JP7526800B2 - Aluminum member for current collector, and lithium ion capacitor, electric double layer capacitor, semi-solid battery, solid battery, and secondary battery using non-aqueous electrolyte - Google Patents

Description

The present invention relates to an aluminum collector member, and a lithium ion capacitor, an electric double layer capacitor, a semi-solid battery, a solid battery, and a secondary battery using a non-aqueous electrolyte, each of which has the aluminum collector member.

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

It is known that an aluminum plate 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 the surface of this aluminum plate current collector can be coated with an active material, activated carbon, or the like as an electrode material and used as a positive or negative electrode.

For example, Patent Document 1 describes a method for manufacturing an aluminum plate having an aluminum base material with a plurality of through holes in the thickness direction, the method comprising an oxide film formation process in which an oxide film is formed by subjecting the surface of an aluminum base material having a thickness of 5 to 1000 μm to an oxide film formation treatment, and a through hole formation process in which, after the oxide film formation process, an electrochemical dissolution process is performed to form through holes.

Patent Document 2 describes an aluminum plate having a plurality of through holes penetrating in the thickness direction,
An aluminum plate is described in which the average opening diameter of the through holes is 1 μm to 100 μm, the density of the through holes is 50 pcs/mm ² to 2000 pcs/mm ² , and the distance between adjacent through holes is 300 μm or less.

Patent Document 3 describes an aluminum foil for a current collector film of a lithium ion secondary battery, on whose surface pits having an average pit diameter of 0.05 to 0.10 μm are formed at an average density of 100 to 500 pits/ ^μm2 .

Patent document 4 describes an aluminum foil for use as a current collector in lithium-ion batteries, on whose surface a barrier-type anodized film having a thickness of 5 to 1,000 nm is formed.

International Publication No. 2015/115531 International Publication No. 2016/051976 JP 2000-113892 A JP 2007-250376 A

It is desirable for the current collector to have high adhesion to the electrode material and low contact resistance with the electrode material. Patent documents 1 to 3 describe roughening the surface of an aluminum plate to improve adhesion to the electrode material. However, it has been difficult to achieve both sufficient adhesion and reduced contact resistance. Furthermore, the effect is not sufficient relative to the cost of the roughening treatment, and it has rarely been put to practical use.

Patent Document 4 also describes that the adhesion is improved by forming an anodized film having fine pores on the surface of the aluminum foil. However, since the anodized film has poor electrical conductivity, there is a problem that the presence of an anodized film on the surface increases the contact resistance with the electrode material.

Therefore, the present invention aims to provide an aluminum member for a current collector that has high adhesion to an electrode material and low contact resistance with the electrode material, as well as a lithium ion capacitor, an electric double layer capacitor, a semi-solid battery, a solid battery, and a secondary battery that uses a non-aqueous electrolyte.

The present invention solves the problem by the following configuration.

[1] An aluminum member for a current collector having an aluminum substrate and an anodized coating film on the aluminum substrate,
The anodized film has many micropores.
The coverage of the anodized film on at least one surface of the aluminum base material is 1 to 80%;
An aluminum member for a current collector, wherein the anodized film has a number density of micropores of 600 pores/ ^μm2 or more.
[2] The aluminum member for a current collector according to [1], wherein the anodized film is present in an island shape on the aluminum base material.
[3] The aluminum member for a current collector according to [1] or [2], wherein the average diameter of the micropores is 1 nm to 100 nm.
[4] The aluminum member for a current collector according to any one of [1] to [3], wherein the anodized coating has a thickness of 1 nm to 30 nm.
[5] The aluminum member for a current collector according to any one of [1] to [4], wherein the aluminum base has a granular intermetallic compound on a surface thereof.
[6] The aluminum member for a current collector according to [5], wherein the surface of the aluminum base has 500 granular intermetallic compounds/ ^mm2 or more.
[7] The aluminum member for a current collector according to any one of [1] to [6], wherein the aluminum base has a thickness of 5 μm to 100 μm.
[8] The aluminum member for a current collector according to any one of [1] to [7], which is in a plate shape.
[9] A lithium ion capacitor having the aluminum member for a current collector according to any one of [1] to [8].
[10] An electric double layer capacitor comprising the aluminum member for a current collector according to any one of [1] to [8].
[11] A semi-solid battery comprising the aluminum member for a current collector according to any one of [1] to [8].
[12] A solid-state battery comprising the aluminum member for a current collector according to any one of [1] to [8].
[13] A secondary battery using a non-aqueous electrolyte, comprising the aluminum member for a current collector according to any one of [1] to [8].

According to the present invention, it is possible to provide an aluminum member for a current collector that has high adhesion to an electrode material and low contact resistance with the electrode material, as well as a lithium ion capacitor, an electric double layer capacitor, a semi-solid battery, a solid battery, and a secondary battery that uses a non-aqueous electrolyte.

FIG. 1 is a cross-sectional view that illustrates an example of an aluminum member for a current collector of the present invention. FIG. 2 is a top view of the aluminum member for a current collector shown in FIG. 1 . FIG. 2 is a cross-sectional view that illustrates a schematic diagram of another example of the aluminum member for a current collector of the present invention. FIG. 1 is a schematic cross-sectional view illustrating an example of a preferred method for producing an aluminum member for a current collector of the present invention. FIG. 1 is a schematic cross-sectional view illustrating an example of a preferred method for producing an aluminum member for a current collector of the present invention. FIG. 1 is a schematic cross-sectional view illustrating an example of a preferred method for producing an aluminum member for a current collector of the present invention. FIG. 2 is a schematic cross-sectional view illustrating another example of a preferred method for producing an aluminum member for a current collector of the present invention. FIG. 2 is a schematic cross-sectional view illustrating another example of a preferred method for producing an aluminum member for a current collector of the present invention. FIG. 1 is a conceptual diagram for illustrating an example of a production apparatus for carrying out a preferred production method for an aluminum member for a current collector of the present invention. 1 is a SEM image of an aluminum member for a current collector in an example. FIG. 2 is a partially enlarged SEM image of an aluminum member for a current collector in an example. FIG. 2 is a partially enlarged SEM image of an aluminum member for a current collector of a comparative example. FIG. 2 is a diagram showing a schematic diagram of a measuring device for measuring peel strength. FIG. 1 is a schematic diagram showing an apparatus for measuring resistance.

The present invention will be described in detail below.
The following description of the components may be based on representative 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.

[Aluminum member for current collector]
The aluminum member for a current collector of the present invention is
An aluminum member for a current collector having an aluminum substrate and an anodized film on the aluminum substrate,
The anodized film has many micropores.
The coverage of the anodized film on at least one surface of the aluminum base material is 1 to 80%;
The aluminum member for a current collector has an anodized film having a number density of micropores of 600 pores/μm ² or more.

The configuration of the aluminum member for the current collector of the present invention is explained using Figures 1 and 2.

Fig. 1 is a schematic cross-sectional view showing one example of a preferred embodiment of the aluminum current collector member of the present invention. Fig. 2 is a top view of the aluminum current collector member shown in Fig. 1. Fig. 2 is a diagram showing the contours of the aluminum base material and the anodized film in an image obtained by observing the surface of the aluminum current collector member in the examples described later with a scanning electron microscope (SEM).
1 and 2, in the aluminum member 10 for a current collector, anodized films (hereinafter also referred to as island-shaped anodized films) 14 are formed in an island shape on each of the two main surfaces of the aluminum base 1. The main surfaces refer to the largest surfaces of a plate-shaped (sheet-shaped) member.

The island-shaped anodic oxide film 14 is an aluminum oxide film that is formed by anodizing and contains aluminum oxide such as aluminum oxide (Al ₂ O ₃ ).

In the present invention, the island-shaped anodic oxide film 14 has a large number of micropores, as shown in the SEM (scanning electron microscope) image of the embodiment shown in FIG. 11 described later. The number density of the micropores is 600/μm ² or more. The anodic oxide film 14 is present in an island shape on the aluminum base 1. Here, the presence in an island shape does not mean a uniform layer, but an amorphous structure divided into countless parts as shown in FIG. 2. When the coverage rate of the anodic oxide film is high, the part without the anodic oxide film has an amorphous structure divided into countless parts. The coverage rate of the island-shaped anodic oxide film 14 on the surface of the aluminum base 1 is 1 to 80%.

The aluminum member 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.

As described above, it is desirable for the current collector to have high adhesion to the electrode material and low contact resistance with the electrode material. However, even if the surface of the aluminum base material is roughened in order to improve adhesion with the electrode material, a sufficient adhesion effect cannot be obtained, and it has not been possible to achieve both adhesion and low resistance at the same time.
It has also been proposed to improve adhesion by forming an anodized film having fine pores on the surface of an aluminum base material. However, since anodized films have poor electrical conductivity, having an anodized film on the surface increases the contact resistance with the electrode material, making it impossible to achieve both adhesion and low resistance.

In contrast, the aluminum member for current collector of the present invention has an anodized film 14 in an island shape on the aluminum substrate 1. In the portion of the aluminum substrate 1 covered with the anodized film 14 having micropores with a number density of 600 pores/ ^μm2 or more, adhesion to the electrode material can be improved. On the other hand, in the portion of the aluminum substrate 1 not covered with the anodized film 14, contact resistance with the electrode material can be reduced. By setting the coverage rate of the island-shaped anodized film 14 on the surface of the aluminum substrate 1 to 80%, it is possible to achieve both adhesion to the electrode material and low resistance.

Here, from the viewpoint of achieving both adhesion to the electrode material and low resistance, the coverage rate of the island-shaped anodized film 14 on the surface of the aluminum base material 1 is preferably 1 to 65%, more preferably 3 to 50%, and even more preferably 3 to 30%.

The coverage of the island-like anodic oxide film 14 on the surface of the aluminum base 1 is measured as follows.
The surface of the aluminum member for current collector is photographed at 10,000 times magnification using an SEM, and the anodized film portion and the aluminum base material portion are binarized using image analysis software to determine the area ratio of the anodized film. A general image analysis software such as ImageJ or Image Factory can be used. Figure 2, which will be described later, is an SEM photograph of the aluminum member for current collector prepared in the examples, and Figure 2 is a contour diagram obtained using ImageJ.

In addition, when the aluminum member for the current collector has through holes, the coverage rate is the area ratio of the anodized film on the surface of the aluminum base material excluding the through holes.

From the viewpoint of adhesion to the electrode material, the number density of the micropores in the anodized film 14 is preferably 600 to 1100 pores/μm ² , more preferably 800 to 1100 pores/μm ² , and even more preferably 900 to 1100 pores/μm ² .

In addition, from the viewpoint of adhesion to the electrode material, the average diameter of the micropores in the anodized film 14 is preferably 1 nm to 100 nm, more preferably 10 nm to 30 nm, and even more preferably 20 nm to 30 nm.

The number density and average diameter of the micropores in the anodic oxide film 14 are measured as follows.
The presence or absence of micropores can be determined by photographing the surface of the aluminum member for current collector at 50,000 times magnification using an SEM. If micropores are present, the number of micropores within the area of the anodized film can be measured using image analysis software to determine the number per unit area of the anodized film, i.e., the number of micropores per ¹ μm2 of the area of the anodized film. The average diameter can be determined by measuring and averaging the diameters of the micropores present within the area of the anodized film.

In addition, from the viewpoint of reducing contact resistance with the electrode material, the thickness of the anodized film 14 is preferably 1 nm to 30 nm, more preferably 5 nm to 30 nm, and even more preferably 10 nm to 30 nm.

The thickness of the anodic oxide film 14 is measured as follows.
Using a sample stage that can be used to mount an observation sample at a 75 degree incline with an SEM, the thickness of the anodized film can be determined from the boundary between the anodized film and the aluminum base material in a photograph taken at 50,000 times the surface of the aluminum member for the current collector.

Here, in the example shown in Figure 1, the anodized coating 14 is configured to be formed on both main surfaces of the aluminum base material 1, but this is not limited to this and it may be configured to be formed on only one of the main surfaces.

In the aluminum member for current collector of the present invention, the portion of the aluminum base material that is not covered with the anodized film may be covered with a natural oxide film. The natural oxide film has a lower contact resistance with the electrode material than the anodized film. Therefore, even if the portion of the aluminum base material that is not covered with the anodized film is covered with the natural oxide film, it is possible to achieve both adhesion with the electrode material and low resistance.
Natural oxide films do not generally have many micropores, so whether a film is an anodic oxide film or a natural oxide film can be determined by observing the presence or absence of micropores using an SEM.

In addition, from the viewpoint of reducing the contact resistance with the electrode material, the thickness of the natural oxide film is preferably 10 nm or less, more preferably 1 nm to 5 nm, and even more preferably 1 nm to 3 nm.

The aluminum member for a current collector of the present invention may have through holes.
FIG. 3 is a cross-sectional view showing a schematic diagram of another example of the aluminum member for a current collector of the present invention.
The aluminum current-collector member 10b shown in FIG. 3 has an anodized film 14 present in an island shape formed on each of the two main surfaces of an aluminum base 3 having through-holes 5 thereon.

The through hole 5 is a through hole that penetrates the aluminum base material 3 and the anodized coating 14 in the thickness direction.

The aluminum member for the current collector has multiple through holes penetrating in the thickness direction, which facilitates the movement of lithium ions when used as a current collector. In addition, the presence of a large number of through holes improves adhesion to the active material.

The average opening diameter of the through holes is preferably 0.1 μm or more and less than 100 μm, more preferably more than 1 μm and 80 μm or less, even more preferably more than 3 μm and 40 μm or less, and particularly preferably 5 μm or more and 30 μm or less.
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 or the like to the aluminum collector member, and to improve the adhesion of the applied active material. Furthermore, even if the aluminum collector member has a large number of through holes, it is possible to ensure that the aluminum collector member has sufficient tensile strength.

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

The average opening ratio of the through holes is preferably 0.5% to 30%, more preferably 1% to 30%, further preferably 2% to 20%, and particularly preferably 3% to 10%.
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 collector member, improve adhesion to the applied active material, and even if the aluminum collector member has a large number of through holes, it is possible to ensure sufficient tensile strength.

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

The surface of the aluminum member for the current collector may be roughened. By providing a rough surface, the surface area of both the aluminum base material and the anodized coating increases, and the area in contact with the active material layer increases, further improving adhesion.

In the present invention, the aluminum base preferably has a large number of granular intermetallic compounds dispersed in a film on its surface. In the following description, the granular intermetallic compounds are also simply referred to as "intermetallic compounds."
Anodized films have higher insulating properties than aluminum substrates. Although natural oxide films have lower insulating properties than anodized films, they have higher resistance than aluminum metal alone. In the following description, anodized films and natural oxide films are collectively referred to as oxide films. In contrast, when an aluminum substrate has an intermetallic compound, the oxide film formed on its surface also contains the intermetallic compound. It has been found that intermetallic compounds are the starting point for reducing the insulating properties of the oxide film. By having an intermetallic compound that is the starting point for reducing the insulating properties, the insulating properties of the oxide film can be reduced, and the contact resistance of the oxide film can be reduced.

The intermetallic compound of the oxide film preferably has an element ratio of oxygen to aluminum, O/Al, of 2 to 4. The number density of the granular intermetallic compound is preferably 500 pieces/mm ² or more.

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, AlFeMnSi, _Mg2Si , and _TiB2 . Among these, the intermetallic compounds containing Al contain Al, so that an aluminum oxide film is formed on the surface. Therefore, the surface layer of the intermetallic compound containing Al contains oxygen element (O).

In the aluminum member for current collector of the present invention, so long as the oxide film on the surface of the intermetallic compound has granular intermetallic compounds having an oxide film with an element ratio O/Al of 2 or more and 4 or less at a density of 500 pieces/mm2 ^or more, the oxide film in the outermost layer may have granular intermetallic compounds with an element ratio O/Al other than 2 or more and 4 or less. In other words, the oxide film in the outermost layer may have granular intermetallic compounds with an element ratio O/Al of less than 2 or more than 4.

Furthermore, when the oxide film is mainly composed of aluminum oxide (Al ₂ O ₃ ) and does not contain hydrates, the element ratio O/Al in the portion of the oxide film other than the intermetallic compounds is less than 2, and is about 1.3 to 1.5.

From the viewpoint of lowering the electrical resistance of the aluminum component for the current collector, the average element ratio O/Al of the oxide film on the surface 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.

The element ratio O/Al in the outermost layer of the intermetallic compound is measured as follows.
When the surface of the oxide film is observed with a high-resolution scanning electron microscope (SEM), the intermetallic compounds can be visually recognized as being distinct from the other portions of the oxide film that are not intermetallic compounds.
First, the surface of the oxide film is photographed at a magnification of 5000 times using a high-resolution scanning electron microscope (SEM), and at least 20 intermetallic compounds are extracted from the obtained SEM photograph.
Next, elemental analysis is performed from the outermost surface to the depth direction at the position of the extracted intermetallic compound using field emission Auger electron spectroscopy (FE-AES). The analysis in the depth direction is performed by repeating measurement and surface removal by sputtering. The elemental ratio O/Al in the outermost surface layer is obtained from the elemental distribution in the depth direction by FE-AES.

From the viewpoint of lowering the electrical resistance of the aluminum member for current collector, the density of the granular intermetallic compound is preferably 1,000 pcs/mm ² to 300,000 pcs/mm ² , and more preferably 5,000 pcs/mm ² to 200,000 pcs/mm ² .

The density of the granular intermetallic compound is measured as follows.
First, the surface of the aluminum member for a current collector is photographed from directly above at a magnification of 5000 times using a high-resolution scanning electron microscope (SEM), and granular intermetallic compounds are extracted from a field of view (five locations) of 1.2 mm × 1.2 mm in the obtained SEM photograph.
Next, the element ratio O/Al of each intermetallic compound extracted by elemental analysis using FE-AES is determined. The number of granular intermetallic compounds having an element ratio O/Al of 2 to 4 is counted, and the number density is calculated from the number of granular intermetallic compounds in the visual field and the area of the visual field (geometric area), and the average value of the five visual fields is calculated as the density.

Here, it is preferable that the granular intermetallic compound has an equivalent circle diameter of 1 μm or less. Intermetallic compounds with an equivalent circle diameter of 1 μm or less are easily exposed on the surface of the aluminum member for the current collector. When small intermetallic compounds are exposed on the surface of the aluminum member for the current collector, the surface area relative to the volume of the intermetallic compound becomes large. As a result, it is believed 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.

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.

The outermost oxide film preferably contains aluminum oxide (Al ₂ O ₃ ) in an amount of 70% by mass or more, more preferably 80% to 100% by mass, and even more preferably 90% to 100% by mass.
By making the content of non-hydrated _aluminum oxide ( _Al2O3 ) in the oxide film 70 mass% or more, the density of the oxide film can be increased, and therefore the oxide film can be prevented from thickening over time, which is preferable in that the oxide film can be prevented from becoming thick and increasing the electrical resistance.

The proportion of aluminum oxide (Al ₂ O ₃ ) in the oxide film can be calculated by measuring the film density of the oxide film as follows.
The film density of the oxide film is measured using a high resolution RBS analyzer HRBS500 (High Resolution Rutherford Backscattering Spectrometry; HR-RBS) manufactured by Kobe Steel, Ltd. He+ ions with energy of 450 keV are incident on the sample at 62.5 degrees to the normal of the sample surface (surface of the oxide film of the aluminum electrode member), and the scattered He+ ions are detected at a scattering angle of 55 degrees by a deflection magnetic field type energy analyzer to obtain the surface density. The obtained surface density (atoms/ ^cm2 ) is converted to mass surface density (g/ ^cm2 ), and the density (g/ ^cm3 ) of the oxide film is calculated from this value and the film thickness measured by a transmission electron microscope (TEM).
Aluminum oxide films consist of non-hydrated aluminum oxide and hydrated aluminum oxide (there are monohydrate and trihydrate), each of which has a different density. For convenience, the density of the hydrate is taken as the average of the monohydrate and trihydrate, and the weighted average of this with the density of the non-hydrate is considered to be the density calculated above, from which the proportion of non-hydrated aluminum oxide is calculated.

There are no particular restrictions on the shape of the aluminum member for the current collector as long as it can be used as a current collector, but it is preferable for it to be plate-shaped.

<Aluminum substrate>
The aluminum base material that is the base material of the aluminum member for the current collector is not particularly limited, and may be, for example, a known aluminum base material such as alloy numbers 1N30, 3003, and 1085 described in JIS standard H4000. If aluminum containing a large amount of intermetallic compounds is used, the above-mentioned effect of reducing electrical resistance can be expected. However, the present application is not limited to aluminum materials. The aluminum base material is an alloy plate containing aluminum as the main component and trace amounts of other elements.

[Method of manufacturing aluminum member for current collector]
Next, the method for producing the aluminum member for current collector of the present invention will be described.
An example of a method for producing an aluminum member for a current collector of the present invention includes the following steps:
an electrolysis step of forming an anodized film on the surface of the aluminum base material;
a partial removal process of partially removing the anodized film to form the anodized film in an island shape;
The present invention relates to a method for producing an aluminum member for a current collector having the above structure.

The method for producing an aluminum member for a current collector may also include a through-hole forming step of forming through-holes that penetrate the aluminum base material and the anodized film.
The method for producing an aluminum member for a current collector may also include a surface roughening step of roughening the surface of the aluminum base.
The through-hole forming step and/or the surface roughening step may be carried out simultaneously with the electrolysis step of forming the anodized film.

After the partial removal process, it is preferable to carry out a cleaning and drying process in which the aluminum member for the current collector is cleaned and dried.

It is also preferable to have a washing process in which a washing treatment is performed and a drying process in which a drying treatment is performed after each process is completed.

Below, using the aluminum collector member shown in Figure 1 and the aluminum collector member having a through hole shown in Figure 3 as examples, each step of the manufacturing method for the aluminum collector member will be explained using Figures 4 to 8. After explaining each step of the manufacturing method for the aluminum collector member, each step will be described in detail.

4 to 6 are schematic cross-sectional views showing an example of a preferred embodiment of the method for producing the aluminum member for current collector shown in FIG.
As shown in FIGS. 4 to 6 , one example of a method for producing an aluminum member for a current collector is a production method including an electrolysis step ( FIGS. 4 and 5 ) in which both main surfaces of an aluminum base 1 are subjected to an electrolytic treatment to form a uniform anodic oxide film 2, and a partial removal step ( FIGS. 5 and 6 ) in which, after the electrolysis step, the anodic oxide film is partially removed to form island-like anodic oxide films 14.

4 and 5 and 7 and 8 are schematic cross-sectional views showing an example of a preferred embodiment of the method for producing the aluminum member for current collector shown in FIG.
As shown in FIGS. 4 to 5 and 7 to 8 , one example of a method for producing an aluminum member for a current collector is a production method including an electrolysis step ( FIGS. 4 and 5 ) of subjecting both main surfaces of an aluminum base 1 to electrolysis to form a uniform anodized film 2, a through hole formation step ( FIGS. 5 and 7 ) of forming through holes that penetrate the anodized film 2 and the aluminum base 1, and a partial removal step ( FIGS. 7 and 8 ) of partially removing the anodized film to form island-like anodized films 14.

[Electrolysis process]
The electrolysis process is a process for forming a uniform anodic oxide film on the surface of the aluminum base material.
In the present invention, in order to form an anodic oxide film having a number density of micropores of 600 pores/μm ² or more, it is preferable to carry out the anodizing treatment using an aqueous solution containing nitric acid and sulfuric acid.

The anodizing treatment method can be the same as the conventionally known anodizing treatment, except that an aqueous solution containing nitric acid and sulfuric acid is used. For the anodizing treatment, the conditions and apparatus described in paragraphs [0063] to [0073] of JP 2012-216513 A can be appropriately adopted.

In the present invention, the conditions for the anodizing treatment vary depending on the electrolyte used and cannot be determined in general, but generally, an electrolyte concentration of 0.2 to 80 mass %, a solution temperature of 5 to 70° C., a current density of 0.5 to 60 A/ ^dm2 , a voltage of 1 to 100 V, and an electrolysis time of 1 second to 20 minutes are appropriate, and are adjusted so as to obtain the desired amount of oxide film.

In addition, 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 preferably 0.5 to 60 A/ ^dm2 , and more preferably 1 to 40 A/ ^dm2 . When the anodizing treatment is performed continuously, it is preferable to use a liquid power supply system in which power is supplied to the aluminum substrate via an electrolytic solution.

[Through hole forming process]
The through hole forming step is a step of forming through holes in the aluminum base material.
The method for forming the through holes in the through hole forming step is not particularly limited, and a mechanical method such as punching or an electrochemical method such as electrolytic dissolution can be used. The method for forming the through holes by electrolytic dissolution is preferable because it can easily form through holes having 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 electrolysis step.

<Electrolytic dissolution treatment>
The electrolytic dissolution treatment is not particularly limited, and may use direct or alternating current and an acidic solution as the electrolyte. Among them, it is preferable to use an electrolyte mainly containing nitric acid, and it is more preferable to carry out the electrochemical treatment using at least one mixed acid selected from sulfuric acid, phosphoric acid, and oxalic acid in addition to these acids.

In the present invention, in addition to the above acids, the acidic solution serving as the electrolyte may be any of the electrolytes described in the specifications of U.S. Patent Nos. 4,671,859, 4,661,219, 4,618,405, 4,600,482, 4,566,960, 4,566,958, 4,566,959, 4,416,972, 4,374,710, 4,336,113, and 4,184,932.

The concentration of the acidic solution is preferably 0.1 to 2.5% by mass, and more preferably 0.2 to 2.0% by mass. The temperature of the acidic solution is preferably 20 to 80°C, and more preferably 30 to 60°C.

The aqueous solution mainly containing the above-mentioned acid can be used by adding at least one of a nitric acid compound having a nitrate ion, such as aluminum nitrate, sodium nitrate, or ammonium nitrate, a hydrochloric acid compound having a hydrochloric acid ion, such as aluminum chloride, sodium chloride, or ammonium chloride, or a sulfate compound having a sulfate ion, such as aluminum sulfate, sodium sulfate, or ammonium sulfate, in an amount ranging from 1 g/L to saturation to an aqueous solution of the acid having a concentration of 1 to 100 g/L.
The acid-based aqueous solution may also contain dissolved metals contained in aluminum alloys, such as iron, copper, manganese, nickel, titanium, magnesium, silica, etc. It is preferable to use a solution in which aluminum chloride, aluminum nitrate, aluminum sulfate, or the like has been added to an aqueous solution having an acid concentration of 0.1 to 2 mass % so that the aluminum ion concentration is 1 to 100 g/L.

DC current is mainly used for electrochemical dissolution treatment, but when AC current is used, the AC power wave is not particularly limited, and sine waves, square waves, trapezoidal waves, triangular waves, etc. can be used, of which square waves or trapezoidal waves are preferred, and trapezoidal waves are particularly preferred.

(Nitric acid electrolysis)
In the present invention, by electrochemical dissolution treatment using an electrolyte containing nitric acid as a main component (hereinafter also referred to as "nitric acid dissolution treatment"), it is possible to easily form through holes having an average opening diameter of 0.1 μm or more and less than 100 μm and an average opening ratio of 0.5% to 30%.
Here, the nitric acid dissolution treatment is preferably an electrolytic treatment using a direct current under conditions of an average current density of 1 A/ ^dm2 or more and an amount of electricity of 50 C/ ^dm2 or more, because this makes it easier to control the dissolution point for forming through holes. The average current density is preferably 100 A/ ^dm2 or less, and the amount of electricity is preferably 10,000 C/ ^dm2 or less.
In addition, the concentration and temperature of the electrolyte in nitric acid electrolysis are not particularly limited. Electrolysis can be performed at 30 to 60° C. using a nitric acid electrolyte having a high concentration, for example, a nitric acid concentration of 15 to 35% by mass, or at a high temperature, for example, 80° C. or higher, using a nitric acid electrolyte having a nitric acid concentration of 0.7 to 2% by mass.
Furthermore, electrolysis can be performed using an electrolyte obtained by mixing the above-mentioned nitric acid electrolyte with at least one of sulfuric acid, oxalic acid, and phosphoric acid at a concentration of 0.1 to 50 mass %.

[Surface roughening process]
The surface roughening step is a step of subjecting the aluminum base material to electrochemical surface roughening treatment (hereinafter also abbreviated as "electrolytic surface roughening treatment") to roughening the front and back surfaces of the aluminum base material.
By roughening the surface of the aluminum base material through electrolytic roughening treatment, adhesion to the layer containing the active material is improved, and the increased surface area also increases the contact area, thereby increasing the capacity retention rate of an electricity storage device using the aluminum current collector member.
For the electrolytic roughening treatment, for example, the conditions and apparatus described in paragraphs [0041] to [0050] of JP-A-2012-216513 can be appropriately adopted.

<Nitric acid electrolysis>
In the present invention, by electrochemical roughening treatment using an electrolytic solution mainly containing nitric acid (hereinafter also referred to as "nitric acid electrolysis"), recesses having an average opening diameter of 0.5 μm to 100 μm can be easily formed at an area ratio of 1% or more.
Here, since the nitric acid electrolysis enables the formation of uniform and dense recesses, it is preferable that the electrolysis is performed using an alternating current under conditions of a peak current density of 30 A/ ^dm2 or more, an average current density of 13 A/ ^dm2 or more, and an amount of electricity of 150 C/ ^dm2 or more. Note that the peak current density is preferably 100 A/ ^dm2 or less, the average current density is preferably 40 A/ ^dm2 or less, and the amount of electricity is preferably 400 C/ ^dm2 or less.
In addition, the concentration and temperature of the electrolyte in nitric acid electrolysis are not particularly limited. Electrolysis can be performed at 30 to 60° C. using a high-concentration nitric acid electrolyte having a nitric acid concentration of, for example, 15 to 35% by mass, or at a high temperature of, for example, 80° C. or higher using a nitric acid electrolyte having a nitric acid concentration of 0.7 to 2% by mass.

<Hydrochloric acid electrolysis>
In the present invention, even by electrochemical graining treatment using an electrolytic solution mainly containing hydrochloric acid (hereinafter also abbreviated as "hydrochloric acid electrolysis"), it is possible to form recesses having an average opening diameter of 0.05 μm to 100 μm at an area ratio of 1% or more.
Here, in the hydrochloric acid electrolysis, because uniform and dense recesses can be formed, it is preferable to use an alternating current, set the peak current density to 30 A/ ^dm2 or more, set the average current density to 13 A/ ^dm2 or more, and set the quantity of electricity to 30 C/ ^dm2 or more. The peak current density is preferably 100 A/ ^dm2 or less, the average current density is preferably 40 A/ ^dm2 or less, and the quantity of electricity is preferably 400 C/ ^dm2 or less.

[Partial Removal Process]
The partial removal step is a step in which the anodized film formed on the surface of the aluminum base material is partially removed to set the coverage rate of the anodized film to 1 to 80%.
The method for partially removing the anodized film is not particularly limited, but examples include a method for partially removing the anodized film by a chemical dissolution treatment using an alkaline aqueous solution (hereinafter also referred to as an "alkaline etching treatment"), and a method for partially removing the anodized film by passing an aluminum base material having an anodized film through a metal roll and then rubbing the surface with a brush roll (hereinafter also referred to as a "mechanical partial removal treatment").

<Alkaline Etching Treatment>
The alkaline etching treatment is a treatment in which the anodized film is brought into contact with an alkaline aqueous solution to partially remove the anodized film.
When an anodized film is brought into contact with an alkaline aqueous solution, the alkaline aqueous solution penetrates the anodized film and dissolves the aluminum metal, allowing the anodized film to be partially peeled off. The anodized film itself can also be dissolved. This results in the formation of island-shaped anodized film. The alkaline etching treatment can also enlarge the micropores in the anodized film.

Examples of the alkali used in the alkaline aqueous solution include caustic alkali and alkali metal salts. Specifically, examples of caustic alkali include sodium hydroxide (caustic soda) and caustic potassium. Examples of the alkali metal salt 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, solutions of caustic alkali and solutions containing both caustic alkali and alkali metal aluminates are preferred because of their fast etching rate and low cost. In particular, an aqueous solution of sodium hydroxide is preferred.

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 preferably 10 to 90°C. The treatment time is preferably 0.5 to 30 seconds.

Methods for bringing the anodized film into contact with an alkaline solution include, for example, passing the aluminum substrate having the anodized film through a tank containing an alkaline solution, immersing the aluminum substrate having the anodized film in a tank containing an alkaline solution, and spraying the alkaline solution onto the surface of the anodized film.

<Mechanical Partial Removal Treatment>
The mechanical partial removal process is a process for mechanically removing a portion of the anodized film.
An example of the mechanical partial removal treatment is a method in which pressure is applied to the anodized film to generate cracks in the anodized film, and then the anodized film is partially removed from the cracks as initiation points.

Methods for pressing the anodized film include passing the aluminum substrate having the anodized film between a pair of rolls. In this case, multiple pairs of rolls may be used. Metal rolls are preferred as the pair of rolls.

One method for partially removing a cracked anodized coating is to rub the surface with a rotating brush roll.

[Washing and drying process]
The cleaning and drying step is a step of cleaning and drying the surface of the aluminum base material from which the anodized film has been partially removed.
In the washing and drying process, it is preferable to wash the substrate in the order of water washing, acid washing, and water washing. After washing, a drying process is performed.

(Water washing process)
For washing, pure water, well water, tap water, etc. may be used. A nip device may be used to prevent the processing solution from being carried over to the next process.

(Pickling process)
Nitric acid, sulfuric acid, etc. can be used for pickling. A nip device may be used to prevent the treatment liquid from being carried over to the next process. Pickling with nitric acid or sulfuric acid is preferred because it is easy to passivate the natural oxide film formed after pickling.

(Drying process)
There is no limitation on the drying method, and any known drying method such as a method of blowing off moisture with an air knife or the like, a method of heating, etc. Also, a plurality of drying methods may be used.

FIG. 9 is a schematic diagram showing an example of a manufacturing apparatus for carrying out such a manufacturing method.
9 is a manufacturing apparatus that produces an aluminum member 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 process while transporting the aluminum base 1 in the longitudinal direction. That is, the manufacturing apparatus 50 is a manufacturing apparatus that produces an aluminum member for a current collector by carrying out each process in a roll-to-roll (RtoR) manner.

The manufacturing apparatus 50 has a rotating shaft 52 on which a substrate roll 70 is loaded, an electrolysis process section 56 which performs an electrolysis process, a partial removal process section 58 which performs a partial removal process, a cleaning and drying process section 60 which performs a cleaning and drying process, and a winding shaft 54 which winds up the aluminum member 10 for current collector produced by each process into a roll 72. The electrolysis process section 56, the partial removal process section 58 and the cleaning and drying process section 60 are arranged on the path along which the aluminum substrate 1 is transported from the rotating shaft 52 to the winding shaft 54.

In the manufacturing apparatus 50, the aluminum substrate 1 is fed from the substrate roll 70 and the aluminum member 10 for the current collector is wound up on the winding shaft 54 in a synchronized manner, 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 processes in each process section.

In addition, a through hole forming process section that performs a through hole forming process and/or a roughening process section that performs a roughening process may be provided upstream or downstream of the electrolysis process section 56. Furthermore, the electrolysis process section 56 may perform a through hole forming process and/or a roughening process in addition to the electrolysis process.

In addition, in the manufacturing apparatus 50, each process is performed in a roll-to-roll manner using a long aluminum base material 1, but this is not limited thereto, and each process may be performed using a sheet-shaped aluminum base material 1. Also, each process may be performed in a separate apparatus.

[Current collector]
As described above, the aluminum member 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").
The current collector has an island-shaped anodized coating, which enables it to achieve both improved adhesion to the electrode material and low resistance. This contributes to reducing internal resistance and also suppresses partial peeling between the electrode material (active material) and the current collector, even after a long period of time and many repeated charge and discharge cycles.

<Electrode material (active material)>
The active material is not particularly limited, and any known active material used in conventional electricity storage devices can be used.
Specifically, when the aluminum member for a current collector is used as a current collector for a positive electrode, the active material and the conductive material, the binder, the solvent, and the like that may be contained in the active material layer are described in JP-A-2012-231262. Materials described in paragraphs [0077] to [0088] of Japanese Patent Publication No. 216513 can be appropriately employed, the contents of which are incorporated herein by reference.
In addition, when the aluminum member for a current collector is used as a current collector for a negative electrode, the active material may be appropriately selected from the materials described in paragraph [0089] of JP-A-2012-216513. The contents are incorporated herein by reference.

[Positive electrode]
A positive electrode using the aluminum member for current collector of the present invention as a current collector is a positive electrode having a positive electrode current collector using the aluminum member for current collector as the positive electrode, 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, the materials described in paragraphs [0077] to [0088] of JP2012-216513A can be appropriately adopted, the contents of which are incorporated herein by reference.

[Negative electrode]
A negative electrode using the aluminum member for a current collector of the present invention as a current collector is a negative electrode having a negative electrode current collector using the aluminum member for a current collector as a negative electrode, and a layer containing a negative electrode active material formed on the surface of the negative electrode current collector.
Here, for the negative electrode active material, materials described in paragraph [0089] of JP2012-216513A can be appropriately adopted, the contents of which are incorporated herein by reference.

[Electricity storage device]
An electrode that utilizes the aluminum member for a current collector of the present invention as a current collector can be used as a positive electrode or a negative electrode of an electricity storage device such as a lithium ion battery, a lithium ion capacitor, an electric double layer capacitor, a semi-solid battery, a solid battery, or a secondary battery that uses a non-aqueous electrolyte.
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 by reference into this specification.

[Electric double layer capacitor]
An electric double layer capacitor is a capacitor having a capacitor structure of facing electrodes with an electric double layer as a dielectric. An electric double layer occurs spontaneously between a solid and a liquid, and is a state in which electrons or holes attract each other and are aligned by charging. The specific configuration of an electric double layer capacitor is described, for example, in JP 2020-064971 A.
The aluminum member for current collectors of the present invention can be used as current collectors for the positive and/or negative electrodes of an electric double layer capacitor.

[Lithium-ion capacitor]
A lithium ion capacitor is a capacitor in which lithium ions are doped into a negative electrode while using the principle of a general electric double layer capacitor. A specific configuration of a lithium ion capacitor is described in, for example, International Publication No. WO 2016/084704.
The aluminum member for current collectors of the present invention can be used as current collectors for positive and/or negative electrodes of lithium ion capacitors.

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

[Semi-solid battery]
A semi-solid battery is a battery in which a semi-solid (gel-like, clay-like) electrolyte is responsible for the conduction of ions between the anode and cathode. A specific configuration of a semi-solid battery is described in U.S. Pat. No. 9,484,569 and the like.
The aluminum member for a current collector of the present invention can be used as a current collector for the positive electrode and/or the negative electrode of a semi-solid battery.

[Secondary battery using non-aqueous electrolyte]
A secondary battery using a non-aqueous electrolyte is a secondary battery that uses a non-aqueous electrolyte as an electrolyte between an anode and a cathode. A specific configuration of a secondary battery using a non-aqueous electrolyte is described in JP 2017-068978 A and the like.
The aluminum member 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.

The present invention will be described in more detail below based on examples. The materials, amounts used, ratios, processing contents, processing 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 interpreted as being limited by the examples shown below.

[Preparation of Aluminum Member for Current Collector]
An aluminum substrate having an alloy number of 1085 or 1N30 and a thickness of 20 μm was used as the aluminum substrate, and the aluminum members for current collectors, current collectors A to S, were fabricated by carrying out the electrolytic treatment and the partial removal treatment or the coating removal treatment described below. Current collectors F to O correspond to examples of the present invention.

<Electrolytic Treatment A>
An anodized film was formed on the surface of the aluminum substrate by electrolytic treatment using an aqueous solution (liquid temperature: 50° C.) containing 20 g/l nitric acid and 20 g/l sulfuric acid, with the aluminum substrate as the anode. The electrolytic treatment was performed using a DC power source. The conditions for the electrolytic treatment were a DC current density of 5 A/dm ² , a DC voltage of 8 V, and an application time of 30 seconds. The anodized film formed by this electrolytic treatment has micropores with diameters of 1 to 30 nm.

<Electrolytic Treatment B>
AC electrolysis was performed in an aqueous solution containing 10 g/l of hydrochloric acid (liquid temperature 35° C.) to form a rough surface on the surface. After rinsing with water, an aqueous solution containing 20 g/l of nitric acid and 20 g/l of sulfuric acid (liquid temperature 50° C.) was used as the anode to perform electrolysis, and an anodized film was formed on the surface of the aluminum substrate. The electrolysis was performed using a DC power source. The electrolysis conditions were a DC current density of 5 A/dm ² , a DC voltage of 8 V, and an application time of 120 seconds. The anodized film formed by this electrolysis has micropores with a diameter of 1 to 30 nm.

<Electrolytic Treatment C>
An aqueous solution (liquid temperature: 50° C.) containing 20 g/l of nitric acid and 20 g/l of sulfuric acid was used to perform electrolytic treatment with the aluminum substrate as the anode, forming an anodized film on the surface of the aluminum substrate and forming through-holes penetrating the aluminum substrate. The electrolytic treatment was performed using a DC power source. The conditions for the electrolytic treatment were a DC current density of 5 A/dm ² , a DC voltage of 8 V, and an application time of 120 seconds. The anodized film formed by this electrolytic treatment has micropores with diameters of 1 to 30 nm.

<Electrolytic Treatment D>
An anodized film was formed on the surface of the aluminum substrate by electrolysis using a solution (liquid temperature 50°C) with 170 g/l sulfuric acid and 5% Al ion concentration, with the aluminum substrate as the anode. The electrolysis was performed using a DC power source. The conditions for the electrolysis were a DC current density of 25 A/ ^dm2 , a DC voltage of 15 V, and an application time of 16 seconds.

<Electrolytic Treatment E>
An anodized film was formed on the surface of the aluminum substrate by electrolytic treatment using a solution (liquid temperature 50°C) with 170 g/l sulfuric acid and 5% Al ion concentration, with the aluminum substrate as the anode. The electrolytic treatment was performed using a DC power source. The conditions of the electrolytic treatment were DC current density 5 A/ ^dm2 , DC voltage 3 V, and application time 27 seconds. After the electrolytic treatment, if partial removal treatment was not performed, the substrate was washed with water and dried.

<Electrolytic Treatment F>
An electrolytic treatment was performed using a solution with a sulfuric acid concentration of 30% (liquid temperature: 0°C) with the aluminum substrate as the anode, to form an anodized film on the surface of the aluminum substrate. The electrolytic treatment was performed using a DC power source. The electrolytic treatment conditions were a DC current density of 3 A/ ^dm2 , a DC voltage of 50 V, and an application time of 30 minutes, twice. After the electrolytic treatment, the aluminum substrate was washed with water and dried.

<Partial Removal Process A>
The surface was washed for 5 seconds with an aqueous solution containing 75 g/l of NaOH (liquid temperature: 35° C.), followed by water washing, acid washing and water washing, and drying.

<Partial Removal Process B>
The surface was washed for 10 seconds with an aqueous solution containing 75 g/l of NaOH (liquid temperature: 35° C.), followed by water washing, acid washing and water washing, and drying.

<Partial Removal Process C>
The surface was washed for 5 seconds with an aqueous solution containing 75 g/l of NaOH (liquid temperature: 25° C.), followed by water washing, acid washing and water washing, and drying.

<Partial Removal Process D>
After passing through a pair of metal rolls (hard chrome plated, diameter 50 mm, passing speed 10 m/s), the surface was rubbed with a rotating brush roll to partially remove the anodized film, followed by pickling, rinsing with water, and drying.

<Film Removal Treatment A>
The anodized film was removed by immersing the plate in phosphoric acid at 30° C. for 30 minutes, followed by rinsing with water and drying.

<Film Removal Treatment B>
The anodized film was removed by immersing the plate in a solution (liquid temperature 35° C.) containing 5% (50 g/l) NaOH and 0.5% (5 g/l) aluminum ion concentration for 3 seconds, followed by rinsing with water and drying.

After each aluminum member for current collector was produced, the coverage of the anodized film, the number density and average diameter of the micropores, and the thickness of the anodized film were measured by the methods described above.
Table 1 shows the treatment of each aluminum member for the current collector, as well as the coverage, thickness, number density and average diameter of the anodized film.
11 shows an SEM image of current collector F, and Fig. 12 shows an SEM image of current collector S. It can be seen that the anodized film 214 of current collector S, which is a comparative example, has non-uniform micropores compared to the anodized film 14 of current collector F, which is an example.

[Examples 1 to 10, Comparative Examples 1 to 9]
The positive electrode slurry described below was applied to the prepared aluminum members for current collectors (current collectors A to S) to form active material layers, and the adhesion and resistance were evaluated.

<Preparation of Positive Electrode Slurry>
The following materials were prepared as the positive electrode slurry.
Positive electrode active material: Powdered activated carbon made from coconut shells (YP: manufactured by Kuraray Co., Ltd.)
88% by mass
Binder: Acrylic resin (AZ-9129: manufactured by Zeon Corporation)
3% by mass
Conductive additive: acetylene black (Denka Black: manufactured by Denki Kagaku Kogyo Co., Ltd.) 15% by mass
Thickener: CMC (manufactured by Daicel FineChem Co., Ltd.) 1% by mass
Water 220% by mass

The materials other than the binder and water were mixed using a variable-rotation mixer (Mazerustar, manufactured by Kurabo Industries, Ltd.). Next, they were mixed using a high-speed homogenizer. Finally, the binder was added and mixed again using the variable-rotation mixer to obtain the slurry for the positive electrode.

<Application of Positive Electrode Slurry>
The positive electrode slurry was applied to one side of an aluminum member for a current collector so that the mass of activated carbon after drying was 3 mg/ ^cm2 . After application and drying, the surface was smoothed by passing through a calendar roll. In this manner, an active material layer was formed on one side of the aluminum member for a current collector.

In addition, for Comparative Example 2, before applying the positive electrode slurry, an undercoat layer of conductive material was formed as follows.

<Formation of Undercoat Layer>
A graphite material (Bunny Height, manufactured by Nippon Graphite Industries Co., Ltd.) was applied with an applicator to a thickness of 3 μm and dried at a drying temperature of 100° C. for 10 minutes to form an undercoat layer.

[evaluation]
<Adhesion>
A peel test was carried out on the aluminum current collector member on which the active material layer was formed, in order to evaluate the adhesion between the aluminum current collector member and the active material layer.
The peel test was performed using a peel tester manufactured by Imada Co., Ltd. The peel test was performed by attaching a digital force gauge 162 to a vertical test stand, fixing the sample S with the active material layer side facing up on an attachment stand 154 on a slide table 152 for 90-degree peel test with double-sided tape 156, and measuring the load when peeling off the adhesive tape 158 attached to the active material layer. In order to evaluate the adhesion of the interface between the aluminum member for the current collector and the active material layer, an adhesive tape with a width of 25 mm having sufficient adhesive strength was used. The evaluation was performed based on the average value of the load measured by the digital force gauge 162 during peeling. A schematic diagram of the peel test evaluation device is shown in FIG. 13.

<RESISTANCE>
For the resistance evaluation, as shown in FIG. 14 , each current-collector aluminum member 10 having an active material layer 106 formed thereon was sandwiched between a pressure-type conductive terminal 102 and a pressure-type insulating terminal 104, and the resistance was measured for one sample, N=7, using a resistance measuring device 100 (HIOKI3541 manufactured by Hioki Corporation).
The initial resistance was evaluated after storing the sample in a dry box for 24 hours or more before the evaluation.
Next, a forced resistance evaluation over time was performed. Each aluminum member for a current collector was stored in an environment at a temperature of 30° C. and a humidity of 80%, and after two weeks, the electrode slurry was applied and dried by the above-mentioned method, and the resistance was evaluated. Similarly, the resistance was evaluated after storing the aluminum member for four weeks in an environment at a temperature of 30° C. and a humidity of 80%.
The results are shown in Table 2.

From Table 2, it can be seen that Examples 1 to 10 of the present invention are able to achieve both high adhesion and low resistance compared to Comparative Examples 1 to 9.

Comparative Examples 1, 2, and 6 did not undergo surface treatment, so the surface of the current collector foil was smooth, adhesion to the active material layer was weak, and peel strength was low. Comparative Example 2 was subjected to a carbon undercoat, which improved adhesion to the active material layer slightly but not sufficiently. Comparative Example 7 had unevenness on the surface, but not to a level that could improve adhesion. Comparative Example 7 was produced by a method conforming to Patent Document 3, and although the aluminum member for current collector produced by this method had unevenness on the surface, this shows that the effect of the micropores in the anodized film does not match the adhesion.

Comparative Examples 3, 4, and 5 have a configuration in which the anodized film remains on the entire surface. Because the surface has a micropore structure, the adhesion is superior to that of a current collector foil with a smooth surface, but the resistance is very poor. This means that the resistance of the aluminum current collector member provided with the anodized film shown in Patent Document 4 is not as good as that of the aluminum current collector member of the present invention.

SEM observation of Comparative Example 8 showed that the anodized film with micropores remained over the entire surface, resulting in high peel strength but extremely poor resistance, just like Comparative Examples 3, 4, and 5. SEM observation of Comparative Example 9 showed that the anodized film without micropores covered approximately 30% of the surface. As it had no micropores, it was found to have low adhesion and poor resistance. The reason for the poor resistance is thought to be the thickness of the natural oxide film.

In the examples of the present invention, the anodized surface film formed by each electrolytic treatment is partially removed, exposing the aluminum base material, and it can be seen that the resistance can be reduced. These have lower resistance and are better than Comparative Examples 1 and 6, which do not have a surface treatment. This is thought to be because the surface of an aluminum base material without a surface treatment has a natural oxide film formed during the rolling process of the aluminum base material, which is present, causing the resistance to be high. However, in the examples of the present invention, the natural oxide film formed on the surface of the aluminum base material exposed after partial removal of the anodized film is very thin, which is thought to be why the resistance can be reduced.

The resistance of the example was at the same level as that of a current collecting foil (Comparative Example 2) that had been undercoated with conductive carbon, which is generally performed for the purpose of reducing the resistance between the active material layer and the aluminum member for the current collector.
When an aluminum member for a current collector is stored at high humidity, a natural oxide film grows on the outermost surface of the aluminum base material, which tends to deteriorate the resistance. However, in the examples of the present invention, the deterioration of resistance due to high humidity storage was suppressed to the same level or less than that in the comparative examples.
In addition, since through holes are formed in Examples 7 and 10, it is considered that a part of the active material layer enters the holes, and the adhesion is slightly improved compared to Example 1.

[Examples 11 to 16, Comparative Example 10]
A positive electrode active material of a semi-solid battery was used as the active material layer in Examples 11 to 16 and Comparative Example 10. Current collectors F to K were used in Examples 11 to 16, respectively, and current collector A was used in Comparative Example 10.
The positive electrode material described below was applied to an aluminum member for a current collector to form an active material layer, and the adhesion and resistance were evaluated.

<Preparation of positive electrode material>
The following materials were prepared as the positive electrode materials.
Positive electrode active material: Lithium cobalt oxide (LiCoO ₂ ) 99% by mass
Conductive additive: acetylene black (Denka Black: manufactured by Denki Kagaku Kogyo Co., Ltd.) 1% by mass
The electrolyte used was ethylene carbonate to which 1.5 mol/kg of electrolyte salt _LiPF6 was added.

The positive electrode active material and conductive additive were mixed, electrolyte was added, and the mixture was further mixed to prepare a clay-like positive electrode material.

<Application of positive electrode material>
The positive electrode material was applied to one side of an aluminum member for a current collector by placing a 2 mm thick stainless steel plate with a square opening of 75 mm in length and 50 mm in width on each aluminum member for a current collector cut to a length of 150 mm and a width of 70 mm, placing the active material in the opening of the stainless steel plate, and applying the active material to a thickness of about 2 mm using a squeegee.

[evaluation]
<Adhesion>
The aluminum current collector member coated with the positive electrode material was wound around a stainless steel round bar having a diameter of 50 mm with the active material layer facing outward, and then unwound, and the state of peeling between the active material layer and the aluminum current collector member was visually observed.
When no peeling occurred at the interface between the active material layer and the aluminum member for current collector, the sample was rated as A, and when peeling occurred, the sample was rated as B.
The results are shown in Table 3.

The results in Table 3 show that the examples did not experience peeling and had high adhesion.

[Examples 17 to 19, Comparative Example 11]
Semi-solid battery cells were prepared in Examples 17 to 19 and Comparative Example 11. In Examples 17 to 19, the positive electrodes prepared in Examples 11 to 13 were used as the positive electrodes, and in Comparative Example 11, the positive electrode prepared in Comparative Example 10 was used as the positive electrode. The negative electrode was prepared as follows.

<Preparation of negative electrode>
The following materials were prepared as negative electrode materials.
Negative electrode active material: Graphite 99% by mass
Conductive assistant: acetylene black (Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.) 1% by mass
The electrolyte used was ethylene carbonate to which 1.5 mol/kg of electrolyte salt _LiPF6 was added.

The negative electrode active material and conductive additive were mixed, electrolyte was added, and the mixture was further mixed to prepare a clay-like negative electrode material.

A 10 μm thick copper foil (electrolytic copper foil) was prepared as a negative electrode current collector, and the negative electrode material was applied to one side of this copper foil with a squeegee to form an active material layer approximately 2 mm thick to produce the negative electrode.

<Preparation of semi-solid battery cells>
After welding the tabs, the positive and negative electrodes were combined and sealed in a pouch to create a semi-solid battery cell.

[evaluation]
<Internal resistance increase rate and capacity retention rate>
The prepared semi-solid battery cell was charged at 20° C. with a constant current of 1 mA up to 4.2 V, and then discharged to 3 V. This charge/discharge cycle was repeated 110 times, and the capacity and internal resistance at the 10th and 110th cycles were recorded. The internal resistance increase rate and capacity retention rate at the 110th cycle were evaluated, with the capacity and resistance at the 10th cycle being set to 100%, respectively.
The results are shown in Table 4.

From Table 4, it can be seen that the examples of the present invention have capacity retention rates and internal resistance increase rates equal to or higher than those of the comparative examples.
From the above, the effects of the present invention are clear.

REFERENCE SIGNS LIST 1 Aluminum substrate 2 Anodized film 3 Aluminum substrate having through-hole 4 Anodized film having through-hole 5 Through-hole 10, 10b Aluminum member for current collector 14 Island-shaped anodized film 50 Manufacturing device 52 Rotating shaft 54 Winding shaft 56 Electric field process section 58 Partial removal process section 60 Cleaning and drying process section 70 Substrate roll 72 Roll 100 Resistance measuring device 102 Pressure-type conductive dedicated terminal 104 Pressure-type insulating terminal 106 Active material layer 150 Slide rail 152 Slide table 154 Pasting stand 156 Double-sided tape 158 Adhesive tape 160 Clamp 162 Digital force gauge 164 Tension device 201 Aluminum substrate 214 Anodized film S Evaluation sample

Claims (13)

An aluminum member for a current collector having an aluminum substrate and an anodized coating film on the aluminum substrate,
The anodic oxide coating has a large number of micropores,
a coverage of the anodized coating on at least one surface of the aluminum base is 1 to 80%;
The anodized coating has a number density of the micropores of 600 pores/ ^μm2 or more ,
The anodized film is present on the aluminum base material in the form of a plurality of divided islands . An aluminum member for a current collector having an aluminum substrate and an anodized coating film on the aluminum substrate,
The anodic oxide coating has a large number of micropores,
a coverage of the anodized coating on at least one surface of the aluminum base is 3 to 28%;
The number density of the micropores in the anodized film is 600/μm ² The aluminum member for a current collector is as described above. The aluminum member for current collector according to claim 1 or 2, wherein the average diameter of the micropores is 1 nm to 100 nm. The aluminum member for a current collector according to any one of claims 1 to 3, wherein the thickness of the anodized film is 1 nm to 30 nm. The aluminum member for a current collector according to any one of claims 1 to 4, wherein the aluminum base has a granular intermetallic compound on the surface. 6. The aluminum member for a current collector according to claim 5, wherein the surface of the aluminum base has the granular intermetallic compound at a density of 500 particles/ ^mm2 or more. The aluminum member for a current collector according to any one of claims 1 to 6, wherein the thickness of the aluminum base is 5 μm to 100 μm. The aluminum member for a current collector according to any one of claims 1 to 7, wherein the aluminum member for a current collector is plate-shaped. A lithium ion capacitor having an aluminum member for a current collector according to any one of claims 1 to 8. An electric double layer capacitor having an aluminum member for a current collector according to any one of claims 1 to 8. A semi-solid battery having the aluminum member for a current collector according to any one of claims 1 to 8. A solid-state battery having the aluminum member for a current collector according to any one of claims 1 to 8. A secondary battery using a non-aqueous electrolyte, comprising the aluminum collector member according to any one of claims 1 to 8.

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