JP5654911B2 - Rolled copper foil for lithium ion secondary battery current collector - Google Patents

Description

  The present invention relates to a rolled copper foil for a lithium ion secondary battery current collector having resin adhesion suitable for a current collector of a lithium ion secondary battery.

  Lithium ion secondary batteries are used as batteries for electronic devices such as mobile personal computers and portable terminals because they can obtain high voltage and have high energy density. In addition, research and development are actively conducted as driving batteries for hybrid vehicles and electric vehicles.

  This lithium ion secondary battery is based on a mechanism in which charging and discharging are repeated by moving lithium ions in an electrolyte between a positive electrode plate and a negative electrode plate insulated by a separator. It is important to find materials for electrolytes, separators, positive plates, and negative plates that can realize this mechanism with high cycle characteristics.

  A negative electrode plate used for a lithium ion secondary battery is generally composed of a negative electrode current collector made of copper foil and a negative electrode active material layer formed on the current collector. The copper foil constituting this negative electrode current collector is produced by electrodepositing metal copper from a rolled copper foil produced by casting a thick strip produced by casting or an electrolytic solution containing copper ions. Electrolytic copper foil is used. This rolled copper foil is characterized in that the copper crystal structure of the copper foil or copper alloy foil can be controlled by combining rolling and heat treatment.

  The negative electrode active material layer formed on the surface of the copper foil is formed with a film thickness of about 100 μm. This negative electrode active material layer is obtained by adding carbon particles such as artificial graphite, natural graphite, or coke together with a binder such as polyvinylidene fluoride (PVdF) and a conductive additive to a solvent such as N-methyl 2-pyrrolidone (NMP). After mixing to make a slurry, this is applied to the surface of the copper foil and dried and solidified.

  In lithium-ion secondary batteries, when charging and discharging are repeated, carbon easily peels from the copper foil due to the expansion and contraction of carbon particles accompanying the insertion and extraction of lithium, and the short-circuit battery capacity between electrodes and cycle characteristics deteriorate. May be incurred. For this reason, as copper foil for negative electrode collectors, the high adhesiveness with the carbon which comprises a negative electrode active material layer is requested | required. The adhesion with carbon can be improved to some extent if the binder ratio in the slurry is increased, but it is not an effective means because the conductivity of the electrode is lowered.

  Therefore, in order to solve this problem, a roughening process for forming irregularities on the surface of the copper foil is performed. As a method of this roughening treatment, methods such as blasting, rolling with a rough surface roll, mechanical polishing, electrolytic polishing, chemical polishing, and plating of electrodeposited grains are known, and among these, electrodeposited grains are particularly preferable. Is often used.

  However, non-uniform and high-roughness roughened particles, on the contrary, have a poor anchoring effect, and high adhesion cannot be obtained between the negative electrode current collector and the negative electrode active material. Therefore, a technique of performing a plurality of plating treatments and reflow treatments has been taken in order to give a rough structure on the surface of the copper foil with low-roughness roughening particles (see, for example, Patent Document 1). .

2009-87561

  However, since the method described in Patent Document 1 is expensive, it leads to an increase in the price of the lithium ion secondary battery, which hinders the general spread of the lithium ion secondary battery to electronic devices and electric vehicles.

  The objective of this invention is providing the rolled copper foil for lithium ion secondary battery electrical power collectors which improved the adhesiveness with resin stably and efficiently.

  The inventors of the present invention conducted an eager study to achieve the above object, and found that there was a certain correlation between the orientation and orientation state of the crystal grains on the rolled surface in the rolled copper foil and the resin adhesion of the copper foil. If used, it becomes clear that the resin adhesion of the copper foil is increased without subjecting the copper foil surface to a roughening treatment such as plating of electrodeposited grains, and an unexpected result can be obtained. I learned that an excellent product that does not cause problems can be formed.

[1] That is, the present invention is an element group consisting mainly of Cu and consisting of Cr, Zr, Sn, Mg, Ag, Fe, Co, Ni, Zn, Ti, Si, B, Bi, Sb, and Mn. a copper alloy composition containing and one or more additive elements and inevitable impurities selected from among diffraction peak intensity of {220} _Cu direction of the copper crystals obtained by the X-ray diffraction 2 [theta] / theta measured I _{{220 } To} {200} _Cu- direction diffraction peak intensity I _{200} is a rolled copper foil for a lithium ion secondary battery current collector, characterized in that I _{220} / I _{200} > 2. is there.

[2] The diffraction peak in the {220} _Cu direction of the copper crystal obtained by X-ray diffraction 2θ / θ measurement after heating at a temperature of 200 ° C. or less for 1 minute to 20 hours in the invention according to [1] above The ratio between the intensity I _{220} and the diffraction peak intensity I _{{200} in the} {200} _Cu direction is I _{220} / I _{200} > 2.

[3] In the invention described in [1] or [2] above, the total amount of the additive elements is 0.5% by weight or less.

[4] The invention according to any one of [1] to [3] above, wherein the rolled copper foil for a lithium ion secondary battery current collector has a thickness of 20 μm or less.

  ADVANTAGE OF THE INVENTION According to this invention, the adhesiveness with resin is favorable and the rolled copper foil for lithium ion secondary battery collectors which can be implement | achieved stably and efficiently is obtained.

It is a flowchart which shows the flow of the manufacturing process of the copper alloy foil for lithium ion secondary battery electrical power collectors which concerns on suitable embodiment of this invention. It is the schematic which shows the relationship of the incident X-ray in X-ray diffraction, a detector, a sample, and a scanning axis. {200} It is a figure which shows typically the atomic arrangement | sequence of the rolling surface at the time of _Cu surface orientation. It is a figure which shows typically the atomic arrangement | sequence of the rolling surface at the time of {220} _Cu surface orientation. It is a figure which shows typically an example of the preparation procedures of a peel test piece.

  Preferred embodiments of the present invention will be specifically described below with reference to the accompanying drawings.

(Rolled copper foil components)
The rolled copper foil in this embodiment is suitably used as a material for a lithium ion secondary battery current collector. This rolled copper foil has Cu (copper) as a parent phase, Cr (chromium), Zr (zirconium), Sn (tin), Mg (magnesium), Ag (silver), Fe (iron), Co (cobalt), Selected from the element group consisting of Ni (nickel), Zn (zinc), Ti (titanium), Si (silicon), B (boron), Bi (bismuth), Sb (antimony), and Mn (manganese) A basic composition component includes one or more additive elements and the balance of inevitable impurities. As Cu, tough pitch copper or oxygen-free copper can be used.

(About more preferable upper limit value of additive element)
The total amount of one or more additional elements selected from the element group consisting of Cr, Zr, Sn, Mg, Ag, Fe, Co, Ni, Zn, Ti, Si, B, Bi, Sb, and Mn is 0. It is preferable that the amount be 5% by weight or less. Even if the total amount of these additive elements is more than 0.5% by weight, there is no further effect of improving the heat resistance.

  Furthermore, since resistance increases when adding more than 0.5 weight%, it causes deterioration of the characteristics of the lithium ion secondary battery such as the discharge rate characteristics of the lithium ion secondary battery manufactured using this copper foil. There is a fear.

(About more preferable lower limit value of additive element)
Among these additive elements, the content of Cr, Zr, Sn, Ag, Ti, and Sb is preferably set to 0.02% by weight or more. When the content of these additive elements is less than 0.02% by weight, sufficient heat resistance cannot be obtained.

  On the other hand, the contents of Mg, Fe, Co, Ni, Zn, Si, B, Bi, and Mn are more preferably set to 0.1% by weight or more. This is because when these additive elements are less than 0.1% by weight, the heat resistance may be lowered.

  The thickness of the rolled copper foil is preferably 20 μm or less. The lithium ion secondary battery manufactured using the rolled copper foil having a thickness of the rolled copper foil exceeding 20 μm has a large volume ratio occupied by the rolled copper foil and cannot be sufficiently filled with the negative electrode active material. Therefore, the volume energy density may be lowered, which is not preferable.

(Method for producing rolled copper foil)
Referring to FIG. 1, FIG. 1 shows a typical manufacturing process for manufacturing a rolled copper foil according to this embodiment. The process of manufacturing this rolled copper foil includes a series of a melting process, a hot rolling process, a cold rolling process, an intermediate annealing process, a dough annealing process, a final cold rolling process (finish rolling process), and a negative electrode plate manufacturing process. (Steps 100 to 106, hereinafter, steps are referred to as “S”). By carrying out the treatment in order in these steps, the initial intended rolled copper foil can be obtained effectively.

(Melting process)
In this melting step, an element group consisting of Cu and 0.5 wt% or less of Cr, Zr, Sn, Mg, Ag, Fe, Co, Ni, Zn, Ti, Si, B, Bi, Sb, and Mn One or more additive elements selected from the above are melted using a melting furnace to produce an ingot (ingot) that becomes a copper alloy material (S100 in FIG. 1).

(Hot rolling process)
In this hot rolling step, the ingot is hot rolled at a predetermined temperature to form a plate material (S101 in FIG. 1).

(Cold rolling process, intermediate annealing process, and dough annealing process)
In this cold rolling step and intermediate annealing step, cold rolling and intermediate annealing that alleviates work hardening by cold rolling are appropriately repeated on the plate after hot rolling (S102 to S104 in FIG. 1). . Thereby, a copper strip called “dough” is manufactured. In this dough annealing process, it is desirable that the processing strain before the dough annealing process is sufficiently relaxed.

(Final cold rolling process)
In this final cold rolling process, a finish rolling process is performed on the annealed material (S105 in FIG. 1). Thereby, the rolled copper foil (finished copper foil) of predetermined thickness is manufactured. The total degree of processing is preferably 85% or more and less than 95%. Thereby, the total number of passes of a rolling process can be reduced with respect to the conventional high workability rolling copper foil. In addition to this, it is possible to avoid the difficulty of controlling the rolling process due to excessive work hardening, and to contribute to reducing the load on the manufacturing facility and reducing the manufacturing cost. It is possible to achieve both high resin adhesion and reduced cost in the rolled copper foil.

(Negative electrode plate manufacturing process)
The rolled copper foil after the final cold rolling process produces the next negative electrode plate without performing a roughening treatment such as plating of electrodeposited grains. In this negative electrode plate manufacturing process, for example, a heat treatment at 100 to 200 ° C. is performed in a drying process after application of the negative electrode active material and a drying process after incorporation of the lithium ion secondary battery (S106 in FIG. 1).

In the manufacturing method of the rolled copper foil, a copper crystal obtained by X-ray diffraction 2θ / θ measurement immediately after the final cold rolling step or after that is heated at a temperature of 200 ° C. or lower for 1 minute to 20 hours. Of {220} _Cu direction diffraction peak intensity I _{220} and {200} _Cu direction diffraction peak intensity I _{200} (hereinafter referred to as “diffraction intensity ratio”) is I _{220} / I _{{ 200}} > 2 is important to control. Here, I _{220} and I _{200} are the X-ray diffraction intensities of the {220} crystal plane and {200} crystal plane in the rolled surface of the rolled copper foil.

In the final cold rolling step, by performing cold rolling at a high workability of 85% or more and less than 95%, in the state immediately after the final cold rolling step, the rolled surface of the copper foil has a {220} _Cu surface. The orientation is strong and the orientation of the {200} _Cu plane is weak, and the upper limit of the diffraction intensity ratio is not particularly limited, but the relationship of the diffraction intensity ratio I _{220} / I _{200} > 2 is satisfied. More preferably, it is desirable to satisfy the relationship of the diffraction intensity ratio I _{220} / I _{200} > 5. This orientation can be determined by an X-ray diffraction method such as the θ-2θ method.

Referring to FIG. 2, FIG. 2 shows the relationship among incident X-rays, detectors, samples, and scanning axes in X-ray diffraction. In the X-ray diffraction apparatus, the θ axis is generally called a sample axis. The measurement in which the sample 1 and the detector 2 are scanned with the θ axis with respect to the incident X-ray, the scanning angle of the sample 1 is scanned with θ, and the scanning angle of the detector 2 with 2θ is referred to as 2θ / θ measurement. It is possible to evaluate which crystal plane is dominant in the sample surface (rolled surface) of the rolled copper foil which is a polycrystal by the intensity of the diffraction peak by the 2θ / θ measurement. Since the crystal structure of copper is cubic, the angle formed by the {200} _Cu face and the {220} _Cu face is 45 °. “{}” Represents an equivalent surface.

As described above, this rolled copper foil is selected from the element group consisting of Cr, Zr, Sn, Mg, Ag, Fe, Co, Ni, Zn, Ti, Si, B, Bi, Sb, and Mn. The heat resistance can be improved by adding the total amount of one or more additional elements at 0.5% by weight or less. Therefore, even in the state after heating for 1 minute to 20 hours at a temperature of 200 ° C. or lower after the final cold rolling step, orientation in the {200} _Cu direction hardly occurs, and the diffraction intensity ratio I _{220} / I _{{ 200}} > 2 is satisfied.

In the final cold rolling process, by obtaining a stronger orientation in the rolling texture {220} _Cu direction, it was heated immediately after or after the final cold rolling process at a temperature of 200 ° C. for 1 minute to 20 hours. Even in the state, orientation in the {200} _Cu direction hardly occurs on the rolled surface, and a rolled copper foil having good resin adhesion characteristics can be stably obtained.

(Discussion on the mechanism of high resin adhesion)
Depending on the orientation and orientation state of the crystal grains on the rolled surface in the rolled copper foil, the state of atomic arrangement seen on the copper foil surface varies, and the interatomic distance on the copper foil surface changes. On the {220} _Cu plane, as shown in FIG. 3, atoms are arranged at a distance between the closest points in a certain direction and a direction perpendicular thereto. On the other hand, on the {200} _Cu plane, as shown in FIG. 4, atoms are arranged at a distance between nearest neighbors in a certain direction and at a distance between next neighbors in a direction perpendicular thereto.

  The resin applied to the copper foil surface is solidified on the copper foil surface in a stable state determined by the atomic force between the atoms on the copper foil surface and the atoms constituting the resin, and the intermolecular force between the resins. It is thought.

  Therefore, by improving the matching between the specific periodic molecular structure of the resin, which is an organic compound, and the interatomic distance of the copper foil surface, the stable state of the resin solidified on the copper foil surface can be improved. It is considered that the stability can be further improved, and the resin adhesion of the copper foil is improved.

  Hereinafter, examples and comparative examples will be described in detail as more specific embodiments of the present invention. In addition, in this Example, a typical example of the rolled copper foil which is the said embodiment is given, and it is needless to say that the present invention is not limited to these Examples and Comparative Examples.

The rolled copper foil of Examples 1 to 15 and the rolled copper foil of Comparative Examples 1 to 4 were produced without performing a roughening treatment such as plating of electrodeposited grains, and the obtained rolled copper foil was compared and evaluated. It was. Compositions of rolled copper foils in Examples 1 to 15 and Comparative Examples 1 to 4, heat treatment conditions after final cold rolling, X-ray diffraction intensity ratio I _{220} / I _{200} , peel strength, and grid The test results are summarized in Table 1 below.

  As a method for evaluating adhesion, a representative polyvinylidene fluoride (PVdF) was applied as a binder resin solvent to the rolled copper foils of Examples 1 to 15 and Comparative Examples 1 to 4. A peel test and a cross-cut test were performed on what was dried and the binder was dried and solidified on the copper foil surface (hereinafter referred to as “binder-coated copper foil”).

(Production of rolled copper foil)
Using oxygen-free copper as a base material, copper alloys having the alloy components shown in Table 1 below were melted and cast into ingots. The plate material obtained by hot rolling the ingot was subjected to cold rolling and fabric annealing in order, and then subjected to final cold rolling at a high workability of 85% or more and less than 95%. Thereby, Examples 1-15 which are rolled copper foil of thickness 10 micrometers, and Comparative Examples 1-4 were obtained.

(X-ray diffraction for rolled copper foil)
For the X-ray diffraction 2θ / θ measurement on the rolled surface of the rolled copper foil, an X-ray diffraction apparatus (manufactured by Rigaku, model Ultimate IV) was used. The measurement results are summarized in Table 1 below.

(Peel test)
FIG. 5 schematically shows an example of a procedure for producing a peel test piece. A copper foil (binder-coated copper foil) 4 coated with the binder film 3 was cut into a rectangular strip having a width of 12.5 mm and a length of 80 mm, and the strip-shaped binder-coated copper foil 4 was bonded to the reinforcing plate 5. A strong adhesive tape 6 is affixed to half the length of the strip of the binder-coated copper foil 4. By pulling the strong adhesive tape 6, a part of the binder film 3 was peeled off from the binder-coated copper foil 4 to obtain a peel test piece. Then, the peeled portion of the binder film 3 was grasped together with the strong adhesive tape 6 by the chuck of the peel tester, and the peel strength was measured by setting the speed at the time of pulling up in the vertical direction to 5 mm / min. The measurement results are summarized in Table 1 below.

(Cross cut test)
100 pieces of each of the rolled copper foils of Examples 1 to 15 and the rolled copper foils of Comparative Examples 1 to 4 were prepared as test pieces. In accordance with JIS H 8602, 25 test pieces (1 mm square) were formed on the binder film 3 of the binder-coated copper foil 4 by using 100 test pieces, and cellophane tape was applied to the binder film 3. After sticking and adhering, the binder film 3 was peeled off, and the adhesiveness was evaluated by the number of grids that were not peeled off. Here, the case where none of the squares were peeled was evaluated as “◯”, the case where only 1 to 5 squares were peeled was regarded as “Δ”, and the case where 6 squares or more were peeled off was evaluated as “X”. The evaluation results are summarized in Table 1 below.

From the results shown in Table 1 below, Examples 1 to 15 are elements of Cr, Zr, Sn, Mg, Ag, Fe, Co, Ni, Zn, Ti, Si, B, Bi, Sb, and Mn. One or more additive elements selected from the above are set to 0.5% by weight or less, and immediately after the final cold rolling step or after that, heated at a temperature of 200 ° C. or less for 1 minute to 20 hours. By controlling the diffraction intensity ratio to have a relationship of I _{220} / I _{200} > 2, the initial intended rolled copper foil can be stably obtained, and good resin adhesion can be realized. I understood that.

On the other hand, as in Comparative Examples 1 and 2, when the additive element such as Cr is not contained, even after the final cold rolling step, after being heated at a temperature of 200 ° C. or lower for 1 minute to 20 hours, { 200} Orientation in the _Cu direction occurs, and the diffraction intensity ratio cannot satisfy the relationship of I _{220} / I _{200} > 2. As a result, in Comparative Examples 1 and 2, it can be understood that the peel strength is lower than in Examples 1 to 15 and it is difficult to achieve good resin adhesion.

Further, as in Comparative Examples 3 and 4, even when the additive element such as Cr is included within the specified range, if the heat treatment conditions after the final cold rolling process deviate from the initial target specification, the diffraction intensity ratio Cannot satisfy the relationship of I _{220} / I _{200} > 2. As a result, in Comparative Examples 3 and 4, it can be understood that the peel strength is lower than in Examples 1 to 15 and it is difficult to achieve good resin adhesion.

  Therefore, as in Comparative Examples 1 to 4, even if the content of the additive element is within the specified range, if the heat treatment temperature and time conditions after the final cold rolling step deviate from the initial target specification, It turned out that the rolled copper foil with favorable adhesiveness with resin cannot be obtained stably.

  From the above, the rolled copper foil for the lithium ion secondary battery current collector of the present invention is a copper foil having good adhesion to the resin, and can contribute to the long life and safety of the lithium ion battery. It was proved to have a very effective effect.

As is clear from the above description, a typical configuration example of the rolled copper foil for a lithium ion secondary battery current collector of the present invention has been described with reference to the above embodiment, examples, and illustrated examples. The above-described embodiments, examples, and illustrated examples do not limit the invention according to the claims. It should be noted that not all the combinations of features described in the above embodiments, examples, and illustrated examples are essential to the means for solving the problems of the present invention. Of course, various configurations are possible within the scope of this technical idea.

DESCRIPTION OF SYMBOLS 1 ... Sample, 2 ... Detector, 3 ... Binder film, 4 ... Copper foil, 5 ... Reinforcement board, 6 ... Strong adhesive tape

Claims (3)

The Cu as the main component, Cr, Zr, Sn, Mg , C o, Ni, Zn, Ti, Si, B, Bi, and one or more additive element selected from the element group consisting of Sb, and Mn Having a copper alloy composition containing inevitable impurities,
The ratio of the diffraction peak intensity I {220} in the {220} Cu direction and the diffraction peak intensity I {200} in the {200} Cu direction of the copper crystal obtained by X-ray diffraction 2θ / θ measurement is I {220} / I {200}> are two der,
Lithium-ion secondary battery current collector rolled copper foil total amount of the additional element, wherein 0.1 to 0.5 wt% der Rukoto.   After heating at a temperature of 200 ° C. or lower for 1 minute to 20 hours, the diffraction peak intensity I {220} in the {220} Cu direction and the diffraction peak in the {200} Cu direction of the copper crystal obtained by X-ray diffraction 2θ / θ measurement 2. The rolled copper foil for a lithium ion secondary battery current collector according to claim 1, wherein the ratio of the strength I {200} is I {220} / I {200}> 2. The rolled copper foil for a lithium ion secondary battery current collector according to claim 1 or 2 , wherein the rolled copper foil has a thickness of 20 µm or less.

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