JP2007273114A - Method of manufacturing electrode for nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an electrode for a nonaqueous electrolyte secondary battery capable of manufacturing a nonaqueous electrolyte secondary battery that reduces rupture and cracks in a strip of collector in a compression process even if the strip of collector is thinned, improves a manufacturing yield, and has a high capacity, in manufacture through a process for compressing the electrode for a nonaqueous electrolyte secondary battery after applying active material mix slurry onto the strip of collector for drying by a die-coating method. <P>SOLUTION: The method of manufacturing the electrode for the nonaqueous electrolyte secondary battery has a process for applying the active material mix slurry onto the strip of collector 21 for drying before compression. In the manufacturing method, a reinforced substance layer 26 that is controlled to be thinner than the thickness of the active material mix slurry after compression is continuously applied and formed along edges at both the sides of the strip of collector 21, and then an active material mix slurry layer 27 is formed by applying the active material mix slurry between the reinforced substance layers 26 on the strip of collector 21 without any gaps. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing an electrode for a non-aqueous electrolyte secondary battery, and in particular, a process of applying an electrode for a non-aqueous electrolyte secondary battery on a strip-shaped current collector by applying an active material mixture slurry by a die coating method, and then compressing it. During manufacturing, even if the thickness of the strip-shaped current collector is reduced, the strip-shaped current collector is less broken or cracked during the compression process, and the production yield is improved and a high-capacity nonaqueous electrolyte secondary battery is manufactured. The present invention relates to a method for producing an electrode for a nonaqueous electrolyte secondary battery.

  With the rapid spread of portable electronic devices, the required specifications for the batteries used for them are becoming stricter year by year, and in particular, small, thin, high capacity, excellent cycle characteristics and stable performance are required. . In the field of secondary batteries, lithium ion non-aqueous electrolyte secondary batteries, which have a higher energy density than other batteries, are attracting attention. The proportion of lithium ion non-aqueous electrolyte secondary batteries accounts for a significant increase in the secondary battery market. Is shown.

  FIG. 2 is a perspective view showing a conventional cylindrical non-aqueous electrolyte secondary battery cut in the vertical direction. In this nonaqueous electrolyte secondary battery 10, a wound electrode body 14 in which a positive electrode 11 and a negative electrode 12 are wound via a separator 13 is disposed, and insulating plates 15 and 16 are disposed above and below the wound electrode body 14, respectively. Then, it is housed in a steel cylindrical battery outer can 17 also serving as a negative electrode terminal, and the current collecting tab 12a of the negative electrode 12 is welded to the inner bottom portion 17a of the battery outer can 17 and the current collecting tab 11a of the positive electrode 11 is welded. Is welded to the bottom plate portion of the current interrupting sealing body 18 incorporating the safety device, a predetermined nonaqueous electrolyte is injected from the opening of the battery outer can 17, and then the battery outer can 17 is attached by the current interrupting sealing body 18. Manufactured by sealing.

  And said winding electrode body 14 is normally produced with the following manufacturing methods. First, a negative electrode active material is intermittently applied along the longitudinal direction on both surfaces of a strip-shaped negative electrode current collector, processed into a predetermined thickness and width, and a negative electrode material in which a large number of negative electrodes are continuous. A positive electrode active material is intermittently applied to both surfaces of the positive electrode current collector along the longitudinal direction, and processed into a predetermined thickness and width to form a positive electrode material in which a large number of positive electrodes are continuous. The negative electrode material and the positive electrode material are sent to a predetermined winding position together with two separators interposed therebetween.

  At the winding position, the negative electrode portion to be wound around the core from the negative electrode material is cut out, the positive electrode portion to be wound around the core from the positive electrode material is cut out, and the first and second separators are also wound around the core. The length used for one wound electrode body to be rotated is cut out, and a negative electrode material, a first separator, a positive electrode material, and a second separator are stacked in this order on a cylindrical or elliptical cylindrical core provided at this position. However, the negative electrode material is wound inside, and a substantially cylindrical or elliptical cylindrical electrode body is sequentially formed. Further, the negative electrode tab and the positive electrode tab for taking out the potential are welded or molded to the uncoated portions of the negative electrode material and the positive electrode material immediately before winding. In the case of manufacturing a rectangular battery, a cylindrical or elliptical columnar electrode body is further crushed so as to be sandwiched from the radial direction by using a predetermined pressing device to form a flat electrode body.

  As a method for producing a strip-shaped electrode material used as such an electrode, a method of applying a positive electrode or negative electrode active material mixture slurry to a strip current collector by a die coating method (also referred to as an extrusion method) is known. (See Patent Documents 1 to 3 below). This die coating method is a method in which an active material mixture slurry for positive electrode or negative electrode is discharged from a nozzle of a die coater and applied onto a traveling strip current collector, and the amount of application of the active material mixture slurry is regulated. It can be performed by setting the discharge rate of the constant flow pump, and since the active material mixture slurry hardly touches the outside air until it is applied, the concentration of the active material mixture slurry does not change due to evaporation of the solvent, and the slurry There is an advantage that there is no need to adjust the coating thickness in accordance with the viscosity change, the coating can be performed more stably than other methods, and there is little variation in product performance.

JP-A-11-31502 (Claims, paragraphs [0004], [0013] to [0019] JP-A-10-64521 (claims, paragraphs [0004], [0011] to [0026], FIGS. 1 and 2) JP 2000-251942 A (claims, paragraphs [0005] to [0007], [0016] to [023], FIGS. 2 to 6)

  Such a belt-shaped body to be dried is coated with an active material mixture slurry that is not necessarily coated with an active material mixture slurry because the active material mixture slurry is intermittently applied to the surface of the belt-shaped current collector. In addition, when the active material mixture slurry is continuously applied to the surface of the strip-shaped current collector, the active material is attached to the current collector tab or separately to form an electrical connection with the battery terminal. There are portions to be coated where the mixture slurry is not coated. In addition, the band-shaped object to be dried, in which the active material mixture slurry is applied to the surface of the band current collector by such a die coating method, increases the packing density of the active material mixture and increases the capacity of the battery. After drying, it is compressed by a roller press device (see Patent Documents 2 and 3 above).

  On the other hand, in order to achieve further increase in capacity of the non-aqueous electrolyte secondary battery, it is necessary to increase the amount of active material applied on the strip-shaped current collector, but the volume limit of the battery outer can is limited. There are limits to being. In addition, the increase in battery capacity based on the improvement of the packing density of the active material mixture by the compression treatment as described above is theoretically the higher the pressure during compression, the larger the packing density of the active material mixture. However, at present, it is difficult to increase the pressure during compression beyond the current level due to the thickness and strength of the belt-like current collector.

  Therefore, in order to increase the battery capacity beyond this, it is considered necessary to reduce the thickness of the band-shaped current collector, but because the strength decreases by the thickness of the band-shaped current collector, Since the pressure at the time of compression needs to be lower than the pressure currently adopted, the effect of improving the packing density of the active material mixture is limited, and when the pressure at the time of compression is set to the same level as the present May cause a decrease in yield due to the rupture of the band-shaped current collector or mixing of cracked products.

As a result of investigating the fracture state in the compression process, in which the inventors of the present application particularly have a high possibility of fracture or crack generation of the strip-shaped current collector, it has been found that the following phenomenon occurs.
(1) A crack is generated at the boundary between the uncoated portion and the coated portion of the active material mixture slurry along the end portions on both sides of the belt-shaped body to be dried.
(2) When the active material mixture slurry is intermittently applied, the band-shaped current collector is in direct contact with the compression roll in the unapplied portion, and thus breakage is likely to occur.
(3) As a measure against the above (1), if a method of applying and reinforcing a peeling tape along the end portions on both sides of the belt-like object to be dried as disclosed in Patent Document 3 above, Because it is difficult to paste along the edges on both sides of the dry zone without any gaps,
(3-1) If there is a part covered with the release tape on the active material mixture slurry, the adhesive material of the release tape protrudes during compression at the part covered with the release tape, and the adhesive material adheres to the compression roll and reverses. In some cases, the strip current collector may break.
(3-2) If there is a gap between the active material mixture slurry and the peeling tape, wrinkles and cracks are generated in the band-like current collector at that portion.

  In addition, in the said patent document 3, as a countermeasure of said (1), the edge part of the both sides of a strip | belt-shaped to-be-dried body other than the method of affixing a peeling tape along the both-ends of a strip | belt-shaped to-be-dried body is reinforced. Although an annealing process or an unevenness forming process is also shown, a special process is required in which only the end portions on both sides of the belt-shaped body to be dried are subjected to an annealing process or an unevenness forming process to make it easy to stretch. In addition, conventional electrode manufacturing apparatuses cannot be used as they are, and these methods do not always have a predetermined effect even if they are used as they are when the thickness of the belt-like current collector is thin. Because it is not, it is difficult to adopt it immediately.

  Moreover, in the said patent document 2, when an active material mixture slurry is intermittently apply | coated on a strip | belt-shaped collector, a pair of compression roll contacts the surface of a strip | belt-shaped collector in the non-application part of an active material mixture slurry. In order to avoid this, an example in which a gap is provided between a pair of compression rolls is shown. However, this is not always effective for the measure (1) above, and the band-shaped current collector is particularly thin. However, it was difficult to prevent the strip-shaped current collector from being broken or cracked even if it was adopted as it was.

  The inventors of the present application have conducted various experiments in order to obtain a manufacturing method that does not cause breakage or cracking during compression even if the thickness of the strip-shaped current collector is made thinner than the thickness conventionally employed. After forming a reinforcing material layer that is thinner than the thickness of the compressed active material mixture slurry along the ends on both sides of the current collector, the active material mixture is formed without any gaps between the reinforcing material layers on the belt-like current collector. The present inventors have found that the problem can be solved by applying an agent slurry, and have completed the present invention.

  That is, the present invention provides the thickness of the strip current collector when the electrode for a non-aqueous electrolyte secondary battery is manufactured through a process in which an active material mixture slurry is applied onto the strip current collector and dried and then compressed. Provides a method for producing an electrode for a nonaqueous electrolyte secondary battery that can produce a high-capacity nonaqueous electrolyte secondary battery while improving the production yield with less rupture and cracking of the strip current collector during production The purpose is to do.

  In order to achieve the above object, the invention of a method for producing an electrode for a nonaqueous electrolyte secondary battery according to claim 1 of the present application is a process in which an active material mixture slurry is applied onto a band-shaped current collector, dried and then compressed. In the method for manufacturing an electrode for a non-aqueous electrolyte secondary battery having a reinforcing material layer controlled to be thinner than the thickness of the active material mixture slurry layer after compression along end portions on both sides of the strip-shaped current collector After the continuous application and formation, the active material mixture slurry is applied with no gap between the reinforcing material layers on the strip-shaped current collector.

  The invention according to claim 2 is the method for producing an electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the reinforcing material layer contains the same solvent as the active material mixture slurry. .

  The invention according to claim 3 is the method for producing an electrode for a nonaqueous electrolyte secondary battery according to claim 2, wherein the reinforcing material layer is a polymer material that is soluble in the same solvent as the active material mixture slurry. It is characterized by using.

  The invention according to claim 4 is the method for producing an electrode for a non-aqueous electrolyte secondary battery according to claim 3, wherein the polymer material is selected from polyvinylidene fluoride, polyimide, and ethylene propylene diene rubber. It is characterized by being.

  The invention according to claim 5 is the method for producing an electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the active material mixture slurry is intermittently applied to the belt-like current collector by a die coating method. It is characterized by that.

  The invention according to claim 6 is the method for producing an electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the active material mixture slurry is a positive electrode active material mixture slurry, The strip current collector is made of aluminum.

  The invention according to claim 7 is the method for producing an electrode for a non-aqueous electrolyte secondary battery according to claim 6, wherein the thickness of the strip-shaped current collector is 8 μm or more and 12 μm or less.

  The present invention has the following excellent effects by adopting the above manufacturing method. That is, according to the first aspect of the invention, since the active material mixture slurry is applied before the reinforcing material layer is dried, the active material mixture layer and the reinforcing material layer are substantially separated at the boundary between them. Since both ends of the belt-shaped current collector are reinforced by the reinforcing material layer, the drying process and the compression process are performed after applying the active material mixture slurry on the belt-shaped current collector. Even after passing, the possibility of cracks occurring at both end portions of the belt-shaped current collector or breaking of the belt-shaped current collector is greatly reduced.

  Furthermore, in this invention, since no gap is generated between the active material mixture layer and the reinforcing material layer, there is a gap between the active material mixture slurry and the reinforcing material layer as in the conventional example. During the compression process, the band-shaped current collector is extremely less likely to be wrinkled or cracked. In addition, since the reinforcing material layer in the present invention is dried before compression, the band-shaped current collector due to the adhesive material of the peeling tape as in the conventional example does not occur.

  Further, according to the invention according to claim 2, since the reinforcing material layer contains the same solvent as the active material mixture slurry, the reinforcing material layer is provided on both sides after the reinforcing material layer is provided along the end portions on both sides of the belt-like current collector. When the active material mixture slurry is applied between the reinforcing material layers, the solvents of the reinforcing material layer and the active material mixture layer mix with each other, and it is difficult for gaps to form between the reinforcing material layer and the active material mixture layer. Such a band current collector is extremely less likely to be wrinkled or cracked during the compression process due to the presence of a gap between the active material mixture slurry and the reinforcing material layer.

  According to the invention of claim 3, since the reinforcing material layer uses a polymer material that is soluble in the same solvent as the active material mixture slurry, the reinforcing material layer is reinforced along the end portions on both sides of the belt-like current collector. When the active material mixture slurry is applied between the reinforcing material layers on both sides after the physical layer is provided, not only the solvent of the reinforcing material layer and the active material mixture layer but also the polymer material are mixed with each other. A gap is less likely to occur between the active material mixture layer.

  Further, according to the invention according to claim 4, as long as it can be dissolved in a solvent as a polymer material used in the reinforcing material layer, not only those normally used as a binder in the active material mixture slurry, but also other than that However, when one kind selected from polyvinylidene fluoride, polyimide, and ethylene propylene diene rubber is adopted, these polymers are used as an electrode active material mixture for non-aqueous electrolyte secondary batteries. Since it is normally mixed in the slurry as a binder, it has a particularly good effect.

  In addition, when the active material mixture slurry is intermittently applied and the reinforcing material layer is not present, the compression roll is in direct contact with the belt-like current collector in the uncoated portion of the active material mixture slurry in the compression step. However, according to the invention according to claim 5, since the compression roll in the compression step rides on the dried reinforcing material layer provided along the end portions on both sides of the belt-like current collector, The contact with the belt-shaped current collector is eliminated, and cracking or breakage of the belt-shaped current collector due to direct contact between the compression roll and the belt-shaped current collector as in the conventional example is prevented.

According to the invention of claim 6, the method for producing a nonaqueous electrolyte secondary battery electrode of the present invention can be adopted as any method of producing a positive electrode and a negative electrode, but a lithium transition metal composite oxide such as LiCoO ₂ is used. In the case of using a positive electrode active material mixture slurry having a product as a positive electrode active material, since the aluminum having low strength is used as the band-shaped current collector, the effect of the present invention is particularly prominent.

  Further, when aluminum is used as the strip-shaped current collector for the positive electrode of the non-aqueous electrolyte secondary battery, a conventional one having a thickness of about 20 μm is conventionally used. According to the invention according to claim 6, 8 μm or more and 12 μm or less can be used, and the amount of the positive electrode and negative electrode active material that can be accommodated in the battery can be increased by reducing the thickness of the strip current collector for positive electrode. Therefore, the capacity of the nonaqueous electrolyte secondary battery can be increased as compared with the conventional example. In the case where the thickness of the aluminum as the band-shaped current collector exceeds 12 μm, the increase in the amount of the active material is small at the time of manufacturing the battery as compared with the conventional one, so there is no effect of reducing the thickness. Further, if the thickness of the aluminum is less than 8 μm, even if the reinforcing material layer of the present invention is provided, cracks or breaks increase, which is not preferable.

  Embodiments of the present invention will be described below with reference to the drawings. However, in the following examples, the production of a positive electrode using a lithium transition metal composite oxide such as lithium cobaltate as a positive electrode active material as an electrode for a non-aqueous electrolyte secondary battery for embodying the technical idea of the present invention. It is intended to illustrate a method, and is not intended to specify the present invention as a method for producing a negative electrode for a non-aqueous electrolyte secondary battery, but also as a method for producing a negative electrode using a carbonaceous material as an active material. It is equally applicable.

[Preparation of sample]
A slurry in which 95% by mass of lithium cobaltate, 2% by mass of acetylene black as a conductive agent, and 3% by mass of polyvinylidene fluoride PVdF powder as a binder was dispersed in N-methylpyrrolidone NMP as a solvent was prepared. An agent slurry was obtained. Further, an NMP solution of PVdF was used as a reinforcement. Using this reinforcing material and the positive electrode active material mixture slurry, the sample was applied to the surface of an aluminum core using the following coating apparatus to prepare the samples of Example and Comparative Example 1.

  A schematic perspective view of the coating apparatus 20 used is shown in FIG. In this coating apparatus 20, a strip-shaped current collector 21 made of aluminum having a thickness of 12 μm is continuously transferred in the direction of the arrow through the first roll 22 and the second roll 23, and is positioned opposite the first roll 22. Further, a first coating die 24 for applying a reinforcing material is provided, and a second coating die 25 is provided at a position facing the second roll 23. In the embodiment, in the first coating die 24, the thickness after drying is continuously smaller than the thickness after compression of the active material mixture layer along both end sides of the surface of the strip-shaped current collector 21. The reinforcing material layer 26 is formed by applying an experimentally determined coating amount so as to have a thickness (for example, 5 μm). In the second coating die 25, the positive electrode active material mixture slurry is applied to the belt-like current collector 21. The belt-shaped body to be dried of the example having the positive electrode active material mixture layer 27 was prepared by applying the film so that the thickness after drying was 90 μm so that no gap was formed between the reinforcing material layers 26 on both sides. Further, in Comparative Examples 1 and 2, the positive electrode active material mixture slurry having the same thickness and the same thickness as in the example was used without using the first coating die 24 for applying the reinforcing material and using only the second coating die 25. The strip-shaped materials to be dried of Comparative Examples 1 and 2 having only the positive electrode active material mixture layer 27 were applied so as to have the same width.

  Thereafter, the belt-like objects to be dried in Examples and Comparative Examples 1 and 2 were dried by continuously passing them through a drying furnace (not shown) for drying by blowing warm air, and the Examples and Comparative Examples 1 and 2 were dried. A belt-like dried body was produced. Next, the belt-like dried bodies of Examples and Comparative Example 1 were directly compressed through a pair of opposing compression rolls so that the applied active material mixture had a thickness of 60 μm. Moreover, about the strip | belt-shaped dry body of the comparative example 2, after reinforce | strengthening the location where the active material mixture of the both ends is not apply | coated with an adhesive tape, a pair of opposition is carried out similarly to the case of an Example and the comparative example 1. It compressed so that the thickness of the apply | coated active material mixture might be set to 60 micrometers through between compression rolls. And the crack, the fracture | rupture state, and the generation | occurrence | production state of a wrinkle at the time of letting each sample of an Example and the comparative examples 1 and 2 pass between a pair of compression rolls over length 100m were confirmed visually. The results are summarized in Table 1.

  As is apparent from the results shown in Table 1, in the sample of the example in which the end portions on both sides of the belt-like current collector 21 were all covered with the reinforcing material layer 26 made of PVdF, even if the compression treatment was performed over 100 m, the cracks, There were no breaks or wrinkles. However, in the sample of Comparative Example 1 in which no reinforcement layer was provided, wrinkles did not occur at the boundary between the coated portion and the coated portion of the positive electrode active material mixture, but breakage occurred frequently (27 locations). Further, in the sample of Comparative Example 2 in which the end portions on both sides of the strip-shaped current collector 21 are reinforced with an adhesive tape during compression, it is difficult to uniformly adhere the adhesive tape along the application portion of the active material mixture. Therefore, the adhesive tape glue material adhered to the compression roll, and the glue material stuck to the surface of the sample of Comparative Example 2, or a gap was created between the adhesive tape and the material-applying portion. There were frequent wrinkles and breaks (8 breaks, 34 wrinkles).

  From the results shown above, it can be seen that very good results are obtained with the sample of the example in which both ends of the belt-like current collector are covered with the reinforcing material 26 made of PVdF. In addition, in the Example, although the example using the same solvent and polymer material as the solvent and binder of a positive electrode active material mixture slurry was used as a reinforcement, these solvents and polymer materials are different from each other. May be. However, since there is no advantage of using different solvents and polymer materials, it is better to use a material containing the same solvent and polymer material as the positive electrode active material mixture slurry and binder as the reinforcing material. .

  Furthermore, as the polymer material used for the reinforcing material layer, not only PVdF but also a polymer material used as a binder for the positive electrode and the negative electrode can be used as long as it dissolves in a solvent. In this case, when one kind selected from PVdF, polyimide, and ethylene propylene diene rubber, which are commonly used as a binder in the active material mixture slurry, is adopted, the boundary between the reinforcing material layer and the active material mixture layer is Very good results can be obtained because they melt together and virtually no boundary is created between them.

  Further, in the examples, the example in which the reinforcing material layer is continuously provided at the both end portions of the belt-shaped current collector and the positive electrode active material mixture layer is continuously provided is shown, but the positive electrode active material mixture layer is intermittent. It may be provided. In this way, when the reinforcing material layer is continuously provided at both end portions of the strip-shaped current collector and the positive electrode active material mixture layer is provided intermittently, even in a place where the positive electrode active material mixture layer is not provided. Since the compression roll does not come into direct contact with the belt-like current collector in the compression step, the effect is particularly prominent as compared with the conventional example in which no reinforcing material layer is provided.

  The above shows an example in which a positive electrode active material mixture slurry made of a lithium composite oxide such as lithium cobalt oxide is applied to a strip-shaped current collector, but a negative electrode active material using a carbon material such as graphite as a negative electrode active material Even when the mixture slurry is applied to the belt-like current collector, the same tendency occurs even if the degree is different. Therefore, according to the present invention, the quality and productivity of the nonaqueous electrolyte secondary battery can be improved, and its industrial value is great.

It is a schematic perspective view of a coating device. It is a perspective view which cuts the cylindrical nonaqueous electrolyte secondary battery produced conventionally from the lengthwise direction.

Explanation of symbols

20 Coating Device 21 Band Current Collector 22 First Roll 23 Second Roll 24 First Coating Die 25 Second Coating Die 26 Reinforcement Layer 27 Positive Electrode Active Material Mixture Layer

Claims (7)

  In the method of manufacturing an electrode for a non-aqueous electrolyte secondary battery including a step of applying an active material mixture slurry onto a strip current collector, drying and then compressing, along the end portions on both sides of the strip current collector, After continuously forming the reinforcing material layer controlled to be thinner than the thickness of the active material mixture slurry layer after compression, the active material mixture slurry without gaps between the reinforcing material layers on the strip-shaped current collector The manufacturing method of the electrode for nonaqueous electrolyte secondary batteries characterized by apply | coating.   The method for producing an electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the reinforcing material layer contains the same solvent as the active material mixture slurry.   The method for producing an electrode for a non-aqueous electrolyte secondary battery according to claim 2, wherein the reinforcing material layer contains a polymer material soluble in the same solvent as the active material mixture slurry.   The method for producing an electrode for a non-aqueous electrolyte secondary battery according to claim 3, wherein the polymer material is one selected from polyvinylidene fluoride, polyimide, and ethylene propylene diene rubber.   The method for producing an electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the active material mixture slurry is intermittently applied to the strip-shaped current collector by a die coating method.   The electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the active material mixture slurry is a positive electrode active material mixture slurry, and the band-shaped current collector is made of aluminum. Production method. 6. The method for producing an electrode for a nonaqueous electrolyte secondary battery according to claim 5, wherein the thickness of the strip-shaped current collector is 8 μm or more and 12 μm or less.

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