Method for producing aluminum perforated foil

Abstract

According to the present invention, it is possible to provide a method for producing an aluminum perforated foil which has a plurality of through holes penetrating therethrough in the thickness direction, the method including a through hole forming step in which an aqueous composition that contains 1-30 mass% of halide ions and 0.1-20 mass% of an oxidizing agent is brought into contact with the surface of an aluminum foil so as to form the through holes in the thickness direction of the aluminum foil.

Description

Manufacturing method of perforated aluminum foil

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

[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 a carbon material, similar to that used in lithium ion secondary batteries, for the negative electrode, and can achieve both high output density and high energy density. However, to achieve high capacity, efficient pre-doping of lithium ions is required, and therefore perforated aluminum foils are formed with a large number of fine through-holes. Etching technology is known as a method for forming fine through-holes. For example, Patent Document 1 describes a method for forming through-holes in aluminum foil by electrolytic etching using an aqueous solution containing hydrochloric acid as an electrolyte. Furthermore, Patent Document 2 describes a method in which a film of aluminum oxide or aluminum hydroxide is formed on the surface of an aluminum foil, the film is removed by laser processing from the portion where a through-hole is to be formed, and then an aqueous solution containing sulfuric acid and nitric acid is used as an electrolyte to form a through-hole in the aluminum foil by electrolytic etching.

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

[0004] There is a need for the development of a technology for easily producing perforated aluminum foil suitable for use as a current collector for an electricity storage device.

[0005] The present invention relates to the following methods for producing perforated aluminum foil. <1> A method for producing perforated aluminum foil having a plurality of through holes penetrating in the thickness direction, comprising a through hole forming step of contacting the surface of an aluminum foil with an aqueous composition containing 1 to 30 mass% of halide ions and 0.1 to 20 mass% of an oxidizing agent to form the through holes in the thickness direction of the aluminum foil. <2> A method for producing perforated aluminum foil according to <1> above, in which the halide ions are chloride ions. <3> A method for producing perforated aluminum foil according to <1> above, in which the oxidizing agent is one or more selected from the group consisting of hydrogen peroxide and nitric acid. <4> A method for producing perforated aluminum foil according to <1> above, in which the thickness of the aluminum foil is 1 μm or more and 50 μm or less. <5> A method for producing perforated aluminum foil according to <1> above, in which the aluminum purity of the aluminum foil is 98 mass% or more but less than 99.9 mass%. <6> The method for producing a perforated aluminum foil according to any one of <1> to <5> above, 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 10 seconds or higher and 150 seconds or lower.

[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 chemical etching.

[0007] 1. Method for Producing Perforated Aluminum Foil The present invention is a method for producing a perforated aluminum foil having a plurality of through holes penetrating in the thickness direction, characterized by including a through hole forming step of contacting the surface of an aluminum foil with an aqueous composition containing 1 to 30 mass% halide ions and 0.1 to 20 mass% oxidizing agent to form the through holes in the thickness direction of the aluminum foil. According to the present invention, through holes can be formed in an aluminum foil by a simple method of contacting the surface of the aluminum foil with an aqueous composition containing specific components. According to a preferred embodiment, the obtained perforated aluminum foil has excellent uniformity in the pore size of the through holes and is suitable for use as a current collector for an electricity storage device, particularly as a current collector for a lithium ion capacitor.

[0008] 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, 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, 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 A1000 series and A8000 series are preferred, and A1N30, A8011, A8021, or A8079 may also be used.

[0009] 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.

[0010] <Through-hole forming step> In the through-hole forming step, an aqueous composition containing 1 to 30% by mass of halide ions and 0.1 to 20% by mass of an oxidizing agent is brought into contact with the surface of the aluminum foil to form the through-holes in the thickness direction of the aluminum foil.

[0011] The 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 halide ions cause pitting corrosion of the passivation film of the aluminum foil, thereby forming through-holes in the aluminum foil.

[0012] 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 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 23% by mass, and particularly preferably 5.0% by mass to 20% by mass. In addition, the range of the content of halide ions contained in the aqueous composition may have a lower limit of 1.0 mass%, 2.0 mass%, 3.0 mass%, or 5.0 mass%, and an upper limit of 30 mass%, 25 mass%, 23 mass%, or 20 mass%.

[0013] The aqueous composition used in the through-hole forming step contains 0.1 mass % to 20 mass % of an oxidizing agent. The oxidizing agent is thought to have the effect of promoting a reaction with halide ions, thereby contributing to the formation of through-holes in the aluminum foil.

[0014] The type of oxidizing agent is not particularly limited, and examples thereof include hydrogen peroxide, nitric acid, persulfate, peracetic acid, ozone, hypochlorite, chlorite, chlorate, perchlorate, chromate, and permanganate. Hydrogen peroxide and nitric acid are preferred from the viewpoints of ease of handling and economy. The oxidizing agent may be used alone or in combination with two or more. The content of the oxidizing agent contained in the aqueous composition is 0.1% by mass to 20% by mass, preferably 0.2% by mass to 15% by mass, more preferably 0.3% by mass to 12% by mass, and particularly preferably 0.5% by mass to 10% by mass. The range of the content of the oxide contained in the aqueous composition may be 0.1% by mass, 0.2% by mass, 0.3% by mass, or 0.5% by mass as the lower limit, and 20% by mass, 15% by mass, 12% by mass, or 10% by mass as the upper limit.

[0015] The aqueous composition may contain additives as components other than the halide ions and the oxidizing agent, as long as the effects of the present invention are exhibited. Examples of additives include organic solvents, surfactants, pH adjusters, etc. The concentration of the additives that may be contained in the aqueous composition is preferably 10% by mass or less, more preferably 5.0% by mass or less, even more preferably 2.0% by mass or less, and particularly preferably 1.0% by mass or less.

[0016] The aqueous composition contains water, particularly ion-exchanged water or ultrapure water. The water content, which is the remainder of the aqueous composition, is preferably 70% by mass or more, more preferably 80% by mass or more, and may be 85% by mass or more. The upper limit of the water content may be 98% by mass or less, 95% by mass or less, or 90% by mass or less.

[0017] The treatment temperature (temperature of the aqueous composition) in the through hole forming step 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 30°C or higher and 40°C or lower. When the temperature of the 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 aqueous composition is 50°C or lower, changes in the liquid composition can be suppressed and etching conditions can be maintained constant. In addition, the work can be carried out safely.

[0018] The method of contacting the aqueous composition with the aluminum foil is not particularly limited. For example, a wet method (wet etching method) such as dropping (sheet spin treatment) or spraying (atomization treatment) of the aqueous composition, contacting with the aluminum foil, or immersing the aluminum foil in the aqueous composition can be adopted.

[0019] The treatment time in the through-hole formation step is preferably 10 seconds or more and 150 seconds or less, more preferably 30 seconds or more and 140 seconds or less, and even more preferably 60 seconds or more and 120 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 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, which is advantageous. Here, the treatment time refers to the time during which the 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 aqueous composition, or the time from when the aqueous composition is sprayed on the surface of the aluminum foil to when the aqueous composition is removed with water or the like.

[0020] <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 and oxidizing agents 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.

[0021] According to the above-mentioned method, perforated aluminum foil can be obtained essentially by a single-step 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, allowing for efficient production of perforated aluminum foil. Furthermore, according to a preferred embodiment of the present invention, the through-holes can be formed with a uniform diameter. Continuous processing of perforated aluminum foil using a roll-to-roll process in which a roll-shaped long current collector is passed through a conveying line for continuous processing can further improve production efficiency. For example, a dripping device, spraying device, or immersion device for an 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, the aqueous composition is passed near the device, and optionally water for removing the aqueous composition is supplied. 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.

[0022] 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 preferably characterized in that the thickness of the perforated aluminum foil is 1 μm or more and 50 μm 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."

[0023] The thickness of the perforated aluminum foil is preferably 1 μm or more and 50 μm or less, more preferably 40 μm or less, and particularly preferably 25 μm or less. 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.

[0024] The average pore size of the pores in the perforated aluminum foil is preferably 10 μm or more and 110 μm or less, more preferably 20 μm or more and 100 μm or less, and particularly preferably 23 μm or more and 96 μm or less. When the average pore size 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.

[0025] The number of holes in the perforated aluminum foil is preferably 0.5×10 ３ pieces / cm ２ 10 x 10 or more ３ pieces / cm ２ is preferably 0.7×10 or less. ３ pieces / cm ２ Above 7.0 x 10 ３ pieces / cm ２ Below, particularly preferably 1.0 × 10 ３ pieces / cm ２ Above 5.0 x 10 ３ 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.

[0026] The aperture ratio of the perforated aluminum foil is preferably 26% or less, more preferably 10% or less, and particularly preferably 5.0% or less. The lower limit of the aperture ratio is preferably 0.2% or more, more preferably 0.5% or more, and even more preferably 0.7% 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.

[0027] The average pitch of the holes in the perforated aluminum foil is preferably 100 μm or more and 350 μm or less, more preferably 120 μm or more and 320 μm or less, and particularly preferably 140 μm or more and 310 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.

[0028] These physical properties can be measured according to the methods described in the examples.

[0029] 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.

[0030] The features of the present invention will be described in more detail below with reference to examples and comparative examples, although the scope of the present invention is not limited to the following examples.

[0031] <Analysis of pores> The perforated aluminum 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 image was binarized using image analysis software (WinROOF2018, manufactured by Mitani Shoji Co., Ltd.), and the number of pores [number / cm] within the observation area of ​​3570 × 2230 μm was calculated. ２ ], average pore diameter [μm], average pitch [μm], and opening ratio [%] were calculated. (Number of pores) Number of pores [pcs / cm ２ ] was calculated by the following formula: (Average Pore Diameter) The average pore diameter [μm] was calculated by the following formula. (Average Pitch) The average pitch [μm] was calculated by the following formula. (Opening ratio) The opening ratio [%] was calculated by the following formula.

[0032] Example 1 An etching solution (aqueous composition) was prepared by adding hydrogen peroxide (as an oxidizing agent) in an amount to give a final concentration of 0.5% by mass (2.8 g of 35% by mass hydrogen peroxide) and hydrochloric acid (as halide ions) in an amount to give a final concentration of 12% by mass (69 g of 35% by mass hydrochloric acid). An aluminum foil (A1N30 (soft), thickness 20 μm, width 30 mm, length 30 mm) was immersed in the obtained etching solution at the temperature and time shown in Table 1 below to carry out an etching treatment. The foil was then washed with water and thoroughly dried to obtain a perforated aluminum foil. The obtained perforated aluminum foil was analyzed for pores. Number of pores [holes / cm ２ The results of the average pore size [μm], average pitch [μm], and opening ratio [%] are shown in Table 1 below.

[0033] (Examples 2 to 8) Apertured aluminum foils were obtained in the same manner as in Example 1, except that the etching solution used, the treatment temperature, and the treatment time were changed as shown in Table 1 below. ２ The results of the average pore size [μm], average pitch [μm], and opening ratio [%] are shown in Table 1 below.

[0034] (Example 9) To 98 g of pure water, nitric acid (as an oxidizing agent) was added in an amount to give a final concentration of 10 mass % (33 g of 60 mass % nitric acid) and hydrochloric acid (as halide ions) in an amount to give a final concentration of 12 mass % (69 g of 35 mass % hydrochloric acid) to prepare an etching solution (aqueous composition). Using the obtained etching solution, an etching treatment was carried out at the temperature and for the time shown in Table 1 below, and perforated aluminum foil was obtained in the same manner as in Example 1. Number of holes [holes / cm ２ The results of the average pore size [μm], average pitch [μm], and opening ratio [%] are shown in Table 1 below.

[0035] Comparative Example 1 An etching solution was prepared without using an oxidizing agent, and perforated aluminum foil was obtained in the same manner as in Example 1, except that the treatment temperature and treatment time were changed as shown in the following Table 1. The perforated aluminum foil obtained had zero pores.

[0036]

Claims

1. A method for producing a porous aluminum foil having a plurality of through holes penetrating in the thickness direction, comprising a through hole forming step of contacting the surface of the aluminum foil with an aqueous composition containing 1 to 30 mass % of a halide ion and 0.1 to 20 mass % of an oxidizing agent 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 halide ion is a chloride ion.

3. The method for producing perforated aluminum foil according to claim 1, wherein the oxidizing agent is at least one selected from the group consisting of hydrogen peroxide and nitric acid.

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 through hole forming step is 10°C or higher and 50°C or lower, and the treatment time is 10 seconds or higher and 150 seconds or lower.

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