JP2006278928A - Capacitor and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly reliable capacitor which is high in energy density and output using a metal oxide for an anode, and improves cycle property, and to provide its manufacturing method. <P>SOLUTION: The capacitor comprises the anode mainly consisting of metal oxide powder and conductive powder, a cathode mainly consisting of a material capable of occluding/discharging lithium, and a non-aqueous system electrolyte formed by dissolving a lithium salt into a non-aqueous solvent. The metal oxide powder contained in the anode is 2 μm or less in average particle size, and/or 1 m<SP>2</SP>/g or more in specific surface area by BET method, a weight ratio of the metal oxide powder/the conductive powder contained in the anode is 3/7 to 7/3, and a uniform region representing a distributed degree is 30 μm or less inside the conductive powder within the anode of the metal oxide powder. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a capacitor having both high capacity and high output, and a method for manufacturing the same.

  In recent years, midnight power storage systems, home-use distributed power storage systems based on solar power generation technology, and power storage systems for electric vehicles have attracted attention from the viewpoint of the conservation of the global environment and the effective use of energy for resource conservation. Yes.

  Among them, in a combination of a high-efficiency engine and a power storage system (for example, a hybrid electric vehicle) or a combination of a fuel cell and a power storage system (for example, a fuel cell electric vehicle), the engine or the fuel cell operates at maximum efficiency. In order to cope with load-side output fluctuations or energy regeneration, high-power discharge characteristics and / or high-rate charge acceptance characteristics are required in the power storage system.

  At present, as a high power storage device, there is an electric double layer capacitor using activated carbon as an electrode, and a large capacitor having an output characteristic exceeding 2 kW / l has been developed. However, since the energy density is only about 1 to 10 Wh / l, for example, in the case of configuring the above-described power storage system, it is cited as a practical issue that the volume is increased. An energy density of 3 to 5 times that of a double layer capacitor is desired.

  In addition to the approach to improve the performance of the electric double layer capacitor itself, there is a concept to actively use the pseudo capacity associated with the electrochemical reaction that is overwhelmingly advantageous in terms of energy density. There have been many attempts to apply metal oxides such as ruthenium oxide, vanadium oxide and manganese oxide on carbon and apply them to capacitors.

For example, vanadium-based oxides are one of the promising positive electrode materials for capacitors because of their large capacity and low cost. V ₂ O ₅ sol and a carbon material are mixed, and metal foam nickel is immersed in this. The electrode obtained by drying has a capacity of 250 mAh / g (based on V ₂ O ₅ ) at an output of 100 C level (for example, see Non-Patent Document 1). Also disclosed is a material in which amorphous manganese oxide is coated on acetylene black by reducing MnO ₄ ⁻ ions in an aqueous sodium permanganate solution under ultrasonic irradiation. The material is reported to have a capacity of 363 mAh / g (see Non-Patent Document 2).

  When the above-described material is put into practical use, first, as a characteristic required for the electrode, an electrode thickness or density of a certain level or more is required. However, a capacitor using an electrode having a practical thickness (for example, a thickness of 20 μm or more) using the above material has a problem that although the energy density is improved, the output characteristics that are characteristic of the capacitor cannot be obtained.

On the other hand, when a metal oxide (for example, lithium vanadium oxide) that generates the pseudo capacity is mixed with activated carbon, the capacity is larger than when activated carbon alone is used, and the capacity of the capacitor is reduced when the charging voltage is low. Although it has been reported to be large, there is no description regarding the output characteristics from the practical viewpoint. (For example, see Patent Document 1).
Mitsuhiro Hibino et al. Compositing vanadium oxide gel and carbon particles for supercapacitor positive electrode, “Production Research”, September 2001, Vol. 53, September / October, p2-8 Kawakazu Hirokazu et al., Sonochemical Synthesis of Amorphous Manganese Oxides and Electrochemical Capacitor Characteristics "Abstracts of the 43rd Battery Conference", October 2002, 2C02 p406-407 JP 2000-138142 A

  Although the above prior art suggests the possibility of a capacitor using a metal oxide for the positive electrode, it is unsatisfactory in energy density or output characteristics from the viewpoint of practical use. Accordingly, the main object of the present invention is to provide a capacitor having a high energy density and high output using a metal oxide for the positive electrode, improved cycle characteristics, and high reliability, and a method for manufacturing the same. .

The present inventor conducted research while paying attention to the problems of the prior art as described above, and as a result, a metal oxide powder having an average particle diameter of 2 μm or less and / or a specific surface area by the BET method of 1 m ² / g or more. Has been found to be able to achieve the above-mentioned object by dispersing it in the positive electrode with a conductive powder at a certain level or higher, and the present invention has been completed.

The capacitor according to claim 1 is a non-aqueous system in which a positive electrode mainly composed of metal oxide powder and conductive powder, a negative electrode mainly composed of a material capable of inserting and extracting lithium, and a lithium salt are dissolved in a non-aqueous solvent. In a capacitor having an electrolytic solution, the metal oxide powder contained in the positive electrode has an average particle diameter of 2 μm or less and / or a specific surface area by the BET method of 1 m ² / g or more. The weight ratio of the conductive powder is 3/7 to 7/3, and the uniform region representing the degree of dispersion of the metal oxide powder in the conductive powder in the positive electrode is 30 μm or less.

  The capacitor according to claim 2 is characterized in that the porosity of the positive electrode is 30% or more and 70% or less.

  The capacitor according to claim 3 is characterized in that the thickness of the positive electrode is 20 μm or more.

  The capacitor according to claim 4, wherein the metal oxide powder contained in the positive electrode is at least one selected from the group consisting of Group VA, Group VIA, Group VIIA, Group VIII transition metal oxides. It is characterized by being.

  The capacitor according to claim 5 is characterized in that the metal oxide powder contained in the positive electrode is a composite oxide containing lithium.

  The capacitor according to claim 6 is characterized in that the metal oxide powder contained in the positive electrode is an oxide mainly composed of manganese.

  The capacitor according to claim 7 is characterized in that the conductive powder contained in the positive electrode is at least one selected from the group consisting of acetylene black and ketjen black.

  The capacitor according to claim 8 is characterized in that the negative electrode is mainly composed of activated carbon.

  According to the configuration of the first to eighth aspects, a capacitor having a high energy density and a high output can be obtained.

  The capacitor manufacturing method according to claim 9 is the capacitor according to any one of claims 1 to 8, wherein in the positive electrode manufacturing step, the mixture containing the metal oxide powder, the conductive powder and the binder is dispersed by a roll. It is a feature.

  According to the above manufacturing method, a capacitor having high energy density, high output, and good cycle characteristics can be easily manufactured.

As described above, the capacitor of the present invention comprises a positive electrode mainly composed of metal oxide powder and conductive powder, a negative electrode mainly composed of a material capable of inserting and extracting lithium, and a lithium salt dissolved in a non-aqueous solvent. In a capacitor having a non-aqueous electrolyte, the metal oxide powder contained in the positive electrode has an average particle diameter of 2 μm or less and / or a specific surface area by the BET method of 1 m ² / g or more, and the powder / conductivity contained in the positive electrode The weight ratio of the powder is 3/7 to 7/3, and the uniform region representing the degree of dispersion of the metal oxide powder in the conductive powder in the positive electrode is 30 μm or less. Therefore, even in a practical capacitor configuration (electrode thickness, electrode density), it is possible to provide a capacitor having a high energy density and a high output with a time rate discharge (discharge rate) of 100 C level. .

  One embodiment of the present invention will be described as follows.

The capacitor of the present invention comprises a positive electrode mainly composed of a metal oxide powder and a conductive powder, a negative electrode mainly composed of a material capable of occluding and releasing lithium, and a non-aqueous electrolyte solution in which a lithium salt is dissolved in a non-aqueous solvent. In the capacitor, the powder contained in the positive electrode has an average particle diameter of 2 μm or less and / or a specific surface area by the BET method of 1 m ² / g or more, and the weight ratio of the powder / conductive powder contained in the positive electrode is 3/7 to 7/3, and the uniform region representing the degree of dispersion of the metal oxide powder in the conductive powder in the positive electrode is 30 μm or less.

The metal oxide powder used for the positive electrode of the present invention is not particularly limited as long as lithium is a material that can be reversibly occluded / released. However, in order to develop output characteristics, the average particle diameter is 2 μm or less and / Or specific surface area by BET method is 1 m ² / g or more. The particle diameter used in the present invention means an average particle diameter. When the average particle diameter exceeds 2 μm and the specific surface area by the BET method is less than 1 m ² / g, sufficient output characteristics cannot be obtained even if the particles are sufficiently dispersed in the conductive powder. In the present invention, it is described as a metal oxide powder for the sake of convenience, but the shape is not particularly limited. For example, the shape may be fibrous, and in that case, the fiber diameter corresponds to the particle diameter. The method for obtaining these metal oxide powders is not particularly limited. For example, the metal oxide powder can be pulverized and classified if necessary to obtain a metal oxide powder having a predetermined particle size.

The metal oxide powder that can be used in the present invention is preferably at least one selected from the group consisting of Group VA, Group VIA, Group VIIA, Group VIII transition metal oxides, Specifically, vanadium oxide, chromium oxide, manganese oxide, iron oxide, cobalt oxide, nickel oxide, cobalt nickel composite oxide, etc., or LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , LiMn _x Examples include composite oxides containing lithium such as Ni _y O ₂ , and composite oxides containing different elements such as Al and B in addition to these metal oxides or lithium-containing composite oxides. More preferably, it is an oxide mainly composed of manganese, in particular, a LiMnxOy system (a composite material of transition metals such as LiMn ₂ O ₄ , Ni, and Co in which Li is excessive from the stoichiometric value, Al, B, etc. A material in which different elements are combined is preferable.

The conductive powder in the present invention is not particularly limited as long as it is a powder having electronic conductivity such as a carbon material powder, a metal material powder, a metal oxide powder, or the like, but preferably has a specific surface area of 10 m ² / g. More preferably, it is a carbon material of 50 m ² / g or more and 3000 m ² / g or less, and specifically, a carbon material such as acetylene black, ketjen black, activated carbon or the like is preferable, and in particular, acetylene black, ketjen black, etc. It is preferable to use a material having an average particle diameter of 1 μm or less.

The weight ratio of metal oxide powder / conductive powder capable of inserting and extracting lithium in the positive electrode of the present invention is 3/7 to 7/3. When the weight ratio is less than 3/7, the conductive powder is too much with respect to the amount of the metal oxide powder, so that although the output characteristics are obtained, the energy density is lowered. On the other hand, if the weight ratio is larger than 7/3, the conductive powder is too small relative to the amount of the metal oxide powder, so that the cycle characteristics indicating the charge / discharge performance of the capacitor are deteriorated. This weight ratio is appropriately determined depending on the specific gravity, specific surface area, particle diameter, etc. of the metal oxide powder and conductive powder used for the positive electrode, but the average particle diameter is 2 μm or less and / or the specific surface area by the BET method is 1 m ² / g or more. It is important that the metal oxide powder is sufficiently dispersed in the positive electrode using the conductive powder, that is, a ratio that allows the uniform region representing the degree of dispersion to be 30 μm or less.

  Usually, when a metal oxide powder is used as a battery electrode, a conductive powder such as acetylene black is added in an amount of about several to 10%. However, in the electrode prepared by such a conventional method, even if the particle diameter is 2 μm or less, the dispersion of the metal oxide powder in the conductive powder becomes insufficient, for example, 20 μm or more. In a positive electrode having a practical thickness, it is difficult to obtain a 100 C level output required for a capacitor. Therefore, it is necessary to add a conductive powder (a conductive powder not coated or supported with a metal oxide) to a material in which a metal oxide according to the prior art is coated or supported on a conductive powder. As a result, an extra conductive powder carbon material for coating and supporting the metal oxide is required, which is disadvantageous in terms of energy density.

  The method for producing the positive electrode of the present invention is not particularly limited, and may be produced by a method in which the metal oxide powder can be sufficiently dispersed in the conductive powder in the positive electrode. A method of forming a powder into an electrode by adding a small amount of solvent as necessary, dispersing it with a ball mill, two rolls, three rolls, etc., and then adding a binder (may be added at the time of dispersion if necessary), A method in which a metal oxide powder and a conductive powder are dispersed in a solvent using a disper, a self-revolving disperser, etc., and then a binder is added (may be added at the time of dispersion if necessary) to form an electrode. Is mentioned.

  As a preferable production method, a mixture containing a metal oxide powder, a conductive powder and a binder is added after a solvent such as alcohol and acetone is added and sufficiently dispersed using a roll such as a two-roll or a three-roll, and then obtained. A method of forming the dispersion mixture to be formed into a predetermined thickness and shape.

  The binder is not particularly limited, and examples thereof include fluorine resins such as polyvinylidene fluoride and polytetrafluoroethylene, and polyolefins such as fluorine rubber, SBR, acrylic resin, polyethylene, and polypropylene. Further, when a binder is added and dispersed and molded using the rolls mentioned as the preferred production method described above, a strong electrode can be obtained with a small amount of polytetrafluoroethylene as the binder, so that it can be preferably used.

  In the present invention, the thickness of the positive electrode is appropriately determined depending on the required characteristics (capacitance / output) of the capacitor, but is preferably 20 μm or more. For example, when the thickness of the positive electrode is less than 20 μm, when an actual capacitor is designed, the ratio between the current collector and the separator becomes high, and sufficient capacity (energy density) cannot be obtained, thereby achieving the object of the present invention. Becomes difficult. Here, the thickness of the positive electrode is the thickness of the electrode layer that does not include the current collector, and when formed on both sides of the current collector, or when using a current collector having holes such as a metal net, The thickness obtained by subtracting the value obtained by subtracting the thickness of the current collector from the thickness (in the case of a current collector having holes such as a metal net, the pores are assumed to be 0%) is ½.

  In the present invention, the metal oxide powder needs to be sufficiently dispersed in the conductive powder in the positive electrode. This degree of dispersion can be evaluated based on the dispersibility evaluation method described in JP 2000-155089 A, and the uniform region of the metal oxide powder is 30 μm or less. When the uniform region representing the degree of dispersion of the metal oxide powder exceeds 30 μm, even if the average particle diameter of the metal oxide powder and the weight ratio of the metal oxide powder / conductive powder are within a predetermined range, Sufficient output characteristics cannot be obtained.

  The uniform region is described in detail in Japanese Patent Application Laid-Open No. 2000-155089. However, the uniform region is expressed by “imagining the distribution state of a predetermined substance contained in the sample to be evaluated, Divided evenly into regions, find the smallest region where no significant difference is found in the average value of the detected intensity in each region, defined as `` absolute value representing the size of the smallest region '', distribution of the predetermined substance As a method for imaging the state, (a) a method based on EPMA mapping analysis, (b) a method based on SEM imaging, (c) a method in which an atomic force is measured using a scanning probe microscope, and (d) Examples include a method by Auger electron microscope mapping analysis, (e) a method by X-ray photoelectron spectroscopy mapping analysis, and (f) a method by fluorescent X-ray analysis mapping analysis.

The porosity of the positive electrode of the present invention is 30% or more and 70% or less. The pores in the positive electrode are impregnated with an electrolytic solution at the time of manufacturing the capacitor. However, since the electrolytic solution needs to be sufficiently provided in the vicinity of the metal oxide powder particles dispersed in the positive electrode, the porosity is 30. If it is less than%, it is difficult to obtain the output characteristic of the present invention. If it exceeds 70%, the absolute amount of the metal oxide powder in the positive electrode is insufficient, so the energy density characteristic of the present invention is reduced. Tend to. The porosity of the positive electrode refers to the ratio of the voids (holes) excluding solid components (metal oxide powder, conductive powder, binder) per electrode unit volume (not including the current collector). The porosity of can be calculated from the actual density of the positive electrode and the true density of the metal oxide powder, conductive powder and binder. Incidentally, the true density of each material constituting the positive electrode, metal oxides (lithium-manganese composite oxide) 4.0 g / cm ^3, the conductive powder (acetylene black) is 2.0 g / cm ^3, binder (poly 4 Ethylene fluoride) is 2.2 g / cm ³ .

  The capacitor of the present invention can use a negative electrode mainly composed of a material capable of inserting and extracting lithium, but in order to obtain a high output, it is preferable to use a carbon-based material having a relatively high specific surface area. And activated carbon.

  The positive electrode and negative electrode used in the capacitor of the present invention are formed on the current collector, or the current collector is bonded to the current collector by pressure bonding or using a conductive adhesive. A body-integrated electrode is also possible. The material of the current collector is not particularly limited, and stainless steel and aluminum can be used for the positive electrode, and copper, iron, stainless steel, and the like can be used for the negative electrode. Furthermore, a structure in which an electrode can be formed on a metal foil or in a gap between metals, for example, an expanded metal, a mesh material, or the like can be used as a current collector.

  In the capacitor of the present invention, as a separator interposed between the positive electrode and the negative electrode, for example, polyolefins such as polyethylene and polypropylene, polyamide, kraft paper, glass, and cellulosic materials can be used.

The capacitor of the present invention uses a nonaqueous electrolytic solution in which a lithium salt is dissolved in a nonaqueous solvent. As the non-aqueous electrolyte solution used in the present invention, a non-aqueous electrolyte solution containing a lithium salt can be used. According to the use conditions such as the type of the positive electrode material, the property of the negative electrode material, the charging voltage, etc. It is determined. Examples of the non-aqueous electrolyte containing a lithium salt include lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, dimethoxyethane, γ-butyrolactone, acetic acid. What was melt | dissolved in the organic solvent which consists of 1 type, or 2 or more types, such as methyl and methyl formate, can be used.

  The shape of the capacitor of the present invention is not particularly limited, and can be appropriately determined according to the purpose, such as a coin shape, a cylindrical shape, a square shape, and a film shape. An object of the present invention is to provide a capacitor having a high energy density and a high output. Although the energy density depends on the size and shape of the capacitor, for example, the capacitor manufactured based on the above description was considered based on the volume of the positive electrode, negative electrode, current collector, and separator, excluding the exterior. In this case, a power density of 30 Wh / l or more, preferably 40 Wh / l or more can be obtained, and an output density of 2 kW / l or more, preferably 3 kW / l or more, more preferably 4 kW / l or more can be obtained. . Also, the average voltage of the capacitor of the present invention is preferably 2.5 V or more, more preferably 3 V or more.

  Hereinafter, examples will be shown to further clarify the features of the present invention, but the present invention is not limited to the examples.

(1) 50 parts by weight of a spinel-type lithium manganese composite oxide (Li _1.08 Mn _1.92 O ₄ ) having an average particle diameter of 0.7 μm, which is a metal oxide powder, and a specific surface area by BET method of 8 m ² / g, and conductive powder By mixing 50 parts by weight of acetylene black (Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.) and 8 parts by weight of polytetrafluoroethylene powder as a binder, adding acetone appropriately, and passing it 10 times while turning back on a biaxial roller, The lithium manganese composite oxide was dispersed in acetylene black. Subsequently, a sheet electrode (capacitor positive electrode) having a thickness of 70 μm was obtained by forming into a sheet using a roll.

The density of the positive electrode obtained was 1.0 g / cm ³ , and the porosity calculated from the density of this positive electrode and the true density of lithium manganese composite oxide, acetylene black and polytetrafluoroethylene was 61%. It was. The degree of dispersion of the lithium manganese composite oxide in the electrode was examined. The uniform area obtained by EPMA mapping analysis of Mn atoms was 27 μm.

The sheet-like positive electrode obtained above was attached to a 20 μm aluminum foil with a graphite conductive adhesive to obtain a positive electrode.
(2) The negative electrode is activated carbon (specific surface area: 1950 m ² / g), polyvinylidene fluoride (10% with respect to 100 parts by weight of activated carbon) as a binder, and acetylene black (10% with respect to 100 parts by weight of activated carbon) as a conductive material. The mixture was mixed in methylpyrrolidone and formed on a copper foil having a thickness of 18 μm. The electrode layer had a thickness of 96 μm and a density of 0.55 g / cm ³ .
(3) The positive electrode (size: 14 × 20 mm) and the negative electrode (size: 15 × 21 mm) are opposed to each other through a separator (polyethylene microporous film having a thickness of 25 μm), and ethylene carbonate and diethyl carbonate are used as an electrolyte solution in a ratio of 3: A capacitor was assembled by using LiPF ₆ dissolved at a concentration of 1 mol / l in a solvent mixed at a weight ratio of 7%. Further, metallic lithium was bonded to the negative electrode in advance, and the negative electrode activated carbon was doped after electrolyte injection.

  This capacitor is charged to a voltage of 4.2 V with a current of 0.96 mA, and then a constant voltage and a constant current charge in which a constant voltage (4.2 V) is applied is performed for 2 hours, and then 0.96 mA (current corresponding to a time rate discharge 1 C). The battery was discharged to 3.0V. The capacity at this time was 0.97 mAh, and the discharge average voltage was 3.95V. Next, in order to confirm the output characteristics, when the same charge was performed and the battery was discharged at 96 mA (current equivalent to 100C hour rate discharge), 20 seconds of discharge was possible.

  When considered based on the volume of the positive electrode, the negative electrode, the current collector, and the separator, the energy density was 55 Wh / l, and the output density at 96 mA (current corresponding to a time rate discharge of 100 C) was 4.6 kW / l.

  Further, FIG. 1 shows the charge / discharge performance of this capacitor in terms of cycle characteristics. The cycle characteristics are 50C-CC cycles (between 4.2V and 3.0V), and the measurement conditions are charging: 4.2V for 2 hours, charging at a constant current of 50C, discharging: 1C constant up to a final voltage of 3.0V. Discharge with current, measurement temperature: 25 ° C.

  As shown in FIG. 1, it can be seen that even when charging and discharging are repeated 10,000 times or more at a current equivalent to 50 C, the discharge capacity hardly changes and the cycle characteristics are dramatically improved.

Comparative Example 1

As a comparison, an electric double layer capacitor using activated carbon for the positive electrode and the negative electrode was made as a trial and the energy density was compared.
(1) Activated carbon used in Example 1 (specific surface area: 1950 m ² / g), polyvinylidene fluoride as binder (10% with respect to 100 parts by weight of activated carbon), acetylene black as conductive material (10% with respect to 100 parts by weight of activated carbon) ) Was mixed in N-methylpyrrolidone and formed on an aluminum foil having a thickness of 20 μm. The electrode layer had a thickness of 80 μm and a density of 0.55 g / cm ³ .
(2) The above electrode is opposed to a positive electrode (size: 14 × 20 mm) and a negative electrode (size: 14 × 20 mm) through a separator (electrolytic capacitor paper having a thickness of 50 μm), and 1.0 mol of propylene carbonate as an electrolytic solution is used as an electrolytic solution. A capacitor was prepared using a solution in which tetraethylammonium · BF ₄ was dissolved at a concentration of 1 / l.

  The capacitor was charged to 2.5 V with a current of 0.65 mA, and then a constant current and constant voltage charge for applying a constant voltage of 2.5 V was performed for 2 hours. Subsequently, the battery was discharged to 0 V with a constant current of 0.65 mA. The discharge capacity was 0.65 mAh, and the discharge average voltage was 1.25V. Next, in order to confirm the output characteristics, the same charging was performed and discharging was performed at 60 mA (equivalent to 100 C), and discharging for 25 seconds was possible.

  When considered based on the volume of the positive electrode, the negative electrode, the current collector, and the separator, the energy density was 11 Wh / l, and the output density at 60 mA (100 C equivalent current) was 1.0 kW / l.

  The volumes of the positive electrode, negative electrode, current collector, and separator of the inventive capacitor of Example 1 and the electric double layer capacitor of the comparative example are substantially the same. From this result, it is clear that the capacitor of the present invention has a higher energy density, higher output, and improved cycle characteristics as compared with the conventional electric double layer capacitor.

Comparative Example 2

(1) 50 parts by weight of a spinel-type lithium manganese composite oxide having an average particle diameter of 0.7 μm and a specific surface area by BET method of 8 m ² / g used in Example 1 and acetylene black (electrochemical industry) (Made by Denka Black) 50 parts by weight and 8 parts by weight of polytetrafluoroethylene powder as a binder are mixed, acetone is added as appropriate, and the mixture is passed through a biaxial roller twice, and then rolled into a sheet. A sheet electrode (capacitor positive electrode) having a thickness of 70 μm was obtained by molding.

The density of the positive electrode obtained was 0.83 g / cm ³ , and the porosity calculated from the density of this positive electrode and the true density of lithium manganese composite oxide, acetylene black and polytetrafluoroethylene was 67%. It was. The degree of dispersion of the lithium manganese composite oxide in the electrode was examined. The uniform region obtained by EPMA mapping analysis of Mn atoms was 36 μm.

The sheet-like positive electrode obtained above was attached to a 20 μm aluminum foil with a graphite conductive adhesive to obtain a positive electrode.
(2) The negative electrode was activated carbon (specific surface area: 1950 m ² / g) as in Example 1, polyvinylidene fluoride (10% with respect to 100 parts by weight of activated carbon) as a binder, and acetylene black (10 with respect to 100 parts by weight of activated carbon) as a conductive material. %) Was mixed in N-methylpyrrolidone and formed on a 18 μm thick copper foil. The electrode layer had a thickness of 96 μm and a density of 0.55 g / cm ³ .
(3) The positive electrode (size: 14 × 20 mm) and the negative electrode (size: 15 × 21 mm) are opposed to each other through a separator (polyethylene microporous film having a thickness of 25 μm), and ethylene carbonate and diethyl carbonate are used as an electrolyte solution in a ratio of 3: A capacitor was assembled by using LiPF ₆ dissolved at a concentration of 1 mol / l in a solvent mixed at a weight ratio of 7%. Further, metallic lithium was bonded to the negative electrode in advance, and the negative electrode activated carbon was doped after electrolyte injection.

  This capacitor is charged to 4.2 V with a current of 0.8 mA, and then subjected to constant voltage and constant current charging to apply a constant voltage (4.2 V) for 2 hours, and then 3.0 V at 0.8 mA (1 C equivalent current). Discharged until. The capacity at this time was 0.8 mAh, and the discharge average voltage was 3.95V. Next, in order to confirm the output characteristics, the same charge was performed and the battery was discharged at 80 mA (current equivalent to 100 C), but the voltage drop was large and a sufficient output could not be obtained.

  If the uniform region representing the degree of dispersion of the metal oxide powder exceeds 30 μm and the dispersion is insufficient, the average particle diameter of the metal oxide powder and the weight ratio of the metal oxide powder / conductive powder are within a predetermined range. However, sufficient output characteristics and cycle characteristics cannot be obtained.

  FIG. 2 shows the relationship between the uniform area and the discharge capacity. When Example 1 and Comparative Example 2 are compared, in Comparative Example 2, when the number of times the roller passes is as small as 2 times, the uniform area becomes 36 μm and the dispersibility is improved. Without this, only 0.217 mAh discharge capacity at 100 C discharge can be obtained.

  On the other hand, in Example 1, by passing 10 times through the roller, the uniform area becomes 27 μm and the dispersibility is improved, and the discharge capacity at 100 C discharge is greatly improved to 0.537 mAh.

  Furthermore, when it is passed through the roller six times, the uniform area becomes 30 μm, and the discharge capacity at 100 C discharge is 0.375 mAh, so that a practically sufficient discharge capacity can be obtained.

  From this, it can be seen that in order to improve the dispersibility and make the uniform region 30 μm or less, it is necessary to pass through the roller at least six times.

Comparative Example 3

(1) Spinel-type lithium manganese composite oxide having an average particle size of 5.6 μm and a specific surface area by BET method of 0.8 m ² / g and acetylene black (Denka Black, manufactured by Denki Kagaku Kogyo) as conductive powder ) Mixing 50 parts by weight and 8 parts by weight of polytetrafluoroethylene powder as a binder, adding acetone appropriately, and passing the mixture 10 times while folding it back on a biaxial roller, thereby dispersing the lithium manganese composite oxide in acetylene black I let you. Subsequently, a sheet electrode (capacitor positive electrode) having a thickness of 65 μm was obtained by forming into a sheet using a roll.

The density of the positive electrode obtained was 1.0 g / cm ³ , and the porosity calculated from the density of this positive electrode and the true density of lithium manganese composite oxide, acetylene black and polytetrafluoroethylene was 61%. It was. The degree of dispersion of the lithium manganese composite oxide in the electrode was examined. The uniform region obtained by EPMA mapping analysis of Mn atoms was 28 μm.

The sheet-like positive electrode obtained above was attached to a 20 μm aluminum foil with a graphite conductive adhesive to obtain a positive electrode.
(2) The negative electrode is activated carbon (specific surface area: 1950 m ² / g), polyvinylidene fluoride (10% with respect to 100 parts by weight of activated carbon) as a binder, and acetylene black (10% with respect to 100 parts by weight of activated carbon) as a conductive material. The mixture was mixed in methylpyrrolidone and formed on a copper foil having a thickness of 18 μm. The electrode layer had a thickness of 96 μm and a density of 0.55 g / cm ³ .
(3) The positive electrode (size: 14 × 20 mm) and the negative electrode (size: 15 × 21 mm) are opposed to each other through a separator (polyethylene microporous film having a thickness of 25 μm), and ethylene carbonate and diethyl carbonate are used as an electrolyte solution in a ratio of 3: A capacitor was assembled by using LiPF ₆ dissolved at a concentration of 1 mol / l in a solvent mixed at a weight ratio of 7%. Further, metallic lithium was bonded to the negative electrode in advance, and the negative electrode activated carbon was doped after electrolyte injection.

  This capacitor is charged to 4.2 V with a current of 1.0 mA, and then a constant voltage and constant current charge for applying a constant voltage (4.2 V) is performed for 2 hours, and then 3.0 V at 1.0 mA (1 C equivalent current). Discharged until. The capacity at this time was 1.01 mAh, and the discharge average voltage was 3.95V. Next, in order to confirm the output characteristics, when the same charge was performed and the battery was discharged at 100 mA (equivalent to 100 C), it was discharged only for 8 seconds, and the initial voltage drop was 0.6 V, which was larger than that in Example 1.

When the particle diameter is large and the BET specific surface area is less than 1 m ² / g, high output and cycle characteristics can be obtained even if the weight ratio of metal oxide powder / conductive powder or the uniform region is within the range of the present invention. Becomes difficult.

(1) 50 parts by weight of a spinel-type lithium manganese composite oxide having an average particle diameter of 0.7 μm and a specific surface area by BET method of 8 m ² / g used in Example 1 and acetylene black (electrochemical industry) 50 parts by weight of Denka Black (manufactured by Denka Black) were dispersed in a nylon ball mill, and 100 parts by weight of this dispersion was mixed with 8 parts by weight of polytetrafluoroethylene powder as a binder, and acetone was added as appropriate. The sample was further dispersed by passing it 10 times while turning it back. Subsequently, a sheet electrode (capacitor positive electrode) having a thickness of 75 μm was obtained by forming into a sheet using a roll.

The density of the positive electrode obtained was 1.23 g / cm ³ , and the porosity calculated from the density of this positive electrode and the true density of lithium manganese composite oxide, acetylene black and polytetrafluoroethylene was 37%. It was. The degree of dispersion of the lithium manganese composite oxide in the electrode was examined. The uniform area obtained by EPMA mapping analysis of Mn atoms was 27 μm.

The sheet-like positive electrode obtained above was attached to a 20 μm aluminum foil with a graphite conductive adhesive to obtain a positive electrode.
(2) As in Example 1, the negative electrode was activated carbon (specific surface area: 1950 m ² / g), polyvinylidene fluoride (10% with respect to 100 parts by weight of activated carbon) as a binder, and acetylene black (10 with respect to 100 parts by weight of activated carbon) as a conductive material. %) Was mixed in N-methylpyrrolidone and formed on a 18 μm thick copper foil. The electrode layer had a thickness of 96 μm and a density of 0.55 g / cm ³ .
(3) The positive electrode (size: 14 × 20 mm) and the negative electrode (size: 15 × 21 mm) are opposed to each other through a separator (polyethylene microporous film having a thickness of 25 μm), and ethylene carbonate and diethyl carbonate are used as an electrolyte solution in a ratio of 3: A capacitor was assembled by using LiPF ₆ dissolved at a concentration of 1 mol / l in a solvent mixed at a weight ratio of 7%. Further, metallic lithium was bonded to the negative electrode in advance, and the negative electrode activated carbon was doped after electrolyte injection.

  The capacitor was charged to 4.2 V with a current of 1.1 mA, and then a constant voltage and constant current charge for applying a constant voltage (4.2 V) was performed for 2 hours, and then 3.0 V at 1.1 mA (1 C equivalent current). Discharged until. The capacity at this time was 1.14 mAh, and the discharge average voltage was 3.95V. Next, in order to confirm the output characteristics, when the same charge was performed and the battery was discharged at 110 mA (100 C equivalent current), a discharge of 13 seconds was possible. Further, the cycle characteristic is 10,000 times or more at a current equivalent to 50 C, which is improved in the same manner as in the first embodiment.

  When considered based on the volume of the positive electrode, the negative electrode, the current collector, and the separator, the energy density was 61 Wh / l, and the output density at 110 mA (100 C equivalent current) was 5.0 kW / l.

  Although the porosity of the positive electrode decreases and the discharge capacity due to a current equivalent to 100 C tends to decrease, it can be used practically. From this, it is considered that a porosity of the positive electrode of at least 30% or more is necessary.

(1) 60 parts by weight of a spinel-type lithium manganese composite oxide having an average particle diameter of 0.7 μm and a specific surface area by BET method of 8 m ² / g used in Example 1, and acetylene black (electrochemical industry) (Made by Denka Black) 40 parts by weight, 8 parts by weight of polytetrafluoroethylene powder as a binder are mixed, and acetone is added as appropriate. Dispersed in acetylene black. Subsequently, a sheet electrode (capacitor positive electrode) having a thickness of 68 μm was obtained by forming into a sheet using a roll.

The density of the positive electrode obtained was 1.04 g / cm ³ , and the porosity calculated from the density of this positive electrode and the true density of lithium manganese composite oxide, acetylene black and polytetrafluoroethylene was 62%. It was. The degree of dispersion of the lithium manganese composite oxide in the electrode was examined. The uniform area obtained by EPMA mapping analysis of Mn atoms was 27 μm.

The sheet-like positive electrode obtained above was attached to a 20 μm aluminum foil with a graphite conductive adhesive to obtain a positive electrode.
(2) As in Example 1, the negative electrode was activated carbon (specific surface area: 1950 m ² / g), polyvinylidene fluoride (10% with respect to 100 parts by weight of activated carbon) as a binder, and acetylene black (10 with respect to 100 parts by weight of activated carbon) as a conductive material. %) Was mixed in N-methylpyrrolidone and formed on a 18 μm thick copper foil. The electrode layer had a thickness of 96 μm and a density of 0.55 g / cm ³ .
(3) The positive electrode (size: 14 × 20 mm) and the negative electrode (size: 15 × 21 mm) are opposed to each other through a separator (polyethylene microporous film having a thickness of 25 μm), and ethylene carbonate and diethyl carbonate are used as an electrolyte solution in a ratio of 3: A capacitor was assembled by using LiPF ₆ dissolved at a concentration of 1 mol / l in a solvent mixed at a weight ratio of 7%. Further, metallic lithium was bonded to the negative electrode in advance, and the negative electrode activated carbon was doped after electrolyte injection.

  The capacitor was charged to 4.2 V with a current of 1.1 mA, and then a constant voltage and constant current charge for applying a constant voltage (4.2 V) was performed for 2 hours, and then 3.0 V at 1.1 mA (1 C equivalent current). Discharged until. The capacity at this time was 1.1 mAh, and the discharge average voltage was 3.95V. Next, in order to confirm the output characteristics, the same charge was performed and the battery was discharged at 110 mA (100 C equivalent current), and 16 seconds of discharge was possible. Further, the cycle characteristic is 10,000 times or more at a current equivalent to 50 C, which is improved in the same manner as in the first embodiment.

  When considered based on the volume of the positive electrode, the negative electrode, the current collector, and the separator, the energy density was 61 Wh / l, and the output density at 110 mA (100 C equivalent current) was 5.4 kW / l.

Comparative Example 4

(1) 80 parts by weight of a spinel-type lithium manganese composite oxide having an average particle diameter of 0.7 μm and a specific surface area by BET method of 8 m ² / g used in Example 1 and acetylene black (electrochemical industry) (Made by Denka Black) 20 parts by weight, 8 parts by weight of polytetrafluoroethylene powder as a binder are mixed, and acetone is added as appropriate. Dispersed in acetylene black. Subsequently, a sheet electrode (capacitor positive electrode) having a thickness of 68 μm was obtained by forming into a sheet using a roll.

The density of the positive electrode obtained was 1.49 g / cm ³ , and the porosity calculated from the density of this positive electrode and the true density of lithium manganese composite oxide, acetylene black and polytetrafluoroethylene was 53%. It was. The degree of dispersion of the lithium manganese composite oxide in the electrode was examined. The uniform region obtained by EPMA mapping analysis of Mn atoms was 28 μm.

The sheet-like positive electrode obtained above was attached to a 20 μm aluminum foil with a graphite conductive adhesive to obtain a positive electrode.
(2) As in Example 1, the negative electrode was activated carbon (specific surface area: 1950 m ² / g), polyvinylidene fluoride (10% with respect to 100 parts by weight of activated carbon) as a binder, and acetylene black (10 with respect to 100 parts by weight of activated carbon) as a conductive material. %) Was mixed in N-methylpyrrolidone and formed on a 18 μm thick copper foil. The electrode layer had a thickness of 96 μm and a density of 0.55 g / cm ³ .
(3) The positive electrode (size: 14 × 20 mm) and the negative electrode (size: 15 × 21 mm) are opposed to each other through a separator (polyethylene microporous film having a thickness of 25 μm), and ethylene carbonate and diethyl carbonate are used as an electrolyte solution in a ratio of 3: A capacitor was assembled by using LiPF ₆ dissolved at a concentration of 1 mol / l in a solvent mixed at a weight ratio of 7%. Further, metallic lithium was bonded to the negative electrode in advance, and the negative electrode activated carbon was doped after electrolyte injection.

  This capacitor is charged to 4.2 V with a current of 1.9 mA, and then a constant voltage and constant current charge is applied to apply a constant voltage (4.2 V) for 2 hours, and then 3.0 V at 1.9 mA (1 C equivalent current). Discharged until. The capacity at this time was 1.9 mAh, and the discharge average voltage was 3.95V. Next, in order to confirm the output characteristics, when the same charge was performed and the battery was discharged at 190 mA (100 C equivalent current), only 3 seconds could be discharged. The initial voltage drop was also as large as 0.7V.

  As described above, when the amount of acetylene black as the conductive powder as the conductive powder is too small relative to the amount of the lithium manganese composite oxide as the metal oxide powder, the average particle size of the metal oxide powder, the BET method Even if the specific surface area and the uniform region are within the predetermined ranges, sufficient output characteristics and cycle characteristics cannot be obtained.

(1) 60 parts by weight of a spinel-type lithium manganese composite oxide (Li _1.14 Mn _1.86 O ₄ ) having an average particle diameter of 2.55 μm, which is a metal oxide powder, and a specific surface area by a BET method of 3.5 m ² / g and conductivity Mix 40 parts by weight of acetylene black (Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.) and 8 parts by weight of polytetrafluoroethylene powder as a binder, add acetone as appropriate, and pass 10 times while turning it back on a biaxial roller. Thus, the lithium manganese composite oxide was dispersed in acetylene black. Subsequently, a sheet electrode (capacitor positive electrode) having a thickness of 70 μm was obtained by forming into a sheet using a roll.

The density of the positive electrode obtained was 1.0 g / cm ³ , and the porosity calculated from the density of this positive electrode and the true density of lithium manganese composite oxide, acetylene black and polytetrafluoroethylene was 68%. It was. The degree of dispersion of the lithium manganese composite oxide in the electrode was examined. The uniform area obtained by EPMA mapping analysis of Mn atoms was 27 μm.

The sheet-like positive electrode obtained above was attached to a 20 μm aluminum foil with a graphite conductive adhesive to obtain a positive electrode.
(2) The negative electrode is activated carbon (specific surface area: 1950 m ² / g), polyvinylidene fluoride as a binder (10% with respect to 100 parts by weight of activated carbon), and acetylene black as a conductive material (10% with respect to 100 parts by weight of activated carbon)
Were mixed in N-methylpyrrolidone and formed on a copper foil having a thickness of 18 μm. The electrode layer had a thickness of 96 μm and a density of 0.55 g / cm ³ .
(3) The positive electrode (size: 14 × 20 mm) and the negative electrode (size: 15 × 21 mm) are opposed to each other through a separator (polyethylene microporous film having a thickness of 25 μm), and ethylene carbonate and diethyl carbonate are used as an electrolyte solution in a ratio of 3: A capacitor was assembled by using LiPF ₆ dissolved at a concentration of 1 mol / l in a solvent mixed at a weight ratio of 7%. Further, metallic lithium was bonded to the negative electrode in advance, and the negative electrode activated carbon was doped after electrolyte injection.

  This capacitor is charged to 4.2 V with a current of 0.95 mA, and then a constant voltage and constant current charge for applying a constant voltage (4.2 V) is performed for 2 hours, and then 0.90 mA (current equivalent to 1 C of time rate discharge). The battery was discharged to 3.0V. The capacity at this time was 0.92 mAh, and the average discharge voltage was 3.95V. Next, in order to confirm the output characteristics, when the same charge was performed and the battery was discharged at 95 mA (current equivalent to 100C hour rate discharge), 17 seconds of discharge was possible. Further, the cycle characteristic is 10,000 times or more at a current equivalent to 50 C, which is improved in the same manner as in the first embodiment.

  When considered based on the volume of the positive electrode, the negative electrode, the current collector, and the separator, the energy density was 52 Wh / l, and the output density at 95 mA (current corresponding to a time rate discharge of 100 C) was 4.6 kW / l.

  Examples of the use of the capacitor of the present invention include use as an output power storage device such as a hybrid electric vehicle and a fuel cell electric vehicle. It can also be used to absorb peak current loads in portable electronic / information devices, small motor drive devices, machines, and the like. This capacitor can achieve both high energy density and high output, both of which have been the subject of the prior art, and further improves cycle characteristics, contributing to the reduction in size and weight of the output power storage device.

It is a figure which shows the relationship between cycling characteristics and discharge capacity. It is a figure which shows the relationship between a uniform area | region and discharge capacity.

Claims (9)

A positive electrode mainly composed of metal oxide powder and conductive powder;
In a capacitor having a negative electrode mainly composed of a material capable of inserting and extracting lithium and a non-aqueous electrolyte solution in which a lithium salt is dissolved in a non-aqueous solvent,
The metal oxide powder contained in the positive electrode has an average particle size of 2 μm or less and / or a specific surface area by the BET method of 1 m ² / g or more,
The weight ratio of metal oxide powder / conductive powder contained in the positive electrode is 3/7 to 7/3, and
A capacitor, wherein a uniform region representing a degree of dispersion of the metal oxide powder in the conductive powder in the positive electrode is 30 μm or less. 2. The capacitor according to claim 1, wherein the porosity of the positive electrode is 30% or more and 70% or less. The capacitor according to claim 1, wherein the positive electrode has a thickness of 20 μm or more. 2. The metal oxide powder contained in the positive electrode is at least one selected from the group consisting of Group VA, Group VIA, Group VIIA, and Group VIII transition metal oxides. The capacitor according to any one of? The capacitor according to claim 4, wherein the metal oxide powder contained in the positive electrode is a composite oxide containing lithium. 6. The capacitor according to claim 4, wherein the metal oxide powder contained in the positive electrode is an oxide mainly composed of manganese. The capacitor according to claim 1, wherein the conductive powder contained in the positive electrode is at least one selected from the group consisting of acetylene black and ketjen black. The capacitor according to claim 1, wherein the negative electrode is mainly composed of activated carbon. 9. The method of manufacturing a capacitor according to claim 1, wherein, in the positive electrode manufacturing process, a mixture containing metal oxide powder, conductive powder and a binder is dispersed by a roll.