Copper foil with improved corrosion resistance, electrode comprising the same, secondary battery comprising the same, and method for manufacturing the same

Abstract

To provide an electrolytic copper foil capable of ensuring secondary batteries with increased capacity and stable capacity retention and performance.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 moisture absorption rate of 0.1% or less. The first moisture absorption rate is expressed by formula 1: (first moisture absorption rate)=[(weight after 24-hour immersion)-(weight before immersion)] / (weight after 24-hour immersion)×100, where the immersion in formula 1 refers to immersing a specimen in water at room temperature for 24 hours.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 with improved corrosion resistance, 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] 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 their size and weight compared to other secondary batteries. Therefore, lithium secondary batteries are preferably used in the field of information and communication devices 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 charge and discharge cycle. When operating any device with a fully charged lithium secondary battery, the lithium-ion secondary battery must have a high charge-discharge capacity in order to increase the operating time of the device. Therefore, research is continuously required to meet the increasing 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. 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 that can increase the capacity of the secondary battery and guarantee stable capacity retention and performance is required.

[0007] In addition, in secondary batteries, there is a problem that the active material and external moisture penetrate into the copper foil, causing corrosion of the copper foil, and research to prevent this is being continuously conducted.

Summary of the Invention

Problems to be Solved by the Invention

[0008] Therefore, the present invention relates to a copper foil capable of preventing 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 manufacturing method thereof.

[0009] 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 description.

Means for Solving the Problems

[0010] 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 water absorption rate of 0.1% or less. The first water absorption rate is represented by the following formula 1, [Formula 1] First water absorption rate = (weight after 24-hour immersion - weight before immersion) / (weight after 24-hour immersion) x 100 The immersion in Formula 1 means immersing the test piece in water at room temperature for 24 hours.

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

[0012] According to 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 disposed between the cathode and the anode that provides an environment in which lithium ions can move; and a separator that electrically insulates the cathode and the anode.

Advantages of the Invention

[0013] The copper foil according to the present invention can have an excellent capacitance retention rate by having a low water absorption rate and high corrosion resistance.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0015] 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.

[0016] 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. The same components throughout the specification may be referred to by the same reference numerals. In describing the present invention, when it is determined that a specific description of related known technologies may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

[0017] When terms such as "comprising", "having", "consisting of", etc. mentioned in this specification are used, other parts may be added as long as the expression "only" is not used. 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 the error range even without separate explicit description.

[0018] In the case of an explanation of the 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 as long as the expressions "immediately" or "directly" are not used.

[0019] 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 the 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.

[0020] In the case of an explanation regarding the relationship of time, for example, when the time sequence relationship is described by "after ~", "subsequent to ~", "next to ~", "before ~", etc., cases including those that are not continuous can be included as long as the expressions "immediately" or "directly" are not used.

[0021] The first, second, etc. are used to describe various components, but these components are not limited by these terms. These terms are merely 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.

[0022] 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" may 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 among the first item, the second item, and the third item.

[0023] The respective features of various embodiments of the present invention can be partially or entirely 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.

[0024] FIG. 1 is a cross-sectional view of a copper foil 110a according to an embodiment of the present invention.

[0025] 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 to this, and the protective layer 112 can be disposed on both sides of the copper film (111) (see FIG. 2).

[0026] 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 during the electroplating process and a matte surface on the opposite side thereof.

[0027] 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.

[0028] The copper foil 110 to be described later can correspond to the copper foils 110a and 110b according to FIGS. 1 to 2.

[0029] According to an embodiment of the present invention, the copper foil 110 can have a first water absorption rate of 0.1% or less. Specifically, when the first water absorption rate of the copper foil 110 is 0.1% or less, corrosion of the copper foil 110 due to the active material and moisture flowing in from the outside can be prevented when it is left outside for a long time. As a result, the copper foil 110 can have an excellent capacity retention rate.

[0030] On the other hand, when the first water absorption rate of the copper foil 110 exceeds 0.1%, the copper foil 110 can absorb the active material and moisture flowing in from the outside, and thereby corrosion may occur in the copper foil 110. As a result, the stable capacity retention and performance of the secondary battery can be reduced.

[0031] Also, according to an embodiment of the present invention, the copper foil 110 can have a second water absorption rate of 0.15% or less. Specifically, when the second water absorption rate of the copper foil 110 is 0.15% or less, corrosion of the copper foil 110 due to the active material and moisture flowing in from the outside can be prevented when it is left outside for a long time. As a result, the copper foil 110 can have an excellent capacity retention rate.

[0032] On the one hand, when the second water absorption rate of the copper foil 110 exceeds 0.15%, the copper foil 110 can absorb the active material and the moisture flowing in from the outside, which may cause corrosion of the copper foil 110. As a result, the stable capacity retention and performance of the secondary battery can be reduced.

[0033] 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, the production of the copper foil 110 having a thickness of less than 4 μm causes a decrease in workability.

[0034] 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.

[0035] 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.

[0036] FIG. 3 is a cross-sectional view of a secondary battery electrode 100a according to an embodiment of the present invention. FIG. 4 is a cross-sectional view of a secondary battery electrode 100b according to another embodiment of the present invention.

[0037] As shown in FIG. 3, the secondary battery electrode 100a according to an embodiment of the present invention includes any one of the copper foils 110 and the active material layer 120 of the foregoing embodiments of the present invention.

[0038] FIG. 3 shows a configuration in which the active material layer 120 is formed on one surface of the copper foil 110. However, an embodiment of the present invention is not limited thereto. Referring to FIG. 4, the active material layer 120 can also be formed on both surfaces of the copper foil 110.

[0039] 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.

[0040] According to an embodiment of the present invention, the secondary battery electrode 100 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.

[0041] In order to ensure 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, preferably Si and / or Sn.

[0042] FIG. 5 is a schematic cross-sectional view of a secondary battery according to an embodiment of the present invention.

[0043] 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 in the electrolyte 350.

[0044] 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.

[0045] The anode 340 includes an anode current collector 341 and an anode active material layer 342, and the copper foil 110 can be used as the anode current collector 341.

[0046] According to an embodiment of the present invention, the copper foil 110 shown in FIGS. 1 to 2 can be used as the negative electrode current collector 341. Further, the secondary battery electrodes 100a and 100b shown in FIG. 3 or FIG. 4 can be used for the negative electrode 340 of the secondary battery shown in FIG. 5.

[0047] Hereinafter, with reference to FIGS. 6 and 7, the manufacturing method of the copper foil 110 of the present invention will be specifically described.

[0048] 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.

[0049] 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 arranged to be separated from each other in the electrolytic solution 20 in the electrolytic cell 10.

[0050] 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.

[0051] 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.

[0052] The current density provided by the first and second positive electrode plates 31 and 32 can be 30 to 130 ASD.

[0053] 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.

[0054] 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.

[0055] The surface characteristics of the copper film 111 can be changed depending on 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.

[0056] In the process of forming 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.

[0057] 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.

[0058] 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.

[0059] In an 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.

[0060] 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 within the range of 15 to 25 ppm.

[0061] 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.

[0062] Collagen and gelatin according to an embodiment of the present invention are added to adjust the normal temperature heat resistance deformation index and 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 high temperature heat resistance deformation index 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.

[0063] 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, collagen can have a molecular weight of 2,000 to 10,000, and gelatin can have a molecular weight of 10,000 to 100,000.

[0064] When the concentration ratio of collagen and gelatin contained in the electrolytic solution 20 is outside the above range, there may be a problem that gelatin with a large molecular weight becomes excessively large and the strength is too high, or there may be a problem that collagen with a small molecular weight becomes excessively large compared to gelatin and the strength is too low.

[0065] According to an embodiment of the present invention, the electrolytic solution 20 may contain an organic additive.

[0066] The organic additive contained in the electrolytic solution 20 includes at least one of a brightener (component A) and a retarder (component B).

[0067] The organic additive may include one or more of a brightener (component A) and a retarder (component B), or may include both components.

[0068] 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.

[0069] The brightener (Component A) can increase the charge amount of the electrolytic solution 20 to 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.

[0070] 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-[(amino-iminomethyl)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.

[0071] 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.

[0072] The retarder (Component B) reduces the copper electrodeposition rate to prevent 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.

[0073] If the concentration of the retarder (Component B) is less than 0.1 ppm, there may be 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 almost no 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 wasting raw materials, the concentration of the retarder (Component B) can be adjusted to the range of 0.1 to 15 ppm.

[0074] The retarder (Component B) may contain at least one non-ionic 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 non-ionic water-soluble polymers that can be used in the manufacture of the high-strength copper foil 110 can be used as the retarder.

[0075] When the copper film 111 is formed, the flow rate of the electrolytic solution 20 supplied into the electrolytic cell 10 can be 41 to 45 m 3 / hour.

[0076] FIG. 7 is a schematic diagram showing the circulation process of the electrolytic solution according to the present invention.

[0077] According to an embodiment of the present invention, the step of manufacturing the electrolytic solution may include filtering (C / F) the first electrolytic solution transferred from the storage tank using carbon to form a second electrolytic solution, and adding collagen and gelatin to the filtered second electrolytic solution to form an electrolytic solution.

[0078] Specifically, the first electrolytic solution transferred from the storage tank may contain copper ions, sulfuric acid, chlorine, organic additives, etc.

[0079] The step of filtering (C / F) the first electrolyte using carbon means the step of removing organic impurities and inorganic impurities present in the first electrolyte.

[0080] According to an embodiment of the present invention, the second electrolyte means the electrolyte obtained by filtering the first electrolyte using carbon.

[0081] According to an embodiment of the present invention, collagen and gelatin can be added to the second electrolyte to form an electrolyte. Since the additives contained in the electrolyte have been described above, the description is omitted. Specifically, collagen and gelatin are added after the filtering (C / F) step. When collagen and gelatin are added after the filtering (C / F) step, it is possible to prevent collagen and gelatin from deteriorating, which is effective for improving the physical properties according to the present invention.

[0082] The electrolyte 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.

[0083] Also, for the cleanliness of the electrolyte 20, the copper wire used as the raw material of the electrolyte 20 can be washed.

[0084] According to an embodiment of the present invention, the step of manufacturing the electrolyte 20 may include the steps of heat-treating the copper wire, pickling the heat-treated copper wire, washing the pickled copper wire with water, and putting the washed copper wire into sulfuric acid for the electrolyte.

[0085] More specifically, in order to maintain the cleanliness of the electrolytic solution 20, 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 copper wire heat-treated for 10 to 20 minutes using a 10% sulfuric acid solution is pickled, and the pickled copper wire is washed with distilled water in sequence, and copper for manufacturing the electrolytic solution 20 can be manufactured. The washed copper wire is added to sulfuric acid for the electrolytic solution, and the electrolytic solution 20 can be manufactured.

[0086] 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 concentration of total organic carbon (TOC) of 300 ppm or less.

[0087] The copper film 111 manufactured in this way can be washed in a washing tank.

[0088] 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.

[0089] Next, a protective layer 112 is formed on the copper film 111.

[0090] 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.

[0091] As described above, the rust preventive liquid 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.

[0092] In addition, the protective layer 112 can also contain a silane compound by silane treatment and can also contain a nitrogen compound by nitrogen treatment.

[0093] The copper foil 110 is manufactured by forming such a protective layer 112.

[0094] 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 on one or both surfaces of the copper foil 110 of the present invention manufactured through the above method, whereby the electrode for secondary battery of the present invention (i.e., the negative electrode) can be manufactured.

[0095] 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 for the 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.

[0096] A secondary battery can be manufactured using the electrode for secondary battery (negative electrode) of the present invention manufactured by the above method together with a normal positive electrode, electrolyte, and separator.

[0097] 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.

[0098] Examples 1 to 4 and Comparative Examples 1 to 4 A copper foil was produced 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 apart from the rotating negative electrode drum 40. The electrolytic solution 20 was a copper sulfate solution. The concentration of copper ions in the electrolytic solution 20 was set to 87 g / L, the concentration of sulfuric acid was 110 g / L, the temperature of the electrolytic solution was 55°C, and the current density was 60 ASD.

[0099] Also, the concentration of chlorine (Cl) contained in the electrolytic solution 20 was maintained at 20 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.

[0100] Among the organic additives, bis-(3-sulfopropyl)-disulfide disodium salt (SPS) was used as a brightening agent (Component A), polyethylene glycol (PEG) was used as a retarder (Component B), and the molecular weights of collagen and gelatin were 3,500 and 10,000, respectively.

[0101] 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 a copper film 111. Next, the copper film 111 was immersed in a rust preventive solution for about 2 seconds, and a chromate treatment was performed on both surfaces of the copper film 111 to form a 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.

[0102] 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.

[0103] [Table 1] [Table 2] [Table 3] For the copper foils of Examples 1 to 4 and Comparative Examples 1 to 4 manufactured as described above, (i) the weight of the sample before immersion, (ii) the weight of the sample after 24 hours of immersion, (iii) the weight of the sample after 72 hours of immersion, and (iv) the volume retention rate were confirmed.

[0104] The copper foil was cut to obtain a 10 cm x 10 cm sample.

[0105] (i) Measurement of the weight of the sample before immersion The sample of the manufactured copper foil was dried in an oven set at a temperature of 50 °C for 24 hours, cooled in a desiccator for 24 hours, and then the weight of the sample was measured immediately.

[0106] (ii) Measurement of the weight of the sample after 24 hours of immersion The sample of the manufactured copper foil was immersed in water at a temperature of 23 °C for 24 hours, then the sample was blotted with gauze, left at room temperature for 2 hours, and then the weight was measured.

[0107] (iii) Measurement of the weight of the sample after 72 hours of immersion It was measured in the same manner except that the sample was immersed in water for 72 hours in the measurement of the weight of the sample after 24 hours of immersion.

[0108] (iv) Volume retention rate 2 parts by weight of SBR (styrene-butadiene rubber) and 2 parts by weight of CMC (carboxymethyl cellulose) were mixed with 100 parts by weight of commercially available carbon for negative electrode active material. 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 a negative electrode was manufactured by performing a pressing step (pressure: 1 ton / cm 2 ).

[0109] Lithium manganese oxide (Li 1.1 Mn 1.85 Al 0.05Lithium manganese oxide (o-LiMnO2) with a tetragonal (O4) and orthorhombic crystal structure was mixed at a weight ratio of 90:10 to produce 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 produce a slurry. The slurry was applied to both sides of an aluminum foil with a thickness of 20 μm and then dried to produce a positive electrode.

[0110] Also, a basic electrolyte was prepared by dissolving 1 M of LiPF6 as a solute in a non-aqueous organic solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a weight ratio of 1:2. 99.5 wt% of this basic electrolyte and 0.5 wt% of succinic anhydride were mixed to produce an electrolyte.

[0111] A secondary battery was manufactured using the negative electrode, positive electrode, and electrolyte thus produced.

[0112] Next, for the secondary battery thus manufactured, the capacity per gram 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.

[0113] [Formula 3] Capacity retention rate (%) = (discharge capacity at the 50th cycle / discharge capacity at the first cycle) × 100 Referring to Tables 1 to 4, for the copper foils according to Examples 1 to 4, the first water absorption rate satisfied the range of 0.1% or less, 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 first water absorption rate did not satisfy the range of 0.1% or less, and the capacity retention rate of the secondary battery did not satisfy 90% required in the industry.

[0114] The present invention described above is not limited by the aforementioned embodiments and the accompanying drawings, and it will be apparent to those having ordinary knowledge in the technical field to which the present invention pertains that various substitutions, modifications, and changes are possible within the scope not deviating 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

[0115] 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 first water absorption rate of 0.1% or less: The first water absorption rate is represented by the following formula 1, [Formula 1] First water absorption rate = (weight after 24-hour immersion - weight before immersion) / (weight after 24-hour immersion) x 100 The immersion in Formula 1 means immersing the test piece in water at room temperature for 24 hours.

2. The copper foil according to Claim 1, having a second water absorption rate of 0.15% or less: The second water absorption rate is represented by the following formula 2, [Formula 2] Second water absorption rate = (weight after 72-hour immersion - weight before immersion) / (weight after 72-hour immersion) x 100 The immersion in Formula 2 means immersing the test piece in water at room temperature for 72 hours.

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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