TW201414602A - Surface-treated copper foil, method for manufacturing surface-treated copper foil, and negative electrode material for negative electrode current collector and nonaqueous secondary cell - Google Patents

Abstract

An object of the present invention is to provide a surface-treated copper foil that decreases little in tensile strength even when subjected to a high-temperature heat treatment for a long period of time, a method for manufacturing the surface-treated copper foil, and a negative electrode material for a current collector and a nonaqueous secondary cell that use the surface-treated copper foil. To achieve this object, provided is a surface-treated copper foil comprising zinc-containing surface-treated layers, 20 mg/m2 to 1000 mg/m2 per side, on both sides of a copper foil containing trace constituents of one, two, or more components selected from carbon, sulfur, chlorine, and nitrogen, the total of these components being 100 ppm or more; the surface-treated copper foil characterized in being subjected to a pre-annealing treatment of heating in a temperature range of 200 to 280 DEG C.

Description

Surface treatment copper foil, method for producing surface treated copper foil, cathode current collector, and cathode material for nonaqueous secondary battery

The present invention relates to a surface-treated copper foil, a method of producing a surface-treated copper foil, a cathode current collector, and a cathode material of a non-aqueous secondary battery. In particular, there is a surface-treated copper foil used for a cathode current collector of a lithium ion secondary battery or the like which has a small decrease in tensile strength even when heated at a high temperature for a long period of time, a method for producing the same, and a method for producing the same The cathode current collector and cathode material of the surface treated copper foil.

Previously, copper foil was used as a circuit forming material for various electronic parts including printed wiring boards. In addition, the copper foil is not limited to these circuit forming materials, and is also used as a cathode current collector of a nonaqueous secondary battery such as a lithium ion secondary battery.

In general, a cathode material of a lithium ion secondary battery is composed of a cathode mixture layer containing a cathode active material, a conductive material, and a binder on the surface of a current collector made of a conductive material. When the lithium ion secondary battery is charged and discharged, when the cathode active material occludes and discharges lithium, the cathode mixture layer expands and contracts with this. Since the cathode mixture layer is adhered to the surface of the current collector, and the lithium ion secondary battery repeats the charge and discharge cycle, the repeated stress is applied between the cathode mixture layer and the current collector. Therefore, the extension of the collector When the strength is low, the current collector is stretched to cause deformation such as wrinkles or breakage due to a change in the volume of the cathode mixture. When the current collector is stretched to cause wrinkles or the like, there is a short circuit between the anode and the cathode, or a change in the distance between the anode and the cathode to hinder the uniform electrode reaction, resulting in a low durability of the charge and discharge cycle. Sex. Further, in the case where the current collector is broken, the capacity per unit volume is decreased, and the battery characteristics of the lithium ion secondary battery are lowered. Therefore, when a copper foil is used as a current collector, the copper foil is required to have high tensile strength.

However, in the step of manufacturing the cathode material, when the cathode mixture layer is formed on the surface of the current collector, the collector system is loaded with heat at a high temperature. In the case of a normal copper foil, when heat of a high temperature is applied, crystal grains are coarsened due to recrystallization of copper, and mechanical strength such as tensile strength is lowered. Therefore, the copper foil used for the current collector is required to maintain high tensile strength even after high-temperature heat treatment. As such a copper foil, for example, Patent Document 1 (International Publication No. 2012/070589) and Patent Document 2 (International Publication No. 2012/070591) disclose that 40 kgf/ can be maintained even after heating at 350 ° C for 60 minutes. mm ² or more for 60 minutes after heating also possible to maintain 35kgf / mm ² in tensile strength between the surface-treated copper foil at least 400 ℃.

However, when manufacturing a cathode material of a lithium ion secondary battery, the current collector is heated in a temperature range of 350 ° C to 400 ° C for more than 1 hour. At this time, the tensile strength of the surface-treated copper foil disclosed in Patent Document 1 or Patent Document 2 is low, and the tensile strength at a sufficient level cannot be maintained depending on the heating time.

Therefore, an object of the present invention is to provide a surface-treated copper foil, a method of producing a surface-treated copper foil, and a current collection using the surface-treated copper foil, in which a reduction in tensile strength is small even when a high-temperature heat treatment is performed for a long period of time. The cathode material of the body and the non-aqueous secondary battery.

As a result of intensive studies, the inventors of the present invention have come up with a surface-treated copper foil which has a small reduction in tensile strength even when subjected to a high-temperature heat treatment for a long period of time.

The surface-treated copper foil of the present invention contains both sides of a copper foil containing 100 ppm or more of a trace component selected from the group consisting of carbon, sulfur, chlorine, and nitrogen in a total amount, and each surface includes 20 mg/m. A surface-treated copper foil of a surface treatment layer of zinc of ² to 1000 mg/m ² , characterized in that it is subjected to pre-annealing treatment by heating at a temperature ranging from 200 ° C to 280 ° C.

The surface-treated copper foil of the present invention exhibits a tensile strength of 45 kgf/mm ² or more after heating at 350 ° C for 5 hours.

In the surface-treated copper foil of the present invention, the surface treatment layer is preferably a metal element containing copper and/or copper which has a faster diffusion rate than zinc, in addition to zinc.

In the surface-treated copper foil of the present invention, the aforementioned metal element is preferably tin.

In the surface-treated copper foil of the present invention, the surface treatment layer preferably contains tin of from 1 mg/m ² to 200 mg/m ² per side.

In the surface-treated copper foil of the present invention, the average crystal grain size of the copper constituting the copper foil is preferably 1.0 μm or less.

In the surface-treated copper foil of the present invention, the copper foil preferably has a normal tensile strength of 50 gf/mm ² or more.

In the surface-treated copper foil of the present invention, the pre-annealing treatment is preferably carried out at a temperature within the above temperature range for 2 hours or more and 25 hours or less.

The surface-treated copper foil of the present invention contains both sides of a copper foil containing 100 ppm or more of a trace component selected from the group consisting of carbon, sulfur, chlorine, and nitrogen in a total amount, and each surface includes 20 mg/m. A surface-treated copper foil of a surface treatment layer of zinc of ² to 1000 mg/m ² , which is characterized in that the tensile strength after heating at 350 ° C for 5 hours is 50 kgf / mm ² or more.

A method for producing a surface-treated copper foil according to the present invention, comprising: a surface treatment step of containing one or more kinds of trace components selected from the group consisting of carbon, sulfur, chlorine, and nitrogen in an amount of 100 ppm or more based on the total amount. a surface of the copper foil having a surface treatment layer containing 20 mg/m ² to 1000 mg/m ² of zinc on each side; and a pre-annealing step of heating at a temperature ranging from 200 ° C to 280 ° C after the surface treatment step .

In the method for producing a surface-treated copper foil according to the present invention, the heating time in the pre-annealing step is preferably 2 hours or longer and 25 hours or shorter.

The cathode current collector of the present invention is characterized by using the surface-treated copper foil according to any one of the above.

The cathode material of the nonaqueous secondary battery of the present invention is characterized in that the cathode current collector is used.

The surface-treated copper foil of the present invention can be easily produced by forming a surface treatment layer containing zinc on both surfaces of a copper foil, and can provide a tensile strength after being subjected to a high-temperature heat treatment for a long period of time. Reduce the copper foil that is also less.

Fig. 1 is a FIB-SIM image showing an example of the cross-sectional crystal structure of the sample 1 after performing pre-annealing treatment at 200 ° C for 8 hours and heating at 350 ° C for 5 hours.

Fig. 2 is a FIB-SIM image showing an example of the cross-sectional crystal structure of the comparative sample 1 after heating at 350 ° C for 5 hours.

Hereinafter, embodiments of the surface-treated copper foil, the method for producing a surface-treated copper foil, the cathode current collector, and the cathode material of the non-aqueous secondary battery of the present invention will be described in order.

Surface treatment copper foil

First, an embodiment of the surface-treated copper foil of the present invention will be described. The surface-treated copper foil of the present invention comprises a surface treatment layer containing zinc (in this embodiment, a zinc adhesion layer) on both sides of the copper foil, and after the formation of the zinc adhesion layer, by pre-annealing, even if it is long After the time is subjected to the high-temperature heat treatment, the decrease in tensile strength can also be suppressed. In addition, in the present specification, the term "high temperature" means a temperature equal to or higher than the temperature at which recrystallization of copper occurs, and mainly refers to a temperature in the range of about 300 ° C to 400 ° C. Further, the term "long time" refers to a time greater than one hour, which mainly means a time of more than 5 hours. Hereinafter, in the present embodiment, In the case where the surface-treated copper foil is used as a cathode current collector of a non-aqueous secondary battery such as a lithium ion secondary battery, the surface-treated copper foil of the present invention is not limited to the lithium ion secondary battery. It is needless to say that the cathode current collector of the nonaqueous secondary battery can be used as a material for manufacturing a printed wiring board.

(1) Copper foil

First, the copper foil will be described. In the present invention, the zinc adhesion layer is provided on both surfaces of a copper foil containing 100 ppm or more of a trace component selected from the group consisting of carbon, sulfur, chlorine, and nitrogen.

Here, the term "copper foil" as used in the present invention means an untreated copper foil which is not subjected to various treatments such as the above surface treatment, and the term "surface-treated copper foil" means zinc which is used to form the zinc adhesion layer. Adhesive treatment, pre-annealing, and various surface treated copper foils. In addition, the copper foil may be an electrolytic copper foil or a rolled copper foil. However, it is preferable to use an electrolytic copper foil from the viewpoint of easily obtaining a copper foil having fine crystal grains and excellent mechanical properties with high tensile strength. In the following, an electrolytic copper foil is mainly described as an example. However, in the following description, only the "copper foil" is used, and the copper foil is not only "electrolyzed copper foil" but also "rolled copper foil".

In the present invention, the copper foil contains one or more kinds of trace components selected from the group consisting of carbon, sulfur, chlorine, and nitrogen in an amount of 100 ppm or more in total. When the content of the trace components is 100 ppm or more in total, the crystal structure (crystal grains) of the copper constituting the copper foil is easily refined, and the mechanical strength with high tensile strength is easily obtained. Copper foil.

Here, the copper foil used in the present invention contains 100 ppm or more of the trace component in total, and contains carbon in the range of 20 ppm to 470 ppm, sulfur in the range of 5 ppm to 600 ppm, and 15 ppm to 600 ppm. The range contains chlorine, and it is preferred to contain nitrogen in the range of 5 ppm to 600 ppm. By containing an appropriate amount of such a trace component in the crystal structure of the copper foil, it is easier to refine the crystal structure of the copper, and it is possible to obtain a copper foil having excellent tensile strength and high mechanical strength. Specifically, by including each trace component in the above range, the copper foil can have an average crystal grain size of 1.0 μm or less, a normal tensile strength of 50 kgf/mm ² or more, and a normal elongation of 3 %~15% of copper foil with excellent mechanical strength.

When the content of each of the minor components is less than the lower limit, for example, it is difficult to obtain an extremely fine crystal structure having an average crystal grain size of 1.0 μm or less and a copper foil having a higher tensile strength cannot be obtained. On the other hand, when the content of each of the minor components in the copper foil is larger than the upper limit, it is not preferable from the viewpoint of the following. When the carbon content is more than 470 ppm, it is not preferable because the graphite is coarsened and cracks are likely to occur. When the sulfur content is more than 600 ppm, although the tensile strength of the copper foil becomes high, the elongation is low and embrittlement is not preferable. When the chlorine content is more than 600 ppm, when the copper foil is electrolyzed, the precipitation surface becomes thick. At this time, since it is difficult to uniformly adhere the cathode active material or the like to the surface thereof, the volume change amount at the time of repeated charge and discharge becomes uneven in the plane and is locally broken, which is not preferable. In addition, when the nitrogen content is more than 180 ppm, the nitrogen compound becomes excessive, and the effect of refining the precipitation structure of the copper foil is saturated, and the meaning of increasing the nitrogen content is lost, which is not preferable.

However, in the present invention, a unit called "ppm" which is used to indicate the content of a trace component in the copper foil is synonymous with "mg/kg", and the trace component is contained in a total amount of 100 ppm or more. Means in the copper foil The total amount of the trace component contained per 1 kg is 100 mg or more.

Average crystal grain size: Next, the average crystal grain size of the crystal grains of copper constituting the crystal structure of the copper foil will be described. First, the average crystal grain size is preferably 1.0 μm or less, and more preferably 0.8 μm or less. When the average crystal grain size is more than 1.0 μm, it is difficult to maintain the tensile strength required as a cathode current collector of a nonaqueous secondary battery such as a lithium ion secondary battery. Further, the crystal grains constituting the copper of the copper foil are preferably fine and uniform. Since the crystal grains are uniform, the crystal grain boundaries are uniformly distributed in the copper foil, and the load applied to the copper foil is dispersed without being biased to specific crystal grains, and mechanical strength with high tensile strength can be obtained. Excellent copper foil. However, the average crystal grain size referred to herein means the average crystal grain size of the copper foil in a normal state, and can be obtained from the particle diameter of the crystal grains which are observed in the cross section when the cross section of the copper foil is observed.

Normal tensile strength: The normal tensile strength of the copper foil is preferably 50 kgf/mm ² or more. However, the "normal state" in the present invention refers to a state in which it is managed at a normal temperature or a state before being heat-treated. By using a copper foil having a normal tensile strength of 50 kgf/mm ² or more, a surface-treated copper foil exhibiting high tensile strength can be obtained even after high-temperature heat treatment. However, even in the copper foil having a high normal tensile strength, the tensile strength after the heat treatment is remarkably lowered. Therefore, in the present invention, it is not preferable that the normal tensile strength of the copper foil itself is higher, regardless of the value of the normal tensile strength, and the surface-treated copper foil is subjected to heat treatment. A higher value of the tensile strength is preferred.

Thickness: The thickness of the copper foil is not particularly limited. A copper foil having a suitable thickness may be used in accordance with the use of the surface-treated copper foil. E.g, When the surface-treated copper foil of the present invention is used as a cathode current collector of a nonaqueous secondary battery such as a lithium ion secondary battery, the thickness of the copper foil is usually in the range of 5 μm to 35 μm (meter thickness). . Moreover, when this surface-treated copper foil is used for the manufacture of a printed wiring board, the thickness of this copper foil is the range of 5 micrometer - 120 micrometer (meter thickness). The surface-treated copper foil of the present invention has a tensile strength of a standard which is required as a cathode current collector of a lithium ion secondary battery even in a thin copper foil of 5 μm to 35 μm.

(2) Zinc adhesion layer (surface treatment layer)

Next, the zinc adhesion layer will be described. The surface-treated copper foil of the present invention is on both sides of the above-mentioned copper foil, and each side includes a zinc adhesion layer containing zinc of 20 mg/m ² to 1000 mg/m ² . The zinc in the zinc adhesion layer provided on both sides of the copper foil diffuses in the copper foil and reacts with the above-mentioned trace components in the crystal structure while passing through. The zinc and the above-mentioned trace component are precipitated at the crystal grain boundary, and when the copper foil is loaded with heat, the effect of preventing the crystal grain from growing and suppressing the coarsening of the crystal grain can be exhibited. In the present invention, by forming a zinc adhesion layer on both surfaces of the copper foil, a pre-annealing treatment to be described later is performed, and it is possible to use a speed which is balanced with industrial production efficiency, not only to diffuse zinc to the surface layer portion of the copper foil, but also Spread to the inside (central part). Therefore, according to the present invention, the surface-treated copper foil can be used in a subsequent use process, and even when heat treatment is performed for a long period of time at a high temperature, the fine crystal structure can be maintained after the heat treatment and the tensile strength of the copper foil can be suppressed from being lowered. .

Here, the zinc content in the zinc adhesion layer, that is, the adhesion amount of zinc to the surface of the copper foil is less than 20 mg/m ² per side, because the amount of zinc diffused in the copper foil is small and cannot be sufficiently suppressed. It is not preferable that the crystal grains are coarsened and it is difficult to maintain a fine crystal structure. From this viewpoint, the adhesion amount of zinc is preferably 25 mg/m ² or more, and more preferably 50 mg/m ² or more. On the other hand, when the adhesion amount of zinc is more than 1000 mg/m ² , even if the amount of adhesion of zinc is increased, the effect of the amount of adhesion is not obtained, which is a waste of resources, which is not preferable. From this point of view, the adhesion amount of zinc is preferably 500 mg/m ² or less, more preferably 300 mg/m ² or less, and still more preferably 200 mg/m ² or less.

Here, since each side of the zinc adhesive layer-based copper foil contains zinc in the above range, the total adhesion amount of zinc to the copper foil is in the range of 40 mg/m ² to 2000 mg/m ² . Further, from the same viewpoint as described above, the total adhesion amount of zinc is preferably 50 mg/m ² or more, and more preferably 100 mg/m ² or more. Further, the upper limit is preferably 1000 mg/m ² or less, and more preferably 600 mg/m ² or less. However, the adhesion amount of the zinc is assumed to be the amount of zinc (the amount of conversion) of the average unit area when the surface of the copper foil is completely flat.

The zinc adhesion layer may be a zinc alloy layer of a metal element having a diffusion rate faster than zinc in copper and/or copper in addition to zinc, in addition to the zinc layer composed of zinc. For example, a metal element having a higher diffusion rate in copper than zinc at a temperature of 300 ° C or higher (hereinafter referred to as "dissimilar metal element") may, for example, be Bi, Cd, Sn, Pb, Sb, In, or Al. , As, Ga, Ge. In addition, the zinc adhesion layer may be a zinc-based composite layer in which a zinc layer and a dissimilar metal containing at least one or two or more of the above-described dissimilar metal elements are laminated. In this case, the order of lamination of the zinc layer and the dissimilar metal layer is not particularly limited, and the surface of the copper foil may be laminated in the order of the zinc layer or the dissimilar metal layer, or may be formed on the surface of the copper foil according to the dissimilar metal layer or the zinc layer. The order is layered. By setting the zinc adhesion layer to contain the above-mentioned heterogeneous metal element with zinc In the copper foil, the dissimilar metal element can be diffused simultaneously with zinc. Since the diffusion rate of the dissimilar metal elements is faster than that of the zinc, the dissimilar metal elements are in the thickness direction of the copper foil, faster than zinc and reach a deeper position. Further, these dissimilar metal elements react with the above-mentioned trace components in the same manner as zinc to form a compound, and suppress coarsening of crystal grains of copper. Therefore, by using a structure in which the zinc adhesion layer contains a dissimilar metal element simultaneously with zinc, even when heat treatment is performed for a long period of time at a high temperature, the entire thickness direction of the copper foil can be more effectively suppressed. The coarsening of the crystal grains of copper. Further, zinc refers to zinc having a purity of 99% or more. Further, the term "zinc alloy" means a mixture of zinc and other elements, a solid solution, a eutectic, a compound, and the like.

In the present invention, when the zinc adhesion layer is a zinc alloy layer or a zinc-based composite layer, among the above-mentioned different metal elements, tin is particularly preferably used. In this case, it is preferable to carry out surface treatment so that the amount of adhesion of tin on each of the above surfaces is 1 mg/m ² to 200 mg/m ² in the above-described conversion amount. In this case, the zinc content ratio calculated by {[zinc adhesion amount] / [zinc-tin alloy adhesion amount]} × 100 is preferably 30% by mass or more. When the amount of zinc adhering to the surface of the copper foil is within the above range, and the zinc content ratio in the zinc adhesive layer is less than 30% by mass, the amount of tin relative to the amount of zinc becomes excessive. Therefore, the presence of tin hinders the diffusion of zinc in the copper foil, and it becomes difficult to sufficiently diffuse zinc inside the copper foil, and the above effects are not obtained, which is not preferable. Moreover, these zinc adhesion layers can be formed, for example, using an anti-rust treatment agent containing zinc or zinc-tin, and can function as a rust-preventing treatment layer.

(3) Other layer structures

The surface treated copper foil of the present invention is in addition to the above zinc adhesion layer Further, other surface treatment layers such as a roughening treatment layer, a chromate treatment layer, and an organic agent treatment layer may be optionally included as necessary.

For example, when the surface-treated copper foil is used as a cathode current collector of a lithium ion secondary battery by providing a roughening treatment layer, the adhesion between the surface of the surface-treated copper foil and the cathode active material can be changed. good.

Further, by including the chromate treatment layer and/or the organic agent treatment layer, oxidation of the surface of the copper foil can be suppressed by the zinc adhesion layer and the layers. Moreover, it is possible to make the adhesion to the cathode active material of the lithium ion secondary battery or the like more favorable. Further, examples of the organic agent treatment layer include a decane coupling agent treatment layer, an organic rustproof treatment layer, and the like.

(4) Pre-annealing treatment

The surface-treated copper foil of the present invention can be obtained by subjecting the surface treatment to the both surfaces of the copper foil, followed by pre-annealing treatment in a temperature range of 200 ° C to 280 ° C. By performing this pre-annealing treatment, it is possible to diffuse zinc in the copper foil while suppressing recrystallization of copper. Therefore, when the surface-treated copper foil is loaded with heat of a temperature higher than the temperature at which the copper is recrystallized, the compound precipitated at the grain boundary can exhibit the effect of preventing the growth of the crystal grains and suppressing the coarsening of the crystal grains. Further, the pre-annealing treatment will be described later. In the following, the copper foil after the surface treatment described above is referred to as a "surface-treated copper foil" before the pre-annealing treatment.

(5) Mechanical properties

The surface-treated copper foil of the present invention is subjected to the pre-annealing treatment on the surface-treated copper foil, and the tensile strength after heating at 350 ° C for 5 hours in an inert gas atmosphere is 45 kgf/mm ² or more; The conditions of the pre-annealing treatment are adjusted to appropriate conditions in accordance with the amount of adhesion of copper foil and zinc (and tin), and the tensile strength after the heat treatment is 50 kg/mm ² or more. In the present invention, in particular, the tensile strength after heating at 350 ° C for 5 hours is preferably 50 kgf / mm ² or more by adjusting the conditions of the pre-annealing treatment.

Further, the surface-treated copper foil of the present invention preferably has a tensile strength after heating at 350 ° C for 5 hours with respect to the tensile strength in a normal state, and is preferably in the range of 90% to 100%. The tensile strength maintenance ratio is preferably in the range of 95% to 100%. According to the present invention, the maintenance rate of the tensile strength after the heat treatment can be improved by performing the pre-annealing treatment as compared with the case where the pre-annealing treatment is not performed.

2. Method for producing surface treated copper foil of the present invention

Next, an embodiment of a method for producing a surface-treated copper foil of the present invention will be described. The surface-treated copper foil of the present invention described above can be obtained by producing a surface-treated copper foil by the following method. Hereinafter, each step will be described.

(1) Preparation of copper foil

In the present invention, a copper foil containing 100 ppm or more of a trace component selected from the group consisting of carbon, sulfur, chlorine, and nitrogen in one or more amounts is prepared. Here, the content of each of the minor components is preferably within the above respective ranges. Further, the average crystal grain size of the copper constituting the copper foil is preferably 1.0 μm or less, and the average crystal grain size is preferably 0.8 μm or less. Further, it is preferable to use a copper foil having a normal tensile strength of 50 kgf/mm ² or more as described above. The copper foil which satisfies such a condition is not particularly limited, and the copper foil which satisfies the above conditions can be easily obtained by adjusting various additives in the electrolytic solution, etc., and copper is produced by electrolysis. Foil is better.

(2) roughening processing steps

Next, when the roughened layer is provided on the surface of the copper foil, the surface of the copper foil is subjected to a roughening treatment. In the present invention, the roughening treatment layer is an arbitrary layer structure, and the roughening treatment method and the roughening treatment conditions are not particularly limited. Further, it is not necessary to perform the treatment before the roughening treatment to perform the pickling treatment on the surface of the copper foil or the like. However, the roughening treatment method and the roughening treatment conditions are not particularly limited, and suitable methods and conditions of the conventional methods may be employed depending on the desired surface characteristics of the copper foil.

(3) Zinc adhesion step (surface treatment step)

Next, a surface treatment (hereinafter referred to as "zinc adhesion treatment") is applied to the surface of the copper foil using a surface treatment agent containing zinc to form a zinc-containing zinc adhesion layer. In the zinc adhesion treatment step, any method can be used as long as the zinc adhesion layer can be formed on the surface of the copper foil so that the amount of adhesion of zinc is within the above range. For example, an electrochemical vapor deposition method such as electrolytic plating or electroless plating, or a physical vapor deposition method such as sputtering vapor deposition or chemical vapor phase reaction can be used. However, when considering the production cost, it is preferable to use an electrochemical method. Further, the surface treatment agent may contain other metal elements in addition to zinc as described above, and the other metal elements are preferably tin, as described above.

Electrolytic plating method:

When the zinc adhesion treatment is applied to the surface of the copper foil by the electrolytic plating method, a zinc pyrophosphate plating bath, a zinc cyanide plating bath, a zinc sulfate plating bath, or the like can be used as the zinc plating solution. For example, when a zinc pyrophosphate plating bath is used, specifically, a bath having a zinc concentration of 5 g/l to 30 g/l, a potassium pyrophosphate concentration of 50 g/l to 500 g/l, and a pH of 9 to pH 12 is used. The copper foil itself is polarized to a cathode in a solution having a liquid temperature of 20 to 50 ° C and electrolyzed under the conditions of a current density of 0.3 A/dm ² to 10 A/dm ² A to form a zinc adhesion layer on the surface of the copper foil.

(4) chromate treatment

The chromate treatment can be optionally applied to the surface of the zinc adhesion layer. The chromate treatment is electrolytic chromate treatment and impregnation chromate treatment, and any method can be used. However, when considering the thickness deviation of the chromate film, the stability of the adhesion amount, etc., it is preferable to use electrolytic chromate treatment. The electrolysis conditions in the electrolytic chromate treatment are not particularly limited, and appropriate and appropriate conditions can be employed.

(5) Organic agent treatment

Further, the surface of the zinc adhesion layer may be treated with an organic agent. The organic agent treatment referred to herein is a decane coupling agent treatment, an organic rustproof treatment, or the like.

Decane coupling agent treatment:

In the present invention, the treatment of the decane coupling agent is not required, and the treatment which is required for the copper foil to be adhered to the insulating resin substrate or the cathode active material of the lithium ion secondary battery is appropriately performed, and can be suitably employed. Appropriate and appropriate conditions and methods.

Organic anti-rust treatment:

Further, in order to further enhance the rust prevention effect, for example, benzotriazole-based tolyltriazole, aminobenzotriazole, carboxybenzotriazole, benzo can be used. A surface treatment is carried out with an organic agent such as triazole. Further, as other organic agents, aliphatic carboxylic acids, alkylamines, benzoic acids, imidazoles, and trisole may also be used. Mercaptans and the like. The organic rustproof treatment is not particularly limited, and appropriate and appropriate conditions and methods can be employed.

(6) Drying step

At the end of the various surface treatments of the copper foil, a drying step is performed to dry the copper foil in the wet state of the various surface treatment steps described above. The drying conditions are not particularly limited. However, when the organic agent treatment is carried out, heat treatment such as prevention of thermal decomposition of the decane coupling agent and/or the organic rust preventive agent adhering to the surface of the copper foil and adhesion of the chemicals to the surface of the copper foil in a good state can be employed. Conditions (temperature, time, etc.) can be.

(7) Pre-annealing step

Next, the pre-annealing step will be described. In the pre-annealing step, the copper foil subjected to the step up to the drying step is subjected to heat treatment in a temperature range of 200 C to 280 ° C to diffuse zinc from the zinc adhesion layer side in the copper foil to obtain a surface treatment of the present invention. The step of copper foil.

temperature:

In the present invention, the copper foil is not easily coarsened by heating even in the temperature range of 200 ° C to 280 ° C by the presence of the above-mentioned minor component. Further, when the copper foil is heated at a normal temperature and the copper foil having a zinc adhesion layer on the surface is heated in the above temperature range, zinc can be used in the copper foil at a speed which is more balanced with industrial production efficiency. Diffusion, but also to make the distribution of zinc in the copper foil more uniform. Therefore, by performing the pre-annealing treatment, even if the surface-treated copper foil continues to be subjected to a high-temperature heat for a long period of time, the effect of suppressing the coarsening of the crystal grains of copper can be enhanced, and the pre-annealing treatment can be performed more than when the pre-annealing treatment is not performed. The reduction in tensile strength is sufficiently suppressed.

Processing time:

Secondly, the time for performing the pre-annealing treatment (hereinafter, "When processing" ()" to explain. When the surface-treated copper foil is pre-annealed at a normal temperature, the amount of zinc diffusion in the copper foil can be increased, and the tensile strength can be suppressed even after the heat treatment is performed at a high temperature. . However, from the viewpoint of not only the surface layer portion of the copper foil but also a sufficient amount of zinc diffused inside the copper foil, the treatment time is preferably 2 hours or longer and 25 hours or shorter. Further, from the viewpoint of more sufficiently diffusing zinc inside the copper foil and making the distribution of zinc in the copper foil more uniform, the treatment time is preferably 8 hours or longer and 25 hours or shorter. On the other hand, when the treatment time is less than 2 hours, the amount of zinc diffusion in the inside of the copper foil is small, and when the high-temperature heat treatment is performed for a long period of time, the crystal grains inside the copper foil may be coarsened, and the film may not be sufficiently suppressed. The case where the tensile strength is lowered. Further, when the pre-annealing time is 25 hours or longer, even if the pre-annealing treatment is performed, the effect of suppressing the coarsening of the crystal grains of copper is saturated. Moreover, the cost of heat treatment and the like are also increased. Therefore, from these viewpoints, the pre-annealing time is preferably set to be within 25 hours.

However, the pre-annealing conditions are different depending on the crystal structure of the copper foil, the content of the trace component in the copper foil, the adhesion amount of zinc to the copper foil, and the like, and the optimum heating temperature and/or time for the diffusion of zinc. Therefore, it is preferable to appropriately set the pre-annealing conditions appropriately in the temperature and time within the above range in accordance with the above.

<Embodiment of Cathode Current Collector of the Present Invention>

Next, an embodiment of the cathode current collector of the present invention will be described. In the cathode current collector of the present invention, the surface-treated copper foil of the present invention can be used as a current collector which is a cathode material in contact with the inside of a nonaqueous secondary battery such as a lithium ion secondary battery. The current collection system of the present invention is used in addition to The surface-treated copper foil is not particularly limited. Since the current collecting system of the present invention uses the surface-treated copper foil described above, it is excellent in mechanical properties such as tensile strength.

<Embodiment of Cathode Material of Nonaqueous Secondary Battery of the Present Invention>

Next, an embodiment of a cathode material of a nonaqueous secondary battery of the present invention will be described. Here, the non-aqueous secondary battery is a generic term for a secondary battery using an electrolyte other than an aqueous solution, and is a secondary use of an organic electrolytic solution, a polymer gel electrolyte, a solid electrolyte, a polymer electrolyte, or a molten salt electrolyte. battery. The cathode material of the present invention is not particularly limited as long as it is a current collector. For example, a cathode material such as a lithium ion secondary battery can be configured to include a cathode mixture layer on the surface of the current collector. Moreover, in this case, the cathode mixture layer can be configured to contain, for example, a cathode active material, a conductive agent, and a binder.

As described above, the surface-treated copper foil of the present invention has a higher effect of suppressing the decrease in tensile strength and a higher retention rate of tensile strength after heat treatment than when the pre-annealing treatment is not performed. As a result, even if they are heated in an inert gas atmosphere at 350 ℃ 5 hours, and also possible to maintain 45kgf / mm ² or more, preferably ² or more and tensile strength of 50kgf / mm. Therefore, even if a stress is repeatedly applied to the current collector due to repeated charge and discharge cycles such as a lithium ion secondary battery, the possibility that the current collector is deformed or broken due to wrinkles or the like is small, and the lithium ion secondary battery can be maintained. Electrical characteristics. Further, in the case of manufacturing a cathode material of a lithium ion secondary battery, a step of forming a cathode mixture layer on the surface of the current collector, the collector system is loaded with heat of a high temperature. Even at this time, it has a sufficient level of tensile strength.

Hereinafter, the present invention will be described more specifically by way of examples and comparative examples. The copper foil is surface treated, but the present invention is not limited by the following examples.

[Example 1]

In the present Example 1, the copper foil of the present invention was produced and compared with Comparative Example 1 described later. Hereinafter, the steps will be described in order.

Preparation of copper foil:

First, an electrolytic copper foil having a total amount of the above-mentioned trace elements in the copper foil of 100 ppm or more (44 ppm of carbon, 14 ppm of sulfur, 54 ppm of chlorine, 11 ppm of nitrogen, and an average crystal grain size of 0.64 μm) was prepared. Specifically, an electrolytic copper foil having a thickness of 12 μm which was not subjected to surface treatment used for manufacturing a VLP copper foil manufactured by Mitsui Mining Co., Ltd. was prepared.

Roughing process steps:

Then, the copper foil is immersed in a copper plating solution having a free sulfuric acid concentration of 200 g/l, a copper concentration of 8 g/l, and a liquid temperature of 35 ° C to polarize the copper foil itself into a cathode. Further, electrolysis was carried out under the conditions of the burnt copper plating of a current density of 25 A/dm ² to precipitate and adhere the fine copper particles to the cathode surface side surface of the copper foil. Next, in order to prevent the fine copper particles from falling off, the copper foil itself is polarized into a cathode in a copper plating solution having a free sulfuric acid concentration of 110 g/l, a copper concentration of 70 g/l, and a liquid temperature of 50 ° C, and is in a current. Electrolysis was performed under smooth plating conditions of a density of 25 A/dm ² to complete the roughening treatment on the cathode surface side.

Zinc adhesion treatment steps:

A surface treatment agent containing zinc and tin is used on both surfaces of the copper foil after the roughening treatment, and a zinc adhesion layer made of a zinc-tin alloy is formed on both surfaces of the copper foil. First, a method of forming a zinc adhesion layer will be described.

In this example, a zinc pyrophosphate-tin plating bath was used to form a zinc-copper alloy layer on both sides of the copper foil as a zinc adhesion layer. The bath composition of the zinc pyrophosphate-tin plating bath is set to have a zinc concentration of 1 g/l to 6 g/l, a tin concentration of 1 g/l to 6 g/l, a potassium pyrophosphate concentration of 100 g/l, and a pH of 10.6. In the zinc pyrophosphate-tin plating bath of this composition, the copper foil itself was polarized to a cathode by a liquid temperature of 30 ° C, and the current density and the electrolysis time were appropriately adjusted to obtain zinc on each side of the copper foil. The adhesion amount was 50 mg/m ² , and the adhesion amount of tin was 5 mg/m ² of copper foil, and this was set as the sample 1.

Pre-annealing steps:

Next, the sample 1 was subjected to a pre-annealing treatment under the conditions shown in Table 1, and this was carried out to carry out the sample 1. However, in the pre-annealing treatment, each sample was placed in an oven and the temperature inside the chamber was raised at 5 ° C / min. Then, heating was carried out under the treatment conditions applicable to the sample 1 of Table 1. Further, in Table 1, the column indicated by "○" means that the pre-annealing treatment is performed on the sample indicated by the parentheses in the column in the condition (temperature, processing time).

[Embodiment 2]

In the second embodiment, the sample 2 was produced in the same manner as in Example 1 except that the amount of adhesion on each side of the tin was 15 mg/m ² , and then pre-annealing was performed under the conditions shown in Table 1. Sample 2 was carried out.

[Example 3]

In the third embodiment, the sample 3 was produced in the same manner as in Example 1 except that the amount of adhesion on each side of the tin was 30 mg/m ² , and then pre-annealing was performed under the conditions shown in Table 1. Sample 3 was carried out.

[Example 4]

In the fourth embodiment, the sample 4 was produced in the same manner as in Example 1 except that the amount of adhesion of each side of the tin was 15 mg/m ² and the total amount of zinc adhered was 100 mg/m ² . The conditions shown in Table 1 were subjected to a pre-annealing treatment to carry out the sample 4.

[Example 5]

In the fifth embodiment, the sample 5 was produced in the same manner as in Example 1 except that the amount of adhesion of each side of the tin was 15 mg/m ² and the total amount of zinc adhered was 150 mg/m ² . The conditions shown in Table 1 were subjected to a pre-annealing treatment to carry out the sample 5.

[Embodiment 6]

Next, the description will be given of the sixth embodiment. In Example 6, the other copper foil of the present invention was produced as follows. Hereinafter, the steps will be described in order.

Copper foil manufacturing:

In Example 6, an electrolytic copper foil produced under the conditions shown below was used. First, as a sulfuric acid-based copper electrolytic solution, copper ions are contained at a concentration of 80 g/l, sulfuric acid is contained at a concentration of 250 g/l, chloride ions are contained at a concentration of 2.7 ppm, and gelatin is contained at a concentration of 2 ppm. The electrolytic solution (50 ° C) was electrolyzed at a current density of 50 A/dm ² to obtain an electrolytic copper foil having a thickness of 12 μm. The content of the trace component in the electrolytic copper foil was 49 ppm of carbon, 26 ppm of sulfur, 24 ppm of chlorine, and 11 ppm of nitrogen, and the average crystal grain size was 0.58 μm.

Roughing process steps:

Then, the copper foil was subjected to a roughening treatment in the same manner as in the first embodiment.

Zinc adhesion step:

The electrolytic copper foil after the roughening treatment was carried out in the same manner as in Example 1 except that the amount of adhesion of tin on each side was 25 mg/m ² and the adhesion amount of zinc was 150 mg/m ² . A sample of the sample 6 was produced by forming a zinc adhesion layer on both surfaces of the copper foil. Then, in the same manner as in Example 1, the pre-annealing treatment was carried out under the conditions shown in Table 1, and the sample after the pre-annealing treatment was used as the sample 6 to be carried out.

[Embodiment 7]

In Example 7, a surface-treated copper foil was produced in the same manner as in Example 1 except that a zinc layer was formed as a zinc adhesion layer. The zinc layer is formed using a zinc pyrophosphate plating bath. Electrolysis was carried out in the same manner as in Example 1 except that the bath composition of the zinc pyrophosphate plating bath was composed of a bath having a zinc concentration of 6 g/l, a potassium pyrophosphate concentration of 125 g/l, and a pH of 10.5, and each side of the copper foil was used. The amount of zinc adhered was 50 mg/m ² of copper foil, and it was set to sample 7. Subsequently, the pre-annealing treatment was carried out in the same manner as in Example 1 under the conditions shown in Table 1, and each pre-annealed sample was subjected to the sample 7.

[Comparative example]

In the comparative example, samples were prepared in the same manner as in the first to seventh embodiments except that the pre-annealing treatment was not carried out, and each of the samples was set as the comparative sample 1 to the comparative sample 7.

In order to easily compare the conditions of the samples produced in the respective examples and comparative examples, Table 2 shows the difference in the total amount of adhesion of tin and zinc and the type of copper foil in each sample. Moreover, in Table 2, the normal tensile strength of each copper foil (A or B) measured by the method mentioned later is shown. In addition, in Table 2, the type A of the copper foil refers to the electrolytic copper foil used in the first to fifth embodiments and the seventh embodiment, and the type B of the copper foil is used in the sixth embodiment. Electrolytic copper foil produced by the method.

[Evaluation] Evaluation method (1) Trace element content

The trace element contents of the trace elements in each of the copper foils used in Examples 1 to 6 and Comparative Examples were measured as follows. First of all, the carbon and sulfur content in the copper foil is based on the carbon of the joint-stock company. Analysis by sulfur analyzer (EMIA-920V). In addition, for the nitrogen content in the copper foil, the oxygen produced by the company is used. Analyzed by a nitrogen analyzer (EMGA-620). Further, the chlorine content in the copper foil was analyzed by a silver chloride turbidimetric method using a spectrophotometer (U-3310) manufactured by Hitachi HIGHTECHNOLOGIES Co., Ltd.

(2) Tensile strength

Each of the samples obtained in Examples 1 to 6 and Comparative Examples was heated at 350 ° C for 5 hours in an inert gas atmosphere, and the tensile strength of each sample after heating was measured.

Further, in the present invention, "tensile strength" means a value obtained by measuring a tensile speed of 50 mm/min using a thin rectangular copper foil sample of 100 mm × 10 mm (distance between points) according to IPC-TM-650. .

(3) Crystalline structure

For each sample obtained in Example 1 and Example 5, Comparative Example 1 and Comparative Example 5, and untreated copper foils (A and B) before roughening treatment, zinc adhesion treatment, etc., in an inert gas atmosphere The crystal grain size after heating at 350 ° C for 5 hours was measured by the following method. Further, for the sample 1 and the sample 5 obtained in the first and fifth embodiments, the pre-annealing treatment was carried out for 8 hours under the treatment conditions (1) (200 ° C).

For the measurement of the crystal grain size of the copper foil, a FE-type scanning electron microscope (SUPRA 55VP, manufactured by Carl Zeiss AG) equipped with an EBSD evaluation device (manufactured by OIM Analysis, TSL Solutions Co., Ltd.) and an attached EBSD analysis were used. Device. The image data of the pattern of the cross-sectional crystal state of the copper foil was obtained by the EBSD method, and the EBSD analysis program (OIMAnalysis, manufactured by TSLSolutions Co., Ltd.) was used for the sample. The image data was quantified by the average crystal grain size. In this evaluation, the difference in orientation of 5° or more is regarded as a crystal grain boundary. The conditions of the scanning electron microscope at the time of observation were acceleration voltage: 20 kV, aperture: 60 mm, High Current mode, and sample angle: 70°. Further, the observation magnification, the measurement region, and the displacement size were measured by appropriately changing the conditions according to the size of the crystal grains.

2. Evaluation results (1) Tensile strength

First, in Tables 3 to 7, the tensile strength of each of the sample and the comparative sample after heat treatment at 350 ° C for 5 hours was shown. Further, Table 7 shows the tensile strengths of Comparative Sample 5 and Comparative Sample 6 after heating at 350 ° C for 1 hour. Further, in each of the tables, the maintenance ratio of the tensile strength after heat treatment of each sample with respect to the normal tensile strength was expressed as a percentage.

As shown in Tables 3 to 6, the sample 1 to the sample 7 of the present invention is displayed in any one of the tensile strengths after heating at 350 ° C for 5 hours regardless of the processing conditions at the time of performing the pre-annealing treatment. A value of 45 kgf/mm ² or more, and a tensile strength of 79% to 102% of the normal tensile strength can be maintained. In addition, by adjusting the amount of adhesion of zinc, the amount of adhesion of tin, etc. according to the content of a trace component of the copper foil, etc., and by using preferable pre-annealing conditions, it is possible to maintain 50 kgf/mm after heating at 350 ° C for 5 hours. ^When the tensile strength of ² or more is confirmed, the tensile strength reduction rate can be suppressed to 10% or less, preferably 5% or less.

Further, when the sample 1 was carried out, the sample 6 was carried out, and the sample 7 was carried out, it was confirmed that when the zinc adhesion layer was made of a zinc layer containing no tin, when the zinc adhesion layer was a zinc-tin alloy layer, The value of the tensile strength after heat treatment is higher, and the maintenance rate is also increased.

On the other hand, as shown in Table 7, when comparing the sample 1 to the comparative sample 7, the tensile strength after heating at 350 ° C for 5 hours can be confirmed, and although the value of 45 kgf / mm ² or more is also exhibited, the tensile strength is obtained. The maintenance rate is 65% to 87%, and the tensile strength of either one is reduced by more than 10%. For example, although the tensile strength of each of Comparative Sample 5 and Comparative Sample 6 after heating at 350 ° C for 1 hour was 51.5 kgf / mm ² and 58.8 kgf / mm ² , the temperature was reduced to 47.3 after heating at 350 ° C for 5 hours. Kgf/mm ² , 40kgf/mm ² . On the other hand, the observation sample 5 and the sample 6 are observed. For example, as shown in Table 3, even after the pre-annealing treatment is performed for 8 hours at the lowest temperature treatment condition (1) (200 ° C), 51.3 kgf can be maintained. / mm ² , tensile strength of 46.9 kgf / mm ² . Further, as shown in Table 5, the treatment time was, for example, 2 hours, and the tensile strength of the sample 5 and the sample 6 at the time of the treatment condition (3) (250 ° C) showed 50.7 kgf/mm ² , 49.3 kgf/mm ² ; treatment conditions (5) (275 ° C) each showed 50.9 kgf / mm ² , 49.2 kgf / mm ² . Therefore, it can be confirmed that even if the pre-annealing treatment is performed at a low temperature or a short time, the effect of suppressing the decrease in tensile strength can be obtained even after heating at a high temperature for a long period of time.

[table 3]

(2) Crystal structure

Next, referring to Fig. 1 and Fig. 2, the sample 1 and the crystal structure of the comparative sample 1 were compared. Fig. 1 and Fig. 2 show FIB-SIM images of the crystal structures of the sample 1 and the comparative sample 1 which were each heated at 350 °C for 5 hours. In addition, in Table 8, the values of the average crystal grain size of the sample 1, the sample 5, the comparative sample 1, and the comparative sample 5 which were heated at 350 ° C for 5 hours were shown. Further, as described above, the sample 1 and the sample 5 were subjected to pre-annealing treatment (heating under treatment conditions (1) (200 ° C) for 8 hours) before heating at 350 ° C for 5 hours. As shown in Figures 1 and 2, it can be confirmed that compared to The crystal structure of the sample 1 was compared, and the crystal grain system of the crystal structure of the sample 1 was finely formed as a whole. Further, as shown in Table 8, it was confirmed that the sample 1 and the sample 5 were placed in any of the surface layer portion and the center portion of the copper foil, and the average crystal grain size was 1.0 μm or less, and was heated at 350 ° C for 5 hours. Thereafter, a fine crystal structure can be maintained as a whole in the thickness direction of the copper foil. On the other hand, the comparative sample 1 and the comparative sample 5 were confirmed to be heated at 350 ° C for 5 hours, and the average crystal grain size in any of the regions was more than 1.0 μm, and the crystal grains in the central portion of the copper foil were The tendency to be big is high. Therefore, it can be confirmed that the pre-annealing treatment of each sample allows zinc (and dissimilar metal elements) to diffuse not only to the surface layer portion of the copper foil but also to the central portion of the copper foil, even if the heat is applied for a long time. At the same time, coarsening of crystal grains of copper can also be suppressed.

Industrial availability

The surface copper foil of the present invention can be easily produced by performing the above-described surface treatment on the surface of the copper foil, and can provide a reduction in tensile strength even after heat treatment for a long period of time at a high temperature. There is also less copper foil. Therefore, it can be suitably used to be exposed at the time of manufacture. In the use of a high-temperature environment, a cathode current collector or a printed wiring board which is a nonaqueous secondary battery such as a lithium ion secondary battery can be suitably used.

Claims (15)

A surface-treated copper foil comprising, on a total surface, a copper foil containing 100 ppm or more of one or more kinds of trace components selected from the group consisting of carbon, sulfur, chlorine, and nitrogen, each surface comprising 20 mg/m ² to 1000 mg The surface treatment layer of zinc of /m ² is characterized in that it is subjected to pre-annealing treatment heated at a temperature ranging from 200 ° C to 280 ° C. The surface-treated copper foil according to claim 1, wherein the tensile strength after heating at 350 ° C for 5 hours is 45 kgf / mm ² or more. The surface-treated copper foil according to claim 1, wherein the surface treatment layer contains a metal element having a higher diffusion rate in copper and/or copper than zinc, in addition to zinc. The surface-treated copper foil according to claim 3, wherein the metal element is tin. The surface-treated copper foil according to claim 4, wherein the surface treatment layer contains 1 mg/m ² to 200 mg/m ² of tin per side. The surface-treated copper foil according to claim 1, wherein the copper foil has a normal crystal grain size of 1.0 μm or less in a normal state. The surface-treated copper foil according to claim 1, wherein the copper foil has a normal tensile strength of 50 gf/mm ² or more. The surface-treated copper foil according to claim 1, wherein in the pre-annealing treatment, the temperature in the temperature range is heated for 2 hours or more and 25 hours or less. A surface-treated copper foil comprising, on a total surface, a copper foil containing 100 ppm or more of one or more kinds of trace components selected from the group consisting of carbon, sulfur, chlorine, and nitrogen, each surface comprising 20 mg/m ² to 1000 mg The zinc surface treatment layer of /m ² is characterized in that the tensile strength after heating at 350 ° C for 5 hours is 50 kgf / mm ² or more. A method for producing a surface-treated copper foil, comprising: a surface treatment step of copper containing one or more kinds of trace components selected from the group consisting of carbon, sulfur, chlorine, and nitrogen of 100 ppm or more in total amount. The two sides of the foil form a surface treatment layer containing 20 mg/m ² to 1000 mg/m ² of zinc on each side; and a pre-annealing step of heating at a temperature ranging from 200 ° C to 280 ° C after the surface treatment step. The method for producing a surface-treated copper foil according to claim 10, wherein the heating time in the pre-annealing step is 2 hours or longer and 25 hours or shorter. A cathode current collector characterized by using the surface-treated copper foil as described in claim 1. A cathode current collector characterized by using the surface-treated copper foil according to claim 9 of the patent application. A cathode material for a nonaqueous secondary battery, characterized in that a cathode current collector according to claim 12 of the patent application is used. A cathode material for a nonaqueous secondary battery, characterized in that a cathode current collector according to claim 13 of the patent application is used.