Copper foil

Abstract

One embodiment of the present invention provides a copper foil comprising a copper thin film having a matte surface and a glossy surface, and a protective layer disposed on the copper thin film, wherein the copper foil has an indentation creep rate of 2.0 to 6.0%. The indentation creep rate is measured using a nanoindenter.

Description

Technical Field

[0001] This invention relates to a copper foil, an electrode comprising the same, a secondary battery comprising the same, and a method for manufacturing the same. More specifically, this invention relates to a copper foil with improved corrosion resistance, an electrode comprising the same, a secondary battery comprising the same, and a method for manufacturing the same. Prior Technology

[0002] A rechargeable battery is a type of energy conversion device that converts electrical energy into chemical energy, stores the chemical energy, and then converts the chemical energy back into electrical energy to generate electricity when needed. Rechargeable batteries are used as an energy source for portable home appliances such as mobile phones and laptops, as well as electric vehicles. Because rechargeable batteries can be repeatedly charged, they are also called "rechargeable batteries."

[0003] Secondary batteries, which have economic and environmental advantages over disposable primary batteries, include lead-acid batteries, nickel-cadmium secondary batteries, nickel-metal hydride secondary batteries, and lithium secondary batteries.

[0004] In particular, compared to other rechargeable batteries, lithium-ion batteries can store a relatively large amount of energy relative to their size and weight. Therefore, lithium-ion batteries are ideal for information and communication devices that emphasize portability and mobility, and their applications are also expanding to energy storage devices for hybrid and electric vehicles.

[0005] Lithium-ion batteries are reused by performing a charging and discharging cycle. When any device operates using a fully charged lithium-ion battery, the battery must have a high charge / discharge capacity to increase the device's operating time. Therefore, continuous research is needed to meet the growing consumer demand for higher charge / discharge capacity in lithium-ion batteries.

[0006] In particular, to increase the capacity of lithium-ion batteries, composite active materials with Si or Sn added to carbon active materials have been proposed as anode active materials. However, these composite active materials have a relatively large coefficient of thermal expansion compared to traditional anode active materials. The rapid contraction and expansion of the composite active material caused by the charging and discharging of lithium-ion batteries promotes the separation of the electrolytic copper foil from the anode active material, thereby reducing the charge and discharge capacity retention rate of the lithium-ion battery. Furthermore, when electrolytic copper foil is coated with the anode active material and then dried at high temperature, the surface of the electrolytic copper foil is oxidized, further promoting the separation of the anode active material. The weaker the adhesion between the copper foil and the anode active material, the more severe the reduction in the charge and discharge capacity retention rate of the lithium-ion battery.

[0007] When the charging / discharging capacity of a secondary battery decreases rapidly with repeated charging / discharging cycles (i.e., the secondary battery has a low capacity retention rate or a short lifespan), consumers will need to replace the secondary battery frequently, which will cause inconvenience to consumers and waste resources. Summary of the Invention

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

[0009] According to one embodiment of the present invention, a copper foil with improved adhesion to active materials and an indentation creep rate of 2.0 to 6.0% is provided.

[0010] According to another embodiment of the present invention, a copper foil with excellent charge / discharge characteristics and an indentation creep rate of 2.0 to 6.0% is provided.

[0011] According to another embodiment of the present invention, an electrode for a secondary battery comprising the copper foil is provided, and a secondary battery comprising the electrode for a secondary battery is provided.

[0012] According to yet another embodiment of the present invention, a method for manufacturing a copper foil with improved adhesion to active materials is provided.

[0013] In addition to the various aspects of the present invention described above, other features and advantages of the present invention will be clearly understood from the following description or from the description by those skilled in the art to which the present invention pertains.

[0014] One embodiment of the present invention provides a copper foil comprising a copper thin film having a matte surface and a glossy surface, and a protective layer disposed on the copper thin film, wherein the indentation creep rate of the copper foil is 2.0 to 6.0%. The indentation creep rate is measured using a nano-indenter. Simple Explanation of the Diagram

[0015] The accompanying drawings are incorporated herein to provide a further understanding of the invention and are incorporated in and constitute a part of this application. They illustrate various embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings:

[0016] Figure 1 is a cross-sectional view of a copper foil according to an embodiment of the present invention;

[0017] Figure 2 is a cross-sectional view of a copper foil according to another embodiment of the present invention;

[0018] Figure 3 is a cross-sectional view of an electrode for a secondary battery according to another embodiment of the present invention;

[0019] Figure 4 is a cross-sectional view of an electrode for a secondary battery according to yet another embodiment of the present invention;

[0020] Figure 5 is a cross-sectional schematic diagram of a secondary battery according to yet another embodiment of the present invention;

[0021] Figure 6 illustrates an apparatus for manufacturing copper foil according to yet another embodiment of the present invention; and

[0022] Figure 7 is a diagram illustrating the pressing depth and the path of load change over time when a load is applied to the pressure head to press the copper foil during the process of measuring the physical properties of the copper foil according to the present invention. Implementation

[0023] Hereinafter, several embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, it should be understood that these embodiments described below are for illustrative purposes only to facilitate a clear understanding of the invention and are not intended to limit the scope of the invention.

[0024] The shapes, dimensions, proportions, angles, quantities, etc., disclosed in the drawings to illustrate these embodiments of the invention are illustrative, and therefore the invention is not limited to the details shown in the drawings. Throughout the specification, the same elements may be represented by the same element symbols. In describing the invention, detailed descriptions of related known technologies will be omitted where they are deemed likely to unnecessarily obscure the gist of the invention.

[0025] When using terms such as "comprising," "having," and "consisting of" as used in this specification, additional parts may be added unless the term "only" is used herein. When an element is represented in the singular, it may include the plural form unless otherwise specified. In interpreting elements, even if not explicitly stated, it is interpreted as including a range of tolerances.

[0026] When describing positional relationships, for example, when the positional relationship between two parts is described as "on," "above," "below," "beside," etc., one or more other parts may be located between the two parts unless "immediately" or "directly" is used.

[0027] Spatial relative terms such as "below," "under," "lower part," "above," and "upper part" may be used herein to describe the relationship between one part or element and another part or element as shown in the diagram. It should be understood that, in addition to the orientation shown in the diagram, spatial relative terms are intended to also encompass different orientations of the parts in use or operation. For example, when the parts in the diagram are flipped, a part described as "above" or "upper part" relative to another part will become "below" or "lower part" relative to that other element. Therefore, the exemplary term "below" can encompass both "above" and "below" orientations. Similarly, the exemplary terms "above" or "upper part" can encompass both "above" and "below" orientations.

[0028] When describing temporal relationships, for example, when the temporal relationship is described as "after", "following", "next", "before", etc., non-continuous cases may also be included unless "immediately" or "directly" is used.

[0029] In describing various elements, terms such as "first" and "second" are used, but these elements are not limited to these terms. These terms are only used to distinguish one element from another. Therefore, within the technical spirit of the present invention, the first element described below can also be a second element.

[0030] 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 the first, second, and third items" can mean not only each of the first, second, and third items, but also all combinations of two or more possible items of the first, second, and third items.

[0031] The various features of the various embodiments of the present invention may be partially or wholly coupled or combined with each other, and may be connected and driven in various technical ways. Each of these embodiments of the present invention may be implemented independently of each other, or may be implemented together in a related relationship.

[0032] Figure 1 is a cross-sectional view of copper foil 110a according to an embodiment of the present invention.

[0033] Referring to FIG1, the copper foil 110a of the present invention comprises a copper film 111 containing 99.9% by weight or more copper. Referring to FIG1, the copper foil 110a of the present invention comprises a copper film 111 and a protective layer 112 disposed on the copper film 111. FIG1 illustrates the protective layer 112 disposed on one surface of the copper film 111. An embodiment of the present invention is not limited thereto, and the protective layer 112 may be disposed on both surfaces of the copper film 111 (see FIG2).

[0034] The copper thin film 111 can be formed on the rotating cathode drum by electroplating, and can have a bright surface that is in direct contact with the rotating cathode drum during the electroplating process and a matte surface opposite to the bright surface.

[0035] A protective layer 112 can be formed by electrodepositing an anti-corrosion material onto a copper thin film 111. The anti-corrosion 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 thin film 111 and improves heat resistance, thereby extending the service life of the copper foil 110 itself and the service life of the final product containing the copper foil 110.

[0036] The copper foil 110 described below may correspond to copper foils 110a and 110b according to Figures 1 and 2.

[0037] According to one embodiment of the present invention, the copper foil 110 may have an indentation creep rate (CIT) of 2.0 to 6.0%. Specifically, when the indentation creep rate (CIT) of the copper foil 110 is 2.0 to 6.0%, the copper foil 110 can exhibit stability under external pressure and excellent adhesion to active materials. For example, when the copper foil 110 is coated with an active material, the copper foil 110 can exhibit high stability under the load applied during the coating of the active material.

[0038] When the indentation creep rate (CIT) exceeds 6.0%, the copper foil 110 may deform excessively when external force is applied, potentially reducing its mechanical stability. Furthermore, repeated physical changes occur during the charging and discharging processes of lithium-ion batteries. In this case, when the indentation creep rate (CIT) of the copper foil exceeds 6.0%, the adhesion to the active material may decrease. Additionally, because the copper foil is prone to deformation over time, there is a risk that the portions bonded to the active material may easily peel off.

[0039] Furthermore, when the indentation creep rate (CIT) of copper foil is less than 2.0%, the copper foil may have difficulty elastically deforming under external pressure. For example, since copper foil with an indentation creep rate (CIT) of less than 2.0% hardly deforms, it is highly likely that fine cracks or peeling will occur in the copper foil when continuous pressure or impact is applied. This can lead to mechanical defects in the copper foil during long-term use. Moreover, copper foil with an indentation creep rate (CIT) of less than 2.0% may lack sufficient flexibility, resulting in poor bonding strength when coated with active materials.

[0040] According to the present invention, the indentation creep rate (CIT) is measured using a nano indenter.

[0041] According to the present invention, the indentation creep rate (CIT) is measured under the following conditions:

[0042] - Temperature: 23 ± 2℃

[0043] - Humidity: 45 ± 5% RH

[0044] Manufacturer: Helmut Fischer

[0045] Model Name: HM 2000

[0046] - Load: 8 mN

[0047] - Load ramp-up time: 10 seconds

[0048] - Uninstallation time increased by 10 seconds

[0049] - Creep Time: 3 seconds

[0050] - Indenter type: Vickers indenter (correction factor: 0.75)

[0051] The indentation creep rate (CIT) according to the present invention refers to the proportion of additional indentation depth after the maximum load is reached, when the load is maintained for a set time (creep time: 3 seconds), as shown in Figure 7.

[0052] According to one embodiment of the present invention, the copper foil 110 may have an elastic modulus (nIT) of 25 to 50%. Specifically, when the elastic modulus (nIT) of the copper foil 110 is 25 to 50%, the copper foil 110 can exhibit stability under external pressure and excellent adhesion to active materials. For example, when the copper foil 110 is coated with an active material, the copper foil 110 can exhibit high stability under the load applied during the coating of the active material.

[0053] When the elastic modulus (nIT) of the copper foil is less than 25%, the copper foil 110 may easily deform when external force is applied, which may lead to a decrease in the mechanical stability of the copper foil. Furthermore, repeated physical changes occur during the charging and discharging processes of lithium-ion batteries. In this case, when the elastic modulus (nIT) of the copper foil is less than 25%, the adhesion to the active material may decrease. Moreover, because the copper foil is prone to deformation over time, there is a risk that the parts bonded to the active material may easily peel off.

[0054] Furthermore, when the elastic modulus (nIT) of the copper foil is greater than 50%, the copper foil may have difficulty elastically deforming under external pressure. For example, since copper foil with an elastic modulus (nIT) exceeding 50% hardly deforms, fine cracks or peeling are highly likely to occur in the copper foil under sustained pressure or impact. This can lead to mechanical defects in the copper foil during long-term use. Additionally, copper foil with an elastic modulus (nIT) exceeding 50% may lack sufficient flexibility, resulting in poor bonding strength when coated with active materials.

[0055] According to the present invention, the elastic modulus (nIT) is measured by a nanoindenter.

[0056] According to the present invention, the modulus of elasticity (nIT) can be measured under the same measurement conditions as the indentation creep rate (CIT).

[0057] According to the invention, the modulus of elasticity (nIT) can be defined as the percentage of the work done when the pressure head is removed relative to the sum of the work done during the press-release phase and the work done when the pressure head is removed, as shown in the graph of Figure 7.

[0058] According to one embodiment of the present invention, the copper foil 110 has a thickness of 3 to 35 μm. When the copper foil 110 is used as a current collector in an electrode of a secondary battery, the thinner the copper foil 110, the more current collectors can be accommodated in the same space, which is beneficial to increasing the capacity of the secondary battery. However, manufacturing a copper foil 110 with a thickness of less than 3 μm will result in reduced processability.

[0059] On the other hand, when a secondary battery is manufactured using a copper foil 110 with a thickness of more than 35 μm, it is difficult to achieve a high capacity due to the thick copper foil 110.

[0060] The present invention will now be described in detail as follows: an electrode 100 comprising a copper foil 110 and a secondary battery comprising the electrode 100.

[0061] Figure 3 is a cross-sectional view of an electrode 100a for a secondary battery according to an embodiment of the present invention. Figure 4 is a cross-sectional view of an electrode 100b for a secondary battery according to another embodiment of the present invention.

[0062] As shown in FIG3, an electrode 100a for a secondary battery according to an embodiment of the present invention comprises a copper foil 110 and an active material layer 120 according to any of the above embodiments of the present invention.

[0063] Figure 3 illustrates a configuration in which the active material layer 120 is formed on one surface of the copper foil 110, but this is not a limitation of one embodiment of the invention. Referring to Figure 4, the active material layer 120 may be formed on both surfaces of the copper foil 110.

[0064] In lithium secondary batteries, aluminum foil is generally used as a cathode current collector combined with the cathode active material, and copper foil 110 is generally used as an anode current collector combined with the anode active material.

[0065] According to one embodiment of the present invention, the electrode 100 for the secondary battery is the anode, and the copper foil 110 is used as the anode current collector. In this case, the active material layer 120 comprises an anode active material.

[0066] To ensure high capacity of the secondary battery, the active material layer 120 of the present invention may be formed of a composite of carbon and metal. For example, the metal may include at least one of Si, Ge, Sn, Li, Zn, Mg, Cd, Ce, Ni and Fe, preferably Si and / or Sn.

[0067] Figure 5 is a cross-sectional schematic diagram of a secondary battery according to an embodiment of the present invention.

[0068] 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 where ions can move, and a separator 360 for electrically insulating the anode 340 and the cathode 370. Here, the ions moving between the cathode 370 and the anode 340 are, for example, lithium ions. The separator 360 separates the cathode 370 and the anode 340 to prevent the charge generated at one electrode from unnecessarily being consumed by moving through the interior of the secondary battery 105 to the other electrode. Referring to Figure 5, the separator 360 is disposed within the electrolyte 350.

[0069] The cathode 370 includes a cathode current collector 371 and a cathode active material layer 372. Here, aluminum foil can be used as the cathode current collector 371.

[0070] The anode 340 includes an anode current collector 341 and an anode active material layer 342. Here, copper foil 110 can be used as the anode current collector 341.

[0071] According to an embodiment of the present invention, the copper foil 110 shown in FIG. 1 and FIG. 2 can be used as the anode current collector 341. Furthermore, the electrode 100a or electrode 100b shown in FIG. 3 or FIG. 4 for the secondary battery can be used as the anode 340 of the secondary battery shown in FIG. 5.

[0072] Hereinafter, the method for manufacturing the copper foil 110 of the present invention will be described in detail with reference to FIG6.

[0073] The method for manufacturing copper foil 110 of the present invention includes: forming a copper thin film 111, and forming a protective layer 112 on the copper thin film 111.

[0074] The method of the present invention comprises: forming a copper thin film 111 on a rotating cathode drum 40 by conducting current between an anode plate 30 and a rotating cathode drum 40, wherein the anode plate 30 and the rotating cathode drum 40 are separated from each other in an electrolyte 20 in an electrolytic cell 10.

[0075] As shown 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.

[0076] The step of forming a copper thin film 111 can be performed by conducting current between the first anode plate 31 and the rotating cathode drum 40 to form a seed layer, and then by conducting current between the second anode plate 32 and the rotating cathode drum 40 to grow the seed layer.

[0077] The current density provided by each of the first anode plate 31 and the second anode plate 32 can be 40 to 130 ASD (A / dm2).

[0078] When the current density provided by each of the first anode plate 31 and the second anode plate 32 is less than 40 ASD, the adhesion strength 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.

[0079] On the other hand, when the current density provided by each of the first anode plate 31 and the second anode plate 32 is greater than 130 ASD, the coating of active material may not be performed smoothly due to the rough surface of the copper foil 110.

[0080] The surface properties of the copper thin film 111 can vary depending on the degree of buffing or polishing of the surface of the rotating cathode drum 40. For example, the surface of the rotating cathode drum 40 can be polished using a polishing brush with a grit size of #800 to #3000.

[0081] During the formation of the copper thin film 111, the electrolyte 20 is maintained at a temperature between 40°C and 65°C. More specifically, the temperature of the electrolyte 20 can be maintained above 45°C. At this time, the physical, chemical, and electrical properties of the copper thin film 111 can be controlled by adjusting the composition of the electrolyte 20.

[0082] According to one embodiment of the present invention, electrolyte 20 may contain copper ions, sulfuric acid, chlorine and organic additives.

[0083] In order to promote the formation of copper thin film 111 through copper electrodeposition, the concentrations of copper ions and sulfuric acid in electrolyte 20 were adjusted to 70 g / L to 150 g / L and 80 g / L to 130 g / L, respectively.

[0084] According to one embodiment of the present invention, chlorine (Cl) comprises both chloride ions (Cl-) and chlorine atoms present in the molecule. For example, chlorine (Cl) can be used to remove silver (Ag) ions introduced into the electrolyte 20 during the process of forming the copper thin film 111. Specifically, chlorine (Cl) can cause silver (Ag) ions to precipitate as silver chloride (AgCl). This silver chloride (AgCl) can be removed by filtration.

[0085] When the concentration of chlorine (Cl) is less than 15 ppm, the removal of silver (Ag) ions cannot be performed smoothly. On the other hand, when the concentration of chlorine (Cl) is greater than 25 ppm, excessive chlorine (Cl) may cause unnecessary reactions. Therefore, the concentration of chlorine (Cl) in electrolyte 20 is controlled within the range of 15 ppm to 25 ppm.

[0086] According to one embodiment of the present invention, the electrolyte 20 may contain organic additives.

[0087] The organic additives contained in electrolyte 20 include brightener (component A), modifier (component B) and roughness modifier (component C).

[0088] Brightener (component A) contains sulfonic acid or its metal salt. Brightener (component A) may have a concentration of 1 ppm to 15 ppm in electrolyte 20.

[0089] The brightener (component A) increases the amount of charge in electrolyte 20, thereby increasing the copper deposition rate, improving the curling properties of the copper foil, and enhancing the gloss of the copper foil 110. When the concentration of brightener (component A) is less than 1 ppm, the gloss of the copper foil 110 deteriorates. On the other hand, when the concentration of brightener (component A) is greater than 15 ppm, the weight or surface roughness of the copper foil 110 may change after immersion.

[0090] For example, brighteners may contain 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, and o-ethyldithiocarbonato-S-(3-sulfopropyl)-ester sodium salt. Sodium salt of 3-(benzothiazolyl-2-mercapto)-propyl-sulfonic acid and sodium salt of ethylenedithiodipropylsulfonic acid.

[0091] The moderating agent (component B) comprises a nonionic water-soluble polymer. The moderating agent (component B) may be present in electrolyte 20 at a concentration of 0.1 ppm to 15 ppm.

[0092] The moderating agent (component B) reduces the copper deposition rate to prevent a rapid increase in the roughness and a decrease in the strength of the copper foil 110. This moderating agent (component B) is also known as an inhibitor or suppressor.

[0093] When the concentration of the modifier (component B) is less than 0.1 ppm, the roughness of the copper foil 110 may increase rapidly, and changes in the surface condition of the copper foil 110 may occur. On the other hand, even when the concentration of the modifier (component B) is greater than 15 ppm, the physical properties of the copper foil 110, such as appearance, gloss, roughness, strength, and elongation, remain almost unchanged. Therefore, the concentration of the modifier (component B) can be adjusted to a range of 0.1 ppm to 15 ppm without unnecessarily increasing the concentration of the modifier (component B), thereby increasing manufacturing costs and wasting raw materials.

[0094] For example, the modifier (component B) may contain at least one nonionic water-soluble polymer selected from polyethylene glycol (PEG), polypropylene glycol, polyethylene-polypropylene copolymer, glycerol, polyethylene glycol dimethyl ether, hydroxyvinyl cellulose, polyvinyl alcohol, polyethylene glycol stearate, and polyethylene glycol stearate. However, the type of modifier is not limited thereto, and other nonionic water-soluble polymers that can be used to manufacture high-strength copper foil 110 may be used as modifiers.

[0095] The roughness modifier (component C) contains a nitrogen-containing heterocyclic quaternary ammonium salt or its derivative.

[0096] The roughness modifier (component C) improves the gloss and flatness of the copper foil 110. The roughness modifier (component C) may be present in the electrolyte 20 at a concentration of 1 to 15 ppm.

[0097] When the concentration of the roughness modifier (component C) is less than 1 ppm, the improvement effect on the gloss and flatness of the copper foil 110 is not apparent. On the other hand, when the concentration of the roughness modifier (component C) is greater than 15 ppm, the surface gloss of the copper foil 110 may become uneven and the surface roughness of the copper foil 110 may increase rapidly.

[0098] The roughness modifier (component C) may contain a compound represented by any of the following chemical formulas 1 to 5.

[0099] [Chemical Formula 1]

[0100] [Chemical Formula 2]

[0101] [Chemical Formula 3]

[0102] [Chemical Formula 4]

[0103] [Chemical Formula 5]

[0104] In chemical formulas 1 to 5, ℓ1 to ℓ4, m1 to m4 and n1 to n5 each represent repeating units and are integers greater than or equal to 1, and their equality can be the same or different from each other.

[0105] According to one embodiment of the invention, each of the compounds represented by chemical formulas 1 to 5 has a number average molecular weight of 500 to 12,000.

[0106] When the average molecular weight of the compounds represented by chemical formulas 1 to 5 used as roughness modifiers is less than 500, the proportion of monomers may increase, thereby increasing the surface roughness of copper foil 110. When the content of roughness modifier is low, the surface roughness of copper film 111 may increase, which leads to deterioration of gloss and flatness.

[0107] When the average molecular weight of the compounds represented by chemical formulas 1 to 5 is greater than 12,000, the surface roughness deviation of the copper foil 110 increases. In this case, even if the concentration of other additives is adjusted, it is still difficult to suppress the increase in the surface roughness deviation of the copper foil 110.

[0108] Compounds represented by chemical formulas 1 to 5 can be manufactured, for example, by polymerization or copolymerization using diallyl dimethyl ammonium chloride (DDAC).

[0109] Compounds represented by chemical formula 1 include, for example, PAS-2451 (Mw: 30,000, Nittobo Corporation).

[0110] Compounds represented by chemical formula 2 include, for example, PAS-84 (Mw: 20,000, Nittobo Corporation).

[0111] Compounds represented by chemical formula 3 include, for example, PAS-2351 (Mw: 25,000, Nittobo Corporation).

[0112] Compounds represented by chemical formula 4 include, for example, PAS-A-1 (Mw: 5,000, Nittobo Corporation) and PAS-A-5 (Mw: 4,000, Nittobo Corporation).

[0113] Compounds represented by chemical formula 5 include, for example, PAS-J-81 (Mw: 180,000, Nittobo Corporation).

[0114] When the copper thin film 111 is formed, the flow rate of the electrolyte 20 supplied to the electrolytic cell 10 can be 41 to 45 m3 / hour.

[0115] According to one embodiment of the present invention, before forming a copper thin film 111 on the rotating cathode drum 40 by immersing the rotating cathode drum 40 in the electrolyte 20 prepared as described above, the surface of the rotating cathode drum 40 may be rinsed or washed with a cleaning agent.

[0116] According to the present invention, the cleaning agent is an aqueous solution comprising 8% (w / w) to 12% (w / w) sulfuric acid and 0.1% (w / w) to 0.3% (w / w) brightener (component A). In this case, the brightener (component A) may comprise any of the various types of brightener (component A) described above.

[0117] According to the present invention, when the surface of the rotating cathode drum 40 is rinsed with a cleaning agent, the sulfuric acid in the cleaning agent reacts with the oxides present on the surface of the rotating cathode drum 40 to effectively dissolve or remove the oxides.

[0118] Furthermore, titanium (Ti) may be present on the surface of the rotating cathode drum 40 after the oxide has been removed. When the titanium (Ti) present on the surface of the rotating cathode drum 40 is exposed to air, an oxide film can form on the surface of the rotating cathode drum 40. Since such a titanium oxide film is insulating, it may impede the flow of current, which may make it difficult to achieve a uniform current distribution during the electroplating process. Moreover, as the titanium oxide film thickens, the surface of the rotating cathode drum 40 becomes irregular, which may make it impossible to maintain the required thickness and flatness during the electroplating process.

[0119] At this point, the brightener (component A) in the cleaning agent can coat the surface of the rotating cathode drum 40 before the titanium (Ti) present on the surface of the rotating cathode drum 40 is exposed to air. Therefore, the formation of a titanium oxide film on the surface of the rotating cathode drum 40 can be prevented.

[0120] That is, if the surface of the rotating cathode drum 40 is not rinsed or washed with a cleaning agent before immersing the rotating cathode drum 40 in the electrolyte 20 to form a copper film 111 on the rotating cathode drum 40, the surface of the manufactured copper foil may be irregular and more defects may exist in the copper foil. Therefore, the copper foil may have an indentation creep rate outside the range of 2.0 to 6.0%.

[0121] Therefore, in order to make the copper foil 110 have an indentation creep rate in the range of 2.0 to 6.0%, the surface of the rotating cathode drum 40 must be rinsed or washed with a cleaning agent before immersing the rotating cathode drum 40 in the electrolyte 20 to form a copper film 111 on the rotating cathode drum 40.

[0122] According to the present invention, in order to enable the copper foil 110 to have an indentation creep rate in the range of 2.0 to 6.0%, the brightener (component A) in the cleaning agent needs to be maintained in the concentration range of 0.1% (w / w) to 0.3% (w / w).

[0123] When the concentration of brightener (component A) in the cleaning agent is less than 0.1% (w / w), the pretreatment effect on the rotating cathode drum 40 may be insufficient due to the insufficient amount of brightener (component A) in the cleaning agent. Therefore, the copper foil may have an indentation creep rate falling outside the range of 2.0% to 6.0%.

[0124] Furthermore, when the concentration of brightener (component A) in the cleaning agent exceeds 0.3% (w / w), brightener (component A) may be excessively adsorbed onto the rotating cathode drum 40. When brightener (component A) is excessively adsorbed onto the rotating cathode drum 40 as described above, it occupies the space that other organic additives would otherwise be adsorbed onto the rotating cathode drum 40. Therefore, the chance of other organic additives being adsorbed onto the rotating cathode drum 40 is reduced. A proper adsorption balance between organic additives must be maintained to obtain the physical properties of the copper foil 110 according to the present invention. In this case, when brightener (component A) is excessively adsorbed onto the rotating cathode drum 40, this balance may be disrupted. That is, the gloss of the copper foil may be improved, but the moderating agent (component B) and roughness modifier (component C) that improve the surface properties of the copper foil may not be sufficiently adsorbed onto the rotating cathode drum 40, which may lead to problems such as deterioration of the surface properties of the copper foil. Therefore, there may be more defects in the copper foil, and the copper foil may have an indentation creep rate that falls outside the range of 2.0 to 6.0%.

[0125] According to the present invention, in order to enable the copper foil 110 to have an indentation creep rate in the range of 2.0 to 6.0%, the sulfuric acid in the cleaning agent needs to be maintained in the concentration range of 8% (w / w) to 12% (w / w).

[0126] When the concentration of sulfuric acid in the cleaning agent is less than 8% (w / w), the sulfuric acid may not be sufficiently effective in reacting with the oxides present on the surface of the rotating cathode drum 40 to dissolve or remove the oxides. Therefore, the surface of the manufactured copper foil may be irregular, and more defects may be present in the copper foil. Consequently, the copper foil may have an indentation creep rate falling outside the range of 2.0% to 6.0%.

[0127] Furthermore, when the concentration of sulfuric acid in the cleaning agent exceeds 12% (w / w), sulfuric acid may be present at a high concentration on the surface of the rotating cathode drum 40, thereby excessively increasing the current density, which may make it difficult to obtain copper foil with the desired quality. In addition, when the concentration of sulfuric acid in the cleaning agent is excessive, uneven defects may appear on the surface of the copper foil, which may make it difficult to obtain the physical properties of the copper foil 110 according to the invention. Therefore, the surface of the manufactured copper foil may be irregular, and more defects may exist in the copper foil. Consequently, the copper foil may have an indentation creep rate falling outside the range of 2.0 to 6.0%.

[0128] According to the present invention, even when the surface of the rotating cathode drum 40 is rinsed with a cleaning agent, the brightener (component A) in the electrolyte 20 may still have a concentration of 1 to 15 ppm, and the sulfuric acid may still have a concentration of 70 to 150 g / L.

[0129] To ensure the cleanliness of electrolyte 20, the copper wire (Cu wire) used as the raw material for electrolyte 20 can be cleaned.

[0130] According to one embodiment of the present invention, the preparation of electrolyte 20 may include: heat-treating copper wire, cleaning the heat-treated copper wire with acid, cleaning the acid-cleaned copper wire with water, and immersing the water-cleaned copper wire in sulfuric acid for use as electrolyte.

[0131] More specifically, to maintain the purity of electrolyte 20, high-purity (99.9% or higher) copper wire is heat-treated in an electric furnace at 750°C to 850°C to burn off various organic impurities on the copper wire. Next, the heat-treated copper wire is cleaned with a 10% sulfuric acid solution for 10 to 20 minutes, and then cleaned with distilled water. Through these sequential processes, copper for manufacturing electrolyte 20 can be prepared. The water-cleaned copper wire can be mixed with sulfuric acid used for the electrolyte to prepare electrolyte 20.

[0132] The copper film 111 manufactured in this manner can be cleaned in a cleaning tank.

[0133] For example, acid cleaning can be performed sequentially to remove impurities (such as resin components or natural oxides) from the surface of the copper film 111, followed by water cleaning to remove the acid solution used in the acid cleaning. The cleaning process can be omitted.

[0134] Next, a protective layer 112 is formed on the copper thin film 111.

[0135] Referring to Figure 6, the method of the present invention may further include immersing the copper film 111 in the anti-corrosion solution 60 of the anti-corrosion treatment tank 50. When the copper film 111 is immersed in the anti-corrosion solution 60, the copper film 111 may be guided by the guide roller 70 disposed in the anti-corrosion solution 60.

[0136] As described above, the anti-corrosion solution 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.

[0137] Meanwhile, the protective layer 112 may contain silane compounds treated with silane, and may also contain nitrogen compounds treated with nitrogen.

[0138] Copper foil 110 is formed by forming such a protective layer 112.

[0139] An electrode (i.e., an anode) for a secondary battery of the present invention can be manufactured by coating one or more anode active materials selected from the group consisting of carbon, Si, Ge, Sn, Li, Zn, Mg, Cd, Ce, Ni or Fe, alloys containing metal (Me), oxides of metal (Me) (MeOx), and complexes of metal (Me) and carbon onto one or two surfaces of the copper foil 110 of the present invention manufactured by the method described above.

[0140] For example, 1 to 3 parts by weight of styrene-butadiene rubber (SBR) and 1 to 3 parts by weight of carboxymethyl cellulose (CMC) are mixed with 100 parts by weight of carbon for use as an anode active material, and then distilled water as a solvent is added to the mixture to prepare a slurry. Subsequently, the slurry is coated onto copper foil 110 with a thickness of 20 to 60 μm using a doctor blade, and pressed at 110 to 130°C with a pressure of 0.5 to 1.5 tons per square centimeter (ton / cm2).

[0141] The secondary battery can be manufactured using the electrode (anode) of the secondary battery used in this invention, which is manufactured by the method described above, together with a conventional cathode, electrolyte, and separator.

[0142] The present invention will now be described in detail with reference to examples and comparative examples. However, it should be understood that the examples described below are provided only to aid in understanding the invention and are not intended to limit the scope of the invention.

[0143] [Example] [1] [To Example] [4]

[0144] Copper foil is manufactured using an electroplating machine comprising an electrolytic cell 10, a rotating cathode drum 40 disposed within the electrolytic cell 10, and an anode plate 30 disposed spaced apart from the rotating cathode drum 40. The electrolyte 20 is a copper sulfate solution. The concentration of copper ions in the electrolyte 20 is set to 87 g / L, the concentration of sulfuric acid is set to 110 g / L, the temperature of the electrolyte is set to 55°C, and the current density is set to 60 ASD.

[0145] Furthermore, the concentration of chlorine (Cl) contained in electrolyte 20 was maintained at 20 ppm, and the concentrations of organic additives are shown in Table 1 below.

[0146] In the organic additives, disodium bis-(3-sulfopropyl)-disulfide (SPS) is used as a brightener (component A), polyethylene glycol (PEG) is used as a modifier (component B), and trimethylethylammonium ethyl sulfide maleic acid copolymer (PAS-2451TM, Nittobo Corporation, Mw.:30,000) is used as a roughness modifier (component C).

[0147] Before immersing the rotating cathode drum 40 in the electrolyte 20, the surface of the rotating cathode drum 40 is washed with a cleaning agent. An aqueous solution containing sulfuric acid and a brightener (component A) is used as the cleaning agent. Disodium bis-(3-sulfopropyl)-disulfide (SPS) is used as the brightener (component A) in the cleaning agent. The concentrations of sulfuric acid and brightener (component A) in the cleaning agent are shown in Table 1 below.

[0148] A copper thin film 111 is manufactured by applying a current with a current density of 60 ASD between a rotating cathode drum 40 and an anode plate 30. Next, the copper thin film 111 is immersed in an anti-corrosion solution for approximately 2 seconds, and a chromate treatment is performed on both surfaces of the copper thin film 111 to form a protective layer 112, thereby manufacturing a copper foil. An anti-corrosion solution containing chromic acid as the main component is used as the anti-corrosion solution, and the concentration of chromic acid is 5 g / L.

[0149] Therefore, copper foils of Examples 1 to 4 were manufactured. At this time, the thickness of the manufactured copper foil was 8 μm.

[0150] [Comparative Example] [1] [and comparative examples] [2]

[0151] The concentrations of organic additives, whether the drum is washed, and the concentration of polish in the detergent are shown in Table 1 below.

[0152] The copper foils of Comparative Examples 1 and 2 were manufactured in the same manner as those of Examples 1 to 4. The thickness of the manufactured copper foil was 8 μm.

[0153] [Comparative Example] [3] [and comparative examples] [4]

[0154] The concentration of organic additives and whether the drum needs to be washed are shown in Table 1 below.

[0155] The copper foil was manufactured in the same manner as in Examples 1 to 4, except that the surface of the rotating cathode drum 40 was rinsed with a cleaning agent before immersing the rotating cathode drum 40 in the electrolyte 20 to form a copper film 111 on the rotating cathode drum 40. At this time, the thickness of the manufactured copper foil was 8 μm.

[0156] [Table 1] SPS (ppm) PEG (ppm) PAS-2451 (ppm) Should the drum be washed? Sulfuric acid in cleaning agents (%) Polishing agent (%) Example 1 10 10 13 O 8 0.15 Example 2 11 6 8 O 10 0.2 Example 3 12 6 8 O 11 0.3 Example 4 10 4 3 O 12 0.1 Comparative Example 1 10 0 0.1 O 5 0.01 Comparative Example 2 11 6 5 O 15 0.5 Comparative Example 3 12 6 5 X - - Comparative Example 4 10 16 17 X - -

[0157] [Table 2] category Indentation creep rate (CIT) (%) Modulus of elasticity (%) Peel strength (N / mm2) Capacity retention rate (%) Example 1 2.51 46.2 26.1 93 Example 2 2.18 27.3 24.5 94 Example 3 2.73 34.7 25.4 95 Example 4 2.04 43.2 24.4 95 Comparative Example 1 6.92 22.1 11.9 89 Comparative Example 2 6.05 55.3 11.5 88 Comparative Example 3 1.52 23.7 10.4 87 Comparative Example 4 1.79 51.5 12.2 88

[0158] The following were verified for the copper foils of Examples 1 to 4 and Comparative Examples 1 to 4 manufactured as described above: i) indentation creep rate (CIT), ii) elastic modulus, iii) peel strength and iv) capacity retention.

[0159] A sample measuring 10 cm × 10 cm was obtained by cutting copper foil.

[0160] [i] [)Indentation creep rate () [C, IT , ] [)]

[0161] Indentation creep rate (CIT) was measured using a nano-indenter. Specific measurement conditions are as follows.

[0162] - Temperature: 23 ± 2℃

[0163] - Humidity: 45 ± 5% RH

[0164] Manufacturer: Helmut Fischer

[0165] Model Name: HM 2000

[0166] - Load: 8 mN

[0167] - Load ramp-up time: 10 seconds

[0168] - Uninstallation time increased by 10 seconds

[0169] - Creep time: 3 seconds

[0170] - Indenter type: Vickers indenter (correction factor: 0.75)

[0171] [ii] [) Modulus of elasticity () [nIT] [)]

[0172] The modulus of elasticity (nIT) was measured using a nano-indenter. The specific measurement conditions are as follows.

[0173] - Temperature: 23 ± 2℃

[0174] - Humidity: 45 ± 5% RH

[0175] Manufacturer: Helmut Fischer

[0176] Model Name: HM 2000

[0177] - Load: 8 mN

[0178] - Load ramp-up time: 10 seconds

[0179] - Uninstallation time increased by 10 seconds

[0180] - Creep time: 3 seconds

[0181] - Indenter type: Vickers indenter (correction factor: 0.75)

[0182] [iii] Peel strength

[0183] Two parts by weight of styrene-butadiene rubber (SBR) and two parts by weight of carboxymethyl cellulose (CMC) were mixed with 100 parts by weight of commercially available carbon to serve as the anode active material. Subsequently, distilled water was added to the mixture as a solvent to prepare a slurry. The slurry was applied to the surface of an electrolytic copper foil (width: 10 cm) to a thickness of approximately 60 μm using a doctor blade, dried at 120°C for 10 minutes, and then pressed (pressure: 1 ton / cm²) to manufacture the anode.

[0184] After attaching double-sided tape to the active material attachment surface of the anode sample (width: 12.7 mm), the copper foil was peeled off at a 90° angle using a Universal Material Testing Machine (UTM) according to IPC-TM-650 standard (measurement speed: 50 mm / min) to measure the peel strength between the copper foil and the active material.

[0185] [iv] [) Capacity retention rate

[0186] Two parts by weight of styrene-butadiene rubber (SBR) and two parts by weight of carboxymethyl cellulose (CMC) were mixed with 100 parts by weight of commercially available carbon to serve as the anode active material. Subsequently, distilled water was added to the mixture as a solvent to prepare a slurry. The slurry was applied to the surface of an electrolytic copper foil (width: 10 cm) to a thickness of approximately 60 μm using a doctor blade, dried at 120°C for 10 minutes, and then pressed (pressure: 1 ton / cm²) to manufacture the anode.

[0187] A cathode active material was prepared by mixing lithium manganese oxide (Li1.1Mn1.85Al0.05O4) and lithium manganese oxide with an orthorhombic crystal structure (o-LiMnO2) at a weight ratio of 90:10. A slurry was prepared by mixing the cathode active material, carbon black, and polyvinylidene fluoride (PVDF) in NMP as an organic solvent at a weight ratio of 85:10:5. The slurry was coated onto both surfaces of an aluminum foil with a thickness of 20 μm and then dried to fabricate the cathode.

[0188] Furthermore, a basic electrolyte was prepared by dissolving 1 M LiPF6 as a solute in a non-aqueous organic solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) mixed in a 1:2 weight ratio. Subsequently, 99.5% by weight of the basic electrolyte was mixed with 0.5% by weight of succinic anhydride to prepare the electrolyte.

[0189] A secondary battery is manufactured using the cathode, anode, and electrolyte produced as described above.

[0190] Next, the capacitance per gram (g) of the cathode of the secondary battery manufactured as described above was measured at a charging operating voltage of 4.3 V and a discharging operating voltage of 3.4 V, and a total of 50 charge / discharge cycles were performed at 50°C with a charge / discharge rate of 0.2C. Then, the capacity retention rate of the secondary battery was calculated according to Equation 1 below.

[0191] [Equation 1]

[0192] Capacity retention rate (%) = (Discharge capacity at the 50th discharge / Discharge capacity at the 1st discharge) × 100

[0193] Referring to Tables 1 and 2, the indentation creep rate in the copper foil according to Examples 1 to 4 is within the range of 2.0% to 6.0%, resulting in a capacity retention rate of over 90% for the secondary battery. However, the indentation creep rate in the copper foil according to Comparative Examples 1 to 4 is not within the range of 2.0% to 6.0%, resulting in a peel strength between the copper foil and the active material that is too low, even failing to reach 13 N / mm². Therefore, the capacity retention rate of the secondary battery does not meet the industry-required 90% capacity retention rate.

[0194] According to an embodiment of the present invention, the copper foil can have an indentation creep rate of 2.0 to 6.0%, thereby improving adhesion to active materials.

[0195] According to an embodiment of the present invention, the copper foil can have an indentation creep rate of 2.0 to 6.0%, and therefore has excellent charge / discharge characteristics.

[0196] It will be apparent to those skilled in the art that the present invention is not limited to the embodiments and accompanying drawings described above, and that various substitutions, modifications, and variations can be made to the invention without departing from its spirit and scope. Therefore, the scope of the invention is defined by the appended claims, and all variations and modifications derived from the meaning, scope, and equivalent concepts of the claims are intended to fall within the scope of the invention.

[0197] 10: Electrolytic cell 20: Electrolytes 30: Anode plate 31: First anode plate 32: Second anode plate 40: Rotating cathode drum 50: Anti-corrosion treatment tank 60: Anti-corrosion solution 70: Guide roller 100a: Electrode 100b: Electrode 110: Copper foil 110a: Copper foil 110b: Copper foil 111: Copper Thin Film 112: Protective layer 120: Active material layer 340: Anode 341: Anode current collector 342: Anode active material layer 350: Electrolyte 360: Isolation membrane 370: Cathode 371: Cathode current collector 372: Cathode active material layer

Claims

1. A copper foil comprising: a copper film having a matte surface and a glossy surface; and a protective layer disposed on the copper film, wherein the copper foil has an indentation creep rate of 2.0 to 6.0%, and the indentation creep rate is measured using a nanoindenter under conditions including a load of 8 mN, a load increase time of 10 seconds, an unload increase time of 10 seconds, and a creep time of 3 seconds.

2. The copper foil as claimed in claim 1, having an elastic modulus of 25 to 50%, wherein the elastic modulus is measured using the nanoindenter and defined as the percentage of work done during unloading relative to the sum of work done during loading and work done during unloading.

3. The copper foil as claimed in claim 1, wherein the protective layer comprises at least one of a chromium compound, a silane compound, and a nitrogen compound.

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