CN108270016B

CN108270016B - Electrolytic copper foil, electrode, secondary battery and method for manufacturing same

Info

Publication number: CN108270016B
Application number: CN201810007187.6A
Authority: CN
Inventors: 蔡荣昱; 安重圭; 崔成勋; 李廷吉; 金兑炫
Original assignee: SK Nexilis Co Ltd
Current assignee: KCF Technologies Co Ltd
Priority date: 2017-01-04
Filing date: 2018-01-04
Publication date: 2021-03-26
Anticipated expiration: 2038-01-04
Also published as: JP6652548B2; KR20180080514A; JP2018109227A; CN108270016A

Abstract

Provided are an electrolytic copper foil having high corrosion resistance and good adhesion to an active material, an electrode including the same, a secondary battery including the same, and a method of manufacturing the same. The electrolytic copper foil of the present invention comprises a first surface and a second surface opposite to the first surface, wherein the first surface obtained immediately before and after the constant temperature and humidity test is 5 or less in CIE 1976L a b color difference (Δ E), and a sample of the electrolytic copper foil is maintained for 24 hours under an accelerated test condition of a temperature of 70 ℃ and a relative humidity of 80% in the constant temperature and humidity test; a difference in glossiness of the first surface with respect to an incident angle of 60 f, which is obtained immediately before and after performing a constant temperature and humidity test in which the sample is maintained under an accelerated test condition of a temperature of 70 ℃ and a relative humidity of 80% for 24 hours, is 50 or less; and the chromium (Cr) content of each of the first and second protective layers ranges from 1to 5mg/m²。

Description

Electrolytic copper foil, electrode, secondary battery and method for manufacturing same

Cross Reference to Related Applications

The present application claims priority and benefit of korean patent application No. 2017-0001310, filed on 4/1/2017, the disclosure of which is incorporated herein by reference in its entirety.

Technical Field

The present invention relates to an electrolytic copper foil, an electrode including the electrolytic copper foil, a secondary battery including the electrolytic copper foil, and a method of manufacturing the electrolytic copper foil, and more particularly, to an electrolytic copper foil having good marketability due to its high corrosion resistance and capable of ensuring a secondary battery having a high capacity retention rate due to its good adhesion to an active material, an electrode including the electrolytic copper foil, a secondary battery including the electrolytic copper foil, and a method of manufacturing the electrolytic copper foil.

Background

A secondary battery is an energy conversion device that converts electric energy into chemical energy, stores the chemical energy, and generates electricity by converting the chemical energy into electric energy when electric power is required, and is used as an energy source for electric vehicles and portable devices such as mobile phones, laptop computers, and the like.

Lead-acid batteries, nickel-cadmium secondary batteries, nickel-hydrogen secondary batteries, lithium secondary batteries, and the like are secondary batteries that are economically and environmentally favorable compared to primary batteries.

The lithium secondary battery can store a relatively large amount of energy with respect to its size and weight, as compared to other secondary batteries. Therefore, in the field of information communication devices where portability and mobility are important, a lithium secondary battery is preferable, and the application range thereof is also expanding to include energy storage devices for hybrid vehicles and electric vehicles.

An electrolytic copper foil used as a negative electrode current collector of a lithium secondary battery has an antirust coating formed on the surface of the electrolytic copper foil to prevent corrosion.

When the rust inhibitive coating is excessively thin, surface oxidation of the copper layer of the electrolytic copper foil rapidly proceeds under a high temperature and high humidity environment, resulting in poor appearance. Such defective appearance results in a decrease in marketability of the electrolytic copper foil.

On the other hand, as the anticorrosive coating becomes thicker, the corrosion resistance of the electrolytic copper foil increases. However, the rust inhibitive coating layer functions as a foreign substance between the copper layer of the electrolytic copper foil and the negative active material, thus reducing the adhesion between the copper layer and the negative active material and further increasing the risk of separation of the negative active material.

Specifically, in order to increase the capacity of a lithium secondary battery, a method of using a composite active material in which Si or Sn is added to a carbon active material as an anode active material has been proposed. Such a composite active material has a relatively large thermal expansion coefficient compared to a conventional anode active material. The separation of the electrolytic copper foil and the negative active material is promoted due to rapid expansion and contraction of the composite active material caused when the lithium secondary battery is charged or discharged, and thus the charge and discharge capacity retention rate of the lithium secondary battery is reduced. When the electrolytic copper foil is coated with the negative active material and then dried at a high temperature of 80 ℃ or more for 1 hour or more, the surface of the electrolytic copper foil is oxidized, promoting the separation of the negative active material. As the adhesive strength between the copper foil and the negative active material is reduced, the charge and discharge capacity retention rate of the lithium secondary battery is significantly reduced.

When the charge and discharge capacity of the secondary battery is rapidly decreased due to repeated charge and discharge cycles (i.e., when the capacity retention rate of the secondary battery is low or the life thereof is short), consumers will need to frequently replace the secondary battery, which causes inconvenience and waste of resources to consumers.

Disclosure of Invention

The present invention is directed to an electrolytic copper foil capable of preventing problems caused by the limitations and disadvantages of the related art, an electrode including the same, a secondary battery including the same, and a method of manufacturing the same.

The present invention also relates to an electrolytic copper foil which has good marketability due to its high corrosion resistance and can ensure a high capacity retention rate of a secondary battery due to its good adhesion to an active material.

The present invention also relates to an electrode capable of ensuring a secondary battery having a high capacity retention rate due to high adhesive force between an electrolytic copper foil and an active material.

The present invention also relates to a secondary battery having a high capacity retention rate.

The present invention also relates to a method of manufacturing an electrolytic copper foil having good marketability due to its high corrosion resistance and capable of securing a high capacity retention rate of a secondary battery due to its good adhesion to an active material.

In addition to the above-described aspects of the present invention, other features and advantages of the present invention will be described below or will become apparent to those skilled in the art from the following description.

According to an aspect of the present invention, there is provided an electrolytic copper foil including a first surface and a second surface opposite to the first surface, the electrolytic copper foil including: a copper layer comprising a matte surface facing the first surface and a glossy surface facing the second surface; a first protective layer on the matte surface; and a second protective layer on the glossy surface, wherein: each of the first protective layer and the second protective layerIncluding chromium (Cr) and Benzotriazole (BTA); a color difference (Δ E) of 5 or less in CIE 1976L a b of the first surface obtained immediately before and after performing a constant temperature and humidity test in which a sample of the electrolytic copper foil is maintained under an accelerated test condition of a temperature of 70 ℃ and a relative humidity of 80% for 24 hours; a difference in gloss of the first surface with respect to a 60 th incident angle, which is obtained immediately before and after performing a constant temperature and humidity test in which the sample is maintained under an accelerated test condition of a temperature of 70 ℃ and a relative humidity of 80% for 24 hours, is 50 or less; and a chromium (Cr) content of each of the first and second protective layers ranges from 1to 5mg/m²。

The difference between the chromium (Cr) content of the first protective layer and the chromium (Cr) content of the second protective layer may be 2mg/m²Or smaller.

The surface roughness (Rz) of each of the first surface and the second surface may range from 0.5 to 2.5 μm.

The electrolytic copper foil may have a tensile strength of 30kgf/mm at room temperature²Or greater, the elongation may be 2% or greater.

The electrolytic copper foil may have a thickness of 1to 70 μm.

According to another aspect of the present invention, there is provided a secondary battery electrode including: an electrolytic copper foil including a first surface and a second surface opposite to the first surface; and a first active material layer on the first surface, wherein the electrolytic copper foil includes: a copper layer comprising a matte surface facing the first surface and a glossy surface facing the second surface; a first protective layer on the matte surface; and a second protective layer on the glossy surface, each of the first protective layer and the second protective layer including chromium (Cr) and BTA, a peel strength between the electrolytic copper foil and the first active material layer being 20N/mm²Or larger.

The chromium (Cr) content of each of the first and second protective layers may range from 1to 5mg/m²And the chromium (Cr) content of the first protective layerThe difference from the chromium (Cr) content of the second protective layer may be 2mg/m²Or smaller.

The surface roughness (Rz) of each of the first and second surfaces may range from 0.5 to 2.5 μm.

The electrolytic copper foil may have a thickness of 30kgf/mm at room temperature²Or greater tensile strength and 2% or greater elongation.

The electrolytic copper foil may have a thickness of 1to 70 μm.

The secondary battery electrode may further include a second active material layer on the second surface, wherein each of the first and second active material layers includes one or more active materials selected from the group consisting of carbon, a metal such as Si, Ge, Sn, Li, Zn, Mg, Cd, Ce, Ni, or Fe, an alloy containing the metal, an oxide of the metal, and a composite of the metal and carbon.

Each of the first and second active material layers may include at least one of Si and Sn.

According to still another aspect of the present invention, there is provided a secondary battery including a cathode, an anode including an electrode of the secondary battery, an electrolyte configured to provide an environment in which lithium ions move between the cathode and the anode, and a separator configured to electrically insulate the cathode from the anode.

According to still another aspect of the present invention, there is provided a method of manufacturing an electrolytic copper foil, the method including forming a copper layer and forming a protective layer on the copper layer, wherein the forming of the copper layer includes: preparing an electrolyte containing 60 to 120g/L of copper ions, 80 to 150g/L of sulfuric acid, and 50ppm or less of chlorine; and by making the electrode plate and the rotary electrode drum arranged at a distance from each other in the electrolyte at 30 to 80A/dm²The current density of (a) is conductive to perform electroplating, and the forming the protective layer includes: preparing an antirust solution by mixing a chromate solution and a BTA solution; and immersing the copper layer in the rust inhibitive solution. The temperature in the electrolyte may be 40 to 60 ℃ during electroplating.

The electrolyte may further include at least one organic additive selected from the group consisting of hydroxyethyl cellulose (HEC), organic sulfides, organic nitrides, and thiourea-based compounds.

The rust preventive solution may include 0.1 to 2g/L of chromium (Cr) and 1to 100mg/L of BTA, and the pH of the rust preventive solution may be in the range of 1.0 to 3.0.

When the protective layer is formed, the temperature of the rust inhibitive solution may be maintained at 20 to 60 ℃.

The copper layer may be immersed in the rust inhibitive solution for 1to 10 seconds.

The general description of the invention set forth above is intended only to illustrate or explain the invention and is not intended to limit the scope of the invention.

Drawings

The above and other objects, features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the attached drawings, in which:

fig. 1 is a sectional view of an electrode for a secondary battery according to an embodiment of the present invention; and

fig. 2 is a view of an apparatus for manufacturing an electrolytic copper foil according to an embodiment of the present invention.

Detailed Description

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 modifications and variations can be made in the present invention without departing from the spirit and scope of the invention. Accordingly, this invention includes all modifications and alterations coming within the scope of the invention as defined by the appended claims and equivalents thereof.

A lithium secondary battery includes a cathode, an anode, an electrolyte providing an environment in which lithium ions can move between the cathode and the anode, and a separator electrically insulating the cathode from the anode to prevent electrons generated at one electrode from being inefficiently consumed by moving to the other electrode through the inside of the secondary battery.

Fig. 1 is a sectional view of an electrode for a secondary battery according to an embodiment of the present invention.

As shown in fig. 1, a secondary battery electrode 100 according to an embodiment of the present invention includes: an electrolytic copper foil 110 having a first surface S1 and a second surface S2 opposite to the first surface S1; the first active material layer 120a on the first surface S1; and a second active material layer 120b on the second surface S2. In fig. 1, an example is shown in which

active material layers

120a and 120b are formed on the first surface S1 and the second surface S2 of the electrolytic copper foil 110, respectively, but the present invention is not limited thereto, and the secondary battery electrode 100 of the present invention may include only one of the first active material layer 120a and the second active material layer 120b as an active material layer.

Generally, in a lithium secondary battery, aluminum foil is used as a positive electrode (cathode) current collector coupled to a positive electrode (cathode) active material, and electrolytic copper foil is used as a negative electrode (anode) current collector coupled to a negative electrode (anode) active material.

According to an embodiment of the present invention, the secondary battery electrode 100 serves as an anode of a lithium secondary battery, the electrolytic copper foil 110 serves as a negative electrode (anode) current collector, and the first and second

active material layers

120a and 120b each include a negative electrode (anode) active material.

As shown in fig. 1, the electrolytic copper foil 110 of the present invention includes a copper layer 111 having a matte surface MS and a glossy surface SS, a first protective layer 112a on the matte surface MS of the copper layer 111, and a second protective layer 112b on the glossy surface SS of the copper layer 111.

The matte surface MS is a surface of the copper layer 111 facing the first surface S1 of the electrolytic copper foil 110, and the glossy surface SS is a surface of the copper layer 111 facing the second surface S2 of the electrolytic copper foil 110. That is, the first surface S1 of the electrolytic copper foil 110 is a surface adjacent to the matte surface MS of the copper layer 111, and the second surface S2 of the electrolytic copper foil 110 is a surface adjacent to the glossy surface SS of the copper layer 111.

The copper layer 111 of the present invention can be formed on the rotating electrode drum by performing electroplating thereon. The glossy surface SS thereof means a surface which is in contact with the rotating electrode drum during the plating process, and the matte surface MS means a surface opposite to the glossy surface SS.

Generally, the glossy surface SS has a lower surface roughness (Rz) than the matte surface MS, but the present invention is not limited thereto, and the surface roughness (Rz) of the glossy surface SS may be higher than or equal to the surface roughness (Rz) of the matte surface MS.

The electrolytic copper foil 110 of the present invention may have a kgf/mm at room temperature (25 ℃ C.) of 30²Or greater tensile strength and 2% or greater elongation. Tensile strength and elongation were measured using a Universal Testing Machine (UTM) in which the width of the sample was 12.7mm, the distance between the grips was 50mm, and the measuring speed was 50 mm/min.

When the tensile strength is less than 30kgf/mm²Or an elongation of less than 2%, the risk of deformation and/or breakage of the electrode 100 due to expansion and contraction of the negative active material caused when the secondary battery is charged or discharged is high.

The electrolytic copper foil 110 of the present invention may have a thickness of 1to 70 μm.

Each of the first and second

active material layers

120a and 120b may include at least one selected from the group consisting of carbon, a metal such as Si, Ge, Sn, Li, Zn, Mg, Cd, Ce, Ni, or Fe, an alloy containing the metal, an oxide of the metal, and a composite of the metal and carbon as an anode active material.

In order to increase the charge and discharge capacity of the secondary battery, each of the first and second

active material layers

120a and 120b may include at least one of Si and Sn.

As described above, as the secondary battery repeats charge and discharge, the

active material layers

120a and 120b alternately expand and contract. This causes the

active material layers

120a and 120b to be separated from the electrolytic copper foil 110, thereby reducing the charge and discharge efficiency of the secondary battery. Therefore, in order for the secondary battery to have a certain or higher degree of capacity retention and life (i.e., in order to suppress deterioration of charge and discharge efficiency of the secondary battery), the electrolytic copper foil 110 should have good coatability with respect to the active material such that the adhesive strength between the electrolytic copper foil 110 and the

active material layers

120a, 120b is high.

The adhesive strength between the electrolytic copper foil 110 and the

active material layers

120a and 120b can be improved by controlling the surface roughness (Rz) of the electrolytic copper foil 110. The surface roughness (Rz) can be measured according to Japanese Industrial Standard (JIS) B0601-: 4mm (excluding the truncated part) ].

According to an embodiment of the present invention, the surface roughness (Rz) of each of the first surface S1 and the second surface S2 of the electrolytic copper foil 110 may be in the range of 0.5 to 2.5 μm. When the surface roughness (Rz) is less than 0.5 μm, the contact area with the negative electrode active material is too small, and sufficient adhesion between the electrolytic copper foil 110 and the negative electrode active material cannot be secured. On the other hand, when the surface roughness (Rz) exceeds 2.5 μm, since the first surface S1 and the second surface S2 of the electrolytic copper foil 110 are excessively uneven, the coating uniformity of the negative active material is reduced, and thus the adhesive force between the electrolytic copper foil 110 and the first active material layer 120a and the second active material layer 120b is significantly reduced.

However, the electrolytic copper foil 110, the surface roughness (Rz) of which is appropriately adjusted, does not necessarily satisfy a certain level of adhesion between the electrolytic copper foil 110 and the

active material layers

120a and 120b required in specifications. That is, the electrolytic copper foil 110 having a surface roughness (Rz) of 0.5 to 2.5 μm cannot always secure a capacity retention rate of 90% or more of a secondary battery (after 50 charging and discharging) which is industrially required.

Specifically, it is known that when the

active material layers

120a and 120b include at least one of Si and Sn to increase the capacity of the secondary battery, the relationship between the surface roughness (Rz) of the electrolytic copper foil 110 and the capacity retention rate of the secondary battery is weak.

According to the present invention, it is known that the materials of the first and second

protective layers

112a and 112b of the electrolytic copper foil 110 and the contents thereof are important factors when ensuring that the adhesive force between the electrolytic copper foil 110 and the

active material layers

120a and 120b is sufficiently large to ensure a capacity retention rate of 90% or more in the secondary battery.

The first protective layer 112a and the second protective layer 112b of the present invention are formed to prevent corrosion of the copper layer 111 and improve heat resistance thereof, and include chromium (Cr).

Each of the first protective layer 112a and the second protective layer 112bThe chromium (Cr) content is preferably from 1to 5mg/m²And the difference between the chromium (Cr) content of the first protective layer 112a and the chromium (Cr) content of the second protective layer 112b is preferably 2mg/m²Or smaller.

When the chromium (Cr) content of each of the first and second

protective layers

112a and 112b is less than 1mg/m²When oxygen easily penetrates through the first and second

protective layers

112a and 112b to oxidize the surface of the copper layer 111, and there may not be sufficient chemical bonding between the electrolytic copper foil 110 and the negative active material due to the surface oxidation of the copper layer 111, and therefore, when the electrolytic copper foil 110 is coated with the negative active material and then dried at a high temperature of 80 ℃ or more for 1 hour or more, the adhesive force between the electrolytic copper foil 110 and the

active material layers

120a and 120b may also be inevitably low. On the other hand, when the chromium (Cr) content is more than 5mg/m²In the case, although the corrosion resistance of the electrolytic copper foil 110 is good, the hydrophobicity of the surface of the electrolytic copper foil 110 increases, and the chemical affinity for the negative electrode active material decreases. As a result, sufficient chemical bonding may not be provided between the electrolytic copper foil 110 and the negative active material, and thus sufficient adhesion may not be ensured between the electrolytic copper foil 110 and the

active material layers

120a and 120 b.

When the difference between the chromium (Cr) content of the first protective layer 112a and the chromium (Cr) content of the second protective layer 112b is more than 2mg/m²When the electrolytic copper foil 110 is curled, workability thereof may be reduced, and a large difference in adhesion to the anode active material may be generated between the first surface S1 and the second surface S2 of the electrolytic copper foil 110, thereby causing a reduction in capacity retention rate of the secondary battery.

According to the present invention, each of the first and second

protective layers

112a and 112b includes Benzotriazole (BTA) in addition to chromium (Cr). Since the first and second

protective layers

112a and 112b include chromium (Cr) and BTA, higher corrosion resistance than the electrolytic copper foil 110 to which only chromium (Cr) is applied may be ensured, and adhesion to the negative active material may be further improved.

The corrosion resistance of the electrolytic copper foil 110 can be quantified by the difference in CIE 1976L a b color difference (Δ E) and glossiness (incident angle: 60 light) caused by the constant temperature and humidity test.

In the present invention, the constant temperature and humidity test is performed by maintaining the electrolytic copper foil 110 for 24 hours under the accelerated test condition of the temperature of 70 ℃ and the relative humidity of 80%.

CIE 1976L a b color difference (Δ E) represents a perceived difference of two perceived colors, and the color difference can be obtained by calculating a geometric distance between two points in L a b color space (CIE 1976) based on the following equation 1.

Equation 1: Δ E { (Δ L {)²+(Δa*)²+(Δb*)²}^1/2

The perceived color of the surface of the electrolytic copper foil 110 was measured immediately before and after the constant temperature and humidity test using a spectrophotometer, and the measured value was used to calculate the CIE 1976L a b color difference (Δ E).

Further, the gloss of the surface of the electrolytic copper foil 110 with respect to the incident angle of 60 ° was measured using a gloss meter immediately before and after the constant temperature and humidity test, and the difference between the measured values was calculated.

Since the first and second

protective layers

112a and 112b include BTA in addition to chromium (Cr), the electrolytic copper foil 110 of the present invention has good corrosion resistance, and thus the CIE 1976L a b color difference (Δ E) of the surfaces S1, S2 of the electrolytic copper foil 110 immediately before and after the constant temperature and humidity test is 5 or less, and the gloss difference of the surfaces S1 and S2 of the electrolytic copper foil 110 with respect to 60 at an incident angle immediately before and after the constant temperature and humidity test is 50 or less.

Therefore, according to the present invention, since the surface of the copper layer 111 can be prevented from being oxidized even when the electrolytic copper foil 110 is coated with the negative active material and then dried at a high temperature of 80 ℃ or more for 1 hour or more, it is possible to provide sufficient chemical bonding between the electrolytic copper foil 110 and the negative active material.

The adhesion between the electrolytic copper foil 110 and the

active material layers

120a and 120b can be confirmed by measuring the peel strength between the electrolytic copper foil 110 and the

active material layers

120a and 120 b.

According to the present invention, since the first and second

protective layers

112a and 112b are formed of chromium (Cr) in addition to chromium (Cr)Including BTA, the peel strength between the electrolytic copper foil 110 and each of the

active material layers

120a and 120b is 20N/mm²Or larger.

Hereinafter, the method of manufacturing the electrolytic copper foil 110 of the present invention will be described in detail with reference to fig. 2.

The method of the present invention includes forming a copper layer 111 and forming

protective layers

112a and 112b on the copper layer 111.

First, in the electrolytic cell 10, an electrolytic solution 20 containing 60 to 120g/L of copper ions, 80 to 150g/L of sulfuric acid, and 50ppm or less of chlorine is prepared.

The electrolyte 20 may further include at least one organic additive selected from the group consisting of hydroxyethyl cellulose (HEC), an organic sulfide (e.g., bis (3-sulfopropyl) -disulfide (SPS)), an organic nitride, and a thiourea-based compound. The content of the organic additive in the electrolytic solution 20 may be in the range of 1to 10 ppm.

Next, the electrode plate 30 and the rotary electrode drum 40, which are spaced apart from each other in the electrolyte 20 at 40 to 60 ℃, are set at 30 to 80A/dm²Is electrically conducted and is plated to form a copper layer 111 on the rotating electrode drum 40.

As shown in fig. 2, the electrode plate 30 may include a first electrode plate 31 and a second electrode plate 32 electrically insulated from each other.

The formation of the copper layer 111 may be performed by making the first electrode plate 31 and the rotary electrode drum 40 conductive to form a seed layer and by making the second electrode plate 32 and the rotary electrode drum 40 conductive to grow the seed layer.

The degree of polishing of the surface of the rotating electrode drum 40, for example, the surface on which copper is deposited by electroplating, is a factor in controlling the surface roughness (Rz) and the amount of chromium (Cr) adhesion of the second surface S2 of the electrolytic copper foil 110. According to the present invention, the surface of the rotary electrode drum 40 is polished with an abrasive brush having a particle size of #800 to # 1500.

Can be between 31 and 45m³Continuous (or circulating) filtration is performed at a flow rate of/hr to remove solid impurities from the electrolyte 20 while electroplating is performed. When the flow velocity is less than 31m³At/hr, the flow rate decreases, the overvoltage increases, and it is not uniformA copper layer 111 is formed. On the other hand, when the flow velocity is more than 45m³At/hr, the filter is damaged and foreign matter is introduced into the electrolyte.

An antirust solution 60 is prepared in the treatment bath 50 to form

protective layers

112a and 112b on the copper layer 111. The rust preventive solution may contain 0.1 to 2g/L of chromium (Cr) and 1to 100mg/L of BTA.

When the chromium (Cr) concentration is less than 0.1g/L, the rust-preventive treatment should be performed for a long time, which is not desirable in terms of productivity. On the other hand, when the chromium (Cr) concentration is more than 2g/L, the thickness of the

protective layers

112a and 112b increases, and thus the corrosion resistance is improved, but the adhesion to the active material is reduced.

When the BTA concentration is less than 1mg/L, the effect of the invention is not significant due to the addition of BTA. On the other hand, when the BTA concentration exceeds 100mg/L, the excessive BTA suppresses the formation of the

protective layers

112a and 112b, thereby reducing both the corrosion resistance of the electrolytic copper foil 110 and the adhesion to the active material.

The pH of the rust inhibitive solution 60 may be in the range of 1.0 to 3.0. When the pH of the rust inhibitive solution 60 is less than 1.0, pores and/or defects are generated in the

protective layers

112a and 112b, and the corrosion resistance and the adhesion to the active material of the electrolytic copper foil 110 are deteriorated. On the other hand, when the pH of the rust inhibitive solution 60 is more than 3.0, the formation speed of the

protective layers

112a and 112b is low, which is not preferable in terms of productivity.

Next, the copper layer 111 is immersed in the rust preventive solution 60. When the copper layer 111 is immersed in the rust preventive solution 60, the copper layer 111 can be guided by the guide roller 70 provided in the rust preventive solution 60.

When the

protective layers

112a and 112b are formed, the temperature of the rust inhibiting solution 60 may be maintained at 20 to 60 ℃. When the temperature of the rust inhibitive solution 60 is less than 20 ℃, the formation speed of the

protective layers

112a and 112b is low, which is not preferable in terms of productivity. On the other hand, when the temperature of the rust inhibiting solution 60 is higher than 60 ℃, the thickness of the

protective layers

112a and 112b increases and the corrosion resistance is improved, but the thickness uniformity and the adhesion to the active material are reduced.

The copper layer 111 may be immersed in the rust inhibitive solution 60 for 1to 10 seconds. If the immersion time is less than 1 second, it is difficult to form the

protective layers

112a and 112b, and the surface of the copper layer 111 is easily oxidized. On the other hand, when the immersion time exceeds 10 seconds, the corrosion resistance and the adhesive force with the active material of the electrolytic copper foil 110 are not increased any more, and the productivity is remarkably lowered compared to the obtainable effect.

A portion of the copper layer 111 immersed in the rust inhibitive solution 60 is dissolved to generate hydrogen, the hydrogen reduces hexavalent chromium (Cr) to trivalent chromium (Cr), and the trivalent chromium (Cr) reacts with chromic acid, so that gelled hydrate is deposited on the copper layer 111, and BTA is adsorbed on the gelled hydrate to form the

protective layers

112a and 112b of the present invention.

When the copper concentration in the rust inhibitive solution 60 is higher than a certain level, the

protective layers

112a and 112b may not be formed smoothly. Therefore, it is preferable to periodically replace the rust preventing solution 60.

One surface or both surfaces of the electrolytic copper foil 110 of the present invention manufactured by the above method are coated with a metal (Me) selected from carbon, such as Si, Ge, Sn, Li, Zn, Mg, Cd, Ce, Ni, or Fe, an alloy containing the metal (Me), an oxide (MeO) of the metal (Me)_x) And one or more negative active materials of the group consisting of the metal (Me) and carbon composite to produce the secondary battery electrode (i.e., anode) of the present invention.

For example, 1to 3 parts by weight of styrene-butadiene rubber (SBR) and 1to 3 parts by weight of carboxymethyl cellulose (CMC) are mixed in 100 parts by weight of carbon for a negative active material, and then distilled water is used as a solvent to prepare a slurry. Next, the electrolytic copper foil 110 was coated with the slurry to have a thickness of 20 to 60 μm using a doctor blade and 0.5 to 1.5ton cm at a temperature of 110 to 130 ℃²Is pressed under pressure.

A lithium secondary battery may be manufactured using a conventional cathode, electrolyte and separator, and the secondary battery electrode (or anode) of the present invention manufactured as described above.

Hereinafter, the present invention will be described in detail with reference to examples and comparative examples. However, the following examples are only examples to aid understanding of the present invention, and the scope of the present invention is not limited to these examples.

Examples 1to 4 andcomparative examples 1to 5

By arranging electrode plates and a rotary electrode drum spaced from each other in an electrolyte at 60A/dm²The current density of (a) is conductive to form a copper layer. The electrolyte contained 75g/L of copper ions, 100g/L of sulfuric acid and 2ppm of chloride ions and was maintained at a temperature of 55 ℃. While electroplating, at 37m³The flow rate of/hr is subjected to continuous filtration for removing solid impurities from the electrolyte.

Next, the copper layer was immersed in an antirust solution, and then dried to prepare an electrolytic copper foil. The chromium (Cr) concentration of the rust inhibitive liquids of examples 1to 4 and comparative examples 1to 5, the BTA concentration of the rust inhibitive liquid, the temperature of the rust inhibitive liquid, the pH of the rust inhibitive liquid, and the immersion time for manufacturing the electrolytic copper foil are shown in table 1.

[ Table 1]

The chromium (Cr) adhesion amount per first surface (the surface of the electrolytic copper foil adjacent to the matte surface of the copper layer), the chromium (Cr) adhesion amount per second surface opposite to the first surface of the electrolytic copper foil (i.e., the chromium (Cr) content of the protective layer formed on the first surface and the second surface), and the color difference (Δ E) and the gloss difference (Δ Gs60 °) of the first surface before and after the constant temperature and humidity test in the examples and comparative examples manufactured as described above were obtained. Further, the active material peel strength of the anodes manufactured using the electrolytic copper foils of examples and comparative examples and the capacity retention rate of the secondary batteries including the anodes were obtained as follows. The measurement results are shown in table 2.

²Chromium (Cr) deposition (mg/m)

The second surface of the electrolytic copper foil was masked with a tape and cut to obtain a sample of 10cm × 10 cm. Then, the first surface S1 of the electrolytic copper foil 110 was dissolved in an aqueous nitric acid solution (a one-to-one ratio mixture of normal nitric acid and water) while taking care not to form holes in the electrolytic copper foil 110. The resulting solution was diluted with water to give 50mL of diluted solution. The diluted solution was then analyzed by an inductively coupled plasma emission spectrometer (ICP-OES, model 720ES manufactured by Agilent) at 25 ℃ to measure the amount of chromium (Cr) attached on the first surface S1 of the electrolytic copper foil 110. Next, the amount of chromium (Cr) attached to the second surface of the electrolytic copper foil was measured in the same manner.

Color difference (. DELTA.E) and gloss difference (. DELTA.Gs 60 °)

The electrolytic copper foil was cut to obtain a sample of 10cm × 10 cm. The sample was placed on an acrylic plate with its first surface facing upward, placed in a constant temperature and humidity chamber (SH-221 manufactured by ESPEC corporation, japan), and allowed to stand under accelerated test conditions of a temperature of 70 ℃ and a relative humidity of 80% for 24 hours.

The perceived color (L a b) of the first surface was measured immediately before and after the constant temperature and humidity test using a spectrophotometer (CM-5 manufactured by Konika Minolta, japan), and the measured result thereof was used to calculate CIE 1976L a color difference (Δ E) based on the following equation 1.

[ equation 1]]：ΔE＝{(ΔL*)²+(Δa*)²+(Δb*)²}^1/2

Further, the glossiness (Gs60 °) of the first surface with respect to the incident angle of 60 ° was measured immediately before and after the constant temperature and humidity test using a gloss meter (VG 7000 manufactured by Nippon Denshoku corporation) according to JIS Z8741 standard, and the difference (Δ Gs60 °) between the measured values was calculated.

²Peel strength (N/mm)

2 parts by weight of SBR and 2 parts by weight of CMC were mixed in 100 parts by weight of commercially available carbon as an anode active material. Next, a slurry was prepared by adding distilled water as a solvent to the mixture. The surface (width: 10cm) of the electrolytic copper foil was coated with the slurry to have a thickness of about 60 μm using a doctor blade and dried at 120 ℃ for 10 minutes, and then by performing a rolling process (pressure: 1 ton/cm)²) And (4) preparing an anode.

The active material-adhered surface of the anode sample (width: 12.7mm) was adhered with a double-sided tape, and then the peel strength between the electrolytic copper foil and the active material was measured while peeling the copper foil at 90 ℃ using UTM according to IPC-TM-650 standard (measuring speed: 50 mm/min).

Capacity retention ratio (%)

2 parts by weight of SBR and 2 parts by weight of CMC were mixed in 100 parts by weight of commercially available carbon as an anode active material. Next, a slurry was prepared by adding distilled water as a solvent to the mixture. The surface (width: 10cm) of the electrolytic copper foil was coated with the slurry to have a thickness of about 60 μm with a doctor blade and dried at 120 ℃ for 10 minutes, and then by performing a rolling process (pressure: 1 ton/cm)²) And (4) preparing an anode.

Lithium manganate (Li)_1.1Mn_1.85Al_0.05O₄) And lithium manganate (o-LiMnO) having an orthorhombic crystal structure₂) Mixed at a weight ratio of 90:10 to prepare a positive electrode active material. A positive electrode active material, carbon black, and polyvinylidene fluoride (PVDF) were mixed with N-methyl-2-pyrrolidone (NMP) as an organic solvent at a weight ratio of 85:10: 5to prepare a slurry. Both surfaces of an aluminum foil having a thickness of 20 μm were coated with the slurry and dried to prepare a cathode.

In addition, by mixing 1M LiPF₆An alkaline electrolyte was obtained as a solute dissolved in a nonaqueous organic solvent in which Ethylene Carbonate (EC) and Ethyl Methyl Carbonate (EMC) were mixed in a weight ratio of 1: 2. The electrolyte solution was prepared by mixing 99.5 wt% of an alkaline electrolyte solution and 0.5 wt% of succinic anhydride.

The anode, the cathode and the electrolyte prepared as described above were used to prepare a secondary battery.

Next, for the secondary battery manufactured as described above, the capacity per gram of cathode was measured at a charge operating voltage of 4.3V and a discharge operating voltage of 3.4V, 500 charge and discharge experiments were performed at a charge-discharge rate of 0.2C at 50 ℃, and the capacity retention ratio of the secondary battery was calculated according to the following equation 2.

[ equation 2] capacity retention rate (%) (50 th discharge capacity/1 st discharge capacity) × 100

[ Table 2]

As shown in Table 2, the electrolytic copper foil at the first surface or the second surface has a chromium (Cr) attachment amount of less than 1mg/m²In the case of (comparative examples 1 and 2) and in the case of not adding BTA to the rust-preventive solution (comparative example 5), the corrosion resistance of the electrolytic copper foil was not good, the CIE 1976L a b color difference (Delta E) was more than 5, the gloss difference was more than 50, and the peel strength between the electrolytic copper foil and the active material was low and was not more than 13N/mm²Therefore, the capacity retention rate of the secondary battery does not satisfy the 90% value required by the industry.

Further, when the chromium (Cr) attachment amount of the electrolytic copper foil at each of the first surface and the second surface is more than 5mg/m²In comparative examples 3 and 4, the electrolytic copper foil was excellent in corrosion resistance. However, the electrolytic copper foil has a low peel strength from the active material, and the peel strength is not more than 13N/mm²Therefore, the capacity retention rate of the secondary battery does not satisfy the 90% value required by the industry. .

Since the electrolytic copper foil of the present invention has good marketability due to its high corrosion resistance and good adhesion to an active material, the electrolytic copper foil can be suitably used for manufacturing a high-capacity secondary battery, i.e., a secondary battery including a composite active material to which Si or Sn is added as a negative electrode active material.

In particular, according to the present invention, a long-life secondary battery capable of maintaining a high charge and discharge capacity for a long time despite repeated charge and discharge cycles can be manufactured. Therefore, it is possible to minimize inconvenience and resource waste to the consumer of electronic products due to frequent replacement of the secondary battery.

Claims

1. An electrolytic copper foil comprising a first surface and a second surface opposite the first surface, the electrolytic copper foil comprising:

a copper layer comprising a matte surface facing the first surface and a glossy surface facing the second surface;

a first protective layer on the matte surface; and

a second protective layer on the glossy surface,

wherein:

each of the first protective layer and the second protective layer includes chromium Cr and benzotriazole BTA;

a color difference Δ E of 5 or less in CIE 1976L a b of the first surface obtained immediately before and after the performance of a constant temperature and humidity test in which a sample of the electrolytic copper foil was maintained for 24 hours under accelerated test conditions of a temperature of 70 ℃ and a relative humidity of 80%,

a difference in glossiness of the first surface with respect to an incident angle of 60 ° obtained immediately before and after the constant temperature and humidity test in which the sample is held for 24 hours under an accelerated test condition of a temperature of 70 ℃ and a relative humidity of 80% is performed, is 50 or less; and

the chromium Cr content of each of the first and second protective layers ranges from 1to 5mg/m²。

2. The electrolytic copper foil according to claim 1, wherein the difference between the chromium Cr content of the first protective layer and the chromium Cr content of the second protective layer is 2mg/m²Or smaller.

3. The electrolytic copper foil according to claim 1, wherein a surface roughness Rz of each of the first surface and the second surface ranges from 0.5 to 2.5 μm.

4. The electrolytic copper foil according to claim 1, wherein the tensile strength of the electrolytic copper foil at room temperature is 30kgf/mm²Or more, and an elongation of 2% or more.

5. The electrolytic copper foil according to claim 1, wherein the electrolytic copper foil has a thickness of 1to 70 μm.

6. A secondary battery electrode comprising:

an electrolytic copper foil including a first surface and a second surface opposite to the first surface; and

a first active material layer on the first surface,

wherein:

the electrolytic copper foil includes:

a first protective layer on the matte surface; and

a second protective layer on the glossy surface,

each of the first protective layer and the second protective layer includes chromium Cr and benzotriazole BTA; and

the peel strength between the electrolytic copper foil and the first active material layer is 20N/mm²Or larger.

7. The secondary battery electrode according to claim 6, wherein:

the chromium Cr content of each of the first and second protective layers ranges from 1to 5mg/m²(ii) a And

the difference between the Cr content of the first protective layer and the Cr content of the second protective layer is 2mg/m²Or smaller.

8. The secondary battery electrode according to claim 6, wherein a surface roughness Rz of each of the first surface and the second surface ranges from 0.5 to 2.5 μm.

9. The electrode for a secondary battery according to claim 6, wherein the electrolytic copper foil has 30kgf/mm at room temperature²Or greater tensile strength and 2% or greater elongation.

10. The secondary battery electrode according to claim 6, wherein the electrolytic copper foil has a thickness of 1to 70 μm.

11. The secondary battery electrode according to claim 6, further comprising: a second active material layer on the second surface,

wherein each of the first active material layer and the second active material layer includes one or more active materials selected from the group consisting of carbon, a metal such as Si, Ge, Sn, Li, Zn, Mg, Cd, Ce, Ni, or Fe, an alloy containing the metal, an oxide of the metal, and a composite of the metal and carbon.

12. The secondary battery electrode according to claim 11, wherein each of the first active material layer and the second active material layer includes at least one of Si and Sn.

13. A secondary battery comprising:

a cathode;

an anode comprising the secondary battery electrode according to any one of claims 6 to 12;

an electrolyte configured to provide an environment in which lithium ions move between the cathode and the anode; and

a separator configured to electrically insulate the cathode from the anode.

14. A method of manufacturing an electrolytic copper foil, the method comprising:

forming a copper layer; and

forming a protective layer on the copper layer,

wherein:

forming the copper layer includes:

preparing an electrolyte containing 60 to 120g/L of copper ions, 80 to 150g/L of sulfuric acid, and 50ppm or less of chlorine; and

by arranging spaced apart in the electrolyteThe electrode plate and the rotary electrode drum are at 30 to 80A/dm²Is electrically conductive for electroplating, and

the forming of the protective layer includes:

preparing an antirust solution by mixing a chromate solution and a benzotriazole BTA solution; and

immersing the copper layer in the anti-tarnish solution,

wherein the rust preventive solution contains 0.1 to 2g/L of Cr and 1to 100mg/L of BTA;

the pH range of the antirust solution is 1.0 to 3.0;

the temperature of the rust inhibitive solution is maintained at 20 to 60 ℃ when the protective layer is formed; and

immersing the copper layer in the rust inhibitive solution for 1to 10 seconds.

15. The method of claim 14, wherein the electrolyte further comprises at least one organic additive selected from the group consisting of hydroxyethyl cellulose HEC, organic sulfides, organic nitrides, and thiourea-based compounds.