JP7472612B2 - Energy Storage Devices - Google Patents

Description

This disclosure relates to an electricity storage device.

Conventionally, proposed energy storage devices have an active material that includes a silicon compound and a nitrogen-containing compound, with the basic skeleton being a structure in which multiple six-membered rings made of silicon atoms are linked together, and this active material is charged and discharged by absorbing and releasing anions (see Patent Documents 1 to 3). In addition, proposed energy storage devices have an active material that includes a repeating structure in which an organic compound such as 4,4'-bipyridine is coordinated to a metal ion, and the repeating structure is charged and discharged by absorbing and releasing anions (see Patent Document 4). In addition, proposed energy storage devices use an alkali metal organic structure that includes a structure in which a substituent is introduced into each of the two nitrogens of 4,4'-bipyridine (see, for example, Patent Document 5).

JP 2012-221885 A JP 2012-221886 A JP 2012-22924 A JP 2016-154086 A JP 2019-99543 A

However, although Patent Documents 1 to 5 provide electricity storage devices that can be charged and discharged by absorbing and releasing anions, it has been desired to provide a new electricity storage device that can be charged and discharged by absorbing and releasing anions. Patent Documents 4 and 5 disclose metal organic structures having a 4,4'-bipyridine skeleton, but the discharge capacity is sometimes small.

This disclosure has been made to solve these problems, and its main objective is to provide a new electricity storage device.

In order to achieve the above-mentioned object, the inventors have conducted extensive research and discovered that a metal-organic framework having an organic framework layer containing 4,4'-bipyridinium and a dicarboxylate anion and a transition metal element layer has various properties and is chemically and structurally stable. In addition, the inventors discovered that an electricity storage device having a negative electrode containing such a metal-organic framework, a positive electrode containing a positive electrode active material capable of donating and receiving anions, and an ion-conducting medium capable of conducting anions has a large discharge capacity, which led to the completion of the present disclosure.

That is, the electricity storage device of the present disclosure is
a three-dimensional structure including an organic framework layer including a heterocyclic compound having 4,4'-bipyridinium and a dicarboxylate anion, and a transition metal element layer in which a transition metal element is coordinated to the carboxylate anion to form a framework, and an anion that forms a pair with the three-dimensional structure; and a negative electrode including a metal organic framework including:
a positive electrode including a positive electrode active material capable of donating and receiving the anion;
an ion-conductive medium interposed between the positive electrode and the negative electrode and capable of conducting the anions;
It is equipped with the following:

This disclosure can provide a novel electricity storage device. This electricity storage device has a higher discharge capacity than, for example, a device in which the organic compound coordinated to the metal ion is 4,4'-bipyridine without a dicarboxylate anion. This is presumably because 4,4'-bipyridinium with a dicarboxylate anion has higher redox activity. This electricity storage device also has a higher discharge capacity than, for example, a device in which lithium ions are coordinated to an organic compound. This is presumably because an organic compound coordinated to a transition metal has a more stable structure and higher redox activity.

FIG. 1 is a schematic diagram showing an example of a structure of a metal-organic framework. FIG. 2 is a schematic diagram showing an example of an oxidation-reduction state of a metal-organic framework. FIG. 2 is a cross-sectional view illustrating a schematic configuration of an electricity storage device 20. FIG. 1 is a schematic diagram showing an example of the operating principle of an electricity storage device. 1 shows the results of thermogravimetric analysis (TG) for Experimental Example 1. XRD profiles of samples of Experimental Examples 1 and 2. IR spectra of samples from Experimental Examples 1 to 3. UV spectra of samples from Experimental Examples 1 to 3. FIG. 1 is a relationship diagram of the direct transition band gap of the samples of Experimental Examples 1 to 3. FIG. 1 is a graph showing the relationship between the indirect transition band gaps of the samples of Experimental Examples 1 to 3. 4 is a charge/discharge curve during single-electrode charge/discharge of an electrode using the sample of Experimental Example 2. Charging and discharging curves of the electricity storage device of Experimental Example 4. Charging and discharging curves of the electricity storage device of Experimental Example 5.

The power storage device of the present disclosure includes a negative electrode including a metal organic framework as a negative electrode active material, the metal organic framework including a three-dimensional structure including an organic framework layer and a transition metal element layer, and an anion paired with the three-dimensional structure; a positive electrode including a positive electrode active material capable of donating and receiving the above-mentioned anion; and an ion conductive medium interposed between the negative electrode and the positive electrode and capable of conducting at least the above-mentioned anion. Being capable of donating and receiving anion means that one or both of the following conditions are satisfied: the anion can be absorbed and released inside, or the anion can be adsorbed and desorbed on the surface. In this power storage device, the metal organic framework included in the negative electrode is provided with an anion that serves as a carrier ion in advance, and during charging, the anion is released or desorbed from the negative electrode and the anion is absorbed or adsorbed to the positive electrode, and during discharging, the anion is released or desorbed from the positive electrode and the anion is absorbed or adsorbed to the negative electrode.

In the power storage device of the present disclosure, the negative electrode contains a metal organic framework as a negative electrode active material. The metal organic framework has a three-dimensional structure having an organic framework layer and a transition metal element layer, and an anion that pairs with the three-dimensional structure. Whether or not the metal organic framework is a three-dimensional structure can be determined, for example, by the peak shape that appears in the XRD profile.

The organic skeleton layer includes a heterocyclic compound having 4,4'-bipyridinium and a dicarboxylate anion. The organic skeleton layer may include a heterocyclic compound having carboxylic acids directly or indirectly bonded to both ends of a basic skeleton including 4,4'-bipyridinium. In the organic skeleton layer, the basic skeleton including 4,4'-bipyridinium may include one or more 4,4'-bipyridiniums, but preferably includes one 4,4'-bipyridinium. In the heterocyclic compound, the carboxylate anion is preferably indirectly bonded to the basic skeleton including 4,4'-bipyridinium via an alkylene chain or aromatic hydrocarbon chain that may have a branch. The alkylene chain preferably has a main chain with 1 to 3 carbon atoms, and more preferably a methylene group. In the branched alkylene chain, the branch may be at least one of a methyl group and an ethyl group. The alkylene chain may have a carbon number of 1 to 3, regardless of whether it has a branch or not. The aromatic hydrocarbon chain is preferably composed of 1 to 3 phenylene groups.

The transition metal element layer is a portion where a transition metal element is coordinated to the carboxylate anion of the organic framework layer to form a framework. This transition metal element layer preferably contains, for example, one or more of Cu, Fe, Co, Ni, and Mn, of which Cu is preferred. In addition, the transition metal contained in this transition metal element layer is preferably a divalent transition metal.

The anion paired with the three-dimensional structure may be, for example, a monovalent or divalent or higher anion, but may be a monovalent anion. The anion may be, for example, tetrafluoroborate (BF ₄ ^- ), hexafluorophosphate (PF ₆ ^- ), hexafluorosilicate (SiF ₆ ^2- ), hexafluoroantimonate (SbF ₆ ^- ), perchlorate (ClO ₄ ^- ), tetracyanoborate (B(CN) ₄ ^- ), tris(pentafluoroethyl)trifluorophosphate ([(C ₂ F ₅ ) ₃ PF ₃ ] ^- ), dicyanamide ([(CN) ₂ N] ^- ), trifluoromethanesulfonate (CF ₃ SO ₃ ^- ), trifluoroacetate (CF ₃ CO ₂ ^- ), bis(fluorosulfonyl)imide (N(FSO ₂ ) ₂ ^- ), bis(trifluoromethanesulfonyl)imide (N(CF ₃ SO ₂ ) ₂ ^{- ).} ), bis(pentafluoroethanesulfonyl)imide (N(C ₂ F ₅ SO ₂ ) ₂ ^- ). The anion may be BF ₄ ^- , PF ₆ ^- , SiF ₆ ^2- , SbF ₆ ^- , ClO ₄ ^- , CF ₃ SO ₃ , or the like. Such anions have a larger ionic radius than halogen anions such as F ^- , Cl ^- , Br ^- , and I ^- , and have a relatively small interaction with heterocyclic compounds and other anions, so it is believed that the stability of the metal organic framework can be further improved. In addition, since the ionic radius is not too large, it is believed that the anion can exist in a good state in the gaps in the structure of the heterocyclic compound. Among these, the anion may be BF ₄ ^- , PF ₆ ^- , CF ₃ SO ₃ ^- , or the like. For example, if the anion is BF ₄ ^- , it is preferable because the molecular weight is small and the ionic conductivity is high, so that the theoretical capacity per unit weight of the electrode active material can be increased. Also, PF ₆ ^- and CF ₃ SO ₃ ^- have a larger molecular weight than BF ₄ ^- and thus reduce the theoretical capacity per unit weight of active material, but have high ionic conductivity and are believed to be able to improve low-temperature characteristics.

The metal organic framework may be, for example, represented by formula (1). In formula (1), ^A- is an anion, M is a transition metal, R is an alkylene chain or an aromatic hydrocarbon chain which may have a branch, and m is 0 or 1. The metal organic framework may be represented by formula (2) or formula (3).

The metal organic framework may be a three-dimensional structure including an organic framework layer in which at least two carboxylate anions are directly or indirectly bonded to a basic framework of 4,4'-bipyridinium, and a transition metal element layer in which a transition metal is bonded to oxygen contained in the carboxylate anion. In such a three-dimensional structure, a space is generated in the organic framework layer to which the transition metal element is bonded, and an anion is considered to exist in this space. This metal organic framework may be a layered structure, or may be formed in a layered form by π-electron interaction of a heterocyclic compound. This metal organic framework may have a structure in which a transition metal is bonded to oxygen of a carboxylate anion possessed by two or four metal organic frameworks. FIG. 1 shows an example of a structure of a metal organic framework including a three-dimensional structure of a heterocyclic compound and an anion. In the metal organic framework of FIG. 1, the anion is ^A- , and the transition metal is ^M2+ . In addition, the metal organic framework is configured such that a carboxylate anion is bonded to nitrogens at both ends of the basic framework of 4,4'-bipyridinium via methylene groups having no substituents.

The metal organic structure may have a peak top with maximum intensity in the range of 5°≦2θ≦30° in an XRD profile using CuKα radiation. This metal organic structure belongs to a specified space group and has a peak that is not broad like an amorphous structure. This metal organic structure may have a peak with maximum intensity in the range of 2θ=5 to 30° and other peaks in an XRD profile.

The metal organic structure may have a band gap calculated from a UV spectrum in the range of 0.5 eV to 3.0 eV. The metal organic structure may not exhibit insulating properties and may have semiconducting properties. The metal organic structure may have a direct transition band gap in the range of 1.0 eV to 3.0 eV, 2.0 eV or less, or 1.5 eV or less. The metal organic structure may have an indirect transition band gap in the range of 0.5 eV to 2.5 eV, 1.0 eV or less, or 0.75 eV or less.

The metal organic framework is capable of donating and receiving anions, which are carrier ions. It is believed that this metal organic framework releases anions from the structure of the metal organic framework during charging and is reduced, and that this anion is absorbed and released within the structure of the metal organic framework during discharging. At this time, in the metal organic framework, a space is generated in the organic framework layer bonded to the transition metal element, and it is believed that anions are absorbed and released in this space. FIG. 2 shows a schematic diagram of an example of the state of oxidation and reduction of the metal organic framework during charging and discharging. FIG. 2 shows an example of a metal organic framework in which the transition metal M is Cu and the anion is BF ₄ ^- . As shown in FIG. 2, it is believed that with the release of BF ₄ ^- , in the viologen framework of 4,4'-bipyridinium, the charge of oxidation and reduction is compensated, and the carboxylate Cu contributes to the formation of the framework.

The metal-organic framework may be manufactured by the following manufacturing method. This manufacturing method includes a precursor manufacturing step and a structure manufacturing step. The manufacturing method may also include a heating step after the structure manufacturing step.

In the precursor preparation process, a solution in which a heterocyclic compound in which a dicarboxylic acid is connected to 4,4'-bipyridinium and an alkali metal compound are dissolved is dried to obtain a powder. The heterocyclic compound may be one in which a carboxylic acid is directly or indirectly bonded to both ends of a basic skeleton containing 4,4'-bipyridinium. Examples of the alkali metal compound include one or more hydroxides, chlorides, sulfates, and nitrates of lithium, sodium, potassium, etc. Among these, it is preferable to use lithium hydroxide. The heterocyclic compound and the alkali metal compound may be appropriately selected according to the target metal organic framework. The basic skeleton of the heterocyclic compound may be the same as the basic skeleton in the above-mentioned metal organic framework. The bond between the carboxylic acid and the basic skeleton may be the same as the bond between the carboxylate anion and the basic skeleton in the above-mentioned metal organic framework. The anion may be the same as the anion in the above-mentioned metal organic framework.

In this step, a solution may be prepared, or a solution that has already been prepared may be prepared. The solvent of the solution is not particularly limited, and may be an aqueous solvent or an organic solvent, but is preferably water. In this step, it is preferable to use a solution in which the molar ratio B/A, which is the ratio of the molar number B (mol) of the alkali metal cation of the alkali metal compound to the molar number A (mol) of the heterocyclic compound, is 2.0 or more and 2.5 or less. In this range, a crystalline metal-organic framework can be obtained more reliably. In this step, it is preferable to prepare a solution in which the concentration of the heterocyclic compound is 0.1 mol/L or more, more preferably 0.2 mol/L or more. In this step, it is preferable to prepare a prepared solution in which the concentration of the heterocyclic compound is 5 mol/L or less. In such a concentration range, the processing in the next step is easier to perform.

In the structure preparation step, a preparation solution is prepared by dissolving the precursor powder obtained in the precursor preparation step, transition metal element ions, and anions, and then a metal organic framework is obtained. The metal organic framework comprises a three-dimensional structure including an organic framework layer containing a heterocyclic compound having 4,4'-bipyridinium and a dicarboxylate anion, a transition metal element layer in which a transition metal element is coordinated to a carboxylate anion to form a framework, and an anion paired with the three-dimensional structure. The transition metal element ion and the anion are preferably salts of these. Examples of the transition metal element include one or more of Cu, Fe, Co, Ni, and Mn, and among these, Cu is preferred. Examples of the anion include one or more of _BF4- ^, _PF6- , ^SiF62- , _SbF6- ^, _ClO4- ^, B(CN) _{4- ,} [( _{C2F5 ) 3PF3} ] ^- , [(CN) _2N ] ^{- ,} _CF3SO3- ^{, CF3CO2- ,} _N ( _FSO2 ) _2- ^, N( _CF3SO2 ) _2- , and N( _C2F5SO2 ) _2- ^, among which _BF4- ^is preferred. Examples of the salts include Cu( _BF4 ) ² . _The solvent of the preparation solution _{is not} particularly limited, _and may be an _aqueous solvent or an organic solvent _, but is preferably _water . In this step, it is preferable to use a solution in which the molar ratio Y/X, which is the ratio of the number of moles Y (mol) of the transition metal element ion to the number of moles X (mol) of the heterocyclic compound, is 2.0 or more and 2.5 or less. In this range, a crystalline metal-organic framework can be obtained more reliably. In this step, it is preferable that the concentration of the heterocyclic compound is 0.1 mol/L or more, more preferably 0.2 mol/L or more. In this step, it is preferable to prepare a preparation solution in which the concentration of the heterocyclic compound is 5 mol/L or less. In such a concentration range, the metal-organic framework can be more easily precipitated.

In this step, it is preferable to generate the metal-organic framework by adding alcohol to the preparation solution in which water is used as a solvent. This method can further suppress the effects on the framework caused by heating and drying. Examples of alcohol include methanol, ethanol, propanol, and butanol, and among these, ethanol is preferred.

In the heating step, the metal organic framework obtained in the structure preparation step may be heated at a temperature range of 40°C to 150°C. The heating temperature is preferably 40°C or higher, more preferably 60°C or higher, and may be 70°C or higher. When the heating temperature is 40°C or higher, the obtained metal organic framework can be sufficiently dried. This heating temperature is preferably 150°C or lower, more preferably 120°C or lower, more preferably 100°C or lower, and may be 80°C or lower. When the heating temperature is 150°C or lower, the structure of the metal organic framework is less adversely affected, which is preferable. In addition, this heating step may be performed under normal pressure or under vacuum. When the heating treatment is performed under normal pressure, the burden on the structure is less, which is preferable. In addition, when the heating treatment is performed under vacuum, the treatment time can be further shortened, which is preferable. In this step, the heating time for the heat treatment may be an appropriate time for removing water and the like from the metal organic framework, and for example, a range of 1 hour to 24 hours or less is preferable, and a range of 3 hours to 12 hours or less is more preferable. In this way, a metal-organic framework having a three-dimensional structure and anions can be produced.

The negative electrode may be formed, for example, by mixing a metal organic framework, which is a negative electrode active material, with a conductive material and a binder as necessary, adding an appropriate solvent to form a paste-like electrode mixture, applying it to the surface of a current collector, drying it, and compressing it to increase the electrode density as necessary. The conductive material is not particularly limited as long as it is an electronically conductive material that does not adversely affect the electrode performance, and for example, a mixture of one or more of graphite such as natural graphite (scale graphite, scale graphite) or artificial graphite, acetylene black, carbon black, ketjen black, carbon whisker, needle coke, carbon fiber, and metals (copper, nickel, aluminum, silver, gold, etc.) can be used. Among these, carbon black and acetylene black are preferred as conductive materials from the viewpoint of electronic conductivity and coatability. The binder plays a role of binding the active material particles and the conductive material particles, and can be, for example, fluorine-containing resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine rubber, or thermoplastic resins such as polypropylene and polyethylene, ethylene-propylene-diene mer (EPDM), sulfonated EPDM, natural butyl rubber (NBR), etc., used alone or as a mixture of two or more kinds. As a solvent for dispersing the active material, conductive material, and binder, for example, organic solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran can be used. In addition, a dispersant, a thickener, etc. can be added to water, and the active material can be slurried with latex such as SBR. As a thickener, for example, polysaccharides such as carboxymethylcellulose and methylcellulose can be used alone or as a mixture of two or more kinds. Examples of application methods include roller coating such as applicator rolls, screen coating, doctor blade method, spin coating, bar coater, etc., and any of these can be used to obtain any thickness and shape. The current collector of this electrode can be made of copper, nickel, stainless steel, titanium, aluminum, baked carbon, conductive polymers, conductive glass, Al-Cd alloys, etc., or, for example, copper whose surface has been treated with carbon, nickel, titanium, silver, etc. for the purpose of improving adhesion, conductivity, and reduction resistance. The surfaces of these can also be oxidized. The shape of the current collector can be foil, film, sheet, net, punched or expanded, lath, porous, foamed, fiber group formed, etc. The thickness of the current collector is, for example, 1 to 500 μm.

In the power storage device of the present disclosure, the positive electrode includes a positive electrode active material capable of receiving and transferring anions, which are carrier ions. In other words, the positive electrode includes a positive electrode active material capable of being charge compensated by anions, which are carrier ions. The positive electrode active material is not particularly limited as long as it is capable of receiving and transferring anions, and examples thereof include carbon materials, anion exchange conductive polymers, metal oxides, and the like. Examples of carbon materials include activated carbon, graphite, carbon black, and the like. The carbon material may be, for example, a material mainly composed of activated carbon, or a material mainly composed of graphite. Here, "mainly composed of activated carbon" means that the material contains 50% by mass or more, preferably 90% by mass or more, and more preferably 95% by mass or more of activated carbon. The same applies to the case of graphite. As the activated carbon, for example, a material made from phenol resin, coal, charcoal, coconut shell, or the like can be used. The activated carbon preferably has a specific surface area of 1000 m ² /g or more, and more preferably 1500 m ² /g or more. When the specific surface area is 1000 m ² /g or more, the discharge capacity can be further increased. The specific surface area of the activated carbon is preferably 3000 m ² /g or less, more preferably 2000 m ² /g or less, from the viewpoint of ease of preparation. Examples of graphite include natural graphite (scale graphite, flake graphite) and artificial graphite, and artificial graphite is preferable in that it can further increase the potential of the power storage device and increase the energy density. Furthermore, it is preferable to use artificial graphite activated with alkali, since the gap between the graphite layers is widened, making it easier for ions to enter and exit, and improving the output characteristics. Specifically, alkali activation can be performed by adding an alkali such as Na or K to graphite and treating it at a high temperature of 600°C to 1000°C in an inert atmosphere. Examples of anion-exchange conductive polymers include viologen polymers. If activated carbon, graphite, or anion-exchange conductive polymer is used as the positive electrode active material, it is preferable because it is easy to reversibly give and receive anions.

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 material, applying it to the surface of a current collector, drying it, and compressing it to increase the electrode density as necessary. The conductive material, binder, solvent, etc. used in the positive electrode may be the same as those exemplified for the electrode for the electric storage device. As the current collector for the positive electrode, in addition to aluminum, titanium, stainless steel, nickel, iron, baked carbon, conductive polymer, conductive glass, etc., aluminum or copper whose surface is treated with carbon, nickel, titanium, silver, etc. for the purpose of improving adhesion, conductivity, and oxidation resistance may be used. The surface of these may also be subjected to an oxidation treatment. The shape of the current collector may be the same as that of the electrode for the electric storage device.

In this electricity storage device, the ionically conductive medium may be any medium capable of conducting anions, which are carrier ions, and may be a non-aqueous electrolyte solution containing a supporting salt or a non-aqueous gel electrolyte solution. This ionically conductive medium may contain an ionic liquid or an organic solvent such as a carbonate-based solvent. If the medium contains a carbonate-based organic solvent, freezing at low temperatures can be prevented, and low-temperature characteristics such as output characteristics at low temperatures can be improved. Furthermore, the addition of a carbonate-based organic solvent can reduce the viscosity and improve the output characteristics. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate, and chloroethylene carbonate; chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl-n-butyl carbonate, methyl-t-butyl carbonate, di-i-propyl carbonate, and t-butyl-i-propyl carbonate; cyclic esters such as γ-butyl lactone and γ-valerolactone; chain esters such as methyl formate, methyl acetate, ethyl acetate, and methyl butyrate; ethers such as dimethoxyethane, ethoxymethoxyethane, and diethoxyethane; nitriles such as acetonitrile and benzonitrile; furans such as tetrahydrofuran and methyltetrahydrofuran; sulfolanes such as sulfolane and tetramethylsulfolane; and dioxolanes such as 1,3-dioxolane and methyldioxolane. Of these, a combination of cyclic carbonates and chain carbonates is preferred.

Ionic liquids are salts of cations and anions that are molten at room temperature. Examples of the cations include imidazolium, ammonium, choline, pyridinium, and piperidinium. Examples of the imidazolium include 1-(hydroxyethyl)-3-methylimidazolium and 1-methyl-3-octylimidazolium. Examples of the ammonium include N,N-dimethylammonium and tetrabutylammonium. Examples of the pyridinium include 1-butyl-3-methylpyridinium and 1-butylpyridinium. Examples of the piperidinium include 1-ethyl-1-methylpiperidinium. Examples of the anion include one or more of BF ₄ ^- , PF ₆ ^- , ClO ₄ ^- , CF ₃ SO ₃ ^- , TFSI ^- , BETI ^- , Br ^- , Cl ^- , and F ^- . Specific examples of the anion that is BF ₄ ^- include diethylmethyl(2-methoxyethyl)ammonium.BF ₄ . Specific examples of the anion TFSI include N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP13TFSI), 1-ethyl-3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide (EMITFSI), N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPATFSI), and N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide. Among these, diethylmethyl(2-methoxyethyl) _ammonium.BF4 is preferred. When the ionic liquid is mixed with an organic solvent, the concentration of the ionic liquid is preferably 0.5M or more and 2.0M or less.

The supporting salt may have, for example, an alkali metal cation or a nonmetallic cation. The alkali metal cation may be, for example, Li ⁺ , Na ⁺ , or K ⁺ . The nonmetallic cation may be a quaternary ammonium cation, specifically, a chain-like saturated compound such as a tetraethylammonium cation (Et ₄ N ⁺ ), a triethyl-methylammonium cation, a tetrabutylammonium cation, a diethyl-methyl-(2-methoxyethyl)ammonium cation, or a trimethyl-propylammonium cation. The quaternary ammonium cation may be a chain-like unsaturated compound such as an iminium cation or a diazonium cation, a cyclic unsaturated compound such as an imidazolium cation or a pyridinium cation, or a cyclic saturated compound such as a pyrrolidinium cation or a piperidinium cation. The cyclic quaternary ammonium cation may be a monocyclic or polycyclic type, and in the case of a polycyclic type, it may be a condensed polycyclic type or a spiro type such as a spiro-(1,1')-bipyrrolidinium cation. The quaternary ammonium cation may have, for example, a molecular weight of 18 to 500. The supporting salt preferably has an alkali metal cation, more preferably Li ⁺ . The mobility of the alkali metal cation (particularly Li ⁺ ) is reduced by solvation compared to that of the anion, resulting in high anion mobility, which is suitable for an anion migration type electricity storage device. In the supporting salt, the anion paired with the cation may be, for example, BF ₄ ^- , PF ₆ ^- , SiF ₆ ^2- , SbF ₆ ^- , ClO ₄ ^- , B(CN) ₄ ^- , [(C ₂ F ₅ ) ₃ PF ₃ ] ^- , [(CN) ₂ N] ^- , CF ₃ SO ₃ ^- , CF ₃ CO ₂ ^- , N(FSO ₂ ) ₂ ^- , N(CF ₃ SO ₂ ) ₂ ^- , or N(C ₂ F ₅ SO ₂ ) ₂ ^- . The supporting salt may be, for example, LiBF ₄ or Et ₄ NBF ₄ . The concentration of this supporting salt in the non-aqueous electrolyte is preferably 0.1 mol/L or more and 5 mol/L or less, more preferably 0.5 mol/L or more and 2 mol/L or less. When the concentration of the supporting salt is 0.1 mol/L or more, a sufficient current density can be obtained, and when the concentration is 5 mol/L or less, the electrolyte can be more stabilized. The anions contained in the supporting salt and the ionic liquid are preferably the same as the anions contained in the metal organic framework. A phosphorus-based, halogen-based, or other flame retardant may be added to the nonaqueous electrolyte.

The power storage device of the present disclosure 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 of the separator include glass filters made of glass fibers, polymer nonwoven fabrics such as polypropylene nonwoven fabrics and polyphenylene sulfide nonwoven fabrics, and thin microporous membranes of olefin resins such as polyethylene and polypropylene. Of these, glass filters have good wettability with electrolytes such as BF4-based ionic liquids, and can facilitate the movement of anions. These may be used alone or in combination.

The shape of the electricity storage device of the present disclosure is not particularly limited, and examples thereof include coin type, button type, sheet type, laminated type, cylindrical type, flat type, and square type. In addition, it may be applied to large ones used in electric vehicles and the like. An example of this electricity storage device is shown in FIG. 3. FIG. 3 is a cross-sectional view showing an outline of the configuration of the electricity storage device 20. This electricity storage device 20 includes a cup-shaped battery case 21, a positive electrode 22 provided inside the battery case 21, a negative electrode 23 provided at a position opposite to the positive electrode 22 via a separator 24, a nonaqueous electrolyte 27 containing a supporting salt, a gasket 25 formed of an insulating material, and a sealing plate 26 disposed at the opening of the battery case 21 and sealing the battery case 21 via the gasket 25. The negative electrode 23 includes the above-mentioned metal organic structure, and the positive electrode 22 includes a positive electrode active material capable of receiving and transferring anions, which are carrier ions. The non-aqueous electrolyte 27 is capable of conducting anions, which are carrier ions, and contains, for example, a supporting salt having an alkali metal cation or a supporting salt having a non-metal cation.

Figure 4 shows a schematic diagram of an example of the operating principle of a capacitor using an anion-releasing negative electrode, which is an example of an electricity storage device of the present disclosure. In a capacitor using an anion-releasing negative electrode, anions are released from the negative electrode during charging and are adsorbed to the positive electrode, and anions are released from the positive electrode during discharging and are absorbed by the negative electrode.

The present disclosure described above in detail can provide a new electricity storage device. The metal organic framework can transfer anions. Therefore, a new electricity storage device can be provided in which the movement of anions charges and discharges the anions, and the anions serve as charge carriers. The reason for obtaining such an effect is presumed to be as follows. For example, the metal organic framework contained in the negative electrode is presumed to form a three-dimensional structure using a transition metal, forming a network in the structure, and forming a path within the structure that allows anions to be transferred, thereby enabling reversible charging and discharging by transfer of anions. In addition, since the electricity storage device disclosed herein is an electricity storage device that uses anions as carriers, the occurrence of short circuits due to overload can be significantly reduced compared to, for example, Li-ion batteries. In addition, since the electricity storage system transfers anions in and out with a capacitor-like behavior, high output is expected. In addition, since the electrodes that are constructed are all stable in the air, the manufacturing process is very easy. Furthermore, since a three-dimensional structure is formed using transition metal elements, the metal organic framework can be produced without going through special or specific processes. In addition, when forming a three-dimensional structure using an alkali metal element, alkali metal ions and anions preferentially form salts, so a specific manufacturing method such as a spray drying method is required, and the synthesis of the desired crystals is relatively difficult. Furthermore, in the energy storage device disclosed herein, since it is anions that are involved in charging and discharging at the positive and negative electrodes, the risk of alkali metal precipitation is extremely low compared to lithium ion batteries, and the device is safer. Furthermore, since the charging and discharging reaction proceeds only through the movement of anions and the change in the anion concentration in the electrolyte is small, the amount of electrolyte can be reduced compared to reserve batteries, and the energy density can be increased.

It goes without saying that the present disclosure is in no way limited to the above-described embodiments, and may be implemented in various forms as long as they fall within the technical scope of the present disclosure.

For example, in the above-described embodiment, the metal organic framework is used in the technical field of electricity storage devices, but the use is not particularly limited thereto, and the metal organic framework may be used as a material for devices utilizing semiconductor properties. Alternatively, the metal organic framework of the present disclosure may be used as a material for an adsorbent, catalyst, or catalyst carrier, utilizing the specific surface area and pores generated by the network present in the three-dimensional structure.

Below, a reference example is described in which a metal-organic framework used in the negative electrode of the electricity storage device of the present disclosure is specifically synthesized and its characteristics are examined. In addition, a working example is described in which a electricity storage device of the present disclosure is specifically fabricated and a charge/discharge test is performed. Experimental examples 1 to 3 correspond to reference examples, and experimental examples 4 and 5 correspond to working examples.

1. Synthesis of metal-organic frameworks and characterization (synthesis of copper viologen dicarboxylate)
[Experimental Example 1]
According to the following synthesis scheme, viologen dicarboxylic acid, which is a raw material of the metal organic framework of the present disclosure, and viologen dicarboxylate copper, which is a metal organic framework of the present disclosure, were synthesized.

(1) 7.0 g of 4,4'-bipyridine and 15.0 g of ethyl bromoacetate were dissolved in 200 mL of acetonitrile and heated under reflux for 24 hours. After cooling to room temperature, the mixture was filtered and washed with ethanol to obtain synthetic intermediate (1).

(2) 21.0 g of synthetic intermediate (1) was dissolved in 120 mL of 10% aqueous hydrochloric acid and heated under reflux for 24 hours, cooled to room temperature, and the solvent was distilled off to obtain synthetic intermediate (2). Synthetic intermediate (2) is a known material (Dalton Trans., 2010, vol.39, pp7714-7722).

(3) 16.0 g of synthetic intermediate (2) was dissolved in 100 mL of water, and 50 mL of water containing 13.8 g of lithium tetrafluoroborate was added and stirred. The resulting powder was filtered and washed with ethanol to obtain synthetic intermediate (3).

(4) 15.42 g of synthetic intermediate (3) was dissolved in 150 mL of water, and 50 mL of water containing 1.64 g of lithium hydroxide was added and stirred. This solution was evaporated to dryness at room temperature. 4.59 g of the resulting powder was taken and dissolved in 60 mL of water. 2.37 g of copper tetrafluoroborate was added to this solution, stirred, and dissolved. Ethanol was added to this prepared solution, and the resulting powder was filtered. The resulting powder was blue-green. This powder was used as the metal-organic framework of Experimental Example 1.

[Experimental Examples 2 and 3]
The metal-organic framework of Experimental Example 1 was dried at 70° C. for 6 hours at 2 Pa using a vacuum dryer to obtain a metal-organic framework of Experimental Example 2. The metal-organic framework of Experimental Example 1 was dried at 120° C. for 6 hours at 2 Pa using a vacuum dryer to obtain a metal-organic framework of Experimental Example 3.

(Single crystal X-ray structure analysis)
A single crystal X-ray structure analysis was performed on the powder of the metal organic framework of Experimental Example 1. This measurement was performed using CuKα radiation (wavelength 1.54051 Å) and an X-ray diffractometer (Ultima IV manufactured by Rigaku). The measurement was performed using a graphite single crystal monochromator to monochromatize the X-rays, with an applied voltage of 40 kV and a current of 30 mA, a scanning speed of 5°/min, and an angle range of 2θ = 5° to 60°. Table 1 summarizes the crystal system, lattice constant, and space group obtained from the measurement results. As shown in Table 1, it was revealed that Experimental Example 1 has a tetragonal system, lattice constants of a = 28.8026(5) Å, c = 10.8477(2) Å, V = 8999.1(3) Å ³ , and a structure of space group I4 ₁ /acd(#142) (see the structure in Figure 1).

(Thermogravimetric analysis (TG))
Thermogravimetric analysis was performed on the powder of the metal organic framework of Experimental Example 1. The thermogravimetric analysis was performed using a Shimadzu TGA-50 with a sample amount of 0.0365 g, a heating rate of 10°C/min, and a temperature range of 20°C to 900°C. FIG. 5 shows the measurement results of thermogravimetric analysis (TG) of Experimental Example 1. As shown in FIG. 5, when Experimental Example 1 was heated, weight loss was observed to continue up to about 600°C. Furthermore, in Experimental Example 1, a mass loss of 12% by mass was observed at 86°C. This was a mass corresponding to six molecules of water incorporated in the crystal. From this measurement result, it was inferred that the metal organic framework of Experimental Example 1 is preferably heated at 200°C or less, preferably 150°C or less, more preferably 120°C or less, and even more preferably 80°C or less.

(X-ray diffraction measurement)
X-ray diffraction measurements were performed on the powders of the metal organic frameworks of Experimental Examples 1 and 2. The measurements were performed using CuKα radiation (wavelength 1.54051 Å) and an X-ray diffractometer (Ultima IV manufactured by Rigaku). The measurements were performed using a graphite single crystal monochromator to monochromatize the X-rays, with an applied voltage of 40 kV and a current of 30 mA, a scanning speed of 5°/min, and an angle range of 2θ = 5° to 80°. FIG. 6 shows the XRD profiles of the samples of Experimental Examples 1 and 2. In Experimental Example 2, which was vacuum dried at 70°C, the powder changed from blue-green to black. As shown in FIG. 6, the peak intensity changed due to the heat treatment, but the peak position was almost unchanged. In Experimental Examples 1 and 2, peaks were present between 2θ of 5° and 35°. The powder of Experimental Example 1 was also examined after heat treatment at 90°C, and it was confirmed that the structure was almost unchanged.

(IR Spectrum Measurement)
Infrared absorption (IR) spectrum measurement was performed on Experimental Examples 1 and 2. This measurement was performed in the range of 600 to 4000 cm ⁻¹ using an Avatar 360 FT-IR manufactured by Thermo Nicolet. FIG. 7 shows the IR spectrum of the samples of Experimental Examples 1 to 3. FIG. 7A also shows the IR spectrum of the intermediate synthetic product (3). FIG. 7B also shows the IR spectrum of the metal organic framework obtained in the same manner as in Experimental Example 3 except that the heating temperature during drying was changed to 40° C., 60° C., 80° C., and 100° C. As shown in FIG. 7A, in Experimental Examples 1 to 3 and the intermediate synthetic product (3), absorption attributable to BF ₄ anion was confirmed near 1000 cm ⁻¹ . This means that in the synthesis of the intermediate synthetic product (3), bromo ion was exchanged with BF ₄ anion. In addition, the absorption attributable to the carboxy group was observed from 1400 cm ^-1 to 1750 cm ^-1 , but in Experimental Examples 1 to 3, the absorption attributable to COOH confirmed in the intermediate synthetic product (3) was not confirmed, and the absorption attributable to the carboxy group of COOCu was confirmed at 1630 cm ^-1 . This indicates that Cu is coordinated to the carboxylate anion in Experimental Examples 1 to 3. In Experimental Examples 2 and 3 obtained by vacuum drying, a change in the absorption peak corresponding to water near 3430 cm ^-1 was confirmed compared to Experimental Example 1. Therefore, it was confirmed that water in the crystals disappeared in Experimental Examples 2 and 3 compared to Experimental Example 1. As for the disappearance of water in the crystals, as shown in Figures 7A and 7B, it was found that as the heating temperature increases to 40°C, 60°C, and 70°C, more water is removed, which is preferable. In addition, since the absorption peak corresponding to water hardly changed between the heating temperatures of 70°C and 100°C, it was found that the heating temperature is preferably 70°C or more and 100°C or less.

(UV Spectrum Measurement)
Ultraviolet absorption (UV) spectrum measurements were performed for Experimental Examples 1 and 2. This measurement was performed in the wavelength range of 200 to 1600 nm using a V-780 manufactured by JASCO. FIG. 8 shows the UV spectrum of the samples of Experimental Examples 1 to 3. Using this measurement result, the band gap was estimated. The band gap was calculated using formula (1). In formula (1), α is the absorption coefficient, ν is the optical frequency, A is a proportionality constant, and Eg is the band gap (eV). In formula (1), n is determined by the transition of the measured sample, and for direct transition, n=1, formula (2), and for indirect transition, n=4, formula (3). Using formulas (2) and (3), the direct transition band gap and the indirect transition band gap were calculated. FIG. 9 is a relationship diagram of the direct transition band gap of the samples of Experimental Examples 1 to 3. FIG. 10 is a relationship diagram of the indirect transition band gap of the samples of Experimental Examples 1 to 3. As shown in Figures 9 and 10, the band gap can be estimated from the intersection of the approximation line obtained from the measurement results of the UV spectrum and the X-axis. The obtained values are summarized in Table 2. In the metal-organic frameworks of Experimental Examples 1 to 3, when the drying temperature was changed within a range of 70°C, 120°C, etc., the band gap was in the range of 0.5 to 3.0 eV, suggesting that Experimental Examples 1 to 3 have semiconducting properties. It was found that in this metal-organic framework, the band gap can be adjusted to any value within the above range by changing the heat treatment temperature.

(Preparation of viologen dicarboxylate Cu electrode)
An electrode mixture was prepared by adding and dispersing 70% by mass of viologen dicarboxylate Cu of Experimental Example 2 prepared by the above method, 25% by mass of carbon black (TB5500, Tokai Carbon) as a particulate carbon conductive material, 5% by mass of polyvinylidene fluoride (PTFE, KF Polymer, manufactured by Kureha) as a binder, and an appropriate amount of N-methyl-2-pyrrolidone as a dispersant. 10 mg of this electrode mixture was pressed against a stainless steel mesh to form a ² cm2 disk-shaped electrode.

(Preparation of bipolar evaluation cell)
A non-aqueous electrolyte was prepared by adding _LiBF4 as a supporting electrolyte to a non-aqueous solvent in a volume ratio of 30:40:30. The viologen dicarboxylate Cu electrode of Experimental Example 2 prepared by the above method was used as a working electrode, lithium metal foil (thickness 300 μm) was used as a counter electrode, and a separator (manufactured by Toray Tonen Co., Ltd.) impregnated with the above non-aqueous electrolyte was sandwiched between the two electrodes to prepare a bipolar evaluation cell.

(Charge/discharge test)
Using the bipolar evaluation cell described above, the cell was reduced to 1.5 V at 0.05 mA (equivalent to 0.1 C) in a temperature environment of 20° C., and then oxidized to 3.0 V at 0.05 mA. This reduction and oxidation operation was repeated 10 times in total. The reduction capacity and oxidation capacity in each operation were determined, and the reduction capacity was taken as the discharge capacity, and the oxidation capacity was taken as the charge capacity. The initial capacity Q ₁ (mAh/g) was determined from the charge/discharge curve of the first cycle, and the capacity retention rate (%) was calculated from the formula Q ₁₀ /Q ₁ ×100 using the initial capacity Q ₁ (mAh/g) and the capacity Q ₁₀ (mAh/g) at the 10th cycle.

(Results and discussion)
FIG. 11 is a charge/discharge curve during single-electrode charge/discharge of a bipolar evaluation cell using the electrode of Experimental Example 2. Table 2 summarizes the heat treatment conditions, band gap, and charge/discharge characteristics of each experimental example. From Table 2 and the measurement results of X-ray diffraction, it was inferred that in maintaining the three-dimensional structure, the heat treatment is preferably 150° C. or less, more preferably 120° C. or less, and even more preferably 80° C. or less. In addition, as shown in FIG. 11, in the bipolar evaluation cell using the viologen dicarboxylic acid Cu electrode of Experimental Example 2, charge/discharge corresponding to the redox of viologen was confirmed from 1.5 V to 3.0 V. It was confirmed that this viologen dicarboxylic acid Cu electrode has a relatively large capacity and can perform stable charge/discharge.

In Experimental Examples 1 to 3, it was inferred that the metal-organic framework had a structure as shown in Figure 1, based on the crystallinity and the structural formula. That is, it was inferred that the metal-organic framework was a three-dimensional structure having an organic framework layer in which carboxylate anions were directly or indirectly bonded to both ends of a basic framework, and a transition metal element layer in which a transition metal was bonded to oxygen contained in the carboxylate anion. In such a three-dimensional structure, for example, a space is generated in the organic framework layer to which the transition metal is bonded, and anions are thought to be absorbed and released in this space. It was inferred that this three-dimensional structure was formed in layers by the π-electron interaction of an aromatic heterocyclic compound, had a structure in which the organic framework layer was bonded by a transition metal element, and had a structure in which four oxygen atoms of different carboxylate anions were bonded to one transition metal element.

2. Preparation of an electricity storage device and charge/discharge test [Experimental Example 4]
(Preparation of viologen dicarboxylate copper electrode)
An electrode mixture was prepared by adding and dispersing 70% by mass of viologen dicarboxylate Cu of Experimental Example 2 prepared by the above method, 25% by mass of carbon black (Tokai Carbon, TB5500) as a particulate carbon conductive material, 5% by mass of polyvinylidene fluoride (PTFE, KF Polymer, manufactured by Kureha) as a binder, and an appropriate amount of N-methyl-2-pyrrolidone as a dispersant. 10 mg of this electrode mixture was pressed against a stainless steel mesh to form a ² cm2 disk-shaped electrode.

(Preparation of activated carbon electrodes)
90% by mass of activated carbon (Cataler, EXC011G), 4% by mass of acetylene black (Denka, Denka Black), 1% by mass of carboxymethylcellulose (Daicel, CMC2200), and 5% by mass of styrene butadiene copolymer (JSR, TRD102A) were mixed, and an appropriate amount of water was added as a dispersant and dispersed to form a slurry mixture. This slurry mixture was uniformly applied to a 10 μm thick copper foil current collector so that the activated carbon per unit area was 3 mg/cm ² , and then heated and dried to prepare a coated sheet. The coated sheet was then subjected to a pressure press treatment and punched out to an area of 2 cm ² to form a disk-shaped electrode.

(Preparation of Li-based non-aqueous electrolyte)
A Li-based nonaqueous electrolyte solution was prepared by adding LiBF ₄ as a supporting electrolyte to a nonaqueous solvent in a volume ratio of 30:40:30, so as to have a concentration of 1.1 mol/L.

(Fabrication of Electricity Storage Device)
A power storage device (two-electrode evaluation cell) was produced by using a viologen dicarboxylate copper electrode as the negative electrode, an activated carbon electrode as the positive electrode, and a separator (manufactured by Toray Tonen Co., Ltd.) impregnated with a Li-based nonaqueous electrolyte between the two electrodes.

(Charge/discharge test)
The above-mentioned bipolar evaluation cell was charged to 2.7 V at 0.049 mA (equivalent to 0.1 C) in a temperature environment of 20° C., and then discharged to 0.0 V at 0.049 mA, and this charge and discharge operation was repeated a total of 10 times. The initial capacity _Q1 (mAh/g) was determined from the charge/discharge curve of the first cycle, and the capacity retention rate (%) was calculated from the initial capacity _Q1 (mAh/g) and the capacity _Q10 (mAh/g) of the 10th cycle according to the formula _Q10 / _Q1 ×100.

[Experimental Example 5]
An electricity storage device was produced in the same manner as in Experimental Example 4, except that a non-Li-based non-aqueous electrolyte prepared as described below was used instead of the Li-based non-aqueous electrolyte, and a charge/discharge test was performed.

(Preparation of non-Li-based non-aqueous electrolyte)
A supporting electrolyte, tetraethylammonium tetrafluoroborate (Et ₄ NBF ₄ ) was added to the propylene carbonate solvent to give a concentration of 1.0 mol/L to prepare a non-Li based non-aqueous electrolyte solution.

[Results and discussion]
FIG. 12 shows the charge/discharge curve of the power storage device of Experimental Example 4, and FIG. 13 shows the charge/discharge curve of the power storage device of Experimental Example 5. Table 3 also summarizes the power storage device configuration (negative electrode active material, positive electrode active material, supporting salt) and charge/discharge characteristics (initial capacity Q ₁ , capacity Q ₁₀ , capacity maintenance rate) of each experimental example. As shown in FIG. 12, a reversible charge/discharge reaction was confirmed in a power storage device prepared using a viologen dicarboxylate copper (hereinafter also referred to as CuViBF ₄ ) electrode as the negative electrode, an activated carbon (hereinafter also referred to as AC) electrode as the positive electrode, and a Li-based nonaqueous electrolyte. As shown in FIG. 13, a reversible charge/discharge reaction was also confirmed in a power storage device prepared using a viologen dicarboxylate copper electrode as the negative electrode, an activated carbon electrode as the positive electrode, and a non-Li-based nonaqueous electrolyte. Thus, since reversible charging and discharging was also achieved in Experimental Example 5 using an electrolyte solution not containing Li, it was presumed that the carrier ions involved in charge compensation in the negative and positive electrodes were mainly _BF4- ^anions . From the above, it was presumed that the charge and discharge reaction formulas in the positive and negative electrodes of the electricity storage devices in Experimental Examples 4 and 5 are expressed by the following formulas. In the following formulas, the reaction to the right corresponds to charging, and the reaction to the left corresponds to discharging.

That is, in the power storage devices of Experimental Examples 4 and 5, it was presumed that the viologen dicarboxylate copper of the negative electrode releases BF ₄ ^- anions during charging and receives BF ₄ ^- anions during discharging, while the activated carbon of the positive electrode receives the BF ₄ ^- anions released from the negative electrode during charging and releases these BF ₄ ^- anions during discharging. As a result, it was presumed that in the power storage devices of Experimental Examples 4 and 5, charging and discharging proceeds by a rocking chair mechanism in which the BF ₄ ^- anions move back and forth between the positive and negative electrodes. In addition, it was presumed that in the power storage devices of the present disclosure, not limited to Experimental Examples 4 and 5, charging and discharging proceeds by a rocking chair mechanism in which anions, which are carrier ions, move back and forth between the positive and negative electrodes.

As shown in Table 3, in Experimental Example 4 using a Li-based nonaqueous electrolyte, the initial capacity _Q1 was 66 mAh/g, the capacity _Q10 was 52 mAh/g, and the capacity retention rate was 79%. In Experimental Example 5 using a non-Li-based nonaqueous electrolyte, the initial capacity _Q1 was 87 mAh/g, the capacity _Q10 was 50 mAh/g, and the capacity retention rate was 57%. From these results, it was found that from the viewpoint of increasing the initial capacity _Q1 , it is preferable to use a supporting salt having an alkali metal cation such as Li cation, and from the viewpoint of increasing the capacity retention rate, it is preferable to use a supporting salt having a nonmetallic cation such as ammonium cation.

This disclosure can be used in the technical field of electricity storage devices.

20: power storage device, 21: battery case, 22: positive electrode, 23: negative electrode, 24: separator, 25: gasket, 26: sealing plate, 27: nonaqueous electrolyte.

Claims (7)

a three-dimensional structure including an organic framework layer including a heterocyclic compound having 4,4'-bipyridinium and a dicarboxylate anion, and a transition metal element layer in which a transition metal element is coordinated to the carboxylate anion to form a framework, and an anion that forms a pair with the three-dimensional structure; and a negative electrode including a metal organic framework including:
a positive electrode including a positive electrode active material capable of donating and receiving the anion;
an ion-conductive medium interposed between the positive electrode and the negative electrode and capable of conducting the anions;
In the negative electrode, the metal organic framework has a structure represented by formula (1) .

a three-dimensional structure including an organic framework layer including a heterocyclic compound having 4,4'-bipyridinium and a dicarboxylate anion, and a transition metal element layer in which a transition metal element is coordinated to the carboxylate anion to form a framework, and an anion that forms a pair with the three-dimensional structure; and a negative electrode including a metal organic framework including:
a positive electrode including a positive electrode active material capable of donating and receiving the anion;
an ion-conductive medium interposed between the positive electrode and the negative electrode and capable of conducting the anions;
In the negative electrode, the metal organic framework has a structure represented by formula (2) or formula (3).

The power storage device according to claim 1 , wherein in the positive electrode, the positive electrode active material is activated carbon. The electricity storage device according to claim 1 , wherein the ionically conductive medium includes a supporting salt having an alkali metal cation. The electricity storage device according to claim 1 , wherein the ionically conductive medium includes a supporting salt having a nonmetallic cation. The electricity storage device _according to _any one _of ^{claims 1 to 5, wherein the anion is one or more of BF4-, PF6-, SiF62-} _{, SbF6- ,} ^ClO4- _, ^{B ( CN} ₎ ^4- _{, [} ^{( C2F5)3PF3]-, [(CN)2N]-} _{, CF3SO3- ,} ^CF3CO2- _{, N} ⁽ _{FSO2 )} 2- _{, N} ⁽ _CF3SO2 ⁾ _2- , and _N ( _C2F5SO2 ⁾ _2- . The power storage device according to any one of claims 1 to 6, wherein in the negative electrode, the transition metal element layer contains one or more of Cu, Fe, Co, Ni, and Mn.

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