Electrode material for aluminum secondary batteries and aluminum secondary batteries

Abstract

To provide an electrode material for an aluminum secondary battery that can impart a good cycle life to the aluminum secondary battery, and an aluminum secondary battery equipped with such an electrode material. [Solution] An aluminum secondary battery comprising an electrode material for an aluminum secondary battery containing 40% by mass or more of a water-insoluble polymer as a binder for the active material, relative to 100% by mass of the binder, a positive electrode containing the aluminum secondary battery electrode material, a negative electrode containing aluminum, a separator, and an electrolyte. The active material is preferably a positive electrode active material. The water-insoluble polymer has an SP value of 30 (MPa). 1 / 2 The following applies especially to 22.0-28.0 (MPa) 1 / 2 It is preferable that it be a polymer.

Description

[Technical Field]

[0001] This invention relates to an electrode material for aluminum secondary batteries and an aluminum secondary battery. [Background technology]

[0002] Rechargeable secondary batteries have long been used for various applications. Among them, lithium-ion secondary batteries have seen a surge in demand in recent years due to their superior energy density. Along with this, technological innovations have been remarkable, and while the battery capacity of recent lithium-ion secondary batteries is approaching its theoretical capacity, significant performance improvements are becoming increasingly difficult. Furthermore, because lithium-ion secondary batteries use rare metals such as lithium, cobalt, and nickel as positive electrode active materials, there are concerns regarding the supply of raw materials. For these reasons, there is a need 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 about four times greater per unit volume than lithium, is chemically more stable than lithium, and is less prone to dendrite formation, making it suitable as a battery material. It has long been used as an electrode in primary batteries, and in recent years, the development of aluminum-ion secondary batteries has also progressed.

[0004] For example, Patent Documents 1 and 2 describe aluminum or an aluminum compound as the negative electrode material, a carbon-based material as the positive electrode material, and Al2Cl7 as the electrolyte. -Aluminum ion batteries using non-aqueous solutions containing aluminum bis(trifluoromethanesulfone)imide, etc., have been disclosed. In recent years, secondary batteries using an aluminum negative electrode and an aqueous electrolyte have also been studied (Patent Document 3, Non-Patent Documents 1 and 2). Secondary batteries using aqueous electrolytes are advantageous in terms of safety and cost. However, since aluminum is less reducible than hydrogen, it is not easy to reversibly electrodeposit it in water. Nevertheless, since aluminum has a high hydrogen overpotential and partial electrodeposition to the interface layer between the electrode surface and the electrolyte can occur, electrodeposition from an aqueous electrolyte is also possible (Non-Patent Document 1).

[0005] Furthermore, aluminum-sulfur batteries, which use sulfur as the positive electrode along with aluminum as the negative electrode, are currently being studied, although this is still at the academic research stage (for example, 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 promising as next-generation batteries. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2016-213101 [Patent Document 2] Japanese Patent Publication No. 2017-168234 [Patent Document 3] Japanese 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] G. A. Elia, et al., Journal of Power Sources, 481, 228870(2021)

Summary of the Invention

Problems to be Solved by the Invention

[0008] As described above, aluminum-ion batteries and aluminum-sulfur batteries can be said to be secondary batteries with a large theoretical capacity and great potential. However, the aluminum secondary batteries developed to date have the problem of a short cycle life, and it is difficult to say that their original battery characteristics are fully utilized. In particular, when using an aqueous electrolyte excellent in terms of safety and cost, the cycle life of an aluminum secondary battery tends to be short.

[0009] The present invention has been made in view of the above problems, and an object thereof is to provide an electrode material for an aluminum secondary battery that can impart a good cycle life to an aluminum secondary battery, and an aluminum secondary battery including such an electrode material.

Means for Solving the Problems

[0010] As a result of intensive studies, the present inventors have found that, in an aluminum secondary battery, by using an electrode material containing a predetermined amount or more of a water-insoluble polymer as a binder for an active material, battery characteristics such as cycle life can be improved.

[0011] That is, the present invention provides the following (1) to (10). (1) An electrode material for an aluminum secondary battery, which contains 40% by mass or more of a water-insoluble polymer with respect to 100% by mass of the binder as a binder for an active material. (2) The electrode material for an aluminum secondary battery according to (1) above, wherein the active material is a positive electrode active material. (3) The electrode material for an aluminum secondary battery according to (1) or (2) above, wherein the water-insoluble polymer has an SP value of 30 (MPa) 1 / 2 The following polymer. (4) The non-water-soluble polymer is one or more polymers selected from the group consisting of alkyd resin, phthalic resin, melamine resin, melamine formaldehyde resin, amino alkyd co-condensation resin, urea resin, polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, polyvinyl butyral, epoxy resin, polyurethane, polyester, vinyl ester resin, phenolic resin, rosin-modified maleic acid resin, silicone resin, acrylic silicone resin, polytetrafluoroethylene, polyvinylidene fluoride, polybutadiene, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, ABS resin, coumarone resin, alkoxysilane polycondensate, thermosetting acrylic resin, oil-soluble acrylic resin, rosin resin, shellac resin, nitrocellulose, cellulose acetate, cellulose acetate butyrate, ethyl cellulose, amorphous polylactic acid, polyamide, polyimide, and polyamideimide, and is the electrode material for an aluminum secondary battery of any one of (1) to (3) above. (5) The positive electrode active material contains one or more chemical species selected from the group consisting of carbon-based materials, metal oxides, metal carbides, metal nitrides, fluorides of transition metals, coordination polymers, polyacetylene, polythiophene, imine-based polymers, anthraquinone-based organic substances, sulfur, and metal sulfides, and is the electrode material for an aluminum secondary battery of (2) etc. above. (6) The electrode material for an aluminum secondary battery of (2) or (5) etc. above further contains one or more conductive aids selected from the group consisting of carbon black, ketjen black, acetylene black, graphite, graphene, carbon nanotubes, metals, metal oxides, and conductive ceramics. (7) An aluminum secondary battery comprising a positive electrode containing the electrode material for an aluminum secondary battery of (2) or (5) etc. above, a negative electrode containing aluminum, a separator, and an electrolytic solution. (8) The electrolytic solution of the aluminum secondary battery of (7) above 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. (9) The aluminum secondary battery according to (7) or (8) above, wherein the aluminum salt contains one or more salts selected from the group consisting of aluminum triperfluoroalkyl sulfonate, 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). (10) Further comprising an outer casing, wherein the negative electrode, the positive electrode, the separator, and the electrolyte are housed in the outer casing, An aluminum secondary battery according to any of (7) to (9) above, wherein the exterior material comprises 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 electrode material for aluminum secondary batteries of the present invention can impart a good cycle life to the aluminum secondary battery. Therefore, the aluminum secondary battery of the present invention equipped with such electrode material has a good cycle life. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic cross-sectional view of an aluminum secondary battery according to one embodiment of the present invention. [Modes for carrying out the invention]

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

[0015] ≪Electrode material for aluminum secondary batteries≫ The electrode material for aluminum secondary batteries of this embodiment is characterized by containing 40% by mass or more of a water-insoluble polymer as a binder for the active material, relative to 100% by mass of the binder. As shown in the examples described later, aluminum secondary batteries equipped with such electrode materials exhibit a good cycle life.

[0016] <Active materials, etc.> Electrode materials for secondary batteries are composed of active materials such as metals and carbon, or of an active material and a current collector. For example, in an aluminum secondary battery, aluminum or its alloy is used as the negative electrode active material, and carbon-based materials such as graphite or metal oxides are used as the positive electrode active material. Here, due to their excellent conductivity, aluminum (alloys) and graphite can not only function as active materials but also as current collectors. Therefore, for example, it is possible to use plates or foils of aluminum or graphite as electrode materials that serve as both negative electrode active material or positive electrode active material and current collector. On the other hand, thin films or powders of active materials such as aluminum or carbon-based materials can also be bonded to a current collector to form negative electrode materials or positive electrode materials. The electrode material for aluminum secondary batteries in this embodiment is useful as the latter type of electrode material.

[0017] In addition to carbon-based materials, low-conductivity materials such as metal oxides and sulfur are also frequently used as positive electrode active materials for aluminum secondary batteries. Unlike the aluminum (alloy) used as the negative electrode material, these low-conductivity positive electrode active materials are preferably bonded to a current collector and are also preferably used in combination with conductive additives such as carbon black. Therefore, the electrode material for aluminum secondary batteries of this embodiment is particularly useful as an electrode material in which the positive electrode material, i.e., the active material, is a positive electrode active material.

[0018] The electrode material for the aluminum secondary battery of this embodiment is also preferably an electrode material, i.e., a positive electrode material, in which the positive electrode active material contains 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 polymers, anthraquinone-based organic materials, sulfur, and metal sulfides.

[0019] Furthermore, the electrode material for the aluminum secondary battery of this embodiment is preferably a positive electrode material further comprising one or more conductive additives selected from the group consisting of carbon black, Ketjenblack, acetylene black, graphite, graphene, carbon nanotubes, metals, metal oxides, and conductive ceramics. While some of the conductive additives exemplified here may overlap in scope with others in a broad sense, they do not limit other conductive additives, nor do they require or prohibit the combined use of multiple conductive additives. Other conductive additives may also be used or combined.

[0020] <Binder> The positive electrode active material or negative electrode active material described above can be bound together with a conductive additive as desired using a binder to form a positive electrode material or negative electrode material. In this embodiment, a binder containing 40% by mass or more of a water-insoluble polymer is used. As shown in the examples and comparative examples described later, when water-soluble polymers such as carboxymethylcellulose (CMC), polyacrylic acid, or sodium alginate are used as the binder for the active material, the cycle life of the aluminum secondary battery can sometimes become extremely short. On the other hand, by using a binder containing 40% by mass or more of a water-insoluble polymer, the cycle life of the aluminum secondary battery, especially the aluminum secondary battery using an aqueous electrolyte, can be improved.

[0021] (Water-insoluble polymer) There are no particular restrictions on the water-insoluble polymers, and any known polymer can be used. For example, polymers with a water solubility of 10 g / 100 g or less, especially polymers with a solubility of 5 g / 100 g or less, and particularly polymers with a solubility of 1 g / 100 g or less, are examples, but the material is not limited to these. It may also be a mixture of multiple types of water-insoluble polymers, and it may also contain water-soluble polymers as long as the water-insoluble polymer makes up 40% by mass or more, preferably 60% by mass or more, more preferably 80% by mass or more, and particularly 90% by mass or more, relative to 100% by mass of the total binder.

[0022] (SP value) Although the non - water - soluble polymer itself is already known, whether a certain polymer is water - insoluble or not can also be estimated based on the SP value (solubility parameter). Substances with close SP values are likely to mix, while substances with widely separated SP values are difficult to mix. Therefore, for water with an SP value of about 48 (MPa) 1 / 2 (POLYMER HANDBOOK, 4th Edition, edited by A.ABE and D.R.BLOCH, JOHN WIELY, 1999; Fundamental of New Rubber Technology, edited by Japan Rubber Association, 1999; ENCYCLOPEDIA of POLYMER SCIENCE and TECHNOLOGY, by H.F.Mark et al., Interscience Publishers, 1964 - 1977), polymers with an SP value of about 33 (MPa) 1 / 2 The following polymers are generally water - insoluble. Among them, polymers with an SP value of about 30 (MPa) 1 / 2 Especially about 27 (MPa) 1 / 2 The following polymers are mostly water - insoluble. Therefore, in this embodiment, it is preferable to use polymers with an SP value of 30 (MPa) 1 / 2 as the binder.

[0023] In this embodiment, more preferably, polymers with an SP value of 20 - 30 (MPa) 1 / 2 (about 9.8 - 14.7 cal 1 / 2 / cm 3 / 2 ) are used. Even more preferably, polymers with an SP value of 22.0 - 28.0 (MPa) 1 / 2 are used. Particularly preferably, polymers with an SP value of 22.5 - 27.0 (MPa) 1 / 2 are used. By using polymers with such SP values as the binder of the electrode material, the cycle life of the aluminum secondary battery becomes even better, and the battery characteristics such as the initial battery capacity may also be improved.

[0024] Although this invention is not limited by any particular theory, one reason why the electrode material for aluminum secondary batteries of this embodiment is effective is that the polymer used as a binder is less likely to dissolve in the electrolyte. The electrolyte of aluminum secondary batteries, whether aqueous or non-aqueous, tends to exhibit high polarity. On the other hand, water-soluble polymers are generally highly polar and tend to dissolve not only in aqueous solvents but also in highly polar non-aqueous solvents and organic solvents. Therefore, if a water-soluble polymer is used as a binder for the active material, it may dissolve even if the electrolyte is non-aqueous, potentially leading to a reduction in lifespan due to the loss of the active material. On the other hand, non-water-soluble polymers, especially those with an SP value of 30 (MPa) 1 / 2 In electrode materials using the following polymers as binders, the binder does not dissolve into the electrolyte, preventing the loss of active material. Even if some loss occurs, the amount is minimal, thus improving the cycle life.

[0025] Furthermore, when electrolyte permeates the binder, the exchange of electrons and ions between the active material and the electrolyte tends to increase. Therefore, as long as the polymer used as the binder for the electrode material is non-water soluble, it is considered that the higher the polarity and SP value, the easier it is to improve the battery characteristics of the aluminum secondary battery. In the electrode material for the aluminum secondary battery of this embodiment, the binder has an SP value of 20-30 (MPa). 1 / 2 Especially 22.0~28.0 (MPa) 1 / 2 It is presumed that this is why battery characteristics such as initial battery capacity are easily improved when using this type of polymer.

[0026] (Specific examples of water-insoluble polymers) In this embodiment, the polymer that can be used as a binder may be any polymer that is non-water soluble as described above. Specific examples are listed below, but are not limited to these. Note that the following specific examples include natural products and mixtures, and therefore may overlap in scope with other examples depending on the breadth or narrowness of the definition. However, this does not limit the range of other resins, nor does it require or prohibit the combined use of multiple types of polymers. Other polymers may also be used or combined. Furthermore, the numerical values ​​in parentheses in the following examples are SP values ​​(unit: (MPa)) quoted from the aforementioned POLYMER HANDBOOK, New Edition Fundamentals of Rubber Technology, and ENCYCLOPEDIA of POLYMER SCIENCE and TECHNOLOGY, etc. 1 / 2 )

[0027] Alkyd resins (19-21), phthalic acid resins (21-22), melamine resins (24-25), melamine formaldehyde resins (15-25), amino alkyd cocondensation resins (19-24), urea resins (25-27), polyvinyl chloride (19-22), polyvinyl acetate (19-26), vinyl chloride / vinyl acetate copolymers (21-22), polyvinyl butyral (21-27), epoxy resins (20-26), polyurethane (19-23), polyester (18-25), vinyl ester resins (19-23), phenolic resins (21-28), rosin-modified maleic acid resins (15-22), silicone resins (14-16), acrylic silicone resins, polytetrafluoroethylene (12.7), polyfluoroethylene Vinylidene (23.2), polybutadiene (15-18), styrene-butadiene copolymer (16-18), acrylonitrile-butadiene copolymer (17-22), ABS resin, coumarone resin (19-21), alkoxysilane polycondensate (14-15), thermosetting acrylic resin (18-21), oil-soluble acrylic resin (18-21), rosin resin (19-24), shellac resin (23-28), nitrocellulose (cellulose nitrate: 21-26), cellulose acetate (19-27), cellulose acetate butyrate (18-26), ethylcellulose (20-21), polylactic acid (21-25), polyamide (22-28), polyimide (27-28), and polyamideimide (27-28).

[0028] In this embodiment, the water-insoluble polymer is preferably one or more polymers selected from the group consisting of the above. More preferably, shellac resin, polyvinyl butyral, polyvinylidene fluoride (PVDF), polylactic acid (PLA), cellulose acetate butyrate, cellulose acetate, vinyl chloride / vinyl acetate copolymer, ethylcellulose, etc. are preferred, among which shellac resin, PVDF, polyvinyl butyral containing 15-25 mol% hydroxyl units and 65-85 mol% acetal units, PVDF, amorphous polylactic acid, cellulose acetate with a degree of acetation of 55% or more (e.g., cellulose diacetate, cellulose triacetate), and cellulose acetate butyrate with a hydroxyl group content of 1-2% are preferred.

[0029] The water-insoluble polymer is preferably a curable polymer, such as a thermosetting polymer. Since polymers tend to become less soluble in solvents and more stable after curing, when used as a binder in electrode materials, they are less likely to cause a decrease in battery performance with repeated charging and discharging. For example, shellac resin and phenolic resin may dissolve in basic aqueous solutions or hot water in their untreated state, but become water-insoluble after thermocuring, so problems such as the binder dissolving into aqueous electrolytes and the active material falling off are less likely to occur. For this reason, they are suitable as binders for electrode materials for aluminum secondary batteries. In this embodiment, the water-insoluble polymer is any polymer that exhibits water insolubility when formed in the electrode material, and includes polymers that may exhibit water solubility before curing, such as shellac resin and phenolic resin, as well as emulsion-type polymers.

[0030] If an electrode material for an aluminum secondary battery contains the above-mentioned water-insoluble polymer in an amount of 40% by mass or more, preferably 60% by mass or more, more preferably 80% by mass or more, and particularly 90% by mass or more, relative to 100% by mass of the total binder, then the elution of the binder in the electrolyte is less likely to occur, making it easier to form an aluminum secondary battery with a good cycle life.

[0031] Furthermore, among the polymers mentioned above, those with an SP value of 20-30 (MPa) 1 / 2 , especially 22.0~28.0 (MPa) 1 / 2 , especially 22.5~27.0 (MPa) 1 / 2 If the electrode material uses a polymer as a binder, it becomes easier to form an aluminum secondary battery that also has excellent characteristics such as initial battery capacity.

[0032] ≪Method for manufacturing electrode materials≫ The electrode material for the aluminum secondary battery of this embodiment can be manufactured, for example, by mixing a positive electrode active material or a negative electrode active material with the above-mentioned polymer or its precursor or varnish, along with an optional conductive additive, to form a paste (ink), which is then applied to a current collector and dried or cured. For example, polyvinylidene fluoride may be dissolved in a solvent such as N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMA), or dimethyl sulfoxide (DMSO), then mixed with the active material and conductive additive to make a paste, which is then applied to a current collector and dried. Alternatively, an aqueous solution or aqueous dispersion of shellac resin or phenolic resin may be mixed with the active material and conductive additive to form a paste, which is then applied to a current collector, dried, and then heat-cured. An emulsion such as an epoxy prepolymer may be mixed with the active material and conductive additive, and this mixture may be applied, dried, and then cured.

[0033] Furthermore, the paste containing the binder and active material may also contain additives such as viscosity modifiers, dispersants, surfactants, antioxidants, and curing agents.

[0034] <Current collectors, etc.> There are no particular restrictions on the material of the current collector; any material used in aluminum secondary batteries may be used. Examples include, but are not limited to, aluminum, aluminum alloys, graphite, niobium, tantalum, molybdenum, nickel, nickel alloys, glassy carbon, titanium nitride, titanium carbonitride, titanium carbide, copper, and copper alloys.

[0035] Furthermore, as the negative electrode material, as described above, it is convenient to use foil or plate-like material of aluminum or aluminum alloy as both the negative electrode active material and the negative electrode current collector. On the other hand, the positive electrode material is preferably manufactured by applying a paste, which is a mixture of the positive electrode active material, binder, and optional components such as conductive additives, onto the current collector. The material of the positive electrode current collector is preferably copper or a copper alloy. A non-water-soluble polymer, especially one with an SP value of 20-30 (MPa), is preferred. 1 / 2 This is because it exhibits excellent adhesion to binders containing polymers.

[0036] As the positive electrode active material, carbon-based materials and metal oxides as described above can be used, but more specifically, carbon-based materials such as particulate or fibrous activated carbon, Ketjenblack, acetylene black, graphite, carbon nanotubes, and graphene; 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; fluorides of transition metals; coordination polymers such as ferric ferrocyanide (Prussian blue); polyacetylene, polythiophene, imine polymers, anthraquinone organic materials; and metal sulfides such as sulfur, copper sulfide, and molybdenum sulfide. There are no particular restrictions on its shape, and positive electrode active materials in any desired shape, such as particulate or fibrous, can be used.

[0037] The current collector may also have a reinforcing material, such as ceramics, glass, carbon-based materials, or polymer materials, attached to one side. For example, by laminating a current collector made of a metal film onto a ceramic or glass reinforcing plate, the corrosion resistance around the electrodes can be further improved. Furthermore, by using a polymer sheet current collector with a metal or graphite vapor-deposited onto it, it is possible to reduce the weight and cost of aluminum secondary batteries.

[0038] Aluminum rechargeable battery The present invention also includes an aluminum secondary battery comprising an electrode containing the above-described aluminum secondary battery electrode material, a separator, and an electrolyte. This embodiment, in particular, is an aluminum secondary battery comprising a positive electrode containing the above-described aluminum secondary battery electrode material, a negative electrode containing aluminum, a separator, and an electrolyte. The following will further describe such an aluminum secondary battery embodiment based on a typical embodiment shown in Figure 1.

[0039] In the aluminum secondary battery 1 of this embodiment, for example, a negative electrode 11 containing aluminum and / or an aluminum alloy, a positive electrode current collector 12 provided opposite the negative electrode 11, a positive electrode active material 13 disposed on the positive electrode current collector 12, and a separator and electrolyte (for example, a separator 14 impregnated with electrolyte) disposed between the negative electrode 11 and the positive electrode current collector 12.

[0040] In the embodiment shown in Figure 1, the separator 14 is in almost complete contact with the main surface of one of the negative electrode 11 and positive electrode active material 13 layers, the electrolyte is impregnated into the separator 14, and they are housed in the outer casing material 15. However, the present invention is not limited to this embodiment. For example, the outer casing material 15 is not an essential component. Furthermore, a liquid, gel-like, or solid electrolyte may be housed inside a frame-shaped or grid-shaped separator. Moreover, instead of the flat plate shape shown in Figure 1, the aluminum secondary battery may be cylindrical, for example, a wound-type aluminum secondary battery. The electrode area may also be larger on the negative electrode side than on the positive electrode side. If the negative electrode is larger than the positive electrode, it becomes easier to prevent electrodeposition of aluminum ions at the negative electrode end. Furthermore, single cells as shown in Figure 1 may be connected in series or parallel to form a battery pack. The following describes more specific aspects of the aluminum secondary battery of this embodiment.

[0041] <Aluminum-ion battery> An aluminum-ion battery can be constructed using the positive electrode current collector 12 and positive electrode active material 13 described above, and a negative electrode 11 containing aluminum and / or an aluminum alloy. An aluminum-ion battery is a secondary battery in which charging and discharging occur through the movement of aluminum ions between the positive electrode and the negative electrode. Compared to lithium-ion batteries, it has the advantages of being able to achieve high capacity, being highly safe, and being made from abundant resources. Here, "aluminum ions" also include aluminum complex ions such as ACO complex ions and cluster-shaped ions containing aluminum. The aluminum secondary battery of the present invention encompasses such aluminum-ion batteries.

[0042] <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 also be an aluminum-sulfur battery. As mentioned 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, an even larger charge and discharge capacity is achieved compared to conventional products, and the inherent characteristics of aluminum batteries can be utilized.

[0043] 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. As conductive additives in aluminum-sulfur batteries, carbon-based materials as described above, or copper or its compounds can be used. It is also possible to use sulfur coated with carbon.

[0044] <Electrolyte> The electrolyte for an aluminum secondary battery can be any liquid containing ions that include the element aluminum as an electrolyte. Furthermore, the same electrolyte can be used in both the aluminum-ion battery and the aluminum-sulfur battery described above. In this invention, the term "electrolyte" broadly includes colloidal solutions. That is, the "electrolyte" in this invention also includes, for example, gel-like electrolytes.

[0045] The electrolyte is a liquid containing, for example, one or more solvents selected from the group consisting of water, organic solvents, deep eutectic solvents, and ionic liquids, and an aluminum salt. In this embodiment, since the binder of the electrode material is a water-insoluble polymer, the improvement in cycle life is particularly noticeable in aluminum secondary batteries using an electrolyte containing a highly polar solvent. As a highly polar solvent, for example, one with an SP value of 30 (MPa) 1 / 2 In particular, 35 (MPa) 1 / 2 The above, especially 40 (MPa) 1 / 2The solvents listed above, specifically (the numbers in parentheses are in MPa) 1 / 2 Examples of electrolytes (SP values ​​shown in units) include ethylene carbonate (30.1), ethylene glycol (32.8), methylformamide (32.9), glycerol (33.8), formamide (39.3), and water (47.9), but are not limited to these. Water-based electrolytes are particularly preferred.

[0046] (electrolyte) There are no particular restrictions on ions containing aluminum as an electrolyte. For example, aluminum-containing ion sources include, but are not limited to, one or more salts selected from the group consisting of aluminum triperfluoroalkyl sulfonates, including aluminum tri(trifluoromethanesulfonate) (Al(OTF)3), aluminum bis(fluorosulfonyl)imide (Al-FSI), aluminum halides, including aluminum bromide and aluminum iodide, aluminum perchlorate, aluminum tris(hexafluorophosphate) (Al(PF6)3), and aluminum tris(tetrafluoroborate) (Al(BF4)3). Al derived from aluminum sulfate or aluminum nitrate. 3+ Ions can also be used. Furthermore, multiple types of these ions may be included.

[0047] Among these electrolytes, aluminum triperfluoroalkyl sulfonate, aluminum bis(fluorosulfonyl)imide, aluminum tris(hexafluorophosphate), and aluminum tris(tetrafluoroborate) are preferred. Using an electrolyte containing these electrolytes will result in better cycle characteristics for aluminum secondary batteries. However, aluminum chloride electrolyte may corrode some positive electrode materials (e.g., copper), so it is preferable not to include it in the electrolyte. More preferably, aluminum triperfluoroalkyl sulfonate or aluminum bis(fluorosulfonyl)imide is used as the electrolyte. With these electrolytes, stable charge and discharge characteristics are more easily achieved even if the electrolyte is aqueous. In particular, aluminum tri(trifluoromethanesulfonate) is preferred.

[0048] (Electrolyte solvent) As mentioned above, the solvent for the electrolyte is preferably a highly polar solvent, such as water, a deep eutectic solvent, and / or an ionic liquid. Among these, an aqueous solution, particularly an aqueous solution, is preferred. If the main solvent is water, a higher level of safety can be ensured compared to using organic solvents, and it is also advantageous in terms of cost. More preferably, an aqueous solution containing aluminum triperfluoroalkyl sulfonate or aluminum bis(fluorosulfonyl)imide is used. With these aqueous electrolytes, particularly an aqueous solution of aluminum tri(trifluoromethanesulfonate), the water solvent is less likely to be electrolyzed during charging, and the characteristics of a secondary battery are more easily exhibited (Non-Patent Literature 1). Furthermore, it becomes possible to reversibly intercalate aluminum aco complexes or trifluoromethanesulfonate complexes in the carbon-based positive electrode active material (Non-Patent Literature 2).

[0049] A "deep eutectic solvent" is a solvent that is liquid at room temperature, obtained by mixing a hydrogen bond donor compound and a hydrogen bond acceptor compound in a certain ratio. By combining donor and acceptor compounds, solvents with any desired properties can be created, and various 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] (Concentration of electrolyte solution) There are no particular restrictions on the concentration of the electrolyte in the electrolyte 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 electrolyte solution. On the other hand, from the viewpoint of preventing an increase in the viscosity of the electrolyte solution and maintaining ionic conductivity, it is preferable to keep the concentration of the electrolyte solution low. A balance between these two is possible, and the concentration of the electrolyte solution may be, for example, 0.1 to 15 mol / L, or even 0.5 to 10 mol / L, and especially around 1 to 5 mol / L.

[0051] (Additives) The electrolyte may also contain various additives as optional components. For example, negative or positive electrode protective film forming agents such as vinyl group-containing compounds, γ-butyrolactone, ethylene sulfide, cyclic sulfonic acid esters, methyl benzoate, succinic anhydride, polydimethylsiloxane, AgPF6, Cu(CF3SO3)2; overcharge prevention agents such as 2,4-difluoroanisole; and flame retardants such as phosphate esters, phosphazenes, and imidazole salts may be included in an amount of about 0.01 to 5% by mass, particularly about 0.1 to 1% by mass.

[0052] <Separator> The aluminum secondary battery 1 of this embodiment includes a separator 14 placed between the positive electrode and the negative electrode to prevent short circuits between the two electrodes. There are no particular restrictions on the form of the separator; for example, it may be frame-shaped or lattice-shaped with a certain thickness to isolate the positive electrode and the negative electrode. It is also possible to use a gel electrolyte or a solid electrolyte as the separator. However, from the viewpoint of more reliably preventing short circuits between the two electrodes, it is preferable that the separator 14 is in contact with almost the entire surface of the main surface of one of the negative electrode 11 and the positive electrode active material 13 layers, as shown in the embodiment in Figure 1. Furthermore, from the viewpoint of maintaining high ionic conductivity between the positive and negative electrodes, it is preferable that the separator 14 holds an electrolyte, and is preferably in the form of a porous film or fibers.

[0053] There are no particular restrictions on the material or shape of the separator; any material can be used, such as glass, ceramics, cellulose fibers, paper (like Japanese paper), fluoropolymers, polyolefins like polyethylene or polypropylene, porous materials such as PET, aromatic polyamides, polyacrylonitrile, and polyimide, or woven or nonwoven fabrics, or gel-like separators.

[0054] <Battery type> Aluminum secondary batteries with the above configuration can be used as single cells, or multiple units can be connected in series or parallel to form a battery pack (module). There are no particular restrictions on the size or the number of single cells in the battery pack; any desired size and number can be adopted according to the purpose. For example, a positive electrode, negative electrode, and separator with a thickness of approximately 1 μm to 2 mm, especially 10 to 500 μm, can be stacked to form a single cell, or 1 to 1,000 such single cells, especially 10 to 100, can be connected to form a battery pack.

[0055] There are no particular restrictions on the type or shape of aluminum secondary batteries; for example, in addition to the flat plate type shown in Figure 1, they can be cylindrical, coin-shaped, button-shaped, and even laminated types as shown below.

[0056] <Laminated Batteries> Another embodiment of the present invention is an aluminum secondary battery, for example, as shown in Figure 1, further comprising an outer casing, wherein a negative electrode, a positive electrode (positive electrode active material and positive electrode current collector, etc.), a separator, and an electrolyte are housed in the outer casing, and the outer casing has an ethylene vinyl acetate resin layer, an ethylene vinyl alcohol resin layer, a polyacrylonitrile resin layer, and / or a polyethylene terephthalate resin layer.

[0057] The aluminum secondary battery of this embodiment is more preferably a laminated battery. A laminated battery is a battery in which a number of batteries (single cells) equipped with a positive electrode, a negative electrode, and a separator are optionally connected in series and then housed in an outer casing made of laminate film. Also called laminated electrode or pouch battery, it has advantages such as being lightweight, having high energy density, high safety, and being easy to form into a battery pack. Therefore, it is a suitable form for making secondary batteries more practical.

[0058] In this embodiment, the shedding of active materials and other components is suppressed, improving cycle life. Furthermore, the outer casing is less prone to deformation or deterioration, making it a practical secondary battery with a long lifespan. For this reason, it is suitable as a secondary battery for vehicles such as automobiles, personal computers, mobile devices, various home appliances, and medical equipment. [Examples]

[0059] 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 specified above.

[0060] [Example 1] An aluminum secondary battery was fabricated using the positive electrode, negative electrode, and electrolyte prepared as described below. • Positive electrode: An ink prepared by mixing 5g of graphite (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 3g of titanium dioxide (TiO2, manufactured by Ishihara Sangyo Co., Ltd.) with 10g of a 10% by mass aqueous solution of shellac resin (manufactured by Gifu Shellac Manufacturing Co., Ltd.) was applied to a positive electrode current collector (size 30 x 35 mm) made of pure copper (tough pitch copper with a purity of 99.94% and a specific gravity of 8.93) using a bar coater, then heated and dried at 120°C for 20 minutes, and further heat-cured at 80°C for 10 minutes. • Negative electrode: A thin sheet of general-purpose A1050 aluminum (size 25 x 35 mm) was used. • Electrolyte: An aqueous electrolyte was used, as differences in cycle life are relatively more easily observed. Aluminum tri(trifluoromethanesulfonate) (Al(OTF)3) was dissolved in purified water to prepare a 2 mol / L aqueous solution.

[0061] The electrolyte prepared above was impregnated into a glass filter separator, and the negative and positive electrodes were placed on each side of the separator and secured with plastic clips to form an aluminum secondary battery.

[0062] The obtained aluminum secondary batteries were subjected to 100 charge-discharge cycles at a potential window of 0.2 to 1.8 V and 0.1 C, and their battery capacity (charge-discharge capacity) was measured. The measurements were performed using a potentiostat / galvanostat HA series manufactured by Hokuto Denko Co., Ltd. In this example, all experimental procedures were performed in air, and battery capacity measurements were performed with n=3. The battery capacities at cycles 1, 25, and 100, along with the SP values ​​of the shellac resin, are shown in Table 1 below.

[0063] [Example 2] The procedure was the same as in Example 1, except that 10 g of a 10% by mass isopropanol solution of polyvinyl butyral (approximately 19 mol% hydroxyl groups, approximately 76 mol% acetal groups; manufactured by Sekisui Chemical Co., Ltd.) was used as the binder for the positive electrode instead of the shellac resin solution, and no heat curing treatment was performed. The battery capacity measurement results, along with the SP values ​​of the polymers, are shown in Table 1 below.

[0064] [Comparative Example 1] The procedure was the same as in Example 2, except that 10 g of a 1% aqueous solution of carboxymethylcellulose (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was used as the binder for the positive electrode instead of the polyvinyl butyral solution. The battery capacity measurement results, along with the SP values ​​of the polymer, are shown in Table 1 below, but the battery capacity after 100 cycles was 0. Visual inspection of the positive electrode after measurement revealed that the binder had dissolved and the positive electrode active material had detached into the electrolyte.

[0065] [Examples 3-8] The procedure was the same as in Example 2, except that polyvinylidene fluoride (N-methylpyrrolidone solution, Example 3), amorphous polylactic acid (ethyl lactate solution, Example 4), cellulose acetate butyrate (ethyl lactate solution, Example 5), cellulose acetate (ethyl lactate solution, Example 6), vinyl chloride / vinyl acetate copolymer (methyl ethyl ketone solution, Example 7), or ethyl cellulose (ethanol solution, Example 8) was used as the binder for the positive electrode instead of polyvinyl butyral. The polymers used in each example, their SP values, and the battery capacity measurement results are shown in Table 1 below.

[0066] [Example 9] The same procedure as in Examples 1 and 2 was followed, except that a positive electrode prepared as described below was used. The battery capacity measurement results, along with the SP values ​​of the polymer, are shown in Table 1 below. • Positive electrode: An ink prepared by mixing 4g of graphite (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 15g of a 1% aqueous solution of carboxymethylcellulose (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and 0.25g of 40% concentration SBR latex (BM451B manufactured by Nippon Zeon Co., Ltd.) was applied to a pure copper positive electrode current collector, the same as in Example 1, using a bar coater, and then heat-treated at 100°C for 20 minutes.

[0067] [Table 1]

[0068] In Comparative Example 1, which used carboxymethylcellulose, a water-soluble polymer, as the binder, the initial battery capacity was good, but after 100 cycles, the battery capacity dropped to zero. As mentioned above, it is presumed that in Comparative Example 1, the binder polymer leached out, causing the battery to cease functioning after several tens of charge-discharge cycles. On the other hand, in Examples 1 to 8, which used a non-water-soluble polymer as the binder, the battery capacity was maintained at around 80% to 90% of the initial value even after 100 cycles.

[0069] Furthermore, in Example 9, where a binder was a mixture of 60% by mass of carboxymethylcellulose, a water-soluble polymer, and 40% by mass of SBS, a water-insoluble polymer, the battery capacity was maintained after 100 cycles. This demonstrates that an aluminum secondary battery with a good cycle life can be obtained by using an electrode material containing 40% by mass or more of a water-insoluble polymer relative to the total binder mass of 100%.

[0070] Among the above examples 1 to 8, the SP value was 22.0 (MPa). 1 / 2 Examples 1-6 using the above polymers, particularly those with an SP value of 22.5-26 (MPa) 1 / 2 In Examples 1-5, which used the polymer, the battery capacity increased significantly from the initial stage to 100 cycles.

[0071] As described above, it has been shown that by using an electrode material containing 40% by mass or more of a water-insoluble polymer as a binder for the active material according to the present invention, an aluminum secondary battery with a good cycle life can be manufactured. Furthermore, as a water-insoluble polymer, an SP value of 20-30 (MPa) 1 / 2 To the extent, especially 22.0 (MPa) 1 / 2 It has become clear that by employing polymers of a certain quality or higher, it is possible to create aluminum secondary batteries that have not only a good cycle life but also good battery capacity. [Explanation of Symbols]

[0072] 1. Aluminum secondary battery 11 Negative electrode 12 Positive electrode current collector 13 Cathode active material 14 Separators 15 Exterior materials

Claims

1. An electrode material for an aluminum secondary battery, comprising 40% by mass or more of a water-insoluble polymer as a binder for the active material, relative to 100% by mass of the binder.

2. The electrode material for an aluminum secondary battery according to claim 1, wherein the active material is a positive electrode active material.

3. The aforementioned water-insoluble polymer has an SP value of 30 (MPa). １／２ The electrode material for an aluminum secondary battery according to claim 1 or 2, wherein the polymer is as follows:

4. The non-water-soluble polymer is one or more polymers selected from the group consisting of alkyd resins, phthalic acid resins, melamine resins, melamine-formaldehyde resins, amino-alkyd cocondensate resins, urea resins, polyvinyl chloride, polyvinyl acetate, vinyl chloride / vinyl acetate copolymers, polyvinyl butyral, epoxy resins, polyurethanes, polyesters, vinyl ester resins, phenolic resins, rosin-modified maleic acid resins, silicone resins, acrylic silicone resins, polytetrafluoroethylene, polyvinylidene fluoride, polybutadiene, styrene / butadiene copolymers, acrylonitrile / butadiene copolymers, ABS resins, coumarone resins, alkoxysilane polycondensates, thermosetting acrylic resins, oil-soluble acrylic resins, rosin resins, shellac resins, nitrocellulose, cellulose acetate, cellulose acetate butyrate, ethylcellulose, amorphous polylactic acid, polyamides, polyimides, and polyamideimides, as described in claim 1 or 2.

5. The electrode material for an aluminum secondary battery according to claim 2, wherein the positive electrode active material comprises 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 polymers, anthraquinone-based organic materials, sulfur, and metal sulfides.

6. The electrode material for an aluminum secondary battery according to claim 2, further comprising one or more conductive additives selected from the group consisting of carbon black, Ketjenblack, acetylene black, graphite, graphene, carbon nanotubes, metals, metal oxides, and conductive ceramics.

7. An aluminum secondary battery comprising a positive electrode containing the electrode material for aluminum secondary batteries described in claim 2, a negative electrode containing aluminum, a separator, and an electrolyte.

8. The aluminum secondary battery according to claim 7, wherein the electrolyte 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.

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

10. The device further comprises an outer casing, and the negative electrode, the positive electrode, the separator, and the electrolyte are housed within the outer casing. The aluminum secondary battery according to claim 7, wherein the exterior material comprises 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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