JP2006048973A - Secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a secondary battery in which charge and discharge characteristics are kept superior, in which energy density is high, and which has voltage a characteristic of 1.2 V. <P>SOLUTION: As for the secondary battery, charge and discharge characteristics are superior because a positive electrode using polyfluorene or its derivative and an electrolytic solution composed of an acidic aqueous solution are used, and energy density is high because the dope and de-dope of ions are used as an electricity storage mechanism, and the secondary battery having the voltage characteristic of 1.2 V which is the highest voltage as a battery using an aqueous electrolytic solution can be provided because a positive electrode is actuated in a state of p-doped oxidation-reduction potential which is higher than that of a conventional conductive polymer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a secondary battery, and more particularly to a secondary battery having excellent output and cycle characteristics and high voltage characteristics.

  In recent years, due to environmental problems on the earth, there are increasing expectations for electric vehicles and hybrid vehicles in place of engine-driven gasoline vehicles and diesel vehicles. In these electric vehicles and hybrid vehicles, electrochemical elements such as secondary batteries and electric double layer capacitors having high energy density and high output density characteristics are used as a power source for driving the motor.

An electric double layer capacitor which is such an electrochemical element uses a polarizable electrode such as activated carbon as positive and negative electrodes and an acidic aqueous solution as an electrolyte. In such an electric double layer capacitor, the electric double layer generated at the interface between the electrode surface and the electrolyte has a capacitance, and there is no reaction involving ions like a battery. Little capacity degradation due to discharge cycle. Furthermore, since an acidic aqueous solution having high ion conductivity is used, a large current can be obtained during charging and discharging. However, the energy density due to the double layer capacity is lower than that of the battery, and it is significantly insufficient as a power source for electric vehicles. On the other hand, there is an example in which an additive is used in the electrolytic solution for the purpose of increasing the capacity. (Patent Document 1)
Japanese Patent Laid-Open No. 2002-1000039

   However, there is a limit in increasing the capacity of an electric double layer capacitor using an electric double layer capacity. Therefore, the present invention uses a secondary solution having a voltage characteristic of 1.2 V, which is an electrolysis voltage of water, in which charge / discharge characteristics are kept good using an acidic aqueous solution, as in the case of an electric double layer capacitor, and the energy density is high. The object is to provide a battery.

  In order to solve the above-mentioned problems, the present invention has been studied on a conductive polymer as an electrode material. As a result, when a positive electrode using polyfluorene or a derivative thereof and an electrolytic solution composed of an acidic aqueous solution are used, charge / discharge characteristics are obtained. Was maintained well, the energy density was high, and a secondary battery having a voltage characteristic of 1.2 V was found to be obtained.

    A secondary battery using a positive electrode using polyfluorene or a derivative thereof, a negative electrode that absorbs and desorbs protons such as a quinoxaline-based polymer as a negative electrode, and an acidic aqueous solution as an electrolytic solution uses an acidic aqueous solution. Since the discharge characteristics are good and the energy storage mechanism is ion doping or dedoping, the energy density is high, and the positive electrode operates in a state where the p-doped redox potential is higher than that of conventional conductive polymers. A secondary battery having a voltage characteristic of 1.2 V, which is the highest voltage, can be provided as a battery using a liquid.

As a derivative of polyfluorene, the substituent at the 9-position of fluorene is an alkyl group, a carboxyl group, a nitro group, a cyano group, an alkyl cyano group, a phenyl group (-Ph), a halogen atom (-X), -CX ₃ It is preferable to use a halogenated phenyl group, an alkylphenyl group, or an alkylhalogenated phenyl group.

    In addition, when a solution in which a doped polyfluorene or a derivative thereof is dissolved in a basic solvent is attached to a current collector, the solvent is evaporated, and an electrode in which a film of polyfluorene or a derivative thereof is formed on the current collector is used. A thin and uniform electrode film can be formed, and the resistance of the electrode can be reduced to keep the discharge voltage high, so that high voltage characteristics can be obtained.

    As described above, when a positive electrode using polyfluorene or a derivative thereof and an electrolytic solution made of an acidic aqueous solution are used, the charge / discharge characteristics are kept good, the energy density is high, and the secondary voltage characteristic is 1.2V. A battery can be obtained.

    The polyfluorene or a derivative thereof of the present invention can be obtained by polymerizing a monomer of fluorene or a derivative thereof by chemical polymerization or electrolytic polymerization. In the case of chemical polymerization, it is possible to form a polymer layer by polymerizing on a current collector using a solution of these monomers and an oxidizing agent to form an electrode. Alternatively, the current collector can be used as an electrode for electropolymerization to perform electropolymerization, and a polymer layer can be formed on the current collector to form an electrode. Moreover, after mixing polyfluorene or its derivative (s), and conductive materials, such as carbon, it can also shape | mold and use as an electrode.

    Furthermore, polyfluorene or a derivative thereof is obtained by polymerizing a monomer of fluorene or a derivative thereof by chemical polymerization or electrolytic polymerization, and in a state doped with this polyfluorene or a derivative thereof, such as chloroform, tetrahydrofuran, N-methylpyrrolidone, etc. Dissolve in basic solvent to make a solution. Then, this solution is applied to a current collector and dried to form a layer of polyfluorene or a derivative thereof. Since the electrode formed in this way is thin and uniform, the resistance of the electrode is reduced, the IR drop during discharge is reduced, and the voltage of the electrode can be kept high.

    The polyfluorene or its derivative thus polymerized is in an oxidized state by doping with anions in the polymerization solution, and this is used as the positive electrode. This positive electrode causes a discharge reaction and a reduction reaction by undoping an anion.

  Furthermore, a self-doped positive electrode can be obtained by reacting fluorene or a derivative thereof with an anion that can be covalently bonded to fluorene such as alkyl sulfonic acid or alkyl phosphonic acid. This positive electrode causes a discharge reaction and an oxidation reaction by doping with a cation in the electrolytic solution.

Here, the polyfluorene derivative is preferably a derivative having a substituent at the 9-position of fluorene. This is because the electron conductivity is not lowered and the reaction of the anion and cation doped by this substituent is accelerated and the output characteristics are improved. In addition, as a substituent, an alkyl group, a carboxyl group, a nitro group, a cyano group, an alkyl cyano group, a phenyl group (-Ph), a halogen atom (-X), -CX ₃ , a halogenated phenyl group, an alkylphenyl group, It is preferable to use an alkyl halogenated phenyl group.

    Among these polyfluorene derivatives, it is preferable that the substituent at the 9-position is an alkyl group or a substituent having a phenyl group, since the reaction of the anion and cation to be doped becomes faster and the output characteristics are improved. The former includes 9,9-dimethylfluorene, 9,9-dioctylfluorene, and the latter includes 9-methyl-9-phenylfluorene, 9-methyl-9-benzylfluorene, benzalfluorene, benzhydrylidinefluorene, and the like. be able to. Especially, when using as a positive electrode of a self-doping type | mold which dopes and dedopes a cation with a big molecule | numerator, the alkyl group of n = 1-8 is preferable.

  The secondary battery of the present invention can be formed using the above electrode and the electrolytic solution. As the electrolytic solution, an aqueous electrolytic solution using protons as cations is used. As anions, inorganic acids such as sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, tetrafluoroboric acid, hexafluorophosphoric acid, hexafluorosilicic acid, saturated monocarboxylic acid, aliphatic carboxylic acid, oxycarboxylic acid, p-toluenesulfone The anion which forms organic acids, such as an acid, polyvinylsulfonic acid, and lauric acid with a proton can be mentioned.

    The secondary battery of the present invention is formed using a positive electrode using polyfluorene or a derivative thereof, a negative electrode that adsorbs and desorbs protons such as a quinoxaline polymer as a negative electrode, and an acidic aqueous solution as an electrolyte. Can do. Since this secondary battery uses an acidic aqueous solution, the charge / discharge characteristics are good, and since ion storage and doping are used as a power storage mechanism, the energy density is high, and the positive electrode is more p-doped than conventional conductive polymers. Therefore, it has a voltage characteristic of 1.2 V which is the highest voltage as a battery using an aqueous electrolyte.

  Furthermore, when a self-doped positive electrode is used, only the cations are involved in the reaction in the same amount in the charge / discharge reaction, so that the cation and anion concentrations in the electrolytic solution do not change and the conductivity of the electrolytic solution is kept constant. be able to.

The present invention will be described more specifically with reference to the following examples.

After dissolving the fluorene derivative in acetonitrile, a sufficient amount of iron (III) chloride was dissolved and stirred for 72 hours to proceed the polymerization. Next, the reaction solution was filtered under reduced pressure, and the filtrate was vacuum dried with 60 C 2 ^O for about 12 hours to obtain a crude product. This crude product was dissolved in chloroform to be saturated, and methanol was added to reprecipitate the product. The reprecipitate was again filtered under reduced pressure, and the filtrate was vacuum-dried with 60 C 2 ^O for about 12 hours to obtain a purified polyfluorene derivative.

Subsequently, 1.2 g of the obtained polyfluorene derivative was dissolved in 1 L of tetrahydrofuran solvent, and this solution was dropped on a current collector made of carbon and dried. By repeating the dropping and drying, a polyfluorene derivative film was formed on the current collector. This current collector / polyfluorene derivative film was used as an electrode made of a polyfluorene derivative. A secondary battery was prepared using this electrode, and a constant current charge / discharge test was conducted. The charge / discharge current was set to 0.5 mA cm ^-2 and charge / discharge was repeated. The electrodes and operating voltage used are shown in (Table 1). In addition, only the monomer name was described about the polymer used as an electrode.

As described above, the secondary battery of the present invention exhibits an operating voltage of 1.2V. The charge / discharge characteristics at this operating voltage were also good up to 10,000 cycles.

Claims (3)

A secondary battery comprising a positive electrode using polyfluorene or a derivative thereof and an electrolytic solution comprising an acidic aqueous solution. The 9-position substituent of the polyfluorene derivative is alkyl group, carboxyl group, nitro group, cyano group, alkyl cyano group, phenyl group (-Ph), halogen atom (-X), -CX ₃ , halogenated phenyl group, The secondary battery according to claim 1, which is an alkylphenyl group. Claims using an electrode in which a solution of doped polyfluorene or a derivative thereof in a basic solvent is attached to a current collector, the solvent is evaporated, and a film of polyfluorene or a derivative thereof is formed on the current collector. The secondary battery according to 1 or 2.