JP2004311138A - Manufacturing method and manufacturing device of lithium-ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method and manufacturing device used for it improving yield and reliability for a lithium-ion secondary battery made sealing in a case a wound-round element formed by folding a laminated body of a positive electrode, a negative electrode, and a separator one or more times in the same direction and filling electrolyte solution in it. <P>SOLUTION: In forming a wound-round element, an initial part of winding of the laminated body 5 is virtually in a folded state, and so damage such as a crack occurs at that part. Since the positive electrode and the negative electrode constituting the laminated body 5 are formed by coating of slurries containing powder of an electrode active material and a binder, a solvent dissolving the binder is coated with the use of a solvent coating unit 7 on a part where the laminated body 5 is folded for the first time and then the body is folded. With this, the binder at the part is swollen to manifest elongation and flexibility, so that damage accompanying bending and folding hardly occurs. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a manufacturing method and a manufacturing apparatus for a lithium ion secondary battery, and more particularly to a method for winding a strip electrode and an apparatus used therefor.
[0002]
[Prior art]
In recent years, in order to meet the demand for downsizing and weight reduction in portable communication devices typified by mobile phones and notebook personal computers, secondary batteries have also been rapidly downsized. Among them, lithium ion secondary batteries are remarkably widespread because they have the following excellent features.
[0003]
(1) Since the energy density is higher than that of a conventional nickel cadmium battery or nickel metal hydride battery, the weight and volume can be reduced to half or less. (2) A high voltage approximately three times that of a nickel cadmium battery or a nickel metal hydride battery can be obtained. (3) There is no so-called memory effect in which the discharge capacity decreases when charging and discharging are repeated. (4) High safety against overcharge and high heat. (5) Does not include materials with high environmental impact such as cadmium, lead, and mercury.
[0004]
And the general manufacturing method of a lithium ion secondary battery is as follows. First, for each of the positive electrode and the negative electrode, an electrode active material, a binder, and a solvent for dissolving the binder are mixed and stirred at a required ratio to prepare a slurry.
[0005]
The slurry is applied to one or both sides of a current collector made of a metal foil, compressed to a required thickness by removing the solvent, and then cut into the required dimensions to form strip-like positive electrode and negative electrode. obtain. Next, the positive electrode and the negative electrode are laminated via a separator and wound in accordance with the shape of the case to obtain a winding element called a jelly roll.
[0006]
Next, the winding element is inserted into the case. In many cases, the case is made of metal and functions as a negative electrode terminal. Therefore, the tabs respectively connected to the positive electrode and the negative electrode of the winding element are the positive electrode terminal provided on the case lid and the negative electrode terminal. Connect to the case.
[0007]
Next, the case and the lid are sealed by laser welding, and an electrolytic solution is injected from an inlet provided in the lid. Thereafter, the inlet is sealed by welding, the case surface is washed, and necessary items such as a lot number are printed, and a finished product is obtained.
[0008]
As the positive electrode active material, lithium cobaltate (LiCoO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium nickelate (LiNiO ₂ ) or the like is used, and as the negative electrode active material, graphite powder or coke type is used. A carbon material such as powder is used. In addition, the current collector uses a lot of aluminum foil on the positive electrode side and copper foil on the negative electrode side, and the separator is a porous polymer made of a material that allows lithium ions to pass freely and is not affected by the electrolyte. A film is used.
[0009]
FIG. 3 is a perspective view of the lithium ion secondary battery obtained as described above, with a part thereof broken when the case has a square shape. In FIG. 3, 1 is a positive electrode, 2 is a negative electrode, 3 is a separator, 9 is a winding element, and 10 is a case also serving as a negative electrode terminal. Reference numeral 11 denotes a positive electrode terminal. The positive electrode 1 and the negative electrode 2 are connected to the positive terminal 11 and the case 10 via tabs not shown in the figure.
[0010]
FIG. 4 is a diagram schematically showing a state in which a winding element is formed. As shown in FIG. 4, the positive electrode 1 and the negative electrode 2 are stacked via a separator 3 to form a stacked body 5. The laminated body is wound with the end portions sandwiched between the winding cores 4a and 4b to form a winding element.
[0011]
In order to form an electrode, as described above, a slurry obtained by mixing a powdered active material, a polymer material serving as a binder, and a solvent is applied to a current collector with a doctor blade or the like. The current collector and the separator are each 20 to 30 μm thick, and the entire electrode is about 100 μm thick. Therefore, the overall thickness of the laminate 5 is about 200 to 300 μm.
[0012]
When this laminated body is formed into a winding element, the winding start of the winding element is close to a state of bending with a very small radius of curvature. For this reason, in the part enclosed with the broken line of FIG. 4, the part extended by a big ratio arises, and it will result in a crack producing a electrode or a fracture | rupture.
[0013]
As an example of such a lithium ion secondary battery, Patent Document 1 discloses a technique relating to a lithium ion battery in which a winding element is housed in a rectangular case and a manufacturing method thereof. However, the technical content of Patent Document 1 is that between the positive electrode and the negative electrode in the longitudinal direction of the winding element cross section in order to avoid obstacles such as a short circuit when an external pressure or bending force is applied. In addition, an insulator is interposed, and there is no disclosure of countermeasures for breaking the bent portion.
[0014]
[Patent Document 1]
Japanese Patent Laid-Open No. 2001-266946
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to prevent a breakage of an electrode portion when a laminated body composed of a positive electrode, a negative electrode, and a separator is formed into a wound element, and to improve the yield. And a manufacturing apparatus used therefor.
[0016]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides the electrode with flexibility and large elongation so that the laminate composed of the positive electrode, the negative electrode, and the separator does not break even when bent with a small radius of curvature. It was made as a result of examination.
[0017]
That is, the present invention provides a belt-like positive electrode in which a layer of a positive electrode active material containing lithium is formed on at least one surface of a belt-like positive electrode current collector and carbon on at least one surface of the belt-like negative electrode current collector. Forming a laminated body obtained by laminating a strip-shaped negative electrode formed with a layer of a negative electrode active material containing a material via a separator, and forming the winding element by bending the laminated body at least once in the same direction; In the method of manufacturing a lithium ion secondary battery in which the wound element is sealed in a case, an electrolyte is injected, the positive electrode and the negative electrode are connected to the positive electrode terminal and the negative electrode terminal, and then the case is sealed. The method for producing a lithium ion secondary battery is characterized in that at least the first folding of the laminate is performed after a solvent is applied to a portion to be folded.
[0018]
The present invention also provides a belt-like positive electrode in which a layer of a positive electrode active material containing lithium is formed on at least one surface of a belt-like positive electrode current collector, and at least one surface of the belt-like negative electrode current collector. An apparatus for manufacturing a lithium ion secondary battery having a winding device for bending a laminate formed by laminating a strip-like negative electrode having a negative electrode active material layer containing a carbon material on a separator in the same direction The winding device is a device for manufacturing a lithium ion secondary battery, comprising a device for applying a solvent to the bent portion of the laminate.
[0019]
As described above, as a method for forming an electrode, a method of applying a slurry made of an electrode active material, a binder, and a solvent for dissolving the binder to the surface of a metal foil used as a current collector is frequently used. In general, a polymer material is used as the binder, but when a good solvent is applied to the polymer material, the polymer material swells and becomes plastic, and can be stretched to some extent.
[0020]
Therefore, even when the laminate of the electrode and the separator is formed into a wound element as described above, the polymer material contained as a binder in the electrode swells by applying a solvent in advance to the portion and bending it. Thus, it becomes possible to exhibit flexibility and prevent the electrode from being damaged.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, when the winding element is bent, the solvent is applied to the portion having the smallest radius of curvature, that is, the first bent portion. If necessary, the solvent is applied to the second and subsequent bent portions. May be. The solvent may be applied by, for example, adding a solvent to a porous member such as a sponge and press-contacting the required portion of the laminate, or using a nozzle to apply the solvent to the required portion of the laminate. You may spray.
[0022]
Further, when the laminate is formed into a wound element, it is necessary to cut the laminate to an appropriate length. However, the cutting and the application of the solvent may be performed by separate devices or separate devices. It is also possible to use a method of interlocking and a method of applying and cutting at the same time by incorporating a coating and cutting unit in the same apparatus.
[0023]
Next, specific examples of the present invention will be described with reference to the drawings.
[0024]
(Example)
FIG. 1 is a diagram schematically showing a manufacturing apparatus according to an embodiment of the present invention. In FIG. 1, 7 is a solvent application unit, and here, a sponge is used. Reference numerals 6a and 6b denote cutting units, and the lower cutting unit 6b is attached to the frame 8 together with the solvent application unit so that the solvent is applied to the laminate 5 and the laminate 5 is simultaneously cut. It has become.
[0025]
Here, a mesh in which a copper wire having a diameter of 24 μm is plain woven was used as the current collector on the positive electrode side. Lithium cobaltate powder as the positive electrode active material, polyvinylidene fluoride having an average molecular weight of 11000 (hereinafter referred to as PVDF) as the binder, so that the lithium cobaltate powder and PVDF are 90/10 by weight. Weighed and mixed, and N-methyl-2-pyrrolidone was added as a solvent to prepare a slurry. The slurry was applied to the current collector using a squeegee so that the thickness after removal of the solvent was 100 μm.
[0026]
Further, as the current collector on the negative electrode side, a mesh in which an aluminum wire having a diameter of 24 μm was plain woven was used. Graphite powder is used as an electrode active material on the negative electrode side, PVDF having an average molecular weight of 11000 is used as a binder, graphite powder and PVDF are weighed and mixed so that the weight is 90/10, and N-methyl-2 is used as a solvent. -A slurry was prepared by adding pyrrolidone. The slurry was applied to the current collector using a squeegee so that the thickness after removal of the solvent was 100 μm.
[0027]
Next, a porous polypropylene film having a thickness of 20 μm was prepared as a separator, and sandwiched between the positive electrode and the negative electrode obtained as described above to obtain a laminate. This laminate was wound into a shape that could be stored in a square case to obtain a wound element. FIG. 2 shows a part of the cross section of the winding element.
[0028]
The radius of curvature of the winding start portion of the laminate, that is, the portion surrounded by the broken line in FIG. 2, is 220 μm on the positive electrode side and 100 μm on the negative electrode side on the bent side. Here, the solvent application unit 6 of the apparatus shown in FIG. 1 was used to apply the bending process after applying N-methyl-2-pyrrolidone to the part that was first bent at the beginning of winding of the laminate.
[0029]
Then, a tab for connecting the positive electrode and the negative electrode to the terminals is attached, inserted into the case, the tab and the terminal are connected, the electrolyte is injected, the case is sealed, and the lithium ion secondary battery of the example Got. In addition, the electrolyte solution used the propylene carbonate solution of lithium perchlorate.
[0030]
For the purpose of comparison, a lithium ion secondary battery of a comparative example was prepared under the same conditions as in the above example, except that the solvent was not applied to the part that was first bent at the beginning of the laminate. Ten lithium ion secondary batteries of the example and the comparative example were each disassembled, and the initial winding start portion of the laminate was observed with a microscope. In the example, damage such as cracks was not observed at all in the corresponding portion. Although it was not, the crack was recognized about two pieces in the comparative example.
[0031]
【The invention's effect】
As described above, according to the present invention, a manufacturing method for obtaining a wound element of a laminate of a positive electrode, a negative electrode, and a separator in a lithium ion secondary battery with a high yield and a manufacturing apparatus used therefor are obtained. . This makes it possible to improve the manufacturing yield and reliability of a particularly thin prismatic lithium ion secondary battery.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing a manufacturing apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram showing a part of a cross section of a winding element.
FIG. 3 is a perspective view in which a part of a lithium ion secondary battery having a square case is broken.
FIG. 4 is a diagram schematically showing a state in which a winding element is formed.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4a, 4b Winding core 5 Laminated body 6a, 6b Cutting unit 7 Solvent application unit 8 Frame 9 Winding element 10 Case 11 Positive terminal

Claims (2)

A belt-like positive electrode in which a layer of a positive electrode active material containing lithium is formed on at least one surface of the belt-like positive electrode current collector, and a negative electrode active material containing a carbon material on at least one surface of the belt-like negative electrode current collector And forming a wound element by bending the laminated body at least once in the same direction to form a wound element. In the method of manufacturing a lithium ion secondary battery in which a positive electrode terminal and a negative electrode terminal are connected to a positive electrode terminal and a negative electrode terminal, and then the case is sealed, The first time is a method of manufacturing a lithium ion secondary battery, which is performed after a solvent is applied to a portion to be bent. A strip-shaped positive electrode in which a layer of a positive electrode active material containing lithium is formed on at least one surface of the strip-shaped positive electrode current collector, and a negative electrode including a carbon material on at least one surface of the strip-shaped negative electrode current collector In a manufacturing apparatus of a lithium ion secondary battery having a winding device for bending a laminate formed by laminating a strip-like negative electrode formed with an active material layer via a separator in the same direction, the winding device is An apparatus for manufacturing a lithium ion secondary battery, comprising a solvent application device for a bent portion of the laminate.

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