Aluminum deposition method, ionic liquid, electrolyte and battery

Abstract

To provide a method that allows aluminum to be deposited inexpensively and efficiently.SOLUTION: An aluminum deposition method includes a step of preparing a mixture of aluminum halide and one or more alkali halide salts containing a halogen element different from a halogen element of the aluminum halide, and a step of depositing aluminum by applying a voltage to the mixture.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an aluminum deposition method, an ionic liquid, an electrolyte, and a battery. [Background technology]

[0002] Although aluminum is a highly chemically reactive metal, the oxide film that forms on aluminum when exposed to the atmosphere is extremely stable, and so it is used in a variety of applications. For example, the use of aluminum for plating processing has been investigated (Patent Document 1). Patent Document 1 describes the use of an ionic liquid produced by mixing anhydrous aluminum chloride with an organic ionic liquid as an aluminum electroplating solution. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2012 / 043129 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the organic ionic liquid used in Patent Document 1 has a large molecular weight and contains only a small amount of ions per unit volume, which can prevent the reduction of aluminum ions from proceeding sufficiently, resulting in inefficient plating. Furthermore, the high cost of organic ionic liquids makes it difficult to perform plating at low cost.

[0005] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an aluminum deposition method, an ionic liquid, an electrolyte, and a battery that are capable of depositing aluminum inexpensively and efficiently. [Means for solving the problem]

[0006] The method for depositing aluminum according to the present invention includes the steps of preparing a mixture of an aluminum halide and one or more alkali halide salts containing a halogen element different from the halogen element of the aluminum halide, and applying a voltage to the mixture to deposit aluminum.

[0007] In certain embodiments, the mixture comprises an ionic liquid.

[0008] In one embodiment, the aluminum halide includes aluminum chloride, and the alkali halide salt includes at least one of potassium bromide and sodium bromide.

[0009] In one embodiment, the molar ratio of the aluminum halide to the mixture is 50% or greater.

[0010] In one embodiment, in the step of depositing aluminum, the aluminum is deposited at the negative electrode of a battery.

[0011] In one embodiment, the aluminum deposition method further comprises melting the mixture at 353K or less.

[0012] The ionic liquid according to the present invention is produced by melting a mixture containing an aluminum halide and an alkali halide salt containing a halogen atom different from that of the aluminum halide.

[0013] In one embodiment, the aluminum halide includes aluminum chloride, and the alkali halide salt includes at least one of potassium bromide and sodium bromide.

[0014] In one embodiment, the molar ratio of the aluminum halide to the mixture is 50% or greater.

[0015] The electrolyte according to the present invention comprises the ionic liquid described above.

[0016] The battery according to the present invention comprises an electrolyte produced by melting a mixture containing an aluminum halide and an alkali halide salt containing a halogen element different from the halogen element of the aluminum halide, an aluminum-containing negative electrode, and a positive electrode.

[0017] In one embodiment, the aluminum halide includes aluminum chloride, and the alkali halide salt includes at least one of potassium bromide and sodium bromide.

[0018] In one embodiment, the molar ratio of the aluminum halide to the mixture is 50% or greater.

[0019] In some embodiments, the positive electrode comprises a sulfur-carbon composite electrode.

[0020] In one embodiment, the sulfur-carbon composite electrode comprises polytetrafluoroethylene. [Effects of the Invention]

[0021] According to the present invention, aluminum can be deposited inexpensively and efficiently. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a flow diagram illustrating an aluminum deposition method according to an embodiment of the present invention. [Figure 2] FIG. 1 is a flow diagram illustrating an aluminum deposition method according to an embodiment of the present invention. [Figure 3] (a) and (b) are cyclic voltammograms of the ionic liquid of this embodiment at a temperature of 353K. [Figure 4] 1 is a schematic diagram of a battery according to an embodiment of the present invention; [Figure 5] 1(a) and 1(b) are cyclic voltammograms of a sulfur-carbon composite electrode using the ionic liquid of this embodiment as an electrolyte. [Figure 6] 3 shows charge and discharge curves of the battery of the present embodiment. [Figure 7] 1 is a graph showing the relationship between the number of cycles and the capacity of the battery of the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, embodiments of the aluminum deposition method, ionic liquid, electrolyte, and battery according to the present invention will be described with reference to the drawings, although the present invention is not limited to the following embodiments.

[0024] First, the aluminum deposition method of this embodiment will be described with reference to Fig. 1. The aluminum deposition method of this embodiment includes a mixing step S1 of mixing an aluminum halide and an alkali halide salt, and a voltage application step S2 of applying a voltage to the mixture.

[0025] In the mixing step S1, the aluminum halide and the alkali halide salt are mixed. Typically, a mixture of the aluminum halide and the alkali halide salt is produced by mixing the solid aluminum halide and the solid alkali halide salt.

[0026] First, an aluminum halide and an alkali halide salt are prepared. The halogen element of the aluminum halide is different from the halogen element of the alkali halide salt. For example, if the aluminum halide is chloride, the alkali halide salt is bromide. Alternatively, if the aluminum halide is bromide, the alkali halide salt is chloride.

[0027] In the mixing step S1, it is preferable that there is one or more types of alkali halide salts. When there are two or more types of alkali halide salts, the types of halogen elements in the two or more alkali halide salts may be the same. For example, the alkali halide salts may be sodium bromide and potassium bromide. Alternatively, the alkali halide salts may be sodium chloride and potassium chloride. Alternatively, when there are two or more types of alkali halide salts, the types of halogen elements in the two or more alkali halide salts may be different. In this case, any of the halogens in the two or more alkali halide salts may be the same as the halogen in the aluminum halide.

[0028] Similarly, in the mixing step S1, the aluminum halides are preferably one or more different types.

[0029] For example, an aluminum halide and an alkali halide salt are added to a container. Either the aluminum halide or the alkali halide salt may be added to the container first, or the aluminum halide and the alkali halide salt may be added simultaneously.

[0030] In the mixing step S1, an aluminum halide and an alkali halide salt are mixed in a container. By mixing the aluminum halide and the alkali halide salt, a mixture of the aluminum halide and the alkali halide salt is produced in the container.

[0031] The aluminum halide and the alkali halide salt may be mixed at room temperature. Alternatively, the aluminum halide and the alkali halide salt may be mixed at a temperature higher than room temperature. When mixed at a temperature higher than room temperature, the viscosity of the mixture decreases. Typically, when the aluminum halide and the alkali halide salt are mixed at a temperature higher than room temperature, the viscosity of the mixture decreases and the mixture melts, allowing the aluminum halide and the alkali halide salt to be sufficiently mixed in a short period of time. The mixture may also be melted by placing it at a temperature higher than room temperature.

[0032] The mixture is preferably an ionic liquid having a melting point of 373 K or less. In particular, the mixture is preferably in the form of a liquid or a highly viscous slurry at room temperature. The glass transition temperature of the mixture is preferably room temperature or lower.

[0033] In the voltage application step S2, a voltage is applied to the mixture. By applying a voltage to the molten mixture, aluminum is precipitated from the molten mixture. For example, aluminum is preferably precipitated as nanometer-order thin flakes.

[0034] For example, the mixture may be melted by applying a voltage to the mixture while the mixture is kept at a temperature higher than room temperature. Alternatively, the mixture may be heated and melted by applying a voltage to the mixture. In this manner, aluminum is precipitated by applying a voltage to the molten mixture. Here, the mixture is preferably a mixture of aluminum halide and alkali halide salt, and the mixture is preferably melted at a temperature of 353 K or less.

[0035] According to this embodiment, aluminum is deposited from a mixture of aluminum halide and alkali halide salt, which allows aluminum to be deposited inexpensively and efficiently.

[0036] The 1-ethyl-3-methylimidazolium chloride ([EMI]Cl) used in Patent Document 1 costs about 400 yen / g, whereas sodium bromide (NaBr), an example of an alkali halide salt, costs about 18 yen / g and potassium bromide (KBr) costs about 6 yen / g. Furthermore, when an organic salt is used, if the reaction proceeds in an oxygen-containing atmosphere, superoxide ions (O2 - ) decomposes organic cations, so when using organic salts, the reaction must be carried out under an inert gas atmosphere.

[0037] On the other hand, according to the present embodiment, aluminum is deposited from a mixture of aluminum halide and alkali halide salt without using an organic salt, which makes it less susceptible to the effects of oxygen and allows aluminum to be deposited inexpensively.

[0038] The aluminum deposition method of the present embodiment is suitable for use in aluminum refining. By using a mixture of aluminum halide and alkali halide salt as the electrolyte, aluminum contained in the aluminum halide is deposited on an electrode, thereby obtaining high-purity aluminum.

[0039] In aluminum refining, it is preferable to mix a low-purity aluminum compound with the electrolyte. This allows aluminum contained in the aluminum halide to be deposited on the electrode, and aluminum ions dissolved from the low-purity aluminum compound to be deposited on the electrode. In this way, high-purity aluminum can be deposited using the low-purity aluminum compound.

[0040] In this embodiment, an ionic liquid can be formed from a mixture of aluminum halide and alkali halide salt. Because the ionic liquid is formed by melting the mixture of aluminum halide and alkali halide salt, it exhibits a high carrier ion density and low viscosity, resulting in high ionic conductivity. Therefore, aluminum is easily precipitated. Furthermore, using the ionic liquid as a battery electrolyte can improve battery characteristics.

[0041] According to this embodiment, a mixture of aluminum halide and alkali halide salt is suitably used as an electrolyte capable of depositing aluminum.

[0042] Furthermore, aluminum batteries can be suitably produced using the ionic liquid of this embodiment as an electrolyte. Aluminum is a common metal and is inexpensive. Aluminum batteries are also easy to recycle and handle. The volumetric energy density of aluminum batteries is more than twice as high as that of lithium-ion batteries.

[0043] In an aluminum battery, aluminum is deposited at the battery's electrodes. When the aluminum battery is discharged, aluminum ions are consumed at the positive electrode of the aluminum battery. The aluminum ions in the mixture and aluminum ions dissolved from the aluminum electrode are used in the reaction at the positive electrode. At the negative electrode, aluminum dissolves during discharge and deposits during charge. In this way, the mixture can be used as the battery's electrolyte, and the aluminum deposition method can be performed at the negative electrode during battery charge.

[0044] The aluminum deposition method of this embodiment is also suitable for use in aluminum plating, and the surface of an object can be plated with aluminum by this embodiment.

[0045] The present embodiment is also suitable for use as a battery material other than an electrolyte solution. For example, the precipitate deposited by the aluminum deposition method of the present embodiment may be used as a material for the negative or positive electrode of a battery. For example, the precipitate is used as a negative electrode active material of a lithium ion battery. Alternatively, the precipitate is used as a positive electrode current collector of a lithium ion battery.

[0046] [Aluminum halide] The aluminum halide may be any of aluminum fluoride, aluminum chloride, aluminum bromide, and aluminum iodide. However, when producing an ionic liquid as a mixture, the aluminum halide is preferably any of aluminum chloride, aluminum bromide, and aluminum iodide. Particularly from the viewpoint of cost, the aluminum halide is preferably aluminum chloride (AlCl). The melting point of aluminum chloride is 466K.

[0047] When aluminum chloride is used as the aluminum halide, the mixing, voltage application, and other processes are preferably carried out in an atmosphere with a low water content in order to suppress the generation of hydrogen chloride. For example, the processes are preferably carried out in a glove box.

[0048] Furthermore, two different types of aluminum halides may be used as the aluminum halides.

[0049] [Alkali halide salts] The alkali halide salt is a salt of an alkali metal and a halogen element. For example, the alkali metal preferably has a lower reduction potential than aluminum.

[0050] For example, the metal includes an alkali metal (Group 1 element). The metal may be any of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs). In this case, the alkali halide salt may be any of lithium chloride (LiCl), sodium chloride (NaCl), potassium chloride (KCl), rubidium chloride (RbCl), and cesium chloride (CsCl).

[0051] Alternatively, the alkali halide salt may be any of lithium bromide (LiBr), sodium bromide (NaBr), potassium bromide (KBr), rubidium bromide (RbBr), and cesium bromide (CsBr). Similarly, the alkali halide salt may be any of fluorides or iodides.

[0052] [Mixture] The aluminum halide and the alkali halide salt are mixed to form a mixture. The mixing may be performed at a temperature higher than room temperature to reduce the viscosity of the mixture. For example, the mixture is a liquid or a viscous slurry at room temperature.

[0053] Alkali metals are monovalent metals. Compared to polyvalent metals, alkali metal ions have a smaller positive charge and a weaker bond with negative ions. Therefore, the melting point of the mixture tends to be lower than when polyvalent metal salts are added.

[0054] In one example, when the alkali halide salt contains bromide, a specific complex anion is formed in the mixture. For example, if the aluminum halide is aluminum chloride (AlCl3) and the alkali halide salt contains bromide, the mixture will contain AlCl3, a strong Lewis acid, and Br, a strong Lewis base. -1 and the complex anion [AlCl3Br] - or [Al2Cl6Br] - The complex anion structure increases entropy, making it difficult for the anion to form a solid, lowering the melting point.

[0055] In order for the mixture to become an ionic liquid, it is preferable that complex anions are easily formed in the mixture. To ensure that complex anions are sufficiently formed in the mixture, the molar concentration of aluminum chloride (AlCl3) is preferably 50 mol% or more, and more preferably 60 mol% or more.

[0056] In this way, the difference between the halogen elements of the aluminum halide and the alkali halide salt reduces the symmetry of the mixture, increasing the entropy of the mixture. Therefore, the mixture is less likely to solidify even at relatively low temperatures, and as a result, the melting point of the mixture can be reduced.

[0057] Because the ionic interaction between the alkali metal ions and the complex ions is not very strong, it is possible to obtain inorganic ionic liquids that can be used at temperatures lower than 333 K. This large change in the solution properties is thought to be due to an increase in the entropy of the anion species, which occurs when the type of halogen element in the aluminum halide differs from that in the alkali halide salt.

[0058] It is also possible to use a combination of several aluminum halides as the aluminum halide, and a combination of several alkali halide salts as the alkali halide salt, in which case the entropy of mixing effect occurs, further increasing the fluidity of the mixture.

[0059] The larger the atomic weight of the halogen element in the aluminum halide and the halogen element and alkali metal in the alkali halide salt, the lower the melting point of the mixture tends to be. On the other hand, the larger the atomic weight of the halogen element in the aluminum halide and the halogen element and alkali metal in the alkali halide salt, the lower the ionic conductivity tends to be.

[0060] [Voltage application] In the voltage application step S2, when a voltage is applied to the mixture, aluminum ions in the mixture (melt) are reduced and aluminum is precipitated. The potential applied to the mixture is preferably −1.5 V or more and −0 V or less.

[0061] The voltage may be applied at room temperature. Alternatively, the voltage may be applied at a temperature higher than room temperature. By applying the voltage at a temperature higher than room temperature, aluminum can be efficiently deposited. However, it is preferable that the voltage be applied at a temperature of 373 K or less so that aluminum can be easily deposited.

[0062] The deposited aluminum can be dissolved by applying a high voltage to the mixture. For example, the potential for dissolving aluminum is preferably 0 V or more and 1.0 V or less. The closer the potential for dissolving aluminum is to 0 V, the more preferable it is.

[0063] For example, it is preferable that one of the electrodes used to apply a voltage contains platinum, glassy carbon, or copper. It is also preferable that another of the electrodes used to apply a voltage contains aluminum. Three or more electrodes may be used to apply a voltage. In this case, two or more electrodes may contain aluminum.

[0064] [Precipitated aluminum] The aluminum is formed into a two-dimensional thin film by applying a voltage, and the thickness of the aluminum is preferably on the order of nanometers, for example, 100 nm or less.

[0065] [battery] Aluminum flakes are suitable for use as a negative electrode active material in lithium-ion batteries. Recently, silicon is often used together with graphite in negative electrode active materials for lithium-ion batteries. While the theoretical capacity of silicon is higher than that of aluminum, silicon itself is not electrically conductive, so a conductive additive is required. In contrast, when aluminum flakes are used as a negative electrode active material in lithium-ion batteries, no conductive additive is required, allowing for an effective high capacity. In this case, the negative electrode may have aluminum flakes attached to a mesh-shaped substrate. For example, the substrate may be formed from mesh-shaped copper.

[0066] The aluminum flakes are also suitable for use as a positive electrode current collector for lithium ion batteries. The positive electrode current collector is preferably formed by integrally molding the aluminum flakes with a sulfur substance, a carbon material, and a binder.

[0067] The mixture of aluminum halide and alkali halide salt is preferably used as an electrolyte for aluminum batteries. In this case, an electrode containing aluminum is used as the negative electrode. Expanded graphite may be used as the positive electrode. Expanded graphite can suppress damage to the positive electrode even if aluminum ions enter the positive electrode. Typically, the expanded graphite is used in a state where it is attached to a substrate. For example, the substrate is made of molybdenum. Alternatively, a graphene laminate may be used as the positive electrode.

[0068] Furthermore, an aluminum-sulfur battery may be fabricated using the ionic liquid of this embodiment as an electrolyte. Sulfur is known to exhibit a high theoretical capacity. In this case, the positive electrode may contain a sulfur-carbon composite. When a mixture (melt) of aluminum halide and alkali halide salt is used as the electrolyte of an aluminum-sulfur battery, it is preferable to use a sulfur-carbon composite electrode as the positive electrode.

[0069] Typically, in aluminum-sulfur batteries, sulfur from the electrodes may dissolve into the electrolyte, but the ionic liquid of this embodiment can suppress the dissolution of sulfur from the electrodes. In particular, when the electrolyte of an aluminum-sulfur battery contains bromide, a relatively stable bromine-containing substance is generated as an intermediate, which is thought to suppress the outflow of sulfur.

[0070] [Sulfur-carbon composite electrode] The sulfur-carbon composite electrode includes sulfur powder and a carbon material. For example, the carbon material is carbon nanotubes. The sulfur-carbon composite electrode may further include polytetrafluoroethylene (PTFE). PTFE can improve adhesion to the current collector.

[0071] 1, the mixture is exposed to a high-temperature environment in either the mixing step S1 or the voltage application step S2 so that the mixture melts, but this embodiment is not limited to this. The mixture may also be melted at a timing other than the mixing step S1 or the voltage application step S2.

[0072] Next, the aluminum deposition method of this embodiment will be described with reference to Fig. 2. The aluminum deposition method of this embodiment further includes a melting step S1m in addition to the mixing step S1 and the voltage application step S2.

[0073] The melting step S1m is performed after the mixture is produced in the mixing step S1 and before a voltage is applied to the mixture in the voltage application step S2, by exposing the mixture to an environment at a temperature higher than room temperature to melt the mixture. For example, in the melting step S1m, the mixture may be melted by exposing it to an environment of 373 K or lower, or may be melted by exposing it to an environment of 353 K or lower.

[0074] Thereafter, in the voltage application step S2, a voltage is applied to the mixture in a molten state, thereby depositing aluminum. [Example]

[0075] [Generation of Sample A] Sample A was prepared as follows. First, anhydrous aluminum chloride (manufactured by Nippon Light Metal Co., Ltd.) was prepared as the material for Sample A. Sodium bromide and potassium bromide obtained from Sigma-Aldrich were vacuum dried at 393 K for 48 hours before use. Then, aluminum chloride was gradually added to the sodium bromide and potassium bromide at room temperature to mix aluminum chloride (AlCl), sodium bromide (NaBr), and potassium bromide (KBr) in a molar ratio of 61.0:26.0:13.0.

[0076] The mixture was then heated to 373 K in a sealed glove box filled with argon and containing less than 1 ppm of oxygen and water, to transform into a liquid, and then cooled to room temperature to solidify. Sample A was thus produced. The melting point of Sample A was 339.3 K. When Sample A was left standing and then cooled, it became supercooled and maintained its liquid phase up to around 303 K.

[0077] [Ionic conductivity] The ionic conductivity of sample A was measured at different temperatures. At 373 K, the ionic conductivity of sample A was 100 mScm. -1 At 353 K, the ionic conductivity of sample A is 70 mScm -1 At 323 K, the ionic conductivity of sample A is 30 mScm -1 It was.

[0078] [viscosity] The viscosity of Sample A was measured using a viscometer under different temperature conditions. The viscosity was 11.2 mPas at 373 K and 18.1 mPas at 353 K.

[0079] [Cyclic voltammogram] The cyclic voltammogram of sample A was measured. The sample was used as the electrolyte and three electrodes were inserted to form a three-electrode cell. Aluminum with 99.999% purity was used as the counter electrode and reference electrode, and glassy carbon (GC) or copper (Cu) was used as the working electrode. The glassy carbon (GC) or copper (Cu) was washed with diluted nitric acid before use.

[0080] Cyclic voltammograms were measured at a temperature of 353 K. In this measurement, the electrode potential was linearly swept from the minimum potential to the maximum potential at a sweep rate of 10 mV / s, and then linearly swept from the maximum potential to the minimum potential to measure the response current.

[0081] Figures 3(a) and 3(b) show the results of cyclic voltammetry of sample A at a temperature of 353 K. In the graphs of Figures 3(a) and 3(b), the vertical axis represents current density, and the horizontal axis represents potential. Note that Figure 3(a) shows the change in current density when conductive glassy carbon (GC) is used as the working electrode, and Figure 3(b) shows the change in current density when copper (Cu) is used as the working electrode.

[0082] In both Figures 3(a) and 3(b), when the potential was lowered, a reduction current flowed. At this time, aluminum precipitated in Sample A. On the other hand, when the potential was increased, the aluminum dissolved and an oxidation current flowed. At this time, the aluminum in the sample dissolved.

[0083] As shown in Figure 3(a), when the potential was decreased to approximately -0.1 V, the reduction current increased rapidly and aluminum precipitated. Then, when the potential was increased to +0.0 V, the current increased rapidly again and aluminum dissolved again. The precipitated aluminum did not adhere well to the glassy carbon electrode and partially peeled off from the glassy carbon, so the aluminum dissolution current was smaller than the aluminum deposition current.

[0084] When the potential was increased to approximately 1.8 V, the electrolyte decomposed and the current increased. Bromine was generated from the electrolyte. The potential window of Sample A was 1.9 V.

[0085] As shown in Figure 3(b), when the potential decreased to approximately -0.02 V, the reduction current increased rapidly and aluminum was deposited. Then, when the potential increased to +0.0 V, the current increased rapidly again and aluminum dissolved again. Because aluminum was deposited in close contact with the copper electrode, the aluminum dissolution current was almost equal to the aluminum deposition current. Here, when the potential exceeded approximately 0.4 V, the copper on the electrode dissolved.

[0086] [Construction of an aluminum-sulfur battery] As shown in FIG. 4, an aluminum-sulfur battery 100 was fabricated. FIG. 4 shows a schematic diagram of the aluminum-sulfur battery 100. The aluminum-sulfur battery 100 includes a positive electrode 110, a negative electrode 120, and an electrolyte 130. Sample A was used as the electrolyte 130, a sulfur-carbon composite material fabricated as follows was used as the positive electrode 110, and an aluminum coil was used as the negative electrode 120. The positive electrode 110 was attached to the tip of an L-shaped current collector 112 made of molybdenum. The positive electrode 110 was a thin, cylindrical battery with a thickness of 60 μm and a diameter of 8 mm (the surface area of the main face was 0.5 cm).2 ) and weighed 2.0 mg.

[0087] [Sulfur carbon composite material] Prior to fabricating the sulfur-carbon composite electrode, a sulfur-carbon composite was synthesized. 5.0 g of sulfur powder and 0.10 g of carbon material (Aldrich multi-walled carbon nanotubes) were placed in a 50 mL two-neck flask, and the air in the flask was replaced with Ar. The mixture was then heated to 403 K, maintained at 423 K for 2 hours with stirring, and then allowed to cool naturally. The mixture was then ground at 200 rpm for 1 hour to produce the sulfur-carbon composite.

[0088] [Sulfur-carbon composite electrode] The sulfur-carbon composite material and carbon material (multi-walled carbon nanotubes) were added to a container in a weight ratio of 50:45 and mixed for 3 minutes. Polytetrafluoroethylene (PTFE) was then added to the mixture in a weight ratio of 95:5 and mixed for 3 minutes. The mixture was transferred to an agate mortar and kneaded to produce a 60 μm thick sheet. A circular piece with a diameter of 8 mm and a weight of 2.0 mg was cut from the sheet and used as the sulfur-carbon composite electrode. In this way, an aluminum-sulfur battery 100 was fabricated using Sample A as the electrolyte.

[0089] [Electrochemical measurements of sulfur-carbon composite electrodes] A three-electrode beaker cell was prepared using a sulfur-carbon composite electrode as the working electrode, a coiled Al counter electrode, an Al wire as the reference electrode, and sample A as the electrolyte.

[0090] Figure 5(a) shows the cyclic voltammograms obtained by subjecting the sulfur-carbon composite electrode to 1 to 30 cycles with the electrolyte stirred at 100 rpm, and Figure 5(b) shows the cyclic voltammograms obtained by subjecting the sulfur-carbon composite electrode to 31 to 60 cycles without stirring. In this measurement, the electrode potential was linearly swept from the minimum potential to the maximum potential at a sweep rate of 1 mV / s at 353 K, and then linearly swept from the maximum potential to the minimum potential to measure the response current.

[0091] As shown in Figure 5(a), when Sample A was used as the electrolyte, current continued to flow even after 30 cycles. Furthermore, as shown in Figure 5(b), current continued to flow even after another 30 cycles.

[0092] [Charge and discharge test of aluminum sulfur battery] A charge / discharge test was carried out on the aluminum-sulfur battery 100. Here, the positive electrode 110 had a thin cylindrical shape, a thickness of 80 μm, a diameter of 22 mm (a surface area of the main surface of 3.8 cm ). 2 ) and weighed 21.1 mg.

[0093] Fig. 6 is a graph showing the charge / discharge curves of the aluminum-sulfur battery 100. The graph in Fig. 6 shows the relationship between the specific capacity and voltage of the aluminum-sulfur battery 100 using Sample A as the electrolyte. In Fig. 6, the lower part (solid line) shows the behavior during discharge, and the upper part (dotted line) shows the behavior during charge. The temperature was 353 K, and the current density per 1 g of active material was 1000 mA.

[0094] As shown in Figure 6, the charge and discharge curves after 20 cycles did not change significantly compared to those after 1 cycle. However, the voltage and specific capacity increased slightly with repeated charge and discharge. This is thought to be because the electrolyte had not fully permeated the electrodes at the start of charge and discharge, but the electrolyte became fully permeated into the electrodes as the charge and discharge were repeated.

[0095] Figure 7 is a graph showing the change in the specific capacity and charge / discharge efficiency of the aluminum-sulfur battery 100 versus the number of charge / discharge cycles. In Figure 7, La represents the change in discharge specific capacity. The discharge specific capacity is relatively small when the number of cycles is low, but increases as the number of cycles increases, reaching 650 mAh per gram of active material when the number of cycles approaches 20.

[0096] In addition, in Figure 7, Lb indicates the change in the charge specific capacity. The charge specific capacity is also relatively small when the number of cycles is small, but increases as the number of cycles increases, reaching 650 mAh per 1 g of active material when the number of cycles approaches 20.

[0097] The coulombic efficiency (charge / discharge efficiency) of the battery was approximately 90% when the number of cycles was small, but as the number of cycles increased, it approached 100%. These results demonstrate that the aluminum-sulfur battery 100 exhibits good battery characteristics.

[0098] The embodiments of the present invention have been described above with reference to the drawings (FIGS. 1 to 7). However, the present invention is not limited to the above embodiments and can be embodied in various forms without departing from the spirit and scope of the present invention. Furthermore, various inventions can be formed by appropriately combining multiple components disclosed in the above embodiments. For example, some components may be omitted from all components shown in the embodiments. The drawings mainly show each component in a schematic manner to facilitate understanding, and the number of each component shown may differ from the actual number due to the convenience of drawing. Furthermore, the components shown in the above embodiments are merely examples and are not particularly limited, and various modifications are possible without substantially departing from the effects of the present invention. [Industrial Applicability]

[0099] According to the present invention, aluminum can be deposited inexpensively and efficiently.

Claims

1. preparing a mixture of an ionic liquid obtained by mixing an aluminum halide and two or more alkali halide salts each containing a halogen atom different from the halogen atom of the aluminum halide; applying a voltage to the mixture to deposit aluminum; The aluminum deposition method includes:

2. The aluminum halide includes aluminum chloride, 2. The method of claim 1, wherein the alkali halide salts include potassium bromide and sodium bromide.

3. 3. The method for depositing aluminum according to claim 1, wherein the molar ratio of said aluminum halide to said mixture is 50% or more.

4. 4. The method for depositing aluminum according to claim 1, wherein in the step of depositing aluminum, the aluminum is deposited at a negative electrode of a battery.

5. The method for depositing aluminum according to claim 1 , further comprising the step of melting the mixture at 353 K or less.

6. Aluminum halide, two or more alkali halide salts each containing a halogen element different from the halogen element of the aluminum halide; An ionic liquid produced by melting a mixture containing

7. The aluminum halide includes aluminum chloride, 7. The ionic liquid of claim 6, wherein the alkali halide salts include potassium bromide and sodium bromide.

8. 8. The ionic liquid according to claim 6, wherein the molar ratio of the aluminum halide to the mixture is 50% or more.

9. An electrolyte solution comprising the ionic liquid according to claim 7 or 8.

10. an electrolyte solution containing an ionic liquid produced by melting a mixture containing an aluminum halide and two or more alkali halide salts containing a halogen element different from the halogen element of the aluminum halide; a negative electrode containing aluminum; Positive electrode and A battery.

11. 11. The battery of claim 10, wherein the positive electrode comprises a sulfur-carbon composite electrode.

12. 12. The battery of claim 11 , wherein the sulfur-carbon composite electrode comprises carbon nanotubes and polytetrafluoroethylene.

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