JP6328100B2 - Battery electrode material and battery substrate, storage battery, dye-sensitized solar cell, capacitor, Li ion secondary battery using the same - Google Patents

Description

  Embodiments of the present invention generally relate to battery electrode materials and battery substrates, storage batteries, dye-sensitized solar cells, capacitors, and Li ion secondary batteries using the same.

  Solar cells using sunlight are attracting attention as clean electric energy. As solar cells, those using a single crystal silicon substrate or a polycrystalline silicon substrate are mainly used because of their excellent power generation efficiency. In addition, the use of thin-film amorphous silicon obtained by reducing the thickness of a silicon substrate has been studied for cost reduction. As these non-silicon solar cells, compound semiconductor solar cells using gallium, arsenic, phosphorus, germanium, indium, or the like are also widely known.

  Conventional solar cells have a problem that they are not easily spread due to the high production cost due to the large size of the silicon substrate that receives sunlight and the complexity of the compound synthesis process. On the other hand, for the purpose of reducing production costs, development of organic solar cells using an organic compound in a light absorption layer (photoelectric conversion layer) has been promoted. Among organic solar cells, development of dye-sensitized solar cells using dyes is expected.

  In addition, power generation systems such as solar power generation, thermal power generation, wind power generation, and nuclear power generation can produce electricity but cannot store electric power. Therefore, it is important to proceed with the construction of a system that can store electricity. As an example of a system for storing electricity, there are various types such as a Li ion secondary battery and a capacitor. For example, in Japanese Unexamined Patent Publication No. 2006-261008 (Patent Document 1), various metal oxides are used for a positive electrode material or a negative electrode material. A battery using Li ions, such as a Li ion secondary battery, uses a material capable of delivering Li ions to the positive electrode material or the negative electrode material.

JP 2006-261008 A JP 2012-252872 A JP 2007-335361 A

  Li ion is common to dye-sensitized solar cells and Li ion secondary batteries. That is, a material that can efficiently deliver Li ions is required as a battery electrode material. However, conventional materials are not always satisfactory in properties, and further improvements have been required.

  The problem to be solved by the present invention is to provide a battery electrode material that can reduce internal resistance because it has a high Li storage capacity as a battery electrode material and is efficient in delivering Li ions. .

The battery electrode material according to the embodiment is a battery electrode material made of tungsten oxide powder, wherein the tungsten oxide powder has a hexagonal crystal structure at least partly or entirely, and the tungsten oxide powder has a BET specific surface area of 1 m. ² / g or more der is, when the composition of the tungsten oxide powder was WO _3-[delta], it is characterized in that it is 0.02 ≦ δ ≦ 0.40.

It is a mimetic diagram for illustrating a storage battery concerning an embodiment of the present invention. It is a mimetic diagram for illustrating a capacitor concerning an embodiment of the present invention.

The battery electrode material according to the embodiment is a battery electrode material made of tungsten oxide powder, wherein the tungsten oxide powder has a hexagonal crystal structure at least partly or entirely, and the tungsten oxide powder has a BET specific surface area of 1 m. ² / g or more der is, when the composition of the tungsten oxide powder was WO _3-[delta], it is characterized in that it is 0.02 ≦ δ ≦ 0.40.

Here, the tungsten oxide powder is preferably tungsten trioxide (WO ₃ ). The tungsten trioxide is suitable if the stoichiometric ratio is close to that of WO ₃ , and specifically, if it is in the range of WO _{2.6 to 3.0} , it is regarded as tungsten trioxide. To do.

  The tungsten oxide powder is characterized by having a hexagonal crystal structure at least partially or entirely. Tungsten oxide has various crystal structures such as monoclinic, triclinic and hexagonal. As a battery electrode material, it is necessary that the tungsten oxide powder has at least a part or all of the hexagonal crystal structure. This indicates that there is a portion having a hexagonal crystal structure in one grain of tungsten oxide powder.

By providing the tungsten oxide powder, particularly tungsten trioxide (WO ₃ ) powder, with a hexagonal crystal structure, it is possible to efficiently deliver Li ions and improve the electrode reaction. Tungsten trioxide having a hexagonal crystal structure has a tunnel structure that becomes a diffusion channel of Li ions composed of a six-membered ring of WO ₆ octahedron inside the crystal structure, so that the diffusion of Li in the crystal is fast. Thus, the internal resistance during the charge / discharge reaction can be reduced. In addition, by speeding up the diffusion of Li, various batteries (storage battery, dye-sensitized solar cell, capacitor, Li ion secondary battery) using the tungsten oxide (WO ₃ ) powder according to the embodiment have a higher charge / discharge speed ( It is possible to discharge in a short time and charge in a short time).

As a method of measuring the internal resistance, it can be obtained by a direct current method. This measurement method is a method of calculating internal resistance by performing discharge at a constant current and performing the current density at the time of discharge at two or more levels. Specifically, the internal resistance is calculated from the relationship between the current density during discharge and the discharge start voltage. According to the present embodiment, the internal resistance can be measured in a state where the capacitor is constructed as a capacitor or battery cell incorporating WO ₃ as an electrode. Further, since the diffusion channel also becomes a space for storing Li, about twice as much Li can be stored as compared with monoclinic WO ₃ . When the amount of Li that can be stored is expressed in the form of Li _x WO ₃ , the monoclinic crystal can satisfy x <0.67, whereas the hexagonal crystal structure can satisfy 0 <1.34. Therefore, it is preferable that the tungsten oxide powder has a hexagonal crystal structure of 50% or more by volume, and further 90 to 100%. If the hexagonal crystal structure can be made 50% by volume or more, the x value indicating the amount of Li can be made 0.67 or more. Note that the upper limit of the x value in Li _x WO ₃ is not particularly limited.

  The ratio of hexagonal crystals in the tungsten oxide powder can be determined from the intensity value of the XRD diffraction peak. Here, in order to identify the hexagonal crystal by the XRD diffraction method, it is necessary to match at least five diffraction peaks. From the low angle side, (100), (001), (110), (101), (200 ). Typically, 2θ is 14.01 ± 0.10 °, 27.80 ± 0.10 °, 24.39 ± 0.10 °, 24.86 ± 0.10 °, and 28.23 ± 0. 10 °.

  By comparing these peak intensities with the peak intensities of crystal systems other than hexagonal crystals, the ratio of hexagonal crystals can be determined. Examples of crystals other than hexagonal crystals include monoclinic crystals and cubic crystals. In particular, when exposed to a high temperature of about 370 ° C. or higher, more preferably 500 ° C. or higher, it tends to change to monoclinic crystals.

  In the case of a monoclinic crystal, five peaks (002), (020), (200), (022), and (202) are detected. For example, when both hexagonal crystals and monoclinic crystals exist, the volume ratio of hexagonal crystals can be obtained by obtaining the strongest peak ratio of each. The volume ratio can be calculated by taking an average of the three XRD diffraction intensity values of the three strongest peaks in each of the hexagonal and monoclinic crystal systems and calculating based on a calibration curve measured in advance in both crystal systems. Here, calculation is performed using three peaks of (100), (001), and (200) as hexagonal crystals and three peaks of (002), (020), and (200) as monoclinic crystals. To do.

Further, when the tungsten oxide powder is subjected to Raman spectroscopic analysis, it is preferable that an intensity peak is detected at 690 ± 10 cm ⁻¹ or / and 780 ± 10 cm ⁻¹ . The peak at 780 ± 10 cm ⁻¹ is preferably a sharp peak. As a sharp peak, a half-value width of 50 cm ⁻¹ or less is preferable. When the half width is 50 cm ⁻¹ , or 40 cm ⁻¹ or less, the crystallinity is good. Good crystallinity means that there are no crystal lattice distortions or defects. Due to the improvement in crystallinity, Li can be delivered more efficiently.

Further, it is preferable that no intensity peak is detected at 950 ± 10 cm ⁻¹ . An intensity peak of 950 ± 10 cm ⁻¹ indicates the presence of a hydrate of tungsten oxide powder (WO ₃ ). If a hydrate is present, it may not be suitable for the electrode material depending on the application.

In addition, if the crystallinity is insufficient or hydrates are mixed, the storage capacity is reduced. Also, depending on the application (battery type), there is a possibility that the charge / discharge cycle characteristics may be reduced. In other words, a tungsten oxide (WO ₃ ) powder that has good crystallinity and does not contain hydrates is preferable. As a method for examining the presence of such crystallinity and hydrate, Raman spectroscopy is suitable.

The Raman spectroscopic analysis is performed by the following method. For the apparatus, PDP-320 manufactured by Photon Desing is used. Measurement conditions are: microscopic Raman, measurement magnification of 100 times, beam diameter of 1 μm or less, light source Ar ⁺ laser (wavelength 514.5 nm), laser power 0.5 mW (at tube), diffraction grating Single 600 gr / mm, cross slit 100 μm , Slit 100 μm, detector CCD / Roper 1340 channel. Under this condition, 100 to 1500 cm ⁻¹ is analyzed. The sample form can be measured as tungsten oxide particles.

The tungsten oxide powder preferably has a BET specific surface area of 1 m ² / g or more. When the BET specific surface area is less than 1 m ² / g, the particle size becomes unnecessarily large, so that it may be difficult to make hexagonal crystals with a volume ratio as described above of 50% or more. Therefore, the BET specific surface area is preferably 10 m ² / g or more. In addition, although the upper limit of the BET specific surface area of tungsten oxide powder is not specifically limited, It is preferable that it is 60 m < ² > / g or less. In the case of tungsten oxide (WO ₃ ) powder having a hexagonal crystal structure, since the diffusion rate of Li in the solid is high, the particle size is relatively large, and the internal resistance can be reduced even with a low specific surface area.

In addition, in the case of the tungsten oxide (WO ₃ ) powder having a hexagonal crystal structure according to the embodiment, the powder may have pores. In this case, there is a possibility that the particle size and the specific surface area are not necessarily consistent. That is, even when the apparent particle size is large, the specific surface area may be large when pores are present inside. The particle diameter is preferably 100 μm or less from the relationship of the film thickness of the electrode layer.

  A metal oxide may be provided on the surface of the tungsten oxide powder. The metal oxide provided on the surface may be a part of the surface of the tungsten oxide powder or the entire surface. As will be described later, the battery electrode material according to the embodiment can be used as an electrode material for various batteries such as a storage battery, a dye-sensitized solar battery, a capacitor, and a Li ion secondary battery. As an example of the usage method, a porous electrode layer may be formed using a battery electrode material (powder). At this time, if a metal oxide film is provided, the bonding force between battery electrode materials (powder) can be increased. When the bonding strength is increased, the resistance of the bonding portion between the battery electrode materials (powder) of the porous electrode layer can be reduced.

  Metal oxides include indium oxide, yttrium oxide, titanium oxide, tin oxide, zirconium oxide, magnesium oxide, aluminum oxide, cerium oxide, thulium oxide, manganese oxide, tantalum oxide, niobium oxide, lanthanum oxide, ITO, and oxide. Examples thereof include scandium, samarium oxide, neodymium oxide, and gadolinium oxide. Among these, indium oxide and yttrium oxide are preferable.

  The battery electrode material according to the embodiment as described above can be applied to various batteries.

  First, the present invention is applied to a battery substrate having a porous electrode layer made of the battery electrode material according to the embodiment. The porous electrode layer preferably has a thickness of 1 μm or more and a porosity of 20 to 80% by volume.

  Examples of the substrate used for the battery substrate include a glass substrate and a metal substrate. When a glass substrate is used, an electrode layer is formed on the surface. The electrode layer is preferably a transparent conductive film such as ITO or ATO as the electrode layer in order to obtain a battery in which light needs to reach the porous electrode layer. Moreover, when using for the battery in which light does not need to reach a porous electrical layer, a thing without transparency, such as a metal film, may be sufficient as an electrode layer. In addition, when used in a battery that does not require light to reach the porous electrode layer, use a metal substrate that is resistant to corrosion by the electrolyte, such as titanium (Ti), ruthenium (Ru), and tungsten (W). A structure without an electrode layer may be employed. In the case of using a metal substrate, an insulating film is provided on the back surface side (side where the porous electrode layer is not provided) to ensure insulation.

  It is preferable to form a porous electrode layer having a thickness of 1 μm or more and a porosity of 20 to 80% by volume on the electrode layer or the metal substrate. If the thickness of the porous electrode layer is less than 1 μm, the porous electrode layer is too thin to improve the power generation capacity or the storage capacity. Further, when the porosity is less than 20% by volume, the ratio of the voids is small, so that there is a possibility that the electrolyte does not sufficiently enter the porous electrode layer. On the other hand, when the porosity exceeds 80% by volume, the amount of battery electrode material in the porous electrode layer is relatively small, and thus the power generation capacity or the storage capacity is not improved. Therefore, the porosity should be in the range of 20 to 80% by volume, and more preferably in the range of 30 to 70% by volume.

  For adjusting the thickness and porosity of the porous electrode layer, a first method is to paste a battery electrode material (tungsten oxide powder) and apply and dry. It is effective to adjust the content of the battery electrode material in the paste, the paste viscosity, the drying speed, and the like. It is also effective to repeat these steps.

  In addition, the thickness of the porous electrode layer is measured using an arbitrary cross section corresponding to a viewing angle of the porous electrode layer of at least “thickness of 1 μm or more × width of 10 μm” at the upper end of the porous electrode layer (in contact with the conductive film). Take an enlarged photo (magnification of 5000 times or more) so that you can see the surface opposite to the surface, and take an enlarged photo 1. In the enlarged photo 1, measure the thickness of any part at three locations, and calculate the average value. Let it be the thickness (film thickness).

  In addition, the measurement of the porosity of the porous electrode layer has been expanded so that the upper end portion of the porous electrode layer can be seen in an arbitrary cross section corresponding to a viewing angle of the porous electrode layer of at least “thickness 1 μm or more × width 10 μm” Take a picture (magnification of 100,000 or more) and take an enlarged picture 2. It is possible to distinguish the battery electrode material (tungsten oxide powder) and the gap from the contrast of the enlarged photograph 2. From the enlarged photograph 2, the area of the gap corresponding to “unit area 1 μm × 3 μm” is obtained. When “unit area 1 μm × 3 μm” cannot be photographed in one field of view, photographing is performed a plurality of times until the total becomes “unit area 1 μm × 3 μm”.

  Moreover, the battery substrate provided with the porous electrode layer as described above is suitable for a dye-sensitized solar cell or a storage battery.

  As a dye-sensitized solar cell, a dye is adsorbed on a porous electrode layer and used. Moreover, the general structure of a dye-sensitized solar cell is illustrated by Unexamined-Japanese-Patent No. 2012-252872 (patent document 2) etc. The dye-sensitized solar cell using the battery substrate according to the embodiment can obtain an excellent power generation efficiency of 3% or more.

  The storage battery is illustrated in FIG. In the figure, 11 is a storage battery, 12 and 13 are electrode parts, 14 is a sealing part, 15 is a power storage part, 16 is an electrolyte, 17 is a protection part, and 18 is a reduction part.

  The storage battery 11 includes an electrode part 12 (corresponding to an example of a first electrode part), an electrode part 13 (corresponding to an example of a second electrode part), a sealing part 14, a power storage part 15, an electrolytic solution 16, A protection unit 17 and a reduction unit 18 are provided.

The electrode portion 12 has a plate shape and is made of a conductive material. The electrode part 12 can be formed from metals, such as aluminum, copper, stainless steel, platinum, for example. The electrode portion 13 has a plate shape and is provided to face the electrode portion 12. The electrode part 13 is formed from the material which has electroconductivity. The electrode part 13 can be formed from metals, such as aluminum, copper, stainless steel, platinum, for example. In this case, the electrode part 12 and the electrode part 13 can also be formed from the same material, and the electrode part 12 and the electrode part 13 can also be formed from different materials. The electrode portions 12 and the electrode portion 13, for example, ITO, IZO (Indium Zinc Oxide ), FTO (Fluorine-doped Tin Oxide), may be used a conductive film made of a SnO 2, InO _3.

  Moreover, the electrode part 12 and the electrode part 13 are provided on a board | substrate (not shown). Examples of the substrate include a glass substrate and an insulated metal substrate.

  In addition, the electrode part 13 on the side where the power storage part 15 made of a porous electrode layer is provided serves as a negative electrode. Moreover, the electrode part 12 which opposes the electrode part 13 used as the negative electrode is a positive electrode.

  The sealing part 14 is provided between the electrode part 12 and the electrode part 13 and seals the peripheral part of the electrode part 12 and the peripheral part of the electrode part 13. That is, the sealing part 14 is provided so as to surround the inside of the storage battery 11 along the periphery of the electrode part 12 and the electrode part 13, and the inside of the storage battery 11 is joined by joining the electrode part 12 side and the electrode part 13 side. To seal. Moreover, the thickness of the sealing part 14 is not particularly limited, but is preferably in the range of 1.5 to 30 times the thickness of the power storage part 15 (porous electrode layer). Since the thickness of the sealing portion 14 becomes a space for filling the electrolyte solution 16, it is preferable to have a predetermined range. If it is less than 1.5 times, the electricity stored in the electricity storage unit 15 is easily released, and if it exceeds 30 times, it is difficult to take out the electricity stored in the electricity storage unit 15.

  The sealing part 14 can be comprised so that a glass material may be included. The sealing portion 14 can be formed using, for example, a glass frit that is made into a paste by mixing powder glass, a binder such as an acrylic resin, an organic solvent, or the like. Examples of the powder glass material include vanadate glass and bismuth oxide glass. In this case, the sealing portion 14 can be formed by applying paste-like glass frit to a portion to be sealed and firing it. And the sealing part 14 can be melted by heating the sealing part 14, and sealing can be performed. For example, sealing can be performed by irradiating the formed sealing portion 14 with laser light and melting a portion of the sealing portion 14 irradiated with the laser light. In addition, the sealing part 14 is not necessarily limited to what contains a glass material. For example, the sealing part 14 may include a resin material and be bonded between the electrode part 12 and the electrode part 13.

  The power storage unit 15 is provided inside the sealing unit 14 and on the surface of the electrode unit 13 facing the electrode unit 12. The power storage unit 15 is provided on the electrode unit 13 via the protection unit 17.

  Further, the electrolytic solution 16 is provided inside the sealing portion 14. That is, the electrolytic solution 16 is filled in a space defined by the electrode part 12, the electrode part 13, and the sealing part 14. The electrolytic solution 16 can be, for example, an electrolytic solution containing iodine. As the electrolytic solution 16, for example, a solution obtained by dissolving lithium iodide and iodine in a solvent such as acetonitrile can be used. Moreover, it is preferable that the density | concentration of lithium iodide is the range of 0.5-5 mol / L, and the density | concentration of iodine is the range of 0.01-5 mol / L.

  The protection unit 17 has a film shape and is provided between the power storage unit 15 and the electrode unit 13. The protection part 17 is provided so as to cover the surface of the electrode part 13 defined by the sealing part 14. The protection part 17 is provided in order to prevent the electrode part 13 from being corroded by the electrolytic solution 16. Therefore, the protection part 17 is formed from a material having conductivity and chemical resistance against the electrolytic solution 16. The protection part 17 can be made of, for example, carbon or platinum. The thickness dimension of the protection part 17 can be about 100 nm, for example. In addition, when the electrode part 13 is formed from the material which has chemical resistance with respect to the electrolyte solution 16, the protection part 17 does not necessarily need to be provided.

The reducing unit 18 has a film shape and is provided to cover the surface of the electrode unit 12 defined by the sealing unit 14. The reducing unit 18 is provided to reduce ions contained in the electrolytic solution 16. For example, the reducing unit 18 reduces I ₃ ⁻ ions (triiodide ions) contained in the electrolytic solution 16 to I ⁻ ions (iodide ions). Therefore, the reducing part 18 is formed from a material that takes into consideration conductivity, chemical resistance to the electrolytic solution 16 and reduction of ions contained in the electrolytic solution 16. The reducing unit 18 can be formed of, for example, carbon or platinum. The thickness dimension of the reduction part 18 can be about 80 nm, for example.

Further, such storage battery to the power storage capacity 1000 C-/ ^{m 2} or more, further it is also possible to 10000C / ^{m 2} or more. Moreover, the storage battery 11 shall cover the outer periphery with an insulating member (not shown).

  Moreover, the battery electrode material according to the embodiment is also suitable for an electrode material of a Li ion secondary battery. A general structure of a Li ion secondary battery is exemplified in Japanese Patent Application Laid-Open No. 2007-335361 (Patent Document 3). The battery electrode material of the embodiment can be used for either the positive electrode or the negative electrode, but the charge capacity can be improved by using it for the negative electrode. In other words, when the battery electrode material according to the embodiment is used for a Li ion secondary battery, it is preferably used for a negative electrode. Moreover, when using for the negative electrode of a Li ion secondary battery, mixing with carbon powder and using it is also effective.

  The battery electrode material according to the embodiment can also be used for a capacitor. FIG. 2 illustrates a capacitor. In the figure, 22 is a capacitor, 23 is an electrode layer (negative electrode side electrode layer), 24 is a negative electrode layer, 25 is a separator layer, 26 is a positive electrode layer, and 27 is an electrode layer (positive electrode side electrode layer).

  The electrode layer 23 and the electrode layer 27 are made of a conductive metal such as an aluminum foil. A negative electrode layer 24 is provided on the electrode layer 23. The negative electrode layer 24 uses the battery electrode material according to the embodiment. At this time, a porous electrode layer made of a battery electrode material (tungsten oxide powder) is preferable. The porous electrode layer preferably has a thickness of 1 μm or more and a porosity of 20 to 80% by volume.

Next, a separator layer is formed. The separator layer is a layer in which the negative electrode layer 24 and the positive electrode layer 26 are provided with a gap at regular intervals and impregnated with an electrolytic solution. The separator layer is made of, for example, a polyethylene porous film, and is preferably impregnated with an electrolytic solution containing Li ions. In addition, a positive electrode layer 26 and an electrode layer 27 are provided on the separator layer 25. The positive electrode layer 26 may be a porous layer made of a Li composite oxide such as LiCoO ₂ .

Next, a separator layer is provided. The separator layer is a layer in which the negative electrode layer 24 and the positive electrode layer 26 are provided with a gap at regular intervals and impregnated with an electrolytic solution. The separator layer is made of, for example, a polyethylene porous film or a polypropylene porous film, and is preferably impregnated with an electrolytic solution containing Li ions. Further, a positive electrode layer 26 and a current collector layer 27 are provided on the separator layer 25. The positive electrode layer 26 is formed of a porous layer made of LiCoO ₂ , LiMnO ₂ , LiNiO ₂ and a Li composite oxide having a mixed composition thereof.

  Moreover, various things, such as an organic solvent and an ionic liquid, are applicable as electrolyte solution. Examples of the organic solvent include propylene carbonate, ethylene carbonate, and γ-butyl lactone. Examples of the ionic liquid include ethyl methyl imidazolium bistrifluoromethanesulfonate.

  The capacitor has such a laminated structure. It is also possible to improve the storage capacity by stacking a plurality of such stacked structures. Further, a long laminated structure may be wound to improve the storage capacity. In addition, when a capacitor is used, such a laminated structure is stored in a storage container (such as a metal can).

With such a capacitor, the initial electric capacity can be 50 mAh / g or more. In addition, the capacity retention rate after repeating charge and discharge 1000 times can be improved to 50% or more. Also, the internal resistance value can be reduced to 22 Ω · cm ² or less. If the electric capacity is improved, the amount of WO ₃ powder used can be reduced for the same electric capacity. In other words, when the usage amount of the WO ₃ powder is the same, a capacitor having a high electric capacity can be produced. In addition, the speed of electricity exchange with the WO3 powder can be increased by reducing the internal resistance value. That is, there is an effect that a capacitor with high instantaneous power can be manufactured.

  As described above, the battery electrode material according to the embodiment can be suitably used for electrode materials for storage batteries, dye-sensitized solar cells, Li ion secondary batteries, and capacitors. In particular, when applied to a battery using an electrolytic solution containing Li ions, the power generation efficiency and power storage efficiency of the battery can be significantly increased.

  Next, the manufacturing method of the battery electrode material according to the embodiment will be described. As long as the battery electrode material according to the embodiment has the above-described configuration, the manufacturing method is not particularly limited, but the following method may be mentioned as a method for efficiently manufacturing.

  First, in order to produce tungsten oxide powder having a hexagonal crystal structure, a synthesis method using a liquid phase reaction is preferable. There is a synthesis method using a plasma flame for producing tungsten oxide powder, but exposure to a high temperature of 500 ° C. or more is not preferable because the hexagonal crystal is likely to change to a monoclinic crystal. Therefore, it is preferable to use a low-temperature reaction using a liquid phase reaction and a heat treatment temperature of less than 500 ° C. during the production process. In order to further promote the growth in the liquid phase, a production method using a hydrothermal reaction under pressure is also possible. Moreover, you may implement the heat processing below 500 degreeC in air | atmosphere.

Moreover, as a manufacturing method using a liquid phase reaction, there are various methods, but the following method is given as an example. Tungstic acid (H ₂ WO ₄ ) is used as a starting material, and the pH is adjusted using an alkaline solution such as sodium hydroxide (NaOH) and an acidic solution such as ammonium hydrogen carbonate (NH ₄ HCO ₃ ). Thereafter, heat treatment is carried out in an autoclave container (hydrothermal reaction) to promote the reaction and to produce.

Alternatively, tungsten oxide can be precipitated by dissolving metallic tungsten with aqueous hydrogen peroxide and adjusting the pH with ammonia, hydrochloric acid, or the like. By subjecting the reaction product thus obtained to a heat treatment at a temperature of 250 ° C. or higher and lower than 500 ° C., hexagonal WO ₃ having a reduced hydrate content can be obtained.

Here, the reason for setting the heat treatment temperature to less than 500 ° C. is to avoid a phase change to monoclinic crystal. As starting materials, it is also effective to use Na ₂ WO ₄ , Li ₂ WO ₄ , (NH ₄ ) ₁₀ [H ₂ W ₁₂ O ₄₂ ] · 4H ₂ O, ATP (ammonium paratungstate), and the like. Two or more tungstic acids may be used as starting materials. In addition, after the liquid phase reaction, filtration, washing with water and drying are performed. A tungsten oxide (WO ₃ ) powder having a hexagonal crystal structure can be obtained by performing a liquid phase reaction and performing an appropriate heat treatment. In addition, the obtained tungsten oxide powder is sufficiently dried.

In the production of the Li _x WO ₃ powder, a ratio of tungsten oxide (WO ₃₎ powder having a hexagonal crystal structure, method of dipping in a solution containing Li ions. In addition, a step of forming tungsten oxide (WO ₃ ) powder having a hexagonal crystal structure in a porous electrode layer (thickness 1 μm or more, porosity 20 to 80% by volume) and then immersing it in a solution containing Li ions May be performed.

It is also effective to subject the obtained tungsten oxide (WO ₃ ) powder to heat treatment in oxygen or heat treatment in nitrogen. The heat treatment in oxygen is effective in reducing oxygen defects in the WO ₃ powder. The electrical capacity can be increased by reducing oxygen defects in the WO ₃ powder. Further, the heat treatment in nitrogen has an effect of increasing oxygen defects. By increasing oxygen defects, the internal resistance value can be reduced. By reducing the internal resistance value, it becomes easier for electricity to flow, and the speed at which electricity flows from the capacitor to the outside increases. That is, a capacitor with higher instantaneous power can be manufactured. For this reason, when the amount of WO ₃ powder used is the same, it is effective to use a material having few oxygen defects in order to improve electric capacity and to use a material having many oxygen defects to reduce internal resistance.

Tungsten oxide containing oxygen defects is generally described in the form of WO _3-δ , and the δ value represents the amount of oxygen defects. As a method for measuring the amount of oxygen defects, for example, a KMnO ₄ solution is used to quantitate the amount of KMnO ₄ required to oxidize all low-electricity W (W ⁴⁺ , W ⁵⁺ ) ions to W ⁶⁺ by chemical analysis. Can be obtained. Further, the coloring state of the powder changes depending on the amount of oxygen defects, and when oxygen defects increase, the color changes from yellow to blue.

The amount of oxygen defects can be reduced by heat-treating tungsten oxide synthesized by heat treatment at a temperature lower than 500 ° C. for 1 hour or more at 350 ° C. or higher in an oxygen atmosphere. Within this temperature range, the oxygen defect amount δ can be easily controlled to 0.01 or less. In other words, WO ₃ powder having an oxygen defect amount in the range of 0.01 or less is preferable in order to improve the electric capacity.

On the other hand, the amount of oxygen defects can be increased by heat-treating tungsten oxide synthesized by heat treatment at a temperature lower than 500 ° C. at 350 ° C. or higher for 1 hour or longer in a nitrogen atmosphere. If it is this range, it will be easy to control oxygen defect amount (delta) value to 0.02 or more. In other words, WO ₃ powder having an oxygen defect amount in the range of 0.02 or more is preferable in order to reduce internal resistance. Note that the δ value is preferably 0.40 or less, and more preferably 0.10 or less, because the electric capacity decreases when there are many oxygen defects.

Further, the heat treatment in nitrogen also has an effect of reducing OH groups remaining on the surface of the WO ₃ powder. As described above, it is preferable to use an alkaline solution for producing hexagonal WO ₃ powder. For this reason, OH groups remain on the surface of the finished WO ₃ powder. If the OH group remains, it affects the electricity exchange of the WO ₃ powder, leading to a decrease in the electric capacity. The OH group can be decomposed by heat treatment in nitrogen.

(Example)
(Examples 1-5)
A tungsten oxide powder having a hexagonal crystal structure was prepared using a liquid phase reaction. The starting material was ammonium paratungstate ((NH ₄ ) ₁₀ · (H ₂ W ₁₂ O ₄₂ ) · 4H ₂ O), and 1N solution of hydrochloric acid (1N) was added to adjust the pH to a range of 6-8. The product was reacted at room temperature for 100 hours to synthesize a WO ₃ compound. The product precipitated by the reaction was washed, filtered and dried at 100 ° C. to obtain a WO ₃ precursor powder containing hydrate, ammonium compound and the like. Further, the obtained WO ₃ precursor powder was heated at 300 ° C. to 460 ° C. for 1 hour to remove hydrates and ammonia compounds, thereby producing WO ₃ powder. The heat treatment temperature is 370 ° C in Example 1, 400 ° C in Example 2, 430 ° C in Example 3, 460 ° C in Example 4, and 300 ° C in Example 5. This WO ₃ powder was used.

(Comparative Examples 1-2)
A precursor powder of WO ₃ was obtained in the same manner as in Example 1. However, WO ₃ powder obtained in a dry state at 100 ° C. without being subjected to heat treatment was designated as Comparative Example 1, and the heat treatment condition set at 500 ° C. × 1 hour was designated as WO ₃ powder according to Comparative Example 2.

(Examples 6 to 8)
Sodium tungstate powder was dissolved in pure water to prepare an aqueous solution of sodium tungstate. The aqueous solution was mixed with a 1N (1N) hydrochloric acid solution. The mixed solution was reacted at 5 ° C. for 48 hours to obtain a gel-like compound. After centrifuging this compound, the supernatant was removed, and the operation of adding pure water was repeated three times to remove impurity elements such as Na. Next, the washed compound was dissolved again in pure water and reacted in an autoclave at 120 ° C. and 10 atm for 20 hours. The solution after the reaction was centrifuged, filtered, and dried at 100 ° C. to prepare a WO ₃ precursor compound. Further, the obtained WO ₃ precursor powder was heated at 200 ° C. to 400 ° C. for 1 hour to remove hydrates, thereby producing WO ₃ powder. The heat treatment temperature was 370 ° C. as Example 6, the 400 ° C. as Example 7, and the 460 ° C. as WO ₃ powder according to Example 8.

(Comparative Examples 3-4)
A precursor powder of WO ₃ was obtained in the same manner as in Example 4. However, the WO ₃ powder obtained in the dry state at 100 ° C. without being subjected to heat treatment as Comparative Example 3, also as Comparative Example 4 of WO ₃ powder obtained by 500 ° C. × 1 hour heat treatment conditions.

(Comparative Example 5)
As Comparative Example 5, WO ₃ powder prepared using a plasma flame (high temperature of 500 ° C. or higher) was prepared as Comparative Example 5.

To WO ₃ powder according to Examples 1 to 8 and Comparative Examples 1 to 5 prepared as described above, was investigated BET specific surface area were both 1~60m ² / g. Moreover, all the compositions were in the range of WO _{2.6 to 3.0} .

In addition, the constituent phases of the WO ₃ powders according to Examples 1 to 8 and Comparative Examples 1 to 5 were identified by the XRD diffraction method and the Raman spectroscopic analysis method.

  When the XRD diffraction method is performed, five peaks (100), (001), (200), (101), and (200) are detected in the case of hexagonal crystal. In the case of a monoclinic crystal, five peaks (002), (020), (200), (022), and (202) are detected.

  In the case of having a constituent phase in which hexagonal crystal and monoclinic crystal are mixed, it can be determined by the ratio of the hexagonal strongest peak to the monoclinic strongest peak. The hexagonal crystal has an average value (average peak intensity) of three peaks of (100), (001), and (200), and the monoclinic crystal has three (002), (020), and (200). The average value of the peaks (average peak intensity) was determined. Measurement was performed using a calibration curve measured in advance.

In addition, when Raman spectroscopy is performed, intensity peaks are detected at different positions due to the crystal structure and the presence of hydrates. Specifically, in the hexagonal crystal, an intensity peak is detected at 690 ± 10 cm ⁻¹ or / and 780 ± 10 cm ⁻¹ . In the monoclinic crystal, an intensity peak is detected at 720 ± 10 cm ⁻¹ or / and 800 ± 10 cm ⁻¹ . Among these, 690 ± 10 cm ^-1 hexagonal, since 720 ± 10 cm ^-1 is determined easily monoclinic, it is preferable to determine presence or absence of the two peaks. In the case of a hydrate, an intensity peak is detected at 950 ± 10 cm ⁻¹ .

The results are shown in Table 1.

As is apparent from the results shown in Table 1, the tungsten oxide (WO ₃ ) powder according to each example had a hexagonal crystal structure, particularly a hexagonal crystal structure of 50% by volume or more. Moreover, the presence of hydrates in the tungsten oxide (WO ₃ ) powder according to each example was not confirmed.

On the other hand, Comparative Example 1 and Comparative Example 3 prepared in the drying step at 100 ° C. without heat treatment had insufficient reaction to WO ₃ or formed hydrates. Further, in Comparative Example 2, Comparative Example 4 and Comparative Example 5 in which the heat treatment temperature was 500 ° C. or higher, it was a tungsten oxide (WO ₃ ) powder composed only of monoclinic crystals.

(Examples 9 to 12)
Next, an example in which heat treatment in oxygen is performed will be described.

WO ₃ powders according to Example 1, Example 2, Example 6, and Example 7 were prepared. Next, the heat treatment shown in Table 2 was performed. For these, the presence or absence of oxygen defects was examined.

The oxygen defect analysis method uses a KMnO ₄ solution to quantitate the amount of KMnO ₄ required to oxidize all the low-electricity W (W ⁴⁺ , W ⁵⁺ ) ions to W ⁶⁺ by chemical analysis. It went by. By this analysis, it was replaced with WO _3-δ and the δ value was determined. This δ value was defined as the amount of oxygen defects.

  As is clear from the results shown in Table 2, oxygen defects were reduced by performing heat treatment in an oxygen atmosphere. In Examples 9 to 12, the hexagonal crystal ratio was not changed from that before the heat treatment with respect to the Raman light peak.

(Examples 13 to 16)
Next, an example in which heat treatment in nitrogen is performed will be described. WO ₃ powders according to Example 1, Example 2, Example 6, and Example 7 were prepared. Next, the heat treatment shown in Table 3 was performed. For these, the amount of oxygen defects was examined by the same method as in Examples 9-12. The results are shown in Table 3.

  As is clear from the results shown in Table 3 above, oxygen defects increased by heat treatment in a nitrogen atmosphere. In Examples 13 to 16, the hexagonal crystal ratio was not changed from that before the heat treatment with respect to the Raman light peak.

(Examples 1A to 8A and Comparative Example 5A)
Next, the storage battery shown in FIG. 1 was produced using the WO ₃ powders of Examples 1 to 8 and Comparative Example 5.

In forming the porous electrode layer, the surface of the WO ₃ powder was coated with yttrium oxide (Y ₂ O ₃ ).

Moreover, the storage battery provided the electrode part 12 (ITO layer) and the reduction | restoration part 18 (Pt layer) on the glass substrate of the surface side. Moreover, the porous electrode layer shown in Table 2 as the electrode part 13 (ITO layer) and the electrical storage part 15 was formed on the glass substrate of the back side. As the electrolytic solution, an acetonitrile solvent obtained by adding lithium iodide at a ratio of 0.8 mol / L and iodine at a ratio of 0.1 mol / L was used. The basis weight of the WO ₃ powder on the glass substrate was adjusted to 12 mg / cm _2, and the film thickness after drying was adjusted to 50 μm and the porosity was 50% by volume.

The storage capacity (C / m ² ) of each storage battery was investigated. The results are shown in Table 4.

The storage capacity is measured using an external power source, and the storage batteries of Examples and Comparative Examples are charged at 0.74 V for 640 seconds, and then the current value flowing to the connected 510Ω resistor is used per active material application area. The storage capacity was calculated. Furthermore, performed in two conditions of the discharge test ^{1mA / cm 2, 5mA / cm} 2 after charging was calculated internal resistance (Ω · cm ²⁾ from the relationship between the discharge start voltage and load current.

As is clear from the results shown in Table 4 above, the storage batteries according to the respective examples exhibited excellent power storage performance. In Examples 1A, 2A, 6A, and 7A, in which the constituent phase was 100% by volume of hexagonal crystals, the storage capacity was large. This is because by increasing the hexagonal crystal structure, the delivery of Li ions is made more efficient and the internal resistance is reduced. Moreover, when Example 1A and Example 2A were compared, Example 2A improved the storage capacity. This is because the crystallinity of the WO ₃ powder is improved and the internal resistance is reduced as the heat treatment temperature is higher.

(Examples 1B to 16B and Comparative Examples 1B to 5B)
Next, the capacitor shown in FIG. 2 was produced. A paste was prepared by mixing acetylene black as a conductive additive and PolyVinylidene DiFluoride (polyvinylidene fluoride) as a conductive additive to the WO ₃ powder according to Examples 1 to 16 and Comparative Examples 1 to 5. This paste was printed on an aluminum foil (negative electrode layer 23) having a thickness of 15 μm and dried to obtain a negative electrode sheet (negative electrode layer 26).

On the other hand, using LiCoO ₂ powder as the positive electrode, a paste was prepared by the same method as the above negative electrode, applied onto an aluminum foil (positive electrode side electrode layer 27) having a thickness of 15 μm, dried, and then positive electrode sheet (positive electrode layer 26). Was made. The electrode area was 1 cm ² . Further, WO ₃ mixing ratio of powder and acetylene black (weight ratio), WO ₃ powder: acetylene black = 100: 10. Further, the basis weight of the negative electrode material obtained by adding the WO ₃ powder and acetylene black was adjusted to 12 mg / cm ^2, and the film thickness after drying was 20 μm and the porosity was 50%. In addition, the basis weight of the positive electrode material was set to an amount having a sufficient margin for the electric capacity of the negative electrode material.

A polyethylene porous film (film thickness 20 μm) was used as the separator layer (separator layer 25). These laminates of electrodes and separator layers were assembled in an aluminum cell, impregnated with an electrolytic solution, defoamed and sealed to produce a capacitor. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ as an electrolyte in an EC / DEC solution was used. EC is an abbreviation for Ethylene Carbonate, and DEC is an abbreviation for Diethyl Carbonate.

  Using the capacitor, the charge / discharge characteristics were investigated. First, in order to measure electric capacity, a charge / discharge test was performed in a voltage range from 1.5 V to 3.0 V using a charge / discharge device. Charging was first performed in the constant current mode, and when 3.0V was reached, the mode shifted to the 3.0V constant voltage mode, and charging was continued until the current amount decreased to a constant value. After charging, the battery was discharged at a constant current, and the capacitance of the capacitor was determined from the capacitance at the time of discharge. As the value of the electric capacity, the electric capacity (mAh / g) per 1 g of the negative electrode material was obtained as the initial electric capacity.

Next, the internal resistance was measured by the direct current method. Discharging at a constant current was performed under conditions where the amount of current was changed at two levels of 1 mA and 5 mA, and the internal resistance value (Ω · cm ² ) was determined from the relationship between each discharge start voltage and the amount of load current.

  Furthermore, in order to investigate the charge / discharge cycle characteristics of the capacitor, the charge / discharge test similar to the method for measuring the capacitance was repeated 1000 times to evaluate the capacity retention rate. The capacity after 1000 cycles was compared with the initial capacity, and the capacity retention rate after the cycle test was determined. The capacity retention rate after the cycle test was obtained by (electric capacity after cycle test / initial electric capacity) × 100 (%).

Table 5 shows the initial electric capacity, the capacity retention ratio after the cycle test, and the internal resistance value.

As is clear from the results shown in Table 5, the capacitors according to the respective examples exhibited excellent charge / discharge characteristics. This is because the WO ₃ powder has a hexagonal crystal structure, so that the delivery of Li ions is efficient. Further, WO ₃ powder used in the negative electrode layer of the capacitor according to the embodiments _{it has} been a _{Li x WO 3, 0 <x} <1.34.

  Moreover, since the oxygen defect reduced in what performed the heat processing in oxygen like Examples 9-12, the improvement of the electrical capacitance was seen. Moreover, since the oxygen defect increased in what heat-processed in nitrogen like Examples 13-16, internal resistance value reduced. For this reason, it is found that it is effective to perform heat treatment in oxygen when increasing the electric capacity, while performing heat treatment in nitrogen when reducing internal resistance.

  On the other hand, since the hydrate remained in Comparative Example 1, all characteristics were deteriorated. Moreover, even if it had a hexagonal crystal structure as in Comparative Example 3, the hydrate remained, although the initial electric capacity was high, the capacity retention rate was low because the crystal structure was weak. Those in which the hydrate remains as in Comparative Example 3 is considered to be a mixed phase of a hexagonal crystal structure and a hydrate, and the interposition of the hydrate becomes a weak chain of the hexagonal network structure. Is considered to be the starting point of change (deterioration). Further, the monoclinic crystals of Comparative Example 2, Comparative Example 4 and Comparative Example 5 are because the crystal structure changes (monoclinic → tetragonal → cubic) with the insertion of Li ions.

  As described above, it is apparent that the battery electrode material according to the embodiment of the present invention can be applied to various batteries, that is, storage batteries, dye-sensitized solar cells, capacitors, and Li ion secondary batteries.

  As mentioned above, although several embodiment of this invention was illustrated, these embodiment is shown as a structural example, and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, changes, and the like can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and equivalents thereof. Further, the above-described embodiments can be implemented in combination with each other.

DESCRIPTION OF SYMBOLS 11 ... Storage battery, 12, 13 ... Electrode part, 14 ... Sealing part, 15 ... Power storage part (porous electrode layer), 16 ... Electrolytic solution, 17 ... Protection part, 18 ... Reduction part, 22 ... Capacitor, 23 ... Electrode Layer (negative electrode side electrode layer), 24 ... negative electrode layer, 25 ... separator layer, 26 ... positive electrode layer, 27 ... electrode layer (positive electrode side electrode layer).

Claims (10)

In the battery electrode material comprising a tungsten oxide powder, the tungsten oxide powder has at least part or all of a hexagonal crystal structure, the tungsten oxide powder has a BET specific surface area of 1 m ² / g or more, and the tungsten oxide powder A battery electrode material characterized in that 0.02 ≦ δ ≦ 0.40, where WO _3−δ is the composition. 2. The battery electrode material according to claim 1, wherein the tungsten oxide powder has a hexagonal crystal structure of 50% or more by volume. The battery electrode material according to any one of claims 1 to 2, wherein a metal oxide is provided on a surface of the tungsten oxide powder. When performing Raman spectroscopy with respect to the tungsten oxide powder, 690 any of claims 1 to 3, characterized in that a peak is detected within a range of ± 10 cm ^-1 and / or 780 ± 10 cm ^-1 The battery electrode material according to item 1. A battery substrate comprising a porous electrode layer made of the battery electrode material according to any one of claims 1 to 4 . The battery substrate according to claim 5, wherein the porous electrode layer has a thickness of 1 μm or more and a porosity of 20 to 80% by volume. A storage battery using the battery substrate according to any one of claims 5 to 6 . A dye-sensitized solar cell using the battery substrate according to any one of claims 5 to 6 . A capacitor using the battery substrate according to any one of claims 5 to 6 . A lithium ion secondary battery using the battery electrode material according to any one of claims 1 to 4 .

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