Aquatic batteries

Abstract

Water-based batteries, which charge and discharge by the deposition and dissolution of zinc at the negative electrode, have room for improvement in terms of cycle characteristics and charge / discharge stability. [Solution] The aqueous battery of the present disclosure comprises a positive electrode, an aqueous electrolyte, and a negative electrode. The aqueous electrolyte comprises water, potassium polyphosphate dissolved in the water, and one or both of zinc phosphate and zinc polyphosphate dissolved in the water. The negative electrode comprises zinc.

Description

[Technical Field]

[0001] This application discloses an aqueous battery. [Background technology]

[0002] Aqueous batteries are known in which charging and discharging are performed by the deposition and dissolution reaction of zinc at the negative electrode. Patent Document 1 discloses an aqueous electrolyte containing water and zinc sulfate dissolved in the water. It is believed that by combining such an aqueous electrolyte with a negative electrode containing zinc, an aqueous battery that utilizes the deposition and dissolution reaction of zinc can be constructed. Patent Document 2 discloses an aqueous electrolyte containing water and potassium pyrophosphate, etc., dissolved in the water, and also discloses that an aqueous battery can be constructed by combining this aqueous electrolyte with a negative electrode containing zinc. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2024-089305 [Patent Document 2] U.S. Patent Application Publication No. 2003 / 077512 [Overview of the project] [Problems that the invention aims to solve]

[0004] Water-based batteries, which charge and discharge by the deposition and dissolution of zinc at the negative electrode, have room for improvement in terms of cycle characteristics and charge / discharge stability. [Means for solving the problem]

[0005] This application discloses several embodiments as means for solving the above-mentioned problems. <Aspect 1> A water-based battery having a positive electrode, an aqueous electrolyte, and a negative electrode, The aforementioned aqueous electrolyte, Water and, the potassium polyphosphate dissolved in the water, one or both of zinc phosphate and zinc polyphosphate dissolved in the water, , the negative electrode comprises zinc, aqueous battery. <Aspect 2> The aqueous battery according to Aspect 1, wherein the potassium polyphosphate is potassium pyrophosphate, aqueous battery. <Aspect 3> The aqueous battery according to Aspect 1 or 2, wherein the aqueous electrolyte comprises the zinc polyphosphate dissolved in the water, aqueous battery. <Aspect 4> The aqueous battery according to Aspect 3, wherein the zinc polyphosphate is zinc pyrophosphate, aqueous battery. <Aspect 5> The aqueous battery according to any one of Aspects 1 to 4, wherein the potassium ion concentration of the aqueous electrolyte is more than 9.5 mol / L, aqueous battery. <Aspect 6> The aqueous battery according to any one of Aspects 1 to 5, wherein the pH of the aqueous electrolyte is 3 or more and 14 or less, aqueous battery. <Aspect 7> The aqueous battery according to any one of Aspects 1 to 6, wherein the positive electrode comprises an oxide as a positive electrode active material, aqueous battery. <Aspect 8> The aqueous battery according to any one of Aspects 1 to 7, wherein the aqueous electrolyte comprises the potassium polyphosphate dissolved at a concentration of 4 mol or more per 1 kg of the water, aqueous battery. <Aspect 9> The aqueous battery according to any one of Aspects 1 to 8, wherein the aqueous electrolyte has no freezing point at -40°C or higher, aqueous battery. <Aspect 10> A water-based battery according to any of embodiments 1 to 9, One or both of the positive electrode and the negative electrode have a current collector containing Al. water-based battery. [Effects of the Invention]

[0006] The aqueous battery disclosed herein performs charging and discharging by the deposition and dissolution of zinc in the negative electrode, and exhibits excellent cycle characteristics and charge / discharge stability. [Brief explanation of the drawing]

[0007] [Figure 1] A schematic example of the configuration of a water-based battery is shown. [Figure 2] A schematic example of the configuration of a water-based battery is shown. [Figure 3A] This shows the relationship between the concentration of potassium ions in an aqueous electrolyte (corresponding to the solubility of potassium pyrophosphate) and the concentration of zinc ions (corresponding to the saturation solubility of zinc salts). [Figure 3B] This shows the relationship between the potassium ion concentration in an aqueous electrolyte (corresponding to the solubility of potassium pyrophosphate) and the zinc ion concentration (zinc ion concentration when 0.5 mol of zinc salt is added per 1 kg of water). [Figure 4A] This is a cyclic voltammogram of an aqueous electrolyte solution prepared by dissolving 1 mole of potassium pyrophosphate and 0.5 moles of zinc pyrophosphate per kilogram of water. [Figure 4B] This is a cyclic voltammogram of an aqueous electrolyte solution prepared by dissolving 2 moles of potassium pyrophosphate and 0.5 moles of zinc pyrophosphate per kilogram of water. [Figure 4C] This is a cyclic voltammogram of an aqueous electrolyte solution prepared by dissolving 3 moles of potassium pyrophosphate and 0.5 moles of zinc pyrophosphate per 1 kg of water. [Figure 4D]This is a cyclic voltammogram of an aqueous electrolyte solution prepared by dissolving 4 moles of potassium pyrophosphate and 0.5 moles of zinc pyrophosphate per 1 kg of water. [Figure 4E] This is a cyclic voltammogram of an aqueous electrolyte solution prepared by dissolving 5 moles of potassium pyrophosphate and 0.5 moles of zinc pyrophosphate per 1 kg of water. [Figure 4F] This is a cyclic voltammogram of an aqueous electrolyte solution to which 0.5 mol of zinc pyrophosphate was added per 1 kg of water. [Figure 5A] This figure illustrates the ΔV in a cyclic voltammogram for an aqueous electrolyte solution prepared by dissolving 1 mole of potassium pyrophosphate and 0.5 moles of zinc pyrophosphate per kilogram of water. [Figure 5B] This figure illustrates the ΔV in a cyclic voltammogram for an aqueous electrolyte solution prepared by dissolving 5 moles of potassium pyrophosphate and 0.5 moles of zinc pyrophosphate per 1 kg of water. [Figure 5C] This shows the relationship between the concentration of potassium pyrophosphate aqueous solution and the potential difference ΔV. [Figure 6] The peak current values ​​on the oxidation side of the CV (Cylindrical Voltage) are shown for aqueous electrolytes prepared by adding a saturating amount of zinc pyrophosphate or zinc sulfate to an aqueous solution of potassium pyrophosphate at various concentrations. [Figure 7A] This is a DSC curve for an aqueous electrolyte solution prepared by dissolving 5 moles of potassium pyrophosphate and 0.5 moles of zinc pyrophosphate per 1 kg of water. [Figure 7B] This is a DSC curve for an aqueous electrolyte solution prepared by dissolving 5 moles of potassium pyrophosphate and a saturated concentration of zinc pyrophosphate per 1 kg of water. [Figure 7C] This is a DSC curve for an aqueous electrolyte solution prepared by dissolving 4 moles of potassium pyrophosphate and 0.5 moles of zinc pyrophosphate per 1 kg of water. [Figure 7D] This is a DSC curve for an aqueous electrolyte solution prepared by dissolving 3 moles of potassium pyrophosphate and 0.5 moles of zinc pyrophosphate per 1 kg of water. [Figure 7E] This is a DSC curve for an aqueous electrolyte solution prepared by dissolving 4 moles of potassium pyrophosphate and 1.0 mole of zinc pyrophosphate per 1 kg of water. [Figure 7F] This is a DSC curve for an aqueous electrolyte solution prepared by dissolving 4 moles of potassium pyrophosphate and a saturated concentration of zinc sulfate per 1 kg of water. [Figure 8] For aqueous electrolytes, the relationship between potassium ion concentration and zinc ion concentration detected by ICP and the concentration range in which antifreeze properties are exhibited is shown. [Figure 9A] This shows the DSC evaluation results for saturated zinc pyrophosphate aqueous solution. [Figure 9B] This shows the DSC evaluation results for a zinc sulfate aqueous solution with a concentration of 4 mol / kg. [Figure 10A] The relationship between ionic conductivity and potassium pyrophosphate concentration is shown for each concentration of potassium pyrophosphate aqueous solution, and for an aqueous solution obtained by adding 0.5 mol / kg of zinc pyrophosphate to the potassium pyrophosphate aqueous solution. [Figure 10B] The relationship between viscosity and potassium pyrophosphate concentration is shown for each concentration of potassium pyrophosphate aqueous solution, and for each aqueous solution obtained by adding 0.5 mol / kg of zinc pyrophosphate to the potassium pyrophosphate aqueous solution. [Figure 10C] The relationship between pH and potassium pyrophosphate concentration is shown for each concentration of potassium pyrophosphate aqueous solution, and for each aqueous solution obtained by adding 0.5 mol / kg of zinc pyrophosphate to the potassium pyrophosphate aqueous solution. [Figure 11] This shows the results of charge and discharge tests of aqueous batteries using various aqueous electrolytes. [Figure 12] This shows the results of charge and discharge tests of aqueous batteries using various aqueous electrolytes. [Modes for carrying out the invention]

[0008] An embodiment of the aqueous battery of the present disclosure will be described below with reference to the drawings, but the technology of the present disclosure is not limited to the following embodiment.

[0009] As shown in Figure 1, an aqueous battery 100 according to one embodiment has a positive electrode 10, an aqueous electrolyte 20, and a negative electrode 30. The aqueous electrolyte 20 contains water, potassium polyphosphate dissolved in the water, and one or both of zinc phosphate and zinc polyphosphate dissolved in the water. The negative electrode contains zinc.

[0010] 1. Positive electrode Any known positive electrode for a water-based battery can be used for the positive electrode 10. As shown in Figure 1, the positive electrode 10 may comprise a positive electrode active material layer 11 and a positive electrode current collector 12.

[0011] 1.1 Cathode active material layer The positive electrode active material layer 11 contains positive electrode active material. The positive electrode active material layer 11 is impregnated with an aqueous electrolyte 20. In addition to the positive electrode active material, the positive electrode active material layer 11 may also contain conductive additives, binders, etc. Furthermore, the positive electrode active material layer 11 may also contain various other additives. The content of each component in the positive electrode active material layer 11 can be appropriately determined according to the desired battery performance. For example, with the entire positive electrode active material layer 11 (total solid content) as 100% by mass, the content of positive electrode active material may be 40% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more, or 100% by mass or less, or 90% by mass or less. The shape of the positive electrode active material layer 11 is not particularly limited, and for example, it may be a sheet-shaped positive electrode active material layer having a substantially flat surface. The thickness of the positive electrode active material layer 11 is not particularly limited and may be, for example, 0.1 μm or more, 1 μm or more, or 10 μm or more, or 2 mm or less, 1 mm or less, or 500 μm or less.

[0012] As the positive electrode active material, any substance that can function as a positive electrode active material for an aqueous battery can be adopted. The positive electrode active material can be appropriately selected in consideration of the potential window and the like of the aqueous electrolyte solution 20 described later. Further, in the present embodiment, various ions derived from the aqueous electrolyte solution can serve as charge compensation ions. Specifically, the charge compensation ions deintercalated and intercalated by the positive electrode active material may be, for example, one or more of protons, potassium ions, zinc ions, anions derived from the electrolyte, and hydroxide ions. The positive electrode active material is, for example, Ni(OH)₂ which is a layered nickel hydroxide compound (for example, JP 2023-154313 A), or A x K y Ni 1-z M z O 2±δ ·nH₂O (A is at least one selected from Li, Na, Rb, Cs, Mg, Ca, Sr, and Ba and Sc, M is at least one selected from transition metal elements, Group 2A elements, Group 3A elements, Group 2B elements, and Group 3B elements, 0≦x<0.5, 0<y≦0.5, 0≦z≦0.5, 0<n≦2, and the relationship (α·x)+y≦0.5 is satisfied, where α is the valence of the cation of A. For example, JP 2023-132287 A), manganese spinel (for example, LiMn₂O₄), various hydroxides and oxides such as nickel-manganese-cobalt-containing composite oxide (NMC). In particular, when the positive electrode contains an oxide as the positive electrode active material, effects such as higher potential, higher capacity, and improved energy density of the aqueous battery are likely to be obtained. Further, the positive electrode active material may be an oxide containing an alkali metal element, a polyanion, or the like. More specifically, it may be a composite oxide of an alkali metal element and a transition metal. The composite oxide is an alkali metal cobalt composite oxide (such as AmCoO₂, where "Am" is an alkali metal element; the same applies hereinafter), an alkali metal nickel composite oxide (such as AmNiO₂), an alkali metal nickel titanium composite oxide (AmNi 1 / 2 Ti 1 / 2 O₂, etc.), an alkali metal nickel manganese composite oxide (AmNi 1 / 2 Mn 1 / 2 O₂, AmNi 1 / 3 Mn 2 / 3O2, etc.), alkali metal manganese composite oxides (AmMnO2, AmMn2O4, etc.), alkali metal iron manganese composite oxides (Am 2 / 3 Fe 1 / 3 Mn 2 / 3 O2, etc.), alkali metal nickel-cobalt-manganese composite oxide (AmNi 1 / 3 Co 1 / 3 Mn 1 / 3 The positive electrode active material may be at least one selected from alkali metal iron composite oxides (such as O2), alkali metal iron composite oxides (such as AmFeO2), alkali metal chromium composite oxides (such as AmCrO2), alkali metal iron phosphate compounds (such as AmFePO4), alkali metal manganese phosphate compounds (such as AmMnPO4), and alkali metal cobalt phosphate compounds (AmCoPO4). Alternatively, the positive electrode active material may be one or both of manganese oxide and vanadium oxide. Alternatively, the positive electrode active material may be an active material such as Prussian blue. Alternatively, the positive electrode active material may be at least one selected from alkali metal titanium composite oxides, TiO2, sulfur (S), etc., which exhibit a nobler charge-discharge potential compared to the negative electrode active material described later. The positive electrode active material may de-insert and de-insert charge compensation ions by intercalation, or by conversion reactions, alloying reactions, etc. Only one positive electrode active material may be used alone, or two or more may be used in combination.

[0013] The shape of the positive electrode active material is limited to any shape that can function as the positive electrode active material of a battery. The positive electrode active material may be, for example, particulate. The positive electrode active material may be solid, hollow, have voids, or be porous. The positive electrode active material may be primary particles or secondary particles formed by the aggregation of multiple primary particles. The average particle diameter D50 of the positive electrode active material may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and may also be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. In this application, the average particle diameter D50 refers to the particle diameter (median diameter) at 50% of the cumulative value in the volume-based particle size distribution determined by laser diffraction-scattering.

[0014] Examples of conductive additives that may be included in the positive electrode active material layer 11 include carbon materials such as vapor-processed carbon fiber (VGCF), acetylene black (AB), Ketjenblack (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF); and metallic materials that are poorly soluble in electrolytes containing nickel, titanium, aluminum, stainless steel, etc. The conductive additive may be in the form of parts or fibers, and its size is not particularly limited. One type of conductive additive may be used alone, or two or more types may be used in combination.

[0015] Examples of binders that may be included in the positive electrode active material layer 11 include butadiene rubber (BR) binders, butylene rubber (IIR) binders, acrylate butadiene rubber (ABR) binders, styrene butadiene rubber (SBR) binders, polyvinylidene fluoride (PVdF) binders, polytetrafluoroethylene (PTFE) binders, and polyimide (PI) binders. A single binder may be used alone, or two or more binders may be used in combination.

[0016] 1.2 Positive electrode current collector As shown in Figure 1, the positive electrode 10 may include a positive electrode current collector 12 that contacts the positive electrode active material layer 11. The positive electrode current collector 12 contacts the aqueous electrolyte 20. Any positive electrode current collector capable of functioning as a positive electrode current collector in an aqueous battery can be used. The positive electrode current collector 12 may contain Al or may not contain Al. In this embodiment, one or both of the positive electrode 10 and the negative electrode 30 may have a current collector containing Al. The leaching of Al from the current collector into the aqueous electrolyte is particularly likely to occur on the positive electrode side, which is at the oxidation potential. However, with the aqueous battery 100 of this disclosure, even if the positive electrode current collector 12 contains Al, the leaching of Al from the positive electrode current collector 12 into the aqueous electrolyte 20 can be suppressed. That is, in the aqueous battery 100, at least the positive electrode 10 may have a current collector containing Al.

[0017] If the positive electrode current collector 12 contains Al, the positive electrode current collector 12 may be made entirely of Al, or at least a portion of its surface may be made of Al. For example, the positive electrode current collector 12 may be made of Al foil, or the surface of a metal foil or some substrate may be coated with Al. The positive electrode current collector 12 may have Al present on at least a portion of the surface that comes into contact with the aqueous electrolyte 20, or Al may be present throughout the entire surface that comes into contact with the aqueous electrolyte 20.

[0018] The positive electrode current collector 12 may be in the form of foil, plate, mesh, perforated metal, or foam. The positive electrode current collector 12 may be composed of metal foil or metal mesh. Metal foil is particularly easy to handle. The positive electrode current collector 12 may consist of multiple foils. Examples of metal materials constituting the positive electrode current collector 12 include those containing at least one element selected from the group consisting of Cu, Ni, Al, V, Au, Pt, Mg, Fe, Ti, Pb, Co, Cr, Zn, Ge, In, Sn, and Zr. In particular, as mentioned above, it is preferable for the positive electrode current collector 12 to contain Al. The positive electrode current collector 12 may be a metal foil or a substrate on which the above metals are plated or deposited. Furthermore, if the positive electrode current collector 12 consists of multiple metal foils, there may be some kind of layer between the multiple metal foils. The thickness of the positive electrode current collector 12 is not particularly limited. For example, the thickness may be 0.1 μm or more, or 1 μm or more, or 1 mm or less, or 100 μm or less.

[0019] 2.Aqueous electrolyte The aqueous electrolyte 20 comprises water, potassium polyphosphate dissolved in the water, and one or both of zinc phosphate and zinc polyphosphate dissolved in the water. The aqueous electrolyte 20 is, for example, in contact with the positive electrode current collector 12 described above, contained in the positive electrode active material layer 11 described above, in contact with the negative electrode current collector 32 described below, contained in the negative electrode active material layer 31 described below, and held between the positive electrode 10 and the negative electrode 30 by the separator 40.

[0020] 2.1 Solvent The aqueous electrolyte 20 contains water as a solvent. The solvent mainly consists of water. That is, water accounts for 50 mol% to 100 mol% of the total amount of solvent constituting the aqueous electrolyte, based on 100 mol%. Water may account for 70 mol% or more, 90 mol% or more, or 95 mol% or more of the total amount of solvent. On the other hand, there is no particular upper limit to the proportion of water in the solvent. The solvent may consist only of water (100 mol% water).

[0021] The solvent may contain, for example, a solvent other than water, in addition to water, to the extent that it can solve the above problems, such as from the viewpoint of forming an SEI (Solid Electrolyte Interphase) on the surface of the active material. Examples of solvents other than water include one or more organic solvents selected from ethers, carbonates, nitriles, alcohols, ketones, amines, amides, sulfur compounds, and hydrocarbons. The solvent other than water may account for 50 mol% or less, 30 mol% or less, 10 mol% or less, or 5 mol% or less, based on the total amount of solvent constituting the electrolyte (100 mol%).

[0022] 2.2 Electrolytes The aqueous electrolyte 20 contains an electrolyte that can dissociate into cations and anions in the aqueous electrolyte 20. In the aqueous electrolyte 20, the cations and anions may be in close proximity to each other and form aggregates.

[0023] 2.2.1 Potassium polyphosphate The aqueous electrolyte 20 contains potassium polyphosphate dissolved in the water. "Potassium polyphosphate" refers to a salt in which at least some of the hydrogen atoms of polyphosphate are replaced with potassium. In other words, "potassium polyphosphate" is a concept that includes potassium hydrogen polyphosphate. A specific example of potassium polyphosphate is potassium pyrophosphate (K 4-x H x P2O7, x<4), potassium tripolyphosphate (K 5-y H y P3O 10Examples include potassium pyrophosphate (K) as potassium polyphosphate. 4-x H x When P2O7 (x<4) is used, the low molecular weight of potassium polyphosphate allows the charge-discharge reaction to proceed more smoothly, making it easier to ensure even higher performance. In the aqueous electrolyte 20, "potassium polyphosphate dissolved in water" may exist as potassium ions, polyphosphate ions, aggregates of these ions, or aggregates with ions derived from potassium hydrogen phosphate, phosphoric acid, polyphosphate, and carboxylic acid, as described later. In the aqueous electrolyte 20, the "concentration of potassium polyphosphate dissolved in water" can be determined by converting the ions and aggregates contained in the aqueous electrolyte 20 to potassium polyphosphate. In this application, "potassium polyphosphate dissolved in water" may also refer to the ions and aggregates formed in the aqueous electrolyte 20 as a result of separately adding a cation source (e.g., a potassium compound) and an anion source (e.g., polyphosphate) to the aqueous electrolyte 20.

[0024] The concentration of potassium polyphosphate in the aqueous electrolyte 20 is not particularly limited. According to the inventors' new findings, when the aqueous electrolyte 20 contains potassium polyphosphate dissolved at a concentration of 1 mol or more per 1 kg of water, in particular when it contains potassium polyphosphate dissolved at a concentration of 3 mol or more per 1 kg of water, and even more specifically when it contains potassium polyphosphate dissolved at a concentration of 4 mol or more per 1 kg of water, and even more specifically when it contains potassium polyphosphate dissolved at a concentration of 4 mol or more and 6 mol or less per 1 kg of water, it can be expected that the electrochemical stability of the electrolyte will be improved, and the electrolyte will be more easily imparted with antifreeze properties. Furthermore, when the concentration of potassium pyrophosphate in the aqueous electrolyte 20 is 4 mol or more per 1 kg of water, it is easier to obtain an aqueous electrolyte 20 that does not have a freezing point above -40°C. On the other hand, when the aqueous electrolyte 20 contains potassium polyphosphate dissolved at a concentration of 1 mol to 4 mol per kg of water, and more particularly when it contains potassium polyphosphate dissolved at a concentration of 1 mol to 3 mol per kg of water, and even more particularly when it contains potassium polyphosphate dissolved at a concentration of 1 mol to 2 mol per kg of water, the viscosity of the aqueous electrolyte 20 tends to decrease and the ionic conductivity tends to increase.

[0025] 2.2.2 Zinc phosphate and / or zinc polyphosphate The aqueous electrolyte 20 contains one or both of zinc phosphate and zinc polyphosphate dissolved in the water. "Zinc phosphate" refers to a zinc phosphate salt in which some of the hydrogen atoms of phosphoric acid are replaced with zinc. In other words, "zinc phosphate" is a concept that includes zinc hydrogen phosphate. Specific examples of zinc phosphate include, for example, those represented by Zn3(PO4)2 and Zn(H2PO4)2. "Zinc polyphosphate" refers to a zinc polyphosphate salt in which at least some of the hydrogen atoms of polyphosphate are replaced with zinc. In other words, "zinc polyphosphate" is a concept that includes zinc hydrogen polyphosphate. Specific examples of zinc polyphosphate include zinc pyrophosphate (Zn 2-x H 2xExamples include P2O7, x<2), and zinc tripolyphosphate. In particular, when the aqueous electrolyte 20 contains zinc polyphosphate dissolved in water, and more specifically, when it contains zinc pyrophosphate dissolved in water, it is easier to ensure excellent performance, such as being able to lower the pH of the aqueous electrolyte 20. Zinc phosphate and zinc polyphosphate are not easily soluble in water on their own, but as mentioned above, in an aqueous solution in which potassium polyphosphate is dissolved, the saturation solubility of zinc phosphate and zinc polyphosphate increases as the concentration of potassium polyphosphate increases. In other words, the concentration of zinc in the aqueous electrolyte 20 can be increased. In the aqueous electrolyte 20, "zinc phosphate dissolved in water" and "zinc polyphosphate dissolved in water" may exist as zinc ions, phosphate ions, polyphosphate ions, aggregates of these ions, or aggregates with ions derived from potassium polyphosphate, potassium hydrogen phosphate, phosphoric acid, polyphosphate, and carboxylic acid, as described below. In the aqueous electrolyte 20, the "concentration of zinc phosphate dissolved in water" and the "concentration of zinc polyphosphate dissolved in water" can be determined by converting the ions and aggregates contained in the aqueous electrolyte 20 into zinc phosphate and zinc polyphosphate. In this application, "zinc phosphate dissolved in water" and "zinc polyphosphate dissolved in water" may refer to ions and aggregates formed in the aqueous electrolyte 20 as a result of separately adding a cation source (e.g., a zinc compound) and an anion source (e.g., phosphoric acid or polyphosphate) to the aqueous electrolyte 20.

[0026] When zinc is not present in the aqueous electrolyte, the reaction proceeds during charging of the aqueous battery by consuming electricity for the hydrogen generation reaction from the aqueous electrolyte, but in this case, plateau disturbance occurs. In contrast, when zinc is dissolved in the aqueous electrolyte 20 as in this embodiment, the reaction proceeds smoothly when the aqueous battery 100 is charged by the deposition (electrodeposition) of zinc contained in the aqueous electrolyte 20 onto the negative electrode 30, thereby suppressing plateau disturbance. Furthermore, the polarization during zinc deposition and dissolution on the negative electrode 30 can be reduced, allowing the zinc deposition and dissolution reactions to proceed smoothly. In particular, such effects are easily obtained when the aqueous electrolyte 20 contains a high concentration of potassium polyphosphate. As described above, the aqueous battery 100 according to this embodiment has excellent charge and discharge stability.

[0027] Zinc phosphate and zinc polyphosphate have strong cation-anion bonding forces and are poorly soluble in water. In this embodiment, potassium polyphosphate is dissolved together with zinc phosphate or zinc polyphosphate in the aqueous electrolyte 20, thereby forming a complex between potassium polyphosphate and zinc phosphate or zinc polyphosphate in the aqueous electrolyte 20. In other words, by dissolving potassium polyphosphate together with zinc phosphate or zinc polyphosphate in water, the soluble concentration of zinc in the aqueous electrolyte can be increased. As a result, as described above, plateau disturbances during charging and discharging are suppressed, and stability during charging and discharging is enhanced.

[0028] Furthermore, it is possible to ensure the stability of the charge and discharge of an aqueous battery by preparing an aqueous electrolyte with a high zinc concentration using a zinc compound that is easily soluble in water (for example, zinc sulfate or zinc halide), and then using that aqueous electrolyte to manufacture an aqueous battery. However, if an aqueous battery is constructed using an aqueous electrolyte in which only zinc sulfate is dissolved in water, the aqueous battery tends to have poor cycle characteristics. Also, if an aqueous battery is constructed using an aqueous electrolyte in which only zinc halide is dissolved in water, a side reaction is likely to occur on the positive electrode side during charging and discharging of the aqueous battery, generating halogen gas. In contrast, as in this embodiment, when an aqueous battery 100 is constructed using an aqueous electrolyte 20 containing potassium polyphosphate dissolved in water and zinc phosphate and / or zinc polyphosphate dissolved in water, the aqueous battery 100 will have excellent cycle characteristics. In addition, as described above, the dissolution of the current collector is easily suppressed, and the aqueous electrolyte 20 may also have antifreeze properties.

[0029] The concentrations of zinc phosphate and zinc polyphosphate (or their total concentration if both are included) in the aqueous electrolyte solution 20 are not particularly limited. As mentioned above, in the aqueous electrolyte solution 20, the saturation solubility of zinc phosphate and zinc polyphosphate increases as the concentration of potassium polyphosphate increases. The concentrations of zinc phosphate and zinc polyphosphate in the aqueous electrolyte solution 20 are greater than 0 mol per kg of water and less than or equal to the saturation concentration, and may be between 0.001 mol and 4.0 mol, between 0.01 mol and 3.5 mol, or between 0.1 mol and 3.0 mol.

[0030] 2.2.3 Acids or Bases The pH of the aqueous electrolyte 20 may be adjusted by adding various acids or bases to the aqueous electrolyte 20. For example, by adding an acid to the aqueous electrolyte 20 to lower the pH, an improvement in performance can be expected. Alternatively, the pH may be increased by adding a base such as potassium hydroxide to the aqueous electrolyte 20. The acid may be an inorganic acid or an organic acid. For example, the aqueous electrolyte 20 may contain at least one of orthophosphoric acid, metaphosphoric acid (polyphosphoric acid), and carboxylic acid dissolved in the water. According to the inventor's new findings, at least orthophosphoric acid, metaphosphoric acid (polyphosphoric acid), and carboxylic acid can lower the pH of the aqueous electrolyte 20 while ensuring the effects of potassium polyphosphate and zinc phosphate and / or zinc polyphosphate mentioned above. Furthermore, the interaction with potassium polyphosphate, etc. mentioned above may further enhance the effect of suppressing the dissolution of the current collector. "Metaphosphoric acid (polyphosphoric acid)" is, for example, pyrophosphoric acid (H4P2O7) and tripolyphosphoric acid (H5P3O7). 10 ) may be one or both of the above. In particular, when pyrophosphate (H4P2O7) is used as polyphosphate, it is easier to ensure even higher performance. "Carboxylic acid" may be monocarboxylic acid or polycarboxylic acid, for example, acetic acid. In the aqueous electrolyte 20, "orthophosphate (H3PO4) dissolved in water" is H + , PO4 3- In addition, it may exist as an aggregate with ions derived from potassium polyphosphate, etc., as mentioned above, for example, KPO4 2- HPO4 2- , K2PO4 - H2PO4 - , KHPO4 - It may exist as an ion, and "metaphosphoric acid (polyphosphoric acid) dissolved in water" is H + It may exist as a polyphosphate anion, or as an aggregate with ions derived from the aforementioned potassium polyphosphate, and "carboxylic acid dissolved in water" is H +It may also exist as an aggregate with a carboxylic acid anion or an ion derived from the potassium polyphosphate mentioned above. In the aqueous electrolyte 20, the "concentration of orthophosphoric acid dissolved in water," the "concentration of metaphosphoric acid dissolved in water," and the "concentration of carboxylic acid dissolved in water" can be determined by converting the ions and aggregates contained in the aqueous electrolyte 20 into orthophosphoric acid, metaphosphoric acid, and carboxylic acid.

[0031] The concentration of acid in the aqueous electrolyte 20 is not particularly limited and can be adjusted as appropriate according to the desired pH. In the aqueous electrolyte 20, the molar ratio of the total of orthophosphoric acid, metaphosphoric acid, and carboxylic acid to potassium polyphosphate ([orthophosphoric acid + metaphosphoric acid + carboxylic acid] / potassium polyphosphate) may be, for example, 0 to 20.00, 0 to 15.00, 0 to 10.00, 0 to 8.50, 0 to 7.00, 0 to 5.00, 0 to 3.00, or 0 to 1.00.

[0032] 2.2.4 Cation The aqueous electrolyte 20 may contain potassium ions as cations. In the aqueous electrolyte 20, a portion of the potassium ions contained in the aqueous electrolyte 20 can be converted into "dissolved potassium polyphosphate." However, the aqueous electrolyte 20 may contain more potassium ions than the concentration at which it can be converted into potassium polyphosphate. For example, when producing the aqueous electrolyte 20, if potassium polyphosphate and other potassium ion sources (e.g., KOH, CH3COOK, K3PO4, etc.) are added to water and dissolved, the aqueous electrolyte 20 will contain more potassium ions than the concentration at which it can be converted into potassium polyphosphate. As mentioned above, potassium ions may form aggregates with other ions. In this embodiment, the higher the potassium ion concentration in the aqueous electrolyte 20, the lower the freezing point of the aqueous electrolyte 20. For example, if the potassium ion concentration of the aqueous electrolyte 20 (the amount of potassium ions contained in 1 L of aqueous electrolyte) is greater than 9.5 mol / L, and especially greater than 11.2 mol / L, the aqueous electrolyte 20 is likely to lack a freezing point at temperatures above -40°C.

[0033] The aqueous electrolyte 20 may contain zinc ions as cations. In the aqueous electrolyte 20, some of the zinc ions contained in the aqueous electrolyte 20 can be converted into "dissolved zinc phosphate" or "dissolved zinc polyphosphate." However, the aqueous electrolyte 20 may contain more zinc ions than the concentration at which it can be converted into zinc phosphate or zinc polyphosphate. For example, when manufacturing the aqueous electrolyte 20, if a zinc ion source other than zinc phosphate or zinc polyphosphate is added to water and dissolved, the aqueous electrolyte 20 will contain more zinc ions than the concentration at which it can be converted into zinc phosphate or zinc polyphosphate. As mentioned above, zinc ions may form aggregates with other ions.

[0034] The aqueous electrolyte 20 may contain other cations to the extent that the above problems can be solved. For example, it may contain alkali metal ions other than potassium ions, alkaline earth metal ions, transition metal ions, etc. Furthermore, the aqueous electrolyte 20 naturally contains protons.

[0035] 2.2.5 Anion The aqueous electrolyte 20 may contain polyphosphate ions (which may exist in a state bonded to a cation, as described above) and phosphate ions (which may exist in a state bonded to a cation, as described above) as anions. The aqueous electrolyte 20 may also contain other anions to the extent that the above problems can be solved. For example, it may contain anions derived from other electrolytes, which will be described later. In addition, the aqueous electrolyte 20 naturally contains hydroxide ions.

[0036] 2.2.6 Other components that may be contained in aqueous electrolytes The aqueous electrolyte 20 may contain electrolytes other than potassium polyphosphate, zinc phosphate, and zinc polyphosphate, for example, other potassium salts and other zinc salts. Examples of other potassium salts include at least one selected from KPF6, KBF4, K2SO4, KNO3, (CF3SO2)2NK, KCF3SO3, (FSO2)2NK, K2HPO4, KH2PO4, KPO3, etc. The other electrolytes may account for 50 mol% or less, 30 mol% or less, or 10 mol% or less, based on the total amount of electrolyte dissolved in the electrolyte (100 mol%). In addition to the electrolytes mentioned above, the aqueous electrolyte 20 may contain various additives.

[0037] 2.3 Other properties As long as the aqueous electrolyte 20 contains the above-mentioned solvent and electrolyte, there are no particular restrictions on its other properties. Examples of other properties of the aqueous electrolyte 20 are described below.

[0038] 2.3.1 Freezing point The aqueous electrolyte 20 may not have a freezing point above -40°C. Here, the presence or absence of a "freezing point" in the aqueous electrolyte 20 is confirmed by differential scanning calorimetry (DSC). The sweep rate of the DSC is set to 1°C / min, and the sweep range is set to cool from room temperature to any temperature T. The atmosphere in the DSC is an inert gas atmosphere such as Ar, and the pressure is equivalent to atmospheric pressure. However, since a sealed aluminum container is used for evaluation, the atmosphere inside the container is the air sealed under atmospheric pressure. If the aqueous electrolyte is measured under the above conditions and no crystallization peak temperature (freezing point temperature) is confirmed above -40°C, the aqueous electrolyte is considered to "not have a freezing point above -40°C". The aqueous electrolyte 20 may not have a freezing point above -60°C, or above -80°C, or above -100°C, or above -120°C. In the aqueous battery 100 of this disclosure, in order to achieve the condition that "the aqueous electrolyte 20 does not have a freezing point at -40°C or above," it is effective to increase the concentration of potassium polyphosphate, zinc phosphate and zinc polyphosphate, and other additives in the aqueous electrolyte 20, and in particular, to increase the concentration of potassium polyphosphate. Since the aqueous electrolyte 20 does not have a freezing point at -40°C, the effect of suppressing the dissolution of the current collector is more easily enhanced. Furthermore, since the aqueous electrolyte 20 does not have a freezing point at -40°C, the aqueous battery 100 can be used even at extremely low temperatures. In other words, the aqueous battery 100 will operate properly even in cold regions.

[0039] 2.3.2 Presence or absence of salt precipitation The aqueous electrolyte 20 may not undergo salt precipitation when cooled from 0°C to -40°C. The absence of salt precipitation due to temperature changes in the aqueous electrolyte 20 enables stable ion conduction even at low temperatures. For example, the aqueous battery 100 can be used even in extremely low temperatures such as in cold regions. As described above, the aqueous electrolyte 20 contains water and potassium polyphosphate dissolved in the water. According to the inventors' knowledge, the saturation solubility of potassium polyphosphate in water has little temperature dependence and hardly changes at temperatures below 0°C. Therefore, even if the aqueous electrolyte 20 is cooled from 0°C to -40°C, salt precipitation in the aqueous electrolyte 20 is unlikely to occur.

[0040] 2.3.3 Viscosity If the viscosity of the aqueous electrolyte 20 is too high, the ionic conductivity of the aqueous electrolyte 20 may decrease. On the other hand, if potassium polyphosphate or the like is dissolved in the aqueous electrolyte 20 at a high concentration, the aqueous electrolyte 20 may have a viscosity above a certain level. From the above viewpoint, the aqueous electrolyte 20 may have a viscosity of 10 mPa·s to 400 mPa·s at 25°C. This viscosity may be 350 mPa·s or less, 300 mPa·s or less, 250 mPa·s or less, or 200 mPa·s or less.

[0041] 2.3.4 pH The pH of the aqueous electrolyte 20 is not particularly limited. However, setting the pH of the aqueous electrolyte 20 within a predetermined range makes it easier to widen the oxidation potential window of the aqueous electrolyte. Also, avoiding the aqueous electrolyte 20 becoming extremely acidic or extremely alkaline broadens the range of choices for various components that make up the battery. In this respect, the pH of the aqueous electrolyte 20 may be between 3 and 14. As mentioned above, since the aqueous electrolyte 20 contains potassium polyphosphate dissolved in water, it is easy to adjust the pH to such a range. The pH of the aqueous electrolyte 20 may be 4 or higher, 5 or higher, 6 or higher, or 7 or higher, and may be 13 or lower, 12 or lower, 11 or lower, 10 or lower, or 9 or lower.

[0042] 2.4 Variations In one embodiment, the aqueous electrolyte 20 may have the following configuration. That is, the aqueous electrolyte 20 according to one embodiment is characterized by containing water, polyphosphate ions, potassium ions, and zinc ions.

[0043] 3.Negative electrode In this embodiment, the aqueous battery 100 is charged and discharged by causing the deposition and dissolution of zinc in the negative electrode 30. Therefore, in this embodiment, the aqueous battery 100 contains zinc in the negative electrode 30. For example, as shown in Figure 1, if the negative electrode 30 comprises a negative electrode active material layer 31 and a negative electrode current collector 32, at least the negative electrode active material layer 31 contains zinc.

[0044] 3.1 Negative electrode active material layer The negative electrode active material layer 31 contains negative electrode active material. The negative electrode active material layer 31 is impregnated with an aqueous electrolyte 20. In addition to the negative electrode active material, the negative electrode active material layer 31 may also contain conductive additives, binders, etc. Furthermore, the negative electrode active material layer 31 may also contain various other additives. The content of each component in the negative electrode active material layer 31 can be appropriately determined according to the desired battery performance. For example, with the entire negative electrode active material layer 31 (total solid content) as 100% by mass, the content of the negative electrode active material may be 40% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more, or 100% by mass or less, or 90% by mass or less. The shape of the negative electrode active material layer 31 is not particularly limited, and for example, it may be a sheet-shaped negative electrode active material layer having a substantially flat surface. The thickness of the negative electrode active material layer 31 is not particularly limited and may be, for example, 0.1 μm or more, 1 μm or more, or 10 μm or more, or 2 mm or less, 1 mm or less, or 500 μm or less.

[0045] As described above, the negative electrode active material contains zinc. The "zinc" contained in the negative electrode 30 may exist as elemental zinc (metallic zinc), as a zinc alloy, or as a zinc compound. In one embodiment, the negative electrode 30 contains metallic zinc. In another embodiment, at least the negative electrode active material layer of the negative electrode 30 may be made of metallic zinc foil. Alternatively, in another embodiment, the negative electrode active material layer of the negative electrode 30 may contain zinc powder.

[0046] Furthermore, in this embodiment, the negative electrode 30 may further contain other negative electrode active materials besides zinc. The charge compensation ions of the other negative electrode active materials may be various ions derived from an aqueous electrolyte. Specifically, the charge compensation ions that the other negative electrode active materials deintercalate may be, for example, one or more of potassium ions, zinc ions, protons, anions derived from the electrolyte, and hydroxide ions. The other negative electrode active materials may be, for example, alkali metal-transition metal composite oxides; titanium oxide; metal sulfides such as Mo6S8; elemental sulfur; alkali metal-titanium composite phosphate compounds; NASICON type compounds; WO3, etc. Alternatively, the other negative electrode active materials may be hydrogen storage alloys. Alternatively, the other negative electrode active materials may be inorganic compounds having a crystal structure belonging to space group I23. Inorganic compounds having a crystal structure belonging to space group I23 may, for example, contain elements A, M, and O. Here, element A is at least one of Bi and La, and element M is at least one of Bi, Mn, Fe, Co and Ni, and both element A and element M may be Bi. The other negative electrode active material may de-insert and de-insert charge compensation ions by intercalation, or by conversion reaction, alloying reaction, etc. The other negative electrode active material may be used alone, or two or more may be used in combination.

[0047] The shape of the negative electrode active material is limited to any shape that can function as the negative electrode active material of a battery. Zinc as the negative electrode active material may be in the form of a sheet (foil), particulate matter, or other shapes. Other negative electrode active materials may be in the form of particulate matter.

[0048] Examples of conductive additives that may be included in the negative electrode active material layer 31 include carbon materials such as vapor-processed carbon fiber (VGCF), acetylene black (AB), Ketjenblack (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF); and metallic materials that are poorly soluble in electrolytes containing nickel, titanium, aluminum, stainless steel, etc. The conductive additive may be in the form of parts or fibers, and its size is not particularly limited. One type of conductive additive may be used alone, or two or more types may be used in combination.

[0049] Examples of binders that may be included in the negative electrode active material layer 31 include butadiene rubber (BR) binders, butylene rubber (IIR) binders, acrylate butadiene rubber (ABR) binders, styrene butadiene rubber (SBR) binders, polyvinylidene fluoride (PVdF) binders, polytetrafluoroethylene (PTFE) binders, and polyimide (PI) binders. A single binder may be used alone, or two or more binders may be used in combination.

[0050] 3.2 Negative electrode current collector As shown in Figure 1, the negative electrode 30 may include a negative electrode current collector 32 that contacts the negative electrode active material layer 31. The negative electrode current collector 32 contacts the aqueous electrolyte 20. Any negative electrode current collector capable of functioning as a negative electrode current collector in an aqueous battery can be used. The negative electrode current collector 32 may contain Al or may not contain Al. If the negative electrode current collector 32 contains Al, the negative electrode current collector 32 may be entirely made of Al, or at least a portion of its surface may be made of Al. For example, the negative electrode current collector 32 may be made of Al foil, or the surface of a metal foil or some substrate may be coated with Al. The negative electrode current collector 32 may have Al present on at least a portion of the surface that contacts the aqueous electrolyte 20, or Al may be present throughout the entire surface that contacts the aqueous electrolyte 20.

[0051] The negative electrode current collector 32 may be in the form of foil, plate, mesh, perforated metal, or foam. The negative electrode current collector 32 may be composed of metal foil or metal mesh. Metal foil is particularly good in terms of handling. The negative electrode current collector 32 may consist of multiple foils. Examples of metal materials constituting the negative electrode current collector 32 include those containing at least one element selected from the group consisting of Cu, Ni, Al, V, Au, Pt, Mg, Fe, Ti, Pb, Co, Cr, Zn, Ge, In, Sn, and Zr. In particular, it is preferable that the negative electrode current collector 32 contains at least one element selected from the group consisting of Al, Ti, Pb, Zn, Sn, Mg, Zr, and In, and as mentioned above, it is preferable that it contains Al. Al, Ti, Pb, Zn, Sn, Mg, Zr, and In all have low work functions, and it is considered unlikely that electrolysis of the aqueous electrolyte 20 will occur even if the negative electrode current collector 32 comes into contact with the aqueous electrolyte 20 at the reduction potential. The negative electrode current collector 32 may be a metal foil or a substrate on which the above metals are plated or deposited. Also, if the negative electrode current collector 32 consists of multiple metal foils, there may be some kind of layer between the multiple metal foils. The thickness of the negative electrode current collector 32 is not particularly limited. For example, it may be 0.1 μm or more or 1 μm or more, or 1 mm or less or 100 μm or less.

[0052] 4. Other configurations In the aqueous battery 100, various ions derived from the aqueous electrolyte 20 can function as carrier ions and charge compensating ions. The aqueous battery 100 may be an aqueous battery in which protons function as carrier ions and charge compensating ions (aqueous proton battery), an aqueous battery in which potassium ions function as carrier ions and charge compensating ions (aqueous potassium ion battery), an aqueous battery in which zinc ions function as carrier ions and charge compensating ions (aqueous zinc ion battery), an aqueous battery in which hydroxide ions function as carrier ions and charge compensating ions (aqueous hydroxide ion battery), an aqueous battery in which polyphosphate anions function as carrier ions and charge compensating ions (aqueous polyphosphate anion battery), or an aqueous battery in which other ions derived from the aqueous electrolyte 20 function as carrier ions and charge compensating ions. In the aqueous battery 100, multiple types of ions derived from the aqueous electrolyte 20 may function as carrier ions and charge compensating ions. In addition to the basic configuration described above, the aqueous battery 100 may have other configurations, such as the following.

[0053] 4.1 Separator As described above, in the aqueous battery 100, a separator 40 may be present between the positive electrode 10 and the negative electrode 30. The separator 40 may be a separator used in conventional aqueous electrolyte batteries (nickel-metal hydride batteries, zinc-air batteries, etc.). For example, it may be a hydrophilic separator such as a nonwoven fabric made of cellulose. The thickness of the separator 40 is not particularly limited and may be, for example, 5 μm or more and 1 mm or less.

[0054] 4.2 Bipolar Structure As described above, the aqueous battery 100 may have both the positive electrode current collector 12 and the negative electrode current collector 32 containing Al. In this regard, in the aqueous battery 100, an Al-containing current collector may be used as a bipolar current collector that serves both as the positive electrode current collector 12 and the negative electrode current collector 32. That is, the positive electrode 10 and the negative electrode 30 may share a single current collector. Figure 2 shows an example of a bipolar structure. As shown in Figure 2, the aqueous battery 100 may have a bipolar structure, and a positive electrode active material layer 11 may be formed on one side of the Al-containing current collector 50 (a bipolar current collector that functions as both the positive electrode current collector 12 and the negative electrode current collector 32), and a negative electrode active material layer 31 may be formed on the other side of the current collector 50. In this case, the current collector 50 containing Al may be impermeable to liquid, that is, it may not allow the aqueous electrolyte 20 to pass from the positive electrode active material layer 11 through the current collector 50 to the negative electrode active material layer 31, and vice versa.

[0055] 4.3 Terminals etc. The aqueous battery 100 may also include terminals, a battery case, etc., in addition to the above configuration. The other configurations are obvious to those skilled in the art who have referred to this application, and therefore are not described here.

[0056] 5. Method for manufacturing aqueous batteries The aqueous battery 100 disclosed herein can be manufactured, for example, as follows:

[0057] 5.1 Method for producing aqueous electrolyte The aqueous electrolyte 20 can be produced, for example, by mixing water, potassium polyphosphate, and one or both of zinc phosphate and zinc polyphosphate. Alternatively, it can be produced by mixing water with a potassium ion source, a zinc ion source, and a polyphosphate ion source. The mixing method is not particularly limited, and known mixing methods can be used. Simply filling a container with water, potassium polyphosphate, and one or both of zinc phosphate and zinc polyphosphate and leaving it to stand will cause them to mix with each other, ultimately yielding the aqueous electrolyte 20.

[0058] 5.2 Manufacturing of the positive electrode The positive electrode 10 is manufactured, for example, as follows: A positive electrode mixture paste (slurry) is obtained by dispersing the positive electrode active material and other materials constituting the positive electrode active material layer 11 in a solvent. The solvent used in this case is not particularly limited, and water or various organic solvents can be used. The positive electrode mixture paste (slurry) is applied to the surface of the positive electrode current collector 12 using a doctor blade or the like, and then dried to form the positive electrode active material layer 11 on the surface of the positive electrode current collector 12, thereby forming the positive electrode 10. In addition to the doctor blade method, electrostatic coating, dip coating, spray coating, etc. can also be used as coating methods.

[0059] 5.3 Manufacturing of the negative electrode The negative electrode 30 is manufactured, for example, as follows: A negative electrode mixture paste (slurry) is obtained by dispersing the negative electrode active material and other materials constituting the negative electrode active material layer 31 in a solvent. The solvent used in this case is not particularly limited, and water or various organic solvents can be used. The negative electrode mixture paste (slurry) is coated onto the surface of the negative electrode current collector 32 using a doctor blade or the like, and then dried to form the negative electrode active material layer 31 on the surface of the negative electrode current collector 32, thereby forming the negative electrode 30. In addition to the doctor blade method, electrostatic coating, dip coating, spray coating, etc. can also be used as coating methods. Alternatively, as described above, the negative electrode 30 may be constructed using zinc foil.

[0060] 5.4 Storage in the battery case, etc. The aqueous electrolyte 20, positive electrode 10, and negative electrode 30 are housed in a battery case to form an aqueous battery 100. For example, a separator 40 is sandwiched between the positive electrode 10 and the negative electrode 30 to obtain a laminate having a positive electrode current collector 12, a positive electrode active material layer 11, a separator 40, a negative electrode active material layer 31, and a negative electrode current collector 32 in this order. Other components such as terminals are attached to the laminate as needed. The aqueous battery 100 can be obtained by housing the laminate in a battery case, filling the battery case with the aqueous electrolyte 20, and sealing the laminate and electrolyte in the battery case so that the laminate is immersed in the aqueous electrolyte 20.

[0061] 6. Effects In the aqueous battery 100 of this disclosure, zinc is dissolved in the aqueous electrolyte 20, and when the aqueous battery 100 is charged, the zinc contained in the aqueous electrolyte 20 is deposited (electrodeposited) on the negative electrode 30, allowing the reaction to proceed smoothly and suppressing plateau disturbance. Furthermore, the polarization during zinc deposition and dissolution at the negative electrode 30 can be reduced, and the zinc deposition and dissolution reactions can proceed smoothly. In other words, the aqueous battery 100 has excellent charge and discharge stability. In addition, in the aqueous battery 100 of this disclosure, the aqueous electrolyte 20 contains potassium polyphosphate dissolved in water and zinc phosphate and / or zinc polyphosphate dissolved in water, which gives the aqueous battery 100 excellent cycle characteristics.

[0062] Furthermore, in the aqueous battery 100, the dissolution of potassium polyphosphate in the aqueous electrolyte 20 can also provide the following effect of suppressing the dissolution of current collectors containing Al.

[0063] During charging and discharging of a battery, the potential of the positive electrode becomes the potential of the oxidation side. Therefore, the Al contained in the positive electrode current collector becomes more likely to release electrons and dissolve. Specifically, the Al contained in the positive electrode current collector coordinates with anions and water molecules contained in the aqueous electrolyte and dissolves into the aqueous electrolyte. Here, potassium polyphosphate is dissolved in the aqueous electrolyte 20 of the aqueous battery 100 of this disclosure. In other words, anions derived from potassium polyphosphate, such as polyphosphate ions, may be present in the aqueous electrolyte 20. Therefore, in the aqueous battery 100 of this disclosure, during charging and discharging of the battery, the Al contained in the positive electrode current collector 12 easily coordinates with anions derived from potassium polyphosphate. Here, for example, aluminum polyphosphate has extremely low solubility in the aqueous electrolyte 20. Therefore, the Al that coordinates with anions derived from potassium polyphosphate rapidly precipitates as a solid. In other words, an insoluble or sparingly soluble Al compound precipitates near the surface of the positive electrode current collector 12, and this Al compound adheres to the surface of the positive electrode current collector 12, forming a protective film (passivation film) on that surface. As a result, in the aqueous battery 100 of this disclosure, the elution of Al from the positive electrode current collector 12 into the aqueous electrolyte 20 can be suppressed by this protective film.

[0064] During charging and discharging of a battery, the potential of the negative electrode becomes the reducing potential. As a result, the aqueous electrolyte in contact with the negative electrode is electrolyzed, generating hydroxide ions, and the pH of the aqueous electrolyte near the negative electrode tends to increase. When the pH of the aqueous electrolyte near the negative electrode increases, the solubility of Al in the aqueous electrolyte increases, making it easier for Al contained in the negative electrode current collector to dissolve into the aqueous electrolyte. In contrast, in the aqueous battery 100 of this disclosure, as described above, potassium polyphosphate is dissolved in the aqueous electrolyte 20. Therefore, in the aqueous battery 100 of this disclosure, even if Al contained in the negative electrode current collector 32 dissolves into the aqueous electrolyte 20 during charging and discharging of the battery, it quickly coordinates with anions derived from potassium polyphosphate and precipitates as a solid Al compound. In other words, an insoluble or sparingly soluble Al compound precipitates near the surface of the negative electrode current collector 32, and this Al compound adheres to the surface of the negative electrode current collector 32, forming a protective film (passivation film) on that surface. As a result, in the aqueous battery 100 of this disclosure, the elution of Al from the negative electrode current collector 32 into the aqueous electrolyte 20 can be suppressed by the protective film.

[0065] 7. Applications of aqueous batteries As described above, the aqueous battery of this disclosure exhibits excellent charge-discharge stability and cycle characteristics. Such an aqueous battery can be suitably used in at least one type of vehicle selected from, for example, hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs). That is, the technology of this disclosure also has the aspect of a vehicle having an aqueous battery, wherein the aqueous battery has a positive electrode, an aqueous electrolyte, and a negative electrode, wherein the aqueous electrolyte contains water, potassium polyphosphate dissolved in the water, and one or both of zinc phosphate and zinc polyphosphate dissolved in the water, and the negative electrode contains zinc. Details of the aqueous electrolyte and battery configuration are as described above. [Examples]

[0066] The technology of this disclosure will be described in more detail below with reference to examples, but the technology of this disclosure is not limited to the following examples.

[0067] 1. Preparation of aqueous electrolyte A first aqueous solution was obtained by dissolving potassium pyrophosphate (K4P2O7) in pure water. Various zinc salts were dissolved in the first aqueous solution to obtain aqueous electrolytes for evaluation. Multiple aqueous electrolytes were prepared by varying the concentration of potassium pyrophosphate and the type and concentration of zinc salts in the aqueous electrolytes. The aqueous electrolyte with zinc salts dissolved at saturation concentration was prepared as follows: A zinc salt was added to the first aqueous solution in an excess amount that left some solid content, and after standing in a 25°C constant temperature bath for one week, the supernatant solution was used after confirming that some solid content remained.

[0068] 2. Cyclic voltammetry 2.1 Cell creation Evaluations were conducted using an SB1A cell (manufactured by EC Frontier) with metal foils facing each other. A nickel foil was used as the working electrode, a zinc foil as the counter electrode, and a silver-silver chloride electrode as the reference electrode. Various aqueous electrolytes prepared using the method described above were used as the electrolyte.

[0069] 2.2 CV Evaluation Criteria CV evaluation was performed in a constant temperature chamber controlled at 25°C using a VMP3 (BioLogic). The evaluation was performed using cyclic voltammetry. The conditions were as follows: the sweep rate was 1 mV / sec, and the sweep range started from the OCP towards the base potential, first sweeping to -1.1V vs. SHE, then reversing the sweep towards the noble potential and sweeping back to OCP. After repeating this for two cycles, the sweep range on the base potential side was gradually expanded to -1.2V, -1.3V, and -1.4V vs. SHE, with two cycles performed for each. The CV curves shown are the CV curves from the second cycle of each sweep range.

[0070] 3. Confirmation of freezing point by DSC An aluminum sealed pan was used as the container, and the freezing point of the aqueous electrolyte was evaluated by starting the sweep at room temperature at a sweep rate of 1°C / min, sweeping down to -100°C, then reversing the sweep and sweeping down to 30°C.

[0071] 4. Charge / Discharge Evaluation Conditions 4.1 γ-type K x Synthesis of NiO2·nH2O The following soft chemical method is used to produce γ-type K x NiO2·nH2O was synthesized.

[0072] A mixed powder was obtained by mixing LiOH·H2O and Ni(OH)2 in a mortar in a mass ratio of 1.1:1. Next, this mixed powder was spread thinly in an alumina crucible and heated in a furnace at a rate of 10°C / min to 700°C, and held at 700°C for 6 hours. Before heating, oxygen gas was flowed into the furnace at a rate of 5 L / min for 1 hour, and then at a rate of 1 L / min during heating. After natural cooling, ultrapure water was poured directly into the crucible, and the supernatant was filtered to extract the powder. The filtered powder was dried in a vacuum at 80°C for 24 hours. The dried powder was a precursor, layered LiNiO2. Subsequently, LiNiO2 was mixed with a 0.6 mol / L sulfuric acid aqueous solution in a molar ratio of 2.5 to H2SO4, and the mixture was stirred at 300 rpm at room temperature for 24 hours to perform a chemical delithiation treatment. This treatment yielded NiO2 (see formula (1) below). 2LiNiO2+4H + → NiO2+Ni 2+ +2Li + +2H2O …(1)

[0073] The delithiated NiO2 was dispersed in a 0.4 mol / L KCl aqueous solution, and 8 mol / L KOH was added to adjust the pH of the solution to approximately 12. The K in this solution... + The molar ratio of NiO2 to K was set to 0.9, and the mixture was stirred at 300 rpm for 24 hours at room temperature. As a result, K + H2O molecules were inserted between the NiO2 layers (see equation (2) below). NiO2 + xKOH + nH2O → K x NiO2·nH2O+x / 4O2+x / 2H2O …(2)

[0074] The final obtained powder is washed with water, vacuumed at room temperature and dried overnight to obtain γ-type K as a positive electrode active material. x NiO2·nH2O was obtained.

[0075] 4.2 Electrode Coating Synthesized γ-type K as a coating material and as a positive electrode active material x An electrode for evaluation was obtained by coating NiO2·nH2O or Ni(OH)2, acetylene black (LI400, manufactured by Denka) as a conductive material, SBR (TRD2001, manufactured by ENEOS Material) as a binder, and CMC (Cellulogen BSH-6, manufactured by Daiichi Kogyo Seiyaku) as a thickener onto a Ti foil (thickness: 15 μm, manufactured by Niraco). Specifically, the positive electrode active material, conductive material, binder, and thickener were mixed in a mass ratio of 75:20:4.5:0.5, water was added, and the mixture was kneaded for 1 minute at 2000 rpm using a planetary mixer (THINKY) to create a slurry. The slurry was dropped onto the Ti foil placed on a glass plate, and the gap of the blade was adjusted using a doctor blade to coat the electrode to the predetermined coating weight. The coated electrode was air-dried for 3 hours, and then dried overnight at 60°C. After drying, the electrodes were punched out to the specified size and pressed with a 1-ton press to obtain electrodes for evaluation.

[0076] 4.3 Charge / Discharge Evaluation For charge / discharge evaluation, we used two types of cells: the SB9 cell (manufactured by EC Frontier), a coin-type evaluation system that uses a separator, and the liquid-rich SB1A cell (manufactured by EC Frontier) which does not use a separator. Metallic zinc foil was used as the negative electrode, and γ-type K was used as the positive electrode active material. x For the case using NiO2·nH2O, SB9 was used to begin evaluation from the discharge side. For the case using Ni(OH)2 as the positive electrode active material, SB1A, which is rich in solution, was used to begin evaluation from the charge side, as electrodeposition of Zn in the solution occurs during the first charge. A GA-100 glass filter (manufactured by ADVANTEC, 440 μm thick) that allows penetration of a high-concentration potassium pyrophosphate aqueous solution was used as the separator. Spring pressure was applied inside the cell. The charge / discharge evaluation current was ±0.1 mA / cm2 The settings were configured as follows: the cutoff conditions were 0 to +1.05V vs. SHE for the positive electrode and -1.5 to +0.2V vs. SHE for the negative electrode. Note that the γ-type K x Since NiO2·nH2O is a charged material, the evaluation began with discharging, followed by three charge-discharge cycles.

[0077] 5. Evaluation Results 5.1 Potassium ion concentration and zinc ion concentration in aqueous electrolyte Figure 3A shows the relationship between the potassium ion concentration (corresponding to the solubility of potassium pyrophosphate) and the zinc ion concentration (corresponding to the saturation solubility of zinc pyrophosphate) in an aqueous electrolyte. As shown in Figure 3A, only 4 ppm of zinc ions were detected in pure water without added potassium pyrophosphate, which is almost 0 when converted to a molar concentration (mol / L). In contrast, it was found that the amount of zinc that could be dissolved increased as the concentration of potassium pyrophosphate increased. As shown in Figure 3A, the zinc concentration increased linearly with increasing potassium pyrophosphate concentration, and it was confirmed that the zinc concentration reached its maximum of 2.9 mol / L when 4 mol of potassium pyrophosphate was dissolved per 1 kg of water. Since the maximum zinc concentration in a typical potassium hydroxide aqueous solution is about 0.6 mol / L, it is clear that zinc pyrophosphate has high solubility in potassium pyrophosphate aqueous solution. Zinc pyrophosphate is sparingly soluble in water, but it is thought to dissolve in the presence of potassium pyrophosphate in the form of a complex (K6Zn(P2O7)2).

[0078] Figure 3B shows the relationship between the potassium ion concentration (corresponding to the solubility of potassium pyrophosphate) and the zinc ion concentration (zinc ion concentration when 0.5 mol of zinc pyrophosphate is added per 1 kg of water) in an aqueous electrolyte. For the aqueous electrolyte used in CV evaluation (with 0.5 mol of zinc pyrophosphate added per 1 kg of water), the potassium ion concentration and zinc ion concentration show the relationship shown in Figure 3B.

[0079] 5.2 CV Evaluation Results Figures 4A to 4F show the cyclic voltammograms of each aqueous electrolyte. Figure 4A is the cyclic voltammogram for an aqueous electrolyte prepared by dissolving 1 mol of potassium pyrophosphate and 0.5 mol of zinc pyrophosphate per 1 kg of water. Figure 4B is the cyclic voltammogram for an aqueous electrolyte prepared by dissolving 2 mol of potassium pyrophosphate and 0.5 mol of zinc pyrophosphate per 1 kg of water. Figure 4C is the cyclic voltammogram for an aqueous electrolyte prepared by dissolving 3 mol of potassium pyrophosphate and 0.5 mol of zinc pyrophosphate per 1 kg of water. Figure 4D is the cyclic voltammogram for an aqueous electrolyte prepared by dissolving 4 mol of potassium pyrophosphate and 0.5 mol of zinc pyrophosphate per 1 kg of water. Figure 4E is the cyclic voltammogram for an aqueous electrolyte prepared by dissolving 5 mol of potassium pyrophosphate and 0.5 mol of zinc pyrophosphate per 1 kg of water. Figure 4F is a cyclic voltammogram of an aqueous electrolyte solution to which 0.5 mol of zinc pyrophosphate was added per 1 kg of water.

[0080] As shown in Figures 4A-E, oxidation peaks associated with the oxidation and dissolution of zinc were observed at all potassium pyrophosphate concentrations from 1 to 5 mol / kg. Therefore, the reduction current observed when sweeping towards the lower potential is thought to be mainly due to the electrodeposition of zinc in the solution. From these results, it was confirmed that this solution functions well as an electrolyte for an aqueous battery that utilizes the deposition and dissolution of zinc at the negative electrode. On the other hand, as shown in Figure 4F, when potassium pyrophosphate was not added, the zinc concentration was also low, so the reduction current was consumed only for hydrogen generation, and no oxidation current was observed.

[0081] Figures 5A and 5C show the results of a comparison of polarization when currents for zinc electrodeposition and dissolution flow. Figure 5A is a cyclic voltammogram for an aqueous electrolyte containing 1 mol of potassium pyrophosphate and 0.5 mol of zinc pyrophosphate per 1 kg of water, and Figure 5B is a cyclic voltammogram for an aqueous electrolyte containing 5 mol of potassium pyrophosphate and 0.5 mol of zinc pyrophosphate per 1 kg of water. Note that the CV measurement range in Figure 5B is 0.1 V narrower than that in Figure 4E, but this does not pose a practical problem in terms of data interpretation. As shown in Figures 5A and 5B, the shape of the CV when the zinc dissolution current begins to flow after the zinc electrodeposition current flows changes slightly as the concentration of potassium pyrophosphate increases, and it was observed that the potential difference between reduction and oxidation decreases with increasing concentration. Figure 5C plots this potential difference ΔV against the concentration of the potassium pyrophosphate aqueous solution. As shown in Figure 5C, a tendency for the ΔV value to shift was observed at a potassium pyrophosphate aqueous solution alone at a concentration of 4 mol / kg, where antifreeze properties are confirmed (described later). This suggests that when the concentration of potassium pyrophosphate increases to create a water-in-salt electrolyte that exhibits antifreeze properties, the polarization during the transition from zinc precipitation to dissolution decreases, meaning that the energy barrier for coordination is relaxed.

[0082] Figure 6 shows the oxidative peak current values ​​of the CV for aqueous electrolytes prepared by adding a saturating amount of zinc pyrophosphate or zinc sulfate to aqueous potassium pyrophosphate solutions of various concentrations. The oxidative peak current value can serve as a simple indicator for determining the amount of eluted zinc, provided that the rate of elution during electrodeposited zinc does not differ significantly. When zinc sulfate is added to an aqueous potassium pyrophosphate solution, the oxidative peak current value decreases sharply when the potassium pyrophosphate concentration exceeds 4 mol / kg. This is thought to be because, once potassium pyrophosphate is in a water-in-salt state, the amount of free H2O sufficient to dissolve zinc sulfate decreases, preventing the zinc ion concentration from increasing even with the addition of zinc sulfate. Therefore, to achieve both the antifreeze properties of aqueous electrolytes and good electrodeposition characteristics as an electrolyte for batteries, it is preferable that the anion type be at least of the same phosphoric acid type.

[0083] 5.3 DSC Evaluation Results Figures 7A to 7F show the DSC curves for each aqueous electrolyte. Figure 7A is the DSC curve for an aqueous electrolyte prepared by dissolving 5 moles of potassium pyrophosphate and 0.5 moles of zinc pyrophosphate per 1 kg of water. Figure 7B is the DSC curve for an aqueous electrolyte prepared by dissolving 5 moles of potassium pyrophosphate and a saturated concentration of zinc pyrophosphate per 1 kg of water. Figure 7C is the DSC curve for an aqueous electrolyte prepared by dissolving 4 moles of potassium pyrophosphate and 0.5 moles of zinc pyrophosphate per 1 kg of water. Figure 7D is the DSC curve for an aqueous electrolyte prepared by dissolving 3 moles of potassium pyrophosphate and 0.5 moles of zinc pyrophosphate per 1 kg of water. Figure 7E is the DSC curve for an aqueous electrolyte prepared by dissolving 4 moles of potassium pyrophosphate and 1.0 mole of zinc pyrophosphate per 1 kg of water. Figure 7F shows the DSC curve for an aqueous electrolyte solution prepared by dissolving 4 moles of potassium pyrophosphate and a saturated concentration of zinc sulfate per 1 kg of water. As shown in Figures 7A-F, adding zinc polyphosphate to the potassium polyphosphate aqueous solution did not change the trend of low-temperature stability of the potassium polyphosphate aqueous solution, and the heat of suggestion associated with freezing disappeared when the concentration of the potassium polyphosphate aqueous solution was 4 mol / kg or higher. From this, it can be said that an aqueous electrolyte solution with a potassium pyrophosphate concentration of 4 mol / kg or higher can exhibit sufficient performance without impairing antifreeze properties.

[0084] Figure 8 shows the relationship between the potassium ion concentration and zinc ion concentration detected by ICP for each aqueous electrolyte and the concentration range in which antifreeze properties were exhibited. In the figure, plots indicated by black circles (●) indicate that antifreeze properties were confirmed, and plots indicated by white circles (○) indicate that antifreeze properties were not confirmed (frozen). As shown in Figure 8, it became clear that the aqueous electrolyte exhibited antifreeze properties when the potassium ion concentration in the aqueous electrolyte exceeded 9.5 mol / L, preferably exceeding 11.2 mol / L. Furthermore, the inventors conducted comparative experiments with a concentrated aqueous solution of pyrophosphate and confirmed that the antifreeze properties of the potassium pyrophosphate aqueous solution cannot be achieved solely by the presence of pyrophosphate anions, but that the presence of potassium ions is also important. This is thought to be because the presence of weakly Lewis acidic K in the network state space between H2O and P2O7 suppressed aggregation. Figure 9A shows the DSC evaluation results of a saturated zinc pyrophosphate aqueous solution. Figure 9B also shows the DSC evaluation results for a zinc sulfate aqueous solution with a concentration of 4 mol / kg. In the aqueous solutions without potassium pyrophosphate shown in Figures 9A and 9B, freezing was observed at around -20°C.

[0085] 5.4 Ionic conductivity, viscosity and pH Figure 10A shows the relationship between ionic conductivity and potassium pyrophosphate concentration for potassium pyrophosphate aqueous solutions of various concentrations, and for aqueous solutions to which 0.5 mol / kg of zinc pyrophosphate has been added. Figure 10B shows the relationship between viscosity and potassium pyrophosphate concentration for potassium pyrophosphate aqueous solutions of various concentrations, and for aqueous solutions to which 0.5 mol / kg of zinc pyrophosphate has been added. Figure 10C shows the relationship between pH and potassium pyrophosphate concentration for potassium pyrophosphate aqueous solutions of various concentrations, and for aqueous solutions to which 0.5 mol / kg of zinc pyrophosphate has been added. As shown in Figures 10A and B, ionic conductivity and viscosity do not change significantly even in the presence of zinc, but as shown in Figure 10C, the pH decreases from approximately 12 to 11 at potassium pyrophosphate concentrations of 4 mol / kg or higher, where antifreeze properties are exhibited, resulting in a milder state.

[0086] 5.5 Charge / Discharge Evaluation Results Figure 11 shows K as the positive electrode active material. x The charge-discharge results of nickel-zinc batteries using NiO2·nH2O, metallic zinc foil as the negative electrode, and either (1) an aqueous electrolyte containing 5 mol / kg potassium pyrophosphate and 0.5 mol / kg zinc pyrophosphate, or (2) an aqueous electrolyte containing 2 mol / L zinc sulfate, are shown. As shown in Figure 11, it was found that charging and discharging was more stable when using aqueous electrolyte (1) than when using aqueous electrolyte (2), which is a general neutral zinc aqueous solution. This is thought to be due to the decrease in capacity on the positive electrode side, as seen in the cycle degradation behavior of zinc sulfate, suggesting that the effect is not due to dendrite growth of zinc, but rather to leaching due to a weakly acidic atmosphere. In other words, it is thought that the mild pH of aqueous electrolyte (1), around 11, contributed to the improvement in cycle characteristics.

[0087] Figure 12 shows the charge-discharge results of a nickel-zinc battery using an aqueous electrolyte containing 5 mol / kg of potassium pyrophosphate but no dissolved zinc pyrophosphate, and the charge-discharge results of a nickel-zinc battery using an aqueous electrolyte containing 5 mol / kg of potassium pyrophosphate and a saturated concentration of zinc pyrophosphate. As shown in Figure 12, even without dissolving zinc, the electrochemical reaction proceeds during the initial charge due to the consumption of electricity by the hydrogen generation reaction in the liquid, but the shape of the plateau is disrupted. In contrast, the presence of zinc in the liquid allows the reaction to proceed even during the initial charge due to the electrodeposition of zinc in the liquid, and the plateau is not disrupted. The potential difference between the plateaus during charging and discharging is also smaller when zinc is present in the liquid, which is advantageous for the charge-discharge reaction. From these results, it was confirmed that a zinc battery can operate even without zinc in the liquid, but the reactivity is better and the charge-discharge is more stable when zinc is present in the liquid.

[0088] 6. Summary Based on the above results, it can be said that a water-based battery with the following configuration exhibits excellent cycle characteristics and charge / discharge stability. (1) It has a positive electrode, an aqueous electrolyte, and a negative electrode. (2) The aqueous electrolyte comprises water, potassium polyphosphate dissolved in the water, and one or both of zinc phosphate and zinc polyphosphate dissolved in the water. (3) The negative electrode contains zinc. [Explanation of Symbols]

[0089] 10 positive electrode 11 Cathode active material layer 12 Positive electrode current collector 20 Aqueous electrolyte 30 negative electrode 31 Negative electrode active material layer 32 Negative electrode current collector 40 Separators 100 Water-based batteries

Claims

1. A water-based battery having a positive electrode, an aqueous electrolyte, and a negative electrode, The aforementioned aqueous electrolyte, Water and, The potassium polyphosphate dissolved in the aforementioned water, One or both of the zinc phosphate and zinc polyphosphate dissolved in the aforementioned water, Includes, The negative electrode contains zinc, water-based battery.

2. A water-based battery according to claim 1, The aforementioned potassium polyphosphate is potassium pyrophosphate. water-based battery.

3. A water-based battery according to claim 1, The aqueous electrolyte contains zinc polyphosphate dissolved in the water. water-based battery.

4. A water-based battery according to claim 3, The aforementioned zinc polyphosphate is zinc pyrophosphate. water-based battery.

5. A water-based battery according to any one of claims 1 to 4, The potassium ion concentration of the aqueous electrolyte is greater than 9.5 mol / L. water-based battery.

6. A water-based battery according to any one of claims 1 to 4, The pH of the aqueous electrolyte is 3 or higher and 14 or lower. water-based battery.

7. A water-based battery according to any one of claims 1 to 4, The positive electrode contains an oxide as the positive electrode active material. water-based battery.

8. A water-based battery according to any one of claims 1 to 4, The aqueous electrolyte contains potassium polyphosphate dissolved at a concentration of 4 mol or more per 1 kg of water. water-based battery.

9. A water-based battery according to any one of claims 1 to 4, The aqueous electrolyte does not have a freezing point at -40°C or above. water-based battery.

10. A water-based battery according to any one of claims 1 to 4, One or both of the positive electrode and the negative electrode have a current collector containing Al. water-based battery.

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