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

Abstract

To provide a copper foil excellent in adhesion to an active material thereby capable of ensuring a secondary battery with a high capacity retention rate.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 room-temperature thermal deformation index ranging from 15 to 50. The room-temperature thermal deformation index is expressed by formula 1: (room-temperature thermal deformation index)=[(room-temperature thermal expansion coefficient) / (ppm / °C)+(room-temperature elongation) / (%)] / (surface area ratio).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. Specifically, the present invention relates to a copper foil having excellent adhesion to an active material, 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 in 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] Examples of secondary batteries that have economic and environmental advantages compared to disposable primary batteries include lead-acid batteries, nickel-cadmium secondary batteries, nickel-metal hydride secondary batteries, and lithium secondary batteries.

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

[0005] A lithium secondary battery is repeatedly used with one cycle of charging and discharging. 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 expectations (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. With the increase in the accommodation for secondary batteries, as the demand for high-capacity, high-efficiency, and high-quality secondary batteries increases, an electrolytic copper foil capable of improving the characteristics of the secondary battery is required. In particular, an electrolytic copper foil capable of increasing the capacity of the secondary battery and guaranteeing stable capacity retention and performance is required.

[0007] Even if the secondary battery has a sufficiently high charge-discharge capacity, if the charge-discharge capacity of the secondary battery rapidly decreases as the charge-discharge cycle is repeated (that is, when the capacity retention rate is low or the life is short), consumers need to frequently replace the secondary battery, which causes inconvenience to consumers and waste of resources.

Summary of the Invention

Problems to be Solved by the Invention

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

[0009] Another embodiment of the present invention is to provide a copper foil having excellent adhesion to an active material and capable of guaranteeing a secondary battery having a high capacity retention rate.

[0010] In addition to the aspects 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 having ordinary knowledge in the technical field to which the present invention belongs from such descriptions.

Means for Solving the Problems

[0011] One embodiment of the present invention provides a copper foil including a copper film containing 99.9% by weight or more of copper; and a protective layer on the copper film, having a normal temperature heat resistance deformation index in the range of 15 to 50. The normal temperature heat resistance deformation index is represented by the following formula 1.

[0012] [Equation 1] Normal temperature heat resistance deformation index = (Normal temperature thermal expansion coefficient / (ppm / °C) + Normal temperature elongation rate / (%)) / (Surface area ratio) 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.

[0013] 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 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.

Advantages of the Invention

[0014] According to the present invention, it is possible to manufacture a long-life secondary battery having excellent adhesion to an active material and capable of maintaining a high capacity retention rate for a long time. Therefore, it is possible to minimize the inconvenience to electronic product consumers and the waste of resources due to frequent replacement of secondary batteries.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the embodiments described below are presented for illustrative purposes only to assist in a clear understanding of the present invention and do not limit the scope of the present invention.

[0017] The shapes, sizes, ratios, angles, numbers, etc. disclosed in the drawings for explaining the embodiments of the present invention are exemplary, so the present invention is not limited to the matters illustrated in the drawings. The same components throughout the specification may be referred to by the same reference numerals. In explaining the present invention, when it is determined that a detailed description of related known technologies may unnecessarily obscure the gist of the present invention, the detailed description thereof is omitted.

[0018] When terms such as "including", "having", "consisting of", etc. are used in this specification, 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.

[0019] 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., unless the expressions "immediately" or "directly" are used, one or more other parts can be located between both parts.

[0020] Spatially relative terms such as "below", "beneath", "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 relative to each other 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 can 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 "upper" can include all directions of up and down.

[0021] In the case of descriptions regarding time relationships, for example, when time front and back relationships are described by "after", "subsequent to", "next to", "before", etc., cases where it is not continuous can also be included as long as the expressions "immediately" or "directly" are not used.

[0022] 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 idea of the present invention.

[0023] 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 presented from among the first item, the second item, and the third item.

[0024] Each feature of various embodiments of the present invention can be partially or wholly combined or combined with each other, enabling various technical linkages and drives. Each embodiment may be implemented independently of each other or may be implemented together in a related relationship.

[0025] FIG. 1 is a cross-sectional view of a copper foil 110a according to an embodiment of the present invention.

[0026] 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 both sides of the copper film 111. However, an embodiment of the present invention is not limited thereto, and the protective layer 112 can be disposed on both sides of the copper film (111) (see FIG. 2).

[0027] The copper film 111 may be formed on a rotating negative electrode drum through electroplating, and may have a shiny surface that directly contacts the rotating negative electrode drum and a matte surface on the opposite side during the electroplating process.

[0028] 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 life of the copper foil 110 as well as the life of the final product including it.

[0029] The copper foil 110 to be described later can correspond to the copper foils 110a and 110b in FIGS. 1 to 2.

[0030] According to an embodiment of the present invention, the copper foil 110 can have a normal temperature heat resistance deformation index in the range of 15 to 50. The normal temperature heat resistance deformation index is represented by the following formula 1.

[0031] [Formula 1] Normal temperature heat resistance deformation index = (Normal temperature thermal expansion coefficient / (ppm / °C) + Normal temperature elongation rate / (%)) / (Surface area ratio) The normal temperature thermal expansion coefficient in Formula 1 means the thermal expansion coefficient measured while raising the temperature from 30°C to 330°C at a rate of 5°C / min using a thermomechanical analyzer (TMA).

[0032] The normal temperature elongation rate in Formula 1 means the elongation rate measured at normal temperature (25 ± 3°C).

[0033] When the copper foil 110 according to an embodiment of the present invention has a normal temperature heat resistance deformation index value in the range of 15 to 50, even if there is a change in the external environment, a secondary battery excellent in the adhesive force between the copper foil 110 and the active material and having a high capacity retention rate can be manufactured.

[0034] On the other hand, when the normal temperature heat resistance deformation index value of the copper foil 110 is less than 15, compared with a certain surface area ratio, the dimensional change due to the temperature rise may be small, or wrinkles may occur due to low strength. Also, compared with a certain thermal expansion coefficient and elongation rate, the surface area ratio of the copper foil may be very large. As a result, the adhesive force between the copper foil and the active material may decrease, and it may not have a high capacity retention rate.

[0035] Also, when the normal temperature heat resistance deformation index value of the copper foil 110 exceeds 50, compared with a certain surface area ratio, since the thermal expansion coefficient or elongation rate is too high, wrinkles or tears may occur in the copper foil due to a high-temperature or high-pressure environment during the secondary battery manufacturing process. And compared with a certain thermal expansion coefficient and elongation rate, the surface area ratio of the copper foil may be very small. As a result, the adhesive force between the copper foil and the active material may decrease, and it may not have a high capacity retention rate.

[0036] According to an embodiment of the present invention, the copper foil 110 can have a high temperature heat resistance deformation index in the range of 20 to 55. The high temperature heat resistance deformation index is represented by the following Formula 2.

[0037] [Formula 2] High temperature heat resistance deformation index = (High temperature thermal expansion coefficient / (ppm / °C) + High temperature elongation rate / (%)) / (Surface area ratio) The high-temperature coefficient of thermal expansion of Formula 2 means the coefficient of thermal expansion measured using a thermomechanical analyzer (TMA) while heating from 30°C to 330°C at a rate of 5°C / min after heat-treating the copper foil at 190°C for 1 hour and then allowing it to cool naturally to room temperature.

[0038] The high-temperature elongation rate of Formula 2 means the elongation rate measured after heat-treating at 190°C for 1 hour.

[0039] When the copper foil 110 according to an embodiment of the present invention has a high-temperature heat-resistant deformation index value in the range of 20 to 55, a secondary battery with excellent adhesion between the copper foil 110 and the active material and a high capacity retention rate can be manufactured even in a high-temperature and high-pressure external environment.

[0040] On the other hand, when the high-temperature heat-resistant deformation index value of the copper foil 110 is less than 20, compared to a certain surface area ratio, the dimensional change may be small in a high-temperature and high-pressure environment, or wrinkles may occur due to low strength. Also, compared to a certain coefficient of thermal expansion and elongation rate, the surface area ratio of the copper foil may be very large. As a result, the adhesion between the copper foil and the active material may decrease, and it may not have a high capacity retention rate.

[0041] Moreover, when the high-temperature heat-resistant deformation index value of the copper foil 110 exceeds 55, compared to a certain surface area ratio, the coefficient of thermal expansion or elongation rate is too high, so 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. And, compared to a certain coefficient of thermal expansion and elongation rate, the surface area ratio of the copper foil may be very small. As a result, the adhesion between the copper foil and the active material may decrease, and it may not have a high capacity retention rate.

[0042] 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 advantageous for increasing the capacity of the secondary battery. However, manufacturing a copper foil 110 with a thickness of less than 4 μm causes a decrease in workability.

[0043] On the other hand, when manufacturing a secondary battery using a copper foil 110 exceeding 35 μm, it becomes difficult to embody a high capacity due to the thick copper foil 110.

[0044] 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.

[0045] FIG. 3 is a cross-sectional view of an electrode 100a for a secondary battery according to an 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.

[0046] As shown in FIG. 3, the electrode 100a for a secondary battery according to an 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.

[0047] FIG. 3 shows a configuration in which the active material layer 120 is formed on one surface of the copper foil 110. However, in one embodiment of the present invention, 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.

[0048] 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.

[0049] According to an 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 contains a negative electrode active material.

[0050] In order to guarantee a high capacity of the secondary battery, the active material layer 120 of the present invention can 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 Si and / or Sn.

[0051] FIG. 5 is a schematic cross-sectional view of a secondary battery according to an embodiment of the present invention.

[0052] 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 through the inside of the secondary battery 105 to the other electrode. Referring to FIG. 5, the separator 360 is disposed within the electrolyte 350.

[0053] The cathode 370 includes a cathode current collector 371 and a cathode active material layer 372, and aluminum foil can be used as the cathode current collector 371.

[0054] The anode 340 includes an anode current collector 341 and an anode active material layer 342, and copper foil 110 can be used as the anode current collector 341.

[0055] 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.

[0056] Hereinafter, the manufacturing method of the copper foil 110 of the present invention will be specifically described with reference to FIGS. 6 and 7.

[0057] 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.

[0058] 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 disposed apart from each other in an electrolytic solution 20 in an electrolytic cell 10.

[0059] As shown in FIG. 6, the positive electrode plate 30 may include first and second positive electrode plates 31 and 32 that are electrically insulated from each other.

[0060] The step of forming the copper film 111 can 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.

[0061] The current density provided by the first and second positive electrode plates 31 and 32 can be 30 to 130 ASD.

[0062] 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.

[0063] 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.

[0064] The surface characteristics of the copper film 111 can be changed depending on the surface buff finish 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.

[0065] 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 characteristics of the copper film 111 can be controlled.

[0066] 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.

[0067] To facilitate the formation of the copper film 111 by copper electrodeposition, the concentrations of copper ions and sulfuric acid in the electrolytic solution 20 are adjusted to 70 - 150 g / L and 80 - 150 g / L, respectively.

[0068] 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.

[0069] 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 may occur due to excessive chlorine (Cl). Therefore, the concentration of chlorine (Cl) in the electrolytic solution 20 is controlled in the range of 15 - 25 ppm.

[0070] 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 - 15 ppm of collagen and 0.1 - 5 ppm of gelatin.

[0071] Collagen and gelatin according to an embodiment of the present invention are added to adjust the normal temperature heat resistance deformation index and the high temperature heat resistance deformation index values of the copper foil according to the present invention. In order to obtain the physical properties of the normal temperature heat resistance deformation index and the high temperature heat resistance deformation index according to the present application invention, it is necessary for the electrolytic solution 20 to contain 1 - 15 ppm of collagen and 0.1 - 5 ppm of gelatin.

[0072] More preferably, the collagen and gelatin contained in the electrolytic solution 20 need to be added at a ratio of 10:1 to 3:1 based on the concentration. 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.

[0073] 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.

[0074] According to an embodiment of the present invention, the electrolytic solution 20 may contain an organic additive.

[0075] The organic additive contained in the electrolytic solution 20 contains at least one of a brightener (Component A) and a retarder (Component B).

[0076] The organic additive may contain one or more of a brightener (Component A) and a retarder (Component B), or may contain both components.

[0077] The brightener (Component A) contains 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.

[0078] The brightener (Component A) can increase the charge amount of the electrolytic solution 20 to increase the electrodeposition rate of copper, 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, and if it exceeds 15 ppm, there may be a problem that the weight of the copper foil 110 changes after immersion or the surface roughness changes.

[0079] The brightening agent may contain at least one of, for example, 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.

[0080] 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 electrolyte 20.

[0081] The retarder (Component B) reduces the electrodeposition rate of copper and prevents a rapid 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.

[0082] If the concentration of the retarder (Component B) is less than 0.1 ppm, there may occur a problem that the roughness of the copper foil 110 rapidly increases and the surface state of the copper foil 110 changes. On the other hand, even if the concentration of the retarder (Component B) exceeds 15 ppm, there are hardly any physical property changes such as the appearance, gloss, roughness, strength, elongation rate, etc. of the copper foil 110. Therefore, without the need to increase the manufacturing cost by unnecessarily increasing the concentration of the retarder (Component B) and waste raw materials, the concentration of the retarder (Component B) can be adjusted within the range of 0.1 to 15 ppm.

[0083] 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 stearyl alcohol polyglycol ether. However, the type of the retarder is not limited thereto, and other nonionic water-soluble polymers that can be used in the production of the high-strength copper foil 110 can be used as the retarder.

[0084] 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.

[0085] FIG. 7 is a schematic diagram showing the circulation process of the electrolytic solution according to the present invention.

[0086] According to an embodiment of the present invention, the step of manufacturing the electrolytic solution may include a step of filtering (C / F) the first electrolytic solution transferred from the storage tank using carbon to form a second electrolytic solution, and a step of adding collagen and gelatin to the filtered second electrolytic solution to form the electrolytic solution.

[0087] Specifically, the first electrolytic solution transferred from the storage tank may contain copper ions, sulfuric acid, chlorine, organic additives, etc.

[0088] The step of filtering (C / F) the first electrolytic solution using carbon means a step of removing organic impurities and inorganic impurities present in the first electrolytic solution.

[0089] 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.

[0090] According to an embodiment of the present invention, collagen and gelatin can be added to the second electrolytic solution to form an electrolytic solution. Since the additives contained in the electrolytic solution have been described above, the description is 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, it is possible to prevent the degradation of collagen and gelatin, which is effective for improving the physical properties according to the present invention.

[0091] The electrolytic 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.

[0092] Also, for the cleanliness of the electrolytic solution 20, the copper wire used as the raw material of the electrolytic solution 20 can be washed.

[0093] According to an embodiment of the present invention, the step of manufacturing the electrolytic 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 electrolytic solution.

[0094] More specifically, in order to maintain the cleanliness of the electrolytic 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 going through the process of washing the pickled copper wire with distilled water, copper for manufacturing the electrolytic solution 20 can be manufactured. The washed copper wire is administered to sulfuric acid for the electrolytic solution to manufacture the electrolytic solution 20.

[0095] According to an 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 be 300 ppm or less. That is, the electrolytic solution 20 can have a total organic carbon (TOC) concentration of 300 ppm or less.

[0096] The copper film 111 thus manufactured can be washed in a washing tank.

[0097] For example, acid cleaning for removing impurities on the surface of the copper film 111, such as resin components or natural oxide, and water cleaning for removing the acidic solution used in the acid cleaning can be sequentially performed. The cleaning process may be omitted.

[0098] Next, a protective layer 112 is formed on the copper film 111.

[0099] Referring to FIG. 6, 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.

[0100] 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 1 - 10 g / L potassium dichromate solution at room temperature for 1 - 30 seconds.

[0101] Note that the protective layer 112 can also include a silane compound by silane treatment and can also include a nitrogen compound by nitrogen treatment.

[0102] The copper foil 110 is manufactured by forming such a protective layer 112.

[0103] 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) such as 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.

[0104] 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.

[0105] 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, electrolyte, and separator.

[0106] 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 rights of the present invention is not limited to these examples.

[0107] 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.

[0108] Also, the concentration of chlorine (Cl) contained in the electrolytic solution 20 was maintained at 22 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 into the filtered electrolytic solution after filtering the electrolytic solution using carbon.

[0109] Among the organic additives, bis-(3-sulfopropyl)-disulfide disodium salt (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.

[0110] 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 a 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.

[0111] As a result, the 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.

[0112]

Table 1

Table 2

Table 3

Table 4

[0113] The copper foil was cut to obtain samples of 5 mm x 5 mm.

[0114] (i) Coefficient of thermal expansion at room temperature The coefficient of thermal expansion at room temperature means the coefficient of thermal expansion measured while heating from 30 °C to 330 °C at a rate of 5 °C / min using a thermomechanical analyzer (TMA).

[0115] At this time, the specific measurement conditions for the coefficient of thermal expansion are as follows.

[0116] - 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) Coefficient of thermal expansion at high temperature The coefficient of thermal expansion at high temperature means the coefficient of thermal expansion measured after heat treatment at 190 °C.

[0117] Specifically, the sample is heat-treated at 190 °C for 1 hour. After cooling the sample, the coefficient of thermal expansion of the sample is measured in the same way as the measurement method for the coefficient of thermal expansion at room temperature. The process of cooling the sample proceeds by leaving it at room temperature.

[0118] (iii) Elongation rate at room temperature The elongation rate at room temperature means the elongation rate measured at room temperature (25 ± 3 °C).

[0119] Specifically, it can be measured by a universal testing machine (UTM) according to the method specified in the IPC-TM-650 Test Method Manual. Equipment from Instron can be used. At this time, the width of the copper foil sample for measuring the elongation rate is 12.7 mm, the distance between the grips is 50 mm, and the measurement speed is 50 mm / min.

[0120] (iv) Elongation rate at high temperature The elongation rate at high temperature means the elongation rate measured after heat treatment at 190 °C for 1 hour.

[0121] Specifically, the samples heat-treated at 190°C for 1 hour can be measured using a universal testing machine (UTM) by the method specified in the IPC-TM-650 Test Method Manual. Equipment from Instron can be used. At this time, the width of the sample for measuring the elongation rate is 12.7 mm, the distance between the grips is 50 mm, and the measuring speed is 50 mm / min.

[0122] (v) Surface area ratio of one side and two sides The surface area ratio of one side and two sides was measured using KEYENCE's VK-9710. At this time, the surface area ratio of one side and two sides means the ratio of the three-dimensional surface area of one side and two sides to the two-dimensional surface area of one side and two sides, respectively. Specifically, a copper foil was cut into 1 cm x 1 cm to produce a test piece, and the copper foil test piece was observed at a magnification of 50 times using KEYENCE's color 3D laser microscope VK-9710 to observe the three-dimensional surface area. The "surface area ratio of one side and two sides" is the value obtained by dividing the three-dimensional surface area of the copper foil test piece measured in three dimensions 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 to focus.

[0123] (vi) Surface area ratio The surface area ratio according to the examples of the present invention means the average value of the surface area ratios of one side and two sides. Specifically, it means the value obtained by adding the surface area ratios of one side and two sides and then dividing by 2.

[0124] (vii) Capacity retention rate To 100 parts by weight of commercially available carbon for the negative electrode active material, 2 parts by weight of SBR (styrene-butadiene rubber) and 2 parts by weight of CMC (carboxymethyl cellulose) were mixed. Next, a slurry was produced by adding distilled water as a solvent to this mixture. The slurry was applied onto the surface of an electrolytic copper foil (width: 10 cm) to a thickness of about 60 μm using a doctor blade, dried at 120°C for 10 minutes, and then subjected to a pressing process (pressure: 1 ton / cm2 The negative electrode was manufactured by performing

[0125] Lithium manganese oxide (Li 1.1 Mn 1.85 Al 0.05 O4) and orthorhombic crystal structure lithium manganese oxide (o-LiMnO2) were mixed at a weight ratio of 90:10 to manufacture a positive electrode active material. The positive electrode active material, carbon black, and polyvinylidene fluoride (PVDF) were mixed with NMP as an organic solvent at a weight ratio of 85:10:5 to manufacture a slurry. The slurry was applied to both sides of an aluminum foil with a thickness of 20 μm and then dried to manufacture a positive electrode.

[0126] Also, a non-aqueous organic solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a weight ratio of 1:2 was used as a basic electrolyte by dissolving 1 M of LiPF6 as a solute. 99.5% by weight of this basic electrolyte and 0.5% by weight of succinic anhydride were mixed to manufacture an electrolyte.

[0127] A secondary battery was manufactured using the negative electrode, positive electrode, and electrolyte thus manufactured.

[0128] Next, for the secondary battery thus manufactured, the capacity per g of the positive electrode was measured at a charging operating voltage of 4.3 V and a discharging operating voltage of 3.4 V, and a charge-discharge experiment was performed 50 times at a charge-discharge rate of 0.2 C at 50°C. The capacity retention rate of the secondary battery was calculated by the following formula 3.

[0129] [Formula 3] Capacity retention rate (%) = (discharge capacity at the 50th cycle / discharge capacity at the 1st cycle) × 100 Referring to Tables 1 to 4, for the copper foils according to Examples 1 to 4, the heat-resistant deformation index at room temperature satisfied the range of 15 to 50, the adhesion between the copper foil and the active material was excellent, and the capacity retention rate of the secondary battery satisfied 90% or more. However, for the copper foils according to Comparative Examples 1 to 4, the heat-resistant deformation index at room temperature did not satisfy the range of 15 to 50, the adhesion between the copper foil and the active material decreased, and the capacity retention rate of the secondary battery did not satisfy 90% required in the industry.

[0130] The present invention described above is not limited by the foregoing examples 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 not departing 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

[0131] 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

1. A copper film containing 99.9 wt% or more of copper; and A protective layer on the copper film, A copper foil having a normal temperature heat resistance deformation index in the range of 15 to 50: The normal temperature heat resistance deformation index is represented by the following formula 1. [Formula 1] Normal temperature heat resistance deformation index = (Normal temperature thermal expansion coefficient / (ppm / °C) + Normal temperature elongation rate / (%)) / (Surface area ratio)

2. The copper foil according to claim 1, having a high temperature heat resistance deformation index in the range of 20 to 55: The high temperature heat resistance deformation index is represented by the following formula 2, [Formula 2] High temperature heat resistance deformation index = (High temperature thermal expansion coefficient / (ppm / °C) + High temperature elongation rate / (%)) / (Surface area ratio) The high temperature thermal expansion coefficient means the thermal expansion coefficient measured after heat treatment at 190°C for 1 hour, The high temperature elongation rate means the elongation rate measured after heat treatment at 190°C for 1 hour.

3. 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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