Copper foil and method for manufacturing the same

Abstract

One embodiment of the present invention provides a copper foil comprising a copper film including a matte surface and a glossy surface, wherein the hydrogen vacancy density at a depth of 30 nm to 45 nm from the matte surface ranges from 80 to 250 counts, and the hydrogen vacancy density at a depth of 3 nm to 45 nm from the glossy surface ranges from 3 to 20 counts. The hydrogen vacancy density refers to the number of hydrogen ions measured using time-of-flight secondary ion mass spectrometry (TOF-SIMS) at a specific sputtering depth from each of the matte and glossy surfaces.

Description

Copper foil and method for manufacturing the same The present invention relates to a copper foil, an electrode comprising the copper foil, a secondary battery comprising the copper foil, and a method for manufacturing the copper foil. More specifically, the present invention relates to a copper foil that prevents curling, an electrode comprising the copper foil, a secondary battery comprising the copper foil, and a method for manufacturing the copper foil. Secondary batteries are a type of energy conversion device that converts electrical energy into chemical energy, stores the chemical energy, and then converts the chemical energy back into electrical energy when power is needed, thereby generating electricity. Secondary batteries are used as energy sources for electric vehicles and portable electronic devices such as mobile phones and laptops. Secondary batteries are rechargeable and are therefore also called rechargeable batteries. Secondary batteries that have economical and environmental advantages over disposable primary batteries include lead-acid batteries, nickel-cadmium secondary batteries, nickel-metal hydride secondary batteries, and lithium secondary batteries. In particular, lithium secondary batteries can store a relatively large amount of energy relative to their size and weight compared to other secondary batteries. Therefore, they are ideal for information and communication devices, where portability and mobility are important. Their application has also expanded to energy storage devices for hybrid and electric vehicles. Lithium secondary batteries are used repeatedly through each cycle, including charge and discharge. When a device operates using a fully charged lithium secondary battery, the battery must have a high charge / discharge capacity to extend the device's operating time. Therefore, continued research is required to meet consumers' growing expectations (demand) for higher charge / discharge capacity in lithium secondary batteries. Such secondary batteries include a negative electrode current collector made of copper foil, and electrolytic copper foil is widely used as the negative electrode current collector of secondary batteries among various copper foils. As the demand for secondary batteries increases, the demand for secondary batteries with high capacity, high efficiency, and high quality is also increasing. Therefore, there is a need for copper foil that can improve the characteristics of secondary batteries. In particular, there is a need for electrolytic copper foil that can ensure high capacity of secondary batteries and enable them to stably maintain capacity and performance. Meanwhile, when the thickness of copper foil becomes smaller, the amount of active material that can be contained in the same space can be increased, the number of current collectors can be increased, and thus the capacity of the secondary battery can be improved. However, when the thickness of copper foil becomes smaller, curling occurs. As a result, when the copper foil is wound, defects such as tearing or wrinkling of the copper foil occur due to the curled edges, making it difficult to produce copper foil in the form of ultra-thin films. Therefore, in order to produce copper foil with an ultra-thin thickness, curling of the copper foil should be prevented. Therefore, the present invention relates to a copper foil, an electrode including the copper foil, a secondary battery including the copper foil, and a method for manufacturing the copper foil, which can prevent the problems caused by the limitations and disadvantages of the related prior art. According to one embodiment of the present invention, a copper foil is provided that prevents wrinkling or tearing by controlling the hydrogen vacancy density at a depth of 30 nm to 45 nm from a matte surface to be in the range of 80 to 250 counts and the hydrogen vacancy density at a depth of 30 nm to 45 nm from a bright surface to be in the range of 3 to 20 counts. According to another embodiment of the present invention, a copper foil is provided that prevents wrinkling or tearing by controlling the hydrogen vacancy density at a depth of 60 nm to 75 nm from a matte surface to be in the range of 15 to 60 counts and the hydrogen vacancy density at a depth of 60 nm to 75 nm from a bright surface to be in the range of 1.0 to 10 counts. According to yet another embodiment of the present invention, an electrode for a secondary battery including a copper foil and a secondary battery including the electrode for a secondary battery are provided. According to yet another embodiment of the present invention, there is provided a method of manufacturing a copper foil, the method preventing the occurrence of curling, wrinkling, or tearing. In addition to the various aspects of the present invention described above, other features and advantages of the present invention will be described in the following embodiments, and those skilled in the art will clearly understand the present invention. According to one embodiment of the present invention, a copper foil is provided, comprising a copper thin film having a matte surface and a shiny surface, wherein the hydrogen vacancy density at a depth of 30 nm to 45 nm from the matte surface ranges from 80 to 250 counts, and the hydrogen vacancy density at a depth of 30 nm to 45 nm from the shiny surface ranges from 3 to 20 counts. The hydrogen vacancy density refers to the number of hydrogen ions measured at a specific sputtering depth from each of the matte and shiny surfaces using a time-of-flight secondary ion mass spectrometer (TOF-SIMS). According to yet another embodiment of the present invention, a method for manufacturing copper foil is provided, the method comprising preparing an electrolyte containing copper ions, forming a copper thin film, and forming a protective layer on the copper thin film, wherein the step of forming the copper thin film comprises forming the copper thin film on a rotating anode drum by energizing a cathode plate and a rotating anode drum, the cathode plate and the rotating anode drum being disposed spaced apart from each other in an electrolyte in an electrolytic cell, wherein the electrolyte comprises: copper ions having a concentration of 70 g / L (grams per liter) to 150 g / L, sulfuric acid having a concentration of 80 g / L to 150 g / L, chlorine (Cl) having a concentration of 15 ppm to 25 ppm, collagen having a concentration of 1 ppm to 15 ppm, gelatin having a concentration of 0.1 ppm to 5 ppm, and an organic additive, wherein the organic additive comprises one or more of a polishing agent (ingredient A) and a moderator (ingredient B), wherein the polishing agent (ingredient A) comprises sulfonic acid or a metal salt thereof, and the moderator (ingredient B) comprises a non-ionic water-soluble polymer. Hereinafter, multiple embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, these embodiments described below are only for illustrative purposes to facilitate a clear understanding of the present invention and do not limit the scope of the present invention. The shapes, sizes, proportions, angles, quantities, etc. disclosed in the drawings for describing the embodiments of the present invention are illustrative, and the present invention is not limited to the details shown in the drawings. Throughout the specification, the same elements may be represented by the same symbols. When describing the present invention, detailed descriptions of related known technologies will be omitted when it is determined that they may unnecessarily obscure the gist of the present invention. When using the terms "including," "having," and "consisting of" in this specification, other parts may be added unless the term "only" is used herein. When an element is expressed in the singular, the plural form is included unless otherwise specified. Furthermore, when explaining an element, even if it is not explicitly stated, it is interpreted as including a range of error. When describing a positional relationship, for example, when the positional relationship of two parts is described as "on", "above", "below", "beside", etc., unless "immediately" or "directly" is used, one or more other parts may be located between the two parts. To facilitate describing the relationship of one part or element to another part or element as illustrated in the drawings, spatially relative terms such as "under," "below," "lower," "over," and "upper" may be used herein. It will be understood that the spatially relative terms are intended to encompass different orientations of the part in use or operation in addition to the orientation depicted in the drawings. For example, when the parts in the drawings are turned over, a part described as being "over" or "upper" relative to another part would become "under" or "under" relative to the other element. Thus, the exemplary term "under" may encompass both an orientation of above and below. Similarly, the exemplary terms "over" or "upper" may encompass both an orientation of above and below. When describing a temporal relationship, for example, when the temporal relationship is described as "after", "subsequently", "next", "before", etc., non-sequential situations may also be included unless "immediately" or "directly" is used. Terms such as "first" and "second" are used to describe various components, but these components are not limited to these terms. These terms are merely used to distinguish one component from another. Therefore, within the technical spirit of the present invention, the first component described below may also be the second component. The term "at least one" should be understood to include all possible combinations of one or more related items. For example, "at least one of a first item, a second item, and a third item" may mean all combinations of two or more of the first item, the second item, and the third item, as well as each of the first item, the second item, and the third item. The features of various embodiments of the present invention may be coupled or combined with each other in part or in whole, and may be connected or operated in various technical ways. Each of these embodiments may be implemented independently of each other or may be implemented together in an associated relationship. FIG. 1 is a cross-sectional view of a copper foil 110 a according to one embodiment of the present invention. Referring to Figure 1 , copper foil 110a of the present invention includes a copper thin film 111 containing copper at a weight percentage (wt%) of 99.9% or greater. Referring to Figure 2 , copper foil 110a of the present invention includes copper thin film 111 and a protective layer 112 formed on copper thin film 111. Figure 2 illustrates a configuration in which protective layer 112 is disposed on one surface of copper thin film 111. However, one embodiment of the present invention is not limited thereto, and protective layer 112 may be disposed on each of both surfaces of copper thin film 111 (see Figure 3 ). The copper film 111 may be formed on the rotating anode drum by electroplating and may include a bright surface that is in direct contact with the rotating anode drum during the electroplating process and a matte surface opposite to the bright surface. Protective layer 112 is formed by electrodepositing a resist material onto copper thin film 111. The resist material may include at least one of a chromium compound, a silane compound, and a nitrogen compound. Protective layer 112 prevents oxidation and corrosion of copper thin film 111 and improves its heat resistance, thereby increasing the lifespan of the final product including copper foil 110 itself and the lifespan of copper foil 110 itself. The copper foil 110 described below may correspond to the copper foils 110 a , 110 b , and 110 c of FIG. 1 to FIG. 3 . According to one embodiment of the present invention, the copper foil 110 includes a copper thin film 111 having a matte surface 111 a and a shiny surface 111 b , wherein the hydrogen vacancy density at a depth of 30 nm to 45 nm from the matte surface 111 a ranges from 80 to 250 counts, and the hydrogen vacancy density at a depth of 30 nm to 45 nm from the shiny surface 111 b ranges from 3 to 20 counts. In this case, the hydrogen vacancy density refers to the number of hydrogen ions measured at a specific sputtering depth from each of the matte surface and the shiny surface using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Specifically, when the hydrogen vacancy density at a depth of 30 nm to 45 nm from the matte surface 111 a ranges from 80 to 250 counts, and the hydrogen vacancy density at a depth of 30 nm to 45 nm from the bright surface 111 b ranges from 3 to 20 counts, the surface properties of each of the matte surface 111 a and the bright surface 111 b of the copper thin film 111 can be stabilized, thereby preventing the occurrence of wrinkles or tears and eliminating curling in the copper foil 110. On the other hand, when the hydrogen vacancy density at a depth of 30 nm to 45 nm from the matte surface 111 a falls outside the range of 80 to 250 counts, or when the hydrogen vacancy density at a depth of 30 nm to 45 nm from the bright surface 111 b falls outside the range of 3 to 20 counts, the difference in surface properties between the matte surface 111 a and the bright surface 111 b increases, which may cause significant warping during the manufacturing process, thereby causing wrinkles, tears, or curling in the copper foil 110. Furthermore, according to one embodiment of the present invention, the hydrogen vacancy density at a depth of 60 nm to 75 nm from the matte surface 111 a may range from 15 to 60 counts, and the hydrogen vacancy density at a depth of 60 nm to 75 nm from the bright surface 111 b may range from 1.0 to 10 counts. Specifically, when the hydrogen vacancy density at a depth of 60 nm to 75 nm from the matte surface 111 a ranges from 15 to 60 counts and the hydrogen vacancy density at a depth of 60 nm to 75 nm from the bright surface 111 b ranges from 1.0 to 10 counts, wrinkles, tears, or curling can be prevented from occurring in the copper foil 110 . On the other hand, when the hydrogen vacancy density at a depth of 60 nm to 75 nm from the matte surface 111 a falls outside the range of 15 to 60 counts, or when the hydrogen vacancy density at a depth of 60 nm to 75 nm from the bright surface 111 b falls outside the range of 1.0 to 10 counts, the difference in surface properties between the matte surface 111 a and the bright surface 111 b increases, which may cause significant warping during the manufacturing process, thereby causing wrinkles, tears, or curling in the copper foil 110. According to one embodiment of the present invention, the depth of the hydrogen component in the matte surface 111 a of the copper thin film 111 may be less than 35 nm. Here, the depth of the hydrogen component refers to the depth at which the number of hydrogen ions measured from the matte surface 111a using TOF-SIMS is 200 or more. Specifically, the depth of the hydrogen component refers to the distance from the surface of the matte surface 111a to the point at which the number of hydrogen ions is 200 or more. When the depth of hydrogen components in the matte surface 111a of the copper film 111 is greater than or equal to 35 nm, hydrogen can penetrate deeper than the matte surface 111a of the copper film 111, which may cause a difference in surface properties between the matte surface 111a and the shiny surface 111b. As a result, significant warping may occur during the manufacturing process, resulting in wrinkles, tears, or curling in the copper foil 110. Copper foil 110 according to one embodiment of the present invention has a thickness of 4 to 35 μm. When copper foil 110 is used as a current collector for an electrode in a secondary battery, as the thickness of copper foil 110 decreases, more current collectors can be accommodated in the same space, which contributes to a higher capacity of the secondary battery. However, manufacturing copper foil 110 with a thickness of less than 4 μm can result in reduced workability. On the other hand, when a secondary battery is manufactured using the copper foil 110 having a thickness exceeding 35 μm, it becomes difficult to achieve a high capacity due to the thick copper foil 110 . Hereinafter, the electrode 100 including the copper foil 110 and the secondary battery including the electrode 100 according to the present invention will be described in detail. 4 is a cross-sectional view of an electrode 100a for a secondary battery according to one embodiment of the present invention. FIG5 is a cross-sectional view of an electrode 100b for a secondary battery according to another embodiment of the present invention. As shown in FIG. 4 , an electrode 100 a for a secondary battery according to one embodiment of the present invention includes a copper foil 110 and an active material layer 120 according to one of the aforementioned embodiments of the present invention. 4 shows a structure in which the active material layer 120 is formed on one surface of the copper foil 110. However, the present invention is not limited thereto, and referring to FIG. 5 , the active material layer 120 may be formed on each of both surfaces of the copper foil 110. Generally, in a lithium secondary battery, an aluminum foil is used as a cathode current collector coupled to a cathode active material, and the copper foil 110 is used as an anode current collector coupled to an anode active material. According to one embodiment of the present invention, the electrode 100 for a secondary battery is an anode, the copper foil 110 is used as an anode current collector, and the active material layer 120 includes an anode active material. To ensure high capacity in the secondary battery, the active material layer 120 of the present invention may be formed from a composite of carbon and metal. For example, the metal may include at least one of silicon (Si), germanium (Ge), tin (Sn), lithium (Li), zinc (Zn), magnesium (Mg), cadmium (Cd), cerium (Ce), nickel (Ni), and iron (Fe). Preferably, it may include Si and / or Sn. FIG6 is a schematic cross-sectional view of a secondary battery according to an embodiment of the present invention. 6 , a secondary battery includes a cathode 370, an anode 340, an electrolyte 350, and a separator 360. The electrolyte 350 is disposed between the cathode 370 and the anode 340 to provide an environment in which ions can move. The separator 360 electrically insulates the cathode 370 and the anode 340. For example, the ions moving between the cathode 370 and the anode 340 are lithium ions. The separator 360 separates the cathode 370 and the anode 340 to prevent charge generated in one electrode from moving through the interior of the secondary battery to the other electrode and being unnecessarily consumed. Referring to FIG6 , the separator 360 is disposed within the electrolyte 350. 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 . 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 . According to one embodiment of the present invention, the copper foil 110 disclosed in Figures 1 to 3 can be used as the anode current collector 341. In addition, the electrode 100a or 100b for a secondary battery shown in Figures 4 or 5 can be used as the anode 340 of the secondary battery shown in Figure 6. Hereinafter, a method for manufacturing the copper foil 110 of the present invention will be described in detail with reference to FIG. 7 and FIG. 8 . The method for manufacturing the copper foil 110 of the present invention includes forming a copper thin film 111 and forming a protective layer 112 on the copper thin film 111 . The method of the present invention includes forming a copper thin film 111 on a rotating anode drum 40 by energizing a cathode plate 30 and the rotating anode drum 40 , the cathode plate 30 and the rotating anode drum 40 being disposed spaced apart from each other in an electrolyte 20 in an electrolytic cell 10 . As shown in FIG. 7 , the cathode plate 30 may include a first cathode plate 31 and a second cathode plate 32 that are electrically insulated from each other. The step of forming the copper thin film 111 may be performed by forming a seed layer through electrical conduction between the first cathode plate 31 and the rotating anode drum 40 , and then growing the seed layer through electrical conduction between the second cathode plate 32 and the rotating anode drum 40 . The current density provided by each of the first cathode plate 31 and the second cathode plate 32 may be 30 to 130 amperes per square inch (ASD, A / dm 2 ). When the current density provided by each of the first and second cathode plates 31 and 32 is less than 30 ASD, the surface roughness of the copper foil 110 may be reduced, and thus adhesion between the copper foil 110 and the active material layer 120 may be insufficient. On the other hand, when the current density provided by each of the first cathode plate 31 and the second cathode plate 32 is greater than 130 ASD, the surface of the copper foil 110 may be rough, and thus the active material may not be smoothly coated. The surface properties of the copper film 111 may vary depending on the degree of buffing or polishing of the surface of the rotating anode drum 40. For example, the surface of the rotating anode drum 40 may be polished using a polishing brush having grit of #800 to #3000. During the process of forming the copper thin film 111, the electrolyte 20 is maintained at a temperature of 40°C to 60°C. More specifically, the temperature of the electrolyte 20 can be maintained at 50°C or higher. In this case, the physical, chemical, and electrical properties of the copper thin film 111 can be controlled by adjusting the composition of the electrolyte 20. According to one embodiment of the present invention, the electrolyte 20 may include copper ions, sulfuric acid, chloride (Cl), collagen, gelatin, and organic additives. To promote the formation of the copper thin film 111 through copper electrodeposition, the concentrations of copper ions and sulfuric acid in the electrolyte 20 are adjusted to be in the range of 70 g / L to 150 g / L and 80 g / L to 150 g / L, respectively. 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 introduced into electrolyte 20 during the process of forming copper thin film 111. Specifically, chlorine (Cl) can precipitate silver (Ag) ions in the form of silver chloride (AgCl). Silver chloride (AgCl) can be removed by filtration. When the chlorine (Cl) concentration is less than 15 ppm, silver (Ag) ions cannot be effectively removed. On the other hand, when the chlorine (Cl) concentration exceeds 25 ppm, unnecessary reactions may occur due to the excess chlorine (Cl). Therefore, the chlorine (Cl) concentration in the electrolyte 20 is controlled within the range of 15 ppm to 25 ppm. According to one embodiment of the present invention, the electrolyte 20 may include collagen and gelatin. Specifically, the electrolyte 20 may include 1 ppm to 15 ppm of collagen and 0.1 ppm to 5 ppm of gelatin. Collagen and gelatin according to one embodiment of the present invention are added to control the hydrogen vacancy density of each of the matte and shiny surfaces of the copper thin film according to the present invention. To achieve the hydrogen vacancy density properties according to the present invention, the electrolyte 20 needs to contain 1 ppm to 15 ppm of collagen and 0.1 ppm to 5 ppm of gelatin. More preferably, the collagen and gelatin contained in the electrolyte 20 need to be added at a concentration ratio of 10: 1 to 3: 1. In this case, the collagen may have a molecular weight of 2,000 to 10,000, and the gelatin may have a molecular weight of 10,000 to 100,000. When the concentration ratio of collagen and gelatin contained in the electrolyte 20 falls outside the above range, an excessively high content of high molecular weight gelatin may result in excessively high strength, while an excessively high content of low molecular weight collagen relative to gelatin may result in excessively low strength. According to one embodiment of the present invention, the electrolyte 20 may contain organic additives. The organic additive contained in the electrolyte 20 includes at least one of a polishing agent (ingredient A) and a moderator (ingredient B). The organic additive may include one or more of a polishing agent (ingredient A) and a softening agent (ingredient B), or may include both of them. The polishing agent (ingredient A) contains sulfonic acid or a metal salt thereof. The polishing agent (ingredient A) in the electrolyte 20 may have a concentration of 1 ppm to 15 ppm. The polishing agent (component A) can increase the amount of charge in the electrolyte 20 to improve the copper electrodeposition rate, improve the curling properties of the copper foil, and increase the glossiness of the copper foil 110. When the concentration of the polishing agent (component A) is less than 1 ppm, the glossiness of the copper foil 110 may be reduced, and when the concentration of the polishing agent (component A) exceeds 15 ppm, the weight of the copper foil 110 may change after immersion, or problems such as changes in surface roughness may occur. For example, the polishing agent may include bis-(3-sulfopropyl)-disulfide disodium salt, 3-mercapto-1-propanesulfonic acid, 3-(N,N-dimethylthiocarbamoyl)-thiopropanesulfonate sodium salt, 3-[(amino-iminomethyl)thio]-1-propanesulfonate sodium salt, O-ethyldithiocarbonato-S-(3-sulfopropyl)-ester sodium salt, salt), 3-(benzothiazolyl-2-mercapto)-propyl-sulfonic acid sodium salt, and ethylenedithiodipropylsulfonic acid sodium salt. The moderator (ingredient B) includes a nonionic water-soluble polymer. The moderator (ingredient B) may have a concentration of 0.1 ppm to 15 ppm in the electrolyte 20 . The moderator (component B) reduces the copper electrodeposition rate to prevent the roughness of the copper foil 110 from increasing rapidly and the strength from decreasing. The moderator (component B) is called an inhibitor or suppressor. When the concentration of the moderator (component B) is less than 0.1 ppm, the roughness of copper foil 110 may increase rapidly, and the surface condition of copper foil 110 may change. On the other hand, even if the concentration of the moderator (component B) exceeds 15 ppm, the physical properties of copper foil 110, such as appearance, gloss, roughness, strength, and elongation, are hardly changed. Therefore, the concentration of the moderator (component B) can be adjusted within the range of 0.1 ppm to 15 ppm without increasing manufacturing costs or wasting raw materials due to unnecessary increases in the concentration of the moderator (component B). For example, the moderator (ingredient B) may include at least one nonionic water-soluble polymer selected from polyethylene glycol (PEG), polypropylene glycol, polyethylene-polypropylene copolymer, polyglycerin, polyethylene glycol dimethyl ether, hydroxyethylene cellulose, polyvinyl alcohol, stearic acid polyglycol ether, and stearyl alcohol polyglycol ether. However, the type of moderator is not limited thereto, and other nonionic water-soluble polymers that can be used to manufacture the high-strength copper foil 110 may be used as the moderator. When forming the copper thin film 111, the flow rate of the electrolyte 20 supplied to the electrolytic cell 10 may be 41 cubic meters per hour (m 3 / hour) to 45 cubic meters / hour. FIG. 8 is a schematic diagram illustrating an electrolyte circulation process according to the present invention. According to one embodiment of the present invention, preparing the electrolyte may include transferring a first electrolyte from a storage tank by carbon filtration (C / F) to form a second electrolyte, and adding collagen and gelatin to the filtered second electrolyte to prepare the electrolyte. Specifically, the first electrolyte delivered from the storage tank may include copper ions, sulfuric acid, chlorine, organic additives, and the like. The process of carbon filtering (C / F) the first electrolyte is to remove organic and inorganic impurities present in the first electrolyte. According to one embodiment of the present invention, the second electrolyte is an electrolyte obtained by filtering the first electrolyte with carbon. According to one embodiment of the present invention, collagen and gelatin may be added to the second electrolyte to form the electrolyte. Since the additives included in the electrolyte have been described above, their description is omitted. Specifically, the collagen and gelatin are added after the filtration (C / F) process. Adding the collagen and gelatin after the filtration (C / F) process prevents degradation of the collagen and gelatin, effectively improving the properties of the present invention. An electrolyte formed by adding collagen and gelatin is contained in an electrolytic cell 10 , and copper foil is manufactured using a foil manufacturing machine including a rotating anode drum 40 disposed in the electrolytic cell 10 and a cathode plate 30 spaced apart from the rotating anode drum 40 . Furthermore, in order to maintain the cleanliness of the electrolyte 20 , the copper (Cu) wire used as a raw material of the electrolyte 20 may be cleaned. According to one embodiment of the present invention, preparing the electrolyte 20 may include heat-treating the copper wire, pickling the heat-treated copper wire, washing the pickled copper wire, and placing the washed copper wire in sulfuric acid for the electrolyte. More specifically, to maintain the cleanliness of the electrolyte 20, a high-purity (99.9% or higher) copper wire is heat-treated in an electric furnace at 750°C to 850°C to burn various organic impurities adhering to the copper wire. The heat-treated copper wire is then pickled for 10 to 20 minutes using a 10% sulfuric acid solution, and then the pickled copper wire is washed with distilled water to prepare copper for manufacturing the electrolyte 20. The washed copper wire is then placed in sulfuric acid for the electrolyte to prepare the electrolyte 20. According to one embodiment of the present invention, in order to meet the characteristics of the copper foil 110 , the total organic carbon (TOC) concentration in the electrolyte 20 is controlled to be less than 300 ppm. In other words, the electrolyte 20 may have a TOC concentration of less than 300 ppm. The copper thin film 111 thus prepared may be cleaned in a cleaning tank. For example, an acid pickling process for removing impurities such as resin components or natural oxides on the surface of the copper film 111 and a water washing process for removing the acid solution used for the pickling process may be sequentially performed. The washing process may be omitted. Next, a protection layer 112 is formed on the copper film 111 . 7 , the method may further include immersing the copper film 111 in a resist solution 60 in the resist tank 50 . When the copper film 111 is immersed in the resist solution 60 , the copper film 111 may be guided by a guide roller 70 disposed in the resist solution 60 . As described above, the resist solution 60 may include at least one of a chromium compound, a silane compound, and a nitrogen compound. For example, the copper film 111 may be immersed in a 1 g / L to 10 g / L potassium dichromate solution at room temperature for 1 to 30 seconds. Meanwhile, the protective layer 112 may include a silane compound treated with silane or a nitrogen compound treated with nitrogen. The copper foil 110 is formed by forming the protective layer 112 . At least one anode active material selected from the group consisting of a metal (Me) of carbon, Si, Ge, Sn, Li, Zn, Mg, Cd, Ce, Ni, or Fe, an alloy containing the metal (Me), an oxide (MeOx) of the metal (Me), and a composite of the metal (Me) and carbon is coated on one or both surfaces of the copper foil 110 of the present invention prepared by the method described above to prepare an electrode (i.e., an anode) for the secondary battery of the present invention. For example, 1 to 3 parts by weight of styrene butadiene rubber (SBR) and 1 to 3 parts by weight of carboxymethyl cellulose (CMC) are mixed with 100 parts by weight of carbon as the anode active material, and distilled water is used as a solvent to prepare a slurry. Subsequently, the slurry is coated on a copper foil 110 with a thickness of 20 μm to 60 μm using a doctor blade and heated at 110 ° C to 130 ° C at a pressure of 0.5 tons / cm 2 Up to 1.5 tons / cm 2 pressure suppression. A secondary battery can be manufactured using the electrode (anode) for the secondary battery of the present invention prepared by the method described above together with a conventional cathode, electrolyte, and separator. Hereinafter, the present invention will be described in detail with reference to examples and comparative examples. However, the examples described below are only intended to help understand the present invention, and the scope of the present invention is not limited to these manufacturing examples. Example 1 To Example 4 and comparative examples 1 To comparative example 4 Copper foil was produced using a foil manufacturing machine comprising an electrolytic cell 10, a rotating anode drum 40 disposed in the electrolytic cell 10, and a cathode plate 30 spaced apart from the rotating anode drum 40. The electrolyte 20 was a copper sulfate solution. The copper ion concentration in the electrolyte 20 was set to 87 g / L, the sulfuric acid concentration was set to 110 g / L, the electrolyte temperature was set to 55°C, and the current density was set to 60 ASD. The concentration of chlorine (Cl) in the electrolyte 20 was maintained at 20 ppm, and the concentrations of collagen, gelatin, and organic additives were as shown in Table 1. At this time, the electrolyte was filtered using carbon, and then collagen and gelatin were added to the filtered electrolyte. Among the organic additives, bis-(3-sulfopropyl)-disulfide disodium salt (SPS) was used as a polishing agent (ingredient A), PEG was used as a buffer (ingredient B), and the molecular weights of collagen and gelatin were 3,500 and 10,000, respectively. A current with a current density of 60 ASD was applied between the rotating anode drum 40 and the cathode plate 30 to prepare a copper thin film 111. Subsequently, the copper thin film 111 was immersed in an anti-etching solution for approximately 2 seconds to form a protective layer 112 on both surfaces of the copper thin film 111 with chromium, thereby preparing a copper foil. The anti-etching solution used was a solution containing chromic acid as a main component, and the concentration of the chromic acid was 5 g / L. Therefore, copper foils of Examples 1 to 4 and Comparative Examples 1 to 4 were prepared. At this time, the thickness of the manufactured copper foil was 8 μm. [Table 1] [Table 2] [Table 3] [Table 4] [Table 5] [Table 6] For the copper foils of Examples 1 to 4 and Comparative Examples 1 to 4 manufactured as described above, i) the hydrogen vacancy density according to the depth of each of the matte surface and the shiny surface, ii) the depth of the hydrogen component in the matte surface, and iii) the occurrence of warping were confirmed. The copper foil was cut into 2 cm x 2 cm samples. After removing the protective layer from the copper film, the hydrogen vacancy density and hydrogen content depth were measured on both the matte and shiny surfaces of the copper film. To remove the protective layer, the copper film was immersed in a 10% sulfuric acid solution for 30 seconds, then rinsed with distilled water for 30 seconds to remove the acidic solution, and then dried. i) Measurement of hydrogen vacancy density corresponding to the depth of each of the matte surface and the shiny surface The hydrogen vacancy density corresponding to the depth of each of the matte surface and the shiny surface refers to the number of hydrogen ions measured at a specific sputtering depth from each of the matte surface and the shiny surface of the copper film using TOF-SIMS. In this case, a map can be obtained by measuring the hydrogen vacancy density at each depth. Specific sputtering conditions and analysis conditions are as follows. Sputtering conditions - Sputter ion (SpI): Cs - Energy: 3 keV - Current: 26.0 nA - Area: 300 × 300 μm 2 - SpIDD: 5.41E+16 Ion / cm 2 Analysis conditions - Primary ion (PI): Bi3 - Energy: 25 keV - Current: 0.300 PA - Area: 100 × 100 μm 2 - PIDD: 3.83E+12 Ion / cm 2 ii) Depth of hydrogen content in the matte surface The depth of hydrogen components in the matte surface refers to the depth at which the number of hydrogen ions measured from the matte surface using TOF-SIMS reaches 200 counts or more. Specifically, from the map of hydrogen vacancy density measured in i), the depth of the point where the number of hydrogen ions (counts) is 200 counts or more is calculated. In the case of "unmeasurable" in Table 6, it means that the point where the hydrogen ion count exceeded 200 counts was too deep from the matte surface to be measured. iii) Occurrence of curling After 100 charge and discharge cycles, the secondary battery was disassembled to observe whether wrinkles or tears occurred on the copper foil. When wrinkles or tears occurred on the copper foil, the copper foil was marked as "occurred", and when there were no wrinkles or tears on the copper foil, the copper foil was marked as "not occurred". Referring to Tables 1 and 2, the copper foils of Examples 1 to 4 did not curl, while the copper foils of Comparative Examples 1 to 4 all curled. According to the present invention, by controlling the hydrogen vacancy density at a depth of 30 nm to 45 nm from the matte surface of the copper foil to 80 to 250 counts and the hydrogen vacancy density at a depth of 30 nm to 45 nm from the shiny surface of the copper foil to 3 to 20 counts, the copper foil can be prevented from wrinkling or tearing during the manufacturing process. Furthermore, by using the copper foil to manufacture intermediate components and final products such as flexible printed circuit boards (FPCBs) and secondary batteries, the productivity of both the intermediate components and the final products can be improved. It will be apparent to those skilled in the art that the present invention is not limited to the embodiments and accompanying drawings described above and that various modifications, variations, and alterations may be made to the present invention without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention is defined by the appended claims, and it is intended that all variations and modifications derived from the meaning, scope, and equivalents of the claims fall within the scope of the present invention. 10: Electrolytic cell 100: Electrode 110, 110a, 110b, 110c: Copper foil 111: Copper thin film 111a: Matt surface 111b: Shiny surface 112: Protective layer 120: Active material layer 20: Electrolyte 30: Cathode plate 31: Cathode plate 32: Second cathode plate 340: Anode 341: Anode current collector 342: Anode active material layer 350: Electrolyte 360: Separator 370: Cathode 371: Cathode current collector 372: Cathode active material layer 40: Rotating anode drum 50: Anti-etching tank 60: Anti-etching solution 70: Guide roller The accompanying drawings are included here to provide a further understanding of the present invention and are incorporated in and constitute a part of this application, illustrating several embodiments of the present invention and together with the description serve to explain the principles of the present invention. In the drawings: FIG1 is a cross-sectional view of a copper foil according to one embodiment of the present invention; FIG2 is a cross-sectional view of a copper foil according to another embodiment of the present invention; FIG3 is a cross-sectional view of a copper foil according to yet another embodiment of the present invention; 4 is a cross-sectional view of an electrode for a secondary battery according to yet another embodiment of the present invention; 5 is a cross-sectional view of an electrode for a secondary battery according to yet another embodiment of the present invention; 6 is a schematic cross-sectional view of a secondary battery according to yet another embodiment of the present invention; FIG7 is a diagram of an apparatus for manufacturing copper foil according to yet another embodiment of the present invention; and FIG. 8 is a schematic diagram illustrating an electrolyte circulation process according to the present invention. 110a: Copper foil 111: Copper film 111a: matte surface 111b: Bright surface

Claims

1. A copper foil comprising a copper thin film having a matte surface and a bright surface, wherein the hydrogen vacancy density at a depth of 30 nm to 45 nm from the matte surface ranges from 80 to 250 counts, and the hydrogen vacancy density at a depth of 30 nm to 45 nm from the bright surface ranges from 3 to 20 counts, and wherein the hydrogen vacancy density refers to the number of hydrogen ions measured using a time-of-flight secondary ion mass spectrometer (TOF-SIMS) at a specific sputtering depth from each of the matte surface and the bright surface.

2. The copper foil as claimed in claim 1, wherein the hydrogen vacancy density at a depth of 60 nm to 75 nm from the matte surface ranges from 15 to 60 counts, and the hydrogen vacancy density at a depth of 60 nm to 75 nm from the glossy surface ranges from 1.0 to 10 counts.

3. The copper foil as claimed in claim 1, wherein a depth of a hydrogen component in the frosted surface is less than 35 nm, wherein the depth of the hydrogen component in the frosted surface refers to the depth of a point where the number of hydrogen ions measured from the frosted surface using a time-of-flight secondary ion mass spectrometer is more than 200.

4. The copper foil as described in claim 1 further includes a protective layer disposed on the copper film.

5. The copper foil as claimed in claim 4, wherein the protective layer comprises at least one of a chromium compound, a silane compound, and a nitrogen compound.

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