Electrolyte for aluminum secondary battery

Abstract

To provide a new electrolyte that is aqueous yet usable in aluminum secondary batteries, capable of forming aluminum secondary batteries exhibiting stable charge-discharge characteristics and improved cycle characteristics, and to provide an aluminum secondary battery based on the electrolyte.SOLUTION: An electrolyte for an aluminum secondary battery includes an aqueous solution containing one or more chemical species selected from the group consisting of aluminum halide, aluminum nitrate, aluminum sulfate, aluminum perfluoroalkanesulfonate, and aluminum bis(perfluoroalkanesulfonyl)imide, and their ions and a deep eutectic solvent. Also provided is an aluminum secondary battery including the electrolyte.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrolyte for an aluminum secondary battery and an aluminum secondary battery comprising the electrolyte. [Background technology]

[0002] Secondary batteries, which can be repeatedly charged and discharged, have traditionally been used for a variety of purposes. Demand for lithium-ion secondary batteries, in particular, has surged 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 and cobalt 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 in reserves, are being considered. Aluminum has a capacity per volume approximately four times that of lithium, is chemically more stable than 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 development of aluminum-ion secondary batteries is also underway (e.g., Patent Documents 1 to 4, Non-Patent Document 1).

[0004] Additionally, aluminum-sulfur batteries, which use sulfur in the positive electrode, have also been investigated (e.g., Non-Patent Documents 1 and 2). Aluminum-sulfur batteries have an extremely high theoretical capacity, about 7 to 8 times that of lithium-ion batteries, and are particularly expected to be next-generation batteries. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 9-120816 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-213101 [Patent Document 3] Japanese Patent Publication No. 2023-156753 [Patent Document 4] Patent Publication No. 2021-174732 [Non-patent literature]

[0006] [Non-Patent Document 1] GA Elia, et al.,Journal of Power Sources,481,228870(2021) [Non-patent document 2] Jasmin Smajic, et al.,Applied Energy Materials,3,p6805-6814(2020) Summary of the Invention [Problem to be solved by the invention]

[0007] However, aluminum secondary batteries have drawbacks, such as low discharge voltage and low charge / discharge efficiency, susceptible electrode degradation, and short cycle life. Furthermore, aluminum is less easily reduced than hydrogen, making it difficult to use aqueous electrolytes in aluminum secondary batteries; non-aqueous electrolytes are generally used (Patent Documents 1-3, Non-Patent Document 1). This poses safety and sanitation issues, such as fires caused by organic solvents, as well as workability and environmental hygiene issues. Even if a flame-retardant non-aqueous electrolyte is used, handling under special conditions, such as a nitrogen atmosphere, may be necessary, which can lead to reduced workability and increased costs.

[0008] Several development examples have also been reported for aluminum secondary batteries using aqueous electrolytes. For example, Patent Document 4 discloses an aqueous electrolyte for aluminum secondary batteries containing perfluorosulfonimide. However, the cycle characteristics of secondary batteries using this electrolyte have not been fully confirmed. The electrolyte described in Patent Document 4 requires perfluorosulfonimide, a substance similar to PFAS, and also uses aluminum perfluorosulfonimide salts as the electrolyte, raising concerns about environmental and cost issues.

[0009] Aluminum secondary batteries based on aqueous electrolytes also have drawbacks, such as a short cycle life and poor reproducibility of charge / discharge characteristics. As shown in the examples and comparative examples described below, aluminum batteries using a general-purpose aluminum halide aqueous solution as the electrolyte may also exhibit some degree of repeated charge / discharge characteristics. However, even when charging and discharging are performed under the same conditions, the reproducibility is low, making it difficult to obtain stable characteristics as a secondary battery. Considering the current energy situation, there is an urgent need to develop an aluminum secondary battery based on an aqueous electrolyte that has a long life and stable charge / discharge characteristics.

[0010] The present invention has been made in view of the above problems, and has an object to provide a new electrolyte solution that is aqueous but can be used in aluminum secondary batteries, and that can constitute an aluminum secondary battery that exhibits stable charge / discharge characteristics and also has improved cycle characteristics, as well as an aluminum secondary battery based on the electrolyte solution. [Means for solving the problem]

[0011] As a result of extensive research, the present inventors have found that by using an electrolyte solution containing an aqueous solution of a specific aluminum salt and a deep eutectic solvent, an aluminum secondary battery can be obtained that has excellent charge / discharge characteristics and reproducibility thereof, as well as good cycle characteristics.

[0012] That is, the present invention provides the following (1) to (8). (1) An electrolyte for an aluminum secondary battery, comprising an aqueous solution containing one or more chemical species selected from the group consisting of aluminum halide, aluminum nitrate, aluminum sulfate, aluminum perfluoroalkanesulfonate, and aluminum bis(perfluoroalkanesulfonyl)imide, and ions thereof, and a deep eutectic solvent. (2) The electrolyte solution according to (1) above, wherein the deep eutectic solvent contains an ammonium halide. (3) The electrolyte solution according to (2), wherein the deep eutectic solvent further contains a compound having one or more carboxy groups and / or a compound having two or more hydroxy groups. (4) The electrolyte solution according to (1), wherein the deep eutectic solvent contains choline chloride and / or a hydroxycarboxylic acid. (5) 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 solution selected from any one of (1) to (4) above. (6) The aluminum secondary battery according to (5) above, wherein the positive electrode active material contains one or more selected from the group consisting of carbonaceous materials, metal oxides, metal carbides, metal nitrides, transition metal fluorides, coordination polymers, sulfur, and metal sulfides. (7) The aluminum secondary battery according to (5) or (6), wherein the positive electrode current collector is made of one or more materials selected from the group consisting of nickel-based alloys, nickel, molybdenum, glassy carbon, titanium nitride, titanium carbonitride, and titanium carbide. (8) The battery further includes an exterior packaging material, and 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; The aluminum secondary battery according to any one of the above (5) to (7), wherein the exterior material has an ethylene vinyl acetate resin layer, an ethylene vinyl alcohol resin layer, and / or a polyacrylonitrile resin layer. [Effects of the Invention]

[0013] The electrolyte solution for aluminum secondary batteries of the present invention is aqueous, yet can be used in aluminum secondary batteries. Furthermore, aluminum secondary batteries of the present invention using this electrolyte solution can exhibit stable charge-discharge characteristics and good cycle characteristics. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram showing an example of a cyclic voltammogram of the aluminum ion battery of Example 1 according to the present invention. [Figure 2] FIG. 1 is a diagram showing an example of a cyclic voltammogram of an aluminum ion battery of Comparative Example 1 according to the prior art. [Figure 3] FIG. 1 shows a cyclic voltammogram of the deep eutectic solvent used in Example 1. [Figure 4] 1 is a cross-sectional view of an aluminum secondary battery according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, the electrolyte solution for an aluminum secondary battery and the aluminum secondary battery of the present invention will be described in detail based on embodiments, but the present invention is not limited to these embodiments.

[0016] The aluminum secondary battery itself is well known. The electrolyte for an aluminum secondary battery of the present invention can be used for any type of secondary battery as long as the battery uses aluminum or an aluminum compound in the negative electrode.

[0017] <Electrolyte for aluminum secondary batteries> A first embodiment of the present invention is an electrolyte solution for an aluminum secondary battery, comprising an aqueous solution containing one or more chemical species selected from the group consisting of aluminum halide, aluminum nitrate, aluminum sulfate, aluminum perfluoroalkanesulfonate, and aluminum bis(perfluoroalkanesulfonyl)imide, and ions thereof, and a deep eutectic solvent.

[0018] <Electrolytes> The electrolyte solution for aluminum secondary batteries of this embodiment contains, as an electrolyte, one or more chemical species selected from the group consisting of aluminum halide, aluminum nitrate (Al(NO3)3), aluminum sulfate (Al2(SO4)3), aluminum perfluoroalkanesulfonate, and aluminum bis(perfluoroalkanesulfonyl)imide, as well as ions thereof. The use of an electrolyte solution containing such an electrolyte improves the cycle characteristics of aluminum secondary batteries. Furthermore, even if the electrolyte solution is aqueous, it is possible to exhibit stable charge / discharge characteristics. While all of these chemical species are known substances, some of them will be described in detail below.

[0019] (Aluminum halides and their ions) Aluminum halides and their ions are useful chemical species as electrolytes for the electrolyte solution for the aluminum secondary battery of the present invention. There are no particular limitations on these chemical species, and any compound or ion of aluminum and various halogens may be used. Examples include AlCl3, AlBr3, AlI3, and AlCl4. - , AlBr4 - ,AlI4 - , Al2Cl7 - , Al2Br7 - , Al2I7 - , Al3Cl 10 - , Al3Br 10 - , Al3I 10 - Examples include, but are not limited to, chemical species containing multiple halogen elements or other anions, such as nitrate ions. For example, AlClBr3 - , AlClI3 - , AlCl2BrI - , AlClBr2I - , AlClBrI2 - , Al2Cl6Br - Two or more types of aluminum halides and their ions can also be used in combination.

[0020] Among the above aluminum halides and their ions, AlCl4 - , AlBr4 - , Al2Cl7 - , and Al2Br7 - is preferred because it tends to stabilize the charge / discharge characteristics. In addition, aluminum chloride and the like are strong Lewis acids, so they form deep eutectic solvents with oxygen-donating amides such as urea, methyl urea, ethyl urea, acetamide, or ethyl pyridine, as described below. These deep eutectic solvents include AlCl4 - For example, [AlCl2(urea)2] + etc. (Patent Document 3, Non-Patent Document 1), it is suitable as the electrolyte solution in this embodiment.

[0021] (Aluminum perfluoroalkanesulfonate) Aluminum perfluoroalkanesulfonate is Al(R f SO3)3(R f = perfluoroalkyl group). There is no particular limitation on the number of carbon atoms in the perfluoroalkyl group, and multiple chemical species with different numbers of carbon atoms may be mixed. Considering ease of availability, those with 1 to 4 carbon atoms are preferred, and trifluoromethanesulfonate is particularly preferred.

[0022] (Aluminum bis(perfluoroalkanesulfonyl)imide) Aluminum bis(perfluoroalkanesulfonyl)imide is Al(N(SO2R f )2)3(R f= perfluoroalkyl group). Here again, there is no particular limitation on the number of carbon atoms in the perfluoroalkyl group, and multiple chemical species with different numbers of carbon atoms may be mixed. Considering ease of availability, those with 1 to 4 carbon atoms are preferred, and examples include aluminum bis(trifluoromethanesulfonyl)imide, aluminum bis(pentafluoroethanesulfonyl)imide, aluminum bis(heptafluoropropanesulfonyl)imide, and aluminum bis(nonafluorobutanesulfonyl)imide. Aluminum bis(trifluoromethanesulfonyl)imide is particularly preferred.

[0023] (aqueous solution) The electrolyte solution for the aluminum secondary battery of this embodiment contains the above-mentioned electrolyte in the form of an aqueous solution. Here, there are no particular limitations on the "aqueous solution," and any solution may be used as long as it is a solution containing a solvent that is primarily water, for example, 50% by mass or more, particularly 80% by mass or more of water. For example, safety can be ensured by using a solution in which the solvent is entirely water. Furthermore, it is also possible to further stabilize the charge / discharge characteristics by using a solution in which the solvent is, for example, 50% by mass or more, particularly 80% by mass or more, of a water-soluble organic solvent such as alcohol, THF, or dioxane.

[0024] The concentration of the electrolyte in the aqueous solution is not particularly limited and can be set arbitrarily depending on the configuration and characteristics of the target aluminum secondary battery, the type of electrolyte, and the type and amount of deep eutectic solvent used in combination. However, from the viewpoint of further stabilizing charge / discharge characteristics, it is preferable to reduce the amount of water contained in the electrolyte, and therefore it is preferable to set the electrolyte concentration higher. For example, the concentration of the electrolyte in the aqueous solution may be set within the range of 0.2 to 20 mol / L, preferably 0.5 to 15 mol / L, and particularly 1 to 10 mol / L.

[0025] <Deep eutectic solvent> The electrolyte solution for an aluminum secondary battery of this embodiment contains a deep eutectic solvent in addition to the aqueous solution. Deep eutectic solvents (DES) themselves are known and are solvents that are liquid at room temperature and are obtained by mixing a hydrogen bond donor compound and a hydrogen bond acceptor compound in a certain ratio. By combining donor compounds and acceptor compounds, solvents with any physical properties can be created, and various combinations have been reported (Patent Document 3, Non-Patent Document 1).

[0026] Here, the inclusion of a deep eutectic solvent as a component of the electrolyte is an important requirement of the present invention. This makes it possible to provide an aluminum secondary battery based on a new aqueous electrolyte solution that exhibits excellent charge / discharge characteristics and their reproducibility, as well as favorable cycle characteristics. Deep eutectic solvents, like ionic liquids, also have low vapor pressure and flame retardancy, making them suitable as components of the electrolyte solution. Furthermore, they generally have the advantages of good thermal stability and electrochemical stability, excellent solubility, and many are inexpensive and environmentally friendly.

[0027] Although the present invention is not limited by any particular theory, it is believed that the first reason why the present invention is effective is that the hydrogen overvoltage of aluminum increases in the presence of a deep eutectic solvent. Because aluminum has a reduction potential less noble than hydrogen, when electrodeposition from an aqueous electrolyte is attempted, hydrogen generation takes precedence, and aluminum often does not electrodeposit (see, for example, Patent Document 1). However, hydrogen generation from the free surface of metallic aluminum requires a large overvoltage. Therefore, hydrogen actually evolves from an aqueous electrolyte at a significantly less noble potential, creating room for aluminum to be electrodeposited. This is similar to the reason why zinc, which has a reduction potential less noble than hydrogen, is electrodeposited from an aqueous solution. In an aluminum secondary battery using the electrolyte of this embodiment, the hydrogen overvoltage of aluminum may be further increased, creating an environment in which aluminum or an aluminum compound can be stably electrodeposited.

[0028] The second possible reason is the interaction between aluminum ions and the components of the deep eutectic solvent. As mentioned above, deep eutectic solvents contain hydrogen bond donor compounds and hydrogen bond acceptor compounds, which can interact with metals such as aluminum through, for example, complex formation. As a result, the reduction potential of aluminum-based ions may change, enabling stable electrodeposition from aqueous solutions.

[0029] A third possibility is that the oxide film on the surface of the aluminum negative electrode is removed by components in the deep eutectic solvent. Because aluminum has a strong affinity for oxygen, a natural oxide film often forms on the surface of the negative electrode. This oxide film can make it difficult for aluminum to dissolve during discharge, resulting in reduced discharge characteristics (see, for example, Patent Document 1). On the other hand, many deep eutectic solvents contain carboxylic acids, which can also dissolve and remove the metal oxide film on the surface. As a result, aluminum dissolution is not hindered in aluminum secondary batteries using deep eutectic solvents, which may improve charge / discharge characteristics, their reproducibility, and cycle characteristics.

[0030] There is no particular limitation on the deep eutectic solvent that can be used in the electrolyte solution of this embodiment, and any combination of hydrogen bond donor compounds and hydrogen bond acceptor compounds may be used as long as they are liquid at room temperature. Examples include the above-mentioned combinations of aluminum chloride and oxygen donor amides such as ureas, acetamides, or ethylpyridine; sugars and hydroxycarboxylic acids, diols and hydroxycarboxylic acids, fatty acids and long-chain fatty acids, urea and sulfamic acid, ammonium halides and urea, ammonium halides and thiourea, ammonium halides and carboxylic acids, ammonium halides and hydroxycarboxylic acids, ammonium halides and diols, and other compounds with two or more hydroxy groups, ammonium halides and amides, ammonium halides and fluorinated alcohols, etc., but are not limited thereto.

[0031] (Ammonium halide) Preferably, a deep eutectic solvent containing an ammonium halide is used. Such a deep eutectic solvent can further stabilize the charge / discharge characteristics of an aluminum secondary battery. In addition, the electrolyte can be easily prepared in air, rather than in a special environment such as a nitrogen atmosphere. There is no limitation on the type of ammonium halide, and examples include tetramethylammonium chloride, tetraethylammonium chloride, tetrapropylammonium chloride, tetrabutylammonium chloride, and choline chloride ((CH3)3N). + (CH2)2OHCl - Choline halides such as choline chloride (e.g., choline chloride), trimethyl(hydroxymethyl)ammonium chloride, trimethyl(hydroxypropyl)ammonium chloride, trimethyl(hydroxybutyl)ammonium chloride, triethyl(hydroxymethyl)ammonium chloride, triethyl(hydroxyethyl)ammonium chloride, triethyl(hydroxypropyl)ammonium chloride, triethyl(hydroxybutyl)ammonium chloride, etc. can be used. In particular, choline chloride is known to form deep eutectic solvents with various compounds such as urea, amides, glycols, carboxylic acids, alcohols, imidazoles, and sugars, and can also be preferably used in this embodiment.

[0032] (Compounds having one or more carboxy groups) The deep eutectic solvent used in this embodiment may contain a compound having one or more carboxy groups. The compound having one or more carboxy groups is not particularly limited, and examples thereof include, but are not limited to, fatty acids and long-chain fatty acids such as octanoic acid, nonanoic acid, decanoic acid, and lauric acid; dicarboxylic acids such as oxalic acid, fumaric acid, and maleic acid; and hydroxycarboxylic acids. Deep eutectic solvents containing hydroxycarboxylic acids as one of their components are particularly preferred because they can further stabilize the charge / discharge characteristics of aluminum secondary batteries.

[0033] Examples of hydroxycarboxylic acids include, but are not limited to, aliphatic hydroxycarboxylic acids such as glycolic acid, lactic acid, tartronic acid, glyceric acid, hydroxybutyric acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid, gamma-hydroxybutyric acid, malic acid, tartaric acid, citramalic acid, citric acid, isocitric acid, leucic acid, mevalonic acid, pantoic acid, ricinoleic acid, ricinelaideic acid, cerebronic acid, quinic acid, and shikimic acid; and aromatic hydroxycarboxylic acids such as salicylic acid, vanillic acid, syringic acid, pyrocatechuic acid, resorcylic acid, protocatechuic acid, gentisic acid, orselliic acid, gallic acid, mandelic acid, benzilic acid, atrolactic acid, mellotic acid, phloretic acid, coumaric acid, umbellic acid, caffeic acid, ferulic acid, and sinapic acid. Multiple hydroxycarboxylic acids can also be used in combination.

[0034] (Compounds with two or more hydroxy groups) The deep eutectic solvent used in this embodiment may contain a compound having two or more hydroxy groups. The deep eutectic solvent preferably contains, in addition to the above-mentioned ammonium halide, a compound having one or more carboxy groups and / or a compound having two or more hydroxy groups. Such a deep eutectic solvent also allows the preparation of an electrolyte solution in air at room temperature, rather than in a special environment such as a nitrogen atmosphere. The compound having two or more hydroxy groups is not particularly limited, and examples include, but are not limited to, ethylene glycol, propanediol, and glycerol. Sugars such as xylitol, glucose, sucrose, lactose, and maltose can also be used.

[0035] The deep eutectic solvent used in this embodiment preferably contains choline chloride and / or a hydroxycarboxylic acid, and particularly preferably both. Among these deep eutectic solvents, combinations of choline chloride and lactic acid, choline chloride and citric acid, choline chloride and tartaric acid, choline chloride and glycolic acid, choline chloride and various organic acids, choline chloride and urea, and choline chloride and thiourea are preferred, with choline chloride and citric acid being particularly preferred.

[0036] The ratio of each component in these deep eutectic solvents can be determined by referring to various literature. For example, choline chloride and citric acid can be mixed in a molar ratio of about 3:1 to 1:3, preferably about 2:1 to 1:2, and particularly about 1:1 to form a deep eutectic solvent.

[0037] <Electrolyte composition> The electrolyte solution for an aluminum secondary battery according to this embodiment contains the above-described electrolyte, a solvent such as water, and a deep eutectic solvent, but the contents thereof are not particularly limited. For example, the molar concentration of the electrolyte in the entire electrolyte solution may be about 0.2 to 15 mol / L, preferably about 0.5 to 10 mol / L, and particularly about 1 to 5 mol / L. The mixing ratio of the aqueous solvent and the deep eutectic solvent is also not particularly limited. From the viewpoint of stabilizing the charge / discharge characteristics of an aluminum secondary battery, it is preferable to keep the water content low, for example, about 50% by mass or less, and particularly about 40% by mass or less, based on the total mass of the electrolyte solution. From the viewpoints of workability and cost, it is preferable to keep the water content at least about 1% by mass, preferably about 10% by mass or more, and particularly about 20% by mass or more, based on the total mass of the electrolyte solution.

[0038] (Other ingredients) The electrolyte solution for aluminum secondary batteries of this embodiment may contain other components in addition to those described above. For example, the electrolyte solution may contain solvents such as the above-mentioned alcohols, THF, dioxane, and other water-soluble organic solvents such as ketones, esters, and carbonates; and ionic liquids containing imidazolium or other components, in an amount of up to about 10% by weight, particularly about 1 to 5% by weight, based on the total weight of the electrolyte solution. The electrolyte solution may also contain various additives as optional components. For example, the electrolyte solution may contain about 0.01 to 5% by weight, particularly about 0.1 to 1% by weight, of the following additives: anode or cathode protective film-forming agents such as vinyl group-containing compounds, γ-butyrolactone, ethylene sulfide, cyclic sulfonic acid esters, methyl benzoate, succinic anhydride, polydimethylsiloxane, AgPF6, and Cu(CF3SO3)2; overcharge inhibitors such as 2,4-difluoroanisole; and flame retardants such as phosphate esters, phosphazenes, and imidazole salts.

[0039] In the electrolyte solution for an aluminum secondary battery of this embodiment, the aluminum-based ions as the electrolyte and the components in the deep eutectic solvent, as well as other additive components, may form aluminum complex ions such as carboxylates. The electrolyte solution for an aluminum secondary battery of this embodiment may contain such a reaction product.

[0040] The electrolyte solution for the aluminum secondary battery of this embodiment may also be a colloidal solution, for example, by adjusting the composition of the deep eutectic solvent or by adding a colloidal agent such as a water-soluble polymer, and may be used in the form of a gel or xerogel.

[0041] The electrolyte solution of this embodiment as described above is water-based, yet can be used in aluminum secondary batteries. For example, a cyclic voltammogram of the electrolyte solution for aluminum secondary batteries of Example 1, which is the electrolyte solution of this embodiment and will be described later, is shown in Figure 1. Unlike the cyclic voltammograms of an electrolyte solution not containing a deep eutectic solvent (Comparative Example 1, which will be described later) and the deep eutectic solvent itself (Figures 2 and 3), the electrolyte solution of this embodiment exhibits redox peaks that are not derived from the electrolysis of water.

[0042] As described above, the electrolyte solution of this embodiment can be used in aluminum secondary batteries, and can improve their cycle life to a practical level. Furthermore, since it can be prepared from relatively low-cost raw materials that are safe and hygienic, it is also advantageous in terms of the environment and cost. Aluminum secondary batteries containing the electrolyte solution of this embodiment have excellent charge / discharge characteristics and their reproducibility, and can exhibit good cycle characteristics. These aluminum secondary batteries will be described below.

[0043] <Aluminum secondary battery> A second embodiment of the present invention is an aluminum secondary battery comprising: a negative electrode containing aluminum and / or an aluminum alloy; a positive electrode current collector disposed 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 the above-described electrolyte solution.

[0044] The aluminum secondary battery of this embodiment will be further described based on the typical embodiment shown in Fig. 4. 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, and a separator and an electrolyte (for example, a separator 14 impregnated with an electrolyte) disposed between the negative electrode 11 and the positive electrode current collector 12.

[0045] In the embodiment shown in FIG. 4 , 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, which is then housed in a housing 15. However, the present invention is not limited to this embodiment. For example, the housing 15 is not an essential component. A liquid, gel, or solid electrolyte may be housed inside a frame-shaped or lattice-shaped separator. Furthermore, the aluminum secondary battery may be cylindrical rather than flat as shown in FIG. 4 . 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, electrodeposition of aluminum ions at the negative electrode end can be prevented. Furthermore, unit cells such as those shown in FIG. 4 may be connected in series or in parallel to form a battery pack. Below, each component constituting the aluminum secondary battery of this embodiment is described.

[0046] <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, and can also function as a current collector. For example, an aluminum foil or an aluminum alloy plate can be used as a negative electrode that serves as both a negative electrode active material and a current collector.

[0047] The negative electrode 11 is also composed of a current collector and an active material, and may optionally contain a conductive additive, a binder, and / or a solid electrolyte. 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 have any configuration, as long as it is capable of precipitation and dissolution of aluminum or dealloying and alloying of aluminum ions from an aluminum alloy.

[0048] The aluminum alloy material is not particularly limited, and examples 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-bismuth alloy, aluminum-tin alloy, aluminum-zinc alloy, and even aluminum-silicon alloy, aluminum-iron alloy, and aluminum-copper 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.

[0049] 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 its 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. Aluminum or a nickel-based alloy is preferably used.

[0050] 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 facilitates the 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.

[0051] The negative electrode 11 may have a reinforcing layer made of ceramics, glass, carbon material, polymer material, or the like. 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 these reinforcing layers.

[0052] <Positive electrode> In the aluminum secondary battery 1 of this embodiment, the positive electrode includes a positive electrode current collector 12 disposed opposite the 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.

[0053] (Cathode active material) In the aluminum secondary battery 1 of this embodiment, a positive electrode active material 13 is disposed on a positive electrode current collector 12. There are no particular limitations on the type of positive electrode active material 13, and any material that is used as a positive electrode active material for aluminum secondary batteries may be used. From the viewpoint of charge / discharge characteristics, a positive electrode active material containing one or more materials selected from the group consisting of carbonaceous materials, metal oxides, metal carbides, metal nitrides, transition metal fluorides, coordination polymers, sulfur, and metal sulfides is preferred.

[0054] Specific examples of preferred positive electrode active materials include, but are not limited to, carbon-based materials such as particulate or fibrous activated carbon, Ketjen black, 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); and metal sulfides such as sulfur, copper sulfide, and molybdenum sulfide.

[0055] (Positive electrode current collector) The material of the positive electrode current collector 12 is not particularly limited, and may be, for example, niobium or tantalum, which are commonly used in aluminum secondary batteries. From the viewpoint of charge / discharge characteristics, the positive electrode current collector is preferably made of one or more materials selected from the group consisting of nickel-based alloys, nickel, molybdenum, glassy carbon, titanium nitride, titanium carbonitride, and titanium carbide. These materials are less expensive than niobium and tantalum, and are therefore advantageous in terms of cost.

[0056] (Positive electrode current collector - nickel alloy) There are no particular limitations on the nickel-based alloy suitable for the positive electrode current collector 12, and various known alloys can be used. Examples include, but are not limited to, nickel-molybdenum alloys, nickel-chromium alloys, nickel-molybdenum-chromium alloys, nickel-titanium alloys, nickel-copper alloys, nickel-copper-aluminum alloys, nickel-chromium-iron alloys, nickel-molybdenum-chromium-iron alloys, nickel-molybdenum-chromium-copper alloys, nickel-tungsten alloys, and nickel-manganese alloys. Alloys based primarily on metals other than nickel, such as austenitic stainless steel, may also be used, and may contain carbon, silicon, manganese, niobium, and the like. Of course, the alloys may contain unavoidable impurities that are mixed in during alloy production, and various commercially available nickel-based alloys can also be used.

[0057] Commercially available nickel-based alloys (nickel alloys) include, but are not limited to, Hastelloy (registered trademark), Inconel, Monel, Incoloy, Woodimet, Waspaloy, Nichrome, PC Permalloy, Nitinol, Nimonic, DASALOY (registered trademark), and austenitic stainless steel (STAINLESS) (registered trademark). From the viewpoint of corrosion resistance, the nickel-based alloy is preferably one or more alloys selected from the group consisting of Hastelloy, Inconel, Monel, Incoloy, and austenitic stainless steel; in particular, one or more alloys selected from the group consisting of typical nickel alloys, Hastelloy, Inconel, Monel, and Incoloy.

[0058] The nickel-based alloy preferably contains 1 to 30 mass% molybdenum, 10 to 25 mass% chromium, 1 to 50 mass% iron, and / or approximately 0 to 35 mass% copper. Among these, nickel-based alloys having a nickel content of 55 to 90 mass%, particularly 60 to 80 mass%, a molybdenum content of 0 to 30 mass%, for example, 2 to 25 mass%, particularly 5 to 20 mass%, a chromium content of 0 to 25 mass%, particularly 10 to 20 mass%, and an iron content of 0 to 50 mass%, particularly 10 to 20 mass%, have extremely good corrosion resistance and are therefore suitable as materials for the positive electrode current collector 12 in this embodiment.

[0059] (Positive electrode current collector - nickel molybdenum) In this embodiment, the positive electrode current collector 12 may be made of pure nickel. Nickel is a metal that itself has excellent corrosion resistance, and is therefore suitable as a material for the positive electrode current collector 12. Nickel normally contains small amounts of impurities such as iron, manganese, carbon, and silicon, but in this embodiment, nickel containing these unavoidable impurities is also included in the term "pure nickel."

[0060] In this embodiment, the positive electrode current collector 12 may be made of molybdenum. Molybdenum has good electrical conductivity and excellent corrosion resistance, making it suitable as a material for the positive electrode current collector 12. In this embodiment, molybdenum also includes molybdenum containing unavoidable impurities.

[0061] (Positive electrode current collector - glassy carbon) Glassy carbon is SP 2 Glassy carbon is a non-graphitizable carbon composed of carbon, and is characterized by high hardness and low density. It also has high electrical conductivity and excellent corrosion resistance against various chemicals, making it suitable as a current collector material. Glassy carbon typically contains about 1% by mass of impurities such as silicon, but in this embodiment, any of various known glassy carbons can be used, including those containing such unavoidable impurities.

[0062] (Positive electrode current collector - titanium-based material) The positive electrode current collector 12 in this embodiment may be made of a titanium-based material such as titanium nitride, titanium carbonitride, or titanium carbide. Titanium nitride is a ceramic material represented by the composition formula TiN. It is widely used as a coating for various parts and for medical parts. Because of its high hardness and excellent wear resistance, it is often used as a coating material, particularly for cutting tools. However, its excellent conductivity and corrosion resistance make it suitable as a current collector material.

[0063] Titanium carbonitride is a ceramic material represented by the formula Ti(C,N). There are no particular limitations on the molar ratio of carbon atoms to nitrogen atoms, and various known titanium carbonitrides can be used, such as titanium carbonitrides with a C:N ratio of about 1:10 to 10:1, particularly about C:N = 1:3 to 3:1. Because it is harder than titanium nitride, it is often used as a coating material for cutting tools, but because it also has excellent conductivity and corrosion resistance, it is also suitable as a current collector material.

[0064] Titanium carbide is a ceramic material with the formula TiC. Like titanium nitride, it has high hardness and excellent wear resistance, making it widely used as a coating material for cutting tools, but its excellent electrical conductivity and corrosion resistance make it suitable as a current collector material.

[0065] (Configuration of positive electrode current collector) In addition to being made of the above-mentioned materials, the positive electrode current collector 12 may have a reinforcing material, such as ceramics, glass, carbon, or polymeric material, attached to one side. For example, by laminating a positive electrode current collector 12 made of a nickel-based alloy, nickel, or molybdenum film on a ceramic or glass reinforcing plate, the corrosion resistance around the positive electrode can be further improved. Furthermore, by forming the positive electrode current collector 12 by vapor-depositing a nickel-based alloy or the like onto a polymeric sheet, it is possible to reduce the weight and cost of the aluminum secondary battery. Titanium nitride, titanium carbonitride, titanium carbide, and the like are commonly used materials for coating, as described above. In this embodiment, the positive electrode current collector 12 can be formed by coating a reinforcing material made of another metal using techniques such as PVD or CVD.

[0066] There are no particular limitations on the manufacturing method of the positive electrode current collector 12, and various known methods can be used depending on the desired shape and the materials used. From the standpoint of ease of manufacturing, metal materials, particularly nickel-based alloys and nickel, and particularly nickel-based alloys, are preferred. Nickel-based alloys are easier to process than molybdenum and generally have superior corrosion resistance to acids compared to pure nickel, making them particularly excellent current collector materials. Nickel-based alloys also have the advantage of being less expensive than molybdenum, titanium nitride, and the like. Therefore, they are suitable as materials for mass-produced batteries. In particular, when the aluminum secondary battery is an aluminum ion battery, i.e., when the positive electrode active material described below does not contain sulfur, the positive electrode current collector is preferably made of a nickel-based alloy.

[0067] The positive electrode of the aluminum secondary battery 1 of this embodiment may also contain, in addition to the positive electrode current collector 12 and the positive electrode active material 13, optional conductive additives, binders, solid electrolytes, and the like. For example, a powder of a positive electrode active material such as manganese dioxide and a conductive additive may be mixed with a solution or emulsion containing a binder such as a polymer, and the mixture may be applied to the positive electrode current collector 12 and dried to form the positive electrode of the aluminum secondary battery 1. Alternatively, the positive electrode active material 13 may be formed by vapor-depositing graphite or the like on one side of the positive electrode current collector 12 made of the above-mentioned material such as a nickel-based alloy.

[0068] (Conductive additive) As the conductive aid, general-purpose conductive aids such as carbon materials such as carbon black, ketjen black, acetylene black, graphite, metals, metal oxides, conductive ceramics, etc. can be used. From the viewpoint of corrosion resistance, carbon materials are particularly preferred.

[0069] (binder) The binder serves to bind the positive electrode active material and conductive additive. Examples of commonly used binders include polyvinylidene fluoride (PVDF), vinylidene fluoride copolymers, polytetrafluoroethylene (PTFE), tetrafluoroethylene copolymers, fluororubbers, ethylene-propylene-diene rubbers, styrene-butadiene copolymers (SBR, SBS), acrylonitrile-butadiene copolymers (NBR), cellulose-based resins, ethylene-vinyl alcohol resins, polyvinyl alcohol (PVAL), and poly(meth)acrylic acid. In the present invention, any of these and other known binders can be used. From the viewpoint of resistance to the electrolyte, binders based on fluorine-based polymers, ethylene-vinyl alcohol resins, SBR, or polyvinyl alcohol are preferred.

[0070] The positive electrode active material 13, conductive additive, and binder described above can be dissolved and / or dispersed in a solvent and applied to the positive electrode current collector. The solvent used here is not limited, and any solvent commonly used in the field of battery materials can be used, such as N-methyl-2-pyrrolidone (NMP), ethylene carbonate (EC), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), ethyl propionate, methyl propionate, propylene carbonate (PC), γ-butyrolactone (γ-BL), acetonitrile (AN), ethyl acetate (EA), tetrahydrofuran (THF), dioxane, acetone, toluene, xylene, and methyl acetate (MA). A mixture of multiple solvents can also be used. Furthermore, additives such as viscosity modifiers, dispersants, surfactants, and antioxidants can be added.

[0071] An aqueous solvent can also be used as the solvent. When an aqueous binder is used as the binder, an active material layer of sufficient thickness can be formed on the current collector. There are no particular limitations on the type of aqueous binder, and known binders can be used. Examples include, but are not limited to, carboxymethyl cellulose, SBR latex, NBR latex, (meth)acrylic latex (emulsion), polyvinyl alcohol, alginic acid, gelatin, and chitosan. These conductive additives, binders, solvents, etc. can also be used when producing the negative electrode 11.

[0072] <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 electrodes, along with the above-described electrolyte solution. The separator may be in any shape, such as a frame or lattice shape with a certain thickness, which 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 electrodes, it is preferable that the separator 14 be in contact with substantially the entire surface of each of the negative electrode 11 and the positive electrode active material layer 13, as in the embodiment shown in FIG. 4 . Furthermore, from the viewpoint of maintaining high ionic conductivity between the positive and negative electrodes, the separator 14 preferably holds the electrolyte solution and is preferably in the form of a porous film, fiber, or the like.

[0073] There are no particular limitations on the material or shape of the separator, and any material can be used, including glass, ceramics, cellulose fiber, paper such as Japanese paper, porous materials such as fluorine-based polymers, polyolefins such as polyethylene or polypropylene, PET, aromatic polyamides, polyacrylonitrile, and polyimides, woven or nonwoven fabrics, or gel separators. A gel obtained by adding a gelling agent to the electrolytic solution of the previous embodiment can also be used as the separator.

[0074] <Battery type> The aluminum secondary battery of this embodiment may be any type of secondary battery, such as an aluminum ion battery or an aluminum sulfur battery.

[0075] (aluminum ion battery) Aluminum ion batteries are secondary batteries that are charged and discharged by the movement of aluminum ions between a positive electrode and a negative electrode. In the positive electrode of an aluminum ion battery, the above-mentioned carbon-based materials, metal oxides, carbides, nitrides, coordination polymers, transition metal fluorides, etc. are generally used as the positive electrode active material. In this case, however, it is preferable to use a nickel-based alloy as the positive electrode current collector from the viewpoint of maintaining the high cost performance of aluminum ion batteries.

[0076] (Aluminum-sulfur battery) In the aluminum secondary battery of this embodiment, when the positive electrode active material contains sulfur or a metal sulfide such as copper sulfide, the secondary battery becomes an aluminum-sulfur battery. Aluminum-sulfur batteries have an extremely high theoretical capacity and are expected to be next-generation batteries.

[0077] Since sulfur and metal sulfides generally have low electrical conductivity at room temperature, it is preferable to use a conductive additive in combination. The conductive additive in an aluminum-sulfur battery can be the carbon material described above, or copper or its compounds. It is also possible to use sulfur after coating it with carbon. Specifically, a composite of sulfur and a carbon material such as acetylene black, a composite of sulfur and metallic copper and a carbon material, or a composite of sulfur and a copper Chevrel phase (Cu2Mo4S 7.8 A composite of the aluminum-sulfur battery and a carbon material is dispersed in the binder described above, and the resulting mixture is applied to a positive electrode current collector made of a nickel alloy or the like and dried to produce a positive electrode material for an aluminum-sulfur battery. Positive electrode active materials and binders for lithium-sulfur batteries or sodium-sulfur batteries may also be used.

[0078] The aluminum secondary battery of this embodiment can be used as a single cell as is, or a plurality of cells can be connected in series or parallel to form a battery module. There are no particular limitations on the size or the number of cells in the battery module, and any size and number can be used depending on the purpose. For example, a single cell can be formed by stacking 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.

[0079] There are no particular limitations on the type or shape of the aluminum secondary battery, and various types are possible, including a flat type as shown in FIG. 4, a cylindrical type, a coin type, a button type, a laminated type, etc. Here, a laminated type aluminum secondary battery is a battery in which a single cell or a battery pack is housed in a laminated exterior material, as described above. By housing an aluminum secondary battery in such an exterior material, it becomes possible to use it as a more practical secondary battery.

[0080] <Laminated battery> The aluminum secondary battery of the present embodiment also encompasses secondary batteries that further include an exterior packaging material 15, as shown in FIG. 4, in which the negative electrode 11, the positive electrode active material 13, the positive electrode current collector 12, the separator 14, and the electrolyte are housed in the exterior packaging material 15, and the exterior packaging material 15 has an ethylene vinyl acetate resin layer, an ethylene vinyl alcohol resin layer, and / or a polyacrylonitrile resin layer.

[0081] Secondary batteries are often used in the form of laminated batteries in practical applications such as those installed in vehicles, personal computers, and mobile terminals. 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 then housed in an exterior material made of laminated film. Also known as 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. The aluminum secondary battery of this embodiment can also be used in the form of such a laminated battery.

[0082] In the embodiment shown in FIG. 4 , the negative electrode 11 and the positive electrode current collector 12 extend in opposite directions to form a negative electrode tab and a positive electrode tab, respectively. However, the present invention is not limited to this embodiment. For example, the negative electrode 11 and the positive electrode current collector 12 may be the same size as the separator 14, and metal plates such as aluminum or nickel alloy may be bonded to each electrode to form electrode tabs. Alternatively, the negative electrode tab and the positive electrode tab may be attached in the same direction. In FIG. 4 , the exterior material 15 houses the unit cell while separated from the negative electrode 11 and the positive electrode current collector 12. However, the exterior material 15 may be attached to a part or the entire surface of the unit cell by, for example, heat fusion. If desired, components such as insulating materials, heat-retaining materials, and buffer materials may be attached to the exterior material 15.

[0083] (exterior materials) As described above, the aluminum secondary battery (laminate battery) of the embodiment shown in Fig. 4 preferably further includes an exterior packaging material, and the exterior packaging material preferably has an ethylene vinyl acetate resin layer, an ethylene vinyl alcohol resin layer, and / or a polyacrylonitrile resin layer. If such an exterior packaging material has an ethylene vinyl acetate resin layer, an ethylene vinyl alcohol resin layer, and / or a polyacrylonitrile resin layer, deformation such as swelling or deterioration is unlikely to occur when applied to an aluminum secondary battery, and it is also possible to obtain a battery with a longer life.

[0084] Ethylene vinyl acetate (resin) is a copolymer of ethylene and vinyl acetate (VA) containing -CH2CH(OCOCH3)- units, and is also referred to as EVA. Various types of EVA are known, including copolymers with a VA content of approximately 4 mol% or less, copolymers with a VA content of approximately 4 to 30 mol%, and copolymers with a VA content of approximately 30 mol% or more, particularly copolymers with a VA content of approximately 60 mol% or more that can become rubbery. Any EVA can be used in this embodiment. It may be partially or completely hydrolyzed (saponified) to have a structure similar to that of an ethylene-vinyl alcohol copolymer, for example. Multiple types of EVA can also be used in combination.

[0085] Ethylene vinyl alcohol (EVOH) is a copolymer of ethylene and vinyl alcohol containing -CHCH(OH)- units. EVOH is generally obtained by saponifying the above-mentioned EVA, and various commercial products are available on the market, such as EVAL (registered trademark) from Kuraray Co., Ltd. and Soarlite (registered trademark) from Mitsubishi Chemical Corporation. EVOH has excellent moldability and gas barrier properties.

[0086] The physical properties and processability of EVOH can be controlled by the copolymerization ratio and degree of polymerization of ethylene and vinyl alcohol, but any EVOH can be used in this embodiment. It may also be a terpolymer in which a third monomer having a carboxyl group or an epoxy group is copolymerized. It is also possible to further enhance the resistance of EVOH by crosslinking the functional groups on the third monomer component. Hydroxy groups on EVOH may be esterified or etherified, or acetalized by reacting with an aldehyde such as formaldehyde or benzaldehyde in the presence of an acid to enhance water resistance.

[0087] From the viewpoint of heat resistance of aluminum secondary batteries, EVA or EVOH with a low ethylene content is preferred, while EVA or EVOH with a high ethylene content is preferred from the viewpoint of cold resistance. Depending on the type of electrolyte, for example, fully saponified EVOH in which approximately 99% or more of the vinyl acetate units are saponified may be used, or partially saponified EVA with a saponification degree of approximately 1 to 95%, particularly approximately 10 to 90% may be used. Furthermore, EVA or EVOH with an ethylene content of approximately 0.1 to 30.0 mol%, particularly approximately 1.0 to 20.0 mol%, is preferred. When used in aluminum secondary batteries, exterior materials having such EVA and / or EVOH in the resin layer are less likely to cause deformation such as swelling or deterioration.

[0088] Polyacrylonitrile (PAN) is a polymer of acrylonitrile, and PAN resin is a polymer containing 50 mol% or more of -CHCH(CN)- units. Various PAN resins with different acrylonitrile copolymerization ratios and molecular weights are commercially available from various companies, and any resin can be used in the present invention. Multiple types of PAN resins may be used in combination. Preferably, a PAN resin with an acrylonitrile copolymerization ratio of 80 mol% or more, or even 90 mol% or more, particularly an acrylonitrile homopolymer, is used. In general, the higher the acrylonitrile copolymerization ratio, the better the corrosion resistance and the more useful it is as a battery component, etc.

[0089] (Laminate structure) The exterior material in this embodiment preferably has an ethylene vinyl acetate resin layer, an ethylene vinyl alcohol resin layer, or a layer containing a resin or polyacrylonitrile resin as the inner (battery-side) layer. It is also possible to have an exterior layer containing EVA, EVOH, and / or PAN resin. The exterior material may have a metal intermediate layer, resin inner and outer layers, and an adhesive layer positioned between these layers. The resin of the outer layer may be polyolefin such as polyethylene or polypropylene, polyamide such as nylon, polyester such as PET, etc. The material of the metal layer is not particularly limited, and any metal used in general-purpose exterior materials (laminate materials) can be used, but aluminum or stainless steel, especially aluminum, is preferably used. Aluminum is lightweight, flexible, and cost-effective, making it a suitable material for the intermediate layer of an exterior material (laminate material).

[0090] There are no particular limitations on the thickness of each layer of the exterior material, and the total thickness can be set to a desired thickness 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 and outer 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 this is not intended to be limiting. An adhesive layer having a thickness of about 1 to 10 μm may also be attached.

[0091] The laminated battery of this embodiment can be produced by housing, for example, the aluminum secondary battery of the above-described embodiment in the exterior material. After housing the aluminum secondary battery, it is preferable to pouch at least the end of the exterior material. The pouching process can be performed by, for example, thermocompression bonding (heat sealing). The entire laminated battery may also be pouched by thermocompression bonding.

[0092] The laminated battery of this embodiment obtained in this manner has an improved cycle life due to suppressed corrosion of the electrodes, etc., and is less susceptible to deformation or deterioration of the exterior material, making it a practical secondary battery with a long life. Furthermore, because aluminum and / or an aluminum alloy is used as the negative electrode material, it is safer and less expensive than lithium-ion batteries, and there are no concerns about the supply of raw materials. Therefore, it is suitable as a secondary battery for vehicles such as automobiles, personal computers, mobile terminals, various home appliances, and medical devices. [Example]

[0093] 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.

[0094] [Example 1] A deep eutectic solvent was prepared by dissolving and mixing citric acid monohydrate and choline chloride in a molar ratio of 1:1 at 80°C. Separately, a 5 mol / L aqueous solution of AlCl3·6H2O was prepared, and this solution was mixed with the deep eutectic solvent in a mass ratio of 8.8:6.0 to prepare an electrolyte (electrolyte concentration: 3.6% by mass).

[0095] The obtained electrolyte solution was subjected to cyclic voltammetry (CV) measurement. All operations from preparation of the electrolyte solution to measurement were carried out in air. For the CV measurement, a two-electrode device equipped with a positive electrode having graphite on Hastelloy foil and an aluminum negative electrode was used. The measurement results are shown in Figure 1. A significant redox peak appeared at a low potential of 1.0 to 1.6 V, indicating that the electrolyte solution of this example can be used in secondary batteries.

[0096] [Comparative Example 1] The aqueous solution (AlCl concentration: 5 mol / L) prepared in Example 1 was subjected to CV measurement in the same manner as in Example 1. The measurement results are shown in Figure 2. Although the electrolyte solution of this comparative example had a higher concentration of the electrolyte itself than the electrolyte solution of Example 1, only a small peak was observed at a high potential of 1.2 to 1.8 V. This suggests that an electrolyte solution without a deep eutectic solvent would cause hydrogen generation to take precedence over aluminum precipitation, making it difficult to function as an aluminum secondary battery.

[0097] [Control Example 1] The deep eutectic solvent prepared in Example 1 was subjected to CV measurement in the same manner as in Example 1. The measurement results are shown in Figure 3. No peaks were observed in the CV, making it clear that the redox peaks in Example 1 were not derived from the deep eutectic solvent itself.

[0098] [Example 2] An aluminum secondary battery was fabricated using the electrolyte solution prepared in Example 1. The electrolyte solution prepared in Example 1 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 a battery. A general-purpose A1050 aluminum plate (25 x 35 mm) was used as the negative electrode. The positive electrode was fabricated by applying an ink containing 15 g of a 1% aqueous solution of carboxymethyl cellulose (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), 0.25 g of 40% SBR latex (BM451B manufactured by Nippon Zeon Co., Ltd.), and 4 g of graphite (manufactured by Fujifilm Corporation, Wako Pure Chemical Industries, Ltd.) to a Hastelloy C-276 plate (25 x 35 mm) using a bar coater, followed by heat treatment at 100°C for 20 minutes.

[0099] 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 was measured. The measurements were performed using a potentiostat / galvanostat HA series manufactured by Hokuto Denko Corporation. In this example, all experimental operations were performed in air, and battery capacity measurements were performed with n=3, but good reproducibility was obtained. The battery capacities at the 1st, 20th, and 100th cycles are shown in Table 1 below.

[0100] Comparative Example 2 The aqueous solution (AlCl concentration: 5 mol / L) prepared in Example 1 was used as the electrolyte, and the same operation as in Example 2 was carried out. The results of the battery capacity measurements varied greatly depending on the battery lot, but the results that were relatively better among them are shown in Table 1 below.

[0101] [Control Example 2] The deep eutectic solvent prepared in Example 1 was used as the electrolyte, and the same operation as in Example 2 was carried out. Although there were some lots for which the battery capacity could not be measured, the results were relatively good and are shown in Table 1 below.

[0102] [Table 1]

[0103] The aluminum secondary battery of Example 2, which uses an electrolyte containing an aluminum compound and a deep eutectic solvent according to the present invention, exhibited a large battery capacity with good reproducibility despite being a simple prototype. On the other hand, Comparative Example 2, which uses an electrolyte without a deep eutectic solvent, did not exhibit stable battery characteristics, and even though the measurement results were relatively good, the battery capacity significantly decreased with repeated charge-discharge cycles. Considering this result, it can be seen that Example 2 according to the present invention also exhibited good cycle characteristics. Furthermore, comparison with Control Example 2 demonstrated the necessity for the electrolyte to contain both an aluminum-based chemical species electrolyte and a deep eutectic solvent in order to exhibit secondary battery characteristics. The reason that Control Example 2 exhibited some battery characteristics is thought to be because the choline chloride in the deep eutectic solvent and the aluminum ions eluted slightly during discharge functioned as electrolytes.

[0104] As described above, it has been demonstrated that the electrolyte solution of the present invention, although aqueous, can be used in aluminum secondary batteries, and can constitute aluminum secondary batteries that exhibit stable charge-discharge characteristics and also have improved cycle characteristics. [Explanation of symbols]

[0105] 1. Aluminum secondary battery 11 Negative electrode 12 Positive electrode current collector 13 Cathode active material 14 Separator 15 Exterior materials

Claims

1. an aqueous solution containing one or more chemical species selected from the group consisting of aluminum halides, aluminum nitrate, aluminum sulfate, aluminum perfluoroalkanesulfonate, and aluminum bis(perfluoroalkanesulfonyl)imide, and ions thereof; Deep eutectic solvents and An electrolyte for an aluminum secondary battery comprising:

2. 10. The electrolyte of claim 1, wherein the deep eutectic solvent comprises an ammonium halide.

3. The electrolyte solution according to claim 2 , wherein the deep eutectic solvent further comprises a compound having one or more carboxy groups and / or a compound having two or more hydroxy groups.

4. 2. The electrolyte solution according to claim 1, wherein the deep eutectic solvent contains choline chloride and / or a hydroxycarboxylic acid.

5. 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 the electrolytic solution according to any one of claims 1 to 4.

6. 6. The aluminum secondary battery according to claim 5, wherein the positive electrode active material contains one or more selected from the group consisting of carbonaceous materials, metal oxides, metal carbides, metal nitrides, transition metal fluorides, coordination polymers, sulfur, and metal sulfides.

7. 6. The aluminum secondary battery according to claim 5, wherein the positive electrode current collector is made of one or more materials selected from the group consisting of nickel-based alloys, nickel, molybdenum, glassy carbon, titanium nitride, titanium carbonitride, and titanium carbide.

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

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