JP2012178265A - Electrode for battery and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for a battery capable of easily matching both end positions of a mixture layer formed on front and back surfaces of a collector of metal foil and such without introducing complication of a manufacturing process, and improving a rate of non-defective product of electrode manufacturing.SOLUTION: Electrodes for a battery 1 and 5 are provided with mixture layers 3 and 7 formed with a slurry form mixture coated on surfaces of collectors 2 and 6, on which a coating setting region A1 preset as an area to which a mixture is to be coated has higher surface tension than a non-coat setting region A2 preset as an area to which the mixture is not to be coated.

Description

  The present invention relates to an electrode used for a battery such as a secondary battery used in a vehicle-mounted battery, and more particularly to an electrode for a battery and a secondary battery that are optimal for a lithium ion secondary battery.

  Due to the emergence of environmental problems such as global warming, there is a need to reduce carbon dioxide emissions from automobiles. Electric vehicles powered by electric energy and energy generated when the automobile decelerates are regenerated to restore power. Development of hybrid vehicles to be used as departments is proceeding at a rapid pace. In particular, a lithium ion secondary battery using a lithium ion occlusion / release reaction at an electrode is attracting attention as a secondary battery for automobiles. The characteristics of the lithium ion secondary battery, particularly the input / output characteristics that are important in the in-vehicle lithium ion secondary battery, depend greatly on the performance of the electrode that occludes and releases lithium ions when the secondary battery is charged and discharged.

  In order to realize a high capacity, it is known to form a mixture containing an active material on the surface of a metal foil constituting a current collector as a shape of an electrode that absorbs and releases a large amount of lithium ions. (Patent Document 1). The mixture is generally formed by diluting and dispersing an active material, conductive material, binder resin, etc. in water or a solvent, and applying the slurry to the surface of the metal foil and drying. .

JP 2010-15851 A

  By the way, when a slurry-like mixture is applied to the surface of the metal foil, it is applied at a certain width on the surface to form an uncoated region for the current collecting tab on the side edge of the metal foil. It has been broken. At that time, the application width of both surfaces of the metal foil and the positions of both ends thereof are matched. If the coating width on both sides of the metal foil and the positions of both ends thereof do not match, the positions of the mixture layers formed on both sides of the metal foil are aligned when the positive and negative electrodes are overlapped with each other through the separator. And the area where the mixture layers of the positive electrode and the negative electrode overlap each other is reduced, which may cause a reduction in battery capacity.

  The conventional method of matching both ends of the mixture layer on both sides of the metal foil is controlled by adjusting the alignment of a machine that applies the slurry mixture onto the surface of the metal foil. However, in this conventional method, after applying the slurry-like mixture on the metal foil, it is impossible to control the fluctuation amount of the application width due to the flow, and there is a possibility that the end portions of the mixture layer are inconsistent. That is, the slurry-like mixture has high viscosity and low fluidity, but since it is applied thickly on the surface of the metal foil, it may flow after application and the outline of the mixture layer may shift. In particular, the slurry-like mixture changes in viscosity according to the environment such as temperature and humidity, the flow after application is not constant, and the controllability is not good.

  The present invention has been made in view of such problems, and the object of the present invention is a mixture formed by coating on both surfaces of a metal foil without performing complicated and fine mechanical alignment adjustment of the manufacturing process. An object of the present invention is to provide a battery electrode capable of easily matching the positions of both ends of a layer and improving the yield of non-defective electrodes, and a secondary battery using this electrode.

  In order to solve the above problems, for example, the configuration described in the claims is adopted. The present application includes a plurality of means for solving the above-mentioned problems. To give an example, a battery electrode in which a slurry mixture is applied to the surface of a current collector to form a mixture layer is provided. Of the surface of the current collector, the application setting area that is preset as the area where the mixture is applied is more than the non-application setting area that is preset as the area where the mixture is not applied. It is characterized by a large surface tension.

  According to the present invention, both end positions of the mixture layer formed on both surfaces of a current collector such as a metal foil can be easily matched. Therefore, the non-defective product rate in the electrode manufacturing process can be improved, and a high quality battery electrode can be provided. Moreover, a secondary battery with high capability can be formed using this electrode. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

The disassembled perspective view of the state which fractured | ruptured a part of cylindrical lithium ion secondary battery using the battery electrode which concerns on this invention. The figure which shows the surface of the metal foil which comprises the electrode of the lithium ion secondary battery of FIG. The figure which shows the state by which the mixture was apply | coated to the surface of the metal foil which comprises the electrode of the lithium ion secondary battery of FIG. The figure which shows the state which divided | segmented the metal foil with which the mixture of FIG. 3 was apply | coated. The figure which shows the cross section of an electrode typically.

  Hereinafter, an embodiment of a cylindrical lithium ion secondary battery using a battery electrode according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is an exploded perspective view of a state in which a part of a cylindrical lithium ion secondary battery using a battery electrode according to the present invention is broken. As shown in FIG. 1, the battery electrode according to the present embodiment is used as a positive electrode 1 and a negative electrode 5 of a lithium ion secondary battery D.

  The positive electrode 1 includes a positive electrode metal foil 2 made of a metal foil such as aluminum as a current collector, and a positive electrode mixture layer 3 formed by applying a slurry-like positive electrode mixture on both surfaces of the positive electrode metal foil 2. Consists of The positive electrode metal foil 2 has a plurality of positive electrode tabs 4, 4.

  The negative electrode 5 includes a negative electrode metal foil 6 composed of a metal thin film such as copper as a current collector, and a negative electrode mixture layer 7 formed by applying a slurry-like negative electrode mixture on both surfaces of the negative electrode metal foil 6. Consists of The negative electrode metal foil 6 is provided with a plurality of negative electrode tabs 8, 8...

  The positive electrode 1 and the negative electrode 5 are wound around a resin shaft 11 through a porous and insulating separator 10, and the outermost separator 10 is stopped with a tape 12 to constitute an electrode group 15. . At this time, the innermost periphery in contact with the shaft core 11 is the separator 10, and the outermost periphery is the separator 10 covering the negative electrode metal foil 6 and the negative electrode mixture layer 7. A positive electrode current collecting member 16 and a negative electrode current collecting member 17 are fixed to both ends of the tubular shaft core 11 in the axial direction by fitting.

  A plurality of positive electrode tabs 4, 4... Of the positive electrode 1 are welded to the positive electrode current collecting member 16 by, for example, an ultrasonic welding method. Similarly, negative electrode tabs 8 of the negative electrode 5 are welded to the negative electrode current collecting member 17 by, for example, an ultrasonic welding method. Inside the battery container 18 also serving as the negative electrode terminal, a positive electrode current collecting member 16 and a negative electrode current collecting member 17 are housed by being attached to an electrode group 15 wound around a resin shaft 11. When the electrode group 15 is accommodated in the battery container 18, the electrolytic solution is also injected into the battery container 18.

  Further, on the positive electrode current collecting member 16, there is an upper lid portion having conductivity provided so as to seal the opening of the battery container 18, and the upper lid portion includes an upper lid 19 and an upper lid case 20. One of the positive electrode leads 16a of the positive electrode current collecting member 16 is welded to the upper cover case 20, and the other is welded to the positive electrode current collecting member 16, whereby the upper cover part and the positive electrode 1 of the electrode group 15 are electrically connected. A gasket 21 is provided between the battery container 18 and the upper lid case 20, and the gasket 21 seals the opening of the battery container 18 and electrically insulates the upper lid 19 and the upper lid case 20. The negative electrode current collecting member 17 is electrically connected to the bottom of the battery container 18 by welding.

  The positive electrode mixture constituting the positive electrode mixture layer 3 includes a positive electrode active material, a positive electrode conductive material, and a positive electrode binder resin. As the positive electrode active material, lithium oxide is preferable. Specific examples include lithium cobaltate, lithium manganate, lithium nickelate, lithium iron phosphate, lithium composite oxide (lithium oxide containing two or more selected from cobalt, nickel, and manganese).

  The positive electrode conductive material can be used without particular limitation as long as it is a substance that can assist the transmission of electrons generated by the occlusion / release reaction of lithium ions in the positive electrode mixture to the positive electrode. Examples of the positive electrode conductive material include graphite and acetylene black. Further, the positive electrode binder resin is not particularly limited as long as it is capable of binding the positive electrode active material, the positive electrode conductive material, and the positive electrode metal foil, and does not deteriorate significantly by contact with the electrolytic solution. Examples of the positive electrode binder resin include polyvinylidene fluoride (PVDF) and fluororubber.

  The negative electrode mixture constituting the negative electrode mixture layer 7 usually has a negative electrode active material, a negative electrode binder resin, and a thickener. The negative electrode mixture may optionally have a negative electrode conductive material such as acetylene black. Examples of the negative electrode active material include carbon materials such as graphite, soft carbon, and hard carbon. As the negative electrode binder resin, PVDF or the like can be used similarly to the positive electrode, or styrene-butadiene copolymer rubber (SBR) or the like is also applicable.

  In order to dispose the positive electrode mixture layer 3 and the negative electrode mixture layer 7 on the surface of the positive electrode metal foil 2 and the surface of the negative electrode metal foil 6, a dispersion solution of substances constituting the mixture is prepared and made into a slurry. The process of apply | coating a slurry on the surface of the positive electrode metal foil 2 and the negative electrode metal foil 6, and drying is required. Examples of the coating method include a slit die coating method and a roll coating method. Moreover, N-methylpyrrolidone (NMP), water, etc. can be used as a solvent of a dispersion solution. Furthermore, examples of the drying method include hot air circulation, infrared heating, and a mixing method thereof.

  2 is a view showing the surface of the metal foil constituting the electrode of the lithium ion secondary battery of FIG. 1, FIG. 3 is a view showing a state in which a mixture is applied to the surface of the metal foil, and FIG. FIG. 5 is a diagram schematically illustrating a cross section of an electrode. FIG. 5 is a diagram illustrating a state in which a metal foil to which a mixture of 3 is applied is divided. In the following description, the case of the positive electrode 1 will be mainly described as an example, and the negative electrode 5 will be described in detail by omitting the reference numerals in parentheses in the drawing.

  As shown in FIG. 3, the positive electrode mixture layer 3 is formed by applying a slurry-like positive electrode mixture on the surface of the positive electrode metal foil 2. As shown in FIG. 5, the positive electrode mixture layer 3 is applied on both surfaces of the positive electrode metal foil 2 so that the application width and the both end positions thereof coincide. After the positive electrode mixture is dried, as shown in FIG. 4, the positive electrode 1 is cut at the central portion of the positive electrode metal foil 2 along the longitudinal direction along the cutting line S, and the blank portion is formed into the shape of the positive electrode tabs 4, 4. It is formed by processing.

  As shown in FIG. 2, the positive electrode metal foil 2 has a coating setting area A <b> 1 that is set in advance as an area where the positive electrode mixture is applied and a non-application area that is set in advance as a non-application area. It has a coating setting area A2. In the present embodiment, the application setting area A1 is set so as to extend along the longitudinal direction at the center in the width direction, leaving margins on both sides in the width direction of the positive electrode metal foil 2, and the non-application setting area A2 It is set along both sides in the width direction of the setting area A1.

  The application setting area A1 and the non-application setting area A2 have a configuration in which the application setting area A1 has a larger surface tension than the non-application setting area A2. In the present embodiment, the non-application setting area A2 of the positive electrode metal foil 2 is subjected to a surface treatment for making the surface tension of the positive electrode metal foil 2 smaller than that of the application setting area A1, before the mixture application, and the application setting area A1 is subjected to a surface treatment that increases the surface tension of the positive electrode metal foil 2 more than the non-application setting area A2 before applying the mixture.

  The surface treatment for reducing the surface tension is not necessarily performed over the entire non-application setting area A2, and may be performed so as to extend with a constant width along the boundary portion with the application setting area A1. .

  The application setting area A1 having a large surface tension has high wettability and the slurry-like mixture is likely to adhere thereto. On the contrary, the non-application setting area A2 having a small surface tension has low wettability and the slurry-like mixture is difficult to adhere. It has become. For this reason, when a slurry-like positive electrode mixture is applied to the surface of the positive electrode metal foil 2, the slurry does not protrude into the non-application setting area A2 having a small surface tension, but falls within the application setting area A1, which is a desired position. The outline of the mixture layer 3 is prevented from protruding along a predetermined edge.

  In a conventional method of applying a slurry-like mixture on the surface of a metal foil, the application width of the mixture changes depending on the fluidity of the mixture from immediately after application until it is dried. The amount of change is difficult to control because factors such as the viscosity of the mixture, the surface tension of the metal foil, and the drying conditions are complexly correlated. Therefore, it has been difficult to accurately form the contour of the mixture layer.

  In contrast, in the present embodiment, the surface treatment of the positive electrode metal foil 2 is performed in advance for each region before the application of the positive electrode mixture, and the surface tension of the positive electrode metal foil 2 is increased in the application setting region A1. Since it is large, the slurry-like mixture spreads out and is dammed up at the boundary with the non-application setting area A2 having a small surface tension, and does not protrude into the application setting area A1. Therefore, the mixture can be applied only to the application setting area A1, and can be prevented from being applied to the non-application setting area A2.

  As a surface treatment method for reducing the surface tension of the non-application setting region A2, for example, a solution containing a fluorine-based compound, a silicone-based compound, etc. is thinly applied on the surface of the positive electrode metal foil 2 and dried. A surface treatment method for coating the non-application setting area A2 can be mentioned. As the solvent of the solution, alcohols such as IPA, methanol, ethanol and the like are used, and examples of the coating method include a die slit coating method. The step of controlling the surface tension of the metal surface is desirably performed immediately before the mixture slurry application step. Further, the coating of the solution can be performed in a state where the application setting area A1 is masked and only the non-application setting area A2 is exposed.

  As a surface treatment method for increasing the surface tension of the coating setting region A1, UV (ultraviolet light) treatment for irradiating ultraviolet rays, plasma treatment for blowing plasma gas, and physical treatment method for degreasing the surface of the positive electrode metal foil 2 Is mentioned. In the UV treatment or plasma treatment, the non-application setting area A2 may be masked, and surface treatment such as irradiation may be performed with only the application setting area A1 exposed.

  Since the above-described surface treatment method does not change the position accuracy due to fluidity, the surface treatment can be accurately performed on the application setting region, and the processing operation itself can be easily performed. When the positive electrode mixture is applied after such processing, the positive electrode mixture flows only in the predetermined application setting area A1 on both surfaces of the positive electrode metal foil 2, and does not flow in the non-application setting area A2. Therefore, it is possible to form the positive electrode material mixture layer 3 whose end positions coincide with each other with high positional accuracy.

  In the above-described embodiment, the case where the surface treatment is performed on both the application setting area A1 and the non-application setting area A2 has been described as an example. However, the surface tension is increased only in the application setting area A1 of the positive electrode metal foil 2. A surface treatment may be performed. The positive electrode metal foil 2 that constitutes the electrode has a large surface tension, but mechanical oil or the like adheres in the manufacturing process formed as a foil, and the surface tension of the entire foil is reduced. The positive electrode mixture is difficult to adhere. Thus, in the state where the surface tension of the entire surface of the metal foil 2 is small, the positive electrode mixture layer 3 is applied to the central portion of the metal foil by applying a surface treatment for increasing the surface tension to the central portion of the metal foil that is the application setting region A1. The positive electrode mixture layer 3 can be made difficult to form at both ends of the metal foil, and the contour of the end portion of the positive electrode mixture layer 3 can be formed with high accuracy.

  The battery electrodes 1 and 5 of the present invention configured as described above are applied to the center in the width direction of the metal foils 2 and 6 before the mixture is applied to the surfaces of the metal foils 2 and 6 constituting the electrodes 1 and 5. Since the set application setting area A1 is surface-treated so that the surface tension is larger than the non-application setting area A2 set at the end in the width direction of the metal foils 2 and 6, the non-application setting is performed. The wettability of the region A2 is low, and the slurry-like mixture is difficult to adhere, and the positional accuracy of the mixture layers 3 and 7 can be improved.

  And surface treatment can be performed by a simple method compared with application of a mixture. For this reason, the alignment accuracy of the mixture layers 3 and 7 applied to one surface of the metal foils 2 and 6 and the mixture layers 3 and 7 applied to the other surface is improved, and the positive electrode and the negative electrode The position accuracy of the battery can be improved, and the capacity of a battery or secondary battery using this electrode can be improved.

  In this way, before the mixture slurry is applied, the surface of the metal foil is subjected to a surface treatment that increases the surface tension of the metal foil in the application setting region, while the surface tension is reduced in the region where the mixture is not applied. By performing an appropriate surface treatment, the slurry-like mixture can be easily placed on the metal foil with high positional accuracy, and a mixture layer can be formed.

  According to the present invention, in the manufacturing process of forming the mixture layer on the surface of the metal foil, the positions of both ends of the mixture layer can be easily matched without performing complicated and fine mechanical alignment adjustment, and the yield rate of electrode manufacturing can be improved. Can be improved.

  As mentioned above, although embodiment of this invention was explained in full detail, this invention is not limited to the structure of the above-mentioned embodiment, A various design change can be performed in the range which does not deviate from the meaning of this invention. Is. For example, in the above-described embodiment, an example of an electrode of a lithium ion secondary battery has been shown, but it can also be used for an electrode of a primary battery such as a lithium battery or an electrode of a nickel hydride secondary battery.

  Moreover, it is not restricted to a lithium battery, Of course, it can be used as an electrode of another primary battery or a secondary battery.

1 Positive electrode (electrode)
2 Positive metal foil (current collector)
3 Positive mix layer 4 Positive electrode tab 5 Negative electrode (electrode)
6 Negative metal foil (current collector)
7 Negative electrode mixture layer 8 Negative electrode tab 10 Separator 11 Axle core 12 Tape 15 Electrode group 16 Positive electrode current collecting member 17 Negative electrode current collecting member 18 Battery container 19 Upper lid 20 Upper lid case 21 Gasket A1 Application setting area A2 Non-application area D Lithium ion 2 Secondary battery

Claims (6)

A battery electrode in which a slurry mixture is applied to the surface of a current collector to form a mixture layer,
Of the surface of the current collector, the non-application setting area in which the application setting area preset as the area where the mixture is applied is preset as the area where the mixture is not applied. A battery electrode having a surface tension greater than that of the battery.   2. The battery electrode according to claim 1, wherein the non-application setting region is subjected to a surface treatment for making the surface tension smaller than that of the application setting region.   3. The battery electrode according to claim 1, wherein the coating setting region is subjected to a surface treatment that has a surface tension larger than that of the non-coating setting region.   The surface treatment for reducing the surface tension is a surface treatment in which a solution containing a fluorine-based compound, a silicone-based compound, or the like is applied to the non-application setting region and dried, and the non-application setting region is coated with the compound. The battery electrode according to claim 2.   The battery electrode according to claim 3, wherein the surface treatment for increasing the surface tension is a surface treatment for performing a UV treatment for irradiating the coating setting region with ultraviolet rays or a plasma treatment for spraying a plasma gas.   A secondary battery using the battery electrode according to any one of claims 1 to 5 as at least one electrode for a positive electrode or a negative electrode.

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