JP2011018687A - Method of manufacturing electrode sheet, and method of manufacturing electrode body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an electrode sheet having strength with good productivity without using any organic solvent, and to provide a method of manufacturing an electrode body using the electrode sheet manufactured by the method.SOLUTION: A binder and water are added to and mixed with a first mixture obtained by mixing a powdery active material and a conductivity auxiliary together. The second mixture which is obtained by the mixing is kneaded so as to be viscous while being applied with shearing force which is large enough to crush the binder in the second mixture, and then the mixture is loosened and the loosened mixture is molded into a sheet to obtain the electrode sheet. A metal foil is stuck on the obtained electrode sheet and dried to obtain the electrode body.

Description

  The present invention relates to an electrode sheet manufacturing method and an electrode body manufacturing method used in the field of electric double layer capacitors and secondary batteries.

  An electric double layer capacitor (capacitor) has a large capacity and is excellent in charge / discharge cycle characteristics, and therefore, its use as various backup power sources including automobiles is being studied. When used as a backup power source for automobiles or the like, a large capacitance is required. Therefore, as a polarizable electrode used in such an electric double layer capacitor, a long sheet-like one is required. . Therefore, various methods have been proposed as a method for manufacturing this type of polarizable electrode.

  For example, Patent Document 1 discloses a method for manufacturing a sheet-like polarizable electrode as follows. In Patent Document 1, a binder made of an organic solvent such as IPA (isopropyl alcohol) is added to a binder made of a fluororesin such as PTFE (polytetrafluoroethylene) in advance to swell the binder. It is disclosed that a powdered active material such as activated carbon and a conductive auxiliary agent such as carbon black are added and mixed and kneaded, and the obtained kneaded material is divided into particles and classified to form a molding material. It is disclosed that a thin sheet-shaped polarizable electrode is manufactured by forming, molding and rolling the molding material into a sheet. Furthermore, this Patent Document 1 discloses that IPA is added again to a kneaded material before molding to soften the kneaded material so that the molding material can be easily formed into a sheet shape. It is also disclosed that a polarizable electrode is obtained by molding into a sheet shape, and the polarizable electrode is dried in order to remove IPA remaining on the polarizable electrode.

  However, when an organic solvent is used as an auxiliary agent for the binder, the environmental load is increased and explosion-proof equipment is required, which increases the equipment investment burden. In addition, in the method for producing a polarizable electrode disclosed in Patent Document 1, it is necessary to add IPA to the kneaded material again before forming the molding material into a sheet shape, and it is difficult to control the concentration and the production efficiency is not good. . Therefore, a method that does not use an organic solvent has been considered.

  A method for producing a polarizable electrode without using an organic solvent is disclosed in Patent Document 2, for example. In Patent Document 2, first, a powdery active material such as activated carbon and a conductive auxiliary agent such as carbon black are mixed by a medium type pulverizer, and then PTFE as a binder and an auxiliary agent for the binder are added to the mixture. It is disclosed that water is added and mixed again, and the resulting mixture is formed into a sheet to produce a polarizable electrode.

JP 2004-186190 A JP 2007-258611 A

  However, in the method for producing a polarizable electrode (electrode sheet) disclosed in Patent Document 2, water is used as an auxiliary agent for the binder. Therefore, compared with a production method using an organic solvent as an auxiliary agent for the binder. Even if kneading is performed, the binder is not easily fiberized, and the mixture (kneaded material) is less likely to be viscous. As a result, the method for producing a polarizable electrode disclosed in Patent Document 2 has a powdery active material, a conductive aid, and a binder, as compared with a method for producing a polarizable electrode using an organic solvent as a binder aid. The bond is weak and the shaped polarizable electrode is also weak. Further, since the bond between the powdery active material, the conductive auxiliary agent and the binder is weak, there is a problem that nests, cracks, tears and the like are likely to occur in the polarizable electrode after molding.

  The present invention has been made in view of the above circumstances, and its purpose is to manufacture an electrode sheet having strength with a high productivity without using an organic solvent, and a manufacturing method thereof. It is providing the manufacturing method which manufactures an electrode body using the made electrode sheet.

  In order to achieve the above object, according to the first aspect of the present invention, the first mixture step obtained by mixing the powdery active material and the conductive auxiliary agent and the first mixture step obtained by the first mixing step are provided. The binder in the second mixture is added to the second mixture obtained by adding the binder and water, mixing the first mixture, the binder and water, and the second mixture step. A kneading step of kneading the second mixture so as to generate viscosity in the second mixture while applying a shearing force to crush the mixture, and a step of loosening the kneaded product having viscosity obtained through the kneading step And the electrode sheet is formed through a forming step of forming the kneaded material loosened through the unwinding step into a sheet shape.

An electrode body used for an electric double layer capacitor and a secondary battery is generally formed by bonding an electrode sheet to a metal foil.
Among the raw materials for the electrode sheet, activated carbon is mainly used as the powdery active material, but carbon nanotubes, fibrous carbon, metal compounds, and the like may be used. In the case of activated carbon, the average diameter of the grains is about 3-5 μm. Examples of the metal compound include lithium cobaltate and lithium manganate. As the conductive auxiliary agent, a material excellent in conductivity and finer than the powdered active material, for example, carbon black is used. Carbon black has an average particle diameter of about 0.5 μm. As the binder, PTFE (polytetrafluoroethylene) is used, and an aqueous PTFE dispersion using an acrylic resin dispersant is more preferable. Examples of the metal foil include an aluminum sheet, an aluminum sheet whose surface is etched, and a sheet made of copper.

  The first mixture is obtained by mixing the powdered active material and the conductive auxiliary agent, and the second mixture is obtained by mixing the first mixture, the binder and water. In obtaining the second mixture, water is added and mixed when the first mixture and the binder are mixed, whereby the first mixture and the binder are easily mixed uniformly. Furthermore, by kneading this second mixture, a kneaded material with a viscosity can be obtained. An electrode sheet is manufactured by loosening this kneaded material and forming it into a sheet. As described above, in the present invention, since the electrode sheet is formed without using an organic solvent as a raw material, the environmental load is reduced, and it is not necessary to provide an explosion-proof facility, thereby reducing the capital investment burden. Moreover, in this invention, it is not necessary to perform the process of adding an organic solvent to a kneaded material again before shape | molding a shaping | molding material like a manufacturing method of the polarizable electrode (electrode sheet) of patent document 1 in a sheet form.

Generally, when a shearing force is applied to the binder, the binder is fibrillated (viscosity is generated in the binder).
In the method for producing an electrode sheet of the present invention, the powdered active material and the conductive auxiliary are mixed as described above, and the binder and water are further added and mixed. And the binder are uniformly mixed. Thereafter, in the kneading step, the binder is moderately crushed and fiberized by applying a shearing force to the mixture so as to crush the binder. As a result, the kneaded product obtained in the kneading step has an appropriate viscosity.

  As described above, in the method for producing an electrode sheet of the present invention, since the kneaded product has an appropriate viscosity, the bonding force between the powdery active material, the conductive auxiliary agent, and the binder is large, and the strength of the electrode sheet is increased. In addition, it is possible to prevent as much as possible the occurrence of nests, cracks, tears, etc. in the electrode sheet.

  In the method for producing an electrode sheet of the present invention, since the binder is appropriately crushed and a shearing force is applied, the binder is fiberized and the powdery active materials are bonded to each other. Thereby, the electrode sheet formed by the method for producing an electrode sheet of the present invention is narrower in the gap between the powdered active materials than the electrode sheet formed of the powdered active material mixed by the medium pulverizer, The packing density of the powdered active material is increased. Therefore, the contact between the powdery active materials increases, the electrical resistance of the electrode sheet can be reduced, and the electrode density of the electrode sheet can be increased.

  In addition, by loosening the kneaded product obtained in the kneading step in the unraveling step, the forming raw material (the loosened kneaded product) is sized. Thereby, it can suppress that a nest, a crack, a tear, etc. generate | occur | produce in the shape | molded electrode sheet.

The invention of claim 2 is characterized in that the kneaded product having viscosity obtained through the kneading step is divided into fine particles in the loosening step.
By dividing the kneaded material having an appropriate viscosity obtained in the kneading step into fine particles in the unraveling step, the kneaded material is further loosened and the molding raw material is further sized. Thereby, it can suppress more that a nest, a crack, a tear, etc. generate | occur | produce in the shape | molded electrode sheet.

  In the invention of claim 3, the kneading step is performed by applying the second mixture to the second mixture supplied between the rollers by a pair of rollers having a rotation axis arranged in parallel and a slight gap. The second mixture is kneaded so that the second mixture has viscosity while applying a shearing force that crushes the binder in the mixture.

  According to the manufacturing method of claim 3 described above, the second mixture obtained by mixing the powdery active material, the conductive auxiliary agent, the binder and water is supplied between the pair of rollers, whereby the second mixture is obtained. A shearing force that crushes the binder can be easily applied to the mixture. The thickness dimension of the kneaded material obtained by applying a shearing force that crushes the binder to the second mixture is smaller than the thickness dimension of the second mixture before the shearing force is applied.

  Further, since the second mixture is kneaded while being crushed by the roller, the binder can be easily fiberized. In addition, since the second mixture that is crushed by the roller can escape (extend) in the molding direction, a moderately strong shearing force can be applied to the second mixture, and the resulting kneaded product can be excessive. There is no stickiness.

  Further, when the kneading of the second mixture is carried out with a batch-type kneader (for example, see Japanese Patent Application Laid-Open No. 2004-186191, FIG. 3) as in the conventional method for producing a polarizable electrode (electrode sheet), the batch Therefore, it is difficult to improve productivity, and it is difficult to set kneading conditions such as controlling the degree of binder fiberization to an appropriate state. That is, when the kneading time is short, the binder is segregated without being uniformly dispersed, and characteristics such as electrode density and electric resistance of the formed electrode sheet may vary depending on the part of the electrode sheet. In addition, if the kneading time is long, the fiberization of the binder proceeds too much, the binder is broken, the binding force of the powdered active material particles is reduced, and the molded electrode sheet has nests, cracks, tears, etc. May occur.

However, in the method for producing an electrode sheet of the present invention, since the second mixture is supplied and kneaded between a pair of rollers, the binder is pressurized with a constant force, and a constant shearing force is applied to the binder. Therefore, the electrode sheet manufactured by the manufacturing method of the present invention can obtain the same characteristics regardless of the portion of the electrode sheet.
Further, in the method for producing an electrode sheet of the present invention, the magnitude of the shearing force applied to the mixture of the powdered active material, the conductive auxiliary agent and the binder is determined by the distance between the rollers, the rotational speed of the rollers, and the roller surface temperature. It can be easily controlled by adjusting.

  The invention of claim 4 is obtained by a laminating step of laminating an electrode sheet obtained by the electrode sheet manufacturing method according to any one of claims 1 to 3 and a metal foil, and a laminating step. The electrode body is manufactured through a drying step of drying the obtained laminate.

  By drying in the state of the electrode sheet, the drying time when manufacturing the electric double layer capacitor and the secondary battery can be shortened, and the productivity can be improved.

The figure which shows one Example of this invention and is a figure explaining the manufacturing process at the time of manufacturing an electrode body Side view of rollers used in the kneading process Schematic diagram of the kneaded material obtained in the kneading process The figure which shows the contrast of the characteristic of the example product and the comparative product

Embodiments of the present invention will be described below with reference to the drawings.
The electrode body is formed through the steps shown in FIG.
The raw material used when manufacturing the electrode sheet of an electrode body uses activated carbon as a powdery active material, carbon black as a conductive auxiliary, PTFE powder as a binder, and water.

(First mixing step)
First, in the first mixing step, 80% by mass of activated carbon and 20% by mass of carbon black are put into a container of a mixer, and these are mixed by a rotating stirring blade. Thereby, the 1st mixture which activated carbon and carbon black mixed as uniformly as possible can be obtained.

(Second mixing step)
Next, a mixture of PTFE and water is put into the container of the mixer and mixed with the first mixture. The mass ratio of the first mixture to PTFE is preferably 80 to 90% by mass for the first mixture and 10 to 20% by mass for PTFE. The amount of water to be added is preferably 50 to 100% of the total mass of the first mixture and PTFE.
Thereby, activated carbon, carbon black, and PTFE are mixed, and a second mixture in which PTFE is fibrillated and the activated carbon and carbon black are entangled can be obtained.

(Kneading process)
Next, as shown in FIG. 2, the second mixture 1 is kneaded so that the second mixture 1 has viscosity while applying a shearing force that crushes the PTFE 8 contained in the second mixture 1. Then, a kneading step for obtaining a sheet-like kneaded product 2 is performed.
In the kneading step, a pair of work rollers 3 and 3 that are arranged in parallel with a rotation axis and disposed through a slight gap, and a backup roller 4 that contacts each work roller 3 and rotates the work roller 3; Is used.

The backup roller 4 is operated by a motor (not shown) so that the second mixture 1 supplied between the work rollers 3 and 3 flows downstream (in the direction of arrow A, ie, the molding direction). 3 is driven in the direction (arrow C direction) opposite to the rotation direction (arrow B direction).
Since the configuration is such that the backup roller 4 is rotated by a motor (not shown) and the work roller 3 is rotated by the rotation of the backup roller 4, the work roller 3 is deformed rather than kneading alone without the backup roller 4. Can be corrected.

  When a shearing force is applied to the PTFE 8, the PTFE 8 becomes a fiber, and the kneaded material 2 comes to have an appropriate viscosity. Further, since the second mixture 1 crushed by the work rollers 3 and 3 can escape (extend) in the forming direction (arrow A direction), an appropriate shearing force can be applied to the second mixture 1. . Thereby, the sheet-like kneaded material 2 which has moderate viscosity is shape | molded.

  FIG. 3 is a schematic diagram showing an enlarged surface of the sheet-like kneaded product 2 obtained in the kneading step. In FIG. 3, it can be seen that activated carbon 6 and carbon black 7 smaller than this are entangled with PTFE 8 having a fibrous shape.

(Unraveling process)
Next, the sheet-like kneaded product 2 obtained in the kneading step is loosened into fine particles by a rotating knife blade to obtain a granular forming raw material in which the kneaded product 2 is loosened. By performing the loosening step, the forming raw material is sized.

(Molding process)
Next, the molding raw material obtained in the unraveling process is put into a hopper (not shown) of a calendar molding machine, and this molding material is passed between two rollers (not shown) to be molded into a sheet ( Calendar molding process). Next, the sheet-shaped molded body formed into a sheet is wound up by a winding roller. At this time, the gap between the rollers used in the calendar molding process is adjusted in advance so that the thickness of the obtained sheet-like molded body becomes, for example, 200 μm.

(Rolling process)
Next, the sheet-like molded body is rolled through two rollers (not shown) (roll rolling process). By performing this roll rolling process a plurality of times, an electrode sheet having a predetermined thickness, for example, 160 μm is formed. In the final step of the roll rolling, both end portions in the width direction of the electrode sheet are cut with a cutter to align the end portions. Thereby, the electrode sheet which has intensity | strength can be manufactured without using an organic solvent.

(Lamination process)
Next, the formed electrode sheet is bonded to a metal foil, for example, an aluminum sheet, which becomes a current collector, using a water-soluble adhesive to form a sheet-like laminate.

(Drying process)
Finally, a drying process is performed to remove moisture contained in the laminate.
By performing the first mixing step to the drying step, an electrode body using the above electrode sheet can be manufactured.

  In order to confirm the effect of the present invention, an electrode sheet sample (Example product 1) molded by the above-described manufacturing method of the present invention and an electrode sheet sample molded by the conventional manufacturing method shown below (Comparison) The characteristics of the example products 1 and 2) were compared. In this test, measurement of electrode density, measurement of electrode tensile strength, measurement of capacitance, measurement of internal resistance, observation of electrode surface for samples (Example product 1, Comparative product 1 and 2) In addition, the wettability of the electrolyte was measured.

(Production method of comparative product 1)
The electrode sheet of Comparative Example Product 1 is formed by a manufacturing method disclosed in JP 2007-258611 A (see Patent Document 2). The material of Comparative Example Product 1 is the same as that of Example Product 1, and the mass ratio of the materials is also the same.

  In the production method of Comparative Example Product 1, first, activated carbon as a powdery active material and carbon black as a conductive auxiliary agent are mixed by a medium pulverizer such as a ball mill (primary mixing step). Next, the mixture obtained in the primary mixing step is taken out from the medium grinder, transferred to another mixer, and PTFE as a binder and water as a liquid lubricant (auxiliary for binder) are added to this mixture. And mixing again (secondary mixing step). Thereafter, the same molding process as that of the manufacturing method of the example product 1 is performed. Thereby, an electrode sheet (comparative product 1) is formed.

(Production method of Comparative Example Product 2)
The electrode sheet of Comparative Example Product 2 is formed by the manufacturing method disclosed in Japanese Patent Application Laid-Open No. 2004-186190 (see Patent Document 1). In the material of Comparative Example Product 2, activated carbon as a powdery active material, carbon black as a conductive aid, PTFE as a binder, and IPA (isopropyl alcohol) as an organic solvent as a binder aid are used. In this case, the IPA of Comparative Example Product 2 is adjusted to an appropriate amount. The activated carbon, carbon black, and PTFE of Comparative Example Product 2 are the same materials as Example Product 1 and Comparative Example Product 1, and the mass ratio of the materials is also the same.

  In the manufacturing method of Comparative Example Product 2, first, activated carbon and carbon black are put into a mixer container and mixed (primary mixing step). Next, PTFE and IPA mixed in advance to swell PTFE are put into the container of the mixer. Then, the mixture obtained in the primary mixing step and the swollen PTFE are mixed (secondary mixing step). Next, the mixture obtained in the secondary mixing step is accommodated in a container of a kneader (kneader) described in, for example, Japanese Patent Application Laid-Open No. 2004-186191 (see FIG. 3 of the same publication), covered and heated. The blade is rotated while kneading (kneading step). The temperature of the container, lid and blade of the kneader during kneading is controlled to 90 ° C.

  Thereafter, the mixture obtained in the kneading step is finely divided into fine particles in the same manner as in the loosening step of the production method of Example Product 1. Next, the obtained particles are sieved and classified so that the particle size becomes 1.0 μm or less. The same molding process as that of the manufacturing method of Example Product 1 is performed on the classified granular kneaded product. I do. However, in Comparative Example Product 2, IPA was added again to the kneaded product before the calendar molding step in this molding step and mixed. Moreover, in the comparative example product 2, the sheet-like molded product obtained in the molding process is dried by passing it through a drying chamber of a dryer (drying process) to remove the remaining IPA. By performing the primary mixing step to the drying step, an electrode sheet (Comparative Example Product 2) is formed.

  In Comparative Example 2, since an organic solvent is used as an auxiliary agent for the binder, as described above, the environmental load becomes large, an explosion-proof facility is required, and the capital investment burden increases. There is a desire not to use the comparative product 2 too much. Therefore, the test results of Comparative Example Product 2 are described for reference.

Next, with reference to FIG. 4, it analyzes about the test result of the samples 1-3.
The “X direction” in FIG. 4 is the forming direction of the electrode sheet of each sample obtained in the forming process, and the “Y direction” is the width direction of the electrode sheet (the direction perpendicular to the forming direction “X direction”). ).
The liquid used in the capacitance, internal resistance, and electrolyte wettability tests is the same as the actual electrolyte used in the electric double layer capacitor.

  As a result of the electrode density, the comparison between Example Product 1 and Comparative Product 1 shows that Example Product 1 has activated carbon because PTFE 8 contained in the electrode sheet is crushed by the shearing force of work rollers 3 and 3 in the kneading process. The clearance gap between 6 becomes narrow and the packing density of the activated carbon 6 becomes high. Thereby, the electrode density of Example product 1 is increased. In addition, since the comparative example product 2 is strongly kneaded, the electrode density increases.

  From the comparison of Example Product 1 and Comparative Product 1 in the results of the electrode tensile strength, Example Product 1 is kneaded while applying a shearing force that crushes PTFE 8, and the PTFE 8 is easily fibrillated. Since it has viscosity, the electrode tensile strength is larger than that of Comparative Example 1. The comparative product 2 has a directionality in the tensile strength.

  From the comparison between the results of capacitance and the results of internal resistance, the product of Example 1 according to the comparison between the product of Example 1 and the products of Comparative Examples 1 and 2 is that the PTFE 8 contained in the electrode sheet is sheared by the rollers 3 and 3 in the kneading process. Since the material is crushed by force and becomes moderately viscous, the gap between the activated carbons 6 is reduced, showing a high value as the capacitance and also reducing the internal resistance.

  FIG. 4 shows the electrode surface of each sample observed visually. In the example product 1, no segregated PTFE8 was found. On the other hand, in the comparative products 1 and 2, PTFE segregated material having a diameter of about 0.5 to 1 mm was present.

  In the electrolyte wettability test, when the contact angle of the electrolyte solution of Example Product 1 is α, the contact angle of the electrolyte solution of Comparative Example Product 1 is β, and the contact angle of the electrolyte solution of Comparative Product 2 is γ Since the density of the activated carbon 6 (electrode density) is higher in the example product 1 than in the comparative example product 1, the electrolyte is less likely to penetrate into the electrode sheet and the contact angle is increased (contact angle α> contact angle β). . In addition, since the activated carbon is more densely present in the comparative example product 2 than in the example product 1, the contact angle is the largest as compared with the example product 1 (contact angle γ> contact angle α).

The present invention is not limited to the embodiment described above and shown in the drawings, and the following modifications and expansions are possible.
Between the unraveling step and the molding step, the kneaded product may be finely divided into fine particles in the unraveling step, followed by sieving the particles to perform classification.
The present invention can be implemented with appropriate modifications within a range not departing from the gist.

  In the drawings, 1 is a second mixture, 2 is a kneaded product, 3 is a work roller (roller), 6 is activated carbon (powdered active material), 7 is carbon black (conductive auxiliary agent), and 8 is PTFE (binder). Indicates.

Claims (4)

A first mixing step of mixing the powdery active material and the conductive auxiliary;
A second mixing step of adding a binder and water to the first mixture obtained through the first mixing step, and mixing the first mixture, the binder and water;
The second mixture obtained through the second mixing step is applied with a shearing force that crushes the binder in the second mixture, and the second mixture is made viscous. A kneading step of kneading the mixture of 2;
A step of loosening the kneaded product having viscosity obtained through the kneading step;
An electrode sheet is formed through a forming step of forming the kneaded material loosened through the unraveling step into a sheet shape.   The method for producing an electrode sheet according to claim 1, wherein the loosening step divides the kneaded material having viscosity obtained through the kneading step into fine particles.   In the kneading step, a pair of rollers arranged in parallel with a rotation axis and disposed through a slight gap is added to the second mixture supplied between the rollers in the second mixture. The method for producing an electrode sheet according to claim 1 or 2, wherein the second mixture is kneaded so as to cause the second mixture to become viscous while applying a shearing force that crushes the binder. . A laminating step of obtaining a laminate by bonding the electrode sheet obtained by the method for producing an electrode sheet according to claim 1 and a metal foil;
An electrode body is manufactured through the drying process which dries the laminated body obtained at the said lamination process, The manufacturing method of the electrode body characterized by the above-mentioned.

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