Aluminum secondary battery

Abstract

The purpose of the present invention is to provide an aluminum secondary battery which has a high charge / discharge capacity and a good cycle life, and is advantageous in terms of cost. This aluminum secondary battery comprises: a negative electrode that contains aluminum and / or an aluminum alloy; a positive electrode current collector that is provided so as to face the negative electrode; a positive electrode active material that is disposed on the positive electrode current collector; a separator that is disposed between the negative electrode and the positive electrode current collector; and an electrolyte solution. The positive electrode current collector is formed of copper and / or a copper alloy. It is preferable that the copper or the copper alloy has a specific gravity of 8.50-8.96.

Description

Aluminum secondary battery

[0001] The present invention relates to an aluminum secondary battery.

[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. Aluminum has long been used as an electrode for primary batteries, and in recent years, development of aluminum-ion secondary batteries has also progressed.

[0004] For example, Patent Documents 1 to 4 disclose a carbonaceous material as a positive electrode active material and AlCl as an electrolyte. ４ － Aluminum ion batteries using aluminum bis(trifluoromethanesulfone)imide or the like as a cathode current collector and molybdenum or platinum or the like have been disclosed. Aluminum ion secondary batteries using 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. This makes it possible to form secondary batteries using aqueous electrolytes.

[0005] Furthermore, aluminum-sulfur batteries, which use sulfur in the positive electrode, are currently being studied, although at the academic research level (see, 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 expected to be next-generation batteries.

[0006] JP 2014-222609 A JP 2016-213101 A JP 2021-174732 A JP 2017-168234 A

[0007] Jasmin Smajic, et al. , Nanomaterials, 11, 3235 (2021) Jasmin Smajic, et al. , Adv. Mater. Interfaces, 2101733 (2021) G. A. Elia, et al. , Journal of Power Sources, 481, 228870 (2021)

[0008] As described above, aluminum-ion batteries and aluminum-sulfur batteries have large theoretical capacities and are considered to be promising secondary batteries. However, aluminum secondary batteries developed to date have issues such as small charge / discharge capacities, low discharge voltages and charge / discharge efficiencies, and short cycle lives, making it difficult to say that their inherent battery characteristics are being fully utilized. Furthermore, because typical aluminum secondary batteries primarily use extremely expensive metal materials such as niobium, tantalum, platinum, and molybdenum for the positive electrode current collector (see, for example, Patent Documents 1 to 4), reducing costs is also an issue.

[0009] The present invention has been made in view of the above problems, and has an object to provide an aluminum secondary battery that has a large battery capacity (charge / discharge capacity), a good cycle life, and is cost-effective.

[0010] As a result of extensive research, the present inventors have found that by using copper and / or a copper alloy as the positive electrode current collector of an aluminum secondary battery, physical properties such as charge / discharge capacity and cycle life can be improved.

[0011] That is, the present invention provides the following (1) to (7): (1) An aluminum secondary battery comprising a negative electrode containing aluminum and / or an aluminum alloy, a positive electrode current collector provided so as to face the negative electrode, a positive electrode active material disposed on the positive electrode current collector, a separator disposed between the negative electrode and the positive electrode current collector, and an electrolyte, wherein the positive electrode current collector is made of copper and / or a copper alloy. (2) The aluminum secondary battery according to (1) above, wherein the copper or copper alloy has a specific gravity of 8.50 to 8.96. (3) The aluminum secondary battery according to (1) or (2) above, wherein the copper or copper alloy has a copper content of 80 to 100 mass %. (4) The aluminum secondary battery according to any one of (1) to (3) above, wherein the electrolyte is a liquid containing an aluminum salt and one or more solvents selected from the group consisting of water, organic solvents, deep eutectic solvents, and ionic liquids. (5) The aluminum salt is selected from the group consisting of aluminum triperfluoroalkylsulfonate, 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 (6) The aluminum secondary battery according to any one of (1) to (5) above, wherein 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-based polymers, anthraquinone-based organic substances, sulfur, and metal sulfides. (7) The aluminum secondary battery according to any one of (1) to (6) above, further comprising an exterior packaging material, wherein the negative electrode, the positive electrode active material, the positive electrode current collector, the separator, and the electrolyte are housed in the exterior packaging material, and the exterior packaging 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.

[0012] The aluminum secondary battery of the present invention has a large charge / discharge capacity, a good cycle life, and is advantageous in terms of cost.

[0013] 1 is a cross-sectional view of an aluminum secondary battery according to one embodiment of the present invention.

[0014] 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] <Aluminum Secondary Battery> Figure 1 is a cross-sectional schematic diagram of an aluminum secondary battery according to one embodiment of the present invention. The aluminum secondary battery 1 of this embodiment includes a negative electrode 11 containing aluminum and / or an aluminum alloy, a positive electrode current collector 12 disposed opposite the negative electrode 11, a positive electrode active material 13 disposed on the positive electrode current collector 12, a separator 14 disposed between the negative electrode and the positive electrode current collector, and an electrolyte, and the positive electrode current collector 12 is made of copper and / or a copper alloy.

[0016] 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, and the separator 14 is impregnated with an electrolyte. However, the present invention is not limited to this embodiment. For example, a liquid, gel, or solid electrolyte may be contained inside a frame-shaped or lattice-shaped separator. Furthermore, the aluminum secondary battery may be cylindrical rather than flat as shown in FIG. 1 . The area of ​​the electrodes 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, 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 constituting the aluminum secondary battery of the present invention is described.

[0017] <Negative Electrode> In the aluminum secondary battery 1 of this embodiment, the negative electrode 11 contains aluminum and / or an aluminum alloy. Here, the aluminum and / or aluminum alloy functions as a negative electrode active material capable of releasing aluminum ions, but can also function as a current collector. For example, it is possible to use an aluminum foil or an aluminum alloy plate as a negative electrode that serves as both the negative electrode active material and the current collector.

[0018] The negative electrode 11 may also be composed of a current collector and an active material, and may optionally contain a conductive additive, a binder, and / or a solid electrolyte. Although not particularly limited, one example is a layered negative electrode in which a thin film or powder of aluminum and / or an aluminum alloy is applied to a current collector. The negative electrode 11 may be made of any material or configuration as long as it is capable of precipitation / dissolution of aluminum or dealloying / alloying of aluminum ions from an aluminum alloy.

[0019] The aluminum alloy material is not particularly limited, and examples thereof include, but are not limited to, aluminum-gold alloy, aluminum-gallium alloy, aluminum-indium alloy, aluminum-manganese alloy, aluminum-nickel alloy, aluminum-platinum alloy, aluminum-magnesium alloy, aluminum-iron alloy, aluminum-bismuth alloy, aluminum-tin alloy, aluminum-zinc alloy, and even aluminum-silicon alloy. Alloys containing two or more elements other than aluminum may also be used. For example, aluminum-magnesium-silicon alloy, aluminum-copper-magnesium alloy, aluminum-magnesium-zinc alloy, etc. can be used as the negative electrode material.

[0020] When the negative electrode 11 includes a current collector, the material of the current collector is not particularly limited. For example, aluminum and / or an aluminum alloy may be used as the current collector, with a negative electrode active material such as aluminum powder disposed on the surface. Examples of negative electrode current collector materials other than aluminum include, but are not limited to, carbon materials such as graphite and glassy carbon, stainless steel, platinum, molybdenum, nickel, nickel-based alloys, and even titanium nitride, titanium carbonitride, and titanium carbide. Preferably, aluminum or a nickel-based alloy is used.

[0021] In a more preferred embodiment, the negative electrode 11 is made of a plate, sheet, or film of aluminum and / or an aluminum alloy. Such a negative electrode configuration allows for easy fabrication of an aluminum secondary battery. Using a general-purpose aluminum plate or aluminum foil as the negative electrode 11 is particularly advantageous in terms of cost.

[0022] The negative electrode 11 may have a reinforcing layer made of ceramics, glass, carbon material, polymer material, etc. Such a reinforcing layer is particularly useful when the negative electrode active material and the negative electrode current collector are thin layers of aluminum and / or aluminum alloy, such as aluminum foil. The negative electrode 11 can also be formed by vapor-depositing aluminum onto such a reinforcing layer.

[0023] <Positive Electrode> In the aluminum secondary battery 1 of this embodiment, the positive electrode includes a positive electrode current collector 12 provided to face the above-described negative electrode 11, 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.

[0024] [Positive Electrode Current Collector] In the aluminum secondary battery 1 of this embodiment, the positive electrode current collector 12 is made of copper and / or a copper alloy (hereinafter, may be referred to as "copper (alloy)"). This is an important requirement in this embodiment. In an aluminum secondary battery, if the positive electrode current collector is made of copper (alloy), a larger charge / discharge capacity and a longer cycle life can be achieved compared to cases where other metal materials are used. Copper (alloy) is not as expensive as niobium or tantalum, and therefore has a cost advantage. Furthermore, because copper (alloy) is generally a soft material, it can also have the advantage of making it easier to process the positive electrode current collector.

[0025] Although the present invention is not limited by any particular theory, it is believed that the reason why the aluminum secondary battery of this embodiment exhibits a large charge / discharge capacity is that the positive electrode current collector made of copper (alloy) exhibits high electrical conductivity. Copper (alloy) tends to exhibit higher electrical conductivity than metals such as niobium, tantalum, and molybdenum. In particular, the electrical conductivity of copper is approximately 6×10, although it depends on the purity, etc. ７ This is the second highest value after silver, at about S / m. It is thought that the positive electrode current collector has such high conductivity that electrons are smoothly exchanged with the positive electrode active material, resulting in a large charge / discharge capacity.

[0026] Copper (alloy) is also softer than tantalum and other materials, and therefore more easily accommodates the expansion and contraction of the positive electrode active material during charge and discharge. As a result, adhesion between the positive electrode current collector and the positive electrode material is more easily maintained, potentially extending the cycle life. Copper (alloy) also has the advantage of excellent corrosion resistance, although not as much as niobium or tantalum. Therefore, during repeated charge and discharge cycles, the positive electrode current collector is less likely to be oxidized, resulting in a decrease in conductivity, which may be contributing to the long cycle life.

[0027] From the viewpoint of further improving the charge / discharge capacity and cycle life of aluminum secondary batteries, it is preferable that the copper (alloy) has a specific gravity (≒ density) of about 8.50 to 8.96, for example, about 8.60 to 8.94. Copper (alloy) with such a specific gravity exhibits high conductivity and is suitable as a material for the positive electrode current collector of aluminum secondary batteries. The specific gravity can be measured, for example, by the underwater displacement method in accordance with JIS Z8807 or JIS K7112.

[0028] From the viewpoint of charge / discharge capacity and cycle life, it is preferable that the copper (alloy) has a copper content of 80 to 100 mass %, for example, about 90 to 99.99 mass %. The higher the copper content of copper (alloy), the better the conductivity and the more suitable it tends to be for a positive electrode current collector. In addition, the copper amount per unit volume, i.e., the copper content (infinite number with 1 as the unit) and the density, is, for example, 6.80 to 8.96 g / cm ３ , particularly 7.50 to 8.94 g / cm ３ Copper (alloy) of this order is preferred. More preferably, copper, particularly high-purity copper called pure copper, is used.

[0029] (Copper) There are no particular limitations on the copper material that can be used for the positive electrode current collector 12, and various known materials can be used. Typical examples include, but are not limited to, oxygen-free copper (OCF, specific gravity 8.94 to 8.95) with a purity of 99.96% or more, deoxidized copper (specific gravity approximately 8.94) with a purity of 99.90% or more, and tough pitch copper (specific gravity 8.89 to 8.94). Pure copper with a purity of 99% or more is preferred, but copper with a purity of less than 99%, for example, a specific gravity of approximately 8.8 to 8.9, known as blister copper, can also be used.

[0030] From the viewpoint of electrical conductivity, pure copper having a specific gravity of 8.90 or more, particularly oxygen-free copper (JIS number C1020), is preferred, but from the viewpoint of cost, deoxidized copper such as dephosphated copper (C1220) or tough pitch copper (C1100), particularly tough pitch copper, is preferred. For example, by forming the positive electrode current collector from tough pitch copper having a specific gravity of 8.90 or more, more preferably a specific gravity of 8.91 to 8.93, an aluminum secondary battery can be obtained that is low in cost yet has good charge / discharge capacity and cycle life.

[0031] (Copper Alloy) The type of copper alloy is not particularly limited. Examples include, but are not limited to, copper alloys with zinc (brass, brass, red brass; specific gravity 7.9 to 8.9), copper alloys with tin (bronze, bronze; specific gravity 7.5 to 8.8), copper alloys with tin and phosphorus (phosphor bronze; specific gravity 8.8 to 8.9), copper alloys with aluminum (aluminum bronze; specific gravity 7.4 to 7.7), copper alloys with zinc and aluminum (aluminum brass; specific gravity 8.1 to 8.4), copper alloys with nickel or the like (cupronickel; specific gravity 8.8 to 9.0), copper alloys with zinc and nickel (nickel silver; specific gravity 8.3 to 8.8), copper alloys containing beryllium (beryllium copper; specific gravity 8.3 to 8.8), copper alloys containing magnesium, copper alloys containing silicon, and the like.

[0032] Among these copper alloys, alloys with a specific gravity of 8.50 to 8.96 are preferred, with those with a specific gravity of 8.60 to 8.94 being particularly preferred, and those with a specific gravity of 8.70 to 8.90 being particularly preferred. Copper alloys with such specific gravities have the advantages of high electrical conductivity and excellent workability. Copper alloys with a copper content of 80% by mass or more, for example 85 to 99% by mass, particularly 90 to 95% by mass are also preferred. Alloys with such copper contents have the advantage of being low cost yet exhibiting high electrical conductivity. The amount of copper per unit volume is 6.80 to 8.96 g / cm ３ , especially 7.30 to 8.50 g / cm ３ Approximately, especially 7.50 to 8.00 g / cm ３ Copper alloys of this order may also be used.

[0033] Specific examples of preferred copper alloys include C2100, which contains about 95% by mass of copper and about 5% by mass of zinc; C2200, which contains about 90% by mass of copper and about 10% by mass of zinc; C2300, which contains about 85% by mass of copper and about 15% by mass of zinc; C2400, which contains about 80% by mass of copper and about 20% by mass of zinc; C2600, which contains about 70% by mass of copper and about 30% by mass of zinc; C2700, which contains about 60% by mass of copper and about 40% by mass of zinc; Examples of such alloys include, but are not limited to, C2800, which contains approximately 80-90% by mass of copper, approximately 5-12% by mass of aluminum, and approximately 1-9% by mass of iron, manganese, nickel, etc.; C6161 and C6191, which contain approximately 73-79% by mass of copper, approximately 20-25% by mass of zinc, approximately 2% by mass of aluminum, and approximately 1-2% by mass of tin.

[0034] (Configuration of Positive Electrode Current Collector) The positive electrode current collector 12 is made of copper (alloy) as described above, but one side of the positive electrode current collector 12 may be provided with a reinforcing material made of ceramics, glass, carbon material, polymer material, or the like. For example, by laminating the positive electrode current collector 12 made of a copper (alloy) film on a ceramic or glass reinforcing plate, the corrosion resistance around the positive electrode can be further improved. In addition, the positive electrode current collector 12 can be configured by vapor-depositing copper (alloy) onto a polymer sheet, thereby reducing the weight and cost of the aluminum secondary battery.

[0035] There are no particular limitations on the method for manufacturing the positive electrode current collector 12, and various known methods can be used depending on the desired shape and the materials used. Copper (alloy) has superior conductivity compared to tantalum and molybdenum, is low cost, and is soft and easy to process, making it suitable as a material for mass-produced batteries.

[0036] [Positive Electrode Active Material] In the aluminum secondary battery 1 of this embodiment, a positive electrode active material 13 is disposed on the 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. Examples include, but are not limited to, 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.

[0037] More specifically, examples of carbon-based materials that can be used include particulate or fibrous activated carbon, Ketjen black, acetylene black, graphite, carbon nanotubes, and graphene. Examples of metal oxides that can be used include manganese dioxide, lead dioxide, silver oxide, iron oxide, molybdenum oxide, vanadium oxide, and titanium oxide. Examples of metal carbides include titanium carbide. Examples of metal nitrides include titanium nitride. Examples of metal fluorides include fluorides of lanthanum and cerium. Examples of coordination polymers include ferric ferrocyanide (Prussian blue). Examples of metal sulfides include copper sulfide, molybdenum sulfide, and lithium sulfide.

[0038] 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, etc. 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 form the positive electrode of the aluminum secondary battery 1. Alternatively, graphite or the like may be vapor-deposited on one side of the positive electrode current collector 12 made of copper (alloy) to form the positive electrode active material 13.

[0039] (Conductive Aid) Incidentally, as the conductive aid, a general-purpose conductive aid can be used, such as a carbon material such as carbon black, ketjen black, acetylene black, graphite, carbon nanotube, etc., a metal, a metal oxide, a conductive ceramic, etc. From the viewpoint of corrosion resistance, a carbon material is particularly preferable.

[0040] (Binder) The binder plays a role in binding the positive electrode active material and the conductive additive, and commonly used binders include, for example, polyvinylidene fluoride (PVDF), vinylidene fluoride copolymers, polytetrafluoroethylene (PTFE), tetrafluoroethylene copolymers, fluororubber, ethylene propylene diene rubber, styrene butadiene copolymers, cellulose-based resins, ethylene vinyl alcohol resins, polyvinyl alcohol (PVAL), poly(meth)acrylic acid, etc. In the present invention, any of these and other known binders can be used.

[0041] The positive electrode active material 13, the conductive additive, and the binder as described above can be applied to the positive electrode current collector by dissolving and / or dispersing them in a solvent, for example. The solvent used here is not limited, and a mixture of multiple solvents can also be used. Furthermore, additives such as a viscosity modifier, a dispersant, a surfactant, and an antioxidant may also be added.

[0042] An aqueous solvent can also be used as the solvent. The type of aqueous binder is not particularly limited, and examples thereof include, but are not limited to, carboxymethyl cellulose, SBR latex, NBR latex, (meth)acrylic latex (emulsion), polyvinyl alcohol, alginic acid, gelatin, and chitosan.

[0043] The conductive additive, binder, solvent, etc. can also be used when producing the negative electrode 11 .

[0044] <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 facing them. Aluminum ion batteries are secondary batteries that are charged and discharged by the movement of aluminum ions between the positive and negative electrodes. Compared to lithium ion batteries, aluminum ion batteries have the advantages of being able to achieve higher capacity, being highly safe, and being abundant in resources. 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.

[0045] <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 copper (alloy) as the positive electrode current collector, a larger charge / discharge capacity than conventional products is achieved, making it possible to utilize the inherent characteristics of aluminum batteries.

[0046] 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 above-mentioned carbon materials, copper, and copper compounds. Sulfur can also be used after being coated with carbon.

[0047] Specifically, a composite material of sulfur and a carbon material such as acetylene black, a composite material of sulfur and metallic copper and a carbon material, or a composite material of sulfur and a copper Chevrel phase (Cu ２ Mo ４ S ７．８The composite material of the aluminum-sulfur battery and a carbon material is dispersed in the binder described above, and the resulting dispersion is applied to a positive electrode current collector made of a nickel alloy and dried to produce a positive electrode material for the aluminum-sulfur battery. Positive electrode active materials and binders for lithium-sulfur batteries and sodium-sulfur batteries may also be used.

[0048] <Electrolyte> The electrolyte for an aluminum secondary battery may be any liquid containing ions containing aluminum element as an electrolyte. Similar electrolytes can be used in both the aluminum ion battery and the aluminum sulfur battery described above. The electrolyte is preferably a liquid 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 "electrolyte" broadly encompasses colloidal solutions. In other words, the term "electrolyte" in the present invention also encompasses, for example, gel-like electrolytes.

[0049] [Electrolyte] There is no particular limitation on the aluminum-containing ion source used as the electrolyte. For example, aluminum tri(trifluoromethanesulfonate) (Al(OTF) ３ aluminum triperfluoroalkylsulfonates such as aluminum triperfluoroalkylsulfonates (Al-PF), aluminum bis(fluorosulfonyl)imide (Al-FSI), aluminum halides such as aluminum bromide and aluminum iodide, aluminum perchlorate, aluminum tris(hexafluorophosphate) (Al(PF)), ６ ) ３ ), and aluminum tris(tetrafluoroborate) (Al(BF ４ ) ３ ) salts derived from aluminum sulfate or aluminum nitrate. ３＋ It is also possible to use ions, and a plurality of types of these ions may be contained.

[0050] 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 copper (alloys), 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.

[0051] [Solvent for Electrolyte Solution] As described above, the solvent for the electrolyte solution may be any solvent that can generate ions containing aluminum elements in the electrolyte solution, such as water, an organic solvent, a deep eutectic solvent, etc., and the type is not particularly limited. Although not necessarily corresponding to a solvent in the narrow sense, it may also include an ionic liquid.

[0052] (Organic Solvent) Examples of organic solvents that can be used in the electrolyte solution include, but are not limited to, aromatic hydrocarbons, ethers, ketones, acetates, carbonates, sulfone-based solvents, and the like. More specifically, examples include glyme-based solvents that are commonly used in batteries as ether-based solvents; dimethoxyethane (DME), ethoxymethoxyethane (EME), diethoxyethane (DEE); tetrahydrofuran, dioxane, dioxolane, crown ethers; and fluorinated ethers. Examples of carbonate esters (carbonates) include alkyl(ene)carbonates such as ethylene carbonate (EC) and propylene carbonate (PC); and fluorinated carbonates. In addition to these, esters such as γ-butyrolactone and methyl acetate; and polyalkylene oxides such as polyethylene oxide (PEO) can also be used.

[0053] (Ionic Liquid) In the aluminum secondary battery of this embodiment, the electrolyte may contain an ionic liquid. An "ionic liquid" is a salt that exists in a liquid state even at room temperature and has characteristics such as high ionic conductivity, low volatility, and high thermal stability. Therefore, an aluminum secondary battery whose electrolyte contains an ionic liquid is less likely to cause problems. In particular, an electrolyte in which an electrolyte and a solvent form an ionic liquid is preferred, and such an electrolyte allows the aluminum secondary battery to be used even at high temperatures of around 300°C.

[0054] (Deep eutectic solvent) In the aluminum secondary battery of this embodiment, the electrolyte may also contain a deep eutectic solvent. A "deep eutectic solvent" is a solvent that is liquid at room temperature and is obtained by mixing a hydrogen bond donor compound and a hydrogen bond acceptor compound in a certain ratio. By combining a donor compound and an acceptor compound, it is possible to create a solvent with any physical properties, and various combinations have been reported.

[0055] Specific examples of deep eutectic solvents that can be used as solvents for electrolytes 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, urea / sulfamic acid systems, etc. Among these, deep eutectic solvents composed of hydroxycarboxylic acid and one or more compounds selected from sugars, carboxylates, and hydroxyalkylammonium salts, such as monosaccharide / hydroxycarboxylic acid systems, are suitable as solvents for electrolytes because they are made from components derived from natural products and are excellent in terms of safety and hygiene.

[0056] (Aqueous Electrolyte) In the aluminum secondary battery of this embodiment, the electrolyte is preferably an aqueous solution, particularly an aqueous solution. If the solvent is mainly water, high safety can be ensured and it is also advantageous in terms of cost compared to when an organic solvent or the like is used. More preferably, an aqueous solution containing aluminum triperfluoroalkylsulfonate or aluminum bis(fluorosulfonyl)imide is used.

[0057] The use of such aqueous electrolytes, particularly aqueous aluminum tri(trifluoromethanesulfonate), makes it difficult for the water solvent to be electrolyzed during charging, making it easier for secondary batteries to exhibit their characteristics (Non-Patent Document 1). One of the reasons why reversible electrodeposition of aluminum in water is difficult is the presence or generation of passive aluminum oxide on the surface of the aluminum negative electrode (Non-Patent Document 2). Because such aluminum oxide is easily soluble in aqueous solutions containing perfluoroalkylsulfonates or bis(fluorosulfonyl)imides, it is likely that these electrolytes remove it from the negative electrode surface, resulting in the development of excellent secondary battery characteristics.

[0058] Furthermore, the anions of the electrolyte, particularly perfluoroalkylsulfonates and bis(fluorosulfonyl)imides, can form complexes with aluminum ions in aqueous solutions. This may facilitate ion migration and intercalation into the electrode active material during charging and discharging, resulting in excellent secondary battery characteristics. For example, it has been reported that in aluminum secondary batteries whose electrolyte contains aluminum tri(trifluoromethanesulfonate), aluminum aquo complexes and trifluoromethanesulfonate complexes reversibly intercalate into the carbon-based positive electrode active material (Non-Patent Document 2).

[0059] There are no particular limitations 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 about 0.5 to 10 mol / L, and particularly about 1 to 5 mol / L.

[0060] (Additives) The electrolyte may also contain various additives as optional components, such as vinyl group-containing compounds, γ-butyrolactone, ethylene sulfide, cyclic sulfonic acid esters, methyl benzoate, succinic anhydride, polydimethylsiloxane, and AgPF ６ , Cu(CF ３ SO ３ )２ The present invention can contain about 0.01 to 5 mass %, particularly about 0.1 to 1 mass %, of a negative electrode or positive electrode protective film forming agent such as those described above; an overcharge inhibitor such as 2,4-difluoroanisole; or a flame retardant such as a phosphate ester, a phosphazene, or an imidazole salt.

[0061] <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 one of the main surfaces of the negative electrode 11 and the positive electrode active material 13 layer over substantially the entire surface, 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.

[0062] The material and shape of the separator are not particularly limited, and any material can be used, such as glass, ceramics, cellulose fiber, paper such as Japanese paper, fluorine-based polymers, polyolefins such as polyethylene or polypropylene, PET, aromatic polyamides, polyacrylonitrile, polyimides, or other porous materials, woven or nonwoven fabrics, or gel-like separators.

[0063] <Battery Type> The 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 desired size and number can be used depending on the purpose. For example, a single cell can be formed by stacking a positive electrode, a negative electrode, and a separator 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.

[0064] There are no particular limitations on the type or shape of the aluminum secondary battery, and various types may be used, 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.

[0065] <Laminate Battery> Yet another embodiment of the present invention is an aluminum secondary battery further including an exterior packaging material, in which the negative electrode, the positive electrode active material, the positive electrode current collector, the separator, and the electrolyte are housed, and the exterior packaging 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.

[0066] 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. For this reason, secondary batteries are often used in the form of a laminated battery.

[0067] In typical laminate batteries, such as lithium-ion batteries, laminate films are used in which layers of polyolefins such as polyethylene and polypropylene, polyamides, etc. are laminated on both sides of a metal layer. However, when these polyolefin or polyamide laminate films are used in aluminum secondary batteries, deformation such as swelling may occur. Therefore, in this embodiment, an exterior material having a resin layer such as an ethylene vinyl acetate resin layer on both sides of a metal layer made of, for example, aluminum or stainless steel (SUS) is preferably used. The exterior material may further be provided with components such as an adhesive layer, an insulating material, a heat-insulating material, or a cushioning material.

[0068] Here, there are no particular limitations on the thickness of each layer and the total thickness of the exterior material, and the thickness can be set as desired depending on the environment in which the aluminum secondary battery is used, etc. For example, a metal layer having a thickness of about 1 to 300 μm, particularly about 10 to 100 μm, can be sandwiched between inner surface-side layers and outer surface-side layers having thicknesses of about 10 to 500 μm, particularly about 30 to 300 μm, to form an exterior material having a total thickness of about 25 μm to 1 mm, particularly about 50 to 500 μm, but the embodiment is not limited to this.

[0069] The laminated battery of the present embodiment can be produced by housing, for example, the aluminum secondary battery of the above-described embodiment in the exterior packaging material. After housing the aluminum secondary battery, it is preferable to pouch at least the end portion of the exterior packaging material.

[0070] 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.

[0071] 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.

[0072] Example 1: An aluminum secondary battery was fabricated using a positive electrode, a negative electrode, and an electrolyte prepared as follows. Positive electrode: 4 g of graphite (manufactured by Fujifilm Corporation, Wako Pure Chemical Industries, Ltd.) was mixed with 15 g of a 1% aqueous solution of carboxymethyl cellulose (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) and 0.25 g of 40% SBR latex (BM451B manufactured by Zeon Corporation). The ink was then applied to a positive electrode current collector (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, followed by heat treatment at 100°C for 20 minutes. Negative electrode: A general-purpose A1050 aluminum plate (25 x 35 mm) was used. Electrolyte: An aqueous electrolyte was used, which is relatively susceptible to differences in battery characteristics depending on the material of the positive electrode current collector. Aluminum tri(trifluoromethanesulfonate) (Al(OTF) ３) was dissolved in purified water to prepare an aqueous solution with a concentration of 1 mol / L.

[0073] The electrolyte prepared above was impregnated into a separator, and the negative electrode and positive electrode were placed on each side of the separator and fixed with plastic clips to form an aluminum secondary battery.

[0074] The resulting aluminum secondary battery was subjected to 100 charge / discharge cycles at 0.1 C over a potential window of 0.2 to 2.1 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, 20th, and 100th cycles are shown in Table 1 below.

[0075] [Examples 2 and 3] The same operation as in Example 1 was carried out except that the concentration of the electrolyte solution was 3 mol / L (Example 2) or 5 mol / L (Example 3). The measurement results of the battery capacity (cycle test results) are shown in Table 1 below.

[0076] Comparative Examples 1 to 12 The same operations as in Examples 1 to 3 were carried out, except that a positive electrode current collector made of molybdenum, tantalum, Hastelloy (C-276), or stainless steel (SUS304) was used instead of copper. The measurement results of the battery capacity are shown in Table 1, along with the material of the positive electrode current collector.

[0077]

[0078] In Examples 1 to 3, which used a copper positive electrode current collector according to the present invention, a higher battery capacity was achieved at any cycle number than in Comparative Examples 1 to 12, which used a positive electrode current collector made of molybdenum, tantalum, etc. Furthermore, no significant decrease in battery capacity was observed at the 100th cycle, as in Comparative Examples 2 and 3.

[0079] [Examples 4 to 9] The same operations as in Examples 1 to 3 were carried out, except that the concentration of the electrolyte was set to 2 mol / L and the positive electrode current collector was made of the material shown below. The results of measuring the battery capacity are shown in Table 2, along with the material of the positive electrode current collector, and the results of Examples 1 and 2 and some comparative examples. Copper (pure copper): the same as that used in Examples 1 to 3; tough pitch copper with a purity of 99.94% and a specific gravity of 8.93. 6% Al copper: aluminum bronze containing approximately 6% by mass of aluminum and approximately 94% by mass of copper; specific gravity 7.60. 8% Al copper: aluminum bronze containing approximately 8% by mass of aluminum and approximately 92% by mass of copper; specific gravity 7.50. 10% brass: brass containing approximately 10% by mass of zinc and approximately 90% by mass of copper; specific gravity 8.70. 30% brass: brass containing approximately 30% by mass of zinc and approximately 70% by mass of copper; specific gravity 8.40. Al brass: alloy containing approximately 2% by mass of aluminum, approximately 22% by mass of zinc, and approximately 76% by mass of copper; specific gravity 8.10.

[0080]

[0081] Not only pure copper positive electrode current collectors, but also copper alloy positive electrode current collectors generally provided larger battery capacities than Hastelloy or stainless steel positive electrode current collectors. In particular, Examples 4 and 7, which used pure copper or 10% brass with a specific gravity of 8.50 to 8.96 and a copper content per unit volume of 7.50 or more, provided larger battery capacities. In addition, from Examples 1 to 4, it was found that Al(OTF) ３ There was a tendency that the higher the concentration, the greater the battery capacity.

[0082] As described above, it has been demonstrated that, according to the present invention, an aluminum secondary battery having a large charge / discharge capacity and a good cycle life can be produced by using copper (alloy), which is cost-effective, as the material for the positive electrode current collector.

[0083] REFERENCE SIGNS LIST 1 aluminum secondary battery 11 negative electrode 12 positive electrode current collector 13 positive electrode active material 14 separator

Claims

1. An aluminum secondary battery comprising a negative electrode containing aluminum and / or an aluminum alloy, a positive electrode current collector disposed opposite the negative electrode, a positive electrode active material disposed on the positive electrode current collector, a separator disposed between the negative electrode and the positive electrode current collector, and an electrolyte, wherein the positive electrode current collector is made of copper and / or a copper alloy.

2. The aluminum secondary battery according to claim 1, wherein the copper or copper alloy has a specific gravity of 8.50 to 8.

96.

3. The aluminum secondary battery according to claim 1 or 2, wherein the copper or copper alloy has a copper content of 80 to 100 mass %.

4. The aluminum secondary battery according to claim 1 or 2, wherein the electrolyte solution is a liquid containing an aluminum salt and one or more solvents selected from the group consisting of water, organic solvents, deep eutectic solvents, and ionic liquids.

5. The aluminum salt is 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 5. The aluminum secondary battery according to claim 4, further comprising one or more salts selected from the group consisting of:

6. The aluminum secondary battery according to claim 1 or 2, wherein the positive electrode active material contains 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.

7. The aluminum secondary battery according to claim 1 or 2, further comprising an exterior packaging material, the negative electrode, the positive electrode active material, the positive electrode current collector, the separator, and the electrolyte solution being housed in the exterior packaging material, and the exterior packaging material having 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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