomic ethylene-based polymer, and suitable examples thereof include polyvinylidene fluoride and polytetrafluoroethylene.
The above polysulfone-based polymer refers to a polymer having a sulfonyl group as a repeating unit, and includes, for example, polysulfone (PSU), polyethersulfone (PESU), and polyphenylsulfone (PSSU).
The polyether ketone is a polymer having an ether bond and a ketone bond, and examples thereof include polyether ketone ketone and polyether ether ketone.

The above polymer can be produced, for example, by copolymerizing monomer components forming structural units contained in the polymer in the presence of a radical generator, and optionally graft-modifying the polymer.
The polymerization method of the monomer component is not particularly limited, and examples thereof include aqueous solution polymerization method, emulsion polymerization method, reverse phase suspension polymerization method, suspension polymerization method, solution polymerization method, bulk polymerization method and the like.

The shape of the polymer is preferably a particle shape, and more specifically, fine powder, powder, granules, granules, flakes, polyhedrons, rods, curved surfaces, and the like.
The polymer preferably has an average particle size of 50 nm or more. The average particle size is more preferably 100 nm or more, even more preferably 200 nm or more. Also, the average particle size is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 10 μm or less.
The average particle size is the average particle size in volume-based particle size distribution. ], trade name: NICOMP Model 380).

The polymer preferably has an aspect ratio (length/width) of 1 or more. Also, the aspect ratio (vertical/horizontal) is preferably 8 or less. The aspect ratio (length/width) is more preferably 5 or less, still more preferably 2 or less, and particularly preferably 1.5 or less.
The aspect ratio (vertical/horizontal) can be obtained from the shape of the particles observed by SEM. For example, when the polymer has a rectangular parallelepiped shape, the length can be obtained by dividing the length by the width, with the longest side being the length and the second longest side being the width. In the case of other shapes, a point in the two-dimensional shape formed by placing a part on the bottom surface with the largest aspect ratio and projecting it from the direction with the largest aspect ratio Measure the length of one point farthest from the point, take the longest length as the length, and the shortest length of a straight line passing through the center of the length as the width, and divide the length by the length of the width. be able to.
Particles having an aspect ratio (vertical/horizontal) in the range described above can be produced by, for example, selecting particles having such an aspect ratio, or by optimizing preparation conditions at the stage of producing particles. It can be obtained by a selective obtaining method or the like.

[Inorganic particles]
In this specification, inorganic particles are usually inorganic compound particles that do not have a glass transition temperature. The inorganic particles may be, for example, particles whose entire particles are composed of an inorganic compound, or particles whose surfaces are coated with an inorganic compound.

In the following, first, particles whose entire particles are composed of an inorganic compound will be mainly described, but the same applies to the inorganic compound portion of particles whose surfaces are coated with an inorganic compound.
Various inorganic compounds can be used as the inorganic compound constituting the inorganic particles. For example, at least One type is preferred. In the present specification, hydroxide refers to a compound having a hydroxy group, other than a layered double hydroxide.

Examples of the oxides include lithium oxide, sodium oxide, potassium oxide, magnesium oxide, calcium oxide, barium oxide, scandium oxide, yttrium oxide, lanthanide oxide, titanium oxide, zirconium oxide, niobium oxide, ruthenium oxide, nickel oxide, palladium oxide, copper oxide, cadmium oxide, boron oxide, aluminum oxide, gallium oxide, indium oxide, thallium oxide, silicon oxide, germanium oxide, tin oxide, lead oxide, phosphorus oxide, bismuth oxide, etc., and one of these Or 2 or more types can be used. Among them, those that are stable even in a dispersion liquid during film formation or in a storage battery under alkaline conditions are preferable. Zirconium oxide is more preferred. The zirconium oxide may be one in which an element such as yttrium, scandium, or ytterbium is dissolved, or may have oxygen defects.

Examples of the hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, scandium hydroxide, yttrium hydroxide, lanthanide hydroxide, titanium hydroxide, water Zirconium oxide, niobium hydroxide, ruthenium hydroxide, nickel hydroxide, palladium hydroxide, copper hydroxide, cadmium hydroxide, boric acid, aluminum hydroxide, gallium hydroxide, indium hydroxide, thallium hydroxide, silicic acid, water Germanium oxide, tin hydroxide, lead hydroxide, phosphoric acid, bismuth hydroxide and the like can be mentioned, and one or more of these can be used. Among them, those having low solubility under alkaline conditions are preferable, and for example, magnesium hydroxide, calcium hydroxide, titanium hydroxide, and zirconium hydroxide are preferable, and magnesium hydroxide is more preferable.

The above layered double hydroxide has the following general formula:
[M ¹ _1-x M ² _x (OH) ₂ ](A ⁿ⁻ ) _x/n ·mH ₂ O
( ^M1 represents a divalent metal ion that is any of Mg, Fe, Zn, Ca, Li, Ni, Co, Cu, Mn; ^M2 represents Al, Fe, Mn, Co, Cr, In Represents a trivalent metal ion that is any ^{A n-} represents an anion having a valence of 1 or more and 3 or less, such as Cl ⁻ , NO ₃ ⁻ , CO ₃ ²⁻ , COO ^{− ,} etc. Among them, A ⁿ⁻ is , preferably represents a divalent or less anion, m is a number of 0 or more, n is a number of 1 or more and 3 or less, and x is a number of 0.20 or more and 0.40 or less.) Examples of such layered double hydroxides include hydrotalcite, manassite, motucoleite, stichtite, shoglenite, barbertite, pyroaurite, iomite, chloromagarminite, hydro Calmite, Green Rust 1, Bercherin, Takovite, Liebesite, Honesite, Yeardrite, Meikisenerite and the like can be mentioned, and one or more of these can be used. Among them, hydrotalcite in which ^M1 is Mg and ^M2 is Al in the above general formula is preferable because it is easy to use industrially.
These layered double hydroxides are, for example, compounds dehydrated by firing at 150 ° C. or higher and 900 ° C. or lower, compounds in which anions in the layers are decomposed, anions in the layers to hydroxide ions, etc. It may be a compound exchanged with
A compound having a functional group such as a hydroxyl group, an amino group, a carboxy group, or a silanol group may be coordinated to the layered double hydroxide. Further, the layered double hydroxide may contain an organic substance between the layers.

Examples of the phosphate compound include hydroxyapatite (Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ ), magnesium hydroxyapatite in which part or all of the calcium ions of hydroxyapatite are replaced with magnesium, and strontium hydroxyapatite in which some or all of the calcium ions of hydroxyapatite are replaced with strontium. , barium hydroxyapatite substituted with barium, and the like. Among them, hydroxyapatite and magnesium hydroxyapatite are preferred.

The above inorganic compound is preferably a magnesium-containing compound among others. Moreover, the inorganic compound is preferably a hydroxide, a layered double hydroxide, or a phosphoric acid compound, and more preferably a layered double hydroxide and/or a hydroxide. The inorganic compound is more preferably a hydroxide from the viewpoint of improving the strength of the separator, and a layered double hydroxide from the viewpoint of improving the ionic conductivity of the separator. , and magnesium hydroxide are more preferable, and from the viewpoint of improving the durability of the separator, magnesium hydroxide is particularly preferable.

Examples of the shape of the inorganic particles include fine powder, powder, granular, granular, scaly, polyhedral, rod-like, and curved surface-containing shapes.
The inorganic particles preferably have an average particle size of 2 μm or less. The average particle size is more preferably 1 μm or less, and still more preferably 0.5 μm or less. Also, the average particle size is preferably 0.001 μm or more, more preferably 10 nm or more, and even more preferably 100 nm or more.
The average particle size is the average particle size in the volume-based particle size distribution, and the inorganic particles are diluted with a dispersion medium (ion-exchanged water containing 0.2% sodium hexametaphosphate). The particles are collected in a glass cell and measured using a particle size distribution analyzer (manufactured by Particle Sizing Systems, trade name: NICOMP Model 380) by the dynamic light scattering method.

Particles having a volume-average particle size in the above range can be obtained, for example, by pulverizing the particles with a ball mill or the like, dispersing the obtained coarse particles in a dispersant to obtain a desired particle size, and then drying and solidifying. , In addition to the method of screening the coarse particles by sieving, etc., it is possible to obtain (nano)particles with the desired particle size by optimizing the preparation conditions at the stage of producing particles. .

The inorganic particles may have an aspect ratio (vertical/horizontal) of 1 or more. Also, the aspect ratio (vertical/horizontal) is preferably 8 or less. The aspect ratio (length/width) is more preferably 5 or less, still more preferably 2 or less, and particularly preferably 1.5 or less.
The method for obtaining the aspect ratio (vertical/horizontal) is as described above.
Particles having an aspect ratio (length/width) in the above range can be obtained by the method described above.

As described above, it is a preferred embodiment of the present invention that the separator includes a composite membrane (anion conductive membrane) containing a polymer and inorganic particles.

As used herein, the anion-conducting membrane refers to a membrane that is permeable to anions such as hydroxide ions that participate in the reaction of a bismuth-zinc battery and that includes a polymer and inorganic particles. The anion conductive membrane has selectivity of permeating anions due to the action of inorganic particles and the like. The selectivity of the anions is such that anions such as hydroxide ions are easily permeable, and metal-containing ions (for example, Zn(OH) ₄ ²⁻ ) derived from the active material and having a large ionic radius even for anions Such permeation is sufficiently prevented. In the present specification, anion conductivity means sufficient permeation of anions having a small ionic radius such as hydroxide ions, or permeation performance of the anions. Anions having a large ionic radius, such as metal-containing ions, are more difficult to permeate, and may not be permeated at all.

[Binding component]
The separator may further contain a binding component. The binding component usually refers to a component having a glass transition temperature of less than 60° C., and can contribute to the structural stability of the separator by binding between particles. The binder component preferably has a glass transition temperature of 50° C. or lower.
Also, the binder component is preferably non-particulate.
Further, the binding component preferably binds with other surrounding components (polymer, inorganic particles, porous support, etc.).

The binder component is preferably an amorphous binder polymer having a glass transition temperature of less than 60°C. By being non-crystalline, it is easy to form a bond with surrounding members and functions favorably as a binding component. The binder polymer is preferably fibrous.
Examples of the binder polymer include conjugated diene-based polymers and (meth)acrylic-based polymers, and among them, conjugated diene-based polymers are preferable.

The conjugated diene-based polymer has a monomer unit derived from a conjugated diene-based monomer.
As the conjugated diene-based polymer, the same conjugated diene-based polymer as described above in the positive electrode for storage battery of the present invention can be suitably used.

The (meth)acrylic polymer may have monomer units derived from a monomer having a (meth)acryloyl group. (Meth)acrylic acid ester-based polymer.

Mainly composed of monomer units derived from (meth)acrylic acid ester monomer means that the content of monomer units derived from (meth)acrylic acid ester monomer is 50% by mass or more in 100% by mass of (meth)acrylic acid ester polymer. Say something.
(Meth) acrylic acid ester monomers, specifically, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate , t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, (meth)acrylate nonyl acrylate, decyl (meth)acrylate and the like.

The (meth)acrylic polymer includes, in addition to monomer units derived from (meth)acrylic acid ester monomers, monomer units derived from unsaturated monomers having a carboxy group and/or a carboxylate group which is a salt thereof, and other unsaturated monomers. It may have a monomer unit derived from a monomer.
In 100% by mass of the (meth)acrylic polymer, the mass ratio of monomer units derived from other unsaturated monomers is preferably 30% by mass or less, more preferably 5% by mass or less, and 0.1 % by mass or less is more preferable.

The binder polymer is preferably fibrous as described above, and may be fibrillated by heat, pressure, or the like. By making the polymer fiber, the strength, anion conductivity, etc. of the separator can be suitably adjusted.

[Porous support]
The composite membrane further has a porous support (porous substrate) made of a polyolefin polymer or the like, and the porous support is impregnated with a mixture of the polymer, inorganic particles, and, if necessary, a binding component. It may be a resin-impregnated layer, or a layered structure obtained by bringing the mixture into contact with a porous substrate and drying the mixture as necessary.

The porous support is not particularly limited, but examples thereof include polyethylene, polypropylene, ethylene-propylene copolymers, polyolefin-based polymers such as cyclic polyolefin-based polymers; polyvinyl alcohol-based polymers such as vinylon; aliphatic polyamides; aromatic polyamides; Non-woven fabrics, woven fabrics, microporous films, etc. made of resin materials such as styrene-based polymers, polyester-based polymers, and polyphenylene sulfide-based polymers are preferred. Among them, polyolefin-based polymers and polyvinyl alcohol-based polymers are more preferred. preferable.
The composite membrane is, for example, at least partially integrated with a resin-impregnated layer obtained by impregnating a porous support with the above mixture and a porous support. In the composite membrane, the solid content of the mixture fills at least part of the pores in the porous support.

When the composite membrane contains the porous support, the mass ratio of the porous support is preferably 5% by mass or more, more preferably 10% by mass or more, in 100% by mass of the composite membrane. It is preferably 15% by mass or more, and more preferably 15% by mass or more. Moreover, the mass ratio is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less.

The density of the porous support is preferably 0.05 g/cm ³ or more, more preferably 0.1 g/cm ³ or more, from the viewpoint of impregnation of the mixture. Also, the density is preferably 2.0 g/cm ³ or less, more preferably 1.0 g/cm ³ or less.

The film thickness of the porous support is preferably 300 μm or less, more preferably 200 μm or less, from the viewpoint of improving storage battery performance and strength and suppressing separation from inorganic components during impregnation. Moreover, the film thickness is preferably 5 μm or more, more preferably 20 μm or more.

[Other ingredients]
The composite film may further contain other components such as conventionally known dispersants, thickeners, conductive carbon, and conductive ceramics.
From the viewpoint of strength of the composite membrane, the content of other components in the composite membrane is preferably 10% by mass or less in 100% by mass of the composite membrane. It is more preferably 5% by mass or less, still more preferably 1% by mass or less, and particularly preferably 0.1% by mass or less.

The composite membrane is preferably gas permeable.
The gas permeability means that the air permeability is 10000 seconds or less in terms of Gurley value. The Gurley value is preferably 9500 seconds or less.
The Gurley value is preferably 500 seconds or more, more preferably 1000 seconds or more.
The Gurley value is obtained by measuring the time required for 100 cc of air to permeate using a Gurley measuring instrument according to JIS P 8117. The Gurley value is an index that expresses the ease with which gas can pass through.
In addition, when the separator includes a laminate in which a plurality of composite films are laminated, the Gurley value is the Gurley value measured for the laminate.

The composite membrane preferably has a porosity of 20% by volume or more, more preferably 30% by volume or more. Moreover, the porosity is preferably 90% by volume or less, more preferably 80% by volume or less.
The porosity is expressed by the volume of voids in the composite membrane relative to the volume of the composite membrane, and can be measured with a mercury porosimeter.

The method for producing the composite membrane is not particularly limited. For example, a mixed solution containing inorganic particles and a polymer is coated on a release substrate, dried, and then the resulting composite film is released from the release substrate. When the composite membrane contains a porous support, the method for producing the composite membrane includes, for example, a method of coating the mixed solution on the porous support and drying, and a method of immersing the porous support in the mixed solution. After that, there is a method of drying, a method of coating the mixed solution on a release base material, drying the coating film in contact with a porous support, and then peeling off the release base material.
There are no particular restrictions on the method for preparing the mixed liquid containing the inorganic particles and the polymer. For example, a method of mixing inorganic particles and a polymer with a solvent and using a dispersing device may be used, or a method of mixing inorganic particles with a solvent such as an organic solvent or water and using a dispersing device to prepare a dispersion of inorganic particles. Then, a method of adding and mixing the polymer thereto may be used. As the dispersing device, conventionally known dispersing devices such as ultrasonic waves, ball mills, and paint shakers can be used. A conventionally known dispersant may be used to disperse the inorganic particles.

[Polymer membrane]
The separator may include a polymer membrane instead of or in addition to the composite membrane.
Examples of such polymer films include hydrocarbon moiety-containing polymers such as polyethylene and polypropylene, polytetrafluoroethylene moiety-containing polymers, polyvinylidene fluoride moiety-containing polymers, cellulose, fibrillated cellulose, viscose rayon, cellulose acetate, hydroxyalkyl Cellulose, carboxymethyl cellulose, polyvinyl alcohol-containing polymer, cellophane, polystyrene containing aromatic ring site polymer, polyacrylonitrile site-containing polymer, polyacrylamide site-containing polymer, polyvinyl halide site-containing polymer, polyamide site-containing polymer such as nylon, polyimide Site-containing polymers, poly(meth)acrylic acid site-containing polymers, poly(meth)acrylate site-containing polymers, hydroxyl group-containing polymers such as polyisoprenol and poly(meth)allyl alcohol, carbonate group-containing polymers such as polycarbonate, polyesters Ester group-containing polymers such as polyurethanes, carbamate or carbamide group site-containing polymers such as polyurethanes, ion-exchange membrane polymers, cyclized polymers, sulfonate-containing polymers, quaternary ammonium salt-containing polymers, quaternary phosphonium salt-containing polymers, A cyclic hydrocarbon group-containing polymer, an ether group-containing polymer, and the like can be mentioned, and one or more of these can be used. The polymer contains a specific site/functional group, as long as the polymer contains a monomer unit having the site/functional group in its part, and a unit that does not have the site/functional group. It may contain a mer unit. In other words, the polymer may be a copolymer.
The polymer membrane is preferably, for example, a nonwoven fabric or a microporous membrane composed of the polymer.

When the polymer has functional groups, the functional groups may be on the main chain or side chains. In addition, the main chain is ester bond, amide bond, ionic bond, van der Waals bond, agostic interaction, hydrogen bond, acetal bond, ketal bond, ether bond, peroxide bond, carbon-carbon bond, carbon-nitrogen bond, carbamate bond. , a thiocarbamate bond, a carbamide bond, a thiocarbamide bond, an oxazoline moiety-containing bond, a triazine bond, or the like.
Any number of polymer films can be used as long as the resistance does not increase and the battery performance does not deteriorate.
For example, a separator obtained by laminating the composite film and the polymer film can be used. Among others, it is one of preferred embodiments of the present invention that the positive electrode side of the separator is a water-retentive polymer film. For the water-retaining polymer film, the water-retaining polymer used in the positive electrode for storage battery of the present invention described above can be used, and specifically, cellulose, fibrillated cellulose, viscose rayon, cellulose acetate, hydroxyalkyl cellulose, carboxymethyl cellulose. , Polyvinyl alcohol, poly(meth)allyl alcohol and other hydroxyl group-containing polymers, polyamide site-containing polymers such as nylon, polyimide site-containing polymers, poly(meth)acrylic acid site-containing polymers, poly(meth)acrylate site-containing polymers, etc. and, for example, polyamide site-containing polymers are preferred. For example, the positive electrode side of the separator can be a water-retentive polymer film, and the negative electrode side of the separator can be the composite film. At least the positive electrode side of the separator may be hydrophilically treated by introducing a surfactant or the like.

In the separator, the average film thickness ratio between the composite film and the polymer film is preferably 1:5 to 1:0, preferably 1:2 to 1:0, and 1:1. ~1:0 is more preferred. From the viewpoint of shortening the inter-electrode distance and lowering the inter-electrode resistance, it is preferable not to use the polymer film.

In the case where the separator consists only of the polymer film, the porosity of the polymer film is preferably 90% by volume or less, preferably 80% by volume or less, from the viewpoint of preventing short circuits due to dendrites derived from the negative electrode. It is more preferably 70% by volume or less, and particularly preferably 60% by volume or less.
The porosity is preferably 20% by volume or more, more preferably 30% by volume or more.
Even when the separator is composed of only the polymer film, a certain dendrite suppression effect can be exhibited as long as the polymer film does not dissolve in the electrolyte and lose its structure. Therefore, the polymer film described above can be appropriately used as the separator. For example, water-absorbent resins such as poly(meth)acrylic acid (salts), and cellulose that does not dissolve in water and maintains its structure like cellophane separators can be used as separator materials for batteries containing aqueous electrolytes. It can exhibit a certain dendrite suppression effect.

The separator preferably has an average thickness of 10 μm to 1 mm. Durability can be made more excellent in it being 10 micrometers or more. In addition, if the thickness is 1 mm or less, it is advantageous in terms of cost, and the ability to transmit ions is sufficiently excellent. More preferably, the average film thickness is 20 μm or more. Further, the average film thickness is more preferably 500 μm or less, still more preferably 200 μm or less, and particularly preferably 150 μm or less.
In the present specification, the average film thickness is the average value obtained by measuring arbitrary 10 points using a Digimatic Micrometer (manufactured by Mitutoyo Corporation).

<Electrolyte>
Preferably, the bismuth-zinc storage battery of the invention further comprises an electrolyte.
As the electrolyte, those commonly used as electrolytes for storage batteries can be used, and there are no particular restrictions. Examples thereof include organic solvent-based electrolytes, aqueous electrolytes, solid electrolytes, and the like. Organic solvent-based electrolytes include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, dimethoxymethane, diethoxymethane, dimethoxyethane, tetrahydrofuran, methyltetrahydrofuran, diethoxyethane, dimethylsulfoxide, sulfolane, acetonitrile, Benzonitrile, ionic liquids, fluorine-containing carbonates, fluorine-containing ethers, polyethylene glycols, fluorine-containing polyethylene glycols and the like can be mentioned, and one or more of these can be used. Examples of aqueous electrolytes include potassium hydroxide aqueous solution, sodium hydroxide aqueous solution, lithium hydroxide aqueous solution, zinc sulfate aqueous solution, zinc nitrate aqueous solution, zinc phosphate aqueous solution, zinc acetate aqueous solution, and the like. Among these, alkaline aqueous electrolytes such as an aqueous potassium hydroxide solution, an aqueous sodium hydroxide solution, and an aqueous lithium hydroxide solution are preferred. One or two or more of the aqueous electrolytes may be used. The aqueous electrolytic solution may contain the above organic solvent-based electrolytic solution.

The bismuth-zinc storage battery of the invention may be hermetically sealed. The bismuth-zinc storage battery of the present invention is suitable for hermetic sealing because it does not generate oxygen during charging. Since the bismuth-zinc storage battery of the present invention is hermetically sealed, evaporation of the electrolyte can be sufficiently prevented. In addition, it is possible to sufficiently prevent the mixture of moisture and carbon dioxide in the air, and for example, to suppress the reaction between carbon dioxide in the air and hydroxide ions in the electrolytic solution.

The bismuth-zinc storage battery of the present invention can be manufactured by appropriately using known methods. For example, a bismuth-zinc storage battery can be fabricated by placing a negative electrode in a cell, introducing an electrolyte solution into the cell, further placing a positive electrode, a separator, and the like.

INDUSTRIAL APPLICABILITY The bismuth-zinc storage battery of the present invention can sufficiently prevent the generation of oxygen during charging and can stably stop charging.

(bipolar electrode)
The present invention is also a bipolar electrode characterized by comprising a cathode active material containing bismuth species.
In general, a bipolar electrode serves both as a positive electrode and a negative electrode, and the bipolar electrode of the present invention basically comprises a current collector and a positive electrode active material containing bismuth species disposed on one side of the current collector. and a negative electrode active material containing zinc species disposed on a surface opposite to the surface.
As the positive electrode active material containing bismuth species and its auxiliary component, those described above as the active material, polymer, water retention component, conductive aid, etc. in the positive electrode for storage battery of the present invention can be preferably used. In particular, by using a water-retaining component, it is easy to retain the aqueous electrolyte in the active material layer, and internal short-circuiting is less likely to occur, making it easier to create a bipolar structure.
The current collector in the bipolar electrode separates the positive electrode active material and the negative electrode active material, is electrically conductive, and is substantially impermeable to the electrolytic solution. The term "the current collector is substantially impermeable to the electrolyte" means that the current collector does not permeate the electrolyte when the battery is constructed, so that the current collector does not permeate the electrolyte and cause an internal short circuit of the battery. For example, various metal foils and metal plates described above can be suitably used as current collectors included in the bismuth-zinc storage battery of the present invention. In addition, even if the current collector is a foam metal, a metal mesh (expanded metal), a perforated metal, or the like, it is preferable if the current collector is impregnated with the active material, etc., and the electrolytic solution does not substantially permeate the current collector. Available.
In other words, a current collector that does not have water permeability can be preferably used.

Preferably, the bipolar electrode of the present invention further comprises a negative electrode active material containing zinc species.
As the negative electrode active material containing zinc species and its auxiliary component, the negative electrode active material, polymer, conductive aid, etc. described above as the negative electrode active material contained in the bismuth-zinc storage battery of the present invention can be preferably used. A water-retaining component may be used, for example, from the viewpoint of keeping the aqueous electrolyte in the negative electrode active material layer.

The bipolar electrode of the present invention may further contain a conductive porous body. By including the conductive porous body, the resistance of the storage battery can be reduced. The conductive porous body forms an active material layer together with an electrode active material and the like. The conductive porous body may be arranged only on one surface of the current collector (the surface on the positive electrode active material side or the surface on the negative electrode active material side), or may be arranged on both surfaces of the current collector.

The conductive porous body is composed of, for example, metals such as copper, brass, nickel, silver, indium, lead, tin, and cobalt, metal compounds, conductive carbon, conductive resins, and composites thereof. The conductive porous body may be a metal nonwoven fabric, a foamed metal, a punched metal plate, a metal mesh, or the like, or may be a resin nonwoven fabric plated with a metal.

A method for fabricating a bipolar electrode will be described below.
An insulating paint is applied to the outer periphery of the current collector in a predetermined width, a negative electrode mixture containing a zinc compound, a conductive aid, etc. is applied to one side of the current collector, and the other side is coated with , a bismuth compound, a conductive aid, and the like, and dried as necessary to produce a bipolar electrode having a negative electrode active material layer and a positive electrode active material layer.

Note that the negative electrode active material layer and the positive electrode active material layer may be joined to the current collector by a method such as welding, adhesion, pressure contact, or crimping.

(Laminate)
The present invention is also a laminate of bipolar electrodes, characterized by including the bipolar electrode of the present invention.
A bipolar electrode is typically used as a stack of multiple bipolar electrodes.
FIG. 5 is a schematic diagram illustrating the configuration of a laminate of bipolar electrodes according to the present invention. In FIG. 5, the bipolar electrode 140 includes a bismuth compound 143 that is a positive electrode active material, a positive electrode active material layer containing a water retention component 145, a layer of a current collector 141, and zinc 147 and oxides that are the negative electrode active material. A state in which a negative electrode active material layer containing zinc 149 is included in this order is shown.

FIG. 5 described above shows that the bipolar electrodes are stacked and the separators 130 and 130A are arranged between the bipolar electrodes.
By forming a laminate in this way, the electromotive force of the battery can be increased.
As shown in FIG. 5, the upper bipolar electrode and the lower bipolar electrode of the bipolar electrode 140, which are the bipolar electrodes of the present invention, are those in which the mixture is applied only to one side of the current collector for current collection. may be
The laminate of the present invention includes a current collector that includes the bipolar electrode of the present invention, and a plurality of bipolar electrodes that include the positive electrode active material and/or the negative electrode active material, and the plurality of bipolar electrodes are Lamination is one of the preferred embodiments of the present invention.
In the laminate of the present invention, for example, a seal that connects the outer edges along the outer edges of the laminated current collector or the like so as to seal the power generation unit such as the positive electrode active material layer, the negative electrode active material layer, and the electrolyte. section may be provided. For the sealing portion, conventionally known gaskets, seal rings, sealing agents, etc. can be appropriately used for the purpose of preventing leakage of the electrolytic solution or entry of air or foreign matter from the outside.
By providing the sealing portion, it is possible to omit the exterior material of the battery such as an aluminum laminate film and the housing. The bipolar storage battery of the present invention may be configured such that instead of providing the seal portion on the laminate, or in addition to providing the seal portion on the laminate, the laminate is covered with an exterior material or a housing of the battery.

FIG. 6 is a schematic diagram showing a case where a short circuit occurs in the laminate of the present invention.
As shown in FIG. 6, if the electrolytic solution 150 interferes with the outer periphery of the bipolar electrode, an internal short circuit 160 will occur and a battery with a bipolar structure will not be formed. In order to prevent this, a member such as the above-described seal portion can be provided. Similarly, when the current collector permeates the electrolyte, an internal short circuit occurs, and a battery having a bipolar structure cannot be formed.

The laminate of the present invention may be appropriately provided with a lead wire or a tab terminal for electrically connecting the current collector and the active material layer that is not in direct contact with the current collector. At least some of the bipolar electrodes may be connected substantially in parallel.

(bipolar storage battery)
The present invention also provides a bipolar storage battery comprising the bipolar electrode of the present invention or the laminate of the present invention.
The bipolar storage battery of the present invention uses nickel species as the positive electrode active material.
By connecting the bipolar type storage battery of the present invention in series with the bipolar structure including the laminate of the present invention, the electromotive force of the storage battery can be increased. In addition, unlike a cell that draws out wiring for each cell, a specific current collector is not required for each cell. and resistance loss due to connection can be reduced.
As described above, when the water-retaining component is added to the positive electrode active material layer or the like of the bipolar electrode, it becomes easier for the electrolyte to remain in the positive electrode active material layer or the like, and internal short-circuiting is less likely to occur. becomes easier to make.
Similar to the bismuth-zinc storage battery of the present invention described above, it is also a preferred embodiment of the present invention that the bipolar storage battery of the present invention includes a water retention component for supplying water to the charging reaction of such positive electrode active material. is one of It is also one of the preferred embodiments of the present invention to use a water-retentive polymer film on the positive electrode side of the separator.

In the bipolar storage battery of the present invention, for example, a water-retaining polymer film (water-retaining body) such as a non-woven fabric made of a water-retaining polymer is impregnated with an electrolytic solution and placed on the positive electrode active material side of the bipolar electrode. After that, the electrodes can be stacked via a separator and brought into contact with each other by, for example, applying pressure from both sides. Instead of using a water retainer, for example, a water retainer may be blended in the positive electrode active material layer.

As described above, the bipolar storage battery of the present invention can increase the electromotive force of the storage battery. In addition, since a long-life and safe battery can be realized without requiring rare earths, it can be suitably used for small mobile devices to large-scale applications such as automobiles.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited only to these examples. Unless otherwise specified, "part" means "mass part" and "%" means "mass %".

[Positive electrode for storage battery and bismuth-zinc storage battery]
(Example 1)
A bismuth-zinc storage battery (Fig. 1) was prepared by placing the following negative electrode in a cell, introducing a 7M-KOH aqueous solution saturated with zinc oxide ZnO into the cell as an electrolyte solution, and further placing the following positive electrode and separator below. bottom.
[Positive electrode]
Bismuth oxide, natural graphite, and SBR were mixed at a mass ratio of 40:4:0.5, applied to a nickel mesh (#100) as a current collector, and dried.
[Negative electrode]
Copper foil was used as a current collector, zinc powder (particle size: 75 μm) was applied on the copper foil, and zinc oxide powder (particle size: 300 nm) was further applied thereon. Zinc powder and zinc oxide powder were each dispersed in a slurry obtained by mixing sodium polyacrylate and water and applied.

[Separator]
Magnesium hydroxide (average particle diameter 250 nm) as inorganic particles, PTFE (average particle diameter 300 nm, glass transition temperature 115 ° C.) as polymer, SBR (glass transition temperature -1 ° C.) as binder, volume ratio 5 A nonwoven fabric was impregnated with the slurried dispersion to obtain an organic/inorganic composite film. The above-mentioned mixing is carried out using a tank-type stirring device equipped with a propeller-type stirring blade and a vertical stirrer, with a sufficient distance between the propeller-type stirring blade and the inner wall of the vessel, and at a rotation speed of 100 rpm in a state where shear stress is not applied. Went for 5 minutes. The Gurley value of the composite membrane was about 5000 sec.
As separators, a 100 μm-thick nylon nonwoven fabric was used on the positive electrode side, and a 100 μm-thick organic/inorganic composite film was used on the negative electrode side.

2 is a graph showing the initial discharge capacity of the bismuth-zinc storage battery of Example 1. FIG. FIG. 2 shows the measurement results for 14 times.
The theoretical capacity calculated from the electrochemical reaction formula of bismuth is 345 mAh/g, and the output capacity of the bismuth-zinc storage battery manufactured by the method described in Example 1 was observed to match the theoretical capacity of bismuth. As for the voltage during charging and discharging, the charging and discharging curves for 2 to 10 cycles are superimposed (Fig. 3). The potential curve is very flat during charging, and there is a clear potential change when charging and discharging are stopped (the cycle capacity is slightly lower than the initial discharge capacity).
The bismuth-zinc storage battery of Example 1 was able to sufficiently suppress oxygen generation at the end of charging. In addition, when the battery was fully charged, there was a clear potential change, and the voltage rose very rapidly, so charging could be easily stopped before oxygen was generated. Furthermore, there was almost no change in the amount of charge due to the timing of stopping charging, and the amount of charge could be made uniform.

Furthermore, the bismuth-zinc storage battery of Example 1 was measured for discharge capacity, cyclability, and output performance under the following conditions. Table 1 shows the results.
(discharge capacity)
The discharge capacity is obtained by measuring the capacity when the battery voltage drops to 0.2 V due to discharging at a constant current (10 mA/cm ² ) and dividing it by the weight of the mounted active material. mAh/g was calculated.

(Cyclical)
A charge/discharge test was performed at a rate of 0.5 C to measure the cyclability (the number of charge/discharge cycles until a short circuit occurred). The measurement results are shown in Table 1 below.
Evaluation criteria are as follows.
○: 100 cycles or more △: 50 cycles or more and less than 100 cycles ×: less than 50 cycles

(output performance)
The output performance was evaluated by the maximum current that flowed when the positive electrode and negative electrode of the fully charged battery were short-circuited. The measurement results are shown in Table 1 below.
Evaluation criteria are as follows.
100 mA/ ^cm2 or more: ◎
50 mA/cm ² or more and less than 100 mA/cm ² : ○ More than 10 mA/cm ² and less than 50 mA/cm ² : △
10 mA/cm ² or less: ×

(Examples 2-7)
A bismuth-zinc storage battery was produced in the same manner as in Example 1, except that the positive electrode and separator were changed as shown in Table 1 below, and the discharge capacity, cyclability, and output performance were measured.
The bismuth-zinc storage batteries of Examples 2 to 7 were also able to sufficiently suppress oxygen generation at the end of charging.
In the bismuth-zinc storage batteries of Examples 2 and 3, as in the bismuth-zinc storage battery of Example 1, there is a clear potential change when fully charged, and the voltage rises very rapidly, so oxygen is generated. I was able to stop charging easily before. Furthermore, there was almost no change in the amount of charge due to the timing of stopping charging, and the amount of charge for each charge could be highly uniformed.
In the bismuth-zinc storage batteries of Examples 4 to 7, the voltage increased sharply when the bismuth charging reaction was completed (for example, FIG. 4. FIG. 4 shows the charge/discharge capacity of the bismuth-zinc storage battery of Example 7 It is a graph showing the voltage between terminals.). In the bismuth-zinc storage batteries of Examples 4 to 7, charging could be easily stopped before oxygen was generated. In addition, it was possible to sufficiently suppress large fluctuations in the amount of charge due to the timing of stopping charging, and to sufficiently uniform the amount of charge for each charge.
In Table 1 below, the content of activated carbon is the mass ratio when the total content of bismuth oxide, natural graphite, SBR, and activated carbon, which are positive electrode mixtures, is 100% by mass.

The bismuth-zinc storage batteries of Examples 1 to 7 were able to sufficiently prevent the generation of oxygen during charging and stably stop charging. Among them, the bismuth-zinc storage batteries of Examples 1 and 3 to 7 were able to achieve high cycle performance by using the highly durable organic-inorganic composite film as the separator. In the bismuth-zinc storage batteries of Examples 1, 2, 4 to 7, the discharge reaction requiring water can be accelerated by using a nylon nonwoven fabric on the positive electrode side of the separator or by mixing a water retaining component in the positive electrode mixture. , it is thought that the discharge capacity can be improved.

Examples 4 to 7, in which activated carbon was mixed in the positive electrode mixture, were excellent in output performance.
As shown in FIG. 4, in Examples 4 to 7 in which activated carbon, which is a water-retaining component, was used in the positive electrode mixture, a charge-discharge curve based on the electric double layer capacity was observed, which is thought to improve the output performance.
In addition, since Example 2 does not use an organic-inorganic composite film as a separator, and Examples 3 to 7 do not use nylon as a separator, the distance between electrodes is shorter than that in Example 1, and the storage battery It is considered that the internal resistance is also reduced.
All of the bismuth-zinc storage batteries of Examples 1 to 7 exhibit the effects of the present invention that, as described above, the generation of oxygen during charging can be sufficiently prevented and charging can be stably stopped. . The bismuth-zinc storage battery of Example 2 is relatively inferior in cycle performance, and the bismuth-zinc storage battery of Example 3 is relatively inferior in discharge capacity and output performance, but has certain practical utility.

[Bipolar electrode, laminate, and bipolar bismuth-zinc storage battery]
(Example 8)
(1) Fabrication of bipolar electrode SBR resin was applied as an insulating paint to the outer periphery of nickel foil (4 cm × 4 cm) as a non-permeable current collector in a width of 5 mm, and Zn powder and ZnO were applied to one surface of the SBR resin. An active material containing bismuth oxide and a conductive agent was applied to the other surface to fabricate a bipolar electrode (FIG. 7).
The zinc layer and the bismuth layer have the same composition and preparation method as those described in the first embodiment. The zinc layer and the bismuth layer are electrically connected through the nickel foil.
(2) Fabrication of bipolar bismuth-zinc storage battery A non-woven fabric (vinylon, thickness 100 µm) cut to 3 cm x 3 cm was used as a water retaining body, impregnated with 100 mL of 7M-KOH aqueous solution, and placed on the Bi side of the bipolar electrode. After that, the electrodes were laminated with an organic-inorganic composite separator interposed therebetween, and pressure was applied from both sides to bring them into contact with each other to form a battery (FIG. 8).
In addition, as shown in FIG. 8, the electrodes on both sides (the upper electrode and the lower electrode of the bipolar electrode 240 shown in FIG. 8) are coated with a mixture only on one side of the current collector for current collection. are doing.

FIG. 9 is a graph showing discharge voltage versus discharge capacity in one embodiment of the bipolar bismuth-zinc storage battery of the present invention.
In FIG. 9 , the graph indicated by “3 cells” is a graph showing discharge voltage versus discharge capacity in the bipolar bismuth zinc storage battery of Example 8. In FIG. The graph indicated by "2 cells" is a graph showing discharge voltage versus discharge capacity in a bismuth-zinc storage battery fabricated by stacking electrodes on only one side of the bipolar electrode of Example 8 instead of on both sides. The graph indicated by "1 cell" is a graph showing discharge voltage versus discharge capacity in the bismuth-zinc storage battery having only one bipolar electrode of Example 8.
FIG. 9 shows that stacking bipolar electrodes further increases the voltage.
The measurement was performed by discharging at a constant current of 10 mA/cm ² as in the measurement of the discharge capacity.

(Example 9)
(1) Fabrication of bipolar electrode SBR resin was applied as an insulating paint to the outer periphery of nickel foil (4 cm × 4 cm) as a non-permeable current collector in a width of 5 mm, and Zn powder and ZnO were applied to one surface of the SBR resin. An active material containing bismuth oxide, a conductive aid and activated carbon was applied to the other side to fabricate a bipolar electrode (FIG. 10).
The zinc layer and the bismuth layer have the same composition and preparation method as those described in the fifth embodiment. The zinc layer and the bismuth layer are electrically connected through the nickel foil.
(2) Preparation of bipolar type bismuth zinc storage battery 100 mL of 7M-KOH aqueous solution was soaked into the Bi side of the bipolar electrode, the electrodes were laminated via an organic-inorganic composite separator, and pressure was applied from both sides to make a battery. (Fig. 11).
In addition, as shown in FIG. 11, the electrodes on both sides (the upper electrode and the lower electrode of the bipolar electrode 340 shown in FIG. 11) are coated with a mixture only on one side of the current collector for current collection. are doing.

FIG. 12 is a graph showing discharge voltage versus discharge capacity in one embodiment of the bipolar bismuth-zinc storage battery of the present invention.
In FIG. 12 , the graph indicated by “3 cells” is a graph showing discharge voltage versus discharge capacity in the bipolar bismuth-zinc storage battery of Example 9. In FIG. The graph indicated by "2 cells" is a graph showing the discharge voltage versus the discharge capacity in the bipolar bismuth-zinc storage battery of Example 9 produced by laminating the electrodes on only one side instead of on both sides. The graph indicated by "1 cell" is a graph showing discharge voltage versus discharge capacity in the bismuth-zinc storage battery having only one bipolar electrode of Example 9.
FIG. 12 shows that stacking bipolar electrodes further increases the voltage.
The measurement was performed by discharging at a constant current of 10 mA/cm ² as in the measurement of the discharge capacity.
In Example 9, when activated carbon is added, discharge occurs due to the activated carbon, so the discharge behavior in the carbon-zinc structure overlaps at the beginning and end of discharge.

In Examples 8 and 9, a bipolar bismuth-zinc storage battery that does not generate oxygen was obtained by using a bismuth compound as the positive electrode active material. Moreover, by configuring the battery as a bipolar type storage battery, the disadvantage of the bismuth-zinc storage battery, which has a low voltage per cell, can be overcome, so it is considered to be a more practical configuration.

10: Positive electrode 11: Positive electrode current collector 13, 143, 143a, 243, 243a, 343, 343a: Bismuth compound 15, 145, 145a, 345, 345a: Water retention component (activated carbon)
20: negative electrode 21: negative electrode current collector 23, 147, 147A, 247, 247A, 347, 347A: zinc 25, 149, 149A: zinc oxide 30, 130, 130A, 230, 230A, 330, 330A: separator 41: activated carbon Region 43 where charge-discharge curves based on the charge-discharge reaction of bismuth are observed: Regions 140, 240, 340 where charge-discharge curves based on the charge-discharge reaction of bismuth are observed: Bipolar electrodes 141, 141a, 141A, 241, 241a, 241A , 341, 341a, 341A: current collector 150: electrolyte 160: internal short circuit 231, 231A: non-woven fabric impregnated with electrolyte 260, 360: insulating paint

Claims (12)

A positive electrode used in a storage battery,
A positive electrode for a storage battery, wherein the positive electrode contains an active material containing 50% by mass or more of bismuth. The positive electrode for a storage battery according to claim 1, wherein the positive electrode further contains a water-retaining component. 3. The positive electrode for a storage battery according to claim 2, wherein said water retaining component is a carbon material. 4. The positive electrode for a storage battery according to claim 1, wherein said positive electrode further contains a polymer. 5. The positive electrode for a storage battery according to claim 1, wherein said positive electrode further contains conductive carbon and/or cobalt species as a conductive aid. A bismuth-zinc storage battery comprising the positive electrode for a storage battery according to any one of claims 1 to 5, a negative electrode containing a zinc species, and a separator. 7. The bismuth-zinc battery of claim 6, wherein the separator comprises polymer and inorganic particles. 8. The bismuth-zinc storage battery according to claim 6, further comprising an alkaline aqueous electrolyte. A bipolar electrode comprising a positive electrode active material containing bismuth species. 10. The bipolar electrode of claim 9, further comprising a negative electrode active material containing zinc species. A laminate of bipolar electrodes, comprising the bipolar electrode according to claim 9 or 10. A bipolar storage battery comprising the bipolar electrode according to claim 9 or 10 or the laminate according to claim 11.

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