Manganese oxide zinc secondary battery

Abstract

The present invention provides a means capable of improving discharge capacity in a manganese oxide zinc secondary battery. The present disclosure provides a manganese oxide zinc secondary battery, in which a battery element is sealed inside an outer package body, and the battery element includes a positive electrode active material layer that contains a positive electrode active material containing manganese dioxide or substituted manganese dioxide, a negative electrode active material layer that contains a negative electrode active material containing zinc, and an electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer. The electrolyte layer contains an alkaline aqueous solution and a cation exchange resin.

Description

Manganese oxide zinc secondary battery

[0001] This invention relates to a manganese-zinc oxide secondary battery.

[0002] In recent years, the widespread adoption of various electric vehicles has been anticipated as a way to address environmental and energy problems. As a key element in the proliferation of these electric vehicles, intensive development efforts are underway to create aqueous secondary batteries, such as manganese dioxide zinc oxide secondary batteries, which use manganese dioxide as the positive electrode active material and an electrolyte such as an alkaline aqueous solution, for use as on-board power sources, including motor drive power supplies.

[0003] For example, International Publication No. 2020 / 049901 discloses a zinc secondary battery, such as a manganese-zinc secondary battery, that uses metallic Zn, ZnO, Zn alloy, or Zn compound as the negative electrode active material and an alkali metal hydroxide aqueous solution, such as potassium hydroxide aqueous solution, as the electrolyte. Furthermore, this document proposes a technique in which, in addition to the alkali metal hydroxide aqueous solution, the electrolyte of the manganese-zinc secondary battery further contains proteins and / or derivatives and / or decomposition products that can complex with Zn, or polyphenols and / or derivatives and / or decomposition products that can complex with Zn. According to International Publication No. 2020 / 049901, this configuration can prevent changes in the morphology of the zinc in the negative electrode and the formation of dendrites as the charge-discharge cycle progresses.

[0004] However, our own investigations have revealed that when the technology described in the aforementioned International Publication No. 2020 / 049901 is adopted, sufficient discharge capacity may not be obtained.

[0005] Therefore, the present invention aims to provide a means for improving the discharge capacity of a manganese-zinc oxide secondary battery.

[0006] The inventors of the present invention conducted diligent research to solve the above problems. As a result, they discovered that the above problems could be solved by including a cation exchange resin in addition to an alkaline aqueous solution in the electrolyte layer, and thus completed the present invention.

[0007] In other words, one embodiment of the present invention relates to a manganese-zinc secondary battery in which a battery element comprising a positive electrode active material layer containing manganese dioxide or substituted manganese dioxide, a negative electrode active material layer containing zinc, and an electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer is sealed inside an outer casing. The secondary battery is characterized in that the electrolyte layer contains an alkaline aqueous solution and a cation exchange resin.

[0008] This is a schematic cross-sectional view of a stacked (flat) non-bipolar (internal parallel connection type) manganese-zinc oxide secondary battery.

[0009] One embodiment of the present invention is a manganese-zinc secondary battery in which a battery element comprising a positive electrode active material layer containing manganese dioxide or substituted manganese dioxide, a negative electrode active material layer containing zinc, and an electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer is sealed inside an outer casing, and the electrolyte layer comprises an alkaline aqueous solution and a cation exchange resin. According to this embodiment, the discharge capacity of the manganese-zinc secondary battery can be improved.

[0010] The embodiments of the present invention described above will be explained below with reference to the drawings, but the technical scope of the present invention should be determined based on the claims and is not limited to the following forms. Note that the dimensional ratios in the drawings are exaggerated for illustrative purposes and may differ from the actual ratios. In this specification, "X to Y" indicating a range means "X or more and Y or less". Unless otherwise specified, operations and measurements of physical properties, etc., are performed under conditions of room temperature (20 to 25°C) and relative humidity of 40 to 50% RH.

[0011] Figure 1 is a schematic cross-sectional view of a flat-type (stacked type) non-bipolar (internal parallel connection type) manganese zinc oxide secondary battery (hereinafter also simply referred to as "stacked secondary battery"), which is one embodiment of the manganese zinc oxide secondary battery according to this embodiment.

[0012] As shown in Figure 1, the stacked secondary battery 10a has a structure in which a roughly rectangular battery element 21, where the charge and discharge reaction actually takes place, is sealed inside a laminate film 29. Here, the battery element 21 has a configuration in which a positive electrode, with positive electrode active material layers 13 arranged on both sides of a positive electrode current collector 11', an electrolyte layer 17 containing a polymer electrolyte, and a negative electrode, with negative electrode active material layers 15 arranged on both sides of a negative electrode current collector 12 are stacked. Specifically, the positive electrode, electrolyte layer, and negative electrode are stacked in this order such that one positive electrode active material layer 13 and an adjacent negative electrode active material layer 15 face each other via the electrolyte layer 17.

[0013] As a result, the positive electrode, electrolyte layer, and negative electrode constitute a single cell layer 19. Therefore, the stacked secondary battery 10a shown in Figure 1 can also be said to have a configuration in which multiple single cell layers 19 are stacked and electrically connected in parallel. In addition, the outermost positive electrode current collectors located on both outermost layers of the battery element 21 have a positive electrode active material layer 13 on only one side, but active material layers may be provided on both sides. That is, instead of using a current collector specifically for the outermost layer with an active material layer on only one side, a current collector with active material layers on both sides may be used as the outermost current collector. Furthermore, by reversing the arrangement of the positive and negative electrodes from that in Figure 1, the outermost negative electrode current collectors may be located on both outermost layers of the battery element 21, and the negative electrode active material layer may be provided on one or both sides of the outermost negative electrode current collector.

[0014] The positive electrode current collector 11' and the negative electrode current collector 12 are each fitted with a positive electrode current collector plate 25 and a negative electrode current collector plate 27, which are electrically connected to the respective electrodes (positive and negative electrodes), and are structured to be led out to the outside of the laminate film 29 by being sandwiched between the edges of the laminate film 29. The positive electrode current collector plate 25 and the negative electrode current collector plate 27 may be attached to the positive electrode current collector 11' and the negative electrode current collector 12 of each electrode via positive electrode terminal leads and negative electrode terminal leads (not shown), respectively, by ultrasonic welding, resistance welding, or the like, as needed.

[0015] The following describes the main components of a manganese oxide zinc secondary battery.

[0016] [Current Collector] The current collector has the function of mediating the movement of electrons from the positive electrode active material layer and the negative electrode active material layer, which will be described later. There are no particular restrictions on the materials that make up the current collector. For example, metals or conductive resins can be used as the constituent materials of the current collector.

[0017] Specifically, examples of metals include aluminum, nickel, iron, stainless steel, titanium, and copper. In addition to these, clad materials of nickel and aluminum, or copper and aluminum may be used. Alternatively, a foil in which aluminum is coated on a metal surface may also be used. Among these, aluminum, stainless steel, copper, and nickel are preferred from the viewpoint of electronic conductivity, battery operating potential, and adhesion of the negative electrode active material to the current collector by sputtering. As for conductive resins, examples include resins in which conductive fillers are added to non-conductive polymer materials.

[0018] The current collector may be a single-layer structure made of a single material, or it may be a laminated structure in which layers made of these materials are appropriately combined. From the viewpoint of reducing the weight of the current collector, it is preferable to include at least a conductive resin layer made of a conductive resin. Furthermore, if the positive electrode active material layer and the negative electrode active material layer described later are conductive and can perform the current collecting function on their own, it is not necessary to use a current collector as a separate component from these electrode active material layers. In such a configuration, the positive electrode active material layer described later will constitute the positive electrode, and the negative electrode active material layer described later will constitute the negative electrode.

[0019] [Positive electrode active material layer] <Positive electrode active material> The positive electrode active material layer consists of manganese dioxide (MnO) as the positive electrode active material. ２ ) or substituted manganese dioxide is included. Preferably, the positive electrode active material layer contains manganese dioxide (MnO) as the positive electrode active material. ２ ) includes.

[0020] Manganese dioxide has been widely used as a positive electrode active material in manganese dry cell batteries and the like. Its manufacturing methods include liquid-phase methods such as electrolysis and chemical synthesis, but are not particularly limited.

[0021] Electrolytic manganese dioxide can be produced by conventionally known methods. For example, it can be produced by the method described in Japanese Patent Application Publication No. 2017-179583. Specifically, for example, an electrolytic cell is prepared by using a mixture of an aqueous sulfuric acid solution and an aqueous manganese sulfate solution as the electrolyte, and the anode and cathode are appropriately selected to carry out the electrolytic reaction, thereby depositing electrolytic manganese dioxide onto the anode.

[0022] Chemically synthesized manganese dioxide can be produced by conventionally known methods. Specifically, for example, one method involves dissolving potassium permanganate in an aqueous hydrochloric acid solution and performing hydrothermal synthesis. The heat treatment (calcination) temperature during hydrothermal synthesis is, for example, 140 to 180°C, preferably 150 to 170°C. The heat treatment (calcination) time is, for example, 2 to 24 hours, preferably 6 to 18 hours. Alternatively, for example, it can be synthesized by mixing an aqueous solution of potassium permanganate, an aqueous solution of manganese sulfate, and an aqueous solution of sodium hydroxide.

[0023] Furthermore, manganese dioxide obtained by electrolysis, chemical synthesis, or other methods may be appropriately pulverized to obtain a positive electrode active material having a desired particle size. For pulverization, for example, roller mills, jet mills, etc., can be used, but are not limited to these. In addition, manganese dioxide having a desired average secondary particle size may be produced by classification using a suitable classification device, such as a sieve or classifier.

[0024] Substitutive manganese dioxide is manganese dioxide in which the oxygen element is replaced by one or more substitution elements.

[0025] The type of substitution element is not particularly limited as long as it can exhibit the effects of the present invention and does not adversely affect the performance or safety of the battery. Examples of substitution elements include nitrogen, phosphorus, sulfur, selenium, chlorine, bromine, iodine, and fluorine. Among these, it is preferable that the substitution element contains nitrogen or sulfur.

[0026] Manganese dioxide (MnO ２The proportion of oxygen elements constituting ) that is substituted by the aforementioned substitution element can be appropriately determined as required in consideration of the desired performance. For example, based on 100 mol% of the total amount of oxygen elements constituting manganese dioxide, the substitution ratio of oxygen elements by the aforementioned substitution element is preferably 0.01 to 50 mol%, more preferably 0.02 to 10 mol%, still more preferably 0.03 to 5 mol%, particularly preferably 0.04 to 3 mol%, and most preferably 0.05 to 1 mol%. The value of this substitution ratio shall be the value measured by the molten gas quantification method, in which a sample is placed in a crucible together with a nickel combustion improver, heated to about 2300°C under an argon atmosphere to melt the sample, and then the substitution element is quantified.

[0027] There are no particular limitations on the method for obtaining substituted manganese dioxide (the method for substituting oxygen elements with a substitution element). For example, when nitrogen is employed as the substitution element, nitrogen gas (N ２ ) or ammonia gas (NH ３ ) atmosphere, a gas-phase reaction in which substitution is promoted by heating manganese dioxide can be employed. In this case, the above-mentioned substitution ratio can be increased by extending the reaction time. Further, instead of nitrogen gas, fluorine (F ２ ), chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ ), substitution with these elements can be achieved by carrying out a gas-phase reaction in the presence of such gases.

[0028] Furthermore, substitution is not limited to gas-phase reactions, and substitution via liquid-phase reactions is also possible. For example, in an aqueous solution, in the presence of a nitrogen source such as urea (CO(NH ２ ) ２ ), a metal salt of Mn(II) such as manganese sulfate (MnSO ４ ) can also be oxidized using an oxidizing agent such as sulfuric acid or ammonium persulfate by a hydrothermal synthesis method to obtain substituted manganese dioxide. In this case, the above-mentioned substitution ratio can be increased by extending the reaction time or increasing the amount of the nitrogen source.

[0029] Further, in the case of substitution with an element (such as sulfur or phosphorus) that forms a simple substance having a melting point of 200°C or lower, substituted manganese dioxide substituted with these substitution elements can be obtained by dissolving the simple substance of these substitution elements in an argon atmosphere, heating the resulting mixture together with manganese dioxide to about 200°C and holding the mixture at that temperature. In this case, the above-mentioned substitution ratio can be increased by extending the heating and holding time or increasing the amount of the substitution element in the reaction system during heating.

[0030] The above-mentioned manganese dioxide or substituted manganese dioxide may form secondary particles. Secondary particles mean an aggregate of primary particles. Primary particles mean the particles of the minimum unit among separable solid particles having boundaries between particles. The average secondary particle diameter of manganese dioxide or substituted manganese dioxide is, for example, less than 100 µm, preferably less than 20 µm, more preferably less than 10 µm. In addition, the lower limit of the average secondary particle diameter of manganese dioxide or substituted manganese dioxide is not particularly limited, and may be, for example, 0.1 µm or more, 0.3 µm or more, or 0.6 µm or more. That is, the average secondary particle diameter of manganese dioxide or substituted manganese dioxide is, for example, 0.1 µm or more and less than 100 µm, preferably 0.3 µm or more and less than 20 µm, more preferably 0.6 µm or more and less than 10 µm. In the present specification, the average secondary particle diameter of manganese dioxide or substituted manganese dioxide as a positive electrode active material is measured by a particle size distribution measuring apparatus based on a laser diffraction / scattering method, and is the 50% cumulative diameter based on volume (D ５０ ) which is the calculated value.

[0031] The average primary particle diameter of manganese dioxide or substituted manganese dioxide is not particularly limited, but the crystallite diameter estimated by Scherrer's equation from the 101 peak confirmed by XRD measurement is, for example, 0.005 µm to 1.5 µm. In addition, the value of the ratio of the average primary particle diameter to the average secondary particle diameter of manganese dioxide or substituted manganese dioxide (average secondary particle diameter / average primary particle diameter) is not particularly limited, and is, for example, 1 to 1000.

[0032] The positive electrode active material may contain positive electrode active materials other than manganese dioxide and substituted manganese dioxide. Here, the ratio of the total content of manganese dioxide and substituted manganese dioxide to the total mass of the positive electrode active material is preferably more than 50% by mass, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, particularly preferably 97% by mass or more, and most preferably 100% by mass. In one embodiment, it is preferable that the positive electrode active material does not contain positive electrode active materials other than manganese dioxide and substituted manganese dioxide, and it is even more preferable that the positive electrode active material does not contain positive electrode active materials other than manganese dioxide. That is, it is preferable that the positive electrode active material consists only of manganese dioxide and substituted manganese dioxide, and it is even more preferable that it consists only of manganese dioxide.

[0033] Furthermore, the content of the positive electrode active material in the positive electrode active material layer is preferably 30 to 99% by mass, more preferably 50 to 85% by mass, and even more preferably 60 to 80% by mass, relative to the total mass of the positive electrode active material layer.

[0034] <Additive Components> The positive electrode active material layer preferably further contains a conductive additive, a binder, or a metal (oxide) in addition to the positive electrode active material described above.

[0035] (Conductive additive) Conductive additives have the function of forming electron conduction paths (conductive passages) in the positive electrode active material layer. When such electron conduction paths are formed in the positive electrode active material layer, the internal resistance of the battery can be reduced and the rate characteristics can be improved.

[0036] Examples of conductive additives include particulate carbon materials such as acetylene black, carbon black, channel black, thermal black, and Ketjenblack (registered trademark), and fibrous carbon materials such as carbon nanotubes (single-walled carbon nanotubes and multi-walled carbon nanotubes), carbon nanofibers, vapor-grown carbon fibers, electrospun carbon fibers, polyacrylonitrile-based carbon fibers, and pitch-based carbon fibers. One conductive additive may be used alone, or two or more may be used in combination.

[0037] The amount of conductive additives that may be included in the positive electrode active material layer (the total amount if two or more types are included) is not particularly limited, but it is preferably 1 to 30% by mass, and more preferably 5 to 20% by mass, based on 100% by mass of the total solid content of the positive electrode active material layer.

[0038] (Binder) The binder used in the positive electrode active material layer is not particularly limited, but examples include the following materials: polybutylene terephthalate, polyethylene terephthalate, polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are substituted with other halogen elements), polyethylene, polypropylene, polymethylpentene, polybutene, polyethernitrile, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), ethylene-propylene-diene copolymer, styrene-butadiene-styrene block copolymer and its hydrogenated products, thermoplastic polymers such as styrene-isoprene-styrene block copolymer and its hydrogenated products, polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene Fluororesins such as PCTFE, ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene fluororubber (VDF-HFP fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene fluororubber (VDF-HFP-TFE fluororubber), and vinylidene fluoride-pentafluoropropylene fluororubber (VDF-PFP fluororubber) Examples include vinylidene fluoride-based fluororubbers such as vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubbers (VDF-PFP-TFE-based fluororubbers), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene-based fluororubbers (VDF-PFMVE-TFE-based fluororubbers), vinylidene fluoride-chlorotrifluoroethylene-based fluororubbers (VDF-CTFE-based fluororubbers), epoxy resins, and the like.Among these, polyvinylidene fluoride (PVDF), polyimide, styrene-butadiene rubber, carboxymethylcellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are preferred.

[0039] The binder content (total amount if two or more types are included) that may be contained in the positive electrode active material layer is not particularly limited, but it is preferably 0.5 to 20% by mass, and more preferably 1 to 10% by mass, relative to the total solid content of the positive electrode active material layer.

[0040] (Metals (Oxides)) Metals (oxides) are metals in their elemental form or oxides thereof. Adding metals (oxides) to the positive electrode active material layer of a manganese-zinc secondary battery can improve the charge-discharge efficiency. There are no particular restrictions on the type of such metals (oxides), but examples include bismuth, lead, tin, silver, copper, titanium, nickel, cobalt, iron, manganese, or oxides thereof. These metals (oxides) may be used individually or in combination of two or more. In particular, from the viewpoint of improving charge-discharge efficiency, bismuth or its oxide (bismuth oxide) is preferred, and bismuth oxide is especially preferred.

[0041] The amount of metals (oxides) that may be contained in the positive electrode active material layer (the total amount if two or more types are included) is not particularly limited, but it is preferably 0.5 to 20% by mass, and more preferably 1 to 15% by mass, relative to the total solid content of the positive electrode active material layer.

[0042] The thickness of the positive electrode active material layer is not particularly limited, and conventionally known knowledge regarding batteries can be referenced as appropriate. For example, the thickness of the positive electrode active material layer is usually about 1 to 1000 μm, preferably 20 to 800 μm, more preferably 30 to 500 μm, and even more preferably 40 to 200 μm. The greater the thickness of the positive electrode active material layer, the more it is possible to hold positive electrode active material necessary to exhibit sufficient capacity (energy density). On the other hand, the smaller the thickness of the positive electrode active material layer, the more the discharge rate characteristics can be improved.

[0043] [Negative electrode active material layer] The negative electrode active material layer contains negative electrode active material.

[0044] (Negative Electrode Active Material) The negative electrode active material of a manganese-zinc secondary battery contains zinc. The zinc may be in any form, such as zinc metal, zinc compounds, or zinc alloys, as long as it has electrochemical activity suitable for the negative electrode. Preferred examples of negative electrode active materials include zinc oxide, zinc metal, calcium zincate, etc., but zinc metal or zinc alloys are more preferred.

[0045] As the zinc alloy, a mercury- and lead-free zinc alloy known as a mercury-free zinc alloy can be used. For example, a zinc alloy containing 0.01 to 0.06 mass% indium, 0.005 to 0.02 mass% bismuth, and 0.0035 to 0.015 mass% aluminum is preferred from the viewpoint of suppressing hydrogen gas generation. In particular, indium and bismuth are advantageous in that they improve discharge performance.

[0046] The negative electrode active material layer preferably further contains a thickening agent in addition to the negative electrode active material described above. The inclusion of a thickening agent in the negative electrode active material layer allows it to be made into a gel. Examples of thickening agents include polyvinyl alcohol, polyacrylate, carboxymethylcellulose, and alginic acid, but polyacrylate is preferred because it has excellent chemical resistance to strong alkalis. Furthermore, the negative electrode active material layer may further contain the conductive additive and binder described above as needed.

[0047] The shape of the negative electrode active material is not particularly limited, such as powder or plate, but it is preferably in powder form, as this increases the surface area and enables it to handle high current discharge. The preferred average particle size of the negative electrode active material is in the range of 50 to 1000 μm, more preferably in the range of 70 to 500 μm, and even more preferably in the range of 90 to 210 μm. Within this range, the large surface area makes it suitable for handling high current discharge, and it is also easy to uniformly mix with the electrolyte and the thickener used as needed, and is easy to handle during battery assembly. In this specification, the average particle size of the negative electrode active material is measured by a particle size distribution analyzer using the laser diffraction / scattering method and is calculated as the 50% cumulative diameter (D50) based on volume.

[0048] [Electrolyte Layer] In the manganese zinc oxide secondary battery according to this embodiment, the electrolyte layer is arranged between the positive electrode and the negative electrode. Specifically, it is preferably arranged adjacent to the positive electrode active material layer and the negative electrode active material layer, and in direct contact with the positive electrode active material layer and the negative electrode active material layer, respectively.

[0049] The electrolyte layer contains an alkaline aqueous solution and a cation exchange resin. The cation exchange resin preferably retains the electrolyte, in which case the cation exchange resin may be a gel-like gel polymer electrolyte. Furthermore, it is preferable that a membrane made of the cation exchange resin retaining the electrolyte (cation exchange resin membrane) constitutes the entire electrolyte layer as a separator.

[0050] (Cation Exchange Resin) The cation exchange resin is not particularly limited, but it is preferably one that captures zinc ions. The cation exchange resin captures zinc ions while releasing cations such as hydrogen ions, thereby maintaining the charge balance of the entire cell. As a result, the discharge capacity of the manganese-zinc secondary battery according to this embodiment can be improved. The mechanism by which the above effects are achieved with the configuration according to this embodiment is not fully clear, but the following mechanism is hypothesized.

[0051] In other words, during the discharge of a manganese-zinc secondary battery, the battery reaction at the positive and negative electrodes is thought to proceed as shown in the following reaction equation: Positive electrode: MnO ２ +H ２ O+e － → MnOOH + OH － Negative electrode: Zn→Zn ２＋ +2e － →Zn ２＋ +4OH － = [Zn(OH) ４ ] ２－ → [Zn(OH)] ４ ] ２－ = Zn(OH) ２ +2OH － →Zn(OH) ２ = ZnO + H ２O At this time, Zn produced at the negative electrode ２＋ When the (zinc ions) move through the electrolyte layer towards the positive electrode and reach the surface of the positive electrode active material layer, the positive electrode active material MnO ２ ZnMn ２ O ４ It was discovered that a side reaction occurs that generates a passive layer called a heterolite. Since this passive layer (heterolite) is inert to the battery reaction, its formation can reduce the battery's capacity. In contrast, the manganese-zinc oxide secondary battery according to this embodiment includes a cation exchange resin in the electrolyte layer, which allows zinc ions to be coordinated to the anionic functional groups of the cation exchange resin, thereby trapping the zinc ions. This makes it difficult for zinc ions to move to the positive electrode. As a result, it is believed that the formation of heterolites during discharge is suppressed, and the battery's capacity can be improved. It should be noted that the above mechanism is based solely on speculation, and its accuracy does not affect the technical scope of the present invention.

[0052] As cation exchange resins, for example, polystyrene sulfonic acid-based strongly acidic cation exchange resins, polyacrylic acid-based weakly acidic cation exchange resins, and polymethacrylic acid-based weakly acidic cation exchange resins can be used, but from the viewpoint of efficiently capturing zinc ions, sulfonic acid groups (-SO ３ It is preferable to use a salt containing H) or a salt thereof. Examples of sulfonic acid salts include sodium salts, potassium salts, lithium salts, and so on.

[0053] Furthermore, cation exchange resins are generally classified into so-called Na-type resins that have sodium ions and so-called H-type resins that have hydrogen ions. In this embodiment, either type can be used, and a combination of Na-type and H-type resins may be used, but it is preferable to use a so-called H-type cation exchange resin that has hydrogen ions.

[0054] In a preferred embodiment, the cation exchange resin has an amide group. The presence of an amide group provides excellent alkali resistance. In a preferred embodiment, the cation exchange resin has a sulfonic acid group or a salt thereof and an amide group. In a preferred embodiment, the cation exchange resin has a sulfonic acid group and an amide group.

[0055] In a preferred embodiment, the cation exchange resin is a polymer having the structure of the following formula as described in International Journal of Hydrogen Energy 40 (2015) 6422-6429.

[0056]

[0057] In preferred embodiments, the cation exchange resin is a polymer having an acrylamide monomer as a monomer, which has an anionic group such as a sulfonic acid group or a salt thereof. Examples of acrylamide monomers include N,N-dimethylacrylamide, N-methylacrylamide, N-ethylacrylamide, N-isopropylacrylamide, N-t-butylacrylamide, N-hydroxymethylacrylamide, and 2-hydroxyethylacrylamide. As an acrylamide monomer having an anionic group, for example, one in which at least some of the hydrogen atoms of the alkyl group in the molecule of the acrylamide monomer are substituted with an anionic group can be used. It is preferable that the acrylamide monomer having an anionic group is water-soluble. As an acrylamide monomer having an anionic group, an acrylamide monomer having a sulfonic acid group is preferred, for example, 2-acrylamide-2-methylpropanesulfonic acid (AMPS) can be cited.

[0058]

[0059] Cation exchange resins can be prepared, for example, by polymerizing a mixture containing the above-mentioned monomer, solvent, and polymerization initiator.

[0060] The solvent is not particularly limited, but when using the above-mentioned acrylamide monomer having an anionic group as the monomer, the solvent is preferably water or a mixed solvent of water and another solvent, and more preferably water. Other solvents include hydrophilic solvents such as methanol and lower alcohols such as ethanol. The amount of solvent in the above mixture is not particularly limited, but is, for example, 10 to 80% by mass of the total amount of monomer.

[0061] The polymerization initiators used are not particularly limited and can include thermal polymerization initiators, photopolymerization initiators, etc. Examples of thermal polymerization initiators include 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AAPH), ammonium persulfate (APS), azobisisobutyronitrile (AIBN), 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, 1,1'-azobis(cyclohexanecarbonitride), di-tert-butyl peroxide, tert-butyl hydroperoxide, and benzoyl peroxide. The thermal polymerization initiator is preferably a water-soluble thermal polymerization initiator. The thermal polymerization initiator may be used alone or in a mixture of two or more types.

[0062] Examples of photopolymerization initiators include azo polymerization initiators such as 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AAPH); 2,2-diethoxyacetophenone, 2,4-diethoxyacetophenone, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 1-hydroxycyclohexylphenyl ketone, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one, and 2-hydroxy-4'-(2-hydroxyethoxy)-2 Examples of photopolymerization initiators include acetophenone-based photopolymerization initiators such as methylpropiophenone; benzoin-based photopolymerization initiators such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and benzyldimethyl ketal; and benzophenone-based photopolymerization initiators such as benzophenone, benzoylbenzoic acid, methyl benzoylbenzoate, 4-phenylbenzophenone, hydroxybenzophenone, acrylic benzophenone, and 4-benzoyl-4'-methyldiphenyl sulfide. The photopolymerization initiator is preferably a water-soluble photopolymerization initiator. The photopolymerization initiator may be used alone or in a mixture of two or more types.

[0063] In the above mixture, the content of the polymerization initiator is not particularly limited, but is, for example, 0.5 to 5 mol% relative to the total amount of monomers.

[0064] The above mixture preferably further contains a crosslinking agent. By using a crosslinking agent, the resulting cation exchange resin may have a crosslinked structure. This can improve the mechanical strength of the cation exchange resin. The crosslinking agent is not particularly limited, but examples include polyfunctional (meth)acrylamides such as N,N'-methylenebis(meth)acrylamide, N,N'-ethylenebis(meth)acrylamide, N-[tris(3-acrylamidepropoxymethyl)methyl]acrylamide, N,N',N''-triacryloyldiethylenetriamine, and N,N',N'',N''-tetraacryloyltriethylenetetramine. Among these, N-[tris(3-acrylamidepropoxymethyl)methyl]acrylamide is preferred. N-[tris(3-acrylamidepropoxymethyl)methyl]acrylamide dissolves in a solvent such as water and can form a three-dimensional crosslinked body having a three-dimensional network structure by radical polymerization using a photopolymerization initiator or a thermal polymerization initiator. Therefore, a polymer electrolyte that can be used more stably as an electrolyte layer can be obtained.

[0065]

[0066] In the above mixture, the content of the crosslinking agent is not particularly limited, but the molar ratio of monomer to crosslinking agent is, for example, 25:1 to 100:1, and preferably 40:1 to 60:1.

[0067] The above mixture may further contain additives such as polymerization accelerators.

[0068] The conditions for the polymerization reaction of the above mixture can be appropriately set depending on the type and amount of monomer used, the type of polymerization initiator, etc. For example, when a photopolymerization initiator is used as the polymerization initiator, the polymerization reaction can be carried out by irradiating the above mixture with UV light with a wavelength of 200 to 400 nm.

[0069] When the cation exchange resin has sulfonic acid groups, the amount of sulfonic acid groups contained in the cation exchange resin (the amount of sulfonic acid groups W (mol / g) contained in 1 g of cation exchange resin) is not particularly limited, but for example, it is 0.0005 to 0.005 mol / g, preferably 0.001 to 0.005 mol / g, and more preferably 0.001 to 0.002 mol / g. The effects of the present invention can be obtained even more significantly when the amount is within the above range. The amount of sulfonic acid groups contained in the cation exchange resin can be calculated based on the chemical structure of the cation exchange resin.

[0070] The thickness of the cation exchange resin (polymer electrolyte) used in the electrolyte layer is not particularly limited, but is, for example, 0.1 to 1000 μm, preferably 10 to 100 μm. The electrolyte layer may also further include a cellulose separator, a porous sheet separator, a nonwoven fabric separator, etc., between the cation exchange resin (polymer electrolyte) and the positive electrode active material layer or the negative electrode active material layer.

[0071] The polymer electrolyte may further contain a gelling agent for gelling the electrolyte. As the gelling agent, a polymer that absorbs the solvent of the electrolyte and swells can be used, and polymers such as polyethylene oxide, polyvinyl alcohol, polyacrylamide, and starch can be used.

[0072] (Alkaline Aqueous Solution) As described above, the electrolyte layer of the manganese zinc oxide secondary battery according to this embodiment contains an alkaline aqueous solution. An alkaline aqueous solution is an aqueous solution that exhibits alkalinity when an alkaline substance is dissolved in water. The alkaline aqueous solution is preferably an aqueous solution containing an alkali metal hydroxide. Examples of alkali metal hydroxides include potassium hydroxide, sodium hydroxide, lithium hydroxide, etc., but potassium hydroxide is more preferred. Alternatively, an aqueous solution containing other hydroxides (such as ammonium hydroxide) may be used as the electrolyte. The electrolyte is preferably an alkaline electrolyte. In the manganese zinc oxide secondary battery according to this embodiment, the electrolyte containing the alkaline aqueous solution exists in a state where it has permeated into the cation exchange resin. There is also an electrolyte (alkaline aqueous solution) that is not contained in the cation exchange resin but is sealed inside the outer casing (laminate film). Here, it is preferable that the molar concentration of alkali in the former is equal to or greater than the molar concentration of alkali in the latter. In other words, when X is the molar concentration of alkali in the alkaline aqueous solution contained in the cation exchange resin, and Y is the molar concentration of alkali in the alkaline aqueous solution not contained in the cation exchange resin but sealed inside the outer casing, it is preferable that X ≥ Y, and more preferably that X > Y. This is because satisfying X ≥ Y (and therefore X > Y) makes it easier for zinc ions to move to the negative electrode side during the charging process due to the concentration gradient between X and Y, thereby promoting the progress of the charging reaction and improving the charging capacity. There are no particular restrictions on the specific numerical values ​​of X and Y, but X is preferably 2 to 10 [mol / L], more preferably 3 to 8 [mol / L], and particularly preferably 3 to 5 [mol / L]. Also, Y is preferably 1 to 8 [mol / L], more preferably 2 to 5 [mol / L], and particularly preferably 2 to 3 [mol / L]. Furthermore, the value of the X / Y ratio is preferably 1 or more, more preferably greater than 1, even more preferably 1.3 or more, and particularly preferably 1.6 or more. It is preferable that the values ​​of X, Y, and X / Y are within these ranges, as this can further improve the discharge capacity of the manganese zinc oxide secondary battery. In a preferred embodiment, Y is 2 to 5 [mol / L] when X ≥ Y.In other preferred embodiments, Y is 2 to 3 [mol / L] when X > Y. Furthermore, in these preferred embodiments, X is particularly preferably 3 to 5 [mol / L].

[0073] [Positive electrode current collector plate and negative electrode current collector plate] The material constituting the current collector plates (25, 27) is not particularly limited, and known highly conductive materials conventionally used as current collector plates for secondary batteries can be used. Preferred materials for the current collector plates are metallic materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof. From the viewpoint of lightness, corrosion resistance, and high conductivity, aluminum and copper are more preferred, and aluminum is particularly preferred. The positive electrode current collector plate 25 and the negative electrode current collector plate 27 may be made of the same material, or different materials may be used.

[0074] Although not shown in the diagram, the current collector 11 and the current collector plates (25, 27) may be electrically connected via positive and negative leads. The materials used for the positive and negative leads can be the same as those used in known aqueous secondary batteries. It is preferable to cover the parts removed from the casing with heat-resistant, heat-shrinkable tubing or the like to prevent leakage current from contacting peripheral equipment or wiring and affecting the product (e.g., automotive parts, especially electronic equipment).

[0075] [Battery Enclosure] As the battery enclosure, a known metal can case can be used, or, as shown in Figure 1, a bag-shaped case made of a laminate film 29 containing aluminum that can cover the battery elements can be used. For example, a three-layer laminate film made by laminating PP, aluminum, and nylon in that order can be used, but there are no limitations to these. Laminate film is preferable from the viewpoint of being able to increase output power and have excellent cooling performance, and can be suitably used for batteries in large equipment for EVs and HEVs.

[0076] [Method for Manufacturing a Manganese-Zinc Secondary Battery] The method for manufacturing a manganese-zinc secondary battery according to one embodiment of the present invention is not particularly limited, and conventionally known knowledge may be referenced as appropriate. In the manufacturing of the manganese-zinc secondary battery according to the above embodiment, for example, a manganese-zinc secondary battery comprising a positive electrode containing manganese dioxide or substituted manganese dioxide as a positive electrode active material, a negative electrode containing zinc as a negative electrode active material, and an electrolyte layer disposed between the positive electrode and the negative electrode and containing a cation exchange resin, the process involves absorbing an alkaline aqueous solution into the cation exchange resin by an immersion step before manufacturing the battery elements, and injecting an alkaline aqueous solution into the casing after sealing the battery elements in the casing. In this case, it is preferable that the alkali concentration (X) of the former alkaline aqueous solution and the alkali concentration (Y) of the latter alkaline aqueous solution satisfy X ≥ Y, and more preferably that X > Y.

[0077] Furthermore, the following items are also included in the scope of the present invention: Item 1: A manganese oxide zinc secondary battery in which a battery element comprising a positive electrode active material layer containing manganese dioxide or substituted manganese dioxide, a negative electrode active material layer containing zinc, and an electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer is sealed inside an outer casing, wherein the electrolyte layer comprises an alkaline aqueous solution (preferably an aqueous solution containing an alkali metal hydroxide, more preferably a KOH aqueous solution) and a cation exchange resin; Item 2: The cation exchange resin comprises sulfonic acid groups (-SO ３A manganese zinc oxide secondary battery according to item 1, comprising H) or a salt thereof as an exchange group; item 3: a manganese zinc oxide secondary battery according to item 1 or item 2, wherein the cation exchange resin has an amide group; item 4: a manganese zinc oxide secondary battery according to any one of items 1 to 3, wherein X is the molar concentration of alkali in the alkaline aqueous solution contained in the cation exchange resin, and Y is the molar concentration of alkali in the alkaline aqueous solution not contained in the cation exchange resin but sealed inside the outer casing, such that X ≥ Y; item 5: a manganese zinc oxide secondary battery according to item 4, wherein Y is 2 to 5 [mol / L]; item 6: a manganese zinc oxide secondary battery according to item 4 or item 5, wherein X and Y satisfy X > Y; item 7: a manganese zinc oxide secondary battery according to any one of items 4 to 6, wherein Y is 2 to 3 [mol / L]; item 8: a manganese zinc oxide secondary battery according to any one of items 4 to 7, wherein X is 3 to 5 [mol / L]; Item 9: The manganese zinc oxide secondary battery according to any one of items 1 to 8, wherein the positive electrode active material layer further comprises an element of metal or an oxide thereof (preferably bismuth oxide).

[0078] The present invention will be described in more detail below using examples and comparative examples, but it is not limited in any way to the following examples.

[0079] 《Preparation of Manganese-Zinc Oxide Secondary Battery》 [Example 1] (Preparation of Cation Exchange Resin) 2-acrylamido-2-methylpropanesulfonic acid (AMPS) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), a monomer, and N-[tris(3-acrylamidopropoxymethyl)methyl]acrylamide (FOM-03006, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), a crosslinking agent, were prepared. These were weighed in a molar ratio of AMPS:FOM-03006 = 50:1, dissolved in water, a solvent, and 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AAPH) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), a photopolymerization initiator, was added in an amount of 4 mol% of the total amount of monomer to prepare a reaction solution. The reaction solution was coated onto a PET substrate and dried, and the resulting coated film was irradiated with UV light to polymerize by radical polymerization, obtaining a 2 mm thick cation exchange resin film. The cation exchange resin, a product of radical polymerization, was identified by mass spectrometry. The obtained cation exchange resin is a three-dimensional crosslinked material with a three-dimensional network structure and is insoluble in water.

[0080]

[0081] (Immersion of cation exchange resin in electrolyte) The cation exchange resin prepared above was cut into 2 cm squares and immersed in a 5 mol / L potassium hydroxide (KOH) aqueous solution for 24 hours. The cation exchange resin film immersed in a 5 mol / L potassium hydroxide (KOH) aqueous solution (X = 5 mol / L) in this manner was used as a separator in a manganese zinc oxide secondary battery below.

[0082] (Preparation of the positive electrode) Next, manganese dioxide (MnO ２A powder composition consisting of 62.0 parts by mass of (manufactured by Tosoh Corporation) and 16.7 parts by mass of acetylene black (manufactured by Denka Co., Ltd., Denka Black®; average particle size (primary particle size): 0.023 μm) as a conductive additive was mixed at 2000 rpm for 1 minute using a planetary stirring type mixing and kneading device "Awatori Rentaro" (ARE-310, manufactured by Thinky Co., Ltd.). Next, 13.0 parts by mass of bismuth oxide as an additive was added and mixed at 2000 rpm for 1 minute using the same device. Furthermore, a PTFE aqueous dispersion (60% dispersion) containing polytetrafluoroethylene (PTFE) (8.3 parts by mass) as a binder was added to the above powder composition and mixed at 2000 rpm for 1 minute using the same device. After that, the obtained powder composition was kneaded manually for 5 minutes, then rolled using a roll press, and dried at 60°C for 3 minutes to obtain a positive electrode active material layer. Then, this positive electrode active material layer was cut into 2 cm squares and pressed onto a positive electrode current collector made of nickel foil to produce the positive electrode of this embodiment.

[0083] (Fabrication of manganese oxide zinc secondary battery) A negative electrode was fabricated by laminating zinc foil (300 μm thick) as a negative electrode active material layer onto the surface of a negative electrode current collector made of nickel foil.

[0084] The positive electrode active material layer of the positive electrode and the negative electrode active material layer of the negative electrode, both prepared as described above, were placed facing each other, and the cation exchange resin film prepared as described above was placed between them as a separator to obtain a laminate (battery element). Nickel tabs were then attached to the positive electrode current collector and the negative electrode current collector, and the battery element was placed inside an outer casing made of aluminum laminate film so that these tabs were exposed to the outside. Then, the electrolyte was injected, and the laminate film was vacuum sealed to produce the manganese-zinc oxide secondary battery of this embodiment. As the electrolyte, a potassium hydroxide aqueous solution with a concentration of 3 mol / L (Y = 3 mol / L) was used.

[0085] [Example 2] A manganese zinc oxide secondary battery of this example was fabricated using the same method as in Example 1 described above, except that the concentration of the electrolyte (potassium hydroxide aqueous solution) immersed in the cation exchange resin film as a separator was changed to 3 mol / L (X = 3 mol / L).

[0086] [Example 3] A manganese oxide zinc secondary battery of this example was manufactured using the same method as in Example 1 described above, except that the concentration of the electrolyte (potassium hydroxide aqueous solution) injected into the casing when manufacturing the manganese oxide zinc secondary battery was changed to 5 mol / L (Y = 5 mol / L).

[0087] [Example 4] A manganese oxide zinc secondary battery of this example was manufactured using the same method as in Example 1 described above, except that the concentration of the electrolyte (potassium hydroxide aqueous solution) injected into the outer casing when manufacturing the manganese oxide zinc secondary battery was changed to 8 mol / L (Y = 8 mol / L).

[0088] [Comparative Example 1] A manganese oxide zinc secondary battery of this comparative example was prepared using the same method as in Example 4 described above, except that a vinylon separator was used instead of a cation exchange resin membrane as the separator.

[0089] Evaluation of Manganese-Zinc Oxide Secondary Batteries The manganese-zinc oxide secondary batteries prepared as described above were evaluated for their battery performance (discharge capacity) using the following method. The experiments were conducted in a constant temperature bath at 298 K (25 °C).

[0090] (Charge / Discharge Test Conditions) Charge / discharge test machine: TOSCAT-3000, model TYS-30TU10 (manufactured by Toyo System Co., Ltd.) Charge / discharge conditions (6-hour cutoff for each process): [Discharge process] 0.2C (current density 15mA / g), 1.8V → 1.0V (CC) [Charge process] 0.2C (current density 15mA / g), 1.0V → 1.8V (CC).

[0091] The initial process for the aqueous secondary battery prepared as described above is the discharge process. Here, to eliminate the influence of irreversible capacity, the initial discharge and charge processes were performed under the conditions described above. Next, a discharge process was performed under the same conditions as above, and the discharge capacity (second discharge capacity) was measured. The results are shown in Table 1 below.

[0092]

[0093] A comparison of Examples 1-4 and Comparative Example 1 shown in Table 1 reveals that the manganese-zinc oxide secondary battery configuration according to this embodiment significantly improves the second discharge capacity. This is likely because the cation exchange resin film, positioned as a separator, prevents the movement of zinc ions from the negative electrode to the positive electrode during discharge, thereby suppressing the formation of passivation (heterolite) at the positive electrode and the resulting decrease in discharge capacity.

[0094] Furthermore, it was shown that satisfying X ≥ Y improves the second discharge capacity, and that satisfying X > Y further improves the second discharge capacity.

[0095] This application claims priority to Japanese Patent Application No. 2025-051939, filed on 26 March 2025, the contents of which are incorporated herein by reference in their entirety.

[0096] 10a Stacked secondary battery, 11' Positive electrode current collector, 12 Negative electrode current collector, 13 Positive electrode active material layer, 15 Negative electrode active material layer, 17 Electrolyte layer, 19 Single cell layer, 21 Battery element, 25 Positive electrode current collector plate (positive electrode tab), 27 Negative electrode current collector plate (negative electrode tab), 29 Laminate film.

Claims

1. A manganese oxide zinc secondary battery comprising a battery element enclosed inside an outer casing, the battery element comprising: a positive electrode active material layer containing manganese dioxide or substituted manganese dioxide; a negative electrode active material layer containing zinc; and an electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer, wherein the electrolyte layer comprises an alkaline aqueous solution and a cation exchange resin.

2. The cation exchange resin has sulfonic acid groups (-SO ３ A manganese zinc oxide secondary battery according to claim 1, comprising H) or a salt thereof as an exchange group.

3. The manganese zinc oxide secondary battery according to claim 1 or 2, wherein the cation exchange resin has an amide group.

4. A manganese zinc oxide secondary battery according to claim 1 or 2, wherein X is the molar concentration of alkali in the alkaline aqueous solution contained in the cation exchange resin, and Y is the molar concentration of alkali in the alkaline aqueous solution not contained in the cation exchange resin but sealed inside the outer casing, such that X ≥ Y.

5. The manganese zinc oxide secondary battery according to claim 4, wherein Y is 2 to 5 [mol / L].

6. The manganese zinc oxide secondary battery according to claim 4, wherein X and Y satisfy X > Y.

7. The manganese zinc oxide secondary battery according to claim 6, wherein Y is 2 to 3 [mol / L].

8. The manganese zinc oxide secondary battery according to claim 7, wherein X is 3 to 5 [mol / L].

9. The manganese zinc oxide secondary battery according to claim 1 or 2, wherein the positive electrode active material layer further comprises an element of metal or an oxide thereof.

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