JP6521806B2 - Method of manufacturing aluminum foil - Google Patents

Description

  The present invention relates to a method of producing an aluminum foil by electrolysis, and more particularly to a method of producing a high quality aluminum foil which is easily peeled off from a titanium drum used as an electrolytic cathode.

  In recent years, lithium ion batteries have been developed as batteries for automobiles and personal computers. In a lithium ion battery, an aluminum foil is used as a positive electrode current collector to improve the battery capacity.

  Aluminum foil is conventionally manufactured by rolling an aluminum foil substrate. The lower limit of the thickness of the aluminum foil produced by such a rolling method is usually about 10 μm. In order to further increase the battery capacity of the lithium ion battery and miniaturize it, it is preferable to use an aluminum foil which is as thin as possible, for example, 5 to 10 μm thick. Thus, although thin aluminum foil can be manufactured also by a rolling method, since it is necessary to increase the number of times of a rolling process, there existed a problem that manufacturing cost became expensive.

  By the way, about the copper foil used as a negative electrode collector of a lithium ion battery, the electrolytic copper foil is used for the most at present, and the rolled copper foil is not used. The electrolytic copper foil is manufactured by forming a plating film of copper on a cathode drum as a base material and then peeling the copper plating film from the cathode drum. Here, since the aluminum foil is inferior in strength to the copper foil, it is extremely difficult to separate and take up and collect after being deposited on the cathode drum. Therefore, a method of easily peeling the aluminum foil deposited on the cathode drum is strongly desired.

  Patent Document 1 describes a method of producing an aluminum foil by an electrolytic method. It is important to adjust the surface roughness of the cathode drum in order to efficiently produce a good quality aluminum foil. If deep valleys or high peaks are present in part of the cathode drum surface, aluminum bites into the valleys, and when the bites are peeled off, it becomes a resistance and causes breakage or cutting of the aluminum foil. Although patent document 1 describes that arithmetic mean roughness Ra is described, there is no description about defining maximum height (Ry) and ten-point average roughness (Rz). The present inventors have found that defining Rz is particularly effective for efficiently producing a high-quality aluminum foil. It is because Rz is an index that best represents the degree of the height of the peaks and the depth of the valleys, as well as their number.

JP 2014-80632 A

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method for producing aluminum foil by electrolysis, which is easy to peel from a cathode drum made of titanium and produces high quality aluminum foil. .

  Specifically, the present invention comprises, in claim 1, a step of electrodepositing an aluminum foil on a rotating titanium cathode drum using a molten salt as an electrolytic solution, and a step of peeling and recovering the electrodeposited aluminum foil. The titanium cathode drum has a surface roughness of an arithmetic mean roughness (Ra) of 0.10 to 0.40 μm and a ten point mean roughness (Rz) of 0.20 to 0.70 μm. Method of producing an aluminum foil.

  According to a second aspect of the present invention, in the first aspect of the present invention, the surface roughness of the titanium cathode drum is adjusted by electropolishing.

  Furthermore, according to the present invention, in claim 3 according to claim 1 or 2, the molten salt contains an alkyl imidazolium chloride or an alkyl pyridinium chloride and aluminum chloride.

  In the manufacturing method according to the present invention, by using a titanium cathode drum having a predetermined surface property, it is possible to obtain a high-quality aluminum foil with good releasability.

(A) And (b) is a SEM photograph of the aluminum foil surface obtained by the Example of this invention.

  In the production method according to the present invention, in order to produce an aluminum foil by electrolysis, electrodeposition is performed under appropriate conditions using a cathode drum made of molten salt and titanium to recover the aluminum foil. Hereinafter, the requirements constituting the present invention and the reasons for limitation thereof will be described. In the present invention, unless otherwise specified, "aluminum" refers to pure aluminum and aluminum alloys having a purity of 99.0% or more.

1. Electrolysis First, the electrolysis used in the method for producing an aluminum foil according to the present invention will be described. In this electrolysis, an electrolytic cell containing an electrolytic solution is prepared, and a titanium cathode drum serving as a cathode and an aluminum plate serving as an anode having a curved surface matching the curved surface of the drum are disposed in the electrolyte. The aluminum is electrodeposited on the surface of the rotating titanium cathode drum by supplying a direct current between both electrodes while rotating the.

1-1. Titanium Cathode Drum A titanium cathode drum is used as a cathode for electrolysis used in the method for producing an aluminum foil according to the present invention. Since titanium is excellent in corrosion resistance, it can be used as a cathode drum in the production of an electrodeposited copper foil or an electrodeposited aluminum foil. If high peaks and deep valleys exist on part of the surface of the titanium cathode drum, the deposited aluminum in the valleys bites in the electrodeposition of aluminum. And when peeling off the electrodeposition aluminum which bite in, big peeling resistance generate | occur | produces, and an electrodeposition aluminum foil is damaged or cut | disconnected by this.

  Such peel resistance is affected by the surface roughness of the drum. In the present invention, arithmetic mean roughness (Ra) and ten-point mean roughness (Rz) are defined as indices representing surface roughness. Thus, the peeling resistance is reduced, and the electrodeposited aluminum foil is easily peeled and collected from the titanium cathode drum.

  Ra was extracted from the roughness curve by the reference length in the direction of its average line, the absolute value of the deviation from the average line of the extracted portion to the measurement curve was summed, and the average value was expressed in micrometers (μm) It is a thing. In the present invention, Ra is defined as 0.10 to 0.40 μm. In order to make Ra less than 0.10 μm, a long time is required for the electrolytic treatment, so the electrolytic efficiency is lowered. On the other hand, when Ra exceeds 0.40 μm, it is difficult to peel off and aluminum can not be recovered, and the peelability, appearance and uniformity of the aluminum foil can not be achieved. In addition, Ra is preferably 0.15 to 0.30 μm.

  Rz extracts only the reference length from the roughness curve in the direction of its average line, measures from the average line of this sampling in the direction of longitudinal magnification, and the height of the highest peak to the fifth peak (Yp) The sum of the average of the absolute values and the average of the absolute values of the lowest valley bottom to the fifth lowest valley bottom (Yv) is determined, and this value is expressed in micrometers (μm). Rz is an index that represents the degree and number of high peaks and deep valleys, and is an index of surface roughness that is particularly important in the present invention. In the present invention, Rz is defined as 0.20 to 0.70 μm. If Rz is less than 0.20 μm, the peelability is too good and the aluminum foil peels off during electrolysis, so the uniformity of the aluminum foil is poor. On the other hand, when Rz exceeds 0.70 μm, grain boundaries and cracks occur in the electrodeposited aluminum foil to cause deterioration in quality, and the removability, appearance and uniformity of the aluminum foil can not be achieved. Rz is preferably 0.25 to 0.50 μm.

1-2. Electrolyte The standard electrode potential of aluminum is −1.662 V vs. As understood from being SHE, it is usually not possible to electrodeposit aluminum from an aqueous solution. Therefore, a molten salt as a mixture with an aluminum salt or an organic solvent in which an aluminum salt is dissolved is used as an electrolytic solution for electrodepositing aluminum.

Molten salts can be roughly classified into inorganic molten salts and organic room temperature molten salts. Among organic-based, room-temperature-type molten salts, for example, a mixture of 1-ethyl-3-methylimidazolium chloride (hereinafter referred to as "EMIC") and aluminum chloride (hereinafter referred to as "AlCl ₃ ") The melting point drops to around -50 ° C. Therefore, the electrodeposition of aluminum can be performed in a lower temperature environment by using an organic-based room temperature molten salt as the electrolytic solution. The electrodeposition of aluminum can be carried out in the same manner as EMIC even if 1-butylpyridinium chloride (hereinafter referred to as "BPC") is used in place of the EMIC. Thus, an organic room-temperature-type molten salt composed of an alkyl imidazolium chloride represented by EMIC, an alkyl pyridinium chloride represented by BPC, and an aluminum halide represented by aluminum chloride is used for aluminum electrodeposition. It can be suitably used as an electrolyte solution of From the viewpoint of the viscosity and conductivity of the electrolyte, the combination of EMIC and aluminum chloride is most preferable. The molar ratio of EMIC and _{AlCl 3 (EMIC: AlCl 3)} , and the molar ratio of BPC and AlCl ₃ (BPC: AlCl ₃₎ Both 2: 1 to 1: it is preferable to be 2, 1 More preferably, it is from 1 to 1: 2.

1-3. Additives In order to improve the smoothness of the aluminum foil surface, for example, an organic compound such as 1, 10-phenanthroline may be added to the electrolytic solution. Such an organic compound exerts the function of controlling the surface shape of the aluminum foil electrodeposited on the titanium cathode drum, and as a result, the smoothness of the aluminum foil surface is improved. The concentration of the organic compound in the electrolytic solution is preferably 0.2 to 2.0 g / L (1.1 to 11 mmol / L).

1-4. Electrodeposition Conditions Next, the electrodeposition conditions will be described. First, the electrodeposition temperature, that is, the temperature of the electrolytic bath in electrodeposition is preferably in the range of 10 to 150 ° C. When the electrodeposition temperature is lower than 10 ° C., the viscosity and the resistance of the electrolytic bath increase, so the maximum current density decreases. As a result, the electrodeposition efficiency is lowered, and the problem that aluminum deposition tends to be uneven occurs. On the other hand, when the temperature of the electrolytic bath exceeds 150 ° C., the volatilization of aluminum chloride and the decomposition of EMI ⁺ cations become remarkable, and the composition of the electrolytic solution becomes unstable. Furthermore, energy for maintaining the temperature is also increased, and deterioration of the electrolytic cell is also promoted, which lowers production efficiency. A more preferable temperature of the electrolytic bath is in the range of 25 ° C. to 100 ° C. near room temperature.

Next, the current density of direct current as an electrodeposition condition will be described. The current density is preferably 10 to 400 mA / cm ² , more preferably 20 to 200 mA / cm ² . Since the deposition rate corresponds to the current density, if the deposition rate is less than 10 mA / cm ² , the deposition rate is too slow, resulting in a decrease in production efficiency. On the other hand, it is difficult to exceed the current density of 400 mA / cm ² due to the restriction of the solution resistance of the electrolytic bath, and even if it exceeds 400 mA / cm ² , the electrodeposition speed becomes too high, and the electrodeposited aluminum foil becomes uneven. easy.

2. Peeling and Recovery of Electrodeposited Aluminum Foil As described above, the aluminum foil electrodeposited on the surface of the titanium cathode drum is peeled off, wound around a recovery drum, and continuously recovered. As a recovery method, for example, the electrode drum is first grown to a predetermined foil thickness while the cathode drum is stopped, electrodeposition is suspended once, the cathode drum is rotated, the exposed aluminum foil is peeled off, and the recovery drum is recovered. And a method of winding it while laminating and a method of collecting it as a peeling piece simultaneously with peeling. The thickness of the aluminum foil obtained by the present invention generally ranges from 1 μm to 20 μm, but the thickness may be appropriately selected depending on the application. For example, when using as a positive electrode collector of a lithium ion battery, it is preferable to be 8-12 micrometers.

3. Electropolishing Next, in the present invention, electropolishing is used to adjust the surface roughness Ra and Rz of the titanium cathode drum as described above. Here, the term “electropolishing” refers to a technique of smoothing a metal surface by utilizing the fact that a difference in dissolution rate occurs between the convexes and the concaves of the metal surface when a current is supplied to the metal immersed in the polishing liquid. It is.

  Conventionally, mechanical polishing such as buffing, chemical polishing using an etching agent, and the above-mentioned electrolytic polishing have been used as a method of polishing titanium. Mechanical polishing, in particular, has been widely used to control the surface roughness of titanium cathode drums, but it is difficult to obtain high smoothness of titanium surface, and fine scratches often remain on the surface. . Moreover, in chemical polishing such as etching, there is a disadvantage that the polishing surface becomes uneven. Compared to such mechanical polishing or chemical polishing, high smoothness is obtained in electropolishing, and a strong passive film is also formed on the surface layer, so the removability of the aluminum foil is improved. Furthermore, the surface of the titanium cathode drum whose surface roughness has been adjusted by electropolishing is also inhibited from the adhesion of foreign matter, is excellent in cleanliness, and is advantageous also in terms of the maintainability of the drum.

  The electropolishing process can be performed using an ethylene glycol solution of NaCl or an ethylene glycol solution of KCl. The titanium cathode drum is immersed in these solutions, and the surface of the drum is mirror-polished by voltage application and ultrasonic cleaning. Polishing is performed more effectively by combining high voltage electrolysis corresponding to rough polishing and low voltage electrolysis corresponding to finish polishing. Further, Ra and Rz can be adjusted by the processing time, that is, the application time of the voltage. The preferable electrolysis voltage and processing time of high voltage electrolysis are 30 seconds to 5 minutes at 15 to 60 V, and more preferable electrolysis voltage and processing time are 1 to 3 minutes at 20 to 40 V. The preferable electrolysis voltage and processing time of low voltage electrolysis are 5 to 60 minutes at 6 to 15 V, and the more preferable electrolysis voltage and processing time are 10 to 30 minutes at 8 to 12 V. For the combination, for example, remove dirt and oxide film on the surface layer by the first high-voltage electrolysis, and then perform ultrasonic cleaning, and then alternately perform high-voltage electrolysis and ultrasonic cleaning followed by low-voltage electrolysis and ultrasonic cleaning. Thus, mirror polishing with excellent smoothness can be performed.

  EXAMPLES The present invention will next be described in more detail by way of examples, which should not be construed as limiting the invention thereto.

<Fabrication of titanium cathode drum>
The titanium rod was electropolished to produce a titanium cathode drum having various surface roughness (Ra, Rz). Specifically, a titanium rod having a purity of 99.9%, a diameter of 10 mm and a length of 100 mm is used as an anode, and a SUS316 plate having a width of 100 mm and a length of 100 mm is used as a cathode. A solution in which NaCl was dissolved was used. The cathode SUS316 plate was spaced apart from the curved surface of the anode titanium rod by a substantially constant distance.

  In the electropolishing, the temperature of the electrolyte was set to 25 ° C., and (1) pre-treatment electrolysis was performed at an electrolysis voltage of 25 V for 3 minutes. (2) The product formed on the surface was removed by ultrasonic cleaning the surface of the electrodeposited titanium rod. Next, (3) the temperature of the electrolyte is kept at 25 ° C., and electrolysis is performed for 3 minutes at a high electrolysis voltage of 25 V, and for 30 minutes at a low electrolysis voltage of 10 V, and finally (4) The surface was sonicated. The titanium cathode drum was manufactured by repeating such operations (3) to (4) twice.

<Electrodeposition of aluminum foil>
An aluminum foil was formed by electrodeposition on the surface of the titanium cathode drum electropolished in accordance with the following procedure.

As the electrolytic solution, at a temperature of _{50 ℃, EMIC: AlCl 3 =} 1: was a mixture with 2 molar ratio. An electrolytic solution was placed in the electrolytic cell, and the electrolytically polished titanium cathode drum as the cathode and the 99.9% aluminum plate (width 80 mm, length 200 mm) as the anode were disposed in the electrolytic solution. Here, the aluminum plate of the anode was disposed to be separated from the curved surface of the titanium cathode drum by a substantially constant distance. Then, by performing direct current electrolytic operation at a current density of 40 mA / cm ² for 12 minutes, an aluminum foil of about 10 μm thickness was electrodeposited on the surface of the titanium cathode drum. After the electrolytic operation, the aluminum foil electrodeposited on the surface of the titanium cathode drum was washed with acetone and pure water, and the aluminum foil was peeled off from the titanium cathode drum and wound around a winding roll to be collected as a sample.

  The following evaluation was performed about the aluminum foil sample and titanium cathode drum which were produced as mentioned above.

<Surface roughness of titanium cathode drum>
The surface roughness (Ra, Rz) of the titanium cathode drum was measured by a laser microscope. Ra and Rz respectively represent the arithmetic mean roughness and the ten-point mean roughness defined in JIS B 0601-1994. The results are shown in Table 1.

<Characteristics of aluminum foil>
As the properties of the aluminum foil, peelability, appearance and uniformity were evaluated as follows.
First, for peelability, an aluminum foil sample electrodeposited on the surface of a cathode drum made of titanium is washed with acetone and pure water, and the one that can be peeled off from the drum without touching it is regarded as peelable (acceptable). The thing which was not was made peelability rejection (x). Also in the following evaluations, a pass is made ○ and a fail is made x.

  Next, regarding the appearance, in the surface of the aluminum foil sample (the contact surface of the cathode drum), a field of view of 25 μm × 20 μm was arbitrarily selected at 10 places and observed and evaluated by SEM. Specifically, the appearance was evaluated as ○ when no pinhole was observed in the entire visual field, and the appearance was evaluated as x when one or more pinholes were observed in one or more visual fields. As an example, FIG. 1 (a) is a SEM photograph of Comparative Example 6, and (b) is a SEM photograph of Invention Example 3. In FIG. 1A, a pinhole 2 is observed near the upper center of the figure. On the other hand, in the same figure (b), a pinhole is not observed at all. In addition, 1 of FIG. 1 (a) shows a grain boundary. The lengths of the scale lines in FIGS. 1 (a) and 1 (b) are both 5 μm.

Furthermore, the uniformity was evaluated as follows. From FIG. 1, it was judged that the uniformity was inferior if the color unevenness of the whole was remarkable, and x was not.
The evaluation results of the above-mentioned characteristics of the aluminum foil are shown in Table 1.

<Electrolytic polishing efficiency>
The electropolishing efficiency at the time of obtaining a titanium cathode drum by electropolishing a titanium rod was evaluated as follows. In order to achieve the target surface roughness, the case of exceeding the upper limit of 60 minutes of the preferable processing time of the above-mentioned low voltage electrolysis was regarded as x inferior to the electrolytic polishing efficiency, and the other was judged as o. The results are shown in Table 1.

<Overall evaluation>
The overall evaluation was determined as follows based on the evaluation results of the surface roughness of the titanium cathode drum, the characteristics of the aluminum foil, and the electropolishing efficiency. The case where all of peelability, appearance, uniformity and electropolishing efficiency were judged as ○ was regarded as comprehensive evaluation ○, and the other was judged as x. The results are shown in Table 1.

  In the invention examples 1 to 8, Ra and Rz were within the range defined in the present invention, so the aluminum foil properties (peelability, appearance and uniformity) and the electropolishing efficiency are both good, and the overall evaluation is pass. there were.

  On the other hand, in Comparative Example 1, since Rz was too smaller than the range specified in the present invention, the aluminum foil was peeled off during the electrolysis, and the uniformity was rejected. Moreover, since Ra was too smaller than the range prescribed | regulated by this invention, in order to implement | achieve this, the electropolishing efficiency of titanium became disqualified. As a result, the overall evaluation failed.

  In Comparative Example 2, since Rz was too smaller than the range specified in the present invention, the aluminum foil peeled off during the electrolysis, and the uniformity was rejected. As a result, the overall evaluation failed.

  In Comparative Example 3, since Ra was too smaller than the range specified in the present invention, the electropolishing efficiency of titanium was rejected in order to realize this. As a result, the overall evaluation failed.

  In Comparative Examples 4 to 6, since Rz was larger than the range defined in the present invention, grain boundaries and cracks occurred in the aluminum foil, and the releasability, appearance and uniformity of the aluminum foil were rejected. As a result, the overall evaluation failed.

  In Comparative Example 7, since Ra was larger than the range specified in the present invention, the removability, the appearance and the uniformity of the aluminum foil were rejected. As a result, the overall evaluation failed.

  According to the present invention, a high quality electrolytic aluminum foil can be efficiently produced because it is easily peeled off from a titanium cathode drum, and an industrially remarkable effect can be obtained.

1 ... grain boundary 2 ... pinhole

Claims (3)

  Using a molten salt as an electrolytic solution, and electrodepositing aluminum foil on a rotating titanium cathode drum; and peeling and recovering the electrodeposited aluminum foil, wherein the titanium cathode drum has a diameter of 0.10 to 0.10. A method for producing an aluminum foil characterized by having an arithmetic mean roughness (Ra) of 0.40 μm and a ten point mean roughness (Rz) of 0.20 to 0.70 μm.   The manufacturing method of the aluminum foil of Claim 1 in which the surface roughness of the said titanium cathode drum is adjusted by electropolishing.   The manufacturing method of the aluminum foil of Claim 1 or 2 in which the said molten salt contains an alkyl imidazolium chloride or an alkyl pyridinium chloride, and aluminum chloride.

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