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

Abstract

The invention relates to a copper foil, an electrode comprising the copper foil, a secondary battery comprising the electrode, and a manufacturing method thereof. One embodiment of the present invention provides a copper foil comprising: 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 represented by the following formula 1: [Formula 1] first moisture absorption rate = (weight after 24 hours of impregnation-weight before impregnation) / (weight after 24 hours of impregnation) * 100; the dipping in the formula 1 refers to dipping the test piece in normal-temperature water for 24 hours.

Description

Technical Field

[0001] The present invention relates to a copper foil, an electrode including the copper foil, a secondary battery including the electrode, and a method for manufacturing the same. Specifically, the present invention relates to a copper foil with improved corrosion resistance, an electrode including the copper foil, a secondary battery including the electrode, and a method for manufacturing the same. Background Art

[0002] A secondary battery is a type of energy conversion device that converts electrical energy into chemical energy and stores it, and then converts the chemical energy back into electrical energy when power is needed. Secondary batteries are used not only in portable household appliances such as mobile phones and laptops but also as an energy source for electric vehicles. Since secondary batteries can be recharged repeatedly, they are also called rechargeable batteries.

[0003] As secondary batteries that are more economical and environmentally friendly 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, compared to other secondary batteries, lithium secondary batteries can store relatively more energy relative to their size and weight. Therefore, in the field of information and communication devices where portability and mobility are important, lithium secondary batteries are preferred, and their application scope is also expanding to energy storage devices for hybrid electric vehicles and electric vehicles.

[0005] Lithium secondary batteries are repeatedly used with charging and discharging as one cycle. When operating a device with a fully charged lithium secondary battery, in order to increase the operating time of the device, the lithium-ion secondary battery should have a high charge / discharge capacity. Therefore, there is a continuous need to conduct research to meet the growing needs of users for the charge / discharge capacity of lithium secondary batteries.

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

[0007] On the other hand, in secondary batteries, there is a problem that active substances and external moisture penetrate into the copper foil, causing corrosion of the copper foil. Therefore, research has been continuously carried out to prevent this problem. Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] Accordingly, the present invention relates to a copper foil, an electrode including the copper foil, a secondary battery including the electrode, and a method of manufacturing the same, which can prevent problems caused by the limitations and disadvantages of the related art as described above.

[0010] In addition to the viewpoints of the present invention mentioned above, other features and advantages of the present invention will be described below or can be clearly understood by those with ordinary knowledge in the technical field to which the present invention pertains from such a description.

[0011] Technical solutions for solving the problems

[0012] An 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, and the copper foil has a first moisture absorption rate of 0.1% or less. The first moisture absorption rate is represented by the following formula 1: [Formula 1] First moisture absorption rate = (weight after impregnation for 24 hours - weight before impregnation) / (weight after impregnation for 24 hours) × 100; the impregnation in Formula 1 means immersing a test piece in water at room temperature for 24 hours.

[0013] According to 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.

[0014] According to another embodiment of the present invention, there is provided a secondary battery, including: a cathode that provides lithium ions during charging; an anode that provides electrons and lithium ions during discharging; an electrolyte disposed between the cathode and the anode and providing an environment in which lithium ions can move; and a separator that electrically insulates the cathode and the anode.

[0015] Advantages of the invention

[0016] The copper foil of the present invention has a low moisture absorption rate and high corrosion resistance, and thus can have an excellent capacity retention rate. Description of the drawings

[0017] Figure 1 is a cross-sectional view of a copper foil according to an embodiment of the present invention.

[0018] Figure 2 is a cross-sectional view of a copper foil according to another embodiment of the present invention.

[0019] Figure 3 is a cross-sectional view of an electrode for a secondary battery according to another embodiment of the present invention.

[0020] Figure 4 is a cross-sectional view of an electrode for a secondary battery according to still another embodiment of the present invention.

[0021] Figure 5 It is a schematic cross-sectional view of a secondary battery according to another embodiment of the present invention.

[0022] Figure 6 It is a manufacturing apparatus for a copper foil according to another embodiment of the present invention.

[0023] Figure 7 It is a schematic diagram showing the circulation process of the electrolytic solution of the present invention.

[0024] Explanation of reference numerals

[0025] 100: Electrode for secondary battery

[0026] 110, 110a, 110b: Copper foil

[0027] 111: Copper film

[0028] 112: Protective layer

[0029] 120: Active material layer

[0030] 10: Electrolytic cell

[0031] 20: Electrolytic solution Detailed description of the embodiments

[0032] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the embodiments described below are only presented for the exemplary purpose of helping to clearly understand the present invention and do not limit the scope of the present invention.

[0033] The shapes, sizes, ratios, angles, quantities, etc. disclosed in the drawings for explaining the embodiments of the present invention are exemplary, and thus the present invention is not limited to the matters shown in the drawings. Throughout the specification, the same constituent elements may be denoted by the same reference numerals. When explaining the present invention, in cases where it is judged that a detailed description of related well-known technologies may unnecessarily obscure the gist of the present invention, its detailed description is omitted.

[0034] When using expressions such as "including", "having", "composed of", etc. mentioned in this specification, unless the expression "only" is used, other parts may be added. When a constituent element is expressed in the singular, unless otherwise specifically stated, it includes the plural. And, when interpreting a constituent element, even without other specific explanations, it is interpreted as including an error range.

[0035] When explaining the positional relationship, for example, when explaining the positional relationship between two parts in terms of "on", "above", "below", "beside", etc., unless the expressions "directly" or "exactly" are used, one or more other parts may be provided between the two parts.

[0036] Spatial relative terms such as "below", "beneath", "lower", "above", "upper", etc. can be used to easily describe the relative relationship between one element or component and other elements or components as shown in the figures. Spatial relative terms should be understood to include terms for different directions of an element during use or operation in addition to the directions shown in the drawings. For example, in the case of flipping the element shown in the drawing, an element described as "below" or "beneath" another element can be placed "above" the other element. Therefore, the exemplary term "below" can include all directions of below and above. Similarly, the exemplary terms "above" or "upper" can include all directions of above and below.

[0037] In the case of explaining temporal relationships, for example, in the case of explaining the temporal sequence using terms such as "after", "subsequent to", "successively", "before", etc., unless the expression "exactly" or "directly" is used, it can also include discontinuous cases.

[0038] Although first, second, etc. are used to describe various components, these components are not limited to these terms. These terms are only used to distinguish one component from another. Therefore, the first component mentioned below can also be the second component within the technical concept of the present invention.

[0039] The term "at least one" should be understood to include all combinations that can be suggested from more than one related item. For example, the meaning of "at least one of the first item, the second item, and the third item" not only refers to each of the first item, the second item, or the third item, but can also refer to the combination of all items suggested by two or more of the first item, the second item, and the third item.

[0040] Each feature of the multiple embodiments of the present invention can be partially or fully combined or combined with each other, and can be variously linked and driven technically. Each embodiment can be implemented independently of each other, or can be implemented together in an associated relationship.

[0041] Figure 1 It is a cross-sectional view of the copper foil 110a according to an embodiment of the present invention.

[0042] Refer to Figure 1 , the copper foil 110a of the present invention includes a copper film 111 containing 99.9 wt% or more of copper. Refer to Figure 1 , the copper foil 110a of the present invention includes a copper film 111 and a protective layer 112 on the copper film 111. Figure 1A configuration is shown in which a protective layer 112 is disposed on one side 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 sides of the copper film 111 (see Figure 2 ).

[0043] The copper film 111 can be formed on a rotating cathode drum by electroplating and can have a smooth surface that directly contacts the rotating cathode drum during the electroplating process and a rough surface on the opposite side thereof.

[0044] The protective layer 112 is formed by electrodepositing an anticorrosion material on the copper film 111. The anticorrosion material may include at least one of a chromium compound, a silane compound, and a nitrogen compound. The protective layer 112 prevents oxidation and corrosion of the copper film 111 and improves heat resistance, thereby not only extending the life of the copper foil 110 itself but also extending the life of the finished product including the copper foil 110.

[0045] The copper foil 110 described below may correspond to Figures 1 to 2 the copper foils 110a and 110b.

[0046] According to an embodiment of the present invention, the copper foil 110 may have a first moisture absorption rate of 0.1% or less. Specifically, when the first moisture absorption rate of the copper foil 110 is 0.1% or less, it is possible to prevent corrosion from occurring in the copper foil 110 due to moisture flowing in from the active material and the outside when placed outside for a long time. As a result, the copper foil 110 can have an excellent capacity retention rate.

[0047] On the contrary, when the first moisture absorption rate of the copper foil 110 exceeds 0.1%, the copper foil 110 may absorb moisture flowing in from the active material and the outside, and thus corrosion may occur in the copper foil 110. As a result, the stable capacity retention and performance of the secondary battery may be reduced.

[0048] In addition, according to an embodiment of the present invention, the copper foil 110 may have a second moisture absorption rate of 0.15% or less. Specifically, when the second moisture absorption rate of the copper foil 110 is 0.15% or less, it is possible to prevent corrosion from occurring in the copper foil 110 due to moisture flowing in from the active material and the outside when placed outside for a long time. As a result, the copper foil 110 can have an excellent capacity retention rate.

[0049] On the contrary, when the second moisture absorption rate of the copper foil 110 exceeds 0.15%, the copper foil 110 may absorb moisture flowing in from the active material and the outside, and thus corrosion may occur in the copper foil 110. As a result, the stable capacity retention and performance of the secondary battery may be reduced.

[0050] A 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 thus beneficial to the high-capacity of the secondary battery. However, the manufacture of the copper foil 110 with a thickness less than 4 μm will result in a reduction in workability.

[0051] On the contrary, in the case of manufacturing a secondary battery with a copper foil 110 exceeding 35 μm, it is difficult to achieve high capacity due to the relatively thick copper foil 110.

[0052] 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.

[0053] Figure 3 is a cross-sectional view of a secondary battery electrode 100a according to an embodiment of the present invention. Figure 4 is a cross-sectional view of a secondary battery electrode 100b according to another embodiment of the present invention.

[0054] As shown in Figure 3 a secondary battery electrode 100a according to an embodiment of the present invention includes any one of the copper foils 110 in the above-described embodiments of the present invention and an active material layer 120.

[0055] Figure 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 Figure 4 the active material layer 120 may also be formed on both surfaces of the copper foil 110.

[0056] Generally, in a lithium secondary battery, an aluminum foil is used as a positive electrode current collector combined with a positive electrode active material, and the copper foil 110 is used as a negative electrode current collector combined with a negative electrode active material.

[0057] 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.

[0058] In order to ensure the high capacity of the secondary battery, the active material layer 120 of the present invention may be formed of a composite of carbon and a metal. The metal may include at least one of, for example, Si, Ge, Sn, Li, Zn, Mg, Cd, Ce, Ni, and Fe, and preferably may include Si and / or Sn.

[0059] Figure 5 is a schematic cross-sectional view of a secondary battery according to an embodiment of the present invention.

[0060] Referring to Figure 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 in one electrode from being uselessly consumed by moving inside the secondary battery 105 to the other electrode. Refer to Figure 5 , the separator 360 is disposed within the electrolyte 350.

[0061] The cathode 370 includes a cathode current collector 371 and a cathode active material layer 372. Aluminum foil can be used as the cathode current collector 371.

[0062] The anode 340 includes an anode current collector 341 and an anode active material layer 342. Copper foil 110 can be used as the anode current collector 341.

[0063] According to an embodiment of the present invention, copper foil 110 as disclosed can be used as the anode current collector 341. Additionally, Figures 1 to 2 the disclosed copper foil 110. Further, Figure 3 or Figure 4 the electrodes 100a, 100b for a secondary battery shown can be used as Figure 5 the anode 340 of the secondary battery shown.

[0064] Hereinafter, with reference to Figure 6 and Figure 7 the manufacturing method of the copper foil 110 of the present invention will be specifically described.

[0065] The manufacturing method of the copper foil 110 of the present invention includes the step of forming a copper film 111 and the step of forming a protective layer 112 on the copper film 111.

[0066] The method of the present invention includes the step of forming a copper film 111 on the rotating cathode drum 40 by energizing an anode plate 30 and a rotating cathode drum 40 disposed apart from each other in the electrolytic solution 20 in the electrolytic cell 10.

[0067] As exemplified in Figure 6 , the anode plate 30 may include a first anode plate 31 and a second anode plate 32 that are electrically insulated from each other.

[0068] The step of forming the copper film 111 can be carried out as follows: a seed layer is formed by energizing between the first anode plate 31 and the rotating cathode drum 40, and then the seed layer is grown by energizing between the second anode plate 32 and the rotating cathode drum 40.

[0069] The current density provided through the first anode plate 31 and the second anode plate 32 respectively may be 30 to 130 ASD.

[0070] When the current density provided through the first anode plate 31 and the second anode plate 32 respectively is lower than 30 ASD, the surface roughness of the copper foil 110 is low, so that the adhesion between the copper foil 110 and the active material layer 120 may be insufficient.

[0071] On the contrary, when the current density provided through the first anode plate 31 and the second anode plate 32 respectively exceeds 130 ASD, the surface of the copper foil 110 is rough, so that the coating of the active material may not be achieved smoothly.

[0072] The surface characteristics of the copper film 111 may vary depending on the surface polishing or grinding degree of the rotating cathode drum 40. For example, a grinding brush with a grit of #800 to #3000 may be used to grind the surface of the rotating cathode drum 40.

[0073] During the formation of the copper film 111, the electrolyte 20 is maintained at a temperature of 40 to 60 °C. More specifically, the temperature of the electrolyte 20 may be maintained above 50 °C. At this time, the physical, chemical, and electrical characteristics of the copper film 111 can be controlled by adjusting the composition of the electrolyte 20.

[0074] According to an embodiment of the present invention, the electrolyte 20 may include copper ions, sulfuric acid, chlorine (Cl), collagen, gelatin, and an organic additive.

[0075] In order to smoothly form the copper film 111 by electro-deposition of copper, the copper ion concentration and the sulfuric acid concentration in the electrolyte 20 are adjusted to 70 to 150 g / L and 80 to 150 g / L respectively.

[0076] In an embodiment of the present invention, chlorine (Cl) includes chloride ions (Cl - ) and all the chlorine atoms present in the molecule. For example, chlorine (Cl) can be used to remove silver (Ag) ions flowing into the electrolyte 20 during the formation of the copper film 111. Specifically, chlorine (Cl) can precipitate silver (Ag) ions in the form of silver chloride (AgCl). This silver chloride (AgCl) can be removed by filtration.

[0077] When the concentration of chlorine (Cl) is lower than 15 ppm, silver (Ag) ions cannot be removed smoothly. On the contrary, when the concentration of chlorine (Cl) exceeds 25 ppm, unnecessary reactions may occur due to excessive chlorine (Cl). Therefore, the chlorine (Cl) concentration in the electrolyte 20 is controlled in the range of 15 to 25 ppm.

[0078] According to an embodiment of the present invention, the electrolyte 20 may contain collagen and gelatin. Specifically, the electrolyte 20 may contain 1 to 15 ppm of collagen and 0.1 to 5 ppm of gelatin.

[0079] The collagen and gelatin of 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 of 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 of the present invention, the electrolyte 20 needs to contain 1 to 15 ppm of collagen and 0.1 to 5 ppm of gelatin.

[0080] More preferably, the collagen and gelatin contained in the electrolyte 20 need to be added in a concentration ratio of 10:1 to 3:1. At this time, the collagen may have a molecular weight of 2000 to 10000, and the gelatin may have a molecular weight of 10000 to 100000.

[0081] When the concentration ratio of the collagen and gelatin contained in the electrolyte 20 deviates from the above range, if the gelatin with a larger molecular weight increases excessively, there may be a problem that the strength becomes excessively large. If the collagen with a smaller molecular weight increases excessively compared to the gelatin, there may also be a problem that the strength is excessively reduced.

[0082] According to an embodiment of the present invention, the electrolyte 20 may contain an organic additive.

[0083] The organic additive contained in the electrolyte 20 contains at least one of a brightener (component A) and a retarder (component B).

[0084] The organic additive may contain one or more of a brightener (component A) and a retarder (component B), or may contain both components.

[0085] The brightener (component A) contains a sulfonic acid or its metal salt. The brightener (component A) may have a concentration of 1 to 15 ppm in the electrolyte 20.

[0086] The brightener (component A) increases the charge amount of the electrolyte 20 and increases the copper electrodeposition rate, improves the curling (Curl) characteristics of the copper foil, and can enhance the gloss of the copper foil 110. If the concentration of the brightener (component A) is lower than 1 ppm, the gloss of the copper foil 110 decreases. If it exceeds 15 ppm, there may be problems such as weight change or surface roughness change after impregnating the copper foil 110.

[0087] The brightening agent may include, for example, at least one of sodium bis-(3-sulfopropyl)-disulfide, 3-mercapto-1-propanesulfonic acid, sodium 3-(N,N-dimethylthiocarbamoyl)-thiopropanesulfonate, sodium 3-[(amino-iminomethyl)thio]-1-propanesulfonate, sodium o-ethyl dithiocarbonate-S-(3-sulfopropyl)-ester, sodium 3-(benzothiazole-2

[0088] -mercapto)-propyl-sulfonate, and ethylene dithiodipropyl sulfonic acid sodium salt.

[0089] The retarder (Component B) contains a nonionic water-soluble polymer. The retarder (Component B) may have a concentration of 0.1 to 15 ppm in the electrolyte 20.

[0090] The retarder (Component B) reduces the rate of copper electrodeposition, thereby preventing a sharp increase in the roughness and a decrease in the strength of the copper foil 110. Such a retarder (Component B) is also referred to as an inhibitor or a suppressor.

[0091] If the concentration of the retarder (Component B) is lower than 0.1 ppm, problems such as a sharp increase in the roughness of the copper foil 110 and a change in the surface state of the copper foil 110 may occur. On the contrary, even if the concentration of the retarder (Component B) exceeds 15 ppm, the physical properties of the copper foil 110 such as appearance, gloss, roughness, strength, elongation, etc. hardly change. Therefore, the concentration of the retarder (Component B) can be adjusted to the range of 0.1 to 15 ppm without unnecessarily increasing the manufacturing cost and wasting raw materials by increasing the concentration of the retarder (Component B).

[0092] The retarder (Component B) may include, for example, at least one nonionic water-soluble polymer selected from polyethylene glycol (PEG), polypropylene glycol, polyethylene-polypropylene copolymer, polyglycerol, polyethylene glycol dimethyl ether, hydroxyethyl cellulose, polyvinyl alcohol, polyethylene glycol stearate ether, and polyethylene glycol stearyl ether. However, the types of retarders are not limited thereto, and another nonionic water-soluble polymer that can be used in the manufacture of the high-strength copper foil 110 can be used as the retarder.

[0093] When forming the copper film 111, the flow rate of the electrolyte 20 supplied into the electrolytic cell 10 may be 41 to 45 m 3 / hour.

[0094] Figure 7 is a schematic diagram showing the circulation process of the electrolyte of the present invention.

[0095] According to an embodiment of the present invention, the steps of manufacturing the electrolyte may include the step of forming a second electrolyte by using carbon filtration C / F to transfer the first electrolyte from the storage tank, and the step of adding collagen and gelatin to the filtered second electrolyte to form the electrolyte.

[0096] Specifically, the first electrolyte transferred from the storage tank may contain copper ions, sulfuric acid, chlorine, organic additives, etc.

[0097] The process of carbon filtering the first electrolyte C / F refers to the step of removing organic impurities and inorganic impurities present in the first electrolyte.

[0098] According to an embodiment of the present invention, the second electrolyte refers to the electrolyte obtained by carbon filtering the first electrolyte.

[0099] According to an embodiment of the present invention, collagen and gelatin can be added to the second electrolyte to form the electrolyte. The additives contained in the electrolyte have been described above and are omitted here. Specifically, collagen and gelatin are added after the carbon filtering C / F process. When collagen and gelatin are added after the carbon filtering C / F process, it can prevent the degradation of collagen and gelatin and has the effect of improving the physical properties of the present invention.

[0100] The electrolyte formed by adding collagen and gelatin is filled in the electrolytic cell 10, and a copper foil is manufactured using a foil making machine including a rotating cathode roller 40 disposed in the electrolytic cell 10 and an anode plate 30 disposed at a distance from the rotating cathode roller 40.

[0101] In addition, for the purity of the electrolyte 20, the copper wire (Cu wire) used as the raw material of the electrolyte 20 can be cleaned.

[0102] According to an embodiment of the present invention, the steps of manufacturing the electrolyte 20 may include: the step of heat-treating the copper wire, the step of pickling the heat-treated copper wire, the step of washing the pickled copper wire with water, and the step of putting the washed copper wire into sulfuric acid for the electrolyte.

[0103] More specifically, in order to maintain the purity of the electrolyte 20, copper for manufacturing the electrolyte 20 can be manufactured by sequentially going through the following process: heat-treating high-purity (99.9% or more) copper wire (Cu wire) in an electric furnace at 750°C to 850°C to burn off various organic impurities attached to the copper wire, then pickling the copper wire heat-treated for 10 to 20 minutes with a 10% sulfuric acid solution, and washing the pickled copper wire with distilled water. The washed copper wire can be put into sulfuric acid for the electrolyte to manufacture the electrolyte 20.

[0104] According to an embodiment of the present invention, in order to meet the characteristics of the copper foil 110, the concentration of total organic carbon (TOC) in the electrolyte 20 is controlled to be below 300 ppm. That is, the electrolyte 20 may have a total organic carbon (TOC) concentration of 300 ppm or less.

[0105] The copper film 111 thus manufactured can be cleaned in a cleaning tank.

[0106] For example, acid cleaning for removing impurities such as resin components or natural oxide films on the surface of the copper film 111 and water cleaning for removing the acidic solution used in the acid cleaning can be performed in sequence. The cleaning process can also be omitted.

[0107] Next, a protective layer 112 is formed on the copper film 111.

[0108] Refer to Figure 6 , and it may further include the step of immersing the copper film 111 in an anticorrosion solution 60. When the copper film 111 is immersed in the anticorrosion solution 60, it can be guided by a guide roll disposed in the anticorrosion solution 60.

[0109] 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.

[0110] On the other hand, the protective layer 112 may include a silane compound based on silane treatment or a nitrogen compound based on nitrogen treatment.

[0111] The copper foil 110 is manufactured by forming such a protective layer 112.

[0112] On one or both sides of the copper foil 110 of the present invention manufactured by the method as described above, a negative electrode active material selected from the group consisting of carbon; a metal (Me) such as Si, Ge, Sn, Li, Zn, Mg, Cd, Ce, Ni, or Fe; an alloy containing the metal (Me); an oxide (MeO x ) of the metal (Me); and a composite of the metal (Me) and carbon is coated, thereby enabling the manufacture of an electrode (i.e., a negative electrode) for a secondary battery of the present invention.

[0113] For example, after mixing 1 to 3 parts by weight of styrene-butadiene rubber (SBR) and 1 to 3 parts by weight of carboxymethyl cellulose (CMC) in 100 parts by weight of carbon used as the negative electrode active material, distilled water is used as a solvent to prepare a slurry. Then, 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 a temperature of 110 to 130 °C.

[0114] A secondary battery can be manufactured using a conventional positive electrode, electrolyte, and separator together with the electrode (negative electrode) for a secondary battery of the present invention manufactured by the above method.

[0115] Hereinafter, the present invention will be specifically described through examples and comparative examples. However, the following examples are merely for helping to understand the present invention, and the scope of the rights of the present invention is not limited to these examples.

[0116] Examples 1-4 and Comparative Examples 1-4

[0117] A copper foil was manufactured using a foil-making machine including an electrolytic cell 10, a rotating cathode drum 40 disposed in the electrolytic cell 10, and an anode plate 30 disposed at a distance from the rotating cathode drum 40. The electrolytic solution 20 was a copper sulfate solution. The concentration of copper ions in the electrolytic solution 20 was set to 87 g / L, the concentration of sulfuric acid was set to 110 g / L, the temperature of the electrolytic solution was set to 55 °C, and the current density was set to 60 ASD.

[0118] In addition, the concentration of chlorine (Cl) contained in the electrolytic solution 20 was maintained at 20 ppm, and the concentrations of collagen, gelatin, and organic additives were as shown in Table 1 below. At this time, after filtering the electrolytic solution using carbon, collagen and gelatin were added to the filtered electrolytic solution.

[0119] 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 3500 and 10000, respectively.

[0120] A current was applied between the rotating cathode drum 40 and the anode plate 30 at a current density of 60 ASD to manufacture a copper film 111. Then, the copper film 111 was immersed in an anti-rust solution for about 2 seconds, and chromate treatment was performed on both sides of the copper film 111 to form a protective layer 112, thereby manufacturing a copper foil. An anti-rust solution mainly composed of chromic acid was used as the anti-rust solution, and the concentration of chromic acid was 5 g / L.

[0121] As a result, the copper foils of Examples 1-4 and Comparative Examples 1-4 were manufactured. At this time, the thickness of the manufactured copper foil was 8 μm.

[0122] [Table 1]

[0123]

[0124] [Table 2]

[0125]

[0126] [Table 3]

[0127]

[0128] For the copper foils of Examples 1-4 and Comparative Examples 1-4 manufactured as such, i) the weight of the sample before impregnation; ii) the weight of the sample after 24 hours of impregnation; iii) the weight of the sample after 72 hours of impregnation; and iv) the capacity retention rate were confirmed.

[0129] The copper foil was cut to obtain samples of 10 cm × 10 cm.

[0130] i) Measurement of the weight of the sample before impregnation

[0131] The samples of the manufactured copper foil were 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 samples was immediately measured.

[0132] ii) Measurement of the weight of the sample after 24 hours of impregnation

[0133] The samples of the manufactured copper foil were immersed in water at a temperature of 23 °C for 24 hours, wiped with gauze, placed at room temperature for 2 hours, and then the weight was measured.

[0134] iii) Measurement of the weight of the sample after 72 hours of impregnation

[0135] The measurement was carried out by the same method except that the sample was immersed in water for 72 hours in the measurement of the weight of the sample after 24 hours of impregnation.

[0136] iv) Capacity retention rate

[0137] Relative to 100 parts by weight of commercially available carbon as 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. Then, a solvent, i.e., distilled water, was added to the mixture to prepare a slurry. The slurry was applied to the surface of an electrolytic copper foil (width: 10 cm) with a thickness of about 60 μm using a spatula, dried at 120 °C for 10 minutes, and then a pressing process (pressure: 1 ton / cm 2 ) was carried out to manufacture the negative electrode.

[0138] Lithium manganese oxide (Li 1.1 Mn 1.85Al 0.05 Lithium manganese oxide (o-LiMnO2) with a spinel structure (LiAl 0.05 O4) and an orthorhombic crystal structure was mixed at a weight ratio of 90:10 to produce the positive electrode active material. The positive electrode active material, carbon black, and polyvinylidene fluoride (PVDF) were mixed with an organic solvent, NMP (N-methyl-2-pyrrolidone), 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 the positive electrode.

[0139] In addition, 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, LiPF6 was dissolved as a solute at 1 M to form a basic electrolyte. 99.5 wt% of this basic electrolyte and 0.5 wt% of succinic anhydride were mixed to produce the electrolyte.

[0140] A secondary battery was fabricated using the negative electrode, positive electrode, and electrolyte thus produced.

[0141] Next, for the secondary battery thus fabricated, the capacity per gram of the positive electrode was measured using a charging operating voltage of 4.3 V and a discharging operating voltage of 3.4 V. A charge / discharge experiment was conducted 50 times at a charge / discharge rate of 0.2C at 50 °C, and the capacity retention rate of the secondary battery was calculated according to Equation 3 below.

[0142] [Equation 3]

[0143] Capacity retention rate (%) = (Discharge capacity at the 50th cycle / Discharge capacity at the 1st cycle) × 100

[0144] Referring to Tables 1 to 4, the first moisture absorption rate of the copper foils in Examples 1 to 4 satisfied the range of 0.1% or less, and thus the capacity retention rate of the secondary battery satisfied 90% or more. However, the first moisture absorption rate of the copper foils in Comparative Examples 1 to 4 did not satisfy the range of 0.1% or less, and the capacity retention rate of the secondary battery did not meet the industry requirement of 90%.

[0145] The present invention described above is not limited to the foregoing embodiments and drawings. It is obvious that those with ordinary knowledge in the technical field to which the present invention pertains can make various substitutions, deformations, and changes without departing from the technical idea of the present invention. Therefore, the scope of the present invention is defined by the appended claims and should be interpreted to include all modifications or variations derived from the meaning, scope, and equivalent concepts of the claims.

Claims

1. A copper foil, wherein include: A copper film comprising 99.9% by weight or more of copper; as well as The 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 the following formula 1: Formula 1 First moisture absorption rate = (weight after immersion for 24 hours - weight before immersion) / (weight after immersion for 24 hours) × 100 The immersion in Formula 1 refers to immersing the test piece in water at room temperature for 24 hours.

2. The copper foil according to claim 1, wherein Having a second moisture absorption rate of 0.15% or less, The second moisture absorption rate is expressed by the following formula 2: Formula 2 Second moisture absorption rate = (weight after immersion for 72 hours - weight before immersion) / (weight after immersion for 72 hours) × 100 The immersion in Formula 2 refers to immersing the test piece in water at room temperature for 72 hours.

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

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