WO2019022408A1 - Secondary battery copper foil, manufacturing method therefor, and secondary battery comprising same - Google Patents

Abstract

The present invention relates to: a secondary battery copper foil having excellent oxidation resistance, even without using chromium, and having excellent adhesion to an active material layer after being processed into an electrode collector; a method for manufacturing the secondary battery copper foil; and a secondary battery comprising the same. The secondary battery copper foil according to the present invention has a styrene-butadiene rubber (SBR) layer formed on the surface of an electrodeposited copper foil.

Description

Copper foil for secondary battery, manufacturing method thereof, and secondary battery including the same

The present invention relates to a copper foil for a secondary battery, a method of manufacturing the same, and a secondary battery including the same. More particularly, the present invention relates to a copper foil for a secondary battery, The present invention relates to an electro-deposited copper foil having good performance as a battery-use copper foil, a production method thereof, and a secondary battery comprising the same. This application claims priority to Korean Patent Application No. 10-2017-0094256 filed on July 25, 2017 and Korean Patent Application No. 10-2018-0075894 filed on June 29, 2018 , The disclosure of which is incorporated herein by reference in its entirety.

2. Description of the Related Art In recent years, demand for portable electronic products such as notebook computers, video cameras, and portable telephones has rapidly increased, and electric vehicles, storage batteries for energy storage, robots, and satellites have been developed in earnest. Are being studied actively. Among the currently commercialized secondary batteries, lithium secondary batteries have been in the limelight due to their low charge and discharge, very low self-discharge rate, and high energy density because they have almost no memory effect compared with nickel-based secondary batteries.

Generally, the secondary battery has a structure including a positive electrode and a negative electrode arranged with a separator interposed therebetween, and the positive electrode has a structure in which a positive electrode active material is attached to a positive electrode current collector, and the negative electrode has a negative electrode active material Structure.

In the lithium secondary battery, an electrolytic copper foil is mainly used as the material of the anode current collector. Electrolytic copper foil is used in almost all manufacturers because of its easiness to cope with phase stability, wide response, purity and long winding among various substances used as an anode current collector.

However, electrolytic copper is oxidized from the moment it is exposed to the atmosphere in the electrolytic cell. This oxidation produces CuO and CuO ₂ , which not only act as an impediment to electrical properties but also cause apparent problems. Therefore, conventionally, chromium components as rust prevention elements and surface modification elements of electrolytic copper foil have been widely used through chromium plating or chromate treatment. In particular, the chromate treatment has been used in most of electrolytic copper foils in the market in recent years. When the chromium component is present as a chromium compound, the oxidation number is trivalent or hexavalent. Toxicity to living organisms is much higher than that of hexavalent chromium, and mobility in soil is also high for hexavalent chromium compounds.

As a result, EU (European Union) ELV (Waste Vehicle Disposal Directive) prohibits the use of environmentally hazardous substances such as lead, hexavalent chrome, mercury and cadmium in new vehicles registered in the EU market after July 1, 2003 And the active use of trivalent chromium is being promoted. In addition, from the heightened awareness of the recent environmental problems, there is a concern that even if trivalent chromium is used, it is converted to hexavalent chromium if the waste treatment is carried out incorrectly, or if the analysis method is wrong, it may be judged as hexavalent chromium. In view of such a problem, it is necessary to develop an electrolytic copper foil which does not use a component called chromium itself.

Metal components other than copper treated on the surface of the electrolytic copper foil are generally used to protect the electrolytic copper foil from atmospheric oxidation to secure long-term preservability, as called a rust-preventive treatment layer (rust-preventive layer). However, depending on the kind of the rust-preventive treatment layer, the adhesion to the negative electrode active material layer is greatly influenced after being processed into the negative electrode collector.

Apart from the development of the antirust treatment layer of the electrolytic copper foil, research in the secondary cell electrode manufacturing process is underway. The electrodeposited copper foil has very good hydrophilic properties, but has a limit in adhesion to the negative electrode active material layer. In order to avoid this problem, it is necessary to increase the content of the binder in the current active material slurry composition, to coat the carbon layer with the electrolytic copper foil as a primer, or to make the anode active material coating layer multilayer by the double layer method Are being applied. This method must be accompanied by the solution of battery capacity / cost / equipment investment and adversely affects the overall yield and fairness due to the increase in process control factors.

Therefore, there is a great need for a copper foil for a secondary battery which is excellent in adhesion to the negative electrode active material layer after being processed into an anode current collector, which has antirust properties and oxidation resistance without using chromium in the rust preventive treatment layer of the electrolytic copper foil.

SUMMARY OF THE INVENTION The present invention has been made to overcome the above problems, and it is an object of the present invention to provide a method for manufacturing a negative electrode, which is excellent in oxidation resistance without using chromium, And an excellent secondary battery copper foil.

Another object of the present invention is to provide a method for producing such a copper foil for a secondary battery.

Another object of the present invention is to provide a secondary battery using the copper foil for a secondary battery.

It is to be understood, however, that the present invention is not limited to the above-described problems, and other technical objects not mentioned above may be clearly understood by those skilled in the art from the following description of the present invention.

In order to solve the above problems, a copper foil for a secondary battery according to the present invention is formed by forming a SBR (Styrene Butadiene Rubber) layer on the surface of an electrolytic copper foil.

The SBR layer completely covers the surface of the electrolytic copper foil and is a continuous layer in the thickness direction, the width direction and the longitudinal direction.

The SBR layer is formed on both surfaces of the electrolytic copper foil to prevent rusting, that is, to prevent rust. The electrolytic copper foil contains no chromium element as a rust-preventive surface treatment element.

The SBR layer is directly coated on the electrolytic copper foil surface formed on the drum surface in an electrolytic bath without any other artificial treatment.

The inventors of the present invention found that by positively using SBR as a rust-preventive treatment layer on the surface of an electrolytic copper foil, it is possible to secure excellent oxidation resistance even without employing a chromium-containing rust-preventive treatment layer such as chromate treatment, The present invention has been developed.

Such a copper foil for a secondary battery can be applied to an anode current collector of a secondary battery.

The thickness of the electrolytic copper foil may range from 3 mu m to 30 mu m.

The thickness of the SBR layer may range from 0.5 [mu] m to 5 [mu] m.

In the method for manufacturing a copper foil for a secondary battery according to the present invention, the electrolytic copper foil is electrodeposited on a drum in an electrolytic bath to produce the electrolytic copper foil, and while the electrolytic copper foil is taken out of the electrolytic bath, the electrolytic copper foil is wound on a bobbin can do. Particularly, it is preferable that the SBR surface treatment section is provided with an SBR aqueous solution treatment tank and a hot-air drying furnace in an in-line manner.

The SBR layer is preferably formed by coating an SBR aqueous solution in which SBR is dispersed in water at a concentration of 1 g / l to 10 g / l on the surface of the electrolytic copper foil and drying.

In the method for manufacturing a copper foil for a secondary battery according to the present invention, it is preferable that the drying is performed in a temperature atmosphere of 160 ° C to 200 ° C.

Furthermore, it is preferable to continue the above drying in a temperature atmosphere of 180 to 190 캜 for 30 to 240 minutes to obtain a baking effect together with drying, beyond the concept of simple drying.

Meanwhile, in the secondary battery according to the present invention, the copper foil for a secondary battery according to the present invention is applied as a negative current collector.

The secondary battery includes an electrode assembly including an anode, a cathode, and a separator.

The negative electrode is formed on the current collector with a negative electrode active material layer including a negative electrode active material, a conductive material and a binder. The content of the binder may be 1 to 15 wt% based on the total weight of the negative electrode active material layer. In particular, the binder may be SBR.

Preferably, the negative electrode may consist of an electrolytic copper foil, an SBR layer, and a negative active material layer.

The copper foil for a secondary battery according to the present invention has a SBR layer formed as a rust-preventive treatment layer. The copper foil for a secondary battery having such a rust-preventive treatment layer has an advantage that chromium is not used in the rust-preventive treatment layer of the electrolytic copper foil and no harmful substance is used.

The copper foil for a secondary battery according to the present invention exhibits the same or higher performance than a copper foil subjected to a conventional chromate treatment. The surface roughness is similar to that of the conventional electrolytic copper foil, and when the copper foil for a secondary battery according to the present invention is used as a negative electrode collector of a secondary battery, the secondary battery manufacturing process is not changed , And the adhesion between the negative electrode current collector and the negative electrode active material layer is 40 to 70% higher than that of the conventional electrolytic copper foil.

That is, although the present specification describes only the rust-preventive treatment layer, the presence of the rust-preventive treatment layer improves the adhesion to the negative electrode active material layer. Therefore, there is no need to form a primer coating layer which is to be additionally formed to improve adhesion with the anode active material layer in the case of electrolytic copper foil which has been subjected to the conventional chromate anticorrosion treatment.

As described above, the SBR layer included in the copper foil for a secondary battery according to the present invention functions not only as an anti-rust treatment layer, but also as an adhesive layer that provides excellent adhesion with the negative electrode active material layer. Accordingly, the SBR layer included in the copper foil for a secondary battery according to the present invention may be referred to as an SBR composite functional layer.

When such a copper foil for a secondary battery is used as an anode current collector, the amount of the binder in the anode active material slurry can be reduced. Conventionally, a portion where the binder is moved to the surface of the negative electrode active material layer during drying after coating the negative electrode active material causes a weakening of the adhesive force between the negative electrode active material and the negative electrode active material layer, and the binder content in the negative electrode active material slurry is increased in order to minimize this. The SBR layer included in the secondary battery battery copper foil of the present invention can minimize the movement of the binder in the negative electrode active material layer and ultimately reduce the amount of the binder in the negative electrode active material slurry and increase the amount of the negative electrode active material, Effect.

As described above, according to the present invention, not only is it superior in oxidation resistance, but it also has physical properties such as excellent adhesion with the negative electrode active material layer after being processed into the negative electrode collector, and the capacity of the secondary battery is also increased It is possible to provide a copper foil for a secondary battery.

The copper foil for a secondary battery according to the present invention can be formed by immersing an electrolytic copper foil in an SBR aqueous solution as an antirust treatment layer. Therefore, the process management set in the existing electrolytic copper foil manufacturing process is not complicated and the management cost is not increased.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and, together with the description of the invention given below, serve to further the understanding of the technical idea of the invention, And should not be construed as limiting.

1 is a cross-sectional view showing a copper foil for a secondary battery according to an embodiment of the present invention.

2 is a cross-sectional view of a negative electrode manufactured using the copper foil for a secondary battery of FIG.

3 is an exploded perspective view schematically showing a configuration of a secondary battery according to an embodiment of the present invention.

4 is a perspective view of a secondary battery according to an embodiment of the present invention.

5 is a schematic view of an apparatus for performing a method of manufacturing a copper foil for a secondary battery according to an embodiment of the present invention.

Figure 6 is a side schematic view of the Figure 5 apparatus.

Fig. 7 shows an SBR aqueous solution treatment section which can be included in the Fig. 5 apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS The objects and advantages of the present invention will be understood by the following description and will be more clearly understood by means of the embodiments of the present invention. It will also be readily apparent that the objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms, and the inventor should appropriately interpret the concepts of the terms appropriately It should be interpreted in accordance with the meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined.

Therefore, the embodiments described in the present specification and the configurations shown in the drawings are only the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible.

In the embodiments described below, the secondary battery refers to a lithium secondary battery. Here, the lithium secondary battery is generally referred to as a secondary battery in which lithium ions act as working ions during charging and discharging to cause an electrochemical reaction between the positive electrode and the negative electrode.

On the other hand, even if the name of the secondary battery is changed depending on the type of the electrolyte or separator used in the lithium secondary battery, the type of the battery case that forms the external appearance of the secondary battery, the internal or external structure of the lithium secondary battery, The secondary battery should be interpreted as being included in the category of the lithium secondary battery.

The copper foil for a secondary battery of the present invention is applicable to a secondary battery other than a lithium secondary battery. Therefore, even if the working ion is not lithium ion, any kind of secondary battery to which the technical idea of the present invention can be applied should be interpreted as falling within the scope of the present invention.

The secondary battery is not limited by the number of elements constituting it. Thus, the secondary battery may be a single cell assembly including a single cell including a positive electrode / separator / negative electrode assembly and an electrolyte in one battery case, a module in which a plurality of assemblies are connected in series and / or in parallel, / RTI > and / or parallel connected packs, a plurality of packs connected serially and / or in parallel, and the like.

First, referring to FIG. 1, a copper foil for a secondary battery according to an embodiment of the present invention will be described.

1 is a cross-sectional view showing a copper foil for a secondary battery according to an embodiment of the present invention.

The copper foil 100 for a secondary battery according to an embodiment of the present invention shown in FIG. 1 is preferably used as a negative electrode collector of a secondary battery. That is, in the secondary battery, it is preferable to be used as an anode current collector coupled with the anode active material.

The copper foil 100 for a secondary battery according to an embodiment of the present invention includes an SBR layer 20 formed on the surface of an electrolytic copper foil 10. The SBR layer 20 is formed on both surfaces of the electrolytic copper foil 10 and functions to prevent rusting.

It is preferable that the SBR layer 20 is formed in the form of a continuous film without exposing a part of the electrolytic copper foil 10 evenly and uniformly on the surface of the electrolytic copper foil 10 in the form of a film. Therefore, the SBR layer 20 completely covers the surface of the electrolytic copper foil 10 and is a continuous layer in the thickness direction, the width direction, and the length direction. There is no other layer formed intentionally between the electrolytic copper foil 10 and the SBR layer 20. [ That is, the SBR layer 20 is formed directly on the surface of the electrolytic copper foil 10 without forming a layer such as a chromate treatment. For example, the surface of the electrolytic copper foil 10 formed on the surface of the drum in the electrolytic bath is directly coated with the SBR layer 20 without any other artificial treatment.

It is preferable that the thickness of the electrolytic copper foil 10 is approximately 3 mu m to 30 mu m.

If the thickness of the electrolytic copper foil 10 is too thin to be less than about 3 탆, handling in the secondary battery manufacturing process becomes difficult and the workability may be lowered. Conversely, when the thickness of the electrolytic copper foil 10 is about 30 탆 There is a problem that it becomes difficult to manufacture a secondary battery of a high capacity due to an increase in volume due to the thickness of the negative electrode collector when the negative electrode collector is used.

The SBR layer 20 is formed on the surface of the electrolytic copper foil 10 for anti-corrosive treatment of the electrolytic copper foil 10. Further, the SBR layer 20 can not only provide anti-rust properties to the electrolytic copper foil 10 but also play a role of imparting a binding force increasing property to the negative electrode active material.

The thickness of the SBR layer 20 may range from 0.5 [mu] m to 5 [mu] m. When the thickness of the SBR layer 20 is less than 0.5 占 퐉, it is insufficient to obtain a desired degree of oxidation resistance and adhesion. If it is more than 5 mu m, the amount occupied by the SBR layer 20 relatively increases, which is not good for the battery capacity and can act as a resistance.

The tensile strength and elongation of the secondary battery copper foil 100 are mainly determined by the tensile strength and elongation of the electrolytic copper foil 10 and the tensile strength and elongation of the electrolytic copper foil 10 are not lowered due to the formation of the SBR layer 20. [ For example, the tensile strength of the secondary battery copper foil 100 may be 30 kgf / mm ² to 35 kgf / mm ² , but the SBR layer 20 is formed on the basis of all the electrolytic copper foil, regardless of the tensile strength of the electrolytic copper foil 10 Can be manufactured by further forming. The elongation of the electrolytic copper foil is usually about 5% to 20%, so that the copper foil 100 for a secondary battery manufactured from such electrolytic copper foil can have a similar degree of elongation. For example, the elongation may be from 16% to 18%. Such a tensile strength and elongation can prevent breakage and deformation at the time of manufacturing the copper foil for a secondary battery, and enable a proper level of handling even when the negative electrode active material slurry is coated to be a negative electrode.

In the conventional chromate treatment, there is a problem that the roughness characteristic of the electrolytic copper foil that has already been produced is changed. However, in the present invention, since the SBR layer 20 is formed without chromate treatment, the roughness characteristic of the electrolytic copper foil 10 is maintained almost intact.

It is preferable that the surface roughness of both surfaces of the secondary battery copper foil 100 is approximately 0.2 탆 to 2.5 탆 on the basis of Rz (ten point average roughness). If the surface roughness is less than about 0.2 탆, adhesion between the copper foil 100 for a secondary battery and the negative electrode active material is deteriorated. If the adhesion between the copper foil 100 for a secondary battery and the negative electrode active material deteriorates, The risk of the desorption phenomenon is increased.

On the contrary, when the surface roughness is more than about 2.5 μm, the uniform coating of the negative electrode active material on the surface of the copper foil 100 for the secondary battery can not be performed due to the high roughness, so that the adhesion may be lowered. The discharge capacity retention rate of the produced secondary battery may be lowered.

Preferably, the surface roughness of both surfaces of the copper foil 100 for a secondary battery is 0.835 탆 to 1.115 탆. In general, the electrolytic copper foil 10 is different in roughness from the surface (drum contact surface) on the side contacting the drum to the side (air exposed surface) side exposed to the air on the opposite side. Normally, the surface roughness of the drum contact surface is larger than the surface roughness of the air exposure surface. In the case of the copper foil 100 for a secondary battery according to an embodiment of the present invention, the surface roughness of the drum contact surface may be, for example, 0.84 mu m and the surface roughness of the air exposed surface may be 1.09 mu m, for example.

The copper foil 100 for a secondary battery having the SBR layer 20 is advantageous in that it does not use chromium in the rust preventive treatment layer of the electrolytic copper foil 10 and does not use harmful substances. The copper foil 100 for a secondary battery according to an embodiment of the present invention exhibits the same or higher performance than the electrolytic copper foil subjected to the conventional chromate treatment. In addition to the mechanical properties such as tensile strength and elongation, surface roughness is similar to that of a conventional electrolytic copper foil. When the copper foil for a secondary battery according to the present invention is used as an anode current collector for a secondary battery, Do not.

For example, the copper foil 100 for a secondary battery according to the present invention may have an adhesive force with respect to the negative electrode active material layer. For example, the adhesion strength between the negative electrode active material layer and the negative electrode active material layer may vary depending on the amount of the binder in the negative electrode active material layer. May be 20 gf to 30 gf. When the negative electrode active material layer using the same amount of binder as described above is applied to a conventional electrolytic copper foil, the adhesion force is as low as 40 to 70% of the adhesive strength level of the present invention. In order to exhibit the same level of adhesion as in the present invention in a conventional electrolytic copper foil, it is necessary to increase the amount of the binder. Thus, according to the present invention, it is possible to obtain an adhesive strength of 40 to 70% higher than that of the conventional electrolytic copper foil without the need to increase the amount of the binder.

That is, although the present specification describes only the rust-preventive treatment layer, the presence of the rust-preventive treatment layer improves the adhesion to the negative electrode active material layer. Therefore, in the present invention, there is no need to form a primer coating layer which is to be additionally formed for improving adhesion with the anode active material layer in the case of electrolytic copper foil which has been subjected to the conventional chromate anticorrosion treatment.

As described above, the SBR layer 20 provided in the secondary battery-use copper foil 100 functions not only as an anti-rust treatment layer, but also as an adhesive layer that provides excellent adhesion with the negative electrode active material layer. Therefore, the SBR layer 20 provided in the secondary battery copper foil 100 may be referred to as an SBR composite functional layer.

2 is a cross-sectional view of a negative electrode manufactured using the copper foil for a secondary battery of FIG.

Referring to FIG. 2, the negative electrode 150 includes a negative electrode active material layer 110 formed on the copper foil 100 for a secondary battery. The negative electrode active material layer 110 includes a negative electrode active material 120, for example, graphite, a conductive material 130 and a binder 140.

The negative electrode active material 120 may include one or more carbon selected from the group consisting of crystalline artificial graphite, crystalline natural graphite, amorphous hard carbon, low crystalline soft carbon, carbon black, acetylene black, graphene, Li _x Fe ₂ O ₃ (0? _X? 1), Li _x WO ₂ (0? _X? 1), Sn _x Me _{1 - x} Me _{y y z} (Me: Mn, Fe , Pb, Ge; Me ': Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen; 0? X? 1; 1? Y? Metal complex oxides; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, And Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials; Titanium oxide; Lithium titanium oxide, and the like, but the present invention is not limited thereto.

The conductive material 130 is not particularly limited as long as it has electrical conductivity without causing any chemical change in the secondary battery. For example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used. Concrete examples of commercially available conductive materials include acetylene black series such as Chevron Chemical Company, Denka Singapore Private Limited and Gulf Oil Company products), EC series (Armak Company Vulcan XC-72 (from Cabot Company) and Super P (from Timcal).

The binder 140 may be selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Styrene (SM), butadiene (BD), and butyl acrylate (BA)), polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, SBR, ≪ / RTI > may be various copolymers of one or more monomers selected from the group consisting of < RTI ID = 0.0 >

The negative electrode active material layer 110 is prepared by coating a negative electrode active material slurry containing the negative electrode active material 120, the conductive material 130 and the binder 140 on the copper foil 100 for a secondary battery and drying the same. At this time, a filler may be selectively added to the negative electrode active material slurry as a component for suppressing the expansion of the electrode. Such a filler is not particularly limited as long as it is a fibrous material without causing any chemical change in the secondary battery, and examples thereof include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used. In addition, other components such as a viscosity adjusting agent, an adhesion promoter and the like may be further included as a selective or a combination of two or more. The viscosity modifier may be added up to 30% by weight based on the total weight of the negative electrode active material slurry, as a component for adjusting the viscosity of the negative electrode active material slurry so that the mixing process of the negative electrode active material slurry and the coating process thereof are easy. Examples of such viscosity modifiers include, but are not limited to, CMC and polyvinylidene fluoride.

Generally, the easiest method for realizing a high capacity in a secondary battery is to place a large amount of electrode active material on a current collector. However, in this method, if a certain level of electrode adhesion is not secured, And the secondary cell performance and stability may be deteriorated.

Therefore, studies have been actively made in the related art to improve the electrode adhesive strength in order to manufacture a secondary battery which is excellent in performance and stability while realizing a high capacity, and a binder 140 for improving the electrode adhesion force is now included in the electrode Is widely used.

Generally, electrode active materials, conductive materials, and current collectors constituting the electrode are solid at room temperature, have different surface characteristics and are difficult to easily bond at room temperature. However, when a polymeric binder is used, So that the desorption phenomenon of the electrode can be suppressed during the electrode coating, drying and rolling processes. However, in the process of drying the electrode at a high temperature of 100 DEG C or higher after coating the electrode, the binder contained in the slurry state moves in the direction in which the solvent is volatilized (the direction far from the current collector) due to the temperature condition of Tg or more of the binder, There is a problem that the adhesive force between the electrode current collector and the electrode active material is weakened.

Therefore, conventionally, during coating after the coating of the electrode active material, the binder moves to the surface of the electrode active material layer, thereby weakening the adhesive force between the electrode current collector and the electrode active material layer. In order to minimize this, the binder content in the electrode active material slurry is increased . The adhesion between the copper foil 100 for a secondary battery and the anode active material layer 110 according to an embodiment of the present invention may be 20 gf to 30 gf, which is 40 to 70% higher than that of a conventional electrolytic copper foil. As described above, the SBR layer 20 of the secondary battery 100 can minimize the movement of the binder 140 in the anode active material layer 110, and ultimately reduce the binder 140 in the anode active material slurry, And the capacity of the secondary battery including the cathode 150 is increased.

Since the SBR layer 20 maximizes the bonding between the anode active material 120 and the electrolytic copper foil 10, even if the content ratio of the binder 140 is reduced, a much higher level of adhesive force than conventionally can be obtained. It is possible to use a binder in an amount that is much smaller than the amount of the binder necessary for obtaining the adhesive force, thereby achieving an effect of reducing the cost and exhibiting an effect beyond a certain level in terms of the capacity and conductivity of the electrode.

Particularly, when SBR is used as the binder 140, a predetermined continuity is given to the bonding interface between the SBR layer 20 and the anode active material layer 110 due to the material identity with the SBR layer 20, It is preferable to use a charging / discharging cycle which is frequently used, because structural strength can be achieved.

As described above, the copper foil 100 for a secondary battery has an SBR layer 20 and thus has good adhesion to the anode active material layer 110. Therefore, when the copper foil 100 for a secondary battery is used as an anode current collector, the amount of the binder 140 in the anode active material slurry can be reduced. When the content of the binder 140 is too high, the resistance of the electrode is increased to deteriorate the characteristics of the battery. As the content of the electrode active material and the conductive material is relatively lowered, the capacity and conductivity of the electrode are lowered , Which is undesirable. The amount of the binder 140 may be in the range of 1 to 15% by weight based on the total weight of the anode active material layer 110, since sufficient adhesion can be secured even if the amount of the binder 140 is reduced. If the content of the binder 140 is less than 1% by weight, the effect of the addition of the binder 140 is insignificant. If the content of the binder 140 is more than 15% by weight, it is not preferable from the viewpoint of the capacity and conductivity of the cathode 150.

The conductive material 130 may be present in an amount of 20 to 100 parts by weight based on 100 parts by weight of the binder 140. If the amount of the conductive material 140 is less than 20 parts by weight, the desired degree of conductivity can not be obtained. If the amount of the conductive material 140 is more than 100 parts by weight, the content of the negative electrode active material 120 decreases, Which is undesirable.

Since the cathode 150 includes the SBR layer 20, the anode 150 may have excellent adhesion with the anode active material layer 110. Therefore, it is not necessary to coat the electrolytic copper foil with a carbon layer as a primer or multilayering the active material coating layer by a double layer method to solve the adhesive force, and the cathode 150 is formed of the electrolytic copper foil 10, the SBR layer 20, Can be formed only of the active material layer 110 and can have a very simple and simple structure and a manufacturing process.

Although the anode active material layer 110 is formed on one surface of the secondary battery 100, the anode active material layer 110 is formed on both surfaces of the secondary battery battery 100 The case is also possible.

The secondary battery according to the present invention can be manufactured in the same or similar form as a known secondary battery by including the cathode 150 as a battery element. The secondary battery according to the present invention includes the cathode 150 and a corresponding anode, and a separator is interposed between the cathode 150 and the anode 150. The secondary battery according to the present invention includes a cathode, a cathode, a separator, and an electrolyte. The electrode assembly and the electrolyte having the interposed structure can be sealed in the battery case. For example, a pouch-type secondary battery as shown in FIG.

FIG. 3 is an exploded perspective view schematically illustrating a configuration of a secondary battery according to an embodiment of the present invention, and FIG. 4 is a perspective view of a secondary battery according to an embodiment of the present invention.

Referring to FIGS. 3 and 4, a secondary battery 190 according to an embodiment of the present invention is a pouch type battery including an electrode assembly 180 and a pouch 185.

The electrode assembly 180 is configured such that the cathode 150 and the anode 160 are opposed to each other and a separation membrane 155 is interposed between the cathode 150 and the anode 160. Such an electrode assembly 180 may be configured as a stacked, stacked, folded, or jelly roll type.

The negative electrode 150 is formed as a structure in which the negative electrode current collector is coated with the negative electrode active material slurry on the copper foil 100 for a secondary battery as described above. The anode 160 is also formed with a structure in which a cathode active material slurry is coated on a cathode current collector such as aluminum. An electrode tab corresponding to each electrode is formed on the non-coated portion, and a negative electrode lead 152 is formed on the negative electrode tab and a negative electrode lead is formed on the positive electrode lead, (162) is connected to the outside of the pouch (185).

The pouch 185 is a battery case having a receptacle which is a concave space as indicated by R in the figure and which can accommodate at least a part of the electrode assembly 180 and an electrolyte such as an electrolyte have. In addition, the pouch 185 may be composed of an upper sheet T and a lower sheet B to facilitate insertion of the electrode assembly 180. At this time, the pouch 100 may be formed so as to accommodate both the upper sheet T and the lower sheet B, So that the portion R is formed. Further, the upper sheet T and the lower sheet B may not be separated from each other, but may be connected to each other to form a unit sheet.

The upper sheet T and the lower sheet B are each provided with a sealing portion S at the edge of the inner accommodating space and the sealing portions S are bonded to each other to seal the inner accommodating space have. A sealing tape 170 may further be provided between the upper sheet T and the lower sheet B to further improve adhesion to the leads 152 and 162.

As described above, the pouch 185 seals the electrode assembly 180 and electrolyte contained therein, and protects the electrode assembly 180 from the outside.

The present invention is not limited to the structure and the kind of the secondary battery according to the present invention, and the secondary battery according to the present invention is only required to use the copper foil for a secondary battery according to the present invention as an anode current collector. In addition to the above description, general matters relating to the secondary battery can be referred to the applicant's prior patent documents, and thus a detailed description thereof will be omitted.

Next, a method for manufacturing a copper foil for a secondary battery according to an embodiment of the present invention will be described.

First, the process for manufacturing a copper foil for a secondary battery according to the present invention is carried out by constructing a process line by relatively simple modification such as removing a chromate treatment section of a process line for manufacturing an existing electrolytic copper foil and adding an SBR aqueous solution treatment tank .

Preferably, the electrolytic copper foil is electrodeposited on the drum in an electrolytic bath, and the electrolytic copper foil passes through the SBR surface treatment section and is wound on the bobbin while the electrolytic copper foil is taken out of the electrolytic bath. This will be described in detail below.

5 is a schematic view of an apparatus for performing a method of manufacturing a copper foil for a secondary battery according to an embodiment of the present invention. Figure 6 is a side schematic view of the Figure 5 apparatus. Fig. 7 shows an SBR aqueous solution treatment section which can be included in the Fig. 5 apparatus.

For example, as shown in FIG. 5, in the electrolytic bath 200, iridium-coated titanium (Ir coated Ti) rotating cathode drum 210 and a gap of about 3 to 20 mm The electrolytic copper foil 10 can be manufactured first by using the electrolytic copper foil manufacturing apparatus 300 in which the electrodes are placed.

When the electrolytic copper foil 10 according to the present invention is produced, a copper sulfate electrolytic solution may be added to the electrolytic bath 200 and electrodeposited on the drum 210 by adjusting the current density ratio. The copper sulfate electrolyte typically has a copper concentration of 50 to 350 g / l and a sulfuric acid concentration of 50 to 200 g / l. Gelatin, gelatin, HEC (Hydroxyethyl Cellulose), and polyvinyl alcohol are added to the copper sulfate electrolyte to obtain the electrolytic copper foil 10 having the desired physical properties and to control the mechanical properties and the surface condition of the electrolytic copper foil 10, Sulfide compounds, polyethylene glycols, nitrides, and the like. The temperature of the copper sulfate electrolyte may be 40 to 70 ° C. The current density is adjusted according to various conditions such as the copper concentration, the sulfuric acid concentration, the liquid supply rate, the inter-pole distance, and the temperature of the copper sulfate electrolyte. (Copper plating in the form of layers) and roughening plating (copper plating in the form of a ball-shaped or needle-shaped or hoarfrost-shaped copper) ), And the current density at the boundary between them is defined as the limiting current density, and the current density is maintained within the limit of the normal plating. The current density may be between 10 and 80 A / dm < ² >.

The electrolytic copper foil 10 has good releasability with the drum 210 and is manufactured with excellent phase stability as an anode current collector of a secondary battery. The electrolytic copper foil 10 made in the electrolytic bath 200 of FIG. 5 can be wound on the bobbin 270 through the transfer part 250.

However, the electrolytic copper foil 10 produced by the electrolytic plating proceeds from the moment when it is exposed to the atmosphere in the electrolytic bath 200. This oxidation produces CuO and CuO ₂ , which not only act as an impediment to electrical properties but also cause apparent problems. Therefore, conventionally, a section for the chromate treatment was required in the middle of the transfer unit 250. In the present invention, an SBR surface treatment section 260 is added instead of the chromate treatment section.

6, the electrolytic copper foil 10 made on the surface of the drum 210 in the electrolytic bath 200 passes through the SBR surface treatment section 260 while the surface or the back surface of the electrolytic copper foil 10, The SBR layer 20 is formed on the bobbin 270 to be a copper foil 100 for a secondary battery. Thereafter, the copper foil 100 for a secondary battery is cut to a required length, and then a negative electrode active material layer is formed to be used as a negative electrode.

6, a method of forming the SBR layer 20 on the surface of the electrolytic copper foil 10 in the SBR surface treatment section 260 can be performed by coating the electrolytic copper foil 10 with an SBR aqueous solution and drying the SBR aqueous solution.

SBR can be easily dispersed in water or emulsion form. Thus, the SBR aqueous solution may be a form in which the SBR is dispersed in an emulsion form, or a form in which some or all of the SBR is dissolved. At this time, the SBR content is determined at a level that determines the viscosity of the SBR aqueous solution in consideration of the possibility of mixing with water, the ease of coating, the shape maintenance after coating, and the like. An additive for viscosity control such as CMC may be further included. The SBR aqueous solution is diluted with SBR as a raw material, which is a solvent, to determine the application amount. The electrolytic copper foil 10 may be continuously processed so as to be taken out of the electrolytic bath 200, passed through the SBR surface treatment section 260, and wound around the bobbin 270. Alternatively, the electrolytic copper foil 10 may be wound on the bobbin 270 after a certain period of time in the SBR surface treatment section 260.

Water is inexpensive and can be purchased more easily. In addition, water is more environmentally friendly and is generally easier to store and process. Accordingly, there is no difficulty in maintaining the SBR surface treatment section 260 compared to the conventional chromate treatment.

The SBR aqueous solution may be left in a stirred state. The SBR aqueous solution may begin to cure and / or separate when left alone without stirring.

The coating method may be spraying by spraying an SBR aqueous solution, coating in a coater, dipping, or shedding. In this embodiment, the SBR aqueous solution treatment tank 262 is shown in Fig. 7 as an example of immersion.

For example, an SBR aqueous solution in which SBR is dispersed in water at a concentration of 1 g / l to 10 g / l is contained in the SBR aqueous solution treatment tank 262, and the electrolytic copper foil 10 is immersed in the SBR aqueous solution treatment tank 262 . Then, the electrolytic copper foil 10 treated with the SBR aqueous solution is dried to form the SBR layer 20 on the surface of the electrolytic copper foil 10. At this time, it is preferable to install the hot-air drying furnace 264 at the stage following the SBR aqueous solution treatment tank 262 in an in-line manner. In the drying furnace 264, the SBR aqueous solution coated on the surface of the electrolytic copper foil 10 may be dried by directly contacting hot air. Box type, and tunnel type drying furnace, and infrared heat, high frequency heating, or heating by hot wire may be used as a heat source. For example, the drying furnace 264 may be a linear hot air drying furnace, such as a halogen line heater. When the in-line configuration is adopted, the electrolytic copper foil wound on the bobbin 270 is separately transferred and untwisted so that the SBR treatment is not required, so that the copper foil 100 for a secondary battery can be obtained at low cost with high productivity suited for continuous production .

The drying is preferably performed in a temperature atmosphere of 160 ° C to 200 ° C. Further, it is preferable to continue the above-mentioned drying in a temperature atmosphere of 180 to 190 캜 for 30 to 240 minutes to obtain a baking effect together with drying beyond the concept of simple drying. Here, baking is a process of increasing the adhesive force of the SBR layer 20 on the surface of the electrolytic copper foil 10, in addition to evaporation of water in the coated SBR aqueous solution, as well as tight bonding between the remaining SBRs, This also includes the meaning of relocation of materials and densification of the film for close bonding. Through this drying, the SBR layer 20 is formed in the form of a continuous film without exposing a part of the electrolytic copper foil 10 to the surface of the electrolytic copper foil 10 evenly and with a constant thickness in the form of a film And defects such as fine cracks and pin holes do not occur.

<Experimental Example>

A commercially available electrolytic copper foil (comparative example) having a thickness of 18 mu m and a copper foil (example) sample for a secondary battery according to the present invention were prepared, and mechanical properties, surface roughness and adhesive strength were measured.

The sample was formed by coating an SBR aqueous solution in which SBR was dispersed in water at a concentration of 5 g / l on the surface of an electrolytic copper foil having a thickness of 18 탆 and drying it. The thickness of the SBR layer after drying was approximately 2 mu m.

The specimens were cut out from each copper foil using a tensile punching machine. The tensile strengths of the specimens were measured at 130 ° C for 10 minutes and then at room temperature for 5 minutes. Tensile strength was measured by using a UTM (Universal Test Machine) widely used for measuring mechanical properties, using INSTRON UTM equipment. The specimens were mounted on a UTM facility and subjected to TA (tension annealing) at a speed of 50 mm / min And the force at break was measured and then calculated.

In this tensile test, elongation was measured by measuring elongation length up to just before fracture. If the initial length of the specimen is L ₀ and the length immediately before the fracture is L, ΔL (= L-L ₀ ) is the length of the specimen. The increased amount of the length indicated as a percentage, that is, _{(△ L / L 0) ×} 100 is the elongation.

The surface roughness and the adhesive force were measured for the drum contact surface and the air exposed surface of the electrolytic copper foil, respectively.

The surface roughness was measured by a ten-point average calculation method using a surface roughness meter (Rz roughness). As is well known, the ten-point average calculation method takes a reference length as a section curve and calculates a straight line that is parallel to the average line of the section and does not cut the cross-section curve transversely between the mountain peaks from the highest to the fifth and from the deepest to the fifth To indicate the difference of the average.

For the evaluation of adhesion, an anode active material slurry was prepared, coated on each copper foil, and then dried at room temperature / high temperature, and evaluated before and after rolling. TA meter was used, and specimens with a length of 2.0 mm (W) x 152.4 mm (L) were produced. The anode active material layer was fixed on a slide glass using a double-sided tape, and the specimen was peeled off from the adherend and peeled to determine the state of adhesion (peel test). The pulling angle was varied between 90 ° and 180 °.

Table 1 summarizes tensile strength, elongation, Rz roughness, and adhesion measurement results.

As shown in Table 1, mechanical properties and surface roughness were measured at a similar level in the conventional (comparative) and inventive (embodiment). That is, in the case of the present invention, it is possible to satisfy the electrolytic copper foil specification condition as a negative electrode current collector that has been used in the past.

It is notable that the adhesive strength of the present invention is significantly increased compared with the conventional adhesive. The adhesive strength increased by 42.6% before rolling on the air-exposed surface, and the adhesion increased by 25.3% after the air-exposed surface was rolled. The adhesive force increased by 67.6% before rolling on the drum contact surface and increased by 54.8% after rolling on the drum contact surface. Therefore, according to the present invention, since the adhesive strength to the negative electrode active material layer is greatly improved, the amount of the binder in the negative electrode active material slurry can be reduced.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It is to be understood that various modifications and changes may be made without departing from the scope of the appended claims.

Claims (11)

1. A copper foil for a secondary battery, wherein a layer of SBR (Styrene Butadiene Rubber) is formed on the surface of the electrolytic copper foil.
2. The copper foil for a secondary battery according to claim 1, wherein the electrolytic copper foil contains no chromium element as an antirust surface treatment element.
3. The copper foil for a secondary battery according to claim 1, wherein the surface of the electrolytic copper foil formed on the drum surface in the electrolytic bath is directly coated with the SBR layer without any other artificial treatment.
4. Subjecting the surface of the electrolytic copper foil to a surface treatment with an SBR aqueous solution to form an SBR layer on the surface of the copper foil.
5. 5. The method for manufacturing a copper foil for a secondary battery according to claim 4, wherein the electrolytic copper foil is electrodeposited on a drum in an electrolytic bath to produce the electrolytic copper foil, and the electrolytic copper foil is wound on the bobbin through the SBR surface treatment section while being taken out of the electrolytic bath.
6. The method for manufacturing a copper foil for a secondary battery according to claim 5, wherein the SBR surface treatment section is provided with an SBR aqueous solution treatment tank and a hot air drying furnace in an inline manner.
7. 5. The method for manufacturing a copper foil for a secondary battery according to claim 4, wherein the SBR layer is formed by coating an SBR aqueous solution in which SBR is dispersed in water at a concentration of 1 g / l to 10 g / l on the surface of the electrolytic copper foil, .
8. The secondary battery according to claim 1, wherein the copper foil for a secondary battery is applied as a negative current collector.
9. 9. The method according to claim 8, wherein the thickness of the electrolytic copper foil in the collector is in the range of 3 to 30 mu m, the thickness of the SBR layer is in the range of 0.5 to 5 mu m,

   Wherein the negative electrode comprises a negative electrode active material layer including a negative electrode active material, a conductive material, and a binder on the current collector,

   Wherein the content of the binder is 1 to 15% by weight based on the total weight of the negative electrode active material layer.
10. The secondary battery according to claim 9, wherein the binder is SBR.
11. The secondary battery according to claim 8, wherein the secondary battery includes an electrode assembly including a cathode, a cathode, and a separator, and the anode comprises an electrolytic copper foil, an SBR layer, and an anode active material layer.

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