JPH11162470A - Aluminum foil for current collector, its manufacture current collector, secondary battery and electric double layer capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum foil for a current collector having high adhesiveness to an electrode active material and a low contact resistance value with the electrode active material, to provide its manufacturing method, and to provide a current collector contributing to increasing characters such as the life of a secondary battery and an electric double layer capacitor. SOLUTION: This aluminum foil for a current collector has the average roughness Ra of 0.3-1.5 μm as the roughness of at least one surface and the maximum height Ry of 0.5-5.0 μm. Water or a nonflammable organic solvent is used as a medium, and alumina grains are sprayed to the surface of the aluminum foil to roughen the surface of the aluminum foil, thereby the aluminum foil for a current collector is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery and an electric double layer capacitor, and more particularly to a current collector used for a secondary battery and an electric double layer capacitor, an aluminum foil for the current collector, and a method of manufacturing the same. is there.

[0002]

2. Description of the Related Art In recent years, lithium ion batteries and polymer batteries as high energy efficiency secondary batteries and electric double layer capacitors as capacitors have been widely used in mobile phones, personal computers, cameras and automobiles. Has been used as a power source.

In a lithium ion battery as an example of a secondary battery, a material obtained by coating an aluminum foil as a current collector with an active material made of, for example, carbon, a lithium metal oxide salt, and a fluorine-based binder is used as a positive electrode material. I have. In a polymer battery, as a positive electrode material,
A collector in which a conductive polymer electrode active material such as polyaniline or polyacetylene is coated on an aluminum foil as a current collector is used.

On the other hand, in electric double layer capacitors,
In order to form an electrode, a material obtained by coating a material made of carbon and a polyimide resin on an aluminum foil as a current collector is used.

[0005] As described above, the reason why aluminum foil is used as a material of a current collector of a secondary battery or an electric double layer capacitor is as follows.

(1) Aluminum foil is hardly eroded by an electrolytic solution and is relatively stable as a support.

(2) The aluminum foil has excellent electric conductivity and a small electric resistance, so that it does not adversely affect the electric efficiency of a secondary battery or an electric double layer capacitor.

(3) Since the aluminum foil has a low electric resistance value, heat generation due to the resistance is small.

(4) Aluminum foil is an economic material because of its low production cost. By the way, in order to form a positive electrode of a secondary battery or an electrode of an electric double layer capacitor, an electrode active material or a binder is applied to the surface of an aluminum foil as a current collector. Such a coating material to be applied has a problem that the adhesion to the surface of the aluminum foil is insufficient, and the contact resistance value between the aluminum foil and the electrode active material increases. In addition, due to insufficient adhesion between the coating material and the surface of the aluminum foil, a phenomenon occurs in which a film of the electrode active material peels off during charging and discharging of a secondary battery or an electric double layer capacitor. There is a problem that the characteristics such as the life of the battery and the electric double layer capacitor are greatly affected.

[0010] In order to solve these problems, a pressure treatment or the like is performed industrially after applying a coating material, but it is not always sufficient. Conversely, there may be a problem that the applied film is peeled off at the time of pressing.

Further, attempts have been made to modify the surface of the aluminum foil chemically by etching or the like to increase the adhesive strength between the film to be coated and the surface of the aluminum foil. However, there is a problem in practical use due to a decrease in strength of the aluminum foil and a change with time of the surface layer.

Accordingly, an object of the present invention is to provide an aluminum foil for a current collector capable of improving the adhesion to an electrode active material, and a method for producing the same.

Another object of the present invention is to provide an aluminum foil for a current collector capable of reducing the contact resistance between the electrode active material and a method of manufacturing the same.

A further object of the present invention is to provide a current collector having high adhesion to an electrode active material and low contact resistance.

Another object of the present invention is to provide a secondary battery and an electric double-layer capacitor provided with a current collector which can contribute to enhancing characteristics such as life.

[0016]

The aluminum foil for a current collector according to the present invention has an average roughness Ra of at least 0.3 μm and at most 1.5 μm and a maximum height Ry of at least one surface of at least one surface. It is not less than 0.5 μm and not more than 5.0 μm.

By modifying the surface of the aluminum foil in this way, and particularly by limiting the roughness of the surface, it is possible to improve the adhesion of the film when the film made of an electrode active material or the like is applied. And the characteristics of the original aluminum foil can be fully utilized.

If the average roughness Ra is less than 0.3 μm, the adhesion of the active material film formed on the surface of the aluminum foil is not good, and the contact resistance between the film and the active material increases. . If the average roughness Ra exceeds 1.5 μm, the surface layer of the aluminum foil becomes embrittled. In addition, when a film of an active material or the like is continuously applied, or in a subsequent pressing step, the aluminum foil is easily broken or the film is easily peeled.

When the maximum height Ry is less than 0.5 μm, the effect of roughening the surface of the aluminum foil and the effect of increasing the surface area due to the roughening cannot be obtained.
Adhesion between the active material and the film is insufficient. When the maximum height Ry exceeds 5.0 μm, the thickness of the film of the electrode active material becomes uneven, thereby causing variations in characteristics of the secondary battery and the electric double layer capacitor. further,
The strength of the current collector itself made of aluminum foil is reduced, whereby the aluminum foil is easily broken or bent when a film of the electrode active material is continuously applied or in a subsequent pressure bonding step.

Preferably, the aluminum foil for a current collector according to the present invention has a tensile strength of 98 MPa or more. If the tensile strength is less than 98 MPa, there is a possibility that the aluminum foil may be broken or cracked when roughening the surface of the aluminum foil or during other manufacturing steps, which is not preferable. More preferably, the aluminum foil of the present invention has a tensile strength of 147 MPa or more.

[0021] Preferably, the thickness of the aluminum foil for a current collector of the present invention is 10 µm or more and 150 µm or less. If the thickness is less than 10 μm, the aluminum foil may be broken or cracked when roughening the surface of the aluminum foil or during another manufacturing process. In addition, the thickness is 1
When it exceeds 50 μm, there is no disadvantage in characteristics,
Not only are disadvantages in terms of volume and weight noticeable, but also disadvantageous in terms of manufacturing costs.

The size and shape other than the thickness of the aluminum foil in the present invention are not limited, and there may be intentional perforations. However, perforations are not always necessary. In other words, the current collector aluminum foil according to the present invention, even without perforating the surface,
The required surface area and the required surface roughness of the current collector can be provided.

The preferred composition of the aluminum foil of the present invention is such that aluminum is 99.0% by weight or more, iron, copper and silicon are each 0.5% by weight or less, and the total content of iron, copper and silicon is Less than 1.0% by weight. More preferably, the content of aluminum is 99.3
% By weight, more preferably 99.9% by weight or more. Limiting the composition of the aluminum foil in this way is
The lower the purity of aluminum, and the higher the content of copper, iron and silicon, the greater the amount of aluminum corrosion during charge and discharge by the electrolyte when used as a current collector for secondary batteries and electric double layer capacitors Because.
In particular, when the content of iron, copper, and silicon as impurities exceeds the above range, corrosion of aluminum becomes remarkable. As a result, the life of the electrode is reduced, and the characteristics are significantly deteriorated.

Further, an oxide film having a withstand voltage of 0.5 V or more and 2.0 V or less is formed on the surface of the aluminum foil of the present invention. When the film withstand voltage is less than 0.5 V, the surface of the aluminum foil is not stable, and iron as an impurity component is easily dissolved in the electrolyte during use as a current collector. If the film withstand voltage exceeds 2.0 V, the internal resistance on the surface of the current collector increases, and adverse effects such as deterioration of electric efficiency and heat generation occur.

A current collector according to another aspect of the present invention includes the aluminum foil as described above.

A secondary battery according to the present invention includes the above-described current collector. Furthermore, an electric double layer capacitor according to the present invention includes the above-described current collector.

By using the current collector according to the present invention, characteristics such as the life of the secondary battery and the electric double layer capacitor can be improved.

The method for producing an aluminum foil for a current collector according to the present invention comprises roughening the surface of the aluminum foil by spraying alumina particles on the surface of the aluminum foil through water or a nonflammable organic solvent. Features.

The roughening treatment of the surface of the aluminum foil is as follows.
The surface of the aluminum foil is roughened by spraying a slurry of alumina particles dispersed in water or a nonflammable organic solvent onto the surface of the aluminum foil using compressed air. Thereby, it is confirmed that the residual rolling oil on the surface of the aluminum foil is completely removed, and that a strong oxide film having a withstand voltage of 0.5 to 2.0 V is formed. This processing is called wet blast processing.

As a method for removing residual oil from rolling of aluminum foil, a method by annealing has been generally used for a long time.
This is not preferable because it causes a significant decrease in strength. If the strength is low, it may cause breakage or cracking of the aluminum foil during wet blasting or other manufacturing steps. Therefore, as described above, the tensile strength of the aluminum foil is preferably 98 MPa or more.

The reason for spraying alumina particles on the surface of the aluminum foil is that when other particles are used, the sprayed particles sink into the surface of the aluminum foil, and a local battery is formed by impurities present in the aluminum foil. It is in the same state as using aluminum foil of poor purity,
This is because corrosion of the aluminum foil proceeds.

The solvent used in the wet blast treatment is water or a nonflammable organic solvent, for example, methylene chloride,
Trichloroethylene and the like are preferred. Flammable organic solvents are not suitable in terms of working environment and safety.

The wet blasting process has advantages such as less heat generation of the material, higher cleaning effect, and higher safety because the blasting process is performed by almost completely shutting off air, as compared with a dry process such as a sand blasting process. Have.

After performing the wet blasting treatment, the aluminum foil is heated in air at a temperature of 60 to 200 ° C. for 0.1 to 0.1 ° C.
By drying for 10 hours, the film withstand voltage is 0.5 to
An oxide film of 2.0 V, preferably 1.0 to 1.8 V can be formed. Other methods for adjusting the film withstand voltage include an anodizing method and a method of immersing an aluminum foil in boiling water.

As described above, the method for producing an aluminum foil for a current collector according to the present invention is safe and economical, and is suitable for industrial production.

[0036]

EXAMPLES As described below, aluminum foils having different surface treatments and different aluminum purities were used as current collectors for lithium ion batteries and electric double layer capacitors in Examples 1 to 7 and Comparative Examples 1 to 5. Prepared by In Comparative Examples 6 to 8, copper foil, iron foil and stainless steel were prepared as current collector materials, respectively. The component analysis value of each material indicates a value analyzed by ICP emission spectroscopy.

Example 1 Nominal purity of 99.9% by weight,
The analysis value of the component is 50 ppm for copper and 500 pp for iron.
A wet blast treatment was performed on an aluminum hard foil having a thickness of 200 ppm, a silicon content of 300 ppm, a thickness of 20 μm, and a tensile strength of 200 MPa. The wet blasting treatment was performed by spraying a blast solution in which 18% by volume of alumina particles having passed through a 320-mesh sieve were dispersed in pure water to the surface of the aluminum hard foil at an air pressure of 1.3 kgf / cm ² . . Thereafter, the aluminum hard foil was dried at a temperature of 80 ° C. for 30 minutes.

Example 2 Nominal purity of 99.3% by weight
500 ppm of copper and 4000 p of iron as analytical values of components
Wet blasting was performed on an aluminum hard foil having pm, silicon of 2000 ppm, thickness of 20 μm, and tensile strength of 175 MPa. Wet blast treatment is 32
Alumina particles that have passed through a 0 mesh sieve
2.0 kgf / cm ^{2 of} the blast liquid dispersed in 8% by volume.
By spraying on the surface of the aluminum hard foil at an air pressure of. Thereafter, the aluminum hard foil was dried at a temperature of 80 ° C. for 30 minutes.

Example 3 Nominal purity of 99.7% by weight,
30 ppm of copper and 1500 pp of iron as analytical values of components
A wet blast treatment was performed on an aluminum hard foil having a thickness of 500 m, a silicon content of 500 ppm, a thickness of 15 μm, and a tensile strength of 190 MPa. The wet blast treatment was performed by spraying a blast solution in which 20% by volume of alumina particles having passed through a 320 mesh sieve were dispersed in pure water onto the surface of an aluminum hard foil at an air pressure of 2.5 kgf / cm ² . . Thereafter, the aluminum hard foil was dried at a temperature of 60 ° C. for 60 minutes.

Example 4 Nominal purity: 99.99% by weight, analysis of components: 10 ppm copper, 50 pp iron
Wet blasting was performed on an aluminum hard foil having a m of 35 ppm, a silicon content of 35 ppm, a thickness of 30 μm, and a tensile strength of 210 MPa. The wet blast treatment was performed by spraying a blast solution in which 18% by volume of alumina particles having passed through a 320 mesh sieve was dispersed in pure water at an air pressure of 1.5 kgf / cm ² onto the surface of the aluminum hard foil. . After that, the aluminum hard foil is heated at a temperature of 6
Drying was performed at 0 ° C. for 30 minutes.

Example 5 Nominal purity of 99.1% by weight,
500 ppm of copper and 5000 p of iron as analytical values of components
Wet blasting was performed on an aluminum hard foil having a pm, silicon of 3000 ppm, a thickness of 40 μm, and a tensile strength of 165 MPa. Wet blast treatment is 32
Alumina particles passed through a 0 mesh sieve
2.0 kgf / cm ^{2 of} the blast liquid dispersed 0% by volume.
By spraying on the surface of the aluminum hard foil at an air pressure of. Thereafter, the aluminum hard foil was dried at a temperature of 90 ° C. for 60 minutes.

Example 6 Using the same aluminum hard foil as in Example 3, the surface was subjected to wet blasting. In the case of this embodiment, the wet blast
A blast solution obtained by dispersing 20% by volume of alumina particles passed through a 00 mesh sieve in pure water is 2.5 kgf / cm.
It was performed by spraying on the surface of aluminum hard foil with air pressure of ² . Thereafter, a drying treatment was performed at a temperature of 60 ° C. for 60 minutes.

(Example 7) Using the same aluminum hard foil as in Example 3, the surface was subjected to wet blasting. In the case of this embodiment, the wet blast
A blast solution obtained by dispersing 20% by volume of alumina particles passed through a 00 mesh sieve in pure water is 2.5 kgf / cm.
It was performed by spraying on the surface of aluminum hard foil with air pressure of ² . Thereafter, a drying treatment was performed at a temperature of 60 ° C. for 60 minutes.

(Comparative Example 1) Nominal purity of 98.0% by weight,
As the analysis values of the components, 1000 ppm of copper, 1.3% by weight (13000 ppm) of iron, and 4000 pp of silicon
m, the surface of an aluminum hard foil having a thickness of 20 μm and a tensile strength of 180 MPa was degreased with methylene chloride.

Comparative Example 2 Nominal purity of 99.3% by weight
500 ppm of copper and 4000 p of iron as analytical values of components
The surface of the aluminum hard foil having pm, silicon of 2000 ppm, thickness of 20 μm and tensile strength of 170 MPa was degreased with methylene chloride.

Comparative Example 3 Nominal purity of 99.7% by weight,
30 ppm of copper and 1500 pp of iron as analytical values of components
The surface of a soft aluminum foil having a m of 500 ppm of silicon, a thickness of 15 μm, and a tensile strength of 70 MPa was washed with methanol.

(Comparative Example 4) Nominal purity: 99.99% by weight, analysis values of components: copper: 10 ppm, iron: 50 pp
The surface of an aluminum hard foil having m, silicon of 35 ppm, thickness of 30 μm and tensile strength of 210 MPa was degreased with methylene chloride.

Comparative Example 5 Using the same aluminum hard foil as in Example 3, the surface was subjected to wet blasting. In the case of this comparative example, the wet blast treatment was 4
A blast solution obtained by dispersing 20% by volume of alumina particles passed through a 00 mesh sieve in pure water is 2.5 kgf / cm.
It was performed by spraying on the surface of aluminum hard foil with air pressure of ² . Thereafter, a drying treatment was performed at a temperature of 60 ° C. for 60 minutes.

The average roughness R as a measured value of the composition, thickness and tensile strength of the aluminum foil prepared in Examples 1 to 7 and Comparative Examples 1 to 5 and the surface roughness obtained by the surface treatment was obtained.
Table 1 shows a and the maximum height Ry. Table 1 also shows the results of measuring the withstand voltage of the oxide film formed on the surface of the aluminum foil.

Comparative Example 6 A copper foil having a purity of 99.9% by weight was degreased with methylene chloride. The surface roughness obtained by this surface treatment has an average roughness Ra of 0.19 μm.
m and the maximum height Ry were 0.33 μm.

Comparative Example 7 An iron foil having a purity of 99.9% by weight was degreased with methylene chloride. The surface roughness obtained by this surface treatment has an average roughness Ra of 0.22 μm.
m and the maximum height Ry were 0.28 μm.

Comparative Example 8 Stainless steel (SUS30)
4) was degreased with methylene chloride.

In Table 1, data not measured are indicated by "-". Surface roughness Ra and maximum height R
The measurement of y was in accordance with JIS B 0601 (-1994).

[0054]

[Table 1]

The performance as a current collector was confirmed by performing the following tests 1 to 4 using the current collector material prepared as described above.

(Test 1) Each of the current collector materials prepared in Examples 1 to 7 and Comparative Examples 1 to 8 was placed in a supporting salt electrolyte of a lithium ion battery at 4.5 V VS. Li + / Li was used for constant potential electrolysis, and the amount of metal dissolved in the electrolyte was measured by ICP emission spectroscopy. As the electrolyte, 1 mol LiClO ₄
/ EC (ethylene carbonate) + DEC (diethylene carbonate) was used.

Table 2 shows the measurement results. Examples 1 to 7
It was confirmed that in the current collector material of No. 1, the amount of ions eluted into the electrolyte was maintained at a low level.

(Test 2) Each of the current collector materials prepared in Examples 1 to 7 and Comparative Examples 1 to 8 was added to a 4.5 V VS. Li + / Li was subjected to constant potential electrolysis, and the amount of metal dissolved in the electrolyte was measured by ICP emission spectroscopy. As the electrolyte, 1 mol LiPF ₆ /
EC (ethylene carbonate) + DEC (diethylene carbonate) was used.

Table 2 shows the measurement results. Examples 1 to 7
It was confirmed that in the current collector material of No. 1, the amount of ions eluted into the electrolyte was low.

(Test 3) The surface of each current collector material prepared in Examples 1 to 7 and Comparative Examples 1 to 8 was coated with a positive electrode active material of a lithium ion battery. The composition of the positive electrode active material of the lithium ion battery was such that lithium cobalt oxide was 50% by weight, acetylene black was 10% by weight, PVDF (polyvinyl difluoride) was 5% by weight, and NMP (N-methylpyrrolidone) was 35% by weight. Was. Then, at a temperature of 100 ° C, 1
Dry for 0 minutes. Thus, the thickness after drying is 8
A coating of the positive electrode active material was formed on the surface of each current collector material so as to have a thickness of 0 μm. Thereafter, the coating film was pressed against the surface of each current collector material by applying a pressure of about 20% with a rolling roll. Thus, the adhesion of the coated film after rolling was observed.

The contact resistance between the current collector material and the active material coating was measured. As shown in FIG. 1, the contact resistance is measured by measuring the distance between AB with a digital multimeter while each sample is sandwiched between an upper electrode 1 (weight: 500 g) made of brass and a lower electrode 2. It was done. In this case, strictly, only the contact resistance is not measured, but since the volume resistance of the electrode or the sample is so small as to be negligible, the measured value can be regarded as the contact resistance value.

Table 2 shows the observation results of the adhesion of the coating film and the measurement results of the contact resistance value. The current collector materials prepared in Examples 1 to 7 show good adhesion of the coating film even after rolling,
Also, it can be seen that the contact resistance value with the coating film is low.

(Test 4) The surface of each current collector material prepared in Examples 1 to 7 and Comparative Examples 1 to 8 was coated with an electrode active material of an electric double layer capacitor. The composition of the active material was 15% by weight of phenolic resin-based activated carbon (trade name: Cractiv 10 Kuraray), 5% by weight of polyimide, and 80% by weight of NMP (N-methylpyrrolidone). Then, the coating film was dried. In this way, a coating of the electrode active material of the electric double layer capacitor was formed on the surface of each current collector material so that the thickness after drying became 20 μm. Then, the temperature 200
After baking the coating at 20 ° C. for 20 minutes, the coating was pressed against the surface of each current-collector material by applying a pressure of about 20% with a rolling roll. Thus, the adhesion of the coated film after rolling was observed. Further, the contact resistance between the surface of each current collector material and the coating film of the active material was measured in the same manner as in Test 3.

Table 2 shows the observation results of the adhesion of the coating film and the measurement results of the contact resistance value. The aluminum foils prepared in Examples 1 to 7 had good adhesion of the coating film of the active material even after rolling, and also showed a low contact resistance value with the coating film.

[0065]

[Table 2]

The embodiments disclosed above are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the examples above, and should be construed as including all modifications and alterations within the scope and meaning equivalent to the terms of the claims.

[0067]

As described above, according to the present invention, the aluminum foil for a current collector has excellent adhesive strength to an electrode active material and a binder, and is used as a current collector for a secondary battery or an electric double layer capacitor. Since the amount of elution into the electrolyte is small, it is useful for secondary batteries and electric double-layer capacitors that require stable performance for a long period of time.

The method for producing an aluminum foil for a current collector according to the present invention is safe and economical, and is suitable for industrial production.

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating a method of measuring a contact resistance value performed in an example.

[Explanation of symbols]

 1 upper electrode 2 lower electrode

Claims (9)

[Claims] An average roughness Ra of at least one surface is 0.3 μm or more and 1.5 μm or less and a maximum height R
An aluminum foil for a current collector, wherein y is 0.5 μm or more and 5.0 μm or less. 2. The aluminum foil has a tensile strength of 98M.
The aluminum foil for a current collector according to claim 1, which is Pa or more. 3. The current collector aluminum foil according to claim 1, wherein the thickness of the aluminum foil is 10 μm or more and 150 μm or less. 4. The aluminum foil contains not less than 99.0% by weight of aluminum and not more than 0.5% by weight of each of iron, copper and silicon, and the total content of iron, copper and silicon is 1.0% by weight. %. The aluminum foil for a current collector according to any one of claims 1 to 3, which is less than 5%. 5. An oxide film having a withstand voltage of 0.5 V or more and 2.0 V or less is formed on a surface of the aluminum foil.
The aluminum foil for a current collector according to any one of claims 1 to 4. 6. A current collector comprising the aluminum foil according to any one of claims 1 to 5. 7. A secondary battery comprising the current collector according to claim 6. 8. An electric double layer capacitor comprising the current collector according to claim 6. 9. The method for producing an aluminum foil for a current collector according to any one of claims 1 to 5, wherein alumina particles are sprayed on a surface of the aluminum foil using water or a nonflammable organic solvent as a medium. A method for producing an aluminum foil for a current collector, comprising roughening the surface of an aluminum foil by the method.