JP2012129136A - Lithium ion secondary battery copper foil and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery copper foil which would not be broken by repetitive stresses at charging and discharging time and therefore exhibits improved reliability and can be manufactured easily and a manufacturing method for the same.SOLUTION: A lithium ion secondary battery copper foil constitutes an anode which is wound round via a separator between it and a cathode. The copper foil has crystal grains having a crystal orientation of within 15 degrees from (200) crystal orientation present therein by 50 to 100% as an area ratio viewed from the copper foil surface. The lithium ion secondary battery copper foil used is made by hot-rolling a copper ingot to a predetermined thickness and then cold-rolling and annealing, for strain removal, the hot-rolled material repeatedly until copper plate in a prescribed thickness is formed, which is then cold-rolled, after being annealed, to obtain copper foil. The copper foil is subjected to heat treatment in a nitrogen, or inert gas, atmosphere before being manufactured with a roll working degree of 91 to 99%.

Description

  The present invention relates to a copper foil for a lithium ion secondary battery and a method for producing the same, and more particularly to a copper foil for a lithium ion secondary battery that is used for a negative electrode of a lithium ion secondary battery and that does not break at the time of charge / discharge.

  In recent years, there has been a remarkable spread of information devices such as mobile phones and personal computers, and there is an increasing demand for small and high-capacity secondary batteries. Among secondary batteries, lithium ion secondary batteries are lightweight and have a high energy density, and thus have recently attracted attention not only in information equipment but also in the field of electric vehicles.

  For example, as shown in FIG. 3, the lithium ion secondary battery has a configuration in which a sheet-like positive electrode 1 and a negative electrode 2 are wound with a separator 3 interposed therebetween. Generally, a copper foil is used for the negative electrode 2 of the lithium ion secondary battery, and this type of copper foil can be roughly divided into two according to the production method. One is a rolled copper foil produced by rolling a material produced by casting, and the other is an electrolytic copper foil produced by electrolytic deposition of copper from a solution mainly composed of copper sulfate. is there.

  Copper foils used in lithium ion secondary batteries are increasingly used with a thickness of 10 μm or less as the capacity of batteries increases and miniaturization progresses. The plate property has deteriorated. In particular, in rolled copper foil, the strength after processing is high and the elongation is small, so breakage is likely to occur due to subtle fluctuations in tension applied to the copper foil during the operation of applying carbon to the copper foil in the production line. ing.

  For this reason, when using a rolled copper foil for a lithium ion secondary battery, the copper foil is heated and softened under a certain temperature condition after rolling, so that the elongation of the copper foil is recovered in advance. To the negative electrode production line.

  However, with the increase in capacity of lithium ion secondary batteries, it is becoming increasingly common for copper foils to break during this charge / discharge. Until now, it has been considered that the phenomenon of fracture occurring in copper foil is governed by the elongation of copper foil.

  However, as the capacity of the battery increases, breakage of the copper foil is remarkably generated even in the electrolytic copper foil and the rolled copper foil whose elongation is sufficiently recovered. Examining the cause of the copper foil breakage, in the lithium ion secondary battery, lithium ions move from the positive electrode to the negative electrode during charging, and lithium ions move again from the negative electrode to the positive electrode during discharging. Since the negative electrode material expands and contracts with the movement of lithium ions, the copper foil used as a current collector undergoes repeated stress fluctuations due to charge and discharge, so the copper foil undergoes fatigue deformation and eventually breaks. It has been found.

In order to improve the strength and ductility of the copper foil used for the negative electrode of the lithium ion secondary battery, for example, Cr contains 0.05 to 0.4 mass%, Zr contains 0.01 to 0.25 mass%, and the balance is The number of inclusions with Rz / t, which is the ratio of the maximum peak height Rz and the plate thickness t when scanning copper and an inevitable impurity copper alloy in the rolling direction, is less than 0.2 and whose major axis is 1 μm or more. A precipitation hardening type copper alloy foil having a thickness of 100 pieces / mm ² or less and a thickness of 20 μm or less has been proposed (see Patent Document 1).

  Moreover, in order to produce a negative electrode for a lithium ion secondary battery having an excellent charge / discharge cycle life at low cost, Ni is 1.0 mass% or more and 5 mass% or less, and Si is 0.2 mass% or more and 1.2 mass. % When the copper alloy foil containing copper and the remainder made of copper and inevitable impurities is subjected to tin plating to form a negative electrode for a lithium ion secondary battery, the tin-plating film contains an intermetallic metal in the Sn-Ni equilibrium diagram. It has also been proposed to form a compound (see Patent Document 2).

JP 2009-79282 A JP 2003-257417 A

  However, as described in the above Patent Documents 1 and 2, in the alloy foil in which various elements are added to the copper base material, there are many kinds of additive elements and the concentration is high. There was a problem that it was not a good idea in terms of cost.

  An object of the present invention is to provide a copper foil for a lithium ion secondary battery that can be easily manufactured without fear of breaking due to repeated stress during charge and discharge, and a method for manufacturing the same.

  The copper foil for a lithium ion secondary battery of the present invention is a copper foil that becomes a negative electrode that is wound with a separator interposed between the positive electrode and the copper foil having a crystal orientation within 15 degrees from the (200) crystal orientation. It is characterized in that 50 to 100% of crystal grains having a ratio of area as viewed from the copper foil surface is present.

  Preferably, the copper foil is characterized in that an average crystal grain size before final cold rolling is 50 μm or less, the copper foil is characterized in that at least one surface is subjected to surface treatment, and the copper foil is further characterized in that The foil is characterized by having a thickness of 7 μm to 20 μm, and the copper foil is characterized by being an alloy foil to which Sn is added, and further, the copper foil has carbon applied to this surface. It is a feature.

  The method for producing a copper foil for a lithium ion secondary battery according to the present invention includes hot rolling a copper ingot created by melt casting to a predetermined thickness, and cold rolling the hot rolled material. A copper plate having a predetermined thickness is formed by repeatedly performing strain relief annealing, and after the copper plate is annealed, it is cold-rolled to obtain a copper foil, subjected to a heat treatment in which the copper foil is heated in a nitrogen atmosphere, and a rolling degree of 91- It is characterized by obtaining a copper foil in which 99% of the crystal grains within 15 degrees from the (200) crystal orientation are present in a proportion of 50 to 100% of the surface area.

  Preferably, the copper ingot is tough pitch copper and is rolled at a rolling work degree of 91 to 95%, and the copper ingot is 0.001 to 0.009 mass% in oxygen-free copper. The tin is added and rolled at a rolling degree of 91 to 99%.

  According to the copper foil for a lithium ion secondary battery of the present invention, the occurrence of copper foil breakage can be significantly reduced by repeated stress during charging and discharging of the lithium ion secondary battery, further improving the reliability of the secondary battery. Can be made.

  Moreover, according to the manufacturing method of the copper foil for lithium ion secondary batteries of this invention, copper foil can be manufactured easily and quality control can be performed reliably, and the manufacturing cost of the copper foil for lithium ion secondary batteries can be improved. There are advantages.

(A)-(c) is a schematic diagram which shows the crystal lattice of copper within 15 degree | times from the (200) crystal orientation of the copper foil for lithium ion secondary batteries of this invention. (A) is a gray map photograph created based on the IPF full-color map photograph of the copper foil for lithium ion secondary batteries of this invention, (b) is a gray scale figure of (a), (c) is two of (a). It is a price photograph. It is the schematic which shows the structure of a lithium ion secondary battery.

  Hereinafter, the copper foil for lithium ion secondary batteries of this invention and its manufacturing method are demonstrated using FIG.1 and FIG.2. As a result of various studies on the copper foil for lithium ion secondary batteries, the present inventors have found that the copper foil can sufficiently withstand the repeated stress during charging and discharging. According to the study by the present inventors, the copper foil for a lithium ion secondary battery has a crystal orientation in which the copper crystal grains are within 15 degrees from the (200) crystal orientation, and the ratio of the area viewed from the copper foil surface is 50. If it controls so that it may exist -100%, it can be set as a desirable copper foil.

  In the present invention, the copper crystal grains within 15 degrees from the (200) crystal orientation means that the normal vector of the (200) plane faces the vertical direction of the copper foil in the copper crystal lattice. In this case, the angle formed by the normal vector of the (200) plane of each crystal as shown in FIGS. 1A, 1B, and 1C is within 15 degrees. Here, it should be noted that the (200) plane, that is, the one matching the (200) plane is also included.

  The copper foil for lithium ion secondary batteries of this invention is manufactured, for example with the following procedures. That is, in the manufacture of the copper foil, since the crystal grains within 15 degrees from the (200) crystal orientation are 50 to 100%, first, a copper ingot is created by melt casting, and this copper ingot is hot-rolled. A copper plate is prepared by rolling to a thickness of 13 mm.

  Next, the produced copper plate having a thickness of 13 mm was repeatedly subjected to cold rolling and strain relief annealing to obtain a copper plate having a thickness of 0.2 mm. Furthermore, this 0.2 mm copper plate was annealed at a temperature of 800 ° C. for 30 seconds, and the average crystal grain size at this time was adjusted to 50 μm or less. Then, it cold-rolled to thickness 10micrometer. At the copper foil manufacturing stage so far, the rolling degree is 95%. In addition, although the processing degree of copper foil changes with copper materials used like pure copper or a copper alloy, it is the range of 91%-99% of rolling processing.

  This manufactured copper foil is subjected to a heat treatment at 170 ° C. for 30 minutes in a nitrogen atmosphere as an inert gas in order to grow (200) crystal orientation. As the conditions for the heat treatment after rolling, a treatment for holding for 30 minutes to 10 hours at a temperature of 170 ° C. to 300 ° C. is performed by selecting the treatment conditions depending on the target copper foil. By this heat treatment, the copper foil has a crystal orientation within 15 degrees from the (200) crystal orientation, and a desired copper foil for a lithium ion secondary battery having a surface area ratio of 50 to 100%. can do.

  When a rolled copper foil is used as described above, crystal grains having a (200) crystal orientation are generated and grown as recrystallized grains during heat treatment using the processing strain given by rolling as a driving force. At this time, if the applied processing strain is small, crystal grains having the (200) crystal orientation cannot be sufficiently grown. On the other hand, if the applied strain is excessive, recrystallization occurs during rolling by using the strain as a driving force, and as a result, the recrystallized grains after the heat treatment are different from the (200) crystal orientation. Become a thing.

The amount of processing strain to be applied varies depending on the material used for the copper foil and the heat resistance, and the appropriate range varies. The amount of processing strain is controlled by the degree of rolling during rolling. In addition, the rolling degree of copper foil is represented by the following formula.
Rolling degree (%) = (Thickness before rolling—Thickness after rolling) / (Thickness before rolling) × 100

As the material used for the rolled copper foil, 99.90% or more tough pitch copper containing 0.02 to 0.05% oxygen in the state of Cu ₂ O copper oxide is excellent in electrical and thermal conductivity, and is malleable. And, since the drawing workability is good, when this is used, the rolling work degree is desirably 91 to 95%. In this range, with tough pitch copper, if the degree of rolling is less than 91%, the (200) crystal orientation does not grow sufficiently in the heat treatment after rolling, and if the degree of rolling exceeds 95%, the (200) crystal orientation is This is because recrystallized grains having different orientations are generated.

  Moreover, the copper alloy which added 0.001-0.009 mass% tin (Sn) to oxygen-free copper can be used as a material of rolled copper foil. When this tin-added copper alloy is used, the softening temperature is 10 to 50 ° C. higher than that of tough pitch copper, so that (200) crystal orientation can grow even when a higher degree of rolling work is given. For this reason, the range of a desirable rolling work degree is 91-99%.

  In the case of a rolled copper foil, the proportion of crystal grains having a (200) crystal orientation also changes depending on the temperature and time of the heat treatment. When the heat amount of the heat treatment is insufficient, the rolled structure remains, and conversely, when the heat amount of the heat treatment is excessive, secondary recrystallization causes crystal grains having a crystal orientation different from (200) crystal orientation. appear. The optimum heat treatment conditions for the rolled copper foil vary depending on the conditions such as the material of the copper foil, the atmosphere during heating, and the heating method of the furnace.

  In the production of the copper foil for a lithium ion secondary battery of the present invention, not only the rolled copper foil but also any electrolytic copper foil can be used. In the case of using a rolled copper foil, the copper foil is subjected to a heat treatment in order to grow the (200) crystal orientation after the rolling process as described above.

  In the above-described copper foil for a lithium ion secondary battery according to the present invention, since the fatigue characteristics of the copper foil at the time of charge / discharge are improved by increasing the (200) crystal orientation, the copper foil is difficult to break. Cycle characteristics during discharge can be improved.

  Furthermore, it is desirable that the average crystal grain size of the crystal grains before final cold rolling be 50 μm or less. A line intercept method is used as a method for measuring the average crystal grain size. The sample is measured for the cross-sectional structure in the rolling direction and the cross-sectional structure in the width direction, and the average value is used as the average crystal grain size. By setting the average grain size before the final cold rolling to 50 μm or less, it becomes easier to form a rolling texture during the subsequent cold rolling, and as a result, the (200) crystal orientation of the recrystallized grains can be improved. It becomes possible.

  The copper foil for a lithium ion secondary battery of the present invention may be manufactured using pure copper (containing components are copper and inevitable impurities), for example, Ag, Sn, Ni, Co, Fe, P, Si, Zn, It can also be manufactured using an alloy foil to which one or more of Cr, Zr, Al, and Mn are added. In this case, since the softening temperature of the copper foil changes depending on the additive material and the amount thereof, the crystal having the above crystal orientation can be obtained by adjusting the heat treatment conditions such as the heating time and the heating temperature according to the additive material and the amount thereof. A copper foil having grains can be obtained.

Moreover, the copper foil for lithium ion secondary batteries of this invention can also apply | coat carbon to the heat-treated copper foil as follows, for example, and can also assemble a lithium ion secondary battery. The coating of carbon on the surface of the copper foil is performed using a ratio of 10% of binder to 90% of graphite, and the thickness of the coating substance is set to 100 μm by pressing. As the binder, typically polyvinyl Den fluoride (PVdF) + N _- using methyl pyrrolidone (MNP), and in order to volatilize removing MNP when carbon coating, to implement the drying of about 10 minutes at 80 ° C. .

  And the copper foil for lithium ion secondary batteries of this invention can be used even if it combines with all surface treatments. For example, in order to improve the adhesion with the negative electrode binding material, one side or both sides of the copper foil are roughened, or Ni plating, chromate treatment or benzotriazole treatment is performed to prevent the copper foil surface from being altered by oxidation or the like. You can also. The timing of the surface treatment of the copper foil may be any after the rolling process or after the heat treatment in the case of the rolled copper foil.

  Furthermore, the thickness of the copper foil for lithium ion secondary batteries of this invention is 20 micrometers or less, Preferably it is 18 micrometers-10 micrometers. The optimal thickness of the copper foil varies depending on the configuration of the target lithium ion secondary battery. Generally, when the thickness is small, a large amount of active material can be loaded, which can be advantageous in terms of battery capacity.

  Next, Examples 1 to 4 and Comparative Examples 1 to 4 which are copper foils for lithium ion secondary batteries of the present invention will be described in order. In each of the following Examples and Comparative Examples, the crystal orientation of the copper foil is determined by SEM-EBSP analysis (Scanning Electron Microscope-Electron Backscattering diffraction Pattern: back reflection electron image analysis using a scanning electron microscope). It was measured.

  In the measurement, the target copper foil was cut into a predetermined size, and the oxide on the surface of the copper foil was removed by ion sputtering. Then, this was put into an FE-SEM, and EBSP analysis was performed. The magnification at the time of measurement was 200 times, the EBSP analysis range was 400 μm square in the visual field, and measurement was performed at a measurement pitch of 2 μm.

  From the measured data, the crystal orientation of each crystal grain is analyzed, and the IPF gray map shown in FIG. 2 (a) is based on an IPF (Inverse Pole Figure) full color map photograph that is color-coded according to the crystal orientation. Created a photo. In this IPF gray map photograph, the crystal orientation can be discriminated on the gray scale shown in FIG. 2B. However, in order to further easily discriminate the target crystal grain from the other, the IPF gray map photograph is binary. The binarized photograph shown in FIG. 2C is used to identify the target grain in the black portion. In the actual crystal grain identification work, a computer was used to identify crystal grains having a crystal orientation within 15 degrees from the (200) crystal orientation, and the area ratio within the measurement area was obtained. This is the (200) area ratio.

Example 1
After adjusting the average crystal grain size to 30 μm by annealing at 800 ° C. for 15 seconds using a tough pitch copper (indicated as “TPC”), a copper foil having a rolling work degree of 91% and a thickness of 10 μm is obtained by cold rolling. Produced. The copper foil was washed and removed from the rolling oil on the surface, then cut into a sheet state, and heated at 170 ° C. for 30 minutes in a nitrogen atmosphere as an inert gas in order to obtain desired crystal grains.

Example 2
After adjusting the average crystal grain size to 30 μm by annealing at 800 ° C. for 15 seconds using tough pitch copper (TPC), a copper foil having a rolling degree of 95% and a thickness of 10 μm was produced by cold rolling. This copper foil was washed and removed from the rolling oil on the surface, then cut into a sheet state and similarly heated at 170 ° C. for 30 minutes in a nitrogen atmosphere.

Example 3
After adjusting the average crystal grain size to 45 μm by annealing at 800 ° C. for 40 seconds using tough pitch copper (TPC), a copper foil having a rolling degree of 95% and a thickness of 10 μm was produced by cold rolling. This copper foil was washed and removed from the rolling oil on the surface, then cut into a sheet state and similarly heated at 170 ° C. for 30 minutes in a nitrogen atmosphere.

Example 4
0.001 to 0.009 mass% of tin (Sn) is added to oxygen-free copper, and a cast copper alloy (indicated as “HX _N ”) is used to anneal the average crystal grain size by annealing at 800 ° C. for 35 seconds. Was adjusted to 30 μm, and then a cold-rolled copper foil having a rolling degree of 91% and a thickness of 10 μm was produced. This copper foil was washed and removed from the rolling oil on the surface, then cut into a sheet and heated at 250 ° C. for 1 hour in a nitrogen atmosphere. The tin to be added is added in a necessary amount when pure copper or oxygen-free copper is melted in a high-frequency melting furnace, the obtained molten metal is poured into a mold, continuously cooled, cast, and rolled as described above. A copper foil is manufactured from the copper alloy.

Example 5
Add 0.001 to 0.009 mass% of tin (Sn) to oxygen-free copper, and adjust the average grain size to 30 μm by annealing at 800 ° C. for 35 seconds using a cast copper alloy (HX _N ). Then, a cold-rolled copper foil having a rolling degree of 99% and a thickness of 1 μm was produced. This copper foil was washed and removed from the rolling oil on the surface, cut into a sheet, and similarly heated at 250 ° C. for 1 hour in a nitrogen atmosphere.

Comparative Example 1
After adjusting the average crystal grain size to 30 μm by annealing at 800 ° C. for 15 seconds using tough pitch copper (TPC), a copper foil having a rolling degree of 90% and a thickness of 10 μm was produced by cold rolling. This copper foil was washed and removed from the rolling oil on the surface, cut into a sheet, and heated at 170 ° C. for 30 minutes in a nitrogen atmosphere.

Comparative Example 2
An average crystal grain size was adjusted to 30 μm by annealing at 800 ° C. for 15 seconds using tough pitch copper (TPC), and then a copper foil having a rolling degree of 96% and a thickness of 10 μm was produced by cold rolling. This copper foil was washed and removed from the rolling oil on the surface, then cut into a sheet and heated at 170 ° C. for 30 minutes in a nitrogen atmosphere.

Comparative Example 3
After adjusting the average crystal grain size to 60 μm by annealing at 800 ° C. for 50 seconds using tough pitch copper (TPC), a copper foil having a rolling degree of 95% and a thickness of 10 μm was produced by cold rolling. This copper foil was washed and removed from the rolling oil on the surface, then cut into a sheet and heated at 170 ° C. for 30 minutes in a nitrogen atmosphere.

Comparative Example 4
0.001 to 0.009 mass% of tin (Sn) is added to oxygen-free copper, the average crystal grain size is made 30 μm using a cast copper alloy (HX _N ), and the thickness is reduced to 90% by rolling. A 10 μm copper foil was prepared. This copper foil was washed and removed from the rolling oil on the surface, then cut into a sheet and heated at 250 ° C. for 1 hour in a nitrogen atmosphere.

Comparative Example 5
Add 0.001 to 0.009 mass% of tin (Sn) to oxygen-free copper, and adjust the average grain size to 30 μm by annealing at 800 ° C. for 35 seconds using a cast copper alloy (HX _N ). After that, a copper foil having a rolling degree of 99.5% and a thickness of 10 μm was produced by cold rolling. This copper foil was washed and removed from the rolling oil on the surface, then cut into a sheet and heated at 250 ° C. for 1 hour in a nitrogen atmosphere.

  For the copper foils obtained in Examples 1 to 5 and Comparative Examples 1 to 5 described above, the (200) area ratio and the cycle characteristics were measured, and a good copper foil was marked with a circle. The evaluation was made with crosses. The evaluation results are shown in Table 1.

  Examples 1 and 2 and Comparative Examples 1 to 3 use tough pitch copper (TPC) as a material and change the rolling degree by rolling from different thicknesses to 10 μm. As shown in Table 1, Comparative Example 1 had a rolling degree of 90% and a (200) area ratio of 45%, whereas it was 50% by setting the rolling degree to 91% as in Example 1. As in Example 2, the degree of processing increased to 95% (200) and the area ratio to 67%. However, when the rolling degree is increased to 96% as in Comparative Example 2, the (200) area ratio is greatly reduced. This is because recrystallization occurs during rolling, which ultimately reduces the amount of processing strain imparted to the copper foil, making it difficult for recrystallized grains having a (200) crystal orientation to grow.

Further, in Comparative Examples 1 and 2 in which the (200) area ratio was less than 50%, disconnection was recognized also in the cycle characteristics. The same applies to Examples 4 and 5 and Comparative Examples 4 and 5 using a cast copper alloy. However, the cast copper alloy (HX _N ) has a softening temperature higher than that of tough pitch copper because tin (Sn) is added. That is, since the energy barrier for generating recrystallization is high, the (200) area ratio is maintained up to a higher degree of rolling than that of tough pitch copper.

  In Examples 2, 3 and Comparative Example 3, the average crystal grain size before cold rolling was changed by changing the annealing conditions before cold rolling. In Example 2, the average crystal grain size was 30 μm, whereas in Example 3, it was 45 μm, and in Comparative Example 3, it was 60 μm. As a result, in Example 3, the (200) area ratio decreased to 55%, and in Comparative Example 3, it decreased to 48%. In Comparative Example 3, the cycle characteristics were poor.

  In the copper foil for a lithium ion secondary battery, the negative electrode binder repeatedly expands and contracts, and the copper foil is subjected to repeated deformation stress by a charge / discharge test. This deformation is not so much that the copper foil is plastically deformed, but it is a repetition of deformation close to elastic deformation, that is, close to fatigue deformation. When such deformation is applied, the copper foil tries to eliminate the applied strain by crystal slip. Therefore, when there are many crystal grains having an orientation close to the (200) crystal orientation, this crystal slip is likely to propagate beyond the crystal grain boundary, and no strain is accumulated in the crystal grain boundary. Therefore, as the copper foil for lithium ion secondary batteries of the present invention has a crystal structure having an orientation close to (200) crystal orientation, strain does not accumulate in the copper foil during the charge / discharge test. No breakage occurs.

DESCRIPTION OF SYMBOLS 1 ... Positive electrode, 2 ... Negative electrode, 3 ... Separator.

Claims (9)

  In the copper foil for a lithium ion secondary battery that becomes a negative electrode wound with a separator interposed between the positive electrode and the positive electrode, the copper foil has a crystal grain having a crystal orientation within 15 degrees from the (200) crystal orientation. A copper foil for a lithium ion secondary battery, wherein the copper foil is present in an area ratio of 50 to 100% as viewed from the surface.   2. The copper foil for a lithium ion secondary battery according to claim 1, wherein the copper foil has an average crystal grain size of 50 μm or less before final cold rolling.   3. The copper foil for a lithium ion secondary battery according to claim 1, wherein the copper foil is subjected to a surface treatment on at least one surface.   4. The copper foil for a lithium ion secondary battery according to claim 1, wherein the copper foil has a thickness of 7 μm to 20 μm.   5. The copper foil for a lithium ion secondary battery according to claim 1, wherein the copper foil is an alloy foil to which Sn is added.   6. The copper foil for a lithium ion secondary battery according to claim 1, wherein the copper foil has carbon applied to the surface.   A copper ingot created by melt casting is hot-rolled and rolled to a predetermined thickness, and the hot-rolled material is repeatedly subjected to cold rolling and strain relief annealing to form a copper plate having a predetermined thickness, and the copper plate Is annealed to obtain a copper foil, and the copper foil is subjected to heat treatment in a nitrogen atmosphere to obtain a rolling degree of 91 to 99% and (200) crystal grains within 15 degrees from the crystal orientation. The manufacturing method of the copper foil for lithium ion secondary batteries characterized by obtaining the copper foil which exists in 50 to 100% of surface area.   8. The method for producing a copper foil for a lithium ion secondary battery according to claim 7, wherein the copper ingot is tough pitch copper and is rolled at a rolling degree of 91 to 95%.   8. The lithium ion secondary battery according to claim 7, wherein the copper ingot is formed by adding 0.001 to 0.009% by mass of tin to oxygen-free copper and rolling at a rolling degree of 91 to 99%. Method for producing copper foil.

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