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

Abstract

To provide a copper foil in which curling is prevented, an electrode including the same, a secondary battery including the same, and a method for manufacturing the same.SOLUTION: A copper foil is provided which comprises: a copper film containing 99.9 wt.% or more of copper; and a protective layer on the copper film. The copper foil has a first room-temperature thermal expansion coefficient of 10 ppm / °C to 25 ppm / °C and a high-temperature thermal expansion coefficient of 20 ppm / °C to 35 ppm / °C, where the first room-temperature thermal expansion coefficient is a thermal expansion coefficient measured in an MD direction, and the high-temperature thermal expansion coefficient is a thermal expansion coefficient measured in the MD direction after heat treatment at 190°C.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a copper foil, an electrode containing the same, a secondary battery containing the same, and a method for manufacturing the same. The present invention relates to a copper foil with prevented curl, an electrode containing the same, a secondary battery containing the same, and a method for manufacturing the same.

Background Art

[0002] A secondary battery is a type of energy conversion device that stores electrical energy by converting it into chemical energy and generates electricity by converting the chemical energy back into electrical energy when electricity is needed. It is used not only for portable household appliances such as mobile phones and notebook computers but also as an energy source for electric vehicles. A secondary battery is also referred to as a rechargeable battery because it can be recharged.

[0003] As secondary batteries that have economic and environmental advantages compared to disposable primary batteries, there are lead-acid batteries, nickel-cadmium secondary batteries, nickel-metal hydride secondary batteries, lithium secondary batteries, etc.

[0004] In particular, a lithium secondary battery can store relatively more energy compared to other secondary batteries in terms of size and weight. Therefore, in the field of information and communication equipment where portability and mobility are important, lithium secondary batteries are preferably used, and their application range is also expanding in energy storage devices for hybrid vehicles and electric vehicles.

[0005] A lithium secondary battery is repeatedly used with one charge-discharge cycle. When operating any device with a fully charged lithium secondary battery, in order to increase the operating time of the device, the lithium-ion secondary battery must have a high charge-discharge capacity. Therefore, research is continuously required to meet the increasingly high expected values (needs) of consumers for the charge-discharge capacity of lithium secondary batteries.

[0006] Such a secondary battery includes a negative electrode current collector made of copper foil, and among copper foils, electrolytic copper foil is widely used as the negative electrode current collector of the secondary battery. As the accommodation for secondary batteries increases and the demand for high-capacity, high-efficiency, and high-quality secondary batteries increases, an electrolytic copper foil that can improve the characteristics of the secondary battery is required. In particular, an electrolytic copper foil that can ensure high capacity and stable capacity retention and performance of the secondary battery is required.

[0007] Note that the thinner the copper foil, the more the amount of active material that can be contained in the same space, the more the number of current collectors can be increased, and the more the capacity of the secondary battery can be increased. However, the thinner the copper foil, the more curl occurs, and defects such as tearing or wrinkling of the copper foil due to curl at the edge part occur during winding of the copper foil, so it is difficult to manufacture a copper foil in the form of a very thin film. Therefore, in order to manufacture a copper foil having a very thin thickness, curl of the copper foil must be prevented.

Summary of the Invention

Problems to be Solved by the Invention

[0008] Therefore, the present invention relates to a copper foil that can prevent problems caused by the limitations and disadvantages of the related art as described above, an electrode including the same, a secondary battery including the same, and a method for manufacturing the same.

[0009] One embodiment of the present invention provides a copper foil with wrinkles or tearing prevented by having a first normal temperature thermal expansion coefficient of 10 ppm / °C to 25 ppm / °C and a high temperature thermal expansion coefficient of 20 ppm / °C to 35 ppm / °C.

[0010] Another embodiment of the present invention provides a copper foil with wrinkles or tearing prevented by having a second normal temperature thermal expansion coefficient of 10 ppm / °C to 25 ppm / °C.

[0011] Yet another embodiment of the present invention provides a copper foil with wrinkles or tears prevented by having a high-temperature thermal expansion coefficient greater than the first room-temperature thermal expansion coefficient and the second room-temperature thermal expansion coefficient.

[0012] Another embodiment of the present invention provides an electrode for a secondary battery including such a copper foil, and a secondary battery including such an electrode for a secondary battery.

[0013] Yet another embodiment of the present invention provides a method for manufacturing a copper foil with curl, wrinkles, or tears prevented.

[0014] In addition to the aspects of the present invention mentioned above, other features and advantages of the present invention will be described below or will be clearly understood by those having ordinary knowledge in the technical field to which the present invention pertains from such descriptions.

Means for Solving the Problems

[0015] One embodiment of the present invention provides a copper foil including a copper film containing 99.9 wt% or more of copper and a protective layer on the copper film, having a first room-temperature thermal expansion coefficient of 10 ppm / °C to 25 ppm / °C and a high-temperature thermal expansion coefficient of 20 ppm / °C to 35 ppm / °C. The first room-temperature thermal expansion coefficient is the thermal expansion coefficient measured in the MD direction, and the high-temperature thermal expansion coefficient is the thermal expansion coefficient measured in the MD direction after heat treatment at 190°C.

[0016] According to yet 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.

[0017] According to yet 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 that is disposed between the cathode and the anode and provides an environment in which lithium ions can move, and a separator that electrically insulates the cathode and the anode.

Effects of the Invention

[0018] According to the present invention, the generation of wrinkles or tears is prevented during the manufacturing process of the copper foil. By manufacturing intermediate parts and final products such as flexible printed circuit boards (FPCBs) and secondary batteries using such a copper foil, the productivity of not only the intermediate parts but also the final products can be improved.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0020] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the embodiments described below are merely presented for illustrative purposes to assist in a clear understanding of the present invention and do not limit the scope of the present invention.

[0021] Since the shapes, sizes, ratios, angles, numbers, etc. disclosed in the drawings for explaining the embodiments of the present invention are exemplary, the present invention is not limited to the matters illustrated in the drawings. Throughout the specification, the same components may be referred to by the same reference numerals. In explaining the present invention, if it is determined that a specific explanation of related known technologies may unnecessarily obscure the gist of the present invention, the detailed explanation thereof will be omitted.

[0022] When terms such as "including", "having", "consisting of", etc. mentioned in this specification are used, unless the expression "only" is used, other parts may be added. When a component is expressed in the singular, it includes a plurality unless otherwise explicitly stated. Also, in the interpretation of components, it is interpreted to include an error range even without separate explicit description.

[0023] In the case of an explanation of a positional relationship, for example, when the positional relationship between both parts is explained by "on", "above", "below", "beside", etc., one or more other parts can be located between both parts unless the expressions "immediately" or "directly" are used.

[0024] Spatially relative terms such as "below", "beneath", "lower", "above", "upper", etc. can be used to easily describe the correlation between one element or component and another element or component as illustrated in the drawings. Spatially relative terms should be understood as terms including different directions of elements during use or operation in addition to the directions illustrated in the drawings. For example, when an element illustrated in the drawings is turned over, an element described as "below" or "beneath" another element may be placed "above" the other element. Therefore, the exemplary term "below" can include all directions of up and down. Similarly, the exemplary terms "above" or "on" can include all directions of up and down.

[0025] In the case of the description of the time relationship, for example, when the time sequence relationship is described by “after ~”, “subsequent to ~”, “next to ~”, “before ~”, etc., the expressions “immediately” or “directly” are not used, and cases where it is not continuous can also be included.

[0026] The first, second, etc. are used to describe various components, but these components are not limited by these terms. These terms are simply used to distinguish one component from another. Therefore, the first component mentioned below may be the second component within the technical concept of the present invention.

[0027] The term “at least one” should be understood to include all combinations that can be presented from one or more related items. For example, the meaning of “at least one of the first item, the second item, and the third item” can mean not only each of the first item, the second item, or the third item alone, but also all combinations of two or more items that can be presented from the first item, the second item, and the third item.

[0028] The respective features of the various embodiments of the present invention can be partially or wholly combined or combined with each other, enabling various technical linkages and drives, and each embodiment may be implemented independently of each other or may be implemented together in a related relationship.

[0029] FIG. 1 is a cross-sectional view of a copper foil 110a according to an embodiment of the present invention.

[0030] Referring to FIG. 1, the copper foil 110a of the present invention includes a copper film 111 containing 99.9 wt% or more of copper. Referring to FIG. 1, the copper foil 110a of the present invention includes a copper film 111 and a protective layer 112 on the copper film 111. FIG. 1 shows a configuration in which the protective layer 112 is disposed on one surface of the copper film 111. However, an embodiment of the present invention is not limited thereto, and the protective layer 112 may be disposed on both surfaces of the copper film 111 (see FIG. 2).

[0031] The copper film 111 may be formed on the rotating negative electrode drum through electroplating, and may have a shiny surface that directly contacts the rotating negative electrode drum during the electroplating process and a matte surface on the opposite side thereof.

[0032] 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 extending the lifespan of the copper foil 110 as well as the lifespan of the final product including the same.

[0033] The copper foil 110 to be described later can correspond to the copper foils 110a and 110b shown in FIGS. 1 to 2.

[0034] According to an embodiment of the present invention, the copper foil 110 can have a first normal temperature thermal expansion coefficient of 10 ppm / °C to 25 ppm / °C and a high temperature thermal expansion coefficient of 20 ppm / °C to 35 ppm / °C.

[0035] At this time, the first normal temperature thermal expansion coefficient means the thermal expansion coefficient measured in the MD direction while heating the copper foil from 30°C to 330°C at a rate of 5°C / min using a thermomechanical analyzer (TMA), and the high temperature thermal expansion coefficient means the thermal expansion coefficient measured in the MD direction while heating the copper foil from 30°C to 330°C at a rate of 5°C / min using a thermomechanical analyzer (TMA) after heat-treating the copper foil at 190°C for 60 minutes.

[0036] Specifically, when the first normal temperature thermal expansion coefficient is 10 ppm / °C to 25 ppm / °C and the high temperature thermal expansion coefficient is 20 ppm / °C to 35 ppm / °C, the occurrence of wrinkles or tears is prevented during the manufacturing process of the copper foil 110.

[0037] On the other hand, when the first normal temperature thermal expansion coefficient is less than 10 ppm / °C or the high temperature thermal expansion coefficient is less than 20 ppm / °C, since the dimensional change due to the temperature rise is small, wrinkles or tears may occur due to a high temperature or high pressure environment during the manufacturing process of the secondary battery.

[0038] Further, when the first normal temperature thermal expansion coefficient exceeds 25 ppm / °C or the high temperature thermal expansion coefficient exceeds 35 ppm / °C, since the thermal expansion coefficient is excessively high, wrinkles or tears may occur in the copper foil due to a high temperature or high pressure environment during the manufacturing process of the secondary battery.

[0039] According to an embodiment of the present invention, it is possible to have a second normal temperature thermal expansion coefficient of 10 ppm / °C to 25 ppm / °C.

[0040] At this time, the second normal temperature thermal expansion coefficient means the thermal expansion coefficient measured in the TD direction while raising the temperature from 30°C to 330°C at a rate of 5°C / min using a thermomechanical analyzer (TMA).

[0041] Specifically, when the second normal temperature thermal expansion coefficient of the copper foil 110 according to an embodiment of the present invention is 10 ppm / °C to 25 ppm / °C, the occurrence of wrinkles or tears is prevented during the manufacturing process of the copper foil 110.

[0042] On the other hand, when the second normal temperature thermal expansion coefficient is less than 10 ppm / °C, since the dimensional change due to the temperature rise is small, wrinkles or tears may occur due to a high temperature or high pressure environment during the manufacturing process of the secondary battery.

[0043] Further, when the second normal temperature thermal expansion coefficient exceeds 25 ppm / °C, since the thermal expansion coefficient is excessively high, wrinkles or tears may occur in the copper foil due to a high temperature or high pressure environment during the manufacturing process of the secondary battery.

[0044] Also, according to an embodiment of the present invention, the high temperature thermal expansion coefficient may be greater than the first normal temperature thermal expansion coefficient and the second normal temperature thermal expansion coefficient.

[0045] According to one embodiment of the present invention, the copper foil 110 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 copper foil 110, the more current collectors can be accommodated in the same space, which is advantageous for increasing the capacity of the secondary battery. However, the production of the copper foil 110 having a thickness of less than 4 μm causes a decrease in workability.

[0046] On the other hand, when manufacturing a secondary battery with a copper foil 110 exceeding 35 μm, it becomes difficult to realize a high capacity due to the thick copper foil 110.

[0047] 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.

[0048] FIG. 3 is a cross-sectional view of an electrode 100a for a secondary battery according to one embodiment of the present invention. FIG. 4 is a cross-sectional view of an electrode 100b for a secondary battery according to another embodiment of the present invention.

[0049] As shown in FIG. 3, the electrode 100a for a secondary battery according to one embodiment of the present invention includes any one of the copper foils 110 and the active material layer 120 of the above-described examples of the present invention.

[0050] FIG. 3 shows a configuration in which the active material layer 120 is formed on one surface of the copper foil 110. However, one embodiment of the present invention is not limited thereto. Referring to FIG. 4, the active material layer 120 can also be formed on both surfaces of the copper foil 110.

[0051] In a lithium secondary battery, an aluminum foil is generally used as a positive electrode current collector that binds to a positive electrode active material, and a copper foil 110 is generally used as a negative electrode current collector that binds to a negative electrode active material.

[0052] According to one embodiment of the present invention, the electrode 100 for a secondary battery is a negative electrode, the copper foil 110 is used as a negative electrode current collector, and the active material layer 120 includes a negative electrode active material.

[0053] In order to ensure the high capacity of the secondary battery, the active material layer 120 of the present invention can be formed of a composite of carbon and metal. The metal may include, for example, at least one of Si, Ge, Sn, Li, Zn, Mg, Cd, Ce, Ni, and Fe, and preferably includes Si and / or Sn.

[0054] FIG. 5 is a schematic cross-sectional view of a secondary battery according to an embodiment of the present invention.

[0055] Referring to FIG. 5, 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 at one electrode from being wasted by moving to the other electrode through the inside of the secondary battery 105. Referring to FIG. 5, the separator 360 is disposed in the electrolyte 350.

[0056] The cathode 370 includes a cathode current collector 371 and a cathode active material layer 372, and an aluminum foil can be used as the cathode current collector 371.

[0057] The anode 340 includes an anode current collector 341 and an anode active material layer 342, and a copper foil 110 can be used as the anode current collector 341.

[0058] According to an embodiment of the present invention, the copper foil 110 shown in FIGS. 1 to 2 can be used as the anode current collector 341. Further, the electrodes 100a and 100b for secondary batteries shown in FIG. 3 or FIG. 4 can be used for the anode 340 of the secondary battery shown in FIG. 5.

[0059] Hereinafter, a method for manufacturing the copper foil 110 of the present invention will be specifically described with reference to FIGS. 6 and 7.

[0060] The method for manufacturing 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.

[0061] The method of the present invention includes a step of forming a copper film 111 on the rotating negative electrode drum 40 by energizing a positive electrode plate 30 and a rotating negative electrode drum 40 which are arranged to be separated from each other in the electrolytic solution 20 in the electrolytic cell 10.

[0062] As shown in FIG. 6, the positive electrode plate 30 may include first and second positive electrode plates 31 and 32 which are electrically insulated from each other.

[0063] The step of forming the copper film 111 may be performed by forming a seed layer by energization between the first positive electrode plate 31 and the rotating negative electrode drum 40, and then growing the seed layer by energization between the second positive electrode plate 32 and the rotating negative electrode drum 40.

[0064] The current density provided by the first and second positive electrode plates 31 and 32 may be 30 to 130 ASD.

[0065] When the current density provided by the first and second positive electrode plates 31 and 32 is less than 30 ASD, since the surface roughness of the copper foil 110 is low, the adhesion between the copper foil 110 and the active material layer 120 may not be sufficient.

[0066] On the other hand, when the current density provided by the first and second positive electrode plates 31 and 32 exceeds 130 ASD, the surface of the copper foil 110 becomes rough, and the coating of the active material may not be smooth.

[0067] The surface characteristics of the copper film 111 can be changed by the surface buffing or polishing degree of the rotating negative electrode drum 40. For example, the surface of the rotating negative electrode drum 40 can be polished with a polishing brush having a particle size (Grit) of #800 to #3000.

[0068] During the formation process 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 can be maintained at 50°C or higher. At this time, by adjusting the composition of the electrolytic solution 20, the physical, chemical, and electrical properties of the copper film 111 can be controlled.

[0069] According to an embodiment of the present invention, the electrolytic solution 20 may contain copper ions, sulfuric acid, chlorine (Cl), collagen, gelatin, and an organic additive.

[0070] In order to smooth the formation of the copper film 111 by electroplating of copper, the concentrations of copper ions and sulfuric acid in the electrolytic solution 20 are adjusted to 70 to 150 g / L and 80 to 150 g / L, respectively.

[0071] In one embodiment of the present invention, chlorine (Cl) includes all chlorine ions (Cl - ) and chlorine atoms present in the molecule. Chlorine (Cl) can be used, for example, to remove silver (Ag) ions that have flowed into the electrolytic solution 20 during the formation of the copper film 111. Specifically, chlorine (Cl) can precipitate silver (Ag) ions in the form of silver chloride (AgCl). Such silver chloride (AgCl) can be removed by filtration.

[0072] When the concentration of chlorine (Cl) is less than 15 ppm, the removal of silver (Ag) ions is not smoothly performed. On the other hand, when the concentration of chlorine (Cl) exceeds 25 ppm, unnecessary reactions due to excessive chlorine (Cl) may occur. Therefore, the concentration of chlorine (Cl) in the electrolytic solution 20 is controlled in the range of 15 to 25 ppm.

[0073] According to an embodiment of the present invention, the electrolytic solution 20 may contain collagen and gelatin. Specifically, the electrolytic solution 20 may contain 1 to 15 ppm of collagen and 0.1 to 5 ppm of gelatin.

[0074] According to one embodiment of the present invention, the collagen and gelatin are added to adjust the coefficient of thermal expansion of the copper foil according to the present invention. In order to obtain the physical property of the coefficient of thermal expansion according to the present invention, the electrolytic solution 20 needs to contain 1 to 15 ppm of collagen and 0.1 to 5 ppm of gelatin.

[0075] More preferably, the collagen and gelatin contained in the electrolytic solution 20 need to be added at a concentration ratio of 10:1 to 3:1. At this time, the collagen can have a molecular weight of 2,000 to 10,000, and the gelatin can have a molecular weight of 10,000 to 100,000.

[0076] When the concentration ratio of the collagen and gelatin contained in the electrolytic solution 20 is outside the above range, there may be a problem that the gelatin with a large molecular weight becomes excessively large and the strength is too high, or there may be a problem that the collagen with a small molecular weight becomes excessively large compared to the gelatin and the strength is too low.

[0077] According to one embodiment of the present invention, the electrolytic solution 20 may contain an organic additive.

[0078] The organic additive contained in the electrolytic solution 20 includes at least one of a brightener (component A) and a retarder (component B).

[0079] The organic additive may include one or more of a brightener (component A) and a retarder (component B), or may contain both components.

[0080] The brightener (component A) includes a sulfonic acid or a metal salt thereof. The brightener (component A) can have a concentration of 1 to 15 ppm in the electrolytic solution 20.

[0081] The brightener (Component A) can increase the charge amount of the electrolytic solution 20, increase the copper electrodeposition rate, improve the curl characteristics of the copper foil, and enhance the gloss of the copper foil 110. If the concentration of the brightener (Component A) is less than 1 ppm, the gloss of the copper foil 110 will decrease. If it exceeds 15 ppm, problems may occur such as a change in the weight of the copper foil 110 after immersion or a change in the surface roughness.

[0082] The brightener may include, for example, at least one of bis-(3-sulfopropyl)-disulfide disodium salt, 3-mercapto-1-propanesulfonic acid, 3-(N,N-dimethylthiocarbamoyl)-thiopropanesulfonate sodium salt, 3-[(aminoiminomethyl)thio]-1-propanesulfonate sodium salt, o-ethyldithiocarbonate-S-(3-sulfopropyl)-ester sodium salt, 3-(benzothiazolyl-2-mercapto)-propyl-sulfonic acid sodium salt, and ethylenedithiodipropylsulfonic acid sodium salt.

[0083] The retarder (Component B) contains a nonionic water-soluble polymer. The retarder (Component B) can have a concentration of 0.1 to 15 ppm in the electrolytic solution 20.

[0084] The retarder (Component B) reduces the copper electrodeposition rate and prevents a sharp increase in the roughness and a decrease in the strength of the copper foil 110. Such a retarder (Component B) is also called an inhibitor or a suppressor.

[0085] If the concentration of the retarder (Component B) is less than 0.1 ppm, problems may occur 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. On the other hand, even if the concentration of the retarder (Component B) exceeds 15 ppm, there are almost no physical property changes such as the appearance, gloss, roughness, strength, and elongation rate of the copper foil 110. Therefore, without the need to unnecessarily increase the concentration of the retarder (Component B) and increase the manufacturing cost and waste raw materials, the concentration of the retarder (Component B) can be adjusted to the range of 0.1 to 15 ppm.

[0086] The retarder (Component B) may contain at least one nonionic water-soluble polymer selected from, for example, polyethylene glycol (PEG), polypropylene glycol, polyethylene polypropylene copolymer, polyglycerin, polyethylene glycol dimethyl ether, hydroxyethyl cellulose, polyvinyl alcohol, polyglycol stearate ether, and polyglycol stearyl alcohol ether. However, the types of retarders are not limited to this, and other nonionic water-soluble polymers that can be used in the production of the high-strength copper foil 110 can be used as retarders.

[0087] When the copper film 111 is formed, the flow rate of the electrolytic solution 20 supplied into the electrolytic cell 10 can be 41 - 45 m 3 / hour.

[0088] FIG. 7 is a schematic diagram showing the circulation process of the electrolytic solution according to the present invention.

[0089] According to an embodiment of the present invention, the step of manufacturing the electrolytic solution may include the step of filtering (C / F) the first electrolytic solution transferred from the storage tank using carbon to form a second electrolytic solution, and the step of adding collagen and gelatin to the filtered second electrolytic solution to form the electrolytic solution.

[0090] Specifically, the first electrolytic solution transferred from the storage tank may contain copper ions, sulfuric acid, chlorine, organic additives, etc.

[0091] The step of filtering (C / F) the first electrolytic solution using carbon means the step of removing organic impurities and inorganic impurities present in the first electrolytic solution.

[0092] According to an embodiment of the present invention, the second electrolytic solution means the electrolytic solution obtained by filtering the first electrolytic solution using carbon.

[0093] According to an embodiment of the present invention, collagen and gelatin can be added to the second electrolyte solution to form an electrolyte solution. Since the additives contained in the electrolyte solution have been described above, the description thereof will be omitted. Specifically, collagen and gelatin are added after the filtration (C / F) step. When collagen and gelatin are added after the filtration (C / F) step, deterioration of collagen and gelatin is prevented, which is effective for improving the physical properties according to the present invention.

[0094] The electrolyte solution formed by adding collagen and gelatin is contained in the electrolytic cell 10, and a copper foil is manufactured using a foil manufacturing machine including a rotating negative electrode drum 40 disposed in the electrolytic cell 10 and a positive electrode plate 30 disposed apart from the rotating negative electrode drum 40.

[0095] Also, for the cleanliness of the electrolyte solution 20, the copper wire used as a raw material for the electrolyte solution 20 can be washed.

[0096] According to an embodiment of the present invention, the step of manufacturing the electrolyte solution 20 may include a step of heat-treating a 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 solution.

[0097] More specifically, in order to maintain the cleanliness of the electrolyte solution 20, a high-purity (99.9% or more) copper wire (Cu wire) is heat-treated in an electric furnace at 750°C to 850°C to burn various organic impurities adhering to the copper wire, and then the heat-treated copper wire is pickled with a 10% sulfuric acid solution for 10 to 20 minutes. After sequentially passing through the process of washing the pickled copper wire with distilled water, copper for manufacturing the electrolyte solution 20 can be manufactured. The washed copper wire is administered to sulfuric acid for the electrolyte solution to manufacture the electrolyte solution 20.

[0098] According to one embodiment of the present invention, in order to satisfy the characteristics of the copper foil 110, the concentration of total organic carbon (TOC) in the electrolytic solution 20 is controlled to 300 ppm or less. That is, the electrolytic solution 20 can have a total organic carbon (TOC) concentration of 300 ppm or less.

[0099] The copper film 111 manufactured in this way can be washed in a washing tank.

[0100] For example, acid cleaning for removing impurities on the surface of the copper film 111, such as resin components or natural oxide films, and water cleaning for removing the acidic solution used in the acid cleaning can be sequentially performed. The cleaning process may be omitted.

[0101] Next, a protective layer 112 is formed on the copper film 111.

[0102] Referring to FIG. 6, it may further include a 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.

[0103] As described above, the anticorrosion solution 60 may contain 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.

[0104] Note that the protective layer 112 can also contain a silane compound by silane treatment and can also contain a nitrogen compound by nitrogen treatment.

[0105] By forming such a protective layer 112, the copper foil 110 is manufactured.

[0106] On one or both sides of the copper foil 110 of the present invention manufactured through the method as described above, one or more negative electrode active materials selected from the group consisting of carbon; a metal (Me) of 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 are coated, whereby an electrode (i.e., a negative electrode) for a secondary battery of the present invention can be manufactured.

[0107] 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) with 100 parts by weight of carbon as a negative electrode active material carbon, a slurry is prepared using distilled water as a solvent. Next, the slurry is applied onto 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 at 110 to 130°C.

[0108] A secondary battery can be manufactured using the electrode (negative electrode) for a secondary battery of the present invention manufactured by the above method, together with a normal positive electrode, an electrolyte, and a separator.

[0109] Hereinafter, the present invention will be specifically described based on Examples and Comparative Examples. However, the following Examples are only for helping the understanding of the present invention, and the scope of the rights of the present invention is not limited to these Examples.

[0110] Examples 1 to 4 and Comparative Examples 1 to 4 A copper foil was manufactured using a foil manufacturing machine including an electrolytic cell 10, a rotating negative electrode drum 40 disposed in the electrolytic cell 10, and a positive electrode plate 30 disposed separately from the rotating negative electrode drum 40. The electrolytic solution 20 was a copper sulfate solution. The copper ion concentration in the electrolytic solution 20 was set to 87 g / L, the sulfuric acid concentration was 110 g / L, the temperature of the electrolytic solution was 55°C, and the current density was 60 ASD.

[0111] In addition, the concentration of chlorine (Cl) contained in the electrolytic solution 20 was maintained at 17 ppm, and the concentrations of collagen, gelatin, and the organic additive were as shown in Table 1 below. At this time, collagen and gelatin were added to the filtered electrolytic solution after filtering the electrolytic solution using carbon.

[0112] Among the organic additives, sodium bis-(3-sulfopropyl)-disulfide (SPS) was used as the brightening agent (Component A), polyethylene glycol (PEG) was used as the retarder (Component B), and the molecular weights of collagen and gelatin were 3,500 and 10,000, respectively.

[0113] A current was applied between the rotating negative electrode drum 40 and the positive electrode plate 30 at a current density of 60 ASD to produce the copper film 111. Next, the copper film 111 was immersed in the rust preventive solution for about 2 seconds, and chromate treatment was performed on both sides of the copper film 111 to form the protective layer 112, thereby producing a copper foil. A rust preventive solution mainly composed of chromic acid was used as the rust preventive solution, and the concentration of chromic acid was 5 g / L.

[0114] As a result, copper foils of Examples 1 to 4 and Comparative Examples 1 to 4 were produced. At this time, the thickness of the produced copper foil was 8 μm.

[0115]

Table 1

Table 2

[0116] The copper foil was cut to obtain a 5 mm x 5 mm sample.

[0117] (i) The first room temperature thermal expansion coefficient The first room temperature thermal expansion coefficient means the thermal expansion coefficient measured in the MD direction of the copper foil sample.

[0118] At this time, the measurement conditions for the coefficient of thermal expansion are as follows.

[0119] - Measuring equipment: Thermomechanical analyzer (Product evaluation: Seiko Exstar 6000 (TMA 6100)) - Starting temperature: 30°C - Ending temperature: 330°C - Heating rate: 5°C / min - Load: 0.05 N (ii) Second room temperature coefficient of thermal expansion The second room temperature coefficient of thermal expansion means the coefficient of thermal expansion measured in the TD direction of the copper foil sample.

[0120] At this time, the measurement method for the coefficient of thermal expansion is the same as that for the first room temperature coefficient of thermal expansion, except for the measurement direction.

[0121] (iii) High temperature coefficient of thermal expansion The high temperature coefficient of thermal expansion means the coefficient of thermal expansion measured in the MD direction after heat treatment at 190°C for 60 minutes.

[0122] Specifically, the sample is heat-treated at 190°C for 60 minutes, and after cooling the sample, the coefficient of thermal expansion of the sample is measured in the same manner as the measurement method for the room temperature coefficient of thermal expansion. The process of cooling the sample proceeds by leaving it at room temperature.

[0123] (iv) Presence or absence of curl generation After 100 charge and discharge cycles, the secondary battery was disassembled, and it was observed whether wrinkles or tears occurred on the copper foil. The case where wrinkles or tears occurred on the copper foil was indicated as "occurred", and the case where they did not occur was denoted as "none".

[0124] Referring to Tables 1 to 2, no curl occurred in the copper foils according to Examples 1 to 4, while curl occurred in the copper foils according to Comparative Examples 1 to 4.

[0125] The present invention described above is not limited by the foregoing embodiments and the accompanying drawings, and it will be apparent to those of ordinary skill in the technical field to which the present invention pertains that various substitutions, modifications, and changes are possible within the scope that does not deviate from the technical matters of the present invention. Therefore, the scope of the present invention is represented by the claims described below, and it should be understood that all changes or modified forms derived from the meaning, scope, and equivalent concepts of the claims are included in the scope of the present invention.

Explanation of Reference Numerals

[0126] 100 Electrode for secondary battery 110, 110a, 110b Copper foil 111 Copper film 112 Protective layer 120 Active material layer 10 Electrolytic cell 20 Electrolyte

Claims

Claim 1 A copper film containing 99.9% by weight or more of copper; and A protective layer on the copper film, A copper foil having a first room temperature thermal expansion coefficient of 10 ppm / °C to 25 ppm / °C and a high temperature thermal expansion coefficient of 20 ppm / °C to 35 ppm / °C: The first room temperature thermal expansion coefficient is the thermal expansion coefficient measured in the MD direction, The high temperature thermal expansion coefficient is the thermal expansion coefficient measured in the MD direction after heat treatment at 190°C for 60 minutes. Claim 2 The copper foil according to claim 1, having a second room temperature thermal expansion coefficient of 10 ppm / °C to 25 ppm / °C: The second room temperature thermal expansion coefficient is the thermal expansion coefficient measured in the TD direction. Claim 3 The copper foil according to claim 2, wherein the high temperature thermal expansion coefficient is greater than the first room temperature thermal expansion coefficient and the second room temperature thermal expansion coefficient. Claim 4 The copper foil according to claim 1, wherein the protective layer contains at least one of a chromium compound, a silane compound, and a nitrogen compound.

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