Aqueous battery

Abstract

Disclosed is a technique capable of suppressing elution of Al from a current collector into an aqueous electrolyte solution when the current collector containing Al is used in an aqueous battery. This aqueous battery has a positive electrode, an aqueous electrolyte solution, and a negative electrode. One or both of the positive electrode and the negative electrode has a current collector containing Al. The current collector is in contact with the aqueous electrolyte solution. The aqueous electrolyte solution contains water, potassium polyphosphate dissolved in the water, and silicate dissolved in the water.

Description

Technical Field

[0001] This application relates to aqueous batteries. Background Technology

[0002] Patent documents 1 and 2 disclose an aqueous electrolyte containing water and potassium pyrophosphate dissolved in the water. When constructing an aqueous battery using the aqueous electrolyte disclosed in patent documents 1 and 2, the aqueous electrolyte has a wide reduction potential window and easily suppresses the decomposition of the aqueous electrolyte on the electrode surface during charging and discharging of the aqueous battery.

[0003] Existing technical documents

[0004] Patent documents

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2024-032362

[0006] [Patent Document 2] Japanese Patent Application Publication No. 2019-220294 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] In aqueous batteries using Al-containing current collectors, Al tends to dissolve from the current collector into the aqueous electrolyte during charging and discharging. This application discloses a new technology capable of suppressing Al dissolution from the current collector into the aqueous electrolyte in aqueous batteries.

[0009] Methods for solving problems

[0010] This application discloses the following methods as means of solving the above-mentioned problems.

[0011] <Method 1>

[0012] An aqueous battery comprising a positive electrode, an aqueous electrolyte, and a negative electrode.

[0013] One or both of the positive and negative electrodes have a current collector containing Al.

[0014] The current collector is in contact with the aqueous electrolyte.

[0015] The aqueous electrolyte contains:

[0016] water,

[0017] Potassium polyphosphate dissolved in the water, and

[0018] Silicates dissolved in the water.

[0019] <Method 2>

[0020] As described in Method 1, the aqueous battery

[0021] The silicate is metasilicate.

[0022] <Method 3>

[0023] As described in Method 1, the aqueous battery

[0024] The silicate is potassium metasilicate.

[0025] <Method 4>

[0026] As described in any of methods 1 to 3, the water-based battery

[0027] The aqueous electrolyte contains at least one of orthophosphoric acid, metaphosphoric acid, and carboxylic acid dissolved in the water.

[0028] <Method 5>

[0029] Aqueous batteries as described in any one of methods 1 to 4,

[0030] The aqueous electrolyte contains potassium polyphosphate dissolved at a concentration of more than 1 mol relative to 1 kg of the water.

[0031] <Method 6>

[0032] Aqueous batteries as described in any one of methods 1 to 5,

[0033] The aqueous electrolyte does not have a freezing point above -40°C.

[0034] <Method 7>

[0035] Aqueous batteries as described in any one of methods 1 to 6,

[0036] No salt will precipitate when the aqueous electrolyte is cooled from 0°C to -40°C.

[0037] <Method 8>

[0038] Aqueous batteries as described in any one of methods 1 to 7,

[0039] The aqueous electrolyte has a viscosity of 10 mPa·s or higher and 400 mPa·s or lower at 25°C.

[0040] <Method 9>

[0041] Aqueous batteries as described in any one of methods 1 to 8,

[0042] The pH of the aqueous electrolyte is above 3 and below 13.

[0043] <Method 10>

[0044] Aqueous batteries as described in any one of methods 1 to 9,

[0045] At least the positive electrode has the current collector.

[0046] <Method 11>

[0047] Aqueous batteries as described in any one of methods 1 to 10,

[0048] It has a bipolar structure, with a positive active material layer formed on one side of the current collector and a negative active material layer formed on the other side of the current collector.

[0049] Invention Effects

[0050] According to the aqueous battery disclosed herein, it is easy to suppress the dissolution of Al from the current collector into the aqueous electrolyte. Attached Figure Description

[0051]

【 Figure 1 This illustration shows an example of the structure of an aqueous battery.

[0052]

【 Figure 2 This illustration shows an example of the structure of an aqueous battery.

[0053]

【 Figure 3A The diagram shows the cyclic voltammogram when the Al dissolution inhibition effect is "A".

[0054]

【 Figure 3B The figure shows the cyclic voltammogram when the Al dissolution inhibition effect is "B".

[0055]

【 Figure 3C The diagram shows the cyclic voltammogram when the Al dissolution inhibition effect is "C".

[0056]

【 Figure 3D The diagram shows the cyclic voltammogram when the Al dissolution inhibition effect is "D".

[0057]

【 Figure 4 The charge-discharge curves of the evaluation unit using the aqueous electrolyte of Comparative Example 5 are shown.

[0058]

【 Figure 5 The charge-discharge curves of the evaluation unit using the aqueous electrolyte of Example 48 are shown. Detailed Implementation

[0059] The following description, with reference to the accompanying drawings, illustrates one embodiment of the aqueous battery of this disclosure; however, the technology of this disclosure is not limited to the following embodiment.

[0060] like Figure 1As shown, an aqueous battery 100 according to one embodiment has a positive electrode 10, an aqueous electrolyte 20, and a negative electrode 30. One or both of the positive electrode 10 and the negative electrode 30 have a current collector containing Al. The current collector is in contact with the aqueous electrolyte 20. The aqueous electrolyte 20 contains water, potassium polyphosphate dissolved in the water, and silicate dissolved in the water.

[0061] 1. Positive electrode

[0062] The positive electrode 10 can be a known positive electrode used in aqueous batteries. For example... Figure 1 As shown, the positive electrode 10 may have a positive electrode active material layer 11 and a positive electrode current collector 12.

[0063] 1.1 Positive Electrode Active Material Layer

[0064] The positive electrode active material layer 11 contains positive electrode active material. Additionally, the positive electrode active material layer 11 is impregnated with an aqueous electrolyte 20. Besides the positive electrode active material, the positive electrode active material layer 11 may contain conductive additives, binders, etc. Furthermore, the positive electrode active material layer 11 may contain various other additives. The content of each component in the positive electrode active material layer 11 can be appropriately determined according to the target battery performance. For example, if the total content of the positive electrode active material layer 11 (solid component as a whole) is set to 100% by mass, the content of the positive electrode active material can be set to 40% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more, or it can be set to less than 100% by mass or less than 90% by mass. The shape of the positive electrode active material layer 11 is not particularly limited; for example, it can be a sheet-like positive electrode active material layer with approximately a planar surface. The thickness of the positive electrode active material layer 11 is not particularly limited; for example, it can be 0.1 μm or more, 1 μm or more, or 10 μm or more, and can be less than 2 mm, less than 1 mm, or less than 500 μm.

[0065] For the positive electrode active material, any material capable of functioning as a positive electrode active material in an aqueous battery (e.g., an aqueous battery using an aqueous electrolyte containing alkali metal ions such as lithium ions, sodium ions, and potassium ions, and / or protons) can be used. The positive electrode active material has a higher charge / discharge potential than the negative electrode active material described later, and can be appropriately selected considering factors such as the potential window of the aqueous electrolyte 20 described later. In addition, in this embodiment, various ions from the aqueous electrolyte can serve as charge compensation ions. Specifically, as charge compensation ions capable of detaching from the positive electrode active material, one or more of potassium ions, protons, anions from the electrolyte, and hydroxide ions can be used, for example. As the positive electrode active material, for example, Ni(OH)2 (e.g., Japanese Patent Application Laid-Open No. 2023-154313), a layered nickel hydroxide compound, can be used. x Ky Ni 1-z M z O 2±δ • nH₂O (where A is at least one of Li, Na, Rb, Cs, Mg, Ca, Sr, Ba, and Sc, and M is at least one of a transition metal element, a group 2A element, a group 3A element, a group 2B element, and a group 3B element, with 0 ≦x < 0.5, 0 < y ≦ 0.5, 0 ≦z ≦ 0.5, 0 < n ≦ 2, and satisfying the relationship (α・x) + y ≦ 0.5, where α is the valence of the cation of A. For example, Japanese Patent Application Publication No. 2023-132287), manganese spinel (e.g., LiMn₂O₄), nickel-manganese-cobalt composite oxides (NMC), and various hydroxides and oxides. Additionally, the positive electrode active material can be an oxide containing an alkali metal element, a polyanion, etc. More specifically, it can be a composite oxide of an alkali metal element and a transition metal. The composite oxide can be selected from alkali metal cobalt composite oxides (AmCoO2, etc., where "Am" represents an alkali metal element, as will be the case hereinafter), alkali metal nickel composite oxides (AmNiO2, etc.), and alkali metal nickel-titanium composite oxides (AmNi...). 1 / 2 Ti 1 / 2 O2, etc.), alkali metal nickel-manganese composite oxides (AmNi) 1 / 2 Mn 1 / 2 O2, AmNi 1 / 3 Mn 2 / 3 O2, etc.), alkali metal manganese composite oxides (AmMnO2, AmMn2O4, etc.), alkali metal iron-manganese composite oxides (Am 2 / 3Fe 1 / 3 Mn 2 / 3 O2, etc.), alkali metal nickel-cobalt-manganese composite oxides (AmNi) 1 / 3 Co 1 / 3 Mn 1 / 3 At least one of the following: O2, alkali metal iron composite oxides (AmFeO2, etc.), alkali metal chromium composite oxides (AmCrO2, etc.), alkali metal iron phosphate compounds (AmFePO4, etc.), alkali metal manganese phosphate compounds (AmMnPO4, etc.), and alkali metal cobalt phosphate compounds (AmCoPO4). Alternatively, the positive electrode active material can be an active material such as Prussian blue. Alternatively, the positive electrode active material can be at least one selected from alkali metal titanium composite oxides, TiO2, sulfur (S), etc., which exhibit a higher charge-discharge potential compared to the negative electrode active materials described below. The positive electrode active material can be a substance that detaches the inserted charge compensation ions through intercalation, or a substance that detaches the inserted charge compensation ions through conversion reactions, alloying reactions, etc. Only one type of positive electrode active material can be used alone, or two or more types can be used in combination.

[0066] Regarding the shape of the positive electrode active material, any shape that can function as the positive electrode active material in a battery is acceptable. The positive electrode active material can be, for example, particulate. It can be a solid material, a hollow material, a material with pores, or a porous material. It can be a primary particle or a secondary particle formed by the aggregation of multiple primary particles. The average particle size D50 of the positive electrode active material can be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and can also be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. Furthermore, the average particle size D50 referred to in this application refers to the particle size (median particle size) at which the cumulative value of the particle size distribution based on volume diffraction and scattering methods reaches 50%.

[0067] Conductive additives that can be included in the positive electrode active material layer 11 include, for example, carbon materials such as fumed carbon fiber (VGCF), acetylene black (AB), Ketjen black (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF); and metallic materials that are difficult to dissolve in the electrolyte, such as nickel, titanium, aluminum, and stainless steel. The conductive additives can be in particulate or fibrous form, and their size is not particularly limited. A single conductive additive can be used, or two or more can be used in combination.

[0068] Examples of adhesives that can be included in the positive electrode active material layer 11 include butadiene rubber (BR) based adhesives, butyl rubber (IIR) based adhesives, acrylate butadiene rubber (ABR) based adhesives, styrene butadiene rubber (SBR) based adhesives, polyvinylidene fluoride (PVdF) based adhesives, polytetrafluoroethylene (PTFE) based adhesives, and polyimide (PI) based adhesives. One type of adhesive may be used alone, or two or more may be used in combination.

[0069] 1.2 Positive Current Collector

[0070] like Figure 1As shown, the positive electrode 10 has a positive current collector 12 in contact with the aforementioned positive electrode active material layer 11. The positive current collector 12 is in contact with the aqueous electrolyte 20. For the positive current collector 12, any material capable of functioning as a positive current collector in an aqueous battery can be used. When the negative current collector 32 (described later) is an Al-containing current collector, the positive current collector 12 can be either an Al-containing current collector or an Al-free current collector. Alternatively, when the negative current collector 32 (described later) is an Al-free current collector, the positive current collector 12 is an Al-containing current collector. As described later, Al dissolution from the current collector into the aqueous electrolyte is particularly prone to occur on the positive electrode side, which is the oxidation potential. However, according to the aqueous battery 100 of this disclosure, even if the positive current collector 12 is an Al-containing current collector, the dissolution of Al from the positive 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.

[0071] When the positive current collector 12 is an Al-containing current collector, the entire positive current collector 12 can be made of Al, or at least a portion of its surface can be made of Al. For example, the positive current collector 12 can be a current collector made of Al foil, or a current collector formed by coating the surface of a metal foil or any substrate with Al. The positive current collector 12 can be a current collector in which at least a portion of the surface in contact with the aqueous electrolyte 20 contains Al, or a current collector in which the entire surface in contact with the aqueous electrolyte 20 contains Al.

[0072] The positive current collector 12 can be in the form of foil, plate, mesh, perforated metal, or foam. The positive current collector 12 can be made of metal foil or metal mesh. In particular, metal foil is superior in terms of operability. The positive current collector 12 can be composed of multiple foils. Examples of metal materials constituting the positive current collector 12 include those containing at least one element selected from Cu, Ni, Al, V, Au, Pt, Mg, Fe, Ti, Pb, Co, Cr, Zn, Ge, In, Sn, and Zr. As mentioned above, the positive current collector 12 is particularly preferably composed of Al. The positive current collector 12 can be a current collector obtained by electroplating or vapor-depositing the aforementioned metal onto a metal foil or substrate. Furthermore, when the positive current collector 12 is composed of multiple metal foils, any number of layers can be formed between the multiple metal foils. The thickness of the positive current collector 12 is not particularly limited. For example, it can be above 0.1μm or above 1μm, and it can be below 1mm or below 100μm.

[0073] 2. Aqueous electrolyte

[0074] The aqueous electrolyte 20 contains water, potassium polyphosphate dissolved in the water, and silicate dissolved in the water. The aqueous electrolyte 20 is in contact with the positive current collector 12 and is contained in the positive active material layer 11, and is in contact with the negative current collector 32 (described later) and is contained in the negative active material layer 31 (described later), and can be held between the positive electrode 10 and the negative electrode 30 by the diaphragm 40.

[0075] 2.1 Solvent

[0076] Aqueous electrolyte 20 contains water as a solvent. The solvent contains water as a main component. That is, based on the total amount of solvent constituting the aqueous electrolyte (100 mol%), water accounts for 50 mol% or more and 100 mol% or less. Water can account for 70 mol% or more, 90 mol% or more, or 95 mol% or more of the total solvent. On the other hand, there is no particular upper limit to the proportion of water in the solvent. The solvent can consist of only water (100 mol% water).

[0077] From the perspective of forming an SEI (Solid Electrolyte Interphase) on the surface of the active material, the solvent may contain solvents other than water, provided that the aforementioned problems can be solved. Examples of solvents other than water include one or more organic solvents selected from ethers, carbonates, nitriles, alcohols, ketones, amines, amides, sulfides, and hydrocarbons. Based on the total amount of solvent constituting the electrolyte (100 mol%), 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.

[0078] 2.2 Electrolytes

[0079] An electrolyte is dissolved in the aqueous electrolyte 20, which can dissociate into cations and anions. In the aqueous electrolyte 20, the cations and anions can approach each other and form a compound.

[0080] 2.2.1 Potassium polyphosphate

[0081] The aqueous electrolyte 20 contains potassium polyphosphate dissolved in the water. "Potassium polyphosphate" refers to a salt in which at least a portion of the hydrogen atoms of a polyphosphate are replaced by potassium. That is, the concept of "potassium polyphosphate" includes potassium hydrogen polyphosphate. Specific examples of potassium polyphosphate include potassium pyrophosphate (K...). 4-x H x P2O7, x < 4), potassium tripolyphosphate (K 5-y H y P3O 10 , y < 5), etc. Among them, potassium pyrophosphate (K 4-x Hx When P2O7 (x < 4) is used as potassium polyphosphate, higher performance can be easily ensured. In the aqueous electrolyte 20, "potassium polyphosphate dissolved in water" can exist in the form of potassium ions, polyphosphate ions, and fusions of these ions, as well as fusions formed with ions derived from potassium hydrogen phosphate, phosphoric acid, polyphosphate, and carboxylic acid (described later). In the aqueous electrolyte 20, the "concentration of potassium polyphosphate dissolved in water" can be determined by converting the ions, fusions, etc., contained in the aqueous electrolyte 20 into potassium polyphosphate. In addition, in this application, "potassium polyphosphate dissolved in water" can refer to a substance in which the above-mentioned ions and their fusions are formed in the aqueous electrolyte 20 by adding a cation source (e.g., potassium compound) and an anion source (e.g., polyphosphate).

[0082] The concentration of potassium polyphosphate in the aqueous electrolyte 20 is not particularly limited. According to the inventors' new understanding, when the aqueous electrolyte 20 contains potassium polyphosphate dissolved at a concentration of 1 mol or more relative to 1 kg of water, and further, when it contains potassium polyphosphate dissolved at a concentration of 1 mol to 6 mol relative to 1 kg of water, and further, when it contains potassium polyphosphate dissolved at a concentration of 3 mol to 6 mol relative to 1 kg of water, and further, when it contains potassium polyphosphate dissolved at a concentration of 4 mol to 6 mol relative to 1 kg of water, and further, when it contains potassium polyphosphate dissolved at a concentration of 4 mol to 5 mol relative to 1 kg of water, in addition to suppressing the dissolution of Al from the current collector, it is also expected to improve other properties of the electrolyte, such as electrochemical stability. Furthermore, when the concentration of potassium pyrophosphate in the aqueous electrolyte 20 is such a concentration, it is easy 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 or more and 4 mol or less relative to 1 kg of water, and further, when the aqueous electrolyte 20 contains potassium polyphosphate dissolved at a concentration of 1 mol or more and 3 mol or less relative to 1 kg of water, and further, when the aqueous electrolyte 20 contains potassium polyphosphate dissolved at a concentration of 1 mol or more and 2 mol or less relative to 1 kg of water, the viscosity of the aqueous electrolyte 20 decreases, and it is easier to improve the ionic conductivity.

[0083] 2.2.2 Silicates

[0084] The aqueous electrolyte 20 contains silicates dissolved in the water. "Silicates" can be orthosilicates or metasilicates. In particular, when the silicate is a metasilicate, a more superior Al dissolution inhibition effect is easily obtained. The type of cation constituting the silicate is not particularly limited. In this embodiment, regardless of the type of cation constituting the silicate, the Al dissolution inhibition effect can be ensured by the anion constituting the silicate. The cation constituting the silicate can be, for example, one or more of alkali metal ions and alkaline earth metal ions. In particular, when the silicate is potassium silicate, and especially when the silicate is potassium metasilicate (K₂SiO₃), a more superior Al dissolution inhibition effect is easily obtained. In the aqueous electrolyte 20, the "silicates dissolved in the water" do not necessarily have to completely dissociate into cations and silicate anions (SiO₃). 2- SiO4 4- Various chelates can also be formed, for example, chelates can be formed with ions from the aforementioned potassium polyphosphate and other additives described later. In the aqueous electrolyte 20, the "concentration of silicates dissolved in water" can be determined by converting the ions, chelates, etc. contained in the aqueous electrolyte 20 into silicates. In addition, in this application, "silicates dissolved in water" can refer to substances that generate ions and their chelates in the aqueous electrolyte 20 that can be converted into silicates by adding a cation source (e.g., potassium compound) and an anion source (e.g., orthosilicic acid, metasilicic acid).

[0085] The concentration of silicate in the aqueous electrolyte 20 is not particularly limited. According to the inventors, a higher concentration of silicate in the aqueous electrolyte 20 makes it easier to improve the Al dissolution inhibition effect. On the other hand, an increase in the pH of the aqueous electrolyte 20 may lead to other effects besides battery reactions. The concentration of silicate in the aqueous electrolyte 20 can be selected appropriately based on a balance between the Al dissolution inhibition effect and pH. For example, the concentration of silicate in the aqueous electrolyte 20 can be 1 ppm or more and 1,000,000 ppm or less, 10 ppm or more and 500,000 ppm or less, or 100 ppm or more and 300,000 ppm or less relative to 1 kg of the water.

[0086] 2.2.3 Orthophosphoric acid, metaphosphoric acid (polyphosphoric acid), and carboxylic acids

[0087] The pH of the aqueous electrolyte 20 containing the aforementioned silicates tends to rise. This can be addressed by adding various acids to the aqueous electrolyte 20 to adjust its pH. The acids can be inorganic or organic. 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 inventors' novel insights, at least orthophosphoric acid, metaphosphoric acid (polyphosphoric acid), and carboxylic acid can lower the pH of the aqueous electrolyte 20 while ensuring the Al dissolution inhibition effect provided by the aforementioned potassium polyphosphate and silicates. Furthermore, the Al dissolution inhibition effect can sometimes be further enhanced through interaction with the aforementioned potassium polyphosphate, etc. "Metaphosphoric acid (polyphosphoric acid)" can be, for example, pyrophosphoric acid (H4P2O7) and tripolyphosphoric acid (H5P3O7). 10 One or both of these. Among them, using pyrophosphate (H4P2O7) as the polyphosphate easily ensures higher performance. "Carboxylic acid" can be a monocarboxylic acid or a polycarboxylic acid, such as acetic acid. In the aqueous electrolyte 20, "orthophosphoric acid (H3PO4) dissolved in water" includes H... ＋ PO4 3- In addition, it can exist in the form of a fusion with ions from potassium polyphosphate, etc., for example, it can exist as KPO4. 2- HPO4 2- K2PO4 - H2PO4 - KHPO4 - Phosphoric acid (polyphosphate) dissolved in water exists in ionic form, and can be expressed as H+. ＋ Carboxylic acids dissolved in water can exist in the form of H+ ions, or phosphate anions, or chelates formed with ions from the aforementioned potassium polyphosphate. ＋ It exists in the form of carboxylic acid anions, or fused compounds formed with ions from the aforementioned potassium polyphosphate. In the aqueous electrolyte 20, by converting the ions and fused compounds contained in the aqueous electrolyte 20 into orthophosphoric acid, metaphosphoric acid, and carboxylic acid, the concentrations of orthophosphoric acid dissolved in water, metaphosphoric acid dissolved in water, and carboxylic acid dissolved in water can be determined.

[0088] The concentration of acid in the aqueous electrolyte 20 is not particularly limited and can be appropriately adjusted according to the target pH. According to the inventors' novel insights, excellent Al dissolution inhibition can be achieved in the aqueous electrolyte 20 by dissolving orthophosphoric acid, metaphosphoric acid, and carboxylic acid together with potassium polyphosphate. In the aqueous electrolyte 20, the total molar ratio of orthophosphoric acid, metaphosphoric acid, and carboxylic acid relative to potassium polyphosphate ([orthophosphoric acid + metaphosphoric acid + carboxylic acid] / potassium polyphosphate) can, for example, be greater than 0 and less than 20.00, greater than 0 and less than 15.00, greater than 0 and less than 10.00, greater than 0 and less than 8.50, greater than 0 and less than 7.00, greater than 0 and less than 5.00, greater than 0 and less than 3.00, or greater than 0 and less than 1.00.

[0089] 2.2.4 Cations

[0090] The aqueous electrolyte 20 may contain potassium ions as cations. In the aqueous electrolyte 20, a portion of the potassium ions contained therein can be converted to "dissolved potassium polyphosphate." However, the aqueous electrolyte 20 may contain a higher concentration of potassium ions than that that can be converted to potassium polyphosphate. For example, when manufacturing the aqueous electrolyte 20, if a potassium ion source other than potassium polyphosphate (e.g., KOH, CH3COOK, K3PO4, etc.) is added to water along with the potassium polyphosphate and dissolved, the aqueous electrolyte 20 may contain a higher concentration of potassium ions than that that can be converted to potassium polyphosphate. Within the scope that solves the above-mentioned problems, the aqueous electrolyte 20 may contain other cations. 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.

[0091] 2.2.5 Anions

[0092] The aqueous electrolyte 20 may contain polyphosphate ions (as described above, which may exist in a state bound to cations) and silicate ions (as described above, which may exist in a state bound to cations) as anions. To the extent that the aforementioned problems can be solved, the aqueous electrolyte 20 may contain other anions. For example, it may contain anions from other electrolytes described later. Furthermore, the aqueous electrolyte 20 naturally contains hydroxide ions.

[0093] 2.2.6 Other components that aqueous electrolytes may contain

[0094] The aqueous electrolyte 20 may contain other electrolytes. For example, it may contain at least one selected from KPF6, KBF4, K2SO4, KNO3, (CF3SO2)2NK, KCF3SO3, (FSO2)2NK, K2HPO4, KH2PO4, KPO3, etc. Based on the total amount of electrolyte dissolved in the electrolyte (100 mol%), other electrolytes may account for less than 50 mol%, less than 30 mol%, or less than 10 mol%. In addition to the above-mentioned electrolytes, the aqueous electrolyte 20 may also contain various additives.

[0095] 2.3 Other characteristics

[0096] The aqueous electrolyte 20 can be any aqueous electrolyte having the above-mentioned solvent and electrolyte; there are no particular limitations on its properties. An example of another property of the aqueous electrolyte 20 is described below.

[0097] 2.3.1 Freezing point

[0098] Aqueous electrolyte 20 can be an electrolyte that does not have a freezing point above -40°C. The presence or absence of a "freezing point" in aqueous electrolyte 20 is confirmed by differential scanning calorimetry (DSC). The DSC scan rate is 5°C / min for both cooling and heating, and the scan range is from room temperature down to -120°C, then up to 40°C. The atmosphere in the DSC is an inert gas atmosphere such as Ar, and the pressure is the same as atmospheric pressure. However, since a sealed aluminum container is used in the evaluation, the atmosphere inside the container is atmospheric pressure. If, under the above conditions, no crystallization peak temperature (freezing point temperature) is confirmed above -40°C for the aqueous electrolyte, it is considered that the aqueous electrolyte "does not have a freezing point above -40°C". The aqueous electrolyte 20 can have no freezing point above -60°C, above -80°C, 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 has no freezing point above -40°C," it is effective to keep the concentrations of potassium polyphosphate, silicate, and other additives in the aqueous electrolyte 20 at high concentrations. By ensuring that the aqueous electrolyte 20 has no freezing point at -40°C, the Al dissolution inhibition effect is easily improved. Furthermore, by ensuring that the aqueous electrolyte 20 has no freezing point at -40°C, the aqueous battery 100 can be used even at extremely low temperatures. That is, the aqueous battery 100 can operate well in cold regions.

[0099] 2.3.2 Presence or absence of salt precipitation

[0100] When the aqueous electrolyte 20 is cooled from 0°C to -40°C, salt precipitation does not occur. By preventing salt precipitation in the aqueous electrolyte 20 without temperature changes, stable ion conduction can be achieved at low temperatures. For example, the aqueous battery 100 can be used at extremely low temperatures, such as in cold regions. As described above, the aqueous electrolyte 20 contains water and potassium polyphosphate dissolved in that water. According to the inventors, the saturated solubility of potassium polyphosphate and the like in water has low temperature dependence and hardly changes at low temperatures below 0°C. In this respect, even when the aqueous electrolyte 20 is cooled from 0°C to -40°C, salt precipitation is unlikely to occur in the aqueous electrolyte 20.

[0101] 2.3.3 Viscosity

[0102] If the viscosity of the aqueous electrolyte 20 is too high, its ionic conductivity may decrease. On the other hand, when potassium pyrophosphate or similar substances are dissolved in the aqueous electrolyte 20 at a high concentration, the aqueous electrolyte 20 can have a certain or higher viscosity. Based on these points, the aqueous electrolyte 20 can have a viscosity of 10 mPa·s or higher and 400 mPa·s or lower at 25°C. This viscosity can be 350 mPa·s or lower, 300 mPa·s or lower, 250 mPa·s or lower, or 200 mPa·s or lower.

[0103] 2.3.4 pH

[0104] The pH of the aqueous electrolyte 20 is not particularly limited. As mentioned above, since silicates are dissolved in the aqueous electrolyte 20, the pH is prone to increase. If the pH of the aqueous electrolyte 20 is too high, there is a concern that the oxidation-side potential window of the aqueous electrolyte will narrow. In this regard, the pH of the aqueous electrolyte 20 can be above 3 and below 13. The pH can be above 4, 5, 6, or 7, and can be below 12, 11, 10, or 9.

[0105] 2.4 Variations

[0106] In one embodiment, the aqueous electrolyte 20 may have the following composition. That is, the aqueous electrolyte 20 of one embodiment is characterized by containing water, polyphosphate ions, silicate ions, and potassium ions.

[0107] 3. Negative electrode

[0108] Regarding the negative electrode 30, a known aqueous battery negative electrode can be used. For example... Figure 1 As shown, the negative electrode 30 may have a negative electrode active material layer 31 and a negative electrode current collector 32.

[0109] 3.1 Negative Electrode Active Material Layer

[0110] The negative electrode active material layer 31 contains negative electrode active material. Furthermore, the negative electrode active material layer 31 is immersed in 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 target battery performance. For example, if the total amount of the negative electrode active material layer 31 (solid component as a whole) is set to 100% by mass, the content of the negative electrode active material can be 40% or more by mass, 50% or more by mass, 60% or more by mass, or 70% or more by mass, and can be less than 100% by mass or less than 90% by mass. The shape of the negative electrode active material layer 31 is not particularly limited; for example, it can be a sheet-like negative electrode active material layer with a generally planar surface. The thickness of the negative electrode active material layer 31 is not particularly limited; for example, it can be 0.1 μm or more, 1 μm or more, or 10 μm or more, and can be less than 2 mm, less than 1 mm, or 500 μm.

[0111] For the negative electrode active material, any material capable of functioning as a negative electrode active material in an aqueous battery can be used. The negative electrode active material is one with a lower charge / discharge potential than the aforementioned positive electrode active material, and can be appropriately selected considering factors such as the potential window of the aqueous electrolyte 20. Furthermore, in this embodiment, various ions from the aqueous electrolyte can serve as charge-compensating ions. Specifically, the charge-compensating ions that detach from and insert into the negative electrode active material can be, for example, one or more of potassium ions, protons, anions from the electrolyte, and hydroxide ions. Examples of negative electrode active materials include alkali metal-transition metal complex oxides; titanium oxide; metal sulfides such as Mo6S8; elemental sulfur; alkali metal-titanium complex phosphate compounds; NASICON-type compounds; WO3, etc. Alternatively, the negative electrode active material can be a hydrogen-absorbing alloy. Alternatively, the negative electrode active material can be an inorganic compound with a crystal structure belonging to space group I23. Inorganic compounds with a crystal structure belonging to space group I23 can, for example, contain elements A, M, and O. Wherein, element A is at least one of Bi and La, and element M is at least one of Bi, Mn, Fe, Co, and Ni. Both element A and element M can be Bi. The negative electrode active material can release intercalation charge compensation ions through intercalation, or through conversion reactions, alloying reactions, etc. The negative electrode active material can be a single type or a combination of two or more types.

[0112] The shape of the negative electrode active material can be any shape that allows it to function as a negative electrode active material in a battery. For example, the negative electrode active material can be particle-shaped. It can be solid, hollow, porous, or have voids. It can be primary particles or secondary particles formed by the aggregation of multiple primary particles. The average particle size D50 of the negative electrode active material can be, for example, greater than 1 nm, greater than 5 nm, or greater than 10 nm, or less than 500 μm, less than 100 μm, less than 50 μm, or less than 30 μm.

[0113] The conductive additives that can be contained in the negative electrode active material layer 31 include, for example, carbon materials such as fumed carbon fiber (VGCF), acetylene black (AB), Ketjen black (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF); and metallic materials that are difficult to dissolve in the electrolyte, such as nickel, titanium, aluminum, and stainless steel. The conductive additives can be in particle or fibrous form, and their size is not particularly limited. A single conductive additive can be used, or two or more can be used in combination.

[0114] The adhesive that can be contained in the negative electrode active material layer 31 includes, for example, butadiene rubber (BR) based adhesives, butyl rubber (IIR) based adhesives, acrylate butadiene rubber (ABR) based adhesives, styrene butadiene rubber (SBR) based adhesives, polyvinylidene fluoride (PVdF) based adhesives, polytetrafluoroethylene (PTFE) based adhesives, and polyimide (PI) based adhesives. One type of adhesive can be used alone, or two or more types can be used in combination.

[0115] 3.2 Negative current collector

[0116] like Figure 1 As shown, the negative electrode 30 may have a negative electrode current collector 32 in contact with the aforementioned negative electrode active material layer 31. The negative electrode current collector 32 is in contact with the aqueous electrolyte 20. Any material capable of functioning as a negative electrode current collector in an aqueous battery can be used for the negative electrode current collector 32. If the aforementioned positive electrode current collector 12 contains Al, the negative electrode current collector 32 may or may not contain Al. Conversely, if the aforementioned positive electrode current collector 12 does not contain Al, the negative electrode current collector 32 may contain Al.

[0117] When the negative electrode current collector 32 contains Al, the entire negative electrode current collector 32 can be made of Al, or at least a portion of its surface can be made of Al. For example, the negative electrode current collector 32 can be made of Al foil, or it can be a current collector obtained by coating the surface of a metal foil or any substrate with Al. At least a portion of the surface of the negative electrode current collector 32 in contact with the aqueous electrolyte 20 can contain Al, or the entire surface in contact with the aqueous electrolyte 20 can contain Al.

[0118] The negative electrode current collector 32 can be in the form of foil, plate, mesh, perforated metal, or foam. The negative electrode current collector 32 can be made of metal foil or metal mesh. In particular, metal foil is excellent in terms of operability, etc. The negative electrode current collector 32 can be made of multiple foils. As for the metallic material constituting the negative electrode current collector 32, examples include metallic materials containing at least one element selected from Cu, Ni, Al, V, Au, Pt, Mg, Fe, Ti, Pb, Co, Cr, Zn, Ge, In, Sn, and Zr. In particular, the negative electrode current collector 32 preferably contains at least one element selected from Al, Ti, Pb, Zn, Sn, Mg, Zr, and In; as mentioned above, Al is preferred. It can be assumed that Al, Ti, Pb, Zn, Sn, Mg, Zr, and In all have low work functions, making it difficult for the aqueous electrolyte 20 to electrolyze even when the negative electrode current collector 32 is in contact with it at the reduction potential. The negative electrode current collector 32 can be a material obtained by electroplating or vapor-depositing the aforementioned metals onto a metal foil or substrate. Furthermore, when the negative electrode current collector 32 is composed of multiple metal foils, there can be any number of layers between these foils. The thickness of the negative electrode current collector 32 is not particularly limited. For example, it can be 0.1 μm or more, or 1 μm or more, and can be 1 mm or less, or 100 μm or less.

[0119] 4. Other components

[0120] In the aqueous battery 100, various ions from the aqueous electrolyte 20 can function as carrier ions and charge compensation ions. The aqueous battery 100 can be an aqueous battery that uses protons as carrier ions and charge compensation ions (aqueous proton battery), an aqueous battery that uses potassium ions as carrier ions and charge compensation ions (aqueous potassium-ion battery), an aqueous battery that uses hydroxide ions as carrier ions and charge compensation ions (aqueous hydroxide-ion battery), an aqueous battery that uses polyphosphate anions as carrier ions and charge compensation ions (aqueous polyphosphate anion battery), or an aqueous battery that uses other ions from the aqueous electrolyte 20 as carrier ions and charge compensation ions. In the aqueous battery 100, multiple ions from the aqueous electrolyte 20 can function as carrier ions and charge compensation ions. The aqueous battery 100 can also have other configurations besides the basic configuration described above.

[0121] 4.1 Diaphragm

[0122] 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 existing aqueous electrolyte batteries (nickel-metal hydride batteries, zinc-air batteries, etc.). For example, there are hydrophilic separators such as nonwoven fabrics made of cellulose. The thickness of the separator 40 is not particularly limited; for example, it may be 5 μm or more and 1 mm or less.

[0123] 4.2 Bipolar Structure

[0124] As described above, both the positive current collector 12 and the negative current collector 32 of the aqueous battery 100 may contain Al. In this regard, in the aqueous battery 100, an Al-containing current collector can be used as a bipolar current collector that serves as both the positive current collector 12 and the negative current collector 32. That is, the positive electrode 10 and the negative electrode 30 can share a single current collector. Figure 2 An example of a bipolar structure is shown in the figure. For example... Figure 2 As shown, the aqueous battery 100 has a bipolar structure, in which a positive electrode active material layer 11 is formed on one side of the Al-containing current collector 50 (which functions as both the positive electrode current collector 12 and the negative electrode current collector 32), and a negative electrode active material layer 31 is formed on the other side of the current collector 50. In this case, the Al-containing current collector 50 is not liquid-permeable, that is, the aqueous electrolyte 20 cannot pass through from the positive electrode active material layer 11 to the negative electrode active material layer 31 via the current collector 50, and conversely, it cannot pass through either.

[0125] 4.3 Terminals, etc.

[0126] In addition to the above-described components, the aqueous battery 100 may also include terminals, a battery casing, etc. Other components will be clear to those skilled in the art upon referring to this application, therefore their description is omitted.

[0127] 5. Manufacturing method of aqueous batteries

[0128] The aqueous battery 100 disclosed herein can be manufactured, for example, in the following manner.

[0129] 5.1 Method for manufacturing aqueous electrolyte

[0130] The aqueous electrolyte 20 can be manufactured, for example, by mixing water, potassium polyphosphate, and silicate. Alternatively, it can be manufactured by mixing water, a potassium ion source, a polyphosphate ion source, and a silicate ion source. There is no particular limitation on the mixing method, and known mixing methods can be used. Alternatively, the aqueous electrolyte 20 can be obtained simply by filling a container with water, potassium polyphosphate, and silicate and allowing them to mix together.

[0131] 5.2 Manufacturing of positive electrode

[0132] The positive electrode 10 can be manufactured, for example, as follows: A positive electrode active material constituting the positive electrode active material layer 11 can be dispersed in a solvent to obtain a positive electrode paste (slurry). In this case, the solvent used is not particularly limited; water or various organic solvents can be used. The positive electrode paste (slurry) is coated onto the surface of the positive electrode current collector 12 using a doctor blade or similar tool, 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. As a coating method, in addition to the doctor blade method, electrostatic coating, dip coating, spray coating, etc., can be used.

[0133] 5.3 Manufacturing of the negative electrode

[0134] The negative electrode 30 can be manufactured, for example, as follows: A negative electrode active material constituting the negative electrode active material layer 31 can be dispersed in a solvent to obtain a negative electrode paste (slurry). In this case, the solvent used is not particularly limited; water or various organic solvents can be used. The negative electrode paste (slurry) is applied to the surface of the negative electrode current collector 32 using a doctor blade or similar tool, 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. As a coating method, in addition to the doctor blade method, electrostatic coating, dip coating, and spray coating can be used.

[0135] 5.4 Storage within the battery casing, etc.

[0136] An aqueous battery 100 is formed by housing an aqueous electrolyte 20, a positive electrode 10, and a negative electrode 30 within a battery casing. For example, a separator 40 is sandwiched between the positive electrode 10 and the negative electrode 30, resulting in a stacked structure having a positive current collector 12, a positive active material layer 11, a separator 40, a negative active material layer 31, and a negative current collector 32 in sequence. Other components, such as terminals, can be mounted on the stacked structure as needed. An aqueous battery 100 can also be obtained by housing the stacked structure within a battery casing, filling the battery casing with an aqueous electrolyte 20, immersing the stacked structure in the aqueous electrolyte 20, and sealing the stacked structure and electrolyte within the battery casing.

[0137] 6. Effects of the water-based battery disclosed herein

[0138] According to the aqueous battery 100 of this disclosure, the dissolution of Al from the current collector into the aqueous electrolyte 20 can be suppressed through the following effects.

[0139] 6.1 Effects of the positive current collector containing Al

[0140] During charging and discharging of the battery, the potential of the positive electrode becomes the potential of the oxidation side. Therefore, the Al contained in the positive electrode current collector releases electrons and becomes readily soluble. 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 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, the Al contained in the positive electrode current collector 12 readily coordinates with anions from potassium polyphosphate. Here, for example, aluminum polyphosphate has extremely low solubility in the aqueous electrolyte 20. Therefore, the Al coordinated with anions from potassium polyphosphate rapidly precipitates out in solid form. In other words, insoluble or sparingly soluble Al compounds are deposited near the surface of the positive current collector 12. These Al compounds adhere to the surface of the positive current collector 12, forming a protective film (non-dynamic film) on that surface. As a result, in the aqueous battery 100 of this disclosure, the dissolution of Al from the positive current collector 12 into the aqueous electrolyte 20 can be suppressed by this protective film.

[0141] Furthermore, the aqueous electrolyte 20 of the aqueous battery 100 of this disclosure contains dissolved silicates. According to the inventors' new insights, by dissolving silicates together with potassium polyphosphate in the aqueous electrolyte 20, the solubility of Al reacting with silicates is also very low. Therefore, the aforementioned protective film (non-dynamic film) can be stabilized. Moreover, when the aforementioned protective film (non-dynamic film) peels off, exposing the Al surface of the current collector, polyphosphate ions and silicates can react with Al again, thereby forming a protective film (non-dynamic film), thus significantly improving the Al dissolution inhibition effect.

[0142] Furthermore, the aqueous electrolyte 20 of the aqueous battery 100 of this disclosure may contain at least one of orthophosphoric acid, metaphosphoric acid (polyphosphoric acid), and carboxylic acid. When orthophosphoric acid, metaphosphoric acid, and / or carboxylic acid are dissolved in the aqueous electrolyte 20 along with potassium polyphosphate, the aforementioned non-dynamic effect of potassium polyphosphate can be obtained, and the pH of the aqueous electrolyte 20 can be lowered. Additionally, the effects of mixing polyphosphate anions with other anions in the aqueous electrolyte, and the effects of increased anion concentration, can be considered to be utilized. That is, it is considered that while maintaining the performance of the aqueous electrolyte 20, the non-dynamic film of Al formed on the surface of the current collector can be further stabilized.

[0143] 6.2 Effect of the negative current collector containing Al

[0144] During battery charging and discharging, the potential of the negative electrode becomes the potential of the reduction side. Therefore, electrolysis occurs through the aqueous electrolyte in contact with the negative electrode, generating hydroxide ions, and the pH of the aqueous electrolyte near the negative electrode tends to increase. If the pH of the aqueous electrolyte near the negative electrode increases, the solubility of Al in the aqueous electrolyte increases, and the Al contained in the negative electrode current collector becomes more easily dissolved 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 the Al contained in the negative electrode current collector 32 dissolves into the aqueous electrolyte 20 during battery charging and discharging, it can quickly coordinate with anions from potassium polyphosphate, becoming Al compounds and precipitating in solid form. In other words, insoluble or sparingly soluble Al compounds precipitate near the surface of the negative electrode current collector 32, and these Al compounds adhere to the surface of the negative electrode current collector 32, thereby forming a protective film (non-dynamic film) on that surface. As a result, in the aqueous battery 100 of this disclosure, the protective film can suppress the dissolution of Al from the negative electrode current collector 32 into the aqueous electrolyte 20.

[0145] In addition, in the aqueous battery 100 disclosed herein, as described above, silicates are dissolved in the aqueous electrolyte 20, which can stabilize the above-mentioned protective film (non-dynamic film). Furthermore, it is recorded that when the above-mentioned protective film (non-dynamic film) peels off and exposes the Al surface of the current collector, a protective film (non-dynamic film) can also be formed by silicates, thereby significantly improving the Al dissolution suppression effect.

[0146] Furthermore, in the aqueous battery 100 of this disclosure, as described above, at least one of orthophosphoric acid, metaphosphoric acid (polyphosphoric acid), and carboxylic acid can be dissolved in the aqueous electrolyte 20. When orthophosphoric acid, metaphosphoric acid, and / or carboxylic acid are dissolved in the aqueous electrolyte 20 along with potassium polyphosphate, the pH of the aqueous electrolyte 20 can be lowered while achieving the aforementioned non-dynamic effect of potassium polyphosphate. Additionally, it is believed that the effects of mixing polyphosphate anions with other anions in the aqueous electrolyte, and the effects of increased anion concentration, can be utilized. That is, it is believed that while maintaining the performance of the aqueous electrolyte 20, the non-dynamic film of Al formed on the surface of the current collector can be further stabilized.

[0147] 6.3 Other Effects

[0148] In aqueous electrolyte batteries, materials containing Ti or Ni are used as current collectors to combat corrosion (e.g., Patent Document 1). It has been believed that metals other than these are difficult to use, as they dissolve at positive electrode potentials. Furthermore, Ti and Ni are expensive, so cheaper alternatives are needed to widely popularize aqueous electrolyte batteries. In this regard, the aqueous battery 100 of this disclosure uses an Al-containing material as the current collector, thereby reducing the overall cost of the battery. Moreover, by employing the aforementioned aqueous electrolyte 20, the dissolution of Al from the current collector into the aqueous electrolyte can be suppressed.

[0149] 7. Applications of aqueous batteries

[0150] As described above, the aqueous battery according to this disclosure can suppress the dissolution of Al from the current collector into the aqueous electrolyte. That is, battery degradation is easily suppressed. Such an aqueous battery is well suited for use in at least one of hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs). Specifically, the technology of this disclosure includes a vehicle with an aqueous battery having a positive electrode, an aqueous electrolyte, and a negative electrode, wherein one or both of the positive and negative electrodes have a current collector containing Al, and the aqueous electrolyte contains water, potassium polyphosphate dissolved in the water, and silicates dissolved in the water. Details of the aqueous electrolyte and the battery configuration are described above.

[0151]

Example

[0152] The following embodiments are provided to illustrate the technology of this disclosure in more detail, but the technology of this disclosure is not limited to the following embodiments.

[0153] 1. Preparation and evaluation of aqueous electrolytes

[0154] 1.1 Preparation of aqueous electrolyte

[0155] 1.1.1 Comparative Examples 1-6

[0156] Potassium pyrophosphate (K4P2O7) was dissolved in pure water at a specified concentration to obtain the aqueous electrolytes of Comparative Examples 1 to 6.

[0157] 1.1.2 Examples 1-66

[0158] Prepare a solution containing 50% by mass of potassium metasilicate (K2SiO3) (manufactured by Fujifilm Wako Co., Ltd.). Dilute this solution with pure water as needed to obtain a solution containing potassium metasilicate at a specified concentration (by mass%). Dissolve potassium pyrophosphate (K4P2O7), pyrophosphate (K4P2O7) or acetic acid (CH3COOH) as any component at a specified concentration to obtain the aqueous electrolytes of Examples 1 to 66.

[0159] 1.2 Evaluation Methods for Aqueous Electrolytes

[0160] 1.2.1 Confirmation of K, P, and Si concentrations

[0161] The concentrations of K, P, and Si in the aqueous electrolyte were determined by ICP. The results are shown in Tables 1-3 below.

[0162] 1.2.2 Ion conductivity

[0163] The ionic conductivity of the aqueous electrolyte at room temperature (25°C) was determined using an ionic conductivity meter (Sevenmulti, Made by Mettler-Toledo). The results are shown in Tables 1-3 below.

[0164] 1.2.3 Viscosity

[0165] The viscosity of the aqueous electrolyte at room temperature (25°C) was measured using a viscometer (VM10, manufactured by Sekonic). The results are shown in Tables 1-3 below.

[0166] 1.2.4 pH

[0167] The pH of the aqueous electrolyte was measured at room temperature (25°C) using a pH meter (SevenMulti, manufactured by Mettel TOLEDO). The results are shown in Tables 1-3 below.

[0168] 1.2.5 Low-temperature stability evaluation

[0169] The above-mentioned aqueous electrolyte was kept in a constant temperature bath at -60°C for more than 8 hours, and then the state of the aqueous electrolyte was visually observed to confirm whether it had frozen (whether it had whitened). If the aqueous electrolyte did not freeze, it was considered that the aqueous electrolyte did not have a freezing point above -60°C. The results are shown in Tables 1-3 below.

[0170] 1.2.6 Electrochemical Measurement

[0171] An electrochemical unit (SB1A, manufactured by EC Frontier) was constructed using Al foil as the working electrode, Ni foil as the counter electrode, Ag / AgCl as the reference electrode, and the aforementioned aqueous electrolyte. Cyclic voltammetry was performed on this unit in a 25°C thermostat, scanning from the open circuit potential (OCP) towards the oxidation side at a scan rate of 1 mV / sec, with two cycles at 1.4 V vs. SHE and two cycles at 1.6 V. Following the electrochemical measurements, the degree of dissolution of the Al foil by the aqueous electrolyte was evaluated according to a four-level scale (A-D) based on the cyclic voltammogram from the second cycle. The results are shown in Tables 1-3 below.

[0172] A: As Figure 3A As shown, even when the potential is increased from OCP up to 1.0V, no oxidation current flows out, and even when the scan is reversed, no oxidation current flows out (i.e., the Al foil surface is non-dynamic and no Al foil dissolution occurs).

[0173] B: As Figure 3B As shown, even when the potential is increased from OCP, no oxidation current flows out up to 1.0V. Even when the scan is reversed, the oxidation current is suppressed, but the suppression range is above 0.5V and below 1.0V.

[0174] C: such as Figure 3C As shown, even when the potential is increased from OCP up to 1.0V, no oxidation current flows out. Even when the scan is reversed, the oxidation current is suppressed, but the suppression range is 0.5V.

[0175] D: such as Figure 3D As shown, when scanning from the OCP to the oxidation side, an oxidation current flows out. If the scan is reversed, the oxidation current continues to flow out.

[0176] 1.3 Evaluation Results of Aqueous Electrolytes

[0177]

[0178] As shown in Table 1, the Al foils of Comparative Examples 1-6, which contained only potassium pyrophosphate dissolved in the aqueous electrolyte, exhibited a small dissolution inhibition effect. For example, the cyclic voltammogram of Comparative Example 5 showed that a current accompanying Al foil dissolution flowed out when the potential was increased slightly from OCP, after which the current tended to decrease (de-dynamic). After repeated scans, a small amount of current still flowed out, and no significant change in the shape of the CV curve was observed after two cycles. This suggests that the state of the de-dynamic film formed on the surface of the Al foil was reset due to the potential returning to OCP, and a robust de-dynamic film existed only when a potential was applied, thus potentially inhibiting Al dissolution. Therefore, for the comparative examples, it is believed that the stability of current collectors containing Al has room for improvement.

[0179] In contrast, the results shown in Tables 1-3 indicate that in Examples 1-66, where potassium metasilicate was dissolved along with potassium pyrophosphate in the aqueous electrolyte, the dissolution inhibition effect of the Al foil was significantly improved. It can be considered that the non-dynamic membrane caused by potassium pyrophosphate was stabilized by potassium metasilicate. Furthermore, the results shown in Tables 1-3 show that when pyrophosphate and acetic acid are dissolved along with potassium pyrophosphate and potassium metasilicate in the aqueous electrolyte, the pH of the aqueous electrolyte can be reduced while ensuring an equivalent or better dissolution inhibition effect on the Al foil.

[0180] As shown in Tables 1-3, all aqueous electrolytes of Examples 1-66 exhibit high ionic conductivity exceeding 10 mS / cm. Furthermore, all aqueous electrolytes of Examples 1-66 have a viscosity of 10 mPa·s or higher and 400 mPa·s or lower at 25°C. Additionally, no salt precipitation occurred in any of the aqueous electrolytes of Examples 1-66 when cooled from 0°C to -40°C.

[0181] Furthermore, the above embodiments illustrate the case where potassium pyrophosphate is dissolved as potassium polyphosphate in an aqueous electrolyte. However, the potassium polyphosphate dissolved in the aqueous electrolyte is not limited to potassium pyrophosphate. The inventors have confirmed that the above-described non-dynamic effect on the Al foil surface can also be obtained by dissolving potassium polyphosphate (e.g., potassium tripolyphosphate) in an aqueous electrolyte instead of potassium pyrophosphate, or together with potassium pyrophosphate.

[0182] Furthermore, the above embodiments illustrate the case where potassium metasilicate is dissolved as a silicate in an aqueous electrolyte. However, the silicate dissolved in the aqueous electrolyte is not limited to potassium metasilicate. The inventors have confirmed that the dissolution inhibition effect of the Al foil can also be improved by dissolving a silicate other than potassium metasilicate (e.g., potassium orthosilicate) in the aqueous electrolyte, either instead of potassium metasilicate or together with potassium metasilicate. However, the dissolution inhibition effect of the Al foil is more easily improved when potassium metasilicate is dissolved as a silicate.

[0183] Furthermore, the above embodiments exemplify the case where pyrophosphate and acetic acid are dissolved as components for adjusting the pH of the aqueous electrolyte. However, the acids dissolved in the aqueous electrolyte are not limited to these acids. For example, it has been confirmed that by dissolving metaphosphoric acid (polyphosphoric acid) other than pyrophosphate, carboxylic acids other than acetic acid, and / or orthophosphoric acid, in place of pyrophosphate and acetic acid, or together with them, it is also possible to lower the pH of the aqueous electrolyte while ensuring the dissolution inhibition effect of the Al foil described above.

[0184] 2. Fabrication and Evaluation of Aqueous Batteries

[0185] 2.1 Unit Creation

[0186] Evaluation cells were fabricated using the aforementioned aqueous electrolyte, nickel hydroxide as the positive electrode active material, and La2Ni7 hydrogen-absorbing alloy as the negative electrode active material. For each electrode, a slurry was prepared with a mass ratio of active material:acetylene black:SBR:CMC = 74.5:20:4.5:1, and coated onto metal foils (positive electrode current collector: Al foil, negative electrode current collector: titanium foil) using a doctor blade. The coated electrodes were dried under reduced pressure at 60°C overnight, and then rolled under a linear pressure of 1 ton. The evaluation cells used were EC Frontier SB9 cells, the diaphragm was an Advantech Glass filter, and the reference electrode was Ag / AgCl.

[0187] 2.2 Unit Evaluation Methods

[0188] A full cell was constructed with a negative electrode / positive electrode capacity ratio of 3 or higher. Charge-discharge evaluations were conducted using ±0.1C current values ​​at a positive electrode capacity of 200 mAh / g and positive electrode side cutoff potentials of 0.0–+1.05V vs. SHE or a cutoff capacity of 200 mAh / g. The evaluations were performed in a constant temperature bath at 25°C.

[0189] 2.3 Evaluation Results

[0190] Figure 4 The charge-discharge curves of the evaluation unit using the aqueous electrolyte of Comparative Example 5 are shown. Figure 4 As shown, a reaction of approximately 50 mAh / g was carried out on the charging side, and the results confirmed the decrease in voltage accompanying Al dissolution.

[0191] Figure 5 The charge-discharge curves of the evaluation unit using the aqueous electrolyte of Example 48 are shown. Figure 5 As shown, no abnormalities were found on the mischarge side, confirming that stable charging and discharging can be performed.

[0192] 3. Summary

[0193] The results above show that an aqueous battery with the following structure can suppress the dissolution of Al from the Al-containing current collector into the aqueous electrolyte.

[0194] (1) It has a positive electrode, an aqueous electrolyte and a negative electrode.

[0195] (2) One or both of the positive and negative electrodes have a current collector containing Al.

[0196] (3) The current collector is in contact with the aqueous electrolyte.

[0197] (4) The aqueous electrolyte contains water, potassium polyphosphate dissolved in the water, and silicate dissolved in the water.

[0198] Explanation of reference numerals in the attached figures

[0199] 10 positive electrode

[0200] 11 Positive Electrode Active Material Layer

[0201] 12 positive current collectors

[0202] 20 Aqueous Electrolyte

[0203] 30 negative electrode

[0204] 31 Negative Electrode Active Material Layer

[0205] 32 negative current collector

[0206] 40 diaphragm

[0207] 100 water-based batteries

Claims

1. An aqueous battery comprising a positive electrode, an aqueous electrolyte, and a negative electrode. One or both of the positive and negative electrodes have a current collector containing Al. The current collector is in contact with the aqueous electrolyte. The aqueous electrolyte contains: water, Potassium polyphosphate dissolved in the water, and Silicates dissolved in the water.

2. The aqueous battery as described in claim 1, wherein the silicate is metasilicate.

3. The aqueous battery as described in claim 1, wherein the silicate is potassium metasilicate.

4. The aqueous battery according to any one of claims 1 to 3, wherein the aqueous electrolyte contains at least one selected from orthophosphoric acid, metaphosphoric acid and carboxylic acid dissolved in the water.

5. The aqueous battery according to any one of claims 1 to 4, wherein the aqueous electrolyte contains potassium polyphosphate dissolved at a concentration of 1 mol or more relative to 1 kg of the water.

6. The aqueous battery according to any one of claims 1 to 5, wherein the aqueous electrolyte does not have a freezing point above -40°C.

7. The aqueous battery according to any one of claims 1 to 6, wherein salt will not precipitate when the aqueous electrolyte is cooled from 0°C to -40°C.

8. The aqueous battery according to any one of claims 1 to 7, wherein the viscosity of the aqueous electrolyte at 25°C is 10 mPa·s or more and 400 mPa·s or less.

9. The aqueous battery according to any one of claims 1 to 8, wherein the pH of the aqueous electrolyte is 3 or higher and 13 or lower.

10. The aqueous battery according to any one of claims 1 to 9, wherein at least the positive electrode has the current collector.

11. The aqueous battery according to any one of claims 1 to 10, having a bipolar structure, wherein a positive electrode active material layer is formed on one side of the current collector, and a negative electrode active material layer is formed on the other side of the current collector.

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