JP2000328159A - Copper alloy foil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain copper foil having strength higher than that of tough pitch copper and excellent in flexibility and heat resistance by allowing it to have a compsn. contg. a specified weight ratio of P and moreover contg. one or two kinds of specified weight ratios of Fe and Ag by a specified weight ratio in total, and the balance Cu with inevitable impurities. SOLUTION: This copper foil has a compsn. contg., by weight, 0.001 to 0.05% P and moreover contg. one or two kinds of 0.005 to 0.3% Fe and 0.001 to 0.3% Ag by 0.001 to 0.6% in total, and the balance Cu with inevitable impurities. Preferably, the integrated intensity ratio: I(200)/I(220) lies in the range of 0.01 to 0.40. Its proof stress is the important characteristics for executing rolling working and heat resistance for executing heating and drying for adhering an active material to the copper foil. The proof stress is controlled to >=460 N/mm2, and heat resistance to >=300 deg.C, and, so for the copper alloy foil satisfying this conditions, foil cutting does not occur at the time of rolling and winding working, and the generation of burrs at the time of slittering can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a copper alloy foil used for an electrode of a Li-ion secondary battery.

[0002]

2. Description of the Related Art In recent years, with the miniaturization of electronic devices such as mobile phones and video cameras, conventional batteries, for example, Li-ion batteries realizing higher energy density have been used in place of secondary batteries such as NiCd batteries. It is starting to be done. The Li-ion battery uses a tough pitch copper foil whose surface is coated with carbon or the like on the cathode, and the copper foil is wound with a separate material and an aluminum foil (positive electrode side). FIG. 1 shows a manufacturing process of a Li-ion secondary battery electrode.

[0003]

The life of a battery becomes longer as the number of windings increases, and a thinner foil is required for a longer life. However, when an electrode is manufactured by the process shown in FIG. 1 using a material obtained by thinning a conventional tough pitch copper foil,
There were the following problems. -Since the strength (proof stress) is low, the copper foil is broken during the winding process, and the battery cannot be formed. -When the active material (such as carbon) is coated on the copper foil and then heat-treated and dried for adhesion, the copper foil becomes dull due to low heat resistance, and becomes easily stretched, so that large burrs are generated during slitting. If the burr is large, it causes a short circuit during the winding process. The burr also increases when the anisotropy of the copper foil is large. -While being used as a battery, a repetitive stress due to a temperature change acts on the wound copper foil. However, the flexibility of the copper foil is inferior, resulting in fatigue failure and shortening the life of the battery.

[0004] The present invention has been made in view of the above-mentioned problems of conventional tough pitch copper, and has as its object to obtain a copper foil material having higher strength and superior flammability and heat resistance than tough pitch copper. I do.

[0005]

Means for Solving the Problems The copper alloy foil according to the present invention is a copper alloy foil used for an electrode for a Li-ion secondary battery and contains P: 0.001 to 0.05% by weight, Fe: 0.005 to 0.3% by weight, Ag: 0.001
0.001 to 0.6% by weight of the total amount of one or two of the following, and the balance is unavoidable impurities and C
u.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The following characteristics are required for a copper alloy foil used for an electrode for a Li-ion secondary battery. [Proof Strength, Heat Resistance] The proof strength is an important property for performing the winding process, and the heat resistance is important for performing heating and drying for bringing the active material into close contact with the copper foil. If the proof stress is less than 460 N / mm ² , the foil will break during the winding process, and the battery will not work. Heat resistance (heat resistance: 80% of initial hardness)
When the temperature (which will be described later in detail) is less than 300 ° C., the copper foil and the active material are brought into close contact with each other by heating and drying, so that burrs are generated largely during slitting. Therefore, the proof stress is 460 N / mm ² or more, and the heat resistance is 3
It should be at least 00 ° C. If the copper alloy foil satisfies this condition, when applied to the process of FIG. 1, the foil does not break during the winding process, and the generation of burrs during slitting can be suppressed.

[Flexibility] Flexibility is a characteristic item for evaluating vibration fatigue resistance after winding. When the battery is used or the temperature changes during charging, the wound cathode and anode expand,
It contracts, and thereby stress acts on the cathode and the anode. This repeated stress may cause the copper foil to break down due to fatigue,
To prevent this, excellent flexibility is required. When the number of times until the breakage of the flexibility by the flexibility test described later is used as an index of the flexibility, if the number is less than 100 times, the foil may break due to vibration fatigue after the winding process, and the battery cannot be formed. Therefore, the number of times until the flexible breakage is 10
Zero or more times are required, and if the copper alloy foil satisfies this condition, the foil breakage due to vibration fatigue after winding (during use as a battery) can be avoided.

[Conductivity] A copper alloy foil used in a Li-ion secondary battery is wound around an aluminum foil, and therefore needs to have at least the same conductivity as aluminum.
Therefore, the conductivity of the copper alloy foil is set to 60% IACS or more. [Anisotropy] Anisotropy of a copper alloy foil is a characteristic that affects the generation of burrs during slitting. If the difference in proof stress (anisotropic) between the direction parallel to the rolling direction and the direction perpendicular to the rolling direction exceeds 50 N / mm ² , burrs will be generated significantly during slitting, and the battery will be short-circuited during the winding process. If the copper alloy foil has a proof stress difference (anisotropic) of 50 N / mm ² or less, it is possible to suppress the occurrence of burrs during slitting.

[Integral strength ratio] The integral strength ratio {I (200) / I (220)} in the copper alloy foil represents the anisotropy of the foil (difference in proof stress in the direction parallel to and perpendicular to the rolling direction). And the rolling rate and annealing conditions during the foil manufacturing process. Generally, the larger the heat capacity during annealing (higher annealing temperature and / or longer annealing time) and the greater the number of times of annealing, the smaller the anisotropy. When the integrated intensity ratio is less than 0.01, the anisotropy increases. On the contrary, when the integrated intensity ratio exceeds 0.40, the anisotropy increases, and the material strength also decreases.
It cannot be used as a copper alloy foil for Li batteries. Therefore,
The integrated strength ratio of the copper alloy foil is in the range of 0.01 to 0.40, and more preferably 0.05 to 0.20.

[Stress corrosion cracking resistance] Since tensile stress is applied to the copper foil by the winding process, if the stress corrosion cracking resistance susceptibility is strong, a crack is formed in the weakest grain boundary of the copper foil in the electrolytic solution. It enters and propagates one after another, causing instantaneous foil breakage, making the battery impractical. P is 0.05% by weight
If the content exceeds the above range, the susceptibility to stress corrosion cracking is increased.

Next, the composition of the copper alloy foil will be described in detail.

[P] P is an element mainly contributing to the improvement of the soundness of the ingot (deoxidation, molten metal flow, etc.). Content 0.0
If it is less than 01% by weight, the deoxidizing effect in the molten metal cannot be obtained. On the other hand, if it is added in an amount of 0.05% by weight or more, it becomes a solid solution in the product, which causes a decrease in conductivity and a deterioration in stress corrosion cracking resistance. Therefore, the addition amount of P is desirably 0.05% by weight or less, and a more desirable range is 0.001 to 0.03% by weight.
It is.

[Fe, Ag] These elements have an effect of remarkably improving the material strength and heat resistance when added in a small amount. However, Fe: less than 0.005% by weight, Ag: 0.00
If it is less than 1% by weight, there is no effect, while if it exceeds 0.5% by weight of Fe and 0.3% by weight of Ag, the electrical conductivity decreases and the anisotropy tends to increase. On the other hand, if the total content exceeds 0.6% by weight, not only does the conductivity drop, but also the number of passes during foil rolling increases, which increases processing costs and is disadvantageous in terms of cost. Therefore, these elements are Fe: 0.
005 to 0.5% by weight, Ag: 0.001 to 0.3% by weight.
% By weight. [Inevitable impurities] Ni, Sn,
Si, Zn, Mg, Ca, Mn, Al, Cr, Co, P
d, S, Be, V, Zr, Nb, Mo, In, Ti, H
f, Ta, B, etc., and if one or more of these elements is 0.05% by weight or less in total, the degree of decrease in conductivity is small and does not particularly adversely affect battery performance. . Therefore, these elements have a total amount of 0.05% by weight.
Below is acceptable.

A copper alloy foil satisfying the above-mentioned properties can be produced by subjecting a copper alloy ingot having the above composition to hot rolling, cooling with water, and further repeating cold rolling and intermediate annealing according to a conventional method. The thickness of the copper alloy foil is not particularly limited.
Generally, a foil having a thickness of 5 to 20 μm is often required for an electrode of an i-ion battery, and the copper alloy foil of the present invention can sufficiently cope with such a requirement.

[0015]

EXAMPLES The characteristics of the copper alloy foil according to the present invention will be described below as a comparative example. A copper alloy having the composition shown in Table 1 was melted under a charcoal coating in the air using an electric furnace, a 50 mm × 80 mm × 180 mm ingot was melted, and hot-rolled to form a slab having a thickness of 15 mm. After hot rolling at 820 ° C. to finish to a thickness of 3.3 mm, it was water-cooled. These sheets were cold-rolled to a thickness of 1.2 mm, and then subjected to intermediate annealing at a furnace temperature of 750 ° C. × 20 S → cold-rolled to a thickness of 0.4 mm, and then subjected to an intermediate annealing at a furnace temperature of 700 ° C. × 20 S → thickness of 0 After cold rolling to 0.2 mm, the furnace temperature was 650 ° C
× 20S intermediate annealing, and further cold-rolled to a thickness of 1
A 0 μm copper alloy foil was produced. The impurity elements shown in Table 1 were added to investigate their effects.
The material properties of these materials were evaluated in the following manner, and the differences from the comparative examples were confirmed. However, for the stress corrosion cracking resistance test, 0.125 m
m. Table 2 shows the results.

[0016]

[Table 1]

Strength: Two pieces of JIS No. 5 test pieces each having a longitudinal direction parallel to the rolling direction (LD) and a right angle (TD) were cut out, and tensile strength was measured by performing a tensile test. The proof stress difference between the parallel direction and the perpendicular direction was defined as anisotropic, and the average of all was defined as the proof stress of the copper alloy foil. Conductivity; Conductivity was measured based on JIS H0505. Heat resistance: After holding the sample at a predetermined temperature for 5 minutes, the hardness after water cooling was measured, and the temperature having 80% of the initial hardness (= heat resistant temperature) was measured. Stress corrosion cracking resistance; 0.125mmt x 12.7mmw
4 x 150mm test pieces were cut out and stress corrosion cracking test was performed by Thompson's method (Materials Research & Standa
rds (1961) 1081). That is, the test piece was formed into a loop shape as shown in FIG. 2, then 14 wt% ammonia water was added, and the test piece was exposed to a desiccator filled with saturated steam at a temperature of 40 ° C., and the time until the test piece was broken was measured. did.

Sinterability: According to JIS P 8115, bending angle 135 °, bending radius 0.8 mm, load 1.5 kg
The number of times until breakage was measured using an MIT massaging fatigue tester under the conditions described above. Integrated intensity ratio: X-rays were incident on the surface of the copper alloy foil in the final product state (10 μm), and the intensity from each diffraction surface was measured.
The ratio {I (200) / I (220)} of the diffraction intensities of the (200) and (220) planes was determined. Burr height; 250% with mold clearance of 15%
At a punching speed of m, a lead having a length of 30 mm and a width of 0.5 mm was punched, and the burr height was measured by SEM observation.

[0019]

[Table 2]

As is clear from Table 2, No. 1 having a composition within the specified range of the present invention. The copper alloy foils Nos. 1 to 9 are conventional tough pitch copper (No.
It is superior to that of (19), has a small integrated anisotropy within a predetermined range, has small anisotropy, and has all the necessary characteristics as an electrode of a Li-ion secondary battery. In contrast, N
o. Sample No. 10 has a low yield strength and poor sinterability because the Fe content is below the specified range. No. In No. 11, although the Fe content exceeds the specified range, the strength is improved, but the electrical conductivity is reduced, and the integrated intensity ratio is also out of the specified range, the anisotropy is large and the burr height is high. Further, the number of passes during rolling increases, which is disadvantageous in cost. No. In No. 12, since the Ag content was below the specified range, the yield strength was poor, and the sinterability was also poor. No. In No. 13, since the Ag content exceeds the specified range, the strength is improved, but the conductivity is reduced, and the integrated intensity ratio is also out of the specified range, and the anisotropy is large and the burr height is high. No. In No. 14, the deoxidation was insufficient during melting and casting because the P content was below the specified range, and ingot cracking occurred, so that the subsequent test was abandoned.

No. In No. 15, since the P content exceeds the specified range, the electrical conductivity decreases and the stress corrosion cracking resistance is poor. N
o. In No. 16, since the total amount of Fe and Ag exceeds the specified range, the conductivity is low, and the integrated intensity ratio is out of the specified range, so that the anisotropy is large and the burr height is high. No. No. 17 has a low conductivity, an integral intensity ratio outside the specified range, a large anisotropy and a high burr height since the total amount of unavoidable impurities exceeds 0.05%. No. 18 is phosphorus deoxidized copper, but because of its low proof stress and sinterability, Li
It is insufficient as an electrode for an ion secondary battery. No. No. 19 is a conventional tough pitch copper, but has a low proof stress, heat resistance and sinterability. Li aiming at extending the life as in 18
It is insufficient as an electrode for an ion secondary battery.

[0022]

The copper alloy foil according to the present invention is made of a conventional Li
Compared with tough pitch copper foil used as an electrode of an ion secondary battery, it has excellent strength, heat resistance, sinterability and the like, and its anisotropy and the like are suppressed within the range of use of a Li ion secondary battery. Therefore, the present invention is extremely promising as a copper alloy foil used for a Li-ion secondary battery or the like for extending the life.

[Brief description of the drawings]

FIG. 1 is a view showing a manufacturing process of a Li-ion secondary battery electrode.

FIG. 2 is a view showing a loop-shaped test piece used for a stress corrosion cracking resistance test.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Riichi Tsuno 14-1 Nagafu Minatomachi, Shimonoseki City, Yamaguchi Prefecture F-term in Kobe Steel, Ltd. Chofu Works (reference) 5H017 AA03 CC01 EE01 EE08 HH01

Claims (2)

[Claims] 1. A copper alloy foil used for an electrode for a Li-ion secondary battery, comprising 0.001 to 0.05% by weight of P, 0.005 to 0.3% by weight of Fe, and Ag. :
A copper alloy foil comprising 0.001 to 0.6% by weight of any one or two of 0.001 to 0.3% by weight, and the remainder consisting of unavoidable impurities and Cu. 2. Integral intensity ratio: I (200) / I (22
The copper alloy foil according to claim 1, wherein 0) is in the range of 0.01 to 0.40.