JP2002158141A - Electrode material for electrochemical capacitor, electrochemical capacitor using the same, and manufacturing method of the electrode material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively provide an electrode material for an electrochemical capacitor and an electrochemical capacitor with a large capacity. SOLUTION: At least a metallic element on which oxidation-reduction can be performed is contained in titanium oxide, hydrate oxide, or hydride thereon. An electrode material is made of a material in which an X-ray diffraction image shows an amorphous diffraction pattern, and an electrode of the electrochemical capacitor is formed using the material. When the electrode material is produced, salt, alkoxide, or chelate of titanium and the reducible metal is used as a material to produce fine particles by evaporation to dryness, coprecipitation, or sol-gel process. After the fine particles are burned to produce fine particles of the electrode material, electrochemical process is performed, in which a charging and recharging cycle is repeated in an organic electrolytic solution having lithium salt.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrode material used for an electrode of an electrochemical capacitor, an electrochemical capacitor using the same, and a method of manufacturing the electrode material.

[0002]

2. Description of the Related Art An electric double layer capacitor utilizes an electric storage effect of an electric double layer formed at an interface between two different materials, and generally includes a pair of polarizable electrodes (a positive electrode and a negative electrode) and a pair of these electrodes. Electrolyte solution impregnated in electrodes, porous separator impregnated with electrolyte and ion-permeable and electrically insulating to separate electrodes from each other to prevent short circuit, and current collector bonded to each electrode Etc.
And, for example, in the case of coin type, metal case (can)
Inside, a pair of electrodes, a separator interposed therebetween, and an electrolyte are accommodated, and a metal lid is attached to the case via a gasket having electrical insulation, so that the electrolyte leaks. Not sealed. Such an electric double layer capacitor has an intermediate characteristic between a battery and an electrolytic capacitor, and is small and has a large capacitance. Therefore, in recent years, it has attracted attention as a backup power supply for small electronic devices, for example.

In an electric double layer capacitor, polarizable electrodes are used for the positive electrode and the negative electrode as described above. As this kind of polarizable electrode, conventionally, activated carbon having a large specific surface area has been mainly used. This is because the activated carbon has a large specific surface area and the electric double layer formed on the surface has a large amount of electric charge, so that the capacitance of the electric double layer capacitor can be increased. Note that, as the electrolytic solution, a solvent having a high dielectric constant such as water or carbonates (for example, propylene carbonate) is generally used to dissolve the electrolyte at a high concentration.

[0004]

However, the specific surface area of activated carbon at present is about 3000 m ² / g at maximum at present, and the specific surface area per unit volume of an electric double-layer capacitor using this as a polarizable electrode is limited. It is said that the capacity has almost reached its limit. Therefore, as an electrode material having a larger capacity than activated carbon, ruthenium oxide having a rutile structure,
Electrochemical capacitors using amorphous hydrated ruthenium oxides and their hydrides (for example, RuO ₂ .xH ₂ O) have been proposed. However, an electrochemical capacitor using this type of ruthenium oxide as an electrode has a capacitance per volume of 10% as compared with that using activated carbon.
Although it can be increased by about 50 times, there is a problem that the material cost is high because ruthenium itself is rare.

SUMMARY OF THE INVENTION The present invention addresses the above-mentioned problems, and an object of the present invention is to provide a novel electrode which is inexpensive and has a large capacitance as an electrode material used for an electrode of an electrochemical capacitor. It is to provide materials. Another object of the present invention is to provide a manufacturing method for obtaining such an electrode material. A further object of the present invention is to obtain an inexpensive and large-capacitance electrochemical capacitor using such an electrode material.

[0006]

The present inventors have studied whether other materials than ruthenium compounds can be used as electrode materials for electrochemical capacitors, and as a result, have obtained abundant abundances more abundantly than ruthenium. Focusing on titanium oxide, which is easy to produce, containing a predetermined element and performing electrochemical treatment in an organic electrolyte containing a lithium electrolyte, a large capacity per unit volume and an inexpensive electrode material can be obtained. Was found to be.

That is, the electrode material for an electrochemical capacitor according to the present invention is composed of titanium oxide (TiO ₂ ), hydrated oxide, or a hydride thereof (hereinafter, appropriately referred to as titanium oxide or the like). It is characterized by comprising a compound containing a reducible metal element and having an X-ray diffraction image showing an amorphous diffraction pattern. The electrode material having a redox-reducible metal element-containing titanium oxide or the like as a component has a large capacity, specifically, for example, a capacity of 200 mA or more per gram of the material. Vanadium (V), chromium (C
r), manganese (Mn), iron (Fe), cobalt (C
o), nickel (Ni), copper (Cu), and the like are used. Particularly, when vanadium is used, an electrode material having a large capacity can be obtained. The content of the redox-reducible metal element is preferably 5 to 50 mol% based on the total amount of the titanium oxide and the like and the redox-reducible metal element. If the content is less than this, the capacity will not increase, and if it is too large, it will be difficult for the redox metal element to enter the titanium lattice. Further, as the content of the redox-reducible metal element increases, the capacity also increases. However, if the content exceeds 50%, manufacturing difficulties increase. In consideration of such points, the content of the redox-reducible metal element is more preferably 10 to 50 mol%.

The electrode material of the present invention is a compound having a redox-reducible metal element-containing titanium oxide or the like as a component, and is characterized by its X-ray diffraction image showing an amorphous diffraction pattern. Therefore, the X-ray diffraction image contains, as a main component, titanium oxide or the like showing a diffraction pattern of an amorphous structure (hereinafter, abbreviated as amorphous);
It is important to include a redox metal element as another component. In addition, the diffraction pattern of an amorphous structure as referred to in the present invention means a pattern in which no diffraction line is observed in an X-ray diffraction image and only a halo pattern is formed. The redox-reducible metal element does not need to be one kind. That is, it may contain a plurality of types of redox-reducible metal elements. This is supported by the fact that good results were obtained when tungsten was added as an auxiliary component in addition to vanadium in the examples of the present invention described below. In addition, when the titanium oxide before the electrochemical treatment is made into fine particles, the titanium oxide is converted into an amorphous oxide, which is not excluded.
In addition, when charge and discharge are repeated in an electrochemical capacitor using these as electrodes, titanium oxide and the like take in lithium ions and become amorphous, but this is not excluded.

The electrode material of the present invention can be produced, for example, by the following method. First, a solution containing a redox-reducible metal salt is evaporated to dryness and fired. As a result, fine particles serving as an electrode material are obtained. Next, using a pressed body or a coated body of a mixture of the fine particles (fired product) serving as the electrode material and the electron-conductive carbon powder, an electrochemical treatment of repeating charge and discharge in an organic electrolyte containing a lithium electrolyte is performed. . Thereby, the electrode material of the present invention is obtained. The fine particles serving as the electrode material can be obtained, for example, by drying and firing a solution containing titanium alkoxide, a vanadium salt, and a tungsten salt (for example, a solution of ethylene glycol-nitric acid). It can also be synthesized by another wet method such as a sol-gel method.

A titanium salt or chelate can be used instead of the titanium alkoxide, and vanadium and tungsten alkoxide or chelate can be used instead of the vanadium salt or tungsten salt. Here, as the titanium salt, for example, titanium sulfate, as the alkoxide, for example, tetraisopropoxytitanium, and as the chelate, for example, Ti (IV) acetylacetone chelate can be mentioned. As vanadium salts, for example, ammonium vanadate, vanadyl sulfate and vanadyl chloride, as alkoxides, for example, triisopropoxyvanadyl, and as chelates, for example, V
(IV) Acetylacetone chelates can be exemplified. Examples of the tungsten salt include ammonium tungstate and tungsten chloride, examples of the alkoxide include pentaisopropoxytungsten, and examples of the chelate include W (IV) acetylacetone chelate.

Further, when producing a titanium oxide or the like containing a redox-reducible metal element, the valence of the metal element is controlled (for example, the metal element is added so as to easily enter titanium oxide (TiO ₂ )). To control the valence of the compound to four)
The firing is preferably performed in an inert atmosphere or a reducing atmosphere.

[0012] The electrochemical capacitor of the present invention comprises a pair of positive and negative electrodes each having an electrode material formed on or integrally with a substrate made of an electrode material, with a porous separator interposed therebetween. In the case of being enclosed in a case together with a liquid, the positive electrode and / or the negative electrode contain the above-described redox metal element-containing titanium oxide or the like as a component, and an X-ray diffraction image shows an amorphous diffraction pattern. It is made of an electrode material. In this case, as the base of the electrode, for example, a net made of a metal such as aluminum, stainless steel, titanium, or copper, a punched metal, an expanded metal, a foam metal, or a foil is used.

As a binder for preparing a coated body of a mixture of the fine particles of the electrode material and the electron conductive carbon powder, polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVdF) or the like is used alone or mixed. Can be used.

As the electron conductive carbon powder, for example, carbon black such as acetylene black, natural graphite,
Artificial graphite, Ketjen black, and the like are used. In addition, carbon fiber, metal powder, metal fiber, and the like can be used to increase electron conductivity.

As the electrolyte, a liquid electrolyte (hereinafter referred to as "electrolyte") is usually used. As this type of electrolyte, an organic solvent-based nonaqueous electrolyte in which a solute is dissolved in an organic solvent is used. Although the solvent of the organic solvent-based electrolyte is not particularly limited, for example, ethylene carbonate (EC), propylene carbonate (P
C), butylene carbonate (BC), γ-butyrolactone (γ-BL), ethylene glycol sulphite (EGS), etc., and particularly preferred are those having a cyclic structure such as ethylene carbonate and propylene carbonate, and particularly preferred are cyclic carbonates. preferable. Examples of the solvent that can be used in combination with the above-mentioned ester include, for example, 1,2-dimethoxyethane (1,2-DME),
Examples thereof include 1,3-dioxolan (1,3-DO), tetrahydrofuran (THF), 2-methyl-tetrahydrofuran (2-Me-THF), and diethyl ether (DEE). In addition, an amine-based or imide-based organic solvent, a sulfur-containing or fluorine-containing organic solvent, and the like can also be used.

As a solute of the electrolytic solution, for example, LiCl
O_Four , LiPF₆ , LiBF_Four , LiAsF₆ , LiS
bF₆ , LiCF_Three SO_Three , LiC_Four F₉ SO_Three , Li
CF _Three CO_Two , Li_Two C_Two F_Four (SO_Three )_Two , LiN
(CF_Three SO_Two )_Two , LiC (CF_Three SO_Two )_Three , Li
C_n F_{2n + 1}SO_Three (N ≧ 2) alone or two or more
The above mixture is used. Especially LiPF₆ And LiC_Four F₉ 
SO_Three And the like are preferable because of good charge / discharge characteristics. Electric
The concentration of the electrolyte in the solution is particularly limited.
No, but 0.3 to 1.7 mol / l, especially 0.4 to 1.5
About mol / liter is preferred.

As the separator, a separator having sufficient strength and capable of holding a large amount of electrolyte is preferable. From such a viewpoint, the thickness is 10 to 50 μm and the porosity is 30.
Microporous films or non-woven fabrics made of polypropylene, polyethylene or a copolymer of ethylene and propylene of up to 70% are preferred.

[0018]

According to the production method of the present invention, for example, when vanadium is used as a redox-reducible metal element, a solution containing a vanadium salt is evaporated to dryness and then fired in an inert or reducing atmosphere. By doing so, it is considered that a fine solid solution (Ti _1-x V _x O _y ) composed of titanium oxide (TiO ₂ ) and vanadium is formed.
Using a pressed body or a coated body of a mixture of the fine particles and the electron conductive carbon powder, the titanium oxide and the vanadium are subjected to an electrochemical treatment of repeating charge and discharge in an organic electrolyte containing a lithium electrolyte. Lithium ions are taken into the fine solid solution composed of the following, and a material having high electrochemical reversibility is synthesized. And the X
Since the line diffraction image shows an amorphous diffraction pattern, it is presumed that lithium ions can easily enter and exit inside the structure, and the discharge capacity increases, as is clear from the data of Examples described later. In the case of the present invention, TiO ₂ is more readily available and less expensive than the aforementioned RuO ₂ . Thus, according to the present invention, an electrode material for an electrochemical capacitor having a large capacity per unit volume and being inexpensive can be obtained. Further, by forming an electrode with this electrode material, an inexpensive electrochemical material having a large capacity can be obtained. A capacitor will be obtained.

[0019]

Embodiments of the present invention will be described below. However, it goes without saying that the following embodiments do not limit the present invention.

A solution is prepared in advance by mixing ethylene glycol and nitric acid (16N nitric acid) at a volume ratio of 9: 1, and using this solution, a titanium compound (TiO (C ₂ H ₅ )) is prepared. ), A solution of a tungsten compound (5 (NH ₄ ) O.12WO ₃ .5H ₂ O), and a solution of a vanadium compound (NH ₄ VO ₃ ). In this case, since the solvent containing only ethylene glycol does not dissolve both the tungsten compound and the vanadium compound, the solubility was increased by mixing nitric acid with the solvent as described above. Then, the above solution is mixed with titanium (Ti), tungsten (W), and vanadium (V) by the charged composition ratio (molar ratio, the same applies to the charged composition ratio below).
i: W: V = 5: 5: 5, the components including titanium, tungsten and vanadium were mixed so that the concentration was 0.1 mol / l, and the solution was evaporated to dryness at 200 ° C. for 12 hours. Powder was obtained.

Next, the evaporated dry powder was fired at 700 ° C. for 30 minutes in an Ar inert atmosphere.

The powder obtained by this calcination, acetylene black used as a conductive additive, and polytetrafluoroethylene used as a binder were mixed in a weight ratio of 7%.
The mixture was mixed at a ratio of 9: 10: 1, and the mixture was applied on a platinum mesh which was to be a substrate (base) of an electrode material.

An aluminum lead was attached to the coated electrode thus obtained, lithium metal was used as a counter electrode, and 1M-LiPF ₆ / PC was used as an electrolytic solution. A test electrode was obtained by repeating a cycle of 1 mA charging and 3.5 V termination three times.

The obtained test electrodes are opposed to each other with a separator interposed therebetween, sandwiched between polypropylene plates, and then screwed,
Vacuum dried at 80 ° C. for 12 hours.

In this way, two electrodes are produced, and these are used as a positive electrode and a negative electrode.
Using M-LiPF ₆ / PC, a model cell was prepared by sealing with a glass cell container.

(Comparative Example) The fired powder, which had not been subjected to the electrochemical treatment, was used as the active material (electrode material) for the positive electrode and the negative electrode.
A model cell was prepared in the same manner as in the above-described example except that the model cell was used.

(Evaluation) Fabrication was performed as described above. In addition to examining the charge / discharge characteristics of the delcell, the structural analysis of the electrode material “without electrochemical treatment” (in the case of the comparative example) and the electrode material “with electrochemical treatment” (in the case of the example) was performed by X-ray diffraction. went. These results are shown in FIG. 1 and FIG. In the measurement, using a charge / discharge apparatus (TOSCAT3100U) of Toyo System, the capacity was measured when the battery was charged to 3.5 V at a constant current of 1 mA and then discharged to 0 V at a constant current of 0.1 mA. The measurement was performed at room temperature.

Referring to FIG. 1, the X-ray diffraction image shows a crystalline diffraction pattern for the electrode material “without electrochemical treatment (before electrochemical treatment)” used in the comparative example. "With electrochemical treatment (after electrochemical treatment)" used in the example
It can be seen that the electrode material of Example 2 shows an amorphous diffraction pattern. In addition, as shown in FIG. 2, in the model cell of the comparative example using the electrode material that was not subjected to the electrochemical treatment, only a very small capacity or little capacity was obtained. In the model cell of the embodiment using the electrode material subjected to the electrochemical treatment, about 7 cells per cell were used.
It was confirmed that a high capacity of 0 Wh / kg was obtained.
This is because when the electrochemical treatment is not performed, the electrode active material structure is crystalline, and since the structure does not contain lithium ions, it is predicted that charging and discharging are difficult, but the electrochemical treatment is performed. As a result, it is considered that the structure was changed to amorphous, lithium ions easily came in and out, and the capacity was significantly increased.

Finally, an example of an electrochemical capacitor to which the present invention is applied will be described. FIG. 3 is a partial cross-sectional view showing such an electrochemical capacitor. The electrochemical capacitor shown in FIG. 3 has a pair of positive and negative electrodes 10 and 11 impregnated with an electrolytic solution, and a separator 12 similarly impregnated with the electrolytic solution is provided between them. An annular gasket 13 is provided on a peripheral portion 10 a of the positive electrode 10 with a separator 12 interposed therebetween. A peripheral folded portion of the metal cap 14 is in contact with the inner peripheral side of the annular gasket 13. Then, a can 15 serving as an outer case
The annular gasket 13 is inwardly clamped by the cap 14, the inner peripheral surface of the open end of the can 15, and the peripheral portion 10 of the positive electrode 10 through the separator 12.
a, so that the opening of the can 15 is sealed. In the present invention, the pair of electrodes 10
The use of the above-mentioned electrode materials in (11) realizes a large-capacity and inexpensive electrochemical capacitor.

[0030]

As described above, according to the present invention, a titanium oxide or the like whose X-ray diffraction image shows an amorphous diffraction pattern contains a metal element that can be redox-reduced, so that a large capacity can be obtained. It is possible to obtain an inexpensive electrode material for an electrochemical capacitor, and by using this to form an electrode, an inexpensive and large-capacity electrochemical capacitor can be realized.

[Brief description of the drawings]

FIG. 1 shows X of an electrode material (electrode active material) used in an example of the present invention and an electrode material (electrode active material) used in a comparative example.
It is a line diffraction image (X-ray diffraction spectrum).

FIG. 2 is a graph showing charge and discharge characteristics of electrochemical capacitors (model cells) of Examples and Comparative Examples.

FIG. 3 is a partial cross-sectional view showing one structural example of an electrochemical capacitor to which the present invention is applied.

[Explanation of symbols]

 Reference Signs 10 electrode (positive electrode) 11 electrode (negative electrode) 12 separator 15 can (case)

Claims (5)

[Claims] An electrode material used for an electrode of an electrochemical capacitor, wherein an oxide-reducible metal element is contained in an oxide or hydrated oxide of titanium or a hydride thereof, and X An electrode material for an electrochemical capacitor comprising a compound whose line diffraction image shows an amorphous diffraction pattern. 2. The electrode material for an electrochemical capacitor according to claim 1, wherein the redox-reducible metal element is vanadium. 3. A pair of positive and negative electrodes each having the electrode material formed on or integrally with the base of the electrode material is sealed in a case together with an electrolytic solution with a porous separator interposed therebetween. An electrochemical capacitor comprising:
3. An electrochemical capacitor, wherein the electrode material according to claim 1 is used as an electrode material of the positive electrode and / or the negative electrode. 4. The electrochemical capacitor according to claim 3, wherein an organic electrolyte containing a lithium salt is used as an electrolyte. 5. A method for producing an electrode material used for an electrode of an electrochemical capacitor, comprising using a salt, an alkoxide or a chelate of each of titanium and a redox-reducible metal as a raw material, an evaporation to dryness method, a coprecipitation method. Alternatively, after preparing fine particles by a sol-gel method, firing the fine particles to prepare fine particles of an electrode material, and performing an electrochemical treatment that repeats a charge / discharge cycle in an organic electrolyte using a lithium salt as an electrolyte. Of producing an electrode material for an electrochemical capacitor.