Electrolytic copper foil and electrode and lithium-ion battery comprising the same

Abstract

Provided are an electrolytic copper foil, an electrode comprising the same, and a lithium-ion battery comprising the same. The electrolytic copper foil comprises a drum side and a deposited side opposite each other. The drum side and the deposited side each have a Kurtosis (Sku) in a range of 1.8 to 6.4, a developed interfacial area ratio (Sdr) in a range of 0.06% to 13%, and a texture aspect ratio (Str) in a range of 0.1 to 1. With the surface morphology, the electrolytic copper foil has an improved adhesion strength with the active material, and thus improving the charge-discharge cycle life performance of the lithium-ion secondary battery.

Claims

1. An electrolytic copper foil, comprising: a drum side and a deposited side opposite the drum side; wherein the drum side and the deposited side each have a Kurtosis (Sku) in a range of 1.8 to 6.4, the drum side and the deposited side each have a developed interfacial area ratio (Sdr) in a range of 0.06% to 13%, and the drum side and the deposited side each have a texture aspect ratio (Str) in a range of 0.1 to 1.

2. The electrolytic copper foil as claimed in claim 1, wherein the Young's modulus of the electrolytic copper foil is in a range of 29.4 gigapascals to 88.2 gigapascals.

3. The electrolytic copper foil as claimed in claim 1, wherein the developed interfacial area ratio (Sdr) of the drum side and the developed interfacial area ratio (Sdr) of the deposited side are each in a range of 1.5% to 13%.

4. The electrolytic copper foil as claimed in claim 1, wherein the texture aspect ratio (Str) of the drum side and the texture aspect ratio (Str) of the deposited side are each in a range of 0.1 to 0.95.

5. The electrolytic copper foil as claimed in claim 1, wherein the electrolytic copper foil comprises a raw copper foil and a surface-treated layer on the raw copper foil, and the drum side and the deposited side are outermost sides of the electrolytic copper foil.

6. The electrolytic copper foil as claimed in claim 2, wherein the electrolytic copper foil comprises a raw copper foil and a surface-treated layer on the raw copper foil, and the drum side and the deposited side are outermost sides of the electrolytic copper foil.

7. The electrolytic copper foil as claimed in claim 3, wherein the electrolytic copper foil comprises a raw copper foil and a surface-treated layer on the raw copper foil, and the drum side and the deposited side are outermost sides of the electrolytic copper foil.

8. The electrolytic copper foil as claimed in claim 4, wherein the electrolytic copper foil comprises a raw copper foil and a surface-treated layer on the raw copper foil, and the drum side and the deposited side are outermost sides of the electrolytic copper foil.

9. The electrolytic copper foil as claimed in claim 1, wherein the electrolytic copper foil comprises substantially no roughening-treated layer.

10. The electrolytic copper foil as claimed in claim 2, wherein the electrolytic copper foil comprises substantially no roughening-treated layer.

11. The electrolytic copper foil as claimed in claim 3, wherein the electrolytic copper foil comprises substantially no roughening-treated layer.

12. The electrolytic copper foil as claimed in claim 4, wherein the electrolytic copper foil comprises substantially no roughening-treated layer.

13. An electrode of a lithium-ion battery, comprising the electrolytic copper foil as claimed in claim 1.

14. The electrode of the lithium-ion battery as claimed in claim 13, wherein the Young's modulus of the electrode is in a range of 29.4 gigapascals to 88.2 gigapascals.

15. The electrode of the lithium-ion battery as claimed in claim 13, wherein the developed interfacial area ratio (Sdr) of the drum side and the developed interfacial area ratio (Sdr) of the deposited side are each in a range of 1.5% to 13%.

16. The electrode of the lithium-ion battery as claimed in claim 13, wherein the texture aspect ratio (Str) of the drum side and the texture aspect ratio (Str) of the deposited side are each in a range of 0.1 to 0.95.

17. The electrode of the lithium-ion battery as claimed in claim 13, wherein the electrode comprises a raw copper foil and a surface-treated layer on the raw copper foil, and the drum side and the deposited side are outermost sides of the electrolytic copper foil.

18. The electrode of the lithium-ion battery as claimed in claim 14, wherein the electrolytic copper foil comprises a raw copper foil and a surface-treated layer on the raw copper foil, and the drum side and the deposited side are outermost sides of the electrolytic copper foil.

19. A lithium-ion battery, comprising the electrode as claimed in claim 13.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The sole FIGURE is a schematic view of preparing the electrolytic copper foils of Examples 1 to 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(2) Hereinafter, several examples are described to illustrate the embodiments of an electrolytic copper foil, an electrode, and a lithium-ion battery of the present invention, and several comparative examples are provided for comparison. One person skilled in the art can easily realize the advantages and effects of the present invention from the following examples and comparative examples. Therefore, it should be understood that the descriptions proposed herein are just preferable examples for the purpose of illustrations only, not intended to limit the scope of the present invention. One person skilled in the art can make various modifications and variations in order to practice or apply the present invention in accordance with the ordinary knowledge without departing from the spirit and scope of the present invention.

(3) Electrolytic Copper Foil

Examples 1 to 10: Electrolytic Copper Foil

(4) Electrolytic copper foils of Examples 1 to 10 were produced by using a production apparatus as shown in the sole FIGURE through the substantially identical process including an electrodeposition step and an anti-tarnish treatment step.

(5) As shown in the sole FIGURE, the production apparatus for producing the electrolytic copper foil comprises an electrodeposition equipment 10, a surface treatment equipment 20, and a series of guide rollers. The electrodeposition equipment 10 comprises a titanium cathode drum 11, an insoluble anode 12, a copper electrolyte solution 13 and a feed pipe 14. The titanium cathode drum 11 is rotatable and comprises a surface which is mechanically polished by a buff 111. The insoluble anode 12 is set below the titanium cathode drum 11 and substantially surrounds the lower half of the titanium cathode drum 11. The titanium cathode drum 11 and the insoluble anode 12 are spaced apart from each other to accommodate the copper electrolyte solution 13 introduced through the feed pipe 14. The surface treatment equipment 20 comprises a treatment tank 21 and an anode plate 22 disposed therein. The series of guide rollers comprise a first guide roller 31, a second guide roller 32, a third guide roller 33, and a fourth guide roller 34 for transporting a raw copper foil, the surface-treated copper foil and the product, and finally the electrolytic copper foil 40 is wound on the fourth guide roller 34.

(6) The method for producing the electrolytic copper foils of Examples 1 to 10 by using the production apparatus of the sole FIGURE is described as follows.

(7) First, the copper electrolyte solution used in the electrodeposition step was prepared. During the electrodeposition step, the titanium cathode drum 11 was rotated on a fixed axis at a constant speed and a current flowed between the titanium cathode drum 11 and the insoluble anode 12, so that copper ions of the copper electrolyte solution 13 were electrodeposited on the surface of the titanium cathode drum 11 to form the raw copper foil. Then the raw copper foil was stripped from the titanium cathode drum 11 and guided to the first guide roller 31.

(8) The composition of the copper electrolyte solution and the parameters of the electrodeposition step were described as follows:

(9) (1) The composition of the copper electrolyte solution:

(10) Copper sulfate (CuSO.sub.4.5H.sub.2O): about 340 grams per liter (g/L);

(11) Sulfuric acid: about 80 g/L;

(12) Chloride ions (from hydrochloric acid, purchased from RCI Labscan Ltd.): about 35 mg/L;

(13) Glucose (purchased from JUNSEI CHEMICAL): about 2.9 mg/L to 4.6 mg/L; and

(14) Ethylene thiourea (ETU, purchased from Sigma-Aldrich): about 0.9 mg/L to 2.4 mg/L.

(15) (2) The parameters of the electrodeposition step:

(16) Linear velocity of the titanium cathode drum 11: about 2 meters per minute (m/min);

(17) Temperature of the copper electrolyte solution 13: about 46 C.; and

(18) Current density: about 48 Amperes per square decimeter (A/dm.sup.2).

(19) During the electrodeposition step, while the titanium cathode drum 11 was rotated on the axis, the buff 111 was rotated on a fixed axis with a linear velocity, and reciprocately moved along the extending direction of the fixed axis of the buff 111 with a cross speed at the same time, so the titanium cathode drum 11 was mechanically polished by the buff 111 to remove the oxides (e.g., titanium oxides or titanium dioxides) on the titanium cathode drum 11, so as to modify the surface characteristics of the raw copper foil.

(20) The parameters of the mechanical-polished step were described as follows:

(21) Type of the buff 111: flap buff, manufactured by Kure Grinding Wheel Co., Ltd., which has multiple abrasive sheets radially arranged around the axis;

(22) Grit # of the buff 111: 600 to 3000;

(23) Linear velocity of the buff 111: about 300 m/min; and

(24) Cross speed of the buff 111: about 15 counts per minute (cpm) to 60 cpm.

(25) Subsequently, the raw copper foil was guided to the surface treatment equipment 20 through the first guide roller 31 and the second guide roller 32 to carry out the anti-tarnish treatment. The raw copper foil was immersed in the treatment tank 21 filled with the anti-tarnish solution, and then processed with electrodeposition to form a chromium layer.

(26) The composition of the anti-tarnish solution and the parameters of the anti-tarnish treatment were described as follows:

(27) (1) The composition of the anti-tarnish solution:

(28) Chromic acid (CrO.sub.3): 1.0 g/L.

(29) (2) The parameters of the anti-tarnish treatment:

(30) Temperature of the anti-tarnish solution: 25 C.;

(31) Current density: about 0.5 A/dm.sup.2; and

(32) Processing time: about 2 seconds.

(33) After the aforesaid anti-tarnish treatment, the anti-tarnish treated copper foil was guided to the third guide roller 33 to be dried, and wound on the fourth guide roller 34 to obtain the electrolytic copper foil 40 with a thickness of about 6 micrometers (m).

(34) In the above manufacturing process, the differences among the manufacturing processes of the electrolytic copper foils of Examples 1 to 10 were the cross speed of the buff and the concentration of the glucose and the ETU in the copper electrolyte solution, and the parameters were listed in Table 1 below.

(35) It should be noted that the aforesaid method for producing the electrolytic copper foil is illustrative only for the electrolytic copper foil in the present invention, but the electrolytic copper foil in the present invention is not limited to be produced by the aforesaid method.

(36) It should be noted that, regardless of whether the raw copper foil was performed with surface treatment after the electrodeposition step, two outermost sides of the electrolytic copper foil were defined by the relative positions between the raw copper foil and the titanium cathode drum and between the raw copper foil and the copper electrolyte solution in the electrodeposition step. In an embodiment, for the manufacturing process in which no surface treatment is performed after the electrodeposition step, the electrolytic copper foil is the raw copper foil wound after the electrodeposition step, a side of the raw copper foil near the titanium cathode drum is called drum side, and the other side of the raw copper foil near the copper electrolyte solution is called deposited side, the drum side and the deposited side are the outermost sides of the electrolytic copper foil. In another embodiment, for the manufacturing process in which a surface treatment is performed on a single side of the raw copper foil after the electrodeposition step, the electrolytic copper foil comprises a raw copper foil and a surface-treated layer on the raw copper foil. Taking the surface treatment performed on a single side of the raw copper foil near the titanium cathode drum as an example for illustration, a side of the surface-treated layer opposite a side of the raw copper foil is called drum side, and the other side of the raw copper foil near the copper electrolyte solution is called deposited side, the drum side and the deposited side are the outermost sides of the electrolytic copper foil. In another embodiment, for the manufacturing process in which a surface treatment is performed on double sides of the raw copper foil after the electrodeposition step, the electrolytic copper foil comprises a raw copper foil and two surface-treated layers on the raw copper foil. In this case, drum side is the outermost side of one of the surface-treated layers, and it is opposite to a side of the raw copper foil near the cathode drum during electrodeposition step. Deposited side is the outermost side of another surface-treated layer, and it is opposite to the other side of the raw copper foil near the copper electrolyte solution during electrodeposition step. Herein, the drum side and the deposited side are the outermost sides of the electrolytic copper foil.

Comparative Examples 1 to 9: Electrolytic Copper Foil

(37) The electrolytic copper foils of Comparative Examples 1 to 9 were provided for comparison with the electrolytic copper foils of Examples 1 to 10. The process used to produce the electrolytic copper foils of Comparative Examples 1 to 9 was similar to that of Examples 1 to 10. The differences were the cross speed of the buff and the concentration of the glucose and the ETU in the copper electrolyte solution. Parameters of Comparative Examples 1 to 9 different from those of Examples 1 to 10 were also listed in Table 1.

(38) Besides the differences as described above, the titanium cathode drums used in Comparative Examples 1 to 4 and 6 to 9 were also mechanically polished by flap buff like those in Examples 1 to 10, but the titanium cathode drum used in Comparative Example 5 was mechanically polished by disc buff (manufactured by Kure Grinding Wheel Co., Ltd.). Herein, the disc buff has multiple abrasive sheets arranged in parallel along the longitudinal direction and arranged around the axis. Table 1: The girt # and the cross speed of the buff and the concentration of the glucose and the ETU in the copper electrolyte solution used to produce the electrolytic copper foils of Examples 1 to 10 (E1 to E10) and Comparative Examples 1 to 9 (C1 to C9).

(39) TABLE-US-00001 Example Cross speed Conc. of glucose Conc. of ETU No. Girt # (cpm) (mg/L) (mg/L) E1 2000 30 2.9 1.2 E2 2000 30 4.6 1.2 E3 2000 30 3.8 1.2 E4 2000 30 3.8 2.4 E5 2000 15 3.8 1.2 E6 2000 60 3.8 1.2 E7 800 30 3.8 1.2 E8 3000 30 3.8 1.2 E9 2000 25 3.8 0.9 E10 2000 30 4.6 2.0 C1 2000 30 1.5 1.2 C2 2000 30 6.9 1.2 C3 2000 30 3.8 0.6 C4 2000 30 3.8 3.6 C5 2000 30 3.8 1.2 C6 2000 10 3.8 1.2 C7 2000 80 3.8 1.2 C8 600 30 3.8 1.2 C9 4000 30 3.8 1.2

Test Example 1: Surface Characteristics

(40) In this test example, the electrolytic copper foils of Examples 1 to 10 and Comparative Examples 1 to 9 were adopted as test samples, and measured by a laser microscope to observe the surface textures of the deposited sides and the drum sides and take their images. The surface characteristics (Sku, Sdr, and Str) of the electrolytic copper foils were evaluated according to ISO 25178-2 (2012), and the results were shown in Table 2 below.

(41) The instrument and the analytical method of the surface characteristics were described as follows:

(42) (1) Instrument:

(43) Laser microscope: LEXT OLS5000-SAF (manufactured by Olympus); and

(44) Objective lenses: MPLAPON-100LEXT.

(45) (2) Analytical method:

(46) Light wavelength: 405 nm;

(47) Magnification of the objective lenses: 100;

(48) Optical zoom: 1.0;

(49) Observation area: 129 m129 m;

(50) Resolution: 1024 pixels1024 pixels;

(51) Conditions: auto tilt removal;

(52) Filter: unfiltered;

(53) Temperature: 243 C.; and

(54) Relative humidity: 633%.

Test Example 2: Young's Modulus

(55) In this test example, the electrolytic copper foils of Examples 1 to 10 and Comparative Examples 1 to 9 were cut into a same size to obtain the test samples. According to the method of IPC-TM-650, a material-testing machine was used for a tensile test to obtain the stress-strain curve with the strain () as X-axis and the stress () as Y-axis. A parallel line to the Y-axis was drawn at a strain of 0.5% (i.e., =0.005), and the intersection of the curve with the line was the yield strength (.sub.y).

(56) Subsequently, the Young's modulus of the electrolytic copper foils was calculated by the formula [Young's modulus (E)=yield strength (.sub.y/strain ()], and the results were shown in Table 2 below.

(57) The instrument and the analytical method were described as follows:

(58) (1) Instrument:

(59) Material-testing machine: AG-I, purchased from Shimadzu Corporation.

(60) (2) Analytical method:

(61) Sample size: 100 mm (length)12.7 mm (width);

(62) Temperature: ambient temperature (about 25 C.);

(63) Chuck distance: 50 mm; and

(64) Crosshead speed: 50 mm/min.

(65) Table 2: Sku, Sdr, and Str of the drum sides and the deposited sides and Young's modulus of the electrolytic copper foils of Examples 1 to 10 (E1 to E10) and Comparative Examples 1 to 9 (C1 to C9), and the adhesion strengths between the electrolytic copper foils' drum sides and the negative electrode active materials as well as the deposited sides and the negative electrode active materials and charge-discharge cycle life of lithium-ion batteries of Examples 1B to 10B and Comparative Examples 1B to 9B.

(66) TABLE-US-00002 Surface charact- Electrolytic copper foils Lithium-ion batteries eristics Sku Sdr (%) Str E (GPa) Adhesion strength Cycle life Criteria 1.8 to 6.4 0.06 to 13 0.1 to 1 29.4 to Not peeled off (number) Example Drum Deposited Drum Deposited Drum Deposited 88.2 Drum Deposited >800 No. side side side side side side Total side side Total E1 3.1 1.8 3.74 7.51 0.59 0.71 29.4 1377 E2 3.2 2.9 3.75 0.55 0.58 0.70 59 941 E3 3.1 3.0 3.75 1.55 0.58 0.70 47.7 1085 E4 3.1 6.4 3.74 1.01 0.59 0.71 88.2 809 E5 1.8 3.1 3.74 1.54 0.10 0.10 47.7 1043 E6 6.4 2.9 3.74 1.56 0.94 0.95 47.8 1052 E7 3.2 2.9 12.87 1.56 0.58 0.70 47.8 1174 E8 3.1 3.0 0.06 2.01 0.59 0.70 47.7 844 E9 3.1 2.0 3.73 11.9 0.18 0.19 33.1 1211 E10 3.2 5.9 3.74 0.09 0.58 0.71 64.5 947 C1 3.1 0.9 3.74 12.91 0.59 0.70 21.1 513 C2 3.2 9.8 3.75 0.09 0.58 0.71 98.3 598 C3 3.2 0.2 3.74 14.51 0.59 0.70 24.4 643 C4 3.1 7.9 3.74 0.02 0.58 0.70 103.2 652 C5 0.9 3.0 3.75 1.55 0.06 0.08 47.8 592 C6 0.4 3.0 3.74 1.56 0.06 0.07 47.7 607 C7 8.4 3.1 15.01 2.11 0.94 0.94 47.7 571 C8 3.1 2.9 14.79 2.35 0.59 0.70 47.8 637 C9 3.2 3.0 0.02 1.55 0.58 0.70 47.8 540

(67) Discussion of Surface Characteristics of the Electrolytic Copper Foils

(68) As shown in Table 2 above, the electrolytic copper foils of Examples 1 to 10 had all of the following three surface characteristics: (1) The drum side and the deposited side each have a Sku in a range of 1.8 to 6.4; (2) The drum side and the deposited side each have a Sdr in a range of 0.06% to 13%; and (3) The drum side and the deposited side each have a Str in a range of 0.1 to 1.

(69) In contrast, either the drum side or the deposited side of each of the electrolytic copper foils of Comparative Examples 1 to 9 failed to have all of the three surface characteristics. Specifically, the deposited sides of the electrolytic copper foils of Comparative Examples 1 and 2 had Sku out of the range of 1.8 to 6.4. The drum sides of the electrolytic copper foils of Comparative Examples 8 and 9 had Sdr out of the range of 0.06% to 13%. Also, the deposited sides of the electrolytic copper foils of Comparative Examples 5 and 6 had Str out of the range of 0.1 to 1.

(70) In addition, the deposited sides of the electrolytic copper foils of Comparative Examples 3 and 4 had Sku out of the range of 1.8 to 6.4 and Sdr out of the range of 0.06% to 13%. The drum side of the electrolytic copper foil of Comparative Example 7 also had Sku and Sdr both out of the aforesaid ranges. The drum sides of the electrolytic copper foils of Comparative Examples 5 and 6 had Sku and Str respectively out of the range of 1.8 to 6.4 and the range of 0.1 to 1.

(71) Electrode

Examples 1A to 10A and Comparative Examples 1A to 9A: Negative Electrode

(72) The two outermost opposite sides, i.e., the drum side and the deposited side, of each of the electrolytic copper foils of Examples 1 to 10 and Comparative Examples 1 to 9 may be further coated with a negative electrode slurry containing the negative electrode active substance to produce a negative electrode for a lithium-ion battery.

(73) Specifically, the negative electrode can be produced by the following steps.

(74) Firstly, at a solid-liquid ratio of 100:60, 100 g of negative electrode active material was mixed with 60 g of a solvent (N-methylpyrrolidone (NMP)) to prepare the negative electrode slurry. The composition of the negative electrode active material (the content of each component was based on the entire negative electrode active material as 100 wt %) in the negative electrode slurry was described as follows:

(75) 93.9 wt % of negative electrode active substance (mesophase graphite powders, MGP);

(76) 1 wt % of conductive additive (conductive carbon black powders, Super P);

(77) 5 wt % of a solvent binder (polyvinylidene fluoride, PVDF 6020); and

(78) 0.1 wt % of oxalic acid.

(79) Next, the negative electrode slurry was coated on each of the drum side and the deposited side of the electrolytic copper foil and then dried in an oven. After that, the negative electrode slurry coated on the electrolytic copper foil was pressed by a pressing machine to a density of 1.5 grams per cubic centimeter (g/cm.sup.3), and a negative electrode was obtained.

(80) The parameters for producing the negative electrode were described as follows:

(81) Coating rate: 5 m/min;

(82) Coating thickness: about 200 m;

(83) Drying temperature: about 160 C.;

(84) Pressing speed: 1 m/min;

(85) Pressing pressure: 3000 pounds per square inch (psi);

(86) Size of the rollers in the pressing machine: 250 mm (outside diameter, )250 mm (width);

(87) Hardness of the rollers: 62 to 65 HRC; and

(88) Material of the rollers: high-carbon chromium bearing steel (SUJ2).

(89) The electrolytic copper foils of Examples 1 to 10 and Comparative Examples 1 to 9 could be respectively processed with the aforesaid method to obtain the negative electrodes of Examples 1A to 10A and Comparative Examples 1A to 9A.

Test Example 3: Adhesion Strength

(90) In this test example, the negative electrodes of Examples 1A to 10A were cut into a size of 100 mm50 mm (along the machine direction (MD)along the transverse direction (TD)) to obtain the test samples. Similarly, the negative electrodes of Comparative Examples 1A to 9A could be processed with the aforesaid method to obtain the test samples, which were adopted to evaluate the adhesion strengths between the electrolytic copper foils and the negative electrode active materials.

(91) Next, tapes of a same type respectively were adhered on both outer surfaces of the negative electrode active materials of each test sample, and then a universal testing machine was used to measure adhesion strengths between the drum side of the electrolytic copper foil and the negative electrode active material and between the deposited side of the electrolytic copper foil and the negative electrode active material of each test sample.

(92) If the negative electrode active material was detached from the surface of the electrolytic copper foil while the tape was peeled off from the negative electrode active material, it means that the adhesion strength between the surface of the electrolytic copper foil and the negative electrode active material was insufficient and the result was marked as x in Table 2 above. If the negative electrode active material was not detached from the surface of the electrolytic copper foil while the tape was peeled off from the negative electrode active material, it means that the adhesion strength between the surface of the electrolytic copper foil and the negative electrode active material was good, so the electrolytic copper foil could pass the adhesion strength test, and the result was marked as o in Table 2 above.

(93) The analytical method of the adhesion strength was described as follows:

(94) Universal testing machine: TKS-20N, manufactured by IMADA;

(95) Test temperature: about 15 C. to 35 C.;

(96) Tape: 810 D, purchased from 3M;

(97) Peeling angle: the tape peeled from the surface of the negative electrode active material at 90, and

(98) Peeling speed: 50 mm/min.

(99) Lithium-Ion Battery

Examples 1B to 10B and Comparative Examples 1B to 9B: Lithium-Ion Battery

(100) The aforesaid negative electrodes of Examples 1A to 10A and Comparative Examples 1A to 9A could be further respectively adopted with positive electrodes to prepare the lithium-ion batteries of Examples 1B to 10B and Comparative Examples 1B to 9B.

(101) Specifically, the positive electrode for the lithium-ion battery was obtained in accordance with the method as follows.

(102) Firstly, at a solid-liquid ratio of 100:195, 100 g of the positive electrode active material was mixed with 195 g of NMP to prepare a positive electrode slurry. The composition of the positive electrode active material (the content of each component was based on the entire positive electrode active material as 100 wt %) in the positive electrode slurry was described as follows:

(103) 89 wt % of positive electrode active substance (LiCoO.sub.2);

(104) 5 wt % of conductive additive (flaked graphite, KS6);

(105) 1 wt % of conductive additive (conductive carbon black powders, Super P); and

(106) 5 wt % of polyvinylidene fluoride (PVDF 1300).

(107) Next, the positive electrode slurry was coated on an aluminum foil, and after the solvent was evaporated, the positive electrodes and the negative electrodes were cut into a specific size, and then the positive electrodes and the negative electrodes were alternately stacked with a microporous separator (model: Celgard 2400, manufactured by Celgard Co., Ltd.) sandwiched there between, and then placed in a pressing mold filled with the electrolyte solution (model: LBC322-01H, purchased from Shenzhen Capchem Technology Co., Ltd.), and sealed to form a laminated lithium-ion battery. The laminated lithium-ion battery was in a size of 41 mm34 mm53 mm.

Test Example 4: Charge-Discharge Cycle Life Performance

(108) For the evaluation of the charge-discharge cycle life performance of the lithium-ion battery, each of the lithium-ion batteries of Examples 1B to 10B and Comparative Examples 1B to 9B was adopted as the test sample.

(109) The analytical method of the charge-discharge cycle life performance was described as follows:

(110) Charging mode: constant current-constant voltage (CCCV);

(111) Discharging mode: constant current (CC);

(112) Charging voltage: 4.2 volts (V);

(113) Charging current: 5 C;

(114) Discharging voltage: 2.8 V;

(115) Discharging current: 5 C; and

(116) Test temperature: about 55 C.

(117) The charge-discharge cycle life of the lithium-ion battery was defined as the number of charge and discharge cycles a lithium-ion battery performed when the capacity dropped to 80% of its initial capacity. The results of the charge-discharge cycle life performance test of the lithium-ion batteries of Examples 1B to 10B, which respectively comprise the electrolytic copper foils of Examples 1 to 10, and Comparative Examples 1B to 9B, which respectively comprise the electrolytic copper foils of Comparative Examples 1 to 9, were also shown in Table 2 above.

(118) According to the aforesaid manufacturing process, the differences between the lithium-ion batteries of Examples 1B to 10B and the lithium-ion batteries of Comparative Examples 1B to 9B were the electrolytic copper foils used in the negative electrodes, so the charge-discharge cycle life performance of the lithium-ion battery was mainly attributed to the characteristics of each electrolytic copper foil.

(119) Discussion of Experimental Results

(120) According to the experimental results as shown in Table 2 above, the drum sides and the deposited sides of the electrolytic copper foils of Examples 1 to 10 all had the aforesaid three surface characteristics, i.e., Sku, Sdr, and Str were all controlled in the suitable range, and thus the drum sides and the deposited sides of these electrolytic copper foils could obtain sufficient adhesion strengths with the negative electrode active materials when they were applied to the negative electrodes of Examples 1A to 10A, which means that these electrolytic copper foils could pass the adhesion strength test from their drum sides and their deposited sides, such that the charge-discharge cycle life of the lithium-ion batteries of Examples 1B to 10B could be improved to more than 800 times.

(121) In contrast, since the drum sides and the deposited sides of the electrolytic copper foils of Comparative Examples 1 to 9 failed to have all of the three surface characteristics, at least one of the drum side and the deposited side of each of these electrolytic copper foils had problem of insufficient adhesion strength with the negative electrode active material, and therefore the charge-discharge cycle life of the lithium-ion batteries of Comparative Examples 1B to 9B failed to reach 800 times, or even failed to reach 700 times. That is, the charge-discharge cycle life performance of the lithium-ion batteries of Comparative Examples 1B to 9B was obviously poorer than the charge-discharge cycle life performance of the lithium-ion batteries of Examples 1B to 10B.

(122) From the experimental results of Table 2, the deposited sides of the electrolytic copper foils of Comparative Examples 1 and 2 had Sku respectively lower than the lower limit of 1.8 and higher than the upper limit of 6.4, so the electrolytic copper foils of Comparative Examples 1 and 2 could not pass the adhesion strength test from their deposited sides, and therefore the charge-discharge cycle life of the lithium-ion batteries of Comparative Examples 1B and 2B could not reach more than 700 times. Furthermore, the drum sides of the electrolytic copper foils of Comparative Examples 8 and 9 had Sdr respectively lower than the lower limit of 0.06% and higher than the upper limit of 13%, so the electrolytic copper foils of Comparative Examples 8 and 9 also could not pass the adhesion strength test from their drum sides, and therefore the charge-discharge cycle life of the lithium-ion batteries of Comparative Examples 8B and 9B could not reach 700 times. Furthermore, the deposited sides of the electrolytic copper foils of Comparative Examples 5 and 6 had Str lower than the lower limit of 0.1, so these two electrolytic copper foils also could not pass the adhesion strength test from their deposited sides, and therefore the lithium-ion batteries of Examples 5B and 6B had poor charge-discharge cycle life performance.

(123) According to the results above, if Sku, Sdr, and Str of one of the outermost sides (the drum side or the deposited side) of the electrolytic copper foil were not all controlled in their respective suitable ranges, the outermost side lacked sufficient adhesion strength with the negative electrode active material, such that the negative electrode active material was easily peeled off or detached from the surface of the electrolytic copper foil during charging and discharging, and thus the charge-discharge cycle life of the lithium-ion battery was severely shortened. In other words, the three surface characteristics of Sku, Sdr, and Str of the electrolytic copper foil are all indispensable. For example, if Sku and Sdr of the deposited side of the electrolytic copper foil were controlled but Str was not controlled, resulting in that the deposited side of the electrolytic copper foil (e.g., Comparative Examples 5 and 6) lacked adhesion strength with the negative electrode active material, the charge-discharge cycle life performance of the lithium-ion battery was deteriorated. Similarly, if Sdr and Str of the deposited side of the electrolytic copper foil were controlled but Sku was not controlled, resulting in that the deposited side of the electrolytic copper foil (e.g., Comparative Examples 1 and 2) lacked adhesion strength with the negative electrode active material, the electrolytic copper foil applied to the lithium-ion battery exhibited inferior charge-discharge cycle life performance.

(124) In addition, the surface characteristics of the electrolytic copper foils of Comparative Examples 3 and 4 in Table 2 above showed that Sku and Sdr of the deposited sides of Comparative Examples 3 and 4 were respectively out of the range of 1.8 to 6.4 and the range of 0.06% to 13%, resulting in that the deposited sides of the electrolytic copper foils lacked adhesion strengths with the negative electrode active materials, and thus the lithium-ion batteries of Comparative Examples 3B and 4B could not obtain the desired charge-discharge cycle life performance. Similarly, from the results of the adhesion strength of the electrolytic copper foil of Comparative Example 7 and the charge-discharge cycle life performance of the lithium-ion battery of Comparative Example 7B in Table 2 above, when Sku and Sdr of the drum side of the electrolytic copper foil were not well controlled, the lithium-ion battery of Comparative Example 7B also could not obtain the desired adhesion strength and the desired charge-discharge cycle life performance. Similarly, from the results of the adhesion strengths of the electrolytic copper foils of Comparative Examples 5 and 6 and the charge-discharge cycle life performance of the lithium-ion batteries of Comparative Example 5B and 6B in Table 2 above, when Sku and Str of the drum side of the electrolytic copper foil were not well controlled, the lithium-ion batteries of Comparative Example 5B and 6B also could not obtain the desired adhesion strength and the charge-discharge cycle life performance.

(125) Furthermore, comparing the results of the three surface characteristics of the electrolytic copper foils of Examples 1 to 10, when Sdr of both the deposited side and the drum side was controlled in the range of 1.5% to 13% (e.g., Examples 1, 3, 5 to 7, and 9), the adhesion strengths between the electrolytic copper foils and the negative electrode active materials could be further improved, thereby prolonging the charge-discharge cycle life of the lithium-ion batteries of Examples 1B, 3B, 5B to 7B, and 9B up to more than 1000 times.

(126) In addition to the aforesaid surface characteristics of the electrolytic copper foils, the Young's modulus of the electrolytic copper foils of Comparative Examples 1 to 4 were also out of the range of 29.4 GPa to 88.2 GPa. The electrolytic copper foils of Comparative Examples 1 and 3 had lower Young's modulus, the electrolytic copper foils failed to have good surface characteristics and were prone to wrinkles, and thereby the charge-discharge cycle life of the lithium-ion batteries was shortened. The electrolytic copper foils of Comparative Examples 2 and 4 had extremely high Young's modulus, so the electrolytic copper foils were more brittle and were easily cracked or broken, which also shortened the charge-discharge cycle life of the lithium-ion batteries of Comparative Examples 2B and 4B. In contrast, the Young's modulus of the electrolytic copper foils of Examples 1 to 10 fell into a suitable range, such that these electrolytic copper foils were not easily wrinkle, cracked or broken during the manufacturing process. The results demonstrated again that the lithium-ion batteries of Examples 1B to 10B could have better charge-discharge cycle life performance than those of Comparative Examples 1B to 9B.

(127) In summary, by controlling the three surface characteristics (Sku, Sdr, and Str) of the drum side and the deposited side of the electrolytic copper foil, the adhesion strengths between the drum side and the negative electrode active material as well as between the deposited side and the negative electrode active material can be both improved, thereby prolonging the charge-discharge cycle life and improving overall performance of the lithium-ion battery comprising such electrolytic copper foil.

(128) Even though numerous characteristics and advantages of the instant disclosure have been set forth in the foregoing description, together with details of the structure and features of the disclosure, the disclosure is illustrative only. Changes may be made in the details, especially in matters of material, shape, size, and arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.