JP2015170740A - Conductive polymer composite and method of producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive polymer composite which has high capacity and high conductivity and high durability.SOLUTION: A conductive polymer composite 1 is provided in which a carbon nanofiber 10 is used as a core, and the surface of the carbon nanofiber 10 is covered with polyion complex 20 composed of polyaniline 21 and polyanion 22.

Description

  The present invention relates to a conductive polymer composite and a method for producing the same. In particular, the present invention relates to a conductive polymer composite used for an electrode of a chargeable / dischargeable power storage device and a method for producing the same.

Polyaniline is a conductive polymer with electrochemical oxidation / reduction (redox) activity, and the oxidation / reduction process is reversible. Therefore, it is an electrode material for chargeable / dischargeable power storage devices such as electrochemical capacitors. Attention has been paid. An electrode made of polyaniline may be used in an acidic electrolytic solution such as sulfuric acid because there are few applications in the organic electrolytic solution because of the possibility of elution into the organic electrolytic solution.
In polyaniline, the electrolyte anion is released from the polymer chain in the reduction process (discharge), and the electrolyte anion is again introduced into the polymer chain in the oxidation process (charge). The charge / discharge capacity of an electricity storage device including an electrode made of a conductive polymer depends on the electrolyte ion retention capacity of the conductive polymer. Since the emeraldine type polyaniline in an ideal structure can hold 0.5 mol of electrolyte anion in one molecule, the polyaniline is regarded as a material having a relatively high energy density. Further, since aniline as a raw material is inexpensive, polyaniline is available at a low price.

As shown in FIG. 3, polyaniline has four structures depending on the oxidation-reduction state, and only the emeraldine salt exhibiting a dark green color has conductivity. Polyaniline undergoes proton addition and proton desorption on nitrogen atoms in parallel with the redox process (charge / discharge process). Along with this, the charge of polyaniline changes, and ion exchange occurs to maintain electrical neutrality. An anionic substance serving as a counter ion of the electrochemically active emeraldine cation is called a dopant, and examples of the dopant include inorganic ions such as sulfate ion, chloride ion and phosphate ion, BF ₄ ⁻ and PF ₆ ^{− and the} like. Complex ions, various organic anions, and the like can be used.
Since polyaniline, which is an organic polymer, dissolves in an organic electrolytic solution, when an electrode made of polyaniline is used in the organic electrolytic solution, polyaniline is eluted from the electrode. Therefore, when an electrode made of polyaniline is used in an organic electrolytic solution, there is a problem that the active species (polyaniline which is an electrode active material) are lost and the capacity is lowered by a long-time operation.

By the way, since lowering the electrical resistance of the electricity storage device leads to an improvement in power density, the electrode material for the electricity storage device is required to have high conductivity. Organic polymers are basically insulators, and even conductive polymers often have higher electrical resistance than metals and carbon. For this reason, attempts have been made to mix conductive assistants such as carbon materials as auxiliary agents that improve the conductivity of the conductive polymer.
Specifically, for example, a polyaniline / carbon composite obtained by mixing polyaniline in a non-doped state stably dispersed in a nonpolar solvent with a carbon material such as activated carbon, carbon black, carbon nanotube, and fullerene has been proposed. (Patent Document 1).
However, it is difficult to ensure uniformity at the nano level in the composite of the carbon material and the conductive polymer by mechanical mixing. In order to effectively use the electrochemically active substance, it is necessary to uniformly mix the conductive polymer and the conductive assistant. Therefore, for example, a polyaniline / carbon composite obtained by electrolytic polymerization of aniline in a solution in which activated carbon is suspended has been proposed (Patent Document 2).
In mechanical mixing, the contact between the carbon material and the conductive polymer is limited. Thus, for example, it has been proposed to obtain a polyaniline / carbon composite by chemically polymerizing aniline in an aqueous solution in the presence of a porous carbon material such as activated carbon, and use this for an electrode (Patent Document 3). ).
Also, for example, a composition for use in an electrode for an electrochemical capacitor comprising an electrochemically active material (such as polyaniline) and a carbon nanofiber having a specific surface area greater than about 100 m ² / g. A composition containing it has been proposed (Patent Document 4).

JP 2008-160068 A Japanese Patent Laid-Open No. 7-201676 JP 2002-25865 A Special Table 2002-526913

However, the conductive polymer composites described in Patent Documents 1 to 4, specifically, a composite of a polyaniline as an active material and a carbon material as a conductive assistant cannot provide high conductivity. There is a problem that polyaniline is eluted in the organic electrolyte. When the polyaniline is eluted, the conductive polymer composite is deteriorated, which leads to deterioration of the electrode made of the conductive polymer composite.
The electrode material is required to be a conductive polymer composite having high electrode activity, high power density, and low dissolution in an organic electrolyte. In order to fully exhibit the high charge / discharge capacity function of polyaniline, it is essential to develop a material that ensures high conductivity and at the same time does not elute into the electrolyte.

  Therefore, an object of the present invention is to provide a conductive polymer composite having high capacity and high conductivity and high durability.

In order to solve the above problem, the invention according to claim 1 is a conductive polymer composite,
The carbon nanofiber is used as a core, and the surface is coated with a polyion complex composed of polyaniline and polyanion.

The invention according to claim 2 is the conductive polymer composite according to claim 1,
The carbon nanofiber is characterized in that the carbon layer is a single-walled single-walled carbon nanotube, the carbon layer is a multi-walled multiwalled carbon nanotube, carbon nanofiber, fibrous activated carbon, or a mixture thereof.

The invention according to claim 3 is the conductive polymer composite according to claim 1 or 2,
The polyaniline is a copolymer of aniline and sulfonated aniline.

The invention according to claim 4 is the conductive polymer composite according to any one of claims 1 to 3,
The polyaniline is an emeraldine type polyaniline,
The polyanion is a polymer having a plurality of Bronsted acid groups.

Invention of Claim 5 is a manufacturing method of the conductive polymer composite as described in any one of Claim 1 to 4, Comprising:
A polyaniline precipitation step of depositing the polyaniline on the surface of the carbon nanofibers by chemically polymerizing aniline in an aqueous solution containing the carbon nanofibers;
A polyaniline reduction step of reducing the precipitated polyaniline;
A polyion complex forming step of reacting the reduced polyaniline with the polyanion as a counter ion to form the polyion complex.

Invention of Claim 6 in the manufacturing method of the conductive polymer composite of Claim 5,
A surfactant is added to the aqueous solution containing the carbon nanofibers used in the polyaniline precipitation step.

  According to the present invention, it is possible to provide a conductive polymer composite having high capacity, high conductivity, and high durability.

It is a schematic diagram which shows an example of the conductive polymer composite concerning embodiment of this invention. It is a figure for demonstrating the copolymer of an anion and a sulfonated anion. It is a figure for demonstrating four structures which polyaniline takes. (A) is a TEM image of polyaniline, and (b) is a TEM image of MWCNT. 2 is a TEM image of the sample of Example 1 (PAN / 15% MWCNT / PSS composite). 2 is an FTIR spectrum of the sample of Example 1 (PAN / 15% MWCNT / PSS composite). It is an FTIR spectrum of the sample of Example 2 (PAN / 15% MWCNT / PVS composite). It is a figure which shows the result of the differential thermal analysis of the sample (PAN / 15% MWCNT / PVS composite) of Example 2. 6 is a TEM image of the sample of Example 5 (PAN / 30% MWCNT / PSS composite). 4 is a TEM image of a sample of Comparative Example 1 (P (AN + S-AN) / 20% AB / PSS composite). It is a figure which shows the result of a charging / discharging test. It is a figure which shows the result of a dissolution test. It is a figure which shows the result of a dissolution test.

  Hereinafter, embodiments of the present invention will be described 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.

[Conductive polymer composite]
First, an embodiment of the conductive polymer composite according to the present invention will be described.
FIG. 1 is a schematic diagram showing an example of a conductive polymer composite 1 according to an embodiment of the present invention.
The conductive polymer composite 1 is a composite that can be used for an electrode of a chargeable / dischargeable power storage device such as an electrochemical capacitor, and as shown in FIG. It is a complex formed by coating the surface with the polyion complex 20 substantially uniformly. The polyion complex 20 includes a polyaniline 21 (emeraldine type polyaniline) that is a conductive polymer and a polyanion 22 that is a counter ion.
For example, the conductive polymer composite 1 deposits a polyaniline 21 as an electrode active material around the carbon nanofiber 10 as a conductive auxiliary agent, and forms a polyanion 22 that also serves as a dopant as a counter ion on the polyaniline 21. It can be formed by entanglement.

  The carbon nanofiber 10 is not particularly limited as long as it is a long-chain carbon fiber having a high aspect ratio. For example, a carbon layer having a network structure has a single-walled single-wall carbon nanotube (SWCNT) and a network structure. Multiwall carbon nanotubes (MWCNT), carbon nanofibers, fibrous activated carbon, carbon black, or a mixture of these are used. Both are excellent in conductivity. As the MWCNT, those subjected to an activation treatment such as a KOH treatment for baking together with KOH powder in an inert gas atmosphere are preferably used. By subjecting the MWCNT to an activation treatment, the multilayer wall is peeled off or through-holes are formed in the wall, so that the surface area increases and the electrolyte solution easily enters. Moreover, it is also preferable to mix and use the carbon nanofiber 10 and acetylene black or carbon black.

As the polyaniline 21, a copolymer of aniline and sulfonated aniline (2-sulfonated aniline and / or 3-sulfonated aniline) (see FIG. 2) can be preferably used. The mixing molar ratio of the sulfonated aniline to the aniline when synthesizing the copolymer is preferably in the range of 0.5% to 50%, and more preferably in the range of 1% to 25%.
Of course, the polyaniline 21 may be a homopolymer of aniline or an aniline derivative (including a sulfonated aniline), a copolymer of aniline and an aniline derivative other than the sulfonated aniline, or an aniline. A copolymer of a derivative (including sulfonated aniline) may be used.

  The weight ratio of the carbon nanofibers 10 to the polyaniline 21 in the conductive polymer composite 1 can be selected in the range of 1% to 90%. In order to optimally achieve both high conductivity and high capacitance. A range of 5% to 50% is suitable. If it is lower than 5%, the carbon nanofibers 10 are difficult to spread throughout the conductive polymer composite 1, and thus sufficient conductivity may not be ensured. If it is higher than 50%, the relative abundance ratio of the polyaniline 21 is reduced, which is sufficient. There are cases where the capacitance cannot be secured.

As the polyanion 22, a polyanion having a large negative charge can be preferably used.
The polyanion having a large negative charge includes a polymer having a plurality of Bronsted acid groups. Specifically, sulfonated polymers such as polystyrene sulfonic acid, polyvinyl sulfonic acid and polyaniline sulfonic acid which are proton acids (Bronsted acids), carboxylic acid polymers such as polyacrylic acid, polymethacrylic acid and polymaleic acid, phosphorus Examples include acid polymers such as polyphosphoric acid, polynuclear heteropolyacids such as molybdenum, tungsten, and vanadium. Of these, polyaniline sulfonic acid, which is a conductive polyanion, is more desirable from the viewpoint of improving conductivity.

The electrochemically active polyaniline has a structure of a salt (emeraldine salt) composed of an ion pair of an emeraldine cation and an anion out of the four structures shown in FIG.
In the emeraldine salt, anions such as BF ₄ ⁻ come in and out in order to maintain electrical neutrality against the valence change of polyaniline due to oxidation / reduction during charge and discharge.
On the other hand, when the polyanion 22 having many negative charges in the molecule forms the polyion complex 20 with the polyaniline 21 (emeraldine type polyaniline) as in the conductive polymer composite 1 of the present embodiment. In addition, since the electrostatic bond between the polyaniline 21 and the polyanion 22 is strong, and the molecular size of the polyanion 22 is large, the movement of the anion (polyanion 22) is not easy. Therefore, it is appropriate to perform charge compensation by the movement of small cations (such as Li ⁺ ).

  The polyaniline 21 is not easily eluted by being held by the carbon nanofibers 10. Furthermore, the polyaniline 21 becomes insoluble in an organic solvent (organic electrolyte solution) by forming the polyanion 22 and the polyion complex 20, and since the polyaniline 21 has many ionic bond points with the polyanion 22, it is difficult for the anion to be detached due to dissociation. Become. Therefore, since the conductive polymer composite 1 of the present embodiment is not easily deteriorated, the use of the conductive polymer composite 1 of the present embodiment for an electrode leads to a long life of the electrode.

Thus, since the conductive polymer composite 1 of this embodiment has the polyaniline 21 deposited on the surface of the carbon nanofiber 10, the high capacitor capacity of the polyaniline 21 and the high conductivity of the carbon nanofiber 10 itself. At the same time, the electrolyte solution and the electrolyte quickly move into the three-dimensional network formed by the long-chain carbon nanofibers 10. In addition, by forming the polyion complex 20 using the polyanion 22 as the counter ion of the polyaniline 21, the polyaniline 21 becomes hardly soluble, loss due to elution is suppressed, and the life of the electrode can be extended. Since the polyion complex 20 is composed of a strong electrostatic bond and the molecular size of the polyanion 22 is large, movement is not easy, and charge compensation is performed by movement of small cations (such as Li ⁺ ). Electronic transmission is quick. Due to these effects, a highly durable electricity storage device having a high capacity and power density can be obtained by using the conductive polymer composite 1 of this embodiment as an electrode material for the electricity storage device.

[Method for producing conductive polymer composite]
The manufacturing method of the conductive polymer composite 1 of this embodiment includes (1) a step of dispersing aniline and carbon nanofibers 10 and (2) a step of coating carbon nanofibers 10 with polyaniline 21 (polyaniline precipitation step). ), (3) a step of dedoping the polyaniline 21 (polyaniline reduction step), and (4) a step of forming the polyion complex 20 of the polyaniline 21 and the polyanion 22 (polyion complex formation step). .

The polyaniline 21 that is an electrode active material and the carbon nanofibers 10 that are conductive assistants are not simply mixed, but the polyaniline 21 is uniformly dispersed and supported on the nano-sized network of the carbon nanofibers 10 itself, thereby making the entire system It is possible to provide high conductivity over the range.
As a method for uniformly dispersing and supporting the polyaniline 21 on the nano-sized network of the carbon nanofibers 10, for example, a method in which the carbon nanofibers 10 are highly dispersed in a solvent and aniline is oxidatively polymerized in this dispersion is optimal. When aniline and the dispersion liquid of carbon nanofiber 10 are mixed, aniline is adsorbed on the surface of carbon nanofiber 10 by the affinity due to the π-π interaction of both aromatic rings represented by van der Waals force. Polymerization proceeds. The polyaniline 21 also has a π-π interaction with the aromatic ring on the surface of the carbon nanofiber 10 due to its conjugated structure. Formation of the composite in which the polyaniline 21 is distributed on the surface of the carbon nanofiber 10 can ensure high conductivity by distributing the electrically conductive portion over the entire polyaniline 21.

  In addition, when the hydrophobic carbon nanofibers 10 are dispersed in the aqueous solution, a good dispersion state can be obtained by adding a surfactant. As the surfactant used here, any of quaternary ammonium salts having a long-chain alkyl group such as hexadecyltrimethylammonium salt, anionic surfactants such as alkylbenzenesulfonic acid, and neutral surfactants such as Triton X can be used. Can be used. Furthermore, ultrasonic irradiation is effective for dispersion.

  The polymerization of aniline under the dispersion of carbon nanofibers 10 is most suitably oxidative polymerization with a chemical reagent performed in an aqueous solution from the viewpoint of simplicity and mass synthesis. Electropolymerization is known as a method for polymerizing aniline, but since the electrode area is limited, large-scale synthesis is difficult and it is not suitable for industrial production compared to chemical polymerization. The polymerization of aniline under the dispersion of carbon nanofibers 10 is preferably performed at a low temperature, and most preferably at a temperature of 5 ° C. or less, because the oxidative polymerization of aniline is an exothermic reaction. As the reaction medium, for example, water or an aqueous solution of alcohol having compatibility with water such as water-methanol, water-ethanol, water-propanol and the like is used. At this time, the pH of the reaction medium is preferably 3 or less, more preferably 1 or less. As the acid used for adjusting the pH of the reaction medium, strong acids such as hydrochloric acid, sulfuric acid, perchloric acid, bromic acid, and paratoluenesulfonic acid can be used. In order to increase the polymerization degree of aniline, hydrochloric acid is used. Is the most suitable.

As an oxidizing agent used for oxidative polymerization of aniline, ammonium persulfate ((NH ₄ ) ₂ S ₂ O ₈ ), hydrogen peroxide, ferric sulfate, ferric chloride, dichromic acid, and the like can be used. Ferric sulfate and ferric chloride have a problem in the post-treatment of the resulting precipitate, hydrogen peroxide has a low reaction yield, and dichromic acid has a problem of chromium toxicity. Most suitable is ammonium persulfate, which is water-soluble, does not cause precipitation, and has little environmental impact such as toxicity. The molar ratio of ammonium persulfate to aniline is suitably in the range of 0.2-fold to 2.0-fold, but 0.5-fold to 1.5-fold from the viewpoint of obtaining a high yield and a high degree of aniline polymerization. The double range is most suitable.

  Formation of the polyion complex 20 of the polyaniline 21 and the polyanion 22 deposited around the carbon nanofiber 10 is performed by dispersing the dedope-treated carbon nanofiber / polyaniline complex in an aqueous solution, and proton acid (Bronsted) in the aqueous solution. This is achieved by adding an aqueous solution of acid) and mixing by stirring (or shaking). A proton is added to the polyaniline 21 portion, and a polyanion 22 is introduced as a counter ion. When the polyion complex 20 is formed, the polyaniline 21 deposited around the carbon nanofibers 10 is optimally dedoped with a reducing agent. The addition amount of the polyanion 22 is preferably 1 or more in terms of molar ratio with respect to the polyaniline 21 deposited around the carbon nanofibers 10, and more preferably in the range of 1.5 to 2 times. The stirring time (or shaking time) is preferably 5 hours or more.

  As described above, the method for producing the conductive polymer composite 1 of the present embodiment has a three-dimensional network-like structure by a simple operation of oxidative polymerization of aniline in an aqueous solution in the presence of carbon nanofibers 10 and a surfactant. A composite in which the polyaniline 21 is deposited on the surface of the carbon nanofiber 10 spreading in a simple manner can be produced in a high yield. Moreover, since various polyion complexes 20 can be formed by adding an arbitrary polyanion 22 to the dedope, various complexes can be obtained as the conductive polymer complex 1.

  According to the conductive polymer composite 1 of the present embodiment described above, the carbon nanofiber 10 is used as a core, and the surface thereof is covered with the polyion complex 20 including the polyaniline 21 and the polyanion 22.

Therefore, since the polyaniline 21 is held by the carbon nanofiber 10 in a state where the polyanion 22 and the polyion complex 20 are formed, it is possible to provide a highly durable conductive polymer composite in which the elution of the polyaniline 21 is prevented. it can.
In other words, according to the conductive polymer composite 1 of the present embodiment, 1) the electrode active material polyaniline 21 is prevented from being eluted into the organic electrolyte solution, thereby preventing a decrease in capacity in a long charge / discharge cycle. At the same time, 2) ensure high power density by effective compounding with carbon nanofibers 10 which are highly conductive materials, and 3) electrolyte to carbon network by direct bonding of polyaniline 21 to carbon nanofibers 10. Thus, it is possible to satisfy the three requirements of realizing a high energy density by increasing the effective specific surface area.
Further, since the polyion complex 20 is held by the carbon nanofibers 10, mechanical stability can be ensured.

  In addition, according to the conductive polymer composite 1 of the present embodiment described above, the carbon nanofiber 10 includes a single-wall carbon nanotube with a single-layer carbon layer, a multi-wall carbon nanotube with a multi-layer carbon layer, and a carbon nanofiber. It is also possible to configure such that it is a fibrous activated carbon or a mixture thereof.

  By comprising in this way, it becomes possible to provide the electroconductive polymer composite 1 with higher electroconductivity.

  Moreover, according to the conductive polymer composite 1 of this embodiment described above, the polyaniline 21 can also be configured to be a copolymer of aniline and sulfonated aniline.

  By comprising in this way, it becomes possible to provide the conductive polymer composite 1 with higher performance.

  Further, according to the conductive polymer composite 1 of the present embodiment described above, the polyaniline 21 is an emeraldine type polyaniline, and the polyanion 22 is a polymer having a plurality of Bronsted acid groups. It is also possible to do.

By comprising in this way, it becomes possible to prevent the elution of the polyaniline 21 more effectively.
That is, since polyanion 22 having a large number of anion sites in the molecule, such as polystyrene sulfonic acid, polyethylene sulfonic acid, and polyphosphoric acid, can be used as a counter ion for emeraldine type polyaniline, formation of a large number of ionic bonds. By cross-linking between the polyaniline chains, a polyion complex 20 hardly soluble in the organic electrolyte can be formed, and the elution of the active material (polyaniline 21) into the electrolyte can be more effectively prevented.

  According to the manufacturing method of the conductive polymer composite 1 of this embodiment described above, polyaniline 21 is deposited on the surface of the carbon nanofiber 10 by chemically polymerizing aniline in an aqueous solution containing the carbon nanofiber 10. A polyaniline precipitation step, a polyaniline reduction step of reducing the precipitated polyaniline 21, and a polyion complex formation step of forming a polyion complex 20 by reacting the reduced polyaniline 21 with a polyanion 22 as a counter ion.

  Therefore, a highly durable conductive polymer composite can be produced by a simple method.

  Moreover, according to the manufacturing method of the conductive polymer composite 1 of this embodiment described above, the surfactant is added to the aqueous solution containing the carbon nanofibers 10 used in the polyaniline precipitation step. It is also possible to do.

By comprising in this way, it becomes possible to deposit the polyaniline 21 on the surface of the carbon nanofiber 10 substantially uniformly.
That is, in order to ensure high conductivity by wiring a long-chain network of carbon nanofibers 10 to every corner of polyaniline 21, and to achieve rapid mass transfer to the network, carbon that is a conductive material is used. In complexing with the nanofibers 10, it is necessary to deposit the polyaniline 21 uniformly on the surface of the carbon nanofibers 10, but by adding a surfactant to the aqueous solution containing the carbon nanofibers 10, the carbon nanofibers are added. Since the dispersion state of 10 becomes good, it becomes possible to deposit the polyaniline 21 substantially uniformly on the surface of the carbon nanofiber 10.

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

[Example 1] PAN / 15% MWCNT / PSS complex Aniline hydrochloride (2.6 g) was dissolved in 1 M HCl (100 ml), and MWCNT (300 mg) of untreated (only acid removal was used to remove Co) was added thereto. In addition, ultrasonic irradiation was performed for 30 minutes.
Then, a surfactant (1 g) dissolved in 1M HCl (20 ml) was added, and the mixture was further subjected to ultrasonic irradiation for 30 minutes. Here, CTAB (hexadecyltrimethylammonium bromide) was used as the surfactant.
Next, the mixture was ice-cooled, and ammonium persulfate (NH ₄ ) ₂ S ₂ O ₈ (4.2 g) dissolved in 1M HCl (20 ml) was gradually added with stirring, followed by stirring overnight in a refrigerator.
Next, the mixture was filtered, thoroughly washed with water until bubbles disappeared, further washed with methanol, and then dried at 50 ° C. to obtain a powder.

Methanol (90 ml) and hydrazine (10 ml) were added to this powder and stirred at 60 ° C. for 1 hour.
Subsequently, it filtered with a filter, wash | cleaned, and dried at 50 degreeC, and the PAN / 15% MWMW dedoped body was obtained. The yield of PAN / 15% MWCNT dedope was 1.6 g.

Next, water (20 ml), 1M HCl (10 ml) and sodium polystyrene sulfonate (500 mg) were added to the PAN / 15% MWCNT dedope (800 mg), and the mixture was stirred at room temperature for 5 hours.
Subsequently, it filtered, wash | cleaned with water and methanol, and was made to dry at 50 degreeC, and the PAN / 15% MWMW / PSS composite which is the conductive polymer composite 1 was obtained. The yield of PAN / 15% MWCNT / PSS complex was 930 mg.

Here, a TEM image of polyaniline 21 that is a constituent component of the conductive polymer composite 1 is shown in FIG. 4A, and a TEM image of MWCNT (carbon nanofiber 10) that is a constituent component of the conductive polymer composite 1 is shown in FIG. Is shown in FIG.
Further, a TEM image of the obtained PAN / 15% MWCNT / PSS composite is shown in FIG. From the image of FIG. 5, it can be seen that the surface of the MWCNT, which is the carbon nanofiber 10, is substantially uniformly coated with the polyion complex 20.
FIG. 6 shows the FTIR spectrum of the PAN / 15% MWCNT / PSS composite. From this FTIR spectrum, it can be seen that strong absorption due to the sulfonic acid group of PSS (sodium polystyrene sulfonate) is observed in the vicinity of 1330 cm ⁻¹ . This showed complexation with PSS.

[Example 2] PAN / 15% MWCNT / PVS composite The PAN / 15% MWCNT dedope (800 mg) synthesized in Example 1 was mixed with water (20 ml), 1 M HCl (10 ml), and a 25% sodium polyvinyl sulfonate aqueous solution. (2 g) was added and stirred at room temperature for 5 hours.
Subsequently, it filtered, wash | cleaned with water and methanol, and was dried at 50 degreeC, and the PAN / 15% MWMW / PVS composite which is the conductive polymer composite 1 was obtained. The yield of PAN / 15% MWCNT / PVS composite was 930 mg.

The FTIR spectrum of the obtained PAN / 15% MWCNT / PVS composite is shown in FIG. From this FTIR spectrum, it can be seen that strong and broad absorption due to the sulfonic acid group of PVS (sodium polyvinyl sulfonate) is observed in the vicinity of 1330 cm ⁻¹ . Thereby, the composite with PVS was shown.
The results of differential thermal analysis of the PAN / 15% MWCNT / PVS composite are shown in FIG. From the results of this differential thermal analysis, it can be seen that there is almost no weight phenomenon due to the temperature rise up to 300 ° C.

[Example 3a] PAN / 15% MWCNT (KOH) / PSS composite MWCNT was mixed with KOH powder and heated at 800 ° C. for 1 hour in a nitrogen atmosphere to subject the MWCNT to KOH treatment. Using this KOH-treated MWCNT, a PAN / 15% MWCNT (KOH) / PSS composite as a conductive polymer composite 1 was obtained in the same procedure as in Example 1.

[Example 3b] PAN / 15% MWCNT (aminated) / PSS complex MWCNT was reacted with octylamine to subject the MWCNT to amination. Using this aminated MWCNT, a PAN / 15% MWCNT (aminated) / PSS composite was obtained in the same procedure as in Example 1.

[Example 4a] PAN / 15% MWCNT (KOH) / PVS composite MWCNT was mixed with KOH powder and heated at 800 ° C. for 1 hour in a nitrogen atmosphere to subject the MWCNT to KOH treatment. Using this KOH-treated MWCNT, a PAN / 15% MWCNT (KOH) / PVS composite as a conductive polymer composite 1 was obtained in the same procedure as in Example 2.

[Example 4b] PAN / 15% MWCNT (aminated) / PVS complex MWCNT was reacted with octylamine to subject the MWCNT to amination. Using this aminated MWCNT, a PAN / 15% MWCNT (aminated) / PVS composite was obtained in the same procedure as in Example 2.

[Example 5] PAN / 30% MWCNT / PSS complex Aniline hydrochloride (1.3 g) was dissolved in 2 M HCl (50 ml), and MWCNT (300 mg only) untreated (only acid-washed to remove Co) was added thereto. In addition, ultrasonic irradiation was performed for 30 minutes.
Next, a solution obtained by dissolving CTAB (1 g) as a surfactant in 1 M HCl (20 ml) was added, and ultrasonic irradiation was further performed for 30 minutes.
Next, the mixture was ice-cooled, and ammonium persulfate (NH ₄ ) ₂ S ₂ O ₈ (2.1 g) dissolved in 2M HCl (20 ml) was gradually added with stirring, followed by stirring overnight in a refrigerator.
Next, the mixture was filtered, washed with water, washed with methanol, and dried at 50 ° C. to obtain a powder.

Methanol (40 ml) and hydrazine (10 ml) were added to this powder and stirred at 60 ° C. for 2 hours.
Subsequently, it filtered with a filter, wash | cleaned, and dried at 50 degreeC, and the PAN / 30% MWMW dedope was obtained. The yield of the PAN / 30% MWCNT dedope was 840 mg.

Next, water (20 ml), 1M HCl (10 ml) and sodium polystyrene sulfonate (500 mg) were added to the PAN / 30% MWCNT dedope (840 mg), and the mixture was stirred at room temperature for 5 hours.
Subsequently, it filtered, wash | cleaned with water and methanol, and was made to dry at 50 degreeC, and the PAN / 30% MWCNT / PSS composite which is the conductive polymer composite 1 was obtained. The yield of PAN / 30% MWCNT / PSS composite was 900 mg.
In addition, a TEM image of the obtained PAN / 30% MWCNT / PSS composite is shown in FIG. From the image in FIG. 9, it can be seen that the surface of the MWCNT, which is the carbon nanofiber 10, is substantially uniformly coated with the polyion complex 20.

[Example 6] PAN / 10% SWCNT / PSS complex Aniline hydrochloride (1.3 g) was dissolved in 1 M HCl (100 ml), and untreated (only acid removal was used to remove Co) SWCNT (100 mg). In addition, ultrasonic irradiation was performed for 30 minutes.
Next, a solution obtained by dissolving CTAB (1 g) as a surfactant in 1 M HCl (20 ml) was added, and ultrasonic irradiation was further performed for 30 minutes.
Next, the mixture was ice-cooled, and ammonium persulfate (NH ₄ ) ₂ S ₂ O ₈ (2.1 g) dissolved in 1M HCl (20 ml) was gradually added with stirring, followed by stirring overnight in a refrigerator.
Next, the mixture was filtered, thoroughly washed with water until bubbles disappeared, further washed with methanol, and then dried at 50 ° C. to obtain a powder.

Methanol (90 ml) and hydrazine (10 ml) were added to this powder and stirred at 60 ° C. for 1 hour.
Subsequently, it filtered with a filter, wash | cleaned, and dried at 50 degreeC, and the PAN / 10% SWCNT dedope was obtained. The yield of the PAN / 10% SWCNT dedope was 780 mg.

Next, water (20 ml), 1M HCl (20 ml) and sodium polystyrene sulfonate (500 mg) were added to the PAN / 10% SWCNT dedope (780 mg), and the mixture was stirred overnight at room temperature.
Subsequently, it filtered, wash | cleaned with water and methanol, and was made to dry at 50 degreeC, and the polyaniline / 10% SWCNT / PSS composite_body | complex which is the conductive polymer composite_body | complex 1 was obtained. The yield of polyaniline / 10% SWCNT / PSS composite was 930 mg.

[Example 7] P (AN + S-AN) / 20% MWCNT / PSS complex To a mixed solution of 1M HCl (40 ml) and ethanol (40 ml), MWCNT (300 mg) of untreated (only acid removal was used to remove Co) was added. The mixture was stirred and subjected to ultrasonic irradiation for 30 minutes.
Then, aniline hydrochloride (2.3 g) and 2-sulfonated aniline (350 mg) dissolved in hydrochloric acid (100 ml) were added.
Next, a solution obtained by dissolving CTAB (1 g) as a surfactant in 1 M HCl (20 ml) was added, and ultrasonic irradiation was further performed for 30 minutes.
Next, the mixture was ice-cooled, and ammonium persulfate (NH ₄ ) ₂ S ₂ O ₈ (4 g) dissolved in 1M HCl (20 ml) was gradually added with stirring, followed by stirring for 6 hours under ice-cooling.
Next, the mixture was filtered, washed with water, further washed with methanol, and dried at 50 ° C. to obtain a powder.

Methanol (40 ml) and hydrazine (10 ml) were added to this powder and stirred at 60 ° C. for 4 hours.
Subsequently, the P (AN + S-AN) / 20% MWCNT dedope was obtained by filtering with a filter, wash | cleaning with methanol, and making it dry at 50 degreeC. The yield of P (AN + S-AN) / 20% MWCNT dedope was 1.5 g.

Next, water (20 ml), 1M HCl (20 ml) and sodium polystyrene sulfonate (500 mg) were added to P (AN + S-AN) / 20% MWCNT dedope (1.5 g), and the mixture was stirred overnight at room temperature.
Subsequently, it filtered, wash | cleaned with water and methanol, and dried at 50 degreeC, and obtained P (AN + S-AN) / 20% MWCNT / PSS composite_body | complex which is the conductive polymer composite_body | complex 1. The yield of P (AN + S-AN) / 20% MWCNT / PSS composite was 1.75 g.

[Comparative Example 1] P (AN + S-AN) / 20% AB / PSS complex To a mixed solution of 1M HCl (40 ml) and ethanol (40 ml), acetylene black (300 mg) was added and stirred, followed by ultrasonic irradiation for 30 minutes. .
Then, aniline hydrochloride (2.3 g) and 2-sulfonated aniline (0.35 g) dissolved in hydrochloric acid (100 ml) were added.
Next, a solution obtained by dissolving CTAB (1 g) as a surfactant in 1 M HCl (20 ml) was added, and ultrasonic irradiation was further performed for 30 minutes.
Next, the mixture was ice-cooled, and ammonium persulfate (NH ₄ ) ₂ S ₂ O ₈ (4 g) dissolved in 1M HCl (20 ml) was gradually added with stirring, followed by stirring for 6 hours under ice-cooling.
Next, the mixture was filtered, washed with water, further washed with methanol, and dried at 50 ° C. to obtain a powder.

Methanol (40 ml) and hydrazine (10 ml) were added to this powder and stirred at 60 ° C. for 6 hours.
Then, it filtered with a filter, wash | cleaned with methanol, and dried at 50 degreeC, and obtained the P (AN + S-AN) / 20% AB dedope. The yield of P (AN + S-AN) / 20% AB dedope was 1.6 g.

Next, water (20 ml), 1M HCl (20 ml) and sodium polystyrene sulfonate (500 mg) were added to P (AN + S-AN) / 20% AB dedope (1.0 g), and the mixture was stirred overnight at room temperature.
It was then filtered, washed with water and methanol, and dried at 50 ° C. to obtain a P (AN + S-AN) / 20% AB / PSS complex. The yield of P (AN + S-AN) / 20% AB / PSS complex was 1.2 g.
A TEM image of the obtained P (AN + S-AN) / 20% AB / PSS composite is shown in FIG.

[Comparative Example 2] YP50
Activated carbon (YP50, made by Kuraray Chemical) was prepared.

(Charge / discharge test)
The samples of Examples 1, 2, 3a, 4a, 3b, 4b, 5, 6 and 7 (that is, the conductive polymer composite 1) and the samples of Comparative Examples 1 and 2 were used as the positive electrode active material, and lithium was used as the negative electrode. A lithium ion capacitor was constructed using an electrode made of a metal or a lithium-doped carbon material, and a charge / discharge test was performed.

First, a positive electrode was produced.
Positive electrode active material: conductive auxiliary agent: binder: binder resin = 16: 2: 1: 1. Specifically, a positive electrode active material (240 mg), acetylene black (30 mg) as a conductive additive, a 2% aqueous solution (1500 μL) of CMC (carboxymethyl cellulose) as a binder, and SBR (binder resin) A dispersion of styrene butadiene rubber (7.5 μL, solid content 48%) was mixed and kneaded in a mortar to obtain a positive electrode active material slurry.
Next, the positive electrode active material slurry was applied to the aluminum collector electrode with a thickness of 300 μm by a doctor blade, naturally dried, then dried at 120 ° C. for 20 minutes, and molded by applying a pressure of 10 MPa.
Next, a positive electrode plate was punched into a circular shape having a diameter of 15 mm, and this positive electrode plate was dried under reduced pressure at 80 ° C. for 24 hours to sufficiently remove moisture, thereby obtaining a positive electrode.

Next, a negative electrode was produced.
The graphite sheet was punched into a circular shape having a diameter of 15 mm and dried under reduced pressure at 80 ° C. for 24 hours to sufficiently remove moisture.
Next, a separator (circular polyolefin film (diameter: 20 mm)) was placed on a Li foil punched into a circular shape with a diameter of 15 mm, and an electrolytic solution (LiPF ₆ (electrolyte) was added to the separator with an EC + EMC solution (solvent). ) (Electrolyte concentration: 1 mol / L)) was dropped, and a graphite sheet was placed on the separator impregnated with the electrolytic solution to constitute a cell.
Next, the Li foil (positive electrode) and the graphite sheet (negative electrode) were short-circuited with a resistance of about 0.1Ω, and the graphite sheet was pre-doped with lithium ions to obtain a negative electrode. And the cell was decomposed | disassembled and the pre-doped graphite sheet (negative electrode) was taken out.
In addition, as a negative electrode, a metal lithium electrode etc. can also be used instead of the graphite sheet which pre-doped lithium ion.

Next, assembly work was performed to produce a lithium ion capacitor. 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, and LiPF ₆ (electrolyte) is dissolved in an EC + EMC solution (solvent) using a circular polyolefin film (diameter: 20 mm) as a separator (electrolyte concentration: 1 mol / L). ) Was used as the electrolyte.
A lithium ion capacitor was configured by sandwiching a separator impregnated with an electrolyte between the extracted negative electrode and the prepared positive electrode.

Next, a charge / discharge test was performed to evaluate the characteristics of each capacitor.
For each capacitor using each of the samples of Examples 1, 2, 3a, 4a, 3b, 4b, 5, 6, and 7 and the samples of Comparative Examples 1 and 2 as the positive electrode active material, the constant current method (1 mA / cm ² The charge / discharge test was conducted. FIG. 11 shows the results of the charge / discharge test (cell capacity, internal resistance) and the capacitance determined from the results. Moreover, the result of having confirmed visually whether there exists an elution from a positive electrode during the said charging / discharging test is also shown in FIG.

As shown in FIG. 11, the capacitor using the sample of the example as the positive electrode active material has higher performance than the capacitor using the sample of the comparative example 2 as the positive electrode active material (that is, a standard lithium ion capacitor). It can be seen that the capacitance is high and the internal resistance is low. Among them, the sample using Example 7, that is, the capacitor using the conductive polymer composite 1 in which the polyaniline 21 is a copolymer of aniline and sulfonated aniline as a positive electrode active material is found to have particularly high performance.
Further, as shown in FIG. 11, the capacitor using the sample of Comparative Example 1 as the positive electrode active material performs worse than the capacitor using the sample of Comparative Example 2 as the positive electrode active material (that is, the capacity is low and the internal resistance is low). Is high). The sample of Comparative Example 1 is a conductive polymer composite using acetylene black instead of the carbon nanofibers 10.
From the above, it was found that the combination of polyaniline 21 and carbon nanofiber 10 is more preferable than the combination of polyaniline 21 and acetylene black.
Further, it was found that the polyaniline 21 exhibits sufficient performance even when the polyanion 22 and the polyion complex 20 are formed.

[Elution test 1]
The composite of Example 1 (ie, PAN / 15% MWCNT / PSS composite) and the dedope obtained during the production of the composite of Example 1 (ie, PAN / 15% MWCNT dedope) In addition, 160 mg each of the dedope-treated polyaniline was taken in a beaker, and propylene carbonate (20 ml) in which 0.1 M tetraethylammonium tetrafluoroborate (TEA · [BF ₄ ]) was dissolved was added thereto. .
Subsequently, after stirring overnight, it filtered with the filter paper and the visible absorption spectrum of the filtrate was measured. The result is shown in FIG.

As shown in FIG. 12, absorption having peaks at 600 nm and 320 nm was observed in the filtrate of the PAN / 15% MWCNT dedope and the filtrate of polyaniline subjected to the dedope treatment.
On the other hand, no absorption peak was observed in the PAN / 15% MWCNT / PSS composite filtrate.
Further, it was found that the size of the absorption peak decreases in the order of polyaniline subjected to dedoping treatment> PAN / 15% MWCNT dedope> PAN / 15% MWCNT / PSS composite.
Thereby, it turned out that the polyaniline 21 deposited on the surface of the carbon nanofiber 10 is less likely to elute than the polyaniline 21 alone. This is considered because the polyaniline 21 is held by the carbon nanofibers 10.

  Furthermore, it has been found that the polyaniline 21 deposited on the surface of the carbon nanofiber 10 hardly elutes by forming the polyanion 22 and the polyion complex 20. This is presumably because the polyaniline 21 is held by the carbon nanofibers 10 in a state where the polyanion 22 and the polyion complex 20 are formed.

[Elution test 2]
The composite of Example 7 (ie, P (AN + S-AN) / 20% MWCNT / PSS composite) and the dedope obtained during the preparation of the composite of Example 7 (ie, P (AN + S-AN) ) / 20% MWCNT dedope) in a beaker, and propylene carbonate (20 ml) in which 0.1 M TEA · [BF ₄ ] was dissolved was added thereto.
Subsequently, after stirring overnight, it filtered with the filter paper and the visible absorption spectrum of the filtrate was measured. The result is shown in FIG.

As shown in FIG. 13, the filtrate of P (AN + S-AN) / 20% MWCNT dedope showed absorption peaks at 600 nm and 320 nm.
In contrast, no absorption peak was observed in the filtrate of P (AN + S-AN) / 20% MWCNT / PSS composite.
Thereby, it turned out that P (AN + S-AN) / 20% MWCNT hardly elutes by forming a polyion complex with PSS.

10 carbon nanofiber 20 polyion complex 21 polyaniline 22 polyanion

Claims (6)

  A conductive polymer composite comprising a carbon nanofiber as a core and a surface coated with a polyion complex composed of polyaniline and polyanion.   2. The carbon nanofiber according to claim 1, wherein the carbon layer is a single-walled carbon nanotube having a single carbon layer, a multi-walled carbon nanotube having a carbon layer, a carbon nanofiber, a fibrous activated carbon, or a mixture thereof. The conductive polymer composite described.   The conductive polymer composite according to claim 1 or 2, wherein the polyaniline is a copolymer of aniline and sulfonated aniline. The polyaniline is an emeraldine type polyaniline,
The conductive polymer composite according to any one of claims 1 to 3, wherein the polyanion is a polymer having a plurality of Bronsted acid groups. A method for producing a conductive polymer composite according to any one of claims 1 to 4,
A polyaniline precipitation step of depositing the polyaniline on the surface of the carbon nanofibers by chemically polymerizing aniline in an aqueous solution containing the carbon nanofibers;
A polyaniline reduction step of reducing the precipitated polyaniline;
A polyion complex forming step of reacting the reduced polyaniline with the polyanion as a counter ion to form the polyion complex, and a method for producing a conductive polymer composite.   The method for producing a conductive polymer composite according to claim 5, wherein a surfactant is added to the aqueous solution containing the carbon nanofibers used in the polyaniline precipitation step.