Perforated aluminum foil and method for manufacturing same

Abstract

The present invention relates to: a perforated aluminum foil suitably used for a current collector for a power storage device; and a method for manufacturing same. The present invention provides a method for manufacturing a perforated aluminum foil having a plurality of through-holes penetrating in the thickness direction thereof, the method comprising: an alkaline cleaning step for bringing a first aqueous composition containing 1-10 mass percent inclusive of an alkali into contact with the surface of an aluminum foil; and a through-hole forming step for forming the through-hole in the thickness direction of the aluminum foil by bringing a second aqueous composition containing 1-30 mass percent inclusive of halide ions into contact with the surface of the aluminum foil within 20 minutes after the alkaline cleaning step. Also provided is a perforated aluminum foil having a prescribed breaking strength, average pore diameter, and maximum pore diameter / average pore diameter.

Description

Perforated aluminum foil and its manufacturing method

[0001] The present invention relates to a perforated aluminum foil and a method for producing the same.

[0002] In recent years, demand for power storage devices, particularly lithium ion capacitors (LICs), lithium ion secondary batteries (LIBs), and electric double layer capacitors (EDLCs), has been increasing in mobile information terminals, mobile electronic devices, electric vehicles, hybrid electric vehicles, and even stationary power storage systems. Perforated aluminum foils with through-holes formed therein for pre-doping with lithium ions are known as current collectors for the positive or negative electrodes of these power storage devices. For example, lithium ion capacitors use activated carbon similar to that used in electric double layer capacitors for the positive electrode and carbon materials similar to that used in lithium ion secondary batteries for the negative electrode, enabling them to achieve both high power density and high energy density. However, to achieve high capacity, efficient pre-doping with lithium ions is required, and it is necessary to form a large number of fine through-holes to reduce the air permeability of the perforated aluminum foil. On the other hand, if a large number of through-holes are formed, the tensile strength of the perforated aluminum foil inevitably decreases. If the tensile strength of the perforated aluminum foil becomes too low, continuous processes such as a roll-to-roll process in which a roll-shaped long current collector is continuously processed through a conveying line cannot be adopted, resulting in poor production efficiency. Therefore, there is a need for the development of a technology that can reduce the air permeability of perforated aluminum foil while suppressing a decrease in tensile strength. Etching technology is known as a method for forming fine through-holes. For example, Patent Document 1 describes a method of forming through-holes in aluminum foil by electrolytic etching using an aqueous solution containing hydrochloric acid as an electrolyte. However, this method has issues with operational safety due to the relatively high temperature treatment. Furthermore, forming through-holes at relatively high temperatures and by electrolytic etching is costly. Patent Document 2 describes a method of forming through-holes in the aluminum foil by electrolytic etching using an aqueous solution containing sulfuric acid and nitric acid as an electrolyte, forming through-holes in the aluminum foil, forming through-holes in the aluminum foil, forming through-holes in the aluminum foil, forming through-holes in the aluminum foil, and removing the coating from the desired portion of the through-hole formation area by laser processing. However, this method requires many steps and is costly due to the use of a laser.

[0003] JP 2011-208254 A International Publication No. 2017 / 163913 A

[0004] There is a need for the development of perforated aluminum foil suitable for use as a current collector for electricity storage devices, and a manufacturing technique for the same.

[0005] The present invention relates to the following perforated aluminum foil and a method for producing the same: [1] A method for producing perforated aluminum foil having a plurality of through holes penetrating in the thickness direction, comprising: an alkali washing step of contacting the surface of an aluminum foil with a first aqueous composition containing 1 mass % to 10 mass % of alkali; and a through hole forming step of contacting the surface of the aluminum foil with a second aqueous composition containing 1 mass % to 30 mass % of halide ions within 20 minutes after the alkali washing step to form the through holes in the thickness direction of the aluminum foil. [2] The method for producing perforated aluminum foil according to [1] above, wherein the alkali is a hydroxide of an alkali metal or alkaline earth metal. [3] The method for producing perforated aluminum foil according to [1] or [2] above, wherein the halide ions are chloride ions. [4] The method for producing perforated aluminum foil according to any one of [1] to [3] above, wherein the thickness of the aluminum foil is 1 μm to 50 μm. [5] The method for producing a perforated aluminum foil according to any one of [1] to [4], wherein the aluminum purity of the aluminum foil is 98% by mass or more and less than 99.9% by mass. [6] The method for producing a perforated aluminum foil according to any one of [1] to [5], wherein the treatment temperature in the alkali washing step is 10°C or more and 50°C or less, and the treatment time is 5 seconds or more and 120 seconds or less. [7] The method for producing a perforated aluminum foil according to any one of [1] to [6], wherein the treatment temperature in the through hole forming step is 10°C or more and 50°C or less, and the treatment time is 5 seconds or more and 120 seconds or less. [8] Perforated aluminum foil having a plurality of through holes penetrating in the thickness direction, wherein the thickness of the perforated aluminum foil is 1 μm or more and 50 μm or less, a breaking strength of 4 N / 10 mm or more and 20 N / 10 mm or less, an average pore size of 1 μm or more and 50 μm or less, and a ratio of maximum pore size to average pore size of 4 or less. [9] Number of holes: 1.0 x 10 ３ pieces / cm ２ Above 5.0 x 10 ４pieces / cm ２ The perforated aluminum foil according to [8] above, having an opening ratio of 10% or less and an air permeability of less than 70 seconds.

[10] A current collector for an electricity storage device, comprising the perforated aluminum foil according to [8] or [9] above.

[0006] According to the present invention, a porous aluminum foil suitable for use as a current collector for an electricity storage device can be produced by a simple method using alkaline washing and subsequent chemical etching.

[0007] 1 is a process diagram illustrating a method for producing a porous aluminum foil according to the present invention. FIG.

[0008] 1. Manufacturing Method of Perforated Aluminum Foil The present invention relates to a manufacturing method of a perforated aluminum foil having a plurality of through holes penetrating in the thickness direction, and is characterized by comprising: an alkali cleaning step of contacting the surface of an aluminum foil with a first aqueous composition containing 1% by mass to 10% by mass of alkali; and a through hole forming step of contacting the surface of the aluminum foil with a second aqueous composition containing 1% by mass to 30% by mass of halide ions within 20 minutes after the alkali cleaning step to form the through holes in the thickness direction of the aluminum foil. FIG. 1 is a schematic diagram illustrating the steps of the manufacturing method of the perforated aluminum foil of the present invention. The following description will be made using FIG. 1. As shown in FIG. 1(A), an oxide film (passive film) 2 is usually formed on the surface of aluminum foil 1. In the alkali cleaning step, the surface of this aluminum foil 1 (or the surface of oxide film 2) is contacted with a first aqueous composition containing 1% by mass to 10% by mass of alkali. This partially removes the oxide film 2 on the surface of the aluminum foil, as shown in FIG. 1(B). The oxide film 2 does not need to be completely removed; it is sufficient that the halide ions are removed to an extent that they can react with at least a portion of the surface of the aluminum foil in the next step. After the alkali cleaning step, if necessary, a water rinsing step may be performed in which appropriate washing is performed using water to remove alkali adhering to the surface of the aluminum foil 1. Within 20 minutes after the alkali cleaning step, the aluminum foil 1 is contacted with a second aqueous composition containing 1 mass% to 30 mass% of halide ions. This allows halide ions to react with the surface of the aluminum foil 1 from which the oxide film 2 has been partially removed, and through-holes can be formed in the thickness direction of the aluminum foil 1, as shown in FIG. 1(C). After the through-hole formation, if necessary, a water rinsing step may be performed in which appropriate washing is performed using water to remove halide ions adhering to the surface of the aluminum foil (i.e., perforated aluminum foil) 1.

[0009] As described above, according to the present invention, through-holes can be formed in the thickness direction of the aluminum foil by a simple method in which the surface of the aluminum foil is washed with an alkali and then contacted with an aqueous composition containing halide ions within 20 minutes. According to a preferred embodiment, the obtained perforated aluminum foil has relatively uniform pore sizes of the through-holes, and therefore has an excellent balance between air permeability and tensile strength, and is suitable for use as a current collector for an electricity storage device, particularly as a current collector for a lithium-ion capacitor.

[0010] <Alkali Cleaning Step> In the alkali cleaning step, the surface of the aluminum foil is brought into contact with a first aqueous composition containing 1 mass % to 10 mass % of alkali. This step allows the oxide film (passive film) on the surface of the aluminum foil to be partially removed, making it easier to control the formation of through-holes by subsequent chemical etching.

[0011] The aluminum foil is an alloy plate containing aluminum as the main component and trace amounts of other elements, and is not particularly limited as long as it can be used as a current collector for an electricity storage device. Examples of other elements include Fe, Si, Cu, Mg, Zn, Ti, V, Ga, Cr, Zr, B, Mn, Ni, Li, etc. The aluminum purity is not particularly limited, but is preferably 98% by mass or more, and may be 98.5% by mass or more, 99% by mass or more, 99.3% by mass or more, 99.5% by mass or more, or 99.75% by mass or more. The upper limit is not particularly limited, and may be 100% by mass, but is preferably less than 99.9% by mass, and may be less than 99.8% by mass, less than 99.7% by mass, less than 99.6% by mass, or less than 99.5% by mass. Either hard aluminum foil or soft aluminum foil may be used as the aluminum foil. The aluminum foil is not particularly limited, but is preferably an A1000 series or A8000 series aluminum foil, and may be A1N30, A8011, A8021, or A8079.

[0012] The thickness of the aluminum foil is preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 25 μm or less. The lower limit of the thickness is not particularly limited, but is usually 1 μm or more. When the thickness is within this range, the aluminum foil can be suitably used as a current collector for an electricity storage device, particularly as a current collector for a lithium ion capacitor.

[0013] The first aqueous composition used in the alkaline cleaning step contains an alkali in an amount of 1% by mass to 10% by mass. The alkali is preferably an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, or an alkaline earth metal hydroxide such as magnesium hydroxide, calcium hydroxide, strontium hydroxide, or barium hydroxide, more preferably an alkali metal hydroxide, and particularly preferably sodium hydroxide. Two or more alkalis may be used in combination as needed. The alkali content (concentration) in the first aqueous composition is 1% by mass to 10% by mass, preferably 2.0% by mass to 8.0% by mass, more preferably 3.0% by mass to 7.0% by mass, particularly preferably 4.0% by mass to 6.0% by mass, and even more preferably 4.5% by mass to 5.5% by mass. In addition, the range of the alkali content contained in the first aqueous composition may have a lower limit of 1.0 mass%, 2.0 mass%, 3.0 mass%, 4.0 mass%, 4.5 mass%, or 5.0 mass%, and an upper limit of 10.0 mass%, 8.0 mass%, 7.0 mass%, 6.0 mass%, or 5.5 mass%.

[0014] The first aqueous composition may contain additives as components other than alkali, as long as the effects of the present invention are exhibited. Examples of additives include organic solvents, surfactants, pH adjusters, and reducing agents. The concentration of the additives that may be contained in the first aqueous composition is preferably 10% by mass or less, more preferably 5.0% by mass or less, more preferably 2.0% by mass or less, and particularly preferably 1.0% by mass or less.

[0015] The first aqueous composition contains water, particularly ion-exchanged water or ultrapure water. The water content, which is the remainder of the first aqueous composition, is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 95% by mass or more. The upper limit of the water content is 99% by mass or less, and may be 98% by mass or less, 97% by mass or less, 96% by mass or less, or 95% by mass or less.

[0016] The treatment temperature in the alkaline cleaning step (the temperature of the first aqueous composition) is preferably 10°C or higher and 50°C or lower, more preferably 20°C or higher and 45°C or lower, and even more preferably 25°C or higher and 40°C or lower. When the temperature of the first aqueous composition is 10°C or higher, the cleaning treatment can be carried out efficiently in a short time. On the other hand, when the temperature of the first aqueous composition is 50°C or lower, changes in the liquid composition can be suppressed and the alkaline cleaning conditions can be maintained constant. In addition, the work can be carried out safely.

[0017] The method for contacting the first aqueous composition with the aluminum foil is not particularly limited. For example, the first aqueous composition may be contacted with the aluminum foil by dropping (spinning) or spraying (atomizing), or a wet method (wet etching method) such as immersing the aluminum foil in the first aqueous composition may be used.

[0018] The treatment time in the alkali washing step is preferably 5 seconds to 120 seconds, more preferably 8 seconds to 100 seconds, and even more preferably 10 seconds to 60 seconds. The treatment time may be appropriately determined taking into account various conditions such as the state of the surface of the aluminum foil, the alkali content in the first aqueous composition, the treatment temperature, and the contact method. Here, the treatment time refers to the time during which the first aqueous composition is contacted with the aluminum foil surface. For example, it refers to the time during which the aluminum foil is immersed in the first aqueous composition, the time from when the first aqueous composition is sprayed on the surface of the aluminum foil to when the first aqueous composition is removed with water, or the time from when the first aqueous composition is removed by contacting the second aqueous composition in the subsequent through-hole formation step.

[0019] <Water washing step> After alkali washing, the aluminum foil is preferably washed with water as needed to remove the alkali adhering to the surface of the aluminum foil. The water is preferably one from which metal ions, organic impurities, particles, etc. have been removed by distillation, ion exchange treatment, filtration, various adsorption treatments, etc., and pure water or ultrapure water is particularly preferred.

[0020] <Through-hole forming step> In the through-hole forming step, within 20 minutes after the alkaline cleaning step, a second aqueous composition containing 1% by mass or more and 30% by mass or less of halide ions is contacted with the surface of the aluminum foil to form the through-holes in the thickness direction of the aluminum foil. By contacting the second aqueous composition containing 1% by mass or more and 30% by mass or less of halide ions within 20 minutes after the alkaline cleaning step, through-holes can be formed in the aluminum foil. Here, "within 20 minutes after the alkaline cleaning step" means within 20 minutes after the completion of the alkaline cleaning step, that is, within 20 minutes after the first aqueous composition is removed from the aluminum foil surface. Preferably, the through-hole forming step is performed within 10 minutes, more preferably within 5 minutes, even more preferably within 3 minutes, particularly preferably within 2 minutes or within 1 minute after the alkaline cleaning step. As described above, by performing the through-hole forming step as quickly as possible after the alkaline cleaning step, the treatment can be performed before a new passive film is formed on the aluminum foil surface, which has the effect of forming more uniform through-holes.

[0021] The second aqueous composition used in the through-hole forming step contains 1% by mass or more and 30% by mass or less of halide ions. The oxide film (passive film) is partially removed by alkaline washing, and the halide ions react with the aluminum foil surface in that portion, thereby forming through-holes in the aluminum foil.

[0022] The type of halide ion is not particularly limited and may be, for example, fluoride ion, chloride ion, bromide ion, or iodide ion. However, chloride ion is more preferred from the viewpoints of ease of handling and economy. The halogen compound used as the halide ion source in the second aqueous composition is not particularly limited. Examples include alkali metal halides such as sodium halide and potassium halide, alkaline earth metal halides such as calcium halide, ammonium halide, copper halide, and hydrogen halide. Among these, alkali metal halides or hydrogen halides are preferred, and hydrochloric acid or sodium chloride is more preferred, from the viewpoint of more effective and reliable formation of through-holes. The halogen compounds can be used alone or in combination of two or more. The content of halide ions in the aqueous composition is 1% by mass to 30% by mass, preferably 2.0% by mass to 25% by mass, more preferably 3.0% by mass to 20% by mass, particularly preferably 5.0% by mass to 15% by mass, and even more preferably 8% by mass to 15% by mass. In addition, the range of the content of halide ions contained in the second aqueous composition may have a lower limit of 1.0 mass%, 2.0 mass%, 3.0 mass%, 5.0 mass%, or 8 mass%, and an upper limit of 30 mass%, 25 mass%, 20 mass%, 18 mass%, or 15 mass%.

[0023] The second aqueous composition may contain additives as components other than halide ions, as long as the effects of the present invention are exhibited. Examples of additives include organic solvents, surfactants, pH adjusters, and oxidizing agents. The concentration of the additives that may be contained in the second aqueous composition is preferably 10% by mass or less, more preferably 5.0% by mass or less, more preferably 2.0% by mass or less, and particularly preferably 1.0% by mass or less.

[0024] The second aqueous composition contains water, particularly ion-exchanged water or ultrapure water. The water content, which is the remainder of the second aqueous composition, is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 95% by mass or more. The upper limit of the water content is 99% by mass or less, and may be 98% by mass or less, 97% by mass or less, 96% by mass or less, or 95% by mass or less.

[0025] The treatment temperature (temperature of the second aqueous composition) in the through hole forming step is preferably 10°C or higher and 50°C or lower, more preferably 15°C or higher and 45°C or lower, and even more preferably 20°C or higher and 40°C or lower. When the temperature of the second aqueous composition is 10°C or higher, through holes can be formed efficiently in a short time. On the other hand, when the temperature of the second aqueous composition is 50°C or lower, changes in the liquid composition can be suppressed and etching conditions can be maintained constant. Furthermore, the work can be carried out safely.

[0026] The method of contacting the second aqueous composition with the aluminum foil after the alkali cleaning step is not particularly limited. For example, a method of contacting the aluminum foil with the second aqueous composition by dropping (single-sheet spin treatment) or spraying (spray treatment), or a wet method (wet etching method) such as immersing the aluminum foil in the second aqueous composition can be used.

[0027] The treatment time in the through-hole formation step is preferably 5 seconds or more and 120 seconds or less, more preferably 8 seconds or more and 100 seconds or less, and even more preferably 10 seconds or more and 60 seconds or less. The treatment time may be appropriately determined taking into consideration various conditions such as the state of the surface of the aluminum foil, the content of halide ions in the second aqueous composition, the treatment temperature, and the contact method. Thus, according to the present invention, the formation of through-holes proceeds even without a very long time. Here, the treatment time refers to the time during which the second aqueous composition is contacted with the aluminum foil surface after the alkaline washing step. For example, it is the time during which the aluminum foil is immersed in the second aqueous composition, or the time from when the second aqueous composition is sprayed on the surface of the aluminum foil to when the second aqueous composition is removed with water or the like.

[0028] <Water washing step> The aluminum foil with through holes formed therein (i.e., perforated aluminum foil) is preferably washed appropriately with water as necessary to remove halide ions adhering to the surface of the aluminum foil. The water is preferably water from which metal ions, organic impurities, particles, etc. have been removed by distillation, ion exchange treatment, filtration, various adsorption treatments, etc., and pure water or ultrapure water is particularly preferred.

[0029] According to the above-mentioned method, perforated aluminum foil can be obtained essentially through a two-stage chemical treatment, or by further performing appropriate washing (e.g., water washing) as necessary. According to the present invention, the conditions for each treatment are mild and the required time is short, so that perforated aluminum foil can be produced efficiently. Furthermore, according to a preferred embodiment of the present invention, the through-holes can be formed with a uniform diameter, and the decrease in tensile strength of the resulting perforated aluminum foil can be suppressed. Therefore, production efficiency can be further improved by continuously processing the perforated aluminum foil using a continuous process such as a roll-to-roll process. For example, a dripping device, spraying device, or immersion device for the first aqueous composition and the second aqueous composition is installed between rolls of aluminum foil, and while the aluminum foil is unwrapped and moved from the roll on which the untreated aluminum foil was wrapped using a roll-to-roll process, the first aqueous composition and the second aqueous composition, and optionally water for removing each aqueous composition, are passed near the above-mentioned device, and the perforated aluminum foil with the formed through-holes can be wound up to obtain a roll. The obtained perforated aluminum foil may be subjected to a drying treatment before being wound up on a roll.

[0030] 2. Perforated Aluminum Foil The perforated aluminum foil of the present invention has a plurality of through-holes that penetrate through the foil in the thickness direction, and is characterized in that the thickness of the perforated aluminum foil is 1 μm or more and 50 μm or less, the breaking strength is 4 N / 10 mm or more and 20 N / 10 mm or less, the average pore size is 1 μm or more and 50 μm or less, and the ratio of maximum pore size / average pore size is 4 or less. The perforated aluminum foil of the present invention can be produced by the method described above in "1. Method for producing perforated aluminum foil."

[0031] The thickness of the perforated aluminum foil is from 1 μm to 50 μm, preferably 40 μm or less, and more preferably 25 μm or less. When the thickness is within this range, the foil can be suitably used as a current collector for an electricity storage device, particularly as a current collector for a lithium ion capacitor.

[0032] The breaking strength is 4 N / 10 mm or more and 20 N / 10 mm or less, preferably 4.5 N / 10 mm or more and 15 N / 10 mm or less, more preferably 5 N / 10 mm or more and 12 N / 10 mm or less, and even more preferably 5.5 N / 10 mm or more and 10 N / 10 mm or less. The stress is preferably 20 N / mm ２ 200N / mm or more ２ or less, more preferably 25 N / mm ２ 150N / mm or more ２ More preferably, 30 N / mm ２ More than 100N / mm ２ The breaking elongation is preferably 0.1% or more and 3% or less, more preferably 0.5% or more and 2% or less, and even more preferably 0.7% or more and 1.5% or less. When the breaking strength, stress, and breaking elongation of the perforated aluminum foil are within the above ranges, the foil can withstand continuous processes such as roll-to-roll processes, and the production efficiency of the perforated aluminum foil is improved.

[0033] The average pore size of the pores in the perforated aluminum foil is 1 μm or more and 50 μm or less, preferably 3 μm or more and 30 μm or less, more preferably 5 μm or more and 25 μm or less, and even more preferably 7 μm or more and 20 μm or less. When the average pore size is within the above range, pre-doping of lithium ions can be performed efficiently, making the foil suitable for use as a current collector for lithium ion capacitors. Furthermore, the maximum pore size / average pore size ratio is 4 or less, preferably 3.8 or less, more preferably 3.6 or less, and even more preferably 3.5 or less. When the maximum pore size / average pore size ratio is within the above range, the decrease in tensile strength is suppressed, and the foil can withstand continuous processes such as roll-to-roll processes, improving the production efficiency of the perforated aluminum foil.

[0034] The number of holes in the aluminum foil was 1.0 × 10 ３ pieces / cm２ Above 5.0 x 10 ４ pieces / cm ２ is preferably 3.0×10 or less. ３ pieces / cm ２ Above 4.0 x 10 ４ pieces / cm ２ or less, more preferably 5.0 × 10 ３ pieces / cm ２ Above 3.0 x 10 ４ pieces / cm ２ More preferably, 7.0 × 10 ３ pieces / cm ２ Above 2.0 x 10 ４ pieces / cm ２ When the number of holes is within the above range, the balance between the tensile strength and the efficiency of pre-doping is good, and the material can be suitably used as a current collector for a lithium ion capacitor.

[0035] The aperture ratio of the aluminum foil is 10% or less, preferably 5% or less, more preferably 4% or less, and even more preferably 3% or less. The lower limit of the aperture ratio is preferably 0.10% or more, more preferably 0.15% or more, and even more preferably 0.20% or more. When the aperture ratio is within the above range, the balance between tensile strength and pre-doping efficiency is good, and the foil can be suitably used as a current collector for a lithium ion capacitor.

[0036] The perforated aluminum foil has an air permeability of less than 70 seconds, preferably less than 40 seconds, more preferably less than 30 seconds, and even more preferably less than 20 seconds. The lower limit of the air permeability is preferably 0 seconds or more, more preferably 0.5 seconds or more, and even more preferably 1.0 seconds or more. When the air permeability is within the above range, pre-doping of lithium ions can be performed efficiently, and the foil can be suitably used as a current collector for a lithium ion capacitor.

[0037] The average pitch of the holes in the perforated aluminum foil is preferably 10 μm or more and 500 μm or less, more preferably 30 μm or more and 250 μm or less, even more preferably 50 μm or more and 150 μm or less, and particularly preferably 60 μm or more and 100 μm or less. When the hole pitch is in the above range, the balance between the tensile strength and the efficiency of pre-doping is good, and the foil can be suitably used as a current collector for a lithium ion capacitor.

[0038] The surface roughness (arithmetic mean roughness Ra) of the unopened portions of the perforated aluminum foil is preferably 0.01 μm or more and 0.20 μm or less, more preferably 0.02 μm or more and 0.15 μm or less, even more preferably 0.03 μm or more and 0.10 μm or less, and particularly preferably 0.04 μm or more and 0.07 μm or less. When the surface roughness of the unopened portions is within the above range, a decrease in tensile strength is suppressed and the foil can withstand continuous processes such as roll-to-roll processes, thereby improving the production efficiency of the perforated aluminum foil.

[0039] These physical properties can be measured according to the methods described in the examples.

[0040] 3. Current Collector for Electricity Storage Device The current collector for an electricity storage device of the present invention is composed of the perforated aluminum foil of the present invention described above. Because the perforated aluminum foil has a plurality of through-holes that penetrate through the foil in the thickness direction, when the current collector for an electricity storage device of the present invention is used in, for example, a lithium ion capacitor, pre-doping of lithium ions can be carried out efficiently in a short time and the lithium ions can be dispersed more uniformly, making it possible to accommodate higher capacities and providing an electricity storage device that achieves both high output density and high energy density.

[0041] Next, the present invention will be explained in more detail using examples and comparative examples, but the present invention is not limited to these examples in any way.

[0042] The methods for measuring each physical property were as follows.

[0043] 1. Analysis of pores The aluminum perforated foils obtained in the examples and comparative examples were observed using an optical microscope (MX63L, manufactured by Olympus Corporation) with the attached bottom light turned on. The observation area was 3570 × 2230 μm. The obtained microscope images were binarized using image analysis software (WinROOF2018, manufactured by Mitani Shoji Co., Ltd.), and the number of pores [number] and the maximum pore area [μm] within the observation area of ​​3570 × 2230 μm were calculated. ２ ], total area of ​​pores [μm ２ ] was calculated.

[0044] (1) Number of holes Number of holes [pcs / cm ２ ] was calculated by the following formula:

[0045] (2) Average Pore Diameter The average pore diameter [μm] was calculated by the following formula.

[0046] (3) Maximum Pore Diameter The maximum pore diameter [μm] was calculated by the following formula.

[0047] (4) Average Pitch The average pitch [μm] was calculated by the following formula.

[0048] (5) Opening ratio The opening ratio [%] was calculated using the following formula.

[0049] 2. Measurement of Air Permeability The air permeability of the perforated aluminum foils obtained in the examples was measured by the Oken test method in accordance with JIS P 8117-2009 using a digital Oken air permeability tester (manufactured by Asahi Seiko Co., Ltd., REG02-5 / 6-1M / 2M). Note that the perforated aluminum foils obtained in the comparative examples all had zero pores, so the air permeability was infinite and unmeasurable.

[0050] 3. Measurement of surface roughness of unopened portions The arithmetic mean roughness (Ra) of the raw material aluminum foil (Reference Example) and the perforated aluminum foil obtained in the Examples was measured in accordance with JIS B 0601-2001 using a laser microscope (manufactured by Keyence Corporation, product name "VK-X250"). The measurement points were unopened. Note that since the number of holes in all of the perforated aluminum foils obtained in the Comparative Examples was 0, the surface roughness of the unopened portions was the same as that of the Reference Example (untreated).

[0051] 4. Tensile Test The raw material aluminum foil (Reference Example) and the perforated aluminum foil obtained in the Examples were cut into a width of 10 mm and a length of 140 mm, and the foils were fixed so that the distance between chucks was 100 mm using a Tensilon universal testing machine (manufactured by A&D Co., Ltd., RTG-1210). The test pieces were subjected to a tensile test at a tensile speed of 10 mm / min to measure the breaking strength [N / 10 mm], stress [N / mm ２ The tensile strength [%] and elongation at break [%] were measured five times and the average values ​​were calculated. Note that, since the number of holes in each of the perforated aluminum foils obtained in the comparative examples was zero, the tensile strength was the same as that of the reference example (untreated).

[0052] [Example 1] A first aqueous composition was prepared by adding 2.0 kg of sodium hydroxide to 38.0 kg of pure water to give a final concentration of 5% by mass, and a second aqueous composition was prepared by adding 13.7 kg of 35% by mass of hydrochloric acid (as halide ions) to 26.3 kg of pure water to give a final concentration of 12% by mass. A roll-to-roll apparatus (manufactured by Shinwa Kogyo Co., Ltd., immersion type) capable of alkaline cleaning → water washing → through-hole formation (etching) → water washing → drying was used to treat aluminum foil (A1N30 (soft), thickness 20 μm, width 300 mm, length 10 m) at the temperature and time shown in Table 1 to obtain a perforated aluminum foil. The obtained perforated aluminum foil was subjected to pore analysis, air permeability measurement, surface roughness measurement of unopened portions, and tensile testing.

[0053] Examples 2 and 3 Apertured aluminum foil was obtained in the same manner as in Example 1, except that the temperature and time of treatment in the roll-to-roll apparatus were changed as shown in Table 1.

[0054] [Examples 4 to 6] The first aqueous composition was obtained by adding sodium hydroxide to 142.5 kg of pure water in an amount (7.5 kg) such that the final concentration was 5% by mass, and the second aqueous composition was obtained by adding hydrochloric acid (as halide ions) to 52.6 kg of pure water in an amount (27.4 kg of 35% by mass hydrochloric acid) such that the final concentration was 12% by mass. The roll-to-roll apparatus was a roll-to-roll apparatus (manufactured by Shinwa Kogyo Co., Ltd., up-and-down spray type), and the treatment temperature and time were changed as shown in Table 1. The same treatment as in Example 1 was performed to obtain perforated aluminum foil.

[0055] [Examples 7 to 13] The first aqueous composition was prepared by adding 100 g of sodium hydroxide to 1800 g of pure water so that the final concentration was 5% by mass. The second aqueous composition was prepared by adding 686 g of 35% by mass of hydrochloric acid (as halide ions) to 1314 g of pure water so that the final concentration was 12% by mass. Without using a roll-to-roll apparatus, the first aqueous composition, the second aqueous composition, and pure water were each placed in a tray, and immersed in the following order at the temperature and time shown in Table 1: alkali washing → water washing → through-hole formation (etching) → water washing. Then, the mixture was thoroughly dried, and the aluminum foil was treated in the same manner as in Example 1 to obtain an aluminum foil (thickness 12 μm, width 70 mm, length 140 mm) shown in Table 1.

[0056] Example 14 A first aqueous composition was prepared by adding 10 g of sodium hydroxide to 180 g of pure water so that the final concentration was 5% by mass. A second aqueous composition was prepared by adding 46 g of 35% by mass of hydrochloric acid (as halide ions) to 154 g of pure water so that the final concentration was 8% by mass. Without using a roll-to-roll apparatus, the first aqueous composition, the second aqueous composition, and pure water were each placed in a tray. An aluminum foil (A1N30 (soft), thickness 20 μm, width 30 mm, length 30 mm) was immersed in the following order at the temperatures and for the times shown in Table 1: alkali washing → water washing → through-hole formation (etching) → water washing. The aluminum foil was then thoroughly dried to obtain a perforated aluminum foil.

[0057] [Examples 15 to 20] Apertured aluminum foils were obtained in the same manner as in Example 14, except that the first aqueous composition, the second aqueous composition, the treatment temperature, and the treatment time were changed to those shown in Table 1.

[0058] Comparative Example 1 A perforated aluminum foil was obtained in the same manner as in Example 14, except that the time between Treatment 1 (alkali washing) and Treatment 2 (throughhole formation) was set to 30 minutes, and the first aqueous composition, the second aqueous composition, the treatment temperature, and the treatment time were changed to those shown in Table 1.

[0059] Comparative Example 2 A perforated aluminum foil was obtained in the same manner as in Example 14, except that the time between Treatment 1 (alkali washing) and Treatment 2 (throughhole formation) was set to 30 minutes, drying was performed, and the first aqueous composition, the second aqueous composition, the treatment temperature, and the treatment time were changed to those shown in Table 1.

[0060] Comparative Example 3 A perforated aluminum foil was obtained in the same manner as in Example 14, except that the second aqueous composition for Treatment 2 was not prepared and the treatment time was changed to the time shown in Table 1.

[0061] Comparative Example 4 A perforated aluminum foil was obtained in the same manner as in Example 14, except that the first aqueous composition for treatment 1 was not prepared, and the second aqueous composition for treatment 2 and the treatment time were changed to those shown in Table 1.

[0062]

[0063] As shown in Tables 1 and 2, the method of the present invention allows for the formation of through-holes by a simple method using alkaline washing and subsequent chemical etching. The resulting perforated aluminum foil has uniform pore sizes in the aluminum foil and is excellent in air permeability and tensile strength, making it suitable for use as a current collector for an electricity storage device.

[0064] 1 Aluminum foil 2 Oxide film (passive film) 3 Through hole

Claims

1. A method for producing a porous aluminum foil having a plurality of through holes penetrating in the thickness direction, comprising: an alkali washing step of contacting the surface of the aluminum foil with a first aqueous composition containing 1% by mass or more and 10% by mass or less of alkali; and a through hole forming step of contacting the surface of the aluminum foil with a second aqueous composition containing 1% by mass or more and 30% by mass or less of halide ions within 20 minutes after the alkali washing step, to form the through holes in the thickness direction of the aluminum foil.

2. The method for producing perforated aluminum foil according to claim 1, wherein the alkali is a hydroxide of an alkali metal or an alkaline earth metal.

3. The method for producing perforated aluminum foil according to claim 1, wherein the halide ion is a chloride ion.

4. The method for producing a porous aluminum foil according to claim 1, wherein the thickness of the aluminum foil is 1 μm or more and 50 μm or less.

5. A method for producing perforated aluminum foil as described in claim 1, wherein the aluminum purity of the aluminum foil is 98 mass% or more and less than 99.9 mass%.

6. A method for producing a porous aluminum foil according to any one of claims 1 to 5, wherein the treatment temperature in the alkaline washing step is 10°C or higher and 50°C or lower, and the treatment time is 5 seconds or higher and 120 seconds or lower.

7. A method for producing a porous aluminum foil according to any one of claims 1 to 5, wherein the treatment temperature in the through hole forming step is 10°C or higher and 50°C or lower, and the treatment time is 5 seconds or higher and 120 seconds or lower.

8. A perforated aluminum foil having a plurality of through holes penetrating in the thickness direction, the perforated aluminum foil having a thickness of 1 μm or more and 50 μm or less, a breaking strength of 4 N / 10 mm or more and 20 N / 10 mm or less, an average pore size of 1 μm or more and 50 μm or less, and a maximum pore size / average pore size ratio of 4 or less.

9. Number of holes is 1.0 x 10 ３ pieces / cm ２ Above 5.0 x 10 ４ pieces / cm ２ The perforated aluminum foil according to claim 8, wherein the perforated aluminum foil has an opening ratio of 10% or less and an air permeability of less than 70 seconds.

10. A current collector for an electricity storage device, comprising the perforated aluminum foil according to claim 8 or 9.

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