Non-aqueous magnesium battery

Abstract

This nonaqueous magnesium battery is provided with a positive electrode, a negative electrode, and an electrolyte. The positive electrode contains a positive electrode active material and is capable of occluding and releasing magnesium ions. An electrolytic solution contains a magnesium salt. The positive electrode active material contains nickel oxyhydroxide, and the nickel oxyhydroxide is formed in a layered shape.

Description

[Technical Field]

[0001] The present disclosure relates to non-aqueous magnesium batteries. [Background technology]

[0002] In recent years, research into non-aqueous magnesium batteries has been attracting attention.

[0003] Non-Patent Document 1 describes a magnesium battery using Mo6S8 having a Chevrel phase as the positive electrode active material. Non-Patent Document 2 describes a magnesium battery using V2O5 as the positive electrode active material. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Journal of The Electrochemical Society, 2014, Vol.161, No.4, p.A593-A598 [Non-patent document 2] Nature Chemistry, 2018, Vol.10, p.532-539 Summary of the Invention [Problem to be solved by the invention]

[0005] The present disclosure provides a non-aqueous magnesium battery with a high reaction potential and a high reversible capacity. [Means for solving the problem]

[0006] The present disclosure provides: Positive electrode active material include A positive electrode and a negative electrode; Contains magnesium salts non-aqueous an electrolyte; the positive electrode active material contains nickel oxyhydroxide, The nickel oxyhydroxide is Magnesium ions can be absorbed and released between the layers Na It is layered, A non-aqueous magnesium battery is provided. [Effects of the Invention]

[0007] According to the present disclosure, a non-aqueous magnesium battery having a high reaction potential and a high reversible capacity can be provided. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view schematically showing an example of the configuration of a nonaqueous magnesium battery. [Figure 2A] FIG. 2A is a diagram showing the results of powder X-ray diffraction measurement of the positive electrode active material according to Example 1. FIG. [Figure 2B] FIG. 2B shows the results of powder X-ray diffraction of γ-NiOOH obtained by simulation. [Figure 3] FIG. 3 is a schematic diagram showing a schematic configuration of a beaker cell according to an embodiment. [Figure 4] FIG. 4 is a graph showing the results of a charge-discharge test of the nonaqueous magnesium battery according to Example 1. [Figure 5A] FIG. 5A is a diagram showing the results of powder X-ray diffraction measurement of the positive electrode active material according to Example 2. FIG. [Figure 5B] FIG. 5B shows the results of powder X-ray diffraction of γ-NiOOH obtained by simulation. [Figure 5C] FIG. 5C shows the results of powder X-ray diffraction of β-NiOOH obtained by simulation. [Figure 6] FIG. 6 is a graph showing the results of a charge-discharge test of the nonaqueous magnesium battery according to Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0009] (Findings that led to the present disclosure) In recent years, multivalent ion batteries using multivalent ions as carriers have been actively researched. An example of a multivalent ion battery is Ca2+ Calcium battery using Be as a carrier 2+ Beryllium battery with Mn as carrier, 2+ Manganese battery with Ni as carrier 2+ Nickel battery with Zn as carrier, 2+ Zinc battery with carrier, Y 3+ Yttrium battery with Al as carrier, 3+ Aluminum batteries with Mg as the carrier, 2+ This is a non-aqueous magnesium battery that uses a carrier. Recently, research into non-aqueous magnesium batteries has been attracting attention.

[0010] Magnesium has a large theoretical capacity per unit mass and a large theoretical capacity per unit volume. Magnesium also exhibits a relatively low oxidation-reduction potential. Therefore, batteries using magnesium as the negative electrode are expected to have a high energy density. In particular, the theoretical capacity per unit volume of magnesium is higher than that of lithium. Therefore, non-aqueous magnesium batteries enable the installation of large-capacity batteries in limited spaces, such as electric vehicles. Furthermore, magnesium reserves in the earth's crust are greater than those of lithium. Therefore, non-aqueous magnesium batteries are less susceptible to the resource depletion and cost issues that are the drawbacks of lithium-ion batteries.

[0011] The melting point of magnesium is approximately 650°C. The melting point of lithium is approximately 180°C. The melting point of sodium is approximately 98°C. The melting point of magnesium is much higher than that of lithium and sodium. Because the melting point is an indicator of the stability of a metal, using magnesium in a battery can improve the safety of the battery. Furthermore, lithium and sodium react violently with, for example, moisture in the air. On the other hand, magnesium is stable in air and can be easily handled. For these reasons, non-aqueous magnesium batteries are being actively researched as an alternative to lithium-ion batteries.

[0012] However, there are many challenges to overcome in order to realize multivalent ion batteries such as nonaqueous magnesium batteries. The development of positive electrode materials is particularly important. The Coulombic interaction between multivalent ions and anions contained in the positive electrode material is stronger than the Coulombic interaction between lithium ions and anions contained in the positive electrode material. Therefore, the diffusion rate of multivalent ions in the positive electrode material is slower than that of lithium ions. This can be a major factor limiting the reaction in multivalent ion batteries.

[0013] Non-Patent Document 1 discloses a compound containing a soft base such as sulfur ion and having a Chevrel phase. According to Non-Patent Document 1, the reaction potential and reversible capacity of this compound are about 1.1 V and about 116 mAh / g, respectively. The reaction potential and reversible capacity of this compound cannot be said to be high.

[0014] Non-Patent Document 2 discloses a positive electrode containing the oxide V2O5. According to Non-Patent Document 2, the reaction potential and reversible capacity of this compound are approximately 1.5 V and approximately 75 mAh / g, respectively. Although the reaction potential of V2O5 is higher than that of the compound described in Non-Patent Document 1, it is difficult to say that the reversible capacity of V2O5 is high.

[0015] From the above viewpoints, there is a need to develop a positive electrode material for magnesium batteries that has an excellent diffusion rate of magnesium ions, a high reversible capacity, and a high reaction potential.

[0016] As a result of extensive research, the present inventors have discovered that the above-mentioned problems can be solved by using a compound having a specific composition, and have thus completed the present disclosure.

[0017] (Summary of one aspect of the present disclosure) The nonaqueous magnesium battery according to the first embodiment of the present disclosure includes: a positive electrode including a positive electrode active material and capable of absorbing and releasing magnesium ions; a negative electrode; It includes an electrolyte containing a magnesium salt. The positive electrode active material contains nickel oxyhydroxide, and the nickel oxyhydroxide is layered.

[0018] According to the first aspect, a non-aqueous magnesium battery having a high reaction potential and a high reversible capacity can be provided.

[0019] In the second aspect of the present disclosure, for example, in the non-aqueous magnesium battery according to the first aspect, the nickel oxyhydroxide may contain a compound represented by the composition formula of NiOOH x and may satisfy 0 < x ≦ 1. x may be 0.3 or more and 1 or less.

[0020] In the third aspect of the present disclosure, for example, in the non-aqueous magnesium battery according to the second aspect, the nickel oxyhydroxide may contain a compound represented by the composition formula of NiOOH x and may satisfy 0 < x < 1. x may be 0.3 or more and less than 1.

[0021] In the fourth aspect of the present disclosure, for example, in the non-aqueous magnesium battery according to the first aspect, the nickel oxyhydroxide may contain γ-NiOOH.

[0022] According to the second to fourth aspects, a non-aqueous magnesium battery having a more reliable high reaction potential and a more reliable high reversible capacity can be provided.

[0023] In the fifth aspect of the present disclosure, for example, in the non-aqueous magnesium battery according to any one of the first to fourth aspects, the negative electrode may contain metallic magnesium.

[0024] In the sixth aspect of the present disclosure, for example, in the non-aqueous magnesium battery according to the first to fourth aspects, the negative electrode may contain a negative electrode active material that occludes and releases magnesium ions.

[0025] According to the fifth and sixth aspects, it is possible to provide a nonaqueous magnesium battery that has a more reliably high reaction potential and a more reliably high reversible capacity.

[0026] Hereinafter, a positive electrode active material according to an embodiment and a nonaqueous magnesium battery using the same will be described in detail with reference to the drawings.

[0027] The following descriptions are all comprehensive or provide specific examples. The numerical values, compositions, shapes, film thicknesses, electrical characteristics, and secondary battery structures shown below are merely examples and are not intended to limit the present disclosure. In addition, any components not described in an independent claim showing a top concept are optional components.

[0028] [1. Positive electrode active material] Non-aqueous magnesium batteries are expected to be put to practical use as high-capacity batteries because they can utilize the two-electron reaction of magnesium. However, the strong interaction between divalent magnesium ions and anions in the active material makes it difficult for magnesium ions to move within the active material, making it difficult for electrode reactions in the active material to proceed.

[0029] In response to this, the present inventors have conducted extensive research and have found the following novel positive electrode active material.

[0030] The nonaqueous magnesium battery according to this embodiment includes a positive electrode containing a positive electrode active material, a negative electrode, and an electrolyte. The positive electrode is capable of absorbing and releasing magnesium ions. The electrolyte has, for example, magnesium ion conductivity. In the nonaqueous magnesium battery according to this embodiment, the positive electrode active material includes layered nickel oxyhydroxide. The positive electrode may contain only layered nickel oxyhydroxide as the positive electrode active material, or may also contain other compounds. The layered nickel oxyhydroxide can absorb and release magnesium ions, for example, between the layers of the nickel oxyhydroxide. This allows the nonaqueous magnesium battery to have a high reaction potential and a high reversible capacity.

[0031] The content of layered nickel oxyhydroxide in the positive electrode active material is not limited to a specific value. By appropriately adjusting the content of layered nickel oxyhydroxide, the non-aqueous magnesium battery can have a high reaction potential and a high reversible capacity.

[0032] Layered nickel oxyhydroxide is represented by the composition formula of NiOOH x and may contain a compound satisfying 0 < x ≦ 1. Layered nickel oxyhydroxide may contain only a compound represented by the composition formula of NiOOH x and satisfying 0 < x ≦ 1.

[0033] Alternatively, layered nickel oxyhydroxide is represented by the composition formula of NiOOH x and may contain a compound satisfying 0 < x < 1. Layered nickel oxyhydroxide may contain only a compound represented by the composition formula of NiOOH x and satisfying 0 < x < 1.

[0034] Layered nickel oxyhydroxide may contain γ-NiOOH. γ-NiOOH is a γ-type nickel oxyhydroxide. In γ-NiOOH, for example, the oxidation number of Ni is 3.0 or more and 3.7 or less. According to such a configuration, the non-aqueous magnesium battery can more surely have a high reaction potential and more surely have a high reversible capacity. Incidentally, γ-NiOOH can be obtained, for example, by oxidizing β-NiOOH described later.

[0035] Layered nickel oxyhydroxide may contain β-NiOOH. β-NiOOH is a β-type nickel oxyhydroxide. In β-NiOOH, for example, the oxidation number of Ni is 3.0 or more and 3.7 or less.

[0036] The layered nickel oxyhydroxide may contain γ-NiOOH and β-NiOOH. With this configuration, the nonaqueous magnesium battery can have a more reliably high reaction potential and a more reliably high reversible capacity. The contents of γ-NiOOH and β-NiOOH contained in the positive electrode active material are not limited to specific values. By appropriately adjusting the contents of γ-NiOOH and β-NiOOH contained in the positive electrode active material, the nonaqueous magnesium battery can have a more reliably high reaction potential and a more reliably high reversible capacity.

[0037] In the positive electrode active material, the content of γ-NiOOH may be higher than the content of β-NiOOH. Generally, the oxidation number of nickel in γ-NiOOH is definitely higher than the oxidation number of nickel in β-NiOOH. Therefore, the number of reaction electrons in γ-NiOOH is more than the number of reaction electrons in β-NiOOH. By having a higher content of γ-NiOOH than the content of β-NiOOH, the nonaqueous magnesium battery can have a more reliably high reaction potential and a more reliably high reversible capacity.

[0038] The positive electrode active material may contain γ-NiOOH as a main component. γ-NiOOH has a high Ni oxidation number among nickel oxyhydroxides. Therefore, by including γ-NiOOH as a main component in the positive electrode active material, the nonaqueous magnesium battery can more reliably have a high reaction potential and a high reversible capacity. In the present disclosure, the term "main component" refers to the component that is contained in the largest amount by mass in the positive electrode active material.

[0039] The positive electrode active material may contain only γ-NiOOH, which allows the nonaqueous magnesium battery to have a more reliably high reaction potential and a more reliably high reversible capacity.

[0040] [2. Method for producing positive electrode active material] The positive electrode active material according to this embodiment is produced, for example, by oxidizing nickel (II) hydroxide.

[0041] For example, an alkaline aqueous solution is used for the oxidation treatment. The alkaline aqueous solution can be obtained by mixing an aqueous solution of sodium hypochlorite and an aqueous solution of potassium hydroxide and stirring the mixture at 80° C. For example, a hot stirrer is used for stirring.

[0042] Next, for example, nickel (II) hydroxide powder manufactured by Kojundo Chemical Laboratory Co., Ltd. is added to the alkaline aqueous solution, and the mixture is stirred at 80°C to oxidize the nickel, thereby preparing a nickel oxyhydroxide-containing solution. For example, a hot stirrer is used for stirring.

[0043] The nickel oxyhydroxide-containing solution after stirring contains a precipitate and a supernatant liquid. Therefore, the supernatant liquid is removed from the nickel oxyhydroxide-containing solution and replaced with water to obtain a mixed solution. Thereafter, the mixed solution is allowed to stand.

[0044] The time for leaving the mixture to stand is, for example, 1 hour to 100 hours. After leaving the mixture to stand, the water is removed from the mixture by suction filtration under reduced pressure to obtain a solid. For example, a vacuum pump is used for the suction filtration.

[0045] The solid is washed with water. For example, suction filtration is used for washing. When the pH of the solution obtained by suction filtration is 7 or more and 14 or less, washing of the solid is completed.

[0046] Next, the washed solid is vacuum dried at 60°C to remove moisture from the solid. The dried solid is pulverized and sized to obtain layered nickel oxyhydroxide. For example, a mortar is used to pulverize the solid. For example, a sieve is used to sieve the solid.

[0047] The composition of the layered nickel oxyhydroxide can be determined, for example, by inductively coupled plasma (ICP) atomic emission spectroscopy, and the crystal structure of the layered nickel oxyhydroxide can be determined, for example, by powder X-ray diffraction.

[0048] In the layered nickel oxyhydroxide, the oxidation number of nickel, which is a transition metal, can be determined, for example, by X-ray absorption fine structure (XAFS) analysis using a synchrotron radiation beamline.

[0049] [3. Magnesium battery] [3-1. Overall composition] The positive electrode active material according to this embodiment can be used in a non-aqueous magnesium battery. The non-aqueous magnesium battery includes a positive electrode containing the positive electrode active material, a negative electrode, and an electrolyte having magnesium ion conductivity. The electrolyte contains, for example, a magnesium salt.

[0050] FIG. 1 is a cross-sectional view schematically showing an example of the configuration of a nonaqueous magnesium battery 10. As shown in FIG.

[0051] The nonaqueous magnesium battery 10 includes a positive electrode 21, a negative electrode 22, a separator 14, a case 11, a sealing plate 15, and a gasket 18. The separator 14 is disposed between the positive electrode 21 and the negative electrode 22. The positive electrode 21, the negative electrode 22, and the separator 14 are impregnated with a nonaqueous electrolyte solution, and are housed in the case 11. The case 11 is closed by the gasket 18 and the sealing plate 15.

[0052] The case 11 houses the positive electrode 21, the negative electrode 22, and the separator 14. The shape and material of the case 11 are not limited to a particular embodiment. The case 11 is not limited to the one shown in FIG. 1 , and any known battery case can be appropriately selected and used.

[0053] The structure of the nonaqueous magnesium battery 10 may be cylindrical, square, button, coin, or flat.

[0054] [3-2. Positive electrode] The positive electrode 21 includes a positive electrode current collector 12 and a positive electrode active material layer 13 disposed on the positive electrode current collector 12. The positive electrode active material layer 13 is disposed between the positive electrode current collector 12 and a separator 14.

[0055] The positive electrode active material layer 13 contains the positive electrode active material described above in [1. Positive electrode active material]. With this configuration, it is possible to provide a positive electrode for a nonaqueous magnesium battery having a high reversible capacity, a high reaction potential, and a high energy density.

[0056] The positive electrode active material layer 13 may further contain at least one of a conductive material and a binder, if necessary.

[0057] Examples of conductive materials include carbon materials, metals, inorganic compounds, and conductive polymers. Examples of carbon materials include graphite, acetylene black, carbon black, ketjen black, carbon whiskers, needle coke, and carbon fibers. Examples of graphite include natural graphite and artificial graphite. Examples of natural graphite include block graphite and flake graphite. Examples of metals include copper, nickel, aluminum, silver, and gold. Examples of inorganic compounds include tungsten carbide, titanium carbide, tantalum carbide, molybdenum carbide, titanium boride, and titanium nitride. These materials may be used alone or in combination.

[0058] Examples of binders include fluorine-containing resins, thermoplastic resins, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, and natural butyl rubber (NBR). Examples of fluorine-containing resins include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluororubber. Examples of thermoplastic resins include polypropylene and polyethylene. These materials may be used alone or in combination.

[0059] Examples of solvents for dispersing the positive electrode active material, conductive material, and binder include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran. A thickener may be added to the dispersant. Examples of thickeners include carboxymethyl cellulose and methyl cellulose.

[0060] The positive electrode active material layer 13 is formed, for example, by the following method. First, a positive electrode active material, a conductive material, and a binder are mixed to obtain a mixture of these materials. Next, an appropriate solvent is added to this mixture to obtain a paste-like positive electrode mixture. Next, this positive electrode mixture is applied to the surface of the positive electrode current collector 12 and dried. In this way, the positive electrode active material layer 13 is formed on the positive electrode current collector 12. The positive electrode active material layer 13 may be compressed to increase the electrode density.

[0061] The thickness of the positive electrode active material layer 13 is not limited to a particular value and is, for example, 1 μm or more and 100 μm or less.

[0062] The material of the positive electrode current collector 12 is, for example, a simple metal or an alloy. More specifically, the material of the positive electrode current collector 12 may be a simple metal or an alloy containing at least one selected from the group consisting of copper, chromium, nickel, titanium, platinum, gold, aluminum, tungsten, iron, and molybdenum. The material of the positive electrode current collector 12 may also be stainless steel.

[0063] The positive electrode current collector 12 may be in the form of a plate or foil. The positive electrode current collector 12 may be a laminated film.

[0064] When the case 11 also serves as a positive electrode current collector, the positive electrode current collector 12 may be omitted.

[0065] [3-3. Negative electrode] The negative electrode 22 includes, for example, a negative electrode active material layer 17 containing a negative electrode active material, and a negative electrode current collector 16. The negative electrode active material layer 17 is disposed between the negative electrode current collector 16 and the separator .

[0066] The negative electrode 22 contains a negative electrode active material capable of absorbing and releasing magnesium ions. That is, the negative electrode active material layer 17 contains a negative electrode active material capable of absorbing and releasing magnesium ions. An example of the negative electrode active material is a carbon material. Examples of the carbon material are graphite, non-graphite carbon, and graphite intercalation compounds. Examples of the non-graphite carbon are hard carbon and coke.

[0067] The negative electrode active material layer 17 may further contain at least one of a conductive material and a binder, as necessary. The conductive material, binder, solvent, and thickener may be, for example, the conductive material, binder, solvent, and thickener described in [3-2. Positive electrode].

[0068] The thickness of the negative electrode active material layer 17 is not limited to a particular value and is, for example, 1 μm or more and 50 μm or less.

[0069] Alternatively, the negative electrode active material layer 17 contains a negative electrode active material capable of depositing and dissolving magnesium. In this case, examples of the negative electrode active material include metallic magnesium and magnesium alloys. The magnesium alloy is, for example, an alloy of magnesium with at least one element selected from the group consisting of aluminum, silicon, gallium, zinc, tin, manganese, bismuth, and antimony.

[0070] The material of the negative electrode current collector 16 may be, for example, the same material as that of the positive electrode current collector 12 described in [3-2. Positive electrode]. The negative electrode current collector 16 may be in the form of a plate or foil.

[0071] When the sealing plate 15 also serves as the negative electrode current collector, the negative electrode current collector 16 may be omitted.

[0072] When the negative electrode current collector 16 is made of a material that can deposit and dissolve magnesium on its surface, the negative electrode active material layer 17 may be omitted. That is, the negative electrode 22 may be made of only the negative electrode current collector 16 that can deposit and dissolve magnesium. In this case, the negative electrode current collector 16 may be made of stainless steel, nickel, copper, or iron.

[0073] [3-4. Separator] Examples of materials for the separator 14 include a microporous thin film, a woven fabric, and a nonwoven fabric. The material for the separator 14 may be a polyolefin such as polypropylene or polyethylene. The thickness of the separator 14 is, for example, 10 μm or more and 300 μm or less. The separator 14 may be a single-layer film made of one material, or a composite film or multi-layer film made of two or more materials. The porosity of the separator 14 is, for example, 30% or more and 70% or less.

[0074] [3-5. Electrolytes] The electrolyte can be a material that has magnesium ion conductivity.

[0075] The electrolyte is, for example, a non-aqueous electrolyte solution that includes a non-aqueous solvent and a magnesium salt dissolved in the non-aqueous solvent.

[0076] Examples of the non-aqueous solvent include cyclic ethers, chain ethers, cyclic carbonates, chain carbonates, cyclic carboxylates, chain carboxylates, pyrocarbonates, phosphates, borates, sulfates, sulfites, cyclic sulfones, chain sulfones, nitriles, and sultones.

[0077] Examples of cyclic ethers are 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, crown ethers, and derivatives thereof.

[0078] Examples of the chain ethers include 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and derivatives thereof.

[0079] Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,4,4-trifluoroethylene carbonate, fluoromethylethylene carbonate, trifluoromethylethylene carbonate, 4-fluoropropylene carbonate, 5-fluoropropylene carbonate, and derivatives thereof.

[0080] Examples of the chain carbonate ester include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, and derivatives thereof.

[0081] Examples of cyclic carboxylic acid esters are γ-butyrolactone, γ-valerolactone, γ-caprolactone, ε-caprolactone, α-acetolactone, and derivatives thereof.

[0082] Examples of the chain carboxylic acid ester are methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, and derivatives thereof.

[0083] Examples of pyrocarbonate esters are diethylpyrocarbonate, dimethylpyrocarbonate, di-tert-butyldicarbonate, and derivatives thereof. Examples of phosphate esters are trimethylphosphate, triethylphosphate, hexamethylphosphoramide, and derivatives thereof. Examples of borate esters are trimethylborate, triethylborate, and derivatives thereof. Examples of sulfate esters are trimethylsulfate, triethylsulfate, and derivatives thereof. Examples of sulfite esters are ethylene sulfite and derivatives thereof.

[0084] Examples of cyclic sulfones include sulfolane and its derivatives. Examples of linear sulfones include alkyl sulfones and their derivatives. Examples of nitriles include acetonitrile, valeronitrile, propionitrile, trimethylacetonitrile, cyclopentanecarbonitrile, adiponitrile, pimelonitrile, and their derivatives. Examples of sultones include 1,3-propane sultone and its derivatives.

[0085] As the solvent, only one of the above substances may be used, or two or more of them may be used in combination.

[0086] Examples of magnesium salts are MgBr2, MgI2, MgCl2, Mg(AsF6)2, Mg(ClO4)2, Mg(PF6)2, Mg(BF4)2, Mg(CF3SO3)2, Mg[N(CF3SO2)2]2, Mg(SbF6)2, Mg(SiF6)2, Mg[C(CF3SO2)3]2, Mg[N(FSO2)2]2, Mg[N(C2F5SO2)2]2, MgB 10 Cl 10 , MgB 12 Cl 12, Mg[B(C6F5)4]2, Mg[B(C6H5)4]2, Mg[N(SO2CF2CF3)2]2, Mg[BF3C2F5]2, Mg[PF3(CF2CF3)3]2, and Mg[B(OCH(CF3)2)4]2. As the magnesium salt, only one of the above substances may be used, or two or more may be used in combination.

[0087] The electrolyte may be a solid electrolyte. In this case, an example of the solid electrolyte is Mg 2-1.5x Al x SiO4, Mg 2-1.5y-0.5z Al y-z Zn z SiO4, MgZr4(PO4)6, MgM1PO4, Mg 1-a M2 a M3(M4O4)3 and Mg(BH4)(NH2). x satisfies 0.1≦x≦1. y satisfies 0.5≦y≦1. z satisfies 0.5≦z≦0.9. yz satisfies yz≧0. y+z satisfies y+z≦1. M1 is at least one selected from the group consisting of Zr, Nb, and Hf. M2 is at least one selected from the group consisting of Ca, Sr, Ba, and Ra. M3 is at least one selected from Zr and Hf. M4 is at least one selected from W and Mo. a satisfies 0≦a<1. [Example]

[0088] [Example 1] (Production of positive electrode active material) A mixed solution was prepared by adding 87 mL of a 10% by mass aqueous solution of sodium hypochlorite and 30 mL of a 48% by mass aqueous solution of potassium hydroxide to a glass beaker. The mixed solution was stirred at 80°C using a hot stirrer to obtain an alkaline aqueous solution.

[0089] Next, 6 g of nickel (II) hydroxide powder manufactured by Kojundo Chemical Laboratory Co., Ltd. was added to the alkaline aqueous solution to prepare a mixture. This mixture was stirred at 80°C for 1 hour using a hot stirrer to prepare a nickel oxyhydroxide-containing solution. The nickel oxyhydroxide-containing solution contains a precipitate and a supernatant liquid.

[0090] Next, the supernatant was removed from the nickel oxyhydroxide-containing solution, and water was added. This operation was repeated twice to obtain a mixed solution.

[0091] The mixture was allowed to stand for 60 hours, and then water was removed from the mixture by suction filtration under reduced pressure using a vacuum pump to obtain a solid.

[0092] The solid was washed with water and then vacuum-dried for 12 hours at 60° C. The dried solid was pulverized and sized to obtain the positive electrode active material of Example 1.

[0093] The crystal structure of the positive electrode active material according to Example 1 was identified by analyzing the X-ray diffraction pattern using an X-ray diffractometer MiNi Flex manufactured by Rigaku Corporation.

[0094] FIG. 2A shows the results of powder X-ray diffraction measurement of the positive electrode active material according to Example 1. FIG. 2B shows the results of powder X-ray diffraction of γ-NiOOH obtained by simulation. As shown in FIGS. 2A and 2B, the results of powder X-ray diffraction measurement of the positive electrode active material according to Example 1 closely matched the results of the simulation of the powder X-ray diffraction spectrum of γ-NiOOH. These results confirmed that high-purity γ-NiOOH powder was synthesized.

[0095] (Fabrication of non-aqueous magnesium battery) FIG. 3 is a schematic diagram showing a schematic configuration of the beaker cell according to the first embodiment.

[0096] The beaker cell 30 includes a positive electrode 31, a negative electrode 34, and a non-aqueous electrolyte 35. The non-aqueous electrolyte 35 is stored in a beaker. The positive electrode 31 includes a mesh 32 and a positive electrode mixture 33. The positive electrode mixture 33 is disposed at the tip of the mesh 32. The positive electrode 31 and the negative electrode 34 are immersed in the non-aqueous electrolyte 35.

[0097] The positive electrode active material according to Example 1, acetylene black, and polytetrafluoroethylene were weighed out in a mass ratio of 8:1:1. The weighed raw materials were mixed in a mortar to obtain a positive electrode mixture. The positive electrode mixture was punched out into a 5 mm x 5 mm square. The punched positive electrode mixture was placed on the tip of a 5 mm x 30 mm mesh 32 and pressed with a pressure of 5 MPa. The mesh 32 was made of aluminum. This yielded a positive electrode 31 according to Example 1. The positive electrode 31 was dried under vacuum at 105°C for 6 hours or more.

[0098] A magnesium ribbon with a thickness of 300 μm was cut into a size of 5 mm × 40 mm to obtain a magnesium foil. The surface of the magnesium foil was scraped to remove the oxide film, and the surface was washed with acetone. This resulted in a negative electrode 34.

[0099] Non-aqueous electrolyte 35 was stored in a glass beaker. 1,2-dimethoxyethane (DME) was used as the non-aqueous solvent for non-aqueous electrolyte 35. Mg[B(OCH(CF3)2)4]2·3DME, an organoboron ate complex salt in which 1,2-dimethoxyethane is coordinated, was dissolved in 1,2-dimethoxyethane at a concentration of 0.3 mol / L to obtain non-aqueous electrolyte 35.

[0100] A positive electrode 31 and a negative electrode 34 were immersed in a non-aqueous electrolyte 35 to prepare a beaker cell 30 having the configuration shown in Fig. 3. The non-aqueous magnesium battery was prepared in an argon atmosphere.

[0101] (Charge / discharge test) A charge-discharge test of the fabricated non-aqueous magnesium battery was carried out in an argon atmosphere at a temperature of 60°C.

[0102] FIG. 4 is a graph showing the results of a discharge and charge test of the nonaqueous magnesium battery according to Example 1.

[0103] A charge / discharge test was performed using a charge / discharge device VSP-300 manufactured by Bio-Logic. First, it was assumed that the crystalline structure of the positive electrode active material according to Example 1 was a single phase of nickel oxyhydroxide (NiOOH). The capacity of the positive electrode active material according to Example 1 was assumed to be 461 mAh / g. In this case, the nonaqueous magnesium battery according to Example 1 was discharged at a C-rate of 0.01. Specifically, the nonaqueous magnesium battery according to Example 1 was discharged at a discharge cut-off voltage of 1.0 V. The discharge capacity in the first cycle was 226 mAh / g. After discharge, an open circuit state was maintained for 5 hours. Next, the nonaqueous magnesium battery according to Example 1 was charged at a C-rate of 0.01. The charge capacity in the first cycle was 226 mAh / g. The charge / discharge reaction was confirmed by the above charge / discharge test. After the first cycle of charging, the nonaqueous magnesium battery according to Example 1 was discharged again. The discharge capacity in the second cycle was 26 mAh / g. The discharge capacity in the second cycle was reduced compared to the discharge capacity in the first cycle. This is thought to be because the charge capacity in the first cycle includes the capacity due to oxidative decomposition of the electrolyte. In Example 1, the reaction potential, which is the average value of the charge potential and the discharge potential, was approximately 2.7 V.

[0104] [Example 2] (Production of positive electrode active material) The mixture was stirred for 30 minutes using a hot stirrer to prepare a nickel oxyhydroxide-containing solution, and the positive electrode active material of Example 2 was obtained in the same manner as in Example 1, except that the nickel oxyhydroxide-containing solution was prepared.

[0105] The crystal structure of the positive electrode active material according to Example 2 was identified by analyzing the X-ray diffraction pattern using an X-ray diffractometer MiNi Flex manufactured by Rigaku Corporation.

[0106] FIG. 5A shows the results of powder X-ray diffraction measurement of the positive electrode active material according to Example 2. FIG. 5B shows the results of powder X-ray diffraction of γ-NiOOH obtained by simulation. FIG. 5C shows the results of powder X-ray diffraction of β-NiOOH obtained by simulation. As shown in FIGS. 5A to 5C, the results of powder X-ray diffraction measurement of the positive electrode active material according to Example 2 closely matched the results of the simulation of the powder X-ray diffraction spectrum of γ-NiOOH and the results of the simulation of the powder X-ray diffraction spectrum of β-NiOOH. These results confirmed that a powder containing γ-NiOOH and β-NiOOH was synthesized in Example 2.

[0107] (Fabrication of non-aqueous magnesium battery) A nonaqueous magnesium battery according to Example 2 was obtained in the same manner as in Example 1, except that the positive electrode active material according to Example 2 was used instead of the positive electrode active material according to Example 1.

[0108] (Charge / discharge test) A charge-discharge test of the fabricated non-aqueous magnesium battery was carried out in an argon atmosphere at a temperature of 60°C.

[0109] FIG. 6 is a graph showing the results of a discharge and charge test of the nonaqueous magnesium battery according to Example 2.

[0110] A charge / discharge test was performed using a VSP-300 charge / discharge device manufactured by Bio-Logic. First, the crystal structure of the positive electrode active material according to Example 1 was assumed to be a single phase of nickel oxyhydroxide (NiOOH). The capacity of the positive electrode active material according to Example 2 was assumed to be 461 mAh / g. The nonaqueous magnesium battery according to Example 2 was discharged at a C-rate of 0.01. Specifically, the nonaqueous magnesium battery according to Example 1 was discharged at a cut-off voltage of 1.0 V. The discharge capacity was 147 mAh / g. After discharge, an open circuit state was maintained for 5 hours. Next, the nonaqueous magnesium battery according to Example 2 was charged at a C-rate of 0.01. The charge capacity was 147 mAh / g. However, as with the charge / discharge of the nonaqueous magnesium battery according to Example 1, the charge capacity of the nonaqueous magnesium battery according to Example 2 in the first cycle is thought to include capacity due to oxidative decomposition of the electrolyte. In Example 2, the reaction potential, which is the average value of the charge potential and the discharge potential, was about 2.7V.

[0111] The density of Mo6S8, a sulfide having a Chevrel phase described in Non-Patent Document 1, is 5.2 g / cm 3 According to Non-Patent Document 1, the discharge capacity and reaction potential of Mo6S8 are approximately 116 mAh / g and approximately 1.1 V, respectively. The density of vanadium pentoxide V2O5, an oxide described in Non-Patent Document 2, is 3.4 g / cm 3 According to Non-Patent Document 2, the discharge capacity and reaction potential of V2O5 are about 75 mAh / g and about 1.5 V, respectively. The density of the powder of γ-NiOOH, which is the compound according to Example 1, is 3.8 g / cm 3 The discharge capacity and reaction potential of the positive electrode active material according to Example 1 were 226 mAh / g and about 2.7 V, respectively. The density of the mixed powder of γ-NiOOH and β-NiOOH, which is the compound according to Example 2, was 3.8 g / cm 3 More than 4.1g / cm 3The discharge capacity and reaction potential of the mixed powder of γ-NiOOH and β-NiOOH were 147 mAh / g and about 2.7 V, respectively. The layered nickel oxyhydroxides according to Examples 1 and 2 had high discharge capacities and high reaction potentials.

[0112] The mass energy density of an active material can be calculated by multiplying the discharge capacity by the reaction potential. The mass energy density of Mo6S8 described in Non-Patent Document 1 was approximately 128 mWh / g. The mass energy density of the positive electrode active material according to Example 1 was approximately 610 mWh / g. The mass energy density of the positive electrode active material according to Example 2 was approximately 397 mWh / g. The mass energy density of the positive electrode active material according to Example 1 was approximately 4.8 times that of Mo6S8. The mass energy density of the positive electrode active material according to Example 2 was approximately 3.1 times that of Mo6S8. It was found that a positive electrode active material containing layered nickel oxyhydroxide had a high mass energy density.

[0113] The volumetric energy density of an active material can be calculated by multiplying the density of the compound by the reversible capacity and the reaction potential. The volumetric energy density of Mo6S8 described in Non-Patent Document 1 is about 664 mWh / cm 3 The volumetric energy density of the positive electrode active material according to Example 1 was about 2319 mWh / cm 3 The volumetric energy density of the positive electrode active material according to Example 2 was about 1508 mWh / cm 3 The volumetric energy density of the positive electrode active material according to Example 1 was about 3.5 times that of Mo6S8. The volumetric energy density of the positive electrode active material according to Example 2 was about 2.3 times that of Mo6S8. It was found that a positive electrode active material containing layered nickel oxyhydroxide has a high volumetric energy density. [Industrial Applicability]

[0114] The positive electrode active material of the present disclosure can be used in non-aqueous magnesium batteries. [Explanation of symbols]

[0115] 10. Non-aqueous magnesium battery 11 cases 12 Positive electrode current collector 13 Cathode active material layer 14 Separator 15 Sealing plate 16 Negative electrode current collector 17 Negative electrode active material layer 18 Gasket 21 Positive electrode 22 Negative electrode 30 Beaker Cell 31 Positive electrode 32 mesh 33 Positive electrode mixture 34 Negative electrode 35 Nonaqueous electrolyte

Claims

1. a positive electrode including a positive electrode active material; a negative electrode; a non-aqueous electrolyte containing a magnesium salt, the positive electrode active material contains nickel oxyhydroxide, The nickel oxyhydroxide has a layered structure capable of absorbing and releasing magnesium ions between the layers. Non-aqueous magnesium battery.

2. The nickel oxyhydroxide is NiOOH x The compound includes a compound represented by the formula: 0<x≦1 is satisfied, The nonaqueous magnesium battery according to claim 1 .

3. The nickel oxyhydroxide is NiOOH x The compound includes a compound represented by the formula: 0<x<1 is satisfied, The nonaqueous magnesium battery according to claim 2 .

4. The nickel oxyhydroxide includes γ-NiOOH. The nonaqueous magnesium battery according to claim 1 .

5. The negative electrode contains metallic magnesium. The nonaqueous magnesium battery according to any one of claims 1 to 4.

6. The negative electrode includes a negative electrode active material that absorbs and releases magnesium ions. The nonaqueous magnesium battery according to any one of claims 1 to 4.

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