Aqueous composition, perforated stainless steel foil, and method for producing same

Abstract

The present invention provides an aqueous composition for forming through-holes in the thickness direction of a stainless steel foil, the aqueous composition containing 0.01-20 mass% of hydrogen peroxide and 1-30 mass% of halide ions based on the total amount of the aqueous composition. Also provided is a method for producing a perforated stainless steel foil, the method including a through-hole forming step for forming a plurality of through-holes penetrating the stainless steel foil in the thickness direction, by bringing the aqueous composition and the stainless steel foil into contact.

Description

Aqueous composition, perforated stainless steel foil and method for producing same

[0001] The present invention relates to an aqueous composition for forming through holes in a stainless steel foil, a perforated stainless steel foil, and a method for producing the same.

[0002] Stainless steel foil has excellent corrosion resistance and mechanical properties, and does not alloy with lithium. Therefore, it is expected to be used as a current collector for both the positive and negative electrodes of lithium-ion secondary batteries (LIBs) (see, for example, Patent Documents 1 to 3). In LIBs, charging and discharging are performed by lithium ions moving between the positive and negative electrodes via an electrolyte solution. However, side reactions during charging and discharging consume the lithium ions. Therefore, in LIBs, high capacity is achieved by pre-doping the amount of lithium ions consumed. To pre-dope the lithium ions, through-holes must be formed in the thickness direction of the stainless steel foil for the lithium ions to pass through. Etching is a known method for forming through-holes. For example, Patent Document 1 describes that through-holes can be formed by immersing stainless steel foil in an aqueous solution containing iron chloride and hydrochloric acid. However, the presence of iron chloride can result in uneven pore formation.

[0003] International Publication No. 2019 / 039332 International Publication No. 2016 / 159058 Japanese Patent Application Laid-Open No. 2010-33768

[0004] There is a need for the development of perforated stainless steel foil suitable for use as a current collector for an electricity storage device, particularly as a current collector for both the positive and negative electrodes of an LIB, and a manufacturing technique for the same.

[0005] The present invention relates to the following aqueous compositions, perforated stainless steel foils, and methods for producing the same: [1] An aqueous composition for forming through holes in a stainless steel foil in the thickness direction, the aqueous composition comprising, based on the total amount of the aqueous composition, 0.01 mass % to 20 mass % of hydrogen peroxide and 1 mass % to 30 mass % of halide ions. [2] The aqueous composition according to [1], which comprises, based on the total amount of the aqueous composition, more than 0 mass % to 10 mass % of copper ions. [3] The aqueous composition according to [1], in which the halide ions are chloride ions. [4] A method for producing perforated stainless steel foil, comprising a through-hole forming step of contacting a stainless steel foil with the aqueous composition according to any one of [1] to [3] to form a plurality of through holes penetrating the stainless steel foil in the thickness direction. [5] A method for producing perforated stainless steel foil according to [4], in which the thickness of the stainless steel foil is 1 μm to 50 μm. [6] A method for producing a perforated stainless steel foil according to [4] or [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 30 seconds or higher and 240 seconds or lower. [7] A perforated stainless steel foil having a plurality of through holes passing through in the thickness direction, wherein the thickness of the perforated stainless steel foil is 1 μm or higher and 50 μm or lower, the average pore diameter is 1 μm or higher and 70 μm or lower, and the average number of pores is 1.0 × 10 ２ pieces / cm ２ Above 1.0 x 10 ５ pieces / cm ２ and the coefficient of variation in the number of pores obtained by measuring five points in an area of ​​3570 μm × 2230 μm is 5% or more and 100% or less. [8] A current collector for an electricity storage device, comprising the perforated stainless steel foil according to [7] above.

[0006] By using the aqueous composition of the present invention, through-holes can be formed in a stainless steel foil by a simple method. The resulting perforated stainless steel foil can be suitably used as a current collector for an electricity storage device, particularly as a current collector for both the positive and negative electrodes of an LIB.

[0007] 1. Aqueous Composition An aqueous composition according to one embodiment of the present invention is an aqueous composition for forming through holes in a stainless steel foil in the thickness direction, and contains, based on the total amount of the aqueous composition, 0.01 mass % to 20 mass % of hydrogen peroxide and 1 mass % to 30 mass % of halide ions. Each component of the aqueous composition will be described below.

[0008] [Hydrogen Peroxide] The hydrogen peroxide contained in the aqueous composition is usually used as an aqueous solution of appropriate concentration, mixed with other components. The concentration of hydrogen peroxide in the aqueous hydrogen peroxide solution is not particularly limited and may be, for example, 10 to 90%, preferably 35 to 60% in accordance with industrial standards. Furthermore, hydrogen peroxide may contain up to about 0.01% by mass of a stabilizer; acceptable stabilizers include sulfuric acid and phosphoric acid. There are no limitations on the manufacturing process or source of hydrogen peroxide; for example, hydrogen peroxide manufactured by the anthraquinone method may be used.

[0009] The content of hydrogen peroxide is 0.01% by mass or more and 20% by mass or less, preferably 0.05% by mass or more and 15% by mass or less, more preferably 0.08% by mass or more and 12% by mass or less, and particularly preferably 0.1% by mass or more and 10% by mass or less, based on the total amount (total mass) of the aqueous composition. The lower limit of the content of hydrogen peroxide may be, for example, 0.01%, 0.05%, 0.08%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, or 0.5% by mass, based on the total amount of the aqueous composition. The upper limit of the hydrogen peroxide content may be, for example, 20 mass%, 15 mass%, 12 mass%, 10.0 mass%, 9.0 mass%, 8.0 mass%, 7.0 mass%, 6.0 mass%, 5.0 mass%, 4.0 mass%, 3.0 mass%, 2.5 mass%, 2.0 mass%, 1.5 mass%, 1.2 mass%, or 1.0 mass%, based on the total amount of the aqueous composition. The range of the hydrogen peroxide content can be selected from a range that combines the above-mentioned lower and upper limits.

[0010] By setting the hydrogen peroxide content within the above range, the reaction proceeds locally on the stainless steel foil surface, facilitating the formation of through holes, and even if halide ions, etc., described below, are coexistent in the aqueous composition, the possibility of heat generation or foaming due to decomposition of hydrogen peroxide is suppressed, thereby ensuring work safety.

[0011] [Halide ions] The type of halide ions contained in the aqueous composition is not particularly limited, and may be, for example, fluoride ions, chloride ions, bromide ions, or iodide ions. However, chloride ions are more preferred from the viewpoints of ease of handling and economy. The halogen compound as the halide ion source 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.

[0012] The halogen compounds can be used alone or in combination of two or more. The halogen compounds may also be the copper compounds described below. For example, when a copper halide is used as a source of halide ions, the copper halide also corresponds to the copper compound serving as a copper ion source described below. Copper chloride is preferred as the copper halide.

[0013] The content of halide ions is 1% by mass or more and 30% by mass or less, preferably 2% by mass or more and 28% by mass or more, more preferably 3% by mass or more and 27% by mass or 4% by mass or more and 26% by mass or more, and particularly preferably 5% by mass or more and 25% by mass or less, based on the total amount of the aqueous composition. The lower limit of the content of halide ions may be, for example, 1.0% by mass, 2.0% by mass, 3.0% by mass, 4.0% by mass, 5.0% by mass, 8.0% by mass, 10.0% by mass, or 12.0% by mass, based on the total amount of the aqueous composition. The upper limit of the content of halide ions may be 30% by mass, 29% by mass, 28% by mass, 27% by mass, 26% by mass, or 25% by mass, based on the total amount of the aqueous composition. The range of the content of halide ions can be selected from a range that appropriately combines the above-mentioned lower limit and upper limit.

[0014] By setting the content of halide ions within the above range, it is possible to form fine through-pores in the stainless steel foil, and also to prevent the decomposition reaction of hydrogen peroxide, thereby ensuring safety.

[0015] [Copper Ions] The aqueous composition according to one embodiment of the present invention may optionally contain copper ions in addition to hydrogen peroxide and halide ions. Copper ions in the aqueous composition can be generated by mixing a copper compound as a copper ion source with other components. The type of copper ion source is not particularly limited as long as it is a copper compound that can provide copper ions in the aqueous composition. Examples of copper ion sources include copper sulfates such as cupric sulfate, copper chlorides such as cupric chloride, copper tetrafluoroborate, cupric bromide, cupric oxide, copper phosphate, copper acetate, copper formate, and copper nitrate, which may be anhydrous or hydrated (e.g., monohydrate, trihydrate, or pentahydrate is preferred, and pentahydrate is more preferred). Among these, copper sulfate or copper chloride is preferred, with cupric sulfate or cupric chloride being even more preferred, and cupric sulfate being even more preferred, from the viewpoints of more effectively and reliably achieving the effects of the present invention, ease of handling, and economy. These may be used alone or in combination of two or more.

[0016] It is presumed that the copper ions contained in the aqueous composition cause a substitution reaction with nickel and chromium, which are components of stainless steel, during the through-hole formation process, and that subsequent removal of the substitution reaction product derived from the copper ions makes it easier to form through-holes.

[0017] When the aqueous composition contains copper ions, the copper ion content is preferably more than 0% by mass and not more than 10% by mass, more preferably 0.1% by mass or more and not more than 8% by mass, even more preferably 0.2% by mass or more and not more than 6% by mass, and particularly preferably 0.25% by mass or more and not more than 5% by mass, based on the total amount of the aqueous composition. The lower limit of the copper ion content may be, for example, 0.00001% by mass (0.1 ppm by mass), 0.0001% by mass (1 ppm by mass), 0.001% by mass, 0.01% by mass, 0.02% by mass, 0.03% by mass, 0.05% by mass, 0.07% by mass, or 0.1% by mass, based on the total amount of the aqueous composition. The upper limit of the copper ion content may be, for example, 10.0% by mass, 9.0% by mass, 8.0% by mass, 7.0% by mass, 6.0% by mass, or 5.0% by mass, based on the total amount of the aqueous composition. The range of the copper ion content can be selected from a range that appropriately combines the above-mentioned lower limit and upper limit. By setting the copper ion content within the above range, desired through holes can be efficiently formed in the stainless steel foil. On the other hand, if the copper ion content is too high, it may be difficult to control the average pore size and uniformity of the through holes.

[0018] [Additives] The aqueous composition according to one embodiment of the present invention may contain additives as components other than hydrogen peroxide, copper ions, and halide ions, as long as the effects of the present invention are achieved. Examples of additives include heterocyclic nitrogen compounds (azole compounds), organic solvents, surfactants, pH adjusters, oxidizing agents, etc. These may be used alone or in combination of two or more. Although surfactants, pH adjusters, etc. have been mentioned as additives, it is preferable that these are not included in the aqueous composition of the present invention. The content of additives that may be included 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.

[0019] [Water] The aqueous composition according to one embodiment of the present invention contains water. The water is not particularly limited, but 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 is more preferably pure water, and particularly preferably ultrapure water. The content of water is the remainder of the aqueous composition, and is not particularly limited, but is preferably 50% by mass or more and 98% by mass or less, more preferably 60% by mass or more and 95% by mass or less, even more preferably 75% by mass or more and 93% by mass or less, and particularly preferably 85% by mass or more and 90% by mass or less, based on the total amount of the aqueous composition. The aqueous composition of the present invention is preferably a solution, and preferably does not contain components that are insoluble in the solution composition, such as solid particles such as abrasive particles.

[0020] 2. Method for Producing Perforated Stainless Steel Foil A method for producing a perforated stainless steel foil according to another aspect of the present invention includes a through hole forming step of contacting the aqueous composition with a stainless steel foil to form a plurality of through holes that penetrate the stainless steel foil in the thickness direction. According to this aspect, as described above, a plurality of through holes can be formed in the thickness direction of the stainless steel foil by the simple method of contacting the aqueous composition with the stainless steel foil.

[0021] [Through-hole forming step] The aqueous composition used in this step is as described above in "1. Aqueous composition".

[0022] The stainless steel foil that is the material for the perforated stainless steel foil is not particularly limited as long as it is a stainless steel plate or foil. The thickness of the stainless steel foil is preferably 1 μm or more and 50 μm or less, more preferably 3 μm or more and 45 μm or less, and more preferably 5 μm or more and 40 μm or less. The lower limit of the thickness of the stainless steel foil may be, for example, 1 μm or more, 2 μm or more, 3 μm or more, 4 μm or more, 5 μm or more, 6 μm or more, 7 μm or more, 8 μm or more, or 9 μm or more. The upper limit of the thickness of the stainless steel foil may be, for example, 50 μm or less, 45 μm or less, 40 μm or less, 30 μm or less, 20 μm or less, 15 μm or less, 12 μm or less, or 10 μm or less.

[0023] The type of stainless steel foil is not particularly limited, but examples include chromium-nickel stainless steels defined by JIS G4305, including SUS304, SUS316, SUS321, SUS347, and SUS329J1; ferritic stainless steels (chromium stainless steels) including SUS405, SUS430, SUS434, SUS444, SUS447, and SUSXM27; and precipitation hardening stainless steels (chromium-nickel stainless steels) including SUS630, SUS631, and SUH660. Among these, SUS304, SUS430 series (such as SUS430 and SUS430LX), and SUS444 are more preferred as stainless steel foils.

[0024] The treatment temperature 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. Here, the treatment temperature refers to the temperature when the aqueous composition is brought into contact with the stainless steel foil surface, particularly the liquid temperature of the aqueous composition brought into contact with the stainless steel foil surface. If the treatment temperature is 10°C or higher, through-holes can be formed efficiently in a short time. On the other hand, if the treatment temperature is 50°C or lower, changes in the liquid composition can be suppressed, etching conditions can be maintained constant, and the work can be carried out safely. Thus, according to this embodiment, through-holes can be formed in the stainless steel foil even if the treatment temperature is not very high.

[0025] The treatment time in the through-hole forming step is preferably 30 to 240 seconds, more preferably 40 to 150 seconds, and particularly preferably 50 to 120 seconds. The treatment time can be determined appropriately taking into account various conditions, such as the condition of the stainless steel foil surface, the content of halide ions in the aqueous composition, the treatment temperature, and the contact method. Here, the treatment time refers to the time during which the aqueous composition is brought into contact with the stainless steel foil surface. For example, it refers to the time during which the stainless steel foil is immersed in the aqueous composition, or the time from when the aqueous composition is sprayed onto the stainless steel foil surface to when the aqueous composition is removed with water or the like. Thus, according to this embodiment, through-holes can be formed in the stainless steel foil without a particularly long time.

[0026] The method for contacting the aqueous composition with the stainless steel foil surface is not particularly limited. For example, the aqueous composition may be contacted with the stainless steel foil by dripping (sheet-fed spin treatment) or spraying (atomization), or a wet method (wet etching method) such as immersing the stainless steel foil in the aqueous composition may be used. In this embodiment, either method may be used. For example, the aqueous composition may be sprayed onto a stainless steel foil processed into a specific shape to form through-holes, thereby obtaining a perforated stainless steel foil. Alternatively, a dripping, spraying, or immersion device for the aqueous composition may be installed between rolls of stainless steel foil, and the stainless steel foil may be unrolled from a roll on which an untreated stainless steel foil was wrapped, while the stainless steel foil is being moved, passing the aqueous composition near the device, and the perforated stainless steel foil is then wound up to obtain a roll. The perforated stainless steel foil with through-holes formed therein may be subjected to a treatment such as water washing (cleaning process).

[0027] [Water-Rinsing Step] The stainless steel foil with through holes formed therein (i.e., perforated stainless steel foil) is preferably washed appropriately with water as necessary to remove halide ions and the like adhering to the surface of the stainless steel foil. The water is preferably water from which metal ions, organic impurities, particles, and the like have been removed by distillation, ion exchange treatment, filtration, various adsorption treatments, etc., and pure water or ultrapure water is particularly preferred.

[0028] [Impurity Removal Step] After the through-hole formation step, smut (a mixture containing Cu as the main constituent element and also C, N, S, O, Fe, Cr, Ni, etc.) may form on the surface of the obtained perforated stainless steel foil. If these remain, they may deteriorate the appearance of the product or cause contamination of the production line for current collectors for electrical storage devices. In order to remove these impurities, an impurity removal step for removing smut may be performed on the perforated stainless steel foil as needed after the through-hole formation step. In this step, impurities on the surface of the perforated stainless steel foil obtained by the through-hole formation step are removed by contacting the surface with a treatment liquid selected from an acidic aqueous solution containing hydrogen peroxide or an aqueous solution containing nitric acid. An example of an acidic aqueous solution containing hydrogen peroxide used in this step is a mixed aqueous solution of hydrogen peroxide and sulfuric acid. An example of an aqueous solution containing nitric acid is an aqueous nitric acid solution. The hydrogen peroxide content in the acidic aqueous solution containing hydrogen peroxide is preferably 0.1% by mass to 20% by mass, more preferably 1.0% by mass to 10% by mass, and even more preferably 1.5% by mass to 5.0% by mass. When a mixed aqueous solution of hydrogen peroxide and sulfuric acid is used as the acidic aqueous solution containing hydrogen peroxide, the sulfuric acid content is preferably 0.1% by mass to 20% by mass, more preferably 1.0% by mass to 10% by mass, and even more preferably 1.5% by mass to 8.0% by mass. The nitric acid content in the aqueous solution containing nitric acid is preferably 0.1% by mass to 40% by mass, more preferably 1.0% by mass to 30% by mass, and even more preferably 1.5% by mass to 20% by mass. Furthermore, alcohol may be added to the treatment solution to facilitate the removal of impurities. Examples of the alcohol that can be used include lower alcohols having 1 to 5 carbon atoms, such as methanol, ethanol, and n-propanol. The alcohol content is preferably 0.1% by mass or more and 5.0% by mass or less based on the total amount of the treatment solution. The components other than hydrogen peroxide, any sulfuric acid, and alcohol in the acidic aqueous solution containing hydrogen peroxide, and the components other than nitric acid and any alcohol in the nitric acid aqueous solution are essentially water. Examples of water include the same as those described in the through-hole forming step, with pure water being more preferred and ultrapure water being particularly preferred.The water content is the remainder of the treatment liquid and is not particularly limited, but is preferably 50% by mass or more and 98% by mass or less, more preferably 60% by mass or more and 95% by mass or less, even more preferably 75% by mass or more and 93% by mass or less, and particularly preferably 85% by mass or more and 90% by mass or less, based on the total amount of the treatment liquid.

[0029] The treatment temperature in the impurity removal 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. Here, the treatment temperature refers to the temperature when the treatment liquid is brought into contact with the surface of the perforated stainless steel foil, particularly the liquid temperature of the treatment liquid that is brought into contact with the surface of the perforated stainless steel foil. If the treatment temperature is 10°C or higher, impurities can be removed from the surface of the perforated stainless steel foil efficiently in a short time. On the other hand, if the treatment temperature is 50°C or lower, changes in the liquid composition can be suppressed, the treatment conditions can be kept constant, and the work can be carried out safely.

[0030] The treatment time in the impurity removal step is preferably 5 to 120 seconds, more preferably 10 to 100 seconds, and particularly preferably 20 to 80 seconds. Here, the treatment time refers to the time during which the treatment liquid is brought into contact with the surface of the perforated stainless steel foil. For example, it is the time during which the perforated stainless steel foil is immersed in the treatment liquid, or the time from when the treatment liquid is sprayed onto the surface of the perforated stainless steel foil to when the treatment liquid is removed with water or the like.

[0031] The method for contacting the surface of the perforated stainless steel foil with the treatment liquid is not particularly limited, and can be, for example, a method in which the treatment liquid is brought into contact with the perforated stainless steel foil by dropping (sheet-fed spin treatment) or spraying (atomization), or a wet method (wet etching method) such as immersing the perforated stainless steel foil in the treatment liquid. Examples include a method in which the treatment liquid is sprayed onto the perforated stainless steel foil obtained through the through-hole formation step, and a method in which a dripping device, spraying device, or immersion device for the treatment liquid is installed between rolls of stainless steel foil, and the perforated stainless steel foil obtained through the through-hole formation step is passed near the device by a roll-to-roll technique while being moved, and the perforated stainless steel foil from which surface impurities have been removed is wound up to obtain a roll.

[0032] After removing impurities from the surface of the perforated stainless steel foil in the impurity removal step, a further treatment such as water washing (cleaning step) may be carried out. For details about the water washing treatment, see the above-mentioned "water washing step." Furthermore, if necessary, rubbing the surface of the perforated stainless steel foil as the treated material with a nonwoven fabric wiper or the like will facilitate the removal of impurities such as smut.

[0033] According to the above-described method, a perforated stainless steel foil can be obtained essentially through one or two chemical treatments, or by further performing appropriate washing (e.g., water washing) as needed. According to this aspect, the conditions for each treatment are mild and the required time is short, allowing for efficient production of the perforated stainless steel foil. Furthermore, according to a preferred embodiment, the through-holes can be formed with a uniform diameter, and the tensile strength of the resulting perforated stainless steel foil can be prevented from decreasing. Therefore, continuous processing of the perforated stainless steel foil using a continuous process such as a roll-to-roll process can further improve production efficiency. For example, a dripping, spraying, or immersion device for the aqueous composition is installed between the rolls of stainless steel foil, and the roll-to-roll process involves passing the untreated stainless steel foil through the vicinity of the device while the stainless steel foil is unwrapped and moved from the roll on which it was wrapped. The aqueous composition, optionally water for removing the aqueous composition, and a treatment solution for removing surface impurities are then supplied, and the perforated stainless steel foil with the formed through-holes can be wound up to obtain a roll. The resulting perforated stainless steel foil may be subjected to a drying treatment before being wound up on a roll.

[0034] 3. Perforated Stainless Steel Foil The perforated stainless steel foil according to this embodiment has a plurality of through holes penetrating in the thickness direction, the thickness of the perforated stainless steel foil is 1 μm or more and 50 μm or less, the average pore diameter is 1 μm or more and 70 μm or less, and the average number of pores is 1.0×10 ２ pieces / cm ２ Above 1.0 x 10 ５ pieces / cm ２ and the coefficient of variation in the number of pores obtained by measuring five points in an area of ​​3570 μm × 2230 μm is 5% or more and 100% or less. The perforated stainless steel foil according to this embodiment can be produced by the method described above in "2. Method for producing perforated stainless steel foil."

[0035] In one embodiment, the thickness of the perforated stainless steel foil is 1 μm or more and 50 μm or less, preferably 3 μm or more and 45 μm or less, and more preferably 5 μm or more and 40 μm or less. Within this range, the perforated stainless steel foil can be suitably used as a current collector for an electricity storage device, particularly as a current collector for both the positive and negative electrodes of an LIB.

[0036] In one embodiment, the average pore size of the pores in the stainless steel perforated foil is 1 μm or more and 70 μm or less, preferably 5 μm or more and 65 μm or less, more preferably 7 μm or more and 60 μm or less, and even more preferably 10 μm or more and 55 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 particularly suitably used as a current collector for both positive and negative electrodes of LIB.

[0037] In one embodiment, the average number of pores in the perforated stainless steel foil is 1.0×10 ２ pieces / cm ２ Above 1.0 x 10 ５ pieces / cm ２ or less, preferably 1.1 × 10 ２ pieces / cm ２ Above 5.0 x 10 ４ pieces / cm ２ or less, more preferably 1.2 × 10 ２ pieces / cm ２ Above 3.0 x 10 ４ pieces / cm ２ More preferably, 1.3 × 10 ２ pieces / cm ２ Above 2.0 x 10 ４ pieces / cm ２ When the average number of pores is within the above range, the balance between tensile strength and pre-doping efficiency is good, and the carbon nanotube can be suitably used particularly as a current collector for both positive and negative electrodes of an LIB.

[0038] In one embodiment, the coefficient of variation (CV) of the number of pores obtained by measuring five points in an arbitrary 3570 μm × 2230 μm area of ​​the stainless steel perforated foil is 5% or more and 100% or less, preferably 80% or less, more preferably 70% or less, even more preferably 60% or less, and particularly preferably 50% or less. The lower limit of the CV may be, for example, 5.0% or more, 6.0% or more, or 7.0% or more. The CV range can be selected from a range that appropriately combines the above-mentioned lower limit and upper limit. When the CV is in the above range, the balance between tensile strength and pre-doping efficiency is good, and the foil can be particularly suitable for use as a current collector for both positive and negative electrodes of LIB.

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

[0040] The current collector for an electricity storage device according to this embodiment is composed of the perforated stainless steel foil described above. The perforated stainless steel foil has a plurality of through-holes that penetrate the foil in the thickness direction. Therefore, when the current collector for an electricity storage device according to this embodiment is used as a current collector for both the positive and negative electrodes of an LIB, for example, pre-doping of lithium ions can be performed efficiently in a short time, and the lithium ions can be dispersed more uniformly. This allows for a high capacity, and an electricity storage device that achieves both a high output density and a high energy density can be provided.

[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. Thickness Measurement The thickness values ​​of the treated stainless steel foils obtained in the Examples and Comparative Examples, and the untreated stainless steel foil in the Reference Example, were measured using a digital micrometer (manufactured by Mitutoyo Corporation, MDH-25MB).

[0044] 2. Analysis of pores The treated stainless steel 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 through holes [number] and the total area of ​​the holes [μm ] within the observation area of ​​3570 × 2230 μm were calculated. ２ ] was calculated.

[0045] (1) Average Pore Diameter The average pore diameter [μm] was calculated by the following formula.

[0046] (2) Number of holes Number of holes [pcs / cm ２ ] was calculated by the following formula, and the average of five points and the coefficient of variation (CV) were calculated.

[0047] (3) Hole uniformity The CV of the number of holes was evaluated as follows: ◯ (pass): CV is 100% or less × (fail): CV is more than 100%

[0048] [Example 1] A stainless steel foil made of SUS444 and having a thickness of 10.1 μm and dimensions of 30 mm × 30 mm was prepared (Reference Example 1). 127.8 g of pure water was mixed with hydrogen peroxide in an amount to give a final concentration of 0.5 mass % (1.7 g of a 60 mass % aqueous hydrogen peroxide solution), hydrochloric acid (as halide ions) in an amount to give a final concentration of 12.0 mass % (68.6 g of a 35 mass % aqueous hydrochloric acid solution), and copper ions in an amount to give a final concentration of 0.25 mass % (copper sulfate pentahydrate (CuSO ４ ・5H ２ To an aqueous composition containing 2.0 g of HCl (6.7 g of a 60% by mass aqueous hydrogen peroxide solution), 171.8 g of sulfuric acid (19.6 g of a 46% by mass aqueous sulfuric acid solution), and 1.0 g of n-propanol (2.0 g) were added, respectively, to prepare a treatment solution for removing impurities.

[0049] The stainless steel foil was immersed in the aqueous composition at a liquid temperature of 35°C for 60 seconds to carry out the through-hole forming step. The immersed stainless steel foil was then thoroughly rinsed with pure water, and then immersed in the impurity removal treatment solution at a liquid temperature of 30°C for 30 seconds to carry out the impurity removal step. The immersed stainless steel foil was then thoroughly rinsed with pure water and thoroughly dried to obtain a perforated stainless steel foil. The obtained perforated stainless steel foil was measured according to the method described above, and the thickness was 10.0 μm, the average pore size of the perforations was 17 μm, and the average number of pores was 4.1 × 10 ２ pieces / cm ２ The CV of the number of holes was 22.1%, and the hole uniformity was good (acceptable).

[0050] [Examples 2 to 10, Comparative Examples 1 to 5] Treated stainless steel foils were obtained in the same manner as in Example 1, except that the conditions for the stainless steel foil to be treated, the through-hole forming step, or the impurity removal step were changed as shown in Table 1. In Comparative Examples 1 and 2, iron (III) chloride hexahydrate (FeCl ３ ・6H ２ The through-hole forming step was carried out using aqueous solutions containing 133.0 g and 133.0 g of the compound (II).

[0051] The thickness of the obtained perforated stainless steel foil, the average diameter of the through holes, the average number of holes, the coefficient of variation (CV) of the number of holes, and the results of judging the uniformity of the holes are shown in Table 1. Table 1 also shows the measurement results of an untreated stainless steel foil as a reference example. In the table, "-" means that the step or measurement was not performed.

[0052]

[0053] As shown in Table 1, according to the present invention, a plurality of through holes can be formed in the thickness direction of a stainless steel foil by a simple method. According to a preferred embodiment, the obtained perforated stainless steel foil has a predetermined thickness, average pore diameter, average number of pores, and coefficient of variation of the number of pores, and has excellent pore uniformity, and is therefore suitable for use as a current collector for an electricity storage device, in particular as a current collector for both the positive and negative electrodes of an LIB.

Claims

1. An aqueous composition for forming through holes in the thickness direction of a stainless steel foil, the aqueous composition comprising, based on the total amount of the aqueous composition, 0.01% by mass or more and 20% by mass or less of hydrogen peroxide and 1% by mass or more and 30% by mass or less of halide ions.

2. The aqueous composition according to claim 1, containing copper ions in an amount of more than 0% by mass and not more than 10% by mass, based on the total amount of the aqueous composition.

3. The aqueous composition of claim 1, wherein said halide ion is chloride ion.

4. A method for producing perforated stainless steel foil, comprising a through-hole forming step of contacting a stainless steel foil with the aqueous composition described in any one of claims 1 to 3 to form a plurality of through-holes that penetrate the stainless steel foil in the thickness direction.

5. A method for producing perforated stainless steel foil according to claim 4, wherein the thickness of the stainless steel foil is 1 μm or more and 50 μm or less.

6. The method for producing a perforated stainless steel foil according to claim 4, 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 30 seconds or higher and 240 seconds or lower.

7. A stainless steel perforated foil having a plurality of through holes penetrating in the thickness direction, wherein the thickness of the stainless steel perforated foil is 1 μm or more and 50 μm or less, the average pore diameter is 1 μm or more and 70 μm or less, and the average number of pores is 1.0 × 10 ２ pieces / cm ２ Above 1.0 x 10 ５ pieces / cm ２ and the coefficient of variation in the number of holes obtained by measuring five points in an area of ​​3570 μm × 2230 μm is 5% or more and 100% or less.

8. A current collector for an electricity storage device, comprising the perforated stainless steel foil according to claim 7.

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