Power storage device

Abstract

To provide a power storage device including an aqueous electrolytic solution containing potassium ions as carrier ions, which is inexpensive and exhibits excellent characteristics.SOLUTION: A power storage device includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and an aqueous electrolytic solution interposed between the positive electrode and the negative electrode and containing potassium ions as carrier ions, and satisfies at least one of the following (1) and (2). (1) The positive electrode has an active material that absorbs and releases potassium ions as a positive electrode active material, and one or more of tungsten, aluminum, stainless steel, and nickel as a positive electrode current collector. (2) The negative electrode has an active material that absorbs and releases potassium ions as a negative electrode active material, and one or more of tin, aluminum, stainless steel, and tungsten as a negative electrode current collector.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an electricity storage device. [Background technology]

[0002] Aqueous potassium ion secondary batteries have been proposed as energy storage devices. Potassium ion secondary batteries are considered a battery system with lower resource risk than lithium ion secondary batteries because potassium, the carrier ion, is abundant in nature. Furthermore, the use of aqueous electrolytes rather than nonaqueous electrolytes allows for the avoidance of manufacturing processes in a dry atmosphere, which is expected to reduce CO2 emissions during the manufacturing process. From this perspective, aqueous potassium ion secondary batteries are an attractive battery system. However, there have been few reports on aqueous potassium ion secondary batteries, and most research has focused on the active materials and electrolytes. While there have been studies investigating active materials and electrolytes, such as using titanium, which has a wide potential window, as a current collector (Non-Patent Document 1) and using electrochemically stable gold as a current collector (Non-Patent Document 2), no research has focused on the current collector. While there are examples of using aluminum as a current collector in non-aqueous potassium ion secondary batteries (Patent Document 1), its combination with an aqueous electrolyte has not been investigated. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7281100 [Non-patent literature]

[0004] [Non-Patent Document 1] Nature Energy | VOL 4 | JUNE 2019 | 495-503 [Non-patent document 2] NATURE COMMUNICATIONS | (2019) 10:4292 Summary of the Invention [Problem to be solved by the invention]

[0005] However, because the titanium used in Non-Patent Document 1 and the gold used in Non-Patent Document 2 are expensive, there is a problem that aqueous potassium ion batteries using these materials are also expensive. Furthermore, although the aluminum used in Patent Document 1 is inexpensive, as mentioned above, no consideration has been given to combining it with an aqueous electrolyte solution.

[0006] The present disclosure has been made to solve these problems, and a primary object of the present disclosure is to provide an electricity storage device that includes an aqueous electrolyte solution containing potassium ions as carrier ions, and that is inexpensive and exhibits good characteristics. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the present inventors have discovered that in an electricity storage device including an aqueous electrolyte solution containing potassium ions as carrier ions, using tungsten, aluminum, stainless steel, or nickel for the positive electrode current collector, and using tin, aluminum, stainless steel, or tungsten for the negative electrode current collector, the device exhibits low cost and good characteristics, and have completed the present disclosure.

[0008] That is, the electricity storage device of the present disclosure is The battery comprises a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and an aqueous electrolyte solution interposed between the positive electrode and the negative electrode and containing potassium ions as carrier ions, and satisfies at least one of the following (1) and (2): (1) The positive electrode has, as the positive electrode active material, an active material that absorbs and releases potassium ions, and has, as the positive electrode current collector, one or more of tungsten, aluminum, stainless steel, and nickel. (2) The negative electrode has, as the negative electrode active material, an active material that absorbs and releases potassium ions, and has, as the negative electrode current collector, one or more of tin, aluminum, stainless steel, and tungsten. [Effects of the Invention]

[0009] The present disclosure provides an inexpensive electricity storage device that includes an aqueous electrolyte solution containing potassium ions as carrier ions and exhibits excellent properties. The reasons for this effect are presumed to be as follows. For example, it is presumed that the metals used for the positive electrode current collector and the negative electrode current collector are less expensive than titanium or gold, making it possible to realize an inexpensive electricity storage device. Furthermore, it is presumed that the metals used for the positive electrode current collector and the negative electrode current collector exhibit high overvoltages for water splitting reactions and wide potential windows, thereby exhibiting excellent properties. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram showing an example of an electricity storage device 10. FIG. [Figure 2] Linear sweep voltammetry (LSV) measurement results (Experimental Examples 1 to 12). [Figure 3] Charging and discharging characteristics evaluation results of Experimental Example 13. DETAILED DESCRIPTION OF THE INVENTION

[0011] The electricity storage device of the present disclosure includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and an aqueous electrolyte solution interposed between the positive electrode and the negative electrode and containing potassium ions as carrier ions. The positive electrode may have a positive electrode active material that occludes and releases potassium ions. The negative electrode may have a negative electrode active material that occludes and releases potassium ions. This electricity storage device may be a potassium ion secondary battery, a potassium secondary battery, or a hybrid capacitor such as a potassium ion capacitor.

[0012] The positive electrode may be formed by, for example, mixing a positive electrode active material, a conductive material, and a binder, adding an appropriate solvent to form a paste-like positive electrode mixture, applying it to the surface of a positive electrode current collector, drying it, and compressing it to increase the electrode density as needed. Examples of the positive electrode active material include compounds containing potassium and transition metal elements (cyanides, sulfates, phosphates, oxides). Examples of cyanides containing potassium and transition metal elements include K2Mn[Fe(CN)6], K2Fe[Fe(CN)6], K2Zn3[Fe(CN)6]2, and K 0.3 Ti 0.75 Fe 0.25 [Fe(CN)6] 0.95 2.8H2O, etc. Examples of sulfates containing potassium and transition metal elements include KFeSO4F, etc. Examples of phosphates containing potassium and transition metal elements include K2FeP2O7, etc. Examples of oxides containing potassium and transition metal elements include K 0.7 Fe 0.5 Mn 0.5 O2 and P3-K 0.5Examples of the conductive material for the positive electrode include graphite, such as natural graphite (scale graphite, flake graphite) and artificial graphite, acetylene black, carbon black, ketjen black, carbon whiskers, needle coke, carbon fiber, and metals (copper, nickel, aluminum, silver, gold, etc.), either singly or in combination. Among these, carbon black and acetylene black are preferred as conductive materials from the viewpoints of electronic conductivity and coating properties. The binder serves to bind the active material particles and the conductive material particles together, and examples thereof include fluorine-containing resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluorine-containing rubber, thermoplastic resins such as polypropylene and polyethylene, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, and natural butyl rubber (NBR), either singly or in combination. In addition, aqueous binders such as cellulose-based carboxymethyl cellulose (CMC), styrene-butadiene copolymer (SBR), and aqueous dispersions of polyvinyl alcohol can also be used. Examples of solvents that can be used to disperse the positive electrode active material, conductive material, and binder include organic solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran. Alternatively, a dispersant, thickener, etc. can be added to water, and the active material can be slurried with a latex such as SBR. Examples of thickeners include polysaccharides such as carboxymethyl cellulose and methyl cellulose, either alone or in combination. Examples of application methods include roller coating (e.g., applicator roll), screen coating, doctor blade coating, spin coating, and bar coating. Any of these methods can be used to achieve the desired thickness and shape.

[0013] The positive electrode current collector is preferably one or more of tungsten (W), aluminum (Al), stainless steel (SUS), and nickel (Ni). From the viewpoint of suppressing side reactions, the positive electrode current collector is preferably one or more of stainless steel and nickel, and from the viewpoint of widening the potential window and reducing costs, it is even more preferably stainless steel. The positive electrode current collector may be surface-treated, such as by oxidation, but is preferably untreated from the viewpoint of reducing costs. The positive electrode current collector preferably has a wide potential window on the oxidation side when evaluated by linear sweep voltammetry in an aqueous electrolyte. The potential window on the oxidation side (vs. Ag|AgCl) is preferably 1 V or more, more preferably 1.2 V or more, and even more preferably 1.3 V or more. The potential window on the oxidation side may be, for example, 2 V or less, 1.8 V or less, or 1.7 V or less. The positive electrode current collector may be in the form of a foil, film, sheet, net, punched or expanded material, lath, porous material, foam, or fiber group, with a foil being preferred. The thickness of the positive electrode current collector is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. The thickness of the positive electrode current collector is preferably 500 μm or less, more preferably 100 μm or less, and even more preferably 30 μm or less.

[0014] The negative electrode may be formed by, for example, adhering a negative electrode active material to a negative electrode current collector. Alternatively, the negative electrode active material, a conductive material, and a binder may be mixed, and an appropriate solvent may be added to form a paste-like negative electrode mixture. This paste is then applied to the surface of the negative electrode current collector, dried, and compressed, as necessary, to increase electrode density. Examples of negative electrode active materials include inorganic compounds such as potassium and potassium alloys, carbonaceous materials capable of absorbing and releasing potassium ions, compounds containing potassium and transition metals (phosphates and oxides), and oxides containing transition metals. Examples of carbonaceous materials include graphite, hard carbon, and soft carbon. Examples of phosphates containing potassium and transition metals include KTi2(PO4)3. Examples of oxides containing potassium and transition metals include K2Ti4O9. Examples of oxides containing transition metals include TiO2. The conductive material, binder, solvent, and the like used in the negative electrode may be the same as those exemplified for the positive electrode.

[0015] The negative electrode current collector has one or more of tin (Sn), aluminum (Al), stainless steel (SUS), and tungsten (W). The negative electrode current collector is preferably aluminum from the viewpoints of suppressing side reactions, widening the potential window, and reducing costs. The negative electrode current collector may be surface-treated, such as by oxidation, but is preferably untreated from the viewpoint of reducing costs. The negative electrode current collector preferably has a wide reduction-side potential window when evaluated by linear sweep voltammetry in an aqueous electrolyte. The reduction-side potential window (vs Ag|AgCl) is preferably, for example, -1 V or less, more preferably -1.1 V or less, and even more preferably -1.2 V or less. The oxidation-side potential window may be, for example, -2 V or more, -1.4 V or more, or -1.3 V or more. The negative electrode current collector may be in the form of a foil, film, sheet, net, punched or expanded material, lath, porous material, foam, or fiber group, with a foil being preferred. The thickness of the negative electrode current collector is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. The thickness of the negative electrode current collector is preferably 500 μm or less, more preferably 100 μm or less, and even more preferably 30 μm or less.

[0016] The aqueous electrolyte may contain a supporting salt and water. Examples of supporting salts include inorganic salts such as potassium nitrate (KNO), potassium sulfate (KSO), potassium acetate (CHCOOK), potassium hydroxide (KOH), potassium chloride (KCl), KPF, KBF, and KClO, as well as organic salts such as KCFSO, KN(CFSO), KN(SOF), and KC(CFSO). These supporting salts may be used alone or in combination. Potassium nitrate and potassium sulfate are preferred as supporting salts, with potassium nitrate being even more preferred, from the standpoints of cost reduction, high solubility in water, suppression of side reactions, and optimization of the potential window. In the aqueous electrolyte, the concentration of the supporting salt may be 0.1 M or more, 0.5 M or more, or 1 M or more, or 20 M or less, 10 M or less, or 3 M or less. The pH of the aqueous electrolyte is preferably 3 or more, more preferably 5 or more, from the viewpoint of optimizing the potential window and suppressing side reactions, and is preferably 11 or less, more preferably 8 or less.

[0017] The power storage device may include a separator between the positive electrode and the negative electrode. The separator is not particularly limited as long as it has a composition that can withstand the range of use of the power storage device, and examples thereof include polymer nonwoven fabrics such as polypropylene nonwoven fabrics and polyphenylene sulfide nonwoven fabrics, and thin microporous films of olefin resins such as polyethylene and polypropylene. These may be used alone or in combination.

[0018] The shape of the electricity storage device of the present disclosure is not particularly limited, and examples thereof include coin-shaped, button-shaped, sheet-shaped, laminated, cylindrical, flat, and rectangular shapes. The device may also be applied to large devices used in electric vehicles and the like. FIG. 1 is a schematic diagram showing an example of an electricity storage device 10 of the present disclosure. The electricity storage device 10 includes a positive electrode sheet 13 having a positive electrode active material 12 formed on a positive electrode current collector 11, a negative electrode sheet 18 having a negative electrode active material 17 formed on the surface of a negative electrode current collector 14, a separator 19 disposed between the positive electrode sheet 13 and the negative electrode sheet 18, and an aqueous electrolyte solution 20 filling the space between the positive electrode sheet 13 and the negative electrode sheet 18. The electricity storage device 10 is formed by sandwiching the separator 19 between the positive electrode sheet 13 and the negative electrode sheet 18, winding them up, and inserting them into a cylindrical case 22. A positive electrode terminal 24 connected to the positive electrode sheet 13 and a negative electrode terminal 26 connected to the negative electrode sheet are disposed therein. The positive electrode current collector 11 is made of one or more of tungsten, aluminum, stainless steel, and nickel, and the negative electrode current collector 14 is made of one or more of tin, aluminum, stainless steel, and tungsten.

[0019] In the above-described embodiment, it is possible to provide an inexpensive electricity storage device that has an aqueous electrolyte solution containing potassium ions as carrier ions and that exhibits good characteristics. The reason for this effect is presumed to be as follows. For example, it is presumed that an inexpensive electricity storage device can be realized because the metals used for the positive electrode current collector and the negative electrode current collector are cheaper than titanium (Ti) and gold (Au). It is also presumed that W, Al, SUS, and Ni used for the positive electrode current collector and Sn, Al, SUS, and W used for the negative electrode current collector have a large overvoltage (wide potential window) for the water splitting reaction and therefore exhibit good characteristics. In particular, when SUS or Ni is used for the positive electrode current collector or Al is used for the negative electrode current collector, it is presumed that better characteristics are exhibited because side reactions resulting from the surface coating of the current collector are small. It should be noted that the overvoltage for the water splitting reaction is determined by the carrier ions in the aqueous solution (K in this disclosure). + ) and H + , O.H. -The adsorption structure formed by ions such as HO and the current collector surface has a significant effect. Because this structure is due to the electronic state of the current collector, the water splitting overvoltage varies significantly depending on the metal species and carrier ion species, but it has been difficult to predict the correlation between these. Furthermore, current collector surface coatings are often presumed to be metal oxides or hydroxides, and the electrochemical behavior of these (side reactions resulting from the current collector surface coating) may lead to the irreversible capacity of an electricity storage device. The electrochemical behavior of the current collector surface coating varies significantly depending on the metal species and carrier ion species, but it has also been difficult to predict the correlation between these. The inventors evaluated the overvoltage for the water splitting reaction and the electrochemical behavior of the current collector surface coating and discovered a current collector that is particularly suitable for electricity storage devices equipped with an aqueous electrolyte containing potassium ions as carrier ions. The present disclosure provides an inexpensive electricity storage device that exhibits excellent characteristics by using such a current collector.

[0020] It goes without saying that the present disclosure is not limited to the above-described embodiments, and can be embodied in various forms as long as they fall within the technical scope of the present disclosure.

[0021] For example, in the above-described embodiment, the positive electrode has a material capable of absorbing and releasing potassium ions as a positive electrode active material, and the positive electrode current collector has one or more of W, Al, SUS, and Ni. The negative electrode has a material capable of absorbing and releasing potassium ions as a negative electrode active material, and the negative electrode current collector has one or more of Sn, Al, SUS, and W. However, one of the positive electrode and the negative electrode does not necessarily have to satisfy these requirements. For example, one of the positive electrode active material and the negative electrode active material may be a carbon material used in capacitors. Examples of carbon materials used in capacitors include activated carbons, cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, carbon fibers, carbon nanotubes, and polyacenes. Even in this case, at least one of the electrodes exhibits a large overvoltage and a wide potential window for the water splitting reaction, thereby exhibiting favorable characteristics.

[0022] The present disclosure may be any of the following [1] to [5]. [1] An electricity storage device comprising: a positive electrode having a positive electrode active material; a negative electrode having a negative electrode active material; and an aqueous electrolyte solution interposed between the positive electrode and the negative electrode and containing potassium ions as carrier ions, the device satisfying at least one of the following (1) and (2): (1) The positive electrode has, as the positive electrode active material, an active material that occludes and releases potassium ions, and the positive electrode current collector has one or more of tungsten, aluminum, stainless steel, and nickel; (2) The negative electrode has, as the negative electrode active material, an active material that occludes and releases potassium ions, and the negative electrode current collector has one or more of tin, aluminum, stainless steel, and tungsten. [2] The electricity storage device according to [1], wherein the positive electrode current collector is made of one or more of stainless steel and nickel. [3] The electricity storage device according to [1] or [2], wherein the negative electrode current collector is made of aluminum. [4] The electricity storage device according to any one of [1] to [3], wherein the aqueous electrolyte solution contains potassium nitrate as a supporting salt. [5] The electricity storage device according to any one of [1] to [4], wherein the aqueous electrolyte solution contains a supporting salt at a concentration of 0.1 M or more and 2 M or less. [Example]

[0023] Hereinafter, examples of current collectors suitable for electricity storage devices equipped with an aqueous electrolyte solution containing potassium ions as carrier ions will be described as examples. Experimental Examples 2 to 5, 7 to 11, and 13 correspond to working examples, Experimental Examples 6 and 12 correspond to comparative examples, and Experimental Examples 1 and 9 correspond to reference examples.

[0024] [Experimental Examples 1-12] A three-electrode cell was fabricated using various metal current collector foils (20 μm thick) of Ti, W, Al, SUS (SUS304), Ni, and Sn as the working electrode, a platinum wire as the counter electrode, a silver-silver chloride electrode as the reference electrode, and a 2 M KNO3 nitric acid solution as the electrolyte. The potential window was evaluated by linear sweep voltammetry (LSV). The potential was scanned from the oxidation side to the reduction side at a sweep rate of 2 mV / sec, and the current density of the working electrode was 0.5 mA / cm. 2The electrode potentials at which the potential window reached were defined as the potential windows on the oxidation and reduction sides, respectively.

[0025] Figure 2 shows the LSV measurement results for various current collecting foils. Note that Figure 2B shows the results for the current density I of Figure 2A when it is -0.1 mA / cm. 2 to 0.1mA / cm 2 When the overpotential on both the oxidation and reduction sides is increased, the current rises sharply, reaching 0.5 mA / cm 2 It was inferred that oxygen generation occurred on the oxidation side and hydrogen generation occurred on the reduction side. Because battery degradation progresses rapidly in the potential region where these reactions occur, a current collecting foil with a wide potential window is preferable. The following study was conducted from this perspective. In the LSV measurement results, Experimental Examples 1 to 6 were selected in order of the widest potential window on the oxidation side, and Experimental Examples 7 to 12 were selected in order of the widest potential window on the reduction side.

[0026] The oxidation potential window is shown in Table 1. For Ti, W, and Al, the potential is 0.5 mA / cm even at a potential of 1.8 V vs Ag|AgCl. 2 The potential window did not reach 1.8 V and was higher than 1.8 V. Although Ti exhibits a wide oxidation-side potential window, it is expensive, and Sn has a too low oxidation-side potential window, making them unsuitable for use as a positive current collector foil. Taking into consideration the cost and potential window, it was found that W, Al, SUS, and Ni are suitable as positive current collector foils. Looking at the behavior at the potential before oxygen generation occurs, Al and W exhibit a potential of 0.5 mA / cm 2 Although the current did not reach the threshold, an oxidation current was observed. Although the details of this reaction are unclear, it is presumed to be due to the formation of an oxide on the metal foil surface. Although this reaction does not cause rapid deterioration of the battery, it is presumed to be a factor that reduces battery performance, such as the generation of irreversible capacity. Considering this point, it is presumed that SUS or Ni would be more suitable as a positive electrode current collector foil.

[0027] Table 2 shows the reduction potential window. Ti is expensive, and Ni has a narrow reduction potential window, making them unsuitable for use as a negative electrode current collector foil. W and SUS have reduction potential windows equivalent to Ti, while Al and Sn have wider reduction potential windows than Ti. This indicates that W, SUS, Al, and Sn are suitable for use as a negative electrode current collector foil. When examining the behavior before hydrogen generation, a reduction current was observed for all foils except Al. The cause of this is unclear, but it is presumed to be due to the reduction of an oxide film formed on the surface of the metal foil. Since no such side reaction occurred with Al, and taking into account the reduction in irreversible capacity of the battery, Al is presumed to be even more suitable for use as a negative electrode current collector foil.

[0028] From the above, we found that by using W, Al, SUS, or Ni for the positive electrode current collector and Sn, Al, SUS, or W for the negative electrode current collector, it is possible to provide an inexpensive electricity storage device with an aqueous electrolyte containing potassium ions as carrier ions, which exhibits good performance. In addition, in electricity storage devices using nonaqueous electrolytes, depending on the charge / discharge potential of the active material, the carrier ions may react (e.g., form an alloy) with the current collector foil, and therefore the current collector must be selected while taking into consideration its combination with the active material. In contrast, in electricity storage devices using aqueous electrolytes, reactions between the carrier ions and the current collector foil are unlikely to occur within the potential range used, and therefore it is possible to select an appropriate current collector simply by considering the water splitting reaction, without considering the combination with the active material.

[0029] [Table 1]

[0030] [Table 2]

[0031] [Experimental Example 13] K2Mn[Fe(CN)6] was synthesized as a positive electrode active material by a liquid-phase method. The first solution was prepared by dissolving 3 mmol of K4Fe(CN)6 in 120 ml of saturated KCl aqueous solution with argon bubbling, and the second solution was prepared by dissolving 6 mmol of MnCl2 in 60 ml of saturated KCl aqueous solution with argon bubbling. The second solution was added dropwise to the first solution and stirred for 3 hours. The product was collected by centrifugation, washed with pure water, and dried to obtain K2Mn[Fe(CN)6] powder. A paste-like positive electrode composite was prepared by dispersing 80 parts by weight of K2Mn[Fe(CN)6], 10 parts by weight of carbon black, and 10 parts by weight of polyvinylidene fluoride (PVdF) in N-methyl-2-pyrrolidone (NMP). The resulting positive electrode composite was applied to SUS304 foil, dried, and pressed to prepare a K2Mn[Fe(CN)6] composite electrode. A three-electrode cell was prepared using a K2Mn[Fe(CN)6] composite electrode as the working electrode, SUS304 foil as the counter electrode, an Ag|AgCl electrode as the reference electrode, and a 2 M KNO3 aqueous solution as the electrolyte.

[0032] The electrochemical characteristics were evaluated using this three-electrode cell. Specifically, cyclic voltammetry measurements were performed at 25°C and 2 mV / sec to evaluate the charge / discharge characteristics. Figure 3 shows the results of the charge / discharge characteristics evaluation for Experimental Example 13. As shown in Figure 3, an oxidation-reduction current was observed, indicating a charge / discharge reaction. This indicates that using SUS for the positive electrode current collector can provide a product that exhibits good characteristics at low cost. Note that, although SUS was used as the positive electrode current collector in Experimental Example 13, it is presumed that products that exhibit good characteristics at low cost can also be provided when W, Al, or Ni is used as the positive electrode current collector, or when Sn, Al, SUS, or W is used as the negative electrode current collector. [Industrial Applicability]

[0033] The present disclosure is applicable to the technical field of electricity storage devices. [Explanation of symbols]

[0034] 10 Energy storage device, 11 Positive electrode current collector, 12 Positive electrode active material, 13 Positive electrode sheet, 14 Negative electrode current collector, 17 Negative electrode active material, 18 Negative electrode sheet, 19 Separator, 20 Aqueous electrolyte, 22 Cylindrical case, 24 Positive electrode terminal, 26 Negative electrode terminal.

Claims

1. An electricity storage device comprising: a positive electrode having a positive electrode active material; a negative electrode having a negative electrode active material; and an aqueous electrolyte solution interposed between the positive electrode and the negative electrode and containing potassium ions as carrier ions, wherein the electricity storage device satisfies at least one of the following (1) and (2): (1) The positive electrode has, as the positive electrode active material, an active material that absorbs and releases potassium ions, and has, as the positive electrode current collector, one or more of tungsten, aluminum, stainless steel, and nickel. (2) The negative electrode has, as the negative electrode active material, an active material that absorbs and releases potassium ions, and has, as the negative electrode current collector, one or more of tin, aluminum, stainless steel, and tungsten.

2. The electricity storage device according to claim 1 , wherein the positive electrode current collector is made of one or more of stainless steel and nickel.

3. The electricity storage device according to claim 1 , wherein the negative electrode current collector is made of aluminum.

4. 4. The electricity storage device according to claim 1, wherein the aqueous electrolyte contains potassium nitrate as a supporting salt.

5. 4. The electricity storage device according to claim 1, wherein the aqueous electrolyte solution contains a supporting salt at a concentration of 0.1 M or more and 2 M or less.

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