JP2009130329A - Electrode for electrochemical device and manufacturing method thereof, and electric double-layer capacitor as electrochemical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an electrode for electrochemical devices, which can be dried quickly in manufacture, does not cause its characteristics to deteriorate by the application of voltage even after it becomes a product, and has stable characteristics for a long time. <P>SOLUTION: In the electrode for electrochemical devices, where a coating electrode material obtained by binding at least active carbon and a conductive auxiliary material by a binder is applied onto a collector made of a metal material up to a prescribed thickness for drying and rolling, a water dispersion is used as the binder. The water dispersion contains polytetrafluoroethylene (PTFE) and a copolymer (FEP) of fluoroethylene and fluoropropylene at a ratio of 7:3 to 3:7 (wt.%). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrode for an electrochemical device and a method for producing the same. More specifically, the present invention relates to an electrochemical device obtained by applying a slurry-like coated electrode material on a current collector such as etched aluminum (mainly The present invention relates to an electrode for an electric double layer capacitor) and a manufacturing method thereof.

  Various electrodes have been proposed for use in electrochemical devices such as electric double layer capacitors. As one of them, activated carbon and a conductive auxiliary agent, polyvinylidene fluoride (PVDF) as a binder, N- A coating electrode material using methylpyrrolidone (NMP) as a solvent is known (see Conventional Example 1, for example, Patent Document 1).

  Also known is a coated electrode material using activated carbon, a conductive additive and a dispersion material such as carboxymethyl cellulose (CMC), a styrene butadiene (SBR) rubber or an acrylate rubber as a binder, and water as a solvent ( Conventional example 2, see Patent Document 2, for example).

  Although it is not a method of applying a slurry-like paint, conductive adhesive is attached to the current collector after kneading polytetrafluoroethylene (PTFE) as a binder with an ethanol solvent together with an ethanol solvent into a conductive material. There is also a method of pasting via a material (see Conventional Example 3, for example, Patent Document 3).

JP-A-8-55761 JP 2006-92760 A Japanese Patent Laid-Open No. 1-164017

  However, according to the above-mentioned conventional example 1, since the solvent used is N-methylpyrrolidone (NMP), drying of the paint after application is at a high temperature, so that drying takes a long time. In addition, the obtained electrode has problems such as bending of carbon as a conductive auxiliary agent due to bending or the like.

  In the case of Conventional Example 2, an electrode having a strong binding force is obtained and the solvent is water, so that the drying temperature and drying time are improved. However, when a voltage is applied as a product, In addition, there is a problem that the binder is oxidized on the positive electrode side, resulting in characteristic deterioration.

  Further, in the case of the above conventional example 3, the drying temperature and drying time are improved, the electrode has a good binding force, and even after the voltage is applied as a product, the characteristics are not deteriorated so much, but the electrode body is completed. In order to do so, a step of attaching the sheet-like electrode to the current collector is required, which is not preferable in terms of productivity.

  In addition, since the sheet-like electrode is formed in advance by slicing or the like, there is a limit to the thickness of the obtained electrode, and as an example, it is extremely difficult to reduce the thickness to 80 μm or less, which is a problem in reducing resistance. Become.

  Accordingly, an object of the present invention is to obtain an electrode for an electrochemical device that can be dried in a short time in production, has little characteristic deterioration due to voltage application, and has stable characteristics over a long period of time even when a product is produced. .

  In order to solve the above-mentioned problems, the present invention provides a current collector made of a metal material as a coated electrode material formed by binding at least activated carbon and a conductive auxiliary material with a binder as described in claim 1. In an electrode for an electrochemical device, which is applied to a predetermined thickness, dried and rolled, polytetrafluoroethylene (PTFE) and a copolymer of fluoroethylene and fluoropropylene (FEP) are used as the binder. : An aqueous dispersion containing 3 to 3: 7 (wt%) is used.

  In the present invention, as described in claim 2, the mixing ratio of the binder in the coated electrode material is preferably 5 to 20 wt%.

  Further, in the present invention, as described in claim 3, a coated electrode material formed by binding at least activated carbon and a conductive auxiliary material with a binder is provided on a current collector made of a metal material. In the method for producing an electrode for an electrochemical device formed by applying a thickness, drying and rolling, after dispersing activated carbon, a conductive auxiliary material and a dispersing agent with water, in this liquid, polytetrafluoroethylene (PTFE), A paint obtained by mixing a binder made of an aqueous dispersion containing a copolymer of fluoroethylene and fluoropropylene (FEP) at a ratio of 7: 3 to 3: 7 (wt%) is applied on the current collector, The manufacturing method of the electrode for electrochemical devices characterized by rolling so that the thickness after drying may be set to 30-150 micrometers is also contained.

  The present invention also includes an electric double layer capacitor comprising the electrode for an electrochemical device according to claim 1 or 2 as described in claim 4.

  According to the present invention, by using polytetrafluoroethylene (PTFE) as a binder, deterioration of characteristics can be suppressed over a long period of time. Further, by adding a copolymer (FEP) of fluoroethylene and fluoropropylene, the binding force of the electrode is increased, so that the self-discharge failure due to, for example, dropping of carbon used as a conductive auxiliary material can be reduced.

  In addition, since the strength is higher than that of the polyvinylidene fluoride (PVDF) electrode in Conventional Example 1, a thick electrode can be manufactured. Furthermore, since the amount of binder used can be reduced, a high-capacity electrode can be obtained as a whole.

  Further, since water can be used as the solvent, the drying temperature can be lowered and the drying time can be shortened, and the cost can be reduced as compared with the N-methylpyrrolidone (NMP) solvent used in the above-mentioned Conventional Example 1. Furthermore, a special recovery device for recovering the solvent is not required.

  The electrode for an electrochemical device of the present invention is an aqueous dispersion (dispersion) in which polytetrafluoroethylene (PTFE) is mixed with a copolymer (FEP) of fluoroethylene and fluoropropylene and dispersed together with a surfactant as a binder. Is applied to a current collector such as etching aluminum and dried to a predetermined thickness, for example, by applying activated carbon and slurry as a conductive auxiliary agent together with activated carbon and a predetermined dispersing agent and an aqueous solvent. .

  According to this, the electrode using water as a solvent can be produced. Moreover, since the binding force between the electrode materials is improved, the self-discharge failure is reduced. Even when a voltage is applied, stable characteristics can be obtained with little deterioration.

  In the present invention, a preferred mixing ratio of polytetrafluoroethylene (PTFE) and a copolymer of fluoroethylene and fluoropropylene (FEP) is 7: 3 to 3: 7 (wt%).

  That is, when PTFE exceeds 7 wt%, the adhesion between the coated electrode and the current collector is deteriorated, and the electrode may fall off. Moreover, since the internal resistance after a voltage application test also increases, it is not preferable. On the other hand, if the FEP exceeds 7 wt%, not only the voltage holding property is deteriorated but also the internal resistance is increased, which is not preferable.

  Moreover, in this invention, the preferable mixing ratio of the binder in a coating electrode material is 1-20 wt% by dry weight. When the mixing ratio is less than 1%, the binding force is too weak to serve as a binder. On the other hand, if the mixing ratio exceeds 20%, the internal resistance increases and the amount of activated carbon also decreases, so the capacity decreases.

  The electrode of the present invention is suitable as an electrode of an electric double layer capacitor, but can also be used as an electrode of a lithium battery or an electrochemical capacitor. The current collector is preferably an etched aluminum foil, but may be copper, nickel, an expanded metal thereof, or a porous metal body. In addition, according to this invention, the application | coating thickness of the coating electrode material with respect to a collector can be suitably selected within the range of 30-150 micrometers.

Example 1
First, ketjen black, which is a carbon material as a conductive auxiliary material, and CMC as a dispersion material were mixed and stirred for a predetermined time, and then activated carbon and water were further added and stirred to be sufficiently dispersed. Separately, PTFE and FEP were mixed as a binder at a ratio of 50 wt%, and a surfactant such as polyoxyethylene octylphenyl ether was added thereto and dispersed in water to prepare a dispersion. Then, after adding the above-mentioned dispersion to a dry weight of 10 wt% in the liquid in which the activated carbon and the conductive auxiliary agent prepared in advance are sufficiently dispersed, further adding water and stirring. The electrode material was applied on an etching aluminum foil having a thickness of 30 μm. Then, it dried at 110 degreeC and rolled so that the thickness of the coating electrode might be set to 50 micrometers, and produced the electrode.

Example 2
An electrode was produced in the same manner as in Example 1 except that PTFE and FEP were mixed at 70 wt% PTFE and 30 wt% FEP.

Example 3
An electrode was prepared in the same manner as in Example 1 except that PTFE and FEP were mixed at 30 wt% PTFE and 70 wt% FEP.

<Comparative example 1>
An electrode was manufactured in the same manner as in Example 1 except that PTFE and FEP were mixed at 90 wt% PTFE and 10 wt% FEP.

<Comparative example 2>
An electrode was fabricated in the same manner as in Example 1 except that PTFE and FEP were mixed at 10 wt% PTFE and 90 wt% FEP.

<Comparative Example 3>
First, ketjen black, which is a carbon material as a conductive auxiliary material, and activated carbon were mixed and stirred for a predetermined time, and then an NMP solution of polyvinyl alcohol was added as a dispersing agent and stirred again to be sufficiently dispersed. To this dispersion, PVDF as a binder was added and stirred, and a coated electrode material was applied onto an etching aluminum foil having a thickness of 30 μm. Then, it dried at 200 degreeC and rolled so that the thickness of the coating electrode might be set to 50 micrometers, and produced the electrode.

<Comparative example 4>
First, ketjen black, which is a carbon material as a conductive auxiliary material, and CMC as a dispersion material were mixed and stirred for a predetermined time, and then activated carbon and water were further added and stirred to be sufficiently dispersed. Separately from this, a binder dispersion containing 40 wt% SBR rubber in water was prepared. Then, the coating electrode material formed by adding the binder dispersion liquid to the liquid prepared by sufficiently dispersing the activated carbon and the conductive auxiliary agent, adding water, and stirring the etched aluminum foil having a thickness of 30 μm. It was applied on top. Then, it dried at 110 degreeC and rolled so that the thickness of the coating electrode might be set to 50 micrometers, and produced the electrode.

  In order to evaluate the above Examples 1 to 3 and Comparative Examples 1 to 4, the coated electrode produced in each example was cut into 10 mm × 20 mm and sandwiched between two flexible metal plates, and 90 mm in both the left and right directions. The bending test was performed three times to observe whether the carbon electrode was dropped. Although not shown, a flexible metal plate having a thickness of 2 mm and having a roundness with a curvature of 1 mm at the tip is used so that the electrode does not fall off due to an angular corner.

  In addition, the coated electrode produced in each example was cut into 13 mm × 250 mm, wound with a cellulose separator having a thickness of 50 μm in a spiral shape, and the wound body inside a bottomed cylindrical aluminum case with a diameter of 12.5 mm Then, 1.5 mol / l (liter) of TEMABF4 / PC was injected as an electrolytic solution and vacuum impregnation was performed, followed by sealing with a sealing rubber to produce an electric double layer capacitor.

  Each electric double layer capacitor thus fabricated was tested for measuring the voltage when charged at DC 2.5 V for 24 hours and then allowed to stand for 24 hours to confirm the initial internal resistance and voltage holding characteristics. Thereafter, DC 2.7 V was continuously applied at 70 ° C., and the internal resistance after 100 hours was measured. The results are shown in Table 1 below.

  According to this, it can be seen that Examples 1 to 3 have high binding properties, with no coating electrode falling off. Moreover, the increase in internal resistance after the test was small, and the result that the voltage holding characteristic was good was obtained.

  On the other hand, in Comparative Example 1, since the PTFE exceeds 7 in weight ratio, the coating electrode is dropped. Also, the increase in internal resistance after the test is large. In Comparative Example 2, the coating electrode does not fall off, but the FEP exceeds 7 by weight, so the voltage holding characteristics are slightly poor. Also, the increase in internal resistance after the test is large.

  In Comparative Example 3, the increase in internal resistance was small, but the coated electrode was observed to fall off. In Comparative Example 4, the coating electrode does not fall off and the voltage holding characteristics are good, but on the other hand, the increase in internal resistance is large.

Claims (4)

In the electrode for an electrochemical device formed by applying a coating electrode material formed by binding at least activated carbon and a conductive auxiliary material with a binder to a predetermined thickness on a current collector made of a metal material, drying and rolling,
As the binder, an aqueous dispersion containing polytetrafluoroethylene (PTFE) and a copolymer of fluoroethylene and fluoropropylene (FEP) in a ratio of 7: 3 to 3: 7 (wt%) is used. An electrode for an electrochemical device.   2. The electrode for an electrochemical device according to claim 1, wherein a mixing ratio of the binder in the coated electrode material is 1 to 20 wt% by dry weight. Manufacture of electrodes for electrochemical devices in which a coated electrode material formed by binding at least activated carbon and a conductive auxiliary material with a binder is applied on a current collector made of a metal material to a predetermined thickness, dried and rolled. In the method
After the activated carbon, the conductive auxiliary material and the dispersion material are dispersed with water, polytetrafluoroethylene (PTFE) and a copolymer of fluoroethylene and fluoropropylene (FEP) are added to this liquid in a ratio of 7: 3 to 3: 7. An electrochemistry characterized in that a paint obtained by mixing a binder composed of an aqueous dispersion containing (wt%) is applied on a current collector and rolled so that the thickness after drying is 30 to 150 μm. A method for manufacturing an electrode for a device.   An electric double layer capacitor comprising the electrode for an electrochemical device according to claim 1.