ELECTRODEPOSITED COPPER FOIL AND METHOD OF PRODUCING SAME

Abstract

The present invention provides an electrodeposited copper foil suitable for a lithium-ion secondary battery, in which a tensile strength in an ordinary state is 50 kgf/mm.sup.2 or more and a tensile strength after continuous heat treatment at 190° C. for 24 hours is 35 to 30 kgf/mm.sup.2.

Claims

1. An electrodeposited copper foil, wherein a tensile strength of the copper foil is 50 kgf/mm.sup.2 or more in an ordinary state and 30 kgf/mm.sup.2 or more after being continuously heat-treated at 190° C. for 24 hours.

2. The electrodeposited copper foil according to claim 1, wherein a sulfur content is 10 ppm by mass or more and less than 30 ppm by mass.

3. A method for producing the electrodeposited copper foil defined in claim 1, wherein the method comprises performing electrolytic treatment with a copper sulfate-based electrolyte containing 1 to 2 ppm of gelatin having an average molecular weight of 80,000 to 120,000 g/mol.

4. A method for producing the electrodeposited copper foil defined in claim 2, wherein the method comprises performing electrolytic treatment with a copper sulfate-based electrolyte containing 1 to 2 ppm of gelatin having an average molecular weight of 80,000 to 120,000 g/mol.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0015] FIG. 1A shows a cross-sectional observation photograph of the copper foil of Example (normal state);

[0016] FIG. 1B shows a cross-sectional observation photograph of the copper foil of Example (after heat treatment);

[0017] FIG. 2A shows a cross-sectional observation photograph of the copper foil of Comparative Example (normal state); and

[0018] FIG. 2B shows a cross-sectional observation photograph of the copper foil of Comparative Example (after heat treatment)

DESCRIPTION OF EMBODIMENTS

[0019] An embodiment of the present invention will be described below.

Example

[0020] As Example, an electrodeposited copper foil was produced under the following conditions.

TABLE-US-00001 Copper sulfate solution Copper concentration 80 ± 5 g/L Free sulfuric acid 90 ± 10 g/L Chlorine 2.5 ppm Gelatin 1.5 ppm (Average molecular weight: 100,000) Solution temperature 50 ± 5° C. Current density 45 ± 5 A/dm.sup.2 Copper foil thickness 8 μm

Comparative Example

[0021] For comparison, an electrodeposited copper foil was produced with a copper sulfate solution in which no gelatin was added. The conditions were the same as those of Example except that no gelatin was added.

[0022] The tensile strength and the elongation rate were measured for the electrodeposited copper foils produced. The measurement method was in accordance with IPC-TM-650. Measurements were made for the electrodeposited copper foils in a normal state (20° C.) and after subjected to heat treatment at 190° C. for each predetermined time. Measurement results are shown in Table 1.

TABLE-US-00002 TABLE 1 Example Comparative Example Tensile Elongation Tensile Elongation strength rate strength rate (kgf/mm.sup.2) (%) (kgf/mm.sup.2) (%) Ordinary state 53.0 6 30.0 12 190° C., 1 hr 48.8 7 25.9 11 190° C., 5 hr 47.3 7 25.2 13 190° C., 10 hr 43.5 9 24.5 13 190° C., 15 hr 38.8 9 23.9 14 190° C., 24 hr 32.8 11 22.1 15

[0023] As shown in Table 1, the tensile strength of the electrodeposited copper foil of Example was 53.0 kgf/mm.sup.2 in the normal state and 32.8 kgf/mm.sup.2 after continuous heat treatment at 190° C. for 24 hours. This revealed that, with the electrodeposited copper foil of Example, the tensile strength after continuous heat treatment at 190° C. for 24 hours decreased by 38.1% as compared with the tensile strength in the normal state. In the case of Example, the tensile strength did not greatly decrease after heat treatment at 190° C. for 1 hour and it was found that the tensile strength gradually decreased as the heat treatment time passed. On the other hand, for the electrodeposited copper foil of Comparative Example, the elongation rate exceeded 10% even in the normal state and the tensile strength decreased by heat treatment at 190° C. for 1 hour. The tensile strength after heat treatment for 24 hours was 22.1 kgf/mm.sup.2, which is less than 30 kgf/mm.sup.2, and was found to decrease by 26.3% as compared with the tensile strength in the normal state.

[0024] Next, the observation results of the cross-sectional structures of the respective electrodeposited copper foils will be described. FIG. 1A shows the cross-sectional observation photograph of Example in the normal state, and FIG. 1B shows the cross-sectional observation photograph of Example after continuous heat treatment at 190° C. for 24 hours. FIG. 2A and FIG. 2B show the cases of Comparative Example in the same manner.

[0025] As shown in FIG. 1B, crystal grain growth was slightly observed in the electrodeposited copper foil of Example after continuous heat treatment was performed at 190° C. for 24 hours, but no crystal grain growth which may result in coarse crystal grains was observed. On the other hand, as shown in FIG. 2B, crystal grains were grown to be coarse crystal grains in the electrodeposited copper foil of Comparative Example after continuous heat treatment was performed at 190° C. for 24 hours.

[0026] Finally, the sulfur content in the electrodeposited copper foil was measured for the electrodeposited copper foils of Example and Comparative Example by secondary ion mass spectroscopy (SIMS), and as a result, the sulfur content was 0.1 ppm by mass or less when the copper foil electrolyte containing no gelatin was used, whereas it was 14 ppm by mass in the copper foil electrolyte when gelatin having an average molecular weight of 100,000 was used. It is deemed that this sulfur content is affected by the use of the gelatin having an average molecular weight of 100,000. Moreover, it is assumed from the cross-sectional structure observation that the sulfur content in the copper foil increases by using the gelatin having an average molecular weight of 100,000, and this controls the electrodeposited copper foil structure so as not to be a crystal structure that causes coarsening of crystal grains by continuous heat treatment at 190° C. for 24 hours.