Electric double layer capacitor and method for manufacturing same

An electric double-layer capacitor includes a cylindrical case having a bottom, a side surface, and an opening, a capacitor element accommodated in the case, the capacitor element, a driving electrolyte accommodated in the case, and a terminal plate provided at the opening of the case. The capacitor element includes a first electrode and a second electrode extending in a direction opposite to the first electrode. The second electrode is joined to the bottom of the case. The first and second electrodes are tilted away from the center axis of the capacitor element. In this electric double-layer capacitor, electrodes of the capacitor element are connected to the case and sealing plate reliably.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a method of manufacturing an electric double-layer capacitor that is used for regeneration or power storage of various electronic devices and hybrid vehicles.

(2) Description of Related Art

FIG. 9is a sectional view of a conventional electric double-layer capacitor501disclosed in patent document 1. Hollow portion10A is provided in capacitor element10. A polarizable electrode layer is formed on each of two collectors made of aluminum foil having a strip shape. Positive electrode15A is disposed on one end side in the width direction of one collector. Negative electrode15B is disposed at an end of the other collector in the opposite direction to positive electrode15A. A separator is provided between the collectors. The collectors and the separator are wound around hollow portion10A, providing capacitor element10. Electrodes15A and15B are exposed at end surfaces of capacitor element10opposite to each other.

Cylindrical case11having a bottom, made of metal, such as aluminum, accommodates capacitor element10and a driving electrolyte. Negative electrode terminal11A for external connection is provided unitarily on an outer bottom surface of case11. Projection11B is provided unitarily on an inner bottom surface of case11, and is inserted into hollow portion10A of capacitor element10. Negative electrode15B of capacitor element10accommodated in the case11is joined mechanically and electrically to the inner bottom surface of case11by laser welding.

Positive electrode terminal12A for external connection is provided unitarily on an outer surface of sealing plate12made of aluminum. Projection12B is inserted into hollow portion10A of capacitor element10. The driving electrolyte is put into case11through injection port12C. Pressure regulating valve13regulates the pressure in case11. Positive electrode15A of capacitor element10is joined mechanically and electrically to an inner surface of sealing plate12by, for example, laser welding. An opening edge of case11is wound with a periphery of sealing plate12, thereby being sealed with sealing plate12, which is called a curling process.

In electric double-layer capacitor501, electrodes15A and15B provided on both end surfaces of capacitor element10are joined directly to case11and sealing plate12with small connection resistances, respectively.

FIG. 10is an enlarged sectional view of capacitor element10. Electrodes15A and15B exposed at both end surfaces of capacitor element10are provided at low density because only respective ones of the electrodes are exposed at respective ones of both end surfaces. The low density prevents electrodes15A and15B from being pressed stably on and being welded to case11and sealing plate12.

This welding is performed by radiating a laser beam from the outer bottom surface of case11and the outer surface of sealing plate12while the inner bottom surface of case11and the inner surface of sealing plate12are pressed on electrodes15A and15B. This operation prevents electrodes15A and15B from melting enough to be welded.

In order to weld case11and sealing plate12to electrodes15A and15B reliably, projections are provided on the inner bottom surface of case11and the inner surface of sealing plate12. Electrodes15A and15B are welded with a laser by pressing the projections onto electrodes15A and15B. However, only portions of the electrodes on which the projections are pressed may be welded reliably, but other portions cannot be welded stably.

In electric double-layer capacitor501, electrodes15A and15B are welded to the inner bottom surface of case11and the inner surface of sealing plate12with the laser, thereby joining capacitor element10mechanically and electrically to case11and sealing plate12. Upon being used for vehicles, electric double-layer capacitor501is required to withstand large vibrations.

In electric double-layer capacitor501, a gap is provided between an outer circumferential surface of capacitor element10and an inner surface of case11. When large vibration is applied to electric double-layer capacitor501, capacitor element10moves in case11. This applies a stress to joined portions between electrodes15A and15B and case11and sealing plate12, which can cause the joined portions to break.Patent document 1: Japanese Patent Laid-Open Publication No. 2004-134632

BRIEF SUMMARY OF THE INVENTION

An electric double-layer capacitor includes a cylindrical case having a bottom, a side surface, and an opening, a capacitor element accommodated in the case, the capacitor element, a driving electrolyte accommodated in the case, and a terminal plate provided at the opening of the case. The capacitor element includes a first electrode and a second electrode extending in a direction opposite to the first electrode. The second electrode is joined to the bottom of the case. The first and second electrodes are tilted away from the center axis of the capacitor element.

In this electric double-layer capacitor, electrodes of the capacitor element are connected to the case and sealing plate reliably.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a sectional view of electric double-layer capacitor1001in accordance with Exemplary Embodiment 1 of the present invention.FIGS. 2A,2B,2C are a perspective view, an enlarged sectional view, and an enlarged sectional view of capacitor element1of electric double-layer capacitor1001, respectively.

As shown inFIG. 2A, capacitor element1includes collectors22A and22B made of metal foil, such as an aluminum foil, having strip shapes, polarizable electrode layers23A and23B provided on collectors22A and22B, respectively, and separators24A and24B having insulating property provided on polarizable electrode layers23A and23B, respectively. Collector22B has surface122B contacting polarizable electrode layer23B and surface222B opposite to surface122B. Separator24A has surface224A contacting polarizable electrode layer23A and surface124A opposite to surface224A. Collector22A, polarizable electrode layer23A, separator24A, collector22B, polarizable electrode layer23B, and separator24B are stacked so that surface124A of separator24A contacts surface222B of collector22B. These stacked layers are wound about center axis1F of hollow portion1C in direction1H, thereby providing capacitor element1. Capacitor element1has a cylindrical shape centering on center axis1F (hollow portion1C), and has end surfaces1D and1E opposite to each other in a direction of center axis1F of hollow portion1C. Collectors22A and22B includes electrodes1A and1B exposed from end surfaces1D and1E, respectively. As shown inFIG. 2B, electrode1A is tilted in radial direction1G proceeding away from center axis1F (hollow portion1C). As shown inFIG. 2C, similarly, electrodes1A is tilted in radial direction1G proceeding away from center axis1F (hollow portion1C). Capacitor element1has outer surface1J parallel to center axis1F. In other words, collector22A is wound around center axis1F. Polarizable electrode layer23A is wound around center axis1F, and is provided on collector22A in a direction toward center axis1F. Separator24A is wound around center axis1F, and is provided on polarizable electrode layer23A in the direction toward center axis1F. Collector22B is wound around center axis1F, and is provided on separator24A in the direction toward center axis1F. Polarizable electrode layer23B is wound around center axis1F, and is provided on collector22B in the direction toward center axis1F. Separator24B is wound around center axis1F, and is provided on polarizable electrode layer23B in the direction toward center axis1F. Electrode1A extends from collector22A in parallel to center axis1F. Electrode1B extends from collector22B in parallel to center axis1F in a direction opposite to a direction in which electrode1A extends. Electrodes1A and1B have spiral shapes spread about center axis1F, and extend in parallel to center axis1F from end surfaces1D and1E, respectively.

Case2made of metal, such as aluminum, has a cylindrical shape, and has bottom2D facing end surface1E of capacitor element1, side surface2H facing outer surface1J of capacitor element1, and opening2E facing end surface1D of capacitor element1. Capacitor element1and driving electrolyte8are accommodated in case2. Projection2A is provided unitarily with inner bottom surface2F of case2, and is inserted into hollow portion1C of capacitor element1. Electrode1B provided on end surface1E of capacitor element1is joined mechanically and electrically to inner bottom surface2F of case2by, for example, laser welding.

Terminal plate3having an annular shape has outer circumference surface3D having a step portion including an upper step thereof having a smaller diameter. Projection3A is provided on inner surface3E of terminal plate3. Recess3B is provided in inner surface3E of terminal plate3. Thread3C for external connection is provided on outer surface3F of terminal plate3. Projection3A is inserted into hollow portion1C of capacitor element1. Electrode1A exposed at end surface1E of capacitor element1is joined mechanically and electrically on recess3B of terminal plate3by, for example, laser welding.

Sealing rubber4has a ring shape having a cross section of a reversed-L shape. Inner circumference surface4A of sealing rubber4contacts a flat portion of the step portion of outer circumference surface3D of terminal plate3and a lower portion of outer circumference surface3D connected to the flat portion. Outer circumference surface4B of sealing rubber4contacts an inner surface of case2. A portion of case2which outer circumference surface4B of sealing rubber4contacts has annular shrink portion2B having a diameter thereof locally reduced. Sealing rubber4is compressed with shrink portion2B of case2. Curled section2C bent and curled toward an inside of opening2E is formed at end2G of opening2E of case2, and compresses the flat portion of outer circumference surface4B of sealing rubber4. Thus, sealing rubber4and terminal plate3seal opening2E of case2.

FIGS. 3A and 3Bare schematic diagrams illustrating a method of manufacturing capacitor element1. Capacitor element1is held with a chuck, and is rotated about center axis1F in winding direction1H of collectors22A and22B and separators24A and24B. While capacitor element1is rotated, tip5A of processing device5is moved in direction5B toward hollow portion1C of capacitor element1, and contacts hollow portion1C of capacitor element1. At this moment, tip5A contacts capacitor element1in downward direction5D from center axis1F about which capacitor element1rotates. Then, tip5A contacts hollow portion1C of capacitor element1and is moved outward in horizontal direction5C perpendicular to direction5D. Thus, electrodes1A and1B are tilted from center axis1F in radial direction1G.

As shown inFIG. 2B, electrode1A exposed at end surface1D of capacitor element1has base portion61A that extends from end surface1D and in parallel to center axis1F, and tip portion62A that extends from base portion61A and is tilted away from center axis1F (hollow portion1C). The length of tip portion62A and the angle of tip portion62A with respect to center axis1F are adjusted by an inserted amount of processing device5, a moving speed of device outward in horizontal direction5C, and a rotating speed of capacitor element1.

As shown inFIG. 2C, similarly, electrode1B exposed at end surface1E of capacitor element1has base portion61B that extends from end surface1E and in parallel to center axis1F, and tip portion62B that extends from base portion61B and is tilted away from center axis1F (hollow portion1C). The size of tip portion62B of electrode1B and the angle of tip portion62B with respect to center axis1F are adjusted precisely based on an inserted amount of the processing device, a moving speed of the device outward in the horizontal direction, and the rotating speed of capacitor element1.

FIGS. 4A and 4Bare enlarged sectional views of capacitor element6of an electric double-layer capacitor in accordance with Exemplary Embodiment 2 of the present invention. InFIGS. 4A and 4B, components identical to those of electric double-layer capacitor1001shown inFIGS. 1 to 2Bare denoted by the same reference numerals, and their description will be omitted. The electric double-layer capacitor according to Embodiment 2 includes capacitor element6instead of capacitor element1of electric double-layer capacitor1001according to Embodiment shown inFIGS. 1 to 2B. Capacitor element6has center axis6F and hollow portion6C corresponding to center axis1F and hollow portion1C of capacitor element1, respectively. Capacitor element6has end surfaces6A and6B opposite to each other in a direction of center axis6F corresponding to end surfaces1D and1E of capacitor element1, respectively. Capacitor element6includes electrodes6A and6B that are exposed at end surfaces6D and6E and correspond to electrodes1A and1B of capacitor element1, respectively. Outer surface6G of capacitor element6is parallel to center axis6F, and faces side surface2H of case2while capacitor element6is accommodated in case2.

As shown inFIG. 4A, electrode6A joined to terminal plate3has inner portion76A connected to hollow portion6C (center axis6F), and outer portion86A farther from hollow portion6C (center axis6F) than inner portion76A. Outer portion86A is connected to outer surface6G of capacitor element6. Inner portion76A of electrode6A has inner base portion176A that extends from end surface6D and in parallel to center axis6F, and inner tip portion276A that extends from inner base portion176A and is tilted away from center axis6F (hollow portion6C). Outer portion86A of electrode6A has outer base portion186A that extends from end surface6D and in parallel to center axis6F, and outer tip portion286A that extends from outer base portion186A and is tilted towards center axis6F (hollow portion6C).

As shown inFIG. 4B, electrode6B joined to inner bottom surface2F of case2has base portion176B that extends from end surface6E and in parallel to center axis6F, and tip portion276B that extends from base portion176B and is tilted away from center axis6F (hollow portion6C).

A method of manufacturing capacitor element6will be described below. First, electrodes6A and6B are tilted away from center axis6F (hollow portion6C) with processing device5, similarly to capacitor element1shown inFIGS. 3A and 3B. Then, processing device5contacts outer surface6G and is moved from outer surface6G toward hollow portion6C, thereby tilting outer tip portion286A of electrode6A toward center axis6F (hollow portion6C). The sizes of tip portions276A,286A, and276B of electrodes6A and6B and the angles of the tip portions with respect to center axis1F are adjusted precisely based on an inserted amount of processing device5, a moving speed of device5outward in a horizontal direction, and a rotating speed of capacitor element6. Inner tip portion276A and outer tip portion286A of electrode6A may be formed by pressing a device with a shape analogous to the shape of electrode6A after processing as shown inFIG. 4A.

In the electric double-layer capacitor according to Embodiment 2, outer portion86A of electrode6A of capacitor element6is tilted toward hollow portion6C. This structure prevents electrode6A from contacting case2and from causing short circuit, thus providing the electric double-layer capacitor with high reliability.

FIG. 5is an enlarged sectional view of a capacitor element of an electric double-layer capacitor in accordance with Exemplary Embodiment 3 of the present invention. InFIG. 5, components identical to those of electric double-layer capacitor1001shown inFIGS. 1 to 2Bare denoted by the same reference numerals, and their description will be omitted.

The electric double-layer capacitor according to Embodiment 3 further includes insulating layer7covering outer peripheral portion1K of electrode1A in addition to capacitor1001according to Embodiment 1. Insulating layer7can be formed by winding an insulating tape on outer peripheral portion1K of electrode1A.

Insulating layer7covering outer peripheral portion1K of electrode1A prevents electrode1A from contacting an inner surface of case2and from causing short circuit, thus providing the electric double-layer capacitor with high reliability.

FIG. 6is a sectional view of electric double-layer capacitor2001in accordance with Exemplary Embodiment 4 of the present invention. InFIG. 6, components identical to those of electric double-layer capacitor1001shown inFIGS. 1 to 2Bare denoted by the same reference numerals, and their description will be omitted.

Case102made of metal, such as aluminum, has a cylindrical shape, and has bottom102D facing end surface1E of capacitor element1, side surface102H facing outer surface1J of capacitor element1, and opening102E facing end surface1D of capacitor element1. Capacitor element1and driving electrolyte8are accommodated in case102. Electrode1B provided on end surface1E of capacitor element1is joined mechanically and electrically to inner bottom surface102F of case102by, for example, laser welding.

Annular shrink portions102S and102T having diameters locally reduced are provided near opening102E and bottom102D of case102, respectively. Shrink portions102S and102T press electrodes1A and1B exposed at end surfaces1D and1E of capacitor element1over the entire circumference and fix capacitor element1so as to prevent capacitor element1from moving in case102.

Terminal plate103has terminal103A for external connection. Terminal plate103is inserted into opening102E of case102. Curled section102C bent and curled toward an inside of opening102E is formed at end102G of opening102E of case102. Insulating layer7for insulating case102from electrode1A is provided on outer peripheral portion1K of electrode1A of capacitor element1. Insulating layer7is formed by sticking an insulating tape to outer peripheral portion1K of electrode1A.

In electric double-layer capacitor2001, electrodes1A and1B provided on end surfaces1D and1E of capacitor element1are pressed by shrink portions102S and102T provided in case102, thereby fixing capacitor element1to case102. Even when large vibration is applied, capacitor element1does not move in case102, thus providing electric double-layer capacitor2001with high resistance against vibration.

While capacitor element1is accommodated in case102having shrink portions102S and102T, electrodes1A and1B of capacitor element1may not necessarily be tilted away from center axis1F, but may be parallel to center axis1F.

FIG. 7is a sectional view of electric double-layer capacitor2002in accordance with Exemplary Embodiment 5 of the present invention. InFIG. 7, components identical to those of electric double-layer capacitor2001according to Embodiment 5 shown inFIG. 6are denoted by the same reference numerals, and their description will be omitted.

Four shrink projections102U projecting toward an inside of case102are formed on side surface102H of case102of electric double-layer capacitor2002. Shrink projections102U has a longitudinally long shape having longitudinal direction102W parallel to center axis102P of case102, center axis1F of capacitor element1. Four shrink projections102U are located substantively at an intermediate between shrink portions102S and102T and at equal angular intervals (90 degrees) about center axis1F (102P).

Four shrink projections102U press outer surface1J of capacitor element1, and fix capacitor element1to case102.

If shrink projections102U of case102has an annular shape or a substantively annular shape, shrink projections102U prevent driving electrolyte8impregnated in capacitor element1from circulating. Therefore, shrink projections102U are provided preferably with certain intervals between projections102U.

In electric double-layer capacitor2002, outer surface1J of capacitor element1and electrodes1A and1B provided on end surfaces1D and1E of capacitor element1are pressed with shrink portions102S and102T and shrink projections102U provided in case102, thereby fixing capacitor element1to case102. Even when large vibration is applied, capacitor element1does not move in case102, thus providing electric double-layer capacitor2002with high resistance against vibration.

According to Embodiment 5, the number of shrink projections102U provided in case102is four. However, two or more shrink projections102U may be provided at equal angle intervals about center axis1F (102P), providing the same effects. The shapes of shrink projections102U may not necessarily have the longitudinally long shape.

While capacitor element1is accommodated in case102having shrink portions102S and102T and shrink projections102U, electrodes1A and1B of capacitor element1may not necessarily be tilted away from center axis1F, but may be parallel to center axis1F.

FIG. 8is a sectional view of electric double-layer capacitor2003in accordance with Exemplary Embodiment 6 of the present invention. InFIG. 8, components identical to those of electric double-layer capacitor1002according to Embodiment 5 shown inFIG. 7are denoted by the same reference numerals, and their description will be are omitted.

As shown inFIG. 8, case102of electric double-layer capacitor2003has shrink portion102S and shrink projections102U for pressing electrode1A and outer surface1J of capacitor element1, but does not have shrink portion102T for pressing electrode1B shown inFIG. 7.

In electric double-layer capacitor2003, outer surface1J of capacitor element1and electrode1A disposed on end surface1D of capacitor element1are pressed with shrink portion102S and shrink projections102U provided in case102, thereby fixing capacitor element1to case102. Even when large vibration is applied, capacitor element1does not move in case102, thus providing electric double-layer capacitor2003with high resistance against vibration.

While capacitor element1is accommodated in case102having shrink portion102S and shrink projections102U, electrodes1A and1B of capacitor element1may not necessarily be tilted away from center axis1F, but may be parallel to center axis1F.

INDUSTRIAL APPLICABILITY

An electric double-layer capacitor according to the present invention includes electrodes of a capacitor element connected reliably to a case and sealing plate, hence being useful for an electronic device requiring resistance to vibration.