JP2000182623A - Electrolytic copper foil, copper foil for current collector of secondary battery, and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolytic copper foil used as a current collector of a secondary battery, excellent in the tensile strength and in the rate of elongation at a room temp. and after being heated and a secondary battery equipped with a current collector consisting of such copper foil excellent in overcharging test characteristics. SOLUTION: An electrolytic copper foil containing not more than 5 ppm carbon and not more than 3 ppm sulfur is used as a current collector of a secondary battery, which is furnished with a negative electrode and positive electrode of such a structure that an electrode constituting substance layer is formed on the surface of current collector in plane form, wherein at least one of the plane current collectors of the positive and negative electrodes consists of the electrolytic copper foil.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic copper foil having excellent tensile strength and elongation, a copper foil for a current collector of a secondary battery comprising the copper foil, and a secondary battery using the copper foil.

[0002]

2. Description of the Related Art In recent years, the development of portable electronic devices has been remarkable. For example, telephones, notebook computers, camera-integrated VTRs,
Electronic still cameras and the like have become widespread, and secondary batteries such as nickel-cadmium batteries, nickel-metal hydride batteries, and lithium-ion batteries have been widely used as power sources.

[0003] In particular, lithium ion batteries have attracted attention because of their high energy density and operating voltage, and excellent cycle life characteristics involving charge and discharge. The structure of this lithium ion battery generally has a positive electrode current collector, for example, 2
A positive electrode obtained by kneading a paste of a positive electrode active material, for example, LiCoO ₂ powder with a binder and a non-aqueous solvent on both sides of an aluminum foil having a thickness of about 0 μm, drying, pressing and integrating the mixture. And a negative electrode current collector, for example, 10
Using a copper foil having a thickness of about μm, a negative electrode active material, for example, a carbon powder kneaded with a binder and a non-aqueous solvent in the same manner as the positive electrode to form a paste is applied, dried, pressed and integrated. A negative electrode, which is successively overlapped and wound up into a cylindrical shape between the two electrodes of the positive electrode and the negative electrode via an insulating porous separator. Further, both electrodes are housed in a cylindrical can, a non-aqueous electrolyte is injected, and members such as a switch element, a safety valve, and a terminal are provided to assemble a secondary battery.

As described above, a metal foil having excellent conductivity, for example, a copper foil, is often used for the negative electrode current collector. Rolled copper foils and electrolytic copper foils with different production methods are known as copper foils. Electrodeposited copper foil has been used as a negative electrode current collector material for secondary batteries in the same manner as rolled copper foil because of its advantages of superior mass productivity and relatively low manufacturing cost compared to rolled copper foil. Was.

In general, an electrolytic copper foil is formed by using a sulfuric acid-copper sulfate aqueous solution as an electrolytic solution, and supplying the electrolytic solution between a cylindrical cathode rotating at a constant speed and an anode provided to face the same. Then, copper is deposited on the rotating cathode surface while energizing, and the copper foil having a predetermined thickness is peeled off from the cathode surface to manufacture the cathode foil.

The mechanical and physical properties of the electrolytic copper foil naturally include the composition of the electrolytic solution, various chemicals (additives) added as necessary, the current density, the supply amount of the electrolytic solution, and the like. It is known that the tensile strength and the elongation can be controlled by adding an appropriate amount of an additive depending on the electrolysis conditions.

One of the characteristics strongly required of a secondary battery is that, when overcharging is performed from the viewpoint of safety, the current collector (copper foil) deteriorates with time, causing cracks or the like. It is necessary that failure such as breakage does not occur.
However, the conventional electrolytic copper foil could not sufficiently satisfy the overcharge test characteristics indicating the rupture state of the current collector (copper foil) after overcharge.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an excellent tensile strength at room temperature and after heating which is suitably used as a current collector for a secondary battery, and an excellent elongation at room temperature and after heating. An object of the present invention is to provide an electrolytic copper foil.

Another object of the present invention is to provide a current collector copper foil for a secondary battery which, when used as a current collector for a secondary battery, can provide a secondary battery having excellent overcharge test characteristics. It is in.

Another object of the present invention is to provide a secondary battery having excellent overcharge test characteristics.

[0011]

That is, the present invention relates to an electrolytic copper foil characterized in that the carbon content in the copper foil is 5 ppm or less and the sulfur content is 3 ppm or less.

The present invention also relates to a current collector copper foil for a secondary battery, comprising the above-mentioned electrolytic copper foil.

[0013] The present invention also provides a secondary battery comprising a positive electrode and a negative electrode in which an electrode constituent material layer is formed on the surface of a planar current collector, wherein at least one of the positive and negative electrode planar current collectors is as described above. The present invention relates to a secondary battery characterized by being an electrolytic copper foil.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The electrolytic copper foil of the present invention has a carbon content of 5 ppm or less and a sulfur content of 3 ppm.
pm or less. By controlling the carbon content and the sulfur content in the copper foil in this way, an electrolytic copper foil having excellent tensile strength at normal temperature and after heating and excellent elongation at normal temperature and after heating can be obtained. When the carbon content in the copper foil exceeds 5 ppm, the elongation after heating decreases. On the other hand, if the sulfur content exceeds 3 ppm, the elongation after heating decreases. The preferred range of the carbon content is 0.1 to
4 ppm, and a preferable range of the sulfur content is 0.1 to
2 ppm.

Further, the electrolytic copper foil of the present invention has an oxygen content of 5 ppm or less in the copper foil and a nitrogen content of 0.1 ppm.
It is preferably at most 5 ppm. If the oxygen content in the copper foil exceeds 5 ppm, the elongation after heating tends to decrease, and if the nitrogen content exceeds 0.5 ppm, the elongation after heating tends to decrease. A more preferable range of the oxygen content is 0.1 to 4 ppm, and a more preferable range of the nitrogen content is 0.1 to 0.4 ppm.

Further, in the electrolytic copper foil of the present invention, the total content of carbon, sulfur, oxygen, nitrogen and hydrogen in the copper foil is 15 pp.
m or less. The total amount of this impurity is 1
If it exceeds 5 ppm, the tensile strength at room temperature and the elongation after heating tend to decrease. More preferably, the total content of carbon, sulfur, oxygen, nitrogen and hydrogen is 10 ppm or less.

In the present invention, the measurement of carbon, sulfur, oxygen, nitrogen and hydrogen is performed by an elemental analyzer. The measurement of the content of carbon and sulfur was performed using EMIA-82 manufactured by Horiba, Ltd.
0, the content of oxygen and nitrogen can be measured by EMGA-620 manufactured by Horiba, and the content of hydrogen can be measured by EMGA manufactured by Horiba, Ltd.
-521.

The copper foil of the present invention, in which the content of impurities is controlled as described above, can be obtained, for example, by subjecting the copper foil of the present invention to electrolytic treatment using, as an electrolytic solution used in the production of electrolytic copper foil, a highly-removed organic impurity. can get.

As a method for removing impurities in the electrolytic solution to a high degree, a copper wire, which is a raw material used for producing the electrolytic solution, is used for a 60-degree process.
A method of firing at 0 to 900 ° C. for 30 to 60 minutes, a method of cleaning a copper wire using sulfuric acid or the like, a high-purity copper wire,
A method using copper sulfate or sulfuric acid, a method not using thiourea, gum arabic, gelatin, glue, etc. commonly used in an electrolytic solution, a method using distilled water or pure water as water to be used, etc. Or a method of appropriately combining them.

In addition, a method of removing impurities in the electrolyte by treating the electrolyte with an activated carbon filter or oxidizing and decomposing organic substances present in the solution with an ozone generator can be used.

By producing an electrolytic copper foil using the electrolytic solution obtained by the above-mentioned method from which impurities are highly removed, an electrolytic copper foil having a predetermined element content can be obtained.

The electrodeposited copper foil of the present invention has the carbon content and the sulfur content in the copper foil within the above-mentioned ranges, has excellent tensile strength at room temperature and after heating, and has excellent elongation at room temperature and after heating. And a current collector of a secondary battery.

The surface of the electrolytic copper foil of the present invention may be provided with a rust-preventing layer such as a roughening-treated layer or a chromate-treated layer for rust prevention, if necessary.

The secondary battery of the present invention includes a positive electrode and a negative electrode each having a planar current collector and an electrode constituting material layer formed on the surface thereof. It is used as at least one of the current collectors, preferably as a negative electrode current collector. Thus, by using the electrolytic copper foil of the present invention as a current collector, a secondary battery having excellent overcharge test characteristics can be obtained. The reason is that the electrolytic copper foil of the present invention has a longer tear propagation time indicating the strength of the copper foil after heating as compared with the conventional electrolytic copper foil, and the foil tear of the overcharge test of the secondary battery is less likely to occur. Because.

The electrode constituting materials of the negative electrode of the secondary battery of the present invention include pyrolytic carbons, cokes, graphites, and the like.
Metallic lithium, lithium alloy, polyacetylene, polypyrrole, and the like can be used.

The material constituting the positive electrode of the positive electrode of the secondary battery of the present invention is not particularly limited, and may be LiNiO ₂ , LiCoO ₂ ,
LiMn ₂ O ₄ or the like can be used alone or as a mixture.

As the electrolyte, LiClO ₄ , LiPF ₆
For example, an electrolyte in which a so-called organic electrolyte obtained by dissolving a lithium salt such as in a non-aqueous solvent such as ethylene carbonate or dimethyl carbonate in a polymer solid electrolyte such as polyvinylidene fluoride can be used.

As the separator, for example, a nonwoven fabric, cloth, microporous film, or a combination thereof, containing a polyolefin such as polyethylene or polypropylene as a main component can be used.

FIG. 1 shows a partial cross-sectional front view of an example of a cylindrical lithium ion battery.

[0030]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples of the present invention and Comparative Examples thereof, but the present invention is not limited to these Examples.

Example 1 (1) Production of Electrodeposited Copper Foil A commercially available copper wire as a copper raw material was baked at 700 ° C. for 1 hour, and further subjected to an acid pickling treatment with a 100 g / l sulfuric acid aqueous solution for 20 minutes. Adhering impurities were removed. Next, the calcined and pickled copper wire was dissolved in sulfuric acid to obtain a copper sulfate solution. The copper sulfate solution was filtered by a filtration device using activated carbon to obtain an electrolyte having the following composition. Note that purified sulfuric acid was used as the sulfuric acid. Copper sulfate (CuSO ₄ .5H ₂ O) 280 g / l Sulfuric acid (H ₂ SO ₄ ) 80 g / l Using this electrolytic solution, a noble metal oxide-coated titanium was used as an anode,
Current density of 50 A / d using titanium drum as cathode
Electrolysis was performed under the conditions of m ² and a liquid temperature of 50 ° C. to produce an electrolytic copper foil having a thickness of 10 μm. Using the obtained copper foil as a sample, the amount of impurities in the copper foil was measured and the following characteristic tests were performed. The results are shown in Table 1. (A) Tensile strength Tensile strength after heating at room temperature (23 ° C.) and 130 ° C. for 15 hours was measured based on JIS C 6511. (B) Elongation The elongation after heating at room temperature (23 ° C.) and 130 ° C. for 15 hours was measured based on JIS C 6511. (C) Tear propagation time Tensile strength test after heating at 130 ° C. for 15 hours (crosshead speed 2.0 mm / min, chart speed 200
mm / min), the time (sec) from the start of the cracking of the foil to the completion of the fracture was measured.

(2) Manufacture of Lithium Ion Battery FIG. 1 shows a partial cross-sectional front view of a cylindrical lithium ion battery, wherein 1 is a positive electrode, 2 is a negative electrode, 3 is a separator, 4 is a positive electrode lead, and 5 is a negative electrode lead. , 6 is a positive electrode cover, 7 is a battery can, and 8 is a gasket.

The lithium ion battery shown in FIG. 1 was manufactured as follows. As the positive electrode active material, LiCoO ₂
90 parts by weight, 5 parts by weight of graphite having an average particle size of 1 μm as a conductive aid, and 5 parts by weight of polyvinylidene fluoride (PVDF) as a binder.
5 parts by weight of 2-pyrrolidone was added to prepare a positive electrode mixture paste. Similarly, pitch-based carbon fiber 90 is used as a negative electrode active material.
10 parts by weight of PVDF as a binder and 10 parts by weight of N-methyl-2-pyrrolidone were mixed with the mixture to obtain a negative electrode mixture paste.

Next, the mixture paste for the positive electrode was
And pre-dried at 120 ° C. for 10 minutes, pressure-formed the electrode by a roller press, and vacuum-dried at 130 ° C. for 15 hours to a thickness of 160 μm.
And The coated amount of the positive electrode mixture (excluding the solvent from the paste) per unit area was 25 mg / cm ² , and was cut into a size of 54 mm in width and 437 mm in length to prepare a positive electrode 1. However, the length 10 mm of both ends of the positive electrode 1 is
The positive electrode mixture was not applied and the aluminum foil was exposed, and the positive electrode lead 4 was pressure-bonded to one of the aluminum foil by ultrasonic bonding.

On the other hand, the negative electrode mixture paste was
m on both sides of the copper foil obtained in Example 1,
After pre-drying at 10 ° C. for 10 minutes, the electrode was pressure-formed by a roller press, and then vacuum-dried at 130 ° C. for 15 hours to a thickness of 200 μm. The applied amount of the negative electrode mixture (paste excluding the solvent) per unit area was 13 mg /
Negative electrode 2 was prepared by cutting out into a size of cm ² , 56 mm in width and 480 mm in length. As in the case of the positive electrode 1, the negative electrode 2 was not coated with the mixture for the negative electrode and the copper foil was exposed in the portion having a length of 10 mm, and the negative electrode lead 5 was pressure-bonded to one of the two parts by ultrasonic bonding. .

The separator 3 has a thickness of 25 μm and a width of 5 μm.
An 8 mm polyethylene microporous membrane was used. Then Figure 1
As shown in (1), the positive electrode 1, the separator 3, the negative electrode 2, and the separator 3 were superimposed in this order, and were wound to form an electrode group. This was inserted into a battery can, the negative electrode lead 5 was welded to the bottom of the can, and a throttle portion for caulking the positive electrode lid 6 was provided. Thereafter, an electrolyte obtained by dissolving lithium hexafluorophosphate in a mixed solvent of ethylene carbonate and dimethyl carbonate at a volume ratio of 1: 1 at 1 mol / liter is poured into the battery can 7, and then the positive electrode lead 4 is connected to the positive electrode cover. After welding to 6, a positive electrode lid 6 was attached to obtain a lithium ion battery.

Overcharge test Using the obtained lithium-ion battery, 40
After overcharging for 30 minutes at 3 A and DC for 3 minutes, the batteries were disassembled, and the winding end point of the negative electrode copper foil (5 cm × 5 c
m, 25 cm ² ) was visually observed to determine whether or not the copper foil was broken, and the number thereof was measured. Table 1 shows the results.

Example 2 In the production of an electrolytic copper foil, a copper sulfate solution (electrolytic solution) was prepared except that the copper wire was not fired.
An electrolytic copper foil was manufactured in the same manner as in Example 1. Using this copper foil, measurement of the amount of impurities in the copper foil and each characteristic test of (a) tensile strength, (b) elongation, and (c) tear propagation time were performed in the same manner as in Example 1. As a result, Are shown in Table 1. Further, a lithium ion battery was manufactured using this copper foil in the same manner as in Example 1, and an overcharge test was performed in the same manner as in Example 1. The results are shown in Table 1.

Example 3 In the production of the electrolytic copper foil, except that the pickling treatment of the copper wire was not performed in preparing the copper sulfate solution (electrolytic solution).
An electrolytic copper foil was manufactured in the same manner as in Example 1. Using this copper foil, measurement of the amount of impurities in the copper foil and each characteristic test of (a) tensile strength, (b) elongation, and (c) tear propagation time were performed in the same manner as in Example 1. As a result, Are shown in Table 1. Further, a lithium ion battery was manufactured using this copper foil in the same manner as in Example 1, and an overcharge test was performed in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 1 In the production of an electrolytic copper foil, in preparing a copper sulfate solution (electrolytic solution), no baking treatment and no pickling treatment were performed on the copper wire, and 0.5 ppm of gelatin was contained in the electrolytic solution. Except having made it, it carried out similarly to Example 1, and manufactured the electrolytic copper foil. Using this copper foil, measurement of the amount of impurities in the copper foil and (a) tensile strength, (b) elongation,
(C) Each property test of the tear propagation time was performed, and the results are shown in Table 1. Further, a lithium ion battery was manufactured using this copper foil in the same manner as in Example 1, and an overcharge test was performed in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 2 In the production of an electrolytic copper foil, a copper sulfate solution (electrolytic solution) was prepared in the same manner as in Example 1 except that the electrolytic solution contained 3 ppm of gelatin and 20 ppm of chloride ions. An electrolytic copper foil was manufactured. Using this copper foil, measurement of the amount of impurities in the copper foil and each characteristic test of (a) tensile strength, (b) elongation, and (c) tear propagation time were performed in the same manner as in Example 1. As a result, Are shown in Table 1. Using this copper foil, a lithium ion battery was manufactured in the same manner as in Example 1, and an overcharge test was performed in the same manner as in Example 1. The results are shown in Table 1.
It was shown to.

Comparative Example 3 An electrolytic copper foil was produced in the same manner as in Example 1 except that the electrolytic solution contained 10 ppm of gelatin in producing the copper sulfate solution (electrolytic solution). did. Using this copper foil, measurement of the amount of impurities in the copper foil and (a) tensile strength, (b) elongation,
(C) Each property test of the tear propagation time was performed, and the results are shown in Table 1. Further, a lithium ion battery was manufactured using this copper foil in the same manner as in Example 1, and an overcharge test was performed in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 4 A commercially available rolled copper foil having a thickness of 10 μm [C1100 (JIS)
H 3110, tough pitch copper) and Cu of 99.90% or more], a lithium ion battery was manufactured in the same manner as in Example 1, and an evaluation test was performed in the same manner as in Example 1. The results are shown in Table 1.

[0044]

[Table 1] In Examples 1 to 3, the electrolytic copper foil of the present invention has the total amount of impurities in the copper foil reduced to 15 ppm or less.
The tensile strength and elongation of the copper foil properties are simultaneously increased. In particular, it has a room temperature tensile strength of 55 kgf / mm ² or more and an elongation after heating of 25% or more. In addition, it has a long tear propagation time and is excellent in preventing breakage in a battery overcharge test.

On the other hand, in Comparative Examples 1 to 3, since the total amount of impurities in the copper foil exceeded 15 ppm, the tensile strength and the elongation at room temperature and after heating could not be increased as in the present invention. As is clear from the overcharge test as a secondary battery, the battery lacks reliability. Comparative Example 4
In the case of (rolled copper foil), the tensile strength and room temperature elongation after heating tend to be lower than those of the copper foil of the present invention, and are slightly inferior to those using the copper foil of the present invention in the evaluation of the overcharge test. It turned out that.

[0046]

The electrolytic copper foil of the present invention has excellent tensile strength at room temperature and after heating, and has excellent elongation at room temperature and after heating, and is suitable for use as a current collector copper foil for secondary batteries. .

When the current collector copper foil for a secondary battery of the present invention is used, a secondary battery having excellent overcharge test characteristics can be obtained.

Further, the secondary battery of the present invention has excellent overcharge test characteristics.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional front view of a cylindrical lithium ion battery.

[Explanation of symbols]

 Reference Signs List 1 positive electrode 2 negative electrode 3 separator 4 positive electrode lead 5 negative electrode lead 6 positive electrode cover 7 battery can 8 gasket

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Katsumi Kobayashi 1226 Shimoedashiri, Shimodate City, Ibaraki Pref. Inside the Shimodate Plant of Nihon Electrolysis Co., Ltd. F-term in Shimodate factory (reference) 5H017 AA03 AS10 CC01 EE01 EE08 HH01 5H028 AA01 CC20 EE01 HH01 5H029 AJ02 AK03 AK19 AL06 AL12 AL16 AM01 AM03 AM05 AM07 AM16 BJ02 BJ14 DJ07 EJ01 HJ01

Claims (5)

[Claims] 1. An electrolytic copper foil characterized in that the carbon content in the copper foil is 5 ppm or less and the sulfur content is 3 ppm or less. 2. The copper foil has an oxygen content of 5 ppm or less and a nitrogen content of 0.5 ppm or less.
Electrolytic copper foil as described. 3. The copper foil has a total content of carbon, sulfur, oxygen, nitrogen and hydrogen of 15 ppm or less.
Electrolytic copper foil as described. 4. A copper foil for a current collector of a secondary battery, comprising the electrolytic copper foil according to claim 1, 2 or 3. 5. A secondary battery comprising a positive electrode and a negative electrode in which an electrode constituent material layer is formed on the surface of a flat current collector, wherein at least one of the positive and negative flat current collectors is provided. Or a secondary battery characterized by being the electrolytic copper foil according to 3.