JP2008270795A - Reaction method and metal oxide nano-particles obtained using the method, or metal oxide nanoparticle-dispersed/deposited carbon and electrode containing this carbon and electric chemical element using this electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of promoting and controlling a liquid-phase reaction which conventionally has not existed. <P>SOLUTION: There is provided a reaction method for promoting and controlling a chemical reaction, by exerting shear stress and centrifugal force on reactants containing a reaction inhibitor in a revolving reactor, in a process of a chemical reaction, wherein by a complex is formed by adding a prescribed compound, such as, acetic acid, thereby forming the complex with the metal alkoxide, to the metal alkoxide by 1 to 3 mol per mol of the metal alkoxide, and reaction is inhibited and controlled. Specifically, by using the reactor constituted of a concentric cylinder of an outer cylinder and an inner cylinder, having a through hole on the side face of the inner cylinder, and having a sheathing board disposed in an opening part of the outer cylinder, the reactant containing the reaction inhibitor within the inner cylinder is moved to the inner wall surface of the outer cylinder through the through hole of the inner cylinder by the centrifugal force generated by revolving motion of the inner cylinder, a thin film that contains the reactant, containing the reaction inhibitor, is generated on the inner wall surface of the outer cylinder; and by adding the shear stress and the centrifugal force to this thin film, the chemical reaction is promoted and controlled. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a chemical reaction method in which the production of an insoluble product by a liquid phase reaction is promoted. Further, the present invention relates to a nanoparticle obtained by this method or carbon carrying nanoparticle, an electrode containing this carbon, and this electrode The present invention relates to an electrochemical device using the.

  Conventionally, lithium titanate has been used as a lithium storage / release active material for electrochemical element negative electrodes. Further, a wet method (see Patent Document 1) is known as a method for forming lithium titanate particles having excellent crystallinity, but there is a problem that output characteristics are not sufficient.

Therefore, the present applicants provide a method for accelerating the reaction in an unprecedented liquid phase reaction, and further, the metal oxide nanoparticles prepared by using this reaction method and the electrode material for an electrochemical device. A patent application was previously filed as Japanese Patent Application No. 2005-356845 for the purpose of providing carbon in which metal oxide nanoparticles are highly dispersed and supported and an electrochemical device using this electrode.
JP 2000-36441 A

  However, for example, when a titanium alkoxide is used as a metal salt for causing a hydrolysis reaction using the mechanochemical reaction described in the specification of the prior application as described above, the reaction is too early, and lithium titanate is used. When manufacturing, titanium oxide was formed, and there was a problem that lithium titanate could not be manufactured.

  The present invention has been proposed to solve the problems of the prior art as described above, and its object is to provide a method for promoting and controlling the reaction in an unprecedented liquid phase reaction, and Metal oxide nanoparticles prepared by using this reaction method, carbon in which the metal oxide nanoparticles used as an electrode material for an electrochemical device are highly dispersed and supported, an electrode containing the carbon, and the electrode It is to provide an electrochemical element.

  As a result of intensive studies to solve the above problems, the present inventors have conducted intensive studies on a method for controlling the mechanochemical reaction described in the specification previously filed by the present applicant, etc., The present invention has been completed.

(Reaction inhibitor)
That is, by adding a predetermined compound that forms a complex with the metal alkoxide as a reaction inhibitor to the predetermined metal alkoxide to which the mechanochemical reaction described in the specification of the prior application is applied, the chemical reaction is promoted too much. It has been found that this can be suppressed.

  That is, the reaction can be suppressed and controlled by adding 1 to 3 mol of a predetermined compound such as acetic acid that forms a complex with metal alkoxide to 1 mol of the metal alkoxide to form a complex. I understood that I could do it. It is to be noted that a metal-oxide composite nano-particle, for example, a lithium-titanium oxide composite nano-particle, which is a precursor of lithium titanate, is produced by firing this reaction. Thus, a crystal of lithium titanate is obtained.

  Thus, by adding a predetermined compound such as acetic acid as a reaction inhibitor, it is possible to suppress the chemical reaction from being promoted too much because the predetermined compound such as acetic acid can form a stable complex with the metal alkoxide. It is thought that it is for forming.

  Examples of substances that can form a complex with a metal alkoxide include acetic acid, citric acid, succinic acid, formic acid, lactic acid, tartaric acid, fumaric acid, succinic acid, propionic acid, carboxylic acid such as propionic acid, and EDTA. Examples include complexing agents represented by amino alcohols such as aminopolycarboxylic acid and triethanolamine.

(Baking process)
Moreover, in the baking process of the obtained lithium titanate precursor, rapid heating from room temperature to 800 ° C., rapid cooling to 50 ° C., and rapid heating and rapid cooling are performed within 1 minute to prevent aggregation of lithium titanate. It was found that nanoparticles having a small particle size were formed.

(Metal alkoxide)
As the metal alkoxide to which the reaction inhibitor according to the present invention can be applied, in addition to the above titanium alkoxide, a metal alkoxide having a reaction rate constant of 10 ⁻⁵ mol ⁻¹ sec ⁻¹ or more for hydrolysis reaction of the metal alkoxide Can be mentioned. Examples of such metals include tin, zirconia, and cesium.

(carbon)
In addition, by adding predetermined carbon during the reaction process, carbon in which 5 to 20 nm lithium titanate is highly dispersed and supported can be obtained. That is, a metal salt, the above reaction inhibitor, and a predetermined carbon are introduced into the inner cylinder of the reactor, and the inner cylinder is rotated to mix and disperse the metal salt, the above reaction inhibitor, and carbon. Further, while turning the inner cylinder, a catalyst such as sodium hydroxide is added to cause hydrolysis and condensation reaction to proceed to produce a metal oxide, and the metal oxide and carbon are mixed in a dispersed state. Along with the completion of the reaction, carbon in which metal oxide nanoparticles are supported in a highly dispersed state can be formed.

  Examples of the carbon used here include carbon blacks such as ketjen black and acetylene black, carbon nanotubes, carbon nanohorns, amorphous carbon, carbon fibers, natural graphite, artificial graphite, activated carbon, mesoporous carbon, and the like. Composite materials can also be used.

  Further, the carbon in which the metal oxide nanoparticles obtained according to the present invention are highly dispersed and supported may be calcined, kneaded with a binder, molded, and then an electrode of an electrochemical element, that is, an electrode for storing electric energy. However, this electrode exhibits high output characteristics and high capacity characteristics.

  Here, the electrochemical element which can use this electrode is an electrochemical capacitor and a battery using an electrolytic solution containing lithium ions. That is, the electrode of the present invention can occlude and desorb lithium ions and operates as a negative electrode. Therefore, an electrochemical capacitor and a battery can be configured by using an electrolytic solution containing lithium ions and using, as a counter electrode, activated carbon, carbon that occludes and desorbs lithium, and the like.

(Mechanochemical reaction)
The reaction method used in the present invention is a mechanochemical reaction similar to the method shown in the above specification previously filed by the applicant of the present application, and is performed in a rotating reactor in the course of the chemical reaction. A chemical reaction is promoted by applying shear stress and centrifugal force to an object.

  In this reaction method, mechanical energy of both shear stress and centrifugal force is applied to the reactant at the same time, which seems to be due to the conversion of this energy into chemical energy. Can be promoted.

  And in order to promote such a chemical reaction, the reactor which consists of a concentric cylinder of an outer cylinder and an inner cylinder, is equipped with a through-hole in the side surface of an inner cylinder, and arrange | positions a slat in the opening part of an outer cylinder. In this, the reactant in the inner cylinder is moved to the inner wall surface of the outer cylinder through the through-hole of the inner cylinder by centrifugal force due to the turning of the inner cylinder, and a thin film containing the reactant is generated on the inner wall surface of the outer cylinder. This can be realized by applying shear stress and centrifugal force.

  According to the present invention, there is provided a method for promoting and controlling the reaction in an unprecedented liquid phase reaction, and further, the metal oxide nanoparticles prepared by using this reaction method and the electrode material for an electrochemical device. It is possible to provide carbon on which metal oxide nanoparticles are highly dispersed and supported, an electrode containing the carbon, and an electrochemical device using the electrode.

  Hereinafter, the present invention will be described more specifically with reference to examples.

(1) Composite powder composed of lithium titanate and ketjen black (Example 1)
A mixed solvent was prepared by dissolving acetic acid and lithium acetate in an amount of 1.8 mol of acetic acid and 1 mol of lithium acetate in a mixture of isopropanol and water with respect to 1 mol of titanium alkoxide. This mixed solvent, titanium alkoxide, isopropyl alcohol, ketjen black (Ketjen Black International Co., Ltd., trade name: ketjen black EC600JD, porosity 78 Vol.%, Primary particle size 40 nm, average secondary particle size 337.8 nm) Into the swirl reactor, and the inner cylinder is swirled with a centrifugal force of 66,000 N (kgms ^-2 ) for 5 minutes to form a thin film of the reactant on the inner wall of the outer cylinder. A chemical reaction was promoted by applying centrifugal force to obtain Ketjen Black carrying a highly dispersed lithium titanate precursor.

  The obtained Ketjen black carrying a highly dispersed lithium titanate precursor was dried at 80 ° C. for 17 hours in a vacuum to obtain a composite in which the lithium titanate precursor was carried highly dispersed by Ketjen black. A body powder was obtained.

  The composite powder in which the obtained lithium titanate precursor is highly dispersed and supported on ketjen black is rapidly heated and rapidly cooled in room temperature → 800 ° C. → 50 ° C. within one minute in a vacuum to contain lithium. Crystallization of the titanium oxide was advanced to obtain a composite powder in which lithium titanate nanoparticles were highly dispersed and supported on Ketjen Black.

  A TEM image of the composite thus obtained is shown in FIG. In FIG. 1, it can be seen that 5 to 20 nm lithium titanate nanoparticles are highly dispersed and supported on Ketjen Black.

(Example 2)
Ketjen black carrying a highly dispersed lithium titanate precursor prepared in the same manner as in Example 1 is baked at 800 ° C. for 12 hours to advance crystallization of titanium oxide containing lithium. A ketjen black composite carrying lithium acid was obtained.

  SEM observation of the ketjen black composite on which lithium titanate thus obtained was supported revealed that aggregated particles of lithium titanate of 0.5 μm to 2 μm were generated.

(Comparative Example 1)
A mixed solvent was prepared by dissolving acetic acid and lithium acetate in an amount of 1.8 mol of acetic acid and 1 mol of lithium acetate in a mixture of isopropanol and water with respect to 1 mol of titanium alkoxide. While stirring titanium alkoxide and isopropyl alcohol with a stirrer, the mixed solvent was added dropwise and stirred for 5 hours. The produced lithium titanate precursor was dried in vacuum at 80 ° C. for 17 hours to obtain lithium-containing titanium oxide powder.

  The obtained lithium titanate precursor was baked at 800 ° C. for 12 hours in an oxygen atmosphere to promote crystallization of lithium-containing titanium oxide to obtain a lithium titanate powder.

  When the lithium titanate powder thus obtained was observed with an SEM, lithium titanate particles of 0.5 μm to 2 μm were produced.

(Comparative Example 2)
When it was produced by the same method as in Example 1 without using acetic acid, hydrolysis progressed when the materials were mixed, and the composite could not be produced by ultracentrifugation.

(Measurement result)
The composite powder obtained in Example 1, Example 2 and Comparative Example 1 was put into a SUS mesh welded on a SUS plate to obtain an electrode. A separator, a counter electrode, and a Li foil were placed on the electrode as a reference electrode, and 1M LiPF ₆ EC / DEC was infiltrated as an electrolyte to obtain a cell.

The working electrode is a SUS mesh welded SUS plate having a composite of the above cells, and a voltage range of 1.3 to 2.0 Vvs. Cyclic voltammograms were measured by sweeping at Li / Li ⁺ and a sweep rate of 0.1 mVsec ⁻¹ . The measured cyclic voltammogram is shown in FIG. Further, when the peak potential difference was measured for Example 1, Example 2 and Comparative Example 1, results as shown in Table 1 were obtained.

  As is clear from FIG. 2, it was found that Example 1 had a sharp CV peak. This is presumably because the output characteristics of the electrodes were improved because the output characteristics of the nanoparticles themselves were improved or the output characteristics were improved by improving the crystallinity. Further, as is clear from Table 1, it was found that Example 1 has a high rate characteristic.

(2) Electrochemical capacitor using the electrode of the present invention An electrode using lithium titanate and ketjen black obtained by the above mechanochemical reaction is used as a negative electrode, and a polarizable electrode such as activated carbon is used as a positive electrode. Thus, it was found that an electrochemical capacitor containing a lithium salt in an electrolytic solution in which lithium dendride is not generated can be obtained. Details will be described below.

  The negative electrode of an electrochemical capacitor that contains a lithium salt in a normal electrolyte uses a carbon material that can store and release lithium. However, since the potential at which lithium dendrites are generated is close to the potential at carbon, lithium dendrites May occur. On the other hand, since the potential of the lithium titanate according to the present invention is about 1.5 V higher than the potential at which lithium dendride is generated, dendride is not generated.

  However, when a charge / discharge test was performed using the electrode of the present application, results as shown in FIG. 3 were obtained. That is, when charging was performed from start to A and discharging was performed, only D was discharged, and it was found to have irreversible capacity. In addition, since lithium titanate alone has no irreversible capacity, it was considered that carbon was the cause.

Next, the irreversible capacity | capacitance at the time of charging to A, B, and C was shown in FIG. As can be seen from the figure, the smaller the charge capacity, the smaller the irreversible capacity. The horizontal axis in FIG. 4 represents the charge capacity converted to “x” of Li _{4 + x} Ti ₅ O ₁₂ .

  Further, when the relationship between the amount of carbon in the negative electrode of the present application electrode and the irreversible capacity was examined, the results shown in FIG. 5 were obtained. Further, when the relationship between the amount of carbon and the capacity reduction rate was examined, results as shown in FIG. 6 were obtained. From these results, it was found that the content of carbon is preferably 30 to 50 wt%, more preferably 35 to 45 wt%.

  Moreover, in order to raise the capacity | capacitance of a lithium titanate, to reduce a charging potential, and to reduce an irreversible capacity | capacitance, when the calcination temperature was examined, the result as shown in FIG. 7 was obtained. As can be seen from the figure, the capacity increased from 900 to 1000 ° C. and increased to the theoretical capacity. In order to increase the capacity, it is preferable to use ketjen black having a large specific surface area.

  Based on these results, an electrochemical capacitor was fabricated with a firing temperature of 900 ° C. and a ketjen black content of 40 wt%, and the characteristics were evaluated. The results shown in FIG. 8 were obtained. As is clear from the figure, it was found that an electrochemical capacitor having a higher energy density can be obtained as compared with an electric double layer capacitor using activated carbon for both electrodes.

(Example 3)
A mixed solvent was prepared by dissolving acetic acid and lithium acetate in an amount of 1.8 mol of acetic acid and 1 mol of lithium acetate in a mixture of isopropanol and water with respect to 1 mol of titanium alkoxide. This mixed solvent, titanium alkoxide, isopropyl alcohol, ketjen black (Ketjen Black International Co., Ltd., trade name: ketjen black EC600JD, porosity 78 Vol.%, Primary particle size 40 nm, average secondary particle size 337.8 nm) Into the swirl reactor, and the inner cylinder is swirled with a centrifugal force of 66,000 N (kgms ^-2 ) for 5 minutes to form a thin film of the reactant on the inner wall of the outer cylinder. A chemical reaction was promoted by applying centrifugal force to obtain Ketjen Black carrying a highly dispersed lithium titanate precursor.

  The obtained Ketjen black carrying a highly dispersed lithium titanate precursor was dried at 80 ° C. for 17 hours in a vacuum to obtain a composite in which the lithium titanate precursor was carried highly dispersed by Ketjen black. A body powder was obtained.

  The composite powder in which the obtained lithium titanate precursor is highly dispersed and supported on ketjen black is rapidly heated and rapidly cooled in room temperature → 800 ° C. → 50 ° C. within one minute in a vacuum to contain lithium. Crystallization of the titanium oxide was advanced to obtain a composite powder in which lithium titanate nanoparticles were highly dispersed and supported on Ketjen Black.

  7 parts by weight of the composite powder obtained as described above, 2 parts by weight of binder (polytetrafluoroethylene), and 1 part by weight of carbon nanofiber (VGCF-S, manufactured by Showa Denko) as a conductive material. Kneaded and rolled to form a sheet. This sheet was vacuum dried and then joined to a copper foil to obtain a negative electrode.

  Further, 8 parts by weight of activated carbon (manufactured by Kuraray Chemical Co., Ltd., YP-17), 1 part by weight of binder (polytetrafluoroethylene) and 1 part by weight of ketjen black as a conductive material are kneaded and rolled to obtain a sheet. Formed. This sheet was vacuum dried and then joined to an aluminum foil to form a positive electrode.

(Comparative Example 3)
8 parts by weight of activated carbon (manufactured by Kuraray Chemical Co., YP-17), 1 part by weight of binder (polytetrafluoroethylene) and 1 part by weight of ketjen black as a conductive material were kneaded and rolled to form a sheet. . This sheet was vacuum dried and then joined to an aluminum foil to form a positive electrode and a negative electrode.

These electrodes were made to face each other through a cellulosic separator in a beaker into which LiPF ₄ and a propylene carbonate solution had been injected to produce a cell. When these cells were subjected to a charge / discharge test at a constant current and measured for energy density and power density, results as shown in FIG. 8 were obtained.

  As apparent from FIG. 8, it was found that the energy density was improved as compared with the electric double layer capacitor using the conventional activated carbon.

3 is a drawing-substituting photograph showing a TEM image of the composite of Example 1. FIG. The figure which shows the cyclic voltammogram about an Example and a comparative example. The figure which shows the result of the charging / discharging test using the electrode which concerns on this invention. The figure which shows the relationship between charging potential and an irreversible capacity | capacitance. The figure which shows the relationship between carbon amount and an irreversible capacity | capacitance. The figure which shows the relationship between a carbon amount and a capacity | capacitance reduction rate. The figure which shows the relationship between baking temperature and a capacity | capacitance. The figure which shows the relationship between energy density and power density.

Claims (15)

  In the course of a chemical reaction, a reaction method is characterized in that shear reaction and centrifugal force are applied to a reactant containing a reaction inhibitor in a swirling reactor to promote and control the chemical reaction.   In the course of a chemical reaction, shearing stress and centrifugal force are applied to reactants and carbon containing reaction inhibitors in a swirling reactor to promote and control the chemical reaction, while at the same time dispersing the product and carbon. Characteristic reaction method.   A thin film containing a reactant containing a reaction inhibitor is generated in a rotating reactor, and a shear reaction and a centrifugal force are applied to the thin film to promote and control a chemical reaction. 2. The reaction method according to 2.   The reactor comprises a concentric cylinder of an outer cylinder and an inner cylinder, and has a through-hole on the side surface of the inner cylinder, and a slat plate is disposed at the opening of the outer cylinder, and by centrifugal force due to the turning of the inner cylinder, The reactant containing the reaction inhibitor in the inner cylinder is moved to the inner wall surface of the outer cylinder through the through hole of the inner cylinder, and a thin film containing the reactant containing the reaction inhibitor is formed on the inner wall surface of the outer cylinder. 4. The reaction method according to claim 3, wherein a chemical reaction is promoted and controlled by applying a shear stress and a centrifugal force.   The reaction method according to claim 3 or 4, wherein the thin film has a thickness of 5 mm or less. The reaction method according to claim 4 or 5, wherein a centrifugal force applied to the reactant in the inner cylinder of the reactor is 1500 N (kgms ^-2 ) or more.   The reaction method according to any one of claims 1 to 6, wherein the chemical reaction is a hydrolysis reaction and / or a condensation reaction of a metal salt.   A metal oxide nanoparticle formed by the reaction method according to claim 1.   In the course of a chemical reaction, metal oxide nanoparticles generated by applying shear stress and centrifugal force to the reactant containing the reaction inhibitor in the swirling reactor, and shear stress and centrifugal force are applied in the swirling reactor. And carbon dispersed in such a manner that the metal oxide nanoparticles are supported in a highly dispersed manner.   A carbon characterized in that the metal oxide nanoparticles formed by the reaction method according to any one of claims 2 to 7 are highly dispersed and supported.   11. An electrode comprising carbon on which the metal oxide nanoparticles according to claim 9 or 10 are supported in a highly dispersed manner.   An electrochemical element using the electrode according to claim 11.   The electrochemical capacitor using the electrode according to claim 11 as a negative electrode and using a polarizable electrode as a positive electrode, wherein the metal oxide is lithium titanate.   14. The electrochemical capacitor according to claim 13, wherein ketjen black is used as the carbon of the negative electrode.   The electrochemical capacitor according to claim 14, wherein the content of ketjen black in the negative electrode is 30 to 50 wt%.