Aluminum substrate for current collector, capacitor, secondary battery, and method for manufacturing aluminum substrate for current collector

Abstract

Provided are: an aluminum substrate for a collector having a high adhesion performance with respect to an electrode material and a low contact resistance with an electrode material; a capacitor; a secondary cell; and a method for manufacturing the aluminum substrate for a collector. The present invention has a face in which (C + D) / (A + B + C + D) is 0.5 to 1 inclusive and C / D is 0.1 to 2 inclusive, where A, B, C, and D respectively represent the peak area ratios of Al, Al2O3, Al(OH)3, and AlO(OH) present within 10 nm of the surface layer when measured by X-ray photoelectron spectroscopy.

Description

[Technical Field]

[0001] The present invention relates to an aluminum current collector base, a capacitor and a secondary battery using this aluminum current collector base, and a method for producing an aluminum current collector base. [Background technology]

[0002] In recent years, with the development of portable devices such as personal computers and mobile phones, as well as hybrid vehicles and electric vehicles, there has been an increasing demand for electricity storage devices as power sources therefor, in particular lithium ion capacitors, lithium ion secondary batteries, electric double layer capacitors, and the like.

[0003] It is known that an aluminum substrate can be used as an electrode current collector (hereinafter simply referred to as "current collector") used in the positive and / or negative electrodes of such an electricity storage device. It is also known that an active material, activated carbon, or the like can be applied to the surface of this aluminum substrate current collector as an electrode material, and the current collector can be used as a positive or negative electrode.

[0004] For example, Patent Document 1 discloses a ceramic substrate having an aluminum substrate and an oxide film laminated on at least one main surface of the aluminum substrate, the oxide film having a density of 2.7 to 4.1 g / cm 3 and an aluminum electrode member having a thickness of 5 nm or less.

[0005] Patent Document 2 describes a positive electrode for a secondary battery, which includes a positive electrode current collector, a positive electrode composite layer, and an intermediate layer provided between the positive electrode current collector and the positive electrode composite layer, the intermediate layer having a first intermediate layer containing a non-oxide conductive inorganic compound and a positive electrode active material, and a second intermediate layer containing an insulating inorganic material and a non-oxide conductive inorganic compound, and the conductive inorganic compound becomes an insulating oxide at 300°C or higher. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2018 / 062046 [Patent Document 2] International Publication No. 2018 / 220991 Summary of the Invention [Problem to be solved by the invention]

[0007] It is desirable for a current collector to have high adhesion to the electrode material and low contact resistance with the electrode material. While it is possible to improve adhesion to the electrode material by roughening the surface of an aluminum substrate, it has been difficult to achieve both sufficient adhesion and reduced contact resistance. Furthermore, the cost of the roughening treatment is not sufficiently cost-effective, and the method has rarely been put to practical use.

[0008] In addition, commercially available aluminum foil for current collectors has a natural oxide film formed on its surface during the rolling process and trace amounts of rolling oil remaining on it, which poses issues with contact resistance and adhesion to electrode materials.

[0009] An object of the present invention is to provide an aluminum substrate for a current collector that has high adhesion to an electrode material and low contact resistance with the electrode material, a capacitor, a secondary battery, and a method for producing an aluminum substrate for a current collector. [Means for solving the problem]

[0010] The present invention solves the problems by the following configuration.

[0011] [1] An aluminum substrate for current collectors having a surface in which, when measured by X-ray photoelectron spectroscopy, the peak area ratios of metallic Al, Al2O3, Al(OH)3, and AlO(OH) present within the surface layer of 10 nm are designated as A, B, C, and D, respectively, such that (C+D) / (A+B+C+D) is 0.5 or more and 1 or less, and C / D is 0.1 or more and 2 or less. [2] The aluminum base for a current collector according to [1], wherein the surface roughness Ra of the surface is 10 nm or more and 50 nm or less. [3] The aluminum base for a current collector according to [1] or [2], wherein the maximum difference in height PV of the surface is 100 nm or more and 500 nm or less. [4] The aluminum base for a current collector according to any one of [1] to [3], the surface of which has a granular intermetallic compound. [5] The number density of granular metal compounds is 500 particles / mm 2 The aluminum base for a current collector according to [4], [6] The aluminum base for a current collector according to any one of [1] to [5], which has a thickness of 5 μm to 100 μm. [7] A capacitor comprising the aluminum base for a current collector according to any one of [1] to [6]. [8] A secondary battery comprising the aluminum substrate for a current collector according to any one of [1] to [6]. [9] A method for producing an aluminum base for a current collector according to any one of [1] to [6], comprising: The current flow rate during anodic electrolysis is 10 to 100 C / dm 2 A film forming process in which an anodized film is formed on the surface of the aluminum foil; a removal step of removing an anodized film.

[10] The method for producing an aluminum substrate for a current collector according to [9], wherein the removing step comprises, in this order, a chemical etching step using an alkaline solution, a water washing step, a cleaning step using an acidic solution, and a water washing step.

[11] The method for producing an aluminum base for a current collector according to

[10] , wherein the chemical etching step includes a step of contacting the anodized film with an alkaline solution at 25°C or higher and lower than 50°C for 1 to 10 seconds. [Effects of the Invention]

[0012] The present invention can provide an aluminum substrate for a current collector that has high adhesion to an electrode material and low contact resistance with the electrode material, a capacitor, a secondary battery, and a method for producing an aluminum substrate for a current collector. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic cross-sectional view illustrating an example of a preferred method for producing an aluminum substrate for a current collector of the present invention. [Figure 2] FIG. 1 is a schematic cross-sectional view illustrating an example of a preferred method for producing an aluminum substrate for a current collector of the present invention. [Figure 3] FIG. 1 is a schematic cross-sectional view illustrating an example of a preferred method for producing an aluminum substrate for a current collector of the present invention. [Figure 4] FIG. 1 is a schematic cross-sectional view illustrating an example of a preferred method for producing an aluminum substrate for a current collector of the present invention. [Figure 5] FIG. 1 is a schematic cross-sectional view illustrating an example of a preferred method for producing an aluminum substrate for a current collector of the present invention. [Figure 6] FIG. 6 is an enlarged view of a region R1 in FIG. 5. [Figure 7] FIG. 7 is an enlarged view of a region R2 in FIG. 6. [Figure 8] FIG. 1 is a conceptual diagram illustrating an example of a manufacturing apparatus for carrying out the manufacturing method of an aluminum substrate for current collector of the present invention. [Figure 9] FIG. 1 is a diagram showing a schematic diagram of an apparatus for measuring resistance. [Figure 10] 1 is an SEM image of an aluminum substrate for a current collector according to an example. [Figure 11] 1 is an SEM image of an aluminum substrate for a current collector of a comparative example. [Figure 12] 1 is an SEM image of an aluminum substrate for a current collector of a comparative example. [Figure 13] FIG. 2 is a diagram schematically illustrating a measuring device for measuring peel strength. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below. The following description of the components may be based on typical embodiments of the present invention, but the present invention is not limited to such embodiments. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0015] [Aluminum substrate for current collectors] The aluminum substrate for a current collector of the present invention is The aluminum substrate for current collectors has a surface in which, when measured by X-ray photoelectron spectroscopy, the peak area ratios of metallic Al, Al2O3, Al(OH)3, and AlO(OH) present within the surface layer of 10 nm are designated as A, B, C, and D, respectively, such that (C+D) / (A+B+C+D) is 0.5 or more and 1 or less, and C / D is 0.1 or more and 2 or less.

[0016] The configuration of the aluminum substrate for current collector of the present invention will be described.

[0017] The aluminum substrate for current collector of the present invention has a configuration in which, when measured by X-ray photoelectron spectroscopy (hereinafter also referred to as XPS), the peak area ratios of metallic Al, Al2O3, Al(OH)3, and AlO(OH) present within a surface layer of 10 nm are designated as A, B, C, and D, respectively, so that the aluminum substrate has a surface in which (C+D) / (A+B+C+D) is 0.5 or more and 1 or less, and C / D is 0.1 or more and 2 or less.

[0018] That is, the aluminum base for current collector of the present invention contains, on at least one surface of the aluminum base, a certain amount or more of two hydroxides, aluminum hydroxide Al(OH)3 and aluminum oxide hydrate (boehmite) AlO(OH), and of the hydroxides, the aluminum base contains a certain amount or more of aluminum hydroxide Al(OH)3.

[0019] The aluminum substrate for a current collector of the present invention is used as a current collector, and an active material (electrode material) is applied to the surface to be used as a positive or negative electrode of an electricity storage device or the like.

[0020] As described above, it is desirable for a current collector to have high adhesion to an electrode material and low contact resistance with the electrode material. Therefore, various configurations have been proposed for aluminum substrates for current collectors to improve adhesion to an electrode material and reduce contact resistance with the electrode material.

[0021] For example, it has been proposed to form a rough surface on the surface of an aluminum substrate to improve adhesion with an electrode material and thereby improve resistance. However, even if the surface of the aluminum substrate is roughened to improve adhesion with an electrode material, a sufficient adhesion effect cannot be obtained, and it has not been possible to sufficiently achieve both adhesion and low resistance. In addition, roughening the surface of an aluminum substrate has the disadvantage of complicating the manufacturing process and increasing manufacturing costs.

[0022] It has also been proposed to improve adhesion by forming an anodized film with fine pores on the surface of an aluminum substrate. However, because an anodized film has poor electrical conductivity, the presence of an anodized film on the surface increases the contact resistance with the electrode material, making it impossible to achieve both adhesion and low resistance.

[0023] Another known method is to form a conductive coating film containing carbon or other conductive particles on an aluminum substrate. The conductive particles in the coating film create minute irregularities on the surface of the conductive coating film, which is known to improve adhesion to the electrode material applied thereon and make it less likely to peel. However, the method of applying a conductive coating film in advance has the drawback of requiring a complex manufacturing process and increasing manufacturing costs.

[0024] Furthermore, aluminum substrates usually have a natural oxide film formed on their surface, which contains Al2O3 and its hydrate Al2O3·nH2O. Because the natural oxide film itself is a material with poor conductivity, it is known that by thinning it or specifying the density of the oxide film, it can be made to have low resistance, thereby reducing contact resistance with the electrode material.

[0025] However, according to the investigations of the present inventors, it has been found that there are cases where the improvement in adhesion to the electrode material and the contact resistance with the electrode material is insufficient simply by controlling the thickness and density of the native oxide film.

[0026] In contrast, the aluminum substrate for current collector of the present invention has a configuration in which, when measured by X-ray photoelectron spectroscopy (hereinafter also referred to as XPS), the peak area ratios of metal Al, Al2O3, Al(OH)3, and AlO(OH) present within the surface layer of 10 nm are designated as A, B, C, and D, respectively, so that (C+D) / (A+B+C+D) is 0.5 or more and 1 or less, and C / D is 0.1 or more and 2 or less.

[0027] The inventors have found that hydroxides near the surface of an aluminum substrate, in addition to the thickness of the native oxide film, also affect interfacial resistance. Specifically, they found that two types of hydroxides, AlO(OH) and Al(OH)3, exist near the surface of an aluminum substrate. They found that AlO(OH) (boehmite) adversely affects interfacial resistance. They also found that even if AlO(OH) is present, low resistance can be maintained as long as a certain amount of another hydroxide, Al(OH)3, is present. Therefore, they found that low resistance can be achieved by maintaining a certain ratio of Al(OH)3 among these two hydroxides present within the surface 10 nm. Specifically, for hydroxides present within the outermost 10 nm, a peak area ratio of Al(OH)3 / AlO(OH) of 0.1 or greater is essential to achieving low resistance. A peak area ratio of 2 or less results in good adhesion during bonding, so the upper limit of the peak area ratio is set to 2.

[0028] As will be described in detail later, an aluminum substrate for a current collector having a hydroxide surface layer in the above ratio can be produced by forming an anodized film under appropriate conditions and then removing the anodized film under appropriate conditions. During this process, fine irregularities with a diameter of approximately 10 nm formed at the bottom of the anodized film affect the formation of fine irregularities on the surface of the aluminum substrate. This has been found to improve adhesion.

[0029] The aluminum substrate for current collectors of the present invention, which has low contact resistance with and strong adhesion to electrode materials, contributes to reducing internal resistance when used in secondary batteries such as lithium-ion batteries and electricity storage devices such as capacitors, and can also suppress partial peeling between the electrode material and the current collector even after many charge / discharge cycles over a long period of time. This is particularly effective in all-solid-state batteries and semi-solid-state batteries, which require high adhesion and low resistance, such as those with solid or semi-solid electrolytes.

[0030] Here, we will explain how to measure the peak area ratios A, B, C, and D of metallic Al, Al2O3, Al(OH)3, and AlO(OH) present within the surface layer of 10 nm.

[0031] X-ray photoelectron spectroscopy (XPS) is an analytical method commonly referred to as ESCA (Electron Spectroscopy for Chemical Analysis) or X-ray Photoelectron Spectroscopy (XPS). XPS is an analytical method that utilizes the emission of photoelectrons when the surface of a sample is irradiated with X-rays. It is widely used to analyze the surface of a sample. XPS allows qualitative and quantitative analysis to be performed using the X-ray photoelectron spectroscopy spectrum obtained by analyzing the surface of the sample. The following equation generally holds true between the depth from the sample surface to the analysis position (hereinafter also referred to as "detection depth") and the photoelectron take-off angle: detection depth ≒ electron mean free path × 3 × sin θ. In this equation, the detection depth is the depth at which 95% of the photoelectrons that make up the X-ray photoelectron spectroscopy spectrum are generated, and θ is the photoelectron take-off angle. The above equation shows that the smaller the photoelectron take-off angle, the shallower the region from the sample surface that can be analyzed, and the larger the photoelectron take-off angle, the deeper the region that can be analyzed. Furthermore, in an analysis performed by XPS at a photoelectron take-off angle of 45 degrees, the analysis position is typically the very surface layer, about 10 nm deep from the sample surface. Therefore, in an analysis of the surface of an aluminum current collector substrate using XPS at a photoelectron take-off angle of 45 degrees, it is possible to perform composition analysis of the very surface layer, about 10 nm deep from the surface of the aluminum current collector substrate.

[0032] For the Al2p spectrum obtained by XPS, peak shift correction for Al2O3, Al(OH)3, and AlO(OH) is performed using the peak position of metallic Al as the reference, and then background correction is performed on the data. By fitting the peak height to a fixed peak position and peak width, peaks corresponding to Al, Al2O3, Al(OH)3, and AlO(OH) are obtained. Peak area ratios A, B, C, and D are obtained from each peak.

[0033] As the XPS measurement device, for example, a commercially available measurement device such as QuanteraSXM manufactured by Ulvac-PHI can be used. The measurement conditions may be, for example, as follows. ·X-ray source: AlKα ray (1486.6ev, 25W, 15kV) ·Pass Energy=55ev, Step=0.05ev ·Measurement area: 300μm×300μm Photoelectron take-off angle: 45 degrees

[0034] From the viewpoint of achieving both adhesion to the electrode material and low resistance, (C+D) / (A+B+C+D) is preferably 0.55 or more and 1 or less, and more preferably 0.6 or more and 0.7 or less. Similarly, C / D is preferably 0.12 or more and 2 or less, and more preferably 0.15 or more and 1 or less.

[0035] From the viewpoint of achieving both good adhesion to the electrode material and low resistance, when the peak area ratios of metallic Al, Al2O3, Al(OH)3, and AlO(OH) present within 5 nm of the surface layer as measured by X-ray photoelectron spectroscopy are designated A2, B2, C2, and D2, respectively, it is preferable that (C2 + D2) / (A2 + B2 + C2 + D2) be 0.5 or greater and 1 or less, and C2 / D2 be 0.4 or greater and 1 or less. Furthermore, (C2 + D2) / (A2 + B2 + C2 + D2) is more preferably 0.6 or greater and 1 or less, and even more preferably 0.65 or greater and 0.7 or less. Similarly, C2 / D2 is more preferably 0.5 or greater and 2 or less, and even more preferably 0.7 or greater and 1 or less.

[0036] When performing a composition analysis of a surface layer portion 5 nm deep from the surface of the aluminum base material for current collector, the photoelectron take-off angle in the above-mentioned XPS measurement may be set to 20 degrees.

[0037] From the viewpoint of achieving both good adhesion to the electrode material and low resistance, the surface roughness Ra of the surface of the aluminum substrate for current collector that satisfies the above-mentioned peak area ratio is preferably 10 nm or more and 50 nm or less, more preferably 11 nm or more and 40 nm or less, and even more preferably 11 nm or more and 36 nm or less.

[0038] Furthermore, from the viewpoint of achieving both adhesion to the electrode material and low resistance, the maximum height difference PV of the surface of the aluminum substrate for current collector that satisfies the above-mentioned peak area ratio is preferably 100 nm or more and 500 nm or less, more preferably 120 nm or more and 200 nm or less, and even more preferably 120 nm or more and 160 nm or less.

[0039] The surface roughness Ra and the maximum height difference PV are measured as follows.

[0040] An atomic force microscope (AFM) is used to measure the surface shape of a 1 μm square area of ​​the aluminum substrate, and the surface roughness Ra and maximum height difference PV are calculated from the obtained three-dimensional data using the following equations. Average surface roughness Ra (nm) = 1 / n × Σ|Z(i)-Zc| (Zc is the Z coordinate (height direction) of the center surface) Maximum height difference PV (nm) = Maximum value of Z coordinate within the measurement surface - Minimum value

[0041] The atomic force microscope (AFM) can be, for example, an AFM5100N SPM manufactured by Hitachi High-Tech Science Corp. This device can be used in tapping mode, with an Olympus OMCL-AC200TS-R3 cantilever used to measure three-dimensional data of the surface of the aluminum substrate at a resolution of 256 × 256 pixels. By applying FFT (Fast Fourier Transform) to the obtained data, it is possible to remove three-dimensional data with a period of 0.2 μm or more, for example, and calculate the surface roughness and maximum height difference PV that reflect short-period irregularities. Here, the 3D data that has undergone FFT processing refers to the shape image obtained by performing a fast Fourier transform (FFT) on the obtained data, converting the resulting data into wavenumber space, performing high-pass filtering, and then performing an inverse Fourier transform (FFT) to reconstruct the shape image. By performing high-pass filtering, large waviness components originating from the aluminum foil with wavelengths of 0.2 μm or more are removed. With regard to the surface roughness Ra, which reflects short-period irregularities excluding three-dimensional data with a period of 0.2 μm or more, from the viewpoint of achieving both adhesion to the electrode material and low resistance, it is preferably 5 nm or more and 10 nm or less, more preferably 6 nm or more and 10 nm or less, and even more preferably 6 nm or more and 9 nm or less. Similarly, the maximum height difference PV, which reflects short-period irregularities excluding three-dimensional data with an F period of 0.2 μm or more, is preferably 50 nm or more and 200 nm or less, more preferably 60 nm or more and 100 nm or less, and even more preferably 70 nm or more and 100 nm or less.

[0042] The thickness of the aluminum current collector base is preferably 5 μm to 100 μm, more preferably 10 μm to 30 μm. If the thickness of the aluminum current collector base is too thin, there is a risk of breakage. On the other hand, in order to reduce the overall thickness when used in an electricity storage device or the like, the thickness of the aluminum current collector base is preferably 100 μm or less.

[0043] The aluminum substrate for a current collector of the present invention may have through-holes that penetrate through the aluminum substrate in the thickness direction.

[0044] The aluminum substrate for a current collector having a plurality of through holes penetrating in the thickness direction can facilitate the movement of charged particles when used as a current collector, and the presence of a large number of through holes can improve adhesion to an active material.

[0045] The average opening diameter of the through holes is preferably 0.1 μm or more and 100 μm or less, more preferably 1 μm or more and 80 μm or less, even more preferably 3 μm or more and 40 μm or less, and particularly preferably 5 μm or more and 30 μm or less.

[0046] By setting the average opening diameter of the through holes within the above range, it is possible to prevent the occurrence of voids when applying an active material to the aluminum substrate for current collector, improve adhesion to the applied active material, and ensure that the aluminum substrate for current collector has sufficient tensile strength even when it has a large number of through holes.

[0047] The average opening diameter of the through holes is measured as follows. Parallel light is irradiated from one side of the aluminum substrate for current collector, and the through-holes are photographed with a transmission optical microscope at a magnification of 200. The obtained data is binarized using image analysis software, and the average value of the circle-equivalent diameter of the through-holes is taken as the average opening diameter.

[0048] The average opening ratio of the through holes is preferably 0.5% to 30%, more preferably 0.6% to 20%, further preferably 0.7% to 10%, and particularly preferably 0.8% to 5%.

[0049] By setting the average aperture ratio of the through holes within the above range, it is possible to prevent the occurrence of voids when applying an active material to the aluminum substrate for current collector, improve adhesion to the applied active material, and ensure that the aluminum substrate for current collector has sufficient tensile strength even when it has a large number of through holes.

[0050] The average opening ratio of the through holes is measured as follows. Parallel light is irradiated from one side of the aluminum substrate for the current collector, and the through-holes are photographed with a transmission optical microscope at a magnification of 200x. The obtained data is binarized using image analysis software, and the ratio is calculated as the sum of the opening areas / the observed area x 100 (%).

[0051] In the present invention, the aluminum base for a current collector preferably has on its surface a large number of granular intermetallic compounds dispersed in a film. In the following description, the granular intermetallic compounds will also be simply referred to as "intermetallic compounds."

[0052] Aluminum oxide has a higher resistance than aluminum metal alone. However, if the aluminum base material contains an intermetallic compound, the aluminum oxide will also contain the intermetallic compound, which reduces the insulation properties.

[0053] In the intermetallic compound, the element ratio of oxygen to aluminum, O / Al, is preferably 2 or more and 4 or less. In addition, the number density of the granular intermetallic compound is 500 pieces / mm 2 It is preferable that this is equal to or greater than this.

[0054] Here, the intermetallic compound in the present invention is a compound containing aluminum element (Al) and at least one selected from Fe, Si, Mn, Mg, Ti, B, etc. Specific examples of intermetallic compounds include Al3Fe, Al6Fe, αAlFeSi, and AlFeMnSi. Because the intermetallic compound contains Al, an aluminum oxide film is formed on the surface. Therefore, the surface layer of the intermetallic compound in the present invention contains oxygen element (O).

[0055] The aluminum substrate for a current collector of the present invention is a substrate containing 500 particles / mm of granular intermetallic compounds having an oxide film on the surface thereof in which the element ratio O / Al is 2 or more and 4 or less. 2 As long as the density is equal to or greater than 100%, other granular intermetallic compounds may be present. That is, the surface oxide film may contain granular intermetallic compounds with an element ratio O / Al of less than 2 or more than 4.

[0056] Furthermore, when the oxide film is mainly composed of aluminum oxide (Al2O3) and does not contain hydrates, the element ratio O / Al in the portion of the oxide film other than the intermetallic compound is preferably less than 2, and is preferably about 1.3 to 1.5.

[0057] From the viewpoint of further reducing the electrical resistance of the aluminum base for current collector, the average element ratio O / Al of the oxide film in the surface layer of the intermetallic compound is preferably 2 or more and 4 or less, and more preferably 2.5 or more and 3.5 or less.

[0058] The element ratio O / Al in the surface layer of the intermetallic compound is measured as follows.

[0059] When the surface of an oxide film is observed with a high-resolution scanning electron microscope (SEM), the intermetallic compounds can be visually distinguished from other portions of the oxide film. Therefore, first, the surface of the oxide film is photographed with a high-resolution scanning electron microscope (SEM) at, for example, 5000x magnification, and the location of the intermetallic compounds is identified in the resulting SEM image. Next, elemental analysis is performed at the extracted intermetallic compound locations from the outermost surface to the depth direction using field-emission Auger electron spectroscopy (FE-AES). The depth direction analysis is performed by repeatedly measuring and removing the surface by sputtering. The elemental ratio O / Al in the outermost layer is determined from the elemental distribution in the depth direction obtained by FE-AES.

[0060] From the viewpoint of lowering the electrical resistance of the aluminum substrate for the current collector, the number density of the granular intermetallic compounds is set to 1000 pieces / mm 2 ~300000 pieces / mm 2 is preferable, and 5000 pieces / mm 2 ~200000 pieces / mm 2 is more preferred.

[0061] The number density of the granular intermetallic compound is measured as follows.

[0062] First, a high-resolution scanning electron microscope (SEM) is used to photograph the surface of the aluminum substrate for current collector from directly above at, for example, 5000x magnification, and granular intermetallic compounds are extracted. Next, elemental analysis using FE-AES is performed to determine the element ratio O / Al of each extracted intermetallic compound. The number of granular intermetallic compounds with an element ratio O / Al of 2 to 4 is counted, and the number density is calculated from the number of granular intermetallic compounds within the field of view and the area of ​​the field of view (geometric area). When multiple SEM photographs are used, the average number density of each photograph is calculated as the density.

[0063] Here, the granular intermetallic compound preferably has an equivalent circle diameter of 1 μm or less. Intermetallic compounds with an equivalent circle diameter of 1 μm or less are likely to appear on the surface of the aluminum substrate for current collector. When small intermetallic compounds appear on the surface of the aluminum substrate for current collector, the surface area relative to the volume of the intermetallic compound increases. As a result, it is thought that water molecules are more likely to be adsorbed locally, and the element ratio O / Al of the oxidized intermetallic compound is likely to be 2 or more. As a result, the oxide film of the intermetallic compound becomes a hydrate, which has lower insulating properties than the surrounding aluminum oxide and serves as a starting point for reducing resistance.

[0064] The circle-equivalent diameter of the granular intermetallic compound is calculated by extracting at least 20 intermetallic compounds whose element ratio O / Al has been measured as described above, determining the area of ​​the oxide film surface of the intermetallic compound using image analysis software or the like, determining the circle-equivalent diameter from this area, and averaging these values ​​to obtain the circle-equivalent diameter.

[0065] The shape of the aluminum substrate for current collector is not particularly limited as long as it can be used as a current collector, but a plate shape is preferred.

[0066] <Aluminum substrate> The aluminum substrate serving as the base material for the current collector aluminum substrate is not particularly limited, and known aluminum substrates such as alloy numbers 1N30, 3003, and 1085 described in JIS standard H4000 can be used. The use of aluminum containing a large amount of intermetallic compounds can be expected to achieve the aforementioned effect of reducing electrical resistance. However, the present application is not limited to aluminum materials. The aluminum substrate is an alloy plate containing aluminum as the main component and trace amounts of other elements.

[0067] [Method of manufacturing aluminum substrate for current collector] Next, the method for producing the aluminum substrate for current collector of the present invention will be described.

[0068] The method for producing an aluminum substrate for a current collector of the present invention includes the steps of: The surface of the aluminum foil is electrolyzed with an electric current of 10 to 100 C / dm 2 a film formation process in which an anodic oxide film is formed by The method for producing an aluminum base for a current collector includes a removal step of removing the anodized film after the film formation step.

[0069] In the method for producing an aluminum substrate for a current collector, the anodized film is preferably removed in the removal step by chemical etching with an alkaline solution, washing with water, cleaning with an acidic solution, and washing with water, in that order.

[0070] The method for producing an aluminum substrate for a current collector may also include a through-hole forming step of forming through-holes that penetrate the aluminum substrate. The method for producing an aluminum substrate for a current collector may also include a surface roughening step of roughening the surface of the aluminum substrate. The through-hole forming step and / or the surface roughening step may be carried out simultaneously with or sequentially to the film forming step of forming an anodized film.

[0071] Hereinafter, each step in the method for producing an aluminum substrate for a current collector will be described with reference to FIGS. 1 to 5, and after each step in the method for producing an aluminum substrate for a current collector has been described, each step will be described in detail.

[0072] 1 to 5 are schematic cross-sectional views illustrating an example of a preferred embodiment of the method for producing an aluminum base for a current collector. 1 to 5, one example of a method for producing an aluminum substrate for a current collector includes a film formation step (FIGS. 1 and 2) in which at least one main surface of an aluminum substrate 1 having a natural oxide film 2 is subjected to electrolytic treatment to form an anodic oxide film 3 between the natural oxide film 2 and the aluminum substrate 1, and a removal step (FIGS. 2 to 5) in which the anodic oxide film 3 and the natural oxide film 2 are removed after the film formation step. Although not shown, the aluminum substrate 1 to be subjected to the film formation step may have rolling oil or the like present on the natural oxide film 2.

[0073] The removal process includes the steps of removing the anodic oxide film 3 and the native oxide film 2 by chemical etching with an alkaline solution (see FIGS. 2 and 3, also referred to as the chemical etching process), washing with water after the chemical etching process (see also the water washing process), removing residue 5 (see FIG. 4) remaining on the surface as a result of the chemical etching process by washing with an acidic solution (see FIGS. 4 and 5, also referred to as the pickling process), and washing with water after the pickling process (see also the water washing process).The chemical etching process and the water washing process precipitate aluminum hydroxide on the surface of the aluminum substrate (see FIG. 4).

[0074] [Film forming process] The film formation process is a process of forming an anodized film on the surface of an aluminum substrate. Since the anodized film is formed by converting metallic aluminum, if the aluminum substrate has a natural oxide film on its surface, the anodized film is formed between the natural oxide film and the aluminum substrate. Therefore, it is less susceptible to the influence of the natural oxide film, rolling oil, etc. in the removal process described below.

[0075] The anodizing treatment method for forming the anodized film can be the same as conventionally known anodizing treatments, and for example, the conditions and apparatus described in paragraphs

[0063] to

[0073] of JP 2012-216513 A can be appropriately adopted for the anodizing treatment.

[0076] In the present invention, the conditions for anodizing treatment cannot be determined in general because they vary depending on the electrolyte used, but generally, the electrolyte concentration is 0.2 to 80 mass %, the solution temperature is 5 to 70°C, and the current density is 0.5 to 60 A / dm 2 The voltage is suitably 1 to 100 V and the electrolysis time is suitably 1 second to 20 minutes, and these are adjusted so as to obtain a desired amount of oxide film.

[0077] In the present invention, it is preferable to carry out the anodizing treatment using an aqueous solution containing nitric acid and sulfuric acid. 2 ~100C / dm 2 and 30C / dm2 ~100C / dm 2 is more preferable, and 50C / dm 2 ~100C / dm 2 is more preferable. At this current amount, a thin anodic oxide film is formed. In the production method of the present invention, a thin anodic oxide film is formed on the aluminum substrate, and the removal step (chemical etching step) described below is carried out in a short time. This suppresses dissolution of the metallic aluminum portion and prevents the proportion of AlO(OH) from increasing, making it possible to produce an aluminum substrate for current collector having the above-mentioned hydroxide proportion in the surface layer within the specified range.

[0078] In the anodizing treatment, a direct current or an alternating current may be applied between the aluminum substrate and the counter electrode. When a direct current is applied to the aluminum substrate, the current density is 0.5 to 60 A / dm 2 It is preferable that the current is 1 to 40 A / dm 2 When the anodizing treatment is carried out continuously, it is preferable to carry out the treatment by a liquid power supply system in which power is supplied to the aluminum substrate via an electrolytic solution.

[0079] [Through hole formation process] The through-hole forming step is a step of forming through-holes in the aluminum base material. There are no particular limitations on the method for forming the through holes in the through hole forming step, and mechanical methods such as punching or electrochemical methods such as electrolytic dissolution can be used. The method for forming through holes by electrolytic dissolution is preferred because it allows for easy formation of through holes with an average opening diameter of 0.1 μm or more and less than 100 μm. Furthermore, the formation of the through holes by electrolytic dissolution treatment can be carried out simultaneously with or successively to the anodizing treatment in the film formation step.

[0080] The electrolytic dissolution treatment is not particularly limited, and for example, the method described in paragraphs

[0025] to

[0032] of Japanese Patent No. 6199416 can be used.

[0081] [Surface roughening process] The surface roughening step is a step in which the aluminum base is subjected to electrochemical surface roughening treatment (hereinafter also abbreviated as "electrolytic surface roughening treatment") to roughen the front and / or back surfaces of the aluminum base. Roughening the surface of the aluminum base material through electrolytic graining improves adhesion to the layer containing the active material, and the increased surface area also increases the contact area, resulting in a higher capacity retention rate after long-term use of an electricity storage device that uses an aluminum base material for a current collector. For the electrolytic graining treatment, for example, the conditions and apparatus described in paragraphs

[0041] to

[0050] of JP-A-2012-216513 can be appropriately adopted.

[0082] [Chemical Etching Process] The chemical etching process is a process for removing the anodic oxide film and natural oxide film (hereinafter collectively referred to as oxide film) formed on the surface of the aluminum base material. In the chemical etching process, the oxide film is removed by chemical dissolution treatment using an alkaline aqueous solution.

[0083] Chemical etching is a process in which an oxide film is removed by contacting the oxide film with an alkaline aqueous solution. When the alkaline aqueous solution is brought into contact with the oxide film, the alkaline aqueous solution penetrates the oxide film and dissolves the aluminum metal, allowing the oxide film to be peeled off. The oxide film itself can also be dissolved, resulting in the removal of the oxide film.

[0084] The anodized film has many fine irregularities formed on the bottom surface facing the aluminum substrate, so that the surface of the aluminum substrate from which the anodized film has been removed has many fine irregularities, as shown in Figure 6.

[0085] Furthermore, the chemical etching treatment and the subsequent water washing treatment cause aluminum hydroxide to precipitate on the surface layer 4 of the aluminum base material 1 (see FIG. 4).

[0086] Examples of alkalis used in alkaline aqueous solutions include caustic alkalis and alkali metal salts. Specific examples of caustic alkalis include sodium hydroxide (caustic soda) and caustic potassium. Examples of alkali metal salts include alkali metal silicates such as sodium metasilicate, sodium silicate, potassium metasilicate, and potassium silicate; alkali metal carbonates such as sodium carbonate and potassium carbonate; alkali metal aluminates such as sodium aluminate and potassium aluminate; alkali metal aldonic acid salts such as sodium gluconate and potassium gluconate; and alkali metal hydrogen phosphates such as sodium diphosphate, potassium diphosphate, sodium triphosphate, and potassium triphosphate. Among these, caustic alkali solutions and solutions containing both caustic alkali and alkali metal aluminates are preferred because of their fast etching rate and low cost. In particular, aqueous solutions of sodium hydroxide containing aluminum ions are preferred.

[0087] In the production method of the present invention, by adjusting the concentration (aluminum ion concentration), temperature, and treatment time of the alkaline aqueous solution, when the peak area ratios of metallic Al, Al2O3, Al(OH)3, and AlO(OH), which are present within the surface layer of 10 nm, are designated as A, B, C, and D, respectively, it is possible to achieve a configuration in which (C+D) / (A+B+C+D) is 0.5 or more and 1 or less, and C / D is 0.1 or more and 2 or less.

[0088] The concentration of the alkaline aqueous solution is preferably 0.1 to 50% by mass, more preferably 0.2 to 10% by mass. When aluminum ions are dissolved in the alkaline aqueous solution, the concentration of the aluminum ions is preferably 0.01 to 10% by mass, more preferably 0.1 to 3% by mass. The temperature of the alkaline solution is less than 50°C, preferably 25 to 45°C, more preferably 30 to 40°C. The treatment time is 10 seconds or less, preferably 1 to 8 seconds, more preferably 3 to 6 seconds.

[0089] Examples of methods for bringing the oxide film into contact with the alkaline solution include a method of passing the aluminum substrate having the oxide film through a tank containing the alkaline solution, a method of immersing the aluminum substrate having the oxide film in a tank containing the alkaline solution, and a method of spraying the alkaline solution onto the surface of the oxide film.

[0090] (Water washing process) It is preferable to carry out a water washing step after the chemical etching treatment, which returns the pH of the surface to neutral and allows the formation of a hydroxide layer on the surface.

[0091] For washing, pure water, well water, tap water, etc. may be used. A nip device, an air knife, etc. may be used to prevent the treatment liquid from being carried over to the next step.

[0092] (pickling process) It is preferable to carry out an acid washing step after the chemical etching step and the water washing step. The pickling step is a step of removing residues 5 (see FIG. 4) that are generated on the surface as a result of the chemical etching step by washing with an acidic solution.

[0093] Nitric acid, sulfuric acid, etc. can be used for pickling, with nitric acid being preferred. An air knife, nip device, etc. may be used to prevent the treatment solution from being carried over to the next process. Pickling with nitric acid is particularly preferred because it is easy to passivate the natural oxide film formed after pickling.

[0094] After the pickling step, it is preferable to carry out a water washing step similar to that described above.

[0095] (drying process) A drying step may be performed after each water washing step. The drying method is not limited, and known drying methods such as a method of blowing off moisture with an air knife or a method of heating may be used as appropriate. A combination of multiple drying methods may also be used.

[0096] Ordinary aluminum substrates are rolled to a specified thickness. When a natural oxide film is formed on the aluminum during the rolling process, lubricants such as rolling oil used during the rolling process may remain on the surface. For this reason, it can be difficult to control hydroxides within the surface layer of 10 nm using rolled aluminum substrates as they are.

[0097] Therefore, the present inventors have invented a method for controlling the hydroxide content of the surface layer after removing the natural oxide film and rolling oil formed during rolling. Dissolving the surface with an alkaline or acidic solution is known as a simple method for removing the surface layer of aluminum. Alkaline solutions are particularly effective in production due to their excellent dissolution efficiency. However, it has been difficult to consistently remove the outermost surface of aluminum using an alkaline solution. This is due to the presence of remnants of the natural oxide film and rolling oil remaining on the outermost surface during rolling. While the surface remnants can be completely removed by using an alkaline solution for a sufficient amount of time, the present inventors discovered that in this case, a large amount of AlO(OH) is formed on the surface as a by-product, which adversely affects resistance.

[0098] Therefore, the inventors considered using an electrochemical method to remove the natural oxide film and remaining rolling oil from the outermost surface formed during rolling. First, an anodic oxide film (anodic oxide film) is formed by causing an anodic reaction on aluminum in an acidic solution containing oxoacid. Because the anodic oxide film is formed by converting the aluminum itself into an oxide film from the surface to the interior, the new oxide film is formed deeper than the original natural oxide film and remaining rolling oil that were present on the outermost surface. The anodic oxide film is then removed, removing the original natural oxide film and exposing the pure aluminum inside the aluminum substrate from beneath the newly formed anodic oxide film. A very thin natural oxide film forms on the exposed aluminum surface. During the anodic oxide film removal process, very light washing with an alkaline solution suppresses the formation of AlO(OH) on the surface, resulting in the formation of Al(OH)3. Since Al(OH)3 is formed particularly in the outermost layer, it can reduce the interface resistance even when AlO(OH) is present.

[0099] According to previous findings (e.g., WO18 / 220991), both AlO(OH) and Al(OH)3 are used as insulating particles to provide insulation. However, the inventors have discovered that the Al(OH)3 obtained by the above process is less likely to deteriorate resistance. While the reason for this is not yet clear, it is presumed that most of the hydroxides formed on the surface during the above process do not exist as particles, but rather exist as a film on the very surface.

[0100] As a by-product of the process described above, the tiny protrusions formed at the leading edge of the anodic oxide film as it grows are left as tiny depressions on the aluminum surface. These depressions, several tens of nanometers in diameter, were found to form over almost the entire surface of the aluminum. These minute irregularities improve adhesion when electrode materials are applied. Using an atomic force microscope, these minute irregularities can be quantified as surface roughness, reflecting the irregularities.

[0101] In terms of efficiency and precision, a thinner anodized film is desirable. Regarding efficiency, a thicker anodized film increases the load on the subsequent removal process. Regarding precision, a thinner anodized film can make it difficult to consistently expose the pristine aluminum surface beneath the natural oxide film or to obtain the finely textured surface of the anodized film. Conversely, a thicker anodized film requires a longer chemical etching time in an alkaline solution. In this process, areas where the film dissolves quickly will further dissolve the aluminum metal, resulting in a higher proportion of AlO(OH) in the surface hydroxides formed after rinsing, making these areas unfavorable for achieving low resistance.

[0102] The amount of aluminum dissolved in the chemical etching process is 0.5 g / m 2 Less than 0.3 g / m is preferred 2 The following is more preferred:

[0103] By analyzing the outermost surface of the aluminum substrate 1 using XPS, the peak area ratios of metallic Al, aluminum oxide Al2O3, and Al hydroxide present within the surface layer of 10 nm can be determined (see Figure 7). Two types of Al hydroxide can be detected using this method: Al(OH)3 and AlO(OH). Furthermore, by reducing the XPS photoelectron take-off angle, information on the surface layer can be obtained. For example, by measuring at a photoelectron take-off angle of 45 degrees, information on the surface layer of the inner 10 nm can be obtained, and by setting the photoelectron take-off angle to 20 degrees, information on the surface layer of the inner 5 nm can be obtained.

[0104] FIG. 8 shows a schematic diagram of an example of a manufacturing apparatus for carrying out such a manufacturing method. 8 is a manufacturing apparatus that produces an aluminum base for a current collector by feeding the aluminum base 1 from a base roll 70 formed by winding a long aluminum base 1, and carrying out each step while transporting the aluminum base 1 in the longitudinal direction. That is, the manufacturing apparatus 50 is a manufacturing apparatus that produces an aluminum base for a current collector by carrying out each step in a roll-to-roll (RtoR) manner.

[0105] The manufacturing apparatus 50 has a rotating shaft 52 on which a substrate roll 70 is loaded, a coating process section 56 for carrying out the coating process, a removal process section 58 for carrying out the removal process, and a take-up shaft 54 ​​for winding up the aluminum substrate 10 for current collectors, which has been subjected to each treatment, into a roll 72. The coating process section 56 and the removal process section 58 are disposed on the path along which the aluminum substrate 1 is transported from the rotating shaft 52 to the take-up shaft 54. It is desirable to place a dryer (not shown) between the removal process section 58 and the take-up shaft 54. The dryer may be a hot air type, a heater type, or the like.

[0106] In the manufacturing apparatus 50, the feeding of the aluminum substrate 1 from the substrate roll 70 and the winding of the current collector aluminum substrate 10 on the winding shaft 54 ​​are carried out in synchronization, and the long aluminum substrate 1 is transported in the longitudinal direction along a predetermined transport path while the aluminum substrate 1 is subjected to the above-mentioned respective treatments in each process section. The treatments carried out in each process section are as described above.

[0107] A through-hole forming process section for performing the through-hole forming process and / or a surface roughening process section for performing the surface roughening process may be provided upstream or downstream of the coating process section 56. Alternatively, the coating process section 56 may perform the through-hole forming process and / or the surface roughening process in addition to the coating process.

[0108] Furthermore, in the manufacturing apparatus 50, each step is performed in a roll-to-roll manner using a long aluminum base material 1, but this is not limiting, and each step may be performed using a sheet-like aluminum base material 1. Furthermore, each step may be performed in a different apparatus.

[0109] [Current collector] As described above, the aluminum substrate for a current collector of the present invention can be used as a current collector for an electricity storage device (hereinafter also referred to as a "current collector"). Because the current collector has the above-mentioned ratio of aluminum hydroxide, it is possible to achieve both improved adhesion with the electrode material and low resistance, which contributes to reducing internal resistance and also prevents partial peeling between the electrode material (active material) and the current collector even after many charge / discharge cycles over a long period of time.

[0110] <Electrode material (active material)> The active material is not particularly limited, and known active materials used in conventional electricity storage devices can be used. Specifically, when the aluminum substrate for current collector is used as a current collector for a positive electrode, the conductive material, binder, solvent, and the like that may be contained in the active material and the active material layer may be selected from the materials described in paragraphs

[0077] to

[0088] of JP 2012-216513 A, the contents of which are incorporated herein by reference. Furthermore, when the aluminum substrate for current collector is used as a current collector for a negative electrode, the active material may be any of the materials described in paragraph

[0089] of JP 2012-216513 A, the contents of which are incorporated herein by reference.

[0111] [Positive electrode] A positive electrode using the aluminum base for a current collector of the present invention as a current collector is a positive electrode having a positive electrode current collector using the aluminum base for a current collector and a layer containing a positive electrode active material (positive electrode active material layer) formed on the surface of the positive electrode current collector. Here, for the positive electrode active material, and the conductive material, binder, solvent, and the like that may be contained in the positive electrode active material layer, materials described in paragraphs

[0077] to

[0088] of JP 2012-216513 A can be appropriately adopted, the contents of which are incorporated herein by reference.

[0112] [Negative electrode] A negative electrode using the aluminum current collector base of the present invention as a current collector is a negative electrode having a negative electrode current collector using the aluminum current collector base and a layer containing a negative electrode active material formed on the surface of the negative electrode current collector. Here, as the negative electrode active material, the materials described in paragraph

[0089] of JP 2012-216513 A can be appropriately adopted, the contents of which are incorporated herein by reference.

[0113] [Energy storage devices] An electrode that utilizes the aluminum substrate for a current collector of the present invention as a current collector can be used as a positive electrode or a negative electrode for electricity storage devices such as lithium ion capacitors, electric double layer capacitors, semi-solid batteries, solid batteries, and secondary batteries that use non-aqueous electrolytes. Here, with regard to the specific configuration and application of the electricity storage device (particularly, the secondary battery), the materials and applications described in paragraphs

[0090] to

[0123] of JP 2012-216513 A can be appropriately adopted, and the contents thereof are incorporated herein by reference.

[0114] [Electric double layer capacitor] An electric double layer capacitor is a capacitor with a capacitor structure of opposing electrodes, with an electric double layer as the dielectric. The electric double layer spontaneously forms between a solid and a liquid, and upon charging, electrons or holes attract each other and align. Specific configurations of electric double layer capacitors are described, for example, in JP 2020-064971 A. The aluminum substrate for current collectors of the present invention can be used as a current collector for the positive electrode and / or negative electrode of an electric double layer capacitor.

[0115] [Lithium-ion capacitor] A lithium ion capacitor uses a positive electrode of an electric double layer capacitor as a positive electrode and a negative electrode of a lithium ion battery as a negative electrode, and the negative electrode is doped with lithium ions. Specific configurations of lithium ion capacitors are described, for example, in International Publication No. 2016 / 084704. The aluminum substrate for current collectors of the present invention can be used as a current collector for the positive electrode and / or negative electrode of a lithium ion capacitor.

[0116] [Solid battery] A solid-state battery is a battery in which a solid electrolyte is responsible for ion conduction between an anode and a cathode. A specific configuration of a solid-state battery is described, for example, in JP 2020-123538 A. The aluminum substrate for current collectors of the present invention can be used as a current collector for the positive electrode and / or negative electrode of a solid-state battery.

[0117] [Semi-solid battery] A semi-solid battery is a battery in which ion conduction between the anode and cathode is carried out by a semi-solid (gel-like, clay-like) electrolyte. The specific structure of a semi-solid battery is described in U.S. Patent No. 9,484,569, etc. The aluminum substrate for current collector of the present invention can be used as a current collector for the positive electrode and / or negative electrode of a semi-solid battery.

[0118] [Secondary battery using non-aqueous electrolyte] A non-aqueous electrolyte secondary battery is a secondary battery that uses a non-aqueous electrolyte between the anode and cathode. Examples include Li-ion batteries, Na-ion batteries, K-ion batteries, and multivalent ion batteries using Mg ions and Ca ions. Specific configurations of non-aqueous electrolyte secondary batteries are described in, for example, JP 2017-068978 A. The aluminum substrate for current collectors of the present invention can be used as current collectors for positive and / or negative electrodes of secondary batteries that use non-aqueous electrolytes. [Example]

[0119] The present invention will be described in more detail below with reference to examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the examples shown below.

[0120] [Preparation of aluminum substrate for current collector] Using an aluminum substrate of alloy number 1085 or 1N30 with a thickness of 20 μm, the following electrolytic treatment (film formation step) and removal treatment (removal step) were carried out to produce current collectors A to J, which are aluminum substrates for current collectors. Current collectors A to F correspond to examples of the present invention.

[0121] <Electrolytic Treatment α> An anodized film was formed on the surface of the aluminum substrate by electrolysis using an aqueous solution (liquid temperature 50°C) containing 20 g / L of nitric acid and 20 g / L of sulfuric acid, with the aluminum substrate as the anode. The electrolysis was carried out using a DC power source. The amount of current flowing during the electrolysis was changed as follows: The current flow rate for electrolytic treatment α1 is 5C / dm 2 The current flow rate for electrolytic treatment α2 is 10C / dm 2 The current flow rate for electrolytic treatment α3 is 100C / dm 2 The current flow rate for electrolytic treatment α4 is 135C / dm 2

[0122] <Removal process β> After electrolysis, the specimen was washed with water and then subjected to a removal treatment. The removal treatment consisted of a chemical etching treatment in which an alkaline aqueous solution (5% NaOH solution containing 0.3-0.5% Al ions) was sprayed onto the surface to remove the oxide film, followed by a water rinse, cleaning with nitric acid solution, and another water rinse. The chemical etching treatment conditions were changed as follows: Removal process β1: NaOH concentration 5%, Al ion concentration 0.5%, liquid temperature 35°C, treatment time 5 seconds Removal process β2: NaOH concentration 5%, Al ion concentration 0.5%, liquid temperature 35°C, treatment time 3 seconds Removal process β3: NaOH concentration 5%, Al ion concentration 0.3%, liquid temperature 37°C, treatment time 5 seconds Removal process β4: NaOH concentration 5%, Al ion concentration 0.3%, liquid temperature 37°C, treatment time 40 seconds

[0123] The treatment conditions for each aluminum substrate for current collector are shown in Table 1. Current collector G is an untreated aluminum substrate. That is, it is an aluminum substrate having a natural oxide film formed on its surface during rolling. Current collector J is an aluminum substrate having an undercoat layer formed by applying conductive carbon particles together with a binder to the surface of the untreated aluminum substrate and then drying it.

[0124] The intermetallic compounds in the aluminum substrate are 460 particles / mm 2 , 1N30 material is 7800 pieces / mm 2 It was.

[0125] [Table 1]

[0126] After preparing each aluminum substrate for the current collector, XPS was used to examine the peak area ratio of aluminum hydroxide present within a depth of 10 nm from the surface. This measurement was not performed on current collector J, as the entire surface of the aluminum substrate was coated with a conductive carbon material and binder in advance.

[0127] The measurement conditions by XPS are as follows. ·Equipment: Ulvac-PHI QuanteraSXM ·X-ray source: AlKα ray (1486.6ev, 25W, 15kv) ·Pass Energy=55ev, Step=0.05ev ·Measurement area: 300μm×300μm The obtained Al2P spectrum was subjected to peak shift correction based on the peak position of metallic Al, and then fitting was performed. Peak area ratio: After performing the above fitting, peaks were obtained, and the peak area ratios were calculated for four types of peaks: metallic Al, aluminum oxide Al2O3, aluminum hydroxide Al(OH)3, and boehmite AlO(OH). Photoelectron take-off angle: 45 degrees The results of XPS analysis performed at a photoelectron take-off angle of 45 degrees are shown in Table 2. Six current collectors A, B, C, D, E, and F, in which the peak area ratio of Al(OH)3 / AlO(OH) = C / D is 0.1 or more and 1 or less, are examples, and three current collectors G, H, and I are comparative examples.

[0128] [Table 2]

[0129] Similarly, the results of XPS analysis performed at a photoelectron take-off angle of 20 degrees are shown in Table 3. These are the peak area ratios of aluminum hydroxide present within a depth of 5 nm from the surface layer.

[0130] [Table 3]

[0131] Current collector G is an untreated aluminum substrate, and therefore Al2O3 formed immediately after rolling was detected, but hydroxide was not detected.

[0132] [Examples 1 to 6, Comparative Examples 1 to 4] The produced aluminum substrates for current collectors (current collectors A to J) were designated as Examples 1 to 6 and Comparative Examples 1 to 4, respectively, and were evaluated for adhesion and resistance.

[0133] <Resistance> A carbon material (Bunny Height T602 manufactured by Nippon Graphite) was applied to the aluminum base material for current collector as an electrode material layer to a dry coating thickness of 10 μm, and the aluminum base material for current collector on which the electrode material layer 106 was formed was sandwiched between a pressure-type conductive terminal and a pressure-type insulating terminal as shown in Figure 9, and the resistance was measured for one sample (N = 7) using a resistance measuring machine (HIOKI3541 manufactured by Hioki Corporation). The distance between the measuring terminals was fixed at 50 mm.

[0134] The initial resistance evaluation was performed after storing the sample in a dry box for at least 24 hours before the evaluation.

[0135] Next, a forced resistance evaluation over time was performed. Each aluminum substrate for current collector was stored in an environment with a temperature of 30°C and a humidity of 80%, and after two weeks, an electrode material layer was formed using the method described above, and then the resistance was evaluated. Similarly, after four weeks of storage in an environment with a temperature of 30°C and a humidity of 80%, an electrode material layer was formed using the method described above, and then the resistance was evaluated. The results are shown in Table 4.

[0136] [Table 4]

[0137] As shown in Table 4, Examples 1 to 6 of the present invention are superior to Comparative Examples 1 and 2 in that they have small resistance values ​​both from the initial stage to after storage at high humidity. Furthermore, Example 6 uses an aluminum substrate containing a large amount of intermetallic compounds, and therefore shows less deterioration in resistance after storage at high humidity compared to the other Examples, demonstrating its superiority. Comparative Example 3 has a poor initial resistance compared to the Examples, but because it uses an aluminum base material containing a large amount of intermetallic compounds, the extent of deterioration in resistance after storage at high humidity is better than the other comparative examples. In Comparative Example 4, the substrate was coated with conductive carbon, and the initial resistance and resistance after 2 weeks of storage at high humidity were excellent, just like in the Examples, but the resistance value increased after 4 weeks of storage at high humidity. The reason for this is unclear, but it is presumed that the resistance deteriorated due to changes such as bleeding of the binder used to fix the primer.

[0138] Next, the surface shape of each aluminum substrate for current collector was observed. Fig. 10 is a surface SEM image of Example 3, and Figs. 11 and 12 are surface SEM images of Comparative Examples 1 and 2, respectively. Fig. 10 shows that a fine uneven structure on the order of several tens of nanometers is formed on the surface of the aluminum current collector base of Example 3. On the other hand, it is clear that such a structure is not formed on the aluminum current collector bases of Comparative Examples 1 and 2.

[0139] For the aluminum substrates for current collectors (current collectors A to I) of each example and comparative example, physical properties representing the surface shape were determined using an atomic force microscope (AFM). The surface shape of a 1 μm square was measured, and the surface physical properties were determined from the obtained three-dimensional data. The results are shown in Table 5.

[0140] The measurement conditions using the atomic force microscope are as follows. ·Measurement area: 1μm×1μm Equipment: Hitachi High-Tech Science AFM5100N SPM (used in tapping mode) Cantilever: Olympus OMCL-AC200TS-R3 Resolution: 256 x 256 pixels

[0141] The following two physical properties were determined from the obtained three-dimensional data. Average surface roughness: JPEG0007777577000005.jpg1275 (Zc is the Z coordinate of the center plane (height direction)) Maximum height difference: PV (nm): Maximum value - minimum value of Z coordinate within the measurement surface In addition, as physical property values ​​focusing particularly on irregularities with short pitches, the surface roughness Ra and maximum height difference PV were also determined by using the 3D data obtained using the above method and performing FFT processing to remove irregularities with a period exceeding 0.2 μm. The results are also shown in Table 5. In Table 5, the surface roughness Ra and maximum height difference PV obtained by performing FFT processing and removing irregularities with a period exceeding 0.2 μm are indicated as "with FFT processing."

[0142] [Table 5]

[0143] Current collectors A to F of Examples 1 to 6 have fine irregularities on their surfaces. Therefore, when measured using an atomic force microscope under the above-described measurement conditions, the average surface roughness reflecting the irregularities was measured. Current collector G of Comparative Example 1 is an aluminum foil that has not been subjected to surface treatment, and therefore has a small Ra value. Current collector H of Comparative Example 2 has an anodized film partially remaining on its surface, resulting in only partial minor irregularities, and therefore a small Ra value. However, due to differences in the presence or absence of the anodized film depending on the location, the maximum height difference (PV) value was relatively large. Current collector I of Comparative Example 3 was dissolved in a large amount by the alkaline solution, resulting in no minor irregularities remaining, and therefore a small Ra value. However, as shown in FIG. 12, the surface has a waviness component, resulting in a relatively large maximum height difference (PV) value. The data subjected to FFT processing clearly shows a clear difference in PV between the Examples and Comparative Examples.

[0144] <Adhesion> The aluminum substrates for current collectors of the Examples and Comparative Examples were evaluated in two ways to evaluate the adhesive strength.

[0145] <<Adhesion Evaluation 1>> A peel test adhesive tape (25 mm wide tape "PS1" manufactured by JTS Corporation) 158 was directly attached to the surface of each of the aluminum current collector substrates in Examples 1 to 6 and Comparative Examples 1 to 3. Each aluminum current collector substrate S was fixed with its surface facing up on an attachment stand 154 on a slide table 152 for a 90-degree peel test using double-sided tape 156, and the load required to peel the attached adhesive tape 158 was measured. The peel strength was evaluated using a peel tester 162 manufactured by Imada Corporation, as the maximum force (N / 25 mm) during peeling. A schematic diagram of the peel test evaluation device is shown in FIG. 13.

[0146] <<Adhesion Strength Evaluation 2>> An electrode material made by kneading 95% activated carbon, 4% water, and 0.5% CMC was applied to the surface of each of the aluminum current collector substrates of Examples 1 to 6 and Comparative Examples 1 to 3 to a thickness of approximately 15 μm. After the electrode material dried, the aluminum current collector substrate was cut to 100 mm × 20 mm and wrapped around a stainless steel round bar with a diameter of 20 mm so that the electrode material was on the outside. The aluminum current collector substrate was then unwound, and the state of peeling between the electrode material and the aluminum current collector substrate was visually observed and evaluated according to the following criteria. A: No peeling occurred at the interface between the electrode material and the aluminum substrate for the current collector. B: Peeling occurred in 1 or 2 places C: Peeling occurred in three or more places The results are shown in Table 6.

[0147] [Table 6]

[0148] Table 6 shows that the Examples of the present invention have higher adhesion than the Comparative Examples, and are less likely to peel after application of the electrode material. In the Examples, it is believed that the microstructure of the surface is effective in improving adhesion.

[0149] From the above results, it can be seen that the examples of the present invention can achieve both higher adhesion and lower resistance compared to the comparative examples. From the above, the effects of the present invention are clear. [Explanation of symbols]

[0150] 1. Aluminum substrate 2 Natural oxide film 3 Anodized coating 4. Surface layer where aluminum hydroxide precipitates 5 Residue 50 Manufacturing equipment 52 Rotation axis 54 Winding shaft 58 Removal process section 70 substrate roll 72 rolls 74 Chemical Etching Process Department 76 Washing process department 78 Pickling process department 80 Washing process department 100 Resistance Measuring Instrument 102 Pressure-type conductive terminal 104 Pressure-type insulated terminal 106 Active material layer 150 slide rail 152 Sliding Table 154 Sticking stand 156 double-sided tape 158 adhesive tape 160 Clamp 162 Digital Force Gauge 164 Tensioning Device S Evaluation sample

Claims

1. When measured by X-ray photoelectron spectroscopy, the metal Al and Al present within the surface layer of 10 nm ２ O ３ , Al(OH) ３ and AlO(OH) are designated as A, B, C, and D, respectively, and the surface has such a ratio (C+D) / (A+B+C+D) of 0.5 or more and 1 or less, and C / D of 0.1 or more and 2 or less, An aluminum substrate for a current collector, having a surface roughness Ra of 10 nm or more and 50 nm or less.

2. 2. The aluminum substrate for a current collector according to claim 1, wherein the maximum difference in height P-V of the surface is 100 nm or more and 500 nm or less.

3. 3. The aluminum substrate for a current collector according to claim 1, wherein the surface has a granular intermetallic compound.

4. The number density of the granular metal compound is 500 pieces / mm ２ The aluminum substrate for a current collector according to claim 3 , wherein the aluminum substrate is one of the above.

5. The aluminum base for a current collector according to any one of claims 1 to 4, which has a thickness of 5 µm to 100 µm.

6. A capacitor comprising the aluminum substrate for a current collector according to any one of claims 1 to 5.

7. A secondary battery comprising the aluminum substrate for a current collector according to any one of claims 1 to 5.

8. A method for producing an aluminum substrate for a current collector according to any one of claims 1 to 5, wherein the amount of current flow during anodic electrolysis is 10 to 100 C / dm ２ a film forming step of forming an anodized film on the surface of the aluminum foil, and a removal step of removing the anodized film, In the film forming step, an anodizing treatment is performed using an aqueous solution containing nitric acid and sulfuric acid, the removing step includes a chemical etching step using an alkaline solution, a water washing step, a cleaning step using an acidic solution, and a water washing step in this order; A method for producing an aluminum substrate for a current collector, wherein the chemical etching step comprises a step of contacting the anodized film with an alkaline solution at 25°C or higher and lower than 50°C for 1 to 10 seconds.

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