Positive electrode active material and aqueous battery

Abstract

To provide a novel material that can function as a positive electrode active material in an aqueous battery having an aqueous electrolyte that includes potassium ions.SOLUTION: A positive electrode active material according to the present disclosure is represented by K2Ni2TeO6, and is used in an aqueous battery having an aqueous electrolyte solution containing potassium ions.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] This application discloses a positive electrode active material and an aqueous battery. [Background technology]

[0002] Patent Document 1 discloses a Prussian blue analogue as a positive electrode active material for an aqueous battery using an aqueous electrolyte solution containing potassium ions. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-220294 A Summary of the Invention [Problem to be solved by the invention]

[0004] There is a need for new positive electrode active materials that can be used in aqueous batteries having aqueous electrolytes that contain potassium ions. [Means for solving the problem]

[0005] The present application discloses the following aspects as means for solving the above problems. <Aspect 1> It is represented by K2Ni2TeO6, and Used in aqueous batteries having an aqueous electrolyte solution containing potassium ions, Cathode active material. <Aspect 2> An aqueous battery, A positive electrode active material layer, an aqueous electrolyte solution, and a negative electrode active material layer are included, the positive electrode active material layer comprises the positive electrode active material of aspect 1, The aqueous electrolyte contains potassium ions. water-based battery. <Aspect 3> 3. The aqueous battery of embodiment 2, The aqueous electrolyte solution contains water and potassium polyphosphate dissolved in the water. water-based battery. <Aspect 4> The aqueous battery of embodiment 2, The aqueous electrolyte solution contains water and potassium polyphosphate dissolved in the water at a concentration of 2.0 mol or more per kg of the water. water-based battery. <Aspect 5> The aqueous battery according to any one of aspects 2 to 4, The pH of the aqueous electrolyte is 3 or more and 13 or less. water-based battery. Effect of the Invention

[0006] The positive electrode active material of the present disclosure can be used as a positive electrode active material in an aqueous battery. [Brief description of the drawings]

[0007] [Figure 1] 1 shows a schematic diagram of an example of the configuration of an aqueous battery. [Diagram 2] 3 shows charge / discharge curves of a cell according to an embodiment. [Diagram 3] 4 shows charge / discharge curves of a cell according to a comparative example. [Figure 4] 1 shows the relationship between the potassium pyrophosphate concentration in an aqueous electrolyte and the ionic conductivity of the aqueous electrolyte. [Diagram 5] 1 shows the relationship between the potassium pyrophosphate concentration in an aqueous electrolyte and the pH of the aqueous electrolyte. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] 1.Cathode active material for water-based batteries There are few reported examples of inorganic compounds that can function as active materials in batteries using electrolytes containing potassium ions. There is little knowledge about what inorganic compounds can be used as active materials, and the activity of a number of inorganic compounds is currently being confirmed one by one. In particular, research on aqueous batteries using aqueous electrolytes containing potassium ions is still in its infancy, and there are even fewer reported examples of active materials compared to non-aqueous batteries, with only Prussian blue-based compounds and the like being considered. Prussian blue-based compounds have a large molecular structure, which is disadvantageous in terms of energy density, for example. In this regard, a new positive electrode active material that can be used in aqueous batteries using aqueous electrolytes containing potassium ions is required.

[0009] The present inventors have searched for new materials that function as positive electrode active materials in aqueous batteries that use aqueous electrolytes containing potassium ions, and have found that a composite oxide represented by K2Ni2TeO6 can be used as the positive electrode active material in such aqueous batteries.

[0010] The positive electrode active material of the present disclosure is represented by K2Ni2TeO6 and is used in an aqueous battery having an aqueous electrolyte solution containing potassium ions. The positive electrode active material of the present disclosure is considered to be advantageous in terms of energy density, etc., compared to Prussian blue-based compounds. In addition, the positive electrode active material of the present disclosure has a high charge / discharge capacity. The present inventor has confirmed that when a part of Ni in K2Ni2TeO6 is replaced with another element (for example, Co), the charge / discharge capacity decreases. In other words, the high charge / discharge capacity as a positive electrode active material for an aqueous battery having an aqueous electrolyte solution containing potassium ions can be said to be a remarkable and unique effect when the positive electrode active material is represented by K2Ni2TeO6.

[0011] The shape of the positive electrode active material of the present disclosure may be a general shape as a positive electrode active material for a battery. The positive electrode active material of the present disclosure may be, for example, particulate. In this case, the particle size is not particularly limited, and an appropriate size may be selected according to the design of the battery. The positive electrode active material of the present disclosure may be a primary particle, or a secondary particle in which a plurality of primary particles are aggregated. The average particle size D50 of the positive electrode active material of the present disclosure may be, for example, 1 nm or more and 1000 μm or less, the lower limit may be 5 nm or more or 10 nm or more, and the upper limit may be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. The average particle size D50 in the present application is the particle size (median size) at an integrated value of 50% in the volume-based particle size distribution obtained by a laser diffraction / scattering method.

[0012] The positive electrode active material of the present disclosure may be produced, for example, by mixing a K source, a Ni source, and a Te source, and calcining the mixture under an oxygen-containing atmosphere. The K source may be, for example, potassium carbonate. The Ni source may be, for example, nickel oxide. The Te source may be, for example, tellurium oxide. The calcination temperature may be, for example, 700° C. or more and 900° C. or less, and the calcination time may be, for example, 5 hours or more and 100 hours or less.

[0013] 2. Water-based battery 1, an aqueous battery 100 according to one embodiment includes a positive electrode active material layer 11, an aqueous electrolyte 20, and an anode active material layer 31. The positive electrode active material layer 11 includes the positive electrode active material of the present disclosure, i.e., the positive electrode active material represented by K2Ni2TeO6. The aqueous electrolyte includes potassium ions.

[0014] 2.1 Cathode active material layer The positive electrode active material layer 11 includes the positive electrode active material of the present disclosure. The positive electrode active material layer 11 may be impregnated with an aqueous electrolyte solution 20. The positive electrode active material layer 11 may include a conductive assistant, a binder, various additives, and the like in addition to the positive electrode active material. The content of each component in the positive electrode active material layer 11 may be appropriately determined according to the intended battery performance. The shape of the positive electrode active material layer 11 is not particularly limited, and may be, for example, a sheet-like positive electrode active material layer having a substantially flat surface.

[0015] 2.1.1 Cathode active material The positive electrode active material layer 11 may contain only the positive electrode active material represented by K2Ni2TeO6, or may contain other positive electrode active materials in addition to the positive electrode active material represented by K2Ni2TeO6. The positive electrode active material represented by K2Ni2TeO6 may account for more than 0 mass% and 100 mass% or less, 10 mass% or more and 100 mass% or less, 30 mass% or more and 100 mass% or less, or 50 mass% or more and 100 mass% or less, based on the total amount of the positive electrode active material contained in the positive electrode active material layer 11 (100 mass%). The other positive electrode active material may contain K element. Specifically, oxides and polyanions containing K element may be mentioned. More specifically, it may be a composite oxide of potassium and a transition metal other than K2Ni2TeO6. Note that even if the K site in the composite oxide is composed of other alkali metal elements, it may be possible to insert and remove various ions contained in the aqueous electrolyte solution 20. Alternatively, the other positive electrode active material may be Prussian blue, etc. Alternatively, the other positive electrode active material may be at least one selected from potassium titanate, TiO2, sulfur (S), etc., which exhibit a charge / discharge potential that is more noble than the negative electrode active material described below. The other positive electrode active material may be, for example, particulate. The other positive electrode active material may be primary particles, or secondary particles formed by agglomeration of a plurality of primary particles. The average particle diameter D50 of the other positive electrode active material may be, for example, 1 nm or more and 1000 μm or less, the lower limit may be 5 nm or more or 10 nm or more, and the upper limit may be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less.

[0016] 2.1.2 Conductive additives Examples of the conductive assistant that may be included in the positive electrode active material layer 11 include carbon materials such as vapor grown carbon fiber (VGCF), acetylene black (AB), ketjen black (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF); and metal materials that are poorly soluble in aqueous electrolytes, such as nickel, titanium, aluminum, and stainless steel. The conductive assistant may be, for example, particulate or fibrous, and its size is not particularly limited. Only one type of conductive assistant may be used alone, or two or more types may be used in combination.

[0017] 2.1.3 Binders Examples of binders that can be included in the positive electrode active material layer 11 include butadiene rubber (BR)-based binders, butylene rubber (IIR)-based binders, acrylate butadiene rubber (ABR)-based binders, styrene butadiene rubber (SBR)-based binders, polyvinylidene fluoride (PVdF)-based binders, polytetrafluoroethylene (PTFE)-based binders, polyimide (PI)-based binders, etc. Only one type of binder may be used alone, or two or more types may be used in combination.

[0018] 2.2 Positive electrode current collector As illustrated in FIG. 1, the positive electrode 10 of the aqueous battery 100 may include a positive electrode current collector 12 in contact with the positive electrode active material layer 11. The positive electrode current collector 12 may be in contact with the aqueous electrolyte 20. Any positive electrode current collector that can function as a positive electrode current collector of an aqueous battery can be used. The positive electrode current collector 12 may be in the form of a foil, a plate, a mesh, a punched metal, a foam, or the like. The positive electrode current collector 12 may be made of a metal foil or a metal mesh. In particular, a metal foil is excellent in terms of ease of handling. The positive electrode current collector 12 may be made of a plurality of foils. Examples of the metal material 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. The positive electrode current collector 12 may be a metal foil or a substrate plated or vapor-deposited with the above metal. When the positive electrode current collector 12 is made of a plurality of metal foils, some layer may be present between the plurality of metal foils. The thickness of the positive electrode current collector 12 is not particularly limited. For example, it may be 0.1 μm or more or 1 μm or more, and may be 1 mm or less or 100 μm or less.

[0019] 2.3 Aqueous electrolyte The aqueous electrolyte 20 includes water and an electrolyte dissolved in the water. The aqueous electrolyte 20 includes potassium ions. For example, a potassium ion source can be dissolved in the aqueous electrolyte 20 as an electrolyte. The aqueous electrolyte 20 may be in contact with the above-mentioned positive electrode collector 12, may be included in the above-mentioned positive electrode active material layer 11, may be in contact with the later-described negative electrode collector 32, may be included in the later-described negative electrode active material layer 31, or may be held by the separator 40 between the positive electrode active material layer 11 and the negative electrode active material layer 31.

[0020] 2.3.1 Solvents The aqueous electrolyte 20 contains water as a solvent. The solvent contains water as a main component. That is, based on the total amount of the solvent constituting the aqueous electrolyte (100 mol%), water accounts for 50 mol% or more and 100 mol% or less. Water may account for 70 mol% or more, 90 mol% or more, or 95 mol% or more of the total amount of the solvent. Meanwhile, the upper limit of the proportion of water in the solvent is not particularly limited. The solvent may be composed of only water (100 mol% water). From the viewpoint of forming a solid electrolyte interphase (SEI) on the surface of the active material, the aqueous electrolyte 20 may contain a solvent other than water in addition to water. Examples of the solvent 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 the solvents constituting the aqueous electrolyte solution 20 (100 mol %).

[0021] 2.3.2 Electrolytes An electrolyte may be dissolved in the aqueous electrolyte 20. The electrolyte may be dissociated into cations and anions in the aqueous electrolyte 20. In the aqueous electrolyte 20, the cation may be completely dissociated from the anion, or may be in close proximity to the anion to form an association. For example, the potassium ion contained in the aqueous electrolyte 20 may form an association with the anion. The aqueous electrolyte 20 may contain multiple types of cations. For example, the aqueous electrolyte 20 may contain potassium ions and other cations together with the potassium ions. For example, the aqueous electrolyte 20 may contain alkali metal ions other than potassium ions, alkaline earth metal ions, transition metal ions, and the like. The aqueous electrolyte 20 naturally contains protons. The aqueous electrolyte 20 may contain one or more types of anions. There is no particular limit to the type of anion. The aqueous electrolyte 20 contains, for example, an anion derived from the electrolyte (for example, a polyphosphate anion described later). The aqueous electrolyte 20 naturally contains hydroxide ions. As described above, the aqueous electrolyte solution 20 contains various ions, and at least one of the ions can be a carrier ion. In this embodiment, the carrier ion may be a potassium ion, a proton, a hydroxide ion, an anion derived from an electrolyte (for example, a polyphosphate anion described later), or a combination thereof. The concentration of the electrolyte in the aqueous electrolyte solution 20 is not particularly limited. The concentration of the electrolyte in the aqueous electrolyte solution 20 can be adjusted according to the target performance. According to the findings of the present inventor, the higher the concentration of the electrolyte in the aqueous electrolyte solution 20, the easier it is to expand the potential window of the aqueous electrolyte solution 20. In addition, the higher the concentration, the easier it is to increase the capacity of the aqueous battery 100. Furthermore, the higher the concentration, the easier it is to suppress the elution of the current collector into the aqueous electrolyte solution 20. On the other hand, the lower the concentration, the easier it is to reduce the viscosity of the aqueous electrolyte solution 20.

[0022] The aqueous electrolyte 20 may contain various potassium compounds that can be dissolved in water as an electrolyte. Examples of the electrolyte include KPF6, KBF4, K2SO4, KNO3, CH3COOK, (CF3SO2)2NK, KCF3SO3, (FSO2)2NK, K2HPO4, KH2PO4, KPO3, K4P2O7, and K5P3O 10 , K6P4O 13 , K7P5O 16 , (KPO3)n, and the like.

[0023] According to the findings of the present inventors, when the aqueous electrolyte 20 contains water and a phosphate or acetate of potassium dissolved in the water, particularly when the aqueous electrolyte 20 contains water and a phosphate of potassium dissolved in the water, and particularly when the aqueous electrolyte 20 contains water and potassium polyphosphate dissolved in the water, the performance of the aqueous battery 100 is likely to be improved. "Potassium polyphosphate" refers to a salt in which at least a portion of the hydrogen of polyphosphoric acid is substituted with potassium. In other words, "potassium polyphosphate" is a concept that includes potassium hydrogen polyphosphate. Specific examples of potassium polyphosphate include potassium pyrophosphate (K 4-x H x P2O7), potassium tripolyphosphate (K 5-x H x P3O 10 ), potassium tetrapolyphosphate (K 6-x H x P4O 13 ), potassium heptapolyphosphate (K 7-x H x P5O 16 Among them, potassium pyrophosphate (K 4-x H xWhen an electrolyte such as potassium polyphosphate (P2O7) is used, higher performance is likely to be ensured. When the aqueous electrolyte solution 20 contains potassium polyphosphate as an electrolyte, it may contain other electrolytes together with the potassium polyphosphate. In this case, based on the total amount of electrolytes dissolved in the aqueous electrolyte solution 20 (100 mol%), potassium polyphosphate may account for 50 mol% to 100 mol%, 70 mol% to 100 mol%, or 90 mol% to 100 mol%, and the other electrolytes may account for 0 mol% to 50 mol%, 0 mol% to 30 mol%, or 0 mol% to 10 mol%.

[0024] In the aqueous electrolyte solution 20, the "potassium polyphosphate dissolved in water" can be dissociated into potassium ions and anions. In the aqueous electrolyte solution 20, the potassium ions may be completely dissociated from the anions, or may form associations by coming close to the anions. For example, when the aqueous electrolyte solution 20 contains potassium pyrophosphate dissolved in water, the "potassium pyrophosphate dissolved in water" in the aqueous electrolyte solution 20 is K + , P2O7 4- , KP2O7 3- , K2P2O7 2- , K3P2O7 - or associations of these ions. Also, HO to H + Pull out the HP2O7 3- , H2P2O7 2- , H3P2O7 - Or, H + and K. + and HK2P2O7 - , HKP2O7 2- , H2KP2O7 - In the aqueous electrolyte solution 20, the "concentration of potassium polyphosphate dissolved in water" is determined by converting the ions and associations contained in the aqueous electrolyte solution 20 into potassium polyphosphate. In addition, when the aqueous electrolyte solution 20 contains polyphosphate ions (pyrophosphate ions, as described above, P2O7 4- In addition, KP2O7 3- , K2P2O72- , K3P2O7 - , HP2O7 3- , H2P2O7 2- , H3P2O7 - , HK2P2O7 - , HKP2O7 2- , H2KP2O7 - In the case where the aqueous electrolyte solution 20 contains a pyrophosphate ion source other than K4P2O7 (e.g., H4P2O7, etc., which may be present in a state bound to a cation), a part of the polyphosphate ion contained in the aqueous electrolyte solution 20 may not be calculated as "potassium polyphosphate dissolved". That is, the aqueous electrolyte solution 20 may contain more polyphosphate ions than the concentration that can be calculated as potassium polyphosphate. For example, when the aqueous electrolyte solution 20 is manufactured, if a pyrophosphate ion source other than K4P2O7 (e.g., H4P2O7, etc.) is added and dissolved in water together with K4P2O7, the aqueous electrolyte solution 20 contains more pyrophosphate ions than the concentration that can be calculated as potassium pyrophosphate. On the other hand, in the case where the aqueous electrolyte solution 20 contains a potassium ion source other than a potassium salt (e.g., KOH) and an anion source other than a potassium salt (e.g., H4P2O7), each of which is dissolved in water and dissociated into potassium ions and anions, the potassium ions and anions are calculated as "potassium salt dissolved in water". For example, when KOH and H4P2O7 are dissolved in the aqueous electrolyte 20, they can be converted into potassium pyrophosphate.

[0025] The aqueous electrolyte 20 may contain water and potassium polyphosphate dissolved at a certain concentration or more per 1 kg of water. The concentration of potassium polyphosphate may be, for example, 2.0 mol or more, 2.5 mol or more, 3.0 mol or more, 3.5 mol or more, or 4.0 mol or more per 1 kg of water. The upper limit of the concentration of potassium polyphosphate in the aqueous electrolyte 20 is not particularly limited, but if the concentration is too high, the viscosity of the aqueous electrolyte 20 may be excessively increased. In this regard, the concentration of potassium polyphosphate may be 8.0 mol or less, 7.0 mol or less, or 6.0 mol or less per 1 kg of water. When the concentration of potassium polyphosphate is 2.0 mol or more per 1 kg of water, oxidation and reduction resistance specific to a concentrated aqueous solution system, so-called water-in-salt, is expressed, making the aqueous electrolyte more preferable. In addition, various physical properties described below can be ensured.

[0026] 2.3.3 Other ingredients In addition to the above-mentioned solvent and electrolyte, the aqueous electrolyte solution 20 may contain an acid, a hydroxide, or the like for adjusting the pH of the aqueous electrolyte solution 20. In addition, various additives may be included.

[0027] 2.3.4 Physical properties of aqueous electrolytes (1) The pH of the aqueous electrolyte 20 is not particularly limited. However, if the pH is too high, there is a risk that the oxidation side potential window of the aqueous electrolyte may be narrowed. In this regard, the pH of the aqueous electrolyte may be 3 or more and 13 or less. The pH may be 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, or 10 or more, or may be 12 or less. (2) The aqueous electrolyte 20 may not have a freezing point at -60°C or higher. Here, the presence or absence of the "freezing point" of the aqueous electrolyte 20 is confirmed by differential scanning calorimetry (DSC). The sweep rate by DSC is 5°C / min for both the temperature drop and temperature rise, and the sweep range is from room temperature to -120°C, and then to 40°C. 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 the evaluation, the atmosphere inside the container is air sealed under atmospheric pressure. When the aqueous electrolyte is measured under the above conditions, if the crystallization peak temperature (freezing point temperature) is not confirmed at -60°C or higher, the aqueous electrolyte is deemed to "not have a freezing point at -60°C or higher." In the aqueous battery 100 of the present disclosure, in order to achieve the condition that "the aqueous electrolyte 20 does not have a freezing point at -60°C or higher", it is effective to increase the concentration of the electrolyte (particularly potassium polyphosphate) in the aqueous electrolyte 20. If the aqueous electrolyte 20 does not have a freezing point at -60°C, the amount of free water molecules in the aqueous electrolyte 20 decreases, and metals contained in the current collector are less likely to dissolve into the aqueous electrolyte 20. Furthermore, since the aqueous electrolyte 20 does not have a freezing point at -60°C, the aqueous battery 100 can be used even at extremely low temperatures. That is, the aqueous battery 100 can operate appropriately even in cold regions. (3) It is preferable that the aqueous electrolyte 20 does not cause salt precipitation when cooled from 0°C to -60°C. In this way, since the aqueous electrolyte 20 does not cause salt precipitation due to temperature change, stable ion conduction is possible even at low temperatures. For example, the aqueous battery 100 can be used even at extremely low temperatures such as in cold regions. As described above, the aqueous electrolyte 20 may contain water and potassium polyphosphate dissolved in the water. Here, according to the knowledge of the present inventor, the saturated solubility of potassium polyphosphate in water has little temperature dependency and hardly changes at low temperatures below 0°C. In this regard, even if potassium polyphosphate is dissolved at a high concentration in the aqueous electrolyte 20 at 0°C and the aqueous electrolyte 20 is cooled from 0°C to -60°C, precipitation of potassium polyphosphate in the aqueous electrolyte 20 does not substantially occur. (4) If the viscosity of the aqueous electrolyte solution 20 is too high, the ionic conductivity of the aqueous electrolyte solution 20 may decrease. On the other hand, if an electrolyte is dissolved in the aqueous electrolyte solution 20 at a high concentration, the aqueous electrolyte solution 20 may have a viscosity of a certain level or higher. The aqueous electrolyte solution 20 may have a viscosity of 10 mPa·s or more and 600 mPa·s or less at 20°C.

[0028] 2.4 Negative electrode active material layer The negative electrode active material layer 31 includes a negative electrode active material. The negative electrode active material layer 31 may include a conductive assistant, a binder, various additives, and the like in addition to the negative electrode active material. The negative electrode active material layer 31 may be impregnated with the aqueous electrolyte solution 20. The content of each component in the negative electrode active material layer 31 may be appropriately determined according to the intended battery performance. For example, the content of the negative electrode active material may be 40% by mass or more, 100% by mass or less, or 90% by mass or less, assuming that the entire negative electrode active material layer 31 (total solid content) is 100% by mass. The shape of the negative electrode active material layer 31 is not particularly limited, and may be, for example, a sheet-like negative electrode active material layer having a substantially flat surface.

[0029] 2.4.1 Negative electrode active material The negative electrode active material may be a known negative electrode active material for aqueous batteries having an aqueous electrolyte solution containing potassium ions. The negative electrode active material may include at least one selected from potassium-transition metal composite oxides, titanium oxide, metal sulfides such as Mo6S8, elemental sulfur, KTi2(PO4)3, NASICON-type compounds, WO3, and the like. Alternatively, the negative electrode active material may be a hydrogen storage alloy. Alternatively, the negative electrode active material may be an inorganic compound having a crystal structure belonging to space group I23. The inorganic compound having a crystal structure belonging to space group I23 may include, for example, element A, element M, and O. Here, the element A is at least one of Bi and La, and the element M is at least one of Bi, Mn, Fe, Co, and Ni, and both the element A and the element M may be Bi. The negative electrode active material may be one that de-inserts and inserts ions by intercalation, or one that de-inserts and inserts ions by a conversion reaction, an alloying reaction, or the like. Only one type of negative electrode active material may be used alone, or two or more types may be used in combination. The shape of the negative electrode active material may be any shape that can function as a negative electrode active material of a battery. The negative electrode active material may be, for example, particulate. The negative electrode active material may be primary particles, or secondary particles formed by agglomeration of a plurality of primary particles. The average particle diameter D50 of the negative electrode active material may be, for example, 1 nm or more and 1000 μm or less, the lower limit may be 5 nm or more or 10 nm or more, and the upper limit may be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less.

[0030] 2.4.2 Other ingredients The conductive assistant and the binder that can be contained in the negative electrode active material layer 31 may be appropriately selected from those exemplified as those that can be contained in the positive electrode active material layer 11. The conductive assistant and the binder may each be used alone or in combination of two or more kinds.

[0031] 2.5 Negative electrode current collector As shown in FIG. 1, the negative electrode 30 of the aqueous battery 100 may include a negative electrode current collector 32 in contact with the negative electrode active material layer 31. The negative electrode current collector 32 may be in contact with the aqueous electrolyte 20. Any negative electrode current collector that can function as a negative electrode current collector for an aqueous battery can be used as the negative electrode current collector 32. The negative electrode current collector 32 may be in the form of a foil, a plate, a mesh, a punched metal, a foam, or the like. The negative electrode current collector 32 may be made of a metal foil or a metal mesh. In particular, a metal foil is excellent in terms of ease of handling. The negative electrode current collector 32 may be made of a plurality of foils. Examples of the metal material 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, the negative electrode current collector 32 preferably contains at least one selected from the group consisting of Al, Ti, Pb, Zn, Sn, Mg, Zr, and In, and preferably contains Al. Al, Ti, Pb, Zn, Sn, Mg, Zr, and In all have low work functions, and it is considered that even if the negative electrode current collector 32 contacts the aqueous electrolyte solution 20 at a reduction potential, electrolysis of the aqueous electrolyte solution 20 is unlikely to occur. The negative electrode current collector 32 may be a metal foil or a substrate on which the above metal is plated or vapor-deposited. In addition, when the negative electrode current collector 32 is made of multiple sheets of metal foil, some layer may be present between the multiple sheets of metal foil. 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, and may be 1 mm or less or 100 μm or less.

[0032] 2.6 Other Configurations In addition to the basic configuration described above, the aqueous battery 100 may have other configurations, such as the following. As described above, in the aqueous battery 100, a separator 40 may be present between the positive electrode active material layer 11 and the negative electrode active material layer 31. The separator 40 may be a separator used in conventional aqueous electrolyte batteries (nickel-metal hydride batteries, zinc-air batteries, etc.). For example, the separator 40 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. In addition to the above configuration, the aqueous battery 100 may have terminals, a battery case, etc. Other configurations are obvious to those skilled in the art who have referred to this application, so a description thereof will be omitted here. The aqueous battery 100 may be a secondary battery.

[0033] The aqueous battery 100 of the present disclosure can be manufactured, for example, as follows. (1) The positive electrode active material constituting the positive electrode active material layer 11 is dispersed in a solvent to obtain a positive electrode mixture paste (slurry). The solvent used in this case may be water or various organic solvents. 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 obtaining the positive electrode 10. As the application method, in addition to the doctor blade method, an electrostatic application method, a dip coating method, a spray coating method, or the like may also be adopted. (2) The aqueous electrolyte solution 20 can be produced, for example, by mixing water and an electrolyte. Even if the water and the electrolyte are simply filled into a container and left to stand, they will mix with each other, and the aqueous electrolyte solution 20 will ultimately be obtained. (3) The negative electrode active material constituting the negative electrode active material layer 31 is dispersed in a solvent to obtain a negative electrode mixture paste (slurry). The solvent used in this case may be water or various organic solvents. The negative electrode mixture paste (slurry) is applied to 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 obtaining the negative electrode 30. As the application method, in addition to the doctor blade method, an electrostatic application method, a dip coating method, a spray coating method, or the like may also be used. (4) The positive electrode 10, the aqueous electrolyte 20, and the negative electrode 30 are housed in a battery case to obtain 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, the separator 40, a negative electrode active material layer 31, and a negative electrode current collector 32 in this order. Other members such as terminals are attached to the laminate as necessary. The laminate is housed in a battery case, and the battery case is filled with the aqueous electrolyte 20. The laminate and the electrolyte are sealed in the battery case so that the laminate is immersed in the aqueous electrolyte 20, to obtain the aqueous battery 100. EXAMPLES

[0034] Hereinafter, the technology of the present disclosure will be described in more detail with reference to examples and comparative examples, but the technology of the present disclosure is not limited to these.

[0035] 1. Preparation of Positive Electrode Active Material 1.1 Example K2CO3 (1.92 g), NiO (1.97 g), and TeO2 (2.11 g) were weighed and mixed in an agate mortar to obtain a mixed powder. The obtained mixed powder was spread on an alumina boat. The alumina boat was set in a quartz tubular furnace, and O2 flow was started. The temperature inside the tubular furnace was raised to 800°C at a rate of 200°C / h, and then maintained at 800°C for 24 hours. After being naturally cooled to room temperature, the alumina boat was removed from the tubular furnace and immediately placed in a glove box (GB). The sample on the alumina boat was collected in the GB and crushed in an agate mortar to obtain a positive electrode active material for evaluation. As a result of ICP analysis, the positive electrode active material was found to be K2.00 Ni 2.00 Te 0.98 O 6±δ It was as shown in the figure.

[0036] 1.2 Comparative Example A positive electrode active material was obtained in the same manner as in the example, except that K2CO3 (1.92 g), NiO (0.99 g), CoO (0.99 g), and TeO2 (2.11 g) were weighed and mixed in an agate mortar to obtain a mixed powder. As a result of ICP analysis, the positive electrode active material was found to be K 2.09 Ni 1.02 Co 0.98 Te 1.01 O 6±δ It was as shown in the figure.

[0037] 2. Preparation of Positive Electrode The above positive electrode active material, acetylene black as a conductive additive, and PVdF as a binder were mixed with a solvent in a mass ratio of positive electrode active material:conductive additive:binder=75:20:5 to prepare an ink. The ink obtained was dropped onto a Ti foil surface and then coated with a doctor blade to form a uniform film, thereby obtaining a positive electrode having a Ti foil and a positive electrode active material layer provided on the surface of the Ti foil.

[0038] 3. Preparation of Aqueous Electrolyte An aqueous electrolyte for evaluation was prepared by dissolving 5 mol of K4P2O7 in 1 kg of pure water. The aqueous electrolyte had a pH of 3 to 13, no freezing point above -60°C, no salt precipitation when cooled from 0°C to -60°C, and a viscosity at 20°C of 10 mPa s to 350 mPa s.

[0039] 4. Preparation of Evaluation Cell An evaluation cell (VM4, EC Frontier) was produced using the above positive electrode as a working electrode, a Pt mesh as a counter electrode, Ag / AgCl as a reference electrode, and the above aqueous electrolyte.

[0040] 5. Cell Evaluation The evaluation cell was charged and discharged under the following conditions to obtain a charge-discharge curve. Charge / discharge current value: 0.2mA / cm 2 Cutoff voltage: -1.2~0.95V vs. Ag / AgCl Measurement temperature: 25℃

[0041] 6. Evaluation Results Figure 2 shows the charge / discharge curves of the cell according to the example, and Figure 3 shows the charge / discharge curves of the cell according to the comparative example. As shown in Figures 2 and 3, it can be seen that the positive electrode active material according to the example can be charged and discharged in an aqueous electrolyte solution containing potassium ions, and has a significantly higher charge / discharge capacity than the positive electrode active material according to the comparative example.

[0042] 7. Supplementary Information FIG. 4 shows the relationship between the concentration of an aqueous potassium pyrophosphate solution and ionic conductivity. As shown in FIG. 4, when the concentration of potassium pyrophosphate in the aqueous potassium pyrophosphate solution is more than 0 mol / kg and not more than 8 mol / kg, the aqueous potassium pyrophosphate solution has excellent ionic conductivity. FIG. 5 shows the relationship between the concentration of the aqueous potassium pyrophosphate solution and pH. As shown in FIG. 5, when the concentration of potassium pyrophosphate in the aqueous potassium pyrophosphate solution is more than 0 mol / kg and not more than 8 mol / kg, the pH of the aqueous potassium pyrophosphate solution is 10.0 to 12.0.

[0043] In the above examples, the performance of the active material contained in the positive electrode was simply evaluated using an evaluation cell having a predetermined aqueous electrolyte, a predetermined positive electrode as a working electrode, a Pt mesh as a counter electrode, and Ag / AgCl as a reference electrode. Here, the configuration other than the positive electrode active material is not the essence of the technology of the present disclosure. When actually configuring an aqueous battery, various aqueous electrolytes containing potassium ions and a negative electrode capable of charging and discharging in an aqueous electrolyte containing potassium ions may be used together with a predetermined positive electrode active material. [Explanation of symbols]

[0044] 10: positive electrode, 11: positive electrode 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: separator, 100: aqueous battery

Claims

1. K ２ Ni ２ TeO ６ and Used in aqueous batteries having an aqueous electrolyte solution containing potassium ions, Cathode active material.

2. An aqueous battery, A positive electrode active material layer, an aqueous electrolyte solution, and a negative electrode active material layer are included, The positive electrode active material layer comprises the positive electrode active material according to claim 1 , The aqueous electrolyte contains potassium ions. water-based battery.

3. 3. The aqueous battery of claim 2, The aqueous electrolyte solution contains water and potassium polyphosphate dissolved in the water. water-based battery.

4. 3. The aqueous battery of claim 2, The aqueous electrolyte solution contains water and potassium polyphosphate dissolved in the water at a concentration of 2.0 mol or more per kg of the water. water-based battery.

5. The aqueous battery according to any one of claims 2 to 4, The pH of the aqueous electrolyte is 3 or more and 13 or less. water-based battery.

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