Copper foil, electrode comprising same, secondary battery comprising same, and method for manufacturing same

Abstract

The invention relates to a copper foil, an electrode comprising the copper foil, a secondary battery comprising the electrode, and a manufacturing method thereof. An embodiment of the present invention provides a copper foil comprising: a copper film having a rough surface and a smooth surface; and a protective layer on the copper film, the copper foil having a first surface in the direction of the rough surface and a second surface in the direction of the smooth surface of the copper film, the copper foil satisfying the following Formula 1: [Formula 1] 45 < = [(average 60 DEG glossiness) / (G.U) * (average peak density) / (piece)] / 100 < = 70; the average peak density of formula 1 is the average value of the peak density of the first surface and the peak density of the second surface, the peak density is the value obtained by dividing the peak number roughness (Rpc) by the surface area ratio, and the average 60-degree glossiness of formula 1 is the average value of the 60-degree glossiness of the first surface and the 60-degree glossiness of the second surface.

Description

Technical Field

[0001] The present invention relates to a copper foil, an electrode including the copper foil, a secondary battery including the electrode, and a method for manufacturing the same. Specifically, the present invention relates to a copper foil having excellent adhesion, an electrode including the copper foil, a secondary battery including the electrode, and a method for manufacturing the same. Background Art

[0002] Copper foils are used in the manufacture of various products such as negative electrodes of secondary batteries and flexible printed circuit boards (FPCBs).

[0003] Copper foils can be manufactured by a roll-to-roll (RTR) process using electrolytic plating. Such copper foils are used in the manufacture of negative electrodes for secondary batteries or flexible printed circuit boards (FPCBs) by a roll-to-roll (RTR) process.

[0004] The negative electrode of a secondary battery generally includes a copper foil and an active material laminated on the copper foil. The active material expands or contracts in volume during charge and discharge, so it sometimes detaches from the copper foil, and there is a problem of shortening the life of the secondary battery due to such detachment of the active material. To solve such a problem, it is necessary to increase the adhesion between the copper foil and the active material. Summary of the Invention

[0005] Problems to be Solved by the Invention

[0006] Accordingly, the present invention relates to a copper foil, an electrode including the copper foil, a secondary battery including the electrode, and a method for manufacturing the same, which can prevent problems caused by the limitations and disadvantages of the related art as described above.

[0007] In addition to the viewpoints of the present invention mentioned above, other features and advantages of the present invention will be described below or can be clearly understood by those with ordinary knowledge in the technical field to which the present invention belongs from such a description.

[0008] Technical Solutions for Solving the Problems

[0009] An embodiment of the present invention provides a copper foil, which includes: a copper film having a rough surface and a smooth surface; and a protective layer on the copper film. The copper foil has a first surface in the direction of the rough surface of the copper film and a second surface in the direction of the smooth surface, and the copper foil satisfies the following formula 1. [Formula 1] 45 ≤ [(average 60° glossiness) / (G.U) × (average peak density) / (pcs)] / 100 ≤ 70. The average peak density in Formula 1 refers to the average of the peak density of the first surface and the peak density of the second surface. The peak density refers to the value obtained by dividing the peak number roughness (Rpc) by the surface area ratio. The average 60° glossiness in Formula 1 refers to the average of the 60° glossiness of the first surface and the 60° glossiness of the second surface.

[0010] Another embodiment of the present invention provides a method for manufacturing a copper foil, including: a step of manufacturing an electrolyte containing copper ions; a step of forming a copper film; and a step of forming a protective layer on the copper film. The step of forming the copper film includes: a step of forming a copper film on the rotating cathode drum by applying electricity to an anode plate and a rotating cathode drum disposed apart from each other in the electrolyte in an electrolytic cell. The electrolyte includes: 70 to 150 g / L of copper ions; 80 to 150 g / L of sulfuric acid; 15 to 25 ppm of chlorine (Cl); and an organic additive. The organic additive includes at least one of a brightening agent (component A), a retarder (component B), and a leveling agent (component C). The leveling agent (component C) includes a PEG derivative.

[0011] According to still another embodiment of the present invention, there is provided an electrode for a secondary battery, including: a copper foil; and an active material layer disposed on at least one surface of the copper foil.

[0012] According to still another embodiment of the present invention, there is provided a secondary battery, including: a cathode that provides lithium ions during charging; an anode that provides electrons and lithium ions during discharging; an electrolyte disposed between the cathode and the anode and providing an environment in which lithium ions can move; and a separator that electrically insulates the cathode and the anode.

[0013] Advantages of the Invention

[0014] The copper foil of the present invention can have excellent adhesion. Therefore, when the copper foil of an embodiment of the present invention is used for an electrode of a secondary battery, the adhesion between the copper foil and the active material is improved, thereby improving the life and reliability of the secondary battery. Description of the Drawings

[0015] Figure 1 is a cross-sectional view of a copper foil according to an embodiment of the present invention.

[0016] Figure 2 It is a cross-sectional view of an electrode for a secondary battery according to another embodiment of the present invention.

[0017] Figure 3 It is a cross-sectional view of an electrode for a secondary battery according to still another embodiment of the present invention.

[0018] Figure 4 It is a schematic cross-sectional view of a secondary battery according to still another embodiment of the present invention.

[0019] Figure 5 It is a manufacturing apparatus for a copper foil according to still another embodiment of the present invention.

[0020] Figure 6 It is a schematic diagram showing a circulation process of an electrolyte of the present invention.

[0021] Description of Reference Numerals

[0022] 100: Electrode for secondary battery

[0023] 110: Copper foil

[0024] 111: Copper film

[0025] 111a: Rough surface

[0026] 111b: Smooth surface

[0027] S1: First surface

[0028] S2: Second surface

[0029] 112: Protective layer

[0030] 120: Active material layer

[0031] 10: Electrolytic cell

[0032] 20: Electrolyte Detailed Description of Embodiments

[0033] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the embodiments described below are only presented for the exemplary purpose of helping to clearly understand the present invention and do not limit the scope of the present invention.

[0034] The shapes, sizes, ratios, angles, quantities, etc. disclosed in the drawings for explaining the embodiments of the present invention are exemplary, and thus the present invention is not limited to the matters shown in the drawings. Throughout the specification, the same constituent elements may be denoted by the same reference numerals. When explaining the present invention, in cases where it is judged that a detailed description of related well-known technologies may unnecessarily obscure the gist of the present invention, the detailed description thereof is omitted.

[0035] In cases where terms such as "including", "having", "composed of", etc. mentioned in this specification are used, unless the expression "only" is used, other parts can be added. When a constituent element is expressed in the singular, it includes the plural unless the matter is specifically and clearly stated. Also, when interpreting a constituent element, even without other explicit statements, it is interpreted as including the error range.

[0036] When explaining the positional relationship, for example, in cases where the positional relationship between two parts is described using terms such as "on", "above", "below", "beside", etc., unless the expressions "directly" or "exactly" are used, one or more other parts can be provided between the two parts.

[0037] Spatial relative terms such as "below", "beneath", "upper", "above", etc. can be used to easily describe the relative relationship between one element or constituent element and other elements or constituent elements as shown in the figure. Spatial relative terms should be understood to include terms for different directions of an element during use or operation in addition to the directions shown in the drawings. For example, in the case of flipping the element shown in the drawing, an element described as "below" or "beneath" another element can be placed "above" the other element. Therefore, the exemplary term "below" can include all directions of below and above. Similarly, the exemplary terms "above" or "upper" can include all directions of above and below.

[0038] In cases where the temporal relationship is explained, for example, in cases where the temporal sequence is described using terms such as "after", "subsequent to", "successively", "before", etc., unless the expressions "directly" or "exactly" are used, discontinuous cases can also be included.

[0039] Although first, second, etc. are used to describe various constituent elements, these constituent elements are not limited to these terms. These terms are only used to distinguish one constituent element from another. Therefore, the first constituent element mentioned below can also be the second constituent element within the technical concept of the present invention.

[0040] The term "at least one" should be understood to include all combinations that can be suggested by one or more related items. For example, "at least one of the first item, the second item, and the third item" not only means each of the first item, the second item, or the third item, but can also mean combinations of all items suggested by two or more of the first item, the second item, and the third item.

[0041] The features of various embodiments of the present invention can be combined or combined partially or completely with each other, and can be variously linked and driven technically. Each embodiment can be implemented independently of each other or can be implemented together in an associated relationship.

[0042] Figure 1 is a cross-sectional view of a copper foil 110 according to an embodiment of the present invention.

[0043] Refer to Figure 1 , the copper foil 110 of the present invention includes a copper film 111 containing 99.9% by weight or more of copper. Refer to Figure 1 , the copper foil 110 of the present invention includes a copper film 111 and a protective layer 112 on the copper film 111. Figure 1 shows a configuration in which protective layers 112 are disposed on both sides of the copper film 111. However, an embodiment of the present invention is not limited thereto, and although not illustrated, a protective layer 112 may be disposed on one side of the copper film 111.

[0044] The copper film 111 can be formed on a rotating cathode drum by electroplating, and can have a smooth surface 111b that is in direct contact with the rotating cathode drum during the electroplating process and a rough surface 111a on the opposite side thereof.

[0045] The protective layer 112 is formed by electrodepositing an anticorrosion material on the copper film 111. The anticorrosion material may include at least one of a chromium compound, a silane compound, and a nitrogen compound. The protective layer 112 prevents oxidation and corrosion of the copper film 111 and improves heat resistance, thereby not only extending the life of the copper foil 110 itself but also extending the life of a finished product including the copper foil 110.

[0046] According to an embodiment of the present invention, the copper foil 110 has a first surface S1 in the direction of the rough surface 111a of the copper film 111 and a second surface S2 in the direction of the smooth surface 111b. At this time, the copper foil 110 of an embodiment of the present invention may satisfy the following formula 1.

[0047] [Formula 1]

[0048] 45 ≤ [(average 60° glossiness) / (G.U) × (average peak density) / (pieces)] / 100 ≤ 70

[0049] Specifically, when the copper foil 110 of an embodiment of the present invention satisfies the formula 1, in a minute area of the copper foil 110, while sufficiently ensuring the active specific surface area, the surface uniformity in a wider area of the copper foil 110 is relatively high, and sufficient adhesion can be ensured between the copper foil 110 and the active material.

[0050] On the contrary, when the value of Formula 1 is less than 45, the average peak density may be excessively reduced. As a result, the active specific surface area in a minute area of the copper foil 110 is too small, and sufficient adhesion between the copper foil 110 and the active material cannot be ensured. In addition, the average 60° glossiness may be excessively reduced. As a result, the surface characteristics in a relatively wide area of the copper foil 110 become uneven, and it may be difficult to ensure sufficient adhesion between the copper foil 110 and the active material.

[0051] At this time, even if the value of the peak density of the copper foil 110 increases, it is difficult to consider that the value of the 60° glossiness will necessarily become smaller.

[0052] In addition, when the value of Formula 1 exceeds 70, the average peak density may be excessively high. As a result, the coating uniformity with the active material is reduced, and thus the adhesion between the copper foil 110 and the active material may be significantly reduced. In addition, the average 60° glossiness may be excessively high. As a result, the active specific surface area in a relatively wide area of the copper foil 110 is too small, and sufficient adhesion between the copper foil 110 and the active material cannot be ensured.

[0053] At this time, the 60° glossiness of Formula 1 is the glossiness with respect to an incident angle of 60° of each of the first surface S1 and the second surface S2 measured by using a gloss meter (VG7000, manufactured by Nippon Denshoku Industries Co., Ltd.) according to the JIS Z 8741 standard.

[0054] In addition, the average peak density of Formula 1 means the average of the peak densities of the first surface and the second surface, and the peak density means the value obtained by dividing the peak number roughness (Rpc) of the first surface S1 and the second surface S2 by the surface area ratio.

[0055] At this time, the peak number roughness (Rpc) is the average of the peak number roughnesses (Rpc) at any three positions, and the peak number roughness (Rpc) at each of the positions means the number of effective peaks that protrude upward by 0.5 μm from the upper reference line (C1) in a unit sampling length of 4 mm in the surface roughness profile obtained according to the Steel Test List (SEP 1940) standard. The surface area ratio means the ratio of the three-dimensional surface area of each of the first surface S1 and the second surface S2 to the two-dimensional surface area of each of the first surface S1 and the second surface S2.

[0056] According to an embodiment of the present invention, the difference between the peak density of the first surface S1 and the peak density of the second surface S2 may be 30 or less.

[0057] Specifically, when the difference in peak density between the first surface S1 and the second surface S2 is less than 30, the difference in surface properties between the first surface S1 and the second surface S2 is small, the coating uniformity of the active material is improved, and sufficient adhesion between the copper foil 110 and the active material can be ensured.

[0058] On the contrary, when the difference in peak density between the first surface S1 and the second surface S2 exceeds 30, the difference in surface properties between the first surface S1 and the second surface S2 becomes large, the coating uniformity of the active material decreases, and it may be difficult to ensure sufficient adhesion between the copper foil 110 and the active material.

[0059] The copper foil 110 according to an embodiment of the present invention has a thickness of 4 to 35 μm. When the copper foil 110 is used as a current collector of an electrode in a secondary battery, the thinner the thickness of the copper foil 110, the more current collectors can be accommodated in the same space, which is beneficial to the high-capacity of the secondary battery. However, manufacturing a copper foil 110 with a thickness less than 4 μm results in reduced workability.

[0060] On the contrary, when manufacturing a secondary battery with a copper foil 110 thicker than 35 μm, it is difficult to achieve high capacity due to the thicker copper foil 110.

[0061] Hereinafter, the electrode 100 including the copper foil 110 of the present invention and the secondary battery including the electrode 100 will be specifically described.

[0062] Figure 2 is a cross-sectional view of a secondary battery electrode 100a according to an embodiment of the present invention. Figure 3 is a cross-sectional view of a secondary battery electrode 100b according to another embodiment of the present invention.

[0063] As Figure 2 shown, the secondary battery electrode 100a according to an embodiment of the present invention includes any one of the copper foils 110 in the above embodiments of the present invention and an active material layer 120.

[0064] Figure 2 shows a configuration in which the active material layer 120 is formed on one surface of the copper foil 110. However, an embodiment of the present invention is not limited thereto. Referring to Figure 3 the active material layer 120 may also be formed on both surfaces of the copper foil 110.

[0065] Generally, in a lithium secondary battery, an aluminum foil is used as a positive electrode current collector combined with a positive electrode active material, and the copper foil 110 is used as a negative electrode current collector combined with a negative electrode active material.

[0066] According to an embodiment of the present invention, the secondary battery electrode 100 is a negative electrode, the copper foil 110 serves as a negative electrode current collector, and the active material layer 120 contains a negative electrode active material.

[0067] In order to ensure the high capacity of the secondary battery, the active material layer 120 of the present invention may be formed of a composite of carbon and a metal. The metal may include, for example, at least one of Si, Ge, Sn, Li, Zn, Mg, Cd, Ce, Ni, and Fe, and preferably may include Si and / or Sn.

[0068] Figure 4 is a schematic cross-sectional view of a secondary battery according to an embodiment of the present invention.

[0069] Referring to Figure 4 , the secondary battery includes a cathode 370, an anode 340, an electrolyte 350 disposed between the cathode 370 and the anode 340 to provide an environment in which ions can move, and a separator 360 that electrically insulates the cathode 370 and the anode 340. Here, the ions moving between the cathode 370 and the anode 340 are, for example, lithium ions. The separator 360 separates the cathode 370 and the anode 340 to prevent the charge generated in one electrode from being uselessly consumed by moving inside the secondary battery 105 to the other electrode. Referring to Figure 4 , the separator 360 is disposed within the electrolyte 350.

[0070] The cathode 370 includes a cathode current collector 371 and a cathode active material layer 372, and aluminum foil may be used as the cathode current collector 371.

[0071] The anode 340 includes an anode current collector 341 and an anode active material layer 342, and the copper foil 110 may be used as the anode current collector 341.

[0072] According to an embodiment of the present invention, the copper foil 110 disclosed may be used as the anode current collector 341. Additionally, Figure 1 the secondary battery electrodes 100a, 100b shown in Figure 2 or Figure 3 may be used as the anode 340 of the secondary battery shown in Figure 4 .

[0073] Hereinafter, referring to Figure 5 and Figure 6 the manufacturing method of the copper foil 110 of the present invention will be specifically described.

[0074] The manufacturing method of the copper foil 110 of the present invention includes a step of forming a copper film 111 and a step of forming a protective layer 112 on the copper film 111.

[0075] The method of the present invention includes a step of forming a copper film 111 on the rotating cathode drum 40 by energizing an anode plate 30 and a rotating cathode drum 40 disposed separately from each other in an electrolytic solution 20 in an electrolytic cell 10.

[0076] As Figure 5 illustrated, the anode plate 30 may include a first anode plate 31 and a second anode plate 32 that are electrically insulated from each other.

[0077] The step of forming the copper film 111 may be performed as follows: a seed layer is formed by energization between the first anode plate 31 and the rotating cathode drum 40, and then the seed layer is grown by energization between the second anode plate 32 and the rotating cathode drum 40.

[0078] The current densities provided by the first anode plate 31 and the second anode plate 32 respectively may be 30 to 130 ASD.

[0079] In the case where the current densities provided by the first anode plate 31 and the second anode plate 32 respectively are lower than 30 ASD, the surface roughness of the copper foil 110 is low, so that the adhesion between the copper foil 110 and the active material layer 120 may be insufficient.

[0080] On the contrary, in the case where the current densities provided by the first anode plate 31 and the second anode plate 32 respectively exceed 130 ASD, the surface of the copper foil 110 is rough, so that the coating of the active material may not be achieved smoothly.

[0081] The surface characteristics of the copper film 111 may vary depending on the surface polishing or grinding degree of the rotating cathode drum 40. For example, a grinding brush having a grit of #800 to #3000 may be used to grind the surface of the rotating cathode drum 40.

[0082] During the formation of the copper film 111, the electrolytic solution 20 is maintained at a temperature of 40 to 60 °C. More specifically, the temperature of the electrolytic solution 20 may be maintained above 50 °C. At this time, the physical, chemical, and electrical characteristics of the copper film 111 may be controlled by adjusting the composition of the electrolytic solution 20.

[0083] According to an embodiment of the present invention, the electrolytic solution 20 may contain copper ions, sulfuric acid, chlorine (Cl), and an organic additive.

[0084] In order to smoothly form the copper film 111 by electrodeposition of copper, the copper ion concentration and the sulfuric acid concentration in the electrolytic solution 20 are adjusted to 70 to 150 g / L and 80 to 150 g / L respectively.

[0085] In one embodiment of the present invention, chlorine (Cl) includes all chloride ions (Cl-) and chlorine atoms present in the molecule. For example, chlorine (Cl) can be used to remove silver (Ag) ions that flow into the electrolyte 20 during the formation of the copper film 111. Specifically, chlorine (Cl) can cause silver (Ag) ions to precipitate in the form of silver chloride (AgCl). This silver chloride (AgCl) can be removed by filtration.

[0086] When the concentration of chlorine (Cl) is less than 15 ppm, silver (Ag) ions cannot be removed smoothly. On the contrary, when the concentration of chlorine (Cl) exceeds 25 ppm, unnecessary reactions may occur due to excessive chlorine (Cl). Therefore, the concentration of chlorine (Cl) in the electrolyte 20 is controlled in the range of 15 to 25 ppm.

[0087] According to one embodiment of the present invention, the electrolyte 20 may include an organic additive.

[0088] The organic additives included in the electrolyte 20 include a brightening agent (component A), a retarder (component B), and a leveling agent (component C).

[0089] The brightening agent (component A) includes a sulfonic acid or its metal salt. The brightening agent (component A) may have a concentration of 1 to 20 ppm in the electrolyte 20.

[0090] The brightening agent (component A) increases the charge amount of the electrolyte 20 and thus increases the copper electrodeposition rate, improves the curl characteristics of the copper foil, and can enhance the gloss of the copper foil 110. If the concentration of the brightening agent (component A) is less than 1 ppm, the gloss of the copper foil 110 decreases, and if it exceeds 20 ppm, problems such as weight change or surface roughness change may occur after dipping the copper foil 110.

[0091] The brightening agent may include, for example, at least one of bis-(3-sulfopropyl)-disulfide disodium salt, 3-mercapto-1-propanesulfonic acid, 3-(N,N-dimethylthiocarbonyl)-thiopropanesulfonic acid sodium salt, 3-[(amino-iminomethyl)thio]-1-propanesulfonic acid sodium salt, o-ethyl dithiocarbonate-S-(3-sulfopropyl)-ester sodium salt, 3-(benzothiazole-2-mercapto)-propyl-sulfonic acid sodium salt, and ethylene dithiodi propyl sulfonic acid sodium salt.

[0092] The retarder (component B) includes a non-ionic water-soluble polymer. The retarder (component B) may have a concentration of 0.1 to 10 ppm in the electrolyte 20.

[0093] The retarder (Component B) reduces the electrodeposition rate of copper, thereby preventing a sharp increase in the roughness and a decrease in the strength of the copper foil 110. This retarder (Component B) is also referred to as an inhibitor or a suppressor.

[0094] If the concentration of the retarder (Component B) is less than 0.1 ppm, problems such as a sharp increase in the roughness of the copper foil 110 and a change in the surface state of the copper foil 110 may occur. On the contrary, even if the concentration of the retarder (Component B) exceeds 10 ppm, the physical properties such as the appearance, gloss, roughness, strength, and elongation of the copper foil 110 hardly change. Therefore, the concentration of the retarder (Component B) can be adjusted to the range of 0.1 to 10 ppm without unnecessarily increasing the manufacturing cost and wasting raw materials by increasing the concentration of the retarder (Component B).

[0095] The retarder (Component B) may include, for example, at least one nonionic water-soluble polymer selected from polyethylene glycol (PEG), polypropylene glycol, polyethylene-polypropylene copolymer, polyglycerol, polyethylene glycol dimethyl ether, hydroxyethyl cellulose, polyvinyl alcohol, polyethylene glycol stearate ether, and polyethylene glycol stearyl ether. However, the types of retarders are not limited thereto, and another nonionic water-soluble polymer that can be used for the manufacture of the high-strength copper foil 110 can be used as the retarder.

[0096] The leveling agent (Component C) includes a PEG derivative. The leveling agent (Component C) may have a concentration of 1 to 10 ppm in the electrolyte 20.

[0097] The leveling agent (Component C) prevents the generation of excessive peaks or large protrusions in the copper film 111, making the copper film 111 macroscopically flat. The leveling agent (Component C) may have a concentration of 1 to 10 ppm in the electrolyte 20.

[0098] Specifically, the end group of the PEG derivative in an embodiment of the present invention may be substituted with a saturated hydrocarbon or a functional group. At this time, the functional group may include at least one of a vinyl group, an acrylic group, and a bisphenol group. At this time, PEG refers to polyethylene glycol.

[0099] Specifically, in the case of PEG, generally, a hydroxyl group (-OH) exists at the end group, and the hydroxyl group (-OH) present in the end group may react with other additives added to the electrolyte and may reduce the physical properties of the copper foil.

[0100] At this time, when the end group of the PEG derivative is substituted with a functional group containing at least one of a saturated hydrocarbon, vinyl group, acrylic group, and bisphenol group, the end group of the PEG derivative is stable, and the influence of various by-products in the electrolyte used for a long time may be reduced. Specifically, compared with the unsubstituted PEG derivative, it has the advantage of being able to reduce defects in electroplating such as pinholes.

[0101] If the concentration of the leveling agent (Component C) is less than 1 ppm, the strength of the copper foil 110 decreases, and difficulties may occur during the manufacturing process of the high-strength copper foil 110.

[0102] On the contrary, when the concentration of the leveling agent (Component C) exceeds 10 ppm, the surface roughness of the copper foil 110 excessively increases and the strength may decrease, pinholes or curling (Cu rl) occur on the surface of the copper foil 110, and difficulties may occur during the separation process from the winding machine (WR) after manufacturing the copper foil 110.

[0103] The leveling agent (Component C) may include, for example, at least one of PEG-isodecyl ether, PEG-glyceryl ether, PEG-butyl ether, PEG-hexyleneglycol, PEG-trimethylolpropane, PEG-allylether, PEG-Methacrylate, PEG-Acylate, PEG-bisphenol A ether.

[0104] When forming the copper film 111, the flow rate of the electrolyte 20 supplied into the electrolytic cell 10 may be 41 to 45 m 3 / hour.

[0105] Figure 6 It is a schematic diagram showing the circulation process of the electrolyte of the present invention.

[0106] According to an embodiment of the present invention, the step of manufacturing the electrolyte may include a step of forming a second electrolyte by using carbon filtration C / F to transfer the first electrolyte from the storage tank and a step of adding a leveling agent (Component C) to the filtered second electrolyte to form the electrolyte.

[0107] Specifically, the first electrolyte transferred from the storage tank may contain copper ions, sulfuric acid, chlorine, organic additives, etc.

[0108] The process of using carbon filtration for the C / F first electrolyte refers to the step of removing organic and inorganic impurities present in the first electrolyte.

[0109] According to an embodiment of the present invention, the second electrolyte refers to the electrolyte obtained by carbon filtering the first electrolyte.

[0110] According to an embodiment of the present invention, a leveling agent (Component C) can be added to the second electrolyte to form the electrolyte. The additives included in the electrolyte have been described above, so they will not be elaborated here. Specifically, the leveling agent (Component C) is added after the process of filtering C / F.

[0111] For example, when the leveling agent (Component C) is added before the process of filtering C / F, the leveling agent (Component C) may be deteriorated and the physical properties of the copper foil may be reduced. On the contrary, when the leveling agent (Component C) is added after the process of filtering C / F, the deterioration of the leveling agent (Component C) is prevented and the physical properties of the present invention are improved.

[0112] The electrolyte formed by adding the leveling agent (Component C) is filled in the electrolytic cell 10, and a copper foil is manufactured using a foil making machine including a rotating cathode drum 40 disposed in the electrolytic cell 10 and an anode plate 30 disposed at a distance from the rotating cathode drum 40.

[0113] In addition, for the purity of the electrolyte 20, the copper wire (Cu wire) that is the raw material of the electrolyte 20 can be cleaned.

[0114] According to an embodiment of the present invention, the step of manufacturing the electrolyte 20 may include: a step of heat-treating the copper wire, a step of pickling the heat-treated copper wire, a step of washing the pickled copper wire with water, and a step of putting the washed copper wire into sulfuric acid for the electrolyte.

[0115] More specifically, in order to maintain the purity of the electrolyte 20, copper for manufacturing the electrolyte 20 can be manufactured by sequentially going through the following process: heat-treating high-purity (99.9% or more) copper wire (Cu wire) in an electric furnace at 750°C to 850°C to burn off various organic impurities attached to the copper wire, pickling the copper wire heat-treated for 10 to 20 minutes with a 10% sulfuric acid solution, and washing the pickled copper wire with distilled water. The washed copper wire can be put into sulfuric acid for the electrolyte to manufacture the electrolyte 20.

[0116] According to an embodiment of the present invention, in order to meet the characteristics of the copper foil 110, the concentration of total organic carbon (TOC) in the electrolyte 20 is controlled to be 300 ppm or less. That is, the electrolyte 20 can have a total organic carbon (TOC) concentration of 300 ppm or less.

[0117] The copper film 111 manufactured in this way can be cleaned in a cleaning tank.

[0118] For example, acid cleaning for removing impurities such as resin components or natural oxide on the surface of the copper film 111 and water cleaning for removing the acidic solution used in the acid cleaning can be performed in sequence. The cleaning process can also be omitted.

[0119] Next, a protective layer 112 is formed on the copper film 111.

[0120] Refer to Figure 5 , and it may further include the step of immersing the copper film 111 in an anticorrosion solution 60. When the copper film 111 is immersed in the anticorrosion solution 60, it can be guided by a guide roll disposed in the anticorrosion solution 60.

[0121] As described above, the anticorrosion solution 60 may include at least one of a chromium compound, a silane compound, and a nitrogen compound. For example, the copper film 111 can be immersed in a potassium dichromate solution of 1 to 10 g / L at room temperature for 1 to 30 seconds.

[0122] On the other hand, the protective layer 112 may include a silane compound based on silane treatment or may include a nitrogen compound based on nitrogen treatment.

[0123] The copper foil 110 is manufactured by forming such a protective layer 112.

[0124] On one or both sides of the copper foil 110 of the present invention manufactured by the method as described above, a negative electrode active material selected from the group consisting of carbon; a metal (Me) such as Si, Ge, Sn, Li, Zn, Mg, Cd, Ce, Ni, or Fe; an alloy containing the metal (Me); an oxide (MeO x ) of the metal (Me); and a composite of the metal (Me) and carbon is coated, thereby enabling the manufacture of an electrode (i.e., a negative electrode) for a secondary battery of the present invention.

[0125] For example, after mixing 1 to 3 parts by weight of styrene-butadiene rubber (SBR) and 1 to 3 parts by weight of carboxymethyl cellulose (CMC) in 100 parts by weight of carbon as the negative electrode active material carbon, distilled water is used as a solvent to prepare a slurry. Then, the slurry is applied to the copper foil 110 with a thickness of 20 to 60 μm using a doctor blade and pressed at a pressure of 0.5 to 1.5 ton / cm 2 Pres s.

[0126] A secondary battery can be fabricated by using a conventional positive electrode, electrolyte, and separator together with the electrode (negative electrode) for a secondary battery of the present invention manufactured by the above method.

[0127] Hereinafter, the present invention will be specifically described through examples and comparative examples. However, the following examples are merely for helping to understand the present invention, and the scope of the claims of the present invention is not limited to these examples.

[0128] Examples 1 - 4 and Comparative Examples 1 - 4

[0129] A copper foil was manufactured using a foil-making machine including an electrolytic cell 10, a rotating cathode drum 40 disposed in the electrolytic cell 10, and an anode plate 30 disposed at a distance from the rotating cathode drum 40. The electrolytic solution 20 was a copper sulfate solution. The concentration of copper ions in the electrolytic solution 20 was set to 87 g / L, the concentration of sulfuric acid was set to 110 g / L, the temperature of the electrolytic solution was set to 55 °C, and the current density was set to 60 ASD.

[0130] In addition, the concentration of chlorine (Cl) contained in the electrolytic solution 20 was maintained at 20 ppm, and the concentration of the organic additive was as shown in Table 1 below. At this time, after filtering the electrolytic solution with carbon, a leveling agent was added to the filtered electrolytic solution.

[0131] Among the organic additives, bis-(3-sulfopropyl)-disulfide disodium salt (SPS) was used as a brightening agent (Component A), polyethylene glycol (PEG) was used as a retarder (Component B), and PEG-methacrylate was used as a leveling agent (Component C).

[0132] A current was applied between the rotating cathode drum 40 and the anode plate 30 at a current density of 60 ASD to fabricate a copper film 111. Subsequently, the copper film 111 was immersed in an anti-rust solution for about 2 seconds, and chromate treatment was performed on both sides of the copper film 111 to form a protective layer 112, thereby manufacturing a copper foil. An anti-rust solution mainly composed of chromic acid was used as the anti-rust solution, and the concentration of chromic acid was 5 g / L.

[0133] As a result, copper foils of Examples 1 - 4 and Comparative Examples 1 - 4 were manufactured. At this time, the thickness of the manufactured copper foil was 8 μm.

[0134] [Table 1]

[0135]

[0136] [Table 2]

[0137]

[0138] [Table 3]

[0139]

[0140] For the copper foils of Examples 1-4 and Comparative Examples 1-4 manufactured as such, the following were confirmed: i) the 60° glossiness of the first side and the second side; ii) the number of peaks roughness of the first side and the second side; iii) the surface area ratio of the first side and the second side; iv) the average 60° glossiness; v) the peak density of the first side and the peak density of the second side; vi) the peak density difference between the first side / second side; vii) the average peak density; viii) the value of Formula 1; and ix) the adhesiveness of the active material.

[0141] The copper foil was cut to obtain a 10 cm × 10 cm sample.

[0142] i) The 60° glossiness of the first side and the second side

[0143] The 60° glossiness was measured for both sides of the sample with respect to an incident angle of 60° using a gloss meter (VG7000, Nippon Denshoku Industries Co., Ltd.) according to the JIS Z 8741 standard.

[0144] ii) The number of peaks roughness of the first side and the second side

[0145] The number of peaks roughness (Rpc) is the average of the number of peaks roughness (Rpc) at any three positions. The number of peaks roughness (Rpc) at each of the positions refers to the number of effective peaks that protrude upward by 0.5 μm from the upper criteria line in the surface roughness profile obtained according to the Steel Test List (SEP 1940) standard per 4 mm of the unit sampling length.

[0146] At this time, there is at least one valley deeper than the lower criteria line of -0.5 μm between adjacent effective peaks among the effective peaks. If there is no valley deeper than the lower criteria line of -0.5 μm between adjacent peaks that protrude upward from the upper criteria line, then neither of the adjacent peaks can be an "effective peak" for measuring the number of peaks roughness (Rpc), and the relatively lower peak among the peaks is ignored when obtaining the number of "effective peaks".

[0147] iii) The surface area ratio of the first side and the second side

[0148] The surface area ratio of the first side and the second side was measured using the VK-9710 of KEYENCE Corporation. At this time, the surface area ratio of the first side and the second side respectively refers to the ratio of the three-dimensional surface area of the first side and the second side to the two-dimensional surface area of the first side and the second side. Specifically, a test piece was manufactured by cutting a copper foil into 1 cm × 1 cm, and the copper foil test piece was observed at a magnification of 50 times using a color 3D laser microscope, that is, the VK-9710 of KEYENCE Corporation, and the three-dimensional surface area was observed. The "surface area ratio of the first side and the second side" is the value obtained by dividing the three-dimensional surface area of the three-dimensionally measured copper foil test piece by the two-dimensional planar area (1 cm 2 ) of the copper foil test piece. Here, the three-dimensional surface area is the area obtained by moving the lens of the microscope in the Z-axis direction and focusing.

[0149] iv) Average 60° gloss

[0150] The average 60° gloss refers to the average of the 60° gloss of the measured first side and second side. Specifically, it refers to half of the sum of the 60° gloss of the first side and the second side.

[0151] v) Peak density of the first side and the second side

[0152] The peak density of the first side and the second side refers to the value obtained by dividing the peak number roughness of the measured first side and second side by the surface area ratio of the first side and the second side.

[0153] vi) Peak density difference between the first side / second side

[0154] The peak density difference between the first side and the second side refers to the value obtained by subtracting the peak density value of the second side from the peak density value of the measured first side.

[0155] vii) Average peak density

[0156] The average peak density refers to the average of the peak densities of the measured first side and second side. Specifically, it refers to half of the sum of the peak densities of the first side and the second side.

[0157] viii) Value of Equation 1

[0158] The value of Equation 1 is calculated by the following Equation 1.

[0159] [Equation 1]

[0160] [(Average 60° gloss) / (G.U) × (Average peak density) / (pcs)] / 100

[0161] ix) Adhesion of the active material

[0162] After disposing a negative electrode active material on the copper foils fabricated in Examples 1-4 and Comparative Examples 1-4 to form a negative electrode active material layer, the peel strength between the copper foil and the active material was measured using a universal testing machine (UTM).

[0163] 1) Fabrication of the negative electrode

[0164] 2 parts by weight of styrene-butadiene rubber (SBR) and 2 parts by weight of carboxymethyl cellulose (CMC) were mixed into 100 parts by weight of carbon for the industrially available negative electrode active material, and a slurry of the negative electrode active material was fabricated using distilled water as a solvent. The slurry of the negative electrode active material was applied to the copper foils (Examples and Comparative Examples) having a width of 10 cm with a thickness of 40 μm, dried at 120 °C, and pressed under a pressure of 1 ton / cm 2 to fabricate a negative electrode for a secondary battery.

[0165] 2) Measurement method

[0166] One side of a double-sided tape was attached to a slide glass, and the active material portion of the negative electrode for a secondary battery was attached to the other side of the double-sided tape. After fixing the slide glass at the lower part of the universal testing machine (UTM), the adhesive force was measured while peeling the copper foil.

[0167] - Measuring testing machine: Universal testing machine (UTM)

[0168] - Width of the sample: 12.7 mm

[0169] - Measurement type: 180° peel test

[0170] - Measurement speed: 50 mm / min

[0171] At this time, if the measured adhesive force is 27 N / m or more, the adhesion to the active material is excellent, and it is marked as "good adhesion" in Table 3. If the measured adhesive force is less than 27 N / m, the adhesion to the active material is poor, and it is marked as "poor adhesion" in Table 3.

[0172] Referring to Tables 1 to 3, the copper foils of Examples 1 to 4 have excellent adhesion to the active material, and the copper foils of Comparative Examples 1 to 4 have poor adhesion to the active material.

[0173] The present invention described above is not limited to the foregoing embodiments and drawings, and it is obvious that those with ordinary knowledge in the technical field to which the present invention pertains can make various substitutions, deformations, and changes without departing from the technical idea of the present invention. Therefore, the scope of the present invention is expressed by the appended claims and should be interpreted as including all manners of changes or deformations derived from the meaning, scope, and equivalent concepts of the claims within the scope of the present invention.

Claims

1. A copper foil, wherein: include: Copper film with rough and glossy sides; as well as The protective layer on the copper film, The copper foil has a first surface in the rough surface direction of the copper film and a second surface in the smooth surface direction. The copper foil satisfies the following formula 1: Formula 1 45≤[(average 60° glossiness)×(average peak density)] / 100≤70, In Formula 1, the unit of the average 60° glossiness is GU, and the unit of the average peak density is individual. The average peak density of Formula 1 refers to the average value of the peak density of the first surface and the peak density of the second surface. The peak density refers to the value of the peak number roughness Rpc divided by the surface area ratio. The average 60° glossiness of Formula 1 refers to the average of the 60° glossiness of the first surface and the 60° glossiness of the second surface.

2. The copper foil according to claim 1, wherein The difference between the peak density of the first surface and the peak density of the second surface is 30 or less.

3. The copper foil according to claim 1, wherein The protective layer includes at least one of a chromium compound, a silane compound, and a nitrogen compound.

4. A method for producing a copper foil, wherein: include: The step of preparing an electrolyte solution containing copper ions; a step of forming a copper film; as well as forming a protective layer on the copper film, The step of forming the copper film comprises: The step of forming a copper film on the rotating cathode drum by energizing an anode plate and a rotating cathode drum which are arranged apart from each other in an electrolyte in an electrolytic cell, The electrolyte comprises: 70 to 150 g / L of copper ions; 80 to 150 g / L sulfuric acid; 15 to 25 ppm chlorine Cl; and Organic additives, The organic additives include a glossing agent, i.e. component A, a speed reducer, i.e. component B, and a leveling agent, i.e. component C. The leveler, component C, includes a PEG derivative.

5. The method for producing copper foil according to claim 4, wherein: The brightener, i.e. component A, comprises sulfonic acid or its metal salt, The moderator, component B, includes a non-ionic water-soluble polymer.

6. The method for producing a copper foil according to claim 4, wherein: The terminal group of the PEG derivative is substituted with a saturated hydrocarbon or with a functional group.

7. The method for producing a copper foil according to claim 6, wherein: The functional group is at least one of a vinyl group, an acrylic group and a bisphenol group.

8. The method for producing a copper foil according to claim 4, wherein: The steps of manufacturing the electrolyte include: A step of filtering the first electrolyte transferred from the storage tank with carbon to form a second electrolyte; and A step of adding the leveling agent, namely component C, to the second electrolyte solution to form the electrolyte solution.

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