JP2010238934A - Electric double-layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric double-layer capacitor for attaining both high output and long life at a high level. <P>SOLUTION: The electric double-layer capacitor includes a plurality of electrode bodies comprising a positive electrode 20b and a negative electrode 30b laminated via a separator 40 and being impregnated with an electrolyte solution, wherein the plurality of electrode bodies are electrically connected in series, the positive electrode and the negative electrode comprise an active material having pores, the electrolyte solution includes an electrolyte having a cation and a counteranion of the cation, a ratio of an ion diameter of the counteranion to an average pore diameter of the active material of the positive electrode ranges from 2.5 to 2.8, and a ratio of an ion diameter of the cation to an average pore diameter of the active material of the negative electrode ranges from 1.65 to 1.85. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electric double layer capacitor.

  In recent years, with the increase in output of electronic devices, attempts have been made to improve the working voltage of an electric double layer capacitor as a power source. As one method for improving the working voltage of the electric double layer capacitor, a method of connecting a plurality of cells in series has been proposed (for example, refer to Patent Document 1 below). Patent Document 1 discloses an electric double layer capacitor in which a plurality of capacitor elements are brought into surface contact with a conductive rubber sheet interposed therebetween and are contacted in series and housed in a metal case.

  In such an electric double layer capacitor using cells connected in series, if the holding voltage of each cell varies, the overcharged cell deteriorates along with the charge / discharge cycle. The entire life of the double layer capacitor may be deteriorated. Therefore, it has been studied to suppress such variation in the holding voltage of the cell (for example, see Patent Document 2 below). Patent Document 2 discloses an electric double layer capacitor that suppresses variation in holding voltage caused by a difference in leakage current between individual cells.

JP 2000-208378 A JP 2002-142369 A

  However, in the electric double layer capacitors of Patent Documents 1 and 2, although the output is increased by connecting a plurality of cells in series, the life of the electric double layer capacitor is not sufficient. Therefore, there is a demand for an electric double layer capacitor that can achieve both high output and long life at a high level.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an electric double layer capacitor capable of achieving both high output and long life at a high level.

  The present invention includes a plurality of electrode bodies in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween and impregnated with an electrolyte solution, and the plurality of electrode bodies are electrically connected in series. The electrolyte solution includes an active material having pores, and the electrolyte solution includes an electrolyte composed of a cation and a counter anion of the cation. The ratio of the ion diameter of the counter anion to the average pore diameter of the active material of the positive electrode is 2.5-2. The ratio of the ion diameter of the cation to the average pore diameter of the negative electrode active material is 1.65 to 1.85.

  In the present invention, both high output and long life can be achieved at a high level. The reason for this is not clear, but the present inventors consider as follows. However, the factors are not limited to these.

  When a voltage is applied to the electric double layer capacitor, the counter anion in the electrolyte solution moves to the positive electrode side, and the cation moves to the negative electrode side. The counter anion that has moved to the positive electrode side penetrates into the pores of the active material of the positive electrode and is adsorbed on the inner wall of the pores, and the cation that has moved to the negative electrode side penetrates into the pores of the negative electrode active material and becomes fine. Adsorbs to the inner wall of the hole. The cation and counter anion adsorbed on the inner wall of the pore (hereinafter referred to as “ion” in some cases) retain kinetic energy for a certain period of time, and most of them are deactivated as they are. To desorb from the inner wall of the pore. If the inner walls of the pores of the active material of the positive electrode or the negative electrode are close enough to resorb the desorbed ions (that is, if the average pore diameter is small to some extent), the ions are again adsorbed on the inner walls of the pores. On the other hand, when the average pore diameter is larger than necessary, the desorbed ions are released as they are into the electrolyte solution. For this reason, it is thought that the space | gap which was not ion-adsorbed exists in the active material surface.

  Here, the energy held by the adsorbed ions is given by the charge charged on the active material surfaces of the positive electrode and the negative electrode during charging. In the void portion, there is a possibility that the electrolyte solution is decomposed by charges that could not contribute to ion adsorption. When multiple electrode bodies are connected in series and there is voltage variation among the electrode bodies, the above phenomenon occurs due to the large average pore diameter of the positive electrode active material and the negative electrode active material. As a result, the capacity of some electrode bodies is reduced.

  On the other hand, when the average pore diameter of the positive electrode active material or the negative electrode active material is small, counter anions and cations cannot enter the pores, and the capacity of some electrode bodies is reduced. Further, even if ions can enter the pores, the repulsive force between the ions acts because the distance between the ions is short. For this reason, ions are prevented from adsorbing inside the pores, and the capacity of some electrode bodies is reduced.

  As described above, if the capacity of some electrode bodies is reduced, the load at the time of applying a voltage is increased in the electrode body on the low capacity side. As compared with the case of using, the life of the entire electric double layer capacitor is deteriorated.

  On the other hand, in the present invention, the ionic diameter of the counter anion has a specific size with respect to the average pore diameter of the active material of the positive electrode, and the ionic diameter of the cation corresponds to the average pore diameter of the active material of the negative electrode. It has a specific size. For this reason, counter anions and cations easily penetrate into the pores of the active material of the positive electrode and the active material of the negative electrode and are adsorbed inside the pores. Efficiency is averaged. Thereby, the capacity | capacitance between several electrode bodies will be equalize | homogenized, and the deterioration accompanying the charging / discharging cycle of an electric double layer capacitor can be suppressed. Therefore, it is possible to achieve both high output and long life at a high level.

  The active material of the positive electrode is preferably made of the same material as the active material of the negative electrode. In the case of an electric double layer capacitor, a polarizable electrode is formed by a pair of a positive electrode and a negative electrode. When the electrode active material is the same material for the positive electrode and the negative electrode, it becomes easy to appropriately realize the necessary polarization state.

  The electrolyte is preferably at least one of tetraethylammonium tetrafluoroborate and triethylmonomethylammonium tetrafluoroborate. In this case, higher output and longer life can be achieved at a higher level.

  ADVANTAGE OF THE INVENTION According to this invention, the electrical double layer capacitor which can make high output and long lifetime compatible to a high level is provided.

1 is a perspective view showing a part of an electric double layer capacitor according to an embodiment of the present invention. It is the II-II sectional view taken on the line of FIG.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same or corresponding elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratio in each drawing does not necessarily match the actual dimensional ratio.

  First, the electric double layer capacitor 100 of this embodiment will be described with reference to FIGS. FIG. 1 is a perspective view showing the electric double layer capacitor 100 of the present embodiment with a part thereof cut away. 2 is a cross-sectional view taken along line II-II in FIG.

  The electric double layer capacitor 100 includes a laminated body 8 in which two electrode bodies 4a and 4b are laminated via a partition wall 6, an exterior body 10 that houses the laminated body 8, and leads 50a, 50b, 52a, and 52b. ing.

  The electrode body 4a is a wound body in which a belt-like laminate that is laminated in the order of the belt-like positive electrode 20a / the belt-like separator 40 / the belt-like negative electrode 30a / the belt-like separator 40 is wound in the longitudinal direction. The electrode body 4b is a wound body in which a belt-like laminate that is laminated in the order of the belt-like positive electrode 20b / the belt-like separator 40 / the belt-like negative electrode 30b / the belt-like separator 40 is wound in the longitudinal direction. The electrode bodies 4a and 4b have a substantially elliptical cross section perpendicular to the width direction of the belt-like laminate. The electrode bodies 4 a and 4 b are arranged so that one end in the width direction of the belt-shaped laminate is facing the opening 12 of the exterior body 10, and one side surface of each of the electrode bodies 4 a and 4 b is in contact with the partition wall 6. ing.

  The positive electrode 20a includes a strip-shaped positive electrode current collector 22a and a positive electrode active material layer 24a formed on the front and back surfaces of the positive electrode current collector 22a. The negative electrode 30a includes a strip-shaped negative electrode current collector 32a and a negative electrode active material layer 34a formed on the front and back surfaces of the negative electrode current collector 32a. The positive electrode 20b includes a strip-shaped positive electrode current collector 22b and a positive electrode active material layer 24b formed on the front and back surfaces of the positive electrode current collector 22b. The negative electrode 30b includes a strip-shaped negative electrode current collector 32b and a negative electrode active material layer 34b formed on the front and back surfaces of the negative electrode current collector 32b. In this embodiment, the “positive electrode” is an electrode that adsorbs a counter anion in the electrolyte solution when a voltage is applied to the electric double layer capacitor, and the “negative electrode” is a voltage applied to the electric double layer capacitor. This is an electrode that adsorbs cations in the electrolyte solution when sapphire is applied. In addition, when recharging after applying a voltage to the electric double layer capacitor once in a specific positive / negative direction, charging is usually performed in the same direction as the first and charged by applying a voltage in the opposite direction. There is little to do.

  The positive electrode current collectors 22a and 22b and the negative electrode current collectors 32a and 32b are not particularly limited as long as they are generally highly conductive materials, but metal materials having low electrical resistance are preferably used. Copper, aluminum, nickel or the like is used. The thicknesses of the positive electrode current collectors 22a and 22b and the negative electrode current collectors 32a and 32b are, for example, about 10 to 50 μm. The positive electrode current collectors 22a and 22b and the negative electrode current collectors 32a and 32b are provided with tabs 54 for lead connection. The tabs 54 are located on the opening 12 side of the outer package 10 in the electrode bodies 4a and 4b. Protruding.

  The positive electrode active material layers 24a and 24b and the negative electrode active material layers 34a and 34b include an active material and a binder, and preferably include a conductive additive.

  Examples of the active material include an electron conductive porous body having pores, such as natural graphite, artificial graphite, mesocarbon microbeads, mesocarbon fiber (MCF), cokes, glassy carbon, and organic compound fired body. And carbon materials such as The materials of the positive electrode active material layers 24a and 24b and the negative electrode active material layers 34a and 34b are preferably the same active material.

  The binder is not particularly limited as long as the above active material and preferably the conductive auxiliary agent can be fixed to the current collector, and various binders can be used. Examples of the binder include fluorine resins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR) and water-soluble polymers (carboxymethylcellulose, polyvinyl alcohol, sodium polyacrylate, Dextrin, gluten, etc.) and the like.

  The conductive additive is a material added to increase the electron conductivity of the positive electrode active material layers 24a and 24b and the negative electrode active material layers 34a and 34b. Examples of the conductive aid include carbon materials such as carbon black and acetylene black, fine metal powders such as copper, nickel, stainless steel, and iron, a mixture of carbon materials and fine metal powders, and conductive oxides such as ITO.

  The thicknesses of the positive electrode active material layers 24a and 24b and the negative electrode active material layers 34a and 34b are, for example, about 1 to 200 μm. The positive electrode active material layers 24a and 24b and the negative electrode active material layers 34a and 34b are formed on the current collector so as to avoid the tabs 54 provided with leads. The positive electrode active material layers 24a and 24b and the negative electrode active material layers 34a and 34b can be produced by a known method.

  The separator 40 electrically insulates between the positive electrode 20a and the negative electrode 30a and between the positive electrode 20b and the negative electrode 30b, and is an electrically insulating porous body. The separator 40 is not particularly limited, and various separator materials can be used. For example, the electrically insulating porous body is selected from the group consisting of monolayers and laminates of films made of polyethylene, polypropylene or polyolefin, stretched films of a mixture of the above resins, or cellulose, polyester and polypropylene. Examples thereof include a fiber nonwoven fabric made of at least one constituent material. The thickness of the separator 40 is, for example, about 5 to 50 μm.

  The partition wall 6 is made of a material that does not allow the later-described electrolyte solution contained in each of the two electrode bodies 4a and 4b to pass therethrough. For example, a synthetic resin such as an epoxy resin, or a metal sheet such as aluminum or stainless steel is used as a resin film (polypropylene or the like). It is formed by laminating. The thickness of the partition wall 6 is, for example, about 10 to 100 μm. By providing the partition wall 6, the electrolyte solutions contained in the two electrode bodies 4a and 4b are suppressed from mixing with each other, and the voltage drop of the electric double layer capacitor 100 can be suppressed.

  The leads 50a, 50b, 52a, 52b are conductive members that serve as current input / output terminals for the positive current collectors 22a, 22b and the negative current collectors 32a, 32b, and have a rectangular plate shape. ing. The thickness of the leads 50a, 50b, 52a, 52b is, for example, about 50 to 1000 μm.

  One end in the longitudinal direction of the lead 50a is electrically connected to the positive electrode current collector 22a of the positive electrode 20a in one electrode body 4a, and one end in the longitudinal direction of the lead 52a is the negative electrode of the negative electrode 30a in the electrode body 4a. One end of the lead 50b in the longitudinal direction is electrically connected to the positive electrode current collector 22b of the positive electrode 20b in the other electrode body 4b, and the lead 52b One end in the longitudinal direction is electrically connected to the negative electrode current collector 32b of the negative electrode 30b in the electrode body 4b. The leads 50a, 50b, 52a, 52b and the tab 54 provided on each current collector are fixed by, for example, conductive adhesive, solder, welding, or the like. The leads 50 a, 50 b, 52 a, 52 b extend from the one end of each lead to the outside of the exterior body 10 through the opening 12.

  The lead 50a and the lead 52b protrude from positions opposed to each other in the stacking direction of the electrode bodies 4a and 4b in the opening 12, and are in contact with each other outside the exterior body 10 and are electrically connected. As a result, the leads 50a and 52b connected to the current collectors having different polarities are electrically connected to each other so that the two electrode bodies 4a and 4b are connected in series, and the voltage of the electric double layer capacitor 100 is increased. Can be improved.

  The exterior body 10 seals the electrode bodies 4a and 4b and prevents air and moisture from entering the inside of the case. As the exterior body 10, for example, a synthetic resin such as an epoxy resin or a metal sheet such as aluminum or stainless steel laminated with a resin film (polypropylene, polyethylene, or the like) can be used. The wall thickness of the exterior body 10 is, for example, about 10 to 500 μm.

  A sealing member 60 is disposed around the leads 50a, 50b, 52a, and 52b in the opening 12 of the outer package 10, and the sealing member 60 is in close contact with the inner wall of the outer package 10 and each lead. The opening 12 is sealed. As the sealing member 60, a material having good adhesion to the opening 12 at the time of heat-sealing with the opening 12 may be used. Specifically, an ethylene-vinyl acetate copolymer, ethylene-acrylate is used. A copolymer, a polypropylene polymer, and the like can be used.

  The internal space of the outer package 10 is filled with an electrolyte solution (not shown), and a part thereof is impregnated inside the positive electrodes 20a and 20b, the negative electrodes 30a and 30b, and the separator 40.

As the electrolyte solution, a solution in which an electrolyte is dissolved in an organic solvent is used. The electrolyte has a cation and a counter anion of the cation. As the electrolyte, for example, a quaternary ammonium salt such as tetraethylammonium tetrafluoroborate (TEA-BF ₄ ) or triethylmonomethylammonium tetrafluoroborate (TEMA-BF ₄ ) is preferably used.

  In addition, these electrolytes may be used individually by 1 type, and may use 2 or more types together.

  Moreover, a well-known solvent can be used as an organic solvent. Preferred examples of the organic solvent include propylene carbonate, ethylene carbonate, and diethyl carbonate. These may be used alone or in combination of two or more at any ratio.

  Next, the correlation between the average pore diameter of the positive electrode active material and the ion diameter of the counter anion, and the correlation between the average pore diameter of the negative electrode active material and the cation ion diameter will be described. In the present embodiment, the correlation between the average pore diameter and the ion diameter is satisfied in both the electrode bodies 4a and 4b. The average pore diameter of the active material can be measured with a mercury porosimeter.

  The ratio of the ion diameter of the counter anion to the average pore diameter of the positive electrode active material is 2.5 to 2.8, and the penetration efficiency of the counter anion into the pore of the positive electrode active material and the adsorption to the inner wall of the pore From the viewpoint of increasing efficiency, 2.6 to 2.7 is particularly preferable. The ratio of the cation ion diameter to the average pore diameter of the negative electrode active material is 1.65 to 1.85, and the cation penetration efficiency into the pores of the negative electrode active material and the adsorption efficiency to the inner walls of the pores are determined. From the viewpoint of increasing, 1.7 to 1.8 is particularly preferable.

  The average pore diameter of the positive electrode active material is appropriately selected depending on the counter anion used from the viewpoint of increasing the penetration efficiency of the counter anion into the pores of the positive electrode active material and simultaneously increasing the adsorption efficiency of the counter anion. For example, in the case of a tetrafluoroborate anion (ion diameter: 4.9 Å), 12.7 to 13.7 Å is preferable, and 12.8 to 13.4 Å is more preferable. The average pore diameter of the negative electrode active material is appropriately selected depending on the cation used from the viewpoint of increasing the penetration efficiency of the cation into the pores of the negative electrode active material and at the same time increasing the adsorption efficiency of the cation. For example, in the case of a triethylmonomethylammonium cation (ion diameter: 7.4Å), 11.9 to 13.4Å is preferable, and 12.5 to 13.2Å is more preferable. In the case of a tetraethylammonium cation (ion diameter: 8.1 Å), 13.2 to 15.0 好 ま し く is preferable, and 14.0 to 14.6 Å is more preferable. The average pore diameter of the positive electrode active material and the negative electrode active material can be set to a desired size by changing the treatment time and treatment temperature for the activation treatment using an alkali reagent such as potassium hydroxide and water vapor. The average pore diameter of the active material can be measured using a mercury porosimeter using a mercury intrusion method.

  The ion diameter of the cation should be large enough to be absorbed by the charge on the negative electrode surface, migrate within the electrolyte solution and enter the pores of the negative electrode active material, and adsorb to the inner walls of the pores. From the two viewpoints of ensuring, 5-10 inches are preferable, 7.0-8.5 inches are more preferable, and 7.2-8.3 inches are still more preferable. The ion diameter of the tetraethylammonium cation is 8.1 、, and the ion diameter of the triethylmonomethylammonium cation is 7.4 Å.

  The ion diameter of the counter anion is large enough to be attracted by the charge on the surface of the positive electrode and migrate in the electrolyte solution to ensure mobility so that it can enter the pores of the positive electrode active material and to be adsorbed on the inner walls of the pores. From the two viewpoints of ensuring the above, 4-5.5 mm is preferable, 4.2-5.3 mm is more preferable, and 4.5-5.2 mm is more preferable. The ion diameter of the tetrafluoroborate anion is 4.9 mm.

  In this embodiment, it is preferable to satisfy the correlation regarding the area of the active material layer described below. The area of the active material layer is an area in a state where it is wound and functions as an electric double layer capacitor, but this area is usually equal to the area of the active material layer of the strip-shaped electrode before being wound. It is. In this embodiment, the area of the active material layer of one electrode is the sum of the areas of all the active material layers of one electrode of one electrode body. The area of the active material layer can be easily adjusted by changing the length and width of the current collector, the length and width of the active material layer formed on the current collector, and the like.

  In the present embodiment, in each of the plurality of electrode bodies, the ratio of the area of the positive electrode active material layer to the area of the negative electrode active material layer is preferably 78 to 128%. That is, the ratio of the area of the positive electrode active material layer 24a of the positive electrode 20a to the area of the negative electrode active material layer 34a of the negative electrode 30a in one electrode body 4a and the negative electrode active material of the negative electrode 30b in the other electrode body 4b. The ratio of the area of the positive electrode active material layer 24b of the positive electrode 20b to the area of the material layer 34b is preferably 78 to 128% from the viewpoint that higher output and longer life can be achieved at a higher level. -125% is more preferable, and 81-123% is still more preferable.

  In the two electrode bodies 4a and 4b, the ratio of the maximum value to the minimum value of the area of the positive electrode active material layer 24a of the positive electrode 20a and the area of the positive electrode active material layer 24b of the positive electrode 20b is high output. From the standpoint of achieving higher levels and longer life, 105% or less is preferable, 100 to 105% is more preferable, and 100 to 103% is more preferable. For example, when the area of the positive electrode active material layer 24a of the positive electrode 20a is larger than the area of the positive electrode active material layer 24b of the positive electrode 20b, the area of the positive electrode active material layer 24a with respect to the area of the positive electrode active material layer 24b The ratio is preferably 105% or less.

  Further, in the two electrode bodies 4a and 4b, the ratio of the maximum value to the minimum value of the area of the negative electrode active material layer 34a of the negative electrode 30a and the area of the negative electrode active material layer 34b of the negative electrode 30b is high output. From the standpoint of achieving higher levels and longer life, 105% or less is preferable, 100 to 105% is more preferable, and 100 to 103% is more preferable. For example, when the area of the negative electrode active material layer 34a of the negative electrode 30a is larger than the area of the negative electrode active material layer 34b of the negative electrode 30b, the area of the negative electrode active material layer 34a relative to the area of the negative electrode active material layer 34b The ratio is preferably 105% or less.

  As long as these relationships are satisfied, the shapes of the positive electrode active material layers 24a and 24b and the negative electrode active material layers 34a and 34b and the distribution ratio of the area between the front and back surfaces of the current collectors of these layers are particularly limited. Not. In addition, it is preferable that 24a and 24b and the active material layers 34a and 34b for negative electrodes are the same areas in the surface and the back surface of a collector, respectively.

  In this embodiment, the ion diameter of the counter anion has a specific size with respect to the average pore diameter of the positive electrode active material, and the cation ion diameter is specific to the average pore diameter of the negative electrode active material. It has the size. Therefore, when the counter anion or cation easily enters the pores of the positive electrode active material or the negative electrode active material and is adsorbed inside the pores, and the electrode bodies 4a and 4b are connected in series, The adsorption efficiency is averaged. Thereby, the capacity | capacitance between electrode body 4a, 4b will be equalize | homogenized, and the deterioration accompanying the charging / discharging cycle of the electric double layer capacitor 100 can be suppressed. Therefore, it is possible to achieve both high output and long life at a high level.

  In the present embodiment, in each of the electrode bodies 4a and 4b connected in series, the ratio of the area of the positive electrode active material layer 24a of the positive electrode 20a to the area of the negative electrode active material layer 34a of the negative electrode 30a and the negative electrode 30b The ratio of the area of the positive electrode active material layer 24b of the positive electrode 20b to the area of the negative electrode active material layer 34b is 78 to 128%, respectively, and the area of the positive electrode active material layer 24a of the positive electrode 20a in the electrode body 4a and the electrode body The ratio of the maximum value to the minimum value of the area of the positive electrode active material layer 24b of the positive electrode 20b in 4b is 105% or less, and the area of the negative electrode active material layer 34a of the negative electrode 30a in the electrode body 4a and the electrode body When the ratio of the maximum value to the minimum value of the area of the negative electrode active material layer 34b of the negative electrode 30b in 4b is 105% or less, the difference is due to the difference in area. That the electrode body 4a, generation of variation in the voltage held 4b is suppressed. Therefore, a voltage is equally applied to each of the electrode bodies 4a and 4b, and deterioration accompanying the charge / discharge cycle of the electric double layer capacitor 100 can be suppressed. Therefore, the synergistic effect of the correlation between the average pore diameter and the ion diameter makes it possible to achieve both higher output and longer life at a higher level.

  The present invention is not limited to the above-described embodiment, and various modifications can be made. For example, in the above embodiment, the two electrode bodies 4a and 4b are connected in series, but three or more electrode bodies may be connected in series. When three or more electrode bodies are connected in series, the correlation between the average pore diameter and the ion diameter is satisfied in any of the electrode bodies, and both high output and long life are achieved at a high level. It becomes possible. In any of the electrode bodies, it is preferable to satisfy the correlation regarding the area of the active material layer.

  Each active material layer may be formed only on one surface of each current collector. Furthermore, in the said embodiment, although the electrode bodies 4a and 4b are winding bodies, it is not restricted to this, A laminated body, a 99-fold structure, etc. may be sufficient.

  The electric double layer capacitor of the present invention can also be used for a power source of a self-propelled micromachine, an IC card, or a distributed power source disposed on or in a printed board.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in more detail, this invention is not limited to these Examples at all.

Example 1
First, activated carbon particles (trade name: RP-20, manufactured by Kuraray Chemical Co., Ltd.) as an active material were activated with potassium hydroxide. The activation treatment conditions were a temperature of 850 ° C. and a treatment time of 100 minutes for the positive electrode active material, and a temperature of 850 ° C. and a treatment time of 100 minutes for the negative electrode active material. When the average pore diameter of the activated active material was measured using a mercury porosimeter (manufactured by Shimadzu Corporation, apparatus name: Porosizer PORE SIZER 9320), it was 13.2 mm for the positive electrode active material and 12.9 mm for the negative electrode active material. there were.

  next. The above active material subjected to activation treatment and PVDF as a binder are mixed at a mass ratio of active material: binder = 70: 30, and N-methylpyrrolidone is added to the obtained mixture and kneaded, whereby a positive electrode and a negative electrode Each coating solution was prepared. Each coating solution is applied on both sides of an aluminum foil (thickness: 20 μm) by a doctor blade method and dried, and a sheet in which a positive electrode active material layer having a thickness of 20 μm is laminated on both sides, and a thickness. Sheets each having a 20 μm negative electrode active material layer laminated thereon were obtained. Then, two strip-like electrodes provided with lead connection tabs are punched out from each of the sheets so that the length and width of the active material layer are the values shown in Table 1, and aluminum foil is formed on each electrode tab. Leads made of (thickness: 100 μm) were connected by ultrasonic welding.

Next, after covering both sides of the positive electrode with a non-woven fabric made of regenerated cellulose (thickness: 30 μm, size: 14 mm × 195 mm) as a separator, facing the negative electrode, under conditions of 100 ° C., 1 kg / cm ² , 10 seconds Heating and pressing were performed to obtain a strip-shaped laminate. This laminate was wound in a cylindrical shape from the end, and the end of the winding was stopped with a winding tape to obtain a wound electrode body. Using the remaining two electrodes, another wound-type electrode body was similarly produced.

  Next, an exterior body made of an aluminum laminate film having an opening on one side and partitioned into two spaces by a partition was prepared. And after accommodating the said electrode body one by one in two spaces, the electrolyte solution was inject | poured in the exterior body from the opening part. The electrolyte solution was obtained by dissolving triethylmonomethylammonium tetrafluoroborate as an electrolyte in propylene carbonate (PC) as an organic solvent, and the electrolyte concentration in the electrolyte solution was 1.0 mol / L.

  Next, the lead connected to the electrode body was taken out from the opening of the exterior body, and the opening of the laminate film was heat-sealed using polypropylene as a sealing member with the lead interposed therebetween, and the exterior body was sealed. Then, a pair of leads connected to electrodes having different polarities in the two electrode bodies were electrically connected outside the exterior body, and the two electrode bodies were connected in series. In this way, an electric double layer capacitor having a size of 20 mm × 20 mm × 27 mm having active material layers having the length and width shown in Table 1 on both surfaces of the current collector was obtained.

(Examples 2 to 54, Comparative Examples 1 to 16)
Examples 2 to 54 and Examples 2 to 54 were the same as Example 1 except that the average pore diameter of the active material, the electrolyte, and the length and width of the active material layer were changed to the values of the Examples and Comparative Examples of Tables 1 to 6. The electric double layer capacitors of Comparative Examples 1 to 16 were obtained. The average pore diameter of the active material was adjusted by changing the treatment time of the activation treatment.

  For Examples 1 to 54 and Comparative Examples 1 to 16, the ratio of the ion diameter of the counter anion to the average pore diameter of the positive electrode active material (indicated as “coefficient A” in Tables 4 to 6), and the negative electrode. The ratio of the ion diameter of the cation to the average pore diameter of the active material (expressed as “coefficient B” in Tables 4 to 6) was calculated. The results are shown in Tables 4-6.

<Calculation of area ratio>
For Examples 1 to 54 and Comparative Examples 1 to 16, the length and width values of the active material layer in two electrode bodies (indicated as “+ series” and “−series” in Tables 1 to 3) are used. Thus, the areas of one surface of the active material layer of the positive electrode and the negative electrode were respectively calculated. It is assumed that the negative electrode of the “+ series” electrode body and the positive electrode of the “− series” electrode body are electrically connected. Then, the ratio of the area of the active material layer of the positive electrode to the area of the active material layer of the negative electrode in each of the “+ series” and “− series” electrode bodies, the activity of the positive electrode in the “+ series” and “− series” electrode bodies. The ratio of the maximum value to the minimum value of the area of the material layer and the ratio of the maximum value to the minimum value of the area of the active material layer of the negative electrode in the “+ series” and “− series” electrode bodies were calculated. The results are shown in Tables 1-3.

  In all the above examples and comparative examples, each electrode has an active material layer on both sides of the current collector, so the area of the active material layer of each electrode used for calculating the area ratio is the active material layer The total area of both surfaces of each electrode is the same as that of the active material layer of each electrode used for calculating the ratio of the areas because the areas of both surfaces of the active material layer of each electrode are equal to each other in all examples and comparative examples. Even if the total value of both sides is used or the value of one side is used, the result does not change.

<Capacity retention measurement>
For the electric double layer capacitors of Examples 1 to 54 and Comparative Examples 1 to 16, constant current and constant voltage charge (CC-CV charge) to 5.7 V at 1 A for 5 seconds, and CC-CV discharge to 0 V at 3 A for 5 seconds This process was set to 1 cycle, and this process was performed 5000 cycles. In the CC-CV discharge at the first cycle, the required time from the voltage to 5 V to 3 V was measured, and the initial capacity value (C ₀ ) was calculated using the current value and the required time.

After the 5000 cycles of charging and discharging, constant current (CC) charging was performed at 50 mA up to 5.7 V, and further, constant voltage (CV) charging was performed at 5.7 V for 10 seconds. Next, CC discharge was performed to 0 V at 50 mA, the required time until the voltage reached from 5 V to 3 V was measured, and the capacity value (C ₁ ) was calculated using the current value and the required time. Then, the ratio (= C ₁ / C ₀ × 100) of the capacity value (C ₁ ) to the initial capacity value (C ₀ ) was calculated as the capacity maintenance ratio (%). The results are shown in Tables 4-6. In addition, the case where a capacity maintenance rate was 80% or more was judged to be favorable.

  4a, 4b ... electrode body, 20a, 20b ... positive electrode, 30a, 30b ... negative electrode, 40 ... separator, 100 ... electric double layer capacitor.

Claims (3)

A positive electrode and a negative electrode are laminated with a separator in between, and a plurality of electrode bodies impregnated with an electrolyte solution are provided,
The plurality of electrode bodies are electrically connected in series,
The positive electrode and the negative electrode include an active material having pores,
The electrolyte solution includes an electrolyte having a cation and a counter anion of the cation,
The ratio of the ion diameter of the counter anion to the average pore diameter of the active material of the positive electrode is 2.5 to 2.8,
The electric double layer capacitor, wherein a ratio of an ion diameter of the cation to an average pore diameter of the active material of the negative electrode is 1.65 to 1.85.   The electric double layer capacitor according to claim 1, wherein a material of the active material of the positive electrode is the same material as the active material of the negative electrode.   The electric double layer capacitor according to claim 1, wherein the electrolyte is at least one of tetraethylammonium tetrafluoroborate and triethylmonomethylammonium tetrafluoroborate.

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