Nitrogen battery, fuel synthesis device, and fuel synthesis method

Abstract

To provide a nitrogen battery with a high electrical capacity and a high energy density.SOLUTION: A nitrogen battery comprises: a positive electrode containing nitrogen as a positive electrode active material; a negative electrode; and an ion conducting medium containing lithium bis (fluorosulfonyl) imide as a supporting electrolyte of at least the positive electrode and containing ether as a solvent present on at least the positive electrode side, and conducting an alkali metal ion.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a nitrogen cell, a fuel synthesis device, and a fuel synthesis method. [Background technology]

[0002] Nitrogen batteries, which use nitrogen as the positive electrode active material, are expected to be high-energy density batteries because the theoretical capacity density of nitrogen, calculated from the reduction reaction equivalent to battery discharge, is extremely large at 5740 mAh / g.

[0003] As such a nitrogen battery, Chem, April 13, 2017, Vol. 2, No. 4, pp. 525-532 (Non-Patent Document 1) proposes a battery using lithium metal as the anode, a non-aqueous electrolyte disposed between the cathode and anode, and a nitrogen reduction reaction occurring at the cathode. Furthermore, Japanese Patent Laid-Open Publication No. 2019-145370 (Patent Document 1) discloses a nitrogen battery comprising a cathode using nitrogen as the cathode active material, an anode, and an ion-conducting medium containing a silane compound and conducting alkali metal ions, and using Li(CF3SO2)2N [LiTFSI] as the supporting electrolyte. However, these nitrogen batteries did not necessarily have sufficient discharge voltage or electrical capacity. Furthermore, Patent Document 1 discloses a fuel synthesis device and a fuel synthesis method using the nitrogen battery, but the fuel (ammonia) production efficiency of these devices and methods was not necessarily sufficient.

[0004] Furthermore, Nature Commun., 2012, Vol. 3, p. 1254 (Non-Patent Document 2) discloses a reduction reaction of nitrogen gas at room temperature and pressure using an iron complex as a catalyst. However, in this reduction reaction, nitrogen is silylated in the presence of an Fe catalyst, a silylating agent, and an alkali metal to synthesize a silylamine, and this silylamine is then brought into contact with water to synthesize ammonia, making it difficult to apply this reduction reaction to nitrogen batteries.

[0005] Furthermore, J. Phys. Chem C, 2015, Vol. 119, pp. 6556-6567 (Non-Patent Document 3) discloses the results of a predictive analysis of whether a transition metal serving as the central metal of a metal-organic framework (MOF) functions as an adsorption site for O or N, by calculating and comparing the interatomic distance between the transition metal M and an oxygen atom O or a nitrogen atom N with the interatomic distance between the oxygen atoms of O or the interatomic distance between the nitrogen atoms of N, using first-principles calculations. The predictive analysis results show that, for example, when 2,5-dihydroxyterephthalate (M(dobcd)) of a transition metal M is used as the MOF, the interatomic distance of O adsorbed to the transition metal M tends to increase as the interatomic distance between the MO atoms decreases, compared to the interatomic distance between the O atoms of unadsorbed O. This result suggests that in the reduction reaction of O2, M2(dobcd) reduces the bonding strength between oxygen atoms, and it is predicted that M2(dobcd) acts as a catalyst for the reduction reaction of O2. On the other hand, Non-Patent Document 3 also shows the results of a predictive analysis that, in N2 adsorbed to a transition metal M, even if the M-N interatomic distance decreases, the N-N interatomic distance remains almost the same as the N-N interatomic distance of unadsorbed N2. This result suggests that in the reduction reaction of N2, M2(dobcd) does not reduce the bonding strength between nitrogen atoms, and it is predicted that M2(dobcd) does not act as a catalyst for the reduction reaction of N2. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-145370 [Non-patent literature]

[0007] [Non-Patent Document 1] Chem, April 13, 2017, Vol. 2, No. 4, pp. 525-532 [Non-patent document 2] Nature Commun., 2012, vol. 3, pp. 1254 [Non-patent document 3] J.Phys.Chem C, 2015, Volume 119, pp. 6556-6567 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made in consideration of the problems associated with the above-described conventional techniques, and aims to provide a nitrogen battery having a high electric capacity and a high energy density, as well as a fuel synthesis device and a fuel synthesis method capable of synthesizing ammonia with high efficiency. [Means for solving the problem]

[0009] As a result of intensive research to achieve the above object, the present inventors have found that a nitrogen battery having a high discharge voltage (plateau voltage), a high electric capacity, and a high energy density can be obtained by using an ion-conducting medium that contains lithium bis(fluorosulfonyl)imide (LiFSI) as at least the supporting electrolyte of the positive electrode, and that contains an ether as the solvent present at least on the positive electrode side and that conducts alkali metal ions. They have also found that ammonia can be synthesized with high efficiency by using this nitrogen battery, and have completed the present invention.

[0010] That is, the present invention provides the following aspects. [1] A nitrogen battery comprising a positive electrode using nitrogen as the positive electrode active material, a negative electrode, and an ion-conducting medium that contains at least lithium bis(fluorosulfonyl)imide as a supporting electrolyte for the positive electrode and an ether as a solvent present at least on the positive electrode side, and that conducts alkali metal ions. [2] The nitrogen battery according to [1], wherein the ether present as the solvent on the positive electrode side is a polyethylene glycol ether. [3] The nitrogen battery according to [1] or [2], wherein the ion conducting medium further contains a silane compound as an additive at least on the positive electrode side. [4] The nitrogen battery according to any one of [1] to [3], wherein the ion-conducting medium includes a positive electrode-side ion-conducting medium present on the positive electrode side in contact with the positive electrode, and a negative electrode-side ion-conducting medium present on the negative electrode side in contact with the negative electrode, the positive electrode-side ion-conducting medium containing lithium bis(fluorosulfonyl)imide as a supporting electrolyte for the positive electrode and containing an ether as a solvent present on the positive electrode side, and the negative electrode-side ion-conducting medium containing lithium bis(fluorosulfonyl)imide as a supporting electrolyte for the negative electrode and containing an ether as a solvent present on the negative electrode side. [5] The nitrogen battery according to [4], wherein the ether as the solvent present on the positive electrode side and the ether as the solvent present on the negative electrode side are both polyethylene glycol ethers. [6] The nitrogen battery according to any one of [1] to [5], wherein the positive electrode comprises an electrode catalyst to which transition metal ions are immobilized. [7] The nitrogen battery according to [6], wherein the electrode catalyst is a metal organic framework containing a transition metal ion and an aromatic polycarboxylate ion. [8] The transition metal ion is an Fe ion, and the aromatic polycarboxylic acid ion is represented by the following formula (1):

[0011] [ka]

[0012] [wherein R 1 represents a tetravalent organic group containing an aromatic ring, and X represents O or S. The nitrogen battery according to [7], wherein the aromatic dicarboxylic acid ion is represented by the formula: [9] The nitrogen battery according to [8], wherein at least a portion of the Fe ions are trivalent Fe ions.

[10] A fuel synthesis device using the nitrogen cell according to any one of [1] to [9], wherein the fuel synthesis device obtains ammonia as fuel by treating a nitrogen reduction reaction product obtained after operation of the nitrogen cell with water.

[11] A method for synthesizing fuel using the nitrogen battery according to any one of [1] to [9], wherein ammonia is obtained as fuel by treating a nitrogen reduction reaction product obtained after operation of the nitrogen battery with water.

[0013] Although the reasons why the present invention provides a nitrogen battery having a high electric capacity and a high energy density and further enables highly efficient ammonia synthesis are not entirely clear, the inventors speculate as follows. That is, it is speculated that the nitrogen battery of the present invention contains LiFSI as at least the supporting electrolyte of the positive electrode in the ion conductive medium and contains an ether as the solvent present at least on the positive electrode side, thereby forming a LiFSI-derived coating on the electrode catalyst, and the nitrogen reduction reaction is promoted by the interaction between the electrode catalyst and the coating. It is also speculated that the use of an ion conductive medium containing LiFSI as at least the supporting electrolyte of the positive electrode and containing an ether as the solvent present at least on the positive electrode side results in a high plateau voltage during the discharge reaction, during which the nitrogen reduction reaction is promoted, thereby increasing the electric capacity and improving the ammonia production efficiency.

[0014] Furthermore, when the electrode catalyst is a metal-organic framework (MOF) containing Fe ions and aromatic polycarboxylate ions represented by formula (1), a nitrogen-containing battery with a higher electrical capacity can be obtained, enabling more efficient ammonia synthesis. The reasons for this are unclear, but the inventors speculate as follows. Specifically, the MOF containing Fe ions and aromatic polycarboxylate ions represented by formula (1) as the electrode catalyst has a hexagonal crystal structure as shown in FIG. 1 . When such an MOF is exposed to an oxygen atmosphere (e.g., an air atmosphere), the Fe ions become trivalent. These trivalent Fe ions serve as nitrogen adsorption sites (open metal sites) and are therefore more likely to adsorb nitrogen. When electrons are donated through the MOF, the nitrogen adsorbed on the Fe ions is reduced more efficiently due to the cooperative electrochemical catalytic action of the coating and the MOF. It is speculated that this results in a further increase in electrical capacity, enabling more efficient ammonia synthesis. [Effects of the Invention]

[0015] According to the present invention, a nitrogen battery having a high electric capacity and a high energy density can be obtained, and by using this nitrogen battery, it becomes possible to synthesize ammonia with high efficiency. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram showing the crystal structure of a metal organic framework containing Fe ions and aromatic polycarboxylate ions represented by formula (1). [Figure 2] FIG. 1 is a schematic diagram showing evaluation cells (nitrogen batteries) prepared in Examples and Comparative Examples. [Figure 3] 1 is a graph showing the relationship (discharge curve) between the electric capacity per unit mass of the electrode and the discharge voltage of the evaluation cell (nitrogen battery) produced in Example 1. [Figure 4] 1 is a graph showing the relationship (discharge curve) between the electric capacity per unit mass of the electrode and the discharge voltage of the evaluation cell (nitrogen battery) produced in Example 2. [Figure 5]1 is a graph showing the relationship (discharge curve) between the electric capacity per unit mass of the electrode and the discharge voltage of the evaluation cell (nitrogen battery) produced in Example 3. [Figure 6] 10 is a graph showing the relationship (discharge curve) between the electric capacity per unit mass of the electrode and the discharge voltage of the evaluation cell (nitrogen battery) produced in Example 4. [Figure 7] 10 is a graph showing the relationship (discharge curve) between the electric capacity per unit mass of the electrode and the discharge voltage of the evaluation cell (nitrogen battery) produced in Example 5. [Figure 8] 10 is a graph showing the relationship (discharge curve) between the electric capacity per unit mass of the electrode and the discharge voltage of the evaluation cell (nitrogen battery) produced in Example 6. [Figure 9] 10 is a graph showing the relationship (discharge curve) between the electric capacity per unit mass of the electrode and the discharge voltage of the evaluation cell (nitrogen battery) produced in Example 7. [Figure 10] 1 is a graph showing the relationship (discharge curve) between the electric capacity per unit mass of the electrode and the discharge voltage of the evaluation cell (nitrogen battery) produced in Comparative Example 1. [Figure 11] 1 is a graph showing the relationship (discharge curve) between the electrical capacity per unit mass of the electrode and the discharge voltage of the evaluation cell (nitrogen battery) produced in Comparative Example 2. [Figure 12] 10 is a graph showing the relationship (discharge curve) between the electrical capacity per unit mass of the electrode and the discharge voltage of the evaluation cell (nitrogen battery) produced in Comparative Example 3. [Figure 13] 10 is a graph showing the relationship (discharge curve) between the electric capacity per unit mass of the electrode and the discharge voltage of the evaluation cell (nitrogen battery) produced in Comparative Example 4. [Figure 14] 10 is a graph showing the relationship (discharge curve) between the electric capacity per unit mass of the electrode and the discharge voltage of the evaluation cell (nitrogen battery) produced in Comparative Example 5. [Figure 15] 10 is a graph showing the relationship (discharge curve) between the electric capacity per unit mass of the electrode and the discharge voltage of the evaluation cell (nitrogen battery) produced in Comparative Example 6. [Figure 16]10 is a graph showing the relationship (discharge curve) between the electric capacity per unit mass of the electrode and the discharge voltage of the evaluation cell (nitrogen battery) produced in Example 8. [Figure 17] 10 is a graph showing the relationship (discharge curve) between the electric capacity per unit mass of the electrode and the discharge voltage of the evaluation cell (nitrogen battery) produced in Example 9. [Figure 18] 10 is a graph showing the relationship (discharge curve) between the electric capacity per unit mass of the electrode and the discharge voltage of the evaluation cell (nitrogen battery) produced in Example 10. [Figure 19] 10 is a graph showing the relationship (discharge curve) between the electric capacity per unit mass of the electrode and the discharge voltage of the evaluation cell (nitrogen battery) produced in Example 11. [Figure 20] 1 is a graph showing the electric capacity per unit mass of the electrodes of the evaluation cells (nitrogen batteries) produced in Examples 1 to 7 and Comparative Examples 1 to 6 up to a discharge voltage of 1.0 V. [Figure 21] 1 is a graph showing the energy density of the evaluation cells (nitrogen batteries) produced in Examples 1 to 7 and Comparative Examples 1 to 6 up to a discharge voltage of 1.0 V. [Figure 22] 1 is a graph showing the electric capacity per unit mass of the electrodes of the evaluation cells (nitrogen batteries) prepared in Examples 8 to 11 up to a discharge voltage of 1.0 V in a nitrogen or argon atmosphere. [Figure 23] 1 is a graph showing the amount of ammonium ions produced up to a discharge voltage of 1.0 V in the evaluation cells (nitrogen batteries) produced in Examples 1 to 7 and Comparative Examples 1 to 6. [Figure 24] 1 is a graph showing the amount of ammonium ions produced in the evaluation cells (nitrogen batteries) produced in Examples 8 to 11 up to a discharge voltage of 1.0 V in a nitrogen or argon atmosphere. [Figure 25] 10 is a graph showing the Fe K-edge XAFS spectrum of the positive electrode catalyst after the discharge test in Example 8. [Figure 26] 10 is a graph showing the Ni K-edge XAFS spectrum of the positive electrode catalyst after the discharge test of Example 9. [Figure 27] 10 is a graph showing the Co K-edge XAFS spectrum of the positive electrode catalyst after the discharge test of Example 10. [Figure 28] 10 is a graph showing the Mn K-edge XAFS spectrum of the positive electrode catalyst of Example 11 after a discharge test. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be described in detail below based on preferred embodiments thereof.

[0018] [Nitrogen battery] First, the nitrogen battery of the present invention will be described. The nitrogen battery of the present invention includes a positive electrode using nitrogen as a positive electrode active material, a negative electrode, and an ion-conducting medium that contains at least lithium bis(fluorosulfonyl)imide as a supporting electrolyte for the positive electrode and an ether as a solvent present at least on the positive electrode side, and that conducts alkali metal ions.

[0019] (positive electrode) The positive electrode used in the present invention uses gaseous nitrogen as the positive electrode active material. The gaseous nitrogen may be nitrogen contained in air or nitrogen gas. The positive electrode may also contain a conductive material or a conductive auxiliary. For example, the positive electrode may be formed by pressing an electrode mixture, such as a conductive material or conductive auxiliary, a binder, and the like, onto a current collector to a desired thickness and shape (e.g., by pressing the kneaded electrode mixture onto a mesh-shaped current collector). Alternatively, the positive electrode may be formed by applying a mixture of a conductive material or conductive auxiliary, a binder, and a solvent to a current collector to a desired thickness and shape. The shape of the positive electrode preferably has an interface where the gaseous nitrogen and the ion-conducting medium are uniform, and is preferably, for example, porous or mesh-shaped.

[0020] The conductive material and conductive auxiliary agent are not particularly limited as long as they are conductive, and examples thereof include carbon, conductive fibers, metal powder, and organic conductive materials. Examples of the carbon include carbon blacks such as ketjen black, acetylene black, channel black, furnace black, lamp black, and thermal black; graphites such as natural graphite (e.g., flake graphite), artificial graphite, and expanded graphite; activated carbons made from charcoal or coal; carbon fibers and carbon paper made from carbonized synthetic fibers or petroleum pitch-based materials. Examples of the conductive fibers include metal fibers. Examples of the metal powder include nickel powder and aluminum powder. Examples of the organic conductive material include polyphenylene derivatives. These conductive materials and conductive auxiliary agents may be used alone or in combination. A carbon-based electrode is preferred as a positive electrode containing such a conductive material or conductive auxiliary agent, and a carbon-based porous electrode is more preferred.

[0021] The binder serves to bind the conductive material and the conductive auxiliary. Examples of such binders include fluorine-containing resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluororubber; thermoplastic resins such as polypropylene, polyethylene, and polyacrylonitrile; rubbers such as ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, natural butyl rubber (NBR), and styrene butadiene rubber (SBR); and aqueous binders such as cellulose. These binders may be used alone or in combination of two or more. The binder may be added directly to a solvent or the like, or may be mixed with a solvent or the like as a dispersion. The amount of the binder to be added is preferably 3 to 15 mass% of the total electrode mixture. When the blending amount of the binder is equal to or greater than the lower limit, the strength of the positive electrode can be sufficiently maintained. On the other hand, when the blending amount of the binder is equal to or less than the upper limit, the amounts of the conductive material, the conductive auxiliary, and the electrode catalyst described later do not become too small, and the progress of the electrode reaction is less likely to be hindered.

[0022] Examples of solvents for dispersing the conductive material, conductive auxiliary, 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, tetrahydrofuran, and alcohol (e.g., ethanol). These organic solvents may be used alone or in combination of two or more. Alternatively, a dispersant, a thickener, or the like may be added to water, and the conductive material, conductive auxiliary, and binder may be slurried with a latex such as SBR. Examples of thickeners include polysaccharides such as carboxymethyl cellulose and methyl cellulose.

[0023] Examples of a method for applying the mixture of the conductive material or the conductive auxiliary, the binder, etc., and the solvent to the current collector include roller coating such as an applicator roll, screen coating, a doctor blade method, spin coating, and bar coating.

[0024] Examples of the current collector include metal current collectors such as stainless steel, nickel, and aluminum. The shape of such current collectors is preferably a porous structure such as a net or mesh to promote nitrogen diffusion. The surface of the current collector may be coated with an oxidation-resistant metal or alloy film to inhibit oxidation. Examples of the current collector include transparent conductive materials such as InSnO2, SnO2, ZnO, and In2O3, or impurity-doped materials such as fluorine-doped tin oxide (SnO2:F), antimony-doped tin oxide (SnO2:Sb), tin-doped indium oxide (In2O3:Sn), aluminum-doped zinc oxide (ZnO:Al), and gallium-doped zinc oxide (ZnO:Ga), formed on glass or a polymer. The thickness of the impurity-doped material is not particularly limited, but a thickness of 3 nm to 10 μm is preferred. The glass or polymer may have a smooth or uneven surface.

[0025] The positive electrode used in the present invention preferably includes an electrode catalyst having immobilized transition metal ions, from the viewpoint of increasing the electric capacity and energy density. The content of the electrode catalyst is preferably 10 to 50 mass% of the entire positive electrode. The transition metal is preferably one capable of reducing nitrogen, such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Be, or Mg. Divalent transition metals, such as Fe, Co, Ni, or Mn, are more preferred. Fe is particularly preferred, from the viewpoint that exposing the electrode catalyst to an oxygen atmosphere (e.g., an air atmosphere) increases the valence of the transition metal to nearly trivalent, thereby enhancing the nitrogen reducing power and increasing the electric capacity and the amount of ammonia produced. These transition metals may be used alone or in combination of two or more.

[0026] Furthermore, the electrode catalyst is more preferably a metal-organic framework (MOF) containing the transition metal ion and an aromatic carboxylate ion, from the viewpoint of being less soluble in a non-aqueous electrolyte and being easily immobilized on the positive electrode. Examples of the aromatic carboxylate ion include those represented by the following formula (1):

[0027] [ka]

[0028] [wherein R 1 represents a tetravalent organic group containing an aromatic ring, and X represents O or S. an aromatic dicarboxylic acid ion represented by the following formula (2):

[0029] [ka]

[0030] [wherein R 2 represents a trivalent organic group containing an aromatic ring. Examples of aromatic tricarboxylic acid ions include those represented by the following formula:

[0031] R in the formula (1) 1The following formulas (1a) to (1f):

[0032] [ka]

[0033] Examples of the aromatic ring-containing tetravalent organic group include:

[0034] In addition, R in the formula (2) 2 The following formulas (2a) to (2b):

[0035] [ka]

[0036] Examples of the aromatic ring-containing trivalent organic group include:

[0037] Specific examples of the aromatic dicarboxylate ion represented by the formula (1) include a 2,5-dioxidoterephthalate ion represented by the following formula (3a), a 2,5-disulfide terephthalate ion represented by the following formula (3b), a 3,7-dioxidonaphthalene-2,6-dicarboxylate ion represented by the following formula (4a), a 1,5-dioxidonaphthalene-2,6-dicarboxylate ion represented by the following formula (4b), a 3,3′-dioxido-[1,1′-biphenyl]-4,4′-dicarboxylate ion represented by the following formula (5a), and a 4,4′-dioxido-[1,1′-biphenyl]-3,3′-dicarboxylate ion represented by the following formula (5b).

[0038] [ka]

[0039] Specific examples of the aromatic tricarboxylate ion represented by the formula (2) include a 1,3,5-benzenetricarboxylate ion represented by the following formula (6a) and an aromatic tricarboxylate ion represented by the following formula (6b).

[0040] [ka]

[0041] Examples of the metal organic framework include metal organic frameworks represented by the formula: M2A (wherein M represents a divalent transition metal ion, and A represents an aromatic dicarboxylate ion represented by the formula (1) above), and metal organic frameworks represented by the formula: M2B3 (wherein M represents a divalent transition metal ion, and B represents an aromatic tricarboxylate ion represented by the formula (2) above).

[0042] Among these metal organic frameworks, from the viewpoint of further increasing the electric capacity, energy density, and amount of ammonium ion generated, a metal organic framework containing Fe ions and an aromatic dicarboxylate ion represented by the formula (1) is preferred, a metal organic framework containing Fe ions and at least one of the aromatic dicarboxylate ions represented by the formulas (3a) to (5b) is more preferred, and a metal organic framework containing Fe ions and an aromatic dicarboxylate ion represented by the formula (3a) is particularly preferred. Furthermore, in these metal organic frameworks, from the viewpoint of further increasing the electric capacity, energy density, and amount of ammonium ion generated, it is preferred that at least a portion of the Fe ions are trivalent Fe ions. Such trivalent Fe ions can be generated by exposing the metal organic framework to an oxygen atmosphere (e.g., an air atmosphere).

[0043] (Negative electrode) The negative electrode used in the present invention is an electrode facing the positive electrode. It is not particularly limited as long as it is usable in nitrogen batteries. However, it preferably contains a negative electrode active material capable of absorbing and desorbing alkali metal ions (more preferably lithium ions). Examples of negative electrode active materials capable of absorbing and desorbing lithium ions include alkali metals (e.g., lithium, sodium, and potassium) and alkali metal alloys (e.g., lithium alloys), as well as metal oxides, metal sulfides, and carbonaceous materials capable of absorbing and desorbing lithium. Examples of lithium alloys include alloys of lithium with aluminum, tin, magnesium, indium, calcium, and the like. Examples of metal oxides include tin oxide, silicon oxide, lithium titanium oxide, niobium oxide, and tungsten oxide. Examples of metal sulfides include tin sulfide and titanium sulfide. Examples of carbonaceous materials capable of absorbing and desorbing lithium include graphite, coke, mesophase pitch-based carbon fiber, spherical carbon, and resin-fired carbon.

[0044] (ion conducting medium) The ionically conductive medium used in the present invention conducts alkali metal ions (preferably lithium ions) and contains at least lithium bis(fluorosulfonyl)imide (LiFSI) as a supporting electrolyte for the positive electrode and an ether as a solvent present at least on the positive electrode side. Examples of such ionically conductive medium include a cathode-side ionically conductive medium present at the positive electrode side and in contact with the positive electrode, containing LiFSI as a supporting electrolyte for the positive electrode and an ether as a solvent present on the positive electrode side. When the ionically conductive medium contains LiFSI as a supporting electrolyte for the positive electrode (e.g., when the ionically conductive medium contains a cathode-side ionically conductive medium containing LiFSI as a supporting electrolyte for the positive electrode), the electric capacity and energy density are increased. Furthermore, when the ionically conductive medium contains an ether as a solvent present at least on the positive electrode side (e.g., when the ionically conductive medium contains a cathode-side ionically conductive medium containing an ether as a solvent present on the positive electrode side), the amount of ammonium ions produced is increased. Furthermore, from the viewpoint of increasing the electric capacity and energy density, the concentration of LiFSI in the positive electrode side ion conductive medium is preferably 0.1 to 3.0 mol / L, more preferably 0.5 to 2.0 mol / L, and even more preferably 0.5 to 1.0 mol / L. Moreover, from the viewpoint of increasing the amount of ammonium ions produced, the ion conductive medium and the positive electrode side ion conductive medium are preferably nonaqueous electrolyte solutions.

[0045] The ether present as the solvent on the positive electrode side is preferably a polyethylene glycol ether, and examples of the polyethylene glycol ether include polyethylene glycol monoalkyl ether and polyethylene glycol dialkyl ether. These polyethylene glycol ethers may be used alone or in combination of two or more.

[0046] Although the reason why the amount of ammonium ions produced increases when an ion-conductive medium containing LiFSI as at least the supporting electrolyte of the positive electrode and an ether as the solvent present at least on the positive electrode side is used is not entirely clear, the present inventors speculate as follows. Here, we will explain the case where the ether present on the positive electrode side as the solvent is polyethylene glycol dimethyl ether. That is, the LiFSI contained in the ion-conductive medium in contact with the positive electrode undergoes a reduction reaction at the positive electrode to form LiFSI-derived radicals and sites where Li cations and fluorine anions interact with each other, as follows:

[0047] [ka]

[0048] The LiFSI-derived radical reacts with polyethylene glycol dimethyl ether to form a stable conjugate as follows:

[0049] [ka]

[0050] It is presumed that the site where the Li cation and the fluorine anion interact with each other exhibits catalytic activity for the nitrogen reduction reaction and catalytically accelerates the nitrogen reduction reaction, thereby increasing the amount of ammonium ions produced.

[0051] On the other hand, when an ion-conductive medium containing LiFSI as at least the supporting electrolyte of the positive electrode and containing a carbonate-based solvent as at least the solvent present on the positive electrode side is used, the LiFSI contained in the ion-conductive medium in contact with the positive electrode undergoes a reduction reaction at the positive electrode, forming LiFSI-derived radicals and sites where Li cations and fluorine anions interact, as described above. However, because the LiFSI-derived radicals do not react with the carbonate-based solvent and a stable bond is not formed, it is presumed that the fluorine anions and the LiFSI-derived radicals recombine, resulting in a decrease in the sites where Li cations and fluorine anions interact. As a result, the catalytic activity for the nitrogen reduction reaction is reduced, and the nitrogen reduction reaction is not promoted, resulting in a decrease in the amount of ammonium ions produced. Alternatively, even if a bond is formed by the reaction of the LiFSI-derived radicals with the carbonate-based solvent, it is presumed that the sites where Li cations and fluorine anions interact are not suitable for catalyzing the nitrogen reduction reaction (e.g., the catalytic activity is inhibited by the bond). As a result, it is presumed that the catalytic activity for the nitrogen reduction reaction is reduced, and the nitrogen reduction reaction is not promoted, resulting in a decrease in the amount of ammonium ions produced.

[0052] In addition, when an ionically conductive medium containing Li(CF3SO2)2N [LiTFSI] as at least the supporting electrolyte of the positive electrode and containing an ether as the solvent present at least on the positive electrode side is used, LiTFSI in the ionically conductive medium in contact with the positive electrode is converted into the following formula:

[0053] [ka]

[0054] Therefore, it is presumed that radicals derived from LiTFSI are not generated, and that sites where the Li cation and fluorine anion interact to exhibit catalytic activity in the nitrogen reduction reaction are not generated either. Therefore, it is presumed that the nitrogen reduction reaction is not promoted, and the amount of ammonium ions produced is reduced.

[0055] When the ion-conducting medium used in the present invention includes the positive electrode-side ion-conducting medium, the ion-conducting medium is preferably present on the negative electrode side in contact with the negative electrode, and includes a negative electrode-side ion-conducting medium containing a supporting electrolyte for the negative electrode and a solvent present on the negative electrode side. Furthermore, the negative electrode-side ion-conducting medium is preferably a nonaqueous electrolyte solution.

[0056] The supporting electrolyte for the negative electrode is not particularly limited, but is preferably an alkali metal salt, and more preferably a lithium salt. Examples of the lithium salt include LiPF6, LiClO4, LiAsF6, LiBF4, Li(CF3SO3), Li(CF3SO2)2N [LiTFSI], Li(SO2F)2N [LiFSI], and LiN(C2F5SO2)2. These supporting electrolytes may be used alone or in combination of two or more. The concentration of the supporting electrolyte for the negative electrode in the negative electrode-side ion conductive medium is preferably 0.1 to 3.0 mol / L, more preferably 0.5 to 2.0 mol / L, and even more preferably 0.5 to 1.0 mol / L.

[0057] The solvent present on the negative electrode side is not particularly limited, and examples thereof include organic solvents such as carbonate solvents, ester solvents, ether solvents, nitrile solvents, and ionic liquids. Examples of the carbonate solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; and chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of the ester solvents include cyclic esters such as γ-butyrolactone and γ-valerolactone. Examples of the ether solvents include cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran; and chain ethers such as dimethoxyethane, ethylene glycol dimethyl ether, and polyethylene glycol ethers (e.g., polyethylene glycol monoalkyl ethers and polyethylene glycol dialkyl ethers). Examples of the nitrile solvents include acetonitrile, propylnitrile, and 3-methoxypropionitrile. Examples of the ionic liquid include N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide, N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide, N,N-dimethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethylsulfonyl)imide, etc. These organic solvents may be used alone or in combination of two or more.

[0058] Furthermore, the ion conductive medium used in the present invention preferably further contains a silane compound as an additive on the positive electrode side (for example, the ion conductive medium includes a positive electrode-side ion conductive medium further containing a silane compound as an additive on the positive electrode side). This increases the amount of ammonium ions produced. The ion conductive medium may further contain a silane compound as an additive on the negative electrode side (for example, the ion conductive medium may include a negative electrode-side ion conductive medium further containing a silane compound as an additive on the negative electrode side). Examples of the silane compound include trialkylsilane compounds and their halides. The trialkylsilane compound preferably has a linear or branched alkyl group having 1 to 8 carbon atoms (more preferably 1 to 4 carbon atoms). Examples of the halides of the trialkylsilane compound include compounds in which the hydrogen atoms bonded to the silicon atoms of the trialkylsilane compound are substituted with halogen atoms such as F, Cl, Br, and I, such as chlorotrimethylsilane, chlorotriethylsilane, and chlorotripropylsilane. These silane compounds may be used alone or in combination of two or more. From the viewpoint of increasing the amount of ammonium ions produced, the concentration of the silane compound in the ion-conducting medium (e.g., the positive electrode-side ion-conducting medium and / or the negative electrode-side ion-conducting medium) is preferably 0.5 to 7.5 mol / L, more preferably 0.8 to 3 mol / L, and even more preferably 1 to 2 mol / L.

[0059] Among such ion-conductive media, from the viewpoint of further increasing the electric capacity, energy density, and amount of ammonium ions produced, an ion-conductive medium containing both a positive electrode-side ion-conductive medium containing LiFSI as a supporting electrolyte for the positive electrode and an ether as a solvent present on the positive electrode side, and an anode-side ion-conductive medium containing LiFSI as a supporting electrolyte for the negative electrode and an ether as a solvent present on the negative electrode side, is more preferred, and an ion-conductive medium in which both the ether as the solvent present on the positive electrode side and the ether as the solvent present on the negative electrode side are the polyethylene glycol-based ether is even more preferred.

[0060] (separator) The nitrogen-containing battery of the present invention preferably includes a separator between the positive electrode and the negative electrode. This separator separates an ion-conducting medium in contact with the positive electrode (e.g., the positive-electrode-side ion-conducting medium) from an ion-conducting medium in contact with the negative electrode (e.g., the negative-electrode-side ion-conducting medium) and prevents their mixing. There are no particular limitations on the separator, as long as its composition is durable for use in nitrogen-containing batteries. Examples of such separators include solid electrolytes, polymer nonwoven fabrics such as polypropylene nonwoven fabrics and polyphenylene sulfide nonwoven fabrics, and microporous films made of olefin-based resins such as polypropylene nonwoven fabrics and polyphenylene sulfide nonwoven fabrics. These separators may be used alone or in combination of two or more. Among these separators, solid electrolytes are preferred because they can increase the concentration of LiFSI in the ion-conducting medium on the positive electrode side, thereby improving electrical capacity and energy density. Solid electrolytes that conduct alkali metal ions (more preferably, lithium ions) are more preferred.

[0061] Examples of the solid electrolyte include Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2-based glass ceramics, and the solid electrolytes described in JP-A-2009-122991 (e.g., garnet-type oxide Li 5+X La3(Zr X ,Nb 2-X )O 12 (1.4≦X<2), garnet-type oxide Li7La3Zr2O 12 , garnet-type oxide Li7ALa3Nb2O 12 (A=Ca, Sr, Ba), glass ceramics Li 1.5 Al 0.5 Ge 1.5 (PO4)3[LAGP]) and the like. These solid electrolytes are useful as solid electrolytes that conduct lithium ions.

[0062] (nitrogen battery) The nitrogen battery of the present invention includes the positive electrode, the negative electrode, and the ion conductive medium, and the positive electrode and the negative electrode are arranged opposite each other. The ion conductive medium preferably includes one in contact with the positive electrode (e.g., the positive electrode-side ion conductive medium) and one in contact with the negative electrode (e.g., the negative electrode-side ion conductive medium), and more preferably, the ion conductive medium in contact with the positive electrode and the ion conductive medium in contact with the negative electrode are separated by the separator arranged between the positive electrode and the negative electrode.

[0063] In the nitrogen battery of the present invention, it is preferable that a space for introducing nitrogen is provided above the positive electrode (on the side opposite to the surface facing the negative electrode). Furthermore, when the nitrogen battery of the present invention includes the separator, it is preferable that the positive electrode is pressed against the separator from above (on the side opposite to the surface facing the negative electrode) by a pressing member such as a spring.

[0064] In the nitrogen battery of the present invention, the ion conductive medium in contact with the positive electrode and the ion conductive medium in contact with the negative electrode may have the same or different compositions of components other than LiFSI as the supporting electrolyte of the positive electrode and the ether as the solvent present on the positive electrode side.

[0065] Furthermore, in cases where the negative electrode is lithium metal, the negative electrode and the separator (particularly, the solid electrolyte) may be directly joined together as long as the separator (particularly, the solid electrolyte) is stable with respect to the negative electrode.

[0066] The shape of the nitrogen battery of the present invention is not particularly limited, and examples thereof include coin type, button type, sheet type, laminated type, cylindrical type, flat type, prismatic type, etc. The nitrogen battery of the present invention can be applied to large nitrogen batteries used in electric vehicles, etc.

[0067] In the nitrogen battery of the present invention, discharge and a nitrogen reduction reaction at the positive electrode proceed by contacting nitrogen with the positive electrode while passing a current between the positive electrode and the negative electrode. The nitrogen battery of the present invention uses an ion-conducting medium containing LiFSI as at least the supporting electrolyte of the positive electrode and an ether as the solvent present at least on the positive electrode side. This increases the plateau potential (the potential in the region where the discharge potential is flat). As a result, the electric capacity and energy density increase, and the amount of nitrogen reduction reaction products (e.g., silylamine, lithium nitride) produced also increases. The initial open-circuit voltage also increases to 3.0 V or higher, preferably 3.3 V or higher. In particular, when Fe is used as the transition metal, the initial open-circuit voltage is 3.6 V or higher.

[0068] [Fuel synthesis device and fuel synthesis method] The fuel synthesis apparatus and method of the present invention are an apparatus and method using the nitrogen cell of the present invention, and are capable of obtaining ammonia as fuel by treating a nitrogen reduction reaction product (e.g., silylamine, lithium nitride) obtained after operation of the nitrogen cell with water. Ammonia is generally synthesized at high temperature and pressure, but by using the fuel synthesis apparatus of the present invention and / or employing the fuel synthesis method of the present invention, it is possible to obtain ammonia at room temperature and pressure. Specifically, the nitrogen cell of the present invention is discharged at room temperature and pressure while introducing nitrogen to generate the nitrogen reduction reaction product. An ionically conductive medium containing the nitrogen reduction reaction product is removed from the discharged nitrogen cell, and this ionically conductive medium is treated with water to hydrolyze the nitrogen reduction reaction product, resulting in ammonia being extracted into the water. [Example]

[0069] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0070] Example 1 <Production of evaluation cell (nitrogen battery)> Anhydrous iron chloride (FeCl2) and 2,5-dihydroxyterephthalic acid (dobcd) were added to dimethylformamide (DMF) and refluxed at 120°C. The resulting reaction product was washed with ethanol and then vacuum-dried at 120°C under an argon atmosphere to obtain iron 2,5-dihydroxyterephthalate (Fe2(dobcd)). 50% by mass of the Fe2(dobcd) catalyst was mixed with 45% by mass of carbon black (Ketjen Black, manufactured by Lion Specialty Chemicals Co., Ltd.) as a conductive additive and 5% by mass of polytetrafluoroethylene (PTFE) as a binder. The resulting mixture was molded into a sheet and then punched into a disk (17 mm diameter), which was then pressed onto a stainless steel mesh and used as the positive electrode. A lithium metal plate was used as the negative electrode. The separator used to prevent the electrolyte (ion conducting medium) on the positive and negative electrodes from mixing is made of a Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2 system. + Conductive solid electrolyte sheet (Ohara Corporation's "LICGC" TM The cathode electrolyte (cationically conductive medium) was prepared by dissolving lithium bis(fluorosulfonyl)imide (LiFSI) as a supporting electrolyte in a tetraethylene glycol dimethyl ether (G4) solvent to a concentration of 1.0 mol / L and chlorotrimethylsilane (TMSCl) as an additive in a concentration of 0.5 mol / L. The anode electrolyte (cationically conductive medium) was prepared by dissolving LiFSI as a supporting electrolyte in a G4 solvent to a concentration of 1.0 mol / L.

[0071] Using these, an evaluation cell (nitrogen battery) as shown in Figure 2 was fabricated. That is, a negative electrode 2 was placed on a negative electrode current collector 1, a separator 3 was placed on top of this at a specified distance, and 1.5 ml of a negative electrode-side electrolyte 4 was poured between the negative electrode 2 and the separator 3. A positive electrode 5 was placed on the separator 3, and 0.4 ml of a positive electrode-side electrolyte 6 was poured so that the positive electrode 5 was completely immersed. The positive electrode 5 was pressed down with a SUS spring 7 to fix it on the separator 3, and a positive electrode current collector 8 and a gas cylinder 9 were then placed.

[0072] <Discharge test> The prepared evaluation cell (nitrogen battery) was set in a charge-discharge device (manufactured by Asuka Electronics Co., Ltd., model name 5V / 100MA), nitrogen gas was introduced into the space above the positive electrode 5 at a pressure of 0.05 MPa, and a current density of 0.05 mA / cm was applied between the positive electrode 5 and the negative electrode 2 at a temperature of 25°C. 2 A current was passed through the battery and the battery was discharged until the discharge voltage reached 0.5V.

[0073] Example 2 An evaluation cell (nitrogen battery) was prepared in the same manner as in Example 1, except that the concentration of TMSCl in the positive electrode electrolyte was changed to 1.0 mol / L. Furthermore, a discharge test was performed in the same manner as in Example 1, except that the battery was discharged until the discharge voltage reached 1.0 V.

[0074] Example 3 An evaluation cell (nitrogen battery) was produced in the same manner as in Example 1, except that the concentration of LiFSI in the positive electrode electrolyte was changed to 0.5 mol / L, the solvent of the negative electrode electrolyte was changed to a mixed solvent of 30 vol% ethylene carbonate (EC) and 70 vol% diethyl carbonate (DEC), and the supporting electrolyte of the negative electrode electrolyte was changed to lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Furthermore, the current density was changed to 0.15 mA / cm. 2 A discharge test was carried out in the same manner as in Example 1, except that the above was changed to the following.

[0075] Example 4 An evaluation cell (nitrogen battery) was prepared in the same manner as in Example 3, and the current density was set to 0.05 mA / cm 2 A discharge test was carried out in the same manner as in Example 3, except that the above was changed to the following.

[0076] Example 5 An evaluation cell (nitrogen battery) was prepared in the same manner as in Example 4, except that the positive electrode was changed to a carbon electrode (carbon black / PTFE=95% by mass / 5% by mass) that did not contain a catalyst, and a discharge test was then conducted in the same manner as in Example 4.

[0077] Example 6 An evaluation cell (nitrogen battery) was produced in the same manner as in Example 4, except that TMSCl was not added to the positive electrode electrolyte, and a discharge test was carried out in the same manner as in Example 4, except that the space above the positive electrode 5 was changed to a dry air atmosphere (dew point: −39° C., moisture content: 144 ppm or less).

[0078] Example 7 An evaluation cell (nitrogen battery) was prepared in the same manner as in Example 4, except that TMSCl was not added to the positive electrode electrolyte, and a discharge test was conducted in the same manner as in Example 4, except that the battery was discharged until the discharge voltage reached 1.0 V.

[0079] (Comparative Example 1) An evaluation cell (nitrogen battery) was produced in the same manner as in Example 4, except that the supporting electrolyte of the positive electrode side electrolyte was changed to lithium nitrate (LiNO3). Further, a discharge test was carried out in the same manner as in Example 4.

[0080] (Comparative Example 2) An evaluation cell (nitrogen battery) was produced in the same manner as in Example 6, except that the supporting electrolyte of the positive electrode electrolyte was changed to LiTFSI. Further, a discharge test was carried out in the same manner as in Example 6.

[0081] (Comparative Example 3) An evaluation cell (nitrogen battery) was prepared in the same manner as in Example 4, except that the solvent of the positive electrode electrolyte was changed to a mixed solvent of 30 vol% ethylene carbonate (EC), 40 vol% dimethyl carbonate (DMC), and 30 vol% ethyl methyl carbonate, and the concentration of LiFSI in the positive electrode electrolyte was changed to 1.1 mol / L. Furthermore, a discharge test was performed in the same manner as in Example 4.

[0082] Comparative Example 4 An evaluation cell (nitrogen battery) was produced in the same manner as in Example 4, except that the supporting electrolyte of the positive electrode electrolyte was changed to LiTFSI. Further, a discharge test was carried out in the same manner as in Example 4.

[0083] (Comparative Example 5) An evaluation cell (nitrogen battery) was prepared in the same manner as in Comparative Example 4, except that the positive electrode was changed to a carbon electrode (carbon black / PTFE = 95% by mass / 5% by mass) that did not contain a catalyst, and a discharge test was then conducted in the same manner as in Comparative Example 4.

[0084] (Comparative Example 6) An evaluation cell (nitrogen battery) was produced in the same manner as in Example 4, except that the supporting electrolyte of the positive electrode electrolyte was changed to lithium hexafluorophosphate (LiPF6), and a discharge test was carried out in the same manner as in Example 4.

[0085] Example 8 <Production of evaluation cell (nitrogen battery)> An evaluation cell (nitrogen battery) shown in Figure 2 was fabricated in the same manner as in Example 1, except for the following: Specifically, anhydrous iron chloride (FeCl2) and 2,5-dihydroxyterephthalic acid (dobcd) were added to dimethylformamide (DMF), and a synthesis reaction was carried out under reflux conditions at 120°C. The resulting reaction product was washed with DMF and ethanol and then vacuum-dried at 120°C to obtain iron 2,5-dihydroxyterephthalate (Fe2(dobcd)) in an air atmosphere. 50% by mass of the Fe2(dobcd) was mixed as a positive electrode catalyst, 45% by mass of carbon black (Ketjen Black, manufactured by Lion Specialty Chemicals Co., Ltd.) as a conductive additive, and 5% by mass of polytetrafluoroethylene (PTFE) as a binder. The resulting mixture was molded into a sheet and then punched into a disk (17 mm diameter), which was then pressure-bonded to a SUS mesh and used as the positive electrode. A lithium metal plate was used as the negative electrode. The separator used to prevent the electrolyte (ion conducting medium) on the positive and negative electrodes from mixing is made of a Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2 system. + Conductive solid electrolyte sheet (Ohara Corporation's "LICGC" TMThe cathode electrolyte (cationically conductive medium) was prepared by dissolving lithium bis(fluorosulfonyl)imide (LiFSI) as a supporting electrolyte to a concentration of 1.0 mol / L in tetraethylene glycol dimethyl ether (G4) solvent and chlorotrimethylsilane (TMSCl) as an additive to a concentration of 0.5 mol / L. The anode electrolyte (cationically conductive medium) was prepared by dissolving lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as a supporting electrolyte to a concentration of 1.0 mol / L in a solvent containing ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 50:50.

[0086] <Discharge test> The prepared evaluation cell (nitrogen battery) was set in a charge-discharge device (manufactured by Asuka Electronics Co., Ltd., model name 5V / 100MA), and nitrogen gas or argon gas was introduced into the space above the positive electrode 5 at a pressure of 0.05 MPa. A current density of 0.10 mA / cm was applied between the positive electrode 5 and the negative electrode 2 at a temperature of 25°C. 2 A current was applied to the battery, and the battery was discharged until the discharge voltage reached 1.0 V.

[0087] Example 9 An evaluation cell (nitrogen battery) was produced in the same manner as in Example 8, except that nickel acetate (Ni(CH3COO)2) was used instead of anhydrous iron chloride (FeCl2), and a discharge test was conducted in the same manner as in Example 8.

[0088] Example 10 An evaluation cell (nitrogen battery) was produced in the same manner as in Example 8, except that cobalt acetate (Co(CH3COO)2) was used instead of anhydrous iron chloride (FeCl2), and a discharge test was conducted in the same manner as in Example 8.

[0089] Example 11 An evaluation cell (nitrogen battery) was produced in the same manner as in Example 8, except that manganese acetate (Mn(CH3COO)2) was used instead of anhydrous iron chloride (FeCl2), and a discharge test was conducted in the same manner as in Example 8.

[0090] <Calculation of Capacitance and Energy Density> Based on the discharge test results of the evaluation cells (nitrogen batteries) fabricated in the examples and comparative examples, the relationship (discharge curve) between the capacitance per unit mass of the electrode (positive electrode) and the discharge voltage was determined. The results are shown in FIGS. 3 to 19. Further, based on the discharge curves shown in FIGS. 3 to 19, the capacitance per unit mass and the energy density of the electrode (positive electrode) until the discharge voltage reaches 1.0 V were determined. The results are shown in Tables 1 to 2 and FIGS. 20 to 22.

[0091] <Quantification of Ammonium Ions> 5 ml of a 2 mol / L H2SO4 aqueous solution was added to the electrode (positive electrode) taken out from the evaluation cell (nitrogen battery) after the discharge test. The recovered aqueous solution was filtered using a syringe filter with a pore size of 0.2 μm, and after diluting the filtrate 100-fold, the ammonium ions were quantified using an ion chromatograph (manufactured by Thermo Fisher Scientific Inc., "ICS-5000" + "), and the production amount of ammonium ions per unit area or per unit mass of the electrode (positive electrode) was calculated. The results are shown in Tables 1 to 2 and FIGS. 23 to 24.

[0092] <X-ray Absorption Fine Structure (XAFS) Spectrum Measurement> The K-edge XAFS spectra of the transition metals in the cathode catalyst after discharge testing were measured by transmission spectroscopy using the Toyota Beamline BL33XU at Spring-8. Specifically, the cathode containing the catalyst was removed from the evaluation cell after discharge testing, and the cathode was covered with Kapton tape in a glove box to prepare a measurement sample. Using this measurement sample, the K-edge XAFS spectra of the transition metals in the catalyst were measured using a step scan at 10 min / sample under non-exposed conditions. The results are shown in Figures 25 to 28. The obtained XAFS spectra were normalized and background-subtracted using the XAFS analysis software Athena from Demeter. Figure 25 shows the K-edge XAFS spectra of Fe in FeO, Fe3O4, and α-Fe2O3; Figure 26 shows the K-edge XAFS spectrum of Ni in NiO; Figure 27 shows the K-edge XAFS spectrum of Co in CoO; and Figure 28 shows the K-edge XAFS spectrum of Mn in MnO.

[0093] As shown in FIG. 25, the Fe in the cathode catalyst prepared in Example 8 was found to be in a trivalent state, as its K-edge XAFS spectrum was close to that of trivalent Fe in α-Fe2O3. Furthermore, as shown in FIG. 26, the Ni in the cathode catalyst prepared in Example 9 was found to be in a divalent state, as its K-edge XAFS spectrum was close to that of divalent Ni in NiO. Furthermore, as shown in FIG. 27, the Co in the cathode catalyst prepared in Example 10 was found to be in a divalent state, as its K-edge XAFS spectrum was close to that of divalent Co in CoO. Furthermore, as shown in FIG. 28, the Mn in the cathode catalyst prepared in Example 11 was found to be in a divalent state, as its K-edge XAFS spectrum was close to that of divalent Mn in MnO.

[0094] [Table 1]

[0095] 20-21 and 23, when an electrolyte containing LiFSI and a G4 solvent was used as the positive electrode electrolyte (Examples 1-7), the electric capacity, energy density, and amount of ammonium ion production were all found to be higher than when neither the positive electrode electrolyte nor the negative electrode electrolyte contained LiFSI (Comparative Examples 1-2, 4-6). The reason for this is thought to be that when an electrolyte containing LiFSI and a G4 solvent was used as the positive electrode electrolyte, a plateau region where the discharge curve was flat existed over a wide area, as shown in FIGS. 3-9. However, when neither the positive electrode electrolyte nor the negative electrode electrolyte contained LiFSI (Comparative Examples 1-2, 4-6), the plateau region did not exist or was narrow, as shown in FIGS. 10-11 and 13-15.

[0096] On the other hand, when an electrolyte containing LiFSI and a carbonate-based solvent was used as the positive electrode electrolyte (Comparative Example 3), the electrical capacity and energy density increased compared to when neither the positive electrode nor negative electrode electrolyte contained LiFSI (Comparative Examples 1-2, 4-6), but the amount of ammonium ions produced did not increase, and was significantly reduced compared to when an electrolyte containing LiFSI and a G4 solvent was used as the positive electrode electrolyte (Examples 1-7).

[0097] It was also found that as the LiFSI concentration in the positive electrode electrolyte increased, the electric capacity, energy density, and amount of ammonium ions produced all increased (comparison between Examples 1 and 2 and Examples 4 to 7).

[0098] Furthermore, it was found that when TMSCl was added to the positive electrode electrolyte (Examples 1 to 5), the amount of ammonium ions produced increased compared to when TMSCl was not added (Examples 6 to 7).

[0099] Furthermore, even when carbon was used as the positive electrode, it was found that when LiFSI was used as the supporting electrolyte of the positive electrode-side electrolyte (Example 5), the electrical capacity, energy density, and amount of ammonium ions produced all increased compared to when LiTFSI was used (Comparative Example 5).

[0100] Furthermore, even when dry air was introduced into the positive electrode, it was found that when LiFSI was used as the supporting electrolyte of the positive electrode side electrolyte (Example 6), the electric capacity, energy density, and amount of ammonium ions produced all increased compared to when LiTFSI was used (Comparative Example 2).

[0101] [Table 2]

[0102] 22 and 24, when any of the transition metals Fe, Ni, Co, and Mn was used (Examples 8 to 11), the nitrogen batteries using nitrogen as the positive electrode active material exhibited high values ​​for the electric capacity and the amount of ammonium ion production, but when Fe was used (Example 8), it was found that the values ​​were particularly high compared to when Ni, Co, or Mn was used (Examples 9 to 11). This is thought to be because, as shown in Table 2, when Fe was used (Example 8), the difference between the amount of ammonium ion produced in a nitrogen atmosphere and the amount of ammonium ion produced in an argon atmosphere was larger compared to when Ni, Co, or Mn was used (Examples 9 to 11), and therefore the reduction reaction of nitrogen derived from nitrogen gas proceeded efficiently. The reasons why the reduction reaction of nitrogen derived from nitrogen gas proceeded efficiently when Fe was used are as follows: (1) when Fe was used, as shown in FIG. 16, the plateau potential at which the discharge curve becomes flat is higher in a nitrogen atmosphere than in an argon atmosphere, whereas when Ni, Co, or Mn was used, as shown in FIGS. 17 to 19, the plateau potentials in a nitrogen atmosphere and an argon atmosphere were similar; (2) as is clear from a comparison of FIG. 16 with FIGS. 17 to 19, when Fe was used, the plateau region was wider than when Ni, Co, or Mn was used; and (3) as shown in Table 2 and FIGS. 25 to 28, in the positive electrode catalyst, Ni, Co, and Mn are divalent, whereas Fe is trivalent. Therefore, Fe serves as a nitrogen adsorption site (open metal site), which is thought to catalytically reduce nitrogen derived from nitrogen gas. [Industrial Applicability]

[0103] As described above, according to the present invention, it is possible to obtain a nitrogen battery having a high electric capacity and a high energy density. Therefore, the nitrogen battery of the present invention is useful as a novel nitrogen battery that can be used as an energy device.

[0104] Furthermore, since the fuel synthesis apparatus and method of the present invention use a nitrogen battery having such a high electric capacity and high energy density, it is possible to efficiently reduce nitrogen, efficiently synthesize a nitrogen reduction reaction product, and highly efficiently obtain ammonia. Therefore, the fuel synthesis apparatus and fuel synthesis method of the present invention are useful as an apparatus and method capable of supplying ammonia as a fuel. [Explanation of symbols]

[0105] 1: Negative electrode current collector 2: Negative electrode 3: Separator 4: Negative electrode side electrolyte 5: Positive electrode 6: Positive electrode electrolyte 7: Spring 8: Positive electrode current collector 9: Gas cylinder 10: Connection

Claims

1. a positive electrode having nitrogen as a positive electrode active material; a negative electrode; an ion-conducting medium that contains lithium bis(fluorosulfonyl)imide as at least a supporting electrolyte for the positive electrode and an ether as a solvent present at least on the positive electrode side, and that conducts alkali metal ions; Nitrogen battery with

2. 2. The nitrogen battery according to claim 1, wherein the ether present as the solvent on the positive electrode side is a polyethylene glycol ether.

3. 2. The nitrogen battery according to claim 1, wherein the ion-conducting medium further contains a silane compound as an additive at least on the positive electrode side.

4. the ion conductive medium includes a positive electrode side ion conductive medium present on the positive electrode side and in contact with the positive electrode, and a negative electrode side ion conductive medium present on the negative electrode side and in contact with the negative electrode, the positive electrode-side ion-conducting medium contains lithium bis(fluorosulfonyl)imide as a supporting electrolyte for the positive electrode and an ether as a solvent present on the positive electrode side; 2. The nitrogen battery according to claim 1, wherein the negative electrode side ion conducting medium contains lithium bis(fluorosulfonyl)imide as a supporting electrolyte of the negative electrode and contains an ether as a solvent present on the negative electrode side.

5. 5. The nitrogen battery according to claim 4, wherein the ether as the solvent present on the positive electrode side and the ether as the solvent present on the negative electrode side are both polyethylene glycol ethers.

6. 2. The nitrogen battery according to claim 1, wherein the positive electrode comprises an electrode catalyst having a transition metal ion immobilized thereon.

7. The nitrogen battery according to claim 6, wherein the electrode catalyst is a metal-organic framework containing a transition metal ion and an aromatic polycarboxylic acid ion.

8. The transition metal ion is an Fe ion, and the aromatic polycarboxylic acid ion is represented by the following formula (1): 【Chemical 1】 [wherein R １ represents a tetravalent organic group containing an aromatic ring, and X represents O or S. The nitrogen battery according to claim 7, wherein the aromatic dicarboxylic acid ion is represented by the formula:

9. 9. The nitrogen battery according to claim 8, wherein at least a portion of the Fe ions are trivalent Fe ions.

10. A fuel synthesis device using the nitrogen cell according to any one of claims 1 to 9, A fuel synthesis device for obtaining ammonia as fuel by treating a nitrogen reduction reaction product obtained after operation of the nitrogen cell with water.

11. A method for synthesizing fuel using the nitrogen fuel cell according to any one of claims 1 to 9, A method for synthesizing fuel, comprising treating a nitrogen reduction reaction product obtained after operation of the nitrogen cell with water to produce ammonia, which is then used as fuel.

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