WO2017217085A1

WO2017217085A1 - Electrolytic copper foil, lithium ion secondary cell negative electrode, lithium ion secondary cell, and printed wiring board

Info

Publication number: WO2017217085A1
Application number: PCT/JP2017/014131
Authority: WO
Inventors: 政登胡木; 篠崎　淳
Original assignee: 古河電気工業株式会社
Priority date: 2016-06-14
Filing date: 2017-04-04
Publication date: 2017-12-21
Also published as: TWI767910B; KR102218889B1; CN108026653A; TW201807260A; KR20190003451A

Abstract

The present invention provides an electrolytic copper foil having high strength, high heat resistance, and small elongation anisotropy, a lithium ion secondary cell negative electrode, a lithium ion secondary cell, and a printed wiring board. This surface-treated copper foil is an electrolytic copper foil containing 0.001-0.020% by mass of copper, and is characterized in that the ten-point average roughness (Rz) of the electrolytic copper foil is 1.8 µm or less, the tensile strength of the electrolytic copper foil when the tensile characteristics thereof are measured at normal temperature after the copper foil is heated for 1 hour at 150°C is 400 MPa or greater, the elongation of the copper foil in the width direction (TD) thereof is 2% or greater, and the elongation anisotropy \{[(MD elongation – TD elongation)/MD elongation] × 100\} as a parameter representing the difference between the elongation of the copper foil in the longitudinal direction (MD) and the elongation thereof in the width direction (TD) is 50% or less.

Description

Electrolytic copper foil, negative electrode for lithium ion secondary battery, lithium ion secondary battery and printed wiring board

The present invention relates to an electrolytic copper foil, a negative electrode for a lithium ion secondary battery, a lithium ion secondary battery, and a printed wiring board having the electrolytic copper foil.

In recent years, in order to reduce the size and weight of lithium (Li) ion secondary batteries, studies to reduce the thickness of the copper foil used as a current collector have progressed, and the stress and strain acting on the copper foil have increased accordingly. Tend to. In addition, in order to increase the capacity of lithium ion secondary batteries, active materials are mixed with conventional carbon materials and silicon materials are mixed to try to increase the theoretical capacity, and the active material layer is filled more densely than before. The development of next-generation lithium-ion secondary batteries, such as increasing the capacity per volume, is becoming full-fledged, and as a result, the stress acting on the copper foil as a current collector becomes higher and the restraint situation becomes stronger. Further, wrinkles and foil breakage of the electrolytic copper foil after charge / discharge are more obvious than ever, and there is a concern that the battery characteristics may be deteriorated.

Conventional means for realizing thin copper foil include, for example, higher strength of electrolytic copper foil, and improvement of characteristics that do not easily cause characteristic deterioration such as softening even during heat treatment in the battery manufacturing process (high heat resistance) (For example, Patent Documents 1 to 4 etc.).

The strength and heat resistance of the electrolytic copper foil are increased by adding additives to the electrolyte and incorporating the additive components into the crystal grains and grain boundaries of the matrix during electrodeposition. Generally, it is carried out by increasing the strength by the miniaturization effect or by the pinning effect.

However, even when high strength and high heat resistance can be realized, it is difficult to completely prevent wrinkles and foil breakage in next-generation lithium ion secondary batteries. Further improvement in characteristics from the viewpoint was necessary.

Japanese Patent No. 5771392 JP 2008-285727 A JP 2014-224321 A Japanese Patent No. 5598700 Japanese Patent No. 3850155

An object of the present invention is to provide an electrolytic copper foil, a negative electrode for a lithium ion secondary battery, a lithium ion secondary battery, and a printed wiring board having high strength, high heat resistance and low elongation anisotropy.

The present inventors examined the development of a new electrolytic copper foil based on the above design guidelines, and found that an electrolytic copper foil having high strength and high heat resistance had an elongation anisotropy (elongation value depending on the direction in which the tensile test was performed). However, the details of this phenomenon will be described later, and the reduction in elongation anisotropy effectively reduces the occurrence of wrinkles and foil breaks after charging and discharging, and the occurrence of wrinkles and foil breaks after pressing. We found that it can be reduced.

The electrolytic copper foil generally produces a long product (electrolytic copper foil) by depositing copper on the surface of the titanium cathode drum, continuously peeling it off and winding it. At this time, the rotation direction of the drum, that is, the longitudinal direction of the long product is expressed as MD, and the direction orthogonal to the MD direction, that is, the width direction of the copper foil is expressed as TD.

For conventional conventional electrolytic copper foil and conventional high-strength and high-heat-resistant electrolytic copper foil, specimens cut in the MD and TD directions were prepared, and the stress and strain were measured with a tensile tester. A typical example of the obtained stress-strain curve (SS curve) is shown in FIG. As is clear from FIG. 1, in the conventional high strength and high heat resistance foil, the strain (elongation) in the MD direction is 5.8%, the elongation in the TD direction is 2.0%, and the anisotropy of elongation is about 65.5% ((5.8 -2.0) /5.8×100%), and it is clear that it has become obvious. However, none of Patent Documents 1 to 4 pays attention to the elongation anisotropy of the high-strength, high-heat-resistant electrolytic copper foil, and in such a configuration, wrinkles and foil breakage in the next-generation lithium ion secondary battery are not observed. The occurrence of this cannot be effectively suppressed. The conventional general electrolytic copper foil also has a slight elongation anisotropy of about 11.1%, which is due to surface irregularities caused by the transfer of buff lines present in the electrolytic drum. It is considered that the anisotropy of elongation is small, and it is difficult to cause wrinkles and foil breakage.

Considering that the development of next-generation lithium-ion secondary batteries will become full-scale in the future, it is considered essential to develop high-strength and high-heat-resistant foils, and it is important to reduce the anisotropy of the elongation that becomes apparent along with it. It can be said that it is a difficult task. That is, in the current collector application of a high-capacity lithium ion secondary battery, it is desired to develop a copper foil having high strength, high heat resistance, and low elongation anisotropy.

Also, considering that isotropic stress is applied to the printed wiring board when it is bonded to the resin, it is considered that the elongation anisotropy is preferably smaller. Development is desired.

Then, the present inventors diligently studied, found a method for solving the above-mentioned problems, and completed the present invention. That is, the gist of the present invention is as follows.
(1) An electrolytic copper foil containing 0.001 to 0.020% by mass of carbon, wherein the electrolytic copper foil has a ten-point average roughness (Rz) of 1.8 μm or less, and the electrolytic copper foil is heated at 150 ° C. for 1 hour. Tensile properties when measured at room temperature after that, the tensile strength of the copper foil is 400 MPa or more, the elongation in the width direction (TD) of the copper foil is 2% or more, and the elongation in the longitudinal direction (MD) of the copper foil And an elongation anisotropy {[(MD elongation−TD elongation) / MD elongation] × 100} which is a parameter representing a difference in elongation in the width direction (TD) is 50% or less. .
(2) The electrolytic copper foil according to (1), wherein the elongation anisotropy {[(MD elongation−TD elongation) / MD elongation] × 100} is 30% or less.
(3) The electrolytic copper foil according to (1) or (2), wherein the tensile properties are obtained in a state of an electrolytic copper foil (raw foil) in which a roughening treatment layer is not formed on either side.
(4) A negative electrode for a lithium ion secondary battery comprising the electrolytic copper foil according to any one of (1) to (3) as a current collector.
(5) A lithium ion secondary battery comprising a negative electrode for a lithium ion secondary battery having the electrolytic copper foil according to any one of (1) to (3) as a current collector.
(6) A printed wiring board formed by laminating the electrolytic copper foil according to any one of (1) to (3) above and an insulating film.

According to the present invention, there is provided an electrolytic copper foil containing 0.001 to 0.020% by mass of carbon, the electrolytic copper foil having a ten-point average roughness (Rz) of 1.8 μm or less, and the electrolytic copper foil at 150 ° C. Tensile properties when measured at room temperature after heating for 1 hour are as follows: the tensile strength of the copper foil is 400 MPa or more, the elongation in the width direction (TD) of the copper foil is 2% or more, and the longitudinal direction of the copper foil (MD ) And elongation anisotropy {[(MD elongation−TD elongation) / MD elongation] × 100}, which is a parameter representing the difference between the elongation in the width direction (TD), is 50% or less. It has become possible to provide an electrolytic copper foil with high heat resistance and low elongation anisotropy.

Moreover, if the electrolytic copper foil of the present invention is used for, for example, a lithium ion secondary battery provided with a negative electrode for a lithium ion secondary battery having a current collector, the foil capacity and wrinkle at the time of charging / discharging are prevented, the battery capacity, Since cycle characteristics and safety can be improved, it is suitable for next-generation lithium ion secondary battery applications. Furthermore, if the electrolytic copper foil of the present invention is used for a printed wiring board formed by laminating with an insulating film, foil breakage and wrinkle generation during pressing can be prevented, and the dimensional stability can be improved.

Fig. 1 shows test pieces cut in the MD and TD directions for a conventional general electrolytic copper foil and a conventional high-strength / high-heat-resistant electrolytic copper foil. It is a typical stress-strain curve (SS curve) obtained by measurement. FIG. 2 is a conceptual diagram for explaining a main part of a production apparatus for producing the electrolytic copper foil of the present invention.

Next, embodiments of the present invention will be described below.
The electrolytic copper foil of the present invention is an electrolytic copper foil containing 0.001 to 0.020 mass% of carbon, and the electrolytic copper foil has a ten-point average roughness (Rz) of 1.8 μm or less. Tensile properties when heated at room temperature for 1 hour and then measured at room temperature (20 ° C ± 15 ° C) are as follows: The tensile strength of the copper foil is 400 MPa or more and the elongation in the width direction (TD) of the copper foil is 2% or more. The elongation anisotropy {[(MD elongation−TD elongation) / MD elongation] × 100} which is a parameter representing the difference between the elongation in the longitudinal direction (MD) of the copper foil and the elongation in the width direction (TD) is 50. % Of the electrolytic copper foil.

<Carbon content in copper foil>
In the present invention, the carbon (C) content in the electrolytic copper foil needs to be 0.001 to 0.020 mass%. If the carbon content is less than 0.001% by mass, sufficient strength and heat resistance cannot be obtained, and if the carbon content exceeds 0.020% by mass, the ductility decreases and the foil breaks during handling or charge / discharge. It is easy to occur. Therefore, the carbon content is set to 0.001 to 0.020% by mass. The carbon content in the copper foil can be measured, for example, by using a carbon / sulfur analyzer EMIA-810W (manufactured by Horiba Seisakusho) in an oxygen stream combustion (tubular electric furnace method) -infrared absorption method. .

<10-point average roughness of copper foil surface (Rz)>
In the present invention, it is necessary that the ten-point average roughness (Rz) of the electrolytic copper foil is 1.8 μm or less. When the ten-point average roughness (Rz) exceeds 1.8 μm, the elongation anisotropy due to the surface unevenness of the electrolytic copper foil becomes large and becomes apparent, and the copper foil after the charge / discharge test is noticeably wrinkled. This is because it tends to occur. For this reason, the 10-point average roughness (Rz) of the electrolytic copper foil was set to 1.8 μm or less. The ten-point average roughness (Rz) of the electrolytic copper foil was measured according to JIS B0601: 1994. The measurement surface is the S surface (surface on the cathode (Ti) drum side) of the untreated electrolytic copper foil (raw foil) on which the roughened layer is not formed, and the measurement direction is the buffing direction (= MD direction) ) Direction (= TD direction).

<Tensile property of copper foil when measured at room temperature after heating at 150 ° C for 1 hour>
Furthermore, the electrolytic copper foil of the present invention satisfies the following characteristics in tensile properties when measured at room temperature after heating at 150 ° C. for 1 hour. That is, the tensile strength of the copper foil is 400 MPa or more, the elongation in the width direction (TD) of the copper foil is 2% or more, and the difference between the elongation in the longitudinal direction (MD) of the copper foil and the elongation in the width direction (TD) It is necessary to satisfy that the elongation anisotropy {[(MD elongation−TD elongation) / MD elongation] × 100}, which is a parameter representing the value, is 50% or less.

Conventional general electrolytic copper foils have few demands for high strength and high heat resistance, and high purity electrolytic copper foil (for example, Patent Document 5) that does not use an additive or for smoothing. In general, an electrolytic copper foil (for example, NC-WS manufactured by Furukawa Electric Co., Ltd.) in which the additive is not so much incorporated into the copper foil during the electrodeposition process is added. However, the demand for electrolytic copper foil with high strength and high heat resistance has increased with the increase in capacity, size, and weight of batteries. Therefore, the additive species incorporated into the foil during the electrodeposition process are actively used. Increasing cases (for example, Patent Documents 1 to 4).

The inventors have produced electrolytic copper foil using various additives on the premise that it has high strength and high heat resistance suitable for battery use or printed wiring board use, and Si-based active material is applied to the negative electrode. When a charge / discharge test was conducted on the next-generation lithium ion secondary battery, the copper foil wrinkle after charge / discharge was only improved by improving the properties that were required in the past, such as strength, elongation, and heat resistance. It turns out that it cannot suppress enough. Therefore, as a result of diligent studies for further suppression of wrinkles, it was found that elongation anisotropy becomes obvious in electrolytic copper foil with high strength and high heat resistance, and wrinkles are reduced by reducing the anisotropy of elongation. It was found that it can be effectively suppressed. Hereinafter, the elongation anisotropy will be described.

Elongation anisotropy refers to the property that the elongation value varies depending on the tensile direction in the tensile test. The present inventors investigated the anisotropy of elongation in a plurality of electrolytic copper foils having high strength and high heat resistance, and found that the elongation value when the copper foil was pulled in the longitudinal direction (MD direction) was the most. It was found that the elongation value was the smallest when the copper foil was pulled in the width direction (TD direction). Therefore, in the present invention, as a value representing the magnitude of the elongation anisotropy, the elongation anisotropy which is a parameter representing the difference between the elongation in the longitudinal direction (MD) of the copper foil and the width direction (TD) is { [(MD elongation−TD elongation) / MD elongation] × 100} was calculated and evaluated. Hereinafter, the relationship between elongation anisotropy and wrinkles will be described.

When isotropic stress is applied to the electrolytic copper foil by charging / discharging the battery or pressing with a resin, when the elongation anisotropy is large, the elongation value is low (for example, the width direction (TD) of the copper foil). However, because it reaches the non-uniform deformation region (corresponding to the necking region in the single tensile test) quickly, the uniform deformation region and the non-uniform deformation region are mixed depending on the direction, resulting in local strain bias. Wrinkles are easy to enter. On the other hand, when the elongation anisotropy is small, the uniform deformation region and the non-uniform deformation region as described above are unlikely to be mixed, so that it is considered that wrinkles are unlikely to occur as a result of suppressing the bias of strain.

For this reason, the electrolytic copper foil of the present invention has a high strength by suppressing the tensile strength when measured at room temperature after heating at 150 ° C. for 1 hour, and maintaining the tensile strength at 400 MPa or higher or lower than 400 MPa. In addition, the heat resistance is high, the elongation in the width direction (TD) of the copper foil is 2% or more, and the elongation anisotropy of the copper foil is 50% or less, preferably 30% or less. This is because if the tensile strength after heating is less than 400 MPa, the strength of the thinned copper foil is insufficient and the foil breaks easily. Further, if the elongation in the width direction (TD) of the copper foil after heating is less than 2%, the foil is likely to break. Furthermore, if the elongation anisotropy of the copper foil after heating exceeds 50%, the uniform deformation region and the non-uniform deformation region coexist, resulting in local strain bias, and the copper foil tends to wrinkle. It is.

For this reason, the electrolytic copper foil of the present invention has high strength and high heat resistance by suppressing that the tensile properties measured at room temperature after heating at 150 ° C. for 1 hour are maintained or lowered at a tensile strength of 400 MPa or more. The elongation in the width direction (TD) of the copper foil was 2% or more, and the elongation anisotropy of the copper foil was 50% or less.

Also, the tensile strength (initial strength) measured at room temperature before the heating is preferably in the range of 400 to 900 MPa. If the tensile strength is less than 400 MPa, the initial strength is insufficient, the tensile strength when measured at room temperature after heating at 150 ° C. can not be more than 400 MPa, the foil tends to break, In addition, if the tensile strength exceeds 900 MPa, the elongation is insufficient, and the elongation in the width direction (TD) of the copper foil when measured at room temperature after heating at 150 ° C. cannot be 2% or more. This is because cutting tends to occur easily.

In addition, the electrolytic copper foil used for the formation of printed wiring boards is particularly rough plating as a post-treatment of the manufactured electrolytic copper foil (raw foil) for the purpose of ensuring adhesion with the resin constituting the printed wiring board. In many cases, roughening is performed. Roughening plating generally forms granular copper particles on the order of 0.1 to 1 μm on the surface of electrolytic copper foil by electrolysis at a high current density in a sulfuric acid-copper sulfate plating solution for a relatively short time. To do. On the other hand, the electrolytic copper foil of the present invention has a great feature in tensile properties when measured in a state of an untreated electrolytic copper foil (raw foil) in which no roughening treatment layer is formed on either side. is there. Although depending on the thickness of the rough plating layer, generally, the rough plating layer is present on the surface of the electrolytic copper foil, so that the unevenness on the surface of the electrolytic copper foil becomes coarse. Moreover, generally the electrolysis conditions of roughening plating differ greatly from the electrolysis conditions which manufacture untreated electrolytic copper foil (raw foil). Therefore, the crystal structure and structure of the copper particles formed by the rough plating are different from the crystal structure and structure of the untreated electrolytic copper foil (original foil).
Although the detailed mechanism is not clear, due to these multiple factors, the electrolytic copper foil with the roughened plating layer has an elongation anisotropy compared to the electrolytic copper foil (raw foil) without the roughened plated layer. It may appear larger or smaller in appearance. Therefore, when the electrolytic copper foil of the present invention accurately measures (evaluates) the above-described tensile properties, it is preferable that the electrolytic copper foil does not include a roughening treatment layer by roughening plating.

The tensile test was measured according to the IPC standard (IPC-TM-650). After measuring 10 times for each sample, values obtained by averaging their tensile strength and elongation were adopted as numerical values for strength and elongation. In addition, the numerical value of the tensile strength was not significant because no significant anisotropy was confirmed between the test piece cut out along the longitudinal direction of the copper foil and the test piece cut out along the width direction of the copper foil. In the invention, the tensile strength was measured with a test piece cut out along the longitudinal direction of the copper foil, and the tensile test speed was 50 mm / min.

[Method for producing electrolytic copper foil]
As a result of intensive investigations on methods for reducing elongation anisotropy, the inventors have reduced the flow rate of the electrolyte during copper electrodeposition, ideally by making the foil in an unstirred state. It was found that the directionality is greatly reduced. Although various analyzes have been conducted on the mechanism, no clear difference in the metal structure due to the presence or absence of elongation anisotropy has been confirmed, and the mechanism has not yet been elucidated. However, the elongation anisotropy is not confirmed in an electrolytic copper foil that hardly incorporates an additive such as a conventional foil, and is considered to be a phenomenon peculiar to an electrolytic copper foil having high strength and high heat resistance (see FIG. 1). ). Since it is generally known that the adsorption of the additive component and the subsequent incorporation of the additive component into the copper foil are affected by the flow rate of the electrolytic solution, the electrolytic solution during the production of the electrolytic copper foil is The effect of the additive is somewhat different due to the fact that the copper foil flows at a high speed in the longitudinal direction of the copper foil, and it is assumed that the elongation anisotropy of the copper foil is expressed.

Next, the example of the typical manufacturing method of the electrolytic copper foil according to this invention is demonstrated below.
FIG. 2 is a schematic view showing a main part of a typical production apparatus 1 used for producing the electrolytic copper foil M of the present invention, and an electrolytic cell 3 filled with an electrolytic solution 2 and a cylindrical surface. The cathode drum 4 is mainly composed of a cathode drum 4 having an anode and an anode 5 positioned opposite to the cathode drum 4. As the electrolytic solution 2, a sulfuric acid-copper sulfate aqueous solution is preferably used. The anode 5 is preferably an insoluble anode made of titanium coated with a white metal element or its oxide element.

The electrolytic copper foil M rotates the cathode drum 4 at a constant speed in a state where the electrolytic solution 2 is filled between the insoluble anode 5 and the titanium cathode drum 4 provided to face the anode 5. Then, copper was deposited on the cathode drum surface 4 by applying a direct current between the electrodes 4 and 5, and the deposited copper was peeled off from the surface of the cathode drum 4 to form an electrolytic copper foil M. The electrolytic copper foil is manufactured by winding it with a winding roll 6.

Since the electrolytic solution 2 is supplied from a portion called a distributor 7 provided at the bottom of the electrolytic cell 3, the flow rate direction of the electrolytic solution 2 flows from the distributor 7 to the overflow portions 8 provided on both upper sides of the electrolytic cell 3. It is a direction which goes to the same direction as the longitudinal direction of the copper foil formed on the surface of the cathode drum 4. The flow rate of the electrolyte 2 can be changed as appropriate depending on the pump output or the like, but so-called burnt plating occurs when it is manufactured under electrolysis conditions that are higher than the limit current density. It is necessary to appropriately adjust the electrolytic bath composition, bath temperature, current density, etc. so that the electrolysis conditions are lower than the density. Suitable electrolysis conditions for producing the electrolytic copper foil of the present invention are shown below.

Copper concentration: 120-155 g / L
Sulfuric acid concentration: 30-100 g / L
Chlorine concentration: 60-140 mg / L
Additive concentration: 2-20mg / L
Bath temperature: 65-80 ℃
Current density: 10-35A / dm ²
Flow rate: 0.02 to 0.05m / s

In order to obtain an electrolytic copper foil having high strength and high heat resistance, it is essential to add an additive to the electrolytic solution. As a method for selecting the additive, it is possible to appropriately select and use an effect of adsorbing on the copper surface and making the crystal grains fine and a heat resistance effect incorporated into the grains. Although there are no particular problems with the use of a plurality of additives, it is preferable to use as few as possible in view of economy, production stability, and ease of concentration control. As additives having the above-mentioned effects, it is generally known that those having a functional group having an unshared electron pair such as S, N, and O are effective. In this example, S, N, and O are also effective. Is used, and an additive having both a refinement effect and a heat resistance effect was used. The higher the additive concentration is, the more the additive is taken into the copper foil and the strength and heat resistance are increased. On the other hand, the ductility is lowered, so that the foil breaks easily during handling or charging / discharging. Therefore, there is an optimum concentration range. As the additive, for example, it is preferable to use, for example, polyethylene glycol (PEG), hydroxyethyl cellulose (HEC), thiourea and the like.

In the present invention, compared with the conventional general production conditions, the copper concentration and bath temperature are greatly increased, and the current density is decreased, so that the current density is less than the limit current density even at an extremely low flow rate, ideally even without stirring. It was devised to satisfy the electrolytic conditions. Moreover, the flow rate of the electrolyte in the electrolytic cell was measured between the distributor 7 and the overflow part 8 of the electrolytic cell in a state before electrolysis using a small micro flow meter CM-1SX type (manufactured by Toho Denki Co., Ltd.). Measurement was performed with an anemometer attached at the position. The electrolytic copper foil of this invention can be manufactured by the method mentioned above.

Moreover, if the electrolytic copper foil of the present invention is used for, for example, a lithium ion secondary battery provided with a negative electrode for a lithium ion secondary battery having a current collector, the foil capacity and wrinkle at the time of charging / discharging are prevented, the battery capacity, Cycle characteristics and safety can be improved. Furthermore, if the electrolytic copper foil of this invention is used for the printed wiring board formed by laminating | stacking with an insulating film, generation | occurrence | production of foil cutting at the time of a press, generation | occurrence | production of a wrinkle, and dimensional stability can be improved.

The above description is merely an example of the embodiment of the present invention, and various modifications can be made within the scope of the claims.

(Examples 1 to 7 and Comparative Examples 1 to 8)
Examples 1 to 7 and Comparative Examples 1 to 8 use the electrolytic copper foil manufacturing apparatus shown in FIG. 2 and between the insoluble anode 5 and the titanium cathode drum 4 provided to face the anode 5. In the state where the electrolyte solution 2 is filled, copper is deposited on the cathode drum surface 4 by applying a direct current between the electrodes 4 and 5 while rotating the cathode drum 4 at a constant speed. It peeled off from the surface of the drum 4, and produced the electrolytic copper foil M of thickness 8 micrometers. Table 1 shows the electrolytic bath composition, additive type and amount, bath temperature, current density, and electrolytic flow rate. In Examples 1 to 5 and 7, the reason why the flow rate is 0.02 m / s, not stirring, is to prevent concentration fluctuations due to stagnation of the bath during continuous foil production. Further, the cathode drum 4 has a roughness Rz when measured in a direction perpendicular to the polishing direction (buffing direction) to the same value as the roughness Rz of the electrolytic copper foil (S surface) shown in Table 2. Until the surface was polished with a buff.

(Comparative Examples 9 to 13)
In Comparative Examples 9 to 13, electrolytic copper foils M having a thickness of 8 μm were prepared according to the conditions corresponding to those in Example 1 of Patent Documents 1 to 5, respectively. Since the flow rate was not particularly described, in Comparative Examples 9 to 13, the flow rate of the electrolytic solution was set to 0.5 m / s, which is a general flow rate condition range of the conventional electrolytic copper foil. Further, the cathode drum 4 has a roughness Rz when measured in a direction perpendicular to the polishing direction (buffing direction) to the same value as the roughness Rz of the electrolytic copper foil (S surface) shown in Table 2. Until the surface was polished with a buff.

(Comparative Example 14)
Widely used as a copper foil for lithium ion secondary batteries. Although the additive is added to the electrolyte for smoothing, it is an electrolytic copper foil in which the additive is not taken into the copper foil during the electrodeposition process. “NC-WS” manufactured by Furukawa Electric Co., Ltd. was used.

<Evaluation method>
1. Measurement of carbon content in copper foil The amount of carbon contained in copper foil was measured using a carbon / sulfur analyzer EMIA-810W (manufactured by Horiba Seisakusho) to burn a sample of about 0.5 g and burning in an oxygen stream ( Tubular electric furnace method)-measured by infrared absorption method. Table 2 shows the measured carbon content. When measuring, the copper foil was handled with great care so as not to contaminate the surface, and pretreated such as acetone degreasing as necessary.

2. Measurement of 10-point average roughness Rz of copper foil surface The 10-point average roughness Rz was measured according to JIS B0601: 1994. The measurement surface was the S surface of the copper foil (the copper foil surface on the cathode drum side), and the measurement direction was the direction (= TD direction) perpendicular to the buffing direction (= MD direction).

3. Battery performance test (1) Production of negative electrode for lithium secondary battery Ball mill so that carbon-based active material (containing 20% by mass of silicon-based alloy active material) and acetylene black are in a mass ratio of 8: 1. Was used for pulverization and mixing to prepare a negative electrode material. A negative electrode mixture was prepared by mixing 80% by mass of this negative electrode material and 20% by mass of polyvinylidene fluoride (PVDF) as a binder, and this negative electrode mixture was dispersed in N-methylpyrrolidone (solvent). Active material slurry. Next, the active material slurry was applied to both sides of a strip-shaped electrolytic copper foil (longitudinal direction parallel to the copper foil MD direction) having a thickness of 8 μm produced under the above conditions, and then dried, and this dried surface-treated electrolytic copper foil Was heated at 150 ° C. for 1 hour and then compression molded with a roller press so that the film thickness of the molded negative electrode mixture was 120 μm on both sides to obtain a negative electrode for a lithium secondary battery.

(2) Preparation of positive electrode for lithium secondary battery 0.5 mol of lithium carbonate and 1 mol of cobalt carbonate were mixed and fired in air at 900 ° C. for 5 hours to obtain a positive electrode active material (LiCoO ₂ ). This positive electrode active material (LiCoO ₂ ) was mixed at a ratio of 91% by mass, graphite as a conductive agent at 6% by mass, and PVDF as a binder at a rate of 3% by mass to produce a positive electrode mixture, which was mixed with N-methyl- Dispersed in 2 pyrrolidone (NMP) to form a slurry. Next, this slurry is uniformly applied to both surfaces of a positive electrode current collector made of a strip-shaped aluminum having a thickness of 20 μm, dried and compressed by a roller press so that the thickness of the positive electrode mixture after molding is 95 μm on both surfaces. It shape | molded and the positive electrode for lithium secondary batteries was obtained.

(3) Production of lithium ion secondary battery A lithium ion secondary battery was produced as a kind of nonaqueous electrolyte secondary battery. The positive electrode and negative electrode produced as described above and a separator made of a microporous polypropylene film were laminated to obtain a laminated electrode body. This laminated electrode body was wound many times in a spiral shape with the negative electrode inside along its length direction, and the final end of the separator was fixed to the outermost periphery with a tape to form a spiral electrode body. The prepared spiral electrode body is housed in a nickel-plated iron battery can with insulating plates on both upper and lower surfaces, and an aluminum positive electrode lead is used to collect the positive and negative electrodes. Was extracted from the positive electrode current collector and connected to the battery lid, and a negative electrode lead made of nickel was derived from the negative electrode current collector and connected to the battery can.

A non-aqueous electrolyte solution in which LiPF6 was dissolved at a rate of 1 mol / L in an equal volume mixed solvent of propylene carbonate and diethyl carbonate was poured into a battery can containing the spiral electrode body. Next, the battery can was caulked through an insulating sealing gasket whose surface was coated with asphalt to fix the battery lid, and the airtightness in the battery can was maintained. As described above, a cylindrical lithium secondary battery having a diameter of 18 mm and a height of 65 mm was produced.

The battery in this lithium ion secondary battery was evaluated at a temperature of 25 ° C. by the following method.

(Conditions for charge / discharge test)
Charging: Constant current charging at a current equivalent to 1 C. After reaching 4.2 V, switching to constant voltage charging was completed when the charging current dropped to 0.05 C equivalent.
Discharge: A constant current was discharged at a current equivalent to 1 C, and was terminated when the voltage reached 3.0V.
C is a C rate, which means the amount of current that discharges the entire capacity of the battery in one hour.

(Evaluation of wrinkles and foil breaks after charge / discharge)
Evaluation of the foil breakage after charging / discharging was repeated up to 1000 cycles under the above conditions, the battery was disassembled after the end of the cycle test, and the presence or absence of copper foil wrinkles and foil breakage was visually confirmed. The evaluation of wrinkles and foil breaks in Table 2 is “◎” when no wrinkles and foil breaks are present, “○” when slight wrinkles are generated, and significant wrinkles are generated. "Wrinkle" when the foil is cut, "Foil cut" when the foil is broken, and "Wrinkle, foil cut" when both the wrinkle and the foil are marked.

The surface-treated copper foil which gave the antirust process on the chromate conditions shown below to the electrolytic copper foil manufactured on the said conditions was used as a tension test, roughness measurement, a gas analysis, and a battery evaluation sample.
<Chromate treatment conditions>
Potassium dichromate 1-10g / L
Temperature (℃) 25 ℃
Immersion treatment time 2 to 20 seconds Table 2 shows the evaluation results.

From the results shown in Table 2, in all of Examples 1 to 7, the amount of carbon contained in the copper foil is 0.0015 to 0.018% by mass, which is an appropriate range of the present invention (0.001 to 0.020% by mass), and Rz is 1.0 to 1.7 μm, the proper range of the present invention (1.8 μm or less), and the tensile properties when measured at room temperature after heating at 150 ° C. for 1 hour, that is, the tensile strength is 420 to 653 MPa. The range (400 MPa or more), the width direction elongation (TD) value is 2.1 to 6.1%, which is an appropriate range of the present invention (2% or more), and the elongation anisotropy is 6.2 to 47.5%. (50% or less) and, after the charge / discharge test, almost no significant wrinkles or foil breakage was confirmed. In particular, Examples 1 to 4 had an elongation anisotropy of 30% or less, and wrinkles were not generated at all. There wasn't.

On the other hand, in Comparative Examples 1 to 4, the elongation anisotropy is 57.1 to 63.9%, which exceeds the upper limit (50%) of the appropriate range of the present invention, and significant wrinkles are confirmed in the copper foil after the charge / discharge test. It was done. In addition, since Comparative Examples 3 and 4 have a copper foil widthwise elongation (TD) value of 1.3 to 1.8%, which is smaller than the lower limit (2%) of the proper range of the present invention, The foil breakage was also confirmed. In Comparative Example 5, the carbon content was 0.023% by mass, which is higher than the upper limit (0.02% by mass) of the appropriate range of the present invention, so that the copper foil after the charge / discharge test was confirmed to be broken. In Comparative Example 6, the carbon content is less than 0.0008% by mass and the lower limit of the proper range of the present invention (0.001% by mass), so the tensile strength after heating at 150 ° C. is 370 MPa and the lower limit of the proper range of the present invention ( It was lower than 400 MPa), and it was remarkably softened by the heat treatment, and it was confirmed that the copper foil after the charge / discharge test was broken. Since Comparative Example 7 had a width direction (TD) elongation of the copper foil of 1.3%, which was smaller than the lower limit (2%) of the appropriate range of the present invention, the copper foil after the charge / discharge test was confirmed to be broken. . In Comparative Example 8, since Rz is 2.0 μm, which is larger than the upper limit (1.8 μm) of the appropriate range of the present invention, the anisotropy of elongation due to surface irregularities becomes obvious, and the copper foil after the charge / discharge test is formed. There were noticeable wrinkles. In addition, since the value of the elongation in the width direction (TD) of the copper foil was 1.8%, which was smaller than the upper limit value of the appropriate range of the present invention, it was confirmed that the copper foil after the charge / discharge test was broken. In each of Comparative Examples 9 to 12, the elongation anisotropy was 53.6 to 70.0%, which was larger than the upper limit value of the appropriate range of the present invention, and thus significant wrinkles were confirmed in the copper foil after the charge / discharge test. In addition, in Comparative Examples 9 and 10, since the value of the elongation in the width direction (TD) of the copper foil was 0.9 to 1.3%, which is smaller than the lower limit value of the appropriate range of the present invention, foil breakage was confirmed at the same time. In both Comparative Examples 13 and 14, the tensile strength after heating at 150 ° C. was 251 to 273 MPa, which was lower than the lower limit value of the appropriate range of the present invention.

From the above results, carbon was contained at 0.001 to 0.020% by mass, the 10-point average roughness (Rz) of the electrolytic copper foil was 1.8 μm or less, and the electrolytic copper foil was measured at room temperature after heating at 150 ° C. for 1 hour. Tensile characteristics of the copper foil, that is, the tensile strength of the copper foil is 400 MPa or more, the elongation in the width direction (TD) of the copper foil is 2% or more, and the elongation in the longitudinal direction (MD) of the copper foil and the width direction ( An electrolytic copper foil satisfying an elongation anisotropy {[(MD elongation−TD elongation) / MD elongation] × 100} which is a parameter representing the difference in elongation of TD) is 50% or less, preferably 30% or less. In the lithium ion secondary battery, wrinkles and foil breakage are suppressed during charging and discharging, which is extremely suitable for extending the life of the battery. Moreover, also in the printed circuit board use, it was confirmed that the copper foil which satisfy | fills the said characteristic is effective in suppression of wrinkles and foil breakage in the copper foil after a press.

In addition, the strength and elongation anisotropy after heating are the characteristics of untreated electrolytic copper foil, and even if surface treatment such as rust prevention treatment or silane coupling treatment is applied, the above properties are affected. Absent.

According to the present invention, it is possible to provide an electrolytic copper foil having high strength, high heat resistance, and low elongation anisotropy. Moreover, if the electrolytic copper foil of the present invention is used for, for example, a lithium ion secondary battery provided with a negative electrode for a lithium ion secondary battery having a current collector, the foil capacity and wrinkle at the time of charging / discharging are prevented, the battery capacity, Cycle characteristics and safety can be improved. Furthermore, if the electrolytic copper foil of the present invention is used for a printed wiring board formed by laminating with an insulating film, foil breakage and wrinkle generation during pressing can be prevented, and dimensional stability can be improved.

DESCRIPTION OF SYMBOLS 1 Electrolytic copper foil manufacturing apparatus 2 Electrolyte 3 Electrolysis tank 4 Cathode drum 5 Anode 6 Winding roll 7 Distributor 8 Overflow part

Claims

An electrolytic copper foil containing 0.001 to 0.020% by mass of carbon,
The electrolytic copper foil has a ten-point average roughness (Rz) of 1.8 μm or less,
Tensile properties when the electrolytic copper foil is heated at 150 ° C. for 1 hour and then measured at room temperature are as follows: the copper foil has a tensile strength of 400 MPa or more, and the copper foil has a width direction (TD) elongation of 2% or more. And the elongation anisotropy {[(MD elongation−TD elongation) / MD elongation] × 100} which is a parameter representing the difference between the elongation in the longitudinal direction (MD) of the copper foil and the elongation in the width direction (TD) is 50%. An electrolytic copper foil characterized by:
2. The electrolytic copper foil according to claim 1, wherein the elongation anisotropy {[(MD elongation−TD elongation) / MD elongation] × 100} is 30% or less.
The electrolytic copper foil according to claim 1 or 2, wherein the tensile properties are obtained in a state of an electrolytic copper foil (raw foil) in which a roughening treatment layer is not formed on either side.
A negative electrode for a lithium ion secondary battery comprising the electrolytic copper foil according to any one of claims 1 to 3 as a current collector.
A lithium ion secondary battery comprising a negative electrode for a lithium ion secondary battery having the electrolytic copper foil according to any one of claims 1 to 3 as a current collector.
A printed wiring board formed by laminating the electrolytic copper foil according to any one of claims 1 to 3 and an insulating film.