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 having a first normal temperature coefficient of thermal expansion of 10 ppm / DEG C to 25 ppm / DEG C and a high temperature coefficient of thermal expansion of 20 ppm / DEG C to 35 ppm / DEG C. The first normal-temperature thermal expansion coefficient is a thermal expansion coefficient measured along the MD direction, and the high-temperature thermal expansion coefficient is a thermal expansion coefficient measured along the MD direction after heat treatment at 190 DEG C.

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. The present invention relates to a copper foil having prevented curl, 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 economical and have environmental advantages compared to disposable primary batteries, there are lead-acid batteries, nickel-cadmium secondary batteries, nickel-metal hydride secondary batteries, lithium secondary batteries, etc.

[0004] In particular, 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 foils are 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, as the thickness of the copper foil becomes thinner, the amount of active material that can be contained in the same space increases, and the number of current collectors can be increased, thereby increasing the capacity of the secondary battery. However, as the copper foil becomes thinner, curling occurs, and thus defects such as tearing or wrinkling of the copper foil occur due to curling at the edge portion when winding the copper foil. Therefore, it is difficult to manufacture a copper foil in the form of a very thin film. Thus, in order to manufacture a copper foil having a very thin thickness, curling of the copper foil must be prevented. Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] Accordingly, 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 copper foil, a secondary battery including the electrode, and a method for manufacturing the same.

[0010] One embodiment of the present invention provides a copper foil that prevents wrinkling or tearing by having a first normal-temperature thermal expansion coefficient of 10 ppm / °C to 25 ppm / °C and a high-temperature thermal expansion coefficient of 20 ppm / °C to 35 ppm / °C.

[0011] Another embodiment of the present invention provides a copper foil that prevents wrinkling or tearing by having a second normal-temperature thermal expansion coefficient of 10 ppm / °C to 25 ppm / °C.

[0012] Still another embodiment of the present invention provides a copper foil that prevents wrinkling or tearing by having a high-temperature thermal expansion coefficient greater than the first normal-temperature thermal expansion coefficient and the second normal-temperature thermal expansion coefficient.

[0013] Another embodiment of the present invention provides an electrode for a secondary battery including such a copper foil and a secondary battery including such an electrode for a secondary battery.

[0014] Still another embodiment of the present invention provides a method for manufacturing a copper foil that prevents curling, wrinkling, or tearing.

[0015] In addition to the viewpoints 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 a description.

[0016] Technical Solutions for Solving the Problems

[0017] An embodiment of the present invention provides a copper foil, comprising: a copper film containing 99.9% by weight or more of copper; and a protective layer on the copper film, the copper foil having a first normal temperature thermal expansion coefficient of 10 ppm / °C to 25 ppm / °C and a high temperature thermal expansion coefficient of 20 ppm / °C to 35 ppm / °C. The first normal temperature thermal expansion coefficient is the thermal expansion coefficient measured along the MD direction, and the high temperature thermal expansion coefficient is the thermal expansion coefficient measured along the MD direction after heat treatment at 190°C.

[0018] According to another embodiment of the present invention, there is provided an electrode for a secondary battery, comprising: a copper foil; and an active material layer disposed on at least one surface of the copper foil.

[0019] According to still another embodiment of the present invention, there is provided a secondary battery, comprising: 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, providing an environment in which lithium ions can move; and a separator that electrically insulates the cathode and the anode.

[0020] Advantages of the Invention

[0021] According to the present invention, wrinkles or tears are prevented from occurring during the manufacturing process of the copper foil, and semi-finished and finished products such as flexible printed circuit boards (FPCBs) and secondary batteries are manufactured using such a copper foil, thereby enabling the productivity of the semi-finished and even finished products to be improved. Description of the Drawings

[0022] Figure 1 is a cross-sectional view of a copper foil according to an embodiment of the present invention.

[0023] Figure 2 is a cross-sectional view of a copper foil according to another embodiment of the present invention.

[0024] Figure 3 is a cross-sectional view of an electrode for a secondary battery according to another embodiment of the present invention.

[0025] Figure 4 is a cross-sectional view of an electrode for a secondary battery according to still another embodiment of the present invention.

[0026] Figure 5 is a schematic cross-sectional view of a secondary battery according to still another embodiment of the present invention.

[0027] Figure 6 is a manufacturing apparatus for a copper foil according to still another embodiment of the present invention.

[0028] Figure 7 is a schematic diagram showing the circulation process of the electrolyte solution of the present invention.

[0029] Description of Reference Numerals

[0030] 100: Electrode for secondary battery

[0031] 110, 110a, 110b: Copper foil

[0032] 111: Copper film

[0033] 112: Protective layer

[0034] 120: Active material layer

[0035] 10: Electrolytic cell

[0036] 20: Electrolyte Detailed Description of the Invention

[0037] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying 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.

[0038] 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, if it is judged that the detailed description of related well-known technologies may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

[0039] When using expressions such as "comprising", "having", "consisting 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. Also, when interpreting a constituent element, even without other specific explanations, it is interpreted as including an error range.

[0040] 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.

[0041] 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 figure. Spatial relative terms should be understood to include terms in different directions of the 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, the element described as "below" or "beneath" another element can be placed "above" another 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.

[0042] In the case of explaining temporal relationships, for example, when explaining the temporal sequence relationship with terms such as "after", "then", "subsequently", "before", etc., unless the expression "exactly" or "directly" is used, it can also include discontinuous cases.

[0043] 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 idea of the present invention.

[0044] The term "at least one" should be understood to include all combinations that can be prompted 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 prompted by two or more of the first item, the second item, and the third item.

[0045] Each feature of the multiple embodiments of the present invention can be partially or fully combined or combined with each other, and can be technically variously interlocked and driven. Each embodiment can be implemented independently of each other, or can be implemented together in an associated relationship.

[0046] Figure 1 It is a cross-sectional view of the copper foil 110a of an embodiment of the present invention.

[0047] 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 ).

[0048] The copper film 111 may be formed on a rotating cathode drum by electroplating, and may have a smooth surface that is in direct contact with the rotating cathode drum during the electroplating process and a rough surface on the opposite side thereof.

[0049] 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 a finished product including the copper foil 110.

[0050] The copper foil 110 described below may correspond to Figures 1 to 2 the copper foils 110a and 110b.

[0051] According to an embodiment of the present invention, the copper foil 110 may have a first normal temperature thermal expansion coefficient of 10 ppm / °C to 25 ppm / °C and a high temperature thermal expansion coefficient of 20 ppm / °C to 35 ppm / °C.

[0052] At this time, the first normal temperature thermal expansion coefficient refers to the thermal expansion coefficient measured in the MD direction (Machine Direction, longitudinal direction) while the copper foil is heated from 30°C to 330°C at a rate of 5°C / minute using a thermomechanical analyzer (TMA, Thermomechanical analyzer), and the high temperature thermal expansion coefficient refers to the thermal expansion coefficient measured in the MD direction while the copper foil is heated from 30°C to 330°C at a rate of 5°C / minute using a thermomechanical analyzer (TMA) after being heat-treated at 190°C for 60 minutes.

[0053] Specifically, when the first normal temperature thermal expansion coefficient is 10 ppm / °C to 25 ppm / °C and the high temperature thermal expansion coefficient is 20 ppm / °C to 35 ppm / °C, wrinkles or tears are prevented from occurring during the manufacturing process of the copper foil 110.

[0054] On the contrary, when the first normal temperature thermal expansion coefficient is less than 10 ppm / °C, or the high temperature thermal expansion coefficient is less than 20 ppm / °C, the dimensional change due to temperature increase is small, and wrinkles or tears may occur due to the high temperature or high pressure environment during the secondary battery manufacturing process.

[0055] In addition, when the first normal thermal expansion coefficient exceeds 25 ppm / °C or the high-temperature thermal expansion coefficient exceeds 35 ppm / °C, the thermal expansion coefficient is too high, and wrinkles or tears may occur in the copper foil due to the high-temperature or high-pressure environment during the secondary battery manufacturing process.

[0056] According to an embodiment of the present invention, the second normal thermal expansion coefficient may be 10 ppm / °C to 25 ppm / °C.

[0057] At this time, the second normal thermal expansion coefficient refers to the thermal expansion coefficient measured in the TD direction (Transverse Direction) while heating from 30°C to 330°C at a rate of 5°C / minute using a thermomechanical analyzer (TMA).

[0058] Specifically, when the second normal thermal expansion coefficient of the copper foil 110 in an embodiment of the present invention is 10 ppm / °C to 25 ppm / °C, wrinkles or tears occurring during the manufacturing process of the copper foil 110 are prevented.

[0059] On the contrary, when the second normal thermal expansion coefficient is less than 10 ppm / °C, the dimensional change with increasing temperature is small, and wrinkles or tears may occur due to the high-temperature or high-pressure environment during the secondary battery manufacturing process.

[0060] In addition, when the second normal thermal expansion coefficient exceeds 25 ppm / °C, the thermal expansion coefficient is too high, and wrinkles or tears may occur in the copper foil due to the high-temperature or high-pressure environment during the secondary battery manufacturing process.

[0061] In addition, according to an embodiment of the present invention, the high-temperature thermal expansion coefficient may be larger than the first normal thermal expansion coefficient and the second normal thermal expansion coefficient.

[0062] The copper foil 110 in 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 therefore beneficial for increasing the capacity of the secondary battery. However, manufacturing a copper foil 110 with a thickness less than 4 μm results in reduced workability.

[0063] On the contrary, when manufacturing a secondary battery using a copper foil 110 with a thickness exceeding 35 μm, it is difficult to achieve a high capacity due to the relatively thick copper foil 110.

[0064] 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.

[0065] Figure 3 It is a cross-sectional view of the secondary battery electrode 100a according to an embodiment of the present invention.Figure 4 It is a cross-sectional view of the electrode 100b for a secondary battery according to another embodiment of the present invention.

[0066] As Figure 3 shown, 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 in the above-described embodiments of the present invention.

[0067] 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.

[0068] Generally, in a lithium secondary battery, an aluminum foil is used as the positive electrode current collector combined with the positive electrode active material, and the copper foil 110 is used as the negative electrode current collector combined with the negative electrode active material.

[0069] According to an embodiment of the present invention, the secondary battery electrode 100 is a negative electrode, the copper foil 110 serves as a negative electrode current collector, and the active material layer 120 contains a negative electrode active material.

[0070] 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.

[0071] Figure 5 It is a schematic cross-sectional view of a secondary battery according to an embodiment of the present invention.

[0072] Referring to Figure 5 , the secondary battery includes a positive electrode (cathode) 370, a negative electrode (anode) 340, an electrolyte (electrolyte) 350 disposed between the positive electrode 370 and the negative electrode 340 to provide an environment in which ions can move, and a separator (separator) 360 that electrically insulates the positive electrode 370 and the negative electrode 340. Here, the ions moving between the positive electrode 370 and the negative electrode 340 are, for example, lithium ions. The separator 360 separates the positive electrode 370 and the negative electrode 340 to prevent the charge generated in one electrode from moving through the inside of the secondary battery 105 to the other electrode and being wasted uselessly. Referring to Figure 5 , the separator 360 is disposed in the electrolyte 350.

[0073] The positive electrode 370 includes a positive electrode current collector 371 and a positive electrode active material layer 372, and an aluminum foil may be used as the positive electrode current collector 371.

[0074] The negative electrode 340 includes a negative electrode current collector 341 and a negative electrode active material layer 342, and a copper foil 110 can be used as the negative electrode current collector 341.

[0075] According to an embodiment of the present invention, the disclosed copper foil 110 can be used as the negative electrode current collector 341. Additionally, Figures 1 to 2 or Figure 3 or Figure 4 the secondary battery electrodes 100a and 100b shown can be used as Figure 5 the negative electrode 340 of the secondary battery shown.

[0076] 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.

[0077] 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.

[0078] The method of the present invention includes a 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 an electrolytic solution 20 in an electrolytic cell 10.

[0079] 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.

[0080] The step of forming the copper film 111 can be performed as follows: a seed layer is formed by energization between the first anode plate 31 and the rotating cathode drum 40, and then the seed layer is grown by energization between the second anode plate 32 and the rotating cathode drum 40.

[0081] The current densities provided by the first anode plate 31 and the second anode plate 32 respectively may be 30 to 130 ASD.

[0082] When the current densities provided by the first anode plate 31 and the second anode plate 32 respectively are lower than 30 ASD, the surface roughness of the copper foil 110 is low, and thus the adhesion between the copper foil 110 and the active material layer 120 may be insufficient.

[0083] On the contrary, when the current densities provided by the first anode plate 31 and the second anode plate 32 respectively exceed 130 ASD, the surface of the copper foil 110 is rough, and thus the coating of the active material may not be smoothly achieved.

[0084] The surface characteristics of the copper film 111 can vary depending on the surface polishing or grinding degree of the rotary cathode drum 40. For example, a grinding brush with a grit size of #800 to #3000 can be used to grind the surface of the rotary cathode drum 40.

[0085] 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 can 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.

[0086] 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.

[0087] To smoothly form the copper film 111 by electroplating of copper, the copper ion concentration and sulfuric acid concentration in the electrolyte 20 are adjusted to 70 to 150 g / L and 80 to 150 g / L, respectively.

[0088] In an embodiment of the present invention, chlorine (Cl) includes chloride ions (Cl - ) and all chlorine atoms present in the molecule. For example, chlorine (Cl) can be used to remove silver (Ag) ions that flow 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.

[0089] When the concentration of chlorine (Cl) is less than 15 ppm, silver (Ag) ions cannot be smoothly removed. 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.

[0090] According to an embodiment of the present invention, the electrolyte 20 may include collagen and gelatin. Specifically, the electrolyte 20 may include 1 to 15 ppm of collagen and 0.1 to 5 ppm of gelatin.

[0091] The collagen and gelatin of an embodiment of the present invention are added to adjust the thermal expansion coefficient of the copper foil of the present invention. To obtain the physical property of the thermal expansion coefficient of the present invention, the electrolyte 20 needs to include 1 to 15 ppm of collagen and 0.1 to 5 ppm of gelatin.

[0092] More preferably, the collagen and gelatin contained in the electrolyte 20 need to be added at a ratio of 10:1 to 3:1 based on the concentration. 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.

[0093] When the concentration ratio of collagen and gelatin contained in the electrolyte 20 deviates from the above range, if the amount of gelatin with a larger molecular weight increases excessively, there may be a problem of excessive increase in strength, and if the amount of collagen with a smaller molecular weight increases excessively compared to gelatin, there may also be a problem of excessive decrease in strength.

[0094] According to an embodiment of the present invention, the electrolyte 20 may contain an organic additive.

[0095] The organic additive contained in the electrolyte 20 contains at least one of a brightening agent (component A) and a retarder (component B).

[0096] The organic additive may contain more than one of a brightening agent (component A) and a retarder (component B), or may contain both components.

[0097] The brightening agent (component A) contains a sulfonic acid or its metal salt. The brightening agent (component A) may have a concentration of 1 to 15 ppm in the electrolyte 20.

[0098] The brightening agent (component A) increases the charge amount of the electrolyte 20 to increase the copper electrodeposition rate, improves the curl characteristics of the copper foil, and can enhance the gloss of the copper foil 110. If the concentration of the brightening agent (component A) is less than 1 ppm, the gloss of the copper foil 110 decreases, and if it exceeds 15 ppm, there may be problems such as weight change or surface roughness change after impregnating the copper foil 110.

[0099] The brightening agent may include, for example, bis-(3-sulfopropyl)-disulfide disodium salt, 3-mercapto-1-propanesulfonic acid, 3-(N,N-dimethylthiocarbamoyl)-thiopropanesulfonic acid sodium salt, 3-[(amino-iminomethyl)thio]-1-propanesulfonic acid sodium salt, o-ethyl dithiocarbonate-S-(3-sulfopropyl)-ester sodium salt, 3-(benzothiazole-2

[0100] -mercapto)-propyl-sulfonic acid sodium salt, and at least one of ethylene dithiodipropyl sulfonic acid sodium salt.

[0101] 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.

[0102] The retarder (component B) reduces the copper electrodeposition rate, thereby preventing a sharp increase in the roughness and a decrease in the strength of the copper foil 110. This retarder (component B) is also called an inhibitor or a suppressor.

[0103] If the concentration of the retarder (Component B) is less 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, there is almost no change in the physical properties of the copper foil 110 such as appearance, gloss, roughness, strength, and elongation. 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).

[0104] 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.

[0105] When forming the copper film 111, the flow rate of the electrolytic solution 20 supplied into the electrolytic cell 10 can be 41 to 45 m 3 / hour.

[0106] Figure 7 is a schematic diagram showing the circulation process of the electrolytic solution of the present invention.

[0107] According to an embodiment of the present invention, the step of manufacturing the electrolytic solution may include the step of forming a second electrolytic solution using the first electrolytic solution transferred from the storage tank by carbon filtration C / F and the step of forming the electrolytic solution by adding collagen and gelatin to the filtered second electrolytic solution.

[0108] Specifically, the first electrolytic solution transferred from the storage tank may contain copper ions, sulfuric acid, chlorine, organic additives, etc.

[0109] The process of carbon filtering C / F the first electrolytic solution refers to the step of removing organic impurities and inorganic impurities present in the first electrolytic solution.

[0110] According to an embodiment of the present invention, the second electrolytic solution refers to the electrolytic solution obtained by carbon filtering the first electrolytic solution.

[0111] According to an embodiment of the present invention, collagen and gelatin can be added to the second electrolytic solution to form the electrolytic solution. The additives contained in the electrolytic solution 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 prevents the degradation of collagen and gelatin and has the effect of improving the physical properties of the present invention.

[0112] The electrolyte formed by adding collagen and gelatin is contained in the electrolytic cell 10, and a copper foil is manufactured using a foil-making machine including a rotary cathode drum 40 disposed in the electrolytic cell 10 and an anode plate 30 disposed at a distance from the rotary cathode drum 40.

[0113] In addition, for the purity of the electrolyte 20, the copper wire (Cu wire) that is the raw material of the electrolyte 20 can be cleaned.

[0114] According to an embodiment of the present invention, the step of manufacturing the electrolyte 20 may include: a step of heat-treating the copper wire, a step of pickling the heat-treated copper wire, a step of washing the pickled copper wire with water, and a step of putting the washed copper wire into sulfuric acid for the electrolyte.

[0115] 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, 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.

[0116] 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 below 300 ppm. That is, the electrolyte 20 can have a total organic carbon (TOC) concentration of below 300 ppm.

[0117] The copper film 111 thus manufactured can be cleaned in a cleaning tank.

[0118] For example, acid cleaning for removing impurities such as resin components or natural oxide 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.

[0119] Next, a protective layer 112 is formed on the copper film 111.

[0120] Refer to Figure 6 , and 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.

[0121] 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 may be immersed in a potassium dichromate solution of 1 to 10 g / L at room temperature for 1 to 30 seconds.

[0122] 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.

[0123] The copper foil 110 is manufactured by forming such a protective layer 112.

[0124] 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 ); 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.

[0125] 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 as the negative electrode active material carbon, distilled water is used as a solvent to prepare a slurry. Then, the slurry is applied to 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.

[0126] 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.

[0127] Hereinafter, the present invention will be specifically described by way of 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.

[0128] Examples 1-4 and Comparative Examples 1-4

[0129] 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 apart from the rotating cathode 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 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.

[0130] In addition, the concentration of chlorine (Cl) contained in the electrolyte 20 is maintained at 17 ppm, and the concentrations of collagen, gelatin, and the organic additive are as shown in Table 1 below. At this time, after filtering the electrolyte using carbon, collagen and gelatin are added to the filtered electrolyte.

[0131] Among the organic additives, bis-(3-sulfopropyl)-disulfide disodium salt (SPS) is used as a brightening agent (Component A), and polyethylene glycol (PEG) is used as a retarder (Component B). The molecular weights of collagen and gelatin are 3500 and 10000 respectively.

[0132] A current was applied between the rotating cathode drum 40 and the anode plate 30 at a current density of 60 ASD to fabricate the copper film 111. Subsequently, 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 fabricating 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.

[0133] As a result, copper foils of Example 1-4 and Comparative Example 1-4 were fabricated. At this time, the thickness of the fabricated copper foil was 8 μm.

[0134] [Table 1]

[0135]

[0136] [Table 2]

[0137]

[0138] For the copper foils of Example 1-4 and Comparative Example 1-4 fabricated in this way, i) the first room temperature thermal expansion coefficient; ii) the second room temperature thermal expansion coefficient; iii) the high temperature thermal expansion coefficient; and iv) whether curling (Curl) occurs were confirmed.

[0139] The copper foil was cut to obtain a 5 mm × 5 mm sample.

[0140] i) The first room temperature thermal expansion coefficient

[0141] The first room temperature thermal expansion coefficient refers to the thermal expansion coefficient of the copper foil sample measured in the MD direction.

[0142] At this time, the measurement conditions for the thermal expansion coefficient are as follows.

[0143] - Measuring equipment: Thermomechanical analysis device (trade name: Seiko Exstar 6000 (TMA 6100))

[0144] - Start temperature: 30 °C

[0145] - End temperature: 330 °C

[0146] - Heating rate: 5 °C / min

[0147] - Counterweight: 0.05 N

[0148] ii) Second coefficient of thermal expansion at room temperature

[0149] The second coefficient of thermal expansion at room temperature refers to the coefficient of thermal expansion measured in the TD direction of the copper foil sample.

[0150] At this time, except for the measurement direction, the method for measuring the coefficient of thermal expansion is the same as that of the first coefficient of thermal expansion at room temperature.

[0151] iii) Coefficient of thermal expansion at high temperature

[0152] The coefficient of thermal expansion at high temperature refers to the coefficient of thermal expansion measured in the MD direction after heat treatment at 190 °C for 60 minutes.

[0153] Specifically, the sample is heat-treated at 190 °C for 60 minutes, and after cooling the sample, the coefficient of thermal expansion of the sample is measured in the same way as the method for measuring the coefficient of thermal expansion at room temperature. The process of cooling the sample is carried out by placing it at room temperature.

[0154] iv) Whether curling (Curl) occurs

[0155] After 100 charge and discharge cycles, the secondary battery was disassembled to observe whether wrinkles or tears occurred in the copper foil. The occurrence of wrinkles or tears in the copper foil is indicated as "occurred", and the non-occurrence is indicated as "none".

[0156] Referring to Tables 1 to 2, curling (Curl) did not occur in the copper foils of Examples 1 to 4, and curling (Curl) occurred in the copper foils of Comparative Examples 1 to 4.

[0157] The present invention described above is not limited to the foregoing embodiments and drawings, and 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 as including all manners of changes or deformations 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 normal temperature thermal expansion coefficient of 10 ppm / °C to 25 ppm / °C and a high temperature thermal expansion coefficient of 20 ppm / °C to 35 ppm / °C. The first room-temperature thermal expansion coefficient is the thermal expansion coefficient measured along the MD direction, The high temperature thermal expansion coefficient is a thermal expansion coefficient measured along the MD direction after heat treatment at 190° C. for 60 minutes.

2. The copper foil according to claim 1, wherein has a second normal temperature thermal expansion coefficient of 10ppm / ℃ to 25ppm / ℃, The second room-temperature thermal expansion coefficient is a thermal expansion coefficient measured along the TD direction.

3. The copper foil according to claim 2, wherein The high-temperature thermal expansion coefficient is greater than the first room-temperature thermal expansion coefficient and the second room-temperature thermal expansion coefficient.

4. 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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