Electrolytic copper foil, electrode comprising the same, 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 has a drum side and a deposited side opposing to the drum side, wherein a nanoindentation hardness of the drum side is equal to or larger than 0.5 GPa and equal to or smaller than 3.5 GPa; and a lightness of the drum side is equal to or larger than 25 and equal to or smaller than 75.

Claims

1. An electrolytic copper foil comprising: a drum side and a deposited side opposing to the drum side; wherein a nanoindentation hardness of the drum side is equal to or larger than 0.5 GPa and equal to or smaller than 3.5 GPa; and a lightness (L*) of the drum side is equal to or larger than 25 and equal to or smaller than 75, wherein the lightness (L*) is one of three elements of a color system defined in JIS Z 8729.

2. The electrolytic copper foil as claimed in claim 1, wherein the nanoindentation hardness of the drum side is equal to or larger than 1.0 GPa and equal to or smaller than 3.0 GPa.

3. The electrolytic copper foil as claimed in claim 1, wherein a tensile strength of the electrolytic copper foil is equal to or larger than 34 kgf/mm.sup.2.

4. The electrolytic copper foil as claimed in claim 1, wherein the electrolytic copper foil further comprises an inorganic anti-corrosion layer formed on at least one of the drum side and the deposited side.

5. The electrolytic copper foil as claimed in claim 4, wherein the inorganic anti-corrosion layer comprises a chromate.

6. The electrolytic copper foil as claimed in claim 4, wherein the electrolytic copper foil further comprises another inorganic anti-corrosion layer, the inorganic anti-corrosion layer is formed on the drum side, and said another inorganic anti-corrosion layer is formed on the deposited side.

7. The electrolytic copper foil as claimed in claim 1, wherein the electrolytic copper foil further comprises an organic anti-corrosion layer formed on at least one of the drum side and the deposited side.

8. The electrolytic copper foil as claimed in claim 7, wherein the organic anti-corrosion layer comprises an azole compound.

9. The electrolytic copper foil as claimed in claim 7, wherein the electrolytic copper foil further comprises another organic anti-corrosion layer, the organic anti-corrosion layer is formed on the drum side, and said another organic anti-corrosion layer is formed on the deposited side.

10. An electrode for a lithium ion battery comprising: the electrolytic copper foil as claimed in claim 1, a binder, and an active material.

11. The electrode as claimed in claim 10, wherein the active material comprises a carbon material, a silicon material, a metal, a metal oxide, a metal alloy, a polymer, or any combination thereof.

12. A lithium ion battery comprising: a positive electrode, a negative electrode, and an electrolyte solution; wherein the negative electrode is the electrode as claimed in claim 10.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 is a schematic view of the process to make an electrolytic copper foil of the instant disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

(2) Hereinafter, one skilled in the art can easily realize the advantages and effects of the instant disclosure from the following 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 disclosure. Various modifications and variations could be made in order to practice or apply the instant disclosure without departing from the spirit and scope of the disclosure.

(3) The instrument model used in the following examples:

(4) 1. nanoindentation system: Nano Indenter XPW SYSTEM XPW291 manufactured by MTS;

(5) 2. spectrophotometer: CM-2500c manufactured by Konica Minolta;

(6) 3. α-type surface roughness measuring instrument: SE 1700 manufactured by Kosaka Laboratory;

(7) 4. tensile testing machine: AG-I manufactured by SHIMADZU Corporation;

(8) 5. pressing machine: BCR-250 manufactured by Shyh Horng Machinery Industrial; and

(9) 6. battery cell charge and discharge test system: Series 4000 manufactured by Maccor.

(10) Materials used in the following examples:

(11) 1. low molecular weight gelatin DV: purchased from Nippi Inc.;

(12) 2. sodium 3-mercaptopropanesulphonate: purchased from Hopax Chemicals Manufacturing Company Ltd.;

(13) 3. hydrochloric acid: purchased from RCI Labscan Ltd.;

(14) 4. thiourea: purchased from Panreac Quimica SAU; and

(15) 5. carbon black: Super P® purchased from UBIQ technology.

(16) Manufactures of Electrolytic Copper Foils

(17) Preparation of a copper sulfate electrolyte solution for an electrolytic bath:

(18) A copper wire is dissolved in a 50 wt % sulfuric acid aqueous solution to prepare an essential solution including copper sulfate (CuSO.sub.4.5H.sub.2O) and sulfuric acid. In the essential solution, a concentration of the copper sulfate is 320 g/liter (g/L) and a concentration of the sulfuric acid is 100 g/L. Then, 5.5 mg of low molecular weight gelatin DV, 3 mg of sodium 3-mercaptopropanesulphonate, 0.01 mg of thiourea, and 25 mg of hydrochloric acid are added in each liter of the essential solution to form the copper sulfate electrolyte solution for the electrolytic bath.

(19) Electrolytic Copper Foil of Example 1

(20) With reference to FIG. 1, before the rotating cathode drum 10 was dipped into the electrolytic bath comprising a copper sulfate electrolyte solution 30, a spraying apparatus 40 sprayed a spraying solution 401 of the temperature of 55° C. on a not-yet-dipped region of the surface of the cathode drum 10 with a parabolic distribution at a flow rate of 5 L/min. The spraying apparatus 40 was installed at a distance of about 5 cm from the cathode drum 10 and had an elevation angle of 45 degrees. The spraying solution 401 had the same ingredients of the same concentrations with those of the copper sulfate electrolyte solution 30.

(21) The cathode drum 10 was rotated counterclockwise at a linear velocity of 1 meter/min, and the cathode drum 10 was mechanically polished by a polishing wheel 50 (model number: 2000, manufactured by Kure Grinding Wheel) at a rotational speed of 300 rpm to remove the impurities on the surface of the cathode drum 10. The pressure applied to the cathode drum 10 by the polishing wheel 50 was controlled by a load current of a polishing rotary driving motor (not shown in FIG. 1), and the load current was set to 1.2 A.

(22) In the electrolytic bath set at 50° C., a current with a current density of 50 A/dm.sup.2 flowed between the cathode drum 10 and the anode plate 20 which was disposed along the curved surface of the cathode drum 10. Therefore, copper ions contained in the copper sulfate electrolyte solution 30 were electrodeposited on the curved surface of the cathode drum 10 to fabricate the electrolytic copper foil 70. Subsequently, the electrolytic copper foil 70 was peeled off from the cathode drum 10 and continuously rolled by a series of guiding rolls 60. The electrolytic copper foil 70 had a drum side 701 and a deposited side 702 opposite to the drum side 701. The electrolytic copper foil 70 had a thickness of 8 μm.

(23) In some cases, the electrolytic copper foil 70 might be subsequently treated, such as by surface roughening, with anti-corrosion treatment, and by metal or metal alloy plating. The anti-corrosion treatment might be performed by electric plating with a chromate solution of a temperature of 31.5° C. The chromate solution comprised chromic acid with a concentration of 1.5 g/L. A current used in the electric plating had a current density of 0.5 A/dm.sup.2. After completion of the treatment, the drum side 701 and the deposited side 702 each respectively had an inorganic anti-corrosion layer comprising chromates.

(24) Electrolytic Copper Foil of Example 2

(25) The process used to manufacture the electrolytic copper foil of Example 2 was similar to the process used to manufacture the electrolytic copper foil of Example 1. The differences between the processes were that the polishing wheel with model number 2000 used in Example 1 was replaced by the polishing wheel with model number 1500; and the temperature of the spraying solution changed from 55° C. to 45° C.

(26) Electrolytic Copper Foil of Example 3

(27) The process used to manufacture the electrolytic copper foil of Example 3 was similar to the process used to manufacture the electrolytic copper foil of Example 1. The difference between the processes was that the flow rate of the spraying solution changed from 5 L/min to 10 L/min.

(28) Electrolytic Copper Foil of Example 4

(29) The process used to manufacture the electrolytic copper foil of Example 4 was similar to the process used to manufacture the electrolytic copper foil of Example 2. The difference between the processes was that the flow rate of the spraying solution changed from 5 L/min to 10 L/min.

(30) Electrolytic Copper Foil of Example 5

(31) The process used to manufacture the electrolytic copper foil of Example 5 was similar to the process used to manufacture the electrolytic copper foil of Example 4. The differences between the processes were that the flow rate of the spraying solution changed from 10 L/min to 20 L/min; and the temperature of the spraying solution changed from 45° C. to 55° C.

(32) Electrolytic Copper Foil of Example 6

(33) The process used to manufacture the electrolytic copper foil of Example 6 was similar to the process used to manufacture the electrolytic copper foil of Example 1. The differences between the processes were that the flow rate of the spraying solution changed from 5 L/min to 20 L/min; and the temperature of the spraying solution changed from 55° C. to 45° C.

(34) Electrolytic Copper Foil of Comparative Example 1

(35) Compared to the process used to manufacture the electrolytic copper foil of Example 1, the process used to manufacture the electrolytic copper foil of Comparative Example 1 had the same step to polish the cathode drum and the same step to electrodeposit the electrolytic copper foil, but it did not have the step of spraying the spraying solution onto the surface of the cathode drum. The process used to manufacture the electrolytic copper foil of Comparative Example 1 was as follows.

(36) Before the cathode drum was dipped into the electrolytic bath comprising a copper sulfate electrolyte solution, the cathode drum was rotated counterclockwise at a linear velocity of 1 meter/min, and the cathode drum was mechanically polished by a polishing wheel (model number: 1500, manufactured by Kure Grinding Wheel) at a rotational speed of 300 rpm. The pressure applied to the cathode drum by the polishing wheel was controlled by a load current of a polishing rotary driving motor, and the load current was set to 1.2 A.

(37) In the electrolytic bath whose temperature is 50° C., a current with a current density of 50 A/dm.sup.2 flowed between the cathode drum and the anode plate which was disposed along the curved surface of the cathode drum. Therefore, copper ions contained in the copper sulfate electrolyte solution were electrodeposited on the curved surface of the cathode drum to fabricate the electrolytic copper foil. Subsequently, the electrolytic copper foil was peeled off from the cathode drum and continuously rolled by a series of guiding rolls. The electrolytic copper foil had a thickness of 8 μm.

(38) Electrolytic Copper Foil of Comparative Example 2

(39) The process used to manufacture the electrolytic copper foil of Comparative Example 2 was similar to the process used to manufacture the electrolytic copper foil of Example 3. The difference between the processes was that the temperature of the spraying solution changed from 55° C. to 70° C.

(40) Electrolytic Copper Foil of Comparative Example 3

(41) The process used to manufacture the electrolytic copper foil of Comparative Example 3 was similar to the process used to manufacture the electrolytic copper foil of Example 4. The difference between the processes was that the temperature of the spraying solution changed from 45° C. to 30° C.

(42) Electrolytic Copper Foil of Comparative Example 4

(43) The process used to manufacture the electrolytic copper foil of Comparative Example 4 was similar to the process used to manufacture the electrolytic copper foil of Example 3. The difference between the processes was that the flow rate of the spraying solution changed from 10 L/min to 1 L/min.

(44) Electrolytic Copper Foil of Comparative Example 5

(45) The process used to manufacture the electrolytic copper foil of Comparative Example 5 was similar to the process used to manufacture the electrolytic copper foil of Example 5. The difference between the processes was that the flow rate of the spraying solution changed from 20 L/min to 50 L/min.

(46) Electrolytic Copper Foil of Comparative Example 6

(47) The process used to manufacture the electrolytic copper foil of Comparative Example 6 was similar to the process used to manufacture the electrolytic copper foil of Example 6. The difference between the processes was that the flow rate of the spraying solution changed from 20 L/min to 65 L/min.

(48) Electrolytic Copper Foil of Comparative Example 7

(49) The process used to manufacture the electrolytic copper foil of Comparative Example 7 was similar to the process used to manufacture the electrolytic copper foil of Example 6. The difference between the processes was that the polishing wheel with model number 2000 used in Example 6 was replaced by the polishing wheel with model number 1000.

(50) Electrolytic Copper Foil of Comparative Example 8

(51) The process used to manufacture the electrolytic copper foil of Comparative Example 8 was similar to the process used to manufacture the electrolytic copper foil of Example 6. The difference between the processes was that the polishing wheel with model number 2000 used in Example 6 was replaced by the polishing wheel with model number 2500.

(52) Analysis 1: Nanoindentation Hardness of Surfaces of the Electrolytic Copper Foils

(53) The electrolytic copper foils of Examples 1 to 6 and Comparative Examples 1 to 8 were analyzed for surface hardness of the drum sides and the deposited sides of the electrolytic copper foils by the nanoindentation system.

(54) The nanoindentation system adopted a Berkovich indenter with a curvature radius of equal to or smaller than 50 nm. The indenter pressed the analyzed surfaces of the electrolytic copper foil at a speed of 0.04 mm/sec. Owing to the interference caused by the flatness of the surface, the measured value obtained from initial pressing would be higher than the true value. As the depth of the indentation became deeper, the measured value would gradually become more stable, which was regarded as the true value of the surface hardness. Therefore, the surface hardness of the instant disclosure was represented by the value measured at an indentation depth of 300 nm. The nanoindentation hardness of the drum sides and the deposited sides of the electrolytic copper foils of Examples 1 to 6 and Comparative Examples 1 to 8 was shown in Table 1.

(55) Analysis 2: Lightness of Surfaces of the Electrolytic Copper Foils

(56) According to the standard MS Z 8722(2000), the electrolytic copper foils of Examples 1 to 6 and Comparative Examples 1 to 8 were analyzed for the lightness of the drum sides of the electrolytic copper foils by using the spectrophotometer CM-2500c, which was manufactured by Konica Minolta, and by adopting the mode of “Methods of Colour measurement method-Reflecting and transmitting objects”. The lightness of the drum sides of the electrolytic copper foils of Examples 1 to 6 and Comparative Examples 1 to 8 was shown in Table 1.

(57) Analysis 3: Surface Roughness of the Electrolytic Copper Foils

(58) According to the standard JIS B 0601-1994, the electrolytic copper foils of Examples 1 to 6 and Comparative Examples 1 to 8 were analyzed for the surface roughness of the drum sides and the deposited sides of the electrolytic copper foils by using the α-type surface roughness measuring instrument. The surface roughness of the instant disclosure was represented by ten-point mean roughness (Rz). Rz of the drum sides and the deposited sides of the electrolytic copper foils of Examples 1 to 6 and Comparative Examples 1 to 8 was shown in Table 1.

(59) Analysis 4: Tensile Strength of the Electrolytic Copper Foils

(60) A maximum load of the tensile strength was measured by extracting testing specimens having a length of 100 mm and a width of 12.7 mm from the electrolytic copper foils obtained in Examples 1 to 6 and Comparative Examples 1 to 8, and a tension strength test was performed at a chuck distance of 50 mm and a crosshead speed of 50 mm/min under the standard IPC-TM-650 2.4.18, referred to as room-temperature tensile strength. The room temperature was 25° C. Tensile strengths of the electrolytic copper foils of Examples 1 to 6 and Comparative Examples 1 to 8 were shown in Table 1.

(61) As listed in Table 1, Examples are expressed as E; Comparative Examples are expressed as C; and the nanoindentation hardness of the surface is abbreviated to surface hardness.

(62) TABLE-US-00001 TABLE 1 surface hardness, lightness, Rz, and tensile strength of Examples 1 to 6 and Comparative Examples 1 to 8 Deposited Side of Electrolytic Drum Side of Electrolytic Electrolytic Copper Copper foil Copper foil Foil Surface Surface Tensile Example hardness Light- Rz hardness Rz strength No. (GPa) ness (μm) (GPa) (μm) (kg/mm.sup.2) E1 1.5 59 1.2 1.6 1.6 34.3 E2 0.5 75 1.9 1.8 1.7 34.5 E3 2.5 49 1.3 1.6 1.6 34.4 E4 1.9 63 2.0 1.7 1.8 34.8 E5 3.5 25 1.9 1.7 2.0 34.1 E6 2.6 55 1.2 1.8 1.4 34.7 C1 0.2 80 1.9 1.8 1.9 34.7 C2 4.3 17 1.2 1.7 1.5 34.4 C3 0.3 78 1.9 1.6 1.8 34.3 C4 0.4 82 1.3 1.7 1.5 34.5 C5 0.1 14 2.0 1.8 1.9 34.1 C6 3.0 21 1.3 1.7 1.6 34.2 C7 2.2 15 2.5 1.6 2.6 34.4 C8 2.4 79 1.0 1.7 1.2 34.6

(63) As shown in Table 1, from the comparison results of Examples 1 to 6 and Comparative Examples 1 to 8, a thin layer of the copper sulfate electrolyte solution could be preliminarily formed on the cathode drum by spraying a solution to moisten the surface of the cathode drum before the cathode drum was dipped into the copper sulfate electrolyte solution. With the thin layer of the copper sulfate electrolyte solution, the coverage of nucleation points for copper ions on the surface of the cathode drum would be increased. Therefore, the surface of the cathode drum would have a more uniform electrification effect, so the growth rates of the copper lattice at different positions on the surface of the cathode drum would also be more uniform. As a result, the surface hardness of the drum side of the electrolytic copper foil would increase.

(64) Moreover, it showed that the flow rates and the temperatures of the spraying solution and the model number of the polishing wheel would affect the characteristics of the electrolytic copper foils.

(65) When the flow rate is too low, the obtained thin layer of the copper sulfate electrolyte solution on the surface of the cathode drum would have a too thin thickness or a too small area. Therefore, the effect of increasing the hardness of the drum side of the electrolytic copper foil would not be obvious. On the other hand, if the flow rate is too high, the obtained thin layer of the copper sulfate electrolyte solution on the surface of the cathode drum would have many bubbles attached thereto, so the number of nucleation points for copper would be reduced. Thus, the effect of increasing the hardness of the drum side of the electrolytic copper foil would not be obvious. Preferably, the flow rate of the spraying solution ranges from 1 L/min to 65 L/min; more preferably, the flow rate of the spraying solution ranges from 5 L/min to 20 L/min.

(66) When the temperature of the spraying solution is too low, the condition is unfavorable to generating nucleation points. Therefore, the effect of increasing the hardness of the drum side of the obtained electrolytic copper foil would not be obvious. On the other hand, if the temperature is too high, the surface of the cathode drum would be easily oxidized; accordingly, the lightness of the drum side of the obtained electrolytic copper foil would decrease. Preferably, the temperature of the spraying solution ranges from 30° C. to 70° C.; more preferably, the temperature of the spraying solution ranges from 45° C. to 55° C.

(67) When the model number of the polishing wheel used to polish the cathode drum is too small, the lightness of the drum side of the obtained electrolytic copper foil is too low. On the other hand, when the model number of the polishing wheel used to polish the cathode drum is too large, the lightness of the drum side of the obtained electrolytic copper foil is too high. Preferably, the model number of the polishing wheel is Model 1500 and Model 2000.

(68) Manufactures of Electrodes and Lithium Ion Battery

(69) The electrolytic copper foils of Examples 1 to 6 and Comparative Examples 1 to 8 were respectively used to manufacture the electrodes of Examples 7 to 12 and Comparative Examples 9 to 16 by using the following process.

(70) The negative electrode slurry was composed of 100 parts by weight of negative electrode solid materials and 60 parts by weight of 1-Methyl-2-pyrrolidone (NMP). Based on the total weight of the negative electrode solid materials, the negative electrode solid materials comprised 93.9 wt % of mesophase graphite powder (MGP) as a negative electrode active material, 1 wt % of carbon black, 5 wt % of poly-1,1-difluoroethene (PVDF 6020), and 0.1 wt % of oxalic acid.

(71) The negative electrode slurry was coated on the electrolytic copper foils at a speed of 5 m/min until forming a layer with the thickness of 200 μm on the electrolytic copper foils of Examples 1 to 6 and Comparative Examples 1 to 8 respectively. After a completion of coating, the coated electrolytic copper foils were dried at a temperature of 160° C., and then the electrodes of Examples 7 to 12 and Comparative Examples 9 to 16 were obtained.

(72) Analysis 5: Test of Pressing the Electrolytic Copper Foils

(73) In order to observe whether there was breaking at the boundary between the region coated with the negative electrode slurry and the region not coated with the negative electrode slurry of the electrolytic copper foil, the electrodes of Examples 7 to 12 and Comparative Examples 9 to 16 were rolled by a wheel of the pressing machine at a speed of 1 m/min and a pressure of 3000 pound per square inch (psi). The wheel made from high-carbon chromium bearing steel (SUJ2) had a diameter of 250 mm and a Rockwell hardness (HRC) of 62 to 65 degrees. The results of the electrodes of Examples 7 to 12 and Comparative Examples 9 to 16 were shown in Table 2.

(74) The electrodes of Examples 7 to 12 and Comparative Examples 9 to 16 were respectively used to manufacture the lithium ion batteries by using the following process.

(75) Take the lithium ion battery comprising the electrode of Example 7 as an example:

(76) The positive electrode slurry was composed of 100 parts by weight of positive electrode solid materials and 195 parts by weight of NMP. Based on the total weight of the positive electrode solid materials, the positive electrode solid materials comprised 89 wt % of lithium cobalt oxide (LiCoO.sub.2) as a positive electrode active material, 5 wt % of flaked graphite (KS6), 1 wt % of conductive carbon powder (Super P®), and 5 wt % of poly-1,1-difluoroethene (PVDF 1300).

(77) The positive electrode slurry was coated on aluminum foils to form a layer with the thickness of 250 nm. After completion of coating, the coated aluminum foil was dried at a temperature of 160° C., and then the positive electrode was obtained.

(78) The positive electrodes and the electrodes of Example 7, which were as the negative electrodes, were alternately stacked to form a laminated body with a respective microporous separator between each two successive positive and negative electrodes. The laminated body was deposited in a press mold filled with an electrolyte solution (a volume ratio of EC to DMC was 1:1) and was packaged to form a stacked type lithium ion battery. The stacked type lithium ion battery had a size of 41 mm×34 mm×53 mm.

(79) Analysis 6: Test for Cycle Life of the Lithium Ion Batteries

(80) The lithium ion batteries comprising the electrodes of Examples 7 to 12 and Comparative Examples 9 to 16 respectively were processed with charge and discharge tests at a temperature of 55° C. The charging step was processed under a constant current-constant voltage mode (CCCV), wherein the charging voltage was 4.2 V, and the charging current was 5 C. The discharging step was processed under a constant current mode (CC), wherein the discharging voltage was 2.8 V, and the discharging current was 5 C.

(81) The cycle life was defined as the times of charge and discharge cycles performed when the capacity of the lithium ion battery fell to 80% of its initial capacity.

(82) TABLE-US-00002 TABLE 2 pressing test of the electrodes of Examples 7 to 12 and Comparative Examples 9 to 16 and cycle lives of charge and discharge tests of the lithium ion batteries comprising Examples 7 to 12 and Comparative Examples 9 to 16 Negative Electrolytic Electrode No. copper foil No. Pressing Test Cycle Life (times) E7 E1 Not broken 1124 E8 E2 Not broken 1153 E9 E3 Not broken 1211 E10 E4 Not broken 1192 E11 E5 Not broken 1183 E12 E6 Not broken 1217 C9 C1 Broken — C10 C2 Not broken 653 C11 C3 Broken — C12 C4 Broken — C13 C5 Broken — C14 C6 Not broken 571 C15 C7 Not broken 592 C16 C8 Not broken 478

(83) As shown in Table 2, all electrodes of Examples 7 to 12 were not broken during the pressing process because the electrodes of Examples 7 to 12 respectively comprised the electrolytic copper foils of Examples 1 to 6, and the electrolytic copper foils of Examples 1 to 6 had a certain range of surface hardness and a certain range of lightness of the drum sides. It demonstrates that the electrode of the instant disclosure has a good mechanical property.

(84) As shown in Table 2, all lithium ion batteries comprising the electrodes of Examples 7 to 12 respectively had a longer cycle life. It demonstrates that the lithium ion battery of the instant disclosure has an excellent cycle performance, so the lithium ion battery of the instant disclosure would have a longer service life.

(85) In contrast, the electrodes of Comparative Examples 9, and 11 to 13 which respectively comprised the electrolytic copper foils of Comparative Examples 1, and 3 to 5 still had breaking after pressing. Even though the electrodes of Comparative Examples 10, and 14 to 16, which respectively comprised the electrolytic copper foils of Comparative Examples 2, and 6 to 8, did not break after pressing, the lithium ion batteries comprising the same still had a poor cycle performance.

(86) It demonstrates that the electrodes of Comparative Examples 9 to 16 did not have the same properties as electrodes of Examples 7 to 12 because the electrodes of Comparative Examples 9 to 16 respectively comprised the electrolytic copper foils of Comparative Examples 1 to 8, which did not control their surface hardness and the lightness of the drum sides in the certain range.

(87) Furthermore, the electrolytic copper foils of Examples 1 to 6 could obtain the desired surface hardness and lightness without undergoing multiple forming processes, and the electrolytic copper foils met the requirements of the lithium ion batteries. Therefore, the electrolytic copper foil of the instant disclosure has a higher potential for commerce because it is easy to manufacture.

(88) 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 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.