JP2005104044A - Charging/discharging material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging/discharging material which has a high capacity and a high diffusion constant. <P>SOLUTION: This charging/discharging material comprises a conductive base material and a coating film including a hollow fiber formed on the base material and made of a chemical compound containing a titanium element. In addition, the major axis of the hollow fiber is orientated in parallel with the conductive base material and a cation can be reversibly intercalated and eliminated. Thus it is possible to obtain the charging/discharging material which shows the peak of oxidation current of not less than 0.6 mA/unit area at an intercalation/elimination rate of 400 mV/s when a proton is intercalated and eliminated. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to charge / discharge materials. The present invention can also be applied to technologies such as battery materials, proton conductors, electrochromic elements, photochromic elements, electrochemical sensors, ion immobilization materials, and rust prevention members.

    Batteries, photochromics, electrochromic characteristics, and the like are known as phenomena using intercalation accompanied by oxidation-reduction reactions of materials. For example, titanium oxide is known as a material exhibiting electrochromic and photochromic characteristics (see, for example, Non-Patent Document 1). In order to cause electrochromic, the titanium oxide electrode is subjected to cathodic polarization to intercalate protons and lithium into the oxide, resulting in coloration because the oxide itself is reduced. All of these materials have been studied as polycrystalline electrodes. In order to increase the contact area with cations, the porous formation of these materials has been studied.

By making the shape of the particles into a hollow fiber, the contact area with the outer system is increased, and therefore further improvement in charge / discharge characteristics can be expected. Regarding hollow fibers of titanium oxide or titanic acid, powder materials have already been reported (for example, see Patent Document 1 and Non-Patent Document 2). However, an example in which a hollow fiber is used as a base material has not been reported. Since the hollow fiber of the preceding example has poor dispersibility in a solvent, it is difficult to form a uniform film.
N. Sakai et al. J. Electrochem. Soc., 148, E395 (2001) Japanese Patent Laid-Open No. 10-152323 LM Peng et al., Adv. Mater. 14, 1208 (2002)

Provided is a charge / discharge material having a large capacity and a high diffusion coefficient.

  Consists of a coating containing a conductive substrate and a hollow fiber made of a compound containing titanium element, the long axis of the hollow fiber is oriented parallel to the conductive substrate, and cations are reversibly inserted into the hollow fiber. Provided is a charge / discharge material that is detachable.

  Since the hollow fiber has a large surface area, it has a large capacity during charging and a high cation diffusion coefficient during charging and discharging. Further, by orienting the long axis of the hollow fiber in parallel with the conductive substrate, the adhesion strength of the coating is improved and the contact with the conductive substrate is also increased.

  According to the present invention, there is provided a charge / discharge material that can be applied to various uses such as battery materials, proton conductors, electrochromic elements, photochromic elements, electrochemical sensors, ion immobilization materials, and rust prevention members. it can.

The charge / discharge material referred to in the present invention refers to a material that induces redox of the material itself by insertion and desorption of cations, and temporarily stores and releases energy. This characteristic is necessary for the functions such as battery, electrochromism, photochromic, electrochemical sensor, ion immobilization, and rust prevention.
The charge / discharge material of the present invention comprises a conductive substrate and a coating containing a hollow fiber made of a compound containing titanium element, and the long axis of the hollow fiber is oriented in a direction parallel to the conductive substrate. . Since the hollow fibers are oriented parallel to the conductive base material, there are advantages in that the adhesion strength is high and that many contacts with the electrodes can be obtained. Whether the hollow fiber is oriented with respect to the conductive substrate can be determined, for example, by scanning electron microscope (SEM), transmission electron microscope (TEM), atomic force microscope (AFM), etc. Can be confirmed.

  The cations inserted into and desorbed from the charge / discharge material of the present invention may be ionized in an organic solvent or an aqueous solution, or may be an electrolyte on a gel or a solid electrolyte.

As a conductive base material according to the present invention, any material can be used as long as it has electrical conductivity. For example, copper, iron, platinum, gold, silver, zinc, nickel, palladium, tungsten, lead, cobalt, aluminum, A material imparted with electrical conductivity by containing at least one metal selected from the group consisting of silicon and carbon can be used.
Further, the conductive substrate is at least one transparent selected from the group consisting of indium oxide doped with metal and fluorine, tin oxide doped with metal and fluorine, tin oxide having oxygen defects, and zinc oxide having oxygen defects Those containing various conductive compounds can also be used.

The compound containing a titanium element according to the present invention is at least one selected from titanium oxide, titanium hydroxide, titanate, and amorphous titanium oxide. When the compound containing the titanium element according to the present invention is titanium oxide, rutile type, anatase type, brookite type, and TiO ₂ (B) can be preferably used. When the compound containing the titanium element according to the present invention is titanate, polytitanic acid containing protons such as trititanic acid, tetratitanic acid, pentatitanic acid, hexatitanic acid, heptitanic acid, octatitanic acid, Polyvalent titanates such as potassium titanate, calcium titanate, cesium titanate, sodium titanate, magnesium titanate, aluminum titanate, strontium titanate, and barium titanate may be used. In a particularly preferred embodiment, the compound containing titanium element is composed of a scroll-like layered trititanic acid. The scroll-like layered trititanic acid has a high cation diffusion coefficient due to its layered structure.

  As a method for producing the hollow fiber, for example, a method of hydrothermally treating titanium oxide particles in a sodium hydroxide aqueous solution is preferably used.

As the cation that can be inserted into and removed from the hollow fiber according to the present invention, an alkali metal ion of Li ⁺ , Na ⁺ , K ⁺ , Rb ⁺ , or Cs ⁺ can be preferably used. In a particularly preferred embodiment, protons (H ⁺ ) are used. Since protons have a small ionic radius, protons can be easily inserted and desorbed, and have a high affinity for compounds containing the titanium element.

  In the charge / discharge material of the present invention, the peak of the oxidation current when protons are inserted and desorbed is 0.6 mA or more per unit area at an insertion rate of 400 mV / sec. The peak of the oxidation current can be used as an indicator of proton charge amount and diffusion rate. In a further preferred embodiment of the present invention, the peak of the oxidation current is 1.2 mA or more. When the peak of the oxidation current is 1.2 mA or more, good charge / discharge characteristics are exhibited. The oxidation current can be determined, for example, by measuring a cyclic voltammogram in an aqueous solution containing protons.

In the charge / discharge material of the present invention, the absorbance in the visible light region after cathodic polarization can also be suitably used as an indicator of the proton charge amount. When protons are intercalated by cathodic polarization, tetravalent titanium ions (Ti ⁴⁺ ) are reduced and trivalent titanium ions (Ti ³⁺ ) are generated. Since the level of Ti ³⁺ is generated in the forbidden band of the band structure, absorption appears in the visible light region of 400 nm to 900 nm, and it is colored black visually. The amount of visible light absorption can be measured by, for example, a spectrophotometer.

The hollow fiber according to the present invention has an inner diameter of 3 to 8 nm, an outer diameter of 8 to 30 nm, and a length of 100 nm to 1 μm. As described above, since the surface area is larger than that of the conventional TiO ₂ colloid, it works favorably for insertion and desorption of cations.

  The film thickness range of the coating according to the present invention is preferably 8 nm to 10 μm. The film thickness when a single layer of hollow fibers is arranged as a single particle corresponds to the outer diameter (8 nm) of the hollow fiber. Further, when the film thickness is 10 μm or less, cations sufficiently permeate, so that sufficient charge / discharge characteristics can be exhibited.

  As the method for producing the charge / discharge material of the present invention, it is particularly preferred to produce the charge / discharge material by alternately immersing the conductive substrate in the solution in which the hollow fiber is dispersed and the solution containing the cationic polymer. Since the surface of the hollow fiber is anionic, a single particle film can be easily manufactured by alternately laminating with a cationic polymer, and the film thickness can be precisely controlled by the number of immersions.

  In the manufacturing method, as a method for producing a solution in which hollow fibers are dispersed, for example, after the step of bringing the hollow fibers into contact with an acid aqueous solution, the hollow fibers can be dispersed in an aqueous amine solution. Proton is added to the inside or the surface of the hollow fiber by bringing it into contact with an acid aqueous solution and stabilized, and then a highly dispersed solution can be prepared by using an aqueous amine solution as a solvent. As a method for adding protons to the hollow fiber, a method in which the hollow fiber is brought into contact with an acid aqueous solution is preferably used. Examples of the acid used here include nitric acid, hydrochloric acid, sulfuric acid, perchloric acid, hydrofluoric acid, bromic acid, iodic acid, nitrous acid, acetic acid, and oxalic acid. Examples of the aqueous amine solution include, for example, ammonia, methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, tert-butylamine, n-pentylamine, alkylamine such as n-hexylamine, and halogenated salts thereof, or At least one selected from the group consisting of diamines such as ethylenediamine and propanediamine can be preferably used. In a more preferred embodiment, at least one of quaternary ammonium hydroxides such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide is suitably used as the amine. can do.

  In the manufacturing method, as the cationic polymer aqueous solution, polymers such as polystyrene sulfonic acid (PSS) polydiethyldiallylammonium chloride (PDDA), polyethyleneimine (PEI), polyvinyl sulfate (PVS), polyallylamine (PAH) are preferably used. can do. In order to increase the bulk of the cationic polymer, a salt such as NaCl or KCl may be added to the aqueous cationic polymer solution. Further, after the film formation, the cationic polymer may be removed. The polymer existing between the layers of the hollow fiber can be removed by heat treatment at 50 ° C to 600 ° C.

  As a method for removing the cationic polymer in the production method, ultraviolet irradiation is more preferably performed. In the process of ultraviolet irradiation, the structure of the hollow fiber is not shrunk as compared with the heat treatment, so that the proton diffusion rate of the charge / discharge material from which the cationic polymer has been removed by ultraviolet irradiation is faster.

The charge / discharge material of the present invention has high cation capacity and high mobility. The charge / discharge material of the present invention can be applied to various uses such as batteries, proton conductors, electrochromic elements, photochromic elements, electrochemical sensors, ion immobilization materials, and rust prevention members.

EXAMPLES Next, although an Example demonstrates this invention concretely, it is not restrict | limited to these Examples at all.
1. 1. Preparation of charge / discharge material 1-1. Production of hollow fiber 0.64 g of titanium oxide powder (trade name P25, Nippon Aerosil Co., Ltd., average primary particle size of about 25 nm, specific surface area of about 55 m ^{2 /} g) was put into 80 ml of 10M sodium hydroxide aqueous solution, and placed in a glass rod. For 1 minute to obtain a white suspension. This white suspension was placed in a 100 ml fluororesin container, and the fluororesin container was placed in a stainless steel container. This stainless steel container was put in a drier and kept at 110 ° C. for 20 hours. After completion of the reaction, the stainless steel container was allowed to cool naturally to room temperature, and a solution containing a white precipitate was collected. As a washing step, the supernatant was first removed from the solution containing the white precipitate with a dropper. To the remaining white precipitate, 100 ml of 0.1 M hydrochloric acid aqueous solution was added little by little. After the entire amount of aqueous hydrochloric acid was added, the mixture was allowed to stand at room temperature (20 ° C.) for 3 hours. After standing, the supernatant was removed. This washing step was performed three times in total, and it was confirmed that the supernatant liquid had a pH of 7 or less. After these neutralization operations, the remaining white precipitate was washed twice with distilled water to obtain a white powder. When this white powder was observed with a scanning transmission electron microscope (Hitachi, Ltd., STEM S-5200), at a magnification of 150,000 times, the white powder obtained by this method was an aggregate of hollow fibers. It was confirmed that the center part of the fiber had a hollow structure with a diameter of 3 to 5 nm.

1-2. Preparation of solution containing hollow fiber The white powder prepared by the above method was added to 64 ml of a 2M nitric acid aqueous solution, and stirred with a magnetic stirrer at room temperature for 15 hours. After stirring, the obtained translucent solution was centrifuged at 5000 rpm for 30 minutes with a centrifuge (Sakuma Seisakusho M200-IVD) to obtain a white gel with added protons. Furthermore, this white gel was added to an aqueous solution of 0.1 M tetrabutylammonium hydroxide and stirred with a magnetic stirrer at room temperature for 24 hours to obtain a translucent solution. Further, 100 mmol of hydrochloric acid was added to this solution to adjust the pH to 9.5.

1-3. Preparation of cationic polymer aqueous solution Polyethyleneimine (0.25 g) was dissolved in water (97.5 g) to prepare an aqueous solution having a concentration of 2.5%.
In addition, an aqueous PDDA solution was prepared as a different cationic polymer. A 10% aqueous solution of PDDA (Aldrich) was diluted 20 times with pure water to prepare a 0.25% PDDA aqueous solution. Further, 0.1 M tetrabutylammonium hydroxide aqueous solution was added to this aqueous solution to adjust the pH to 9.5.

1-4. Immobilization on a base material and production of an electrode Using fluorine-doped SnO ₂ coated glass (Nippon Sheet Glass) as a base material, it was ultrasonically cleaned with ethanol and then washed with pure water. This substrate was partially masked for electrode extraction, immersed in the polyethyleneimine aqueous solution for 10 minutes, and then washed with pure water. Further, it was immersed in the solution containing the hollow fiber for 10 minutes and washed with pure water. Further, this substrate was immersed in an aqueous PDDA solution for 10 minutes and washed with pure water. Thereafter, immersion in a solution containing a hollow fiber and an aqueous PDDA solution and washing were repeated to produce a thin film having six hollow fiber layers. The hollow fiber is exposed on the outermost surface. The resulting thin film was subjected to heat treatment at 400 ° C. for 1 hour in the air or ultraviolet irradiation to remove the interlayer cationic polymer. UV irradiation was performed using a 200 W mercury-xenon lamp (LA-210UV, manufactured by Hayashi Watch Industry) for 24 hours. The masking part of the obtained sample and the copper wire were connected using a silver paste, and the connection part was covered with an epoxy resin. The area of the hollow fiber electrode produced as described above is 4.5 cm ² .

1-5. Preparation of Comparative Example The conductive base material cleaned by the cleaning method was dip coated with a titanium alkoxide solution (Nippon Soda, model number: NDH510C). The lifting speed of the dip coat was 5 cm / min. After dip coating, baking was performed in the atmosphere at 500 ° C. for 30 minutes, and anatase-type titanium oxide electrodes were produced in the same manner as in 1-4. The area of the titanium oxide electrode produced as described above was 4.5 cm ² .

2. Structure observation by SEM The surface and cross section were observed with a scanning electron microscope (SEM: Hitachi, Ltd., S-800) for the charge / discharge materials of the present invention and comparative examples. The results are shown in FIG. 1, whereas the particles constituting the anatase-type TiO ₂ thin film of the comparative example are spherical, whereas the thin film of the example is composed of an anisotropic hollow fiber. It was also confirmed that the long axis of the hollow fiber was oriented parallel to the substrate. The film thickness is 50 nm for the six laminated hollow fibers, and 70 nm for the comparative anatase TiO ₂ thin film.

3. Measurement of cyclic voltammogram The cyclic voltammogram in the electrolyte was measured with a potentiostat (Hokuto Denko, HSV-100) for the hollow fiber electrode and the anatase TiO ₂ electrode of the comparative example. The electrolyte was adjusted to a standard phosphate buffer (Wako Pure Chemical Industries, Ltd.) so that Na ₂ SO ₄ had a concentration of 0.1 mol / L. A hollow fiber and an anatase TiO ₂ electrode were connected to the working electrode of the potentiostat, a platinum wire was used as the counter electrode, and a silver-silver chloride electrode was used as the reference electrode. When measuring the cyclic voltammogram, the electrolyte was bubbled with nitrogen. The voltage pulling speed was 50, 100, 200, and 400 mV / sec.
The relationship between current and voltage is shown in FIG. The reduction current that flows when cathodic polarization is attributed to proton intercalation and hydrogen generation. On the other hand, the oxidation current when a reverse potential is applied to the anode is due to reoxidation of intercalated protons. The magnitude of this oxidation current can be used as an indicator of proton charge and diffusion rate. As a result, both of the hollow fiber coating irradiated with UV and the one heat-treated at 400 ° C. exhibited higher oxidation currents than the comparative example. The peak of the oxidation current per unit area at an insertion speed of 400 mV / sec is 2.00 mA when the hollow fiber is irradiated with UV, 1.26 mA when the hollow fiber is heat-treated at 400 ° C., anatase type TiO of the comparative example ₂ was 0.57 mA. That is, it was suggested that the charge / discharge material of the present invention has a higher proton charge amount and a higher proton diffusion rate than conventional TiO ₂ . In particular, the oxidation current of the hollow fiber irradiated with UV is high, but it is expected that protons are more likely to diffuse because the hollow fiber structure does not shrink than the heat treated at 400 ° C.

4). Evaluation of coloration during cathodic polarization Cathode polarization in an electrolyte using a potentiostat (Hokuto Denko, HSV-100) for a hollow fiber electrode irradiated with ultraviolet light and a comparative anatase TiO ₂ electrode . The voltage was -1.5V and the polarization time was 5 minutes. Similarly to the measurement of the cyclic voltammogram, an electrolyte was prepared in a standard phosphate buffer (Wako Pure Chemical Industries) so that Na ₂ SO ₄ had a concentration of 0.1 mol / L. A hollow fiber and anatase TiO ₂ electrode were connected to the working electrode of the potentiostat, a platinum wire was used as the counter electrode, and a silver-silver chloride electrode was used as the reference electrode. After cathodic polarization, immediately after washing with pure water and drying with a blower, the absorbance of the electrode was measured with an ultraviolet-visible spectrophotometer (JASCO, Ubest-55).
The results are shown in FIG. It was revealed that the hollow fiber electrode has a larger absorption in the visible light region. That is, it was suggested that the charge / discharge material of the present invention can insert a larger amount of protons than conventional titanium oxide by cathodic polarization.

  The charge / discharge material of the present invention can be applied to uses such as battery materials, proton conductors, electrochromic elements, photochromic elements, electrochemical sensors, ion immobilization materials, and rust prevention members.

It is a figure which shows the SEM photograph of the cross section of the charging / discharging material of this invention. It is a figure which shows the cyclic voltammogram of the charging / discharging material of this invention. It is a figure which shows the light absorption characteristic of the charging / discharging material of this invention.

Claims (9)

A conductive base material and a coating containing a hollow fiber made of a compound containing titanium element provided on the conductive base material, and the long axis of the hollow fiber is oriented parallel to the conductive base material. A charge / discharge material, wherein cations can be reversibly inserted and removed from the hollow fiber. The charge / discharge material according to claim 1, wherein the compound containing the titanium element is at least one selected from titanium oxide, titanium hydroxide, titanate, and amorphous titanium oxide. The charge / discharge material according to claim 1, wherein the compound containing the titanium element is a scroll-like layered trititanic acid. The charge / discharge material according to any one of claims 1 to 3, wherein a cation that can be inserted into and removed from the hollow fiber is a proton. 5. The charge / discharge material according to claim 4, wherein the peak of the oxidation current when the proton is inserted and desorbed is 0.6 mA or more per unit area at an insertion speed of 400 mV / sec. The charge / discharge material according to any one of claims 1 to 5, wherein the hollow fiber has an inner diameter of 3 to 8 nm, an outer diameter of 8 to 30 nm, and a length of 100 nm to 1 µm. The charge / discharge material according to any one of claims 1 to 6, wherein the film thickness is in a range of 8 nm to 10 µm. It is a method of manufacturing the charging / discharging material as described in any one of Claims 1-7, Comprising: A conductive base material is immersed in the solution in which the said hollow fiber was disperse | distributed, and the solution containing a cationic polymer alternately. The manufacturing method of the charging / discharging material characterized by having the process laminated | stacked by this. It is a manufacturing method of the charging / discharging material of Claim 8, Comprising: The ultraviolet irradiation is performed after the process of laminating | stacking the said hollow fiber and a cationic polymer, The manufacturing method of the charging / discharging material characterized by the above-mentioned.

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