Negative electrode material for aluminum secondary battery and aluminum secondary battery

Abstract

To provide a negative electrode material for an aluminum secondary battery which can impart good battery characteristics to the aluminum secondary battery and is advantageous in terms of cost, and to provide an aluminum secondary battery including the negative electrode material.SOLUTION: A negative electrode material for an aluminum secondary battery includes an aluminum alloy containing 0.50 mass% or more of magnesium, and an aluminum secondary battery includes a negative electrode including the negative electrode material, a positive electrode, a separator, and an electrolytic solution. The aluminum alloy preferably has a magnesium content of from 0.7 to 10.0% by weight and densities of from 2.640 to 2. 700g / cm3.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a negative electrode material for an aluminum secondary battery and an aluminum secondary battery. [Background technology]

[0002] Secondary batteries, which can be repeatedly charged and discharged, have traditionally been used for a variety of purposes. Demand for lithium-ion secondary batteries, in particular, has skyrocketed in recent years due to their excellent energy density. This has been accompanied by remarkable technological innovation, and while the battery capacity of recent lithium-ion secondary batteries is approaching theoretical capacity, it is becoming increasingly difficult to achieve dramatic improvements in performance. Furthermore, because lithium-ion secondary batteries use rare metals such as lithium, cobalt, and nickel as the positive electrode active material, there are concerns about the supply of raw materials. For these reasons, there is a demand for the development of secondary batteries based on materials other than lithium.

[0003] From this perspective, new secondary batteries using aluminum, which is abundant and inexpensive, are being considered. Aluminum has a capacity per volume about four times that of lithium, is chemically stable compared to lithium, and is less likely to develop dendrites, making it an ideal battery material. It has long been used as an electrode in primary batteries, and in recent years, development of aluminum-ion secondary batteries has also been progressing.

[0004] For example, Patent Documents 1 and 2 disclose anode materials using aluminum or aluminum compounds, cathode materials using carbonaceous materials, and electrolytes using Al2Cl7 - Aluminum ion batteries using non-aqueous solutions containing aluminum bis(trifluoromethanesulfone)imide or aluminum bis(trifluoromethanesulfone)imide have been disclosed. In recent years, secondary batteries using aluminum anodes and aqueous electrolytes have also been investigated (Patent Document 3, Non-Patent Documents 1 and 2). Aluminum is less easily reduced than hydrogen, making it difficult to reversibly electrodeposit it in water. However, aluminum has a high hydrogen overvoltage, and partial electrodeposition at the interface between the electrode surface and the electrolyte can occur, making electrodeposition from aqueous electrolytes possible (Non-Patent Document 1).

[0005] Furthermore, aluminum-sulfur batteries, which use sulfur as a positive electrode together with an aluminum negative electrode, are currently being studied, although this is still at the academic research level (e.g., Non-Patent Document 3). Aluminum-sulfur batteries have a theoretical capacity of approximately 1675 Wh / kg, which is about 7 to 8 times that of lithium-ion batteries, and are particularly expected to be next-generation batteries. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-213101 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-168234 [Patent Document 3] Patent Publication No. 2021-174732 [Non-patent literature]

[0007] [Non-Patent Document 1] Jasmin Smajic, et al.,Nanomaterials,11,3235(2021) [Non-patent document 2] Jasmin Smajic, et al.,Adv. Mater. Interfaces,2101733(2021) [Non-patent document 3] GA Elia, et al.,Journal of Power Sources,481,228870(2021) Summary of the Invention [Problem to be solved by the invention]

[0008] As mentioned above, aluminum-ion batteries and aluminum-sulfur batteries have a large theoretical capacity and are considered to be promising secondary batteries. However, aluminum secondary batteries developed to date have issues such as small charge / discharge capacity, low discharge voltage and charge / discharge efficiency, and short cycle life, and it is difficult to say that their inherent battery characteristics are being fully utilized.

[0009] The present invention has been made in view of the above problems, and has an object to provide an anode material for an aluminum secondary battery that can impart a good battery capacity (charge / discharge capacity) and cycle life to the aluminum secondary battery and is also advantageous in terms of cost, and an aluminum secondary battery equipped with such an anode material. [Means for solving the problem]

[0010] As a result of extensive research, the present inventors have found that physical properties such as charge / discharge capacity and cycle life can be improved by using a material containing an aluminum alloy containing a predetermined amount or more of magnesium as a negative electrode material for an aluminum secondary battery.

[0011] That is, the present invention provides the following (1) to (9). (1) A negative electrode material for an aluminum secondary battery, comprising an aluminum alloy containing 0.50 mass % or more of magnesium. (2) The negative electrode material for aluminum secondary batteries according to (1) above, wherein the aluminum alloy has a magnesium content of 0.7 to 10.0 mass %. (3) The negative electrode material for aluminum secondary batteries according to (1) or (2) above, wherein the total content of gallium, vanadium, nickel, boron, and zirconium in the aluminum alloy is 0.05 mass % or less. (4) The aluminum alloy has a viscosity of 2.640 to 2.700 g / cm 3 The negative electrode material for an aluminum secondary battery according to any one of (1) to (3) above, having a density of 0.1 to 0.5. (5) An aluminum secondary battery comprising a negative electrode containing the negative electrode material for aluminum secondary batteries according to any one of (1) to (4) above, a positive electrode, a separator, and an electrolyte. (6) The aluminum secondary battery according to (5) above, wherein the electrolyte solution is a liquid containing one or more solvents selected from the group consisting of water, organic solvents, deep eutectic solvents, and ionic liquids, and an aluminum salt. (7) The aluminum secondary battery according to (6) above, wherein the aluminum salt contains one or more salts selected from the group consisting of aluminum triperfluoroalkylsulfonate, aluminum bis(fluorosulfonyl)imide (Al-FSI), aluminum bromide, aluminum iodide, aluminum perchlorate, aluminum tris(hexafluorophosphate) (Al(PF6)3), and aluminum tris(tetrafluoroborate) (Al(BF4)3). (8) The aluminum secondary battery according to any one of (5) to (7) above, wherein the positive electrode comprises a positive electrode active material containing one or more chemical species selected from the group consisting of carbonaceous materials, metal oxides, metal carbides, metal nitrides, transition metal fluorides, coordination polymers, polyacetylenes, polythiophenes, imine-based polymers, anthraquinone-based organic compounds, sulfur, and metal sulfides. (9) The battery further includes an exterior packaging material, and the negative electrode, the positive electrode, the separator, and the electrolyte are housed in the exterior packaging material; The aluminum secondary battery according to any one of (5) to (8) above, wherein the exterior material has an ethylene vinyl acetate resin layer, an ethylene vinyl alcohol resin layer, a polyacrylonitrile resin layer, and / or a polyethylene terephthalate resin layer. [Effects of the Invention]

[0012] The negative electrode material for aluminum secondary batteries of the present invention can impart good battery capacity (charge / discharge capacity) and cycle life to aluminum secondary batteries, and is low-cost. Therefore, aluminum secondary batteries of the present invention equipped with such a negative electrode material have good cycle life and are cost-effective. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view of an aluminum secondary battery according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, the negative electrode material for an aluminum secondary battery and the aluminum secondary battery of the present invention will be described in detail based on embodiments, but the present invention is not limited to these embodiments.

[0015] <Anode material for aluminum secondary batteries> The negative electrode material for aluminum secondary batteries of this embodiment is characterized by containing an aluminum alloy containing 0.50 mass % or more of magnesium. As will be shown in the examples described later, aluminum secondary batteries equipped with a negative electrode material containing such a magnesium-containing aluminum alloy exhibit good battery capacity and cycle life.

[0016] In addition, general-purpose pure aluminum materials such as A1050 and A1100A may contain magnesium at levels of 0.05% by mass or less, or 0.10% by mass or less. However, at these magnesium contents, the battery characteristics are almost the same as when pure aluminum is used. Furthermore, even when using aluminum alloys with a low magnesium content, the battery characteristics may be at the same level as A1050, etc.

[0017] Although the present invention is not limited by any particular theory, the reason why the aluminum secondary battery negative electrode material of this embodiment is effective is thought to be the involvement of sacrificial oxidation by the magnesium component. It is known that the performance of aluminum batteries declines when passive aluminum oxide forms on the negative electrode surface (Non-Patent Document 2). Here, if magnesium, which is more easily oxidized than aluminum, is contained in the negative electrode at a certain level or more, it is preferentially oxidized, making it difficult for an aluminum oxide film to form. As a result, the battery characteristics, particularly the cycle life of secondary batteries, may be better than when aluminum is used alone.

[0018] Another possible reason is the lattice distortion of the anode material. When magnesium is added to aluminum, the area around the magnesium atoms expands, increasing the lattice constant and creating distortion within the lattice. This distortion is eliminated, making it easier for aluminum ions to be released during charging. This also makes it easier for aluminum elements to be reinserted into the resulting voids during charging, potentially resulting in a greater charge / discharge capacity than a pure aluminum anode.

[0019] <Magnesium-containing aluminum alloy> Aluminum alloys containing 0.50% by mass or more of magnesium (Mg) are well known, and various materials are commercially available. Examples include, but are not limited to, various aluminum-magnesium alloys of the Alloy No. 5000 series, JIS symbols AC7A (Mg content 4.5%), ADC5 (Mg content 6.0%), and ADC6 (Mg content 3.0%). The contents of Mg and other elements in this text are in mass % unless otherwise specified. The average compositions of representative magnesium-containing aluminum alloys of the Alloy No. 5000 series are shown in Table 1 below, along with their densities.

[0020] [Table 1]

[0021] In addition to the above, aluminum-copper-magnesium alloys of alloy number 2000 series, aluminum-manganese alloys of alloy number 3000 series, aluminum-silicon alloys of alloy number 4000 series, aluminum-magnesium-silicon alloys of alloy number 6000 series, aluminum-zinc-magnesium alloys of alloy number 7000 series, etc. can also be used in the negative electrode material of this embodiment as long as they contain 0.50 mass% or more of magnesium. Representative examples of such multi-component aluminum alloys with a magnesium content of 0.50 mass% or more are selected and their compositions and densities are shown in Table 2 below, although other types of alloys can of course also be used.

[0022] [Table 2]

[0023] (Aluminum alloy composition) As described above, in the negative electrode material of this embodiment, the aluminum alloy contains 0.50% by mass or more of magnesium. Such an alloy composition can exhibit excellent battery characteristics. To further improve the performance of an aluminum secondary battery equipped with the negative electrode material of this embodiment, the magnesium content in the aluminum alloy is preferably 0.60% by mass or more. The magnesium content may be, for example, 0.70 to 10.00% by mass, more preferably 0.75 to 5.00% by mass, even more preferably 0.80 to 4.00% by mass, and particularly preferably 1.00 to 3.50% by mass. However, if the magnesium content is too high, the physical properties may differ significantly from those of pure aluminum, making it difficult for the aluminum secondary battery to exhibit good characteristics. Therefore, the magnesium content may be, for example, 0.50 to 5.00% by mass, especially 0.50 to 3.50% by mass.

[0024] The aluminum alloy preferably has a total aluminum and magnesium content of, for example, 90% by mass or more, preferably 95% by mass or more, even more preferably 98% by mass or more, and particularly preferably 99% by mass or more. Other components, such as transition metal elements such as copper, manganese, and zinc, may potentially cause unexpected electrochemical reactions, so their content in the aluminum alloy is preferably 10% by mass or less, preferably 5% by mass or less, even more preferably 2% by mass or less, and particularly preferably 1% by mass or less. For similar reasons, the total content of gallium, vanadium, nickel, boron, and zirconium in the aluminum alloy is preferably 0.05% by mass or less, particularly preferably 0.02% by mass or less, or below the detection limit.

[0025] As shown in Table 1 above, most of the aluminum alloys of the alloy number 5000 series have a magnesium content in the range of 0.50 to 10.0 mass%, particularly 0.70 to 5.00 mass%, and the contents of elements other than Al and Mg are generally 1 to 3 mass% or less, making them suitable for the negative electrode material of this embodiment. Among these, A5005 (Mg content: 0.8%), A5021 (Mg content: 2.5%), A5050 (Mg content: 1.5%), A5052 (Mg content: 2.5%), A5086 (Mg content: 4.0%), A5154 (Mg content: 3.5%), A5251 (Mg content: 2.1%), A5254 (Mg content: 3.5%), and A5754 (Mg content: 3.1%) have magnesium contents in the range of 0.75 to 4.0% by mass, and also have contents of elements other than Al and Mg that are less than 1 to 2% by mass, and are also advantageous in terms of cost, making them particularly suitable as the negative electrode material of this embodiment.

[0026] (Aluminum alloy density) The aluminum alloy in the negative electrode material of this embodiment also has a density of 2.640 to 2.700 g / cm 3 It is preferable that the density (≒ specific gravity) of the aluminum alloy be 2.698 to 2.710. By using a negative electrode material containing a magnesium-containing aluminum alloy with such a density, the physical properties of the aluminum secondary battery, such as the charge / discharge capacity and cycle life, are further improved. Although the reason for this cannot be determined with certainty, it is possible that the expansion and distortion of the aluminum crystal lattice described above are involved. The density of pure aluminum is generally within the range of 2.698 to 2.710, although it depends on the purity and the type and amount of trace impurities contained.

[0027] A more preferred magnesium-containing aluminum alloy has a density of 2.650 to 2.695 g / cm 3 , and even 2.660~2.690g / cm 3 , especially 2.670~2.685g / cm 3Specific examples include, but are not limited to, A5005 (specific gravity 2.70), A5021 (specific gravity 2.68), A5050 (specific gravity 2.69), A5052 (specific gravity 2.68), A5086 (specific gravity 2.66), A5154 (specific gravity 2.66), A5251 (specific gravity 2.69), A5254 (specific gravity 2.66), A5754 (specific gravity 2.67), and ADC6 (specific gravity 2.65).

[0028] <Configuration of negative electrode material for aluminum secondary batteries> The negative electrode material for aluminum secondary batteries of this embodiment may be in any form as long as it contains an aluminum alloy containing a predetermined amount of magnesium. The magnesium-containing aluminum alloy can function as a negative electrode active material capable of releasing aluminum ions, but due to its excellent conductivity, it can also function as a current collector. Therefore, for example, a plate or foil of the aluminum alloy can be used as a negative electrode material that serves as both a negative electrode active material and a current collector. Furthermore, multiple types of aluminum alloys may be used in combination.

[0029] The negative electrode material of this embodiment is also composed of a current collector and an active material, and may optionally contain a conductive additive, a binder, and / or a solid electrolyte, etc. For example, the negative electrode may have a layered structure in which a thin film or powder of an aluminum alloy is applied to a current collector.

[0030] The negative electrode material may also have a reinforcing layer made of ceramics, glass, carbonaceous materials, polymeric materials, etc. Such a reinforcing layer is particularly useful when the negative electrode material includes a thin aluminum alloy layer, such as a foil. Magnesium-containing aluminum may also be vapor-deposited onto such a reinforcing layer to form the negative electrode material of this embodiment.

[0031] In a more preferred embodiment, the negative electrode material is composed of a plate-shaped, sheet-shaped, or film-shaped material of a magnesium-containing aluminum alloy. Such a negative electrode configuration allows for easy production of an aluminum secondary battery, which is also advantageous in terms of cost. In particular, a negative electrode material composed of an aluminum alloy sheet-shaped or film-shaped material, such as a foil, is preferred because it can be easily applied to aluminum secondary batteries of various shapes, such as wound types.

[0032] <Aluminum secondary battery> The present invention also encompasses an aluminum secondary battery comprising a negative electrode containing the above-mentioned negative electrode material for aluminum secondary batteries, a positive electrode, a separator, and an electrolyte.

[0033] The aluminum secondary battery of this embodiment will be further described based on the typical embodiment shown in Fig. 1. The aluminum secondary battery 1 of this embodiment is provided with a negative electrode 11 containing aluminum and / or an aluminum alloy, a positive electrode current collector 12 disposed so as to face the negative electrode 11, a positive electrode active material 13 disposed on the positive electrode current collector 12, and a separator and an electrolyte (for example, a separator 14 impregnated with an electrolyte) disposed between the negative electrode 11 and the positive electrode current collector 12.

[0034] In the embodiment shown in FIG. 1 , the separator 14 contacts substantially the entire surface with one of the main surfaces of the negative electrode 11 and the positive electrode active material layer 13, the separator 14 is impregnated with an electrolyte, and the separator 14 is housed in a housing 15. However, the present invention is not limited to this embodiment. For example, the housing 15 is not an essential component. A liquid, gel, or solid electrolyte may be housed inside a frame-shaped or lattice-shaped separator. Furthermore, instead of the flat shape shown in FIG. 1 , the aluminum secondary battery may be cylindrical, e.g., wound. The area of ​​the electrodes may also be larger on the negative electrode side than on the positive electrode side. Having a larger negative electrode than a positive electrode makes it easier to prevent electrodeposition of aluminum ions at the negative electrode end. Furthermore, unit cells such as those shown in FIG. 1 may be connected in series or in parallel to form a battery pack. Below, each component other than the negative electrode constituting the aluminum secondary battery of this embodiment is described.

[0035] <Positive electrode> In the aluminum secondary battery 1 of this embodiment, the positive electrode includes a positive electrode current collector 12 and a positive electrode active material 13 disposed on the positive electrode current collector 12. The positive electrode may also optionally contain a conductive additive, a binder, a solid electrolyte, etc. For example, the positive electrode may have a layered structure in which the positive electrode active material 13 is mixed with a conductive additive or a binder and applied to the positive electrode current collector 12.

[0036] (Cathode active material) In the aluminum secondary battery 1 of this embodiment, a positive electrode active material 13 is disposed on a positive electrode current collector 12. There are no particular limitations on the type of positive electrode active material 13, and any material that is used as a positive electrode active material for aluminum secondary batteries may be used. From the viewpoint of charge / discharge characteristics, a positive electrode active material containing one or more chemical species selected from the group consisting of carbon-based materials, metal oxides, metal carbides, metal nitrides, transition metal fluorides, coordination polymers, polyacetylenes, polythiophenes, imine-based polymers, anthraquinone-based organic compounds, sulfur, and metal sulfides is preferred.

[0037] Specific examples of preferred positive electrode active materials include, but are not limited to, particulate or fibrous activated carbon, ketjen black, acetylene black, graphite, carbon nanotubes, graphene, and other carbon-based materials; metal oxides such as manganese dioxide, lead dioxide, silver oxide, iron oxide, molybdenum oxide, vanadium oxide, and titanium oxide; metal carbides such as titanium carbide; metal nitrides such as titanium nitride; transition metal fluorides; coordination polymers such as ferric ferrocyanide (Prussian blue); and metal sulfides such as sulfur, copper sulfide, and molybdenum sulfide. There are no particular limitations on the shape of the positive electrode active material, and any desired shape, such as particulate or fibrous, can be used.

[0038] (Positive electrode current collector) The material of the positive electrode current collector 12 is not particularly limited, and is preferably one or more selected from the group consisting of niobium and tantalum, which are commonly used in aluminum secondary batteries, as well as molybdenum, nickel, nickel-based alloys, glassy carbon, titanium nitride, titanium carbonitride, titanium carbide, copper, and copper alloys. These materials have excellent conductivity and corrosion resistance, making them suitable as current collectors for the aluminum secondary battery of this embodiment.

[0039] The positive electrode current collector 12 may have a reinforcing material made of ceramics, glass, carbon-based materials, polymer materials, or the like attached to one side thereof. For example, by laminating the positive electrode current collector 12 made of a metal film on a ceramic or glass reinforcing plate, the corrosion resistance around the positive electrode can be further improved. Also, by configuring the positive electrode current collector 12 by vapor-depositing metal, graphite, or the like onto a polymer sheet, it is possible to reduce the weight and cost of the aluminum secondary battery.

[0040] The positive electrode of the aluminum secondary battery 1 of this embodiment may also contain, in addition to the positive electrode current collector 12 and the positive electrode active material 13, optional conductive additives, binders, solid electrolytes, and the like. For example, a powder of a positive electrode active material such as manganese dioxide and a conductive additive may be mixed with a solution or emulsion containing a binder such as a polymer, and the mixture may be applied to the positive electrode current collector 12 and dried to produce the positive electrode of the aluminum secondary battery 1. The conductive additives and binders are not particularly limited, and commonly used materials for secondary batteries can be used. Specific examples of commonly used conductive additives include, but are not limited to, carbon-based materials such as carbon black, ketjen black, acetylene black, graphite, and carbon nanotubes, as well as metals, metal oxides, and conductive ceramics.

[0041] The conductive additive, binder, etc. can also be used when producing the negative electrode 11.

[0042] <Aluminum-ion battery> An aluminum ion battery can be constructed using the above-described positive electrode current collector 12 and positive electrode active material 13, and the negative electrode 11 containing aluminum and / or an aluminum alloy. Aluminum ion batteries are secondary batteries that are charged and discharged by the movement of aluminum ions between the positive electrode and the negative electrode. Compared to lithium ion batteries, aluminum ion batteries have the advantages of being able to achieve higher capacity, being safer, and being abundantly available. Note that the term "aluminum ions" as used herein also encompasses aluminum complex ions such as aquo complex ions, and cluster-like ions containing aluminum. The aluminum secondary battery of the present invention encompasses such aluminum ion batteries.

[0043] <Aluminum sulfur battery> In the aluminum secondary battery of this embodiment, the positive electrode active material may contain sulfur. That is, the aluminum secondary battery of the present invention may be an aluminum-sulfur battery. As described above, aluminum-sulfur batteries have an extremely high theoretical capacity and are expected to be next-generation batteries. In the aluminum secondary battery of this embodiment, by using a magnesium-containing aluminum alloy as the negative electrode material, a larger charge / discharge capacity than conventional products is achieved, making it possible to utilize the inherent properties of aluminum batteries.

[0044] Examples of positive electrode active materials in aluminum-sulfur batteries include positive electrode active materials containing sulfur itself and positive electrode active materials containing sulfides such as copper sulfide. Since sulfur and sulfides generally have low electrical conductivity at room temperature, it is preferable to use a conductive additive in combination. Examples of conductive additives that can be used in aluminum-sulfur batteries include the carbon-based materials described above, copper, and copper compounds. Sulfur can also be used after being coated with carbon.

[0045] <Electrolyte> The electrolyte solution for an aluminum secondary battery may be any solution containing ions containing aluminum element as an electrolyte. Similar electrolyte solutions can be used in both the aluminum ion battery and the aluminum sulfur battery described above. The electrolyte solution is preferably a solution containing an aluminum salt and one or more solvents selected from the group consisting of water, organic solvents, deep eutectic solvents, and ionic liquids. In the present invention, the term "electrolytic solution" broadly encompasses colloidal solutions. In other words, the term "electrolytic solution" in the present invention also encompasses, for example, gel-like electrolytes.

[0046] (electrolyte) There are no particular limitations on the aluminum-containing ions used as the electrolyte. For example, aluminum-containing ion sources include, but are not limited to, one or more salts selected from the group consisting of aluminum triperfluoroalkylsulfonates such as aluminum tri(trifluoromethanesulfonate) (Al(OTF)3), aluminum bis(fluorosulfonyl)imide (Al-FSI), aluminum halides such as aluminum bromide and aluminum iodide, aluminum perchlorate, aluminum tris(hexafluorophosphate) (Al(PF6)3), and aluminum tris(tetrafluoroborate) (Al(BF4)3). Aluminum ions derived from aluminum sulfate or aluminum nitrate may also be used. 3+ It is also possible to use ions, and a plurality of types of these ions may be contained.

[0047] Among these electrolytes, aluminum triperfluoroalkylsulfonate, aluminum bis(fluorosulfonyl)imide, aluminum tris(hexafluorophosphate), and aluminum tris(tetrafluoroborate) are preferred. The use of an electrolyte solution containing such electrolytes improves the cycle characteristics of aluminum secondary batteries. Aluminum chloride electrolytes may corrode some positive electrode materials (e.g., copper), so it is preferable not to include them in the electrolyte solution. More preferably, aluminum triperfluoroalkylsulfonate or aluminum bis(fluorosulfonyl)imide is used as the electrolyte. These electrolytes enable stable charge / discharge characteristics to be exhibited, even when the electrolyte solution is aqueous. Aluminum tri(trifluoromethanesulfonate) is particularly preferred.

[0048] (solvent for electrolyte) As described above, the solvent for the electrolytic solution may be any solvent that can generate ions containing aluminum elements in the electrolytic solution, such as water, an organic solvent, or a deep eutectic solvent, and the type is not particularly limited. Although not necessarily a solvent in the strict sense, it may also include an ionic liquid.

[0049] A "deep eutectic solvent" is a solvent that is liquid at room temperature and can be obtained by mixing a hydrogen bond donor compound and a hydrogen bond acceptor compound in a certain ratio. By combining donor and acceptor compounds, it is possible to create solvents with any physical properties, and a variety of combinations have been reported. Examples include, but are not limited to, monosaccharide / hydroxycarboxylic acid systems, disaccharide / hydroxycarboxylic acid systems, diol / hydroxycarboxylic acid systems, fatty acid / long-chain fatty acid systems, and urea / sulfamic acid systems.

[0050] In the aluminum secondary battery of this embodiment, the electrolyte is preferably an aqueous solution, particularly an aqueous solution. When the solvent is primarily water, it can ensure high safety and is cost-effective compared to using organic solvents. More preferably, an aqueous solution containing aluminum triperfluoroalkylsulfonate or aluminum bis(fluorosulfonyl)imide is used. These aqueous electrolytes, particularly aqueous aluminum tri(trifluoromethanesulfonate), make it difficult for the water in the solvent to be electrolyzed during charging, making it easier for the secondary battery to exhibit its characteristics (Non-Patent Document 1). Furthermore, it is also possible for aluminum aquo complexes or trifluoromethanesulfonate complexes to reversibly intercalate into carbon-based positive electrode active materials (Non-Patent Document 2).

[0051] (Electrolyte concentration) There are no particular restrictions on the concentration of the electrolyte in the electrolytic solution. From the viewpoint of increasing the charge / discharge capacity and suppressing the electrolysis of water during charging, it is preferable to increase the concentration of the electrolytic solution. On the other hand, from the viewpoint of preventing an increase in the viscosity of the electrolytic solution and maintaining ionic conductivity, it is preferable to keep the concentration of the electrolytic solution low. Striking a balance between these two, the concentration of the electrolytic solution may be, for example, about 0.1 to 15 mol / L, further 0.5 to 10 mol / L, and particularly about 1 to 5 mol / L.

[0052] (Additives) The electrolyte solution may also contain various additives as optional components, such as a vinyl group-containing compound, γ-butyrolactone, ethylene sulfide, cyclic sulfonic acid ester, methyl benzoate, succinic anhydride, polydimethylsiloxane, AgPF6, Cu(CF3SO3)2, or other negative or positive electrode protective film forming agents; overcharge inhibitors such as 2,4-difluoroanisole; and flame retardants such as phosphate esters, phosphazenes, and imidazole salts, in an amount of about 0.01 to 5 mass %, and particularly about 0.1 to 1 mass %.

[0053] <Separator> The aluminum secondary battery 1 of this embodiment includes a separator 14 disposed between the positive electrode and the negative electrode to prevent short-circuiting between the two electrodes. The shape of the separator is not particularly limited, and it may be, for example, a frame-like or lattice-like separator having a certain thickness that separates the positive electrode and the negative electrode. A gel electrolyte or a solid electrolyte may also be used as the separator. However, from the viewpoint of more reliably preventing short-circuiting between the two electrodes, it is preferable that the separator 14 be in contact with substantially the entire surface of each of the negative electrode 11 and the positive electrode active material 13 layer, as in the embodiment shown in FIG. 1 . Furthermore, from the viewpoint of maintaining high ionic conductivity between the positive and negative electrodes, the separator 14 preferably holds an electrolyte solution and is preferably in the form of a porous film, fiber, or the like.

[0054] There are no particular limitations on the material or shape of the separator, and any material can be used, including glass, ceramics, cellulose fibers, paper such as Japanese paper, fluorine-based polymers, polyolefins such as polyethylene or polypropylene, PET, aromatic polyamides, polyacrylonitrile, polyimides, and other porous materials, woven or nonwoven fabrics, or gel-like separators.

[0055] <Battery type> An aluminum secondary battery configured as described above can be used as a single cell as is, or multiple cells can be connected in series or parallel to form a battery module. There are no particular limitations on the size or the number of cells in the battery module, and any size and number can be used depending on the purpose. For example, a single cell can be formed by stacking positive electrodes, negative electrodes, and separators each having a thickness of about 1 μm to 2 mm, particularly about 10 to 500 μm, and about 1 to 1,000 such cells, particularly about 10 to 100, can be connected to form a battery module.

[0056] There are no particular limitations on the type or shape of the aluminum secondary battery, and various types are possible, such as a flat type as shown in FIG. 1, a cylindrical type, a coin type, a button type, and even a laminate type as described below.

[0057] <Laminated battery> Yet another embodiment of the present invention is an aluminum secondary battery as shown in FIG. 1 , which further includes an exterior housing material, in which the negative electrode, positive electrode active material, positive electrode current collector, separator, and electrolyte are housed, and the exterior housing material has an ethylene vinyl acetate resin layer, an ethylene vinyl alcohol resin layer, a polyacrylonitrile resin layer, and / or a polyethylene terephthalate resin layer.

[0058] The aluminum secondary battery of this embodiment is more preferably a laminated battery. A laminated battery is a battery in which a plurality of batteries (single cells) each having a positive electrode, a negative electrode, and a separator are connected in series as desired and housed in an exterior material made of a laminated film. Also called a laminated electrode or pouch battery, it has advantages such as being lightweight, having a high energy density, being highly safe, and being easy to form into a battery pack. Therefore, it is a suitable form for making secondary batteries more practical.

[0059] In the laminate battery of this embodiment, corrosion of the electrodes and the like is suppressed, improving the cycle life, and deformation or deterioration of the exterior material is also unlikely to occur, making it a practical secondary battery with a long life. Therefore, it is suitable as a secondary battery for vehicles such as automobiles, personal computers, mobile terminals, various home appliances, and medical devices. [Example]

[0060] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples except as defined above.

[0061] [Example 1] An aluminum secondary battery was fabricated using a positive electrode, a negative electrode, and an electrolyte solution prepared as follows. Positive electrode: 4g of graphite (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was mixed with 15g of a 1% aqueous solution of carboxymethyl cellulose (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and 0.25g of 40% SBR latex (BM451B manufactured by Zeon Corporation). The ink was then applied with a bar coater to a positive electrode current collector (30 x 35mm) made of pure copper (tough pitch copper with a purity of 99.94% and a specific gravity of 8.93), followed by heat treatment at 100°C for 20 minutes. Negative electrode: General-purpose A5005 aluminum alloy (Mg content 0.8% by mass; Ga, V, Ni, B, and Zr are all below the detection limit (<0.05% by mass); density 2.700 g / cm 3 ) thin plate (size 25 × 35 mm) was used. Electrolyte: An aqueous electrolyte was used, as differences in battery characteristics due to the negative electrode material are relatively easy to see. Aluminum tri(trifluoromethanesulfonate) (Al(OTF)3) was dissolved in purified water to prepare an aqueous solution with a concentration of 2 mol / L.

[0062] The electrolyte prepared above was impregnated into a separator made of a glass filter, and the negative electrode and positive electrode were placed on either side of the separator and secured together with plastic clips to form an aluminum secondary battery.

[0063] The resulting aluminum secondary battery was subjected to 100 charge / discharge cycles at 0.1 C over a potential window of 0.2 to 1.8 V, and the battery capacity (charge / discharge capacity) was measured. The measurements were carried out using a potentiostat / galvanostat HA series manufactured by Hokuto Denko Corporation. In this example, all experimental operations were carried out in air, and battery capacity measurements were carried out with n=3. The battery capacities at the 1st cycle, 25th cycle, and 100th cycle are shown in Table 3 below.

[0064] [Comparative Example 1] As the negative electrode material, general-purpose A1050 aluminum (Mg content ≤ 0.05 mass%; Ga, V, Ni, B, and Zr were all below the detection limit; density 2.705 g / cm) was used instead of A5005. 3 ) was used, the same operations as in Example 1 were carried out. The measurement results of the battery capacity (cycle test results) are shown in Table 3 below.

[0065] [Examples 2 to 3] As the negative electrode material, A5052 (Mg content 2.5 mass%; Ga, V, Ni, B, and Zr were all below the detection limit; density 2.680 g / cm) was used instead of A5005. 3 ) (Example 2) or A5086 (Mg content 4.0 mass%; Ga, V, Ni, B, and Zr were all below the detection limit; density 2.660 g / cm 3 ) (Example 3) was used, the same operation as in Example 1 was carried out. The results of measuring the battery capacity are shown in Table 3 below.

[0066] [Example 4] Except for changing the concentration of the electrolyte to 3 mol / L, the same operation as in Example 2 was carried out. The measurement results of the battery capacity are shown in Table 3 below.

[0067] Comparative Example 2 Except for changing the concentration of the electrolyte to 3 mol / L, the same operation as in Comparative Example 1 was carried out. The measurement results of the battery capacity are shown in Table 3 below.

[0068] [Table 3]

[0069] In Examples 1 to 3, in which A5005, A5052, or A5086 with a Mg content of 0.50% by mass or more and a specific gravity of 2.660 to 2.700 was used as the negative electrode material, the battery capacity at each cycle was approximately double that of Comparative Example 1, in which A1050 with a magnesium content of 0.05% by mass or less was used. In particular, the battery characteristics were particularly good when A5005 or A5052 with a Mg content of 0.8 to 2.5% by mass and a density of 2.680 to 2.700 was used. Furthermore, when the electrolyte concentration was 3 mol / L and the negative electrode material had a Mg content of 2.5% by mass and a density of 2.690 g / cm 3 In Example 4 using A5052, a battery capacity more than double that of Comparative Example 2 using A1050 under the same conditions was achieved.

[0070] As described above, it has been demonstrated that by using a material containing an aluminum alloy containing 0.50 mass % or more of magnesium as a negative electrode material for an aluminum secondary battery according to the present invention, an aluminum secondary battery having a large charge / discharge capacity and a good cycle life can be manufactured. [Explanation of symbols]

[0071] 1. Aluminum secondary battery 11 Negative electrode 12 Positive electrode current collector 13 Cathode active material 14 Separator 15 Exterior materials

Claims

1. A negative electrode material for an aluminum secondary battery, comprising an aluminum alloy containing 0.50 mass % or more of magnesium.

2. 2. The negative electrode material for aluminum secondary batteries according to claim 1, wherein the aluminum alloy has a magnesium content of 0.7 to 10.0 mass%.

3. 3. The negative electrode material for an aluminum secondary battery according to claim 1, wherein the total content of gallium, vanadium, nickel, boron, and zirconium in the aluminum alloy is 0.05 mass% or less.

4. The aluminum alloy has a viscosity of 2.640 to 2.700 g / cm ３ The negative electrode material for an aluminum secondary battery according to claim 1 or 2, having a density of

5. An aluminum secondary battery comprising: a negative electrode containing the negative electrode material for aluminum secondary batteries according to claim 1 or 2; a positive electrode; a separator; and an electrolyte.

6. The aluminum secondary battery according to claim 5, wherein the electrolyte solution is a liquid containing one or more solvents selected from the group consisting of water, organic solvents, deep eutectic solvents, and ionic liquids, and an aluminum salt.

7. The aluminum salt may be aluminum triperfluoroalkylsulfonate, aluminum bis(fluorosulfonyl)imide (Al-FSI), aluminum bromide, aluminum iodide, aluminum perchlorate, aluminum tris(hexafluorophosphate) (Al(PF ６ ) ３ ), and aluminum tris(tetrafluoroborate) (Al(BF ４ ) ３ 7. The aluminum secondary battery according to claim 6, further comprising one or more salts selected from the group consisting of:

8. 6. The aluminum secondary battery according to claim 5, wherein the positive electrode comprises a positive electrode active material containing one or more chemical species selected from the group consisting of carbon-based materials, metal oxides, metal carbides, metal nitrides, transition metal fluorides, coordination polymers, polyacetylenes, polythiophenes, imine-based polymers, anthraquinone-based organic compounds, sulfur, and metal sulfides.

9. the negative electrode, the positive electrode, the separator, and the electrolyte solution are contained in the exterior packaging; 6. The aluminum secondary battery according to claim 5, wherein the exterior material has an ethylene vinyl acetate resin layer, an ethylene vinyl alcohol resin layer, a polyacrylonitrile resin layer, and / or a polyethylene terephthalate resin layer.

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