Method for manufacturing manganese oxide-zinc secondary battery

Abstract

The purpose of the present invention is to provide, in a manganese oxide-zinc secondary battery using a polymer electrolyte, a means capable of improving a current value at a reaction potential.　The present invention provides a method for manufacturing a manganese oxide-zinc secondary battery including: 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 holding an electrolyte solution as a polymer electrolyte, the method including preparing the polymer electrolyte by causing the cation exchange resin to absorb the electrolyte solutions through two or more immersion steps, wherein concentrations of the electrolyte solutions absorbed in the two or more immersion steps are sequentially decreased.

Description

Method for manufacturing a manganese-zinc oxide secondary battery

[0001] This invention relates to a method for producing 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 oxide secondary battery, that uses metallic Zn, ZnO, a Zn alloy, or a Zn compound as the negative electrode active material and an alkali metal hydroxide aqueous solution, such as an aqueous potassium hydroxide solution, as the electrolyte.

[0004] In recent years, research and development have been conducted on secondary batteries that use polymer electrolytes as the electrolyte constituting the electrolyte layer. A polymer electrolyte generally refers to a material in which an electrolyte is held in an ionic conductive polymer. By using a polymer electrolyte, it is possible to prevent leakage, prevent liquid junctions, and obtain a highly reliable secondary battery.

[0005] On the other hand, our own research has shown that in secondary batteries using polymer electrolytes, a sufficient current value may not be obtained at the reaction potential.

[0006] Therefore, the present invention aims to provide a means for improving the current value at the reaction potential in a manganese zinc oxide secondary battery using a polymer electrolyte.

[0007] The inventors of the present invention conducted diligent research to solve the above problems. As a result, they discovered that the above problems can be solved by preparing a polymer electrolyte in the manufacturing of a manganese zinc oxide secondary battery by absorbing an electrolyte into a cation exchange resin through two or more immersion steps, and by gradually decreasing the concentration of the electrolyte during this process, thus completing the present invention.

[0008] In other words, one embodiment of the present invention is a method for producing a manganese zinc oxide 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, containing a cation exchange resin holding an electrolyte as a polymer electrolyte, wherein the method includes preparing a polymer electrolyte by allowing the cation exchange resin to absorb an electrolyte through two or more immersion steps, and the concentration of the electrolyte absorbed in the two or more immersion steps is sequentially decreased.

[0009] This is a schematic cross-sectional view of a stacked (flat) non-bipolar (internal parallel connection type) manganese-zinc oxide secondary battery.

[0010] One embodiment of the present invention is a method for manufacturing a manganese zinc oxide 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, containing a cation exchange resin holding an electrolyte as a polymer electrolyte, wherein the method includes preparing a polymer electrolyte by allowing the cation exchange resin to absorb the electrolyte through two or more immersion steps, and progressively decreasing the concentration of the electrolyte absorbed in the two or more immersion steps. According to this embodiment of the method for manufacturing a manganese zinc oxide secondary battery, the current value at the reaction potential can be improved in a manganese zinc oxide secondary battery using a polymer electrolyte.

[0011] 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.

[0012] 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 manufactured by the manufacturing method of this embodiment.

[0013] As shown in Figure 1, the stacked secondary battery 10a has a structure in which a roughly rectangular power generation element 21, where the charge and discharge reaction actually takes place, is sealed inside a laminate film 29. Here, the power generation 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 the adjacent negative electrode active material layer 15 face each other via the electrolyte layer 17.

[0014] 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 power generation 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 power generation element 21, and the negative electrode active material layer may be provided on one or both sides of the outermost negative electrode current collector.

[0015] 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) as needed, by ultrasonic welding, resistance welding, or the like.

[0016] The following describes the main components of a manganese oxide zinc secondary battery.

[0017] [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.

[0018] 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.

[0019] 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.

[0020] [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.

[0021] 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.

[0022] 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.

[0023] 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, chemically synthesized manganese dioxide can be produced by mixing, for example, an aqueous solution of potassium permanganate, an aqueous solution of manganese sulfate, and an aqueous solution of sodium hydroxide.

[0024] 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.

[0025] Substituted manganese dioxide is obtained by substituting a part of the oxygen element in manganese dioxide with one or more substitution elements.

[0026] There are no particular limitations on the type of substitution element, as long as it can exhibit the functions and effects of the present invention and does not adversely affect the performance or safety of the battery, any such element can be used. Examples of the substitution element include nitrogen, phosphorus, sulfur, selenium, chlorine, bromine, iodine, and fluorine. Among these, the substitution element preferably contains nitrogen or sulfur.

[0027] Manganese dioxide (MnO ２ ), the proportion of the oxygen element constituting manganese dioxide that is substituted by the above substitution element can be appropriately determined in consideration of desired performance. For example, based on 100 mol% of the total oxygen element constituting manganese dioxide, the substitution ratio of the oxygen element by the above 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 is defined as 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.

[0028] The method for obtaining substituted manganese dioxide (the method of substituting oxygen element with a substitution element) is not particularly limited. For example, when nitrogen is used as the substitution element, nitrogen gas (N ２ ) or ammonia gas (NH ３ ), a gas phase reaction in which substitution is promoted by heating manganese dioxide under an atmosphere can be employed. In this case, the substitution ratio described above can be increased by prolonging the reaction time. Further, substitution with these elements can be achieved by carrying out the gas phase reaction in the presence of a gas such as fluorine (F ２ ), chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ ) instead of nitrogen gas.

[0029] Furthermore, substitution is possible not only through gas-phase reactions but also through liquid-phase reactions. For example, urea (CO(NH) in an aqueous solution. ２ ) ２ In the presence of a nitrogen source such as ), manganese sulfate (MnSO4) ４ Substituted manganese dioxide can also be obtained by hydrothermal synthesis, which involves oxidizing metal salts of Mn(II), such as ), using oxidizing agents such as sulfuric acid or ammonium peroxysulfate. In this case, the substitution ratio can be increased by extending the reaction time or increasing the amount of nitrogen source.

[0030] Furthermore, when substituting with elements exhibiting elemental properties with melting points below 200°C (such as sulfur or phosphorus), it is possible to obtain substituted manganese dioxide by dissolving these elemental substitution elements in an argon atmosphere and heating and holding them together with manganese dioxide at approximately 200°C. In this case, the substitution ratio can be increased by extending the heating and holding time or by increasing the amount of substitution element in the reaction system during heating.

[0031] The manganese dioxide or substituted manganese dioxide described above may form secondary particles. Secondary particles refer to aggregates of primary particles. Primary particles refer to the smallest unit of solid particles that are separable and have boundaries between them. The average secondary particle diameter of manganese dioxide or substituted manganese dioxide is, for example, less than 100 μm, preferably less than 20 μm, and more preferably less than 10 μm. Furthermore, there is no particular lower limit to the average secondary particle diameter of manganese dioxide or substituted manganese dioxide, but it may be, for example, 0.1 μm or more, 0.3 μm or more, or 0.6 μm or more. In other words, 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, and more preferably 0.6 μm or more and less than 10 μm. In this specification, the average secondary particle diameter of manganese dioxide or substituted manganese dioxide as the positive electrode active material is measured by a laser diffraction / scattering particle size distribution analyzer, and the 50% cumulative diameter (D) is determined based on volume. ５０ This is the value calculated as follows:

[0032] The average primary particle diameter of manganese dioxide or substituted manganese dioxide is not particularly limited, but the crystallite diameter estimated using Scherrer's formula from the 101 peaks confirmed by XRD measurement is, for example, between 0.005 μm and 1.5 μm. Furthermore, the ratio of the average primary particle diameter to the average secondary particle diameter (average secondary particle diameter / average primary particle diameter) of manganese dioxide or substituted manganese dioxide is not particularly limited, but is, for example, between 1 and 1000.

[0033] 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.

[0034] Furthermore, the content of the positive electrode active material in the positive electrode active material layer (total amount if two or more types are included) is preferably 30 to 99% by mass, more preferably 50 to 85% by mass, and even more preferably 60 to 80% by mass, based on 100% by mass of the total solid content of the positive electrode active material layer.

[0035] <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.

[0036] (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.

[0037] 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.

[0038] 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.

[0039] (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, 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 (PCTFE) ), fluororesins such as ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene fluororubber (VDF-HFP fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene fluororubber (VDF-HFP-TFE fluororubber), vinylidene fluoride-pentafluoropropylene fluororubber (VDF-PFP fluororubber), vinyl Examples include vinylidene fluoride-based fluororubbers such as redene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubbers (VDF-PFP-TFE-based fluororubbers), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene-based fluororubbers (VDF-PFMVE-TFE-based fluororubbers), and vinylidene fluoride-chlorotrifluoroethylene-based fluororubbers (VDF-CTFE-based fluororubbers), as well as epoxy resins.Among these, polyvinylidene fluoride (PVDF), polyimide, styrene-butadiene rubber, carboxymethylcellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are preferred.

[0040] 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.

[0041] (Metals (Oxides)) Metals (oxides) are elements of metals 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. Among these, bismuth or its oxide (bismuth oxide) is preferred from the viewpoint of its high effect in improving charge-discharge efficiency, and bismuth oxide (Bi ２ O ３ It is particularly preferable that ) be used.

[0042] 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.

[0043] 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.

[0044] [Negative electrode active material layer] The negative electrode active material layer contains negative electrode active material.

[0045] (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.

[0046] 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.

[0047] 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.

[0048] The shape of the negative electrode active material is not particularly limited, such as particulate or plate-shaped, but it is preferable to have a particulate shape, as this increases the surface area and enables it to handle high current discharge. When the negative electrode active material is particulate, the preferred average particle diameter 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 surface area is large, making 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 diameter of the negative electrode active material is measured by a particle size distribution analyzer using the laser diffraction / scattering method, and the 50% cumulative diameter (D) is determined based on volume. ５０ This is the value calculated as follows:

[0049] [Electrolyte Layer] In the manganese zinc oxide secondary battery manufactured by the manufacturing method of this embodiment, the electrolyte layer is arranged between the positive electrode and the negative electrode. Specifically, it is arranged adjacent to the positive electrode active material layer and the negative electrode active material layer, respectively.

[0050] The electrolyte layer contains a cation exchange resin holding an electrolyte as a polymer electrolyte. The polymer electrolyte may be gel-like; that is, the polymer electrolyte may be a gel polymer electrolyte.

[0051] (Cation exchange resin) The cation exchange resin is not particularly limited, but it is preferably one that captures zinc ions. The cation exchange resin can maintain the charge balance of the entire cell by capturing zinc ions while releasing cations such as hydrogen ions.

[0052] In a manganese-zinc secondary battery, the battery reaction during discharge 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 ２ O At this time, Zn produced at the negative electrode ２＋ (Zinc ions) move through the electrolyte layer towards the positive electrode, and as a side reaction at 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 passive layer called a heterolite is formed. When a passive layer is formed, it is inactive to the battery reaction, which can reduce the battery capacity. In contrast, by using a cation exchange resin in the electrolyte layer, zinc ions can be coordinated to the anionic functional groups of the cation exchange resin, trapping the zinc ions. This makes it difficult for zinc ions to move to the positive electrode side. As a result, the formation of heterolites during discharge is suppressed, and the battery capacity can be improved.

[0053] 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 salt groups of the sulfonic acid group include sodium salt, potassium salt, lithium salt, and so on.

[0054] 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.

[0055] 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.

[0056] In a preferred embodiment, the cation exchange resin is a polymer having the structure of the following formula as described in the International Journal of Hydrogen Energy 40 (2015) 6422-6429.

[0057]

[0058] 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 or a salt thereof is preferred, for example, 2-acrylamide-2-methylpropanesulfonic acid (AMPS) can be cited.

[0059]

[0060] Cation exchange resins can be prepared, for example, by polymerizing a mixture containing the above-mentioned monomer, solvent, and polymerization initiator.

[0061] 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.

[0062] The polymerization initiators used are not particularly limited and can include thermal polymerization initiators, photopolymerization initiators, etc. Examples of thermal polymerization initiators include ammonium persulfate (APS), azobisisobutyronitrile (AIBN), 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, 1,1'-azobis(cyclohexanecarbonilate), di-tert-butylperoxide, tert-butylhydroperoxide, 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.

[0063] Examples of photopolymerization initiators include acetophenone-based photopolymerization initiators such as 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-methylpropiophenone; benzoin, be Examples of photopolymerization initiators include benzoin-based photopolymerization initiators such as benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and benzyldimethyl ketal; benzophenone-based photopolymerization initiators such as benzophenone, benzoylbenzoic acid, methyl benzoylbenzoate, 4-phenylbenzophenone, hydroxybenzophenone, acrylic benzophenone, and 4-benzoyl-4'-methyldiphenyl sulfide; and 2,2'-Azobis(2-methylpropionamidin) dihydrochloride. 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.

[0064] 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.

[0065] 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 with 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.

[0066]

[0067] 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.

[0068] The above mixture may further contain additives such as polymerization accelerators.

[0069] 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.

[0070] When the cation exchange resin has sulfonic acid groups or salts thereof, the total amount of sulfonic acid groups and salts contained in the cation exchange resin (total amount of sulfonic acid groups and salts contained in 1 g of cation exchange resin V (mol / g)) 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 within the above range. The total amount of sulfonic acid groups and salts contained in the cation exchange resin can be calculated based on the chemical structure of the cation exchange resin.

[0071] In the manganese zinc oxide secondary battery manufactured by the method of this embodiment, the electrolyte is preferably an aqueous solution containing an alkali metal hydroxide as the electrolyte. Examples of alkali metal hydroxides include potassium hydroxide, sodium hydroxide, and lithium hydroxide, 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 manufactured by this embodiment, the electrolyte exists in a state where it has permeated into the cation exchange resin.

[0072] In the polymer electrolyte used in the electrolyte layer of the manganese zinc oxide secondary battery manufactured by the method of this embodiment, the amount of electrolyte held in the cation exchange resin is not particularly limited, but the content of the cation exchange resin relative to the total mass of the cation exchange resin and the electrolyte is, for example, 10 to 80% by mass, preferably 20 to 50% by mass. The content of the electrolyte is, for example, 20 to 90% by mass, preferably 50 to 80% by mass, relative to the total mass of the cation exchange resin and the electrolyte.

[0073] The amount of alkali metal ions retained by the cation exchange resin (the amount of alkali metal ions W (mol / g) contained in the electrolyte absorbed by 1 g of cation exchange resin) (also expressed as the amount of alkali metal ions in the electrolyte retained by the cation exchange resin) is not particularly limited, but for example, it is 0.002 mol / g or more, preferably 0.003 mol / g or more, and more preferably 0.0037 mol / g or more. The effects of the present invention can be obtained even more significantly within the above range. The upper limit of the amount of alkali metal ions retained by the cation exchange resin is not particularly limited, but for example, it is 0.1 mol / g or less, and preferably 0.01 mol / g or less. The amount of alkali metal ions retained by the cation exchange resin can be calculated from the mass of the cation exchange resin before and after immersion in the electrolyte. The amount W (mol / g) of alkali metal ions in the electrolyte held by the cation exchange resin is, for example, 0.002 to 0.1 mol / g, preferably 0.003 to 0.01 mol / g, and more preferably 0.0037 to 0.01 mol / g.

[0074] In a preferred embodiment, the cation exchange resin contains amide groups and sulfonic acid groups or salts thereof, and the electrolyte contains an alkali metal hydroxide, wherein the ratio W / V, which is the ratio of the amount of alkali metal ions in the electrolyte held by the cation exchange resin (W (mol / g)) to the total amount of sulfonic acid groups and salts contained in the cation exchange resin (V (mol / g)), is 2 or more. When a polymer electrolyte is used as the electrolyte constituting the electrolyte layer, the ionic conductivity of the electrolyte layer is generally lower compared to when an electrolyte is used. However, when the W / V value is 2 or more, the electrolyte is in excess of the amount of anionic groups in the polymer electrolyte, so the ionic conductivity is improved and becomes comparable to that when an electrolyte is used. As a result, the current value at the reaction potential is further improved, and the battery performance can be further improved. The W / V value is more preferably 3 or more, and even more preferably 4 or more. The upper limit of the W / V value is not particularly limited, but for example, it is 20 or less. The W / V value is preferably 2 to 20, more preferably 3 to 20, and even more preferably 4 to 20.

[0075] 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.

[0076] The thickness of the polymer electrolyte used in the electrolyte layer is not particularly limited, but is, for example, 0.1 to 2000 μm, for example, 1 to 2000 μm, for example, 1 to 1000 μm, and 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 polymer electrolyte and the positive electrode active material layer or the negative electrode active material layer.

[0077] [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.

[0078] Furthermore, although not shown in the diagram, the current collectors (11', 12) 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 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).

[0079] [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 power generation element can be used. For example, a three-layer laminate film made by laminating polypropylene (PP), aluminum, and nylon in that order can be used, but there are no limitations to these. A laminate film is preferable from the viewpoint of being able to increase power output and have excellent cooling performance, and can be suitably used for batteries in large equipment for EVs and HEVs. Furthermore, a laminate film containing aluminum is more preferable for the enclosure because it is possible to easily adjust the group pressure applied to the power generation element from the outside and to easily adjust to the desired electrolyte layer thickness.

[0080] [Method for Manufacturing a Manganese-Zinc Secondary Battery] One embodiment of the present invention is a method for manufacturing 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 holding an electrolyte as a polymer electrolyte, wherein the method includes preparing a polymer electrolyte by allowing the cation exchange resin to absorb an electrolyte through two or more immersion steps, and the concentration of the electrolyte absorbed in the two or more immersion steps is sequentially decreased.

[0081] Batteries using polymer electrolytes in the electrolyte layer are less prone to leakage and offer superior safety due to the smaller amount of electrolyte used. However, polymer electrolytes generally exhibit less ion diffusion and movement than liquid electrolytes. Therefore, it has been found that using a polymer electrolyte in the electrolyte layer of a manganese-zinc secondary battery can hinder the zinc dissolution reaction, potentially resulting in a lower current value in response to the reaction potential.

[0082] Polymer electrolytes are generally prepared by immersing a polymer in an electrolyte solution and allowing the polymer to absorb the solution. However, even after immersion, the amount of absorbed liquid reaches equilibrium, and the polymer gradually becomes less able to absorb the electrolyte. Furthermore, polymer electrolytes have the problem that ions do not diffuse as easily internally as in electrolytes. This difficulty in ion diffusion can hinder the progress of battery reactions, potentially leading to a decrease in reaction current.

[0083] In this method, a cation exchange resin, acting as a polymer, is first immersed in a high-concentration electrolyte, and then sequentially immersed in electrolytes of lower concentration, repeating this multi-stage immersion process to produce a polymer electrolyte. In this way, osmotic pressure is generated due to the concentration difference between the electrolyte inside and outside the polymer, allowing for greater absorption of the electrolyte. As a result, the ion diffusion and movement state in the resulting polymer electrolyte approaches that of the electrolyte. This is thought to facilitate the elution and extraction reaction of zinc, which is a battery reaction, and potentially increase the current value that responds to the reaction potential.

[0084] In this case, the concentration of the electrolyte in the two or more immersion steps should be controlled so that the concentration of the electrolyte in the first immersion step is the highest, and the concentration decreases sequentially in the second and subsequent steps. There are no particular restrictions on the specific value of the concentration, but it is preferable to prepare it in the range of 0.1 to 15 mol / L. In a preferred embodiment, the concentration of the electrolyte in the first immersion step is 1 mol / L or higher. This can make the effects of the present invention even more pronounced. The concentration of the electrolyte in the first immersion step is preferably 1 to 10 mol / L, more preferably 4 to 10 mol / L, even more preferably 7 to 10 mol / L, and even more preferably 8 to 10 mol / L. Furthermore, the concentration of the electrolyte in the final immersion step is, for example, 0.1 to 6 mol / L, preferably 1 to 5 mol / L, and more preferably 3 to 5 mol / L. Here, the concentration of the electrolyte refers to the concentration of the electrolyte in the electrolyte. For example, when using alkali metal hydroxides such as potassium hydroxide, sodium hydroxide, or lithium hydroxide as the electrolyte, the concentration of the electrolyte refers to the concentration of the alkali metal hydroxide. If the electrolyte contains two or more types of electrolytes, the total concentration of those electrolytes is considered the concentration of the electrolyte.

[0085] In a preferred embodiment, the ratio X / Y of the electrolyte concentration X in the first immersion step to the electrolyte concentration Y in the final immersion step is greater than 1 and less than or equal to 2. When X / Y is 2 or less, the concentration difference of the electrolyte does not become too large, which suppresses the discharge of ions from inside the polymer to the outside due to an excessively large concentration gradient of ions such as alkali metal ions. As a result, the concentration of the electrolyte inside the cation exchange resin can be kept at a high concentration, and a higher reaction current can be obtained. The value of X / Y is more preferably 1.1 to 1.9, even more preferably 1.3 to 1.9, and even more preferably 1.4 to 1.8.

[0086] The immersion process can be carried out in two or more stages, for example, in 2 to 10 stages, preferably 2 to 5 stages. If the number of immersion stages is 10 or less, batteries can be manufactured efficiently.

[0087] The specific form of each immersion step is not particularly limited. The thickness of the cation exchange resin as a polymer is not particularly limited, but is, for example, 0.1 to 2000 μm, for example, 1 to 2000 μm, for example, 1 to 1000 μm, and preferably 10 to 100 μm. The amount of electrolyte used to immerse the polymer is also not particularly limited, as long as it is enough to sufficiently immerse the polymer. The immersion time is also not particularly limited, but the time for the first immersion step is, for example, 1 to 48 hours, preferably 2 to 36 hours, and more preferably 6 to 24 hours. The time for the second and subsequent immersion steps is, for example, 0.1 to 24 hours, preferably 0.5 to 24 hours, and more preferably 1 to 6 hours. The temperature conditions in each immersion step are also not particularly limited, and are, for example, carried out at a temperature of 20 to 40°C. Furthermore, the processing solution containing the polymer and electrolyte may be stirred during immersion. It is preferable to carry out each immersion step continuously, but a rest period may be inserted between each immersion step. The final thickness of the polymer electrolyte is not particularly limited, but is, for example, 1 to 2000 μm, for example, 1 to 1000 μm, and preferably 10 to 100 μm.

[0088] The method for manufacturing a manganese zinc oxide secondary battery of this embodiment includes preparing a polymer electrolyte by allowing an electrolyte to be absorbed into a cation exchange resin through two or more immersion steps, and is not particularly limited as long as the concentration of the electrolyte absorbed in the two or more immersion steps is sequentially decreased, and conventionally known methods can be used as appropriate.

[0089] The following items are also included in the scope of the present invention: Item 1: A method for producing a manganese zinc oxide 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, containing a cation exchange resin holding an electrolyte as a polymer electrolyte, wherein the method includes preparing a polymer electrolyte by allowing the cation exchange resin to absorb the electrolyte through two or more immersion steps, and sequentially decreasing the concentration of the electrolyte absorbed in the two or more immersion steps; Item 2: The method for producing a manganese zinc oxide secondary battery according to Item 1, wherein the cation exchange resin contains amide groups and sulfonic acid groups or salts thereof, the electrolyte contains alkali metal hydroxides, and the ratio W / V, which is the ratio of the amount of alkali metal ions in the electrolyte held by the cation exchange resin to the total amount (V) of sulfonic acid groups and salts contained in the cation exchange resin, is 2 or more; Item 3: A method for manufacturing a manganese zinc oxide secondary battery according to Item 1 or 2, wherein in the two or more immersion steps, the ratio X / Y of the concentration X of the electrolyte in the first immersion step to the concentration Y of the electrolyte in the last immersion step is greater than 1 and less than or equal to 2; Item 4: A method for manufacturing a manganese zinc oxide secondary battery according to Item 3, wherein the concentration X of the electrolyte in the first immersion step is 1 mol / L or more.

[0090] 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.

[0091] [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-methylpropionamide) Dihydrochloride, a photopolymerization initiator, was added in an amount of 4 mol% relative to the total amount of monomer to prepare a reaction solution. The reaction solution was applied to a PET substrate and dried, and the resulting coating film was irradiated with UV light to polymerize by radical polymerization, obtaining a 2 mm thick film-like cation exchange resin. The cation exchange resin, a product of radical polymerization, was identified by mass spectrometry. The obtained cation exchange resin is a crosslinked material with a three-dimensional network structure and is insoluble in water.

[0092]

[0093] (First Immersion Step) The cation exchange resin prepared above was immersed in an 8 mol / L potassium hydroxide (KOH) aqueous solution, which is the electrolyte, for 24 hours. This first immersion step is the first of two immersion steps that allow the cation exchange resin to absorb the electrolyte.

[0094] (Second immersion step) Next, the cation exchange resin was immersed in a 5 mol / L KOH aqueous solution for 1 hour to obtain a polymer electrolyte. This second immersion step is the final of two immersion steps in which the cation exchange resin absorbs the electrolyte.

[0095] (Total amount V of sulfonic acid groups and their salts contained in the cation exchange resin and amount W of potassium ions in the electrolyte held by the cation exchange resin) For the polymer electrolyte obtained as an electrolyte layer, the total amount V (mol / g) of sulfonic acid groups and their salts contained in the cation exchange resin and the amount W (mol / g) of potassium ions in the electrolyte held by the cation exchange resin were determined. The total amount V of sulfonic acid groups and their salts contained in the cation exchange resin (total amount (mol / g) of sulfonic acid groups and their salts contained in 1 g of cation exchange resin) was determined from the mass of the cation exchange resin and the polymerization ratio of the monomers during synthesis. The amount W (amount (mol / g) of potassium ions in the electrolyte absorbed by 1 g of cation exchange resin) was calculated by determining the mass of the absorbed electrolyte from the mass of the polymer electrolyte as the final electrolyte layer and the mass of the cation exchange resin before immersion in the electrolyte. The results are shown in Table 1 below.

[0096] (Measurement of reaction current) A symmetrical cell was prepared by using two Zn foils (20 μm thick) as counter electrodes and the above polymer electrolyte (2 mm thick) as the working electrode, and a reference electrode (Ag / AgCl) was placed on the polymer electrolyte. Cyclic voltammetry (CV) measurements were performed using this cell. CV measurements were performed in the voltage range of -1.5 to 1.5 V at a sweep rate of 10 mV / sec. The Zn of the oxidation side current value obtained by CV measurement was... ２＋ The reaction current (mA / cm²) is calculated by dividing the peak value of the reaction by the area of ​​the polymer electrolyte. ２ The value of ) was used.

[0097] [Example 2] A cell was prepared in the same manner as in Example 1, except that the electrolyte concentration in the first immersion step was 4 mol / L and the electrolyte concentration in the second immersion step was 3 mol / L, and the reaction current was measured.

[0098] [Example 3] A cell was prepared in the same manner as in Example 1, except that the electrolyte concentration in the first immersion step was 7 mol / L and the electrolyte concentration in the second immersion step was 3 mol / L, and the reaction current was measured.

[0099] [Comparative Example 1] A cell was prepared in the same manner as in Example 1, except that the concentration of the electrolyte in the second immersion step was set to 8 mol / L, and the reaction current was measured.

[0100] [Comparative Example 2] A cell was prepared in the same manner as in Example 1, except that the electrolyte concentration in the first immersion step was 6.5 mol / L and the electrolyte concentration in the second immersion step was 6.5 mol / L, and the reaction current was measured.

[0101] [Comparative Example 3] A cell was prepared in the same manner as in Example 1, except that the concentration of the electrolyte in the first immersion step was 5 mol / L, and the reaction current was measured.

[0102] [Comparative Example 4] A cell was prepared in the same manner as in Example 1, except that the electrolyte concentration in the first immersion step was 5 mol / L and the electrolyte concentration in the second immersion step was 8 mol / L, but the reaction current could not be measured.

[0103] The results are shown in Table 1 below.

[0104]

[0105] As shown in Table 1, in Examples 1 to 3, the cation exchange resin was immersed in an electrolyte solution in two stages. The concentration X of the electrolyte solution immersed in the first stage was higher than the concentration Y of the electrolyte solution immersed in the second stage. It was found that this resulted in a higher reaction current compared to Comparative Examples 1 to 3, where the concentration of the electrolyte solution immersed in each stage was the same. Furthermore, in Comparative Example 4, where the concentration Y of the electrolyte solution immersed in the second stage was higher than the concentration X of the electrolyte solution immersed in the first stage, the electrolyte impregnation did not proceed sufficiently, and the reaction current could not be measured.

[0106] In particular, cells in Examples 1 and 2, where the ratio (X / Y) of the electrolyte concentration X in the first immersion step to the electrolyte concentration Y in the second immersion step was greater than 1 and less than or equal to 2, yielded higher reaction currents.

[0107] This application is based on Japanese Patent Application No. 2025-051949, filed on 26 March 2025, the disclosures of which are incorporated herein by reference in their entirety.

[0108] 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 Power generation 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 method for manufacturing a manganese zinc oxide 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 holding an electrolyte as a polymer electrolyte, wherein the method includes preparing a polymer electrolyte by allowing the cation exchange resin to absorb an electrolyte through two or more immersion steps, and progressively decreasing the concentration of the electrolyte absorbed in the two or more immersion steps.

2. The method for producing a manganese zinc oxide secondary battery according to claim 1, wherein the cation exchange resin comprises an amide group and a sulfonic acid group or a salt thereof, the electrolyte comprises an alkali metal hydroxide, and the ratio W / V, which is the ratio of the amount of alkali metal ions in the electrolyte held by the cation exchange resin to the total amount (V) of sulfonic acid groups and salt groups contained in the cation exchange resin, is 2 or more.

3. The method for manufacturing a manganese zinc oxide secondary battery according to claim 1, wherein in the two or more immersion steps, the ratio X / Y of the concentration X of the electrolyte in the first immersion step to the concentration Y of the electrolyte in the last immersion step is greater than 1 and less than or equal to 2.

4. The method for producing a manganese zinc oxide secondary battery according to claim 3, wherein the concentration X of the electrolyte in the first immersion step is 1 mol / L or more.

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