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

Abstract

Provided are an electrodeposited copper foil, a negative electrode that is for a lithium ion secondary battery, and a lithium ion secondary battery into which the electrode is incorporated. The electrodeposited copper foil exhibits good electrical conductivity and superior tensile strength, with no significant decline in tensile strength exhibited even after one hour of heating at 300 C. The negative electrode has heightened cycle properties due to the use of the electrodeposited copper foil as a current collector. Using x-ray diffraction, in the electrodeposited copper foil, in normal conditions, the diffraction intensity (I)<220> in the <220> orientation, the diffraction intensity (I)<200> in the <200> orientation, and the diffraction intensity (I)<111> in the <111> orientation, satisfy the following formula (1):
I<220>/{I<220>+I<200>+I<111>}>0.13(1).

Claims

1. An electrodeposited copper foil for a lithium ion secondary battery, wherein, using x-ray diffraction, in normal conditions, a diffraction intensity I<220> thereof in a <220> orientation, a diffraction intensity I<200> thereof in a <200> orientation, and a diffraction intensity I<111> thereof in a <111> orientation, satisfy the following formula (1):
I<220>/{I<220>+I<200>+I<111>}0.30(1) in normal conditions, a tensile strength thereof is 450 MPa or greater, and in normal conditions, electrical conductivity thereof is 80% IACS or greater measured right after the electrodeposited copper foil is manufactured with an electrolytic method.

2. The electrodeposited copper foil for a lithium ion secondary battery according to claim 1, wherein, in normal conditions, a tensile strength thereof is 500 MPa or greater.

3. The electrodeposited copper foil for a lithium ion secondary battery according to claim 1, wherein a tensile strength thereof after a heating process of one hour at 300 C. is 400 MPa or greater.

4. The electrodeposited copper foil for a lithium ion secondary battery according to claim 1, wherein electrical conductivity thereof after a heating process of one hour at 300 C. is 85% IACS or greater.

5. The electrodeposited copper foil for a lithium ion secondary battery according to claim 2, wherein a tensile strength thereof after a heating process of one hour at 300 C. is 400 MPa or greater.

6. The electrodeposited copper foil for a lithium ion secondary battery according to claim 2, wherein electrical conductivity thereof after a heating process of one hour at 300 C. is 85% IACS or greater.

7. An electrodeposited copper foil for a lithium ion secondary battery, wherein, using x-ray diffraction, in normal conditions, a diffraction intensity I<220> thereof in a <220> orientation, a diffraction intensity I<200> thereof in a <200> orientation, and a diffraction intensity I<111> thereof in a <111> orientation, satisfy the following formula (2):
0.65>I<220>/{I<220>+I<200>+I<111>}>0.30(2) in normal conditions, a tensile strength thereof is 450 MPa or greater, and in normal conditions, electrical conductivity thereof is 80% IACS or greater measured right after the electrodeposited copper foil is manufactured with an electrolytic method.

8. The electrodeposited copper foil for a lithium ion secondary battery according to claim 7, wherein, in normal conditions, a tensile strength thereof is 500 MPa or greater.

9. The electrodeposited copper foil for a lithium ion secondary battery according to claim 7, wherein a tensile strength thereof after a heating process of one hour at 300 C. is 400 MPa or greater.

10. The electrodeposited copper foil for a lithium ion secondary battery according to claim 7, wherein electrical conductivity thereof after a heating process of one hour at 300 C. is 85% IACS or greater.

Description

EXAMPLES

(1) Further detailed description will be given below of the present invention based on Examples; however, the present invention is not in any way limited to the following Examples and it is possible to carry out appropriate changes within a range which does not depart from the gist of the present invention.

(2) [Manufacture of Unprocessed Copper Foil]

(3) An electrolyte for manufacturing a foil was prepared by respectively adding additives with the compositions shown in Table 1 to an acidic copper electrolytic bath of copper 80 g/L-sulfuric acid 40 to 60 g/L. Here, in the Examples, all the chloride ion concentrations are adjusted to 30 ppm; however, the chloride ion concentration is appropriately changed according to the electrolysis conditions and is not limited to this concentration.

(4) Using the prepared electrolyte, unprocessed copper foils of Examples 1 to 25 were manufactured using an electrolytic foil manufacturing method for manufacturing unprocessed copper foil with a thickness of 12 m under conditions of a current density of 40 A/dm.sup.2 and a bath temperature of 45 C. using a precious metal oxide coated titanium electrode for the anode and a rotating drum made of titanium for the cathode.

(5) In addition, also in Comparative Examples 1 to 6, unprocessed copper foils were manufactured so as to be 12 m using electrolytes with the compositions shown in Table 1.

(6) Here, Comparative Example 5 is an electrodeposited copper foil created in accordance with Patent Document 10 and Comparative Example 6 is an electrodeposited copper foil created in accordance with Patent Document 11. Here, MPS is 3-mercapto-1-propanesulfonic acid sodium salt, 2M-5S is 2-mercapto-5-benzimidazole sulfonic acid, SPS is bis-(3-sulfopropyl)-disulfide, DDAC is diallyl dimethyl ammonium chloride, and EUR is N,N-diethylthiourea.

(7) TABLE-US-00001 TABLE 1 Concen- Cl Copper Sulfuric Acid Concentration tration Concentration Concentration Concentration Example Additive (A) Type ppm Additive (B) Type ppm ppm g/L g/L 1 Thiourea 2 Polyethylene glycol 2 30 80 45 2 Thiourea 3 Polyethylene glycol 2 30 80 55 3 Thiourea 6 Polyarylamine 2 30 80 45 4 N-allythiourea 6 Polyarylamine 2 30 80 50 5 Ethylene thiourea 6 Polyarylamine 2 30 80 60 6 Thiourea 5 Polyethylene glycol 10 30 80 47 7 Thiourea 5 Hydroxyethylcellulose 12 30 80 49 8 Thiourea 5 Polyacrylamide 8 30 80 41 9 N,N-dimethylthiourea 5 Polyethylene glycol 10 30 80 57 10 N,N-dimethylthiourea 5 Hydroxyethylcellulose 12 30 80 59 11 N,N-dimethylthiourea 5 Polyacrylamide 8 30 80 51 12 Tetramethylthiourea 5 Polyethylene glycol 10 30 80 42 13 Tetramethylthiourea 5 Hydroxyethylcellulose 12 30 80 44 14 Tetramethylthiourea 5 Polyarylamine 8 30 80 46 15 Ethylene thiourea 6 Polyethyleneimine 15 30 80 52 16 Ethylene thiourea 6 Polyethylene glycol 12 30 80 54 17 Ethylene thiourea 5 Hydroxyethylcellulose 12 30 80 56 18 Ethylene thiourea 5 Polyarylamine 8 30 80 58 Cl Copper Sulfuric Acid Comparative Concentration Concentration Concentration Concentration Concentration Example Additive Type ppm Additive Type ppm ppm g/L g/L 1 Tetramethylthiourea 5 Polyethylene 10 30 80 145 glycol 2 Ethylene thiourea 5 Gelatin 12 30 80 145 3 30 80 90 4 MPS 5 Gelatin 12 30 80 50 Sulfuric Acid Comparative Cl Concentration Copper Concentration Concentration Example Additive Type and Concentration ppm g/L g/L 5 2M-5S 31.3 ppm + SPS 73.0 ppm + DDAC 64.1 ppm 65.7 80 150 6 DDAC 70 ppm + SPS 60 ppm + EUR 3 ppm 60 80 150
[Measurement of Tensile Strength and Electrical Conductivity of Electrodeposited Copper Foil]

(8) The tensile strength Ts (MPa), the 0.2% proof stress (MPa), the elongation (%), and the electrical conductivity EC (% IACS (International Annealed Copper Standard)) were measured at room temperature of each of the electrodeposited copper foils (Examples 1 to 18 and Comparative Examples 1 to 6). The results are shown in Table 2.

(9) In addition, for the tensile strength Ts (MPa), the 0.2% proof stress (MPa), the elongation (%), and the electrical conductivity EC (% IACS), measurement was carried out after performing the heating process for one hour at 300 C. The results are shown in Table 2.

(10) In addition, the ten point average surface roughnesses Rz (m) of the S-surface and the M-surface of each of the electrodeposited copper foils (Examples 1 to 18 and Comparative Examples 1 to 6) were measured. The results are shown in Table 2.

(11) Here, the tensile strength is a value measured using a tensile tester (Model 1122 manufactured by Instron Co.), the electrical conductivity is a value measured according to JIS H 0505, the surface roughness Rz (m) is a ten point average roughness as defined in JIS B 0601-1994, and the 0.2% proof stress and the elongation are values measured using methods defined in JIS K 6251.

(12) [Measurement of <110> Orientation Intensity Ratio]

(13) The X-ray diffraction spectrum of each of the electrodeposited copper foils (Examples 1 to 18 and Comparative Examples 1 to 6) was measured.

(14) Here, using an X-ray apparatus manufactured by Rigaku Denki Co. as the measuring apparatus, the X-ray tube was CuK, the tube voltage was 40 kV, the tube current was 20 mA, the scanning method was a -2 method, and the measurement range was 20 deg to 100 deg.

(15) From each of the diffraction intensities I<220>, I<200>, and I<111> of the obtained X-ray diffraction spectrum, I<220>/{I<220>+I<200>+I<111>} was calculated as the <110> orientation intensity ratio.

(16) The results are shown in Table 2.

(17) TABLE-US-00002 TABLE 2 I<220>/{I<200> + I<220> + I<111>} Room Temperature After Heating Capacity 0.2% 0.2% <110> Retention Proof Proof Rz Intensity Ratio Ts Stress Elongation EC Ts Stress Elongation EC S-surface M-surface Ratio % Evaluation MPa Mpa % % IACS MPa Mpa % % IACS m m Example 1 0.13 70 465 395 5.4 76 352 308 7.6 89 1.98 2.03 2 0.26 72 487 414 5.2 78 365 310 7.3 87 1.99 2.03 3 0.3 75 524 482 4.7 85 416 318 7.0 86 1.56 2.03 4 0.41 79 586 507 4.2 83 421 336 7.2 86 1.54 2.02 5 0.36 78 595 499 4.3 82 435 322 6.7 85 1.45 1.98 6 0.47 82 649 561 3.2 86 427 371 6.0 87 1.89 1.90 7 0.45 81 642 547 3.4 85 422 368 5.5 87 1.86 1.91 8 0.41 75 600 516 4.2 80 389 333 6.6 83 1.63 1.65 9 0.5 81 642 552 3.4 85 422 361 5.9 87 1.90 1.25 10 0.48 79 628 543 3.6 83 411 353 5.6 86 1.96 1.87 11 0.44 76 607 525 4.1 81 395 343 7.0 84 1.49 1.53 12 0.44 83 656 564 3.1 86 432 372 5.4 88 1.22 1.32 13 0.42 82 649 555 3.2 86 427 369 5.6 87 1.64 1.67 14 0.4 81 642 554 3.4 85 422 364 5.6 87 1.30 1.39 15 0.69 87 684 557 2.5 78 484 385 4.2 93 1.58 2.50 16 0.67 85 670 516 2.8 79 473 382 5.4 92 1.56 2.45 17 0.65 84 663 569 2.9 87 438 377 4.2 89 1.89 1.32 18 0.63 83 656 566 3.1 86 432 370 5.8 88 1.87 1.91 Comparative Example 1 0.10 64 X 693 562 2.5 71 388 327 4.6 76 1.53 3.31 2 0.09 60 X 662 554 3.1 73 378 302 5.3 77 1.53 2.58 3 0.09 56 X 408 345 8.2 95 205 169 10.0 98 1.58 3.66 4 0.08 55 X 312 265 10.2 99 220 183 13.5 99 1.45 1.41 5 0.10 55 X 786 624 1.4 34 450 328 4.1 40 1.57 3.04 6 0.10 54 X 483 418 6.7 58 365 310 8.4 66 1.42 1.35
[Chromate Processing]

(18) With respect to Examples 1 to 18 and Comparative Examples 1 to 6, a rust-proofing treated layer was formed and set as a current collector by carrying out chromate processing.

(19) The conditions of the chromate processing of the copper foil surface are as follows.

(20) Chromate processing conditions:

(21) Potassium bichromate: from 1 to 10 g/L

(22) Immersion processing time: from 2 to 20 seconds

(23) [Manufacture of Negative Electrode for Lithium Secondary Battery]

(24) A negative electrode mixture was adjusted by mixing at a ratio of 90 mass % of a powdered Si alloy-based active material (average particle diameter 0.1 m to 10 m) and 10 mass % of a polyimide-based binder as a binder and an active material slurry was set by dispersing the negative electrode mixture in N-methylpyrrolidone (solvent).

(25) Next, the slurry was applied on both surfaces of a strip-shaped electrodeposited copper foil with a thickness of 12 m manufactured in the Examples and Comparative Examples and then compressed and formed by a roller press after drying to form a strip-shaped negative electrode. This strip-shaped negative electrode was formed so that the film thickness of the negative electrode mixture after molding was the same at 90 m on both sides and so that the width and length were 55.6 mm and 551.5 mm, respectively.

(26) [Manufacture of Positive Electrode for Lithium Secondary Battery]

(27) 0.5 mole lithium carbonate and 1 mole cobalt carbonate were mixed and calcined at 900 C. in air for five hours to obtain a positive electrode active material (LiCoO.sub.2).

(28) A positive electrode mixture was made by mixing at a ratio of 91 mass % of this positive electrode active material (LiCoO.sub.2), 6 mass % of graphite as a conductive agent, and 3 mass % of polyvinylidene fluoride as a binder and this positive electrode mixture was dispersed in N-methyl-2-pyrrolidone to form a slurry.

(29) Next, this slurry was applied uniformly to both sides of a positive electrode current collector made of a strip of aluminum with a thickness of 20 m and then compression-molded with a roller press after drying to obtain a strip-shaped positive electrode with a thickness of 160 m. This strip-shaped positive electrode was formed so that the film thickness of the positive electrode mixture after molding was 70 m on both surfaces and so that the width and length were 53.6 mm and 523.5 mm, respectively.

(30) [Manufacture of Lithium Secondary Battery]

(31) The strip-shaped positive electrode and the strip-shaped negative electrode manufactured as described above are laminated with a separator formed of a microporous polypropylene film with a thickness of 25 m and a width of 58.1 mm to form a laminated electrode body. Regarding this laminated electrode body, the negative electrode is wound many times in a spiral form to the inside along the length direction thereof and the final end section of the separator is fixed with tape at the outermost periphery to form a spiral electrode body. The hollow portion of this spiral-shaped electrode body was formed with an inner diameter of 3.5 mm and an outer shape of 17 mm.

(32) In a state where an insulating plate is installed on both upper and lower surfaces of the manufactured spiral-shaped electrode body, the manufactured spiral-shaped electrode body is accommodated in a battery can made of iron and plated with nickel and a positive electrode lead made of aluminum leading from the positive electrode current collector is connected with the battery cover and a negative electrode lead made of nickel leading from the negative electrode current collector is connected with the battery can in order to perform current collection in the positive electrode and the negative electrode.

(33) 5.0 g of a non-aqueous electrolyte, in which LiPF.sub.6 was dissolved at a ratio of 1 mol/l in an equal volume mixed solvent of propylene carbonate and diethyl carbonate, was introduced into the battery can accommodating the spiral-shaped electrode body. Next, the battery cover was fixed by caulking the battery can via an insulating sealing gasket coated with an asphalt surface so as to maintain the airtightness inside the battery can.

(34) By so doing, a cylindrical lithium secondary battery with a diameter of 18 mm and a height of 65 mm was manufactured.

(35) [Measurement of Capacity Retention Ratio by Charge and Discharge Test]

(36) For the secondary batteries of the manufactured Examples 1 to 18 and Comparative Examples 1 to 6, charge and discharge test was performed under a condition of 25 C. and the capacity retention ratio of the 50th cycle with respect to the 2nd cycle was calculated. At that time, after performing charging until the battery voltage reached 4.2 V at a set current density of 1 mA/cm.sup.2, charging was performed until the current density reached 0.05 mA/cm.sup.2 at a set voltage of 4.2 V, and discharging was performed until the battery voltage reached 2.5 V at a set current density of 1 mA/cm.sup.2.

(37) Here, when performing the charging, the utilization rate of the capacity of the negative electrode was 90% and metal lithium was not deposited on the negative electrode.

(38) The capacity retention ratio was calculated as the ratio of the discharge capacity of the 50th cycle with respect to the discharge capacity of the 2nd cycle, that is, as (discharge capacity of 50th cycle/discharge capacity of 2nd cycle)100.

(39) The results of the measured capacity retention ratio are shown in Table 2. In addition, the evaluation with respect to the capacity retention ratio is shown in Table 2. As evaluation, is particularly good, is good, and x is poor.

(40) As shown in Table 2, Examples 3 to 18 were favorable with a <110> orientation intensity ratio greater than 0.13, a tensile strength of 400 MPa, and electrical conductivity of 75% IACS or greater at room temperature and after the heating process, and the capacity retention ratios thereof were also favorable.

(41) Here, for Examples 1 and 2, the <110> orientation intensity ratio was greater than 0.13; however, the tensile strength after the heating process was slightly insufficient. However, as long as the tensile strength after the heating process was 350 MPa or greater, the capacity retention ratio was favorable as an electrode for a lithium secondary battery formed of a normal active material with electrical conductivity, 0.2% proof stress, elongation, and the like, and the evaluation was (good).

(42) On the other hand, for Comparative Examples 1 to 6, since the <110> orientation intensity ratio was less than 0.13, excesses or deficiencies occurred in the tensile strength, the electrical conductivity, the 0.2% proof stress, the elongation and the like after the heating process, the capacity retention ratio was poor, and the evaluation was x (poor).

(43) Here, for Comparative Example 4, despite I.sub.220/I.sub.200 defined in Patent Document 12 being 2.5 or less to 0.03 or greater, I<220>/{I<220>+I<200>+I<111>}>0.13 defined in the present specification was not satisfied, the tensile strength was low at 320 MPa or less, and the capacity retention ratio was poor.

(44) [Evaluation of Negative Electrode Active Material Adhesion]

(45) Furthermore, evaluation of the active material adhesion was carried out as follows with respect to Examples 1, 3, 9, 18, 16, and 15 out of the secondary batteries of the manufactured Examples 1 to 18.

(46) Each of the electrodes was cut into a 10 mm60 mm piece as a test piece and fixed such that negative electrode active material coating surface was up and the copper foil surface was down. Next, tape was stuck onto the negative electrode active material surface and the peel strength was measured when the stuck tape was peeled from the end in a direction at 90 thereto at a speed of 50 mm/min. The measurement was carried out five times and the average values of each of the values are shown in Table 3 as the adhesion strength (N/m). From Table 3, the <110> orientation intensity ratio of Examples 1, 3, 9, and 18 was 0.65 or less, and the active material adhesion was more favorable with an adhesion strength of 30 N/m or greater.

(47) However, Examples 15 and 16 had a <110> orientation intensity ratio of 0.65 or greater and the adhesion strength was 30 N/m or less; however, these Examples were in a range where there were no practical problems.

(48) The overall determination of each of the Examples is shown in the evaluation columns of Table 3 as -particularly good, and -good.

(49) Under conditions where the <110> orientation intensity ratio was greater than 0.65, the surface roughness Rz was greater (refer to Table 2) and it is considered that the unevenness was not preferable with respect to the active material adhesion.

(50) TABLE-US-00003 TABLE 3 I<220>/{I<200> + I<220> + I<111>} Active Cl Copper Sulfuric Acid <110> material Additive (A) Additive (B) Concentration Concentration Concentration Intensity Adhesion Example Type ppm Type ppm ppm g/L g/L Ratio N/m Evaluation 1 Thiourea 2 Polyethylene 2 30 80 45 0.16 31 glycol 3 Thiourea 6 Polyarylamine 2 30 80 45 0.3 33 9 N,N- 5 Polyethylene 10 30 80 57 0.5 35 dimethylthiourea glycol 18 Ethylene thiourea 5 Polyarylamine 8 30 80 58 0.63 36 16 Ethylene thiourea 6 Polyethylene 12 30 80 54 0.67 28 glycol 15 Ethylene thiourea 6 Polyethylene 15 30 80 52 0.69 23 imine

(51) Here, the present embodiment described a case where the active material of the negative electrode was silicon; however, even in a case of using an active material mainly composed of oxide of silicon, carbon, germanium, or tin, it is possible to suppress the generation of deformation such as wrinkles in the current collector due to the charge and discharge, it is possible to prevent short circuiting in the positive electrode and the negative electrode of the lithium ion secondary battery, and it is possible to provide a compact lithium ion secondary battery with a long lifetime where decreases in the capacity retention ratio do not occur even when the charge-discharge cycle is repeated.