KR102492813B1 - Copper foil for high capacity secondary battery with improved handling property, 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-prevention film disposed on the copper layer, wherein a first surface in the direction of the matte surface and a second surface in the direction of the shiny surface are formed. A hardness difference rate (HDR) between the first surface and the second surface is 0.02 or less, and at least one of the first surface and the second surface has a hardness of 1.4 to 1.7 GPa, and the first surface has a hardness of 1.4 to 1.7 GPa. It provides a copper foil having a kinetic coefficient of friction of 0.4 to 0.5, and a difference in kinetic friction coefficient between the first surface and the second surface is 0.2 or less. Here, the hardness difference rate (HDR) is obtained by the following equation.

Description

Copper foil for a high-capacity secondary battery with excellent handling properties, an electrode including the same, a secondary battery including the same, and a manufacturing method thereof FOR MANUFACTURING THE SAME}

The present invention relates to a copper foil having excellent handling properties and capable of 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 generates electricity by converting electrical energy into chemical energy and storing it, and then converting chemical energy back into electrical energy when electricity is needed. The secondary battery is also referred to as a rechargeable battery in that it can be recharged. Among secondary batteries, lithium secondary batteries are currently widely used due to their high operating voltage, high energy density, and excellent lifespan characteristics.

A secondary battery includes a negative current collector made of copper foil, and among copper foils, an electrolytic copper foil is widely used as a negative current collector of a secondary battery.

An electrodeposited copper foil used as an anode current collector typically has a tensile strength of about 30 to 40 kgf/mm ² . Recently, in order to manufacture a high-capacity lithium secondary battery, a metal-based or composite-based active material having high-capacity characteristics has attracted attention. However, metal-based or composite-based active materials exhibit severe volume expansion during charge/discharge processes. Therefore, only when the copper foil can respond to the volume expansion of the active material, the copper foil is not torn even when the active material expands in volume, and the separation of the active material from the copper foil is prevented. In addition, the copper foil must have high-strength characteristics in order to cope with the volume expansion of the active material.

In order to manufacture a high-strength copper foil having a tensile strength of 40 kgf/mm ² or more, for example, there is an electroplating method using a sulfuric acid-based electrolyte solution to which a multi-component additive or a thiourea-based organic additive is added. When the tensile strength of the copper foil increases, it is common that the hardness of the copper foil also increases. However, when a multi-component additive is used, 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 in that wrinkles or curls occur in the copper foil in the roll-to-roll process for coating the active material.

Specifically, when the tensile strength of the copper foil increases, the stress inside the copper foil generally increases, so that the frequency of occurrence of curl in the copper foil increases. When curl occurs in copper foil, in the process of manufacturing copper foil by the Roll to Roll (RTR) process or in the process of manufacturing electrodes for secondary batteries using copper foil, wrinkles occur in the copper foil or the copper foil is torn. Defects occur, resulting in deterioration in handling performance in the manufacturing process of the secondary battery.

Recently, a very thin copper foil having a thickness of 10 μm or less is used for manufacturing an electrode of a secondary battery for high capacity of a secondary battery. When the thickness of the copper foil is reduced to 10 μm or less, there is A slip phenomenon may occur. When the slip phenomenon occurs, wrinkles or tearing occur in the copper foil, making it impossible to perform a continuous process, deteriorating handling in the process of manufacturing electrodes for secondary batteries, and in severe cases, making electrodes and assembling secondary batteries impossible.

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

The inventors of the present invention have found that the slip phenomenon that deteriorates handling properties in the process of manufacturing electrodes and secondary batteries using copper foil is related to the coefficient of dynamic friction on the surface of the copper foil. In copper foil, the coefficient of kinetic friction in the direction of the shiny surface can be determined by the roughness of the buffing brush. The larger the difference between the coefficient of kinetic friction in the direction of the matte and shiny surfaces, the more slippage occurs. As a result, the frequency of wrinkles in the copper foil increases. In particular, the present inventors have confirmed that when the coefficient of kinetic friction in the mat surface direction is out of an appropriate range, the possibility of wrinkles occurring in the copper foil is high. Therefore, it is necessary to control the kinetic friction coefficient in the mat surface direction to an appropriate range.

Therefore, the present inventors use multi-component additives and control the concentration of each additive to adjust the correlation between strength and hardness of copper foil and the range of hardness difference between both sides to an appropriate range, and also to adjust the range of difference in kinetic friction coefficient between both sides to an appropriate range. Development of copper foil that can minimize warpage during the process, improve handling of the roll-to-roll process for manufacturing electrodes and secondary batteries, and maximize the capacity retention rate during charging and discharging to improve the lifespan of secondary batteries. did

One embodiment of the present invention is to provide such a copper foil, an electrode including the same, a secondary battery including the same, and a manufacturing method of 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, an embodiment of the present invention includes a copper layer having a matte surface and a shiny surface and a rust-prevention film disposed on the copper layer, and a first surface in the direction of the matte surface and a second surface in the direction of the shiny surface are formed. A hardness difference rate (HDR) between the first surface and the second surface is 0.02 or less, and at least one of the first surface and the second surface has a hardness of 1.4 to 1.7 GPa, and the first surface has a hardness of 1.4 to 1.7 GPa. It provides a copper foil having a kinetic coefficient of friction of 0.4 to 0.5, and a difference in kinetic friction coefficient between the first surface and the second surface is 0.2 or less. Here, the hardness difference rate (HDR) is obtained by Equation 1 below.

[Equation 1]

The copper foil has a tensile strength of 40 kgf/mm ² or more.

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

The first surface and the second surface each have a surface roughness (Rz JIS) of 0.5 to 2.0 μm.

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

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

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

Another embodiment of the present invention provides a secondary battery electrode 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, a cathode, an anode disposed opposite to the cathode, an electrolyte disposed between the anode and the cathode to provide an environment in which lithium ions can move, and It provides a secondary battery including a separator that electrically insulates the positive electrode and the negative electrode, and the negative electrode includes the copper foil and an active material layer disposed on the copper foil.

In another embodiment of the present invention, a current density of 30 to 80 ASD (A/dm ² ) is applied between an electrode plate and a rotating drum spaced apart from each other in an electrolyte solution containing copper ions to form a copper layer. forming, wherein the electrolyte solution includes 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 is a brightening agent ( component A), a moderator (component B), and at least one of a first leveling agent (component C) and a second leveling agent (component D), wherein the brightener (component A) includes sulfonic acid or a metal salt thereof, The moderator (component B) includes a nonionic water-soluble polymer, the first leveling agent (component C) includes a thiol-based compound or a thio-based compound, and the second leveling agent (component D) includes nitrogen (N ) and a heterocyclic compound (D) having at least one of sulfur (S).

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

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, 3- (N,N-dimethylthiocarbamoyl)-thiopropanesulfonate sodium salt, 3-[(amino-iminomethyl)thio]-1-propanesulfonate sodium salt, o-ethyldithiocarbonate-S-( It includes at least one selected from 3-sulfopropyl)-ester sodium salt, 3-(benzothiazolyl-2-mercapto)-propyl-sulfonic acid sodium salt, and ethylenedithiodipropylsulfonic acid sodium salt.

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

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

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

The first leveling agent (component C) has a concentration of 1 to 10 ppm.

The first leveling agent (component C) is thiourea (TU), diethylthiourea, ethylenethiourea, acetylenethiourea, dipropylthiourea, dibutylthiourea, N-trifluoroacetylthiourea (N -trifluoroacetylthiourea), N-ethylthiourea, N-cyanoacetylthiourea, N-allylthiourea, o-tolylthiourea, N, N'-butylene thiourea, thiazolidinethiol, 4-thiazolinethiol, 4-methyl-2-pyrimidinethiol (4- methyl-2-pyrimidinethiol) and 2-thiouracil (2-thiouracil).

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

The second leveling agent (component D) is 3-(benzotriazole-2-mercapto)-prosulfonic acid), 2-mercaptopyridine, 3(5-mercapto-1H-tetrazole)benzenesulfonate , 2-mercaptobenzothiazole, dimethylpyridine, 2,2'-bipyridine, 4,4'-bipyridine, pyrimidine, pyridazine, pyrinoline, oxazole, thiazole, 1-methylimidazole, 1-benzimidazole, 1-methyl-2methylimidazole, 1-benzyl-2-methylimidazole, 1-ethyl-4-methylimidazole, N-methylpyrrole, N-ethylpyrrole, N -among butylpyrrole, N-methylpyrroline, N-ethylpyrroline, N-butylpyrroline, pyrimidine, purine, quinoline, isoquinoline, N-methylcarbazole, N-ethylcarbazole and N-butylcarbazole contains at least one selected

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

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

According to one embodiment of the present invention, by adjusting the correlation between the strength and hardness of the copper foil and the hardness difference range of both sides of the copper foil to an appropriate range, and also by adjusting the dynamic friction coefficient difference range to an appropriate range, the occurrence of warpage in the copper foil can be prevented. It is possible to minimize and improve the handling of the roll-to-roll process for manufacturing electrodes and secondary batteries. In addition, by using such a copper foil, the lifespan of the secondary battery can be improved by maximizing the capacity retention rate during charging and discharging.

In addition, according to one embodiment of the present invention, by using multi-component additives and controlling the concentration of each additive, the correlation between the strength and hardness of the copper foil and the hardness difference range of both sides are adjusted to an appropriate range, and the dynamic friction of both sides The coefficient difference range can be adjusted to an appropriate range.

A secondary battery manufactured using the copper foil according to an embodiment of the present invention has an excellent capacity retention rate and can realize high capacity.

The accompanying drawings are intended to aid understanding of the present invention and constitute a part of this specification, illustrate embodiments of the present invention, and explain the principles of the present invention together with the detailed description 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 another embodiment of the present invention.
Figure 6 is a schematic diagram of the manufacturing process of the copper foil shown in Figure 2.
Figure 7 is a schematic diagram explaining the measurement of the dynamic friction coefficient of copper foil.
8 is a schematic diagram explaining the measurement of the curl height of copper foil.
9 is a schematic diagram illustrating a wrinkle generation test.

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 described in the claims and equivalents thereof.

The shape, size, ratio, angle, number, etc. disclosed in the drawings to describe the embodiments of the present invention are exemplary, and the present invention is not limited by the details shown in the drawings. Like elements may be referred to by like reference numerals throughout the specification.

When 'includes', 'has', 'consists of', etc. mentioned in this specification is 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, even if there is no separate explicit description, it is interpreted as including the error range.

In the case of a description of a positional relationship, for example, 'on top of', 'on top of', 'at the bottom of', 'next to', etc. Or, unless the word 'directly' is used, one or more other parts may be located between the two parts.

In the case of a description of a temporal relationship, for example, 'immediately' or 'directly' when a temporal precedence relationship is described in terms of 'after', 'following', 'next to', 'before', etc. Unless the expression is used, non-continuous cases may be included.

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

The term “at least one” should be understood to include all possible combinations from one or more related items.

Each feature of the various embodiments of the present invention can be partially or entirely combined or combined with each other, technically various interlocking and driving are possible, and each embodiment can be implemented independently of each other or can 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.

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 came into contact with the rotating drum 12 during the electroplating process, and the matte surface (MS) refers to the surface opposite to the shiny surface (SS).

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

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

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

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

According to an embodiment of the present invention, the anti-rust 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 formed by a rust-preventive solution containing chromium (Cr), that is, a rust-preventive solution containing a chromic acid compound.

According to one embodiment of the present invention, the copper foil 100 has a first surface S1 that is a surface in the direction of the mat surface (MS) and a second surface that is a surface in the direction of the shiny surface (SS) 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 anti-rust film 211, and the second surface S2 is the shiny surface SS. When the anti-rust film 211 is omitted, the matte surface MS of the copper layer 110 becomes the first surface S1 of the copper foil 100 .

According to one embodiment of the present invention, at least one of the first surface (S1) and the second surface (S2) of the copper foil 100 has a hardness of 1.4 to 1.7GPa. Of course, both the first surface S1 and the second surface S2 of the copper foil 100 may have a hardness of 1.4 to 1.7 GPa. Here, hardness is surface hardness. Surface hardness is the hardness of the surface of an object.

When the hardness of the first surface S1 and the second surface S2 of the copper foil 100 is out of the range of 1.4 to 1.7 GPa, adjusting the difference in hardness between the first surface S1 and the second surface S2 It is difficult, and it becomes difficult to adjust the dynamic friction coefficient of the copper foil 100 within a predetermined range. Accordingly, a slip phenomenon may occur during the manufacturing process of the copper foil 100 by a roll to roll (RTR) process or the manufacturing process of a secondary battery electrode using the copper foil 100. When such a slip phenomenon occurs, defects such as wrinkles in the copper foil 100 or tearing of the copper foil may occur.

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

According to one embodiment of the present invention, the hardness difference ratio (HDR) between the first surface (S1) and the second surface (S2) of the copper foil 100 is 0.02 or less. Here, the hardness difference rate (HDR) can be obtained by the following Equation 1.

[Equation 1]

The hardness difference rate can be said to be the ratio of the difference in hardness between both surfaces of the copper foil 100 to the hardness of the first surface S1 of the copper foil 100.

According to one embodiment of the present invention, the first surface (S1) of the copper foil 100 has a dynamic friction coefficient of 0.4 to 0.5. In addition, the difference in kinetic friction coefficient between the first surface S1 and the second surface S2 of the copper foil 100 is 0.2 or less.

Specifically, the dynamic friction coefficient of the first surface S1 of the copper foil 100 may be referred to as "μk1", and the dynamic friction coefficient of the second surface S2 may be referred to as "μk2". Here, μk1 and μk2 satisfy Equations 2 and 3 below.

[Equation 2]

0.4 ≤ µk1 ≤ 0.5

[Equation 3]

|μk1 - μk2| ≤ 0.2

The dynamic friction coefficient of the copper foil 100 may be measured by a Tribogear 14FW model from HEIDON, according to ASTM D1894. Specifically, a stainless steel ball (SUS ball) 630 is brought into contact with the copper foil 100 (CF), and the copper foil 100 is mutually moved while applying a load to the stainless steel 630. The coefficient of dynamic friction of the copper foil 100 can be measured. Yes (see FIG. 7). At this time, a 10 mm stainless steel ball 630 is used, and the dynamic friction coefficient of the copper foil 100 can be measured under the measurement conditions of applying a load of 100 g at a speed of 100 mm / min at a measurement distance of 10 mm. there is. For example, the dynamic friction coefficient may be measured three times, and the average value may be used.

When the coefficient of kinetic friction (μk1) of the first surface (S1) of the copper foil 100 is less than 0.4, a process for manufacturing the copper foil 100 by a roll-to-roll (RTR) process or another product using the copper foil 100, For example, in the process of manufacturing a secondary battery, a slip may occur and wrinkles may occur in the copper foil 100 .

On the other hand, when the coefficient of kinetic friction (μk1) of the first surface (S1) of the copper foil 100 exceeds 0.5, slip generation can be prevented or suppressed, but the surface of the copper foil 100 is excessively rough, e.g. For example, when coating the active material on the copper foil 100 in the manufacturing process of a secondary battery electrode, the coating is made non-uniformly.

On the other hand, if the difference in the coefficient of kinetic friction between the first surface S1 and the second surface S2 of the copper foil 100 exceeds 0.2, a slip phenomenon may occur, and the difference in surface properties of both sides of the copper foil 100 Since is large, the coating of the active material on both sides of the copper foil 100 may not be uniformly performed during the manufacturing process of the electrode for a secondary battery. Therefore, the difference in kinetic friction coefficient between the first surface S1 and the second surface S2 of the copper foil 100 is adjusted to 0.2 or less.

The coefficient of kinetic friction μk1 of the first surface S1 of the copper foil may be controlled by adjusting additives added to the electrolyte during the manufacturing process of the copper layer 110 . In addition, the coefficient of kinetic friction (μk2) of the second surface (S2) of the copper foil can be controlled by adjusting the grain size (roughness) of a brush that buffs (polishing) the surface of the rotating drum in the manufacturing process of the copper layer 110. there is.

According to one embodiment of the present invention, the second surface S2 of the copper foil may have, for example, a kinetic coefficient of friction (μk2) of 0.2 to 0.7.

According to one embodiment of the present invention, the copper foil 100 has a tensile strength of 40 kgf/mm ² or more. The tensile strength at room temperature (25±15° C.) is also referred to as room temperature tensile strength, and the copper foil 100 may have room temperature (25±15° C.) tensile strength of 40 kgf/mm ² or more.

When the copper foil 100 has a tensile strength of less than 40 kgf/mm ² , when the copper foil 100 is used as a current collector for a secondary battery electrode, breakage may occur in the copper foil 100 due to volume expansion of the active material. For example, a metal-based active material containing 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 such 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 bends to the copper foil 100 in a roll-to-roll process for manufacturing a secondary battery electrode or a secondary battery ( curls or creases may occur.

On the other hand, when the tensile strength of the copper foil 100 is excessively high, the brittleness increases and the copper foil 100 breaks during the manufacturing process of the copper foil 100 or during the manufacturing process of a secondary battery electrode or secondary battery using the copper foil 100. It can be. Therefore, the copper foil 100 may have a tensile strength of, for example, 40 to 60 kgf/mm ² .

Tensile strength can be measured by a universal testing machine (UTM) according to the provisions of the IPC-TM-650 Test Method Manual. According to one embodiment of the present invention, the tensile strength is measured by an Instron universal testing machine. 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.

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

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

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

According to one embodiment of the present invention, the first surface (S1) and the second surface (S2) of the copper foil 100 each have a surface roughness (Rz JIS) of 0.5 to 2.0㎛.

The surface roughness (Rz JIS) according to an embodiment of the present invention is also referred to as 10-point average roughness, and can be measured by a surface roughness measuring instrument (M300, Mahr) according to the JIS B 0601-2001 standard.

When the surface roughness (Rz JIS) of the first surface S1 and the second surface S2 of the copper foil 100 is less than 0.5 μm, respectively, when the copper foil 100 is used as a current collector for a secondary battery electrode, the copper foil ( 100) and the active material have low peel strength, and thus, the active material may be separated from the copper foil 100 during charging and discharging of the secondary battery. On the other hand, when the surface roughness (Rz JIS) of the first surface S1 and the second surface S2 exceeds 2.0 μm, when the copper foil 100 is used as a current collector for a secondary battery electrode, the active material is the copper foil 100 ) is not uniformly coated, so current is locally concentrated during charging and discharging of the secondary battery, and thus the charge/discharge cycle characteristics may be deteriorated, and the capacity retention rate of the secondary battery may be deteriorated.

Meanwhile, according to one embodiment of the present invention, the difference in surface roughness (Rz JIS) between the first surface S1 and the second surface S2 of the copper foil 100 may be adjusted to 0.5 μm or less.

According to one embodiment of the present invention, the copper foil 100 may have a thickness of 4 μm to 35 μm. When the copper foil 100 is used as a current collector of a secondary battery electrode, the thinner the copper foil 100 is, the more current collectors can be accommodated in the same space, which is advantageous for higher capacity of the secondary battery. However, when the thickness of the copper foil 100 is less than 4 μm, the handling property is deteriorated during the manufacturing process of a secondary battery electrode 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 secondary battery electrode using the copper foil 100 increases, and this large thickness may cause difficulties in implementing a high capacity secondary battery.

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

To measure the maximum curl height of the copper foil 100, the copper foil 100 is cut into 60 mm X 60 mm, and the copper foil 100 is placed on the support 520 so that the first surface S1 faces upward. After placing, the glass plate 530 is placed on the copper foil 100 . At this time, only half of the copper foil 100 is overlapped with the glass plate 530 by a length of 30 mm of the cut copper foil, set so that only half of the copper foil 100 is positioned between the support 520 and the glass plate 530, and then exposed to the outside of the glass plate 530. The height of the copper foil is measured, and the maximum height is defined as the maximum curl height of the copper foil 100 (see FIG. 8).

When the maximum curl 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 during the manufacturing process of a secondary battery using the copper foil 100 ( defects such as wrinkles may occur. In addition, when a curl occurs in the copper foil 100, it may be difficult to separate the copper foil 100 from the winder WR after manufacturing the copper foil 100.

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

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

For convenience of description, among the two anti-rust films 211 and 212, the anti-rust film 211 disposed on the matte surface MS of the copper layer 110 is referred to as a first protective layer and disposed on the shiny surface SS. The anti-rust 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, which is a surface in the direction of the matte surface (MS), and a second surface, which is a surface in the direction of the shiny surface (SS), 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 surface of 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 difference ratio (HDR) between the first surface (S1) and the second surface (S2) is 0.02 or less. The hardness difference rate (HDR) can be obtained from Equation 1. At least one of the first surface S1 and the second surface S1 of the copper foil 200 has a hardness of 1.4 to 1.7 GPa.

In addition, the first surface S1 of the copper foil 200 has a kinetic friction coefficient of 0.4 to 0.5, and the difference between the kinetic friction coefficient between the first surface S1 and the second surface S2 is 0.2 or less.

The copper foil 200 may have a tensile strength of 40 kgf/mm ² or more, an elongation of 2% or more, a thickness of 4 to 35 μm, and a maximum curl height of 20 mm or less.

The first surface S1 and the second surface S1 of the copper foil 200 each have a surface roughness (Rz JIS) of 0.5 to 2.0 μm.

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

Referring to FIG. 3 , an 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 the copper foil 100 . Here, the copper foil 100 includes a copper layer 110 and an anti-rust 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 has 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 anti-rust 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 a 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, and the Active material layers 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 shown in FIG. 3 includes an electrode active material, and in particular, may include an anode active material. That is, the secondary battery electrode 300 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 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).

As charging and discharging of the secondary battery is repeated, contraction and expansion of the active material layer 310 occur alternately, which causes separation between 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 high 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 though 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 . Therefore, a secondary battery including the secondary battery electrode 300 has excellent charge/discharge efficiency and excellent capacity retention rate.

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

An 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 sides of the copper layer 110 .

Specifically, the secondary battery electrode 400 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 the first active material layer, and the active material layer 320 disposed on the second surface S2 of the copper foil 200 Also referred to as the second active material layer.

The two active material layers 310 and 320 may be made of the same material using the same method, or may be made of different materials or methods.

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

Referring to FIG. 5 , a secondary battery 500 is disposed between a cathode 370, an anode 340 opposite to the anode 370, and a cathode 370 and a cathode 340. An electrolyte 350 providing an environment in which ions can move, and a separator 360 electrically insulating the anode 370 and the cathode 340 are included. 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 in order to prevent the charge generated from one electrode from being unprofitably consumed by moving to the other electrode through the inside of the secondary battery 500 . Referring to FIG. 5 , a separator 360 is disposed within an electrolyte 350 .

The cathode 370 includes a cathode current collector 371 and a cathode active material layer 372 . Aluminum foil may be used as the positive 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 anode 340 includes an anode active material.

As the negative current collector 341, the copper foils 100 and 200 disclosed 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, with reference to FIG. 6, a manufacturing method of copper foil 200 according to another embodiment of the present invention will be described in detail.

FIG. 6 is a schematic diagram of a manufacturing process of the copper foil 200 shown in FIG. 2 .

In order to manufacture the copper foil 200, first, the electrolyte solution 11 containing copper ions is prepared. The electrolyte solution 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 spaced apart from each other in the electrolyte solution 11 containing copper ions to form a copper layer. (110) is formed. The copper layer 110 is formed by the principle of electroplating. The gap between the electrode plate 13 and the rotating drum 12 can 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 rotary drum 12 may be connected to a cathode of the power source.

When the current density applied between the electrode plate 13 and the rotary 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 miniaturization of the crystalline particles is accelerated. The current density can be tuned 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 . To adjust the surface properties in the direction of the shiny surface (SS), the surface of the rotary drum 12 may be polished with a polishing brush having a grit of #800 to #3000, for example.

In the process of forming the copper layer 110, the electrolyte solution 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 one embodiment of the present invention, the physical, chemical and electrical properties of the copper layer 110 can be controlled by adjusting the composition of the electrolyte solution 11 .

According to one embodiment of the present invention, the electrolyte solution 11 includes 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 smoothly form the copper layer 110 by electrodeposition of copper, the concentration of copper ions and the concentration of sulfuric acid in the electrolyte solution 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 chloride. Chlorine (Cl) may be used, for example, to remove silver (Ag) ions introduced into the electrolyte solution 11 during the formation of the copper layer 110 . Chlorine (Cl) can 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 excessive chlorine (Cl). Therefore, the concentration of chlorine (Cl) in the electrolyte solution 11 is managed to 50 ppm or less. More specifically, the concentration of chlorine (Cl) may be managed to 25 ppm or less, for example, it may be managed in the range of 5 to 25 ppm.

The electrolyte solution 11 contains organic additives.

The organic additive includes at least one of a brightening agent (component A), a moderator (component B), and a first leveling agent (component C) and a second leveling agent (component D). That is, the organic additive includes a brightener (component A) and a moderator (component B), and includes at least one of a first leveling agent (component C) and a second leveling agent (component D).

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

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

If the concentration of the brightener (component A) is less than 5 ppm, the gloss of the copper foil 200 is reduced, and if 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 solution 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 , 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 can include

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

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

If the concentration of the moderator (component B) is less than 5 ppm, the roughness of the copper foil 200 increases rapidly and the strength of the copper foil 200 decreases. On the other hand, even if the concentration of the moderator (component B) exceeds 50 ppm, there is little change in physical properties such as appearance, gloss, roughness, strength, and elongation 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 the need to unnecessarily increase the concentration of the moderator (component B) to increase the manufacturing cost and waste raw materials.

The moderator (component B) is, for example, polyethylene glycol (PEG), polypropylene glycol, polyethylene polypropylene copolymer, polyglycerin, polyethylene glycol dimethyl ether, hydroxyethylene cellulose, polyvinyl alcohol, stearic acid polyglycol ether and at least one nonionic water-soluble polymer selected from stearyl alcohol polyglycol ether. However, the type of moderator is not limited thereto, and other nonionic water-soluble polymers that can be used in the manufacture of 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 of the copper foil 200 by the moderator (component B) is insignificant, and if it exceeds 25,000, the moderator (component B) Due to the large molecular weight of the copper layer 110 may not be easily formed.

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 first leveling agent (component C) and the second leveling agent (component D) prevent excessively high peaks or excessively large protrusions from being generated in the copper layer 110, so that the copper layer 110 is macroscopically flat. let it bear

The first leveling agent (component C) includes a thiol-based compound or a thio-based compound. The first leveling agent (component C) improves the strength of the copper foil 200 in addition to the function of planarizing the copper layer 110 .

The first leveling agent (component C) has a concentration of 1 to 10 ppm.

When the concentration of the first leveling agent (component C) is less than 1 ppm, the strength of the copper foil 200 is reduced because high strength of the copper foil 200 is not achieved. When the concentration of the first leveling agent (component C) exceeds 10 ppm, the surface roughness of the copper foil 200 increases, the tensile strength decreases, and a large number of pin holes occur on the surface of the copper foil 200, Difficulty also arises in peeling after manufacturing the copper foil 200 .

The first leveling agent (component C) is thiourea (TU), diethylthiourea, ethylenethiourea, acetylenethiourea, dipropylthiourea, dibutylthiourea, N-trifluoroacetylthiourea (N- trifluoroacetylthiourea), N-ethylthiourea, N-cyanoacetylthiourea, N-allylthiourea, o-tolylthiourea, N ,N'-butylenethiourea (N,N'-butylene thiourea), thiozolidinethiol, 4-thiazolinethiol, 4-methyl-2-pyrimidinethiol (4-methyl -2-pyrimidinethiol) and 2-thiouracil (2-thiouracil).

The second leveling agent (component D) includes a heterocyclic compound (D) having at least one of nitrogen (N) and sulfur (S). The second leveling agent (component D) prevents curl from occurring in the copper foil 200 in addition to the function of planarizing the copper layer 110 .

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

When the concentration of the second leveling agent (component D) is less than 1 ppm, the strength of the copper foil 200 is lowered, making it difficult to implement high strength, and curl occurs in the copper foil 200 . On the other hand, when the concentration of the second leveling agent (component D) exceeds 20 ppm, the strength of the copper foil 200 is increased, but the curl tends to be rather severe.

The second leveling agent (component D) is 3-(benzotriazole-2-mercapto)-prosulfonic acid), 2-mercaptopyridine, 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- selected from butylpyrrole, N-methylpyrroline, N-ethylpyrroline, N-butylpyrroline, pyrimidine, purine, quinoline, isoquinoline, N-methylcarbazole, N-ethylcarbazole and N-butylcarbazole contains at least one

Forming the copper layer 110 may include filtering the electrolyte solution 11 . For filtering the electrolyte solution 11, for example, the electrolyte solution 11 can 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 serving as 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, resin components or natural oxides, and water cleaning for removing an acidic solution used for pickling. ) can be performed sequentially. A cleaning process may be omitted.

Next, antirust films 211 and 212 are formed on the copper layer 110 .

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

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

The anti-rust films 211 and 212 may contain a silane compound by silane treatment or a nitrogen compound by nitrogen treatment.

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

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

Next, after a drying process is performed, the copper foil 200 is wound around 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.

manufacturing example 1-4 and comparative example 1-5

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

The electrolyte solution contains organic additives. Among the organic additives, bis-(3-sulfopropyl)-disulfide disodium salt (SPS) was used as a brightening agent (component A), polyethylene glycol (PEG) was used as a moderator (component B), and a first leveling agent ( Ethylene Thiourea (ETU) was used as component C) and 2-mercapto pyridine (2MP) was used as the second leveling agent (component D). Its content is shown in Table 1.

Meanwhile, the surface of the rotary drum 12 was polished using a drum polishing buffing brush of #2000 roughness. Accordingly, the coefficient of kinetic friction and hardness of the first surface S1 in the direction of the shiny surface SS of the copper layer 110 were maintained almost constant.

While maintaining the temperature of the electrolyte solution 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 manufacture the copper layer 110 . Next, the copper layer 110 was immersed in an anti-rust solution containing chromium for about 2 seconds, and chromate treatment was performed on the surface of the copper layer 110 to form anti-rust 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 manufactured.

Organic additive concentration (ppm) SPS
(Component A) PEG
(component B) ETU
(component C) 2MM
(Component D) Preparation Example 1 20 30 3 10 Preparation Example 2 5 50 10 20 Preparation Example 3 15 5 - 5 Production Example 4 30 20 5 - Comparative Example 1 - 30 12 - Comparative Example 2 20 30 3 25 Comparative Example 3 15 - - 10 Comparative Example 4 - - 15 - Comparative Example 5 - 30 - 10

SPS: Bis(3-Sulfo-Propyl)di-Sulfide

PEG: Polyethylene Glycol

ETU: Ethylene Thiourea

2MP: 2-Mercapto Pyridine

For the copper foils of Preparation Examples 1-4 and Comparative Examples 1-5 prepared as described above, (i) the hardness of the first surface (S1) and the second surface (S2), (ii) the first surface (S1) and the second surface (S1) The kinetic friction coefficient of the second surface (S2), (iii) curl height, (iv) wrinkle generation and (v) capacity retention were measured.

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

The first and second surfaces (S1) and (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 ISO 14577 standards 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 of the first surface S1 and the second surface S2 5 times each, 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 rate (HDR) was calculated according to the following Equation 1 using the hardness of the first surface (S1) and the second surface (S2) of the copper foil.

[Equation 1]

(ii) Measurement of the dynamic friction coefficient of the first surface (S1) and the second surface (S2)

Measure the kinetic friction coefficients of the first surface (S1) and the second surface (S2) of the copper foils prepared in Manufacturing Examples 1-4 and Comparative Examples 1-5 using HEIDON's Tribogear 14FW model according to ASTM D1894. did Figure 7 is a schematic diagram explaining the measurement of the dynamic friction coefficient of copper foil.

Specifically, as shown in FIG. 7, the copper foil (CE) is placed on the substrate 610, the stainless steel ball (SUS ball) 630 and the copper foil (CE) come into contact, and the stainless steel ball 630 The dynamic friction coefficient of the copper foil (CE) was measured while moving the copper foil (CE) in the D1 direction while applying a load. At this time, a stainless steel ball 630 with a diameter of 10 mm was used, and measurement conditions of applying a load of 100 g at a speed of 100 mm/min at a measurement distance of 10 mm were applied. The dynamic friction coefficient was measured three times, and the average value is disclosed in Table 2.

In addition, the difference in kinetic friction coefficient between the first surface (S1) and the second surface (S2) of the copper foil was calculated.

(iii) Measurement of curl height

To measure the curl height of the copper foil 100, copper foil specimens 510 were prepared by cutting the copper foils of Preparation Examples 1-4 and Comparative Examples 1-5 into 60 mm X 60 mm. 8 is a schematic diagram explaining the measurement of the curl height of copper foil.

Referring to FIG. 8 , after the specimen 510 is placed on the support 520 so that the first surface S1 of the specimen 510 faces upward, a glass plate 530 is placed on the specimen 510 . At this time, only half of the specimen 510 was overlapped with the glass plate by 30 mm in length, so that only half of the specimen 510 was positioned between the support 520 and the glass plate 530, and the other half was exposed from the glass plate 530. The height of the specimen 510 exposed to the outside of the glass plate 530 was measured using the measuring means 540 (meter ruler), and the maximum height was defined as the curl 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 curl heights were measured, and then the average value was calculated to calculate the curl height value of the copper foil.

(iv) measurement of wrinkle occurrence

9 is a schematic diagram illustrating a wrinkle generation test.

As shown in FIG. 9, after the copper foils (CF) of Manufacturing Examples 1-4 and Comparative Examples 1-5 were placed on the first roll (R1) and the second roll (R2), 1.5 After artificially generating misalignment in the range of ˚ angle (θ), it was confirmed whether wrinkles were generated when the copper foil was driven in the D1 direction. In Table 2, cases where wrinkles occurred were marked with "○", and cases where wrinkles did not occur were marked with "X".

(v) capacity retention rate evaluation

1) Cathode manufacturing

Commercially available silicon/carbon composite negative electrode material for negative active material Mix 2 parts by weight of styrene butadiene rubber (SBR) and 2 parts by weight of carboxymethyl cellulose (CMC) with 100 parts by weight of a negative active material slurry for negative active material using distilled water as a solvent was prepared. Using a doctor blade, the slurry for negative electrode 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, dried at 120 ° C, and 1 ton / cm A negative electrode for a secondary battery was prepared by applying a pressure of ² .

2) Manufacture of electrolyte solution

A basic electrolyte solution was prepared by dissolving LiPF ₆ as a solute at a concentration of 1 M in a non-aqueous organic solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a ratio of 1:2. A nonaqueous 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 Li _1.1 Mn _1.85 Al _0.05 O ₄ lithium manganese oxide and o-LiMnO ₂ lithium manganese oxide having an orthorhombic crystal structure in a ratio of 90:10 (weight ratio). A slurry was prepared by mixing a cathode active material, carbon black, and PVDF [Poly(vinylidenefluoride)] as a binder in a weight ratio of 85:10:5 (weight ratio) and mixing them with NMP, an organic solvent. The prepared slurry was applied to both surfaces of an Al foil having a thickness of 20 μm and then dried to prepare a positive electrode.

4) Production of lithium secondary battery for testing

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

5) Evaluation of capacity retention rate

Using the lithium secondary battery prepared as described above, the battery was driven at a charging voltage of 4.3V and a discharging voltage of 3.4V, and the capacity per gram of the positive electrode was measured. Next, in order to evaluate the high-temperature lifespan, a capacity retention rate was calculated by performing a charge/discharge experiment 50 times at a high temperature of 50° C. at a current rate (C-rate) of 0.2 C. The capacity retention rate can be calculated by Equation 4 below.

[Equation 4]

Capacity retention rate (%) = [(Capacity after 50 charge/discharge cycles)/(Capacity after charge/discharge cycle once)] 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 for a negative electrode current collector for a lithium ion battery.

The above test results are shown in Table 2.

Hardness (GPa) Dynamic friction coefficient curl
Height
(mm) Volume
retention rate
(%) Presence of wrinkles page 1 page 2 Longitudinal difference rate page 1 page 2 double sided difference Preparation Example 1 1.69 1.65 0.02 0.43 0.32 0.11 9 92 X Preparation Example 2 1.52 1.67 0.1 0.49 0.32 0.17 12 91 X Preparation Example 3 1.42 1.66 0.18 0.46 0.33 0.13 11 90 X Production Example 4 1.57 1.67 0.06 0.41 0.32 0.09 17 91 X Comparative Example 1 1.37 1.66 0.21 0.38 0.33 0.05 30 81 O Comparative Example 2 1.71 1.65 0.03 0.53 0.32 0.21 28 80 O Comparative Example 3 1.32 1.67 0.27 0.56 0.33 0.23 21 78 O Comparative Example 4 1.35 1.66 0.23 0.34 0.32 0.02 25 81 O Comparative Example 5 1.3 1.67 0.28 0.31 0.32 0.01 22 80 O

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

In the copper foil of Comparative Example 1 made of an electrolyte solution containing an excess of the first leveling agent (component C) and not containing a brightening agent (component A) among organic additives, a curl exceeding 20 mm occurred, Comparative Example 1 The secondary battery manufactured using the copper foil of had a capacity retention rate of less than 90%, and wrinkles occurred in the copper foil.

A curl of more than 20 mm occurred in the copper foil of Comparative Example 2 made of an electrolyte containing an excess of the second leveling agent (component D), and the secondary battery manufactured using the copper foil of Comparative Example 2 was less than 90% It has a capacity retention rate of , and wrinkles occurred in the copper foil.

A curl of more than 20 mm occurred in the copper foil of Comparative Example 3 made of an electrolyte solution containing no moderator (component B), and the secondary battery manufactured using the copper foil of Comparative Example 3 had a capacity retention rate of less than 90% , and wrinkles occurred in the copper foil.

A curl of more than 20 mm occurred in the copper foil of Comparative Example 4 made of an electrolyte solution containing only the first leveling agent (component C), and the secondary battery manufactured using the copper foil of Comparative Example 4 had a capacity of less than 90% It had a retention rate, and wrinkles occurred in the copper foil.

A curl of more than 20 mm occurred in the copper foil of Comparative Example 5 made of an electrolyte solution containing no brightener (component A), and the secondary battery manufactured using the copper foil of Comparative Example 5 had a capacity retention rate of less than 90%. and wrinkles occurred in the copper foil.

On the other hand, according to an embodiment of the present invention, at least one of the first leveling agent (component C) and the second leveling agent (component D) is included as organic additives, including a brightening agent (component A) and a moderator (component B). In the copper foils of Preparation Examples 1 to 4 made of the electrolyte solution containing, the height of the curl is 20 mm or less, and the secondary battery manufactured using this copper foil has a capacity retention rate of 90% or more, and no wrinkles occurred on the copper foil. .

The present invention described above is not limited by the foregoing embodiments and the accompanying drawings, and various substitutions, modifications, and changes are possible within the scope of the technical details of the present invention. will be clear to those skilled 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: if it's shiny

Claims (21)

a copper layer having a matte side and a shiny side; and
Including; a rust-preventive film disposed on the copper layer,
It has a first surface in the direction of the matte surface and a second surface in the direction of the shiny surface,
The hardness difference rate (HDR) between the first surface and the second surface is 0.02 or less, where the hardness difference rate (HDR) is obtained by the following equation 1,
[Equation 1]

At least one of the first surface and the second surface has a hardness of 1.4 to 1.7 GPa,
The first surface has a kinetic friction coefficient of 0.4 to 0.5,
Copper foil, wherein the difference in dynamic friction coefficient between the first surface and the second surface is 0.2 or less. According to claim 1,
Copper foil having a tensile strength of 40 kgf/mm ² or more. According to claim 1,
Copper foil having an elongation of 2% or more. According to claim 1,
The first surface and the second surface each have a surface roughness (Rz JIS) of 0.5 to 2.0 μm, copper foil. According to claim 1,
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 rust-preventive film includes at least one of chromium, a silane compound, and a nitrogen compound. copper foil; and
Including; active material layer disposed on at least one surface of the copper foil,
The copper foil is a copper foil according to any one of claims 1 to 7,
Electrodes for secondary batteries. cathode;
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
Including; a separator that electrically insulates the anode and the cathode;
The cathode is
The copper foil according to any one of claims 1 to 7; and
an active material layer disposed on the copper foil;
Including, secondary battery. Forming a copper layer by applying a current density of 30 to 80 ASD (A/dm ² ) between an electrode plate and a rotating drum spaced apart from each other in an electrolyte solution containing copper ions,
The electrolyte is
60 to 120 g/L copper ions;
80 to 150 g/L sulfuric acid;
Chlorine (Cl) less than 50 ppm; and
Including; organic additives,
The organic additive,
brightener (component A);
moderators (component B);
1st leveling agent (component C); and
It includes a second leveling agent (component D),
The brightening agent (component A) includes sulfonic acid or a metal salt thereof,
The moderator (component B) includes a nonionic water-soluble polymer,
The first leveling agent (component C) includes a thiol-based compound or a thio-based compound having a concentration of 1 to 10 ppm,
The second leveling agent (component D) comprises 2-mercaptopyridine having a concentration of 1 to 20 ppm,
Copper foil manufacturing method. According to claim 10,
In the step of forming the copper layer, the temperature of the electrolyte solution is maintained in the range of 40 to 60 ℃, copper foil manufacturing method. According to claim 10,
The brightener (component A) has a concentration of 5 to 100 ppm, copper foil manufacturing method. According to claim 10,
The brightening agent (component A) is bis-(3-sulfopropyl)-disulfide disodium salt [bis-(3-Sulfopropyl)-disulfide disodium salt] (SPS), 3-mercapto-1-propanesulfonic acid, 3- (N,N-dimethylthiocarbamoyl)-thiopropanesulfonate sodium salt, 3-[(amino-iminomethyl)thio]-1-propanesulfonate sodium salt, o-ethyldithiocarbonate-S-( At least one selected from 3-sulfopropyl)-ester sodium salt, 3-(benzothiazolyl-2-mercapto)-propyl-sulfonic acid sodium salt and ethylenedithiodipropylsulfonic acid sodium salt, Copper foil manufacturing method. According to claim 10,
The moderator (component B) has a concentration of 5 to 50 ppm, a method for producing copper foil. According to claim 10,
The moderator (component B) is polyethylene glycol (PEG), polypropylene glycol, polyethylene polypropylene copolymer, polyglycerin, polyethylene glycol dimethyl ether, hydroxyethylene cellulose, polyvinyl alcohol, stearic acid polyglycol ether and stearyl A method for producing a copper foil comprising at least one nonionic water-soluble polymer selected from alcohol polyglycol ethers. According to claim 15,
The nonionic water-soluble polymer has a number average molecular weight of 500 to 25,000, copper foil manufacturing method. delete According to claim 10,
The first leveling agent (component C) is thiourea (TU), diethylthiourea, ethylenethiourea, acetylenethiourea, dipropylthiourea, dibutylthiourea, N-trifluoroacetylthiourea (N -trifluoroacetylthiourea), N-ethylthiourea, N-cyanoacetylthiourea, N-allylthiourea, o-tolylthiourea, N, N'-butylene thiourea, thiazolidinethiol, 4-thiazolinethiol, 4-methyl-2-pyrimidinethiol (4- methyl-2-pyrimidinethiol) and 2-thiouracil (2-thiouracil), including at least one selected from, a method for producing a copper foil. delete delete According to claim 10,
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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