KR102446550B1 - Copper foil for high capacity secondary battery, electrode comprisng the same, secondary battery comprising the same and method for manufacturing the same - Google Patents

Abstract

An embodiment of the present invention includes a copper layer having a matte surface and a shiny surface and a rust preventive film disposed on the copper layer, and has a first surface in the matte surface direction and a second surface in the shiny surface direction, The hardness of the first surface is 1.5 to 1.8 GPa, the difference in hardness between the first surface and the second surface is 0.2 GPa or less, and the tensile strength at room temperature (25±15° C.) is 40 to 65 kgf/mm ² and, Provided is a copper foil having a high-temperature tensile strength of 36 to 58 kgf/mm ² measured after heat treatment at 190° C. for 1 hour.

Description

Copper foil for high capacity secondary battery, electrode including same, secondary battery including same, and manufacturing method thereof

The present invention relates to a copper foil that can be used for manufacturing a high-capacity secondary battery, an electrode including the same, a secondary battery including the same, and a manufacturing method thereof.

A secondary battery is a type of energy conversion device that converts and stores electrical energy into chemical energy, and then converts chemical energy back into electrical energy when electricity is needed to generate electricity. The secondary battery is also referred to as a rechargeable battery in that it can be recharged. Among secondary batteries, a lithium secondary battery has a high operating voltage, high energy density, and excellent lifespan characteristics, and is currently widely used.

A secondary battery includes a negative electrode current collector made of copper foil. Among the copper foils, an electrolytic copper foil is widely used as a negative electrode current collector of a secondary battery. The electrolytic copper foil used as the negative electrode current collector typically has a tensile strength of about 30 to 40 kgf/mm ² . Recently, for the manufacture of a high-capacity lithium secondary battery, a metal-based or composite-based active material having high capacity characteristics has been attracting attention. However, the metal-based or composite-based active material has severe volume expansion during charging and discharging. Therefore, only when the copper foil can cope with the volume expansion of the active material, the copper foil is not torn even when the active material expands in volume, and the active material is prevented from being detached from the copper foil.

In order to cope with the volume expansion of the active material, the copper foil should have high strength properties. In addition, in order to cope with the high temperature drying conditions during the coating process of the active material, it is necessary to maintain the tensile strength of the copper foil at high strength during and after heat treatment.

For example, in order to manufacture a high-strength copper foil having a tensile strength of 40 kgf/mm ² or more, an electroplating method using a sulfuric acid-based electrolyte to which a multi-component additive or a thiourea-based organic additive is added may be used. have. However, when the tensile strength of the copper foil is increased, the stress inside the copper foil is increased and the frequency of occurrence of curl in the copper foil is increased. When the copper foil is curved, in the manufacturing process of the electrode for secondary battery by the Roll to Roll (RTR) process, a problem occurs in the mobility (or runability) of the copper foil, and wrinkles occur in the copper foil or Defects such as tearing of the copper foil may occur. Therefore, it is necessary to select an appropriate additive.

When the tensile strength of the copper foil increases, the hardness of the copper foil also increases. However, in the case of using a multi-component additive, the strength and hardness of the copper foil do not necessarily increase proportionally due to the influence of various additives constituting the electrolyte. In addition, when the difference in hardness between the matte surface direction and the shiny surface direction of the copper layer is large, there is a problem that wrinkles or curls are generated in the copper foil in the roll-to-roll process for coating the active material.

Recently, a very thin copper foil having a thickness of 10 μm or less has been used to manufacture electrodes of secondary batteries in order to increase the capacity of secondary batteries. A very thin copper foil has poor handling properties, so when a battery maker uses copper foil to manufacture electrodes for secondary batteries, workability problems may occur. When handling or workability is severely deteriorated in the electrode manufacturing process for secondary batteries, it may be impossible to manufacture an electrode using copper foil and assemble the secondary battery itself.

Therefore, it is necessary to develop a high-strength copper foil capable of improving handling properties and workability in the manufacturing process of electrodes and secondary batteries using copper foil.

In one embodiment of the present invention, high tensile strength is maintained even through a manufacturing process of a secondary battery subjected to a thermal history, so that handling is excellent, and it is possible to increase the amount of metal-based active material used, thereby increasing the capacity of the secondary battery. would like to provide

In addition, an embodiment of the present invention is to control the crystal structure of the copper foil so that the tensile strength of the high-strength copper foil can be maintained high even after heat treatment. To this end, in one embodiment of the present invention, a specific organic additive is applied in the manufacturing process of the copper foil to prepare a copper foil including crystalline having a denser particle size than that of a conventional electrodeposited copper foil.

In addition, an embodiment of the present invention is to control the strength and hardness of the copper foil and to minimize the occurrence of curvature in the copper foil by adjusting the hardness difference range between the two sides to a predetermined range.

An embodiment of the present invention is to provide a copper foil having these characteristics, an electrode including the same, a secondary battery including the same, and a method of manufacturing the copper foil.

In addition to the aspects of the present invention mentioned above, other features and advantages of the present invention will be described below or will be clearly understood by those skilled in the art from such description.

To this end, in one embodiment of the present invention, a multi-component additive is used, the concentration of each additive is controlled, the range of hardness difference between both sides of the copper foil is adjusted to a predetermined range, and the tensile strength of the copper foil is maintained at high strength at room temperature and high temperature. and to form dense crystalline particles in the crystal structure of the copper foil.

Specifically, an embodiment of the present invention includes a copper layer having a matte surface and a shiny surface and a rust preventive film disposed on the copper layer, a first surface in the mat surface direction and a second surface in the shiny surface direction has a hardness of 1.5 to 1.8 GPa of the first surface, a difference in hardness between the first surface and the second surface of 0.2 GPa or less, and a tensile strength of 40 to 65 kgf/mm at room temperature (25±15° C.) ² , and the high-temperature tensile strength measured after heat treatment at 190° C. for 1 hour is 36 to 58 kgf/mm ² It provides a copper foil.

The copper layer has crystalline particles, and after heat treatment at room temperature and 190° C. for 1 hour before the heat treatment, the crystalline particles have an average particle size of 0.8 to 1.7 μm.

The copper foil has an elongation of 2% or more.

The copper foil has a thickness of 4 to 35㎛.

The copper foil has a maximum curvature height of 20 mm or less.

The rust preventive film includes at least one of chromium, a silane compound, and a nitrogen compound.

Another embodiment of the present invention provides an electrode for a secondary battery including the copper foil and an active material layer disposed on at least one surface of the copper foil.

Another embodiment of the present invention is a positive electrode (cathode), a negative electrode (anode) disposed opposite to the positive electrode (electrolyte) disposed between the positive electrode and the negative electrode to provide an environment in which lithium ions can move and and a separator for electrically insulating the positive electrode and the negative electrode, wherein the negative electrode includes the copper foil and an active material layer disposed on the copper foil.

Another embodiment of the present invention, between the electrode plate and the rotating drum disposed to be spaced apart from each other in the electrolyte containing copper ions, by applying a current at a current density of 30 to 80 ASD (A/dm ² ) to the copper layer wherein the electrolyte comprises 60 to 120 g/L of copper ions, 80 to 150 g/L of sulfuric acid, less than 50 ppm of chlorine (Cl) and an organic additive, wherein the organic additive comprises: It contains a brightening agent (component A), a moderator (component B) and a leveling agent (component C), the brightening agent (component A) contains sulfonic acid or a metal salt thereof, and the moderator (component B) is a nonionic water-soluble polymer Including, the leveling agent (component C) provides a method for producing a copper foil, including a heterocyclic compound having at least one of nitrogen (N) and sulfur (S).

In the step of forming the copper layer, the temperature of the electrolyte is maintained in the range of 40 to 60 ℃.

The brightening agent (component A) has a concentration of 5 to 100 ppm.

The brightening agent (component A) is bis-(3-sulfopropyl)-disulfide disodium salt [bis-(3-Sulfopropyl)-disulfide disodium salt] (SPS), 3-mercapto-1-propanesulfonic acid (MPS) , 3-(N,N-dimethylthiocarbamoyl)-thiopropanesulfonate sodium salt, 3-[(amino-iminomethyl)thio]-1-propanesulfonate sodium salt, o-ethyldithiocarbonate- At least one selected from S-(3-sulfopropyl)-ester sodium salt, 3-(benzothiazolyl-2-mercapto)-propyl-sulfonic acid sodium salt and ethylenedithiodipropylsulfonic acid sodium salt include

The moderator (component B) has a concentration of 5 to 50 ppm.

The moderator (component B) is polyethylene glycol (PEG), polypropylene glycol (PPG), polyethylene polypropylene copolymer, polyglycerin, polyethylene glycol dimethyl ether, hydroxyethylene cellulose, polyvinyl alcohol, polyglycol stearate and at least one nonionic water-soluble polymer selected from ethers and stearyl alcohol polyglycol ethers.

The nonionic water-soluble polymer has a number average molecular weight of 500 to 25,000.

The leveling agent (component C) has a concentration of 1 to 20 ppm.

The leveling agent (component C) is 3-(benzotriazole-2-mercapto)-propylsulfonic acid, 2-mercaptopyridine (2MP), 3(5-mercapto-1H-tetrazole)benzenesulfonate , 2-mercaptobenzothiazole, dimethylpyridine, 2,2'-bipyridine, 4,4'-bipyridine, pyrimidine, pyridazine, pyrinoline, oxazole, thiazole, 1-methylimidazole, 1-benzylimidazole, 1-methyl-2methylimidazole, 1-benzyl-2-methylimidazole, 1-ethyl-4-methylimidazole, N-methylpyrrole, N-ethylpyrrole, N -Butylpyrrole, N-methylpyrroline, N-ethylpyrroline, N-butylpyrroline, purine, quinoline, isoquinoline, at least one selected from N-methylcarbazole, N-ethylcarbazole and N-butylcarbazole includes

The method of manufacturing the copper foil further includes forming a rust preventive film on the copper layer.

The above general description of the present invention is only for illustrating or explaining the present invention, and does not limit the scope of the present invention.

According to an embodiment of the present invention, a multi-component additive is used in the manufacturing process of the copper foil, the strength and hardness of the copper foil are controlled by controlling the concentration of each additive, and the range of hardness difference between the two sides of the copper foil is adjusted to an appropriate range. It is possible to minimize the occurrence of warpage, and by making the copper foil have fine and dense crystalline particles at room temperature and high temperature, it is possible to improve the high strength characteristics of the copper foil at room temperature and high temperature.

In addition, when such a copper foil is used for a secondary battery, the handling property of the roll-to-roll process for manufacturing the secondary battery electrode is improved, and the capacity retention rate during charging and discharging of the secondary battery is maximized, thereby improving the lifespan of the secondary battery.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are intended to aid the understanding of the present invention and constitute a part of this specification, illustrate embodiments of the present invention, and together with the description, explain the principles of the present invention.
1 is a schematic cross-sectional view of a copper foil according to an embodiment of the present invention.
2 is a schematic cross-sectional view of a copper foil according to another embodiment of the present invention.
3 is a schematic cross-sectional view of an electrode for a secondary battery according to another embodiment of the present invention.
4 is a schematic cross-sectional view of an electrode for a secondary battery according to another embodiment of the present invention.
5 is a schematic cross-sectional view of a secondary battery according to still another embodiment of the present invention.
6 is a schematic view of a manufacturing process of the copper foil shown in FIG.
7 is a schematic view for explaining the measurement of the curvature (curl) height of the copper foil.
8 is a schematic diagram illustrating a wrinkle generation test.
9a and 9b show cross-sections of the copper foil prepared in Preparation Example 1 before and after heat treatment, respectively.
10A and 10B show cross-sections of the copper foil prepared in Comparative Example 3 before and after heat treatment, respectively.

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

It will be apparent to those skilled in the art that various changes and modifications of the present invention are possible without departing from the spirit and scope of the present invention. Accordingly, the present invention includes all modifications and variations within the scope of the invention as set forth in the claims and their equivalents.

Since the shapes, sizes, proportions, angles, numbers, etc. disclosed in the drawings for explaining the embodiments of the present invention are exemplary, the present invention is not limited by the matters shown in the drawings. Like elements may be referred to by the same reference numerals throughout the specification.

When 'including', 'having', 'consisting', etc. mentioned in this specification are used, other parts may be added unless the expression 'only' is used. When a component is expressed in the singular, the plural is included unless specifically stated otherwise. In addition, in interpreting the components, it is interpreted as including an error range even if there is no separate explicit description.

In the case of a description of the positional relationship, for example, when the positional relationship of two parts is described as 'on', 'on', 'on', 'beside', etc., 'right' Alternatively, unless the expression 'directly' is used, one or more other parts may be positioned between the two parts.

In the case of a description of a temporal relationship, for example, 'immediately' or 'directly' when a temporal relationship is described as 'after', 'following', 'after', 'before', etc. Unless the expression is used, cases that are not continuous may be included.

To describe various elements, expressions such as 'first', 'second', etc. are used, but these elements are not limited by these terms. These terms are only used to distinguish one component from another. Accordingly, the first component mentioned below may be the second component within the spirit of the present invention.

The term 'at least one' should be understood to include all possible combinations of one or more related items.

Each feature of the various embodiments of the present invention may be partially or wholly combined or combined with each other, technically various interlocking and driving are possible, and each of the embodiments may be implemented independently of each other or may be implemented together in a related relationship. may be

1 is a schematic cross-sectional view of a copper foil 100 according to an embodiment of the present invention.

The copper foil 100 according to an embodiment of the present invention includes a copper layer 110 . The copper layer 110 has a matte surface MS and an opposite shiny surface SS.

The copper layer 110 may be formed on the rotating drum 12 through, for example, electroplating (see FIG. 6 ). At this time, the shiny surface (SS) refers to the surface that was in contact with the rotary drum 12 during the electroplating process, the mat surface (MS) refers to the opposite side of the shiny surface (SS).

In general, the shiny surface (SS) has a lower surface roughness than the mat surface (MS). However, one embodiment of the present invention is not limited thereto, and the surface roughness of the shiny surface SS may be the same as or higher than the surface roughness of the mat surface MS. For example, depending on the degree of polishing of the rotary drum 12 (see FIG. 6 ) used for manufacturing the copper layer 110 , the surface roughness of the shiny surface SS may be lower than the surface roughness of the mat surface MS. and may be high. The surface of the rotating drum 12 may be polished by an abrasive brush having a grit of #800 to #3000.

Referring to FIG. 1 , the copper foil 100 includes a rust preventive film 211 disposed on a copper layer 110 . The rust prevention film 211 may be omitted.

The rust prevention film 211 may be disposed on at least one of the mat surface MS and the shiny surface SS of the copper layer 110 . Referring to FIG. 1 , a rust preventive film 211 is disposed on the mat surface MS. However, one embodiment of the present invention is not limited thereto, and the rust preventive film 211 may be disposed only on the shiny surface SS, or may be disposed on both the mat surface MS and the shiny surface SS.

The rust prevention film 211 may protect the copper layer 110 to prevent the copper layer 110 from being oxidized or deteriorated. Therefore, the rust prevention film 211 is also referred to as a protective layer.

According to an embodiment of the present invention, the rust preventive film 211 may include at least one of chromium (Cr), a silane compound, and a nitrogen compound. For example, the rust preventive film 211 may be made of a rust preventive liquid containing chromium (Cr), that is, a rust preventive liquid containing a chromic acid compound.

According to an embodiment of the present invention, the copper foil 100 has a first surface (S1) that is a surface in the mat surface (MS) direction and a second surface that is a surface in the shiny surface (SS) direction with respect to the copper layer 110 . (S2). Referring to FIG. 1 , the first surface S1 of the copper foil 100 is the surface of the rust preventive film 211 , and the second surface S2 is the shiny surface SS. When the rust preventive film 211 is omitted, the mat surface MS of the copper layer 110 becomes the first surface S1 of the copper foil 100 .

According to an embodiment of the present invention, the first surface S1 of the copper foil 100 has a hardness of 1.5 to 1.8 GPa. Here, the hardness is the surface hardness. Surface hardness is the hardness of the surface of an object. In addition, the difference in hardness between the first surface ( S1 ) and the second surface ( S2 ) of the copper foil 100 is 0.2 GPa or less.

According to an embodiment of the present invention, the hardness of the first surface (S1) and the second surface (S2) of the copper foil 100 is to be measured with a nano indenter (Agilent Technologies Nano Indenter G200) according to the standard of ISO 14577. can Measurement conditions can be set as follows.

Surface Approach Velocity (nm/S): 10

Depth Limit(nm): 1000

Strain Rate Target(1/S): 0.05

Frequency Target(Hz): 45

After measuring the hardness 5 times for each surface, the average value may be determined as the hardness of the first surface (S1) and the second surface (S2) of the copper foil 100, respectively.

When the hardness of the first surface S1 of the copper foil 100 is less than 1.5 GPa, the surface of the copper foil 100 is softer than necessary, and warpage may occur in the copper foil 100 . On the other hand, when the hardness of the first surface S1 of the copper foil 100 exceeds 1.8 GPa, the surface of the copper foil 100 is hardened more than necessary, so that the workability of the copper foil 100 is reduced. It may be difficult to adjust the difference in hardness between the first surface S1 and the second surface S2 of the copper foil 100 to a range of 0.2 GPa or less.

When the difference in hardness between the first side (S1) and the second side (S2) of the copper foil 100 exceeds 0.2 GPa, due to the difference in the surface properties of both sides, the Roll to Roll (RTR) process A slip phenomenon may occur during the manufacturing process of the copper foil 100 or the manufacturing process of the electrode for a secondary battery using the copper foil 100 . When such a slip phenomenon occurs, defects such as curvature or tearing of the copper foil 100 may occur. In addition, when the difference in hardness between the first surface S1 and the second surface S2 of the copper foil 100 exceeds 0.2 GPa and the difference in surface properties of both surfaces is large, the active material is evenly distributed on both sides of the copper foil 100 . Since it is not coated, the performance of the secondary battery using the copper foil 100 may be deteriorated.

Meanwhile, the second surface S2 of the copper foil 100 may have a hardness of 1.3 to 2.0 GPa. More specifically, the second surface S2 of the copper foil 100 may have a hardness of 1.5 to 1.8 GPa.

According to an embodiment of the present invention, the copper foil 100 is 40 to 65 kgf / mm ² of room temperature (25±15℃) tensile strength. The tensile strength at room temperature (25±15℃) is called room temperature tensile strength.

In addition, according to an embodiment of the present invention, the high-temperature tensile strength of the copper foil 100, measured after heat treatment at 190° C. for 1 hour, is 36 to 58 kgf/mm ² . Here, the high-temperature tensile strength refers to the tensile strength measured after the copper foil 100 is heat treated at 190° C. for 1 hour. Considering the measurement conditions, etc., the tensile strength measured after heat treatment at a temperature of 190 ± 5 °C for 1 hour ± 5 minutes may be referred to as high temperature tensile strength.

Tensile strength can be measured by universal testing machine (UTM) according to the provisions of the IPC-TM-650 Test Method Manual. According to an embodiment of the present invention, the tensile strength is measured by a universal tester of Instron. The width of the sample for measuring tensile strength was 12.7 mm, the distance between grips was 50 mm, and the measurement speed was 50 mm/min.

When the tensile strength of the copper foil 100 at room temperature (25±15° C.) is less than 40 kgf/mm ² , when the copper foil 100 is used as a current collector of an electrode for a secondary battery, the volume expansion of the active material causes the copper foil 100 fracture may occur. For example, a metal-based active material including tin (Sn) or silicon (Si) has a very large volume expansion during charging and discharging, and the copper foil attached to the active material may be broken due to this large volume expansion. To prevent this, the copper foil 100 according to an embodiment of the present invention has a tensile strength of 40 kgf/mm ² or more. In addition, when the tensile strength of the copper foil 100 is less than 40 kgf / mm ² , the copper foil 100 is bent ( curl) or wrinkles may occur.

When the tensile strength at room temperature (25±15° C.) of the copper foil 100 exceeds 65 kgf/mm ² , the brittleness increases and the manufacturing process of the copper foil 100 or the electrode or secondary battery using the copper foil 100 The copper foil 100 may be broken during the manufacturing process of the battery.

When the high-temperature tensile strength of the copper foil 100 measured after heat treatment at 190° C. for 1 hour is less than 36 kgf/mm ² , softening occurs in the copper foil 100 under harsh process conditions at high temperature, and wrinkles may occur.

On the other hand, when the high-temperature tensile strength after heat treatment exceeds 58 kgf/mm ² , the brittleness of the copper foil 100 increases under severe conditions such as active material coating or high-temperature drying, so that fracture of the copper foil 100 may occur.

According to an embodiment of the present invention, the copper layer 110 of the copper foil 100 has crystallinity and may include crystalline grains (see FIGS. 9A, 9B, 10A, and 10B). Physical and mechanical properties of the copper foil 100 including the copper layer 110 may vary depending on the crystallinity of the copper layer 110 .

In one embodiment of the present invention, the crystalline (crystalline) particle has a polyhedral shape, or even if it does not have a polyhedral shape, an X-ray diffraction phenomenon can be confirmed by a crystal lattice consisting of a periodic arrangement of atoms. includes all particles.

The crystalline particles included in the copper layer 110 have an average particle size of 0.8 to 1.7 μm after heat treatment at room temperature and 190° C. for 1 hour before heat treatment. More specifically, over the cross-section of the copper layer 110 in which the copper layer 110 is cut in the thickness direction, the average particle size of the crystalline particles is 0.8 both before and after heat treatment at 190° C. for 1 hour. to 1.7 μm.

The average particle size of the crystalline particles included in the copper layer 110 may be measured by an Electron Back Scattered Diffraction (EBSD) method. More specifically, before or after heat treatment, after analyzing the first side (S1) and the second side (S2) of the copper foil 100 by the EBSD method, the average particle size of the crystalline particles can be calculated using the analysis result. can For example, an FE-SEM (Field Emission - Scanning Electron Microscope) device (Hitachi, model name: S-4300SE) is equipped with an EBSD (Electron Backscatter Diffraction) detector (eg, EDAX's EBSD camera). Using, it is possible to measure the average particle size of the crystalline (crystalline) particles included in the copper layer 110 by observing the cross section of the copper foil 100 under the measurement conditions of a voltage of 15 kV, a current of 50 mA, and a magnification of 2000 times.

Before and after heat treatment at 190° C. for 1 hour, when the average particle size of the crystalline particles included in the copper layer 110 is 0.8 to 1.7 μm, the copper foil 100 is 40 to 65 kgf/mm ² at room temperature (25±15). ℃) tensile strength and high-temperature tensile strength of 36 to 58 kgf/mm ² .

On the other hand, when the average particle size of the crystalline particles included in the copper layer 110 is less than 0.8 μm or exceeds 1.7 μm, the tensile strength at room temperature (25±15° C.) of the copper foil 100 is 40 to 65 kgf/mm ² , or the high temperature tensile strength may be out of the range of 36 to 58 kgf/mm ² .

When the crystalline particles included in the copper layer 110 are fine and the average particle size thereof is small, the copper foil 100 may have high strength. Regarding the average particle size of the crystalline particles, the nitrogen (N) or sulfur (S) component derived from the organic additive added to the electrolyte is vacant in the crystal grain structure of the copper layer 110, and even after heat treatment, It exhibits a pin effect that prevents the average particle size of the included crystalline particles from increasing. When the average particle size of the crystalline particles contained in the copper layer 110 at room temperature is less than 0.8 μm, the crystalline particles are too fine and the strength of the copper foil 100 is excessively high, thereby increasing the brittleness of the copper foil 100, and accordingly , the possibility of tearing in the copper foil 100 is increased in the foil making process using the rotating cathode drum. On the other hand, when the average particle size of the crystalline particles included in the copper layer 110 exceeds 1.7 μm, it becomes difficult to implement high strength of the copper foil 100 .

According to an embodiment of the present invention, the size of the crystalline particles included in the copper layer 110 may be maintained without significantly increasing even after heat treatment. Accordingly, the copper foil 100 may have excellent tensile strength even after heat treatment.

According to an embodiment of the present invention, the copper foil 100 has an elongation of 2% or more.

Elongation can be measured by universal testing machine (UTM) according to the method specified in IPC-TM-650 Test Method Manual. According to an embodiment of the present invention, Instron's equipment may be used. At this time, the width of the sample for measuring the elongation is 12.7 mm, the distance between the grips is 50 mm, and the measurement speed is 50 mm/min.

If the elongation of the copper foil 100 is less than 2%, when the copper foil 100 is used as a current collector of a secondary battery, the copper foil 100 is not sufficiently stretched and there is a risk of tearing in response to the large volume expansion of the high-capacity active material. (curl) The copper foil 100 may be broken by deformation. On the other hand, if the elongation is excessively large, the copper foil 100 is easily stretched in the electrode manufacturing process for a secondary battery, and thus the electrode may be deformed. Accordingly, the copper foil 100 may have, for example, an elongation of 2 to 20%.

According to an embodiment of the present invention, the copper foil 100 may have a thickness of 4㎛ to 35㎛. When the copper foil 100 is used as a current collector of an electrode for a secondary battery, the thinner the thickness of the copper foil 100 is, the more the current collector can be accommodated in the same space, so it is advantageous to increase the capacity of the secondary battery. However, when the thickness of the copper foil 100 is less than 4 μm, the handling property is deteriorated in the manufacturing process of the electrode for a secondary battery or a secondary battery using the copper foil 100 .

On the other hand, when the thickness of the copper foil 100 exceeds 35 μm, the thickness of the electrode for a secondary battery using the copper foil 100 increases, and due to such a large thickness, it may be difficult to implement a high capacity of the secondary battery.

According to an embodiment of the present invention, the copper foil 100 has a maximum curvature height of 20 mm or less.

The maximum curvature height of the copper foil 100 may be measured by the method shown in FIG. 7 .

Specifically, the copper foil 100 is cut to 60 mm X 60 mm to prepare a copper foil specimen 510, and the specimen 510 is placed on the support 520 so that the first surface S1 faces upward, A glass plate 530 is placed on the specimen 510 . At this time, only the 30 mm length of the cut specimen 510 overlaps the glass plate 530 , and only half of the specimen 510 is set to be positioned between the support 520 and the glass plate 530 , and then the glass plate 530 . ) The height of the exposed specimen 510 is measured and the maximum height is defined as the maximum curvature height of the copper foil 100 (see FIG. 7 ).

When the maximum curvature height of the copper foil 100 exceeds 20 mm, the copper foil 100 is torn or wrinkled during winding of the copper foil 100 or in the manufacturing process of a secondary battery using the copper foil 100 ( defects such as wrinkle) may occur. In addition, when the copper foil 100 is curved, it may be difficult to separate the copper foil 100 from the winder WR after the copper foil 100 is manufactured.

2 is a schematic cross-sectional view of a copper foil 200 according to another embodiment of the present invention. Hereinafter, descriptions of the already described components will be omitted in order to avoid duplication.

Referring to FIG. 2 , a copper foil 200 according to another embodiment of the present invention has a copper layer 110 and two anti-rust surfaces disposed on the mat surface MS and the shiny surface SS of the copper layer 110 , respectively. membranes 211 and 212 . Compared with the copper foil 100 illustrated in FIG. 1 , the copper foil 200 illustrated in FIG. 2 further includes a rust preventive film 212 disposed on the shiny surface SS of the copper layer 110 .

For convenience of description, the rust preventive film 211 disposed on the mat surface MS of the copper layer 110 among the two rust prevention films 211 and 212 is referred to as a first protective layer, and is disposed on the shiny surface SS. The rust-preventive film 212 is also referred to as a second protective layer.

In addition, the copper foil 200 shown in FIG. 2 has a first surface S1 that is a surface in the mat surface MS direction and a second surface that is a surface in the shiny surface SS direction, based on the copper layer 110 . (S2). Here, the first surface S1 of the copper foil 200 is the surface of the anti-rust film 211 disposed on the mat surface MS, and the second surface S2 is the anti-rust film 212 disposed on the shiny surface SS. ) is the surface of

According to another embodiment of the present invention, each of the two anti-rust films 211 and 212 may include at least one of chromium (Cr), a silane compound, and a nitrogen compound.

In the copper foil 200 according to another embodiment of the present invention, the hardness of the first surface (S1) is 1.5 to 1.8 GPa, the difference in hardness between the first surface (S1) and the second surface (S2) is 0.2 GPa or less. Room temperature (25±15° C.) tensile strength of the copper foil 200 is 40 to 65 kgf/mm ² , and the high-temperature tensile strength measured after heat treatment at 190° C. for 1 hour is 36 to 58 kgf/mm ² .

The copper layer 110 of the copper foil 200 has crystalline particles, and after heat treatment at room temperature and 190° C. for 1 hour before heat treatment, the crystalline particles have an average particle size of 0.8 to 1.7 μm.

In addition, the copper foil 200 has an elongation of 2% or more, has a thickness of 4 to 35 μm, and has a maximum curvature height of 20 mm or less.

3 is a schematic cross-sectional view of an electrode 300 for a secondary battery according to another embodiment of the present invention. The electrode 300 for a secondary battery shown in FIG. 3 may be applied to the secondary battery 500 shown in FIG. 5 , for example.

Referring to FIG. 3 , the electrode 300 for a secondary battery according to another embodiment of the present invention includes a copper foil 100 and an active material layer 310 disposed on at least one surface of the copper foil 100 . Here, the copper foil 100 includes a copper layer 110 and a rust preventive film 211 disposed on the copper layer 110 , and is used as a current collector.

Specifically, the copper foil 100 has a first surface S1 and a second surface S2 , and the active material layer 310 is at least one of the first surface S1 and the second surface S2 of the copper foil 100 . placed in one The active material layer 310 may be disposed on the rust prevention film 211 .

3 shows an example in which the copper foil 100 of FIG. 1 is used as a current collector. However, another embodiment of the present invention is not limited thereto, and the copper foil 200 shown in FIG. 2 may be used as a current collector of the electrode 300 for a secondary battery.

In addition, although the structure in which the active material layer 310 is disposed only on the first surface S1 of the copper foil 100 is shown in FIG. 3 , another embodiment of the present invention is not limited thereto. The active material layer 310 may be respectively disposed on both the first surface S1 and the second surface S2 . In addition, the active material layer 310 may be disposed only on the second surface S2 of the copper foil 100 .

The active material layer 310 illustrated in FIG. 3 includes an electrode active material, and in particular, may include an anode active material. That is, the electrode 300 for a secondary battery shown in FIG. 3 may be used as a negative electrode.

The active material layer 310 may include at least one of carbon, a metal, an oxide of a metal, and a composite of a metal and carbon. As the metal, at least one of Ge, Sn, Li, Zn, Mg, Cd, Ce, Ni, and Fe may be used. Also, in order to increase the charge/discharge capacity of the secondary battery, the active material layer 310 may include silicon (Si) or tin (Sn).

As the charging and discharging of the secondary battery is repeated, contraction and expansion of the active material layer 310 alternately occur, which causes separation of the active material layer 310 and the copper foil 100, thereby reducing the charging and discharging efficiency of the secondary battery. In particular, the active material 310 including silicon (Si) or tin (Sn) has a large degree of expansion and contraction.

According to another embodiment of the present invention, since the copper foil 100 used as the current collector can contract and expand in response to the contraction and expansion of the active material layer 310 , the active material layer 310 contracts and expands. Even so, the copper foil 100 is not deformed or torn. Accordingly, separation does not occur between the copper foil 100 and the active material layer 310 . Accordingly, the secondary battery including the electrode 300 for the secondary battery has excellent charge/discharge efficiency and excellent capacity retention.

4 is a schematic cross-sectional view of an electrode 400 for a secondary battery according to another embodiment of the present invention.

The electrode 400 for a secondary battery according to another embodiment of the present invention includes a copper foil 200 and active material layers 310 and 320 disposed on the copper foil 200 . The copper foil 200 includes a copper layer 110 and anti-rust films 211 and 212 disposed on both surfaces of the copper layer 110 .

Specifically, the electrode 400 for a secondary battery shown in FIG. 4 includes two active material layers 310 and 320 respectively disposed on the first surface S1 and the second surface S2 of the copper foil 200 . Here, the active material layer 310 disposed on the first surface S1 of the copper foil 200 is referred to as a first active material layer, and the active material layer 320 disposed on the second surface S2 of the copper foil 200 is formed. Also referred to as the second active material layer.

The two active material layers 310 and 320 may be made of the same material by the same method, or may be made of a different material or a different method.

5 is a schematic cross-sectional view of a secondary battery 500 according to another embodiment of the present invention. The secondary battery 500 illustrated in FIG. 5 is, for example, a lithium secondary battery.

Referring to FIG. 5 , the secondary battery 500 is disposed between a positive electrode 370 , a negative electrode 340 disposed opposite to the positive electrode 370 , and a positive electrode 370 and a negative electrode 340 . It includes an electrolyte 350 that provides an environment in which ions can move, and a separator 360 that electrically insulates the positive electrode 370 and the negative electrode 340 from each other. Here, ions moving between the positive electrode 370 and the negative electrode 340 are, for example, lithium ions. The separator 360 separates the positive electrode 370 and the negative electrode 340 to prevent the charge generated from one electrode from being uselessly consumed by moving to the other electrode through the interior of the secondary battery 500 . Referring to FIG. 5 , the separator 360 is disposed in the electrolyte 350 .

The positive electrode 370 includes a positive electrode current collector 371 and a positive electrode active material layer 372 . An aluminum foil may be used as the positive electrode current collector 371 .

The negative electrode 340 includes a negative electrode current collector 341 and an active material layer 342 . The active material layer 342 of the negative electrode 340 includes an anode active material.

As the negative electrode current collector 341 , the copper foils 100 and 200 shown in FIG. 1 or 2 may be used. In addition, the secondary battery electrodes 300 and 400 shown in FIG. 3 or 4 may be used as the negative electrode 340 of the secondary battery 500 shown in FIG. 5 .

Hereinafter, a method of manufacturing the copper foil 200 according to another embodiment of the present invention will be described in detail with reference to FIG. 6 .

6 is a schematic diagram of a manufacturing process of the copper foil 200 shown in FIG.

In order to manufacture the copper foil 200, an electrolyte 11 containing copper ions is first prepared. The electrolyte 11 is accommodated in the electrolytic cell 10 .

Next, a current is applied at a current density of 30 to 80 ASD (A/dm ² ) between the electrode plate 13 and the rotating drum 12 disposed spaced apart from each other in the electrolyte 11 containing copper ions to form a copper layer (110) is formed. The copper layer 110 is formed by the principle of electroplating. The distance between the electrode plate 13 and the rotating drum 12 may be adjusted in the range of 8 to 13 mm.

Here, the electrode plate 13 may be connected to an anode of a power source (not shown), and the rotating drum 12 may be connected to a cathode of the power source.

When the current density applied between the electrode plate 13 and the rotating drum 12 is less than 30 ASD, the generation of crystalline particles in the copper layer 110 increases, and when it exceeds 80 ASD, the refinement of the crystalline particles is accelerated. The current density can be adjusted above 40 ASD.

The surface characteristics of the shiny surface SS of the copper layer 110 may vary depending on the degree of buffing or polishing of the surface of the rotary drum 12 . In order to adjust the surface properties in the direction of the shiny surface SS, for example, the surface of the rotary drum 12 may be polished with a polishing brush having a grit of #800 to #3000.

In the process of forming the copper layer 110 , the electrolyte 11 is maintained at a temperature of 40 to 60°C. More specifically, the temperature of the electrolyte 11 may be maintained at 50° C. or higher.

According to an embodiment of the present invention, the physical, chemical and electrical properties of the copper layer 110 may be controlled by adjusting the composition of the electrolyte 11 .

According to an embodiment of the present invention, the electrolyte solution 11 contains 60 to 120 g/L of copper ions, 80 to 150 g/L of sulfuric acid, less than 50 ppm of chlorine (Cl) and organic additives.

In order to facilitate the formation of the copper layer 110 by copper electrodeposition, the copper ion concentration and the sulfuric acid concentration in the electrolyte 11 are adjusted to 60 to 120 g/L and 80 to 150 g/L, respectively.

Chlorine (Cl) includes both chlorine ions (Cl-) and chlorine atoms present in the form of chlorides. Chlorine (Cl), for example, may be used to remove silver (Ag) ions introduced into the electrolyte 11 during the formation of the copper layer 110 . Chlorine (Cl) may precipitate silver (Ag) ions in the form of silver chloride (AgCl). This silver chloride (AgCl) can be removed by filtration.

When the concentration of chlorine (Cl) is 50 ppm or more, an unnecessary reaction may occur due to an excess of chlorine (Cl). Accordingly, the chlorine (Cl) concentration in the electrolyte 11 is managed to be less than 50 ppm. More specifically, the concentration of chlorine (Cl) may be managed to 25 ppm or less, for example, may be managed in the range of 5 to 25 ppm.

The electrolyte solution 11 contains an organic additive.

The organic additive contains a brightening agent (component A), a moderator (component B), and a leveling agent (component C).

The brightening agent (component A) contains sulfonic acid or its metal salt. The brightening agent (component A) may increase the charge amount of the electrolyte 11 to increase the copper electrodeposition rate, improve the curvature characteristics of the copper foil, and enhance the gloss of the copper foil 200 .

The brightening agent (component A) may have a concentration of 5 to 100 ppm in the electrolyte 11 .

If the concentration of the brightening agent (component A) is less than 5 ppm, the gloss of the copper foil 200 is reduced, and when it exceeds 100 ppm, the roughness of the copper foil 200 may be increased and the strength may be reduced. More specifically, the brightener (component A) may have a concentration of 5 to 30 ppm in the electrolyte 11 .

The brightening agent (component A) is, for example, bis-(3-sulfopropyl)-disulfide disodium salt [bis-(3-Sulfopropyl)-disulfide disodium salt] (SPS), 3-mercapto-1-propanesulfonic acid (MPS), 3-(N,N-dimethylthiocarbamoyl)-thiopropanesulfonate sodium salt, 3-[(amino-iminomethyl)thio]-1-propanesulfonate sodium salt, o-ethyldithioca Bornato-S-(3-sulfopropyl)-ester sodium salt, 3-(benzothiazolyl-2-mercapto)-propyl-sulfonic acid sodium salt and ethylenedithiodipropylsulfonic acid sodium salt It may include at least one.

The moderator (component B) contains a nonionic water-soluble polymer. The moderator (component B) reduces the electrodeposition rate of copper to prevent a sudden increase in roughness and decrease in strength of the copper foil 200 . These moderators (component B) are also called suppressors or suppressors.

The moderator (component B) may have a concentration of 5 to 50 ppm in the electrolyte 11 .

When the concentration of the moderator (component B) is less than 5 ppm, the roughness of the copper foil 200 is rapidly increased, and a problem in which the strength of the copper foil 200 is lowered may occur. On the other hand, even if the concentration of the moderator (component B) exceeds 50 ppm, there is almost no change in physical properties such as appearance, gloss, roughness, strength, elongation, etc. of the copper foil 200 . Therefore, the concentration of the moderator (component B) can be adjusted in the range of 5 to 50 ppm without needlessly increasing the concentration of the moderator (component B) to increase the manufacturing cost and wasting raw materials.

The moderator (component B) is, for example, polyethylene glycol (PEG), polypropylene glycol (PPG), polyethylene polypropylene copolymer, polyglycerin, polyethylene glycol dimethyl ether, hydroxyethylene cellulose, polyvinyl alcohol, stearate. It may include at least one nonionic water-soluble polymer selected from ric acid polyglycol ether and stearyl alcohol polyglycol ether. However, the type of the moderator is not limited thereto, and other nonionic water-soluble polymers used in the field of manufacturing the high-strength copper foil 200 may be used as the moderator.

The nonionic water-soluble polymer used as the moderator (component B) may have a number average molecular weight of 500 to 25,000. If the number average molecular weight of the moderator (component B) is less than 500, the effect of preventing the increase in roughness and strength reduction of the copper foil 200 by the moderator (component B) is insignificant, and when it exceeds 25,000, the moderator (component B) Formation of the copper layer 110 may not be easy due to the large molecular weight of .

More specifically, the nonionic water-soluble polymer used as the moderator (component B) may have a molecular weight of 1,000 to 10,000.

The leveling agent (component C) prevents excessively high peaks or excessively large protrusions from being generated in the copper layer 110 so that the copper layer 110 is macroscopically flat. The leveling agent (component C) includes a heterocyclic compound (D) having at least one of nitrogen (N) and sulfur (S). The leveling agent (component C), in addition to the function of planarizing the copper layer 110 , increases the strength of the copper foil 200 and alleviates the occurrence of curvature in the copper foil 200 .

The leveling agent (component C) has a concentration of 1 to 20 ppm.

When the concentration of the leveling agent (component C) is less than 1 ppm, the strength of the copper foil 200 is lowered, making it difficult to implement high strength, and curvature occurs in the copper foil 200 . On the other hand, when the concentration of the leveling agent (component C) exceeds 20 ppm, the strength of the copper foil 200 is increased, but there is a tendency that the curvature is rather severe.

The leveling agent (component C) is 3-(benzotriazole-2-mercapto)-propylsulfonic acid, 2-mercaptopyridine (2MP), 3(5-mercapto-1H-tetrazole)benzenesulfonate, 2-mercaptobenzothiazole, dimethylpyridine, 2,2'-bipyridine, 4,4'-bipyridine, pyrimidine, pyridazine, pyrinoline, oxazole, thiazole, 1-methylimidazole, 1 -Benzylimidazole, 1-methyl-2methylimidazole, 1-benzyl-2-methylimidazole, 1-ethyl-4-methylimidazole, N-methylpyrrole, N-ethylpyrrole, N- At least one selected from butylpyrrole, N-methylpyrroline, N-ethylpyrroline, N-butylpyrroline, purine, quinoline, isoquinoline, N-methylcarbazole, N-ethylcarbazole and N-butylcarbazole; include

Forming the copper layer 110 may include filtering the electrolyte 11 . For filtration of the electrolyte 11, for example, the electrolyte 11 may be circulated at a flow rate of 35 to 45 m ³ /hour. In addition, for the cleanliness of the electrolyte 11 , a copper wire, which is a raw material of the electrolyte 11 , may be heat treated and cleaned.

The copper layer 110 manufactured in this way may be cleaned. For example, acid cleaning for removing impurities on the surface of the copper layer 110 , for example, a resin component or natural oxide, and water cleaning for removing an acid solution used for pickling ) may be sequentially performed. The cleaning process may be omitted.

Next, rust-preventive films 211 and 212 are formed on the copper layer 110 .

Referring to FIG. 6 , the copper layer 110 may be immersed in the rust prevention liquid 31 contained in the rust prevention tank 30 to form the rust prevention films 211 and 212 on the copper layer 110 . The rust preventive solution 31 may include chromium. Chromium (Cr) may exist in an ionic state in the rust preventive solution 31 .

The rust preventive solution 31 may include, for example, 1 to 10 g/L of chromium. In order to form the rust preventive films 211 and 212 , the temperature of the rust preventive liquid 31 may be maintained at 20 to 40°C. The copper layer 110 may be immersed in the rust preventive solution 31 for about 1 to 30 seconds.

The rust preventive films 211 and 212 may include a silane compound by silane treatment or a nitrogen compound by nitrogen treatment.

The copper foil 200 is made by forming the rust-preventing films 211 and 212 .

Next, the copper foil 200 may be cleaned. The cleaning process may be omitted.

Next, after the drying process is performed, the copper foil 200 is wound on the winder WR.

Hereinafter, the present invention will be described in detail through Preparation Examples and Comparative Examples. However, the following Preparation Examples and Comparative Examples are only for helping understanding of the present invention, and the scope of the present invention is not limited by the Preparation Examples or Comparative Examples.

<Preparation Examples 1-4 and Comparative Examples 1-5>

Copper foils were manufactured according to Table 1 by using a maker including an electrolytic cell 10 , a rotary drum 12 disposed in the electrolytic cell 10 , and an electrode plate 13 disposed to be spaced apart from the rotary drum 12 . The electrolyte solution 11 is a copper sulfate solution. The copper ion concentration in the electrolytic solution 11 was 80 g/L, the concentration of sulfuric acid was 100 g/L, and the chlorine concentration was 20 ppm.

The electrolyte contains organic additives. Among the organic additives, 3-mercapto-1-propanesulfonic acid (MPS) was used as a brightening agent (component A), polypropylene glycol (PPG) was used as a moderator (component B), and 2 as a leveling agent (component C) -Mercaptopyridine (2-mercapto pyridine) (2MP) was used. The content is shown in Table 1.

Meanwhile, the surface of the rotary drum 12 was polished using a buffing brush for drum polishing of #2000 roughness. Accordingly, in the copper foils of Preparation Examples 1-4 and Comparative Examples 1-5, the surface properties of the first surface S1 in the direction of the shiny surface SS of the copper layer 110 were maintained substantially the same.

While maintaining the temperature of the electrolyte at 55° C., a current was applied between the rotating drum 12 and the electrode plate 13 at a current density of 50 ASD to form the copper layer 110 . Next, the copper layer 110 was immersed in a rust-preventive solution containing chromium for about 2 seconds to chromate the surface of the copper layer 110 to form rust-preventive films 211 and 212 . As a result, copper foils of Preparation Examples 1-4 and Comparative Examples 1-5 having a thickness of 6 μm were prepared.

Concentration of additives (ppm) MPS
(Component A) PPG
(Component B) 2MP
(component C) Preparation Example 1 15 30 10 Preparation 2 10 20 15 Preparation 3 5 20 20 Preparation 4 30 50 5 Comparative Example 1 - 30 10 Comparative Example 2 15 - 10 Comparative Example 3 15 30 - Comparative Example 4 - - 10 Comparative Example 5 15 30 25

MPS: 3-mercapto-1-propanesulfonic acid

PPG: polypropylene glycol

2MP: 2-mercaptopyridine

For the copper foils of Preparation Examples 1-4 and Comparative Examples 1-5 prepared as described above, (i) hardness of the first side (S1) and the second side (S2), (ii) heat treatment at room temperature and 190°C for 1 hour Tensile strength after (iii) average particle size of crystalline particles after heat treatment at room temperature and 190°C for 1 hour, (iv) height of curvature, (v) elongation, (vi) occurrence of wrinkles, and (vii) capacity retention were measured. .

(i) hardness of the first surface (S1) and the second surface (S2)

The first side (S1) and the second side (S2) of the copper foils prepared in Preparation Examples 1-4 and Comparative Examples 1-5 using a nano indenter (Agilent Technologies Nano Indenter G200) according to the standard of ISO 14577. Hardness was measured. Measurement conditions were set as follows.

Surface Approach Velocity (nm/S): 10

Depth Limit (nm): 1000

Strain Rate Target (1/S): 0.05

Frequency Target (Hz): 45

After measuring the hardness for each of the first surface (S1) and the second surface (S2) 5 times, the average value was determined as the hardness of the first surface (S1) and the second surface (S2) of the copper foil, respectively.

In addition, the hardness difference between the two surfaces was calculated using the hardness of the first surface S1 and the second surface S2.

(ii) Tensile strength after heat treatment at room temperature and 190°C for 1 hour

The room temperature tensile strength of the copper foil was measured at room temperature (25±15° C.), and after the copper foil was heat treated at 190° C. for 1 hour, the high temperature tensile strength of the copper foil was measured.

Specifically, according to the regulations of the IPC-TM-650 Test Method Manual, the tensile strength was measured using an Instron universal testing machine (UTM). The width of the sample for measuring tensile strength was 12.7 mm, the distance between grips was 50 mm, and the measurement speed was 50 mm/min.

(iii) Average particle size of crystalline particles after heat treatment at room temperature and 190°C for 1 hour

Measure the average particle size of the crystalline particles included in the copper layer constituting the copper foil at room temperature (25±15° C.), and measure the average particle size of the crystalline particles included in the copper layer after heat-treating the copper foil at 190° C. for 1 hour did.

At this time, after analyzing the first side (S1) and the second side (S2) of the copper foil according to the Electron Back Scattered Diffraction (EBSD) method, the average particle size of the crystalline particles is calculated using the analysis result did. Specifically, an FE-SEM (Field Emission - Scanning Electron Microscope) device (Hitachi, model name S-4300SE) is equipped with an EBSD (Electron Backscatter Diffraction) detector (eg, EDAX's EBSD camera). Thus, the average particle size of the crystalline particles contained in the copper layer was measured by observing the cross section of the copper foil under the measurement conditions of a voltage of 15 kV, a current of 50 mA, and a magnification of 2000 times.

(iv) curl height

For measuring the curvature height of the copper foil, the copper foils of Preparation Examples 1-4 and Comparative Examples 1-5 were cut to 60 mm X 60 mm to prepare a copper foil specimen 510, and as shown in FIG. 7 , the copper foil was bent. The height was measured.

7 is a schematic view for explaining the measurement of the curvature (curl) height of the copper foil. Referring to FIG. 7 , after placing the specimen 510 on the support 520 so that the first surface S1 of the specimen 510 faces upward, the glass plate 530 is placed on the specimen 510 . At this time, only the 30 mm length of the specimen 510 overlaps the glass plate so that only half of the specimen 510 is positioned between the support 520 and the glass plate 530 and the other half is set to be exposed from the glass plate 530 . The height of the specimen 510 exposed outside the glass plate 530 was measured using a measuring means 540 (meter ruler), and the maximum height was defined as a curvature height value of the copper foil.

Four specimens 510 were prepared for each of the copper foils of Preparation Examples 1-4 and Comparative Examples 1-5, and the bending height was measured, and then the average value was calculated to calculate the curvature height value of the copper foil.

(v) elongation

The elongation was measured by a universal testing machine (UTM) according to the provisions of the IPC-TM-650 Test Method Manual. Specifically, the elongation was measured using a universal tester of Instron. The width of the sample for measuring elongation was 12.7 mm, the distance between grips was 50 mm, and the measurement speed was 50 mm/min.

(vi) generation of wrinkles

8 is a schematic diagram illustrating a wrinkle generation test.

As shown in Figure 8, after the copper foils (CF) of Preparation Examples 1-4 and Comparative Examples 1-5 are mounted on the No. 1 roll (R1) and the No. 2 roll (R2), 1.5 for the No. 2 roll After artificially generating misalignment in the range of ˚ angle (θ), it was checked whether wrinkles occurred when the copper foil was driven in the D1 direction. In Table 2, the case where wrinkles occurred was indicated by "○", and the case where wrinkles did not occur was indicated by "X".

(vii) assessment of capacity retention

1) Cathode manufacturing

2 parts by weight of styrene-butadiene rubber (SBR) and 2 parts by weight of carboxymethyl cellulose (CMC) are mixed with 100 parts by weight of a commercially available silicon/carbon composite anode material for negative electrode active material, and distilled water is used as a solvent to make slurry for negative electrode active material was prepared. A slurry for a negative active material was applied to a thickness of 20 to 60 μm on the copper foils of Preparation Examples 1-4 and Comparative Examples 1-5 having a width of 10 cm using a doctor blade, dried at 120° C., and 1 ton/cm A negative electrode for a secondary battery was prepared by applying a pressure of ² .

2) Preparation of electrolyte

A basic electrolyte solution was prepared by dissolving LiPF ₆ as a solute at a concentration of 1M in a non-aqueous organic solvent mixed with ethylene carbonate (EC) and ethylmethyl carbonate (EMC) in a ratio of 1:2. A non-aqueous electrolyte was prepared by mixing 99.5% by weight of the basic electrolyte and 0.5% by weight of succinic anhydride.

3) Anode manufacturing

A cathode active material was prepared by mixing lithium manganese oxide of Li _1.1 Mn _1.85 Al _0.05 O ₄ and lithium manganese oxide of orthorhombic crystal structure of o-LiMnO ₂ in a ratio of 90:10 (weight ratio). A cathode active material, carbon black, and PVDF [Poly(vinylidenefluoride)] as a binder were mixed in a ratio of 85:10:5 (weight ratio), and mixed with NMP as an organic solvent to prepare a slurry. The slurry thus prepared was applied to both surfaces of an Al foil having a thickness of 20 μm, and then dried to prepare a positive electrode.

4) Manufacture of lithium secondary battery for testing

Inside the aluminum can, a positive electrode and a negative electrode were disposed to be insulated from the aluminum can, and a non-aqueous electrolyte and a separator were disposed between them, thereby manufacturing a coin-type lithium secondary battery. The separator used was polypropylene (Celgard 2325; thickness 25㎛, average pore size φ28 nm, porosity 40%).

5) Capacity retention rate evaluation

Using the lithium secondary battery prepared as described above, the capacity per g of the positive electrode was measured by driving the battery at a charging voltage of 4.3V and a discharge voltage of 3.4V. Next, in order to evaluate the high-temperature lifespan, 50 charge/discharge experiments were performed at a high temperature of 50° C. at a 0.2C rate (current rate, C-rate) to calculate the capacity retention rate. The capacity retention rate can be calculated by Equation 1 below.

[Equation 1]

Capacity retention rate (%) = [(Capacity after 50 charge/discharge)/(Capacity after one charge/discharge)] x 100

The capacity retention rate was measured three times and the average value was adopted. When the capacity retention rate was less than 90%, it was determined that the copper foil was unsuitable as a negative electrode current collector for a lithium ion battery.

The above test results are shown in Table 2. However, since the copper foils of Preparation Examples 1-4 and Comparative Examples 1-5 were all measured to have an elongation of 2% or more, all of them were determined as "Pass", and the elongation was excluded in Table 2.

Hardness (Gpa) The tensile strength
(kgf/㎟) particle size
(μm) warp
Height
(mm) wrinkle
Occur
The presence or absence Capacity retention rate
(%) page 1 page 2 difference room temperature High temperature room temperature High temperature Preparation Example 1 1.59 1.67 0.08 45 39 1.1 1.2 13 X 90 Preparation 2 1.70 1.66 0.04 52 45 1.2 1.5 11 X 91 Preparation 3 1.79 1.68 0.11 57 52 0.8 1.0 18 X 91 Preparation 4 1.50 1.69 0.19 43 38 1.3 1.7 9 X 90 Comparative Example 1 1.41 1.65 0.24 43 39 1.2 1.5 27 O 82 Comparative Example 2 1.37 1.66 0.29 45 40 1.1 2.3 28 O 80 Comparative Example 3 1.32 1.67 0.27 33 27 3.2 4.2 21 O 78 Comparative Example 4 1.35 1.66 0.23 45 37 1.1 2.7 23 O 81 Comparative Example 5 1.75 1.65 0.10 60 54 0.9 1.0 25 O 91

Referring to Tables 1 and 2, the following results can be confirmed.

In the copper foil of Comparative Example 1 made of an electrolyte that does not contain a brightening agent (component A) among organic additives, the difference in hardness between the first side (S1) and the second side (S2) exceeded 0.2, and the warpage exceeded 20 mm (curl) occurred, wrinkles occurred in the copper foil, and the secondary battery manufactured using the copper foil of Comparative Example 1 had a capacity retention rate of less than 90%.

In the copper foil of Comparative Example 2 made of an electrolyte that does not contain a moderator (component B) among organic additives, the difference in hardness between the first surface (S1) and the second surface (S2) exceeded 0.2, and after heat treatment at high temperature The average particle size of the crystalline particles of capacity retention.

In the copper foil of Comparative Example 3 made of an electrolyte that does not contain a leveling agent (component C) among organic additives, the difference in hardness between the first surface (S1) and the second surface (S2) was greater than 0.2, and at room temperature (25± 15 ℃) was less than 40kgf / mm ² , the tensile strength at high temperature after 1 hour heat treatment at 190 ℃ was less than 36kgf / mm ² , the average particle size of the crystalline particles at room temperature exceeded 1.7㎛, heat treatment After that, the average particle size of the crystalline particles at high temperature exceeded 1.7 μm, a curl exceeding 20 mm occurred, wrinkles occurred in the copper foil, and the secondary battery manufactured using the copper foil of Comparative Example 3 was 90 % capacity retention.

In the copper foil of Comparative Example 4 made of an electrolyte containing only the leveling agent (component C) among the organic additives, the difference in hardness between the first surface (S1) and the second surface (S2) exceeded 0.2, and after heat treatment at high temperature The average particle size of the crystalline particles was more than 1.7 μm, a curl exceeding 20 mm occurred, wrinkles occurred in the copper foil, and the secondary battery manufactured using the copper foil of Comparative Example 4 had a capacity of less than 90% had a retention rate.

In the copper foil of Comparative Example 5 made of an electrolyte containing all of a brightening agent (component A), a moderator (component B) and a leveling agent (component C) as organic additives, but having an excessive content of the leveling agent (component C), 20 mm A curvature exceeding , occurred, and wrinkles occurred.

On the other hand, according to an embodiment of the present invention, in the copper foils of Preparation Examples 1 to 4 made of an electrolyte containing a predetermined amount of a brightener (component A), a moderator (component B) and a leveling agent (component C) as an organic additive, according to an embodiment of the present invention The height of the curvature is 20 mm or less, the secondary battery manufactured using this copper foil has a capacity retention rate of 90% or more, and wrinkles do not occur in the copper foil.

9A and 9B respectively show a cross section of the copper foil according to Preparation Example 1 before and after heat treatment, and FIGS. 10A and 10B show a cross section of the copper foil according to Comparative Example 3 before and after heat treatment, respectively. 9A, 9B, 10A and 10B, the upper direction of the drawing is the mat surface MS direction, and the lower direction of the drawing is the shiny surface SS direction.

9A, in the copper foil according to Preparation Example 1, the average particle size of the crystalline particles of the copper layer before heat treatment is 1.1 μm based on the particle diameter, and referring to FIG. 9B, the crystalline quality of the copper layer after heat treatment at 190° C. for 1 hour The average particle size of the particles is 1.2 μm based on the particle size. As such, in the copper foil according to Preparation Example 1, the average particle size of the crystalline particles of the copper layer before and after the heat treatment is in the range of 0.8 to 1.7 μm based on the particle diameter.

On the other hand, referring to FIG. 10A , in the copper foil according to Comparative Example 3, the average particle size of the crystalline particles of the copper layer before heat treatment is 3.2 μm based on the particle diameter, and referring to FIG. 10B , the copper layer after heat treatment at 190° C. for 1 hour The average particle size of the crystalline particles is 4.2㎛ based on the particle size. In the copper foil according to Comparative Example 3, the average particle size of the crystalline particles of the copper layer before and after the heat treatment is not within the range of 0.8 to 1.7 μm based on the particle size, and the average particle size of the crystalline particles of the copper layer by the heat treatment is 1.0 μm increased.

On the other hand, referring to Table 2, in Comparative Examples 2 and 4 as well as Comparative Example 3, it can be confirmed that the average particle size of the crystal grains of the copper layer after the heat treatment is further increased by 1 μm or more compared to before the heat treatment.

The present invention described above is not limited by the above-described embodiments and the accompanying drawings, and it is a technical field to which the present invention pertains that various substitutions, modifications and changes are possible without departing from the technical matters of the present invention. It will be clear to those of ordinary skill in the art. Therefore, the scope of the present invention is expressed by the following claims, and all changes or modifications derived from the meaning, scope, and equivalent concepts of the claims should be construed as being included in the scope of the present invention.

100, 200: copper foil
211, 212: anti-rust film
300, 400: electrode for secondary battery
310, 320: active material layer
500: secondary battery
MS: matte side
SS: Shiny noodles

Claims (18)

a copper layer having a matte surface and a shiny surface; and
Including; a rust preventive film disposed on the copper layer;
It has a first surface in the direction of the mat surface and a second surface in the direction of the shiny surface,
The hardness of the first surface is 1.5 to 1.8 GPa,
The second surface has a hardness of 1.3 to 2.0 GPa,
The difference in hardness between the first surface and the second surface is 0.2 GPa or less,
The tensile strength at room temperature (25±15℃) is 40 to 65kgf/mm ²
High-temperature tensile strength measured after heat treatment at 190 ° C. for 1 hour is 36 to 58 kgf / mm ² of,
copper foil. According to claim 1,
The copper layer has crystalline particles,
After the heat treatment at room temperature before the heat treatment and the heat treatment at 190° C. for 1 hour, the crystalline particles have an average particle size of 0.8 to 1.7 μm, copper foil. According to claim 1,
Copper foil having an elongation of 2% or more. According to claim 1,
A copper foil having a thickness of 4 to 35 μm. According to claim 1,
Copper foil having a maximum curl height of 20 mm or less. According to claim 1,
The anti-rust film is a copper foil comprising at least one of chromium, a silane compound, and a nitrogen compound. copper foil; and
and an active material layer disposed on at least one surface of the copper foil;
The copper foil is the copper foil according to any one of claims 1 to 6,
Electrode for secondary battery. anode;
a cathode disposed opposite to the anode;
an electrolyte disposed between the positive electrode and the negative electrode to provide an environment in which lithium ions can move; and
a separator that electrically insulates the anode and the cathode;
The cathode is
The copper foil according to any one of claims 1 to 6; and
an active material layer disposed on the copper foil;
Including, a secondary battery. Forming a copper layer by applying a current at a current density of 30 to 80 ASD (A/dm ² ) between the electrode plate and the rotating drum spaced apart from each other in an electrolyte containing copper ions to form a copper layer;
The electrolyte is
60 to 120 g/L of copper ions;
80 to 150 g/L sulfuric acid;
less than 50 ppm chlorine (Cl); and
and organic additives;
The organic additive includes a brightening agent (component A), a moderator (component B) and a leveling agent (component C),
3-mercapto-1-propanesulfonic acid (MPS) is included as the brightener (component A),
It contains polypropylene glycol (PPG) as the moderator (component B),
containing 2-mercaptopyridine (2MP) as the leveling agent (component C),
A method for manufacturing copper foil. 10. The method of claim 9,
In the step of forming the copper layer, the temperature of the electrolyte is maintained in the range of 40 to 60 ℃, a method of manufacturing a copper foil. 10. The method of claim 9,
The brightener (component A) has a concentration of 5 to 100 ppm, a method for producing a copper foil. delete 10. The method of claim 9,
The moderator (component B) has a concentration of 5 to 50 ppm, a method for producing a copper foil. delete delete 10. The method of claim 9,
The said leveling agent (component C) has a density|concentration of 1-20 ppm, the manufacturing method of copper foil. delete 10. The method of claim 9,
Further comprising the step of forming a rust preventive film on the copper layer, the manufacturing method of the copper foil.

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