JP4895028B2 - Electric double layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the internal resistance of an electric double-layer capacitor. <P>SOLUTION: A plurality of electrode sheets in each of which a polarizable electrode layer mainly formed of activated carbon is formed on one side or both sides of a collector are stacked with separators therebetween to make a prismatic capacitor. The prismatic capacitor is housed in a prismatic exterior case along with a holding member arranged between the side of the capacitor element and the inner side of the exterior case. Further, when the capacitor is immersed in an electrolyte, it is swollen as it is impregnated with the electrolyte. The swelling of the capacitor gives a specified pressure to the capacitor from the holding member, thus increasing the contact frequency of active carbons inside the polarizing electrode and reducing internal resistance. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to an electric double layer capacitor obtained by impregnating a capacitor element formed by laminating a polarizable electrode, a current collector, and a separator with an electrolytic solution.

  Recently, electric double layer capacitors capable of charging and discharging a large current have attracted attention. An electric double layer capacitor is a capacitor that uses an electric double layer formed by ion polarization at the interface between an electrode and an electrolytic solution, and has a larger capacitance than an electrolytic capacitor and is also compared with a battery. Rapid charge / discharge is possible, and its application is expected.

  In such an electric double layer capacitor, a plate-like electrode sheet having polarizable electrode layers formed on both sides of a current collector is used as a positive electrode sheet and a negative electrode sheet, and these are alternately stacked via separators to form a capacitor element. A multilayer electric double layer capacitor is known which is formed and accommodated in an exterior case made of aluminum or the like and has an opening end sealed with a sealing plate.

  Since such a multilayer electric double layer capacitor can produce a prismatic electric double layer capacitor, the storage efficiency in an electric device can be increased as compared with a wound electric double layer capacitor. There is an advantage.

  In addition, the multilayer electric double layer capacitor is provided with a tab protruding outward from one side of each current collector, and electrically connects the tabs serving as positive electrodes and the tabs serving as negative electrodes, respectively. It is connected to an external electrode embedded in the sealing plate of the multilayer capacitor and is electrically connected to an external circuit. And, as described above, by pulling out the external extraction tab from each current collector, the current capacity at the tab portion can be increased, and charging / discharging with a large current can be performed on the electric double layer capacitor. It becomes possible.

  As described above, the electric double layer capacitor has a large capacitance and can be charged and discharged with a large current. However, an electric double layer capacitor requires a high capacity and a high discharge density. However, when the internal resistance of the capacitor is high, as the current density increases, a sudden drop in voltage at the initial stage of discharge, a so-called IR drop is observed. Therefore, it is required to reduce the internal resistance of the capacitor.

  The internal resistance largely depends on the part depending on the specific resistance of the electrolytic solution of the electric double layer capacitor and the part depending on the electric resistance of the positive electrode and the negative electrode. Among these, the electrical resistance of the positive electrode and the negative electrode is greatly influenced by the contact frequency between the activated carbon powders, and the internal resistance is increased unless the contact frequency between the activated carbon powders is very large. Therefore, it is attempted to reduce the internal resistance by increasing the contact frequency of the activated carbon and increasing the conductive path inside the polarizable electrode layer.

  As a method of increasing the contact frequency between the activated carbon powders of the polarizable electrode layer and reducing the internal resistance, there is a method of increasing the contact frequency between the activated carbon powders by applying a press pressure to the polarizable electrode layer formed in a sheet shape. is there. In addition, a method is also known in which after the capacitor element is housed in the exterior case, the exterior case is deformed inward from the periphery of the exterior case to apply pressure to the polarizable electrode layer (Patent Document 1).

  In addition, after the prismatic capacitor element is housed in the prismatic outer case, the capacitor element is impregnated with an electrolytic solution, and the capacitor element swells due to the impregnation with the electrolytic solution. A method is also known in which the internal resistance of an electric double layer capacitor is reduced by applying pressure (Patent Document 2).

As described above, there are the following documents as well-known documents related to the electric double layer capacitor.
Japanese Patent Application Laid-Open No. 2000-124086 JP 2006-54253 A

  In the method for manufacturing an electric double layer capacitor disclosed in Patent Document 2, the capacitor element is impregnated with the electrolytic solution after the prismatic capacitor element is accommodated in the prismatic outer case, and the capacitor element is impregnated with the electrolytic solution. In order to apply a predetermined pressure to the capacitor element from the inner peripheral surface of the outer case due to the swelling, the effect is further increased by reducing the clearance between the outer case and the capacitor element. However, even in a prismatic outer case, it is impossible to form the corners at right angles, and the corners are formed in an arc shape. For this reason, the length of the radius of the corner formed in the arc shape cannot be accommodated in the outer case unless the capacitor element is made small. This state is shown in FIG.

  In addition, the arcuate size of the corners of the outer case varies depending on the material and thickness of the outer case. The current situation is that the size varies.

  For this reason, it is necessary to form the size of the capacitor element smaller than the inner dimension of the outer case in consideration of the variation of the arcuate size at the corners of the outer case. The clearance could not be completely eliminated. As a result, the effect of applying a predetermined pressure to the capacitor element from the inner peripheral surface of the exterior case could not be sufficiently obtained due to the swelling of the capacitor element accompanying the impregnation of the electrolytic solution.

  Therefore, the present invention provides a structure that can apply a predetermined pressure to the capacitor element from the inner peripheral surface of the outer case more reliably by swelling of the capacitor element accompanying the impregnation of the electrolytic solution.

  According to the first aspect of the present invention, a capacitor element using an electrode sheet in which a polarizable electrode layer mainly composed of activated carbon is formed on one side or both sides of a current collector is housed in an outer case together with a holding member. An electric double layer capacitor in which a predetermined pressure is applied from the holding member to the capacitor element by swelling of the capacitor element with the electrolyte solution impregnated in the capacitor.

  A polarizable electrode used for an electric double layer capacitor is formed into a sheet by kneading activated carbon powder, carbon black, and a binder. The polarizable electrode swells when impregnated with an electrolytic solution. Therefore, a predetermined pressure is applied from the holding member to the capacitor element by utilizing the swelling due to the impregnation of the electrolytic solution. When pressure is applied to the capacitor element, the contact frequency between the activated carbon powders increases, and the internal resistance of the electric double layer capacitor is reduced. In addition, the adhesion strength between the polarizable electrode sheet and the polarizable electrode layer is increased, the contact resistance at this interface is reduced, and the internal resistance of the electric double layer capacitor can be reduced.

The invention according to claim 2 is the electric double layer capacitor according to claim 1, characterized in that the specific surface area of the activated carbon is in the range of 1500 to 3000 m ² / g.

When the specific surface area of the activated carbon used as the material for the polarizable electrode is in the range of 1500 to 3000 m ² / g, it is considered that the activated carbon itself does not absorb the electrolyte and expand. A graphite material having a smaller specific surface area is known in which graphite takes in an electrolyte solution and expands, but this invention does not include a material having a property of expanding a carbon material. The swelling of the polarizable electrode in this invention is considered to swell when the electrolyte enters between the activated carbon powders.

And in the range whose specific surface area of activated carbon is 1500-3000 m < ² > / g, since the contact area of activated carbon and electrolyte solution becomes large, and the area of the electric double layer formed also becomes large, a big electrostatic capacitance is obtained. Be able to.

  The electric double layer capacitor obtained by the manufacturing method of the present invention can further reduce the internal resistance by a simple method. Furthermore, since the capacitor element is fixed by the holding member and the capacitor element does not move inside the outer case, the vibration resistance performance of the electric double layer capacitor is improved.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 4 shows the structure of the electric double layer capacitor of the present invention.

  As an outline of the structure of the electric double layer capacitor, as shown in FIG. 4, the capacitor element 1 formed by alternately laminating the positive electrode sheets 11 and the negative electrode sheets 12 with the separators 13 interposed therebetween together with the holding member 5 is made of metal. The exterior case 3 is housed and the opening end of the exterior case 3 is sealed by the sealing plate 2.

  The positive electrode sheet 11 and the negative electrode sheet 12 are flat electrode sheets in which polarizable electrode layers 14 and 14 mainly composed of activated carbon are formed on both sides of a current collector 13 as shown in FIG. The electrode arranged on the outermost part of the capacitor element may be one in which the polarizable electrode layer 14 is formed only on the inner surface.

The positive electrode sheet 11 and the negative electrode sheet 12 are prepared by kneading activated carbon having a specific surface area of 1500 to 3000 m ² / g, carbon black as a conductive auxiliary agent, and polytetrafluoroethylene powder as a binder in a wet or dry manner. A kneaded product is obtained, and the kneaded product is applied to the current collector 13 and dried to solidify the kneaded product to form the polarizable electrode layers 14 and 14 on the current collector 13. Furthermore, you may press the polarizable electrode layers 14 and 14 so that it may become predetermined thickness with a rolling roll.

  In addition to the above steps, the kneaded product may be formed into a sheet and dried, and this sheet may be attached to a current collector with a conductive adhesive to produce a polarizable electrode. In this case, the thickness may be set to a predetermined thickness with a rolling roll in the state of the sheet, or the thickness may be set to a predetermined thickness with the rolling roll after the sheet is attached to the current collector.

  The current collector 13 can be a metal foil, mesh, or the like, rather than a metal, but it is 40 μm from the viewpoint of corrosion resistance to the electrolyte, conductivity of the current collector itself, and mechanical strength of the current collector. An aluminum foil having a thickness of about can be suitably used. In addition, when using aluminum foil, it is good to form the fine unevenness | corrugation in the surface by the etching process. If there are fine irregularities on the surface, the wettability is improved when the kneaded product is applied to the current collector or when a conductive adhesive is applied to the current collector, and the adhesion strength with the polarizable electrode layer is strong. It will be a thing.

  Further, a tab 15 for external drawing is connected to the current collector 13 in advance. The tab 15 is obtained by projecting a part of the current collector 13 from one side of the current collector 13. The tab 15 may be formed by connecting a member different from the current collector 13 to the current collector by a cold welt method, an ultrasonic welding method, or the like.

  As shown in FIG. 3, the positive electrode sheet 11 and the negative electrode sheet 12 are alternately laminated with a plurality of positive electrode sheets 11 and negative electrode sheets 12 with separators 16 interposed therebetween to form a laminate. As the separator 16, a polypropylene nonwoven fabric or the like can be used. At this time, lamination is performed so that the positive electrode tabs and the negative electrode tabs overlap each other.

  Moreover, the winding tape 17 is wound around the outer periphery of these laminated bodies, and it fixes so that a laminated body may not loosen. The anti-winding tape used here preferably has a stretchability of 4% or more. This is because even if the polarizable electrode of the capacitor element swells, if the swelling of the capacitor element is hindered by the winding tape that circulates around the outer periphery of the capacitor element, a predetermined pressure can be applied to the capacitor element from the holding member. Disappear. Therefore, by setting the winding tape as stretchable, a predetermined pressure can be applied to the capacitor element from the inner peripheral surface of the outer case. As a material for the winding tape having such an extensibility, a polyimide film coated with an adhesive can be used.

  The capacitor element produced as described above is formed in a prismatic shape, and the dimension indicated by the arrow in FIG. 2 is the thickness in the stacking direction.

  Next, the tab derived from the capacitor element and the external connection terminal 21 of the sealing plate 2 are electrically joined. The sealing plate 2 is made of a hard resin and is embedded so that the metal external connection terminals 21 and 21 penetrate therethrough. The connection method of the tab 15 and the external connection terminal 21 is not particularly limited, but one end of the connection lead is attached by overlapping a plurality of tabs, and the other end of the connection lead is connected to the inner end of the external connection terminal. A connection method can be taken.

  Then, the capacitor element 1 connected to the sealing plate 2 is housed in the outer case 3 together with the holding member 5. As shown in FIG. 5, the holding member 5 is made of resin and includes four holding pieces 51 that come into contact with the side surface of the capacitor element 1, and the holding pieces 51 are integrated at the bottom 52. An interval (inside dimension) between the opposing holding pieces 51 is formed slightly smaller than the outer dimension of the capacitor element 1. The horizontal width of the holding piece 51 is narrower than the width of the side surface of the capacitor element. When the capacitor element 1 is housed inside the holding member 5, the corners of the capacitor element 1 are not in contact with the holding member 5.

  The outer case 3 has a prismatic shape, and one end is open. Aluminum or an aluminum alloy can be used as the material of the outer case 3. In order to increase the mechanical strength of the side surfaces, ribs that protrude from the inner side to the outer side may be provided. Further, the inner dimension of the outer case 3 is set to be almost the same as the outer dimension of the holding member 5 or slightly larger than the outer dimension of the holding member 5.

  The size of the capacitor element 1 with respect to the inner dimension of the holding member 5 can be appropriately designed according to the degree of swelling when the capacitor element 1 is impregnated with the electrolytic solution. For example, when the size (swelling degree) after impregnating the electrolytic solution is about 5% larger than the size before impregnating the electrolytic solution with the capacitor element 1, the capacitor before impregnating the electrolytic solution Even when the size of the element is about 96% of the inner dimension of the holding member 5, when the capacitor element is impregnated with an electrolyte and swollen, the pressing pressure can be received from the holding member 5. . Further, when the size of the capacitor element is about 99% of the inner dimension of the holding member 5, even if the swelling degree of the capacitor element is about 1%, the capacitor element receives a pressing pressure from the holding member 5. become. In addition, since the capacitance per volume of the electric double layer capacitor can be increased by increasing the amount of the polarizable electrode with respect to the storage volume of the outer case, in terms of the storage efficiency of the capacitor element, the stacking direction It is preferable that the thickness is 98.5% or more of the inner dimension of the outer case that accommodates the thickness of the outer case.

  When the holding member 5 and the capacitor element 1 are stored in the outer case 3, the holding member 5 enters the gap between the outer case 3 and the capacitor element 1 as shown in FIG. 7. In addition, although it is not necessary to provide a clearance between the holding member 5 and the side surface of the outer case 1, the outer dimension of the holding member 5 is slightly smaller than the inner dimension of the outer case in order to facilitate storage in the outer case. It is sufficient to make it small.

  Then, as shown in FIG. 1 (a), the capacitor element 1 is housed in the outer case 3, and then, the electrolyte solution 4 is injected into the outer case 18 as shown in FIG. 1 (b). Is impregnated in the capacitor element 1. In FIG. 1, the tab of the capacitor element 1 is omitted.

The electrolytic solution used here is a solute composed of cations such as lithium ions and quaternary phosphonium ions, anions such as BF ₄ ⁻ , PF ₆ ⁻ , ClO ₄ ⁻ , CF ₃ SO ₃ ⁻ , propylene carbonate, 1 An organic electrolytic solution composed of an aprotic solvent such as butylene carbonate, sulfolane, acetonitrile, γ-butyrolactone, and dimethylformamide is preferable.

  By injecting the electrolytic solution, the capacitor element 1 is impregnated with the electrolytic solution, and the capacitor element 1 swells. The swelling direction becomes conspicuous with respect to the thickness direction in the stacking direction of the capacitor element 1 in which the electrode sheets as indicated by arrows in FIG. Although it is going to swell also in the horizontal direction, the polarizable electrode layer is bonded to the aluminum foil as the current collector, so that the swelling in the horizontal direction is inhibited.

  When the thickness of the capacitor element in the stacking direction is 98.5% or more of the inner dimension of the holding member to be stored, if a capacitor element having a swelling degree of 2% or more is used, the storage efficiency is good and the capacitor Since the degree of swelling of the element is large, the pressure applied to the capacitor element as a reaction from the inner surface of the holding member can be increased, which is preferable.

  The capacitor element 1 swollen by the electrolytic solution comes into contact with the inner surface of the holding member 5 and further presses the outer case 3. Due to the reaction, the entire capacitor element 1 receives a pressing pressure from the inner surface of the holding member 5. At this time, the holding member 5 has such a strength that it is not deformed by the pressure accompanying the swelling of the capacitor element. Alternatively, if the holding member 5 is deformed, the outer case 3 has such a strength that it is not deformed by pressure due to swelling of the capacitor element 1. If the holding member 5 itself and the outer case 3 are simultaneously deformed by the pressure due to swelling of the capacitor element 1, it becomes impossible to apply an appropriate pressing pressure to the capacitor element 1.

  Since the entire capacitor element 1 receives a pressing pressure, the adhesion frequency between the activated carbon powders in the polarizable electrode layer is increased, and the conductive path in the polarizable electrode is increased, so that the internal resistance of the capacitor element is increased. Can be reduced. Further, the adhesion strength between the current collector of the electrode sheet and the polarizable electrode layer becomes strong, and the contact resistance at these interfaces is also reduced.

  In addition, since the press pressure is applied to the entire capacitor element, the polarizable electrode layer receives the press pressure, and the contact frequency of the activated carbon powder within the polarizable electrode layer is increased substantially uniformly. For this reason, the reduction effect of the internal resistance as a whole becomes large.

  And as shown in FIG.1 (d), an electrical double layer capacitor is completed by sealing the opening edge part of an exterior case with a sealing board.

  In the above-described embodiment, the holding member 5 has four holding pieces 51 and is joined at the bottom 52. However, in the present invention, the bottom 52 of the holding member 5 is an essential configuration. Absent. The holding member 5 may be disposed between the inner side surface of the outer case 3 and the side surface of the capacitor element. Further, the holding member 5 does not need to be disposed on all four side surfaces of the capacitor element 1. For example, the holding pieces may be two sheets facing each other, and the holding pieces may be arranged in the stacking direction of the capacitor elements.

  Further, the shape of the exterior case may not be a prismatic shape. A cylindrical outer case may be used, and a holding member having an arcuate cross section may be used so as to conform to the shape of the inner surface of the cylindrical outer case. That is, the shape of the outer case is arbitrary, and the shape of the holding member can be selected so as to match the shape of the outer case.

  In the electric double layer capacitor described above, the capacitor element receives press pressure from the inner peripheral surface of the outer case, and therefore the capacitor element is in contact with the inner peripheral surface of the outer case. In this state, the capacitor element occupies a large volume in the housing space of the exterior case, and the capacitance per volume of the electric double layer capacitor is also large.

The invention will now be described on the basis of more detailed examples.
(Example)
An activated carbon powder having a specific surface area of 2200 m ² / g, carbon black and tetrafluoroethylene powder were kneaded together with isopropyl alcohol to obtain a kneaded product. The kneaded product was rolled with a rolling roll to obtain a polarizable electrode sheet having a thickness of 100 μm. Next, the polarizable electrode sheet was cut into a size of 108 mm × 47 mm.

  Next, a high-purity aluminum foil having a thickness of 40 μm was cut into a size of 110 mm × 47 mm so that a tab having a width of 13 mm and a length of 20 mm was led out from one of the short sides to obtain a current collector. .

  A polarizable electrode sheet was attached to both surfaces of the current collector with a conductive adhesive to produce an electrode sheet.

  160 layers of electrode sheets were laminated via a 112 mm × 47 mm separator to obtain a laminate. At this time, lamination was performed such that the tabs were alternately led out from one end face.

  Next, the outer periphery of the laminate in which the electrode sheets were laminated was circulated with an adhesive tape in which an adhesive was applied to a polyimide film. This polyimide film is extensible.

  The capacitor element formed as described above had a size of 47 mm × 47 mm × 112 mm.

  Here, in order to observe the degree of swelling when the capacitor element was impregnated with the electrolytic solution, the capacitor element was impregnated with the electrolytic solution. As a result, the capacitor element swelled mainly in the stacking direction of the multilayer body, and the maximum thickness in the stacking direction was 48.2 mm.

  As described above, when the capacitor element is impregnated with the electrolytic solution, the size in the thickness direction of the capacitor element after impregnation is about 2% larger than the size in the thickness direction of the capacitor element before impregnation. It was confirmed that it increased by about 2% due to swelling.

  Next, the capacitor element before impregnating with the electrolytic solution was housed together with the holding member in a bottomed square columnar outer case. The outer case is made of aluminum and has an inner dimension of 50 mm × 50 mm and a length dimension of 130 mm.

  Further, the holding member has four holding pieces having a length dimension of 112 mm, a width dimension of 40 mm, and a thickness of 1.3 mm, and is shaped so that the holding pieces are arranged on a square side. The interval between the holding pieces is 47 mm, which is the same as the width of the side surface of the capacitor element.

  Thus, since the outer diameter of the capacitor element is slightly smaller (0.4 mm in total clearance) than the inner dimension of the outer case, the capacitor element can be easily stored in the outer case.

  Next, an electrolytic solution was injected into the outer case. By impregnating the electrolytic solution, the capacitor element swells, closely contacts the inner surface of the holding member and presses the outer peripheral surface of the capacitor element, and as a reaction, a pressing pressure is applied from the holding member to the capacitor element; Become. Further, even when the holding member tries to spread outward as the capacitor element swells, the holding piece is pressed against the side surface of the outer case.

  And the opening end part of the exterior case was sealed with the sealing plate, and the electric double layer capacitor was completed.

The electric double layer capacitor was rated for a rated voltage of 2.3 V, a rated capacitance of 2700 F, and an internal resistance of 1.0 mΩ.
(Comparative example)
As a comparative example, the same capacitor element as in the example was used, and it was housed in an outer case having an inner dimension of 50 mm × 50 mm and a length dimension of 130 mm. During the storage, the holding member of the above-described embodiment is not used. And electrolyte solution was inject | poured into the exterior case and the capacitor element was impregnated with electrolyte solution. In this case, although the capacitor element swells due to the impregnation with the electrolytic solution, even if the capacitor element swells, it is smaller than the inner dimension of the outer case, and therefore, it does not receive a pressing pressure from the outer case.

  And the opening end part of the exterior case was sealed with the sealing plate, and the electric double layer capacitor was completed.

  This electric double layer capacitor was rated for a rated voltage of 2.3 V, a rated capacitance of 2700 F, and an internal resistance of 1.3 mΩ.

  Comparing the above example and comparative example, it is clear that the rated voltage and the rated capacitance obtained are the same, but there is a difference in the value of the internal resistance, and the internal resistance of the example is lower. It was.

BRIEF DESCRIPTION OF THE DRAWINGS It is drawing explaining the manufacturing method of the electrical double layer capacitor of this invention, (a)-(d) represents each process. It is a perspective view which shows an electrode sheet. It is a perspective view which shows a capacitor element. It is sectional drawing which shows the internal structure of an electrical double layer capacitor. It is a perspective view which shows an example of a holding member. It is sectional drawing of the conventional square-shaped electric double layer capacitor. It is sectional drawing of the electric double layer capacitor of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 0 Electric double layer capacitor 1 Capacitor element 11 Positive electrode 12 Negative electrode 13 Current collector 14 Polarization electrode layer 15 Tab 16 Separator 17 Winding tape 2 Sealing plate 21 External connection terminal 3 Exterior case 4 Electrolytic solution 5 Holding member 51 Holding piece

Claims (2)

  A capacitor element using an electrode sheet in which a polarizable electrode layer mainly composed of activated carbon is formed on one or both sides of a current collector is housed in an outer case together with a holding member, and the capacitor element is made of an electrolyte impregnated in the capacitor element An electric double layer capacitor in which a predetermined pressure is applied from the holding member to the capacitor element by swelling of the capacitor. ^2. The electric double layer capacitor according to claim 1, wherein the activated carbon has a specific surface area of 1500 to 3000 m ² / g.