Copper foil, electrodes containing the same, a secondary battery containing the same, and a method for manufacturing the same.

Abstract

To provide a copper foil excellent in adhesion to an active material thereby capable of ensuring a secondary battery with a high capacity retention rate.SOLUTION: A copper foil is provided which comprises: a copper film containing 99.9 wt.% or more of copper; and a protective layer on the copper film. The copper foil has a room-temperature thermal deformation index ranging from 15 to 50. The room-temperature thermal deformation index is expressed by formula 1: (room-temperature thermal deformation index)=[(room-temperature thermal expansion coefficient) / (ppm / °C)+(room-temperature elongation) / (%)] / (surface area ratio).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a copper foil, an electrode containing the same, a secondary battery containing the same, and a method for manufacturing the same. Specifically, the present invention relates to a copper foil having excellent adhesion to an active material, an electrode containing the same, a secondary battery containing the same, and a method for manufacturing the same.

Background Art

[0002] A secondary battery is a type of energy conversion device that stores electrical energy by converting it into chemical energy and generates electricity by converting the chemical energy back into electrical energy when electricity is needed. It is used not only in portable household appliances such as mobile phones and laptop 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, lithium secondary batteries, and the like.

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

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

[0006] Such secondary batteries include 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 in secondary batteries. As the capacity of secondary batteries increases, the demand for high-capacity, high-efficiency, and high-quality secondary batteries is growing, and there is a need for electrolytic copper foil that can improve the characteristics of secondary batteries. In particular, there is a need for electrolytic copper foil that can increase the capacity of secondary batteries and guarantee stable capacity retention and performance.

[0007] Furthermore, even if a secondary battery has a sufficiently high charge / discharge capacity, if its charge / discharge capacity decreases rapidly as the charge / discharge cycle is repeated (i.e., if the capacity retention rate is low or the lifespan is short), consumers will need to replace the secondary battery frequently, which will result in inconvenience for consumers and waste of resources. [Overview of the project] [Problems that the invention aims to solve]

[0008] Therefore, the present invention relates to copper foil, an electrode containing the same, a secondary battery containing the same, and a method for manufacturing the same, which can prevent problems arising from the limitations and disadvantages of the above-mentioned related technologies.

[0009] Another embodiment of the present invention is to provide a copper foil that has excellent adhesion to the active material and can guarantee a secondary battery with a high capacity retention rate.

[0010] In addition to the embodiments of the present invention mentioned above, other features and advantages of the present invention are described below or can be clearly understood from such description by a person with ordinary skill in the art to which the present invention pertains. [Means for solving the problem]

[0011] One 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, having a room-temperature heat deformation index in the range of 15 to 50. The room-temperature heat deformation index is represented by the following formula 1.

[0012] [Equation 1] Room temperature thermal deformation index = (Coefficient of thermal expansion at room temperature / (ppm / °C) + Elongation at room temperature / (%)) / (Surface area ratio) According to yet another embodiment of the present invention, an electrode for a secondary battery is provided, comprising a copper foil and an active material layer disposed on at least one surface of the copper foil.

[0013] According to yet another embodiment of the present invention, a secondary battery is provided comprising: a cathode that provides lithium ions during charging; an anode that provides electrons and lithium ions during discharge; 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. [Effects of the Invention]

[0014] According to the present invention, it is possible to manufacture a long-life secondary battery that has excellent adhesion to the active material and can maintain a high capacity retention rate for a long period of time. Therefore, it is possible to minimize the inconvenience and waste of resources caused by frequent replacement of secondary batteries for electronic product consumers. [Brief explanation of the drawing]

[0015] [Figure 1] This is a cross-sectional view of copper foil according to one embodiment of the present invention. [Figure 2] This is a cross-sectional view of copper foil according to another embodiment of the present invention. [Figure 3] This is a cross-sectional view of an electrode for a secondary battery according to another embodiment of the present invention. [Figure 4] This is a cross-sectional view of an electrode for a secondary battery according to yet another embodiment of the present invention. [Figure 5] This is a schematic cross-sectional view of a secondary battery according to yet another embodiment of the present invention. [Figure 6] This is a copper foil manufacturing apparatus according to yet another embodiment of the present invention. [Figure 7] This is a schematic diagram showing the electrolyte circulation process according to the present invention. [Modes for carrying out the invention]

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

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

[0018] When terms such as "comprising", "having", "consisting of", etc. are used in this specification, unless the expression "only ~" is used, other parts may be added. When a component is expressed in the singular, it includes a plurality unless otherwise explicitly stated. Also, in the interpretation of components, it is interpreted to include an error range even without separate explicit description.

[0019] In the case of an explanation of a positional relationship, for example, when the positional relationship between both parts is described by "on ~", "above ~", "below ~", "beside ~", etc., unless the expressions "immediately" or "directly" are used, one or more other parts can be located between both parts.

[0020] Spatially relative terms such as "below" or "beneath," "lower," "above," and "upper" can be used to easily describe the correlation between one element or component and another, as illustrated in a drawing. Spatially relative terms should be understood as terms that include not only the directions illustrated in the drawing, but also different directions of elements when in use or operation. For example, if elements illustrated in a drawing are flipped over, an element described as "below" or "beneath" of another element may be placed "above" of that element. Therefore, the exemplary term "below" can include both downward and upward directions. Similarly, the exemplary terms "up" or "above" can include both upward and downward directions.

[0021] When describing temporal relationships, for example, if the temporal sequence is described using phrases such as "after," "following," "next," or "before," it can include cases that are not continuous, unless expressions like "immediately" or "directly" are used.

[0022] While terms such as "first," "second," etc., are used to describe various components, these components are not limited by these terms. These terms are simply used to distinguish one component from another. Therefore, the first component mentioned below may be the second component within the technical concept of the present invention.

[0023] The term "at least one" should be understood to include all possible combinations of one or more related items. For example, "at least one of items 1, 2, and 3" could mean not just each of items 1, 2, or 3 individually, but all possible combinations of items that can be presented from two or more of items 1, 2, and 3.

[0024] The features of each of the various embodiments of the present invention can be partially or entirely combined or combined with one another, enabling a variety of technically diverse interlocking and driving processes. Each embodiment may be implemented independently of the others or together in relation to one another.

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

[0026] Referring to Figure 1, the copper foil 110a of the present invention includes a copper film 111 containing 99.9% by weight or more of copper. Referring to Figure 1, the copper foil 110a of the present invention includes the copper film 111 and a protective layer 112 on the copper film 111. Figure 1 shows a configuration in which the protective layer 112 is arranged on both sides of the copper film 111. However, the embodiment of the present invention is not limited to this, and the protective layer (112) can be arranged on both sides of the copper film (111) (see Figure 2).

[0027] The copper film 111 may be formed on the rotating anode drum through electroplating, and may have a shiny surface that is in direct contact with the rotating anode drum during the electroplating process and a matte surface on the opposite side.

[0028] The protective layer 112 is formed by electrodepositing an anticorrosion material onto the copper film 111. The anticorrosion material may contain 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 its heat resistance, thereby extending the lifespan of the copper foil 110, as well as the lifespan of the final product containing it.

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

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

[0031] [Formula 1] Room temperature thermal deformation index = (Coefficient of thermal expansion at room temperature / (ppm / °C) + Elongation at room temperature / (%)) / (Surface area ratio) The room-temperature thermal expansion coefficient in Equation 1 refers to the thermal expansion coefficient measured using a thermomechanical analyzer (TMA) while increasing the temperature from 30°C to 330°C at a rate of 5°C / min.

[0032] The room-temperature elongation in Equation 1 refers to the elongation measured at room temperature (25±3℃).

[0033] When the copper foil 110 according to one embodiment of the present invention has a room-temperature heat deformation index value in the range of 15 to 50, it is possible to manufacture a secondary battery that has excellent adhesion between the copper foil 110 and the active material and a high capacity retention rate, even when there are changes in the external environment.

[0034] On the other hand, if the room-temperature thermal deformation index of copper foil 110 is less than 15, dimensional changes due to temperature increases may be small compared to a certain surface area ratio, or wrinkles may occur due to low strength. Also, the surface area ratio of the copper foil may be very large compared to a certain thermal expansion coefficient and elongation rate. As a result, the adhesion between the copper foil and the active material may decrease, and it may not have a high capacity retention rate.

[0035] Furthermore, if the room-temperature thermal deformation index of copper foil 110 exceeds 50, the coefficient of thermal expansion or elongation is too high compared to a certain surface area ratio, which can cause wrinkles or tears in the copper foil during the secondary battery manufacturing process due to high temperature or high pressure environments. In addition, the surface area ratio of the copper foil may be very small compared to a certain coefficient of thermal expansion and elongation ratio. As a result, the adhesion between the copper foil and the active material decreases, and it may not have a high capacity retention rate.

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

[0037] [Formula 2] High-temperature thermal deformation index = (High-temperature thermal expansion coefficient / (ppm / °C) + High-temperature elongation rate / (%)) / (Surface area ratio) The high-temperature thermal expansion coefficient in Equation 2 refers to the thermal expansion coefficient measured after heat treatment of copper foil at 190°C for 1 hour, followed by natural cooling at room temperature, and then heating from 30°C to 330°C at a rate of 5°C / min using a thermomechanical analyzer (TMA).

[0038] The high-temperature elongation in Equation 2 refers to the elongation measured after heat treatment at 190°C for 1 hour.

[0039] When the copper foil 110 according to one embodiment of the present invention has a high-temperature heat deformation index value in the range of 20 to 55, it is possible to manufacture a secondary battery that has excellent adhesion between the copper foil 110 and the active material and a high capacity retention rate, even in high-temperature and high-pressure external environments.

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

[0041] Furthermore, if the high-temperature thermal deformation index of copper foil 110 exceeds 55, the coefficient of thermal expansion or elongation is too high compared to a certain surface area ratio, which can cause wrinkles or tears in the copper foil during the secondary battery manufacturing process due to high temperature or high pressure environments. In addition, the surface area ratio of the copper foil may be very small compared to a certain coefficient of thermal expansion and elongation ratio. As a result, the adhesion between the copper foil and the active material decreases, and the battery may not have a high capacity retention rate.

[0042] A copper foil 110 according to one embodiment of the present invention has a thickness of 4 to 35 μm. When the copper foil 110 is used as a current collector for electrodes in a secondary battery, the thinner the copper foil 110, the more current collectors can be accommodated in the same space, which is advantageous for increasing the capacity of the secondary battery. However, manufacturing copper foil 110 with a thickness of less than 4 μm leads to a decrease in workability.

[0043] On the other hand, when manufacturing secondary batteries with copper foil 110 exceeding 35 μm in thickness, achieving high capacity becomes difficult due to the thickness of the copper foil 110.

[0044] The following describes in detail the electrode 100 containing the copper foil 110 of the present invention and the secondary battery containing the electrode 100.

[0045] Figure 3 is a cross-sectional view of electrode 100a for a secondary battery according to one embodiment of the present invention. Figure 4 is a cross-sectional view of electrode 100b for a secondary battery according to another embodiment of the present invention.

[0046] As shown in Figure 3, an electrode 100a for a secondary battery according to one embodiment of the present invention includes one of the copper foils 110 and active material layer 120 from the embodiments of the present invention described above.

[0047] Figure 3 shows a configuration in which the active material layer 120 is formed on one surface of the copper foil 110. However, the present invention is not limited to this, and referring to Figure 4, the active material layer 120 can also be formed on both sides of the copper foil 110.

[0048] In lithium secondary batteries, aluminum foil is commonly used as the positive electrode current collector that bonds with the positive electrode active material, and copper foil 110 is commonly used as the negative electrode current collector that bonds with the negative electrode active material.

[0049] According to one 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.

[0050] To ensure the high capacity of the secondary battery, the active material layer 120 of the present invention can be formed from a carbon-metal composite. 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.

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

[0052] Referring to Figure 5, the secondary battery includes a cathode 370, anode 340, an electrolyte 350 placed between the cathode 370 and anode 340 to provide an environment for ion movement, and a separator 360 that electrically insulates the cathode 370 and anode 340. Here, the ions moving between the cathode 370 and anode 340 are, for example, lithium ions. The separator 360 separates the cathode 370 and anode 340 to prevent the charge generated at one electrode from being wasted by moving to the other electrode through the interior of the secondary battery 105. Referring to Figure 5, the separator 360 is placed within the electrolyte 350.

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

[0054] The negative electrode 340 includes a negative electrode current collector 341 and a negative electrode active material layer 342, and copper foil 110 can be used in the negative electrode current collector 341.

[0055] According to one embodiment of the present invention, the copper foil 110 shown in Figures 1 and 2 can be used as the negative electrode current collector 341. In addition, the secondary battery electrodes 100a and 100b shown in Figure 3 or 4 can be used as the negative electrode 340 of the secondary battery shown in Figure 5.

[0056] The method for manufacturing the copper foil 110 of the present invention will be specifically described below with reference to Figures 6 and 7.

[0057] The method for manufacturing copper foil 110 of the present invention includes the steps of forming a copper film 111 and forming a protective layer 112 on the copper film 111.

[0058] The method of the present invention includes the step of forming a copper film 111 on the rotating negative electrode drum 40 by energizing a positive electrode plate 30 and a rotating negative electrode drum 40 which are arranged spaced apart from each other in an electrolyte 20 within an electrolytic cell 10.

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

[0060] The formation of the copper film 111 can be carried out by forming a seed layer by energizing the first positive electrode plate 31 and the rotating negative electrode drum 40, and then growing the seed layer by energizing the second positive electrode plate 32 and the rotating negative electrode drum 40.

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

[0062] If the current densities provided by the first and second positive electrode plates 31 and 32, respectively, are less than 30 ASD, the adhesion between the copper foil 110 and the active material layer 120 may be insufficient due to the low surface roughness of the copper foil 110.

[0063] On the other hand, if the current densities provided by the first and second positive electrode plates 31 and 32, respectively, exceed 130 ASD, the surface of the copper foil 110 may become rough, making it difficult to coat the active material smoothly.

[0064] The surface properties of the copper film 111 can be varied depending on the degree of surface buffing or polishing of the rotating anode drum 40. For example, the surface of the rotating anode drum 40 can be polished with an abrasive brush having a grit size of #800 to #3000.

[0065] During the formation of the copper film 111, the electrolyte 20 is maintained at a temperature of 40-60°C. More specifically, the temperature of the electrolyte 20 can be maintained at 50°C or higher. In this process, the physical, chemical, and electrical properties of the copper film 111 can be controlled by adjusting the composition of the electrolyte 20.

[0066] According to one embodiment of the present invention, the electrolyte 20 may contain copper ions, sulfuric acid, chlorine (Cl), collagen, gelatin, and organic additives.

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

[0068] In one embodiment of the present invention, chlorine (Cl) is a chloride ion (Cl - This includes all chlorine atoms present in the molecule. Chlorine (Cl) can be used, for example, to remove silver (Ag) ions that have flowed into the electrolyte 20 during the process of forming the copper film 111. Specifically, chlorine (Cl) can precipitate silver (Ag) ions in the form of silver chloride (AgCl). Such silver chloride (AgCl) can be removed by filtration.

[0069] If the chlorine (Cl) concentration is less than 15 ppm, the removal of silver (Ag) ions will not proceed smoothly. On the other hand, if the chlorine (Cl) concentration exceeds 25 ppm, unwanted reactions may occur due to an excess of chlorine (Cl). Therefore, the chlorine (Cl) concentration in the electrolyte 20 is controlled within the range of 15 to 25 ppm.

[0070] According to one 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.

[0071] Collagen and gelatin according to one embodiment of the present invention are added to adjust the room temperature heat deformation index and high temperature heat deformation index values ​​of the copper foil according to the present invention. In order to obtain the room temperature heat deformation index and high temperature heat deformation index properties according to the present invention, the electrolyte 20 needs to contain 1 to 15 ppm of collagen and 0.1 to 5 ppm of gelatin.

[0072] More preferably, the collagen and gelatin contained in the electrolyte 20 should be added in a concentration ratio of 10:1 to 3:1. In this case, the collagen may have a molecular weight of 2,000 to 10,000, and the gelatin may have a molecular weight of 10,000 to 100,000.

[0073] If the concentration ratio of collagen and gelatin contained in the electrolyte solution 20 is outside the range described above, there is a possibility that the amount of gelatin, which has a large molecular weight, will be excessively high, resulting in a problem of excessively high strength, or that the amount of collagen, which has a small molecular weight, will be excessively high compared to gelatin, resulting in a problem of excessively low strength.

[0074] According to one embodiment of the present invention, the electrolyte 20 may contain organic additives.

[0075] The organic additive contained in the electrolyte 20 includes at least one of a brightener (component A) and a moderator (component B).

[0076] The organic additive may contain one or more of the brightener (component A) and the speed reducer (component B), or it may contain both components.

[0077] The glossing agent (component A) contains sulfonic acid or a metal salt thereof. The glossing agent (component A) can have a concentration of 1 to 15 ppm in the electrolyte 20.

[0078] The brightener (component A) increases the charge of the electrolyte 20, thereby increasing the electrodeposition rate of copper, improving the curl characteristics of the copper foil, and enhancing 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 decreases, and if it exceeds 15 ppm, problems may occur where the weight of the copper foil 110 changes or the surface roughness changes after immersion.

[0079] The glossing agent may include, for example, at least one of the following: 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-sulfonate sodium salt, and ethylenedithiodipropylsulfonic acid sodium salt.

[0080] The moderator (component B) contains a nonionic water-soluble polymer. The moderator (component B) can have a concentration of 0.1 to 15 ppm in the electrolyte 20.

[0081] The moderator (component B) reduces the electrodeposition rate of copper, preventing a rapid increase in the roughness and decrease in strength of the copper foil 110. Such a moderator (component B) is also called an inhibitor or suppressor.

[0082] If the concentration of the moderator (component B) is less than 0.1 ppm, the roughness of the copper foil 110 increases rapidly, which can cause problems with changes in the surface condition of the copper foil 110. On the other hand, even if the concentration of the moderator (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 moderator (component B) can be adjusted within the range of 0.1 to 15 ppm without unnecessarily increasing the concentration of the moderator (component B), thereby increasing manufacturing costs and wasting raw materials.

[0083] The moderator (component B) may include, for example, at least one nonionic water-soluble polymer selected from polyethylene glycol (PEG), polypropylene glycol, polyethylene polypropylene copolymer, polyglycerin, polyethylene glycol dimethyl ether, hydroxyethylene cellulose, polyvinyl alcohol, polyglycol stearate ether, and stearyl alcohol polyglycol ether. However, the type of moderator is not limited thereto, and other nonionic water-soluble polymers that can be used in the manufacture of high-strength copper foil 110 can be used as moderators.

[0084] When the copper film 111 is formed, the flow rate of the electrolyte 20 supplied into the electrolytic cell 10 is 41-45 m / s. 3 It could be / hour

[0085] Figure 7 is a schematic diagram showing the electrolyte circulation process according to the present invention.

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

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

[0088] The process of filtering the first electrolyte using carbon (C / F) refers to the step of removing organic and inorganic impurities present in the first electrolyte.

[0089] According to one embodiment of the present invention, the second electrolyte means the electrolyte obtained by filtering the first electrolyte using carbon.

[0090] According to one embodiment of the present invention, collagen and gelatin can be added to the second electrolyte to form an electrolyte. The additives contained in the electrolyte have been described above, so their explanation is omitted. Specifically, collagen and gelatin are added after the filtration (C / F) step. When collagen and gelatin are added after the filtration (C / F) step, degradation of the collagen and gelatin is prevented, which is effective in improving the physical properties according to the present invention.

[0091] An electrolyte solution formed by adding collagen and gelatin is contained within the electrolytic cell 10, and copper foil is manufactured using a foil-making machine that includes a rotating negative electrode drum 40 located in the electrolytic cell 10 and a positive electrode plate 30 located away from the rotating negative electrode drum 40.

[0092] Furthermore, to ensure the cleanliness of the electrolyte 20, the copper wire (Cu wire) that serves as the raw material for the electrolyte 20 can be washed.

[0093] According to one embodiment of the present invention, the steps for producing the electrolyte 20 may include the steps of heat-treating a copper wire, pickling the heat-treated copper wire, washing the pickled copper wire with water, and immersing the washed copper wire in sulfuric acid for the electrolyte.

[0094] More specifically, in order to maintain the cleanliness of the electrolyte 20, copper for the production of the electrolyte 20 can be produced by sequentially following the steps of: heat-treating high-purity (99.9% or higher) 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 heat-treated copper wire with a 10% sulfuric acid solution for 10 to 20 minutes; and rinsing the pickled copper wire with distilled water. The rinsed copper wire can then be added to sulfuric acid for the electrolyte to produce the electrolyte 20.

[0095] According to one embodiment of the present invention, in order to satisfy the properties of the copper foil 110, the concentration of total organic carbon (TOC) in the electrolyte 20 is controlled to be 300 ppm or less. That is, the electrolyte 20 can have a total organic carbon (TOC) concentration of 300 ppm or less.

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

[0097] For example, acid cleaning can be performed sequentially to remove impurities on the surface of the copper film 111, such as resin components or natural oxide films, followed by water cleaning to remove the acidic solution used in acid cleaning. The cleaning step may be omitted.

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

[0099] Referring to Figure 6, the step may further include immersing the copper film 111 in an anticorrosion solution 60. When the copper film 111 is immersed in the anticorrosion solution 60, it may be guided by a guide roll placed in the anticorrosion solution 60.

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

[0101] Furthermore, the protective layer 112 may contain silane compounds obtained by silane treatment, or nitrogen compounds obtained by nitrogen treatment.

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

[0103] The electrode for a secondary battery (i.e., a negative electrode) of the present invention can be manufactured by coating one or more negative electrode active materials selected from the group consisting of carbon; metal (Me) of Si, Ge, Sn, Li, Zn, Mg, Cd, Ce, Ni, or Fe; alloys containing the metal (Me); oxides (MeOx) of the metal (Me); and composites of the metal (Me) and carbon onto one or both sides of the copper foil 110 of the present invention manufactured by the method described above.

[0104] For example, 100 parts by weight of carbon for the negative electrode active material is mixed with 1 to 3 parts by weight of styrene-butadiene rubber (SBR) and 1 to 3 parts by weight of carboxymethylcellulose (CMC), and then a slurry is prepared using distilled water as a solvent. Next, the slurry is applied to the copper foil 110 to a thickness of 20 to 60 μm using a doctor blade, and heated at 110 to 130°C for 0.5 to 1.5 ton / cm². 2 Press with this pressure.

[0105] A secondary battery can be manufactured using the electrode (negative electrode) for the secondary battery of the present invention, manufactured by the method described above, along with a conventional positive electrode, electrolyte, and separator membrane.

[0106] The present invention will be described in detail below based on examples and comparative examples. However, the following examples are provided solely to aid in understanding the present invention, and the scope of the present invention is not limited to these examples.

[0107] Examples 1-4 and Comparative Examples 1-4 Copper foil was manufactured using a foil-making machine that included an electrolytic cell 10, a rotating negative electrode drum 40 positioned in the electrolytic cell 10, and a positive electrode plate 30 positioned away from the rotating negative electrode drum 40. The electrolyte 20 was a copper sulfate solution. The copper ion concentration in the electrolyte 20 was set to 87 g / L, the sulfuric acid concentration to 110 g / L, the electrolyte temperature to 55°C, and the current density to 60 ASD.

[0108] Furthermore, the concentration of chlorine (Cl) in the electrolyte 20 was maintained at 22 ppm, and the concentrations of collagen, gelatin, and organic additives were as shown in Table 1 below. In this process, the collagen and gelatin were added to the filtered electrolyte after filtering the electrolyte using carbon.

[0109] Among the organic additives, bis-(3-sulfopropyl)-disulfide disodium salt (SPS) is used as a brightening agent (component A), polyethylene glycol (PEG) is used as a moderator (component B), and the molecular weights of collagen and gelatin are 3,500 and 10,000, respectively.

[0110] A copper film 111 was produced by applying a current at a current density of 60 ASD between the rotating negative electrode drum 40 and the positive electrode plate 30. Next, the copper film 111 was immersed in a rust-preventive solution for about 2 seconds to perform chromate treatment on both sides of the copper film 111, thereby forming a protective layer 112 and producing copper foil. A rust-preventive solution mainly composed of chromic acid was used, with a chromic acid concentration of 5 g / L.

[0111] As a result, copper foils for Examples 1-4 and Comparative Examples 1-4 were manufactured. The thickness of the manufactured copper foil was 8 μm.

[0112] [Table 1] [Table 2] [Table 3] [Table 4] For the copper foils of Examples 1-4 and Comparative Examples 1-4 manufactured in this manner, (i) the coefficient of thermal expansion at room temperature, (ii) the coefficient of thermal expansion at high temperature, (iii) the elongation at room temperature, (iv) the elongation at high temperature, (v) the surface area ratio of the first and second surfaces, (vi) the surface area ratio, and (vii) the capacity retention rate were confirmed.

[0113] The copper foil was cut to obtain a 5mm x 5mm sample.

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

[0115] The specific measurement conditions for the coefficient of thermal expansion are as follows:

[0116] - Measurement equipment: Thermomechanical analyzer (Product evaluation: Seiko Exstar 6000 (TMA 6100)) -Starting temperature: 30℃ -End temperature: 330℃ - Heating rate: 5℃ / min -Weight: 0.05N (ii) High temperature thermal expansion coefficient The high-temperature thermal expansion coefficient refers to the thermal expansion coefficient measured after heat treatment at 190°C.

[0117] Specifically, the sample is heat-treated at 190°C for 1 hour, and after the sample has cooled, the thermal expansion coefficient of the sample is measured in the same manner as the method for measuring the thermal expansion coefficient at room temperature. The cooling process of the sample is carried out by leaving it at room temperature.

[0118] (iii) Elongation at room temperature Room temperature elongation refers to the elongation rate measured at room temperature (25±3℃).

[0119] Specifically, the measurement can be performed using a universal tester (UTM) according to the method specified in the IPC-TM-650 Test Method Manual. Instron equipment can be used. In this case, the width of the copper foil sample for elongation measurement is 12.7 mm, the distance between the grips is 50 mm, and the measurement speed is 50 mm / min.

[0120] (iv) High temperature elongation High-temperature elongation refers to the elongation measured after heat treatment at 190°C for 1 hour.

[0121] Specifically, a sample heat-treated at 190°C for 1 hour can be measured using a universal tester (UTM) according to the method specified in the IPC-TM-650 Test Method Manual. Instron equipment can be used. In this case, the width of the sample for elongation measurement is 12.7 mm, the distance between grips is 50 mm, and the measurement speed is 50 mm / min.

[0122] (v) Surface area ratio of face 1 and face 2 The surface area ratio of one and two surfaces was measured using KEYENCE's VK-9710. In this context, the surface area ratio of one and two surfaces refers to the ratio of the three-dimensional surface area of ​​one and two surfaces to the two-dimensional surface area of ​​the two surfaces, respectively. Specifically, copper foil was cut into 1cm x 1cm test pieces, and the copper foil test pieces were observed at 50x magnification using KEYENCE's color 3D laser microscope VK-9710 to observe the three-dimensional surface area. The "surface area ratio of one and two surfaces" is calculated by multiplying the three-dimensional surface area of ​​the copper foil test piece by its two-dimensional planar area (1cm²). 2 This is the value obtained by dividing by ). Here, the three-dimensional surface area is the area obtained by moving the microscope lens in the Z-axis direction and focusing it.

[0123] (vi) Surface area ratio In the embodiments of this invention, the surface area ratio refers to the average value of the surface area ratios of surface 1 and surface 2. Specifically, it refers to the value obtained by adding the surface area ratios of surface 1 and surface 2 and then dividing by 2.

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

[0125] Lithium manganese oxide (Li 1.1 Mn 1.85 Al 0.05 A positive electrode active material was prepared by mixing O4 and orthorhombic lithium manganese oxide (o-LiMnO2) in a weight ratio of 90:10. A slurry was prepared by mixing the positive electrode active material, carbon black, and polyvinylidene fluoride (PVDF) with NMP as an organic solvent in a weight ratio of 85:10:5. The positive electrode was prepared by coating both sides of a 20 μm thick aluminum foil with the slurry and then drying it.

[0126] Furthermore, a basic electrolyte was prepared by dissolving 1 M of LiPF6 as a solute in a non-aqueous organic solvent, which was a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a 1:2 weight ratio. This basic electrolyte was then mixed with 0.5% by weight of succinic anhydride to produce another electrolyte.

[0127] A secondary battery was manufactured using the negative electrode, positive electrode, and electrolyte produced in this manner.

[0128] Next, the capacity per g of the positive electrode was measured for the secondary battery manufactured in this manner at a charging operating voltage of 4.3V and a discharging operating voltage of 3.4V. A charge-discharge experiment was performed 50 times at a charge-discharge rate of 0.2C at 50℃, and the capacity retention rate of the secondary battery was calculated using the following Equation 3.

[0129] [Formula 3] Capacity retention rate (%) = (Discharge capacity at 50th discharge / Discharge capacity at 1st discharge) × 100 Referring to Tables 1 to 4, the copper foils from Examples 1 to 4 met the range of 15 to 50 for room temperature heat deformation index, exhibited excellent adhesion between the copper foil and the active material, and achieved a secondary battery capacity retention rate of 90% or more. However, the copper foils from Comparative Examples 1 to 4 did not meet the range of 15 to 50 for room temperature heat deformation index, exhibited reduced adhesion between the copper foil and the active material, and failed to meet the industry requirement of 90% for secondary battery capacity retention.

[0130] The present invention, as described above, is not limited by the embodiments and accompanying drawings, and it will be apparent to those with ordinary skill in the art to which the present invention pertains that various substitutions, modifications, and alterations are possible within the scope of the technical matters of the present invention. Accordingly, the scope of the present invention is expressed by the claims described below, and it should be understood that all modified or altered forms derived from the meaning, scope, and equivalent concepts of the claims are included within the scope of the present invention. [Explanation of symbols]

[0131] 100 Electrodes for secondary batteries 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% by weight or more of copper; and The protective layer on the copper film is included, It has a room temperature heat deformation index in the range of 27.27 to 37.

28. Copper foil for current collectors of secondary batteries having a high-temperature heat deformation index in the range of 35.46 to 39.76: The aforementioned room-temperature heat deformation index is expressed by the following formula 1: [Formula 1] Room temperature thermal deformation index = (Coefficient of thermal expansion at room temperature / (ppm / °C) + Elongation at room temperature / (%)) / (Surface area ratio) The aforementioned high-temperature heat deformation index is expressed by the following formula 2: [Formula 2] High-temperature thermal deformation index = (High-temperature thermal expansion coefficient / (ppm / °C) + High-temperature elongation rate / (%)) / (Surface area ratio) The aforementioned high-temperature thermal expansion coefficient refers to the thermal expansion coefficient measured after heat treatment at 190°C for 1 hour. The aforementioned high-temperature elongation rate refers to the elongation rate measured after heat treatment at 190°C for 1 hour.

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

Images