Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2001-09-25
2003-10-28
Mayes, Curtis (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S229000, C156S244110, C156S244230, C156S244240, C029S025030, C361S502000
Reexamination Certificate
active
06638385
ABSTRACT:
The present invention relates to a process for producing an electrode assembly for an electric double layer capacitor.
The demand for an electric double layer capacitor utilizing an electric double layer formed at the interface between a polarizable electrode and an electrolyte, particularly for a coin shaped one, is rapidly increasing recently, as a memory backup power source. On the other hand, it is desired to develop an electric double layer capacitor having a large capacitance per unit volume (hereinafter referred to as capacitance density), small internal resistance, a high energy density and a high output density, also for a use which requires a large capacity such as a power source for electric cars. Further, with regard to an electric double layer capacitor for memory backup, it is desired to reduce the internal resistance.
In order to reduce the internal resistance, it is necessary to use a material having a low resistance as the material for constituting the electrode and to efficiently collect the electric current. For this purpose, it is common to use an electrode of sheet shape comprising an electroconductive material, as bonded to the surface of a current collector foil having a low resistance. However, if the thickness of the electrode of sheet shape is thick, the resistance can not be made adequately low, and it is necessary to obtain a thin electrode of sheet shape. Further, the capacitance density is higher, as the amount of the electrode material (such as a carbonaceous material having a high specific surface area) as the main material for forming an electric double layer, present per unit volume of the electrode, is larger. Accordingly, it is necessary to increase the density of the electrode of sheet shape.
The electrode for an electric double layer capacitor is prepared, for example, by kneading an activated carbon powder with a solvent for an electrolytic solution such as sulfuric acid, and forming the mixture into a slurry, followed by press forming (U.S. Pat. No. 3,288,641). However, the electrode obtained by this process has a stiff porous structure and thus is likely to be cracked or broken, and it can not be used for a long period of time. On the other hand, a carbon-paste electrode has been proposed which is made of a viscous material having a binder made of a polytetrafluoroethylene (hereinafter referred to as PTFE) added to a mixture comprising an activated carbon powder and an electrolytic solution, as the case requires (JP-B-53-7025, JP-B-55-41015). This electrode is flexible and has crack resistance and break resistance. However, it is inadequate in the shape keeping property, and a cell having a special structure is required to supplement the strength for its use.
In order to obtain an electrode having crack resistance and break resistance, and an excellent shape keeping property, a process has been proposed, which comprises preliminarily molding a kneaded material comprising a carbonaceous material, a binder such as PTFE and a liquid lubricant, followed by stretching or rolling to obtain a formed electrode of sheet shape (JP-A-63-107011, JP-A-2-235320). However, by this process, PTFE is randomly fibrillated by kneading, and a fibrillated portion and a non-fibrillated portion will be formed, and consequently the hardness of the two portions will be different. Therefore, when the sheet electrode is formed into a thin film sheet having, for example, a thickness of at most 0.2 mm, the surface tends to be irregular, and holes are likely to be formed. Therefore, the capacitance density of the electric double layer capacitor can not be made large, and further the internal resistance is large.
As a method for solving the above problems, a method has been proposed wherein a mixture comprising a carbonaceous material, PTFE and a liquid lubricant, is subjected to paste extrusion or screw extrusion, followed by rolling, to obtain an electrode formed into a sheet shape (JP-A-2000-235938, JP-A-11-283887). By such a method, a thin sheet having high strength can be obtained, but the density of the electrode of sheet shape can not be made high, since the electrode of sheet shape is smoothly made thin by rolling. Accordingly, there is a problem that the capacitance density can not be adequately increased.
On the other hand, a method has also been proposed wherein an activated carbon powder and PTFE are mixed and formed into a paste, which is coated on a current collector, dried and then heated to a temperature of at least the melting point of PTFE, followed by press forming to make the electrode thin and also to increase the density (JP-A-9-36005). However, this method has a problem such that the production steps are so complicated that it is difficult to make them continuous, and a part of PTFE melts so that the internal resistance will be high.
The present invention has been made to overcome the above-mentioned problems of the prior art, and it is an object of the present invention to provide a process for producing an electrode having an electrode layer with a high density and a low resistance, formed on a current collector, thereby to provide an electric double layer capacitor having a high capacitance density and low internal resistance, particularly an electric double layer capacitor for an application where a large capacitance and a high power are required.
The present invention provides a process for producing an electrode assembly for an electric double layer capacitor having an electrode layer comprising a carbonaceous material and a first binder, formed on at least one side of a metal current collector foil, which comprises the following steps A to D:
Step A: a step of coating an electroconductive adhesive comprising an electroconductive powder, a second binder and a solvent, on at least one side of a metal current collector foil;
Step B: a step of drying the metal current collector foil coated with the electroconductive adhesive to remove at least a part of the solvent and to form an electroconductive bonding layer;
Step C: a step of preparing a formed product of sheet shape comprising the carbonaceous material and the first binder; and
Step D: a step of placing the formed product of sheet shape on the electroconductive bonding layer to form a laminate comprising the metal current collector foil and the formed product of sheet shape, and rolling the laminate to reduce the thickness of the formed product of sheet shape by from 5 to 60% and to form an electrode layer comprising the formed product of sheet shape.
Now, the present invention will be described in detail with reference to the preferred embodiments.
In this specification, an electrode assembly refers to an assembly having an electrode layer formed on one side or both sides of a metal current collector foil, so that the metal current collector foil and the electrode layer are integrated. When such an electrode assembly is used on a positive electrode side, it will be referred to as a positive electrode assembly, and when it is used on a negative electrode side, it will be referred to as a negative electrode assembly.
The electric double layer capacitor is based on a principle such that an electric double layer is formed at the interface between an electrode material and an electrolyte, thereby to store an electric charge at the electric double layer. In the present invention, a carbonaceous material is used as the electrode material. As the carbonaceous material, a powder of e.g. activated carbon, polyacene or carbon black, is preferred, and carbon fiber, carbon whisker or a fiber or powder of e.g. graphite can also preferably be used. As the activated carbon, a phenol type, a rayon type, an acrylic type, a pitch type or a coconut shell type, may be used.
The above carbonaceous material preferably has a pore volume of from 0.7 to 1.2 cm
3
/g and a specific surface area of from 900 to 2,300 m
2
/g. The specific surface area is particularly preferably from 1,500 to 2,300 m
2
/g. Further, it is more preferred that the pore volume is from 0.75 to 1.1 cm
3
/g, and the specific surface area is
Ikemura Masaaki
Ishikawa Takamichi
Kanetoku Sadao
Shinozaki Yasuo
Asahi Glass Company Limited
Mayes Curtis
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
LandOfFree
Process for producing an electrode assembly for an... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for producing an electrode assembly for an..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for producing an electrode assembly for an... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3130310