JP6553558B2 - Surface treated copper foil, negative electrode current collector, and negative electrode material for non-aqueous secondary battery - Google Patents

Description

  The present invention relates to a surface-treated copper foil, a negative electrode current collector, and a negative electrode material for a non-aqueous secondary battery. In particular, a surface-treated copper foil used for a negative electrode current collector application such as a lithium ion secondary battery with little reduction in tensile strength even when heated for a long time at high temperature, a negative electrode current collector using the surface-treated copper foil The present invention relates to a body and a negative electrode material.

  Conventionally, copper foil has been used as a circuit forming material for various electronic components including printed wiring boards. Further, in recent years, copper foils are used not only for these circuit-forming materials but also as negative electrode current collectors of non-aqueous secondary batteries such as lithium ion secondary batteries.

  Generally, the negative electrode material of a lithium ion secondary battery comprises a negative electrode active material layer, 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 At the time of charge and discharge of the lithium ion secondary battery, when the negative electrode active material occludes and releases lithium, the negative electrode mixture layer expands and contracts. Since the negative electrode mixture layer is in close contact with the surface of the current collector, repetitive stress is applied between the negative electrode mixture layer and the current collector by repeating the charge and 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 be stretched to cause deformation such as wrinkles or breakage due to a change in volume of the negative electrode mixture. When the current collector expands and causes deformation 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 to inhibit uniform electrode reaction, thereby causing charge and discharge. The 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 step of manufacturing the negative electrode material, high temperature heat is applied to the current collector when the negative electrode mixture layer is formed on the surface of the current collector. In the case of a general copper foil, when high temperature heat is applied, recrystallization of copper causes coarsening of crystal grains, and mechanical strength such as tensile strength decreases. 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 copper foils, 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, even after heating at 400 ° C. for 60 minutes, 35 kgf / mm ^{2 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, heating over 1 hour may be performed with respect to a collector in the temperature range of 350 degreeC-400 degreeC. In this case, the tensile strength of the surface-treated copper foil disclosed in Patent Document 1 or Patent Document 2 is lowered, and depending on the heating time, a sufficient level of tensile strength may not be maintained.

  Therefore, an object of the present invention is to provide a surface-treated copper foil with little reduction in tensile strength even when high-temperature heat treatment is performed for a long time, and a collector and non-aqueous secondary battery using the surface-treated copper foil. An object of the present invention is to provide a negative electrode material.

  As a result of intensive researches, the present inventors conceived of a surface-treated copper foil with little reduction in tensile strength even when high temperature heat treatment is performed 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 in total of one or two or more trace components selected from carbon, sulfur, chlorine and nitrogen. A surface-treated copper foil comprising a surface-treated layer containing zinc / m ² , wherein a compound of the zinc in the surface-treated layer and the trace component is precipitated at grain boundaries of the copper foil, the normal tension of the copper foil strength 50 kgf / mm ² or more 62kgf / mm ² or less, a tensile strength after heating for 5 hours at 350 ° C. under an inert gas atmosphere of the surface treated copper foil 50 kgf / mm ² or more, and, the It is characterized in that a retention ratio of tensile strength after heating of the surface treated copper foil to normal tensile strength of the copper foil is 90% to 100% .

  The negative electrode current collector according to the present invention is characterized in that the surface-treated copper foil described in any of the above is used.

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

  The surface-treated copper foil according to the present invention can be easily manufactured by forming a surface-treated layer containing zinc on both sides of the copper foil and performing the above-described 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-section crystal structure of the working sample 1 after heating at 350 degreeC for 5 hours, after pre-annealing treatment for 8 hours at 200 degreeC. It is a FIB-SIM image which shows an example of the cross-section crystal structure of the comparative sample 1 after heating at 350 degreeC for 5 hours.

  Hereinafter, embodiments of a surface-treated copper foil, a method for producing the surface-treated copper foil, an anode current collector, and an anode material of a non-aqueous 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 high-temperature heat treatment is performed for a long time, the reduction in tensile strength can be suppressed. In the present specification, the high temperature refers to a temperature higher than the temperature at which copper recrystallization occurs, and mainly refers to a temperature within the range of about 300 ° C. to 400 ° C. In addition, a long time refers to 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 is described as an example of using the negative electrode current collector of a non-aqueous secondary battery such as a lithium ion secondary battery, but the surface-treated copper according to the present invention is described. The foil is not limited to the negative electrode current collector of the non-aqueous secondary battery such as the lithium ion secondary battery, and of course can be used as a manufacturing material of a printed wiring board.

(1) Copper foil First, copper foil is demonstrated. In the present invention, the above-mentioned zinc adhesion layer is provided on both sides of a copper foil containing 100 ppm or more in total of one or more trace components selected from carbon, sulfur, chlorine and nitrogen.
Here, in the present invention, "copper foil" means an untreated copper foil which has not been subjected to various treatments such as the above surface treatment, and "surface treated copper foil" means the above-mentioned zinc adhesion layer. In addition to zinc adhesion treatment to form W, pre-annealing treatment, copper foil after various surface treatments shall be meant. Further, the copper foil may be an electrolytic copper foil or a rolled copper foil, but it is said that a copper foil having fine crystal grains and excellent in mechanical characteristics with high tensile strength can be easily obtained. From the viewpoint, an electrolytic copper foil is preferable. Hereinafter, although an electrodeposited copper foil is mentioned as an example and explained as an example, when only saying "copper foil" below, not only "electrolytic copper foil" but "rolled copper foil" is contained in the said copper foil Shall be

Minor Component: In the present invention, as described above, the copper foil contains 100 ppm or more in total of one or more minor components selected from carbon, sulfur, chlorine and nitrogen. When the total content of these trace components is 100 ppm or more in total, it is easy to miniaturize the crystal structure (crystal grains) of copper constituting the copper foil, and the copper foil has high mechanical strength with high tensile strength. Is 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 incorporating these trace components in the crystal structure of the copper foil in an appropriate amount, it becomes easier to refine the crystal structure of the copper, and the copper foil is superior in mechanical strength with higher tensile strength and can do. Specifically, when each minor component is contained in the above range, the average crystal grain size of the copper foil is 1.0 μm or less, the normal state tensile strength is 50 kgf / mm ² or more, and the normal state elongation rate is 3%. It can be set as the copper foil excellent in mechanical strength of -15%.

Here, when the content of each minor component is less than the lower limit value, 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 copper having a higher tensile strength. A foil cannot be obtained, which is not preferable. On the other hand, when content of each trace amount 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 is coarsened 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 is reduced, which is not preferable because it becomes brittle. When the chlorine content exceeds 600 ppm, in the case of the electrodeposited copper foil, the deposition surface becomes rough. In that case, it becomes difficult to uniformly adhere the negative electrode active material or the like on the surface thereof, and the volume change amount when charging and discharging are repeated becomes nonuniform in the plane, which is not preferable because it is locally broken. Furthermore, when the nitrogen content exceeds 180 ppm, the nitrogen compound becomes excessive, the refining effect of the precipitation structure of the copper foil is saturated, and the significance of increasing the nitrogen content is not preferable.
However, in the present invention, the unit “ppm” used to represent the content of minor components in the copper foil is synonymous with “mg / kg”, and the total amount of the minor components is 100 ppm or more. It means that the total amount of the said trace component contained per kg of the said 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 the tensile strength of the level required as a negative electrode current collector of a non-aqueous secondary battery such as a lithium ion secondary battery, which is not preferable. . Moreover, it is preferable that the copper crystal grains constituting the copper foil are fine and uniform. Due to the uniformity of the crystal grains, the grain boundaries are uniformly distributed in the copper foil, the load applied to the copper foil is dispersed without being biased to specific crystal grains, and the mechanical strength is high in tensile strength. Copper foil excellent in However, the average crystal grain size referred to here indicates the average crystal grain size in the normal state of the copper foil, and can be determined based on the grain size of crystal grains appearing in the cross section when observing the cross section of the copper foil. .

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, it is possible to obtain a surface-treated copper foil exhibiting high tensile strength even after high-temperature heat treatment. However, even in the case of a copper foil having high tensile strength in the normal state, the reduction in tensile strength after heat treatment may be significant. Therefore, 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 heat treatment is performed regardless of the value of the normal tensile strength. It is preferable that the tensile strength of is 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 using the surface-treated copper foil according to the present invention 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 in the range of 5 μm to 35 μm (gauge thickness) In many cases. Moreover, when using the said surface-treated copper foil when manufacturing a printed wiring board, the thickness of the said copper foil is often carried out in 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 required in the market as an anode current collector of a lithium ion secondary battery.

(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 provided with a zinc adhesion layer containing 20 mg / m ^{2 to} 1000 mg / m ² of zinc per side on both sides of the copper foil. The zinc in the zinc adhesion layer provided on both sides of the copper foil diffuses into the copper foil over time, and reacts with the above-mentioned trace components in the crystal structure. The compound of zinc and the above-mentioned trace component precipitates at grain boundaries, and when heat is applied to the copper foil, it inhibits the growth of crystal grains and exerts the effect of suppressing the coarsening of crystal grains. . In the present invention, after forming a zinc adhesion layer on both sides of the copper foil, by performing a pre-annealing process described later, zinc is not only in the surface layer portion of the copper foil but also in the inside ( Can be diffused to the center). Therefore, according to the present invention, even if the surface-treated copper foil is subjected to heat treatment at a high temperature for a longer time in the subsequent use process, the fine crystalline 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 on the surface of the copper foil is less than 20 mg / m ² per one side, the amount of zinc diffused in the copper foil is small and coarsening of crystal grains It is not preferable because the effect of suppressing the crystal structure can not be obtained sufficiently and it becomes difficult to maintain a fine crystal structure. From this point of view, 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 exceeds 1000 mg / m ² , even if the adhesion amount of zinc is increased, the effect according to the adhesion amount can not be obtained, which is not preferable because it causes waste of resources. From the viewpoint, 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, 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 from the same viewpoint as the above, it is preferable that it is 50 mg / m < ² > or more, and, as for the total adhesion amount of the said zinc, it is more preferable that it is 100 mg / m < ² > or more. The upper limit value is preferably 1000 mg / m ² or less, more preferably 600 mg / m ² or less. However, the adhesion amount of zinc is the adhesion amount (conversion amount) of zinc 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 a metal element having a faster diffusion rate in copper and / or copper than zinc in addition to zinc. For example, Bi, Cd, Sn, Pb, Sb, In, Al, as a metal element having a faster diffusion rate in copper than zinc at a temperature of 300 ° C. or more (hereinafter referred to as “different metal element”). As, Ga, Ge can be mentioned. 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 or more of the above-mentioned dissimilar metal elements are laminated. In this case, the lamination order of the zinc layer and the dissimilar metal layer is not limited, and the zinc layer and the dissimilar metal layer may be laminated in this order on the surface of the copper foil, or the dissimilar metal layer on the surface of the copper foil, zinc It may be laminated in the order of layers. By making the zinc adhesion layer include the above-mentioned foreign metal element together with zinc, it is possible to diffuse the above-mentioned foreign metal element together with zinc in the copper foil. Since the diffusion rate of the dissimilar metal element is higher than that of zinc, these dissimilar metal elements reach a deeper position faster than zinc in the thickness direction of the copper foil. Moreover, these dissimilar metal elements react with the above-mentioned trace components to form a compound in the same manner as zinc, thereby suppressing the coarsening of copper crystal grains. Therefore, by forming the zinc adhesion layer with the zinc together with the zinc, even if the heat treatment is performed at a high temperature for a longer time, coarsening of copper crystal grains is substantially achieved over the entire thickness of the copper foil. Can be suppressed more effectively. Zinc refers to zinc having a purity of 99% or more. In addition, a zinc alloy refers to a mixture, a solid solution, a eutectic, a compound, or the like of zinc and another element.

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 above-mentioned dissimilar metal elements. In this case, in the terms of the amount of the surface treatment so that the amount of deposition of tin per the one side is ^1mg / ^{m 2 ~200mg} / m 2 is is preferably subjected. Moreover, in this case, it is preferable that the zinc content ratio calculated by {[zinc adhesion amount] / [zinc-tin alloy adhesion amount] x 100 is 30 mass% or more. Even if the adhesion amount of zinc to the surface of the copper foil is in the above range, if the zinc content in the zinc adhesion layer is less than 30% by mass, the amount of tin with respect to the amount of zinc is excessive. For this reason, the presence of tin hinders the diffusion of zinc into the copper foil, making it difficult to sufficiently diffuse the zinc into the inside of the copper foil, and the above-mentioned effects can not be obtained, which is not preferable. These zinc adhesion layers can be formed using, for example, a rustproofing agent containing zinc or zinc-tin, and exhibit the function as a rustproofing layer.

(3) Other Layer Configurations The surface-treated copper foil according to the present invention includes, in addition to the above-mentioned zinc adhesion layer, other surface treatment layers such as a roughening treatment layer, a chromate treatment layer, and an organic agent treatment layer, as needed. Can optionally be 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, adhesion between the surface of the surface-treated copper foil and the negative electrode active material is improved. be able to.

  Moreover, by providing a chromate treatment layer and / or an organic agent treatment layer, it is possible to suppress the oxidation of the copper foil surface by these layers together with the zinc adhesion 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 subjecting both surfaces of the above-mentioned copper foil to the above-mentioned surface treatment and then performing pre-annealing treatment in which heating is performed 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. Therefore, when heat is applied to the surface-treated copper foil at a temperature higher than the temperature at which recrystallization of copper occurs, the above-described compound precipitated at grain boundaries prevents the growth of crystal grains and the crystal grains are coarsened. The effect which suppresses this can be exhibited. The pre-annealing process will be described later. Moreover, in the following, it is copper foil after said each surface treatment, Comprising: The thing before a pre-annealing process may be called "the copper foil with surface treatment completed."

(5) Mechanical Properties The surface-treated copper foil according to the present invention has a tensile strength after being heated at 350 ° C. for 5 hours in an inert gas atmosphere by subjecting the surface-treated copper foil to the above-described 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 etc. Indicates 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.

  In addition, the surface-treated copper foil according to the present invention preferably has a tensile strength retention ratio of 90% to 100% after heating at 350 ° C. for 5 hours with respect to the tensile strength in a normal state. The tensile strength retention ratio is more preferably in the range of 95% to 100%. According to the present invention, by performing the pre-annealing process, it is possible to improve the retention ratio of the tensile strength after the heat treatment as compared with the case where the pre-annealing process 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. Each step will be described below.

(1) Preparation of Copper Foil In the present invention, a copper foil containing 100 ppm or more in total of one or more trace components selected from carbon, sulfur, chlorine and nitrogen is prepared. Here, the content of each trace component is preferably within the above-described range. Moreover, it is as having mentioned above that it is preferable that the average grain size of copper which comprises the said copper foil is 1.0 micrometer or less, and it is more preferable that the said average grain size is 0.8 micrometer or less. 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. The manufacturing method is not limited as long as a copper foil satisfying such conditions can be obtained, but a copper foil satisfying the above conditions can be obtained by adjusting various additives and the like in the electrolytic solution. It is preferable to manufacture a copper foil by an electrolytic method from a viewpoint of being easy.

(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 configuration, and there is no particular limitation on the roughening treatment method and the roughening treatment conditions. Moreover, it is needless to say that pretreatment such as acid pickling treatment may be performed on the surface of the copper foil before the roughening treatment. However, the roughening treatment method and the roughening treatment conditions are not limited to this, and conventionally known methods may be appropriately adopted according to the surface characteristics required for the copper foil. Just do it.

(3) Zinc adhesion process (surface treatment process)
Next, the surface of the copper foil is subjected to surface treatment (hereinafter referred to as “zinc adhesion treatment”) using a surface treatment agent containing zinc to form a zinc adhesion layer containing zinc. In the zinc adhesion treatment step, any method may be used as long as the zinc adhesion layer can be formed on the surface of the copper foil so that the adhesion amount of zinc falls within the above range. For example, an electrochemical method such as electrolytic plating or electroless plating, or a physical vapor deposition method such as sputtering deposition or chemical vapor reaction can be used. However, in consideration of production costs, it is preferable to employ an electrochemical method. In addition, it is as having mentioned above that other metal elements other than zinc may be contained in a surface treatment agent, and it is as having mentioned above the point whose tin is preferable as the said other metal element.

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 pyrophosphate zinc 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 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 Layers can be formed.

(4) Chromate treatment The surface of the zinc adhesion layer may be optionally subjected to chromate treatment. 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. The electrolysis conditions in the case of an electrolytic chromate process do not have a limitation in particular, Appropriate conditions can be employ | adopted suitably.

(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, and in view of the adhesion to the insulating resin base material required for copper foil or the negative electrode active material of a lithium ion secondary battery, etc. 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 above-described various surface treatments are completed on the copper foil, a drying step is performed to dry the copper foil in a wet state in the various surface treatment steps. Drying conditions are not particularly limited. However, when organic agent treatment is performed, thermal decomposition etc. of the silane coupling agent and / or organic rust inhibitor attached to the copper foil surface are prevented, and these agents are fixed in a good state on the copper foil surface. The heat treatment conditions (temperature, time, etc.) which can be made to adopt may be adopted.

(7) Pre-annealing step Next, the pre-annealing step will be described. In the pre-annealing process, zinc is diffused from the zinc adhesion layer side into the copper foil from the zinc adhesion layer side by performing heat treatment at a temperature range of 200 ° C. to 280 ° C. to the copper foil which 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 above-mentioned minor component, the copper foil hardly causes coarsening of crystal grains even if it is heated in a temperature range of 200 ° C. to 280 ° C. In addition, if the copper foil provided with a zinc adhesion layer on the surface is heated within the above temperature range, zinc can be contained in the copper foil at a speed commensurate with industrial production efficiency as compared with storage of the copper foil at normal temperature. The zinc distribution in the copper foil can be made uniform. Therefore, by performing the pre-annealing process, 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 subjecting the copper foil after the surface treatment to pre-annealing, the amount of zinc diffused into the copper foil can be increased as compared with the case of storage at normal temperature, and even after heat treatment at high temperature It becomes possible to control the fall of 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 inside of 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 by the inside of copper foil and making distribution of zinc in copper foil more uniform. On the other hand, if the treatment time is less than 8 hours, the amount of zinc diffused into the inside of the copper foil is small, and if high temperature heat treatment is performed for a long time, crystal grains may be coarsened inside the copper foil. In some cases, the reduction in tensile strength can not be sufficiently suppressed. In addition, when the pre-annealing time is 25 hours or more, the effect of suppressing the coarsening of copper crystal grains is saturated even if the pre-annealing treatment is performed more than that. Moreover, the cost etc. concerning heat processing also increase. Therefore, from these viewpoints, the pre-annealing time is preferably within 25 hours.

  However, depending on the crystal structure of the copper foil, the content of minor components in the copper foil, the adhesion amount of zinc to the copper foil, etc., the pre-annealing condition is an optimal heating temperature and / or suitable for zinc diffusion. 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 negative electrode current collector according to the present invention>
Next, an embodiment 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 contact with the negative electrode mixture inside the battery in a non-aqueous secondary battery such as a lithium ion secondary 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 generic term for secondary batteries using electrolytes other than aqueous solution, and secondary batteries using organic electrolytic solution, polymer gel electrolyte, solid electrolyte, polymer electrolyte, molten salt electrolyte, etc. Say The form of the negative electrode material according to the present invention is not particularly limited as long as the above 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, in the surface-treated copper foil according to the present invention, the effect of suppressing the reduction in tensile strength is high as compared with the case where the pre-annealing treatment is not performed, and the maintenance ratio of the tensile strength after heat treatment is high. As a result, even after heating at 350 ° C. for 5 hours in an inert gas atmosphere, it is possible to maintain a tensile strength of 45 kgf / mm ² or more, preferably 50 kgf / mm ² or more. Therefore, even if stress is repeatedly applied to the current collector by repeating charge and discharge cycles in a lithium ion secondary battery etc., there is little risk of deformation such as wrinkles in the current collector or breakage, lithium ion The electrical characteristics of the secondary battery can be maintained. Moreover, when manufacturing the negative electrode material of a lithium ion secondary battery, a high temperature heat | fever is loaded on a collector in 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.

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

  In Example 1, the copper foil according to the present invention was manufactured and compared with Comparative Example 1 described later. The steps will be described below in order.

Preparation of copper foil: First, an electrolytic copper foil was prepared in which the total amount of the above trace elements in the copper foil was 100 ppm or more (carbon 44 ppm, sulfur 14 ppm, chlorine 54 ppm, nitrogen 11 ppm, average crystal grain diameter 0.64 μm). Specifically, a 12 μm-thick non-surface-treated electrolytic copper foil used for manufacturing VLP copper foil manufactured by Mitsui Mining & Smelting Co., Ltd. was prepared.

Roughening treatment step: 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 to a cathode. Electrolysis was carried out under burnt copper plating conditions with a density of 25 A / dm ² to deposit fine copper particles on the surface of the copper foil on the cathode side. Next, in order to prevent the fine copper particles from falling off, the copper foil itself is polarized to 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.degree. It electrolyzed on the smooth plating conditions of density 25 A / dm < ² >, and the roughening process of the cathode surface side was completed.

Zinc adhesion treatment step: A surface treatment agent containing zinc and tin was used on both sides of the copper foil after the roughening treatment to form a zinc adhesion layer made of a zinc-tin alloy on both sides 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-tin alloy layer as a zinc adhesion layer on both sides of the copper foil. The bath composition of the zinc pyrophosphate-tin plating bath was 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 a zinc pyrophosphate-tin plating bath of the composition, the temperature of the solution is 30 ° C., the copper foil itself is polarized to the cathode, and the current density and the electrolysis time are appropriately adjusted to adhere zinc per one side of the copper foil. A copper foil was obtained in a quantity of 50 mg / m ² and a deposition amount of tin of 5 mg / m ² .

Pre-annealing step: Next, the sample 1 was subjected to a pre-annealing process under the conditions shown in Table 1 and used as a working sample 1. However, at the time of pre-annealing treatment, each sample was placed in an oven to raise the temperature inside the chamber at 5 ° C./min. Then, in Table 1, the sample 1 was heated under the corresponding processing conditions. In Table 1, a column displayed as “o” means that the pre-annealing process was performed on the sample of the number indicated in the parenthesis of the column under the condition (temperature, processing time).

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

In Example 3, a sample 3 was produced in the same manner as in Example 1 except that the adhesion amount of tin per one side was set to 30 mg / m ^2, and then a pre-annealing treatment was performed under the conditions shown in Table 1 It was three.

In Example 4, a sample 4 was prepared in the same manner as in Example 1 except that the adhesion amount of tin per one surface was 15 mg / m ² and the total adhesion amount of zinc was 100 mg / m ^2, and then Table 1 Pre-annealing treatment was performed under the conditions shown in FIG.

In Example 5, a sample 5 was prepared in the same manner as in Example 1 except that the adhesion amount of tin per one surface was 15 mg / m ² and the total adhesion amount of zinc was 150 mg / m ^2, and then Table 1 Pre-annealing treatment was performed under the conditions shown in FIG.

  A sixth embodiment will now be described. In Example 6, another copper foil according to the present invention was manufactured as follows. The steps will be described below in order.

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 80 g / l of copper ions and 250 g / l of sulfuric acid, 2.7 ppm of chlorine ions, and 2 ppm of gelatin is used as a sulfuric acid-based copper electrolytic solution. Electrolysis was carried out at a current density of 50 A / dm ² to obtain an electrolytic copper foil with a thickness of 12 μm. The content of minor components in the electrodeposited 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: In the same manner as in Example 1, except that the adhesion amount of tin per one surface is 25 mg / m ² and the adhesion amount of zinc is 150 mg / m ^{2 on} the electrodeposited copper foil after the roughening treatment. A zinc adhesion layer was formed on both sides of the copper foil to prepare sample 6. Then, in the same manner as in Example 1, the pre-annealing process was performed under the conditions shown in Table 1, and the sample after each pre-annealing process was used as a working sample 6.

[Reference example]
In the reference example, 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 bath composition of the pyrophosphate zinc plating bath is the same as in Example 1 except that the bath composition of zinc concentration 6 g / l, potassium pyrophosphate concentration 125 g / l, pH 10.5 is employed, and copper foil A copper foil with an adhesion amount of 50 mg / m ² was obtained as a reference sample. Thereafter, in the same manner as in Example 1, the pre-annealing treatment was performed under the conditions shown in Table 1, and the sample after each pre-annealing was used as a reference sample.

Comparative example

  In the comparative example, samples were prepared in the same manner as in the examples 1 to 6 and the reference sample except that the pre-annealing process was not performed, and they were respectively set as the comparative sample 1 to the comparative sample 7.

  In order to facilitate comparison of the conditions etc. of the samples produced in each example, comparative example and reference example, Table 2 shows the total adhesion amount of tin and zinc in each sample and the type of copper foil. Moreover, in Table 2, the normal-state tensile strength of each copper foil (A or B) measured by the method mentioned later is shown. In Table 2, Type A of the copper foil refers to the electrodeposited copper foil used in Examples 1 to 5 and the reference example, and type B of the copper foil is manufactured by the method described in Example 6. Refers to an electrodeposited copper foil.

[Evaluation]
1. Evaluation method (1) Trace element content Content of the trace element of the trace element in each copper foil used by Example 1- Example 6 and a comparative example was measured as follows. First, the content of carbon and sulfur in the copper foil was analyzed using a carbon / sulfur analyzer (EMIA-920V) manufactured by Horiba, Ltd. Moreover, about content of nitrogen in copper foil, it analyzed using the oxygen and nitrogen analyzer (EMGA-620) by Horiba, Ltd. make. And about content of the chlorine in copper foil, it analyzed using the spectrophotometer (U-3310) made from Hitachi High-Tech Fielding Co., Ltd. by the silver chloride nephelometry.

(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, the “tensile strength” is based on IPC-TM-650, and using a strip-shaped copper foil sample of 100 mm × 10 mm (distance between marks: 50 mm), a tensile speed of 50 mm / min. The value when measured with.

(3) Crystal structure About the untreated copper foil (A and B) before giving each sample and roughening process, zinc adhesion process, etc. which were obtained by Example 1 and Example 5 and Comparative example 1 and Comparative example 5 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 samples 1 and 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 The device was used. The 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 appropriately cross-sectioned using this apparatus, and this image data is used as an 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 accelerating voltage: 20 kV, an aperture diameter: 60 mm, a high current mode, and a sample angle: 70 °. In addition, observation magnification, a measurement area | region, and step size changed the conditions suitably, and measured it according to the magnitude | size of a crystal grain.

2. Evaluation Results (1) Tensile Strength First, Tables 3 to 7 show the tensile strengths of the respective execution samples, comparative samples and reference samples after heat treatment at 350 ° C. for 5 hours. Table 7 shows tensile strengths of Comparative Sample 5 and Comparative Sample 6 after heating at 350 ° C. for 1 hour. In each table, the retention rate of the tensile strength after heat treatment of each sample to the normal tensile strength is shown as a percentage.

As shown in Tables 3 to 6, the practical samples 1 to 6 according to the present invention and the reference sample have tensile strengths after heating for 5 hours at 350 ° C. regardless of the processing conditions for the pre-annealing treatment. All exhibited values of 45 kgf / mm ² or more, and maintained a tensile strength of 79% to 102% of the normal tensile strength. Moreover, according to the content of trace components of copper foil, etc., while adjusting the adhesion amount of zinc, the adhesion amount of tin, etc., 50 kgf even after heating at 350 ° C. for 5 hours by adopting preferable pre-annealing conditions. It was confirmed that it is possible to maintain a tensile strength of at least ² mm ² and suppress the reduction rate of the tensile strength within 10%, more preferably within 5%.

  Further, comparing the practical samples 1 to 6 with the reference sample, the zinc adhesion layer is made a zinc-tin alloy layer, and the heat treatment after the heat treatment is made more than the case where the zinc adhesion layer is a tin layer not containing tin. It was confirmed that the 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 may show a value of 45 kgf / mm ² or more, but maintaining the tensile strength The percentage was 65% to 87%, and it was confirmed that the tensile strength decreased by 10% or more in each 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 Working Sample 5 and Working Sample 6, for example, as shown in Table 3, even if the pre-annealing treatment is performed for 8 hours under the lowest temperature treatment condition (1) (200 ° C.), 51.3 kgf / mm ² , And maintains a tensile strength of 46.9 kgf / mm ² . In addition, as shown in Table 5, when the processing time is 2 hours, for example, the tensile strength of the working sample 5 and the working sample 6 is 50.7 kgf / mm in the case of the processing condition (3) (250 ° C.) 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 has been confirmed that the effect of suppressing the decrease in tensile strength can be obtained even by heating at a high temperature for a long time by performing the pre-annealing process 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 working sample 1 and the comparative sample 1 is compared. 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 also shows values of average crystal grain sizes of Working Sample 1, Working Sample 5, Comparative Sample 1 and Comparative Sample 5 after heating at 350 ° C. for 5 hours. Note that, as described above, the pre-annealing process (heating under the processing condition (1) (200 ° C.) for 8 hours) is performed on the working samples 1 and 5 before heating at 350 ° C. for 5 hours. As shown in FIGS. 1 and 2, when compared with the crystal structure of the comparative sample 1, it can be confirmed that the crystal structure of the working sample 1 is entirely fine. In addition, as shown in Table 8, each of the working sample 1 and the working sample 5 has 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 is 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 Comparative Sample 1 and Comparative Sample 5 are heated at 350 ° C. for 5 hours, the average crystal grain size exceeds 1.0 μm in any region, and in particular, the crystal grains in the central portion of the copper foil are coarsened. It was confirmed that the tendency was high. Therefore, by subjecting each sample to pre-annealing, zinc (and different metal elements) can be diffused not only to the surface layer of copper foil but also to the central part of copper foil, so that high temperature heat is prolonged 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 applying the above-mentioned surface treatment to the surface of the copper foil and then applying the above-mentioned pre-annealing treatment, and performing long-time heat treatment at high temperature. Even after being processed, a copper foil with less reduction in tensile strength can be provided. Therefore, it can be used suitably for the use exposed to high temperature atmosphere at the time of manufacture, and can be especially preferably used as a negative electrode collector of non-aqueous secondary batteries, such as a lithium ion secondary battery, and a manufacturing material of a printed wiring board.

Claims (7)

Surface treatment layer containing 20 mg / m ^{2 to} 1000 mg / m ² of zinc per surface on both sides of a copper foil containing 100 ppm or more in total of one or more trace components selected from carbon, sulfur, chlorine and nitrogen A surface-treated copper foil in which a compound of the zinc in the surface treatment layer and the minor component is deposited at grain boundaries of the copper foil,
Normal tensile strength of the copper foil 50 kgf / mm ² or more 62kgf / mm ² or less,
The tensile strength after heating at 350 ° C. for 5 hours in an inert gas atmosphere of the surface-treated copper foil is 50 kgf / mm ² or more,
In addition, the surface-treated copper foil is characterized in that the retention ratio of tensile strength after heating to tensile strength after heating of the surface-treated copper foil relative to the tensile strength of normal state of the copper foil is 90% to 100%. . The surface-treated copper foil according to claim 1, wherein the surface treatment layer contains a metal element whose diffusion rate in copper and / or copper is faster than zinc. The surface-treated copper foil according to claim 2, wherein the metal element whose diffusion rate into copper and / or copper is faster than zinc is tin . The surface-treated copper foil according to claim 3, 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 4, wherein the copper foil has an average crystal grain size in a normal state of 1.0 µm or less. The negative electrode collector using the surface-treated copper foil as described in any one of Claims 1-5 . A negative electrode material of a non-aqueous secondary battery comprising the negative electrode current collector according to claim 6 .