JP7183395B2 - Aluminum foil, method for producing aluminum foil, current collector, lithium ion capacitor, and lithium ion battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to an aluminum foil, a method for producing this aluminum foil, and a current collector, lithium ion capacitor, and lithium ion battery using this aluminum foil.

In recent years, with the development of portable equipment such as personal computers and mobile phones, hybrid vehicles, electric vehicles, etc., the demand for power storage devices, especially lithium ion capacitors, lithium ion secondary batteries, and electric double layer capacitors, has increased. increasing.

It is known to use an aluminum plate as an electrode current collector (hereinafter simply referred to as "current collector") used for the positive electrode or the negative electrode of such an electricity storage device. It is also known that an active material, activated carbon, or the like is applied as an electrode material to the surface of a current collector made of this aluminum plate, and used as a positive electrode or a negative electrode.

In large-capacity next-generation secondary batteries, the electrodes are doped with a large amount of Li (lithium) ions in advance for the purpose of ensuring capacity, depending on the material of the electrode material. As a method for doping Li ions, a method is known in which Li metal is put into a battery cell and dissolution in the battery cell is promoted to distribute excess Li ions to the electrodes. The electrode material is originally a porous material that allows Li ions to pass through. On the other hand, the current collector, which serves as a support for the electrode material and also as a conductive plate for the input and output of electricity during charging and discharging, is usually made of metal foil, which conducts electricity but blocks ions. Therefore, in order to distribute Li ions to every corner of the electrode material in the battery cell, a metal foil having a large number of through holes for allowing Li ions to pass through is used.

For example, in Patent Document 1, an aluminum substrate and an oxide film laminated on at least one main surface of the aluminum substrate are provided, and the oxide film has a density of 2.7 to 4.1 g/cm ³ . , an aluminum member for an electrode having a thickness of 5 nm or less. It is described that this aluminum member for electrodes has a plurality of through holes penetrating in the thickness direction.

Patent Document 2 discloses an aluminum plate having a plurality of through holes penetrating in the thickness direction, wherein the average opening diameter of the plurality of through holes is 0.1 μm or more and 100 μm or less, and the average opening ratio of the plurality of through holes is 2% or more and 40% or less, the ratio of through holes having an opening diameter of 5 μm or less among the plurality of through holes is 40% or less, and the ratio of through holes having an opening diameter of 40 μm or more among the plurality of through holes is 40% or less, and among the plurality of through holes, the ratio S ₁ /S ₀ of the area S ₁ of the through hole and the area S ₀ of the circle whose diameter is the major axis of the through hole is 0.1 or more An aluminum plate having a percentage of through-holes of 1 or less that is 50% or more is described.

WO2018/062046 WO2017/018462

Here, a current collector made of aluminum has an oxide film because its surface is easily oxidized and is oxidized when exposed to the atmosphere. Since an oxide film has high insulating properties, the presence of a thick oxide film on the surface of the current collector increases electrical resistance.

Accordingly, an object of the present invention is to provide an aluminum foil, a method for producing the aluminum foil, a current collector, a lithium ion capacitor, and a lithium ion battery that can reduce the electric resistance due to the oxide film on the surface.

The present invention solves the problems with the following configurations.

[1] An aluminum foil having a plurality of through holes penetrating in the thickness direction,
The aluminum foil has an oxide film on its surface,
The oxide film has an intermetallic compound in which the element ratio O/Al of oxygen to aluminum is 2 or more and 4 or less,
An aluminum foil having an intermetallic compound density of 500/mm ² or more.
[2] The aluminum foil according to [1], wherein the intermetallic compound has an equivalent circle diameter of 1 μm or less.
[3] The aluminum foil according to [1] or [2], wherein the oxide film contains 70% by mass or more of aluminum oxide.
[4] The aluminum foil according to any one of [1] to [3], wherein the contact angle of the oxide film surface is 20° to 80°.
[5] The aluminum foil according to any one of [1] to [4], wherein the through holes have an average opening diameter of 0.1 μm to 100 μm.
[6] having non-penetrating recesses with an average opening diameter of 0.1 μm to 100 μm,
The aluminum foil according to any one of [1] to [5], wherein the occupancy of the concave portions is 1% or more.
[7] An aluminum foil manufacturing method for manufacturing the aluminum foil according to any one of [1] to [6],
a through-hole forming step of forming through-holes in an aluminum base;
an alkali treatment step of contacting the aluminum substrate with an alkaline aqueous solution to dissolve the outermost layer;
and an acid treatment step of contacting the aluminum base material after the alkali treatment step with an acidic aqueous solution to form an oxide film on the surface of the aluminum base material.
[8] A current collector using the aluminum foil according to any one of [1] to [6].
[9] A lithium ion capacitor using the current collector according to [8].
[10] A lithium ion battery using the current collector according to [8].

According to the present invention, it is possible to provide an aluminum foil, a method for producing the aluminum foil, a current collector, a lithium ion capacitor, and a lithium ion battery that can reduce electrical resistance due to an oxide film on the surface.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows typically an example of the aluminum foil of this invention. FIG. 2 is a top view of the aluminum foil shown in FIG. 1; BRIEF DESCRIPTION OF THE DRAWINGS It is typical sectional drawing for demonstrating an example of the suitable manufacturing method of the aluminum foil of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is typical sectional drawing for demonstrating an example of the suitable manufacturing method of the aluminum foil of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is typical sectional drawing for demonstrating an example of the suitable manufacturing method of the aluminum foil of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is typical sectional drawing for demonstrating an example of the suitable manufacturing method of the aluminum foil of this invention. It is a figure which shows typically the apparatus which measures resistance. 1 is an SEM image of the aluminum foil of Example 1. FIG. It is a graph showing the relationship between the depth and the elemental composition ratio. It is a graph showing the relationship between the depth and the elemental composition ratio. It is a graph showing the relationship between the depth and the elemental composition ratio. It is a graph showing the relationship between the depth and the elemental composition ratio. 4 is an SEM image of the aluminum foil of Comparative Example 3. FIG. It is a graph showing the relationship between the depth and the elemental composition ratio. It is a graph showing the relationship between the depth and the elemental composition ratio. It is a graph showing the relationship between the depth and the elemental composition ratio.

The present invention will be described in detail below.
The description of the constituent elements described below may be made based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.
In this specification, a numerical range represented by "-" means a range including the numerical values before and after "-" as lower and upper limits.

[Aluminum foil]
The aluminum foil of the present invention is
An aluminum foil having a plurality of through holes penetrating in the thickness direction,
The aluminum foil has an oxide film on its surface,
The oxide film has an intermetallic compound in which the element ratio O/Al of oxygen to aluminum is 2 or more and 4 or less,
The aluminum foil has an intermetallic compound density of 500/mm ² or more.
Next, the structure of the aluminum foil of the present invention will be described with reference to FIGS. 1 and 2. FIG.

FIG. 1 is a schematic cross-sectional view showing one preferred embodiment of the aluminum foil of the present invention. 2 is a top view of the aluminum foil shown in FIG. 1. FIG.
As shown in FIG. 1, the aluminum foil 10 has an oxide film 14 formed on both main surfaces (largest surfaces) of the aluminum substrate 3 . The oxide film is an aluminum oxide film containing aluminum oxide such as aluminum oxide (Al ₂ O ₃ ). Further, the aluminum foil 10 has a plurality of through holes 5 penetrating through the aluminum base material 3 and the oxide film 14 in the thickness direction. That is, the aluminum foil 10 has a structure in which an aluminum substrate 3 having through holes penetrating in the thickness direction and an oxide film 14 having through holes penetrating in the thickness direction are laminated.

In the example shown in FIG. 1, the oxide film 14 is formed on both main surfaces of the aluminum base material 3, but is not limited to this, and may be formed on only one main surface. There may be.

The aluminum foil of the present invention is used as a current collector, coated with an active material (electrode material) on the surface, and used as a positive electrode or a negative electrode of an electric storage device.
Since the aluminum foil has a plurality of through-holes penetrating in the thickness direction, lithium ions can easily move when used as a current collector. In addition, by having a large number of through holes, it is possible to improve the adhesion with the active material.

Here, as shown in FIG. 2, in the present invention, the oxide film 14 has many granular intermetallic compounds 16 dispersed in the film. The intermetallic compound 16 has an elemental ratio O/Al of oxygen to aluminum of 2 or more and 4 or less. Also, the density of the intermetallic compound 16 is 500/mm ² or more.

As described above, aluminum is easily oxidized and is oxidized when exposed to the air, so it always has an oxide film. Since the oxide film has a high insulating property, the presence of a thick oxide film on the surface of the aluminum base may increase the electrical resistance between the aluminum base and the active material.

In addition, it is possible to reduce the electrical resistance by thinning the oxide film, but there is a limit to the reduction in electrical resistance by thinning the oxide film, and there is a problem that it is difficult to further reduce the electrical resistance. there were.

On the other hand, in the aluminum foil of the present invention, the oxide film 14 has many granular intermetallic compounds dispersed in the film. The intermetallic compound has an elemental ratio O/Al of oxygen to aluminum of 2 or more and 4 or less. Moreover, the density of the intermetallic compound is 500/mm ² or more.
According to the studies of the present inventors, it has been found that the intermetallic compound having an element ratio O/Al of 2 or more and 4 or less becomes a starting point for lowering the insulating properties of the oxide film. By having the intermetallic compound, which serves as a starting point for lowering the insulation, at a density of 500/mm ² or more, the insulation of the oxide film can be reduced, and the electric resistance of the oxide film can be reduced.
A method of forming an oxide film having an intermetallic compound having an element ratio O/Al of 2 or more and 4 or less at a density of 500/mm ² or more will be described in detail later.

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 and the like. Specifically, the intermetallic compounds include Al ₃ Fe, Al ₆ Fe, αAlFeSi, AlFeMnSi, Mg ₂ Si, and TiB ₂ . Among these, the intermetallic compound containing Al contains Al, so that a natural oxide film of aluminum is formed on the surface.
Therefore, the surface layer of the intermetallic compound containing Al contains oxygen element (O).

In the aluminum foil of the present invention, the oxide film on the surface of the intermetallic compound has an intermetallic compound having an oxide film with an element ratio O/Al of 2 or more and 4 or less at a density of 500/mm ² or more. If so, the outermost oxide film may contain an intermetallic compound other than the element ratio O/Al of 2 or more and 4 or less. That is, the outermost oxide film may have an intermetallic compound with an element ratio O/Al of less than 2 or more than 4.
In the following description, an intermetallic compound in which the element ratio O/Al in the outermost oxide film is 2 or more and 4 or less is defined as an intermetallic compound A, and similarly the element ratio O/Al in the outermost oxide film is less than 2. , or an intermetallic compound of more than 4 is defined as an intermetallic compound B. Moreover, when it is not necessary to distinguish between the intermetallic compound A and the intermetallic compound B, they are collectively called an intermetallic compound.

When the oxide film contains aluminum oxide (Al ₂ O ₃ ) as a main component and does not contain a hydrate, the element ratio O/Al in the portion other than the intermetallic compound of the oxide film is less than 2. It is about 3 to 1.5.

From the viewpoint of lowering the electric resistance of the aluminum foil, the average value of the element ratio O/Al of the oxide film on the surface layer of the intermetallic compound A is preferably 2 or more and 4 or less, and 2.5 or more and 3.5. It is more preferably 5 or less.

The element ratio O/Al of the outermost layer of the intermetallic compound is measured as follows.
Intermetallic compounds (intermetallic compound A and intermetallic compound B) are different from portions other than the intermetallic compound of the oxide film when the surface of the oxide film is observed with a high-resolution scanning electron microscope (SEM). They can be distinguished and visually recognized (see FIGS. 8 and 13).
Therefore, first, from the surface of the oxide film, the surface of the oxide film is photographed using a high-resolution scanning electron microscope (SEM) at a magnification of 5000 times. Extract 20 pieces.
Next, elemental analysis is performed using field emission Auger electron spectroscopy (FE-AES) in the depth direction from the outermost surface at the position of the extracted intermetallic compound. Depth analysis is performed by repeating the measurement and surface removal by sputtering. From the result of element distribution in the depth direction by FE-AES (see FIG. 9, etc.), the element ratio O/Al in the outermost layer is determined.

The density of the intermetallic compound A is preferably 1,000/mm ² to 300,000/mm ² , more preferably 5,000/mm ² to 200,000/mm ² from the viewpoint of lowering the electric resistance of the aluminum foil. .

In addition, the density of the intermetallic compound A is measured as follows.
First, using a high-resolution scanning electron microscope (SEM), the surface of the aluminum foil was photographed from directly above at a magnification of 5000 times. Extract intermetallic compounds.
Next, the elemental ratio O/Al of each intermetallic compound extracted by elemental analysis using FE-AES is determined. Count the number of intermetallic compounds A with an element ratio O/Al of 2 or more and 4 or less, and calculate the number density from the number of intermetallic compounds A in the field of view and the area of the field of view (geometric area). , the average value of five fields of view is calculated as the density.

Here, the equivalent circle diameter of the intermetallic compound A is preferably 1 μm or less. An intermetallic compound having an equivalent circle diameter of 1 μm or less is likely to appear on the surface of the aluminum foil. When a small intermetallic compound appears on the surface of the aluminum foil, the surface area to volume of the intermetallic compound increases. As a result, it is considered that water molecules are easily adsorbed locally, and the element ratio O/Al of the oxidized intermetallic compound tends to be 2 or more.

The circle equivalent diameter of the intermetallic compound A is obtained by extracting at least 20 intermetallic compounds A whose element ratio O/Al is measured as described above, and using image analysis software or the like to measure the oxide film surface of the intermetallic compound A. The area is determined, the equivalent circle diameter is determined from this area, and the average value of these values is calculated as the equivalent circle diameter.

The outermost oxide film preferably contains 70% by mass or more of aluminum oxide (Al ₂ O ₃ ), more preferably 80% to 100% by mass, even more preferably 90% to 100% by mass. .
By setting the content of non-hydrated aluminum oxide (Al ₂ O ₃ ) in the oxide film to 70% by mass or more, the density of the oxide film can be increased, so that the oxide film becomes thicker over time. can be suppressed. Therefore, it is preferable in that it is possible to suppress an increase in electric resistance due to a thick oxide film.

The ratio 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 an energy of 450 keV were incident on the sample at 62.5 degrees with respect to the normal to the sample surface (the surface of the oxide film of the aluminum member for electrode), and the scattered He+ ions were scattered at a position of a scattering angle of 55 degrees in a polarized magnetic field type. Detected by an energy analyzer to obtain areal density. The obtained areal density (atoms/cm ² ) was converted to mass areal density (g/cm ² ), and the density of the oxide film (g/cm ³ ) was calculated from this value and the film thickness measured by a transmission electron microscope (TEM). ) is calculated.
The oxide film of aluminum consists of non-hydrated aluminum oxide and hydrated aluminum oxide (monohydrate and trihydrate exist), and each has a different density. The weighted average of the densities of the monohydrate and the trihydrate and the density of the nonhydrate is considered to be the density determined above, and the proportion of nonhydrated aluminum oxide is determined therefrom.

From the viewpoint of reducing electric resistance, the thickness of the oxide film is preferably 5 nm or less, more preferably 4.5 nm or less, and even more preferably 4 nm or less.

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 less than 80 µm, still more preferably more than 3 µm and less than 40 µm, and particularly preferably more than 5 µm and less than 30 µm.
By setting the average opening diameter of the through-holes within the above range, it is possible to prevent the occurrence of omissions or the like when the active material or the like is applied to the aluminum foil, and the adhesion to the applied active material can be improved. Moreover, even when the aluminum foil has a large number of through-holes, it can have sufficient tensile strength.

The average opening diameter of the through holes is obtained by photographing the surface of the aluminum foil at a magnification of 200 using a high-resolution scanning electron microscope (SEM) from one surface of the aluminum foil. In the photograph, at least 20 through-holes whose periphery is continuous in a ring are extracted, the opening diameters thereof are read, and the average value of these is calculated as the average opening diameter.
For the opening diameter, the maximum value of the distance between the ends of the through-hole portion was measured. That is, since the shape of the opening of the through-hole is not limited to a substantially circular shape, when the shape of the opening is non-circular, the maximum distance between the ends of the through-hole portion is taken as the opening diameter. Therefore, for example, even in the case of a through-hole having a shape in which two or more through-holes are integrated, this is regarded as one through-hole, and the maximum value of the distance between the ends of the through-hole portions is taken as the opening diameter. .

The average open area ratio of the through holes is preferably 0.5% to 30%, more preferably 1% to 30%, even more 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 the active material is applied to the aluminum foil, and to improve the adhesion with the applied active material. Moreover, even when the aluminum foil has a large number of through-holes, it can have sufficient tensile strength.

In addition, the average aperture ratio of the through-holes was obtained by photographing the surface of the aluminum foil from directly above using a high-resolution scanning electron microscope (SEM) at a magnification of 200, and obtaining a 30 mm × 30 mm field of view (5 The through-hole part and the non-through-hole part are observed by binarizing with image analysis software, etc., and the ratio of the total opening area of the through-holes and the area of the field of view (geometric area) (opening area/geometric area) area), and the average value in each field of view (5 locations) was calculated as the average aperture ratio.

Further, the aluminum foil preferably has non-penetrating recesses with an average opening diameter of 0.1 μm to 100 μm on the surface (oxide film). Moreover, it is preferable that the occupancy rate (area ratio) of the concave portions on the surface of the aluminum foil is 1% or more.
By having the concave portion, the surface area is increased, and the area in close contact with the active material layer is increased, thereby further improving the adhesion.

From the viewpoint of adhesion, the average opening diameter of the recesses is preferably 0.1 μm to 100 μm, more preferably 1 μm to 50 μm, even more preferably 2 μm to 30 μm.
In addition, the average opening diameter of the recesses is obtained by photographing the surface of the aluminum foil from directly above at a magnification of 200 using a high-resolution scanning electron microscope (SEM) from one surface of the aluminum foil. At least 20 recesses (pits) having a concavo-convex structure with an annular continuous circumference were extracted, and the maximum diameter was read as the opening diameter, and the average value of these was calculated as the average opening diameter. The maximum diameter is the maximum linear distance between one edge forming the opening of the recess. For example, if the recess is circular, it means the diameter; if the recess is elliptical, it means the major axis; The maximum value of the straight-line distance from the edge of the

From the viewpoint of adhesion, the occupancy of the recesses is preferably 1% or more, more preferably 2% to 5%, and even more preferably 5% to 10%.
The occupancy rate of the recesses was obtained by photographing the surface of the aluminum foil from directly above with a high-resolution scanning electron microscope (SEM) at a magnification of 200 times, and obtaining a SEM photograph of 30 mm × 30 mm field of view (5 locations). Regarding, binarize with image analysis software etc. and observe the recessed part and the non-recessed part, and calculate the ratio (opening area/geometric area) of the total opening area of the recess and the area of the field of view (geometric area) The average value in each visual field (five locations) was calculated as the occupancy.

Further, the water contact angle of the surface of the aluminum foil, that is, the surface of the oxide film is preferably 20° to 80°.
An aluminum foil used as a current collector is used as an electrode after being coated with an electrode material on its surface. Generally, the electrode material is applied to the current collector by making a water-based solvent into a slurry. When applying a water-based electrode material, in order to suppress the electrode material from being repelled and improve the applicability, the surface is subjected to a hydrophilic treatment to make it hydrophilic (that is, to reduce the water contact angle). ) has been performed (eg, WO2011/089722).

However, according to the studies of the present inventors, if the water contact angle on the surface of the aluminum foil is too small, that is, if the affinity with moisture is high, moisture in the air is likely to be adsorbed. Moisture is easily supplied. It has been found that when water is supplied to the oxide film, the oxide film tends to grow, and as a result, the electrical resistance tends to deteriorate over time.

On the other hand, by setting the water contact angle of the surface of the aluminum foil (surface of the oxide film) to 20° or more, the growth of the oxide film due to the adsorption of moisture is suppressed, and the deterioration of the electrical resistance over time is suppressed. can be done. The water contact angle of the surface of the aluminum foil (the surface of the oxide film) is preferably 40° or more, more preferably 50° or more.

In addition, if the water contact angle of the surface of the aluminum foil (the surface of the oxide film) is too high, when a water-based electrode material is applied, it may be repelled by the surface and uniform application may not be possible. On the other hand, by setting the water contact angle of the surface of the aluminum foil (the surface of the oxide film) to 80° or less, the coatability of the electrode material can be improved. The water contact angle of the aluminum foil surface (oxide film surface) is preferably 70° or less.

The water contact angle is measured by the sessile drop method in which water droplets are deposited in the air and the water contact angle is determined. A static contact angle is preferable for measuring the water contact angle, and the sessile drop method can be used for the static contact angle measurement.
As an example, the sessile drop method described in "JIS R 3257:1999 Test method for wettability of substrate glass surface" can be used to measure the water contact angle. The water contact angle can be measured, for example, with a portable contact angle meter PCA-1 (Kyowa Interface Science Co., Ltd.).

<Aluminum substrate>
The aluminum base material that is the base material of the aluminum foil is not particularly limited, and for example, known aluminum base materials such as alloy numbers 1N30 and 3003 described in JIS H4000 can be used. Aluminum containing a large amount of intermetallic compounds is preferred, but the present application is not limited to aluminum materials. The aluminum base material is an alloy plate containing aluminum as a main component and a small amount of foreign elements.

In order to make the density of the intermetallic compound A having an element ratio O/Al of 2 or more and 4 or less in the oxide film formed on the surface of the aluminum base material 500/mm ² or more, the aluminum base material It preferably has 500/mm ² or more intermetallic compounds, more preferably 1,000/mm ² or more and 200,000/mm ² or less, and even more preferably 3,000/mm ² or more and 300,000/mm ² or less.

The equivalent circle diameter of the intermetallic compound having an element ratio O/Al of 2 or more and 4 or less, which is contained in the aluminum substrate, is preferably 1 μm or less.

The thickness of the aluminum substrate is not limited, but preferably 5 μm to 100 μm, more preferably 10 μm to 30 μm.

[Method for producing aluminum foil]
Next, the method for producing the aluminum foil of the present invention will be explained.
The method for producing an aluminum foil of the present invention comprises:
a through-hole forming step of forming a through-hole;
an alkali treatment step of contacting the aluminum substrate after the film forming step with an alkaline aqueous solution to dissolve the outermost surface;
an acid treatment step of contacting the aluminum base material after the alkali treatment step with an acidic aqueous solution to remove residues on the surface of the aluminum base material and to make the natural oxide film formed thereafter non-hydrated. A method for producing an aluminum foil.

By the acid treatment step, most of the surface of the aluminum substrate is formed with a film mainly composed of aluminum oxide with an element ratio O/Al of 1 to 2, while the surface of the intermetallic compound has an element ratio O/Al of 2. An oxide film having a thickness of 4 or less is formed. Further, in the acid treatment step, by using an acidic aqueous solution containing nitric acid as an acidic aqueous solution, a film mainly composed of aluminum oxide having an element ratio O/Al of 1 to 2 is formed on most of the surface of the aluminum substrate. At the same time, an oxide film having an element ratio O/Al of 2 or more and 4 or less can be preferably formed on the surface of the intermetallic compound.

In addition, the alkali treatment step removes unnecessary films, oils, etc. before the acid treatment step, and exposes the aluminum substrate to facilitate the formation of an oxide film.

Moreover, the through-hole forming step can be performed by a known method such as a method using electrolysis or a method of mechanically forming holes.

Moreover, it is preferable to have a water washing step for performing a water washing treatment after each of the alkali treatment step, the acid treatment step, and the through-hole forming step.
Moreover, it is preferable to have a drying step for performing a drying treatment after the water washing treatment after each step.
Here, the drying process after the water washing process after the acid treatment process is preferably carried out on the aluminum substrate using high-temperature air of more than 200° C. and 350° C. or less. By performing the drying step after the acid treatment step under these conditions, the element ratio O/Al of most of the oxide films on the aluminum base material becomes 1 or more and less than 2, and the element ratio O/Al on the surface of the intermetallic compound is preferably 2 or more and 4 or less.

Hereinafter, taking the aluminum foil having through holes shown in FIG. 1 as an example, each step of the aluminum foil manufacturing method will be described with reference to FIGS. 3 to 6, and then each step will be described in detail.

3 to 6 are schematic cross-sectional views showing an example of a preferred embodiment of the aluminum foil manufacturing method.
As shown in FIGS. 3 to 6, the method for producing an aluminum foil includes a film forming step (Fig. 3 and FIG. 4), and a through-hole forming step (FIG. 4) in which the through-holes 5 are formed by performing electrolytic dissolution treatment after the film-forming step, and the aluminum substrate 3 having the through-holes and the film 4 having the through-holes are formed. and FIG. 5), an alkali treatment step (FIGS. 5 and 6) for dissolving and removing the outermost layer including the coating 4 having through holes after the through-hole forming step, and an acid treatment after the alkali treatment step. and an acid treatment step (FIGS. 6 and 1) for forming oxide films on both main surfaces of the aluminum base material 3 having through holes.

[Through hole forming step]
The through-hole forming step is a step of forming through-holes in the aluminum base material.
The method of forming the through-holes in the through-hole forming step is not particularly limited, and mechanical methods such as punching or electrochemical methods such as electrolytic dissolution can be used.
The method of forming through-holes by electrolytic dissolution is preferable in that through-holes having an average opening diameter of 0.1 μm to 100 μm can be easily formed.

In the through-hole forming step in which electrolytic dissolution treatment is performed, after the film forming step of forming a non-homogeneous film in advance, electrolytic treatment (electrolytic dissolution treatment) is performed with a third acidic aqueous solution using the aluminum base material as an anode, and the aluminum base material is This is a step of forming through-holes in the material and the aluminum hydroxide film. The type of film is not particularly limited as long as it is possible to form a difference between areas that are easily dissolved and penetrated during electrolytic treatment and areas that are difficult to dissolve.

<Electrolytic dissolution>
The electrolytic dissolution treatment is not particularly limited, and direct current or alternating current can be used, and an acidic solution (second acidic aqueous solution) can be used as the electrolytic solution. Among them, it is preferable to perform the electrochemical treatment using at least one acid selected from nitric acid and hydrochloric acid. In addition to these acids, the electrochemical treatment is performed using a mixed acid including at least one selected from sulfuric acid, phosphoric acid and oxalic acid. is more preferred.

In the present invention, as the acidic solution which is the electrolytic solution, in addition to the above acids, 4,600,482, 4,566,960, 4,566,958, 4,566,959, 4,416,972, 4,374,710 Electrolyte solutions described in the specifications of No. 4,336,113 and No. 4,184,932 can also be used.

The concentration of the acid solution is preferably 0.1-2.5% by weight, particularly preferably 0.2-2.0% by weight. The temperature of the acidic solution is preferably 20-80°C, more preferably 30-60°C.

Further, the aqueous solution mainly composed of the acid is an aqueous solution of acid with a concentration of 1 to 100 g / L, nitric acid compounds having nitrate ions such as aluminum nitrate, sodium nitrate, ammonium nitrate, or hydrochloric acid such as aluminum chloride, sodium chloride, ammonium chloride, etc. At least one sulfate compound having sulfate ions such as a hydrochloride compound having ions, aluminum sulfate, sodium sulfate, ammonium sulfate, etc. can be added and used in an amount ranging from 1 g/L to saturation.
In addition, metals contained in aluminum alloys, such as iron, copper, manganese, nickel, titanium, magnesium, and silica, may be dissolved in the aqueous solution mainly composed of the acid. It is preferable to use a solution obtained by adding aluminum chloride, aluminum nitrate, aluminum sulfate, or the like to an aqueous solution having an acid concentration of 0.1 to 2% by mass so that aluminum ions are 1 to 100 g/L.

Direct current is mainly used for electrochemical dissolution treatment, but when alternating current is used, the AC power wave is not particularly limited, and sine wave, rectangular wave, trapezoidal wave, triangular wave, etc. are used. Among them, a rectangular wave or a trapezoidal wave is preferable, and a trapezoidal wave is particularly preferable.

(Nitric acid electrolysis)
In the present invention, through-holes having an average opening diameter of 0.1 μm to 100 μm are easily formed by electrochemical dissolution treatment using an electrolytic solution mainly composed of nitric acid (hereinafter also abbreviated as “nitric acid dissolution treatment”). can be formed.
Here, the nitric acid dissolution treatment uses a DC current, an average current density of 5 A/dm ² or more, and an amount of electricity of 50 C/dm ² or more because it is easy to control the dissolution point for forming through holes. It is preferable that the electrolytic treatment is carried out in. The average current density is preferably 100 A/dm ² or less, and the quantity of electricity is preferably 10000 C/dm ² or less.
Further, the concentration and temperature of the electrolytic solution in nitric acid electrolysis are not particularly limited. Electrolysis can be performed at a high temperature, for example, 80° C. or higher using a 7 to 2% by mass nitric acid electrolyte.
Further, electrolysis can be performed using an electrolytic solution obtained by mixing at least one of sulfuric acid, oxalic acid, and phosphoric acid with a concentration of 0.1 to 50% by mass in the nitric acid electrolytic solution.

(hydrochloric acid electrolysis)
In the present invention, through-holes having an average opening diameter of 0.1 μm to 100 μm can be easily formed by electrochemical dissolution treatment using an electrolytic solution mainly composed of hydrochloric acid (hereinafter also abbreviated as “hydrochloric acid dissolution treatment”). can be formed.
Here, the hydrochloric acid dissolution treatment uses a direct current, an average current density of 5 A/dm ² or more, and an amount of electricity of 50 C/dm ² or more because it is easy to control the dissolution point for forming through holes. It is preferable that the electrolytic treatment is carried out in. The average current density is preferably 100 A/dm ² or less, and the quantity of electricity is preferably 10000 C/dm ² or less.
Further, the concentration and temperature of the electrolytic solution in the hydrochloric acid electrolysis are not particularly limited. Electrolysis can be performed at a high temperature, for example, 80° C. or higher using a hydrochloric acid electrolyte of 7 to 2 mass %.
Further, electrolysis can be performed using an electrolytic solution obtained by mixing at least one of sulfuric acid, oxalic acid, and phosphoric acid with a concentration of 0.1 to 50% by mass in the hydrochloric acid electrolytic solution.

[Alkaline treatment step]
The alkali treatment step is a step of dissolving (removing) the outermost layer of the aluminum substrate by performing a chemical dissolution treatment using an alkaline aqueous solution. In addition, once the through-holes are formed by electrolytic treatment, any residue or film remaining on the surface is removed. At that time, the intermetallic compound on the surface layer of the aluminum substrate has a slower dissolution rate in an alkaline aqueous solution than the aluminum substrate, so by appropriately selecting the treatment conditions, the intermetallic compound was slightly embossed on the surface layer of the aluminum substrate. Can be left on the surface in a state.
In the alkali treatment step, the outermost layer of the aluminum base material can be dissolved (removed) by performing, for example, an alkali etching treatment to be described later.

<Alkaline etching treatment>
The alkali etching treatment is a treatment of dissolving the surface layer by bringing the aluminum base material into contact with an alkaline aqueous solution.

Examples of the alkali used in the alkaline aqueous solution include caustic alkalis and alkali metal salts. Specifically, examples of caustic alkalis include sodium hydroxide (caustic soda) and caustic potash. 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; sodium aluminate and aluminum. alkali metal aluminates such as acid potassium; alkali metal aldonic salts such as sodium gluconate and potassium gluconate; dibasic sodium phosphate, dibasic potassium phosphate, tribasic sodium phosphate, tribasic potassium phosphate Alkali metal hydrogen phosphates may be mentioned. Among them, a solution of caustic alkali and a solution containing both caustic alkali and alkali metal aluminate are preferable in terms of high etching rate and low cost. An aqueous solution of sodium hydroxide is particularly preferred.

The concentration of the alkaline aqueous solution is preferably 0.1-50% by mass, more preferably 0.2-10% by mass. When aluminum ions are dissolved in the alkaline aqueous solution, the concentration of 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 10-90°C. The treatment time is preferably 1 to 120 seconds.

Examples of the method of bringing the aluminum substrate into contact with the alkaline solution include a method of passing the aluminum substrate through a tank containing an alkaline solution, a method of immersing the aluminum substrate in a tank containing an alkaline solution, a method of A method of spraying the solution onto the surface of the aluminum substrate can be used.

[Acid treatment process]
In the acid treatment step, the aluminum base material is brought into contact with an acidic aqueous solution (first acidic aqueous solution) to form an oxide film having an element ratio O/Al of 1 or more and less than 2 on the surface or back surface of the aluminum base material. This is a step of forming an oxide film having an element ratio O/Al of 2 or more and 4 or less on the surface of the intercompound.
As described above, an oxide film having an element ratio O/Al of 1 or more and less than 2 is formed on most of the surface of the aluminum substrate, and the surface of the intermetallic compounds present at 500/mm ^{2 or} more has an element ratio O/ By forming an oxide film containing 2 or more and 4 or less Al, the insulating property of the oxide film can be lowered starting from the intermetallic compound, and the electric resistance of the oxide film can be lowered.

In the acid treatment process, the surface of the aluminum base material is washed away with an acidic aqueous solution to remove the residue formed during the alkali treatment process, and the natural oxide film formed on the surface of the aluminum base material is mainly composed of aluminum oxide. It can be a passive film.
Here, since the intermetallic compound composed of aluminum and Fe or Si contained in the aluminum base material contains the aluminum element, an oxide film is formed. At that time, as described above, the intermetallic compound is in a state in which the intermetallic compound is slightly raised on the surface layer of the aluminum base material due to the alkali treatment step, so the ratio of the exposed area to the volume of the intermetallic compound is increased. . As a result, it was found that the oxide film formed on the surface of the intermetallic compound had a large element ratio of oxygen O to aluminum Al=O/Al. This is probably because the surface area of the intermetallic compound is large, so that aluminum oxide does not pass uniformly over the entire surface and, for example, water molecules are easily adsorbed locally. Therefore, it is possible to form an oxide film having 500/mm ² or more intermetallic compounds A with an element ratio O/Al of 2 or more and 4 or less.

As the acidic aqueous solution (first acidic aqueous solution) used in the acid treatment step, nitric acid, sulfuric acid, phosphoric acid, oxalic acid, or a mixed acid of two or more of these is preferably used, and an acidic aqueous solution containing nitric acid is more preferably used. preferable.
The concentration of the acidic aqueous solution is preferably 0.01 to 10% by weight, particularly preferably 0.1 to 5% by weight. Also, the liquid temperature of the acidic aqueous solution is preferably 25 to 70°C, more preferably 30 to 55°C.

Also, the method of bringing the aluminum substrate into contact with the acidic aqueous solution is not particularly limited, and examples thereof include an immersion method and a spray method. The spray method is preferable because it facilitates liquid replacement on the aluminum surface.

The immersion method is a process of immersing the aluminum substrate in the acid solution described above. Stirring during the immersion treatment is preferable because the treatment can be performed evenly.
The immersion treatment time is preferably 15 seconds or longer, more preferably 30 seconds or longer, and even more preferably 40 seconds or longer.

[Washing process]
As described above, in the present invention, it is preferable to have a water washing step after each of the alkali treatment step, the acid treatment step, and the through-hole forming step described above. Pure water, well water, tap water, or the like can be used for washing with water. A nip device may be used to prevent the processing liquid from being brought into the next step.

[Drying process]
As described above, it is preferable to have a drying step for performing a drying treatment after the water washing step after each step.
The drying method is not limited, and known drying methods such as a method of blowing off moisture with an air knife or the like, a method of heating, and the like can be used as appropriate. Moreover, you may perform several drying methods.

Here, it is preferable to have a water washing step for washing the aluminum base material after the acid treatment step, and it is preferable to have a drying step after the water washing step after the acid treatment step. In this case, the drying step is preferably a step of heating the surface of the aluminum base material by applying hot air of more than 200° C. to 350° C. or less.
After forming an oxide film on the surface of the aluminum base material in the acid treatment process, a water washing process is performed to remove the acidic aqueous solution remaining on the surface of the aluminum base material (oxide film). By heating the aluminum substrate to more than 200 ° C. and 350 ° C. or less in the drying step of removing the, an oxide film having an element ratio O / Al of 1 or more and less than 2 is formed on the surface of the aluminum substrate, and an intermetallic compound An oxide film having an element ratio O/Al of 2 or more and 4 or less can be preferably formed on the surface of the .

The heating temperature in the drying step after the acid treatment step is preferably a hot air temperature of 180°C to 350°C, more preferably 240°C to 300°C. The drying time is preferably 1 to 30 seconds, more preferably 3 to 10 seconds.

Here, the water contact angle of the surface of the aluminum foil (the surface of the oxide film) produced by the production method of the present invention is affected by the method of forming the through-holes. Therefore, a step of adjusting the water contact angle may be carried out according to the water contact angle of the aluminum foil surface (oxide film surface) after production (after the acid treatment step). In addition, when the water contact angle of the aluminum foil surface (oxide film surface) after production (after the acid treatment process) is 20° to 80°, after the oxide film is formed (after the acid treatment process), a hydrophilic It is preferable not to apply a hardening treatment. Moreover, it is preferable not to apply a hydrophilization treatment to the electrode material after the production of the aluminum foil.

[Current collector]
As described above, the aluminum foil of the present invention can be used as a current collector for power storage devices (hereinafter also referred to as "current collector").
Since the current collector has a plurality of through holes in the aluminum foil in the thickness direction, for example, when it is used in a lithium ion capacitor, it is possible to pre-dope lithium in a short time, and the lithium is made more uniform. Dispersion becomes possible. In addition, the adhesion to the active material layer and activated carbon is improved, and an electricity storage device having excellent productivity such as cycle characteristics, output characteristics, and coating suitability can be produced.
In addition, since the current collector using the aluminum foil of the present invention has a low electrical resistance of the oxide film, the electrical resistance between the current collector and the active material layer is low, and an efficient electricity storage device can be produced.

<Active material layer>
The active material layer is not particularly limited, and known active material layers used in conventional electricity storage devices can be used.
Specifically, when aluminum foil is used as a current collector of the positive electrode, the conductive material, binder, solvent, etc. that may be contained in the active material and the active material layer are disclosed in JP-A-2012-216513. , paragraphs [0077] to [0088], the contents of which are incorporated herein by reference.
In addition, when aluminum foil is used as the current collector of the negative electrode, the active material may be appropriately selected from the materials described in paragraph [0089] of JP-A-2012-216513. incorporated into the book as a reference.

[Power storage device]
An electrode using the aluminum foil of the present invention as a current collector can be used as a positive electrode or a negative electrode of an electric storage device such as a lithium ion battery or a lithium ion capacitor.
Here, regarding the specific configuration and application of the electric storage device (especially, the secondary battery), the materials and applications described in paragraphs [0090] to [0123] of JP-A-2012-216513 may be used as appropriate. can be adopted, the contents of which are incorporated herein by reference.

[Positive electrode]
The positive electrode using the aluminum foil of the present invention as a current collector includes a positive electrode current collector using the aluminum foil as a positive electrode and a layer containing a positive electrode active material formed on the surface of the positive electrode current collector (positive electrode active material layer). and a positive electrode.
Here, the positive electrode active material and the conductive material, binder, solvent, etc. that may be contained in the positive electrode active material layer are described in paragraphs [0077] to [0088] of JP-A-2012-216513. The materials described can be employed as appropriate, the contents of which are incorporated herein by reference.

[Negative electrode]
A negative electrode using an aluminum foil as a current collector of the present invention is a negative electrode having a negative electrode current collector using an aluminum foil 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 JP-A-2012-216513 can be appropriately employed, the contents of which are incorporated herein by reference.

[Other uses]
The aluminum foil of the present invention can also be used as a current collector for electrolytic capacitors.

The present invention will be described in further detail based on examples below. The materials, amounts used, proportions, treatment details, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the gist of the present invention. Therefore, the scope of the present invention should not be construed to be limited by the examples shown below.

[Examples 1 and 2 and Comparative Examples 1 to 3]
<Preparation of aluminum substrate>
Aluminum substrates A1 and A2 containing an intermetallic compound with an equivalent circle diameter of 1 μm or less and an aluminum substrate B containing no intermetallic compound with an equivalent circle diameter of 1 μm or less were prepared.

The aluminum base A1 is made by melting an aluminum base metal with an Al purity of 99.90%, casting aluminum with 2% Fe added by a DC (Direct Chill) casting method, and then hot rolling and cold rolling to obtain a final plate thickness. It is an aluminum base material finished to 20 μm. In order to adjust the strength, heat treatment was performed when the sheet thickness was 2 mm during the cold rolling.

The aluminum base A2 is an aluminum base obtained by melting an aluminum base metal with an Al purity of 99.90%, casting aluminum to which 0.5% of Fe is added by a continuous casting method, and then cold rolling it to a final plate thickness of 20 μm. It is wood. In order to adjust the strength, heat treatment was performed when the sheet thickness was 2 mm during the cold rolling.

Aluminum base material B is aluminum finished to a final plate thickness of 20 μm by hot rolling and cold rolling in the same manner as aluminum base material A1 after casting an aluminum ingot with an Al purity of 99.90% by a DC casting method. It is the base material.

Each aluminum substrate was subjected to through-hole forming treatment 1 and/or through-hole forming treatment 2 described below to form through-holes.

<Through hole forming treatment 1>
(a-1) Process for Forming Heterogeneous Film As a pretreatment, electrolysis was performed with an acidic solution containing aluminum ions in the solution to deposit aluminum hydroxide having a thickness of 1 μm or more. This becomes an inhomogeneous film.

(b-1) electrolytic dissolution treatment (through-hole forming step)
Next, using an electrolytic solution (nitric acid concentration of 2%, sulfuric acid concentration of 2%, aluminum concentration of 1%) kept at 50 ° C., electrolytic treatment is performed with the aluminum substrate as the anode, and the aluminum substrate and the aluminum hydroxide film are subjected to electrolytic treatment. A through hole was formed. In addition, the electrolytic treatment was performed with a DC power source. The current density was adjusted so that the aperture ratio was about 4%.
After forming the through-holes, washing with water was performed by spraying.

(c-1) Alkaline treatment step Next, an aqueous solution (liquid temperature: 37°C) having a sodium hydroxide concentration of 10% by mass and an aluminum ion concentration of 5% by mass was sprayed onto the aluminum base material after the electrolytic dissolution treatment, and the residue was removed. Removed.
After removing the aluminum film, it was washed with water by spraying.

(d-1) Acid treatment step Next, the aluminum substrate after the alkali treatment step was sprayed with an aqueous solution having a nitric acid concentration of 10% and an aluminum ion concentration of 5% by mass (liquid temperature of 50°C) for 5 seconds, and the surface of the aluminum substrate was treated. An oxide film was formed on the
Then, it was washed with water by spraying.

(e-1) Drying step Next, the moisture remaining on the surface of the aluminum substrate that has been formed with an oxide film and washed with water is removed with an air knife, and further dried by heating with hot air at a drying temperature of 300°C. An aluminum foil was made.

The through holes formed in the through hole forming process 1 are generally formed with an aperture ratio of 4.0%, an average hole diameter of 10 μm, and a density of 100 holes/mm ² .

<Through hole forming treatment 2>
Through holes having an opening ratio of 10% and an average hole diameter of 250 μm were mechanically formed on the surface. An oxide film is formed on the surface of the aluminum substrate in which the through holes are formed by the through hole forming treatment 2 by natural oxidation.
Table 1 shows the type of aluminum base material and the type of through-hole forming treatment used in each example and comparative example.

[evaluation]
<Initial resistance value>
On one surface of the aluminum foil 10 produced in each example and comparative example, a conductive material "Bunny Height" in which carbon particles are dispersed in an aqueous solvent is applied with an applicator and dried at 130 ° C. for 15 minutes to form a carbon layer. 106 was formed. Next, as shown in FIG. 7, the aluminum foil 100 with the carbon layer 106 formed thereon is sandwiched between the pressurized conductive dedicated terminal 102 and the pressurized insulated terminal 104, and the resistance is measured with a resistance measuring machine 100 (HIOKI3541 manufactured by Hioki Co., Ltd.). was measured with one sample N=7.
The initial resistance value was evaluated as A when less than 20 mΩ, B when 20 mΩ or more and less than 30 mΩ, C when 30 mΩ or more and less than 35 mΩ, and D when 35 mΩ or more.

<Forced aging resistance evaluation>
The aluminum foil produced in each example and comparative example was stored in an environment with a temperature of 30° C. and a humidity of 80%. It was measured.
Forced resistance over time is A if the resistance value after holding for 4 weeks is within 50 mΩ, B if the resistance value is within 50 mΩ after holding for 3 weeks and exceeds 50 mΩ after holding for 4 weeks, and within 50 mΩ after holding for 2 weeks and after holding for 3 weeks. If it exceeded 50 mΩ, it was judged as C, and if it exceeded 50 mΩ after holding for 2 weeks, it was judged as D.
Table 1 shows the results.

Below, the surface of the portion where the through hole is not formed (surface of the oxide film) in Example 1 and Comparative Example 3 was observed with SEM using FE-AES (manufactured by JEOL Ltd.), and the oxide film on the surface. The results of the elemental distribution from the outermost surface to the depth direction are exemplified.

FIG. 8 shows an example of an SEM image of Example 1. FIG. As can be seen from FIG. 8, the oxide film has many granular intermetallic compounds. In FIG. 8, the intermetallic compounds are indicated as IMC1 and IMC2, and the portions other than the intermetallic compounds are indicated as A11 and A12.

9 to 12 show the results of elemental analysis in the depth direction for the portions of IMC1, IMC2, A11 and A12 in FIG.
FIG. 9 shows the results of elemental analysis of the IMC1 portion. This intermetallic compound had an equivalent circle diameter of 3 μm or more. FIG. 10 shows the results of elemental analysis of the IMC2 portion. This intermetallic compound had an equivalent circle diameter of 1 μm or less. FIG. 11 shows the results of elemental analysis of the Al1 portion. FIG. 12 shows the results of elemental analysis of the Al2 portion.

As can be seen from FIGS. 9 to 12, there is no great difference in the thickness of the oxide film at any position.
It can be seen that the element ratio O/Al of the outermost layer in the IMC1 portion of FIG. 9, the Al1 portion of FIG. 11, and the Al2 portion of FIG. 12 is 2 or less. On the other hand, it can be seen that the element ratio O/Al of the outermost layer in the portion of IMC2 in FIG. 10 is 2 or more and 4 or less. That is, in the example of the SEM image shown in FIG. 8, the IMC1 portion corresponds to the intermetallic compound B, and the IMC2 portion corresponds to the intermetallic compound A.
When the density of the intermetallic compound A was determined by the above-described method through such elemental analysis, it was 110,000/mm ² .

FIG. 13 shows an example of a SEM image of Comparative Example 3. As shown in FIG. As can be seen from FIG. 13, the oxide film has granular intermetallic compounds. In FIG. 13, the intermetallic compound is indicated as IMC3, and the portions other than the intermetallic compound are indicated as A13 and A14.

14 to 16 show the results of elemental analysis in the depth direction for the portions of IMC3, A13 and A14 in FIG.
FIG. 14 shows the results of elemental analysis of the IMC3 portion. This intermetallic compound had an equivalent circle diameter of 1 μm or more. FIG. 15 shows the results of elemental analysis of the Al3 portion. FIG. 16 shows the results of elemental analysis of the Al4 portion.

As can be seen from FIGS. 14 to 16, there is no great difference in the thickness of the oxide film at any position.
14, Al3 in FIG. 15, and Al4 in FIG. 16, the element ratio O/Al of the outermost layer is 2 or less. That is, the IMC3 portion corresponds to the intermetallic compound B in the example of the SEM image shown in FIG. From Comparative Example 3, no intermetallic compound A having an element ratio O/Al in the outermost layer of 2 or more and 4 or less could not be observed.
The results of elemental analysis are shown in Table 2.

From Tables 1 and 2, it can be seen that the aluminum foil of the present invention having an oxide film having 500/mm ² or more intermetallic compound A with an element ratio O/Al of 2 or more and 4 or less has an initial resistance and low resistance over time.

[Comparative Examples 4 and 5]
Aluminum foils were made using the methods described in Example 5 and Example 11 of WO2017/018462, respectively.
Comparative Example 4 is an example using an aluminum base material with few small intermetallic compounds, and Comparative Example 5 is an example using an aluminum base material containing small intermetallic compounds.

[Example 3]
An aluminum foil was produced in the same manner as in Example 1, except that the treatment conditions in the through-hole forming step were changed in order to obtain substantially the same through-hole physical properties (average opening diameter and average opening ratio) as in Comparative Examples 4 and 5. .

[evaluation]
The initial resistance value and the resistance value after forced aging for 4 weeks were measured in the same manner as described above. Further, using FE-AES in the same manner as described above, the density of the intermetallic compound A was obtained by performing SEM observation and element distribution from the outermost surface of the oxide film on the surface toward the depth direction. Also, the initial value and the value after 4 weeks forced aging were obtained for the film thickness of the oxide film. Also, the density (initial value) of the oxide film was obtained.
Table 3 shows the treatment conditions and the like, and Table 4 shows the results.

As shown in Table 3, Comparative Examples 4 and 5 differ in the type of aluminum base material, the type of acid used in the acid treatment step, and the temperature in the drying step. As shown in Table 4, no intermetallic compound A was observed in the oxide film of Comparative Examples 4 and 5 in which aluminum foils were produced under these conditions. In Comparative Example 4, the maximum element ratio O/Al of the intermetallic compound was 1.3. In Comparative Example 5, the maximum element ratio O/Al of the intermetallic compound was 1.9. On the other hand, in Example 3, the element ratio O/Al of the intermetallic compound was 3.0 on average.

As can be seen from Tables 3 and 4, the initial resistance values of Comparative Examples 4 and 5 are as low as those of Example 3, but the resistance values increase as the film thickness increases over time. On the other hand, in Example 3 of the present invention, although the thickness of the oxide film was large at the initial stage, it was found that the increase in resistance value over time was small. This uses an aluminum base material containing a large amount of small intermetallic compounds as the aluminum base material, and by setting the element ratio O/Al of the small intermetallic compounds in the oxide film to a predetermined range, the intermetallic compound A is This is because it becomes a conduction point and can maintain a low resistance.

[Comparative Example 6]
An aluminum foil was made using the method described in Example 1 of WO2018/062046.
Comparative Example 6 is an example using an aluminum base material with many small intermetallic compounds.

[Example 4]
An aluminum foil was produced in the same manner as in Example 1, except that the treatment conditions in the through-hole forming step were changed in order to obtain substantially the same through-hole physical properties (average opening diameter and average opening ratio) as in Comparative Example 6.

[evaluation]
The initial resistance value, the resistance value after forced aging for 3 weeks, and the resistance value after forced aging for 8 weeks were measured in the same manner as described above. Further, using FE-AES in the same manner as described above, the density of the intermetallic compound A was obtained by performing SEM observation and element distribution from the outermost surface of the oxide film on the surface toward the depth direction. In addition, the initial value, the value after forced aging for 3 weeks, and the value after forced aging for 8 weeks were obtained for the film thickness of the oxide film. Also, the density (initial value) of the oxide film was obtained.
Table 5 shows the treatment conditions and the like, and Table 6 shows the results.

As shown in Table 5, Comparative Example 6 differs in the type of aluminum base material, the type of acid used in the acid treatment step, and the temperature in the drying step. As shown in Table 6, no intermetallic compound A was observed in the oxide film of Comparative Example 6 in which the aluminum foil was produced under these conditions. In Comparative Example 6, the maximum element ratio O/Al of the intermetallic compound was 1.8. On the other hand, in Example 4, the element ratio O/Al of the intermetallic compound was 3.0 on average.

In Comparative Example 6, by controlling the film quality of the oxide film, the film thickness of the oxide film can be suppressed from becoming thicker over time and the film thickness can be kept thin. An increase is seen. On the other hand, in Example 4 of the present invention, the increase in thickness of the oxide film over time is greater than that of the comparative example, but it can be seen that the resistance value can be kept low. Also, by setting the element ratio O/Al of the small intermetallic compounds in the oxide film within a predetermined range, even if the thickness of the entire oxide film increases, this intermetallic compound A becomes a conduction point and reduces the thickness of the oxide film. This is because the resistance can be maintained.

[Example 5]
After producing an aluminum foil in the same manner as in Example 2, it was washed with a solvent (MEK (methyl ethyl ketone)) to produce an aluminum foil.

[Example 6]
An aluminum foil was produced in the same manner as in Example 2, washed with a solvent (MEK (methyl ethyl ketone)), and then packed with untreated aluminum foil (A1085 material, untreated, unwashed) for 1 week. That is, aluminum foil prepared in the same manner as in Example 5 was packed with untreated aluminum foil for one week.
Here, packing and storing with untreated aluminum foil increases the water contact angle because a small amount of rolling oil remaining on the surface of the untreated aluminum foil is transferred to the surface of the aluminum foil. Taking advantage of this point, Examples 6, 7, and 10 were prepared as examples with large contact angles.

[Example 7]
After an aluminum foil was produced in the same manner as in Example 2, it was packed with untreated aluminum foil for one week.

[Example 8]
After an aluminum foil was produced in the same manner as in Example 2, it was subjected to corona treatment once to be hydrophilic to produce an aluminum foil. A treatment apparatus manufactured by Kasuga Denki Co., Ltd. was used for the corona treatment. The power of corona treatment was 600W.

[Example 9]
After an aluminum foil was produced in the same manner as in Example 2, it was subjected to corona treatment twice to be hydrophilic to produce an aluminum foil.

[Example 10]
After an aluminum foil was produced in the same manner as in Example 2, it was packed with untreated aluminum foil for 2 weeks.

Water contact angles were measured for the aluminum foils of Examples 2 and 5 to 10. The water contact angle was measured using a portable contact angle meter PCA-1 (Kyowa Interface Science Co., Ltd.) according to the sessile drop method described in "JISR3257: 1999 Substrate glass surface wettability test method". . The measurement conditions were as follows.
Waiting time until measurement 2000ms
Created liquid volume 1.8 μL
Table 7 shows the measurement results of the water contact angle.

[evaluation]
<Initial resistance and forced aging resistance>
The initial resistance and forced aging resistance of the aluminum foils of Examples 2 and 5 to 10 were measured in the same manner as above, and evaluated according to the same criteria. In addition, as in Examples 6, 7, and 10, for examples in which untreated aluminum is packed and stored, in order to minimize the effects of aging during packing and storage, after storage for a predetermined period in a low-humidity environment, After unpacking, initial resistance and forced aging resistance were measured.

<Applicability>
For the aluminum foils of Examples 2 and 5 to 10, when the electrode material was applied for the measurement of the initial resistance, it was visually confirmed whether the electrode material could be uniformly applied.
Table 7 shows the results.

From Table 7, it can be seen that the coatability becomes uneven when the water contact angle on the surface exceeds 80°. It is considered that this is because the water-based electrode material partially repels due to the surface approaching water repellency, making uniform coating impossible.
Here, Examples 6 and 7 packed and stored with untreated aluminum foil have larger water contact angles than Examples 2 and 5 produced under the same conditions. This is because the untreated aluminum foil was used for packaging and storage, and the slight amount of rolling oil remaining on the surface of the untreated aluminum foil was transferred to the aluminum foil, increasing the water contact angle compared to the original state (before packaging and storage). There is. In addition, Example 10 was packed and stored for a longer period than Example 8. In Example 10, the water contact angle is even greater and exceeds 80° due to the long packing and storage period. As a result, Example 10 had non-uniform coatability compared to other examples.

Further, from Table 7, it can be seen that when the water contact angle on the surface is less than 20°, the initial resistance and forced aging resistance deteriorate. In Examples 8 and 9, the surface was forcibly hydrophilized by corona treatment. As described above, it can be seen that when corona treatment is performed to lower the water contact angle, the resistance deteriorates.
In addition, in Example 10, it is considered that the contact state between the electrode material and the aluminum foil was insufficient due to non-uniform coating properties, and the initial resistance was worse than in Example 2. On the other hand, the forced aging resistance of Example 10 was at the same level as that of Example 2 without much deterioration because the water contact angle of the surface was large and was close to water repellency.
From the above, the effect of the present invention is clear.

REFERENCE SIGNS LIST 1 aluminum substrate 2 aluminum hydroxide film 3 aluminum substrate having through-holes 4 aluminum hydroxide film having through-holes 5 through-holes 10 aluminum foil 14 oxide film 16 intermetallic compound 100 resistance measuring device 102 pressure-type conductive dedicated terminal 104 Pressurized insulated terminal 106 carbon layer

Claims (8)

An aluminum foil having a plurality of through holes penetrating in the thickness direction,
The aluminum foil has an oxide film on its surface,
The oxide film has an intermetallic compound in which the element ratio O/Al of oxygen to aluminum is 2 or more and 4 or less,
The intermetallic compound has a density of 500/mm ² or more,
The aluminum foil having a water contact angle of 20° to 80° on the surface of the oxide film. 2. The aluminum foil according to claim 1, wherein the intermetallic compound has an equivalent circle diameter of 1 [mu]m or less. The aluminum foil according to claim 1 or 2, wherein the oxide film contains 70% by mass or more of aluminum oxide. The aluminum foil according to any one of claims 1 to 3, wherein the through holes have an average opening diameter of 0.1 µm to 100 µm. having non-penetrating recesses with an average opening diameter of 0.1 μm to 100 μm,
The aluminum foil according to any one of claims 1 to 4, wherein the occupancy rate of the concave portions is 1% or more. A current collector using the aluminum foil according to any one of claims 1 to 5. A lithium ion capacitor using the current collector according to claim 6 . A lithium ion battery using the current collector according to claim 6 .

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