JP2005222851A - Electrode active material and electrochemical cell using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery suppressing sharp voltage drop and preventing drop in battery function in reflow soldering in the nonaqueous electrolyte secondary battery using a niobium oxide as a positive active material. <P>SOLUTION: The niobium oxide in which diffraction intensity ratio in X-ray diffraction patterns is in a specific range and average particle size is 3 μm or less is used as the positive active material, a silicon oxide in which an atomic ratio of lithium and oxygen is specified is used as a negative active material, and heat resistant resin such as a liquid crystal polymer is used in a gasket. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrode active material used in an electrochemical cell such as a nonaqueous electrolyte battery.

Coin-type (button-type) electrochemical cells are increasingly used as a power source for equipment backup due to their high energy density and light weight.
The mainstream electrochemical cells for memory and clock backup are those charged at 3V or higher. However, as the operating voltage of devices has been lowered, secondary batteries for memory and clock backup have been required to have a low voltage that can be charged at 3 V or less.

  As batteries that can be charged at a low voltage, those using niobium oxide as the positive electrode active material and lithium aluminum alloy as the negative electrode active material are the mainstream (see, for example, Patent Document 1).

In addition, as a method for mounting an electrochemical cell on a substrate, reflow soldering, in which solder cream or the like is applied between the electrochemical cell and the substrate and introduced into an electric furnace together with the substrate, is attracting attention. At the time of this reflow soldering, the electrochemical cell is exposed to a high temperature of 240 ° C. or more, so heat resistance is also required.
Japanese Unexamined Patent Publication No. 2000-133313 (Section 2-4, FIG. 1)

  Since the conventional electrochemical cell uses niobium oxide with low heat resistance, the electrode active material deteriorates during reflow soldering, and the function as an electrochemical cell is impaired. Further, the cycle characteristics are deteriorated, and battery capacity is deteriorated when left for a long time after charging.

  In addition, the charging voltage and discharging end voltage of a device incorporating an electrochemical cell vary depending on the electronic component used and the power source used. In particular, as the charging voltage is shifting from a 3V system to a 2.5V system, device manufacturers select and use various components according to cost and device functions. The actual condition is that the end-of-discharge voltage (battery operating voltage range) varies from device manufacturer to device manufacturer and from device to device.

  However, in the conventional niobium oxide-lithium aluminum alloy electrochemical cell, as shown in the discharge curve of Comparative Example 1 in FIG. 1, the voltage drops sharply from 2V to about 1.3V, and then the slope of the discharge curve gradually decreases. The battery operating voltage range was very narrow (Comparative Example 1 in FIG. 1 shows a discharge curve of a nonaqueous electrolyte secondary battery using niobium oxide as the positive electrode active material and lithium aluminum alloy as the negative electrode active material. ).

  When a lithium aluminum alloy is used as the negative electrode active material, a device using a voltage of 1.3 V or higher cannot use a sufficient discharge capacity because of a rapid voltage drop.

  Furthermore, if a high voltage is applied excessively during charging, abnormal lithium deposition occurs on the negative electrode, which is a lithium aluminum alloy, causing deterioration of the electrode active material.

  Accordingly, it is an object of the present invention to provide an electrode active material using a highly heat-resistant niobium oxide that solves the above-mentioned problems, and to provide an electrochemical cell that is excellent in heat resistance and cycle characteristics and has a wide battery operating voltage range. .

  The electrode active material according to the present invention is an electrode active material made of niobium oxide and has a diffraction angle of 24 degrees (2θ) in the X-ray diffraction pattern of the niobium oxide measured using CuKα rays (1.5418４). The diffraction peak intensities near and near the diffraction angle of 25 degrees (2θ) are both 20% or less of the diffraction peak intensity near the diffraction angle of 22.6 degrees (2θ).

In the electrode active material of the present invention, the niobium oxide does not have a diffraction peak near a diffraction angle of 24 degrees (2θ) and a diffraction angle of 25 degrees (2θ). Furthermore, the niobium oxide of the present invention is preferably Nb ₂ O ₅ .

  The electrode active material according to the present invention is a niobium oxide and has an average particle size of 3.0 μm or less. The weight reduction rate when the niobium oxide is ignited is 0.3% or less.

  The niobium oxide contained in the electrode active material according to the present invention has a Ta content of 500 ppm or less, an Fe content of 15 ppm or less, and an Si content of 300 ppm or less.

The electrode active material according to any one of claims 1 to 6, wherein the specific surface area of the niobium oxide is preferably in the range of 3.5 m ² / g to 20 m ² / g. Furthermore, the electrode active material is preferably used for the positive electrode.

  In the present invention, an electrochemical cell is prepared using the electrode active material.

  Furthermore, in the electrochemical cell according to the present invention, the negative electrode active material is made of a material containing either silicon or tungsten.

  Preferably, in the present invention, a silicon oxide capable of occluding and releasing lithium ions is used for the negative electrode active material.

  More preferably, when the ratio of the number of atoms of silicon, lithium, and oxygen contained in the silicon oxide is expressed by 1: x: y, x ≧ 0 and 2> y> 0. When the ratio of the number of atoms of silicon, lithium, and oxygen contained in the silicon oxide is expressed by 1: x: y, it is more preferable that 4.5 ≧ x ≧ 4.0 and 2> y> 0. .

  In addition, the electrochemical cell according to the present invention includes the niobium oxide, a nonaqueous solvent having a boiling point of 200 ° C. or higher at normal pressure, a supporting salt containing fluorine, glass fiber, or a heat distortion temperature of 230 ° C. or higher. And a gasket made of a resin having a heat distortion temperature of 230 ° C. or higher.

  Preferably, the non-aqueous solvent according to the present invention contains either ethylene carbonate (EC) or γ-butyrolactone (γBL).

Moreover, the supporting salt of the electrochemical cell according to the present invention contains either lithium hexafluorophosphate (LiPF ₆ ) or lithium borofluoride (LiBF ₄ ).

  The gasket of the electrochemical cell according to the present invention is made of polyphenylene sulfide, liquid crystal polymer (LCP), polyether ether ketone resin (PEEK), polyether nitrile resin (PEN), polyamideimide resin, or tetrafluoroethylene-perfluoroalkyl vinyl ether. One of copolymer resins is used.

  The electrochemical cell according to the present invention has both diffraction peak intensities at a diffraction angle of 24 degrees (2θ) and a diffraction angle of 25 degrees (2θ) in a X-ray diffraction pattern measured using CuKα rays (1.5418 Å). It consists of a positive electrode active material made of niobium oxide that is 20% or less of the diffraction peak intensity of 6 degrees (2θ) and a negative electrode active material containing either silicon or tungsten.

In the present invention, in the X-ray diffraction measurement using CuKα ray (1.5418Å), the diffraction peak intensities near the diffraction angle of 24 degrees (2θ) and 25 degrees OLE_LINK3 (2θ) OLE_LINK3 are both diffraction angles of 22.6 degrees (2θ). Niobium oxide Nb ₂ O ₅ having a diffraction peak intensity of 20% or less in the vicinity is used as the electrode active material. This niobium oxide is excellent in heat resistance and can be reflow soldered. In addition, by using the electrode active material of the present invention, a stable electrochemical cell having excellent cycle characteristics can be obtained.

  Moreover, the electrode active material of this invention can raise the electrical conductivity in a positive electrode active material by making an average particle diameter small as 3.0 micrometers or less.

  By using a niobium oxide having a reduction rate of 0.3% or less as an electrode active material when ignited, it is possible to prevent the mixing of organic impurities that cause a decrease in battery capacity.

  Use of niobium oxide having a Ta content of 500 ppm or less, an Fe content of 15 ppm or less, and an Si content of 300 ppm or less as an electrode active material improves the decrease in battery capacity over time. be able to.

In addition, the reaction between the electrode active material and the electrolytic solution is suppressed by using a niobium oxide having a specific surface area in the range of 3.5 m ² / g to 20 m ² / g as the electrode active material.

  In addition, by using a positive electrode active material made of niobium oxide and a negative electrode active material made of silicon or tungsten for the electrochemical cell, it is possible to prevent a rapid voltage drop of the electrochemical cell during OLE_LINK2 discharge, and the slope of the charge / discharge curve. Becomes constant and a sufficient electric capacity can be used in a wide voltage range. By using silicon oxide capable of occluding and releasing OLE_LINK2 lithium ions as a negative electrode active material, an electrochemical cell capable of using a sufficient electric capacity in a wider voltage range can be realized.

  When the ratio of the number of atoms of silicon, lithium, and oxygen is expressed as 1: x: y, the potential of the negative electrode is lowered by selecting a silicon oxide such that x ≧ 0 and 2> y> 0, and electrochemical The cell voltage can be increased.

  Further, by setting the Li content to 4.0 ≦ x ≦ 4.5, the potential on the negative electrode side can be lowered and the voltage of the electrochemical cell can be increased. An abrupt voltage drop of the electrochemical cell during discharge can be prevented, the slope of the charge / discharge curve is constant, and a sufficient electric capacity can be used in a wide voltage range. At the same time, charging is possible even at a high voltage, but lithium metal does not abnormally deposit on the electrode during charging. An electrochemical cell capable of having a large electric capacity in a wide voltage range can be provided.

  In the electrochemical cell according to the present invention, the nonaqueous solvent has a boiling point of 200 ° C. or higher at normal pressure, the supporting salt contains fluorine, and the separator is glass fiber or a heat distortion temperature of 230 ° C. or higher. And the gasket is made of a resin having a heat distortion temperature of 230 ° C. or higher, thereby improving heat resistance and enabling reflow soldering.

  Furthermore, the nonaqueous solvent contains either ethylene carbonate (EC) or γ-butyrolactone (γBL), thereby increasing the dielectric constant of the nonaqueous solvent and reducing the internal resistance of the electrochemical cell.

Further, by using any one of lithium hexafluorophosphate (LiPF ₆ ) and lithium borofluoride (LiBF ₄ ) as the supporting salt, the electrolytic solution exhibits high conductivity. These supporting salts are both stable under oxidizing and reducing conditions, and are less likely to deteriorate due to charging and discharging of the electrochemical cell.

  Electrochemical cells when polyphenylene sulfide, liquid crystal polymer (LCP), polyether ether ketone resin (PEEK), polyether nitrile resin (PEN), polyamide imide resin, or tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin is used as a gasket. Improves heat resistance. Moreover, since the battery performance is not impaired even in combination with the electrode, an electrochemical cell that can withstand the reflow temperature can be provided.

  The structure of the electrochemical cell of the present invention is shown in a sectional view in FIG. The positive electrode pellet 101 and the negative electrode pellet 102 were obtained by molding a positive electrode active material and a negative electrode active material, respectively. The difference in electrode potential between the positive electrode active material and the negative electrode active material becomes an electromotive force of the electrochemical cell. The separator 103 prevents electrical contact between the positive and negative electrodes. Further, when the negative electrode pellet 102 and the lithium foil 104 are brought into contact with each other and the electrolytic solution 105 is added, an electrochemical reaction occurs, and lithium ions are occluded in the negative electrode pellet. The electrolytic solution 105 includes a non-aqueous solvent and a supporting salt. The electrode pellet and the electrolytic solution are accommodated in a positive electrode case 106 and a negative electrode case 107 and are caulked and sealed through a gasket 108.

The positive electrode active material niobium oxide Nb ₂ O ₅ can be charged at a low voltage and is large in capacity, and is suitable for a battery used in a low voltage region. Further, this Nb ₂ O ₅ has an intensity of a peak near a diffraction angle of 24 degrees (2θ) and an intensity of a peak near 25 degrees (2θ) in the X-ray diffraction measurement using CuKα rays (1.5418 Å). It is desirable that it is 20% or less of the intensity of the peak around 6 degrees (2θ). The diffraction measurement conditions of the present invention are not limited, but it is preferable to use CuKα rays. Specifically, it is preferable to carry out under the conditions described in the following examples.

X-ray diffraction measurement conditions Light source: CuKα ray (1.5418mm)
Output: 40KV, 30mA
Divergent slit: 1.0 °
Scattering slit: 1.0 °
Light receiving slit: 0.1 mm
Step width: 0.05 °
Scan speed: 3 ° / min
X-ray diffraction measurement was performed under the above conditions.

  FIG. 3 shows the diffraction peak of niobium oxide.

It is particularly desirable that there are no prominent peaks other than the background near diffraction angles of 24 degrees (2θ) and 25 degrees (2θ). This is because the crystal structure is an orthorhombic single phase, and since it has a stable crystal structure, there is little deterioration against heat and the charge / discharge cycle characteristics are good. Further, when a battery is produced using this Nb ₂ O ₅ as a positive electrode, the negative electrode containing lithium is stabilized at a high temperature, and there is also an action of suppressing a swelling of the battery and an increase in internal resistance.

Moreover, it is preferable that the Ta content in the niobium oxide Nb ₂ O ₅ is 500 ppm or less, the Fe content is 15 ppm or less, and the Si content is 300 ppm or less. A secondary battery may be left for a long time after being charged when the battery is used. However, if the battery is left for a long time in this charged state, the capacity may be deteriorated. This is because Ta, Fe, Si, which are impurities contained in Nb ₂ O ₅ , elute into the electrolyte solution, and this penetrates into the negative electrode or precipitates on the negative electrode surface, thereby adversely affecting the negative electrode active material. It is possible that Therefore, by setting the Ta content in Nb ₂ O ₅ to 500 ppm or less, the Fe content to 15 ppm or less, and the Si content to 300 ppm or less, it is possible to solve battery capacity deterioration due to long-term standing. It was.

Suppressing the content of other organic impurities also suppresses capacity reduction and leads to improvement of charge / discharge cycle characteristics. Specifically, when the ignition loss of Nb ₂ O ₅ is set to 0.3% or less, the charge / discharge cycle characteristics are improved and the capacity deterioration is suppressed.

Further, the niobium oxide Nb ₂ O ₅ of the present invention defines a specific surface area measured by the BET method or an average particle diameter measured by the brane method. It is necessary to suppress the reaction between the chemically active active material and the electrolytic solution while ensuring the electrical conductivity in the positive electrode active material. For this reason, it has a small specific surface area and a small average particle size. The diameter is desirable. Therefore, the specific surface area by the BET method is preferably 3.5 m ² / g or more and 20 m ² / g or less, and the average particle size is preferably 3.0 μm or less. In particular, those having a specific surface area of 3.5 m ² / g or more and 10 m ² / g or less and an average particle diameter of 1.0 μm or less are particularly preferable because of excellent heat resistance.

  By using a silicon oxide represented by SiOy (2> y> 0) such as SiO or Si as the negative electrode active material, a rapid voltage drop is prevented, and the charge / discharge curve has a constant slope. In particular, by using SiO, a rapid voltage drop of the electrochemical cell can be prevented, and the electric capacity of the electrochemical cell can be effectively used in a wide voltage range. In addition, when a battery is manufactured using SiO, it is necessary to occlude lithium ions to be moved into SiO in advance to obtain a lithium-containing silicon oxide represented by LixSiOy (x ≧ 0, 2> y> 0). In this case, by increasing the lithium content, the electrode potential on the negative electrode side decreases, and the electromotive force of the electrochemical cell increases. In addition, when too much lithium is added, lithium metal is abnormally deposited on the electrode during charging, and therefore x is particularly preferably in the range of 4.0 ≦ x ≦ 4.5. By having the niobium oxide and SiO in the positive and negative electrodes, a secondary battery that can be charged and discharged in a wide region with a low voltage can be obtained. It is also preferable to use a negative electrode active material containing tungsten.

  Examples of the electrolyte electrolyte include γ-butyrolactone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, 1,2-dimethoxyethane, tetrahydrofuran, dioxolane, dimethylformamide, and the like. An organic solvent alone or a mixed solvent can be used.

  In order to perform reflow soldering, it was found that it is stable at the reflow temperature to use a nonaqueous solvent having a boiling point of 200 ° C. or higher at normal pressure as the electrolytic solution. In combination with positive and negative electrodes, propylene carbonate (PC), ethylene carbonate (EC), and γ-butyrolactone (γBL) were used alone or in combination.

  In addition to the organic solvent, a polymer can be used. Examples of the polymer include polyethylene oxide (PEO), polypropylene oxide, crosslinked polyethylene glycol diacrylate, polyvinylidene fluoride, crosslinked polyphosphazene, crosslinked polypropylene glycol diacrylate, crosslinked polyethylene glycol methyl ether acrylate, and polypropylene glycol methyl ether. A crosslinked acrylate or the like is preferably used.

  Examples of main impurities present in the electrolytic solution (nonaqueous solvent) include moisture and organic peroxides (for example, glycols, alcohols, carboxylic acids). Each of the impurities is considered to form an insulating film on the surface of the active material and increase the interface resistance of the electrode. Therefore, the cycle life and capacity may be affected. In addition, self-discharge during storage at high temperatures (60 ° C. or higher) may increase. For this reason, it is preferable to reduce the impurities as much as possible in the electrolyte solution containing the non-aqueous solvent. Specifically, the moisture is preferably 50 ppm or less and the organic peroxide is preferably 1000 ppm or less.

Supported salts include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), lithium trifluorometasulfonate (LiCF) ₃ SO ₃ ), bistrifluoromethylsulfonylimide lithium [LiN (CF ₃ SO ₂ ) ₂ ], lithium salts (electrolytes) such as thiocyanate and aluminum fluoride can be used.
In performing reflow soldering, lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), lithium trifluorometasulfonate, which are fluorine-containing supporting salts, such as LiClO _{4 and} other chlorine-based ones (LiCF ₃ SO ₃ ) was stable both thermally and electrically.

  The amount dissolved in the non-aqueous solvent is preferably 0.5 to 3.0 mol / 1.

  As the separator, an insulating film having a large ion permeability and a predetermined mechanical strength is used. As the pore diameter of the separator, a range generally used for batteries is used. For example, 0.01 to 10 μm is used. The thickness of the separator is generally used in the battery range, for example, 5 to 300 μm is used.

  As the gasket, polypropylene or the like is usually used.

  When performing reflow soldering, polyphenylene sulfide, polyethylene terephthalate, polyamide, liquid crystal polymer (LCP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (PFA), polyether ether ketone resin (PEEK), polyether nitrile resin (PEN), polyetherketone resin (PEK), polyamideimide, polyarylate resin, polybutylene terephthalate resin, polycyclohexanedimethylene terephthalate resin, polyethersulfone resin, polyaminobismaleimide resin, polyetherimide resin, fluorine resin reflow There was no rupture at temperature, and there was no problem of leakage due to deformation of the gasket even during storage after reflow.

  In particular, resins having a heat distortion temperature of 230 ° C. or higher, polyphenylene sulfide, liquid crystal polymer (LCP), polyetheretherketone resin (PEEK), polyethernitrile resin (PEN), polyamideimide resin, or tetrafluoroethylene-perfluoroalkyl The vinyl ether copolymer resin was excellent in terms of leakage resistance.

  Moreover, what added glass fiber, my cow whisker, ceramic fine powder, ceramic whisker, etc. with the addition amount of about 40 weight% or less to this material can be used. In particular, those using potassium titanate whiskers were good.

  As a method for manufacturing the gasket, there are an injection molding method, a thermal compression method, and the like.

  The thermal compression method is a method for obtaining a final molded product by performing thermal compression molding at a temperature equal to or lower than the melting point using a plate material having a thickness larger than the gasket shape of the molded product as a material molded product.

  In general, when a temperature is applied to a thermoplastic resin molded product molded by hot compression molding at a temperature below the melting point from the material molded product, there is a property of returning to the shape of the original material molded product. As a result, a non-aqueous electrolyte is supposed to have a gap between the outer can and the inner can (metal) and the gasket (resin), or a stress sufficient for sealing cannot be obtained between the can and the gasket. By using this gasket for the next battery, there is no gap between the outer can and can (metal) and gasket (resin) due to expansion of the gasket due to heat treatment (reflow soldering, etc.) or sealing between the can and gasket. Sufficient stress can be obtained.

  Further, it has a property of returning to the shape of the original material molded product over time, and is effective in batteries other than reflow soldering.

  In particular, in a gasket using tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (PFA), a heat compression molded one produced by heating and pressing a sheet-like material is more sealed than one produced by injection molding. The property was good. This is because the PFA has rubber elasticity, and the injection molded product shrinks at the reflow temperature, whereas the hot compression molded product tries to return to the thickness of the sheet before molding at the reflow temperature. This is because the internal pressure of the gas increases and further sealing and airtightness can be achieved.

  On the other hand, the injection molding method is the most common gasket molding method. However, when the molding accuracy is sacrificed due to cost reduction or the like, it is essential to supplement the airtightness using a liquid sealant.

  In the case of coins and button batteries, one or a mixture of liquid sealants such as asphalt pitch, butyl rubber, fluorinated oil, chlorosulfonated polyethylene, and epoxy resin is used between the gasket and the positive and negative electrode cans. When the liquid sealant is transparent, it is colored to clarify the presence or absence of application. Examples of the method for applying the sealant include injection of the sealant into the gasket, application to the positive / negative electrode can, and dipping of the gasket into the sealant solution.

  When the battery shape is a coin or a button, the electrode shape is used by compressing a mixture of a positive electrode active material and a negative electrode active material into a pellet shape. In the case of a thin coin or button, an electrode formed in a sheet shape may be punched out. The thickness and diameter of the pellet are determined by the size of the battery.

  As the pellet pressing method, a generally adopted method can be used, but a die pressing method is particularly preferable. The pressing pressure is not particularly limited, but is preferably 0.2 to 5 t / cm2. The pressing temperature is preferably room temperature to 200 ° C.

  A conductive agent, a binder, a filler, or the like can be added to the electrode mixture. The kind of the conductive agent is not particularly limited and may be a metal powder, but a carbon-based one is particularly preferable. Carbon materials are the most common, and natural graphite (scale-like graphite, scale-like graphite, earth-like graphite, etc.), artificial graphite, carbon black, channel black, thermal black, furnace black, acetylene black, carbon fiber, etc. are used. As the metal, metal powder such as copper, nickel, silver, or metal fiber is used. Conductive polymers are also used.

  The amount of carbon added varies depending on the electrical conductivity of the active material, the electrode shape, etc., and is not particularly limited. However, in the case of the negative electrode, it is preferably 1 to 50% by weight, particularly preferably 2 to 40% by weight.

  When the carbon particle size is in the range of 0.5 to 50 μm, preferably in the range of 0.5 to 15 μm, more preferably in the range of 0.5 to 6 μm, the contact between the active materials becomes good. Electron conduction network formation is improved, and active materials that are not involved in electrochemical reactions are reduced.

The binder is preferably insoluble in the electrolytic solution.
Polyacrylic acid and neutralized polyacrylic acid, polyvinyl alcohol, carboxymethylcellulose, starch, hydroxypropylcellulose, regenerated cellulose, diacetylcellulose, polyvinylchloride, polyvinylpyrrolidone, tetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, ethylene-propylene -Diene polymer (EPDM), sulfonated EPDM, styrene butadiene rubber, polybutadiene, fluoro rubber, polyethylene oxide, polyimide, epoxy resin, phenol resin and other polysaccharides, thermoplastic resin, thermosetting resin, rubber elastic polymer, etc. Are used as one or a mixture thereof. The addition amount of the binder is preferably 1 to 50% by weight.

By using a water-soluble binder, the burden on the environment can be reduced. In the production of the positive electrode mixture, when water-soluble polyacrylic acid and polyacrylic acid neutralized product, polyvinyl alcohol, carboxymethyl cellulose, starch, etc. are used, Nb ₂ O ₅ absorbs water, It is necessary to heat-treat the pellet formed with the positive electrode mixture.

  Any filler can be used as long as it is a fibrous material that does not cause a chemical change in the constructed battery. In the present invention, fibers such as carbon and glass are used. Although the addition amount of a filler is not specifically limited, 0 to 30 weight% is preferable.

  It is desirable to use a metal plate having a low electrical resistance as a can that also serves as a current collector for the electrode active material. For example, in addition to stainless steel, nickel, aluminum, titanium, tungsten, gold, platinum, baked carbon, etc., the positive electrode has a surface of aluminum or stainless steel treated with carbon, nickel, titanium or silver. Used. As for stainless steel, duplex stainless steel is effective against corrosion. In the case of a coin or button battery, nickel plating is performed on the outside of the battery. Treatment methods include wet plating, dry plating, CVD, PVD, clad formation by pressure bonding, coating, and the like.

  In addition to stainless steel, nickel, copper, titanium, aluminum, tungsten, gold, platinum, calcined carbon, etc., the negative electrode can has carbon, nickel, titanium or silver treated on the surface of copper or stainless steel. Al-Cd alloy or the like is used. Examples of the treatment method include wet plating, dry plating, CVD, PVD, clad formation by pressure bonding, coating, and the like.

  It is also possible to fix the electrode active material and the current collector can with a conductive adhesive. As the conductive adhesive, a resin in which carbon or metal powder or fiber is added to a resin dissolved in a solvent, or a conductive polymer dissolved therein is used.

  In the case of a pellet-shaped electrode, the electrode is fixed by applying between the current collector and the electrode pellet. The conductive adhesive in this case often includes a thermosetting resin.

  The application of the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, but is suitable for, for example, a backup power source such as a mobile phone and a pager, particularly a device having a battery operating voltage range of about 2.5V to 1.0V. .

  The battery of the present invention is preferably assembled in a dehumidified atmosphere or an inert gas atmosphere. Moreover, it is preferable that the parts to be assembled are also dried in advance. As a method for drying or dehydrating pellets, sheets and other parts, it is preferable to use hot air, vacuum, infrared rays, far infrared rays, electron beams and low-humidity air alone or in combination. The temperature is preferably in the range of 80 to 350 ° C, particularly preferably in the range of 100 to 300 ° C. The water content is preferably 2000 ppm or less for the entire battery, and preferably 50 ppm or less for each of the positive electrode mixture, the negative electrode mixture and the electrolyte from the viewpoint of improving charge / discharge cycle performance.

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

Example 1 is a case where Nb ₂ O ₅ produced by heating niobic acid at 800 ° C. as the positive electrode active material and SiO as the negative electrode active material. A positive electrode, a negative electrode and an electrolytic solution prepared as described below were used. The size of the battery was 4.8 mm in outer diameter and 1.4 mm in thickness.

As Example 1, the positive electrode was produced as follows. Commercially available niobic acid (Nb ₂ O ₅ .nH ₂ O) was heated in the atmosphere at 800 ° C. for 8 hours to obtain Nb ₂ O ₅ . Thereafter, powders having various characteristics were obtained by changing the heating temperature and the heating time.

  Next, the peak intensity ratio of the powder sample was measured by XRD diffraction, the average particle diameter was measured by the brane method, the specific surface area was measured by the BET method, and the contents of Ta, Fe, and Si were measured by atomic absorption analysis. Moreover, the ratio of the weight reduction | decrease amount when it heated until it became constant weight at 800 degreeC was measured, and it was set as the ignition loss.

From the measurement results, the peak intensities near the diffraction angle of 24 degrees (2θ) and 25 degrees (2θ) are 4% and 3.8% of the peak intensity near 22.6 degrees (2θ), respectively, and the BET specific surface area. Nb ₂ O ₅ with 5.8 m 2 / g, average particle size 0.88 μm, loss on ignition 0.22%, Ta content 150 ppm, Fe content 4.7 ppm and Si content 15 ppm was selected.
The Nb ₂ O ₅ pulverized powder is mixed with graphite as a conductive agent and polyacrylic acid as a binder in a weight ratio of Nb ₂ O ₅ : graphite: polyacrylic acid = 78: 20: 2. Next, 5 mg of this positive electrode mixture was pressure-molded into pellets having a diameter of 2.1 mm at 2 ton / cm 2. Thereafter, the positive electrode pellet obtained in this manner was bonded and integrated with the positive electrode case using a conductive adhesive composed of a conductive resin adhesive containing carbon (made into a positive electrode unit), and then the atmosphere was 250 ° C. for 8 hours. Heat treated in.

  The negative electrode was produced as follows. A commercially available SiO pulverized material was used as the active electrode active material. This active material was mixed with graphite as a conductive agent and polyacrylic acid as a binder at a weight ratio of 45:40:15 to obtain a negative electrode mixture. A mixture of 1.4 mg of a mixture at 2 ton / cm @ 2 into 2.1 mm diameter pellets was used. Thereafter, the negative electrode pellet obtained in this way was bonded and integrated with the negative electrode case using a conductive resin adhesive having carbon as a conductive filler (negative electrode unitization), and then in the atmosphere at 250 ° C. for 8 hours. Heat treated. Further, a lithium foil punched out to a diameter of 1.8 mm and a thickness of 0.3 mm on the pellet was pressure-bonded to obtain a lithium-negative electrode pellet laminated electrode.

A non-woven fabric made of glass fiber having a thickness of 0.2 mm was dried and punched out to 3.2 mm to obtain a separator. A gasket made of PP was used. The electrolytic solution is a solution of propylene carbonate (PC): ethylene carbonate (EC): 1,2-dimethoxyethane (DME) in a volume ratio of 1: 1: 2 in which 2 mol / l of lithium perchlorate (LiClO ₄ ) is dissolved. 4.6 μL of the product was placed in a battery can. A positive electrode unit and a negative electrode unit were overlapped and sealed to produce a battery.

A battery was fabricated in exactly the same manner except that commercially available niobic acid (Nb ₂ O ₅ .nH ₂ O) was heated in air at 1000 ° C. for 8 hours to obtain Nb ₂ O ₅ . The powder characteristics of this Nb ₂ O ₅ were measured in the same manner as in Example 1. As a result, in the XRD diffraction measurement, the intensities of the peaks near the diffraction angles of 24 degrees (2θ) and 25 degrees (2θ) were 22.6 degrees (2θ). 38.5% and 36.7% of the intensity of nearby peaks, BET specific surface area 2.0 m2 / g, average particle size 3.8 μm, loss on ignition 0.11%, Ta content 175 ppm, Fe content 4. 7 ppm, Si content was 30 ppm.
(Comparative Example 1)
A battery having a diameter of 4.8 mm and a height of 1.4 mm using Nb ₂ O _{5 as} a commercial positive electrode and a lithium aluminum alloy as a negative electrode was examined.
(Comparative Example 2)
A battery was fabricated in exactly the same manner except that commercially available niobic acid (Nb ₂ O ₅ .nH ₂ O) was heated in the atmosphere at 650 ° C. for 8 hours to obtain Nb ₂ O ₅ . When the powder characteristics of this Nb ₂ O ₅ were measured in the same manner as in Example 1, the intensity of the peak near the diffraction angle of 24 degrees (2θ) and the intensity of the peak near 25 degrees (2θ) in the XRD diffraction measurement were 22.6. 5.8% and 4.2% of the peak intensity in the vicinity of the degree (2θ), BET specific surface area 5.2 m 2 / g, average particle size 0.8 μm, ignition loss 0.3%, Ta content 524 ppm, Fe The content was 15.6 ppm, and the Si content was 312 ppm.
The charge / discharge curve was measured for the battery of Example 1 and the battery of Comparative Example 1. Discharge was performed by constant current discharge of 5 μA and a final voltage of 0.7V. Charging was performed at 25 μA and a final voltage of 2.0V. The discharge capacity is shown in Table 1 for each voltage value.

また、同様の条件で実施例１、実施例２の電池のサイクル特性を調べた結果を表２に示す。

Table 2 shows the results of examining the cycle characteristics of the batteries of Example 1 and Example 2 under the same conditions.

本実施例1の電池は、比較例１の電池に比べどの電圧においても放電容量が大きい。１．３Ｖ以上においては約１．８倍、１．５Ｖ以上においては約５倍の値を示す。実施例１および比較例1の放電カーブを図１に示した。本発明の実施例1の電池は、急激な電圧低下を防ぎ充放電カーブの傾きが一定となっており、電池を組み込む機器の終止電圧がたとえ１．３Ｖであっても半分以上の放電容量を確保できることがわかる。一方、比較例１は、急激な電圧低下が生じており、使用可能な電圧範囲が狭くなっている。

The battery of Example 1 has a larger discharge capacity at any voltage than the battery of Comparative Example 1. The value is about 1.8 times above 1.3V, and about 5 times above 1.5V. The discharge curves of Example 1 and Comparative Example 1 are shown in FIG. The battery of Example 1 of the present invention prevents a sudden voltage drop and has a constant slope of the charge / discharge curve, and has a discharge capacity of more than half even if the end voltage of the device incorporating the battery is 1.3V. It can be seen that it can be secured. On the other hand, in Comparative Example 1, a rapid voltage drop occurs, and the usable voltage range is narrow.

Next, about the battery of the comparative example 1, when charging / discharging from 2.0V to 0.7V was repeated 30 times, it did not function as a battery. This is presumably because the lithium aluminum alloy used as the negative electrode was deteriorated by a deep charge / discharge cycle. In addition, the battery of Example 2 had the same initial characteristics as that of Example 1, but the discharge capacity was reduced when compared at the 30th cycle. This seems to be due to the influence of other crystal phases contained in Nb ₂ O ₅ . Table 2 shows the discharge capacity for each voltage. Here, in terms of cycle performance, ◎ indicates that a sufficient capacity can be obtained, Δ indicates that the capacity is reduced by about 20%, and x indicates that the capacity cannot be obtained. In contrast to the battery of Example 2, the battery of Example 1 did not stop functioning as a battery even after repeated charging and discharging 100 times or more. The 30th charge curve and discharge curve of Example 1 and Example 2 are shown in FIG.

  Next, after the battery of Example 1 and the battery of Comparative Example 2 were allowed to stand at room temperature for 3 months, a charge / discharge test was performed under the previous conditions. The discharge capacity is shown in Table 3 for each voltage.

サイクル性については、先ほどと同じ記号でしめす。比較例２の電池は実施例１に比べて８割程度の容量となり、１．０Ｖをすぎて放電すると、容量が伸びなくなってしまった。また、サイクル性についても劣化が激しかった。これは、不純物による影響と思われる。実施例１の電池と比較例２の電池を３ヶ月間室温放置した後に測定した充電カーブと放電カーブを図５に示す。
（比較例３）
実施例1と同様の方法でニオブ酸（Ｎｂ₂Ｏ_５・ｎＨ₂Ｏ）を熱処理後、ボールミルにて２４時間粉砕を行った以外はまったく同様にして電池を作製した。このＮｂ₂Ｏ_５の粉末特性を実施例１と同様に測定したところ、ＸＲＤ回折において回折角２４度（２θ）付近のピークの強度と２５度（２θ）付近のピークの強度はは２２．６度（２θ）付近のピークの強度の１．７％と１．４％、ＢＥＴ比表面積２４．２ｍ^２／ｇ、平均粒径０．２５μｍ、強熱減量０．１２％、Ｔａ含有量２０３ｐｐｍ、Ｆｅ含有量４．４ｐｐｍ、Ｓｉ含有量４７ｐｐｍであった。

For cycle characteristics, use the same symbols as before. The battery of Comparative Example 2 had a capacity of about 80% compared to Example 1, and when it exceeded 1.0 V and was discharged, the capacity did not increase. Also, the cycle performance was severely degraded. This seems to be the effect of impurities. FIG. 5 shows a charge curve and a discharge curve measured after the battery of Example 1 and the battery of Comparative Example 2 were allowed to stand at room temperature for 3 months.
(Comparative Example 3)
A battery was fabricated in exactly the same manner as in Example 1, except that niobic acid (Nb ₂ O ₅ .nH ₂ O) was heat treated and then ground in a ball mill for 24 hours. When the powder characteristics of this Nb ₂ O ₅ were measured in the same manner as in Example 1, the intensity of the peak near the diffraction angle of 24 degrees (2θ) and the intensity of the peak near 25 degrees (2θ) in XRD diffraction were 22.6. 1.7% and 1.4% of the intensity of the peak near the degree (2θ), BET specific surface area 24.2 m ² / g, average particle size 0.25 μm, loss on ignition 0.12%, Ta content 203 ppm, The Fe content was 4.4 ppm, and the Si content was 47 ppm.

  In order to check whether the battery can withstand the reflow temperature for each of the 10 batteries manufactured as in Example 1 and Comparative Example 3, a reflow test was performed by heating at 180 ° C. for 5 minutes and heating at 240 ° C. for 1 minute. It was. The sample after heating was subjected to battery height measurement, internal resistance measurement, and cycle characteristic measurement in order to investigate swelling. The height was measured using a dial gauge. Internal resistance was measured by an alternating current method (1 kHz). Charging / discharging conditions in the cycle characteristics are as follows: charging is carried out by a constant current constant voltage method with a maximum current of 0.05 mA, a constant voltage value of 2.0 V, and a charging time of 48 hours; I went there. The results are shown in Table 4.

実施例１の電池の膨らみは、全て０．０３ｍｍ以下で問題のないレベルであった。内部抵抗についても、リフローテスト後はテスト前のプラスマイナス２０％以内に入り問題のないレベルであった。これに対して、比較例３の電池は、電池のふくらみは全て０．０３ｍｍ以下だったものの、内部抵抗についてはリフロー前の２倍以上の大きさとなってしまった。また、容量についても大きく劣化してしまった。これは、正極の粒径を細かくしすぎたために、熱を与えた場合に活性化してしまい電解液と反応して劣化しているものと考えられる。また、上記リフローテストを行った実施例１と比較例３の充電カーブと放電カーブを図６に示す。

The bulges of the battery of Example 1 were all 0.03 mm or less, and there was no problem. The internal resistance was within the range of plus or minus 20% before the test after the reflow test, and was at a level with no problem. On the other hand, in the battery of Comparative Example 3, although the swelling of the battery was 0.03 mm or less, the internal resistance was twice as large as that before reflow. In addition, the capacity has greatly deteriorated. It is considered that this is because when the particle size of the positive electrode is made too fine, it is activated when heated and reacts with the electrolytic solution to deteriorate. Moreover, the charge curve and discharge curve of Example 1 and Comparative Example 3 in which the reflow test was performed are shown in FIG.

The discharge curve of the electrochemical cell of this invention and a comparative example. Sectional drawing of the electrochemical cell of this invention. 2 is an X-ray diffraction pattern of niobium oxide according to the present invention. The charge curve and discharge curve of the 30th cycle of the electrochemical cell which concerns on this invention. The charge curve and discharge curve which were measured after leaving for three months the electrochemical cell which concerns on this invention, and a comparative example. The charge curve and discharge curve of the Example after a reflow test, and a comparative example.

Explanation of symbols

101 Positive electrode pellet 102 Negative electrode pellet 103 Separator 104 Lithium foil 105 Electrolytic solution 106 Positive electrode case 107 Negative electrode case 108 Gasket

Claims (18)

An electrode active material made of niobium oxide, which has a diffraction angle of around 24 degrees (2θ) and a diffraction angle of 25 degrees (2θ) in the X-ray diffraction pattern of the niobium oxide measured using CuKα rays (1.5418Å). An electrode active material characterized in that the diffraction peak intensity in the vicinity is 20% or less of the diffraction peak intensity in the vicinity of a diffraction angle of 22.6 degrees (2θ). 2. The electrode active material according to claim 1, wherein the niobium oxide does not have diffraction peaks near a diffraction angle of 24 degrees (2θ) and a diffraction angle of 25 degrees (2θ). The electrode active material according to claim 1, wherein the niobium oxide is Nb ₂ O ₅ . 4. The electrode active material according to claim 1, wherein the niobium oxide has an average particle size of 3.0 μm or less. 5. The electrochemical cell according to any one of claims 1 to 4, wherein a weight reduction rate when the niobium oxide is ignited is 0.3% or less. 6. The niobium oxide has a Ta content of 500 ppm or less, an Fe content of 15 ppm or less, and an Si content of 300 ppm or less. 6. Electrode active material. 7. The electrode active material according to claim 1, wherein the niobium oxide has a specific surface area in the range of 3.5 m ² / g to 20 m ² / g. The electrode active material according to any one of claims 1 to 7, wherein the electrode active material is used for a positive electrode. An electrochemical cell using the electrode active material according to claim 1. 9. An electrochemical cell using the electrode active material according to claim 8, wherein the negative electrode active material is made of a material containing either silicon or tungsten. 11. The electrochemical cell according to claim 10, wherein the negative electrode active material is a silicon oxide capable of occluding and releasing lithium ions. 12. The ratio of the number of atoms of silicon, lithium, and oxygen contained in the silicon oxide is represented by 1: x: y, wherein x ≧ 0 and 2> y> 0. Electrochemical cell. When the ratio of the number of atoms of silicon, lithium and oxygen contained in the silicon oxide is expressed by 1: x: y, 4.5 ≧ x ≧ 4.0 and 2> y> 0, The electrochemical cell according to claim 11. From a nonaqueous solvent having a boiling point of 200 ° C. or higher at normal pressure, a supporting salt containing fluorine, a separator made of glass fiber or a resin having a heat distortion temperature of 230 ° C. or higher, and a resin having a heat distortion temperature of 230 ° C. or higher. The electrochemical cell according to claim 9, further comprising: a gasket. The electrochemical cell according to claim 14, wherein the non-aqueous solvent contains either ethylene carbonate (EC) or γ-butyrolactone (γBL). The electrochemical cell according to claim 14, wherein the supporting salt contains either lithium hexafluorophosphate (LiPF ₆ ) or lithium borofluoride (LiBF ₄ ). The gasket is made of polyphenylene sulfide, liquid crystal polymer (LCP), polyetheretherketone resin (PEEK), polyethernitrile resin (PEN), polyamideimide resin, or tetrafluoroethylene-perfluoroalkylvinylether copolymer resin. The electrochemical cell according to claim 14, wherein the electrochemical cell is used. In the X-ray diffraction pattern measured using CuKα ray (1.5418 Å), the diffraction peak intensities at a diffraction angle of 24 degrees (2θ) and a diffraction angle of 25 degrees (2θ) are both diffraction angles of 22.6 degrees (2θ). An electrochemical cell comprising a positive electrode active material made of niobium oxide having a strength of 20% or less and a negative electrode active material containing either silicon or tungsten.

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