JP2014080636A - Surface-treated copper foil, method of producing surface-treated copper foil, anode collector and anode material for nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface-treated copper foil causing less deterioration of the tensile strength even when subjected to a high-temperature heat treatment for a long time, a method of producing a surface-treated copper foil, a collector using the surface-treated copper foil and an anode material for nonaqueous secondary batteries.SOLUTION: A surface-treated copper foil has a surface-treated layer containing 20 mg/m-1000 mg/m, per side, of zinc on both sides of a copper foil containing a total content of 100 ppm or more of one or more minor ingredients selected from carbon, sulfur, chlorine and nitrogen and is subjected to a pre-annealing treatment in which heating is performed in the temperature range of 200-280°C.

Description

  The present invention relates to a surface-treated copper foil, a method for producing the surface-treated copper foil, a negative electrode current collector, and a negative electrode material for a non-aqueous secondary battery. In particular, even when heated at a high temperature for a long time, the surface-treated copper foil used for negative electrode current collector applications such as lithium ion secondary batteries with little decrease in tensile strength, its production method, and the surface-treated copper foil are used. The present invention relates to a negative electrode current collector and a negative electrode material.

  Conventionally, copper foil has been used as a circuit forming material for various electronic components including printed wiring boards. In recent years, copper foil is not limited to these circuit forming materials, and is also used as a negative electrode current collector for non-aqueous secondary batteries such as lithium ion secondary batteries.

  In general, a negative electrode material of a lithium ion secondary battery is configured to include a negative electrode active material, a conductive material, a negative electrode mixture layer containing a binder (binder) and the like on the surface of a current collector made of a conductive material. The When the negative electrode active material occludes / releases lithium during charge / discharge of the lithium ion secondary battery, the negative electrode mixture layer expands / contracts accordingly. Since the negative electrode mixture layer is in close contact with the surface of the current collector, repeated stress is applied between the negative electrode mixture layer and the current collector by repeating the charge / discharge cycle of the lithium ion secondary battery. For this reason, when the tensile strength of the current collector is low, the current collector may expand due to a change in the volume of the negative electrode mixture, causing deformation such as wrinkles, or breakage. When the current collector stretches and deforms such as wrinkles, a short circuit occurs between the positive electrode and the negative electrode, or the distance between the positive electrode and the negative electrode changes, preventing uniform electrode reaction, and charging / discharging Cycle durability may be reduced. Further, when the current collector is broken, the capacity per unit volume is reduced, and the battery characteristics of the lithium ion secondary battery are deteriorated. For this reason, when using copper foil as a collector, it is calculated | required that the said copper foil has high tensile strength.

By the way, in the process of manufacturing a negative electrode material, when forming a negative mix layer on the surface of a current collector, high-temperature heat is loaded on the current collector. In the case of a general copper foil, when high-temperature heat is applied, crystal grains become coarse due to recrystallization of copper, and mechanical strength such as tensile strength is lowered. For this reason, it is calculated | required that the copper foil used for a collector use maintains high tensile strength, even after high temperature heat processing is performed. As such a copper foil, for example, in Patent Document 1 and Patent Document 2, even after heating at 350 ° C. for 60 minutes, 40 kgf / mm ² or more, and after heating at 400 ° C. for 60 minutes, 35 kgf / mm ^A surface-treated copper foil capable of maintaining ^two or more tensile strengths is disclosed.

International Publication No. 2012/070589 International Publication No. 2012/070591

  However, when manufacturing the negative electrode material of a lithium ion secondary battery, the collector may be heated in a temperature range of 350 ° C. to 400 ° C. for more than 1 hour. In this case, the surface-treated copper foil disclosed in Patent Document 1 or Patent Document 2 has a reduced tensile strength, and depending on the heating time, a sufficient level of tensile strength may not be maintained.

  Therefore, the problem of the present invention is that even when a high-temperature heat treatment is performed for a long time, the surface-treated copper foil with little decrease in tensile strength, a method for producing the surface-treated copper foil, and a current collector using the surface-treated copper foil It is providing the negative electrode material of a body and a non-aqueous secondary battery.

  As a result of diligent research, the present inventors have come up with a surface-treated copper foil with little decrease in tensile strength even when high-temperature heat treatment is applied for a long time by adopting the following technical idea. .

The surface-treated copper foil according to the present invention is 20 mg / m ^{2 to} 1000 mg per side on both sides of a copper foil containing 100 ppm or more of one or more trace components selected from carbon, sulfur, chlorine and nitrogen in total. It is a surface-treated copper foil provided with a surface treatment layer containing / m ² of zinc, and is characterized by being subjected to a pre-annealing treatment that is heated in a temperature range of 200 ° C. to 280 ° C.

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

  The surface-treated copper foil which concerns on this invention WHEREIN: It is preferable that the said surface treatment layer contains the metallic element whose diffusion rate in copper and / or copper is faster than zinc other than zinc.

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

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

  The surface-treated copper foil which concerns on this invention WHEREIN: It is preferable that the average crystal grain diameter of the copper which comprises the said copper foil is 1.0 micrometer or less.

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

  In the surface-treated copper foil according to the present invention, the pre-annealing treatment is preferably performed at a temperature within the temperature range for 2 hours to 25 hours.

The surface-treated copper foil according to the present invention is 20 mg / m ^{2 to} 1000 mg per side on both sides of a copper foil containing 100 ppm or more of one or more trace components selected from carbon, sulfur, chlorine and nitrogen in total. A surface-treated copper foil provided with a surface treatment layer containing zinc of / m ² , characterized in that the tensile strength after heating at 350 ° C. for 5 hours is 50 kgf / mm ² or more.

The manufacturing method of the surface treatment copper foil which concerns on this invention is 20 mg / m per one surface on both surfaces of the copper foil which contains 100 ppm or more of 1 type, or 2 or more types of trace components chosen from carbon, sulfur, chlorine, and nitrogen in the total amount. ^It comprises a surface treatment step for forming a surface treatment layer containing ^{2 to} 1000 mg / m ² of zinc, and a pre-anneal treatment step for heating in a temperature range of 200 ° C. to 280 ° C. after the surface treatment step. .

  In the manufacturing method of the surface-treated copper foil which concerns on this invention, it is preferable that the heating time in the said pre-annealing process process is 2 hours or more and 25 hours or less.

  The negative electrode current collector according to the present invention is characterized by using any of the surface-treated copper foils described above.

  The negative electrode material of the non-aqueous secondary battery according to the present invention is characterized by using the negative electrode current collector.

  The surface-treated copper foil according to the present invention can be easily manufactured by forming a surface treatment layer containing zinc on both sides of the copper foil and performing the pre-annealing treatment, and a high-temperature heat treatment is performed for a long time. Even after being applied, it is possible to provide a copper foil with little decrease in tensile strength.

It is a FIB-SIM image which shows an example of the cross-sectional crystal structure of the implementation sample 1 after performing a pre-annealing process at 200 degreeC for 8 hours, and heating at 350 degreeC for 5 hours. It is a FIB-SIM image which shows an example of the cross-sectional crystal structure of the comparative sample 1 after heating at 350 degreeC for 5 hours.

  Hereinafter, embodiments of the surface-treated copper foil, the method for producing the surface-treated copper foil, the negative electrode current collector, and the negative electrode material of the nonaqueous secondary battery according to the present invention will be described in order.

1. Surface-treated copper foil First, an embodiment of the surface-treated copper foil according to the present invention will be described. The surface-treated copper foil according to the present invention is provided with a surface treatment layer containing zinc (referred to as a zinc adhesion layer in the present embodiment) on both sides of the copper foil, and after the zinc adhesion layer is formed, pre-annealing treatment is performed. Thus, even after a high-temperature heat treatment is performed for a long time, a decrease in tensile strength can be suppressed. In the present specification, the high temperature refers to a temperature equal to or higher than the temperature at which copper recrystallization occurs, and mainly refers to a temperature within a range of about 300 ° C to 400 ° C. Further, the long time means a time exceeding 1 hour and mainly means a time of 5 hours or more. Hereinafter, in the present embodiment, the surface-treated copper foil will be described as an example in which the surface-treated copper foil is used as a negative electrode current collector of a non-aqueous secondary battery such as a lithium ion secondary battery. Of course, the foil can be used not only as a negative electrode current collector of a non-aqueous secondary battery such as the lithium ion secondary battery but also as a material for producing a printed wiring board.

(1) Copper foil First, copper foil is demonstrated. In this invention, the said zinc adhesion layer is provided on both surfaces of the copper foil which contains 100 ppm or more of 1 type, or 2 or more types of trace components chosen from carbon, sulfur, chlorine, and nitrogen in a total amount.
Here, in the present invention, “copper foil” means an untreated copper foil that has not been subjected to various treatments such as the above surface treatment, and “surface treated copper foil” means the zinc adhesion layer. In addition to the zinc adhesion treatment and pre-annealing treatment for forming the copper foil, the copper foil after various surface treatments is meant. Further, the copper foil may be an electrolytic copper foil or a rolled copper foil, but it is easy to obtain a copper foil having fine crystal grains and excellent mechanical properties with high tensile strength. From the viewpoint, an electrolytic copper foil is preferable. Hereinafter, description will be given mainly by taking an electrolytic copper foil as an example, but in the following, when simply described as "copper foil", the copper foil includes not only "electrolytic copper foil" but also "rolled copper foil" Shall be.

Trace component: In the present invention, as described above, the copper foil contains 100 ppm or more of one or more trace components selected from carbon, sulfur, chlorine, and nitrogen in a total amount. When the content of these trace components is 100 ppm or more in total, it is easy to refine the crystal structure (crystal grains) of copper constituting the copper foil, and the copper foil having high tensile strength and excellent mechanical strength. It is because it becomes easy to obtain.

Here, the copper foil used in the present invention contains 100 ppm or more of the total amount of the trace components, and contains 20 ppm to 470 ppm of carbon, 5 ppm to 600 ppm of sulfur, 15 ppm to 600 ppm of chlorine, and 5 ppm to 600 ppm of nitrogen. It is preferable to do. By including an appropriate amount of these trace components in the crystal structure of the copper foil, it becomes easier to refine the copper crystal structure, and the copper foil having higher mechanical strength and tensile strength. can do. Specifically, by including each trace component within the above range, the average crystal grain size of the copper foil is 1.0 μm or less, the normal tensile strength is 50 kgf / mm ² or more, and the normal elongation is 3%. A copper foil excellent in mechanical strength of ˜15% can be obtained.

Here, when the content of each trace component is less than the lower limit value, for example, it is difficult to obtain a very fine crystal structure having an average crystal grain size of 1.0 μm or less, and copper having a higher tensile strength. A foil cannot be obtained, which is not preferable. On the other hand, when content of each trace component in the said copper foil exceeds an upper limit, it is unpreferable from the following viewpoints. If the carbon content exceeds 470 ppm, the graphite becomes coarse and cracks are likely to occur, which is not preferable. When the sulfur content exceeds 600 ppm, the tensile strength of the copper foil is increased, but the elongation rate is lowered and embrittlement is not preferable. When the chlorine content exceeds 600 ppm, the deposited surface becomes rough in the case of an electrolytic copper foil. In that case, it is difficult to adhere the negative electrode active material or the like to the surface without unevenness, and the amount of volume change when charging / discharging is repeated becomes non-uniform in a plane, which is not preferable. Furthermore, if the nitrogen content exceeds 180 ppm, the nitrogen compound becomes excessive, the effect of refining the precipitate structure of the copper foil is saturated, and the significance of increasing the nitrogen content is lost, which is not preferable.
However, in the present invention, the unit of “ppm” used to represent the content of the trace component in the copper foil is synonymous with “mg / kg”, and that the trace component contains 100 ppm or more in total. It means that the total amount of the trace components contained per 1 kg of the copper foil is 100 mg or more.

Average crystal grain size: Next, the average crystal grain size of the copper crystal grains 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 exceeds 1.0 μm, it is difficult to maintain a tensile strength at a level required as a negative electrode current collector of a non-aqueous secondary battery such as a lithium ion secondary battery. . Moreover, it is preferable that the copper crystal grains constituting the copper foil are fine and uniform. Due to the uniform crystal grains, the grain boundaries are evenly distributed in the copper foil, and the load applied to the copper foil is dispersed without being biased to specific crystal grains, and the mechanical strength is high. It can be set as the copper foil excellent in. However, the average crystal grain size here refers to the average crystal grain size in the normal state of the copper foil, and can be determined based on the crystal grain size appearing 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, in the present invention, “normal state” refers to a state managed at normal temperature or a state before heat treatment. By using a copper foil having a normal tensile strength of 50 kgf / mm ² or more, a surface-treated copper foil having a high tensile strength can be obtained even after a high-temperature heat treatment. However, even if the copper foil has a high normal tensile strength, the decrease in tensile strength after the heat treatment may be significant. Accordingly, in the present invention, it is not preferable that the normal tensile strength of the copper foil itself is a higher value, and the surface-treated copper foil after being subjected to heat treatment regardless of the value of the normal tensile strength. The tensile strength of is preferably a higher value.

Thickness: The thickness of the copper foil is not particularly limited. What is necessary is just to employ | adopt the copper foil of appropriate thickness suitably according to the use of the said surface treatment copper foil. For example, when the surface-treated copper foil according to the present invention is used as a negative electrode current collector of a non-aqueous secondary battery such as a lithium ion secondary battery, the thickness of the copper foil is within a range of 5 μm to 35 μm (gauge thickness). And often. Moreover, when using the said surface-treated copper foil when manufacturing a printed wiring board, the thickness of the said copper foil is often made into the range of 5 micrometers-120 micrometers (gauge thickness). Even if the surface-treated copper foil according to the present invention is a thin copper foil of 5 μm to 35 μm, it has a tensile strength of a level required in the market as a negative electrode current collector of a lithium ion secondary battery.

(2) Zinc adhesion layer (surface treatment layer)
Next, the zinc adhesion layer will be described. Surface treatment copper foil present invention, on both sides of the copper foil, and a zinc deposition layer comprising zinc per surface ^{20mg / m 2 ~1000mg / m 2} . Zinc in the zinc adhesion layer provided on both sides of the copper foil diffuses into the copper foil with the passage of time and reacts with the trace components in the crystal structure. This zinc and the compound of the trace component are precipitated at the crystal grain boundary, and when the copper foil is heated, the growth of the crystal grain is prevented and the effect of suppressing the coarsening of the crystal grain is exhibited. . In the present invention, after forming a zinc adhesion layer on both sides of the copper foil, by applying a pre-annealing treatment described later, zinc is not only the surface layer portion of the copper foil but also its inside ( Can be diffused to the center). Therefore, according to the present invention, even if the surface-treated copper foil is subjected to a heat treatment for a longer time at a high temperature in the subsequent use process, a fine crystal structure can be maintained even after the heat treatment. It can suppress and it can suppress that the tensile strength of the said copper foil falls.

Here, when 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, the amount of zinc diffusing into the copper foil is small and the crystal grains are coarsened. This is not preferable because the effect of sufficiently suppressing the above cannot be obtained and it becomes difficult to maintain a fine crystal structure. From this viewpoint, the amount of zinc deposited is preferably 25 mg / m ² or more, and more preferably 50 mg / m ² or more. On the other hand, when the zinc adhesion amount exceeds 1000 mg / m ² , even if the zinc adhesion amount is increased, the effect corresponding to the adhesion amount is not obtained, and it is not preferable because it wastes resources. From this viewpoint, the adhesion amount of zinc is preferably 500 mg / m ² or less, more preferably 300 mg / m ² or less, and further preferably 200 mg / m ² or less.

Here, the zinc deposited layer, since it contains zinc in the range of per side of the copper foil, the total deposition amount of zinc to the copper foil ^will be in the range of ^{40mg / m 2 ~2000mg / m 2} . And the total adhesion amount of the zinc is preferably 50 mg / m ² or more, more preferably 100 mg / m ² or more, from the same viewpoint as described above. The upper limit is more preferably is preferably 1000 mg / ^{m 2} or less, 600 mg / ^{m 2} or less. However, the zinc adhesion amount is the zinc adhesion amount (converted amount) per unit area when it is assumed that the surface of the copper foil is completely flat.

  The zinc adhesion layer may be a zinc layer made of zinc, or may be a zinc alloy layer containing copper and / or a metal element whose diffusion rate in copper is faster than zinc. For example, Bi, Cd, Sn, Pb, Sb, In, Al, a metal element (hereinafter referred to as “foreign metal element”) having a diffusion rate in copper that is faster than that of zinc at a temperature of 300 ° C. or higher. Examples include As, Ga, and Ge. Further, the zinc adhesion layer may be a zinc-based composite layer in which a zinc layer and a dissimilar metal layer containing at least one of the dissimilar metal elements or two or more of them are stacked. In this case, the stacking order of the zinc layer and the dissimilar metal layer is not limited, and the zinc layer and the dissimilar metal layer may be sequentially stacked on the surface of the copper foil, or the dissimilar metal layer and zinc may be stacked on the surface of the copper foil. You may laminate | stack in order of the layer. By making the zinc adhesion layer contain the different metal element together with zinc, the different metal element can be diffused together with zinc in the copper foil. Since the diffusion rate of different metal elements is faster than that of zinc, these different metal elements reach deeper positions faster than zinc in the thickness direction of the copper foil. In addition, these different metal elements react with the above-mentioned trace components in the same manner as zinc to form a compound and suppress the coarsening of copper crystal grains. Therefore, by making the zinc adhesion layer contain a dissimilar metal element together with zinc, even when heat treatment is performed at a high temperature for a longer time, the copper crystal grains become coarse in almost the entire thickness direction of the copper foil. Can be suppressed more effectively. Zinc refers to zinc having a purity of 99% or more. A zinc alloy refers to a mixture, solid solution, eutectic, compound, or the like of zinc and other elements.

In the present invention, when the zinc adhesion layer is a zinc alloy layer or a zinc-based composite layer, it is particularly preferable to use tin among the different metal elements. In this case, in the equivalent amount, the adhesion amount of tin per the one side that the surface treatment is performed so as to ^1mg / ^{m 2 ~200mg} / m 2 preferred. 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. Even if the amount of zinc adhered to the surface of the copper foil is within the above range, if the zinc content in the zinc adhesion layer is less than 30% by mass, the amount of tin is excessive with respect to the amount of zinc. For this reason, the presence of tin inhibits the diffusion of zinc into the copper foil, making it difficult to sufficiently diffuse zinc into the copper foil, and the above-described effects cannot be obtained. In addition, these zinc adhesion layers can be formed using the antirust processing agent containing zinc or zinc-tin, for example, and there exists a function as an antirust processing layer.

(3) Other layer configurations In addition to the zinc adhesion layer, the surface-treated copper foil according to the present invention may have other surface treatment layers such as a roughening treatment layer, a chromate treatment layer, and an organic agent treatment layer as necessary. Can be optionally provided.

  For example, when the surface-treated copper foil is used as a negative electrode current collector of a lithium ion secondary battery by providing a roughened layer, the adhesion between the surface of the surface-treated copper foil and the negative electrode active material is improved. be able to.

  Moreover, it can suppress that the copper foil surface is oxidized by these layers with the said zinc adhesion layer by providing a chromate processing layer and / or an organic agent processing layer. Moreover, the adhesiveness with the negative electrode active material etc. of the said lithium ion secondary battery can be made still better. Examples of the organic agent treatment layer include a silane coupling agent treatment layer and an organic rust prevention treatment layer.

(4) Pre-annealing treatment The surface-treated copper foil according to the present invention is obtained by performing a pre-annealing treatment in which the surface treatment is performed on both surfaces of the copper foil and then heated in a temperature range of 200 ° C to 280 ° C. By performing the pre-annealing treatment, zinc can be diffused into the copper foil in a state where recrystallization of copper is suppressed. For this reason, when the surface treatment copper foil is loaded with heat higher than the temperature at which copper recrystallization occurs, the above-mentioned compounds precipitated at the grain boundaries prevent the growth of crystal grains and the crystal grains become coarse. The effect which suppresses this can be exhibited. The pre-annealing process will be described later. In the following, the copper foil after the above surface treatment and before the pre-annealing treatment may be referred to as “surface-treated copper foil”.

(5) Mechanical properties The surface-treated copper foil according to the present invention has the tensile strength after heating at 350 ° C. for 5 hours in an inert gas atmosphere by subjecting the surface-treated copper foil to the pre-annealing treatment. Is 45 kgf / mm ² or more, and the tensile strength after the heat treatment is 50 kg / mm by adjusting the pre-annealing conditions to appropriate conditions according to the amount of copper foil and zinc (and tin) attached. ² or more. In the present invention, it is particularly preferable that the tensile strength after heating at 350 ° C. for 5 hours is 50 kgf / mm ² or more by adjusting the conditions of the pre-annealing treatment.

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

2. 2. Manufacturing method of surface-treated copper foil which concerns on this invention Next, embodiment of the manufacturing method of the surface-treated copper foil which concerns on this invention is described. The surface-treated copper foil according to the present invention described above can be obtained by producing the surface-treated copper foil by the following method. Hereinafter, each step will be described.

(1) Preparation of copper foil In this invention, the copper foil which contains 100 ppm or more of 1 type, or 2 or more types of trace components chosen from carbon, sulfur, chlorine, and nitrogen in a total amount is prepared. Here, the content of each trace component is preferably within the above-described range. Further, the average crystal grain size of copper constituting the copper foil is preferably 1.0 μm or less, and the average crystal grain size is more preferably 0.8 μm or less as described above. Furthermore, as described above, it is more preferable to use a copper foil having a normal tensile strength of 50 kgf / mm ² or more. If a copper foil satisfying such conditions can be obtained, its production method is not limited, but by adjusting various additives in the electrolyte, a copper foil satisfying the above conditions can be obtained. From the viewpoint of ease, it is preferable to produce a copper foil by an electrolytic method.

(2) Roughening treatment process Next, when providing a roughening process layer on the surface of copper foil, a roughening process is performed with respect to the surface of the said copper foil. In the present invention, the roughening treatment layer has an arbitrary layer structure, and there is no particular limitation on the roughening treatment method and the roughening treatment conditions. Of course, before the roughening treatment, pretreatment such as pickling treatment of the copper foil surface may be performed. However, the roughening treatment method and the roughening treatment conditions are not limited to this, and a conventionally known method can be appropriately adopted according to the surface characteristics required for the copper foil. That's fine.

(3) Zinc adhesion process (surface treatment process)
Next, a surface treatment (hereinafter referred to as “zinc adhesion treatment”) is performed on the surface of the copper foil using a surface treatment agent containing zinc to form a zinc adhesion layer containing zinc. In the said zinc adhesion treatment process, what kind of method may be used if a zinc adhesion layer can be formed in the surface of copper foil so that the adhesion amount of zinc may become in the said range. For example, an electrochemical method such as electrolytic plating or electroless plating, or a physical vapor deposition method such as sputtering vapor deposition or chemical vapor reaction can be used. However, in consideration of production costs, it is preferable to adopt an electrochemical method. In addition, it is as above-mentioned that metal elements other than zinc may be contained in the surface treating agent, and the point that tin is preferable as the other metal elements is also as described above.

Electrolytic plating method: When the zinc adhesion treatment is performed on the surface of the copper foil by the electrolytic plating method, a zinc pyrophosphate zinc plating bath, a zinc cyanide plating bath, a zinc sulfate plating bath, or the like can be used. For example, when a zinc pyrophosphate plating bath is employed, specifically, a bath composition 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 employed. , in a solution of a liquid temperature of 20 to 50 ° C., and polarizing the copper foil itself cathode by electrolysis at a current density of ^{0.3A / dm 2 ~10A / dm 2} a, zinc adhered to the copper foil surface A layer can be formed.

(4) Chromate treatment A chromate treatment may be optionally applied to the surface of the zinc adhesion layer. The chromate treatment includes electrolytic chromate treatment and immersion chromate treatment, and any method may be used. However, in consideration of the thickness variation of the chromate film, the stability of the adhesion amount, etc., it is preferable to employ electrolytic chromate treatment. Electrolytic conditions in the case of electrolytic chromate treatment are not particularly limited, and appropriate conditions can be adopted as appropriate.

(5) Organic agent treatment Moreover, you may perform an organic agent treatment with respect to the surface of a zinc adhesion layer. Examples of the organic agent treatment include silane coupling agent treatment and organic rust prevention treatment.

Silane coupling agent treatment: In the present invention, the silane coupling agent treatment is not essential, considering the adhesiveness with the negative electrode active material of the insulating resin base material or lithium ion secondary battery required for the copper foil. Therefore, appropriate conditions and methods can be adopted as appropriate.

Organic rust prevention treatment: In addition, in order to further improve the rust prevention effect, when organic rust prevention treatment is performed, for example, benzotriazole methylbenzotriazole (tolyltriazole), aminobenzotriazole, carboxyl benzotriazole, benzotriazole Surface treatment can be performed using an organic agent such as. As other organic agents, aliphatic carboxylic acids, alkylamines, benzoic acids, imidazoles, triazine thiols and the like may be used. The organic rust prevention treatment is not particularly limited, and appropriate conditions and methods can be appropriately employed.

(6) Drying step When the various surface treatments are completed on the copper foil, the drying step is performed, and the copper foil in a wet state in the various surface treatment steps is dried. Drying conditions are not particularly limited. However, when the organic agent treatment is performed, the silane coupling agent and / or organic rust preventive agent adhering to the copper foil surface is prevented from being thermally decomposed, and these agents are fixed on the copper foil surface in good condition. What is necessary is just to employ | adopt the heat processing conditions (temperature, time, etc.) which can be made to perform.

(7) Pre-annealing step Next, the pre-annealing step will be described. In the present invention, the pre-annealing step diffuses zinc from the zinc adhesion layer side into the copper foil by performing a heat treatment in the temperature range of 200 ° C. to 280 ° C. on the copper foil that has undergone the steps up to the drying step. This is a step of obtaining the surface-treated copper foil.

Temperature: In the present invention, due to the presence of the trace component, the copper foil is less likely to be coarsened even when heated in a temperature range of 200 ° C. to 280 ° C. In addition, if the copper foil having a zinc adhesion layer on the surface is heated within the above temperature range, the zinc is contained in the copper foil at a rate commensurate with industrial production efficiency as compared with the case where the copper foil is stored at room temperature. The zinc distribution in the copper foil can be made uniform. For this reason, by applying pre-annealing treatment, even when high-temperature heat is applied to the surface-treated copper foil for a long time, the effect of suppressing the coarsening of copper crystal grains can be enhanced, Compared with the case where pre-annealing is not performed, it is possible to sufficiently suppress the decrease in tensile strength.

Processing Time: Next, the time for performing the pre-annealing process (hereinafter referred to as “processing time”) will be described. By performing pre-annealing on the copper foil after the surface treatment, the amount of zinc diffused into the copper foil can be increased compared with the case where it is stored at room temperature, and even after heat treatment at high temperature. It is possible to suppress a decrease in tensile strength. However, from the viewpoint of diffusing a sufficient amount of zinc not only in the surface layer portion of the copper foil but also in the copper foil, the treatment time is preferably 2 hours or more and 25 hours or less. Moreover, it is preferable that the said processing time is 8 hours or more and 25 hours or less from a viewpoint of diffusing zinc fully inside a copper foil, and making more uniform the distribution of zinc in copper foil. On the other hand, if the treatment time is less than 2 hours, the amount of zinc diffusion into the copper foil is small, and if high-temperature heat treatment is performed for a long time, the crystal grains may be coarsened inside the copper foil. In some cases, the decrease in tensile strength cannot be sufficiently suppressed. When the pre-annealing time is 25 hours or longer, the effect of suppressing the coarsening of the copper crystal grains is saturated even if the pre-annealing treatment is further performed. Moreover, the cost etc. concerning heat processing also increase. Therefore, from these viewpoints, the pre-annealing time is preferably within 25 hours.

  However, the pre-annealing conditions are the optimum heating temperature and / or suitable for the diffusion of zinc, depending on the crystal structure of the copper foil, the content of trace components in the copper foil, the amount of zinc attached to the copper foil, etc. Time is different. Accordingly, it is preferable to appropriately set appropriate pre-annealing conditions in the temperature and time within the above range according to these.

<Embodiment of the negative electrode current collector according to the present invention>
Next, embodiments of the negative electrode current collector according to the present invention will be described. The negative electrode current collector according to the present invention is characterized by using the surface-treated copper foil according to the present invention described above, and in a non-aqueous secondary battery such as a lithium ion secondary battery, is in contact with the negative electrode mixture inside the battery. It can be used as a current collector. The current collector according to the present invention is not particularly limited except that the surface-treated copper foil is used. Since the current collector according to the present invention uses the surface-treated copper foil, it has excellent mechanical properties such as tensile strength.

<Embodiment of negative electrode material of non-aqueous secondary battery according to the present invention>
Next, embodiments of the negative electrode material of the non-aqueous secondary battery according to the present invention will be described. Here, the non-aqueous secondary battery is a general term for secondary batteries using an electrolyte other than an aqueous solution, and a secondary battery using an organic electrolyte, a polymer gel electrolyte, a solid electrolyte, a polymer electrolyte, a molten salt electrolyte, or the like. Say. The negative electrode material according to the present invention is not particularly limited as long as the current collector is used. For example, it can be set as the structure provided with the negative mix layer on the surface of a collector like the negative electrode material of a lithium ion secondary battery. In this case, the negative electrode mixture layer can include, for example, a negative electrode active material, a conductive agent, and a binder.

As described above, the surface-treated copper foil according to the present invention has a higher effect of suppressing a decrease in tensile strength than the case where the pre-annealing treatment is not performed, and the retention rate of the tensile strength after the heat treatment is increased. As a result, it is possible to maintain a tensile strength of 45 kgf / mm ² or more, preferably 50 kgf / mm ² or more even after heating at 350 ° C. for 5 hours in an inert gas atmosphere. For this reason, by repeating the charge / discharge cycle in a lithium ion secondary battery or the like, even when a stress is repeatedly applied to the current collector, there is little risk of deformation such as wrinkles or breakage in the current collector. The electrical characteristics of the secondary battery can be maintained. Moreover, when manufacturing the negative electrode material of a lithium ion secondary battery, high temperature heat | fever is loaded on a collector at the process of forming a negative mix layer on the surface of a collector. Even in this case, it has a sufficient level of tensile strength.

  Hereinafter, although an example and a comparative example are given and the surface treatment copper foil concerning the present invention is explained more concretely, the present invention is not limited to the following examples.

  In the present Example 1, the copper foil which concerns on this invention was manufactured, and it was decided to contrast with the comparative example 1 mentioned later. Hereinafter, it will be described in the order of steps.

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

Roughening treatment step: 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. Electrolysis was performed under a burn copper plating condition with a density of 25 A / dm ² , and fine copper particles were deposited on the cathode side surface of the copper foil. Next, in order to prevent the fine copper particles from falling off, the copper foil itself is polarized to the 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. Electrolysis was performed under smooth plating conditions with a density of 25 A / dm ² to complete the roughening treatment on the cathode side.

Zinc adhesion treatment process: Using the surface treating agent containing zinc and tin on both surfaces of the copper foil after the roughening treatment, a zinc adhesion layer made of a zinc-tin alloy was formed on both surfaces of the copper foil. First, the formation method of a zinc adhesion layer is demonstrated.

In this example, a zinc-tin alloy layer was formed as a zinc adhesion layer on both sides of the copper foil using a zinc pyrophosphate-tin plating bath. The bath composition of the zinc pyrophosphate-tin plating bath was such that the zinc concentration was 1 g / l to 6 g / l, the tin concentration was 1 g / l to 6 g / l, the potassium pyrophosphate concentration was 100 g / l, and the pH was 10.6. In a zinc pyrophosphate-tin plating bath of the composition, the liquid temperature is 30 ° C., the copper foil itself is polarized to the cathode, and the current density and electrolysis time are adjusted as appropriate, so that the zinc adheres to one side of the copper foil. A copper foil having an amount of 50 mg / m ² and an adhesion amount of tin of 5 mg / m ² was obtained.

Pre-annealing treatment step: Next, pre-annealing treatment was performed on the sample 1 under the conditions shown in Table 1, and this was designated as an implementation sample 1. However, in the pre-annealing treatment, each sample was put in an oven and the internal temperature was raised at 5 ° C./min. In Table 1, the sample 1 was heated under the corresponding processing conditions. In Table 1, the column labeled “◯” means that the pre-annealing process was performed on the sample with the number indicated in parentheses in the column under the conditions (temperature, processing time).

In Example 2, sample 2 was prepared in the same manner as in Example 1 except that the amount of tin deposited on one side was 15 mg / m ^2, and then pre-annealing was performed under the conditions shown in Table 1. Sample 2 was obtained.

In Example 3, sample 3 was prepared in the same manner as in Example 1 except that the amount of tin deposited on one side was 30 mg / m ^2, and then pre-annealed under the conditions shown in Table 1. It was set to 3.

In Example 4, Sample 4 was prepared in the same manner as in Example 1 except that the adhesion amount per one side of tin was 15 mg / m ² and the total adhesion amount of zinc was 100 mg / m ^2. A pre-annealing treatment was performed under the conditions shown in the following to obtain an implementation sample 4.

In Example 5, Sample 5 was prepared in the same manner as in Example 1 except that the adhesion amount per one side of tin was 15 mg / m ² and the total adhesion amount of zinc was 150 mg / m ^2. A pre-annealing treatment was performed under the conditions shown in the following to obtain an implementation sample 5.

  Next, Example 6 will be described. In Example 6, another copper foil according to the present invention was manufactured as follows. Hereinafter, it will be described in the order of steps.

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

Roughening treatment step: Then, the copper foil was subjected to a roughening treatment in the same manner as in Example 1.

Zinc adhesion step: The same as in Example 1 except that the electrolytic copper foil after the above roughening treatment had a tin adhesion amount of 25 mg / m ² and a zinc adhesion amount of 150 mg / m ² per side. Sample 6 was prepared by forming a zinc adhesion layer on both sides of the copper foil. Then, in the same manner as in Example 1, pre-annealing treatment was performed under the conditions shown in Table 1, and the sample after each pre-annealing treatment was designated as Working Sample 6.

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 the zinc adhesion layer. The zinc layer was formed using a zinc pyrophosphate plating bath. The zinc pyrophosphate plating bath was electrolyzed in the same manner as in Example 1 except that a zinc composition having a zinc concentration of 6 g / l, a potassium pyrophosphate concentration of 125 g / l, and a pH of 10.5 was employed. A copper foil having a zinc adhesion amount of 50 mg / m ² per side was obtained, and this was designated as Sample 7. Thereafter, in the same manner as in Example 1, pre-annealing treatment was performed under the conditions shown in Table 1, and a sample after each pre-annealing was taken as an execution sample 7.

Comparative example

  In the comparative example, a sample was prepared in the same manner as in Examples 1 to 7 except that the pre-annealing treatment was not performed, and Comparative Sample 1 to Comparative Sample 7 were used.

  In order to facilitate the comparison of the conditions and the like of the samples prepared in each Example and Comparative Example, Table 2 shows the total amount of tin and zinc deposited on each sample and the type of copper foil. Table 2 shows the normal tensile strength of each copper foil (A or B) measured by the method described later. In Table 2, type A of copper foil refers to the electrolytic copper foil used in Examples 1 to 5 and Example 7, and type B of copper foil is the method described in Example 6. It refers to the produced electrolytic copper foil.

[Evaluation]
1. Evaluation Method (1) Trace Element Content The trace element content of trace elements in each copper foil used in Examples 1 to 6 and Comparative Example was measured as follows. First, the carbon and sulfur contents in the copper foil were analyzed using a carbon / sulfur analyzer (EMIA-920V) manufactured by Horiba, Ltd. The nitrogen content in the copper foil was analyzed using an oxygen / nitrogen analyzer (EMGA-620) manufactured by Horiba, Ltd. The chlorine content in the copper foil was analyzed by a silver chloride turbidimetric method using a spectrophotometer (U-3310) manufactured by Hitachi High-Tech Fielding Co., Ltd.

(2) Tensile strength Each sample obtained in Examples 1 to 6 and Comparative Example was heated at 350 ° C. for 5 hours in an inert gas atmosphere, and the tensile strength of each sample after heating was measured.
In the present invention, “tensile strength” is based on IPC-TM-650, using a strip-shaped copper foil sample of 100 mm × 10 mm (distance between ratings: 50 mm), and a tensile speed of 50 mm / min. The value when measured with.

(3) Crystal structure About each sample obtained in Example 1 and Example 5, Comparative Example 1 and Comparative Example 5, and untreated copper foil (A and B) before roughening treatment, zinc adhesion treatment, etc. The crystal grain size after heating at 350 ° C. for 5 hours in an inert gas atmosphere was measured by the following method. In addition, about the implementation sample 1 and the implementation sample 5 obtained in Example 1 and Example 5, what performed the pre-annealing process for 8 hours on process conditions (1) (200 degreeC) was used.

  To measure the crystal grain size of copper foil, a scanning electron microscope (SUPRA 55VP, manufactured by Carl Zeiss Co., Ltd.) equipped with an EBSD evaluation device (OIM Analysis, manufactured by TSL Solutions Co., Ltd.) and the attached EBSD analysis A device was used. Using this apparatus, image data of the pattern of the crystal state of the cross section of the copper foil is obtained according to the EBSD method for the sample that has been appropriately cross-section processed, and this image data is obtained from the EBSD analysis program (OIM Analysis, The average crystal grain size was quantified in the analysis menu of TSL Solutions Inc.). In this evaluation, an orientation difference of 5 ° or more was regarded as a crystal grain boundary. The conditions of the scanning electron microscope at the time of observation were an acceleration voltage: 20 kV, an aperture diameter: 60 mm, a high current mode, and a sample angle: 70 °. The observation magnification, the measurement region, and the step size were measured by changing the conditions as appropriate according to the size of the crystal grains.

2. Evaluation results (1) Tensile strength
First, Tables 3 to 7 show the tensile strengths of the respective implementation samples and comparative samples after heat treatment at 350 ° C. for 5 hours. Table 7 shows the tensile strengths of Comparative Sample 5 and Comparative Sample 6 after heating at 350 ° C. for 1 hour. Moreover, each table | surface shows the maintenance rate of the tensile strength after the heat processing of each sample with respect to normal state tensile strength in percentage.

As shown in Tables 3 to 6, the working sample 1 to the working sample 7 according to the present invention have a tensile strength of 45 kgf after heating at 350 ° C. for 5 hours, regardless of the treatment conditions when performing the pre-annealing treatment. / Mm ^{2 and} higher, and maintained a tensile strength of 79% to 102% of the normal tensile strength. Also, by adjusting the zinc adhesion amount, tin adhesion amount, etc. according to the content of the trace component of the copper foil, etc., by adopting preferable pre-annealing treatment conditions, 50 kgf even after heating at 350 ° C. for 5 hours. It was confirmed that the tensile strength of / mm ² or more can be maintained, and the rate of decrease in tensile strength can be suppressed within 10%, more preferably within 5%.

  Moreover, when the implementation sample 1-the implementation sample 6 and the implementation sample 7 are compared, by making a zinc adhesion layer into a zinc-tin alloy layer, it is after heat processing rather than the case where a zinc adhesion layer is made into the zinc layer which does not contain tin. It was confirmed that the value of tensile strength was high and the maintenance rate was also improved.

On the other hand, as shown in Table 7, in the case of Comparative Sample 1 to Comparative Sample 7, the tensile strength after heating at 350 ° C. for 5 hours has a value of 45 kgf / mm ² or more, but the tensile strength is maintained. The rate was 65% to 87%, and it was confirmed that the tensile strength decreased by 10% or more in any case. For example, tensile strength after Comparative Sample 5 and Comparative Sample 6 which was heated at 350 ° C. Each of 51.5kgf ^/ mm 2, but was 58.8kgf / mm ^2, was heated for 5 hours at 350 ° C. It drops each of the ^{47.3kgf / mm 2, 40kgf / mm} 2. On the other hand, looking at the working sample 5 and the working sample 6, for example, as shown in Table 3, 51.3 kgf / mm ² even when pre-annealing treatment was performed for 8 hours under the lowest temperature processing condition (1) (200 ° C.). The tensile strength of 46.9 kgf / mm ² is maintained. Further, as shown in Table 5, when the processing time is 2 hours, for example, in the case of processing condition (3) (250 ° C.), the tensile strengths of the working sample 5 and the working sample 6 are 50.7 kgf / mm, respectively. ² shows a 49.3kgf / mm ^2, respectively in the case of processing conditions (5) (275 ℃) is 50.9kgf ^/ mm 2, a 49.2kgf / mm ^2. Therefore, it was confirmed that the effect of suppressing the decrease in the tensile strength can be obtained even after being heated at a high temperature for a long time by applying the pre-annealing treatment even at a low temperature or for a short time.

(2) Crystal structure Next, with reference to FIG.1 and FIG.2, the crystal structure of the implementation sample 1 and the comparative sample 1 is contrasted. 1 and 2 are FIB-SIM images showing the crystal structures of the working sample 1 and the comparative sample 1 after heating at 350 ° C. for 5 hours, respectively. Table 8 shows the average crystal grain size values of Example 1, Example 5, Comparative Sample 1 and Comparative Sample 5 after heating at 350 ° C. for 5 hours. As described above, the working sample 1 and the working sample 5 are pre-annealed (heated at 200 ° C. for 8 hours) before being heated at 350 ° C. for 5 hours. As shown in FIGS. 1 and 2, it can be confirmed that the crystal structure of the working sample 1 is fine as a whole as compared with the crystal structure of the comparative sample 1. Moreover, as shown in Table 8, the working sample 1 and the working sample 5 have an average crystal grain size of 1.0 μm or less in any of the surface layer portion and the central portion of the copper foil, and are heated at 350 ° C. for 5 hours. It can be confirmed that a fine crystal structure is maintained throughout the thickness direction of the copper foil. On the other hand, when the comparative sample 1 and the comparative sample 5 are heated at 350 ° C. for 5 hours, the average crystal grain size exceeds 1.0 μm in any region, and the crystal grains in the central portion of the copper foil are particularly coarse. It was confirmed that the tendency was high. Therefore, by pre-annealing each sample, zinc (and dissimilar metal elements) can be diffused not only to the surface layer portion of the copper foil but also to the center portion of the copper foil. It was confirmed that coarsening of copper crystal grains can be suppressed even when loaded.

  The surface copper foil according to the present invention can be easily manufactured by subjecting the surface of the copper foil to the surface treatment and then the pre-annealing treatment, and is subjected to a heat treatment for a long time at a high temperature. Even after being applied, it is possible to provide a copper foil with little decrease in tensile strength. Therefore, it can be suitably used for applications exposed to a high-temperature atmosphere during production, and can be particularly preferably used as a material for producing a negative electrode current collector of a non-aqueous secondary battery such as a lithium ion secondary battery and a printed wiring board.

Claims (13)

A surface treatment layer containing 20 mg / m ^{2 to} 1000 mg / m ² of zinc per side on both sides of a copper foil containing 100 ppm or more of one or more trace components selected from carbon, sulfur, chlorine and nitrogen. A surface-treated copper foil comprising:
A surface-treated copper foil, which has been subjected to a pre-annealing treatment to be heated in a temperature range of 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.   3. The surface-treated copper foil according to claim 1, wherein the surface treatment layer contains, in addition to zinc, copper and / or a metal element whose diffusion rate in copper is faster than that of 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-treated layer contains 1 mg / m ^{2 to} 200 mg / m ² of tin per side.   The surface-treated copper foil according to any one of claims 1 to 5, wherein an average crystal grain size of copper in a normal state of the copper foil is 1.0 µm or less. The surface-treated copper foil according to any one of claims 1 to 6, wherein a normal tensile strength of the copper foil is 50 gf / mm ² or more.   The surface-treated copper foil as described in any one of Claims 1-7 heated by the temperature within the said temperature range for 2 hours or more and 25 hours or less in the said pre-annealing process. A surface treatment layer containing 20 mg / m ^{2 to} 1000 mg / m ² of zinc per side on both sides of a copper foil containing 100 ppm or more of one or more trace components selected from carbon, sulfur, chlorine and nitrogen. A surface-treated copper foil comprising:
A surface-treated copper foil characterized by a tensile strength of 50 kgf / mm ² or more after heating at 350 ° C. for 5 hours. A surface treatment layer containing 20 mg / m ^{2 to} 1000 mg / m ² of zinc per side on both sides of a copper foil containing 100 ppm or more of one or more trace components selected from carbon, sulfur, chlorine and nitrogen. Forming a surface treatment step;
After the surface treatment step, a pre-annealing step of heating in a temperature range of 200 ° C. to 280 ° C.,
A method for producing a surface-treated copper foil, comprising:   The manufacturing method of the surface-treated copper foil of Claim 10 whose heating time in the said pre-annealing process is 2 hours or more and 25 hours or less.   A negative electrode current collector using the surface-treated copper foil according to any one of claims 1 to 9.   A negative electrode material for a non-aqueous secondary battery, wherein the negative electrode current collector according to claim 12 is used.