JP6652548B2 - Electrodeposited copper foil having high corrosion resistance and excellent adhesion to active material, electrode including the same, secondary battery including the same, and method of manufacturing the same - Google Patents

Description

  The present invention relates to an electrolytic copper foil, an electrode including the same, a secondary battery including the same, and a method for manufacturing the same. More specifically, the present invention not only has excellent commercial properties due to having high corrosion resistance, The present invention relates to an electrolytic copper foil capable of securing a secondary battery having a high capacity retention rate because of its excellent adhesive strength to an active material, an electrode including the same, a secondary battery including the same, and a method of manufacturing the same.

  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 the chemical energy to electrical energy when needed. It is used as an energy source for electric vehicles as well as portable home appliances such as notebook computers.

  Secondary batteries that are economically and environmentally advantageous compared to disposable primary batteries include lead storage batteries, nickel cadmium secondary batteries, nickel hydride secondary batteries, and lithium secondary batteries.

  Lithium secondary batteries can store relatively more energy relative to size and weight than other secondary batteries. Therefore, in the field of information and communication equipment in which portability and mobility are important, lithium secondary batteries are preferred, and their applications are expanding to energy storage devices for hybrid vehicles and electric vehicles.

  Electrolytic copper foil used as a cathode current collector of a lithium secondary battery has a film formed of a rust preventive substance on its surface for corrosion prevention.

  If the rust-preventive film is excessively thin, the oxidation of the surface of the copper layer of the electrolytic copper foil proceeds rapidly in a high-temperature and high-humidity environment, leading to poor appearance. Decreases the commercial value of foil.

  On the other hand, although the corrosion resistance of the electrolytic copper foil increases as the rust-preventive film is thicker, the film acts as a foreign substance between the copper layer of the electrolytic copper foil and the cathode active material, so that the copper layer and the cathode active material have a larger thickness. The adhesive force between the cathode active materials is reduced to further increase the risk of peeling between the cathode active materials.

  In particular, it has been proposed to use a composite active material obtained by adding Si or Sn to a carbon active material as a cathode active material in order to increase the capacity of a lithium secondary battery. However, such a composite active material has a relatively large coefficient of thermal expansion as compared with a normal cathode active material. The rapid contraction and expansion of the composite active material due to charge and discharge of the lithium secondary battery promotes separation between the electrodeposited copper foil and the cathode active material, thereby lowering the charge / discharge capacity retention rate of the lithium secondary battery. In addition, when the electrodeposited copper foil is coated with the cathode active material and then dried at a high temperature of 80 ° C. or more for 1 hour or more, the surface of the electrodeposited copper foil is oxidized to promote the desorption of the cathode active material. The lower the adhesive strength between the copper foil and the cathode active material, the more seriously the charge / discharge capacity retention rate of the lithium secondary battery decreases.

  If the charge / discharge capacity of the secondary battery decreases rapidly as the charge / discharge cycle is repeated (i.e., if the capacity retention rate is low or the life is short), the consumer will not be able to use the secondary battery. The batteries need to be replaced frequently, which will inconvenience consumers and result in wasted resources.

  Accordingly, the present invention relates to an electrolytic copper foil, an electrode including the same, a secondary battery including the same, and a method of manufacturing the same, which can prevent the problems caused by the limitations and disadvantages of the related art.

  One aspect of the present invention is to provide an electrolytic copper foil that can secure a secondary battery having a high capacity retention rate because of not only having excellent merchantability by having high corrosion resistance, but also having excellent adhesion to an active material. It is to provide.

  Another aspect of the present invention is to provide an electrode capable of securing a secondary battery having a high capacity retention rate by having a high adhesive force between an electrolytic copper foil and an active material.

  Yet another aspect of the present invention is to provide a secondary battery having a high capacity retention rate.

  Yet another aspect of the present invention is to provide a secondary battery having a high capacity retention rate due to its high corrosion resistance, which has not only excellent commercial properties, but also excellent adhesion to an active material. It is to provide a method for producing copper foil.

  In addition to the aspects of the invention described above, other features and advantages of the invention will be described hereinafter or will be apparent from such description to those of ordinary skill in the art to which this invention pertains. Should be.

According to one aspect of the present invention, there is provided an electrolytic copper foil having a first surface and a second surface opposite to the first surface, wherein the matte surface faces the first surface and the second surface. A copper layer including a shiny surface; a first protective layer on the matte surface; and a second protective layer on the shiny surface, wherein each of the first and second protective layers is chromium (Cr) and The CIE1976L ^* a ^* b of the first surface immediately before and immediately after performing a constant temperature and humidity test in which benzotriazole (BTA) is contained and left for 24 hours under an accelerated test condition of a temperature of 70 ° C. and a relative humidity of 80%. ^{* The} color difference (ΔE) is 5 or less, and the temperature is constant for 24 hours under the accelerated test conditions of a temperature of 70 ° C and a relative humidity of 80%. The difference in glossiness with respect to the 60 ° incident angle of the first surface immediately before and immediately after performing the humidity test is 50 or less, and the chromium (Cr) content of each of the first and second protective layers is 1 to 5. An electrolytic copper foil is provided, which is characterized by being 5 mg / m ² .

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

  Each of the first and second surfaces may have a surface roughness Rz of 0.5 to 2.5 μm.

The electro-deposited copper foil may have a tensile strength of 30 kgf / mm ² or more and an elongation of 2% or more at room temperature.

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

According to another aspect of the present invention, there is provided an electrolytic copper foil having 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 comprises the first surface. A first protective layer on the matte surface; and a second protective layer on the shiny surface, wherein the first and second protective layers include a copper layer including a matt surface toward the mating surface and a shiny surface toward the second surface. Each of the electrodes contains chromium (Cr) and benzotriazole (BTA), and the peel strength between the electrolytic copper foil and the first active material layer is 20 N / mm ² or more, wherein the electrode for a secondary battery is provided. Is provided.

The chromium (Cr) content of each of the first and second protective layers may be 1 to 5 mg / m ² , and the chromium (Cr) content of the first protective layer and the chromium (Cr) content of the second protective layer May be less than or equal to ² mg / m ² .

  Each of the first and second surfaces may have a surface roughness Rz of 0.5 to 2.5 μm.

The electro-deposited copper foil may have a tensile strength of 30 kgf / mm ² or more and an elongation of 2% or more at room temperature.

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

  The secondary battery electrode may further include a second active material layer on the second surface, wherein the first and second active material layers are independent of each other; carbon; Si, Ge, Sn, One or more active materials selected from the group consisting of a metal of 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 can be included.

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

  According to another aspect of the present invention, a cathode; an anode comprising the secondary battery electrode; an electrolyte that provides an environment in which lithium ions can move between the anode and the cathode; And a separator that electrically insulates the anode and the cathode from each other.

According to yet another aspect of the present invention, the method includes forming a copper layer; and forming a protective layer on the copper layer, wherein the copper layer forming step includes 60 to 120 g / L copper ions, 80 to 150 g. / L sulfuric acid and 50 ppm or less of chlorine; and preparing an electrode plate and a rotating electrode drum spaced apart from each other in the electrolyte at 40 to 60 ° C. by 30 to 80 A / dm ^2. Performing an electroplating by applying a current at a current density of: wherein the step of forming a protective layer comprises preparing a rust preventive solution by mixing a chromate solution and a benzotriazole (BTA) solution; and A method for producing an electrolytic copper foil is provided, comprising a step of immersing the copper layer in the rust preventive liquid.

  The electrolyte may further include at least one organic additive selected from the group consisting of hydroxyethylcellulose (HEC), organic sulfide, organic nitride, and thiourea-based compound.

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

  When the protective layer is formed, the temperature of the rust preventive liquid may be maintained at 20 to 60C.

  The copper layer may be immersed in the rust preventive liquid for 1 to 10 seconds.

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

  The electrolytic copper foil of the present invention not only has excellent commercial properties due to having high corrosion resistance, but also has a high capacity secondary battery, that is, Si or Sn because of its excellent adhesive strength with the cathode active material. Suitable for manufacturing a secondary battery containing the added composite active material as a cathode active material.

  In particular, according to the present invention, it is possible to manufacture a long-life secondary battery capable of maintaining a high charge / discharge capacity for a long period of time despite repeated charge / discharge cycles. User inconvenience and waste of resources can be minimized.

The accompanying drawings are provided to aid in understanding the present invention and to constitute a part of the specification. Hereinafter, embodiments of the present invention will be exemplified, and the principle of the present invention will be described together with the detailed description of the present invention.
1 is a cross-sectional view of a secondary battery electrode according to an embodiment of the present invention. 1 is a drawing showing an apparatus for manufacturing an electrolytic copper foil according to one embodiment of the present invention.

  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 variations that come within the scope of the invention as claimed and its equivalents.

  Lithium ion secondary batteries include an anode, a cathode, an electrolyte that provides an environment where lithium ions can move between the anode and the cathode, and electrons generated at one electrode. In order to prevent the anode and the cathode from being wasted by moving to another electrode through the inside of the electrode, a separator is provided to electrically insulate the anode and the cathode.

  FIG. 1 is a sectional view of a secondary battery electrode according to one embodiment of the present invention.

  As illustrated in FIG. 1, an electrode 100 for a secondary battery 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, on the first surface S1. And a second active material layer 120b on the second surface S2. FIG. 1 shows an example in which active material layers 120a and 120b are respectively formed on all of the first and second surfaces S1 and S2 of the electrolytic copper foil 110, but the present invention is not limited to this. In addition, the secondary battery electrode 100 of the present invention may include only one of the first and second active material layers 120a and 120b as an active material layer.

  In a lithium secondary battery, an aluminum foil is used as a cathode current collector combined with a cathode active material, and is used as a cathode current collector combined with a cathode active material. In general, electrolytic copper foil is used.

  According to an embodiment of the present invention, the secondary battery electrode 100 is used as a cathode of a lithium secondary battery, the electrolytic copper foil 110 functions as a cathode current collector, and the first and second active material layers are used. 120a and 120b contain a cathode active material.

  As illustrated in FIG. 1, the electrolytic copper foil 110 of the present invention includes a copper layer 111 including a matte surface MS and a shiny surface SS, and a copper layer 111 on the matte surface MS of the copper layer 111. A first protective layer 112a, and a second protective layer 112b on the shiny surface SS of the copper layer 111.

  The matte surface MS is a surface of the copper layer 111 toward the first surface S1 of the electrolytic copper foil 110, and the shiny surface SS is a surface of the copper layer 111 toward 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 adjacent to the shiny surface SS of the copper layer 111. Surface.

  The copper layer 111 of the present invention may be formed on the rotating electrode drum through electroplating. The shiny surface SS indicates a surface that contacts the rotating electrode drum during the electroplating process, and the matte surface MS is the shiny surface. Points to the opposite side of the SS.

  Although the shiny surface SS generally has a lower surface roughness Rz than the matte surface MS, the present invention is not limited to this, and the shiny surface SS has a surface roughness Rz that is lower than the matte surface MS. It may be equal to or higher than Rz.

The electrodeposited copper foil 110 of the present invention can have a tensile strength of 30 kgf / mm ² or more at a normal temperature (25 ° C.) and a stretching ratio of 2% or more. The tensile strength and the stretching ratio are measured using a universal testing machine (UTM). At this time, the width of the sample is 12.7 mm, the distance between the grips is 50 mm, and the measuring speed is 50 mm / min. is there.

If the tensile strength is less than 30 kgf / mm ² or the elongation is less than 2%, the electrode 100 may be deformed and / or broken due to expansion and contraction of the cathode active material caused during charging and discharging of the secondary battery. The danger is great.

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

  The first and second active material layers 120a and 120b are independently of each other carbon; a metal of Si, Ge, Sn, Li, Zn, Mg, Cd, Ce, Ni or Fe; an alloy containing the metal; At least one selected from the group consisting of a metal oxide; and a composite of the metal and carbon may be included as a cathode active material.

  In order to increase the charge / discharge capacity of the secondary battery, the first and second active material layers 120a and 120b may include at least one of Si and Sn.

  As described above, as the charging and discharging of the secondary battery are repeated, the contraction and expansion of the active material layers 120a and 120b alternately occur, which causes the active material layers 120a and 120b to separate from the electrolytic copper foil 110. As a result, the charge / discharge efficiency of the secondary battery is reduced. Therefore, in order for the secondary battery to secure a capacity retention rate and a service life that are equal to or higher than a certain level (that is, to suppress a decrease in the charge / discharge efficiency of the secondary battery), the electrolytic copper foil 110 uses the active material. The adhesive strength between the electrodeposited copper foil 110 and the active material layers 120a and 120b must be high by having excellent coating properties.

  By controlling the surface roughness Rz of the electrolytic copper foil 110, the adhesive strength between the electrolytic copper foil 110 and the active material layers 120a and 120b can be improved. The surface roughness Rz can be measured in accordance with, for example, a JIS B0601 (1994) standard using a Mahrsurf M300 roughness meter manufactured by Mahr [measurement length: 4 mm (excludes cut off section)].

  According to an embodiment of the present invention, the first and second surfaces S1 and S2 of the electrodeposited copper foil 110 may have a surface roughness Rz of 0.5 to 2.5 μm. When the surface roughness Rz is less than 0.5 μm, a sufficient adhesive force between the electrodeposited copper foil 110 and the cathode active material cannot be ensured because the adhesion area with the cathode active material is too small. On the other hand, when the surface roughness Rz exceeds 2.5 μm, the first and second surfaces S1 and S2 of the electrodeposited copper foil 110 are excessively uneven, so that the coating uniformity of the cathode active material decreases. Accordingly, the adhesion between the electrodeposited copper foil 110 and the first and second active material layers 120a and 120b is significantly reduced.

  However, in practice, the electrolytic copper foil 110 having the appropriately adjusted surface roughness Rz does not necessarily satisfy the adhesive force between the electrolytic copper foil 110 and the active material layers 120a and 120b required in the specification. That is, the electrolytic copper foil 110 having a surface roughness Rz of 0.5 to 2.5 μm can always ensure the capacity retention rate (after 50 charge / discharge) of the secondary battery of 90% or more required in the industry. Absent.

  In particular, when the active material layers 120a and 120b include at least one of Si and Sn in order to increase the capacity of the secondary battery, the surface roughness Rz of the electrolytic copper foil 110 and the capacity retention of the secondary battery are reduced. The association between them was shown to be even lower.

  According to the present invention, in securing the adhesive force between the electrolytic copper foil 110 and the active material layers 120a and 120b large enough to ensure a capacity maintenance ratio of the secondary battery of 90% or more, the electrolytic copper foil 110 It was confirmed that the materials and the contents of the first and second protective layers 112a and 112b were important factors.

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

The chromium (Cr) content of each of the first and second protective layers 112a and 112b is preferably 1 to 5 mg / m ² , and the chromium (Cr) content of the first protective layer 112a and the second protective layer The difference in chromium (Cr) content of 112b is preferably ² mg / m ² or less.

If the chromium (Cr) content of the first and second protective layers 112a and 112b is less than 1 mg / m ² , the cathode active material is coated on the electrodeposited copper foil 110 and then at a high temperature of 80 ° C. or more for 1 hour or more. When drying, oxygen easily passes through the first and second protective layers 112a and 112b to induce oxidation of the surface of the copper layer 111, and also oxidizes the surface of the copper layer 111 to form an electrolytic copper foil. Since a sufficient chemical bond cannot be provided between the electrode 110 and the cathode active material, the adhesive strength between the electrolytic copper foil 110 and the active material layers 120a and 120b must be reduced. On the other hand, if the chromium (Cr) content exceeds 5 mg / m ² , the corrosion resistance of the electrodeposited copper foil 110 is excellent, but the hydrophobicity of the surface of the electrodeposited copper foil 110 increases, and the cathode active material increases. , A sufficient chemical bond between the electrodeposited copper foil 110 and the cathode active material cannot be provided, and between the electrodeposited copper foil 110 and the active material layers 120a and 120b. Sufficient adhesive strength cannot be secured.

If the difference between the chromium (Cr) content of the first protective layer 112a and the chromium (Cr) content of the second protective layer 112b exceeds ² mg / m ² , curl of the electrolytic copper foil 110 may cause a reduction in workability. In addition to the above, a large difference occurs between the first and second surfaces S1 and S2 of the electrodeposited copper foil 110 on the side of the adhesive force with the cathode active material, causing a decrease in the capacity retention of the secondary battery.

  According to the present invention, the first and second protective layers 112a and 112b further include benzotriazole (BTA) in addition to chromium (Cr). Since the first and second protective layers 112a and 112b include benzotriazole (BTA) together with chromium (Cr), higher corrosion resistance is ensured compared to the electrolytic copper foil 110 to which only chromium (Cr) is applied. Not only that, the adhesive strength with the cathode active material can be further improved.

The corrosion resistance of the electrodeposited copper foil 110 can be quantified through a CIE1976L ^* a ^* b ^* color difference (ΔE) and gloss (incident angle: 60 °) difference caused by a constant temperature and humidity test.

  In the present invention, the constant temperature / humidity test is performed by leaving the electrolytic copper foil 110 for 24 hours under an accelerated test condition of a temperature of 70 ° C. and a relative humidity of 80%.

The CIE1976 L ^* a ^* b ^* color difference (ΔE) is a numerical representation of the perceived difference between two perceived colors (perceived color). Two points in the L ^* a ^* b ^* color space (CIE 1976) It can be obtained by calculating the geometric distance between them by the following equation 1.

Equation 1: ΔE = {(ΔL ^* ) ² + (Δa ^* ) ² + (Δb ^* ) ² } ^1/2
Immediately before and immediately after the temperature and humidity test, the perceived color of the surface of the electrolytic copper foil 110 is measured using a spectrophotometer, and the CIE1976L ^* a ^* b ^* color difference ( ΔE) is calculated.

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

Since the first and second protective layers 112a and 112b further include benzotriazole (BTA) together with chromium (Cr), CIE1976L of the surfaces S1 and S2 of the electrolytic copper foil 110 immediately before and immediately after the constant temperature and humidity test. ^{* A *} b ^{* The} color difference (ΔE) is 5 or less, and the difference in glossiness with respect to the 60 ° incident angle on the surfaces S1 and S2 of the electrolytic copper foil 110 immediately before and immediately after the constant temperature and humidity test is 50 or less. Thus, the electrolytic copper foil 110 of the present invention has excellent corrosion resistance.

  Therefore, according to the present invention, the surface of the copper layer 111 can be prevented from being oxidized even when the cathode active material is coated on the electrolytic copper foil 110 and then dried at a high temperature of 80 ° C. or more for 1 hour or more. A sufficient chemical bond between the foil 110 and the cathode active material can be provided.

  The adhesive strength between the electrolytic copper foil 110 and the active material layers 120a, 120b can be confirmed by measuring the peel strength between the electrolytic copper foil 110 and the active material layers 120a, 120b.

According to the present invention, the first and second protective layers 112a and 112b further include benzotriazole (BTA) together with chromium (Cr), thereby separating the electrodeposited copper foil 110 and the active material layers 120a and 120b. The strength is 20 N / mm ² or more.

  Hereinafter, a method for manufacturing the electrolytic copper foil 110 of the present invention will be specifically described with reference to FIG.

  The method includes forming a copper layer 111 and forming protective layers 112 a and 112 b on the copper layer 111.

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

  The electrolyte solution 20 further includes at least one organic additive selected from the group consisting of hydroxyethylcellulose (HEC), organic sulfide (eg, SPS), organic nitride, and thiourea-based compound. be able to. The content of the organic additive in the electrolyte solution 20 may be 1 to 10 ppm.

Subsequently, the electrode plate 30 and the rotating electrode drum 40, which are spaced apart from each other in the electrolytic solution 20 at 40 to 60 ° C., are energized at a current density of 30 to 80 A / dm ² to perform electroplating. A layer 111 is formed on the rotating electrode drum 40.

  As illustrated in FIG. 2, the electrode plate 30 may include first and second electrode plates 31 and 32 that are electrically insulated from each other.

  In the step of forming the copper layer 111, a seed layer is formed by energizing the first electrode plate 31 and the rotating electrode drum 40, and then the seed layer is formed by energizing the second electrode plate 32 and the rotating electrode drum 40. This can be done by growing a seed layer.

  The degree of polishing of the surface of the rotating electrode drum 40 (the surface on which copper is deposited by electroplating) is one factor that controls the surface roughness Rz of the second surface S2 of the electrolytic copper foil 110 and the amount of chromium (Cr) attached. It is. According to the present invention, the surface of the rotary electrode drum 40 is polished with a polishing brush having a grain size (Grit) of # 800 to # 1500.

During the electroplating, continuous (or circulating) filtration for removing solid impurities from the electrolytic solution 20 may be performed at a flow rate of 31 to 45 m ³ / hr. If the flow rate is less than 31 m ³ / hr, the flow rate is reduced, the overvoltage is increased, and the copper layer 111 is formed unevenly. On the other hand, if the flow rate exceeds 45 m ³ / hr, the filter may be damaged and foreign matter may flow into the electrolyte.

  In order to form the protective layers 112a and 112b on the copper layer 111, a rust preventive liquid 60 is prepared in the processing bath 50. The rust preventive liquid may include 0.1 to 2 g / L chromium (Cr) and 1 to 100 mg / L benzotriazole (BTA).

  If the chromium (Cr) concentration is less than 0.1 g / L, rust prevention treatment must be performed for a long time, which is not preferable in terms of productivity. On the other hand, when the chromium (Cr) concentration exceeds 2 g / L, the thickness of the protective layers 112a and 112b increases and the corrosion resistance improves, but the adhesive strength with the active material decreases.

  When the concentration of the benzotriazole (BTA) is less than 1 mg / L, the effect of the present invention accompanying the addition of the benzotriazole (BTA) is very small. On the other hand, when the concentration of the benzotriazole (BTA) exceeds 100 mg / L, an excessive amount of the benzotriazole (BTA) suppresses the formation of the protective layers 112a and 112b, and the corrosion resistance of the electrolytic copper foil 110 and the adhesion to the active material. Reduce all power.

  The pH of the rust preventive liquid 60 may be 1.0 to 3.0. When the pH of the rust preventive liquid 60 is less than 1.0, groundwork and / or defects are generated in the protective layers 112a and 112b, so that the corrosion resistance of the electrolytic copper foil 110 and the adhesive strength with the active material are all deteriorated. On the other hand, if the pH of the rust preventive liquid 60 exceeds 3.0, the formation speed of the protective layers 112a and 112b becomes slow, which is not preferable in terms of productivity.

  Subsequently, the copper layer 111 is immersed in the rust preventive liquid 60. When the copper layer 111 is immersed in the rust preventive liquid 60, the copper layer 111 may be guided by a guide roll 70 disposed in the rust preventive liquid 60.

  When the protective layers 112a and 112b are formed, the temperature of the rust preventive liquid 60 may be maintained at 20 to 60C. If the temperature of the rust preventive liquid 60 is lower than 20 ° C., the formation speed of the protective layers 112a and 112b becomes slow, which is not preferable in terms of productivity. On the other hand, when the temperature of the rust preventive liquid 60 exceeds 60 ° C., the thickness of the protective layers 112a and 112b increases and the corrosion resistance improves, but the uniformity of the thickness and the adhesive force with the active material decrease. .

  The copper layer 111 may be immersed in the rust preventive liquid 60 for 1 to 10 seconds. If the immersion time is less than 1 second, the surface of the copper layer 111 is easily oxidized because the protective layers 112a and 112b are hardly formed. On the other hand, if the immersion time exceeds 10 seconds, the corrosion resistance of the electrodeposited copper foil 110 and the adhesive force with the active material will not increase any more, and the reduction in productivity relative to the obtained effect will be greater.

  A part of the copper layer 111 immersed in the rust preventive solution 60 is dissolved to generate hydrogen, and this hydrogen reduces hexavalent chromium (Cr) to trivalent chromium (Cr), The chromium (Cr) reacts with chromic acid to deposit a gelled hydrate on the copper layer 111, and benzotriazole (BTA) is adsorbed on the gelled hydrate to form a protective layer 112a of the present invention. , 112b are formed.

  If the copper concentration in the rust preventive liquid 60 is higher than a certain level, the protective layers 112a and 112b cannot be formed smoothly. Therefore, it is preferable that the rust preventive liquid 60 is periodically replaced.

One side or both sides of the electrodeposited copper foil 110 of the present invention manufactured by the above-described method, carbon; a metal (Me) of Si, Ge, Sn, Li, Zn, Mg, Cd, Ce, Ni or Fe; An alloy containing the metal (Me); an oxide of the metal (Me) (MeO _x ); and at least one cathode active material selected from the group consisting of a composite of the metal (Me) and carbon. Thereby, the electrode (that is, the cathode) for the secondary battery of the present invention can be manufactured.

For example, 1 to 3 parts by weight of styrene butadiene rubber (SBR) and 1 to 3 parts by weight of carboxymethyl cellulose (CMC) are mixed with 100 parts by weight of carbon for a cathode active material, and then distilled water is used as a solvent. Prepare a slurry. Subsequently, the slurry is applied on the electrolytic copper foil 110 to a thickness of 20 to 60 μm using a doctor blade, and pressed at 110 to 130 ° C. at a pressure of 0.5 to 1.5 and ton / cm ² .

  A lithium secondary battery can be manufactured using the usual anode, electrolyte, and separator together with the secondary battery electrode (cathode) of the present invention manufactured by the above method.

  Hereinafter, the present invention will be specifically described through examples and comparative examples. However, the following examples are only for helping to understand the present invention, and the scope of the present invention is not limited to these examples.

Examples 1-4 and Comparative Examples 1-5
A copper layer was formed by applying a current density of 60 A / dm ² to the electrode plate and the rotating electrode drum which were disposed apart from each other in the electrolytic solution. The electrolyte contained 75 g / L of copper ions, 100 g / L of sulfuric acid, and 20 ppm of chlorine, and was maintained at 55 ° C. During the electroplating, continuous filtration was performed at a flow rate of 37 m ³ / hr to remove solid impurities from the electrolyte.

  Subsequently, the copper layer was immersed in a rust preventive liquid, and then dried to complete an electrolytic copper foil. The chromium (Cr) concentration of the rust preventive solution, the benzotriazole (BTA) concentration of the rust preventive solution, the temperature of the rust preventive solution, the pH of the rust preventive solution, and the immersion time are as shown in Table 1 below.

  Amount of chromium (Cr) deposited on the first surface (the surface of the electrolytic copper foil adjacent to the matte surface of the copper layer) and the second surface on the opposite side of the electrolytic copper foils of Examples and Comparative Examples manufactured as described above. (That is, the chromium content of the protective layer formed on the first and second surfaces), the color difference (ΔE) and the gloss difference (ΔGs60 °) of the first surface before and after the constant temperature and humidity test are as follows. I asked for each. In addition, the peel strength of the cathode active materials manufactured from the electrolytic copper foils of the examples and the comparative examples and the capacity retention of the secondary battery including the cathode were determined as follows. The measurement results are shown in Table 2 below.

Chromium (Cr) adhesion amount (mg / m ² )
A 10 cm × 10 cm sample was obtained by masking and cutting the second side of the electrolytic copper foil with a tape. Subsequently, the first surface of the electrolytic copper foil was dissolved with a nitric acid aqueous solution (mixing of nitric acid and water at a ratio of 1: 1) while taking care not to form a hole in the electrolytic copper foil. The solution thus formed was diluted with water to obtain a diluted solution of 50 mL. Subsequently, the diluted solution was analyzed at 25 ° C. by ICP-OES (Inductively Coupled Plasma Optical Emission Spectroscopy) (Agilent, 720ES model) to measure the amount of chromium adhering to the first surface of the electrolytic copper foil. Subsequently, the amount of chromium deposited on the second surface of the electrolytic copper foil was measured in the same manner.

Color difference (ΔE) and gloss difference (ΔGs60 °)
The sample of 10 cm × 10 cm was obtained by cutting the electrolytic copper foil. After attaching the sample to an acrylic plate so that the first surface is on the upper side, the sample is put in a thermo-hygrostat (SH-221, ESPEC Japan) under an accelerated test condition of 70 ° C. and 80% relative humidity. Left for hours.

Immediately before and immediately after the temperature and humidity test, the perceived color (L ^* a ^* b ^* ) of the first surface was measured with a spectral colorimeter (Konica Minolta, Japan, CM-5), and the measured values were used. Then, CIE1976L ^* a ^* b ^* color difference (ΔE) was calculated by the following equation 1.

[Equation 1]: ΔE = {(ΔL ^* ) ² + (Δa ^* ) ² + (Δb ^* ) ² } ^1/2
Immediately before and after the temperature and humidity test, the glossiness (Gs60 °) of the first surface with respect to a 60 ° incident angle was measured using a gloss meter (Nippon Denshoku, VG7000) in accordance with JIS Z8741 standard. The measurement was performed, and the difference (ΔGs60 °) between the measured values was calculated.

Peel strength (N / mm ² )
For a cathode active material, 2 parts by weight of SBR (styrene butadiene rubber) and 2 parts by weight of CMC (carboxymethyl cellulose) were mixed with 100 parts by weight of commercially available carbon. Subsequently, a slurry was produced by adding distilled water as a solvent to the mixture. The slurry is applied to a thickness of about 60 μm on a surface of an electrolytic copper foil (width: 10 cm) using a doctor blade, dried at 120 ° C. for 10 minutes, and then subjected to a pressing step (pressure: 1 ton / cm ^2). ) To produce a cathode.

  After attaching the active material attachment surface of the cathode sample (width: 12.7 mm) with a double-sided tape, the copper foil was peeled at 90 ° using a universal testing machine (UTM) in accordance with the IPC-TM-650 standard. The peel strength between the electrolytic copper foil and the active material was measured while measuring (measuring speed: 50 mm / min).

Secondary battery capacity retention rate (%)
For a cathode active material, 2 parts by weight of SBR (styrene butadiene rubber) and 2 parts by weight of CMC (carboxymethyl cellulose) were mixed with 100 parts by weight of commercially available carbon. Subsequently, a slurry was produced by adding distilled water as a solvent to the mixture. The slurry is applied to a thickness of about 60 μm on a surface of an electrolytic copper foil (width: 10 cm) using a doctor blade, dried at 120 ° C. for 10 minutes, and then subjected to a pressing step (pressure: 1 ton / cm ^2). ) To produce a cathode.

A lithium manganese oxide (Li _1.1 Mn _1.85 Al _0.05 O ₄ ) and a lithium manganese oxide having an orthohombic crystal structure (o-LiMnO ₂ ) were mixed at a weight ratio of 90:10 to prepare an anode active material. Manufactured. The slurry was prepared by mixing the anode active material, carbon black, and polyvinylidene fluoride (PVDF) in a weight ratio of 85: 10: 5 with NMP as an organic solvent. The slurry was applied on both sides of a 20 μm-thick aluminum foil and then dried to produce an anode.

In addition, a non-aqueous organic solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a weight ratio of 1: 2 and 1 M of LiPF ₆ dissolved as a solute as a solute was used as a basic electrolyte. An electrolyte was prepared by mixing 0.5 wt% of succinic anhydride and 0.5 wt% of succinic anhydride.

  A secondary battery was manufactured using the cathode, the anode, and the electrolyte thus manufactured.

  Subsequently, the capacity per gram of the anode was measured at a charging operating voltage of 4.3 V and a discharging operating voltage of 3.4 V, and the charge / discharge of 0.2 C was performed at 50 ° C. A charge / discharge experiment was performed 50 times at a speed, and the capacity retention ratio of the secondary battery was calculated by the following equation 2.

  [Equation 2]: Capacity retention rate (%) = (50th discharge capacity / first discharge capacity) × 100

As can be seen from Table 2 above, when the amount of chromium (Cr) deposited on any one of the first and second surfaces of the electrolytic copper foil is less than 1 mg / m ² (Comparative Examples 1 and 2), Even when benzotriazole (BTA) was not added to the rust preventive liquid (Comparative Example 5), the corrosion resistance of the electrolytic copper foil was poor, and only CIE1976L ^* a ^* b ^* color difference (ΔE) exceeded 5. In addition, the difference in glossiness exceeds 50, the peel strength between the electrolytic copper foil and the active material is so low that the peel strength does not reach 13 N / mm ² , and the capacity maintenance rate of the secondary battery is required in the industry. 90% was not satisfied.

When the amount of chromium (Cr) adhered on the first and second surfaces of the electrolytic copper foil exceeded 5 mg / m ² (Comparative Examples 3 and 4), the corrosion resistance of the electrolytic copper foil was good. The peel strength between the electrodeposited copper foil and the active material is so low that the peel strength does not reach 13 N / mm ² , and the capacity retention of the secondary battery cannot satisfy 90% required in the industry. Was.

Reference Signs List 10: electrolytic cell 20: electrolytic solution 30: electrode plate 40: rotating electrode drum 50: processing tank 60: rust preventive liquid 70: guide roll 100: electrode for secondary battery 110: electrolytic copper foil 111: copper layer 112a: first Protective layer 112b: Second protective layer 120a: First active material layer 120b: Second active material layer

Claims (15)

In an electrolytic copper foil having a first surface and a second surface opposite to the first surface,
A copper layer including a matte surface facing the first surface and a shiny surface facing the second surface;
A first protective layer on the matte surface; and a second protective layer on the shiny surface;
Each of the first and second protective layers includes chromium (Cr) and benzotriazole (BTA);
CIE1976L ^* a ^* b ^* color difference (color difference) of the first surface immediately before and immediately after performing the constant temperature / humidity test which is left for 24 hours under the accelerated test condition of a temperature of 70 ° C. and a relative humidity of 80% ( ΔE) is 5 or less;
The difference in glossiness with respect to the 60 ° incident angle of the first surface immediately before and immediately after performing the constant temperature and humidity test, which is left for 24 hours under the accelerated test conditions of a temperature of 70 ° C. and a relative humidity of 80%, is 50 or less. Yes,
Wherein each of the chromium (Cr) content of the first and second protective layer is characterized by a 1 to 5 mg / ^{m 2,} an electrolytic copper foil. Wherein the difference between the chromium (Cr) content of chromium (Cr) content and the second protective layer of the first protective layer is 2 mg / m ² or less, the electrolytic copper foil according to claim 1.   2. The electrolytic copper foil according to claim 1, wherein each of the first and second surfaces has a surface roughness Rz of 0.5 to 2.5 μm. 3. 2. The electrolytic copper foil according to claim 1, wherein the electrolytic copper foil has a tensile strength of 30 kgf / mm ² or more and an elongation of 2% or more at room temperature. 3.   The electrolytic copper foil according to claim 1, wherein the electrolytic copper foil has a thickness of 1 to 70 m. An electrolytic copper foil having a first surface and a second surface opposite to the first surface; and a first active material layer on the first surface,
The electrolytic copper foil,
A copper layer including a matte surface facing the first surface and a shiny surface facing the second surface;
A first protective layer on the matte surface; and a second protective layer on the shiny surface;
Each of the first and second protective layers includes chromium (Cr) and benzotriazole (BTA);
An electrode for a secondary battery, wherein a peel strength between the electrolytic copper foil and the first active material layer is 20 N / mm ² or more. The first and second protective layers have a chromium (Cr) content of 1 to 5 mg / m ² ,
Wherein the difference between the chromium (Cr) content of chromium (Cr) content and the second protective layer of the first protective layer is 2 mg / m ² or less, a secondary battery electrode according to claim 6 .   The electrode of claim 6, wherein the first and second surfaces have a surface roughness Rz of 0.5 to 2.5 m. The electrolytic copper foil is characterized by having a room temperature at 30 kgf / mm ² or more tensile strength and 2% or more elongation, secondary cell electrode according to claim 6.   The electrode of claim 6, wherein the electrodeposited copper foil has a thickness of 1 to 70 m. A second active material layer on the second surface;
The first and second active material layers are independently formed of carbon; a metal of Si, Ge, Sn, Li, Zn, Mg, Cd, Ce, Ni, or Fe; an alloy containing the metal; The electrode for a secondary battery according to claim 6, further comprising one or more active materials selected from the group consisting of a substance and a composite of the metal and carbon.   The electrode of claim 11, wherein the first and second active material layers include at least one of Si and Sn. Anode;
A cathode comprising the electrode for a secondary battery according to any one of claims 6 to 12.
A secondary battery, comprising: an electrolyte that provides an environment in which lithium ions can move between the anode and the cathode; and a separator that electrically insulates the anode and the cathode. Forming a copper layer; and forming a protective layer on the copper layer;
The copper layer forming step includes:
Preparing an electrolyte solution containing 60 to 120 g / L of copper ions, 80 to 150 g / L of sulfuric acid, and 50 ppm or less of chlorine; and electrodes spaced apart from each other in the electrolyte solution at 40 to 60 ° C. Performing electroplating by energizing the plate and rotating electrode drum at a current density of 30-80 A / dm ² ,
The protection layer forming step includes:
Step chromate (chromate) solution and benzotriazole (BTA) solution were mixed to prepare a rust preventive solution; the step of immersing the copper layer and the rust-liquid seen including,
The rust preventive solution contains 0.1 to 2 g / L of chromium (Cr) and 1 to 100 mg / L of benzotriazole (BTA), and the pH of the rust preventive solution is 1.0 to 3.0,
When the protective layer is formed, the temperature of the rust preventive liquid is maintained at 20 to 60C,
The method for producing an electrolytic copper foil, wherein the copper layer is immersed in the rust preventive liquid for 1 to 10 seconds .   The electrolyte further includes at least one organic additive selected from the group consisting of hydroxyethylcellulose (HEC), organic sulfide, organic nitride, and thiourea-based compound. A method for producing an electrolytic copper foil according to claim 14.