TW201802258A - Electrolytic copper foil for providing a high tensile strength, maintaining a high tensile strength after being heated and realizing an excellent folding resistance - Google Patents

Abstract

The purpose of the present invention is to provide an electrolytic copper foil for providing a high tensile strength, maintaining high tensile strength after being heated and realizing an excellent folding resistance. The electrolytic copper foil is characterized in: the content of carbon (C) being 20 to 150 mass ppm, the content of sulfur (S) being 18 mass ppm or less, the content of nitrogen (N) being 40 mass ppm or less, and the content of chlorine (Cl) being 25 to 200 mass ppm.

Description

Electrolytic copper foil

The present invention relates to an electrolytic copper foil, which is suitable for manufacturing, for example, a negative electrode current collector of a lithium ion secondary battery or a printed circuit board.

Printed circuit boards (hereinafter sometimes referred to simply as "circuit boards") used in negative current collectors of lithium-ion secondary batteries (hereinafter sometimes referred to simply as "batteries") and various electronic devices such as electronic communication devices ) Conductors, copper foil is widely used. Compared with rolled copper foil, electrolytic copper foil is widely used because it is easy to achieve both conductivity and strength, and it can be made thinner at low cost.

In addition, the copper foil is subjected to various stress loads during the manufacture of the lithium ion secondary battery and during the charging and discharging of the battery. Therefore, damage such as wrinkles or cracks may occur on the copper foil, which may cause problems such as degradation of battery cycle characteristics, short circuit, and fire. In order to solve these problems, methods for improving physical properties have been proposed. For example, in a lithium ion secondary battery, the tensile strength of copper foil is set to a predetermined value or more, the tensile strength after heating is set to a predetermined value or more, or The elongation of the copper foil is set to a predetermined value or more (Patent Documents 1 to 3).

In addition, in recent years, with the further development of higher capacity and lighter weight of lithium-ion secondary batteries, the structure of lithium-ion secondary batteries has also changed compared with the past. For example, in order to store the electrodes in the battery case at a higher density, there are more and more cases where copper foil is folded.

Specifically, in a cylindrical battery, in order to prevent winding misalignment of the innermost or outermost electrode terminal portion and ensure safety, the copper foil is sandwiched between the separator or the aluminum foil of the positive electrode, and then folded back. Folding processing.

In addition, in a rectangular or laminated battery, the electrode has been folded back at 180 ° in the past (corresponding to FIG. 4 and curved corner portion 12 of Patent Document 4). However, in recent years, in order to achieve higher density, stricter implementation may be required. Folding processing, such as applying more tension to wind it up, or pressing it after winding, reducing the bending radius, or winding the electrode on the inner layer side within a smaller bending radius.

On the other hand, in recent years, various electronic devices such as portable devices have been rapidly developed in terms of further miniaturization and high density, and requirements for miniaturization and high-density component storage have been demanded for mounted components. In particular, in a flexible printed circuit board, a copper foil is folded in order to accommodate a conductor portion in a narrower frame.

However, such a folding process has a problem that the copper foil may be damaged, such as a gap or a break. In order to avoid this problem, it is necessary to develop a copper foil having good durability for the folding process.

Here, the "folding process" refers to a bending process in which a certain surface of the copper foil is folded back at 180 °. This folding process does not have to be close to the bend, and other parts can be clamped inside the bent portion. In addition, the copper foil durability with respect to such a folding process is hereinafter referred to as "foldability."

In general, the evaluation of the bendability or folding resistance of a copper foil often uses the MIT bending resistance test or the IPC bending test specified in JIS P8115: 2001. For example, in the MIT bending resistance test, a high-speed repeated bending of ± 135 ° is performed with a load applied to the copper foil, and the number of bending times is evaluated. In this method, the tensile strength The higher the degree of copper foil, the more the number of bends before fracture or resistance increase, and it is generally evaluated as having good folding resistance. In addition, the IPC bending test is a 180 ° bending, but the bending radius is large, and the bending is performed within the elastic deformation range of the copper foil. In this method, instead of breaking, the number of bends before the resistance increases to a certain level is usually evaluated.

The folding test is a 180 ° bending test. Compared with the MIT resistance test, the bending radius is small, and the bending is performed within the plastic deformation range of the copper foil. Therefore, the folding resistance is a measurement method in which the load mode is completely different from the MIT folding resistance test or the IPC bending test, and the test results do not necessarily correspond. Therefore, the copper foil disclosed in Patent Document 5 which improves the folding resistance of the MIT folding resistance test and the copper foil disclosed in Patent Document 6 which improves the bendability of the IPC bending test do not necessarily have sufficient folding resistance.

In addition, the copper foil folding test is a bending test accompanying a 180 ° bend, but the phenomenon is different from, for example, a 180 ° bend of a copper strip or a copper plate having a thickness exceeding 50 μm. That is, because copper foil is very thin (for example, 4 to 30 μm), the number of crystal grains in the thickness direction is small, and the difference between the compressive stress and the tensile stress between the inner and outer sides of the bend is also small. Features not found in thick copper strips.

In addition, there is no correspondence between the folding resistance and the extension of the copper foil. For example, Patent Document 7 discloses a technology that achieves a balance between tensile strength and folding resistance by controlling the crystal orientation and work hardening index of a copper foil with large elongation and poor folding resistance. However, this technique is related to the technique of rolling copper foil, and the well-known relationships among copper plates and strips such as the relationship between crystal orientation and bendability cannot be easily applied to electrolytic copper foil. That is, the electrolytic copper foil has an electrodeposited structure, so Aspects such as bit density, dislocation density, and diffusion coefficient are very different from the calendering structure.

In addition, in order to solve the above-mentioned problems, for example, in Patent Document 8 on a printed circuit board, it is proposed to set the elastic modulus and thickness of a resin layer bonded to a metal layer (copper foil) within a fixed range so that the A method in which the surface roughness is less than a predetermined value; Patent Document 9 proposes a method in which the tensile elastic modulus, thickness of a polyimide layer, and the tensile elastic modulus, thickness, and average crystal grain size of a copper foil are fixed. A method within the range; Patent Document 10 proposes a method of controlling the thickness, average crystal grain size, and crystal orientation of each copper foil when the copper foil is bonded to both sides of the polyimide layer within a predetermined range. However, most of these measures benefit from the characteristics of the resin side or the structure of the laminated board to which the copper foil is attached, and the characteristics of the copper foil side have not been sufficiently studied. Therefore, the characteristics of the copper foil side are expected to be improved. If the fold resistance can be improved by relying only on the characteristics of the copper foil side, the freedom of choosing a resin or designing a substrate will be improved, so that a resin with better signal transmission performance can be used, and a more efficient substrate design can be performed. The performance as a flexible printed circuit board is expected to be further improved.

On the other hand, as a method for improving folding resistance in copper foil, it is known that reducing the tensile strength of copper foil can effectively improve folding resistance, but the tensile strength cannot be reduced blindly. That is, as described above, in addition to the folding resistance of lithium ion secondary batteries, the tensile strength of copper foil and the tensile strength after heating need to be more than a certain value. In addition, in flexible substrates, the tensile strength of copper foil When the tensile strength is low, when a flexible printed circuit board that is further thinner is manufactured, the workability is deteriorated during the passage of the plate material and the resin molding step.

As such, it is proposed to improve the folding resistance and improvement of copper foil Tensile strength is the opposite requirement. Therefore, using conventional copper foil, it is difficult to achieve high folding strength while maintaining high tensile strength after heating, and good folding resistance.

[Advanced technical literature]

[Patent Literature]

[Patent Document 1]: Japanese Patent No. 5588607

[Patent Document 2]: Japanese Patent No. 5074611

[Patent Document 3]: Japanese Patent No. 4583149

[Patent Document 4]: Japanese Patent No. 4863636

[Patent Document 5]: Japanese Patent No. 5301886

[Patent Document 6]: Japanese Patent No. 5373970

[Patent Document 7]: International Publication No. 2012/128099

[Patent Document 8]: Japanese Patent Laid-Open No. 2012-006200

[Patent Document 9]: Japanese Patent Laid-Open No. 2014-080021

[Patent Document 10]: Japanese Patent Laid-Open No. 2015-127120

The present invention has been developed in view of the above circumstances, and an object thereof is to provide an electrolytic copper foil that has high tensile strength, maintains high tensile strength after heating, and has good folding resistance.

The inventors have conducted in-depth research on the relationship between the trace components contained in the copper foil, folding resistance, and tensile strength, and found that sulfur (S) in the copper foil Or nitrogen (N) has a good effect of improving tensile strength, but as its content increases, the foldability decreases very significantly, and carbon (C) and chlorine (Cl) in copper foil have no effect on tensile strength. Such a large improvement effect, but after its content is increased, the folding resistance will not be significantly reduced. Compared with sulfur (S) or nitrogen (N), the degree of folding resistance is more moderate. According to the survey results, The content of carbon (C), sulfur (S), nitrogen (N), and chlorine (Cl), which are the trace components contained in the copper foil, are controlled within the specified ranges, respectively, and the excellent folding resistance and high tensile strength are successfully taken into account. The present invention has been completed.

That is, the gist structure of this invention is as follows.

[1] An electrolytic copper foil characterized by a carbon (C) content of 20 to 150 mass ppm, a sulfur (S) content of 18 mass ppm or less, a nitrogen (N) content of 40 mass ppm or less, and chlorine The content of (Cl) is 25 to 200 mass ppm.

[2] The electrolytic copper foil according to the above [1], wherein a ratio of the content of the carbon (C) to the content of the chlorine (Cl) [content of C / content of Cl] is in a range of 0.70 to 1.40 .

[3] The electrolytic copper foil according to the above [1] or [2], wherein the tensile strength measured in a normal state is in a range of 380 to 600 Mpa.

[4] The electrolytic copper foil according to any one of the above [1] to [3], wherein a tensile strength measured in a state after heating at 300 ° C. for 1 hour is in a range of 300 to 550 MPa.

[5] The electrolytic copper foil according to any one of the above [1] to [4], wherein the electrical conductivity is 85% IACS or more.

[6] A lithium ion secondary battery having the electrolytic copper foil according to any one of the above [1] to [5] as a negative electrode current collector.

[7] A printed circuit board having the structure according to any one of the above [1] to [5] The electrolytic copper foil described above is used as the conductor portion.

With the present invention, it is possible to provide an electrolytic copper foil that has high tensile strength, maintains high tensile strength after heating, and can achieve good folding resistance. The electrolytic copper foil according to the present invention is suitable for, for example, manufacturing a negative electrode current collector of a lithium ion secondary battery, and can improve battery capacity, cycle characteristics, and safety. In addition, it is also applicable to, for example, the manufacture of a printed circuit board, and can improve the operability when manufacturing a circuit board and the durability when folding a flexible printed circuit board.

10‧‧‧ Copper foil

20‧‧‧ compartment

30‧‧‧roller

X‧‧‧ dashed area

FIG. 1 is a schematic cross-sectional view schematically showing a scenario when a folding test is performed in the embodiment.

Hereinafter, preferred embodiments of the electrolytic copper foil according to the present invention will be specifically described.

The electrolytic copper foil according to the present invention has a carbon (C) content of 20 to 150 mass ppm, a sulfur (S) content of 18 mass ppm or less, a nitrogen (N) content of 40 mass ppm or less, and chlorine ( The content of Cl) is 25 to 200 mass ppm.

In addition, in the present specification, electrolytic copper foil refers to a copper foil produced by electrolytic treatment, including untreated copper foil without surface treatment after the production of the foil, and copper foil that has been subjected to a surface treatment as required (surface-treated electrolytic copper). Foil). The thickness of the electrolytic copper foil is preferably 30 μm or less, and more preferably 4 to 15 μm. Hereinafter, unless otherwise specified, "copper foil" means "electrolytic copper foil". Mass ppm is the mass fraction, ie mg / kg.

<Ingredient composition>

The following are the composition and functions of the electrolytic copper foil according to the present invention.

In the electrolytic copper foil according to the present invention, the contents of carbon (C), sulfur (S), nitrogen (N), and chlorine (Cl) are controlled within the following specified ranges.

[S content: 18 mass ppm or less] and [N content: 40 mass ppm or less]

S and N are elements that increase the tensile strength, and these elements tend to embrittle the crystal grain boundary of the copper foil, so the folding resistance is significantly reduced.

When the S content exceeds 18 mass ppm, folding resistance is extremely deteriorated. Therefore, the S content is set to 18 mass ppm or less, and preferably 13 mass ppm or less. The lower the S content, the better. The lower limit value is 0 mass ppm, but from the viewpoint of practicality, it may be 1 mass ppm.

When the N content exceeds 40 mass ppm, folding resistance is extremely deteriorated. Therefore, the N content is set to 40 mass ppm or less, and preferably 30 mass ppm or less. The lower the N content, the better. The lower limit value is 0 mass ppm, but from the viewpoint of practicality, it may be 1 mass ppm.

[C content: 20 to 150 mass ppm] and [Cl content: 25 to 200 mass ppm]

Although C and Cl are elements having an effect of improving tensile strength, unlike S or N described above, the effect of embrittlement of the crystal grain boundary of the copper foil is small, and the folding resistance is not significantly reduced.

When the C content is less than 20 mass ppm, the effect of improving the tensile strength cannot be fully exhibited, and when it exceeds 150 mass ppm, the folding resistance tends to decrease. Therefore, from the viewpoint of taking both tensile strength and folding resistance into consideration, the C content should be 20 to 150 mass ppm, preferably 30 to 140 mass ppm, and more preferably 60 to 140 mass ppm.

When the content of Cl is less than 25 mass ppm, the effect of improving the tensile strength cannot be sufficiently exerted, and when it exceeds 200 mass ppm, the folding resistance tends to decrease. Therefore, from the viewpoint of taking both tensile strength and folding resistance into consideration, the Cl content should be 25 to 200 mass ppm, preferably 30 to 180 mass ppm, and more preferably 50 to 150 mass ppm.

In addition, the ratio of the C content to the Cl content [C content / Cl content] is preferably in the range of 0.70 to 1.40, and by controlling the above range, the effect of improving the folding resistance of the copper foil can be further improved. It is well known that Cl is required for effective adsorption of organic additives on copper foil. Its mechanism is not clear, but because the system is said to Cu ⁺ - complex of organic additive will be electrostatically adsorbed on specific adsorption on the surface of the copper substrate Cl ^-, then Cu ⁺ - complex of organic additive via Cl ^- Adsorption On a copper substrate. Then, when Cu ⁺ indirectly adsorbed on the copper substrate is reduced to Cu atoms and precipitated on the copper substrate, the organic additives (C) and Cl adsorbed together also enter the copper foil at the same time. Therefore, the balance of the existence ratio of C and Cl is broken, the existence state of C and Cl in the copper foil is changed, and the effect of improving the folding resistance of the copper foil cannot be sufficiently obtained.

[Other trace ingredients]

To the extent that the effect of the present invention is not impaired, the electrolytic copper foil of the present invention may contain components derived from various additives and unavoidable impurities in addition to the aforementioned components.

In addition, the component derived from various additives mentioned here means a component other than the above-mentioned components among components derived from an organic additive or an inorganic additive used in the production of electrolytic copper foil. The upper limit of the content of the components derived from various additives is preferably 100 mass ppm.

In addition, the term "unavoidable impurities" as used herein means impurities that are inevitably contained in a manufacturing step. The components listed as unavoidable impurities are, for example, iron (Fe), oxygen (O), and the like. The upper limit of the content of the inevitable impurities is preferably 100 mass ppm. Depending on the composition and content of unavoidable impurities, the characteristic value of the copper foil may be lowered. Therefore, it is preferable to further suppress the content.

<Manufacturing method of electrolytic copper foil>

The preferred manufacturing method of the electrolytic copper foil (or surface-treated electrolytic copper foil) according to the present invention is described below.

The electrolytic copper foil of the present invention is produced, for example, by using a sulfuric acid-copper sulfate aqueous solution as an electrolytic solution, and supplying the electrolytic solution between an insoluble anode and a titanium cathode roller provided opposite the anode, The cathode roller is rotated at a fixed speed, and a DC current is applied between the two electrodes, so that copper is precipitated on the surface of the cathode roller, and the precipitated copper is torn off from the surface of the cathode roller and continuously wound. The insoluble anode is Titanium covered with platinum group elements or oxide elements. Moreover, this device is only an example.

In particular, the electrolytic copper foil according to the present invention is manufactured under conditions that do not contain S or N as much as possible in the copper foil made into the foil, and can achieve a sulfur (S) content in the copper foil of 18 mass ppm or less and nitrogen ( N) The state where the content is 40 mass ppm or less.

Generally, in order to increase the strength and heat resistance of copper foil, additives are generally added to the electrolytic solution. Examples of such additives include organic additives and inorganic additives, and organic additives are particularly preferred. The molecular structure of such commonly used organic additives often contains S or N. Organic additives containing S or N in the molecular structure have a strong adsorption on copper foil, so they can be easily absorbed into the copper foil. This phenomenon originates from the unshared electron pairs owned by S and N.

Therefore, as described above, from the viewpoint of obtaining a copper foil in which the contents of S and N in the copper foil are controlled within a predetermined range, it is preferable to use an organic additive that does not include S and N in the molecular structure. By using such an organic additive, S and N derived from the organic additive can be effectively prevented from being absorbed into the copper foil.

Examples of organic additives not containing S and N in the molecular structure include polyethers (polyethylene glycol, polypropylene glycol, etc.), water-soluble polysaccharides (hydroxyethyl cellulose, carboxymethyl cellulose, and the like), and the like. In particular, considering the mass productivity of the electrolytic copper foil, a polymer compound having a tendency to have high stability in an electrolytic solution is preferable to a monomolecular compound.

As described above, from the viewpoint of obtaining a copper foil in which S and N in the copper foil are controlled within a predetermined range, an inorganic additive that does not include S and N in the molecular structure may be used. However, when an inorganic additive is used, the inorganic in the electrolytic solution is inorganic. Additives will precipitate, resulting in deterioration of mass productivity, and lowering of electrical conductivity, which cannot ensure good folding resistance. Therefore, as the additive, the above-mentioned organic additive is preferably used.

Furthermore, as described above, by using an organic additive that does not contain S and N in the molecular structure, the content of S and N in the obtained copper foil can be controlled within the above-mentioned range. However, the S in the copper foil can be further reduced. From the viewpoint of the content of N and N, it is preferable to use a method that reduces the concentration of S and N in the electrolytic solution as much as possible, such as using a high-purity reagent, selecting the type of activated carbon, and pickling before putting in a copper raw material.

Sulfuric acid, copper sulfate reagents, and additives for preparing electrolytes may contain S or N as impurities. In addition, S or N may be contained in attachments or impurities of copper raw materials or activated carbon (the activated carbon treatment used in the production of electrolytic copper foil). Among them, compounds having high reactivity and adsorption properties are removed by appropriate treatment with activated carbon, or are separated by electrolytic reaction. Solution, it is not easy to thicken in the electrolytic solution, and the less reactive compounds are slowly accumulated in the electrolytic solution. Therefore, although the degree of influence is small compared to S and N brought by intentionally added organic additives, it is also desirable to remove S and N brought by reagents, activated carbon, etc. as much as possible.

It should be noted that even if these processes are performed, it is difficult to completely remove impurities containing S or N from the electrolytic solution. If the concentration of S or N in the electrolytic solution is kept to zero, the work load will increase. Therefore, in consideration of practical manufacturing, from the viewpoint of practicality, the contents of S and N in the copper foil may be 1 mass ppm or more, respectively. That is, as long as the content of S is 18 mass ppm or less and the content of N is 40 mass ppm or less, the foldability is not affected much.

In addition, the electrolytic copper foil according to the present invention is manufactured under the condition that the copper foil made of the foil contains appropriate amounts of C and Cl, and the carbon (C) content in the copper foil can be achieved in the range of 20 to 150 mass ppm. And the state of the content of chlorine (Cl) in the range of 25 to 200 mass ppm.

Generally, in order to achieve high strength and high heat resistance of a copper foil, it is desirable that the copper foil absorb a large amount of organic additives (for example, the C content is large). However, compared with organic additives containing S or N, the organic additives not containing S and N have a lower adsorption to copper, and therefore, the amount absorbed into the copper foil tends to be smaller. Therefore, when using organic additives that do not contain S and N, in order to increase the C and Cl content in the copper foil so as to achieve high strength and high heat resistance of the copper foil, for example, the chloride ion (Cl _- ) Concentration is an effective method. It is well known that the chloride ions in the electrolyte interact with the organic additives, so that the organic additives are easily absorbed into the copper foil. On the other hand, when the amount of C and Cl absorbed in the copper foil is excessive, the folding resistance tends to deteriorate.

Therefore, as described above, it is preferable to control the chloride ion concentration in the electrolytic solution from the viewpoint of obtaining a copper foil in which the content of C and Cl in the copper foil is controlled within a predetermined range. Specifically, the chloride ion concentration in the electrolytic solution is preferably 150 to 250 mg / L, and more preferably 150 to 200 mg / L. By controlling the above range, the content of C and Cl in the copper foil can be effectively controlled. On the other hand, when the chloride ion is less than 150 mg / L, the amount of C and Cl contained in the copper foil becomes small, and it is difficult to obtain high strength and high heat resistance effects. In addition, when the chloride ion exceeds 250 mg / L, the amount of C and Cl absorbed in the copper foil increases, and the folding resistance is deteriorated.

In addition, the [C content / Cl content] in copper foil can be managed in principle by using the ratio of the concentration of organic additives in the electrolyte to the concentration of chloride ions. To adjust appropriately.

An example of a preferable composition of the electrolytic solution for manufacturing an electrolytic copper foil is given below.

Copper concentration 50 to 100 g / L

Sulfuric acid concentration of 40 to 120 g / L

Organic additives 0.1 to 100 mg / L

Chloride ion 150 to 250mg / L

As described above, it is important to manufacture under conditions that do not contain S or N as much as possible in the copper foil that is made into the foil, and under conditions that appropriately absorb C or Cl. For this reason, it is preferable and effective to properly control the electrolytic conditions and intentionally add organic additives. method.

Generally, in the manufacture of copper foil, a thyristor DC power supply is generally used. In principle, the output voltage of a thyristor DC power supply will be 50 or 60 Hz. Frequency (pulsation). For example, when a thyristor DC power supply with a pulsation rate of 10% is used, a voltage vibration of 100 or 120 times per second with a maximum height difference of 10% will be generated.

As we all know, this kind of pulsation has a great influence on the potential response of organic additives such as adsorption, absorption behavior and copper precipitation behavior. However, detailed investigation and analysis are extremely difficult. Therefore, pulsation is usually not considered in the manufacture of copper foil. Influence. As a result, due to the influence of pulsation, there may be cases where the organic additive cannot be effectively absorbed, or abnormal segregation occurs at the crystal grain boundary, or the organic additive causes excessive absorption.

Therefore, in the production of the electrolytic copper foil of the present invention, it is preferable to adjust the electrolytic conditions to obtain the original adsorption behavior of the organic additive in a state where there is little external interference. Specifically, it is desirable to manufacture the electrolytic copper foil under electrolytic conditions in which the above-mentioned power supply voltage ripple is not generated as much as possible, and for example, it is preferable to use an inverter-type DC power supply for manufacturing.

The inverter-type DC power supply is controlled in a higher frequency area in principle, so it can be regarded as having substantially no pulsation effect. Therefore, by using an inverter-type DC power supply, it is possible to easily adjust the situation with little external interference with respect to the organic additive.

In addition, when using a thyristor-type DC power supply, it is also possible to obtain electrolytic conditions with less pulsation by performing electrolysis under conditions with as few pulsations as possible, or by selecting additives or electrolytic conditions that are not easily affected by pulsations.

In the present invention, as described above, it is recommended to use an organic additive that does not contain S and N in order to make the copper foil made of foil free of S or N as much as possible, but the organic additive has relatively weak adsorption force for copper. Therefore, the effects of the above pulsations In addition, it is more difficult for organic additives to be absorbed into the copper foil, so it is not preferable to consider the high strength and high heat resistance of the copper foil intuitively. However, as described above, by performing electrolysis using a method that does not generate pulsation as much as possible, even if an organic additive containing no S and N is used, the organic additive can be effectively absorbed into the copper foil, and a relatively uniform structure can be obtained.

In addition, the liquid temperature of the electrolytic solution is preferably 40 to 60 ° C, and the average current density of the cathode electrode surface is 45 to 60 A / dm ² .

The electrolytic copper foil of the present invention is preferably subjected to a surface treatment on at least one of its surfaces as necessary.

As the surface treatment of the copper foil, for example, chromate treatment, or Ni or Ni alloy plating, Co or Co alloy plating, Zn or Zn alloy plating, Sn or Sn alloy plating can be performed, and then chromate can be applied to the above various plating layers. Inorganic antirust treatment such as treatment, or organic antirust treatment using benzotriazole, etc., and silane coupling agent treatment. In addition to rust prevention, the surface treatment described above, for example, when used as a negative electrode current collector of a lithium ion secondary battery, can also play a role of increasing the adhesion strength with an active material, thereby preventing the charge and discharge cycle efficiency of the battery from decreasing. These rust preventive treatments are usually performed with extremely thin thicknesses relative to the thickness of the copper foil. Therefore, it has little effect on folding resistance or tensile strength.

Before performing the surface treatment on the copper foil, the surface of the copper foil may be subjected to a roughening treatment as necessary. As the roughening treatment, for example, a plating method, an etching method, or the like can be preferably used. These roughening treatments have the effect of further improving the adhesion to the circuit board resin when used as a conductor portion of a printed circuit board, and the adhesion to an active material when used as a negative electrode current collector of a lithium ion secondary battery.

As a roughening treatment using a plating method, electrolytic plating can be used Method and electroless plating method. Coarse particles can be formed by metal plating of one metal of Cu, Co, and Ni or alloy plating containing two or more of these metals.

In addition, as the roughening treatment using an etching method, a method such as physical etching and chemical etching is preferable. For example, as the physical etching, a method of etching by sandblasting or the like can be mentioned. Moreover, as a chemical etching, the method of performing an etching using a processing liquid etc. is mentioned. In particular, when performing chemical etching, as the processing liquid, a known processing liquid containing an inorganic or organic acid, an oxidizing agent, and an additive can be used.

<Characteristics of electrolytic copper foil>

The electrolytic copper foil according to the present invention preferably has a tensile strength of 380 MPa or more under normal conditions, more preferably 380 to 600 MPa, and still more preferably 400 to 600 MPa. By controlling within the above range, the operability and durability during battery or circuit board manufacturing can be further improved. In addition, in this specification, the "normal state" includes a state in which the copper foil does not have any thermal history (unheated after being manufactured), and includes a thermal history of 60 ° C or lower (after being heated at 60 ° C). status.

In addition, the electrolytic copper foil according to the present invention preferably has a tensile strength of 300 MPa or more, more preferably 300 to 550 MPa, in a state (after heating at 300 ° C and 1 hour) with a thermal history of 300 ° C and 1 hour. It is more preferably within a range of 350 to 550 MPa. By controlling within the above range, the operability and durability during battery or circuit board manufacturing can be further improved.

The tensile strengths described above are all values measured at room temperature (25 ° C ± 10 ° C) in accordance with IPC-TM-650.

In addition, the electrolytic copper foil according to the present invention preferably has a conductivity of 85% IACS or more, and more preferably 90% IACS or more. High strength of electrolytic copper foil It has a tendency to reduce the conductivity, but the electrolytic copper foil of the present invention absorbs a large amount of C and Cl to achieve high strength, so it is possible to reduce the decrease in conductivity. Since the electrolytic copper foil of the present invention is used as a conductive member, the higher the conductivity, the better. In addition, the said electric conductivity is the value measured based on JISH0505: 1975.

The electrolytic copper foil of the present invention is preferably used for manufacturing at least one of a negative electrode current collector of a lithium ion secondary battery and a conductor portion of a printed circuit board. Especially when used as a negative electrode current collector of a lithium ion secondary battery, it has high strength and high heat resistance, so it has excellent durability and folding resistance during battery manufacturing and charging and discharging, and can achieve higher density. Advantages of electrode storage. In addition, when it is used as a conductor portion of a printed circuit board, since it has high strength and high heat resistance, it has excellent operability and folding resistance when manufacturing a printed circuit board, and has the advantage of enabling higher density mounting. The electrolytic copper foil of the present invention is more preferably used for both a negative electrode current collector of a lithium ion secondary battery and a conductor portion of a printed circuit board. Conditions do not require other production lines, so it has a very economical advantage.

The embodiment of the present invention has been described above. The above embodiment is only an example of the present invention. Within the scope of the present invention, various changes can be made including the concept of the present invention and all forms included in the scope of patent application.

[Example]

Hereinafter, in order to further clarify the effects of the present invention, examples and comparative examples will be described.

(Example 1)

Since the electrolyte is supplied between the insoluble anode and a titanium cathode roller provided opposite the anode, the cathode roller is rotated at a constant speed while A DC current was applied between the electrodes to deposit copper on the surface of the cathode roll, and an untreated copper foil having a thickness of 8 μm was produced. The insoluble anode was composed of titanium covered with a platinum group element or an oxide element thereof.

As the electrolytic solution, a sulfuric acid-copper sulfate-based electrolytic solution was used, in which the copper concentration was adjusted to 80 g / L and the sulfuric acid concentration was adjusted to 80 g / L. Further, in the electrolyte, in Table 1 and adjusting the concentration of the additive, and the chloride ion (Cl ^-) concentration of the DC power supply as shown, using Table 1 as a rectifier, to adjust the temperature of the electrolyte is 50 ℃, current density 40A / dm ² , liquid flow rate is 1.0m / s.

Furthermore, the untreated copper foil produced under the above-mentioned conditions was subjected to a chromate treatment immediately after forming the foil. Specifically, after immersing the untreated copper foil in a 7 g / L chromic anhydride aqueous solution at 45 ° C. for 5 seconds, the liquid was drained and air-dried.

(Examples 2 to 6 and 9)

Examples 2 to 6 and 9 were produced in the same manner as in Example 1 except that at least one of the conditions of the additives and chloride ions and the conditions of the DC power source used as a rectifier was changed as shown in Table 1. Copper foil.

(Examples 7 and 8)

In Examples 7 and 8, the conditions of the additives and chloride ions were changed as shown in Table 1, and roughened under the conditions shown below, except that they were produced in the same manner as in Example 1. Copper foil. The roughening treatment was performed under conditions of a copper concentration of 30 g / L, a sulfuric acid concentration of 180 g / L, a bath temperature of 25 ° C, a current density of 40 A / dm ² , and a treatment time of 4 seconds.

(Comparative Examples 1 to 9)

In Comparative Examples 1 to 9, except for additives and chloride ions The conditions and at least one of the DC power supplies used as a rectifier were changed as shown in Table 1. A copper foil was produced in the same manner as in Example 1.

(Comparative Example 10)

In Comparative Example 10, a sulfuric acid-copper sulfate-based electrolyte adjusted to a copper concentration of 80 g / L and a sulfuric acid concentration of 140 g / L was used. In the electrolytic solution, the additives and their concentrations were adjusted according to Table 1, and the chloride ion concentration was used. The DC power source shown in Figure 1 was used as a rectifier. The temperature of the electrolyte was adjusted to 50 ° C, the current density was 52 A / dm ² , and the liquid flow rate was 0.4 m / s. Method to make copper foil. The comparative example corresponds to Example 1 described in Patent Document 5.

(Comparative Example 11)

In Comparative Example 11, except that the DC power source used as a rectifier was changed as shown in Table 1, a copper foil was produced in the same manner as in Comparative Example 10.

(Comparative Example 12)

In Comparative Example 12, a sulfuric acid-copper sulfate-based electrolytic solution adjusted to a copper concentration of 70 g / L and a sulfuric acid concentration of 100 g / L was used. In the electrolytic solution, the additives and their concentrations, and the chloride ion concentration were adjusted according to Table 1. The DC power source shown in Figure 1 was used as a rectifier to adjust the temperature of the electrolyte to 40 ° C, the current density to 50 A / dm ² , and the liquid flow rate to 0.4 m / s. Method to make copper foil. In addition, this comparative example corresponds to Example 5 described in Patent No. 4976351.

(Comparative Example 13)

In Comparative Example 13, except that the DC power source used as a rectifier was changed as shown in Table 1, a copper foil was produced by the same method as Comparative Example 12.

In addition, among the types of additives described in Table 1, "HEC1" means hydroxyethyl cellulose having a weight average molecular weight of about 30,000, "HEC2" means hydrolyzed hydroxyethyl cellulose having a weight average molecular weight of about 24500, and "PPG "Means polypropylene glycol with a weight average molecular weight of about 6000," 2M5S "means" sodium 2-mercaptobenzimidazole-5-sulfonate "," PEI "means polyethyleneimine with a weight average molecular weight of about 30,000, and" mixture "means A dimethyldiallylammonium chloride polymer, sodium polydithiodipropane sulfonate, and N, N'-diethylthiourea are used as a mixed additive in a weight ratio of 70: 60: 1.

In addition, in the DC power supply described in Table 1, "inverter" indicates the use of inverter-type DC power supply (power supply equipped with a 20kHz high-frequency inverter), and "thyristor" indicates the use of thyristor-type DC power supply (pulsation rate of 10) % Of power).

[Evaluation]

Using the electrolytic copper foils of the above examples and comparative examples, the following characteristics were evaluated. The evaluation conditions of each characteristic are as follows. The results are shown in Table 1.

[1] C content and S content analysis

A carbon-sulfur analyzer (EMIA-810W, manufactured by Horiba, Ltd.) was used, and the measurement was performed by combustion in an oxygen gas flow (tubular electric furnace method) -infrared absorption method. A 0.5 g sample was burned for impurity analysis. Take full care to avoid contamination of the copper foil surface, and perform pretreatment such as acetone degreasing as required.

[2] Analysis of N content

The measurement was performed using an oxygen nitrogen hydrogen analyzer (EMGA-930, manufactured by Horiba, Ltd.) using an inert gas fusion-thermal conductivity method (TCD). A 0.5 g sample was burned for impurity analysis. Take care to avoid copper foil The surface is contaminated, and pretreatment such as acetone degreasing is performed as required.

[3] Cl content analysis

A certain volume of acid (a mixed solution of 1 mol / L sulfuric acid and 20 ml / L of a 35% by mass hydrogen peroxide solution) was used to dissolve a certain weight of copper foil. For this solution, an aqueous silver nitrate solution (0.01 mol / L) was used as the reference solution. Potential difference titration was performed using an automatic titration device COM-1600 (produced by Hiranuma Sangyo Co., Ltd.), and the Cl content in the copper foil was measured.

[4] Tensile test

The tensile test is performed in accordance with the provisions of IPC-TM-650. The measurement was performed using a tensile tester (type 1122, manufactured by Instron) at room temperature (25 ° C ± 10 ° C) with a distance between chucks of 70 mm. Two types of samples were prepared for measurement, each of which was cut to a size of 0.5 inch × 6 inch for each copper foil under normal conditions, and heated at 300 ° C using an inert gas furnace (INH-21CD-S, manufactured by Koyo THERMOS System Co., Ltd.) Samples cut to a size of 0.5 inch × 6 inch after hours were measured under the above-mentioned room temperature conditions.

In this example, the tensile strength measured in the normal state is 380 MPa or more as the acceptable level, and the tensile strength measured in the state after heating at 300 ° C for 1 hour is 300 MPa or more as the acceptable level.

[5] Electrical conductivity

The electrical conductivity was measured according to JIS H 0505: 1975, and was measured by the 4-terminal method.

In this example, a conductivity of 85% IACS or more was evaluated as good.

[6] MIT folding resistance test

The MIT folding resistance test is performed in accordance with JIS P 8115: 2001. The test was performed under the conditions of room temperature (25 ° C ± 10 ° C), a bending radius R of 0.08 mm, a bending angle of ± 135 °, a bending speed of 175 times / minute, and a load of 500 g. In addition, the measurement sample is a sample in which the copper foil was heated at 300 ° C. for 1 hour in an inert gas furnace (same as above), and the heated copper foil was cut into a size of 130 mm in length × 15 mm in width.

In this test, the number of bends before the measurement sample is cut is calculated, and the number of bends when the sample is cut is evaluated.

In this example, the number of bending times of 800 or more was evaluated as good.

[7] Folding test

The folding test was performed at room temperature (25 ° C ± 10 ° C) according to the following steps <S1> to <S5>. <S1> to <S4> in FIG. 1 correspond to the following <S1> to <S4>.

<S1> First, the copper foil was heated at 300 ° C. for 1 hour in an inert gas furnace (same as above), and the heated copper foil was cut to a size of 0.5 inch × 6 inch to prepare a measurement sample.

Then, a polyimide film having a thickness of 100 μm was used as a spacer having a bending radius of 0.2 mm. As shown in FIG. 1, a measurement sample 10 was placed on the spacer 20, and both ends in the longitudinal direction were fixed to the spacer. The interlayer 20 is a laminated body of the interlayer 20 and the copper foil 10.

<S2> Next, as shown in FIG. 1, the spacer 20 is placed on the inside, the laminated body of the spacer 20 and the copper foil 10 is bent at 180 °, and a rubber roller (diameter 95 mm × width 45 mm, weight 2 kg) is used. , Rubber hardness 80Hs, manufactured by Taiyou Machinery Co., Ltd.) 30 load.

<S3> Then, the vicinity of the bent portion (dashed area X) of the copper foil shown in FIG. 1 was observed with an optical microscope (VHX-1000, manufactured by Keynes Corporation). Check for cracks (cracks).

<S4> For the sample that did not break in <S3>, as shown in FIG. 1, the folded laminated body was opened again, and flattened using the roller 30 described above.

<S5> Then, repeat the steps from <S2> to <S4> until a break is observed in the above <S3>, calculate the number of repetitions, and evaluate the number of observations when a break is observed.

In this embodiment, the number of observations of 40 or more times is evaluated as a passing level, and 50 or more times are evaluated as good.

As shown in Table 1, in the electrolytic copper foils according to Examples 1 to 9 of the present invention, the content of carbon (C), sulfur (S), nitrogen (N), and chlorine (Cl) is controlled within a predetermined range, so before and after heating Both have high tensile strength and excellent folding resistance.

In contrast, in the electrolytic copper foils of Comparative Examples 1 to 13, at least one of the contents of carbon (C), sulfur (S), nitrogen (N), and chlorine (Cl) was not controlled within a predetermined range. Compared with the electrolytic copper foils of Examples 1 to 9, at least one of the tensile strength and the folding resistance before and after heating is worse. In particular, the electrolytic copper foils of Comparative Examples 2 to 4, 10, and 11 exhibited excellent bending resistance in the conventional MIT bending resistance test in the past, but did not exhibit sufficient performance in a more severe bending test, namely, a folding test. Bending resistance.

As described above, the electrolytic copper foil of the present invention has high tensile strength, maintains high tensile strength after heating, and can achieve good folding resistance. Therefore, it is suitable for manufacturing a negative electrode current collector or a circuit board of a lithium ion secondary battery. Of electrolytic copper foil.

10‧‧‧ Copper foil

20‧‧‧ compartment

30‧‧‧roller

X‧‧‧ dashed area

Claims (9)

An electrolytic copper foil characterized by a carbon (C) content of 20 to 150 mass ppm, a sulfur (S) content of 18 mass ppm or less, a nitrogen (N) content of 40 mass ppm or less, and chlorine (Cl) The content is 25 to 200 mass ppm. The electrolytic copper foil according to item 1 of the scope of patent application, wherein the ratio of the content of the carbon (C) to the content of the chlorine (Cl) [content of C / content of Cl] is in a range of 0.70 to 1.40. The electrolytic copper foil according to item 1 or 2 of the scope of the patent application, wherein the tensile strength measured in a normal state is in a range of 380 to 600 Mpa. The electrolytic copper foil according to any one of claims 1 to 3, wherein the tensile strength measured in a state after heating at 300 ° C for 1 hour is in a range of 300 to 550 MPa. The electrolytic copper foil according to any one of claims 1 to 4, wherein the electrical conductivity is 85% IACS or more. The electrolytic copper foil according to any one of claims 1 to 5, wherein the copper foil is used for manufacturing a negative electrode current collector of a lithium ion secondary battery. The electrolytic copper foil according to any one of claims 1 to 5, wherein the copper foil is used for manufacturing a conductor portion of a printed circuit board. A lithium ion secondary battery having the electrolytic copper foil according to any one of claims 1 to 6 as a negative electrode current collector. A printed circuit board having the electrolytic copper foil according to any one of claims 1 to 5 and 7 as a conductor portion.