JP4487540B2 - Electrochemical capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrochemical capacitor having a sufficient capacity. <P>SOLUTION: The electrochemical capacitor comprises an anode 10, a cathode 20 and a nonaqueous electrolyte solution 30 contained in a case 50. The anode 10 contains a first conductive polymer and/or a first carbon material as an anode active substance. The cathode 20 contains a second carbon material coated with a second conductive polymer having at least a molecular structure including a repetition unit based on a monomer represented by a formula (I) as a cathode active substance. The oxidation reduction potential E1 [V] of the anode active substance and the oxidation reduction potential E2 [V] of the cathode active substance satisfy conditions of expression (1); 0.20&le;(E2-E1)&le;3.60. <P>COPYRIGHT: (C)2005,JPO&amp;NCIPI

Description

  The present invention relates to an electrochemical capacitor.

  Electrochemical capacitors, such as electric double layer capacitors, utilize the capacitance resulting from the electric double layer generated at the electrode / electrolyte solution interface of the polarizable electrode. The electrochemical capacitor has excellent large current discharge characteristics and cycle characteristics, and can be easily reduced in size and weight. However, the capacity of the electrochemical capacitor is about one tenth of the capacity of a battery such as a lithium ion secondary battery, and the electrochemical capacitor is required to have a higher capacity.

In order to increase the capacity of an electric double layer capacitor, for example, Patent Document 1 proposes to use an electrode including a composite of activated carbon and a conductive polymer.
JP 2002-25868 A

  However, the electric double layer capacitor disclosed in Patent Document 1 uses a sulfuric acid aqueous solution having a narrow potential window as an electrolyte solution, and a sufficient capacity cannot be obtained. For example, there is a possibility that the capacity can be further increased by using a non-aqueous electrolyte solution having a wide potential window. However, the electric double layer capacitor disclosed in Patent Document 1 uses an organic solvent as a conductive polymer constituting the cathode. Uses polyaniline, which is easy to dissolve. Therefore, it has been difficult to construct an electric double layer capacitor of a nonaqueous electrolyte solution using this cathode.

  The present invention has been made in view of the above-described problems of the prior art, and an object thereof is to provide an electrochemical capacitor having a sufficient capacity.

  As a result of intensive studies to achieve the above object, the present inventors have used a non-aqueous electrolyte solution as an electrolyte solution and a carbon material coated with a specific conductive polymer as a cathode active material. It was found that it is effective for increasing the capacity of electrochemical capacitors. Further, the redox potential of the carbon material and the conductive polymer as the anode active material is measured by a specific method, and a material in which the redox potential satisfies a specific condition with respect to the redox potential of the cathode active material is anode-treated. The inventors have found that the object can be achieved by selecting the active material, and have reached the present invention.

［式（Ｉ）中、Ｒ^１およびＲ^２は、それぞれ独立に、水素原子、アルキル基、アリール基およびアルコキシ基からなる群より選ばれる一種を表す。］ The electrochemical capacitor of the present invention includes a current collector and an anode having an anode active material-containing layer formed on the current collector,
A cathode having a current collector and a cathode active material-containing layer formed on the current collector;
A non-aqueous electrolyte solution;
A case for containing the anode, the cathode and the non-aqueous electrolyte solution in a sealed state,
The anode active material-containing layer contains the first conductive polymer and / or the first carbon material as an anode active material,
The cathode active material-containing layer has, as a cathode active material, a second carbon material coated with a second conductive polymer having at least a molecular structure including a repeating unit based on a monomer represented by the following formula (I) Including
An oxidation-reduction potential E1 [V] of the anode active material, the oxidation-reduction potential E2 [V] and the cathode active material meets the conditions of the following formula (1),
The first conductive polymer has at least a molecular structure including a repeating unit based on at least one selected from the group consisting of indole, ethylenedioxythiophene and 3- (4-fluorophenyl) thiophene. And
0.20 ≦ (E2-E1) ≦ 3.60 (1)

[In Formula (I), R ¹ and R ² each independently represent one selected from the group consisting of a hydrogen atom, an alkyl group, an aryl group, and an alkoxy group. ]

By adopting the above specific configuration, a sufficient capacity can be obtained in the electrochemical capacitor of the present invention. Therefore, the electrochemical capacitor of the present invention is suitable as a backup power source for power sources of portable devices and the like and an auxiliary power source for hybrid vehicles. In addition, since the electrochemical capacitor of the present invention uses an anode active material and a cathode active material that are difficult to dissolve in the non-aqueous electrolyte solution, the initial and long-term charge / discharge characteristics are also excellent. The first conductive polymer obtained from the specific monomer has a low redox potential. Therefore, by using the first conductive polymer obtained from the specific monomer for the anode, it is possible to further increase the capacity of the electrochemical capacitor.

Here, the “redox potential” in the present invention is a potential determined by measurement based on an electrochemical measurement method (polarography, cyclic voltammetry, etc.). That is, the “redox potential” in the present invention is measured using an electrochemical cell having the following configuration. The electrochemical cell includes an electrode containing an electrode active material to be measured as a working electrode (electrode punched to 15 mmΦ), lithium metal as a reference electrode and a counter electrode, and a propylene carbonate solution (1 mol·L as a supporting salt) as an electrolyte solution. ⁻¹ LiBF ₄ ). Note that the tip of the Lugin tube of the reference electrode has a diameter of 1 mm, and the distance between the reference electrode and the working electrode is adjusted to 2 mm. Further, the electrode area of the counter electrode is adjusted to be sufficiently larger than the electrode area of the working electrode. And said electrochemical cell is 4.2-1.8 [V vs. The average discharge voltage when discharged to Li / Li ⁺ ] is measured and is defined as the “redox potential” of the present invention. Although the average discharge voltage is a lower value due to polarization than the original oxidation-reduction potential, the present invention focuses on obtaining the potential difference between the cathode and the anode, and at a low current density, with a difference in the average discharge voltage, It can be expressed as a difference in redox potential.

  In the electrochemical capacitor of the present invention, the monomer represented by the formula (I) is at least selected from the group consisting of thiophene, 3-methylthiophene, 3-butylthiophene, 3-phenylthiophene, and 3-methoxythiophene. One type is preferred. The second conductive polymer obtained from the specific monomer has a high redox potential. Therefore, by using the second conductive polymer obtained from the specific monomer for the cathode, it is possible to further increase the capacity of the electrochemical capacitor.

  In the cathode of the present invention, the second conductive polymer is formed on the second carbon material by electrolytic polymerization. By such electrolytic polymerization, the second carbon material can be easily coated with the second conductive polymer.

  The electrolytic polymerization includes a second carbon material having a current collector having electron conductivity and a cathode active material-containing layer containing the second carbon material formed on the current collector. Using the containing electrode as a working electrode, the working electrode is immersed in a solution containing the monomer represented by the above formula (I).

  By carrying out in this way, a second conductive polymer film can be formed also on the second carbon material inside the electrode.

  The electrolytic polymerization is performed by an electrolytic cell using a solution containing the monomer represented by the above working electrode (second carbon material-containing electrode) and the above formula (I). The “electrolysis cell” in this case is not particularly limited as long as the working electrode is used. For example, a so-called bipolar electrolytic cell including a working electrode and a counter electrode serving as a reference electrode may be used. It is also possible to use a so-called tripolar electrolytic cell composed of a working electrode, a reference electrode, and a counter electrode. In any electrolytic cell, by holding the working electrode at a constant potential for a predetermined time, the surface of the working electrode is used as a reaction field where the oxidation reaction proceeds selectively, and the counter electrode is used as a reaction field where the reduction reaction proceeds selectively. can do. However, from the viewpoint of more precisely controlling the potential of the working electrode with respect to the reference electrode and allowing the desired oxidation reaction to proceed more selectively and reliably, it is preferable to use a three-electrode electrolytic cell.

  Moreover, you may perform electrolytic polymerization using the mixed solution containing the monomer represented by the said Formula (I), and said 2nd carbon material. This electrolytic polymerization is performed using the electrolytic cell as described above, but as the working electrode, the second carbon material-containing electrode may be used, and a commonly used electrode such as a platinum electrode or a carbon electrode is used. May be. At this time, the mixed solution is used instead of the solution containing the monomer represented by the formula (I). When electrolytic polymerization is performed using a commonly used electrode, a composite of a second conductive polymer and a second carbon material formed on the electrode is used as the cathode active material.

  In the electrochemical capacitor of the present invention, the first carbon material and the second carbon material are preferably fibrous activated carbon, and the aspect ratio of the fibrous activated carbon is preferably 1.5 or more. . Here, the “aspect ratio” indicates a value (b / a) obtained by dividing the major axis (length) b of the fibrous activated carbon by the minor axis (diameter) a.

  By using such fibrous activated carbon, the internal resistance of the electrode is reduced, and an electrochemical capacitor exhibiting excellent charge / discharge characteristics can be obtained. In the case of fibrous activated carbon, the contact between the activated carbons in the electrodes is often a line contact, and since the contact area between the activated carbons is relatively large, the amount of electricity transmitted between the activated carbons increases and the internal resistance is sufficiently reduced. It is thought. In addition, the activated carbon expands and contracts due to the desorption of electrolyte ions during charge and discharge, and the contact between the activated carbons is easily lost. However, the contact area between the activated carbons is large, and the contact between the activated carbons is sufficiently maintained. Can do. However, this does not limit the shape of the activated carbon.

  In the electrochemical capacitor of the present invention, the anode and the cathode are arranged to face each other, and a separator made of an insulating porous body is arranged between the anode and the cathode, and the nonaqueous electrolyte solution It is preferable that at least a part thereof is contained in the anode, the cathode and the separator.

  In the electrochemical capacitor of the present invention, each of the anode, the cathode, and the separator has a plate shape, and the case is formed using at least a pair of composite packaging films facing each other. And it is preferable that the said composite packaging film has at least the innermost layer made from a synthetic resin which contacts the said nonaqueous electrolyte solution, and the metal layer arrange | positioned above the said innermost layer.

  According to the present invention, an electrochemical capacitor having a sufficient capacity can be provided. Such an electrochemical capacitor is suitable as a backup power source for a power source of a portable device or the like and an auxiliary power source for a hybrid vehicle.

  Hereinafter, preferred embodiments of the electrochemical capacitor of the present invention will be described with reference to the drawings. In the following description, the same or corresponding parts are denoted by the same reference numerals, and duplicate descriptions are omitted.

  FIG. 1 is a front view showing a preferred embodiment of the electrochemical capacitor of the present invention. FIG. 2 is a development view when the inside of the electrochemical capacitor shown in FIG. 1 is viewed from the normal direction of the surface of the anode 10. 3 is a schematic cross-sectional view of the electrochemical capacitor shown in FIG. 1 taken along the line X1-X1 of FIG. 4 is a schematic cross-sectional view showing the main part when the electrochemical capacitor shown in FIG. 1 is cut along the line X2-X2 of FIG. 5 is a schematic cross-sectional view showing the main part when the electrochemical capacitor shown in FIG. 1 is cut along the line YY of FIG.

  As shown in FIGS. 1 to 5, the electrochemical capacitor 1 is mainly composed of a plate-like anode 10 and a plate-like cathode 20 facing each other, and a plate disposed adjacently between the anode 10 and the cathode 20. Separator 40, nonaqueous electrolyte solution 30, case 50 containing these in a sealed state, one end of the anode 10 is electrically connected to the anode 10, and the other end is outside the case 50. The anode lead 12 is protruded, and one end is electrically connected to the cathode 20 and the other end is protruded to the outside of the case 50. Here, for convenience of explanation, the “anode” 10 and the “cathode” 20 are determined based on the polarity at the time of discharging the electrochemical capacitor 1. Accordingly, during charging, “anode 10” becomes “cathode” and “cathode 20” becomes “anode”.

  The electrochemical capacitor 1 has a configuration described below in order to achieve the above-described object of the present invention.

  Details of each component of the present embodiment will be described below with reference to FIGS.

  The case 50 is formed by using a pair of films (a first film 51 and a second film 52) that face each other. Here, as shown in FIG. 2, the first film 51 and the second film 52 in this embodiment are connected. That is, the case 50 in the present embodiment is formed by folding a rectangular film made of a single composite packaging film along a fold line X3-X3 shown in FIG. 2 and a pair of edges of the rectangular film facing each other ( The edge 51B of the first film 51 and the edge 52B of the second film 52 in the figure are overlapped to form an adhesive or heat seal.

  And the 1st film 51 and the 2nd film 52 respectively show the part of this film which has a mutually opposing surface formed when the one rectangular film 53 is bend | folded as mentioned above. Here, in the present specification, the respective edge portions 51B and 52B of the first film 51 and the second film 52 after being joined are referred to as “seal portions”.

  Thereby, since it becomes unnecessary to provide the seal part for joining the 1st film 51 and the 2nd film 52 in the part of bending line X3-X3, the seal part in case 50 can be reduced more. As a result, the volume energy density based on the volume of the space in which the electrochemical capacitor 1 is to be installed can be further improved.

  In the case of this embodiment, as shown in FIGS. 1 and 2, one end of each of the anode lead 12 and the cathode lead 22 connected to the anode 10 is the edge portion 51 </ b> B of the first film 51 described above. And the edge portion 52B of the second film are arranged so as to protrude to the outside from the sealed portion.

  Moreover, the film which comprises the 1st film 51 and the 2nd film 52 is a film which has flexibility as stated above. Since the film is lightweight and easy to thin, the electrochemical capacitor itself can be made into a thin film. Therefore, the original volume energy density can be easily improved, and the volume energy density based on the volume of the space in which the electrochemical capacitor is to be installed can be easily improved.

  The film is not particularly limited as long as it is a flexible film. However, while ensuring sufficient mechanical strength and light weight of the case 50, moisture and air can enter from the outside of the case 50 into the case 50 and the case 50. From the viewpoint of effectively preventing the electrolyte component from escaping from the inside of the case 50 to the outside, the innermost layer made of synthetic resin that contacts the nonaqueous electrolyte solution 30 and the metal disposed above the innermost layer A “composite packaging film” having at least a layer is preferable.

  Examples of the composite packaging film that can be used as the first film 51 and the second film 52 include a composite packaging film having a configuration shown in FIGS. 6 and 7. The composite packaging film 53 shown in FIG. 6 has an innermost layer 50a made of a synthetic resin that contacts the nonaqueous electrolyte solution 30 on the inner surface F53, and the other surface (outer surface) of the innermost layer 50a. And a metal layer 50c to be disposed. Further, the composite packaging film 54 shown in FIG. 7 has a configuration in which an outermost layer 50b made of synthetic resin is further arranged on the outer surface of the metal layer 50c of the composite packaging film 53 shown in FIG.

  The composite packaging film that can be used as the first film 51 and the second film 52 includes two or more layers including one or more synthetic resin layers including the innermost layer described above and a metal layer such as a metal foil. If it is a composite packaging material which has a layer, it will not specifically limit. From the viewpoint of obtaining the same effect as described above more reliably, like the composite packaging film 54 shown in FIG. 7, the innermost layer 50a and the outer surface of the case 50 farthest from the innermost layer 50a. It is composed of three or more layers including an outermost layer 50b made of synthetic resin and at least one metal layer 50c arranged between the innermost layer 50a and the outermost layer 50b. More preferably.

  The innermost layer 50a is a layer having flexibility, and the constituent material thereof can express the above-mentioned flexibility, and the chemical stability (chemical properties) with respect to the non-aqueous electrolyte solution 30 to be used. There is no particular limitation as long as it is a synthetic resin having characteristics that do not cause reaction, dissolution, and swelling) and chemical stability against oxygen and water (water in the air). For the innermost layer 50a, it is preferable to use a material having a low permeability to oxygen, water (water in the air) and the components of the nonaqueous electrolyte solution 30. Examples thereof include engineering plastics and thermoplastic resins such as polyethylene, polypropylene, polyethylene acid modified products, polypropylene acid modified products, polyethylene ionomers, and polypropylene ionomers.

  The “engineering plastic” means a plastic having excellent mechanical properties, heat resistance, and durability, such as those used in mechanical parts, electrical parts, housing materials, and the like. Examples thereof include polyacetal, polyamide, polycarbonate, polyoxytetramethyleneoxyterephthaloyl (polybutylene terephthalate), polyethylene terephthalate, polyimide, polyphenylene sulfide, and the like.

  Further, when a synthetic resin layer such as the outermost layer 50b is further provided in addition to the innermost layer 50a as in the composite packaging film 54 shown in FIG. Constituent materials similar to the innermost layer may be used.

  The metal layer 50 c is preferably a layer formed of a metal material having corrosion resistance against oxygen, water (water in the air), and the non-aqueous electrolyte solution 30. For example, a metal foil made of aluminum, aluminum alloy, titanium, chromium, or the like may be used.

  Moreover, the sealing method of all the sealing parts in the case 50 is not particularly limited, but the heat sealing method is preferable from the viewpoint of productivity.

  Next, the anode 10 and the cathode 20 will be described. FIG. 8 is a schematic cross-sectional view showing an example of the basic configuration of the anode of the electrochemical capacitor 1 shown in FIG. FIG. 9 is a schematic cross-sectional view showing an example of the basic configuration of the cathode of the electrochemical capacitor 1 shown in FIG.

  As shown in FIG. 8, the anode 10 includes a current collector 16 having electron conductivity, and an anode active material-containing layer 18 having electron conductivity formed on the current collector 16. As shown in FIG. 9, the cathode 20 includes a current collector 26 having electron conductivity, and a cathode active material-containing layer 28 having electron conductivity formed on the current collector 26. An undercoat layer that is an adhesive layer may be provided between the current collectors 16 and 26 and the active material containing layers 18 and 28.

［上記式（Ｉ）中、Ｒ^１およびＲ^２は、それぞれ独立に、水素原子、アルキル基（炭素数１〜５のアルキル基が好ましい）、アリール基（炭素数６〜１２のアリール基が好ましい）およびアルコキシ基（炭素数１〜５のアルコキシ基が好ましい）からなる群より選ばれる一種を表す。］ In the present invention, the anode active material-containing layer 18 contains a first conductive polymer and / or a first carbon material having electronic conductivity as an anode active material. Further, the cathode active material-containing layer 26 has at least a molecular structure including a repeating unit based on a monomer represented by the following formula (I), and has a second carbon having an electron conductivity covered with a second conductive polymer. The material is included as a cathode active material. The redox potential E1 [V] of the anode active material and the redox potential E2 [V] of the cathode active material satisfy the condition of the following formula (1).
0.20 ≦ (E2-E1) ≦ 3.60 (1)

[In the above formula (I), R ¹ and R ² are each independently a hydrogen atom, an alkyl group (preferably an alkyl group having 1 to 5 carbon atoms), an aryl group (preferably an aryl group having 6 to 12 carbon atoms). ) And an alkoxy group (preferably an alkoxy group having 1 to 5 carbon atoms). ]

  In the present invention, the non-aqueous electrolyte solution 30 is used as the electrolyte solution, and the anode 10 and the cathode 20 are configured as described above. Therefore, the electrochemical capacitor 1 has a sufficient capacity.

Here, it is more preferable that the oxidation-reduction potential E1 and the oxidation-reduction potential E2 satisfy the condition of the following expression (2), and it is more preferable that the condition of the following expression (3) is satisfied.
0.20 ≦ (E2-E1) ≦ 1.00 (2)
0.25 ≦ (E2-E1) ≦ 0.90 (3)

  If the difference ΔE between the oxidation-reduction potential E1 and the oxidation-reduction potential E2 is less than 0.20 V, it is difficult to obtain a sufficient capacity. Inconveniences such as lack of are likely to occur.

  Although the present invention relates to an electrochemical capacitor, the anode and cathode configurations described above can also be applied to a secondary battery such as a lithium ion secondary battery. It is considered that the capacity of the secondary battery can be improved by adopting the configuration of the anode and the cathode in the secondary battery.

  Hereinafter, the anode 10 will be described in detail. The current collector 16 is not particularly limited as long as it is a good conductor that can sufficiently transfer charges to the anode active material-containing layer 18, and a current collector used in a known electrochemical capacitor should be used. Can do. For example, the current collector 16 may be a metal foil such as aluminum or copper. The thickness of the current collector 16 is preferably 15 to 50 μm, and more preferably 15 to 30 μm, from the viewpoint of reducing the size and weight of the electrode 10.

  Further, the anode active material-containing layer 18 of the anode 10 mainly includes an anode active material and a binder. The anode active material-containing layer 18 may contain a conductive additive.

  The anode active material includes a first conductive polymer and / or a first carbon material having electronic conductivity, and more preferably includes the first conductive polymer and the first carbon material. Here, when the first conductive polymer is included alone as the anode active material, the anode can be configured such that the first conductive polymer is directly formed on the current collector 16. When the first conductive polymer and the first carbon material are included, the first carbon material covered with the first conductive polymer is included in the same manner as the cathode active material described above. Also good.

［式（ＩＩ）中、Ｒ^３は、水素原子またはアルキル基（炭素数１〜５のアルキル基が好ましい）を示し、Ｒ^４およびＲ^５は、それぞれ独立に、水素原子、アルキル基（炭素数１〜５のアルキル基が好ましい）、アリール基（炭素数６〜１２のアリール基が好ましい）およびアルコキシ基（炭素数１〜５のアルコキシ基が好ましい）からなる群より選ばれる一種を表す。］ As a 1st electroconductive polymer, what is hard to melt | dissolve in a nonaqueous electrolyte solution (especially propylene carbonate solution), and should just satisfy | fill the conditions of said Formula (1). For example, a molecular structure containing a repeating unit based on a monomer represented by the following formula (II), or a repeating unit based on at least one selected from the group consisting of indole, ethylenedioxythiophene and 3- (4-fluorophenyl) thiophene It is preferable to have at least a molecular structure containing When an n-type doped conductive polymer is used, the difference (E2-E1) between the redox potential of the anode active material and the redox potential of the cathode active material is increased, and an electrochemical capacitor having a higher capacity can be obtained. It is considered that a higher voltage and higher energy density can be obtained.

[In Formula (II), R ³ represents a hydrogen atom or an alkyl group (preferably an alkyl group having 1 to 5 carbon atoms), and R ⁴ and R ⁵ each independently represent a hydrogen atom, an alkyl group (carbon number 1 to 5 alkyl groups are preferred), an aryl group (preferably an aryl group having 6 to 12 carbon atoms) and an alkoxy group (preferably an alkoxy group having 1 to 5 carbon atoms) are selected. ]

  The monomer represented by the formula (II) is preferably at least one selected from the group consisting of pyrrole, 3-methylpyrrole, 3-butylpyrrole, 3-phenylpyrrole and 3-methoxypyrrole.

  Examples of the first carbon material having electron conductivity include activated carbon, carbon black such as acetylene black and ketjen black, graphite, low-temperature calcined carbon, graphitizable carbon, non-graphitizable carbon, and carbon nanotube. Among these, activated carbon and carbon nanotubes are preferable, and fibrous activated carbon is more preferable.

The density of the activated carbon is preferably 0.1 to 1.0 g / cm ^3, more preferably 0.5~0.8g / cm ^3. If such a density exceeds 1.0 g / cm ³ , the electrode characteristics tend to be insufficient, and if it is less than 0.1 g / cm ³ , it tends to be difficult to produce activated carbon.

The specific surface area of the activated carbon is preferably 1000~3000m ² · ^{g -1,} more preferably 1000 to 2000 ² · ^{g -1,} more preferably a 1500~2000m ² · ^{g -1.} When the specific surface area is less than 1000 m ² · g ⁻¹ , the electrode characteristics tend to be insufficient, and when the specific surface area exceeds 3000 m ² · g ⁻¹ , the electrolyte solution tends to become unstable. .

  The fibrous activated carbon preferably has an aspect ratio (b / a) of 1.5 or more (more preferably 1.5 to 8, more preferably 2 to 6, particularly preferably 2 to 4). When the aspect ratio is more than 8, aggregation flaws are likely to occur in the electrode-forming coating solution used to produce the electrode, and it tends to be difficult to produce the electrode (particularly to make it thinner). On the other hand, when the ratio is less than 1.5, the contact between the activated carbons becomes close to point contact, and the internal resistance of the electrode tends to be insufficiently reduced.

  The short axis a of the fibrous activated carbon is preferably 15 μm or less, more preferably 0.1 to 12 μm, and even more preferably 1 to 10 μm. If the short axis a exceeds 15 μm, it tends to be difficult to make the electrode thin, whereas if it is less than 0.1 μm, it tends to be difficult to produce activated carbon.

  As the material of the activated carbon, raw coal (for example, carbonized petroleum coke or resin produced from a delayed coker made from bottom oil of fluid heavy oil cracking catalytic cracker or residual oil of vacuum distillation equipment) It is preferable to use as a main component what is obtained by activation treatment (such as phenol resin) or carbonized natural material (for example, coconut shell charcoal).

  The carbon nanotube has a diameter of 100 nm or less (preferably 50 nm or less, more preferably 1 to 15 nm). Carbon nanotubes having a diameter exceeding 100 nm tend not to exhibit sufficient electric double layer capacity. The length is not particularly limited, but is 500 μm or less. Here, the carbon nanotube is a substance composed of carbon atoms obtained by rounding a graphite layer into a cylindrical shape. Furthermore, in the present embodiment, the carbon nanotube includes vapor grown carbon fiber.

  The carbon nanotube may be a multi-wall carbon nanotube (MWCNT) or a single-wall carbon nanotube (SWCNT). The structure is not particularly limited, and may be an armchair type, zigzag type, or chiral type structure, or a mixture of these structures. Here, the carbon nanotubes increase the conductivity of the electrode and increase the electric double layer capacity, leading to an improvement in volume energy density. In addition, the conductive polymer has a Faraday pseudocapacitance and increases the capacity of the electrode, which leads to an improvement in volume energy density.

  The binder is not particularly limited as long as it can bind the anode active material particles. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoro Ethylene copolymer (ETFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF) ) And the like. The binder also contributes to binding to the foil (current collector 16).

  The conductive auxiliary agent is not particularly limited, and a known conductive auxiliary agent can be used. Examples thereof include carbon blacks, carbon materials, metal fine powders such as copper, nickel, stainless steel and iron, a mixture of carbon materials and metal fine powders, and conductive oxides such as ITO.

  The anode active material-containing layer 10 has a plate-like shape, and its thickness is preferably 200 μm or less, and more preferably 10 to 100 μm. If the thickness of the anode active material-containing layer 10 exceeds 200 μm, it is difficult to reduce the size of the electrode, and stripes and the like are generated during the electrode preparation, which tends to make the electrode preparation difficult. On the other hand, when it is less than 10 μm, there is a tendency that sufficient volume energy density cannot be obtained.

  Next, the cathode 20 will be described in detail. As the current collector 26 of the cathode 20, a metal material on which a corrosion-resistant passive film is formed can be appropriately selected and used. For example, aluminum foil is preferable.

  The cathode active material-containing layer 28 of the cathode 20 is mainly composed of a cathode active material and a binder. The cathode active material-containing layer 28 may contain a conductive additive.

  The cathode active material-containing layer 28 only needs to contain the second carbon material coated with the above-described second conductive polymer as the cathode active material. The monomer represented by the formula (I) is preferably at least one selected from the group consisting of thiophene, 3-methylthiophene, 3-butylthiophene, 3-phenylthiophene and 3-methoxythiophene. The second carbon material is the same as the first carbon material. Moreover, what is preferable as a 1st carbon material can be used as a preferable thing similarly in a 2nd carbon material.

  The second carbon material coated with the second conductive polymer is a material in which part or all of the second carbon material is covered with the second conductive polymer.

  As long as the cathode active material-containing layer 28 includes the second carbon material coated with the second conductive polymer as the cathode active material, the other constituent conditions are not particularly limited. From the viewpoint of more reliably obtaining the effects of the present invention, the content of the second carbon material coated with the second conductive polymer in the cathode active material-containing layer 28 is the total mass of the cathode active material-containing layer 28. As a reference, it is preferably 3 to 90% by mass, and more preferably 10 to 80% by mass. When the content of the second carbon material coated with the second conductive polymer is less than the lower limit value, the capacity tends to be insufficiently improved. On the other hand, when the content exceeds the upper limit value, There is a tendency that the preparation of a coating solution for producing an electrode becomes difficult.

  The second carbon material coated with the second conductive polymer is formed on the second carbon material by electrolytic polymerization. This electrolytic polymerization is performed using a mixed solution containing the monomer represented by the above formula (I), which is a constituent material of the conductive polymer, and the second carbon material.

Specifically, the electrolytic polymerization uses an electrolytic cell containing the above mixed solution, a commonly used electrode such as a platinum electrode or a carbon electrode as a working electrode, and a constant potential (4.0 to 5.0) for a predetermined time. [V vs. Li / Li ⁺ ] grade). The method of electrolytic polymerization is not particularly limited, and is appropriately selected from constant potential electrolysis, constant current electrolysis, potential sweep, current pulse, potential pulse and the like. In this case, the electrolytic cell may be a bipolar or tripolar system. The mixed solution is used for electrolytic polymerization of an organic solvent (such as propylene carbonate) or an electrolyte (such as LiBF ₄ ) that can disperse or dissolve the monomer represented by the above formula (I) and the second carbon material. Contains necessary ingredients.

  By this electrolytic polymerization, the second carbon material coated with the second conductive polymer, which is a composite of the second conductive polymer and the second carbon material, is deposited on the surface of the working electrode.

  The cathode active material-containing layer 20 has a plate shape, and the thickness thereof is preferably 200 μm or less, and more preferably 10 to 100 μm. If the thickness of the cathode active material-containing layer 20 exceeds 200 μm, it is difficult to reduce the size of the electrode, and streaks or the like are generated during the production of the electrode, which tends to make the production of the electrode difficult. On the other hand, when it is less than 10 μm, there is a tendency that sufficient volume energy density cannot be obtained.

  Further, the cathode active material-containing layer 20 may include an electrode active material other than the second carbon material coated with the second conductive polymer, for example, a carbon material (activated carbon is more preferable), Constituent materials such as a binder may be included. The type and content thereof are not particularly limited. For example, a conductive assistant for imparting conductivity to the carbon powder (including those exemplified for the anode 10), binding, and the like. An agent (similar to those exemplified for the anode 10 may be mentioned) may be added.

  The cathode active material-containing layer 20 is formed on the current collector 26 (or the undercoat layer when there is an undercoat layer) as follows, for example. First, a coating liquid for forming a cathode active material-containing layer containing at least a second carbon material coated with a second conductive polymer, a binder, and a liquid capable of dissolving the binder is prepared. Next, the coating liquid is applied onto the current collector 26. And it is formed by removing the liquid. In addition, it is preferable that the cathode active material-containing layer 28 further contains a conductive auxiliary agent in order to obtain better electronic conductivity.

  When preparing the coating liquid for forming the cathode active material-containing layer, the second carbon material not coated with the second conductive polymer is used instead of the second carbon material coated with the second conductive polymer. A carbon material, that is, a simple second carbon material may be used.

  In this case, the obtained second carbon material-containing electrode (the current collector 26 having electron conductivity and the second carbon material formed on the current collector 26 and having the electron conductivity) The active material-containing layer) does not contain the second carbon material coated with the second conductive polymer, but the carbon material in the carbon material-containing electrode is obtained by the following method. Can be coated with a second conductive polymer.

That is, using the carbon material-containing electrode as a working electrode, the working electrode is immersed in a monomer solution containing the monomer represented by the above formula (I), and electrolytic polymerization is performed by the same method as described above. Thereby, the film | membrane of a 2nd conductive polymer can be formed in the whole electrode as well as the carbon material inside an electrode. Moreover, when immersing a carbon material containing electrode, only the surface of an electrode active material content layer may be immersed, and the whole may be immersed. In addition to the monomer represented by the above formula (I), the monomer solution is subjected to electrolytic polymerization of an organic solvent (such as propylene carbonate) in which the above monomer can be dispersed or dissolved, an electrolyte (such as LiBF ₄ ), and the like. Contains necessary ingredients. Further, as the monomer solution, a mixed solution containing the monomer represented by the above formula (I) and the second carbon material may be used.

  The cathode 20 may be provided with an undercoat layer (not shown). The undercoat layer is a layer disposed between the current collector 26 and the cathode active material-containing layer 28, and is a layer that imparts physical and electrical adhesion of each layer in the cathode 20. The material contains at least conductive particles and a binder capable of binding to the conductive particles. The undercoat layer is formed as follows. That is, first, an undercoat layer-forming coating solution containing conductive particles, a binder, and a liquid capable of dissolving the binder is prepared, and then this is applied onto the surface of the current collector 26. , Formed by removing the liquid.

  The current collector 26 of the cathode 20 is electrically connected to one end of a cathode lead 22 made of, for example, aluminum or tantalum, and the other end of the cathode lead 22 extends to the outside of the case 50. On the other hand, the current collector 18 of the anode 10 is also electrically connected to one end of an anode lead 12 made of, for example, copper, aluminum, or nickel, and the other end of the anode lead 12 extends to the outside of the encapsulating bag 14.

  The separator 40 disposed between the anode 10 and the cathode 20 is not particularly limited as long as it is formed of an insulating porous body, and a separator used in a known electrochemical capacitor can be used. For example, the insulating porous body may be a laminate of films made of polyethylene, polypropylene or polyolefin, a stretched film of a mixture of the above resins, or at least one constituent material selected from the group consisting of cellulose, polyester and polypropylene. The fiber nonwoven fabric which becomes.

  The non-aqueous electrolyte solution 30 is not particularly limited, and a non-aqueous electrolyte solution (electrolyte solution using an organic solvent) used in a known electrochemical capacitor can be used. The non-aqueous electrolyte solution 30 has a large potential window and contributes to increasing the capacity of the electrochemical capacitor 1.

The type of the nonaqueous electrolyte solution 30 is not particularly limited, but is generally selected in consideration of the solubility of the solute, the degree of dissociation, and the viscosity of the solution. The nonaqueous electrolyte solution 30 preferably has a high conductivity and a high potential window (a high decomposition starting voltage). For example, as a typical example, a solution in which a supporting salt such as LiBF ₄ is dissolved in an organic solvent such as propylene carbonate, diethylene carbonate, acetonitrile, γ-butyrolactone, and sulfolane is used. Further, as the supporting salt, a quaternary ammonium salt such as tetraethylammonium tetrafluoroborate can also be used. The non-aqueous electrolyte solution 30 may be a gel solution. In this case, it is necessary to strictly manage the moisture content.

  Further, as shown in FIG. 2 and FIG. 3, the anode lead 12 portion that comes into contact with the sealing portion of the encapsulating bag composed of the edge portion 51 </ b> B of the first film 51 and the edge portion 52 </ b> B of the second film 52 includes An insulator 14 for preventing contact between the anode lead 12 and the metal layer in the composite packaging film constituting each film is coated. Further, the cathode lead 22 and each film are formed in the portion of the cathode lead 22 that comes into contact with the sealing portion of the encapsulating bag composed of the edge 51B of the first film 51 and the edge 52B of the second film 52. An insulator 24 for preventing contact with the metal layer in the composite packaging film is coated.

  The configurations of the insulator 14 and the insulator 24 are not particularly limited, but may be made of, for example, a synthetic resin. It should be noted that the insulator 14 and the insulator 24 may not be disposed as long as the metal layer in the composite packaging film can be sufficiently prevented from contacting the anode lead 12 and the cathode lead 22, respectively.

  According to the present invention, the electrochemical capacitor 1 can be obtained as an electric double layer capacitor having a large capacity while being in the form of a film. These make use of their thin characteristics and can be used for IC cards, IC tags and the like in addition to the above-described applications. In addition, applications for toys and portable devices will be expanded.

  Next, a method for manufacturing the case 50 and the electrochemical capacitor 1 described above will be described.

  The manufacturing method of the element body 60 (a stacked body in which the anode 10, the separator 40, and the cathode 20 are sequentially stacked in this order) is not particularly limited, and a known method employed in manufacturing a known electrochemical capacitor is used. be able to. The cathode 20 uses the above-described electrode of the present invention.

  When the anode 10 is manufactured, first, the above-described constituent components are mixed and dispersed in a solvent in which the binder can be dissolved to prepare a coating liquid (slurry or the like) for forming an anode active material-containing layer. The solvent is not particularly limited as long as the binder can be dissolved and the conductive additive can be dispersed. For example, methyl isobutyl ketone, N-methyl-2-pyrrolidone, N, N-dimethyl Formamide can be used.

  Next, the anode active material-containing layer forming coating solution is applied onto the current collector surface, dried, and rolled to form the anode active material-containing layer 18 on the current collector 16, thereby producing the anode 10. To complete. Here, the method for applying the anode active material-containing layer forming coating solution to the surface of the current collector is not particularly limited, and may be appropriately determined according to the material and shape of the current collector. Examples thereof include a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, and a screen printing method. Moreover, when the anode 10 contains the 1st carbon material coat | covered with the 1st conductive polymer as an anode active material, you may produce an anode by the method similar to the cathode 20. FIG.

  The anode lead 12 and the cathode lead 22 are electrically connected to the produced anode 10 and cathode 20, respectively. The separator 40 is disposed between the anode 10 and the cathode 20 in a contacted state (non-adhered state), and the element body 60 is completed.

  Next, an example of a method for manufacturing the case 50 will be described. First, when the first film and the second film are composed of the composite packaging film described above, known production methods such as a dry lamination method, a wet lamination method, a hot melt lamination method, an extrusion lamination method, etc. It is produced using.

  For example, a film that becomes a synthetic resin layer constituting the composite packaging film, and a metal foil made of aluminum or the like are prepared. The metal foil can be prepared, for example, by rolling a metal material.

  Next, a composite packaging film (multilayer film) is preferably obtained by laminating a metal foil via an adhesive on a film that becomes a layer made of a synthetic resin so as to have a configuration of a plurality of layers described above. Is made. Then, the composite packaging film is cut into a predetermined size to prepare one rectangular film.

  Next, as described above with reference to FIG. 3, one film is folded, and the seal portion 51B (edge portion 51B) of the first film 51 and the seal portion 52B (edge portion) of the second film 52B) is heat-sealed by a desired seal width under a predetermined heating condition using, for example, a sealing machine. At this time, in order to secure an opening for introducing the element body 60 into the case 50, a part where heat sealing is not performed is provided. As a result, the case 50 having an opening is obtained.

  Then, an element body 60 in which the anode lead 12 and the cathode lead 22 are electrically connected is inserted into the case 50 having an opening. Then, the nonaqueous electrolyte solution 30 is injected. Subsequently, with the anode lead 12 and the cathode lead 22 partially inserted into the case 50, the opening of the case 50 is sealed using a sealing machine. In this way, the production of the case 50 and the electrochemical capacitor 1 is completed. In addition, the electrochemical capacitor of this invention is not limited to such a shape, It selects suitably. For example, a cylindrical shape or the like may be used. The electrochemical capacitor 1 described above is particularly suitable as an electric double layer capacitor, but is also suitable as a redox capacitor, pseudocapacitance capacitor, pseudo capacitor, or the like.

EXAMPLES Hereinafter, although an Example , a reference 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.

  First, an electrode was prepared. In preparation of an electrode, first, 80 parts by mass of fibrous activated carbon (trade name FR25, manufactured by Kuraray Chemical Co., Ltd.) and 10 parts by mass of a fluororubber binder were mixed. Next, methyl isobutyl ketone (MIBK) as a solvent was added to the mixture to obtain a slurry-like coating solution for forming an electrode active material-containing layer. The obtained coating solution was applied to an aluminum foil (20 μm) as a current collector by a doctor blade method and dried at 150 ° C. Rolling was performed after drying to obtain an activated carbon-containing electrode. In addition, the fibrous activated carbon of this case was used by processing FR25 into an aspect ratio of 1.5 to 8.

The activated carbon-containing electrode was vacuum dried at 175 ° C. for 12 hours, and then placed in an electrolytic cell (electrolyzer) containing an electrolytic solution. As the electrolyte, a LiBF ₄ in propylene carbonate to a solution at a ratio of 1.0 mol · ^{L -1,} using a monomer solution prepared by dissolving thiophene in a ratio of 0.3 mol · ^{L -1.} The electrolytic cell is 4.4 [V vs. Li / Li ⁺ ] was maintained at a constant potential for 20 minutes to perform electrolytic oxidation polymerization, and an electrode containing fibrous activated carbon coated with polythiophene was obtained. The obtained electrode was designated as electrode 1.

  In addition, instead of 3-phenylthiophene, 3-butylthiophene, indole, pyrrole, ethylenedioxythiophene (PEDOT) as the monomer to be dissolved in the electrolytic solution, fibrous activated carbon coated with a conductive polymer corresponding to each monomer An electrode containing was obtained. The obtained electrodes were referred to as electrodes 2, 3, 4, 5, and 6, respectively. An attempt was made to produce an electrode by using aniline as a monomer to be dissolved in the electrolytic solution. However, in the electrolytic solution mainly composed of propylene carbonate, polyaniline is dissolved in the electrolytic solution, so that the fibrous activated carbon coated with polyaniline is used. It was not possible to produce an electrode containing.

And the oxidation-reduction potential of the obtained electrode was investigated. First, an electrochemical cell was produced. The electrochemical cell is composed of an electrode (15 mmΦ) obtained as a working electrode, lithium metal as a reference electrode and a counter electrode, and a propylene carbonate solution (including ¹ mol·L ⁻¹ LiBF ₄ as a supporting salt) as an electrolyte solution. Is done. In this electrochemical cell, the tip of the Luggin tube of the reference electrode was adjusted to a diameter of 1 mm, and the distance between the reference electrode and the working electrode was adjusted to 2 mm. Further, the electrode area of the counter electrode was adjusted so as to be sufficiently larger than the electrode area of the working electrode. Next, the electrochemical cell was subjected to 4.2 to 1.8 [Vvs. The average discharge voltage when discharging to Li / Li ⁺ ] was measured, and the value was taken as the oxidation-reduction potential. The obtained results are shown in Table 1. Moreover, in Table 1, the electrode 7 is an activated carbon electrode which did not coat | cover activated carbon with a conductive polymer.

An electrochemical capacitor was produced using each of the obtained electrodes, and the discharge capacity was measured.
Example 1
An electrode (electrode 1) containing fibrous activated carbon coated with polythiophene was punched out to 15 mmΦ to form a cathode. In addition, an electrode (electrode 6) containing fibrous activated carbon coated with PEDOT was punched out to 15 mmΦ to be an anode. A 50 μm-thick cellulose separator impregnated with a propylene carbonate solution (containing ¹ mol·L ⁻¹ LiBF ₄ as a supporting salt) was sandwiched between the cathode and the anode and housed in a case to produce an electrochemical capacitor. Then, the obtained electrochemical capacitor was charged with a constant current and a constant voltage of 0.5 mA, discharged from 1.5 V to 0.1 V, and the capacity (mAh) was measured. The obtained results are shown in Table 2. Moreover, the discharge curve of the electrochemical capacitor of Example 1 is shown in FIG.

( Reference Examples 2 to 4 and Comparative Example 1)
An electrochemical capacitor was produced in the same manner as in Example 1 except that the anode and the cathode were replaced with the electrodes shown in Table 2. And with the obtained electrochemical capacitor, constant current constant voltage charge was performed at 0.5 mA, it discharged from 1.5V to 0.1V, and the capacity | capacitance (mAh) was measured. The obtained results are shown in Table 2. Moreover, the discharge curves of the electrochemical capacitors of Reference Examples 2 to 4 and Comparative Example 1 are shown in FIG. For reference, the difference (E2-E1) in the redox potential of the electrodes used for the cathode and the anode is also shown.

As can be seen from the results shown in Table 2, in Example 1 and Reference Examples 2 to 4, an electrochemical capacitor having a sufficient capacity of 0.200 mAh or more was obtained. Particularly, in Example 1 and Reference Example 2, a carbon material whose anode was coated with a conductive polymer was contained as an anode active material, and an extremely high capacity electrochemical capacitor of 0.400 mAh or more was obtained. In Comparative Example 1, it was confirmed that the capacity was low. In addition, since an electrode containing fibrous activated carbon coated with polyaniline could not be produced, an electrochemical capacitor using such an electrode could not be produced.

  The electrochemical capacitor of the present invention can be used as a backup power source for a power source of a portable device (small electronic device) or the like and an auxiliary power source for a hybrid vehicle.

It is a front view which shows suitable one Embodiment of the electrochemical capacitor of this invention. FIG. 2 is a development view when the inside of the electrochemical capacitor shown in FIG. 1 is viewed from the normal direction of the surface of an anode 10. It is a schematic cross section at the time of cut | disconnecting the electrochemical capacitor shown in FIG. 1 along the X1-X1 line | wire of FIG. It is a schematic cross section which shows the principal part at the time of cut | disconnecting the electrochemical capacitor shown in FIG. 1 along the X2-X2 line | wire of FIG. It is a schematic cross section which shows the principal part at the time of cut | disconnecting the electrochemical capacitor shown in FIG. 1 along the YY line of FIG. It is a schematic cross section which shows an example of the basic composition of the film used as the constituent material of the case of the electrochemical capacitor shown in FIG. It is a schematic cross section which shows another example of the basic composition of the film used as the constituent material of the case of the electrochemical capacitor shown in FIG. It is a schematic cross section which shows an example of the basic composition of the anode of the electrochemical capacitor shown in FIG. It is a schematic cross section which shows an example of the basic composition of the cathode of the electrochemical capacitor shown in FIG. It is a graph which shows the discharge curve of the electrochemical capacitor of Example 1 , Reference Examples 2-4 and Comparative Example 1. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electrochemical capacitor, 10 ... Anode, 12 ... Anode lead, 14 ... Insulator, 16 ... Current collector, 18 ... Anode active material content layer, 20 ... Cathode, 22 ... Lead for cathode, 24 ... Insulator, 26 ... current collector, 28 ... cathode active material-containing layer, 30 ... non-aqueous electrolyte solution, 40 ... separator, 50 ... case, 60 ... element body.

Claims (8)

An anode having a current collector and an anode active material-containing layer formed on the current collector;
A cathode having a current collector and a cathode active material-containing layer formed on the current collector;
A non-aqueous electrolyte solution;
A case for containing the anode, the cathode, and the non-aqueous electrolyte solution in a sealed state,
The anode active material-containing layer includes a first conductive polymer and the first carbon material as an anode active material,
The cathode active material-containing layer has, as a cathode active material, a second carbon material coated with a second conductive polymer having at least a molecular structure including a repeating unit based on a monomer represented by the following formula (I) Including
The anode active redox potential E1 [V] of a substance, the oxidation-reduction potential E2 [V] and the cathode active material meets the conditions of the following formula (1),
The first conductive polymer has at least a molecular structure including a repeating unit based on at least one selected from the group consisting of indole, ethylenedioxythiophene and 3- (4-fluorophenyl) thiophene. Electrochemical capacitor.
0.20 ≦ (E2-E1) ≦ 3.60 (1)

[In Formula (I), R ¹ and R ² each independently represent one selected from the group consisting of a hydrogen atom, an alkyl group, an aryl group, and an alkoxy group. ]   The monomer represented by the formula (I) is at least one selected from the group consisting of thiophene, 3-methylthiophene, 3-butylthiophene, 3-phenylthiophene and 3-methoxythiophene. 2. The electrochemical capacitor according to 1. Said second conductive polymer, an electrochemical capacitor according to claim 1 or 2, characterized in that formed on the second carbon material by electrolytic polymerization. The electrolytic polymerization is
A current collector having electron conductivity;
A cathode active material-containing layer containing the second carbon material formed on the current collector, and a second carbon material-containing electrode as a working electrode,
The electrochemical capacitor according to claim 3 , wherein the working electrode is immersed in a solution containing the monomer represented by the formula (I). The electrolytic polymerization is
Carried out using a mixed solution containing the monomer represented by the above formula (I) and the second carbon material,
The electrochemical capacitor according to claim 3 . The electrochemical capacitor according to any one of claims 1 to 5 , wherein the first carbon material and the second carbon material are fibrous activated carbon. The electrochemical capacitor according to any one of claims 1 to 6 , wherein the fibrous activated carbon has an aspect ratio of 1.5 or more. The anode and the cathode are arranged to face each other,
A separator made of an insulating porous body is disposed between the anode and the cathode,
At least a part of the non-aqueous electrolyte solution is contained in the anode, the cathode and the separator;
The electrochemical capacitor according to any one of claims 1 to 7 , wherein:

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