JP6146964B2 - Copper alloy rolled foil for secondary battery current collector and method for producing the same - Google Patents

Description

  The present invention relates to a copper alloy rolled foil applicable to a current collector for a secondary battery, and in particular, a copper alloy rolled foil having a small Young's modulus for tensile stress in directions of 0 °, 45 °, and 90 ° with respect to the rolling direction. And a manufacturing method thereof.

A copper alloy rolled foil may be used for a negative electrode current collector of a secondary battery such as a lithium ion battery. In this case, the copper alloy rolled foil holds the negative electrode active material on the surface thereof and is used as a negative electrode current collector.
With the recent demand for increasing battery capacity, changes in the negative electrode active material from carbon-based to silicon (Si) -based or tin (Sn) -based are being studied. Although these new active materials have a large charge / discharge capacity, they have a feature that the volume expansion / contraction due to charge / discharge is larger than that of carbon. The copper alloy rolled foil deforms following the deformation of the active material, but remains as a permanent deformation when the amount of deformation imposed on the copper foil exceeds its elastic limit. As a result, there were a problem that the active material peeled from the rolled foil, a problem that the rolled foil was broken, and the like. The separation of the active material and the breakage of the current collector lead to an increase in the electric resistance inside the battery, thereby reducing the capacity of the battery.

In order to make permanent deformation difficult even for large deformation, it is desired to lower Young's modulus in addition to high yield stress. Since the active material expands and contracts in all directions in the plane, it is necessary to control to reduce the Young's modulus of the rolled foil in all directions.
In the battery assembly process, a heat treatment at 350 ° C. is performed to imidize the polyamide used to fix the active material having a large deformation amount to the negative electrode current collector. For this reason, when used for a battery, it is calculated | required that copper alloy rolled foil does not soften also by said process.

Several proposals have been made regarding the control of the Young's modulus of a copper alloy rolled foil as follows.
Patent Document 1 describes that when a copper sheet of pure copper is rolled at a rolling rate of 96% and heat-treated at 250 ° C. for one hour, the Young's modulus decreases due to an increase in cube texture. .
In Patent Document 2, the tensile strength and Young's modulus are controlled within a certain range by controlling the tensile strength and Young's modulus within a certain range by controlling the development so that the recrystallization texture after heating at 300 ° C. for 30 minutes does not develop. Propose improvement.
Patent Document 3 proposes that the charge / discharge cycle life of the secondary battery is excellent when the Young's modulus has little anisotropy and has a tensile strength of 400 MPa or more after heating at 300 ° C. for 30 minutes.

JP 55-055454 A JP 2009-108376 A JP 2011-216463 A

The conductor described in Patent Document 1 is one that rolls copper, but has a significantly low yield stress because it is after the copper foil has been completely recrystallized and softened. In addition, because it is a flexible cable application, it is difficult to apply to rolled copper foil for batteries that require a reduction of the Young's modulus including the 45 ° direction only by reducing the Young's modulus in the rolling direction or the vertical direction of rolling. Technology.
Similarly, since the copper foil described in Patent Document 2 is also used for a flexible printed circuit (FPC), only the rolling parallel direction is controlled, and this technique is difficult to apply to the rolled copper foil for batteries.
On the other hand, in Patent Document 3, the Young's modulus is focused, but the anisotropy in the rolling direction is reduced (the ratio of Young's modulus between different directions in the rolling direction is adjusted to 1.3 or less). It does not decrease the Young's modulus itself.

Here, in Patent Documents 2 and 3, the Young's modulus measured by the vibration method is evaluated. However, this method measures the resonance frequency (natural frequency) by applying forced vibration, and calculates the resonance frequency from the resonance frequency. This is a measurement method for calculating the Young's modulus. There are some problems in applying this measuring method to a rolled foil having a plate thickness of about 10 microns, and there are cases where correct evaluation is difficult. For one thing, there was a problem that because the measurement was performed with a small amount of displacement, the elastic vibration was not stabilized due to slight wrinkles or creases in the specimen, and the evaluation results varied greatly. Secondly, since bending stress is applied, there is a problem that the influence of the irregularities in the vicinity of the deformed foil surface layer is strongly influenced and the influence inside the foil is not reflected. Third, when a copper alloy rolled foil is used as a battery, it is compressed and tensioned by the active material applied on both sides, whereas the flexural deformation by the vibration method is compressed on one side and pulled on the other. Therefore, the deformation state that is essentially different from the usage environment was to be evaluated.
The Young's modulus is measured by, for example, the vibration method as described in the Japan Society of Mechanical Engineers, “Technical Data, Elastic Modulus of Metallic Materials”, p19 (1980), Maruzen Publishing. It is known that the evaluation result of Young's modulus is different between the dynamic method represented by 静 的 and the static method represented by the tensile test.

  It is an object of the present invention to provide a copper alloy rolled foil for a secondary battery current collector that can reduce the Young's modulus against tensile stress and improve the electrical characteristics of the secondary battery, and a method for producing the same. .

The above problems have been solved by the following means.
(1) A copper alloy rolled foil containing at least one of Cr, Zr and Ti in a total amount of 0.01 to 0.6% by mass, the balance being made of copper and inevitable impurities,
The copper for a secondary battery current collector, characterized in that in the crystal orientation distribution on the rolling surface, the length of the boundary line of the orientation difference boundary having an orientation difference of 1 ° or more is 1 μm ² or more and less than 10 μm per 1 μm ² Alloy rolled foil.
(2) Containing at least one of Cr, Zr and Ti in a total amount of 0.01 to 0.6% by mass, Sn 0.72% by mass or less , Zn 0.21% by mass or less , Mn 0.03 % by mass % Or less , Mg 0.03 mass% or less , Ag 0.04 mass% or less , Si 0.17 mass% or less , P 0.03 mass% or less , Ni 0.70 mass% or less, and Fe 0.15 mass% or less It is a copper alloy rolled foil containing 0.01 to 0.95% by mass in total of at least one of the above, with the balance consisting of copper and inevitable impurities,
The copper for a secondary battery current collector, characterized in that in the crystal orientation distribution on the rolling surface, the length of the boundary line of the orientation difference boundary having an orientation difference of 1 ° or more is 1 μm ² or more and less than 10 μm per 1 μm ² Alloy rolled foil.
(3) After the heat treatment held at 350 ° C. for 1 hour, the length of the boundary line of the orientation difference boundary having an orientation difference of 1 ° or more in the crystal orientation distribution on the rolled surface is 1 μm or more per 1 μm ^2. The copper alloy rolled foil for a secondary battery current collector according to (1) or (2).
(4) A method for producing a copper alloy rolled foil for a secondary battery current collector,
A copper alloy material having an alloy composition of at least one of Cr, Zr and Ti in a total content of 0.01 to 0.6% by mass and the balance consisting of copper and inevitable impurities is melted (step 1) and cast. The ingot obtained by (Step 2) is subjected to a homogenization heat treatment (Step 3) at 900 to 1030 ° C. for 5 minutes to 4 hours, and hot rolling 1 at a temperature of 700 to 1030 ° C. and a processing rate of 60 to 95%. (Step 4), intermediate cooling (Step 5) with a cooling rate of 6 to 6000 ° C./min, high temperature rolling 2 (Step 6) with a processing rate of 40 to 80% at 300 to 700 ° C., and a cooling rate of 6 to 6000 C / min cooling (step 7), chamfering (step 8), intermediate cold rolling (step 9) with a working rate of 90 to 96% at 0 to 150 ° C., and 0.5 at 300 to 600 ° C. Heat treatment (step 10) for 5 hours and 0-150 In machining rate by applying a 66 to 95% of the finishing foil rolling (step 11),
In the crystal orientation distribution of the rolled surface, a secondary copper alloy foil having a length of a boundary line of an orientation difference boundary having an orientation difference of 1 ° or more is 1 μm ² per 1 μm ² and shorter than 10 μm is obtained. A method for producing a copper alloy rolled foil for a battery current collector.
(5) A method for producing a copper alloy rolled foil for a secondary battery current collector,
Containing at least one of Cr, Zr and Ti in a total of 0.01 to 0.6 mass%, Sn 0.72 mass% or less , Zn 0.21 mass% or less , Mn 0.03 mass% or less , Mg 0.03% by mass or less , Ag 0.04% by mass or less , Si 0.17% by mass or less , P 0.03% by mass or less , Ni 0.70% by mass or less, and Fe 0.15% by mass or less . Obtained by melting (step 1) and casting (step 2) a copper alloy material having an alloy composition containing at least one kind in total of 0.01 to 0.95% by mass and the balance consisting of copper and inevitable impurities The ingot is subjected to homogenization heat treatment (step 3) at 900 to 1030 ° C. for 5 minutes to 4 hours, high temperature rolling 1 (step 4) with a processing rate of 60 to 95% at a temperature of 700 to 1030 ° C., and a cooling rate. Intercooling at 6 to 6000 ° C / min 5), high temperature rolling 2 (step 6) with a processing rate of 40 to 80% at 300 to 700 ° C., cooling at a cooling rate of 6 to 6000 ° C./min (step 7), and face milling (step 8). Intermediate cold rolling (step 9) with a processing rate of 90 to 96% at 0 to 150 ° C., heat treatment for 0.5 to 5 hours at 300 to 600 ° C. (step 10), and processing at 0 to 150 ° C. Finish foil rolling (step 11) with a rate of 66-95%,
In the crystal orientation distribution of the rolled surface, a secondary copper alloy foil having a length of a boundary line of an orientation difference boundary having an orientation difference of 1 ° or more is 1 μm ² per 1 μm ² and shorter than 10 μm is obtained. A method for producing a copper alloy rolled foil for a battery current collector.
(6) After the finish foil rolling (step 11), low temperature annealing (step 12) is performed at 200 to 600 ° C. for 0.1 to 20 hours, (2) according to (4) or (5) Manufacturing method of copper alloy rolled foil for secondary battery current collector.

ADVANTAGE OF THE INVENTION By this invention, the Young's modulus with respect to a tensile stress can be made small, and the copper alloy rolled foil for secondary battery electrical power collectors which can improve the electrical property of a secondary battery, and its manufacturing method can be provided.
According to the present invention, a copper alloy rolled foil which is a current collector as an active material (for example, Sn-based or Si-based) having a large expansion / contraction amount during charge / discharge isotropically deformed. When the current is deformed, the current collector is elastically deformed, so that the current collector can follow the shape change of the active material. Therefore, the active material can be prevented from being detached from the current collector, and the charge / discharge cycle characteristics of the secondary battery can be improved.

It is a typical process drawing of the manufacturing process of the copper alloy rolled foil for controlling crystal orientation. It is the map which analyzed Example 104 of this invention by the EBSD method, and showed the orientation difference boundary of 1 degree or more with the line. It is the map which analyzed the comparative example 303 with the EBSD method, and showed the orientation difference boundary of 1 degree or more with the line. It is a graph which shows distribution of the length of the orientation difference boundary per unit area. It is a graph which shows the relationship of the 0.2% yield strength after a heating with respect to the heating temperature in the copper alloy rolled foil of this invention example 106 and the comparative example 204.

In a preferred embodiment of the present invention, in the copper alloy rolled foil, the length of the boundary line of the misorientation boundary where the misorientation is 1 ° or more in the crystal orientation distribution of the rolling surface is 1 μm ² or more and shorter than 10 μm.
First, the orientation difference boundary will be described.

[Direction difference boundary]
The inventors examined the relationship between the orientation difference boundary length and Young's modulus.
Orientation difference boundaries are formed by processing such as dislocation walls formed by active dislocation deposition, dislocation cell boundaries, boundaries between regions with different slip systems due to crystal fragmentation, small-angle grain boundaries, and large-angle grain boundaries. It means to include the boundary of the metallographic structure. As a result of the study, it has been found that the longer the boundary, the higher the Young's modulus, and by setting it to a specific range, 0 °, 45 °, 90 ° with respect to the rolling direction as well as the specific direction. It has been found that the Young's modulus in the direction can be reduced.
Note that the two regions having different crystal orientations across the orientation difference boundary have different elastic behaviors depending on the orientation, and therefore, an internal stress distribution and a strain distribution are formed at the orientation difference boundary and its vicinity. The rolled copper alloy foil is manufactured by rolling at a high processing rate, but due to the strong strain, many misalignment boundaries are introduced in the internal metal structure. Therefore, when the rolled copper alloy foil is elastically deformed, a large number of internal stresses and strain distributions are distributed in a complicated manner.

In the present invention, the length of the orientation difference boundary having an orientation difference of 1 ° or more in the crystal orientation distribution of the foil after rolling is 1 μm or more and less than 10 μm per 1 μm ² . This length is preferably 3 μm to 9.5 μm, and more preferably 4 μm to 9.5 μm. If it falls below this range, the strength decreases, which is not preferable. Above this range, the Young's modulus due to tensile stress increases, which is not preferable. A long misorientation boundary corresponds to the fact that there are many lattice defects, and if it exceeds this rule, it becomes a factor of reducing the heat resistance when heated at 350 ° C., which is not preferable.

In addition, after finishing foil rolling (step 11), when heated at 350 ° C. for 1 hour, the length of the boundary line of the orientation difference boundary where the orientation difference after heating is 1 ° or more is preferably 1 μm or more per 1 μm ² , 3 μm or more is more preferable, and 5 μm or more is more preferable. The upper limit of the boundary line length of the orientation difference boundary after heating is not particularly limited, but is preferably 10 μm or less.

[analysis method]
The FE-SEM / EBSD method is used for the analysis of the crystal orientation in the present invention. The EBSD method is an abbreviation of Electron Back Scatter Diffraction (Electron Back Scattering Diffraction). Reflected electron Kikuchi line diffraction (Kikuchi pattern) generated when a sample is irradiated with an electron beam in a scanning electron microscope (SEM). ) Is a crystal orientation analysis technique. Since the FE-SEM uses a field emission electron gun, the electron beam is thin and has a high spatial resolution. When a material is strongly distorted by rolling at a high processing rate like a copper alloy rolled foil, the structure has a high orientation gradient, so the FE-SEM / EBSD method is effective as a method for accurately measuring the crystal orientation. . On the other hand, when a tungsten filament electron gun or the like having a large irradiation electron beam diameter is used, a diffraction pattern with a plurality of directions is formed, and it may be difficult to specify the direction.
In this embodiment, a sample area of 700 square μm or more was scanned in steps of 0.05 μm, and the crystal orientation was analyzed. As analysis software, OSL version 5 (trade name) of TSL (Company) is used.

In the present invention, when the orientation is measured at an interval of 0.05 μm and the angle formed between adjacent measurement points is 1 ° or more, the boundary is defined as “the orientation difference boundary where the orientation difference in the crystal orientation distribution is 1 ° or more. ". Then, the total length of the misalignment boundary within the measurement area of 700 square μm or more (the total of all the lengths of the boundary line) is obtained, and this is divided by the measurement area to calculate the misalignment boundary length per 1 μm ² area. To do.
Note that the information obtained in the azimuth analysis by the EBSD method includes azimuth information up to a depth of several tens of nanometers at which the electron beam penetrates the sample, but is sufficiently small with respect to the measured width. Then, it is incorporated as plane information.

  Assuming that the two crystal orientations to be subjected to orientation difference analysis are x and y, the orientation relationship between them is represented by the following rotation matrix a.

The rotation angle θ _xy that is an azimuth difference can be obtained by the following equation. (For example, see Yuichi Ikuhara, “Physics of Ceramic Materials-Crystals and Interfaces”, Nikkan Kogyo Shimbun, 1999.) Normally, such calculation is performed in analysis software.

θ _xy = cos ⁻¹ {(a ₁₁ + a ₂₂ + a ₃₃ −1) / 2}

  In addition to the FE-SEM / EBSD method, a TEM / Kikuchi line analysis method may be used. This method creates a crystal orientation map by analyzing a diffraction pattern in a TEM (Transmission Electron Microscope). Similarly, the length of the orientation difference boundary having an orientation difference of 1 ° or more in the crystal orientation distribution may be obtained from this map.

As a representative example of the orientation difference boundary map of 1 ° or more, FIG. 2 shows the result of the present invention example 104, and FIG. 3 shows the result of the comparative example 303. In the example of the present invention, it can be seen that the orientation difference boundary is controlled to be short.
Moreover, the distribution with respect to the azimuth difference is shown in FIG. It can be seen that the azimuth difference boundary of 1 ° or more is suppressed to be shorter than that of the comparative example 303 (thin line) in the present invention example 104 (thick line) in all angle ranges from the low angle to the high angle.

[Alloy composition and composition]
The copper alloy rolled foil for the secondary battery current collector of the present invention contains 0.01 to 0.6% by mass in total of at least one of Cr, Zr and Ti as a main component in the copper alloy, and the balance Consists of copper and inevitable impurities. Here, inevitable impurities are generally present in raw materials in metal products and inevitably mixed in the manufacturing process, and are essentially unnecessary, but are in very small quantities and are characteristic of metal products. It is an acceptable impurity because it has no effect.
The content of at least one of Cr, Zr, and Ti is preferably 0.01 to 0.35% by mass, and more preferably 0.01 to 0.25% by mass.

  The copper alloy rolled foil of the present invention further contains 0.01 to 0.95 mass% in total of at least one of Sn, Zn, Mn, Mg, Ag, Si, P, Ni and Fe as sub-addition elements. The total content thereof is more preferably 0.01 to 0.55% by mass, and still more preferably 0.01 to 0.19% by mass.

The copper alloy rolled foil for the secondary battery current collector of the present invention contains 0.01 to 0.6% by mass of at least one of Cr, Zr and Ti, without greatly reducing the conductivity. It has the effect of improving strength and heat resistance.
When added in excess of the upper limit of the components defined in each of the above, it is dispersed as a coarse second phase in the form of oxide, precipitate, crystallized product, etc., up to a foil thickness (plate thickness) of 15 μm or less When rolling, it causes pinholes and plate breakage. In addition to this, the conductivity is significantly reduced.
On the other hand, when the total amount of Cr, Zr and Ti is added below the lower limit of the components defined above, the heat resistance is lowered, which is not preferable.

[Young's modulus against tensile stress]
In the present invention, the Young's modulus with respect to tensile stress is measured by measuring the distance between gauge points during a short-axis tensile test with a camera-type non-contact extensometer, measuring strain, and the slope of the linear portion of the elastic region in the stress-strain curve. Is measured and is defined as “Young's modulus against tensile stress”. The camera-type non-contact extensometer uses DVE-201 (trade name) manufactured by Shimadzu Corporation. The elongation is measured by automatically tracking the mark mark from the CCD camera image. The test piece has a strip shape with a width of 13 mm.
Test specimens are taken in three directions of 0 °, 45 °, and 90 ° with respect to the rolling direction, and Young's modulus with respect to tensile stress is measured to obtain three average values (denoted as Eave).

  The preferred range of Young's modulus (average value) for the tensile stress of the copper alloy rolled foil of the present invention is 127 GPa or less, more preferably 120 GPa or less, still more preferably 113 GPa or less, and most preferably 108 GPa or less. is there. The lower limit of the Young's modulus (average value) with respect to tensile stress is not particularly limited, but is preferably 70 GPa or more, and more preferably 80 GPa or more.

[0.2% yield strength after holding at 350 ° C. for 1 hour]
In the present invention, the 0.2% proof stress after being held at 350 ° C. for 1 hour is preferably 400 MPa or more, more preferably 440 MPa or more, and further preferably 510 MPa or more. Although an upper limit is not specifically limited, Preferably it is 700 MPa or less, More preferably, it is 650 MPa or less.

[Manufacturing method for controlling misalignment boundaries]
The manufacturing method for controlling to the condition of the misalignment boundary found to be effective in the embodiment of the present invention will be described. As described above, in the foil after rolling, if the length of the boundary line of the misorientation boundary having an misorientation of 1 ° or more is 1 μm ² per 1 μm ² and less than 10 μm, the production thereof The method is not particularly limited.

The production method of the present invention contains 0.01 to 0.6% by mass of at least one of Cr, Zr and Ti, and the balance has an alloy composition consisting of copper and inevitable impurities, or contains the subcomponents. In the case of containing 0.01 to 0.6% by mass of at least one of Cr, Zr and Ti, and at least one of Sn, Zn, Mn, Mg, Ag, Si, P, Ni and Fe. In an ingot obtained by melting (step 1) and casting (step 2) a copper alloy having an alloy composition of 0.01 to 0.95% by mass with the balance being copper and inevitable impurities. Homogenization heat treatment (step 3) at 10-30 ° C. for 5 minutes to 4 hours, high temperature rolling 1 (step 4) with a processing rate of 60-95% at a temperature of 700-1030 ° C., and a cooling rate of 6 ° C./min. Intermediate cooling (6000 ° C / min) 5), high temperature rolling 2 (step 6) with a processing rate of 40 to 80% at 300 to 700 ° C., cooling at a cooling rate of 6 ° C./min to 6000 ° C./min (step 7), and face milling (step 7). Step 8), intermediate cold rolling (Step 9) at a processing rate of 90 to 96% at 0 to 150 ° C., heat treatment at 300 to 600 ° C. for 0.5 to 5 hours (Step 10), and 0 to 150 It consists of finish foil rolling (step 11) at a processing rate of 66 to 95% at ° C.
With the manufacturing method through such steps, the length of the boundary line of the misorientation boundary where the misorientation in the crystal orientation distribution of the rolled surface is 1 ° or more can be 1 μm per 1 μm ² and shorter than 10 μm. Become.

As a preferred method for producing a copper alloy rolled foil for controlling the misalignment boundary, steps 1 to 11 are basic steps as shown in the process illustrated in FIG.
Below, step 1-11 based on FIG. 1 is demonstrated in order.
Note that the conditions of Step 6 and Step 10 and combinations of these conditions are important.

<Step 1>
Step 1 is a process of melting a copper alloy having a predetermined alloy composition. A copper alloy material is prepared and melted so as to contain 0.01 to 0.6% by mass of copper as a base material and at least one of Cr, Zr and Ti contained in the copper alloy. If necessary, further, at least one of Sn, Zn, Mn, Mg, Ag, Si, P, Ni and Fe is added and dissolved so as to contain 0.01 to 0.95 mass% in total.
Specifically, the above components are used as raw materials and melted in a vacuum melting furnace at a temperature of 1100 to 1300 ° C. over 1 to 10 hours.

<Step 2>
Step 2 is a casting process. In this process, the melted raw material is cooled and cast at a cooling rate of 0.1 to 100 ° C./second, for example, to obtain an ingot (regardless of shape). Thereby, the components in the copper alloy are finally determined.

<Step 3>
Step 3 is a homogenization heat treatment step. This is a step of holding at 900 to 1030 ° C. for 5 minutes to 4 hours. Additive components are sufficiently homogeneously dispersed in the copper alloy matrix to reduce segregation in the casting process.

<Step 4>
Step 4 is a process of performing the first high temperature rolling (high temperature rolling 1). In this step, the material subjected to the homogenization heat treatment in Step 3 is subjected to the high temperature rolling 1 in which the processing rate becomes a specific value, for example, 60 to 95%, in Step 4. Here, high temperature rolling means rolling at a temperature of 700 to 1030 ° C.

<Step 5>
Step 5 is a process of performing intermediate cooling. Cooling methods include water cooling, air cooling, gas cooling and the like. The cooling rate is preferably 6 ° C./min to 6000 ° C./min. What is necessary is just to cool to the processing temperature of step 6.

<Step 6>
Step 6 is a process of performing the second high temperature rolling (high temperature rolling 2).
The processing temperature is 300 ° C to 700 ° C, preferably 350 ° C to 650 ° C. The total processing rate in this temperature range is 40 to 80%. The processing temperature is measured with a radiation thermometer on the upper surface of the material before and after the pass. By processing in a temperature range where the frequency of dynamic recrystallization decreases, randomization of crystal orientation is prevented.
When the temperature is higher than this, the orientation is randomized, and when the temperature is lower than this, edge cracks occur, which is not preferable. If it is less than this total processing rate, the effect is insufficient, and if it is high, cracks on the rolling surface occur, which is not preferable.

<Step 7>
Step 7 is a cooling process. Cooling methods include water cooling, air cooling, gas cooling and the like. The cooling rate is preferably 6 ° C./min to 6000 ° C./min. The cooling rate is more preferably 60 ° C./min to 4500 ° C./min, more preferably 120 ° C./min to 3000 ° C./min.

<Step 8>
Step 8 is a process for chamfering. This is a general process for chamfering to remove oxide scale. Specifically, in order to remove oxides on the surface, surface roughness, etc., the surface is chamfered with a normal chamfering machine. Although there is no restriction | limiting in particular in the surface cutting rate of the one-side surface, Usually, it shall be 0.1-3.0 mm.

<Step 9>
Step 9 is an intermediate cold rolling process. The processing rate is not particularly limited, but is, for example, 90 to 96%. The temperature at the time of the cold rolling step is usually 0 ° C to 150 ° C, preferably 5 ° C to 100 ° C.

<Step 10>
Step 10 is a heat treatment process.
The heat treatment temperature is 300 to 600 ° C, preferably 310 to 550 ° C, more preferably 350 to 550 ° C, and still more preferably 350 to 500 ° C. The heat treatment time is preferably 0.5 to 5 hours. This heat treatment is preferably performed by a batch annealing method.
A temperature lower than 300 ° C. or a holding time of less than 0.5 hours is not preferable because recrystallization is insufficient. If the temperature exceeds 600 ° C. or the holding time is 5 hours or longer, the crystal grains are coarsened and the strength is lowered.
When the heat treatment temperature is 300 ° C., the treatment time is preferably 1 to 5 hours.
Coupled with the effect of step 6 above, the recrystallized texture formed during the heat treatment can suppress the formation of misorientation boundaries during foil rolling.

<Step 11>
Step 11 is a finish foil rolling process, which is a final cold rolling process. The processing rate is not particularly limited, but is set to 66 to 95%, for example. The temperature at the time of the cold rolling step is usually 0 ° C to 150 ° C, preferably 5 ° C to 100 ° C.
In this step, the final thickness of the foil is adjusted.

In the present invention, low temperature annealing (step 12) may be performed after the finish foil rolling (step 11).
The low temperature annealing (step 12) is preferably performed at a temperature of 200 to 600 ° C. for 0.1 to 20 hours. If the heat treatment conditions are not satisfied, particularly when the heat history is high and / or long, the desired metal structure obtained up to the previous step 11 is changed, and the predetermined metal structure and physical properties are changed. It may not be obtained.

[Foil thickness]
The copper alloy rolled foil of the present invention is used for a secondary battery assembly, and for the purpose of improving the energy density of the battery, a copper foil having a thickness of 15 μm or less is particularly targeted, but a copper foil thicker than 15 μm is used. It is also possible to apply. Specifically, the copper foil of the present invention can be applied to those having a thickness of about 5 to 25 μm. In addition, although the minimum of thickness is not specifically limited, Preferably it is 1 micrometer or more, and 5 micrometers or more are more preferable.

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited thereto.

[Manufacturing method of copper alloy rolled foil]
The Example of the manufacturing method of the copper alloy rolled foil for secondary battery collectors concerning this embodiment is demonstrated with reference to FIG. The present invention is not limited to this.

  In Step 1, the raw material was melted in a vacuum melting furnace, and in Step 2, the melted raw material was cooled and cast at a cooling rate of 0.1 to 100 ° C./second to obtain an ingot. The ingot contained the alloy components shown in Table 2 below, and the remainder was formed of inevitable impurities.

In step 3, homogenization heat treatment was performed at 900 to 1030 ° C. for 5 minutes to 4 hours, and in step 4, high temperature rolling 1 with a processing rate of 60 to 95% was performed. Next, after cooling to the processing temperature of step 6 in step 5, high-temperature rolling 2 of step 6 was performed under the conditions shown in Table 1 below. Next, water cooling was performed in Step 7, chamfering was performed for removing oxide scale in Step 8, and intermediate cold rolling with a processing rate of 90 to 96% was sequentially performed in Step 9.
After Step 9, the heat treatment of Step 10 was performed under the manufacturing conditions shown in Table 1 below. In addition, when this heat processing temperature was 300 degreeC, time adjustment was carried out in the range of 1 hour-5 hours.
Next, in step 11, final cold rolling with a processing rate of 66 to 95% was performed to prepare a test material of copper alloy rolled foil having a thickness of 8 to 15 μm.
Among these rolled copper alloy foils, Examples 112 and 113 of the present invention and Comparative Example 305 were further subjected to low temperature annealing at a temperature of 200 to 600 ° C. for 0.1 to 20 hours as Step 11.

The compositions and properties of these inventive examples 101 to 113 and comparative examples 201 to 204 and 301 to 305 are as shown in Table 2.
After each heat treatment and rolling, acid cleaning and surface polishing were performed according to the state of oxidation and roughness of the material surface, and correction with a tension leveler was performed according to the shape. Moreover, the processing temperature in high temperature rolling 1 (step 4) and high temperature rolling 2 (step 6) was measured with the radiation thermometer installed in the entrance side and exit side of a rolling mill.

As described above, as shown in Table 2, in the inventive examples 101 to 113 and the comparative examples 201 to 204, the high temperature rolling 1 (step 6) and the heat treatment (step 10) are performed according to the manufacturing condition A described in the table 1. It went and produced the test material of copper alloy rolled foil. On the other hand, in Comparative Examples 301 to 305, copper alloy rolled foil specimens were produced in the same manner as the inventive examples except that the production conditions H to L described in Table 1 were used.
The following evaluation was performed about each obtained copper alloy rolled foil.

[Length of boundary line of misorientation boundary: (MBL (Missional Boundary Length) before heating))]
By using the FE-SEM / EBSD method, the rolling area of the 700 square μm sample after foil rolling was measured by scanning from the rolling surface in steps of 0.05 μm, and the orientation difference boundary was analyzed. Then, the length of the boundary line of the misorientation boundary per unit area (1 μm ² ) of the observation sample was obtained.
That is, in the state after foil rolling, it measured from the rolling surface by the method mentioned above by EBSD method. The length of the boundary line of the misalignment boundary having a misorientation of 1 ° or more was measured, and it was divided by the measurement area and converted per unit area. In the case where the pattern was not clear because the work-affected layer on the rolled surface was thick, the measurement was performed after the electropolishing time was lengthened and the surface layer was melted around 1 μm thick.

  The analysis software used was OSL version 5 (trade name) of TSL. When an electron beam scans on a misorientation boundary (for example, a grain boundary), diffraction occurs from the regions (crystals) on both sides of the boundary (grain boundary), and diffraction corresponding to a state where two crystal orientations coexist. It becomes a pattern. In that case, the conventional EBSD method may misrecognize a completely different azimuth. When the density of misorientation boundaries is high as in the present invention, special attention should be paid to this effect. In this measurement, the crystal orientation of such a scanning point with low reliability was replaced with the orientation of the adjacent scanning point with high reliability. As a threshold value with sufficient reliability, the CI value (Confidence Index) of the software is 0.05 or more.

FIG. 2 shows the results of Example 104 of the present invention and FIG. 3 shows the results of Comparative Example 303 for the orientation difference boundary map of 1 ° or more. The black line in the map represents the misalignment boundary. Such a boundary appears in a hexagonal shape because analysis by the FE-SEM / EBSD method is performed by scanning with a step of 0.05 μm and one pixel is displayed in a hexagonal shape. Comparing FIG. 2 and FIG. 3, it can be seen that the orientation difference boundary is formed short in the result of FIG.
FIG. 4 shows the distribution of the length of the orientation difference boundary per unit area for the inventive example 104 and the comparative example 303. It can be seen that the azimuth difference boundary of 1 ° or more is suppressed to be shorter than that of the comparative example 303 (thin line) in the present invention example 104 (thick line) in all angle ranges from the low angle to the high angle.

[Average value of Young's modulus against tensile stress: (Eave before heating)]
Using a camera-type non-contact extensometer, the distance between the gauge points during the uniaxial tensile test was measured, and the strain was measured. The slope of the linear portion of the elastic region in the collected stress-strain curve was measured and taken as the Young's modulus for the tensile stress. As the camera-type non-contact extensometer, DVE-201 (trade name) manufactured by Shimadzu Corporation was used. The elongation is measured by automatically tracking the mark mark from the CCD camera image. The test piece was strip-shaped with a width of 13 mm.
Test pieces were sampled in three directions of 0 °, 45 °, and 90 ° with respect to the rolling direction, and the Young's modulus with respect to the tensile stress was measured, and an average value thereof was obtained.
In addition, a pass level is 127 GPa or less.

[Conductivity after rolling: (EC before heating)]
The electrical conductivity (% IACS) of each copper alloy foil after foil rolling was measured by a four-terminal method at room temperature.

[Length of misalignment boundary after heating to 350 ° C .: (MBL after heating)]
The sample after rolling was subjected to a heat treatment that was held at 350 ° C. for 1 hour in an argon (Ar) atmosphere, and then measured by the FE-SEM / EBSD method in the same manner as before heating.
Incidentally, pass level is 1 [mu] m or more per 1 [mu] m ^2.

[0.2% yield strength after heating to 350 ° C .: (YS after heating)]
After performing a heat treatment held at 350 ° C. for 1 hour in an Ar atmosphere, it was measured by a tensile test in the rolling parallel direction according to JIS Z2241.
In order to set the boundary between elastic deformation and plastic deformation for the sake of convenience, the stress corresponding to the yield stress is taken as the proof stress, and the permanent strain at yield of steel is about 0.2% (0.002). The stress at which the permanent set is 0.2% is called 0.2% proof stress.
In addition, a pass level is 400 Mpa or more.

  FIG. 5 shows the relationship of heat resistance (softening curve). In FIG. 5, the relationship of 0.2% yield strength with respect to heating temperature is plotted, and it showed together about the copper alloy rolled foil of this invention example 106 and the comparative example 204. FIG.

[Battery evaluation, discharge capacity maintenance rate]
(I) Positive electrode Using Li ₂ CO ₃ and CoCO ₃ as starting materials, weigh them so that the atomic ratio of Li: Co is 1: 1, mix in a mortar, press this with a mold and pressurize After molding, it was fired in air at 800 ° C. for 24 hours to obtain a LiCoO ₂ fired body. This was pulverized in a mortar to prepare an average particle size of 20 μm.
90 parts by mass of the obtained LiCoO ₂ powder, 5 parts by mass of artificial graphite powder as a conductive agent, and a 5% by mass N-methylpyrrolidone solution containing 5 parts by mass of polyvinylidene fluoride as a binder were mixed, and a positive electrode mixture A slurry was obtained.
This positive electrode mixture slurry was applied onto an aluminum foil as a current collector, dried and then rolled. The obtained product was cut out to obtain a positive electrode.

(Ii) Negative electrode 8.6% by mass of N-methyl containing 80.2 parts by mass of silicon powder (purity 99.9%) having an average particle diameter of 3 μm as an active material and 19.8 parts by mass of polyamic acid as a binder. It mixed with the pyrrolidone solution and it was set as the negative mix slurry.
This negative electrode mixture slurry was applied to the copper alloy rolled foils produced in the respective Examples and Comparative Examples which were current collectors, dried, and then rolled. This was heat-treated at 400 ° C. for 30 hours in an argon atmosphere and sintered to obtain a negative electrode.

(Iii) Battery assembly As an electrolytic solution, a solution obtained by dissolving 1 mol / liter of LiPF ₆ in an equal volume mixed solvent of ethylene carbonate and diethylene carbonate was prepared. A lithium secondary battery was produced using the positive electrode, the negative electrode, and a commercially available electrolyte solution.
The positive electrode and the negative electrode were opposed via a separator.

(Iv) Evaluation of battery characteristics The charge / discharge cycle characteristics of the lithium secondary battery prepared above were evaluated. Each battery was charged to 4.2 V at a current value of 1 mA at 25 ° C., and then discharged to 2.75 V at a current value of 1 mA. The discharge capacity after 50 cycles was measured as the discharge capacity retention rate with respect to the discharge capacity at the first cycle.

  Table 2 shows the measurement results.

As shown in Table 2, the comparative example 201 having a Cr content of less than 0.01% by mass and the comparative example 204 not containing Cr, Zr or Ti have the length of the boundary line of the misalignment boundary before heating ( MBL) each 5.2 .mu.m / [mu] m ^2, was 7.5 [mu] m / [mu] m ^2, although within the scope of the present invention, any short length of the border of misorientation boundary after heating (MBL) is 0 .2% yield strength (YS) is inferior and maintenance rate in battery evaluation is low. On the other hand, in Comparative Example 202 in which the total content% of Cr and Zr exceeds 0.6% by mass, and in Comparative Example 203 in which the subcomponent Sn is as high as 0.97% by mass, the plate was cut, so the processing was stopped. did.

On the other hand, in Comparative Examples 301 to 305, the alloy composition and the content of each component satisfy the scope of the present invention, but in each of Comparative Examples 301 to 304, the length of the misalignment boundary before the heating (MBL) is 10 μm / and the [mu] m ² or more, Comparative example 305 was less than 1 [mu] m / [mu] m ^2, in order to adjust the length of the misorientation boundary before heating (MBL) 1μm / μm ² or more and less than 10 [mu] m / [mu] m ^2, step 6 It can be seen that the combination of the process conditions of step 10 and step 10 is important.

  Comparative Examples 301 to 304 were inferior in average value (Eave) of Young's modulus with respect to tensile stress before heating. Further, Comparative Examples 301 and 305 have a short boundary line length (MBL) after heating, and Comparative Examples 303 and 304 have a long boundary line boundary (MBL) after heating. Of these, Comparative Examples 303 and 305 were inferior in 0.2% yield strength (YS) after heating. Moreover, all of Comparative Examples 301 to 305 had a low maintenance rate in battery evaluation.

  On the other hand, Examples 101 to 113 of the present invention are all excellent in average value (Eave) of Young's modulus with respect to tensile stress before heating and 0.2% proof stress (YS) after heating, and the conductivity is All were 50% IACS or more. Moreover, the discharge capacity retention rate after 50 cycles, which is battery characteristics, was as high as 30% or more.

Claims (6)

It is a copper alloy rolled foil containing at least one of Cr, Zr and Ti in a total amount of 0.01 to 0.6% by mass, and the balance consisting of copper and inevitable impurities,
The copper for a secondary battery current collector, characterized in that in the crystal orientation distribution on the rolling surface, the length of the boundary line of the orientation difference boundary having an orientation difference of 1 ° or more is 1 μm ² or more and less than 10 μm per 1 μm ² Alloy rolled foil. Containing at least one of Cr, Zr and Ti in a total of 0.01 to 0.6 mass%, Sn 0.72 mass% or less , Zn 0.21 mass% or less , Mn 0.03 mass% or less , Mg 0.03% by mass or less , Ag 0.04% by mass or less , Si 0.17% by mass or less , P 0.03% by mass or less , Ni 0.70% by mass or less, and Fe 0.15% by mass or less . It is a copper alloy rolled foil containing at least one kind in a total of 0.01 to 0.95 mass%, with the balance being made of copper and inevitable impurities,
The copper for a secondary battery current collector, characterized in that in the crystal orientation distribution on the rolling surface, the length of the boundary line of the orientation difference boundary having an orientation difference of 1 ° or more is 1 μm ² or more and less than 10 μm per 1 μm ² Alloy rolled foil. The length of the boundary line of the misorientation boundary having an orientation difference of 1 ° or more in the crystal orientation distribution of the rolled surface after the heat treatment held at 350 ° C for 1 hour is 1 µm or more per 1 µm ^2. Or a copper alloy rolled foil for a secondary battery current collector according to 2; A method for producing a copper alloy rolled foil for a secondary battery current collector, comprising:
A copper alloy material having an alloy composition of at least one of Cr, Zr and Ti in a total content of 0.01 to 0.6% by mass and the balance consisting of copper and inevitable impurities is melted (step 1) and cast. The ingot obtained by (Step 2) is subjected to a homogenization heat treatment (Step 3) at 900 to 1030 ° C. for 5 minutes to 4 hours, and hot rolling 1 at a temperature of 700 to 1030 ° C. and a processing rate of 60 to 95%. (Step 4), intermediate cooling (Step 5) with a cooling rate of 6 to 6000 ° C./min, high temperature rolling 2 (Step 6) with a processing rate of 40 to 80% at 300 to 700 ° C., and a cooling rate of 6 to 6000 C / min cooling (step 7), chamfering (step 8), intermediate cold rolling (step 9) with a working rate of 90 to 96% at 0 to 150 ° C., and 0.5 at 300 to 600 ° C. Heat treatment (step 10) for 5 hours and 0-150 In machining rate by applying a 66 to 95% of the finishing foil rolling (step 11),
In the crystal orientation distribution of the rolled surface, a secondary copper alloy foil having a length of a boundary line of an orientation difference boundary having an orientation difference of 1 ° or more is 1 μm ² per 1 μm ² and shorter than 10 μm is obtained. A method for producing a copper alloy rolled foil for a battery current collector. A method for producing a copper alloy rolled foil for a secondary battery current collector, comprising:
Containing at least one of Cr, Zr and Ti in a total of 0.01 to 0.6 mass%, Sn 0.72 mass% or less , Zn 0.21 mass% or less , Mn 0.03 mass% or less , Mg 0.03% by mass or less , Ag 0.04% by mass or less , Si 0.17% by mass or less , P 0.03% by mass or less , Ni 0.70% by mass or less, and Fe 0.15% by mass or less . Obtained by melting (step 1) and casting (step 2) a copper alloy material having an alloy composition containing at least one kind in total of 0.01 to 0.95% by mass and the balance consisting of copper and inevitable impurities The ingot is subjected to homogenization heat treatment (step 3) at 900 to 1030 ° C. for 5 minutes to 4 hours, high temperature rolling 1 (step 4) with a processing rate of 60 to 95% at a temperature of 700 to 1030 ° C., and a cooling rate. Intercooling at 6 to 6000 ° C / min 5), high temperature rolling 2 (step 6) with a processing rate of 40 to 80% at 300 to 700 ° C., cooling at a cooling rate of 6 to 6000 ° C./min (step 7), and face milling (step 8). Intermediate cold rolling (step 9) with a processing rate of 90 to 96% at 0 to 150 ° C., heat treatment for 0.5 to 5 hours at 300 to 600 ° C. (step 10), and processing at 0 to 150 ° C. Finish foil rolling (step 11) with a rate of 66-95%,
In the crystal orientation distribution of the rolled surface, a secondary copper alloy foil having a length of a boundary line of an orientation difference boundary having an orientation difference of 1 ° or more is 1 μm ² per 1 μm ² and shorter than 10 μm is obtained. A method for producing a copper alloy rolled foil for a battery current collector. 6. The secondary battery current collector according to claim 4, wherein low-temperature annealing (step 12) is performed at 200 to 600 ° C. for 0.1 to 20 hours after the finish foil rolling (step 11). 7. Method for producing copper alloy rolled foil.

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