JP2015103602A - Lithium ion capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion capacitor having a high energy density.SOLUTION: A lithium ion capacitor comprises a positive electrode 10, a negative electrode 20, and an electrolyte. The positive electrode 10 contains a conductive high polymer and a redox substance having a redox potential lower than that of the conductive high polymer, as a positive electrode active material.

Description

  The present invention relates to a lithium ion capacitor.

2. Description of the Related Art Conventionally, an electric double layer capacitor (also referred to as “super capacitor”), which is a kind of electrochemical capacitor, is known as an electricity storage device that has an excellent output density, a short full charge / discharge time, and an excellent cycle life. Electric double layer capacitors are mounted on various industrial equipment such as smartphones, forklifts, idle stop cars, OA equipment, home appliances and tools.
However, the conventional electric double layer capacitor has a disadvantage that its energy density is lower than that of a chemical battery such as a lithium ion battery or a nickel metal hydride battery.

Therefore, a lithium ion capacitor having a structure in which a negative electrode of a lithium ion battery and a positive electrode of an electric double layer capacitor are combined has been proposed. This is intended to increase the capacitor voltage and improve the energy density by using a carbon electrode pre-doped with lithium ions as the negative electrode.
However, although the energy density of the conventional lithium ion capacitor is higher than the energy density of the electric double layer capacitor, it still does not reach the energy density of the lithium ion battery. Therefore, it is still insufficient to use a lithium ion capacitor as a consumer battery or the like where energy density is important, and further improvement is desired.

  By the way, as lithium ion batteries having excellent performance, those using an indigo compound as a positive electrode active material (see Patent Document 1), 1,4,5,8-anthracene tetron compound, and 5,7,12,14-pentacene. The thing using a tetron compound as a positive electrode active material (refer patent document 2) etc. is proposed.

JP 2011-103260 A JP 2012-155484 A

  However, even if the configuration of the lithium ion battery described in Patent Documents 1 and 2 is applied to a lithium ion capacitor as it is, a lithium ion capacitor having a practically sufficient energy density cannot be obtained.

  An object of the present invention is to provide a lithium ion capacitor having a high energy density.

（但し、式中Ｒ^１およびＲ^２は、基−ＳＯ_３Ｍ（Ｍは、水素原子、アルカリ金属、または（Ｍ^１）_１／２（Ｍ^１はアルカリ土類金属である。）である。）である。ｎおよびｍは、それぞれ０〜２の整数であり、ｎ個のＲ^１とｍ個のＲ^２とは、それぞれ同一または異なってもよい。） In order to solve the above-mentioned problem, the invention described in claim 1
A lithium ion capacitor,
A positive electrode, a negative electrode, and an electrolyte;
The positive electrode includes, as a positive electrode active material, a conductive polymer, and a redox material having a lower redox potential than the conductive polymer,
The oxidation-reduction substance is an indigo compound represented by the following formula (1).

Wherein R ¹ and R ² are the group —SO ₃ M (M is a hydrogen atom, an alkali metal, or (M ¹ ) _1/2 (M ¹ is an alkaline earth metal). N and m are each an integer of 0 to 2, and n R ¹ and m R ² may be the same or different.

The invention according to claim 2 is the lithium ion capacitor according to claim 1,
N and m in the formula (1) are 0 or 1, respectively.

The invention according to claim 3 is the lithium ion capacitor according to claim 1 or 2,
The indigo compound is at least one selected from indigo and indigo carmine.

The invention according to claim 4 is the lithium ion capacitor according to any one of claims 1 to 3,
The conductive polymer is at least one selected from polyaniline, polypyrrole, and polythiophene.

  According to the present invention, since a pseudo capacitance appears near the redox potential of the conductive polymer and near the redox potential of the redox substance, a lithium ion capacitor having a high energy density can be provided.

It is a disassembled perspective view which shows an example of the lithium ion capacitor concerning embodiment of this invention. It is sectional drawing which shows an example of the lithium ion capacitor concerning embodiment of this invention. (A) is a figure which shows the result of the charging / discharging test performed using the capacitor of Example 1, (b) is a figure which shows the result of the charging / discharging test performed using the capacitor of Example 2. (A) is a figure which shows the result of the charging / discharging test performed using the capacitor of Example 3, (b) is a figure which shows the result of the charging / discharging test performed using the capacitor of Example 4. It is a figure which shows the result of the charging / discharging test done using the capacitor of Example 5. It is a figure which shows the result of the charging / discharging test done using the capacitor of the comparative example 1.

  Embodiments of a lithium ion capacitor according to the present invention will be described below with reference to the drawings. The embodiments described below are provided with various technically preferable limitations for carrying out the present invention, but the scope of the present invention is not limited to the following embodiments and illustrated examples.

FIG. 1 is an exploded perspective view showing an example of a lithium ion capacitor 1 according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view showing an example of the lithium ion capacitor 1 according to an embodiment of the present invention.
As shown in FIGS. 1 and 2, the lithium ion capacitor 1 mainly includes a positive electrode current collector 11 and a negative electrode current collector 21 that are arranged to face each other, and one surface (negative electrode) of the positive electrode current collector 11. The positive electrode active material layer 12 formed on the surface of the current collector 21), the negative electrode active material layer 22 formed on one surface of the negative electrode current collector 21 (the surface on the positive electrode current collector 11 side), and the positive electrode active material The power storage device includes a separator 30 disposed between the material layer 12 and the negative electrode active material layer 22, an electrolytic solution impregnated in the separator 30, and a storage body 40 for storing them. . In addition, in FIG. 1, illustration of the storage body 40 is abbreviate | omitted.
In the case of the laminated type, the positive electrode active material layer 12 and the negative electrode active material layer 22 are coated on both sides of each current collector, and are stacked and packaged in parallel and in series.

The current collectors 11 and 21 serve to electrically connect the active material layers 12 and 22 and an external circuit. The current collectors 11 and 21 are formed with terminals 11a and 21a that are drawn out of the housing 40 and connected to an external circuit. Examples of materials for the current collectors 11 and 21 include (1) excellent electronic conductivity, (2) stable existence inside the capacitor, and (3) reduction in volume inside the capacitor (thinning). (4) The weight per unit volume is small (weight reduction), (5) Easy to process, (6) Practical strength, (7) Adhesion (mechanical adhesion) (8) Any material that has characteristics such as corrosion and dissolution by an electrolyte solution, such as metal electrode materials such as platinum, aluminum, gold, silver, copper, titanium, nickel, iron, stainless steel, etc. It may be a non-metallic electrode material such as carbon, conductive rubber, or conductive polymer. It is also possible to form at least the inner surface of the storage body 40 with a metal electrode material and / or a non-metal electrode material and provide the active material layers 12 and 22 on the inner surface. In this case, the storage body 40 also serves as the current collectors 11 and 21.
Here, the positive electrode 10 of the electrode for the lithium ion capacitor 1 according to the present invention includes a positive electrode current collector 11 and a positive electrode active material layer 12 provided on the surface of the positive electrode current collector 11. Moreover, the negative electrode 20 of the electrode for the lithium ion capacitor 1 according to the present invention includes a negative electrode current collector 21 and a negative electrode active material layer 22 provided on the surface of the negative electrode current collector 21.

The positive electrode active material layer 12 includes a positive electrode active material, a conductive additive, and a binder resin, and is provided on the surface of the positive electrode current collector 11.
In this embodiment, a mixture of a conductive polymer and a redox material having a lower redox potential than that of the conductive polymer is used as the positive electrode active material. Thereby, the electrostatic capacitance of the lithium ion capacitor 1 can be increased in a pseudo manner by the transfer of electrons by the redox reaction of the conductive polymer and the redox substance. Moreover, since the pseudo capacitance is expressed separately near the redox potential of the conductive polymer and near the redox potential of the redox substance, the energy density of the lithium ion capacitor 1 can be increased. In addition, since both of the conductive polymer and the redox substance have high ion entry and exit, a high output density can be obtained.

As the conductive polymer for the positive electrode active material, a polymer obtained by polymerizing at least one polymerizable monomer selected from aniline, pyrrole, and thiophene can be used. Specifically, polyaniline, polypyrrole, or polythiophene may be used as the conductive polymer, or a copolymer of at least two of aniline, pyrrole, and thiophene may be used, or these polymers may be used. May be used in combination.
In addition, when a conductive polymer is synthesized using aniline, pyrrole, or thiophene as a polymerizable monomer, an anionic surfactant, a cationic surfactant, or neutral is added to the polymerizable monomer solution in which the polymerizable monomer is dissolved. It is also possible to add a surfactant.
The conductive polymer for the positive electrode active material is not limited to a polymer obtained by polymerizing at least one polymerizable monomer selected from aniline, pyrrole, and thiophene, and can be arbitrarily changed as appropriate. .

（但し、ａは０以上の整数である。） The redox material for the positive electrode active material can be arbitrarily selected as appropriate according to the type of the conductive polymer for the positive electrode active material. For example, when the conductive polymer for the positive electrode active material is a polymer obtained by polymerizing at least one polymerizable monomer selected from aniline, pyrrole, and thiophene, the redox material for the positive electrode active material An indigo compound represented by the above formula (1) (hereinafter simply referred to as “indigo compound”), a derivative of an acene compound represented by the following formula (2) having at least two ketone structures (Hereinafter simply referred to as “acene compound derivative”), benzoquinone derivatives, and the like can be used.

(However, a is an integer of 0 or more.)

Indigo compounds are preferably those in which n in the above formula (1) is “0” or “1”, and those in which m in the above formula (1) is “0” or “1” are preferable. Indigo compounds in which n and m in the formula (1) are “0” or “1” are preferable in that they have excellent cycle characteristics because elution into a solvent hardly occurs even when charging and discharging are repeated. .
The substitution position of R ¹ and R ² in the above formula (1) is not particularly limited, but the indigo compound in which R ¹ and R ² are substituted at the 5,5′-position, 7,7′-position, etc. Is preferable because it can be easily synthesized by electrophilic reaction.
More preferable examples of the indigo compound include compounds in which n and m in the above formula (1) are each “0”, that is, indigo represented by the following formula (3), and n in the above formula (1). And m are each “1” and R ¹ and R ² in the above formula (1) are each “—SO ₃ Na”, that is, indigo carmine represented by the following formula (4) However, these do not limit the indigo compounds.

The acene compound derivative is preferably such that at least one ring contained in the acene compound represented by the above formula (2) has two ketone structures.
Specifically, the acene compound derivative includes a derivative in which a in the above formula (2) is “0” and one ring has two ketone structures, that is, a naphthoquinone represented by the following formula (5) Or a derivative thereof, a derivative in which a in the above formula (2) is “1” and one ring has two ketone structures, that is, anthraquinone represented by the following formula (6) or a derivative thereof, In the formula (2), a is “3” and each of the two rings has two ketone structures, that is, pentacentetron represented by the following formula (7) or a derivative thereof, the above formula (2) In which a is “1” and the two rings each have two ketone structures, ie, 1,4,5,8-anthracenetetron or a derivative thereof, These are not intended to limit the acene compound derivative.
The acene compound derivative is derived from a multi-electron reaction, has a large theoretical capacity, and can be used effectively as a positive electrode active material. For example, the theoretical capacity of 1,4,5,8-anthracentetron is as large as 450 mAh / g.

Examples of the benzoquinone derivative include dihydroxybenzoquinone represented by the following formula (8) and dimethoxybenzoquinone represented by the following formula (9), but these do not limit the benzoquinone derivative.

The positive electrode active material may further include a porous body in addition to a mixture of a conductive polymer and a redox material having a lower redox potential than the conductive polymer. When the positive electrode active material contains a porous body, not only the capacity increase effect due to the addition of pseudocapacitance associated with the redox reaction of the conductive polymer or redox material, but also the surface of the porous body having a large specific surface area Since the capacity increasing effect due to the formation of the double layer can be enjoyed, the capacity of the lithium ion capacitor 1 can be further increased.
The porous body for the positive electrode active material may be a conductive porous body such as activated carbon or an insulating porous body such as silica, but the conductive porous body is used from the viewpoint of use as an electrode material. preferable. Furthermore, among the conductive porous bodies, a porous body made of a conductive carbon material such as activated carbon, graphene, carbon nanotube, or carbon nanofiber is more preferable from the viewpoint of manufacturing cost. Moreover, an insulating porous body can also be used suitably as a porous body for positive electrode active materials by selecting suitably the kind and quantity of a conductive support agent.
When the positive electrode active material includes a porous body, the positive electrode active material may include one type of porous body or a plurality of types of porous bodies.

The negative electrode active material layer 22 includes a negative electrode active material, a conductive additive, and a binder resin, and is provided on the surface of the negative electrode current collector 21.
In this embodiment, an active material capable of occluding lithium ions is used as the negative electrode active material, and an electrode pre-doped with lithium ions is used as the negative electrode 20. Thereby, since the electric potential of the negative electrode 20 falls, the cell voltage (capacitor voltage) of the lithium ion capacitor 1 can be raised.

Active materials for the negative electrode active material include polyacene organic semiconductors (PAS), graphite materials (natural graphite, artificial graphite, modified graphite), graphitizable carbon, non-graphitizable carbon, low-temperature calcined carbon, coke , Various graphite materials, carbon fibers, resin-fired carbon, pyrolytic vapor-grown carbon, mesocarbon microbeads (MCM), mesophase pitch-based carbon fibers, graphite whiskers, pseudo-isotropic carbon (PIC), fired natural materials , Lithium titanium oxide (LTO) represented by the general formula Li ₄ Ti ₅ O ₁₂ , hydrogen titanium oxide (HTO) represented by the general formula H ₂ Ti ₁₂ O ₂₅ , and the like. The active material for the negative electrode active material is not limited.

Note that the negative electrode active material may include one type of active material or a plurality of types of active materials.
Also, the negative electrode 20 is not limited to an electrode that uses an active material capable of occluding lithium ions as a negative electrode active material, such as a carbon electrode pre-doped with lithium ions, and is pre-doped (pre-occluded) with lithium ions. For example, a lithium electrode made of metallic lithium may be used.

  The conductive assistant contained in the active material layers 12 and 22 plays a role of reducing the internal resistance of the lithium ion capacitor 1. As the conductive auxiliary agent, for example, carbon black such as acetylene black, furnace black, channel black, thermal black, ketjen black and the like can be used.

  The binder resins contained in the active material layers 12 and 22 serve to fix each other in a state where the active material and the conductive additive are mixed. As the binder resin, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), tetrafluoroethylene-propylene (FEPM), an elastomer binder, or the like can be used. Alternatively, after being kneaded by a dry method, the collector electrode (current collector) can be coated.

The separator 30 is disposed between the adjacent positive electrode 10 and the negative electrode 20, and plays a role of preventing the positive electrode 10 and the negative electrode 20 from coming into contact with each other and short-circuiting in the housing 40. As a material of the separator 30, an insulating material capable of holding an electrolytic solution can be used, and it can be properly used depending on whether the electrolytic solution contained in the separator 30 is an aqueous electrolytic solution or a non-aqueous electrolytic solution. preferable. Specifically, as the separator 30, for example, a film of polyolefin, polytetrafluoroethylene (PTFE), polyethylene, cellulose, polyvinylidene fluoride (PVdF), or the like can be used.
The electrolytic solution impregnated in the separator 30 may be an aqueous electrolytic solution or a non-aqueous electrolytic solution.

As the aqueous electrolyte solution, an aqueous solution of a supporting electrolyte can be used.
Typical supporting electrolytes are H ₂ SO ₄ , HCl, KCl, NaCl, KOH, NaOH and the like, but the supporting electrolyte is not limited to this.
The electrolytic solution may contain one type of supporting electrolyte or a plurality of types of supporting electrolytes.

In addition, as the nonaqueous electrolytic solution, a solution obtained by dissolving a supporting electrolyte in a predetermined organic solvent can be used.
Typical supporting electrolytes are TEABF ₄ , TEAPF ₆ , LiPF ₆ , LiBF ₄ , LiClO ₄ , TEABF ₄ , TEAPF _6, etc., but the supporting electrolyte is not limited thereto.
As the predetermined organic solvent, for example, ethylene carbonate (EC), ethyl methyl carbonate (EMC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC) and the like can be used.

The storage body 40 plays a role of storing a stacked body of the current collectors 11 and 21, the active material layers 12 and 22, and the separator 30 that is impregnated and held with the electrolytic solution. Here, the storage body 40 and the current collectors 11 and 21 are insulated.
As a material of the storage body 40, a laminate film material made of aluminum, stainless steel, titanium, nickel, platinum, gold, or the like, or a laminate film material made of an alloy thereof can be used.

Next, an example of the manufacturing method of the lithium ion capacitor 1 of this embodiment is demonstrated.
First, a mixture of a conductive polymer and a redox material having a lower redox potential than the conductive polymer (positive electrode active material), a conductive additive for the positive electrode active material layer 12, and a positive electrode active material layer 12 A binder resin is kneaded to prepare a positive electrode active material slurry. If necessary, the conductive polymer is doped or dedoped, and the conductive polymer is doped or dedoped, and then kneaded with the redox substance, conductive assistant, and binder resin. To do.
Next, the positive electrode active material slurry is placed on the positive electrode current collector 11 and pressurized, and the positive electrode active material layer 12 is formed on the surface of the positive electrode current collector 11, thereby producing the positive electrode 10.

In addition, an active material capable of occluding lithium ions (negative electrode active material), a conductive additive for the negative electrode active material layer 22, and a binder resin for the negative electrode active material layer 22 are kneaded to prepare a negative electrode active material slurry.
Next, the negative electrode active material slurry is placed on the negative electrode current collector 21 and pressurized to form the negative electrode active material layer 22 on the surface of the negative electrode current collector 21, and then lithium ions are pre-doped to obtain the negative electrode 20.
A carbon electrode prepared and pre-doped with lithium ions may be used as the negative electrode 20, or a lithium electrode made of metallic lithium may be prepared and used as it is as the negative electrode 20.

Next, the positive electrode 10 and the negative electrode 20 are arranged so that the positive electrode active material layer 12 and the negative electrode active material layer 22 are opposed to each other, and a separator 30 impregnated with an electrolytic solution is sandwiched therebetween to produce a capacitor body.
Next, the capacitor body is stored in the storage body 40, and the storage body 40 is sealed under reduced pressure. Thereby, the lithium ion capacitor 1 is completed.
1, the positive electrode 10, the negative electrode 20, and the separator 30 illustrate the rectangular lithium ion capacitor 1. However, the shapes of the positive electrode 10, the negative electrode 20, and the separator 30 can be arbitrarily changed as appropriate. For example, it may be circular.

  Hereinafter, the present invention will be described with reference to specific examples, but the present invention is not limited thereto.

  A mixture of a conductive polymer (undoped polyaniline) and a redox substance (indigo compound, acene compound derivative, benzoquinone derivative) having a lower redox potential than the conductive polymer was used as a positive electrode active material. The lithium ion capacitor 1 was composed of the positive electrode 10 and the negative electrode 20 made of a graphite sheet pre-doped with lithium ions, and a charge / discharge test was performed to evaluate the characteristics of the lithium ion capacitor 1.

Specifically, first, the positive electrode 10 was produced.
Using a mixture of undoped polyaniline (that is, undoped polyaniline) and indigo (ID, see formula (3) above), which is a kind of indigo compound, as a positive electrode active material, undoped polyaniline (12 mg) and indigo (12 mg), acetylene black (3 mg) as a conductive assistant, and PTFE (3 mg) as a binder resin were mixed and kneaded in a mortar to obtain a positive electrode active material slurry.
Next, an aluminum mesh (thickness: 100 μm) is used as the positive electrode current collector 11, the positive electrode active material slurry is stretched into a sheet shape, placed on the positive electrode current collector 11, and a pressure of 10 MPa is applied to form. Thus, the positive electrode active material layer 12 was formed on the surface of the positive electrode current collector 11. Then, a circular positive electrode 10 was produced by punching into a circular shape having a diameter of 15 mm. Then, it was made to dry under reduced pressure at 100 degreeC for 24 hours, and the water | moisture content was fully skipped.

Next, the negative electrode 20 was produced.
The graphite sheet was punched into a circular shape having a diameter of 15 mm and dried under reduced pressure at 100 ° C. for 24 hours to sufficiently remove water.
Next, a separator 30 (circular polyolefin film (diameter: 20 mm)) is placed on a Li foil punched into a circular shape with a diameter of 15 mm, and an electrolytic solution (LiPF ₆ (electrolyte)) is added to the separator 30 with an EC + EMC solution. A cell dissolved in (solvent) (electrolyte concentration: 1 mol / L)) was dropped, and a graphite sheet was placed on the separator 30 impregnated with the electrolytic solution to constitute a cell.
Subsequently, between the Li foil (positive electrode) and the graphite sheet (negative electrode) was short-circuited with a resistance of about 0.1Ω, and the negative electrode 20 was obtained by pre-doping lithium ions into the graphite sheet. And the cell was decomposed | disassembled and the pre-doped graphite sheet (negative electrode 20) was taken out.

Next, assembly work was performed to produce the lithium ion capacitor 1. All assembly operations were performed in an argon atmosphere (specifically, in a glove box filled with argon gas). A bipolar flat cell is used as an evaluation cell, a circular polyolefin film (diameter: 20 mm) is used as a separator 30, and LiPF ₆ (electrolyte) is dissolved in an EC + EMC solution (solvent) (electrolyte concentration: 1 mol / mol) L) was used as the electrolyte.
A lithium ion capacitor 1 (hereinafter referred to as “capacitor of Example 1”) was configured by sandwiching a separator 30 impregnated with an electrolyte between the extracted negative electrode 20 and the prepared positive electrode 10.

Moreover, it is the same method as the capacitor of Example 1 except that a mixture of undoped polyaniline and indigo carmine (IC, see formula (4) above), which is a kind of indigo compound, is used as the positive electrode active material. A lithium ion capacitor 1 (hereinafter referred to as “capacitor of Example 2”) was constructed.
Moreover, it is the same method as the capacitor of Example 1 except that a mixture of undoped polyaniline and anthraquinone (AQ, see formula (6) above), which is a kind of acene compound derivative, is used as the positive electrode active material. A lithium ion capacitor 1 (hereinafter referred to as “capacitor of Example 3”) was constructed.
Further, the same method as that of the capacitor of Example 1 except that a mixture of undoped polyaniline and pentacentetron (PCT, see formula (7) above) which is a kind of acene compound derivative is used as the positive electrode active material. Thus, a lithium ion capacitor 1 (hereinafter referred to as “capacitor of Example 4”) was configured.
Moreover, it is the same method as the capacitor of Example 1 except that a mixture of undoped polyarinin and dimethoxybenzoquinone (DMBQ, see the above formula (9)), which is a kind of benzoquinone derivative, is used as the positive electrode active material. A lithium ion capacitor 1 (hereinafter referred to as “capacitor of Example 5”) was constructed.

For comparison, a lithium ion capacitor (hereinafter referred to as “capacitor of Comparative Example 1”) is configured in the same manner as the capacitor of Example 1 except that only undoped polyaniline is used as the positive electrode active material. did.
For comparison, a lithium ion capacitor (hereinafter referred to as “capacitor of comparative example 2”) is the same as the capacitor of example 1 except that only activated carbon (YP50, manufactured by Kuraray Chemical) is used as the positive electrode active material. ) Was configured.
For comparison, the electric double layer was formed in the same manner as the capacitor of Example 1 except that only activated carbon was used as the positive electrode active material and an activated carbon electrode (not pre-doped with lithium ions) was used as the negative electrode. A capacitor (hereinafter referred to as “capacitor of Comparative Example 3”) was constructed.

Next, a charge / discharge test was performed to evaluate the characteristics of each capacitor.
For Examples 1 to 5 and Comparative Examples 1 and 2, as test conditions, charge / discharge current: 1 mA / cm ² , upper limit voltage: 3.8 V, lower limit voltage: 2.0 V are set, and a charge / discharge test is performed by a constant current method. Went. Moreover, about the comparative example 3, the charging / discharging test was done by the constant current method, setting charging / discharging electric current: 1 mA / cm < ² >, upper limit voltage: 2.5V, and lower limit voltage: 0.0V as test conditions. Table 1 shows the energy density obtained from the result of the charge / discharge test. Moreover, the change of the capacitor voltage at the time of the said charge / discharge test is shown in FIGS. In each capacitor, the electrode weights are not exactly the same.

As shown in Table 1, the energy density of the capacitor of Example 1 (that is, a capacitor using a mixture of undoped polyaniline and indigo as the positive electrode active material) is equal to that of the capacitor of Comparative Example 3 (that is, the electric double layer). 7.9 times the energy density of the capacitor), 2.8 times the energy density of the capacitor of Comparative Example 2 (ie, standard lithium ion capacitor), and only the capacitor of Comparative Example 1 (ie, undoped polyaniline is active as the positive electrode). It was found to be 1.3 times the energy density of the capacitor used as the substance.
Moreover, as shown in Table 1, the energy density of the capacitor of Example 2 (that is, the capacitor using a mixture of undoped polyaniline and indigo carmine as the positive electrode active material) is the energy density of the capacitor of Comparative Example 3. 6.6 times, 2.3 times the energy density of the capacitor of Comparative Example 2, and 1.1 times the energy density of the capacitor of Comparative Example 1.
This is because the difference in redox potential between the polyaniline and the indigo compound and the combination of the polyaniline and the indigo compound are compatible with the operating potential of the lithium ion capacitor.

That is, when polyaniline is used as the positive electrode active material, a large pseudo capacitance is generated with anion doping / dedoping.
However, when only polyaniline is used as the positive electrode active material as in the capacitor of Comparative Example 1, the dedoping is completed at 2.5 V or less at the operating potential of 2 to 4 V of the lithium ion capacitor as shown in FIG. The capacitor voltage drops rapidly (see the portion surrounded by the one-dot chain line in FIG. 6).
On the other hand, when a mixture of polyaniline and an indigo compound is used as the positive electrode active material as in the capacitors of Example 1 and Example 2, the oxidation of the indigo compound is performed as shown in FIGS. 3 (a) and 3 (b). Since the reduction potential is in the vicinity of 2.0 to 2.4 V, a pseudo capacitance appears in the vicinity of 2.0 to 2.4 V, and the voltage drop becomes gentle (see the portion surrounded by the one-dot chain line in FIG. 3). Thus, a lithium ion capacitor having a large energy density can be obtained by using a mixture of polyaniline and an indigo compound as a positive electrode active material in the lithium ion capacitor.

Further, as shown in Table 1, the energy density of the capacitor of Example 3 (that is, a capacitor using a mixture of undoped polyaniline and anthraquinone as the positive electrode active material) is equal to the energy density of the capacitor of Comparative Example 3. It was found to be 6.9 times, 2.5 times the energy density of the capacitor of Comparative Example 2, and 1.2 times the energy density of the capacitor of Comparative Example 1.
Further, as shown in Table 1, the energy density of the capacitor of Example 4 (that is, a capacitor using a mixture of undoped polyaniline and pentacentetron as a positive electrode active material) is the energy density of the capacitor of Comparative Example 3. It was found that the energy density of the capacitor of Comparative Example 2 was 4.3 times that of the capacitor of Comparative Example 2 and 2.0 times that of the capacitor of Comparative Example 1.
This is because the difference in redox potential between the polyaniline and the acene compound derivative and the combination of the polyaniline and the acene compound derivative are compatible with the operating potential of the lithium ion capacitor.

That is, when polyaniline is used as the positive electrode active material, a large pseudo capacitance is generated with anion doping / dedoping.
However, when only polyaniline is used as the positive electrode active material as in the capacitor of Comparative Example 1, the dedoping is completed at 2.5 V or less at the operating potential of 2 to 4 V of the lithium ion capacitor as shown in FIG. The capacitor voltage drops rapidly (see the portion surrounded by the one-dot chain line in FIG. 6).
On the other hand, when a mixture of polyaniline and an acene compound derivative is used as a positive electrode active material as in the capacitors of Example 3 and Example 4, as shown in FIGS. 4A and 4B, the acene compound derivative is used. Since the oxidation-reduction potential of 2.0 is in the vicinity of 2.0 to 2.5 V, a pseudocapacitance appears in the vicinity of 2.0 to 2.5 V, and the voltage drop becomes gradual (see the portion surrounded by the one-dot chain line in FIG. 4). . Accordingly, a lithium ion capacitor having a large energy density can be obtained by using a mixture of polyaniline and an acene compound derivative as a positive electrode active material in the lithium ion capacitor.

Further, as shown in Table 1, the energy density of the capacitor of Example 5 (that is, the capacitor using a mixture of undoped polyaniline and dimethoxybenzoquinone as the positive electrode active material) is the energy density of the capacitor of Comparative Example 3. It was found to be 6.8 times that of the capacitor, 2.4 times the energy density of the capacitor of Comparative Example 2, and 1.2 times the energy density of the capacitor of Comparative Example 1.
This is because the difference in redox potential between polyaniline and benzoquinone derivative and the combination of polyaniline and benzoquinone derivative are compatible with the operating potential of the lithium ion capacitor.

That is, when polyaniline is used as the positive electrode active material, a large pseudo capacitance is generated with anion doping / dedoping.
However, when only polyaniline is used as the positive electrode active material as in the capacitor of Comparative Example 1, the dedoping is completed at 2.5 V or less at the operating potential of 2 to 4 V of the lithium ion capacitor as shown in FIG. The capacitor voltage drops rapidly (see the portion surrounded by the one-dot chain line in FIG. 6).
On the other hand, when a mixture of polyaniline and a benzoquinone derivative is used as a positive electrode active material as in the capacitor of Example 5, the redox potential of the benzoquinone derivative is around 2.0 to 2.5 V as shown in FIG. For this reason, a pseudo capacitance appears in the vicinity of 2.0 to 2.5 V, and the voltage drop becomes gentle (see the portion surrounded by the alternate long and short dash line in FIG. 5). Accordingly, a lithium ion capacitor having a large energy density can be obtained by using a mixture of polyaniline and a benzoquinone derivative as a positive electrode active material in the lithium ion capacitor.

  From the results of Table 1 and FIGS. 3 to 6, an electric double layer capacitor (as a positive electrode active material) can be obtained by using a mixture of a conductive polymer and a redox material having a lower redox potential than the conductive polymer. The capacitor of Comparative Example 3), a lithium ion capacitor using activated carbon as the positive electrode active material (capacitor of Comparative Example 2), or a conductive polymer as the positive electrode active material, but having a redox potential higher than that of the conductive polymer. It was found that a lithium ion capacitor having a higher energy density than that of a lithium ion capacitor not containing a low redox substance (capacitor of Comparative Example 1) can be formed.

According to the lithium ion capacitor 1 of the present embodiment described above, the positive electrode 10, the negative electrode 20, and the electrolyte are provided. The positive electrode 10 is composed of a conductive polymer and a conductive polymer as a positive electrode active material. And a redox substance having a low redox potential.
Therefore, since pseudo capacity appears near the redox potential of the conductive polymer and near the redox potential of the redox substance, a lithium ion capacitor having a high energy density can be provided.
Note that the positive electrode active material may contain a plurality of types of redox substances as redox substances having a lower redox potential than the conductive polymer.

In addition, according to the lithium ion capacitor 1 of the present embodiment, the redox substance is a derivative of an acene compound and has at least two ketone structures, and the acene compound is represented by the above formula (2). It is preferable that
Further, the redox substance is more preferably at least one selected from naphthoquinone, anthraquinone, pentacentetron, and derivatives thereof.
By using such a redox substance, it is possible to provide a lithium ion capacitor made of a material with a low environmental burden as a lithium ion capacitor having a high energy density.

Moreover, according to the lithium ion capacitor 1 of this embodiment, it is preferable that the oxidation-reduction substance is an indigo compound represented by the above formula (1).
Furthermore, n and m in Formula (1) are more preferably 0 or 1, respectively.
Furthermore, the indigo compound is most preferably at least one selected from indigo and indigo carmine.
By using such a redox substance, it is possible to provide a lithium ion capacitor made of a material with a low environmental burden as a lithium ion capacitor having a high energy density.

Moreover, according to the lithium ion capacitor 1 of the present embodiment, the conductive polymer is preferably at least one selected from polyaniline, polypyrrole, and polythiophene.
By using such a conductive polymer, it is possible to sufficiently enjoy the capacity increasing effect due to the addition of the pseudo capacitance associated with the oxidation-reduction reaction of the conductive polymer.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 Lithium ion capacitor 10 Positive electrode 20 Negative electrode

Claims (4)

A positive electrode, a negative electrode, and an electrolyte;
The positive electrode includes, as a positive electrode active material, a conductive polymer, and a redox material having a lower redox potential than the conductive polymer,
The lithium ion capacitor, wherein the redox material is an indigo compound represented by the following formula (1).

Wherein R ¹ and R ² are the group —SO ₃ M (M is a hydrogen atom, an alkali metal, or (M ¹ ) _1/2 (M ¹ is an alkaline earth metal). N and m are each an integer of 0 to 2, and n R ¹ and m R ² may be the same or different.   2. The lithium ion capacitor according to claim 1, wherein n and m in the formula (1) are 0 or 1, respectively.   The lithium ion capacitor according to claim 1, wherein the indigo compound is at least one selected from indigo and indigo carmine.   4. The lithium ion capacitor according to claim 1, wherein the conductive polymer is at least one selected from polyaniline, polypyrrole, and polythiophene. 5.

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