JP2009193826A - Electrode active material, and electrode using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode active material which can provide an electrochemical element having a high operating voltage, a large capacity, and high energy density. <P>SOLUTION: The electrode active material is composed of precise polymerization polyfluorene composed of fluorene rings polymerized at 2-position and 7-position practically. The electrode active material includes a capacity greatly larger than that of an electrode active material consisting of bulk polymerization polyfluorene polymerized at an irregular position obtained by polymerization using iron chloride (III) as a catalyst. In the same way as the bulk polymerization polyfluorene, p-doped oxidation-reduction potential is high, and n-doped oxidation-reduction potential is low. Thereby, by the electrode active material composed of the precise polymerization polyfluorene, electrochemical element having a high operating voltage, a large capacity, and high energy density, can be obtained. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrode active material that can provide an electrochemical element having a high operating voltage, a high capacity, and a high energy density, and an electrode using the electrode active material.

  Expectations for low-emission vehicles such as electric vehicles and hybrid vehicles to replace gasoline and diesel vehicles from the viewpoints of reducing oil consumption, mitigating air pollution, and reducing emissions of carbon dioxide that causes global warming. It is growing. As a motor drive power source in such a low pollution vehicle, an electrochemical element such as a secondary battery or an electric double layer capacitor having a high energy density and a high output density is used.

  Secondary batteries include batteries using an aqueous electrolyte and batteries using a non-aqueous electrolyte (organic electrolyte).

  Examples of batteries using acidic or alkaline aqueous electrolyte include lead batteries, nickel / cadmium batteries, nickel metal hydride batteries, and proton batteries. Since these secondary batteries have an electrolysis voltage of water of 1.23 V, a higher operating voltage cannot be obtained. As a power source for an electric vehicle, a high voltage of around 200V is required. To obtain this voltage, many batteries must be connected in series, which is disadvantageous for reducing the size and weight of the power source. is there. However, since the aqueous electrolyte has high ionic conductivity, it has excellent output characteristics that a large current can be obtained during charging and discharging.

On the other hand, lithium ion secondary batteries are well known as batteries using nonaqueous electrolyte solutions. In general, this battery uses a carbon material that occludes and releases lithium ions as a negative electrode, a lithium layered compound such as lithium cobaltate (LiCoO ₂ ) as a positive electrode, and a lithium salt such as lithium hexafluorophosphate (LiPF ₆ ). A solution dissolved in an organic solvent such as ethylene carbonate or propylene carbonate is used as an electrolytic solution. Since such a lithium ion secondary battery has a high electrolysis voltage of the organic solvent, an average operating voltage of 3.6 V can be obtained and the energy density is also high. However, since the charge / discharge reaction is occlusion and release of lithium ions in the electrode, the output characteristics are inferior, and it is disadvantageous as a power source for an electric vehicle that requires a large instantaneous current.

  The electric double layer capacitor uses a polarizable electrode such as activated carbon as positive and negative electrodes, and uses an electric double layer generated at the interface between the electrode surface and the electrolytic solution as a capacitance. An electric double layer capacitor has a high output density, can be rapidly charged and discharged, and has little capacity deterioration even after repeated charging and discharging. This is because in an electric double layer capacitor, electrolyte ions move only in the electrolytic solution along with charging / discharging and are adsorbed / desorbed to / from the electrode interface, and do not involve an electrochemical reaction as in a battery.

  Also in the electric double layer capacitor, there are a capacitor using an aqueous electrolyte and a capacitor using a non-aqueous electrolyte (organic electrolyte).

  Since the operating voltage of an electric double layer capacitor is mainly determined by the electrolysis voltage of the electrolyte, the capacitor using an aqueous electrolyte has a higher operating voltage than the capacitor using a non-aqueous electrolyte (organic electrolyte). It is disadvantageous in terms. However, it has the advantage of high power density and safety.

  On the other hand, an electric double layer capacitor using a non-aqueous electrolyte solution in which a quaternary onium salt such as boron tetrafluoride or phosphorus hexafluoride is dissolved in an organic solvent such as propylene carbonate has an operating voltage of an aqueous electrolyte solution. It is higher than the capacitor, but lower than the secondary battery. In addition, the energy density due to the electric double layer capacity is lower than that of the secondary battery, and the power source of the electric vehicle is greatly insufficient.

  In order to improve such problems, studies on electrode active materials used in electrochemical devices are underway.

  Patent Document 1 (Japanese Patent Application Laid-Open No. 2003-297362) discloses a positive electrode mainly composed of a p-doped conductive polymer, a negative electrode mainly composed of a carbon material capable of inserting and extracting lithium ions, and a lithium salt. A hybrid secondary power source having an organic electrolyte solution is proposed. A secondary power source using a polythiophene having a weight average molecular weight of 50000, a poly (3-methylthiophene) having a weight average molecular weight of 80000, etc. as a positive electrode, an operating voltage of 4.0 V, and a secondary power source using activated carbon as a positive electrode A secondary power source having a capacity equal to or higher than that of the battery and having high charge / discharge cycle reliability is obtained.

  Patent Document 2 (Japanese Patent Application Laid-Open No. 6-104141) discloses an electrolytic double layer for the purpose of increasing the capacity and reducing the internal resistance of an electric double layer capacitor provided with an electrode prepared using a conductive polymer powder paste. An electric double layer capacitor using a conductive polymer film obtained by a legal method as a polarizable electrode is proposed. By using the polypyrrole film obtained by the electrolytic polymerization method, an electric double layer capacitor having an operating voltage of 2.6 V and a higher capacity than an electric double layer capacitor having an electrode using a powder paste has been obtained.

  In order to improve the low energy density of the electric double layer capacitor, an electrochemical capacitor using an additional capacitance due to a redox reaction or a charge transfer reaction on the electrode surface in addition to the electric double layer capacitance has been studied. Yes. As an electrode active material for such an electrochemical capacitor, charge transfer by exchange of π-electrons with metal oxides such as ruthenium oxide, manganese oxide, nickel oxide, etc. where an oxidation-reduction reaction easily occurs, and anions and cations of electrolytes Conductive polymers such as polyaniline, polythiophene, polypyrrole and the like in which the above occurs relatively easily have been studied.

  Patent Document 3 (Japanese Unexamined Patent Publication No. 2000-315527) discloses a conductive polymer containing a thin film of triphenylamine as a repeating unit as a positive electrode and a thin film of 2,2′-bipyridine as a repeating unit. A non-aqueous electrochemical capacitor having a negative electrode made of a conductive polymer has been proposed, and a non-aqueous electrochemical capacitor exhibiting an operating voltage of up to 2.7 V and having an energy density more than three times that of an electric double layer capacitor has been obtained. Yes.

  Further, Patent Document 4 (Japanese Patent Laid-Open No. 2006-48974) discloses an electrode material made of polyfluorene or a derivative thereof, and the n-doped redox potential of the polyfluorene derivative is a conventional conductive polymer. The p-doped redox potential of polyfluorene or its derivatives is higher than that of conventional conductive polymers, indicating that this electrode material has high voltage characteristics. When poly (9,9-dimethylfluorene) obtained by polymerization using iron (III) chloride as a catalyst is used as an electrode active material, a secondary battery and an electrochemical capacitor using poly (3-methylthiophene) It shows that a secondary battery and an electrochemical capacitor having a higher operating voltage can be obtained.

JP 2003-297362 A JP-A-6-104141 JP 2000-315527 A JP 2006-48974 A

  However, there is a constant demand for miniaturization and weight reduction of motor drive power supplies for electric vehicles, etc. Therefore, there is a strong demand for higher operating voltage, higher capacity, and higher energy density for electrochemical elements used as power supplies. There is.

  Accordingly, an object of the present invention is to provide an electrode active material having a higher capacity than a conventional conductive polymer capable of providing an electrochemical element having a high operating voltage, a high capacity and a high energy density, and an electrode using the same Is to provide.

  The inventors proceeded with the study based on the electrode active material composed of polyfluorene disclosed in Patent Document 4, and the above problem can be solved by precisely controlling the reaction point of the fluorene ring in the polymerization of polyfluorene. I found.

  The electrode active material of the present invention is an electrode active material composed of at least one polyfluorene, wherein the fluorene ring of the polyfluorene is substantially polymerized at the 2-position and the 7-position. Hereinafter, polyfluorene in which the fluorene ring is substantially polymerized at the 2-position and the 7-position will be referred to as “precisely polymerized polyfluorene”. The term “substantially polymerized at the 2-position and the 7-position” is 90% or more, preferably 95% or more, more preferably 98% or more, particularly preferably the number of fluorene rings contained in polyfluorene. Means that 100% of the fluorene ring is bonded to the adjacent fluorene ring at the 2nd and 7th positions.

  FIG. 1 (a) shows a fluorene chain in a precisely polymerized polyfluorene as an electrode active material of the present invention, and FIG. 1 (b) uses iron (III) chloride disclosed in Patent Document 4 as a catalyst. The fluorene chain in the polyfluorene obtained by superposition | polymerization is shown.

  In the polymerization using iron (III) chloride as a catalyst, it is difficult to control the reaction point, so that the growth direction becomes irregular as shown in FIG. Hereinafter, polyfluorene in which such a fluorene ring is polymerized at irregular positions is referred to as “bulk polymerized polyfluorene”, but since bulk polymerized polyfluorene has many branching sites and meta-conjugated sites. The charge utilization rate becomes low.

  On the other hand, the highly polymerized polyfluorene shown in FIG. 1 (a) is expected to have a high charge utilization rate because there are almost no branching sites or meta-conjugated sites. As a result of the study, it was found that when the conventional bulk polymerized polyfluorene was changed to the precision polymerized polyfluorene, the redox potential of p-doping and n-doping did not differ significantly, but the capacity increased significantly. . Therefore, by using an electrode active material made of precision polymerized polyfluorene, an electrochemical element having a high operating voltage, a high capacity and a high energy density can be obtained.

  In the range of the precisely polymerized polyfluorene in the present invention, as long as the fluorene ring is substantially polymerized at the 2-position and the 7-position, in addition to the polymer composed only of the unsubstituted fluorene ring, the position not involved in the polymerization Also included is a polymer containing at least one fluorene ring having a substituent. The fluorene ring of the precisely polymerized polyfluorene preferably has one or two substituents at the 9-position. The substituent at the 9-position does not decrease the electronic conductivity of the polymer, and the substituent increases the speed of the anion and cation doping and dedoping reactions and improves the output characteristics. The substituent at the 9-position consists of an alkyl group, a carboxyl group, a nitro group, a cyano group, an alkyl cyano group, a phenyl group, a halogen atom, a halogenated methyl group, a halogenated phenyl group, an alkylphenyl group, and an alkylhalogenated phenyl group. Preferably selected from the group.

  The present invention also provides an electrode having an active material layer containing an electrode active material composed of the above-described precision polymerized polyfluorene. Precision polymerized polyfluorene has a significantly increased capacity over bulk polymerized polyfluorene and has the same high voltage characteristics as bulk polymerized polyfluorene. Therefore, the electrode of the present invention can be suitably used to construct an electrochemical device having a high operating voltage, a high capacity and a high energy density, or as one of a pair of electrodes in a secondary battery, or It can be suitably used as one of a pair of electrodes in an electric double layer capacitor or as at least one of a pair of electrodes in an electrochemical capacitor.

  In the electrode of the present invention, the active material layer preferably contains at least one kind of carbon nanotube. Since carbon nanotubes have a high electrical conductivity, a composite with a high electrical conductivity can be obtained by compounding with an active material. Further, since the outer surface area is large, the contact surface with the active material is widened, and it is possible to impart conductivity with high efficiency. Furthermore, the carbon nanotubes themselves have a capacity in contact with the electrolyte solution. Therefore, by using the precision polymerized polyfluorene and the carbon nanotubes in combination, an electrode having a high impedance and a low impedance characteristic can be obtained.

  The precisely polymerized polyfluorene is preferably supported on carbon nanotubes. Since the contact resistance between the carbon nanotube and the precisely polymerized polyfluorene becomes small, it is possible to obtain an electrode further excellent in low impedance characteristics.

  An electrode active material composed of precision polymerized polyfluorene in which the fluorene ring of the present invention is polymerized substantially at the 2-position and the 7-position has a significantly increased capacity compared to an electrode active material composed of bulk-polymerized polyfluorene, It has the same high voltage characteristics as an electrode active material made of polymerized polyfluorene.

  Accordingly, an electrode having an active material layer containing the electrode active material of the present invention has an electrochemical element such as a secondary battery, an electric double layer capacitor, and an electrochemical capacitor having a high operating voltage, a high capacity and a high energy density. Very useful for building.

  The electrode active material of the present invention comprises precision polymerized polyfluorene in which the fluorene ring is polymerized substantially at the 2nd and 7th positions. The electrode active material made of precision polymerized polyfluorene has a capacity that is significantly increased compared to the electrode active material made of bulk polymerized polyfluorene, and has the same high voltage characteristics as the electrode active material made of bulk polymerized polyfluorene. The precisely polymerized polyfluorene as the electrode active material may be a single material or a mixture of different precisely polymerized polyfluorenes.

  The precision polymerized polyfluorene as the electrode active material of the present invention may be unsubstituted as long as the fluorene ring is substantially polymerized at the 2nd and 7th positions. In addition, at least one fluorene ring constituting the precisely polymerized polyfluorene may have a substituent at a position not involved in the polymerization. When two or more substituents are present in one fluorene ring, these substituents may be the same or different. The precisely polymerized polyfluorene may be composed only of fluorene rings having the same substituent, or fluorene rings having different substituents may be contained in the polymer molecular chain.

  The fluorene ring preferably has 1 or 2 substituents at the 9-position. The substituent at the 9-position does not decrease the electronic conductivity of the polymer, and the substituent increases the speed of the anion and cation doping and dedoping reactions and improves the output characteristics. Fluorene without a substituent at the 9-position is highly reactive with the hydrogen at the 9-position. When a reduction potential is applied, the proton is eliminated, and the reduction potential of this proton is higher than that of the fluorene. It is difficult to use as a negative electrode.

  The substituent at the 9-position of the fluorene ring includes hydroxyl group; nitro group; amino group; alkylamino group such as methylamino, ethylamino, dimethylamino; cyano group; alkylcyano group such as methylcyano, ethylcyano, propylcyano; Halogen atom such as iodine, bromine, chlorine, fluorine; chain or branched alkyl group such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl It is done. The alkyl group may be substituted by a hydroxyl group, a nitro group, an amino group, a cyano group, a halogen atom, an alkoxy group or an aryl group. Examples include chloromethyl, dichloromethyl, trichloromethyl, fluoromethyl, difluoromethyl. , Trifluoromethyl, difluoroethyl, methoxyethyl, ethoxyethyl, benzyl, phenethyl, cumyl, hydrocinnamyl.

  Substituents at the 9-position of the fluorene ring further include cycloalkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, cycloundecyl, cyclododecyl; linear or branched -Like alkoxy groups such as methoxy, ethoxy, propoxy, butoxy, pentyloxy, hexyloxy, heptyloxy, octyloxy, nonyloxy, decyloxy, undecyloxy, dodecyloxy.

  As the substituent at the 9-position of the fluorene ring, an alkenyl group such as ethenyl group, propenyl group, butenyl group, pentenyl group, hexenyl group, cyclopentenyl group, cyclohexenyl group, cyclohexedienyl group; alkynyl group such as Ethynyl, propynyl, butynyl, pentynyl, hexynyl; aromatic groups such as phenyl, naphthyl, anthryl, phenalenyl, phenanthryl, pyrenyl; heterocyclic groups such as pyridyl, pyrazyl, pyrimidyl, pyrrolyl, indenyl, furyl, oxazolyl, thiazolyl, Thienyl is mentioned. These groups may be substituted by hydroxyl group, nitro group, amino group, cyano group, halogen atom, alkyl group, alkoxy group. Examples include styryl, tolyl, xylyl, mesityl, fluorophenyl, fluoromethylphenyl. , Methoxyphenyl, ethoxyphenyl, methylpyridyl, methylpyrazyl.

  As the substituent at the 9-position of the fluorene ring, a carboxyl group; an alkylcarbonyl group such as acetyl, ethylcarbonyl, propylcarbonyl, butylcarbonyl, pentylcarbonyl, hexylcarbonyl; an alkoxycarbonyl group such as methoxycarbonyl, ethoxycarbonyl, Propoxycarbonyl, butoxycarbonyl, pentyloxycarbonyl, hexyloxycarbonyl; alkylcarbonyloxy groups such as acetoxy, ethylcarbonyloxy, propylcarbonyloxy, butylcarbonyloxy, pentylcarbonyloxy, hexylcarbonyloxy; ester groups such as methyl ester, Ethyl ester, phenyl ester; carbamoyl group such as methylcarbamoyl, ethylcarbamoyl, E carbamoylmethyl and the like.

  Examples of the substituent at the 9-position of the fluorene ring include an alkyl group, a carboxyl group, a nitro group, a cyano group, an alkylcyano group, a phenyl group, a halogen atom, a halogenated methyl group, a halogenated phenyl group, an alkylphenyl group, and an alkylhalogen. Preferred is a phenyl group. Particularly, it is preferable that the substituent at the 9-position is a substituent having an alkyl group or a phenyl group, since the doping reaction and dedoping reaction of the anion and cation to be doped are further accelerated and the output characteristics are improved. Examples of the former include 9,9-dimethylfluorene and 9,9-dioctylfluorene, and examples of the latter include 9-methyl-9-phenylfluorene, 9-methyl-9-benzylfluorene, benzalfluorene, and benzhydrylidinefluorene. be able to. Among these, when doping or dedoping a cation having a large molecule, an alkyl group having 1 to 8 carbon atoms is preferable as a substituent.

  The fluorene ring constituting the precisely polymerized polyfluorene can also have a substituent at a position other than the 9-position that is not involved in polymerization. Substituents at these positions can also be selected from the range of groups shown above for the 9-position substituent.

These precision polymerized polyfluorenes are known per se and can be obtained by known methods. For example, a Yamamoto coupling method using a nickel catalyst and a Suzuki-Miyaura coupling method using a palladium catalyst can be used. Formula I below shows an example of production by the Yamamoto coupling method, and Formula II shows an example of production by the Suzuki-Miyaura coupling method.

  These precision polymerized polyfluorenes can be imparted with a conductivity by doping treatment. As the doping process, either a chemical doping process or an electrochemical doping process may be employed.

Acceptors for chemical doping treatment include halogens such as Br ₂ , I ₂ and Cl ₂ , Lewis acids such as SO ₃ , BF ₃ , PF ₅ , AsF ₅ and SbF ₅ , HNO ₃ and H ₂ SO _4. Protonic acids such as HClO ₄ , CF ₃ SO ₃ H, FSO ₃ H, transition metal halides such as FeCl ₃ , MoCl ₅ , WCl ₅ , SnCl ₄ , MoF ₅ , tetracyanoethylene, tetracyanoquinodimethane, chloranil, etc. Organic materials such as Li, Na, K, and Cs can be used as donors.

As an acceptor for electrochemical doping treatment, Lewis acids such as BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ and SbF ₆ ⁻ , and halogen anions such as I ⁻ , Br ⁻ and Cl ⁻ can be used. As the donor, alkali metal ions such as Li ⁺ , Na ⁺ , K ⁺ , and Cs ⁺ , alkylammonium ions such as tetraethylammonium ions and tetrabutylammonium ions, and the like can be used.

  The doping amount is not particularly limited, but is preferably 5 to 100 mol% per fluorene monomer unit, more preferably 20 to 50 mol% per fluorene monomer unit. Polymerization may be performed after doping in a stage before polymerization, a method of doping after polymerization may be used, or doping may be performed by charging after electrode formation.

  The positive electrode active material subjected to these doping treatments undergoes a discharge reaction and a reduction reaction due to anodization of the anion. Further, the negative electrode active material subjected to these doping treatments causes a discharge reaction and an oxidation reaction due to cation dedoping.

  In addition, anion capable of covalently bonding with fluorene such as alkyl sulfonate anion and alkyl phosphonate anion is reacted with fluorene and polymerized to form a self-doped positive electrode active material. Tertiary ammonium cation A cation that can be covalently bonded to fluorene as described above is reacted with fluorene and polymerized to form a self-doped negative electrode active material.

  The self-doped positive electrode active material causes a discharge reaction and a reduction reaction by doping of cations in the electrolytic solution. In addition, the self-doped negative electrode active material undergoes a discharge reaction and an oxidation reaction by doping anions in the electrolytic solution. When a self-doped positive electrode active material or negative electrode active material is used, the same type and amount of cations or anions are involved in the charge transfer reaction, so that the ion concentration in the electrolyte is kept constant, and therefore the conductivity of the electrolyte is constant. Is kept constant.

  An electrode for an electrochemical device can be formed by providing an active material layer containing an electrode active material made of the precisely polymerized polyfluorene of the present invention on a current collector.

  As the current collector, a conductive material such as platinum, gold, nickel, aluminum, titanium, steel, or carbon can be used. As the shape of the current collector, any shape such as a film shape, a foil shape, a plate shape, a net shape, an expanded metal shape, and a cylindrical shape can be adopted.

  The active material layer is formed by dissolving the above-mentioned precisely polymerized polyfluorene in a solvent such as chloroform, tetrahydrofuran, N-methylpyrrolidone, isopropyl alcohol, and applying the resulting solution onto a current collector and drying. Also good. The film-shaped active material layer thus formed has a high capacity, is thin and uniform, and reduces the resistance of the electrode. Therefore, the IR drop during discharge can be reduced and the voltage of the electrode can be kept high. it can. Further, an active material layer may be formed by inserting a current collector into a monomer solution for forming precision polymerized polyfluorene and polymerizing the current collector on the current collector.

  Alternatively, the active material layer may be formed using a mixed material obtained by mixing a binder and a conductive material with the above-described precision polymerized polyfluorene.

  As the binder, known binders such as polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, polyvinyl fluoride, and carboxymethyl cellulose can be used. The content of the binder is preferably 1 to 20% by mass with respect to the total amount of the active material layer. When it is 1% by mass or less, the strength of the active material layer is not sufficient, and when it is 20% by mass or more, electrochemical characteristics such as capacity are insufficient.

  The conductive material may include known conductive materials such as carbon materials such as carbon black, natural graphite and artificial graphite, metal powders such as nickel and iron, and conductive oxides such as ITO. The content of these conductive materials is preferably 1 to 20% by mass with respect to the total amount of the active material layer. When the content is 1% by mass or less, the conductivity of the active material layer is insufficient, and when the content is 20% by mass or more, electrochemical characteristics such as capacity are insufficient.

  Other active materials may be further mixed in the active material layer as necessary. For example, other electrode active materials, for example, electron conductive polymers such as polythiophene, polypyrrole, and polyacene can be included. The amount of the other additive material is preferably 20% by mass or less based on the total amount of the active material layer. When it is 20% by mass or more, electrochemical characteristics such as capacity become insufficient.

  The electrode using the above-mentioned mixed material is obtained by dispersing the electrode active material of the present invention, a conductive material, and optionally other additive substances in a varnish in which a binder is dissolved, and collecting the obtained dispersion by a doctor blade method or the like. It can also be created by coating on top and drying. Alternatively, the obtained mixed material may be sandwiched between a net-like current collector to form an electrode.

  In a preferred form, the active material layer contains precision polymerized polyfluorene and carbon nanotubes. As carbon nanotubes, carbon nanotubes obtained by arc discharge method, laser evaporation method, chemical vapor deposition (CVD) method, etc. can be used, and both single-walled carbon nanotubes and multi-walled carbon nanotubes can be used. These may be used in combination. Since carbon nanotubes have a high electrical conductivity, a composite with a high electrical conductivity can be obtained by compounding with an active material. Further, since the outer surface area is large, the contact surface with the active material is widened, and it is possible to impart conductivity with high efficiency. Furthermore, the carbon nanotubes themselves have a capacity in contact with the electrolyte solution. Therefore, the combined use of precision polymerized polyfluorene and carbon nanotubes provides an electrode having high impedance, high p-doping redox potential, low n-doping redox potential, and low impedance characteristics. .

  An active material layer can be formed by mixing precisely polymerized polyfluorene and carbon nanotubes. At this time, if necessary, the active material layer may be formed by mixing both using a dispersion medium and then drying. However, it is particularly preferable to form an active material layer by supporting precisely polymerized polyfluorene on carbon nanotubes. Loading is performed by immersing carbon nanotubes in a solution of precision polymerized polyfluorene dissolved in a solvent such as chloroform, tetrahydrofuran, N-methylpyrrolidone, isopropyl alcohol, filtering after a predetermined time, collecting the carbon nanotubes, and drying. It can be carried out. After drying, a film of precision polymerized polyfluorene is formed on the surface of the carbon nanotube. In addition to having a high capacity, this film is thin, uniform, and has low resistance, and since the adhesion between the carbon nanotubes and the precision polymerized polyfluorene film is good and the contact resistance is low, IR drop during discharge is further reduced. The electrode voltage can be kept higher.

  The mass ratio of the precisely polymerized polyfluorene and the carbon nanotube is generally in the range of 9: 1 to 1: 9, and preferably in the range of 8: 2 to 2: 8. Exceeding this range results in insufficient electrochemical properties.

  After the active material layer containing the precisely polymerized polyfluorene and the carbon nanotube is molded into a predetermined shape such as a sheet, the obtained molded body and the current collector can be joined to obtain an electrode. For example, an electrode can be obtained by pressure-bonding the obtained molded body on a current collector. In the production of the active material layer, a binder or the like may be added as necessary.

  The electrode of the present invention can be suitably used in an electrochemical device having a pair of electrodes, a separator disposed between the electrodes, and an electrolyte solution.

  As a separator used for an electrochemical element, a polyolefin fiber nonwoven fabric, a glass fiber nonwoven fabric, etc. are used suitably, for example. There are a nonaqueous electrolytic solution and an aqueous electrolytic solution as the electrolytic solution, and they are appropriately selected according to the application.

  As the solvent for the non-aqueous electrolyte, electrochemically stable ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, sulfolane, 3-methyl sulfolane, γ-butyrolactone, acetonitrile, and dimethoxyethane, N-methyl-2-pyrrolidone, dimethylformamide or a mixture thereof can be preferably used.

As a solute of the nonaqueous electrolytic solution, a salt that generates lithium ions when dissolved in an organic electrolytic solution can be used without any particular limitation. For _{example, LiPF 6, LiBF 4, LiClO} 4, LiN (CF 3 SO 2) 2, LiCF 3 SO 3, LiC (SO 2 CF 3) 3, LiN (SO 2 C 2 F 5) 2, LiAsF 6, LiSbF 6 Or a mixture thereof can be preferably used. Further, a quaternary ammonium salt or a quaternary phosphonium salt having a quaternary ammonium cation or a quaternary phosphonium cation can be used as a solute of the nonaqueous electrolytic solution. For example, a cation represented by R ¹ R ² R ³ R ⁴ N ⁺ or R ¹ R ² R ³ R ⁴ P ⁺ (where R ¹ , R ² , R ³ , and R ⁴ have 1 to 6 carbon atoms) Represents an alkyl group), PF ₆ ⁻ , BF ₄ ⁻ , ClO ₄ ⁻ , N (CF ₃ SO ₃ ) ₂ ⁻ , CF ₃ SO ₃ ⁻ , C (SO ₂ CF ₃ ) ₃ ⁻ , N (SO ₂ C _A salt composed of an anion composed of ₂ F ₅ ) ₂ ⁻ , AsF ₆ ^— or SbF ₆ ^— , or a mixture thereof can be suitably used. In particular, a salt using PF ₆ ⁻ , BF ₄ ⁻ , ClO ₄ ⁻ or N (CF ₃ SO ₃ ) ₂ ⁻ as the anion is preferable as the solute.

  Examples of the solute cations in the acidic or alkaline aqueous electrolyte include cations of alkali metals such as sodium and potassium, or protons. Solute anions in aqueous electrolytes include anions of inorganic acids such as sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, tetrafluoroboric acid, hexafluorophosphoric acid, hexafluorosilicic acid, saturated monocarboxylic acids, aliphatic carboxylic acids And anions of organic acids such as oxycarboxylic acid, p-toluenesulfonic acid, polyvinylsulfonic acid and lauric acid.

  The electrode of the present invention can be suitably used as at least one of a pair of electrodes in an electrochemical device. Precision polymerized polyfluorene has a significantly increased capacity over bulk polymerized polyfluorene and, like bulk polymerized polyfluorene, has a high p-doping redox potential and a low n-doping redox potential. Therefore, by using the electrode of the present invention as an electrode of any electrochemical element, an electrochemical element having a high operating voltage, a high capacity and a high energy density can be obtained. Hereinafter, each case where the electrochemical element is a secondary battery, an electric double layer capacitor, or an electrochemical capacitor will be described.

(Secondary battery)
In the case of a lithium secondary battery, a non-aqueous electrolyte solution having a lithium salt as a solute is used as the electrolyte solution. Then, the electrode of the present invention is used as the positive electrode, and an electrode using an electrode active material that occludes and releases lithium ions such as conventional lithium metal or natural graphite, artificial graphite, and petroleum coke is used as the negative electrode. In the positive electrode of the present invention using self-doped precision polymerized polyfluorene as an electrode active material, the same amount of lithium cation participates in the charge / discharge reaction, so that the ion concentration of the electrolyte is kept constant, The conductivity of the liquid can be kept constant.

  The lithium secondary battery having this configuration operates in a state in which the positive electrode of the present invention has a high p-doping oxidation-reduction potential in the same manner as the positive electrode using bulk polymerized polyfluorene as an electrode active material, and further electrolysis of a non-aqueous electrolyte solution. Since the operating voltage can be increased because the voltage is high, the operating voltage is high, the capacity is high, and the energy density is high.

  Further, when the electrode active material of the present invention is used for the negative electrode and a conventional layered compound such as lithium cobaltate or a conductive polymer such as polyaniline or polyphenylene is used as the electrode active material for the positive electrode, lithium ion intercalation is caused. Therefore, a lithium secondary battery with improved output characteristics and cycle characteristics, high operating voltage, high capacity and high energy density can be obtained.

  In the case of forming a proton battery, an acid aqueous solution having protons is used as an electrolytic solution. And the electrode of this invention is used as a positive electrode, and the negative electrode in well-known proton batteries, such as a quinoxaline type polymer, is used as a negative electrode. The proton battery having this configuration uses an electrolytic solution made of an acid aqueous solution, has good charge / discharge characteristics, high energy density, and the positive electrode of the present invention is similar to a positive electrode using bulk-polymerized polyfluorene as an electrode active material. The battery operates at a high p-doping redox potential and shows a maximum operating voltage of 1.2 V in a battery using an aqueous electrolyte.

(Electric double layer capacitor)
As the electrolytic solution for the electric double layer capacitor, any of the above-mentioned non-aqueous electrolytic solution and aqueous electrolytic solution can be used. In an electric double layer capacitor using a non-aqueous electrolyte, the electrode of the present invention is used as a positive electrode or a negative electrode, and the other electrode is an electric material such as activated carbon, carbon fiber, phenol resin carbide, vinylidene chloride resin carbide, or microcrystalline carbon. An electrode having a double layer capacity is used. The positive electrode of the present invention operates in a state where the redox potential of p-doping is high as in the case of the positive electrode using bulk polymerized polyfluorene as the electrode active material, or the negative electrode of the present invention is the same as the negative electrode using bulk polymerized polyfluorene. It operates at a low oxidation-reduction potential of n-doping, has a capacity characteristic greatly increased as compared with a negative electrode using bulk polymerized polyfluorene, and the electrolysis voltage of the non-aqueous electrolyte is high. Since it can be increased, an electric double layer capacitor having a high operating voltage, a high capacity and a high energy density can be obtained.

  In addition, in an electric double layer capacitor using an aqueous electrolyte, the electrode of the present invention is used as a positive electrode, and the other electrode is made of an electric two-layer such as activated carbon, carbon fiber, phenol resin carbide, vinylidene chloride resin carbide, and microcrystalline carbon. An electrode having a multilayer capacity is used. The electric double layer capacitor of this configuration can use acidic, neutral, and alkaline aqueous solutions, has good charge / discharge characteristics, high energy density, and the positive electrode of the present invention uses bulk-polymerized polyfluorene as an electrode active material. As in the case of the positive electrode, it operates with a high p-doping oxidation-reduction potential, and shows a maximum operating voltage of 1.2 V in an electric double layer capacitor using an aqueous electrolyte.

(Electrochemical capacitor)
As an electrolytic solution for the electrochemical capacitor, a nonaqueous electrolytic solution having a quaternary ammonium salt or a quaternary phosphonium salt as a solute is used. Then, the electrode of the present invention can be used as the positive electrode, and an electrode using a conventional conductive polymer such as polyacetylene, polyacene, or polyphenylene having redox reaction characteristics as the negative electrode can be used as the electrode active material. The electrochemical capacitor of this configuration has a significantly increased capacity as compared with the positive electrode using bulk polymerized polyfluorene as the positive electrode of the present invention, as well as the positive electrode using bulk polymerized polyfluorene. Since it operates in a state where the oxidation-reduction potential is high, the operating voltage is high, the capacity is high, and the energy density is high.

  In addition, a conventional conductive polymer such as polyaniline, polyacetylene and polyphenylene having redox reaction characteristics or an electrode using a metal oxide such as ruthenium oxide, manganese oxide and nickel oxide as an electrode active material is used as a positive electrode, and this electrode is used as a negative electrode. The electrode of the invention can also be used. In the electrochemical capacitor of this configuration, the negative electrode of the present invention has a capacity that is significantly increased as compared with a negative electrode using bulk polymerized polyfluorene or metal oxide as an electrode active material, and in addition to a negative electrode using bulk polymerized polyfluorene. Since it operates in a state where the redox potential of n-doping is low, the operating voltage is high, the capacity is high and the energy density is high.

  Further, when the electrode of the present invention is used for both of a pair of electrodes in an electrochemical capacitor, the negative electrode has a low n-doping oxidation-reduction potential, the positive electrode has a high p-doping oxidation-reduction potential, and has high capacity characteristics. Therefore, an electrochemical capacitor having an unprecedented high operating voltage, high capacity, and high energy density can be obtained. In addition, when self-doped precision polymerized polyfluorene is used, the same type and amount of ions are involved in the reaction, so the ion concentration in the electrolyte is kept constant and the conductivity of the electrolyte is constant. Kept.

  Examples of the present invention are shown below, but the present invention is not limited to the following examples.

Example 1: Precision polymerization polyfluorene synthetic 1.2mL dimethylformamide of 1 mmol 2,7-dibromofluorene, NiCl ₂ of 0.05 mmol, 3.1 mmol of Zn, triphenylphosphine 0.1 mmol, 0.05 mmol Of 2,2-bipyridine was added and stirred at 80 ° C. for 20 hours to obtain the product. The product was filtered and washed to obtain a yellow powder precision polymerized polyfluorene represented by the following formula III.

2: Preparation of precision polymerized polyfluorene / carbon nanotube composite electrode Add 20 mg of precisely polymerized polyfluorene powder and 10 mg of carbon nanotube powder (specific surface area: 200 m ² / g) to 50 mL of isopropyl alcohol, and disperse by mechanical stirring. Got. The dispersion was filtered to obtain a sheet of a precisely polymerized polyfluorene / carbon nanotube composite in which precisely polymerized polyfluorene was supported on carbon nanotubes. The sheet was cut to about 2 cm ² and pressed onto an aluminum current collector of the same size to obtain a precisely polymerized polyfluorene / carbon nanotube composite electrode.

3: Cyclic voltammogram evaluation of precision polymerized polyfluorene / carbon nanotube composite electrode Using precision polymerized polyfluorene / carbon nanotube composite electrode as working electrode, using activated carbon sheet as counter electrode, and silver-silver ion electrode as reference electrode, Cyclic voltammograms were measured with a triode cell. As the electrolytic solution, propylene carbonate in which 1M tetraethylammonium tetrafluoroborate was dissolved was used. The potential range was −2 V to +1 V, and the potential scanning speed was 5 mVs ⁻¹ .

Comparative Example 1: Synthesis of bulk-polymerized polyfluorene 10 mmol of FeCl ₃ was added to acetonitrile in which 10 mmol of fluorene monomer was dissolved, and the mixture was stirred at room temperature for 72 hours, filtered and dried (60 ° C. vacuum drying for 24 hours). A bulk-polymerized polyfluorene powder of the tan powder represented by formula IV was obtained.

2: Production of bulk polymerized polyfluorene / carbon nanotube composite electrode Add 50 mg of bulk polymerized polyfluorene powder and 10 mg of carbon nanotube powder (specific surface area: 200 m ² / g) to 50 mL of isopropyl alcohol, and disperse by mechanical stirring. Got. The dispersion was filtered to obtain a bulk polymerized polyfluorene / carbon nanotube composite sheet in which bulk polymerized polyfluorene was supported on carbon nanotubes. The sheet was cut to about 2 cm ² and pressed onto an aluminum current collector of the same size to obtain a bulk polymerized polyfluorene / carbon nanotube composite electrode.

3: Cyclic voltammogram evaluation of bulk polymerized polyfluorene / carbon nanotube composite electrode Using bulk polymerized polyfluorene / carbon nanotube composite electrode for working electrode, activated carbon sheet for counter electrode, and silver-silver ion electrode for reference electrode, Cyclic voltammograms were measured with a triode cell. As the electrolytic solution, propylene carbonate in which 1M tetraethylammonium tetrafluoroborate was dissolved was used. The potential range was −2 V to +1 V, and the potential scanning speed was 5 mVs ⁻¹ .

In FIG. 2, the cyclic voltammogram of an Example and the cyclic voltammogram of a comparative example are shown collectively. Table 1 shows values of the differential capacity and the integral capacity obtained from the results of the cyclic voltammogram of the example and the cyclic voltammogram of the comparative example.

  As is clear from Table 1, the precision polymerized polyfluorene / carbon nanotube composite electrode of the example has an integral capacity of about 2.2 times that of the bulk polymerized polyfluorene / carbon nanotube composite electrode of the comparative example. Have.

(A) is a figure which shows the fluorene ring chain in precision polymerization polyfluorene, (b) is a figure which shows the fluorene ring chain in bulk polymerization polyfluorene. It is a cyclic voltammogram of a polyfluorene / carbon nanotube composite electrode.

Claims (9)

An electrode active material comprising at least one polyfluorene,
An electrode active material, wherein the fluorene ring of the polyfluorene is substantially polymerized at the 2-position and the 7-position.   2. The electrode active material according to claim 1, wherein the polyfluorene contains at least one fluorene ring having a substituent at the 9-position.   The substituent is a group consisting of an alkyl group, a carboxyl group, a nitro group, a cyano group, an alkylcyano group, a phenyl group, a halogen atom, a halogenated methyl group, a halogenated phenyl group, an alkylphenyl group, and an alkylhalogenated phenyl group. The electrode active material according to claim 2, selected from:   The electrode which has an active material layer containing the electrode active material of any one of Claims 1-3.   The electrode according to claim 4, wherein the active material layer contains at least one carbon nanotube.   The electrode according to claim 5, wherein the polyfluorene is supported on the carbon nanotubes.   The electrode according to any one of claims 4 to 6, which is used as one of a pair of electrodes in a secondary battery.   The electrode according to any one of claims 4 to 6, which is used as one of a pair of electrodes in an electric double layer capacitor.   The electrode according to any one of claims 4 to 6, which is used as at least one of a pair of electrodes in an electrochemical capacitor.

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