JP2019021421A - Conductive carbon mixture, electrode arranged by use of the mixture, and power storage device having the electrode - Google Patents

Abstract

To provide a conductive carbon mixture which is used together with an electrode active material in manufacturing an electrode of a power storage device and which enables the achievement of a power storage device with a good cycle life.SOLUTION: A conductive carbon mixture for manufacturing an electrode of a power storage device comprises: a conductive oxidation-processed carbon; and another conductive carbon different from the oxidation-processed carbon, wherein the oxidation-processed carbon covers the surface of the other conductive carbon. A dibutyl phthalate oil absorption per 100 g of the conductive carbon mixture is equal to or less than 70% of a dibutyl phthalate oil absorption per 100 g of the other conductive carbon. The conductive carbon mixture covers the surface of an electrode active material particularly well, elongating the cycle life of a power storage device.SELECTED DRAWING: None

Description

  The present invention relates to a conductive carbon mixture used in the manufacture of an electrode for an electricity storage device. The present invention also relates to an electrode using the conductive carbon mixture and an electricity storage device including the electrode.

  Power storage devices such as secondary batteries, electric double layer capacitors, redox capacitors, and hybrid capacitors are used as power sources for information devices such as mobile phones and laptop computers, as well as motor drive power sources and energy regeneration for low-emission vehicles such as electric vehicles and hybrid vehicles Although these devices are widely studied for systems and the like, in order to respond to the demand for higher performance and smaller size in these power storage devices, improvement in energy density and cycle life is desired.

  In these electricity storage devices, an electrode active material that develops a capacity by a Faraday reaction involving the exchange of electrons with ions in an electrolyte (including an electrolyte solution) or a non-Faraday reaction not involving the exchange of electrons is used for energy storage. Used. These electrode active materials are generally used in the form of a composite material with a conductive agent. As the conductive agent, conductive carbon such as carbon black, natural graphite, artificial graphite, or carbon nanotube is usually used. These conductive carbons are used in combination with active materials with low electrical conductivity to play a role in imparting electrical conductivity to composite materials, but they also act as a matrix that absorbs volume changes associated with active material reactions. Moreover, even if the active material is mechanically damaged, it plays a role of securing an electron conduction path.

  By the way, the composite material of these active materials and conductive carbon is generally manufactured by a method of mixing active material particles and conductive carbon particles. Conductive carbon basically does not contribute to improvement of the energy density of the electricity storage device. Therefore, in order to obtain an electricity storage device having a high energy density, the amount of active material is increased by reducing the amount of conductive carbon per unit volume. There is a need. However, it is difficult to efficiently make the conductive carbon particles enter between the active material particles, and thus it is difficult to increase the amount of the active material per unit volume by bringing the distance between the active material particles closer. Existed.

  In response to this problem, the applicant has proposed a conductive carbon mixture for manufacturing an electrode of an electricity storage device in Patent Document 1 (Japanese Patent Laid-Open No. 2006-96125). This conductive carbon mixture is obtained by dry mixing of an oxidized carbon obtained by subjecting a carbon material having voids to a strong oxidizing treatment and a conductive carbon different from the oxidized carbon. Oxidized carbon that has been subjected to strong oxidation treatment has the property that at least a part thereof changes into a paste when subjected to pressure, but the pressure applied to the oxidized carbon during the dry mixing process causes the paste of the oxidized carbon to have a paste. As a result, the oxidized carbon, at least part of which has been changed into a paste, adheres to the surface of the other conductive carbon.

  The conductive carbon mixture is compatible with the electrode active material, and in the process of manufacturing the electrode material for the electricity storage device by mixing the conductive carbon mixture and the electrode active material, at least a part of the conductive carbon mixture is used. The paste-like oxidized carbon covers the surface of the electrode active material. Then, an active material layer is formed on the current collector using this electrode material, and when an electrode is manufactured by applying pressure to the active material layer, the pressure further increases the paste of oxidized carbon, Covering the surface of the electrode active material with paste-like oxidized carbon further progresses, and between the particles of the electrode active material in which the paste-like oxidized carbon and another conductive carbon coated with each other approach each other Extruded to become dense. As a result, the content of the electrode active material in the active material layer can be increased, and an electrode having a high electrode density can be obtained. In addition, when the electricity storage device is configured using the obtained electrode, the conductive carbon mixture dissolves the electrode active material in the electrolyte even though the impregnation of the electrolyte in the electricity storage device into the electrode is not suppressed. It is known to suppress. Therefore, the energy density and cycle life of the electricity storage device are improved by the conductive carbon mixture.

Japanese Patent Laid-Open No. 2006-96125

  Storage devices are always required to further improve cycle life. Therefore, an object of the present invention is to provide a conductive carbon mixture that further extends the cycle life of the electricity storage device based on the knowledge of Patent Document 1.

  The inventor uses carbon used for evaluating the degree of development of a structure of a conductive carbon mixture obtained by widely changing the strength of dry mixing of oxidized carbon with another conductive carbon. As a result of investigation using the dibutyl phthalate oil absorption per 100 g, it was found that the dibutyl phthalate oil absorption per 100 g of the conductive carbon mixture decreases as the dry mixing strength increases. Here, the dibutyl phthalate oil absorption per 100 g of carbon is a value measured according to JIS K 6217-4. Hereinafter, the dibutyl phthalate oil absorption of 100 g of carbon measured in accordance with this JIS standard is expressed as “DBP oil absorption”, and dibutyl phthalate is expressed as “DBP”. In the present invention, “oxidized carbon” means carbon obtained by subjecting a carbon material having conductivity to a strong oxidation treatment and having a property that at least a part thereof changes into a paste when subjected to pressure. The term “paste-like” means a state where grain boundaries of carbon primary particles are not recognized and non-particulate amorphous carbon is connected in an SEM photograph taken at a magnification of 25000 times. And as a result of intensive studies, the inventors have shown that the DBP oil absorption amount is 70% or less, preferably 40 to 70%, particularly preferably 40 to 65% of the DBP oil absorption amount of the other conductive carbon. It has been found that the cycle life of an electricity storage device can be significantly improved when an electricity storage device is constructed using a conductive carbon mixture, thus completing the invention.

  Therefore, the present invention first includes a conductive oxidized carbon having conductivity and a conductive carbon different from the oxidized carbon, and the oxidized carbon coats the surface of the another conductive carbon. A conductive carbon mixture for producing an electrode of an electricity storage device, wherein the conductive carbon mixture has a DBP oil absorption of 70% or less, preferably 40 to 70% of the DBP oil absorption of the other conductive carbon. In particular, the present invention relates to a conductive carbon mixture characterized by being in the range of 40 to 65%. In the conductive carbon mixture, it is preferable that at least a part of the oxidized carbon is pasty.

  Oxidation treatment in which the other conductive carbon is refined by the pressure received during the dry mixing process of the oxidized carbon and the other conductive carbon, and at least part of the surface of the refined particles is changed into a paste Although carbon is coated, the DBP oil absorption decreases as the mixing strength is increased by, for example, increasing the frequency of a ball mill used for dry mixing or increasing the mixing time. This means that as the mixing strength is increased, the DBP oil absorption amount is reduced by the refinement of the other conductive carbon, and the oxidized conductive carbon that is at least partially changed into a paste is refined. It is considered that this corresponds to a decrease in the adsorption field of DBP. Therefore, the DBP oil absorption amount is a value reflecting the covering state of the surface of the other conductive carbon with the oxidized carbon.

  Then, the DBP oil absorption measured for the conductive carbon mixture obtained by dry mixing, that is, the conductive carbon mixture in which the oxidized carbon coats the surface of the another conductive carbon, is It has been found that the cycle life of the electricity storage device is remarkably improved when it is 70% or less, preferably 40 to 70%, particularly preferably 40 to 65% of the DBP oil absorption of the conductive carbon.

  The oxidized carbon in the conductive carbon mixture preferably contains a hydrophilic portion, and the content of the hydrophilic portion is preferably 10% by mass or more of the entire oxidized carbon. Here, the “hydrophilic portion” of carbon has the following meaning. That is, 0.1 g of carbon is added to 20 mL of an aqueous ammonia solution of pH 11, and ultrasonic irradiation is performed for 1 minute, and the obtained liquid is left for 5 hours to precipitate a solid phase portion. A portion that is not precipitated but is dispersed in an aqueous ammonia solution having a pH of 11 is a “hydrophilic portion”. Moreover, content with respect to the whole carbon of a hydrophilic part is calculated | required with the following method. After precipitation of the solid phase part, the remaining part from which the supernatant has been removed is dried, and the weight of the solid after drying is measured. The weight obtained by subtracting the weight of the solid after drying from the initial weight of 0.1 g of carbon is the weight of the “hydrophilic portion” dispersed in the aqueous ammonia solution at pH 11. The weight ratio of the “hydrophilic portion” to the initial carbon weight of 0.1 g is the content of the “hydrophilic portion” in the carbon.

  The ratio of the hydrophilic portion in the conductive carbon such as carbon black, natural graphite, and carbon nanotube used as the conductive agent in the electrode of the conventional power storage device is 5% by mass or less. However, when the carbon raw material is oxidized, it is oxidized from the surface of the carbon particles, hydroxy groups, carboxy groups and ether bonds are introduced into the carbon, and the carbon conjugated double bonds are oxidized to form carbon single bonds. The carbon-carbon bond is partially broken, and a hydrophilic portion is generated on the particle surface. As the strength of the oxidation treatment is increased, the proportion of the hydrophilic portion in the carbon particles increases and the hydrophilic portion occupies 10% by mass or more of the total carbon. Such oxidation-treated carbon is preferable because it is compressed integrally when it is subjected to pressure, easily spreads in a paste form, and is easily densified.

  The conductive carbon mixture of the present invention is used in a form mixed with an electrode active material for the production of an electrode for an electricity storage device. In the process of obtaining the electrode material by mixing the conductive carbon mixture of the present invention and the electrode active material, pasting of the oxidized carbon progresses to coat the surface of the electrode active material. Further, in the process of forming an active material layer using the electrode material on the current collector and applying pressure to the active material layer to manufacture the electrode, the pressure treatment further increases the paste of oxidized carbon. As a result, the coating of the surface of the electrode active material further proceeds and the conductive carbon mixture becomes dense. The conductive carbon mixture of the present invention having a DBP oil absorption amount of 70% or less, preferably 40 to 70%, particularly preferably 40 to 65% of the DBP oil absorption amount of the other conductive carbon is the electrode material and electrode. In the production process, the surface of the electrode active material is densified while being particularly well coated, so that the cycle life of the electricity storage device including the obtained electrode is prolonged. Therefore, the present invention is also an electrode for an electricity storage device, and has an active material layer including the electrode active material and the conductive carbon mixture of the present invention, and the oxidized carbon covers the surface of the electrode active material. It is related with the electrode characterized by having carried out, Furthermore, it is related with the electrical storage device provided with this electrode.

  In the electrode active material layer, the ratio of the electrode active material and the conductive carbon mixture is not strictly limited, but the conductive carbon mixture coats the surface of the electrode active material particularly well so that the active material layer can be electrically conductive. Therefore, the amount of the electrode active material in the active material layer can be increased. An increase in the electrode active material leads to an improvement in the energy density of the electricity storage device. The ratio of the electrode active material to the conductive carbon mixture is preferably in the range of 95: 5 to 99.5: 0.5 by mass ratio, and in the range of 97: 3 to 99.5: 0.5. Is particularly preferred. When the proportion of the conductive carbon mixture is less than the above range, the conductivity of the active material layer is insufficient, and the coverage of the active material by the conductive carbon mixture tends to be reduced and the cycle characteristics tend to be reduced.

  DBP oil absorption amount in a conductive carbon mixture comprising an oxidized carbon having conductivity and a conductive carbon different from the oxidized carbon, wherein the oxidized carbon coats the surface of the another conductive carbon. The conductive carbon mixture of the present invention having a DBP oil absorption of 70% or less of the above another conductive carbon densifies the electrode material and the surface of the electrode active material in the process of manufacturing the electrode particularly well. Therefore, the cycle life of the electricity storage device provided with the obtained electrode is prolonged.

(1) Conductive carbon mixture The conductive carbon mixture for the production of the electrode of the electricity storage device of the present invention includes an oxidized carbon having conductivity, and a conductive carbon different from the oxidized carbon, The oxidized carbon coats the surface of the other conductive carbon. Preferably, at least a part of the oxidized carbon is pasty. The DBP oil absorption amount of the conductive carbon mixture is 70% or less, preferably 40 to 70%, particularly preferably 40 to 65% of the DBP oil absorption amount of the other conductive carbon.

Oxidized carbon that at least partially changes into a paste during mixing with the other conductive carbon can be obtained by subjecting a carbon material having conductivity to a relatively strong oxidation treatment. There are no particular limitations on the carbon raw material used, but from the viewpoint of easy oxidation, porous carbon powder, ketjen black, furnace black with voids, carbon with voids such as carbon nanofibers and carbon nanotubes are used. Carbon having a void with a specific surface area measured by the BET method of 300 m ² / g or more is preferable. Among these, spherical particles such as ketjen black and furnace black having voids are particularly preferable.

  For the oxidation treatment of the carbon raw material, a known oxidation method can be used without particular limitation. For example, the oxidized carbon can be obtained by treating the carbon raw material in an acid or hydrogen peroxide solution. As the acid, nitric acid, a nitric acid-sulfuric acid mixture, a hypochlorous acid aqueous solution, or the like can be used. Moreover, oxidation-treated carbon can be obtained by heating the carbon raw material in an oxygen-containing atmosphere, water vapor, or carbon dioxide. Furthermore, the carbon raw material is mixed with an alkali metal hydroxide, heated in an oxygen-containing atmosphere, and the alkali metal is removed by washing with water or the like, whereby oxidized carbon can be obtained. Further, oxidized carbon can be obtained by plasma treatment in an oxygen-containing atmosphere of a carbon raw material, ultraviolet irradiation, corona discharge treatment and glow discharge treatment, treatment with ozone water or ozone gas, and oxygen bubbling treatment in water.

  When a carbon raw material, preferably a carbon raw material having voids as described above, is oxidized, it is oxidized from the surface of the carbon particles, and a hydroxy group, a carboxy group or an ether bond is introduced into the carbon, and a conjugated double bond of carbon is oxidized. As a result, a carbon single bond is generated, a carbon-carbon bond is partially broken, and a hydrophilic portion is generated on the particle surface. Oxidized carbon having such a hydrophilic portion easily adheres to the surface of the other conductive carbon, and effectively suppresses aggregation of the other conductive carbon. Then, as the strength of the oxidation treatment is increased, the proportion of the hydrophilic portion in the carbon particles increases, and an oxidation treatment carbon is obtained in which at least a part changes into a paste during mixing with the other conductive carbon. . The content of the hydrophilic portion in the oxidized carbon is preferably 10% by mass or more of the entire oxidized carbon. Such oxidized carbon is easily compressed when subjected to pressure, spreads in a paste-like shape, and is easily densified. It is particularly preferable that the content of the hydrophilic portion is 12% by mass or more and 30% by mass or less of the whole.

The oxidized carbon containing 10% by mass or more of the hydrophilic part of the whole
(A) a step of treating a carbon raw material having voids with an acid,
(B) a step of mixing the product after the acid treatment with the transition metal compound,
(C) pulverizing the obtained mixture to cause a mechanochemical reaction;
(D) heating the product after the mechanochemical reaction in a non-oxidizing atmosphere; and
(E) It can obtain suitably by the manufacturing method including the process of removing the said transition metal compound and / or its reaction product from the product after a heating.

  In the step (a), a carbon material having voids, preferably ketjen black, is immersed in an acid and left standing. You may irradiate an ultrasonic wave in the case of this immersion. As the acid, it is possible to use acids usually used for the oxidation treatment of carbon, such as nitric acid, a nitric acid-sulfuric acid mixture, and a hypochlorous acid aqueous solution. The soaking time depends on the acid concentration and the amount of the carbon raw material to be treated, but is generally in the range of 5 minutes to 5 hours. The acid-treated carbon is sufficiently washed with water and dried, and then mixed with a transition metal compound in the step (b).

  The transition metal compound added to the carbon raw material in the step (b) includes transition metal halides, inorganic metal salts such as nitrates, sulfates, carbonates, formates, acetates, oxalates, methoxides, ethoxides, An organic metal salt such as propoxide or a mixture thereof can be used. These compounds may be used alone or in combination of two or more. You may mix and use the compound containing a different transition metal by predetermined amount. Moreover, as long as the reaction is not adversely affected, a compound other than the transition metal compound, for example, an alkali metal compound may be added together. Oxidized carbon is mixed with the electrode active material in the production of the electrode of the electricity storage device. Therefore, when the compound of the element constituting the electrode active material is added to the carbon raw material, it becomes an impurity to the electrode active material. This is preferable because it is possible to prevent mixing of possible elements.

  In the step (c), the mixture obtained in the step (b) is pulverized to cause a mechanochemical reaction. The transition metal compound acts to promote the oxidation of the carbon raw material by a mechanochemical reaction, and the oxidation of the carbon raw material proceeds rapidly in this process. Examples of the pulverizer for this reaction include a lycaic device, a millstone mill, a ball mill, a bead mill, a rod mill, a roller mill, a stirring mill, a planetary mill, a vibration mill, a hybridizer, a mechanochemical compounding device, and a jet mill. be able to. The pulverization time depends on the pulverizer to be used, the amount of carbon to be treated, and the like, and is not strictly limited, but is generally in the range of 5 minutes to 3 hours. (D) A process is performed in non-oxidizing atmospheres, such as nitrogen atmosphere and argon atmosphere. The heating temperature and the heating time are appropriately selected according to the transition metal compound used. In the subsequent step (e), the transition metal compound and / or the reaction product thereof are removed from the heated product by means such as dissolution with an acid, and then sufficiently washed and dried. Through these steps, oxidized carbon containing a hydrophilic portion of 10% by mass or more, preferably 12% by mass or more and 30% by mass or less of the whole can be obtained.

  The conductive carbon mixture of the present invention can be obtained by dry-mixing the obtained oxidized carbon and conductive carbon different from the oxidized carbon.

  As another conductive carbon mixed with the oxidation-treated carbon, a conductive carbon used for an electrode of a conventional power storage device can be used without any particular limitation. Examples include Ketjen Black, Carbon black such as acetylene black, channel black, furnace black, thermal black, fullerene, carbon nanotube, carbon nanofiber, amorphous carbon, carbon fiber, natural graphite, artificial graphite, graphitized ketjen black, mesoporous carbon, gas phase method Carbon fiber is mentioned. These may be used alone or in combination of two or more. It is preferable to use conductive carbon having a higher conductivity than oxidized carbon that is at least partially pasty, and particularly preferably acetylene black.

  The ratio of the oxidized carbon and the other conductive carbon is preferably in the range of 3: 1 to 1: 3 by mass ratio, and preferably in the range of 2.5: 1.5 to 1.5: 2.5. More preferred. For dry mixing, a lycaic device, a stone mill, a ball mill, a bead mill, a rod mill, a roller mill, a stirring mill, a planetary mill, a vibration mill, a hybridizer, a mechanochemical compounding apparatus, and a jet mill can be used. The dry mixing time varies depending on the total amount of the oxidized carbon and the other conductive carbon subjected to mixing and the mixing apparatus used, but is generally between 10 minutes and 1 hour.

  In the process of dry mixing, at least a part of the oxidized carbon is changed into a paste and covers the surface of the other conductive carbon, so that aggregation of the other conductive carbon can be suppressed. When the DBP oil absorption is measured for the conductive carbon mixture after dry mixing, the higher the mixing strength in dry mixing, in other words, at least part of the surface of the other conductive carbon by paste-like oxidized carbon. As the coating progresses, the DBP oil absorption decreases. The DBP oil absorption of the conductive carbon mixture of the present invention is 70% or less, preferably 40 to 70%, particularly preferably 40 to 65% of the DBP oil absorption of the other conductive carbon. The dry mixing conditions for adjustment can be determined by simple preliminary experiments. Since the conductive carbon mixture of the present invention is densified while coating the surface of the electrode active material particularly well in the process of manufacturing the electrode material and electrode shown below, the cycle of the electricity storage device provided with the obtained electrode The service life is extended. When the dry mixing strength of the oxidized carbon and the another conductive carbon is increased until the DBP oil absorption amount of the conductive carbon mixture is less than 40% of the DBP oil absorption amount of the other conductive carbon, the conductive carbon mixture Although the cycle life of the electricity storage device is prolonged as compared with the case where an insufficient dry mixing strength such that the DBP oil absorption exceeds 70% of the DBP oil absorption of another conductive carbon is adopted, the DBP of the conductive carbon mixture is increased. Compared to the case where a suitable dry mixing strength in which the oil absorption is in the range of 40 to 70% of the DBP oil absorption of another conductive carbon is adopted, a tendency that the cycle life of the electricity storage device is shortened is recognized. At present, the reason is not clear.

(2) Electrode The conductive carbon mixture of the present invention is used for the production of an electrode of an electricity storage device such as a secondary battery, an electric double layer capacitor, a redox capacitor, and a hybrid capacitor, and the electron with the ions in the electrolyte of the electricity storage device. It is used in the form of a mixture with an electrode active material that develops capacity by a Faraday reaction with transfer or non-Faraday reaction without transfer of electrons.

  As the electrode active material used in combination with the conductive carbon mixture of the present invention, an active material used as a positive electrode active material or a negative electrode active material in a conventional electricity storage device can be used without any particular limitation. These active materials may be a single compound or a mixture of two or more compounds.

As examples of the positive electrode active material of the secondary battery, first, layered rock salt type LiMO ₂ , layered Li ₂ MnO ₃ —LiMO ₂ solid solution, and spinel type LiM ₂ O ₄ (wherein M is Mn, Fe, Co, Ni or a combination thereof). Specific examples of these include LiCoO ₂ , LiNiO ₂ , LiNi _4/5 Co _1/5 O ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _1/2 Mn _1/2 O ₂ , LiFeO ₂ , LiMnO ₂ , Li ₂ MnO ₃ —LiCoO _2, Li ₂ MnO ₃ —LiNiO ₂ , Li ₂ MnO ₃ —LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , Li ₂ MnO ₃ —LiNi _1/2 Mn _1/2 O ₂ , Li ₂ MnO ₃ —LiNi _1/2 Mn _1/2 O ₂ —LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMn ₂ O ₄ , LiMn _3/2 Ni _1/2 O ₄ may be mentioned. Also, sulfur and sulfides such as Li ₂ S, TiS ₂ , MoS ₂ , FeS ₂ , VS ₂ , Cr _1/2 V _1/2 S ₂ , selenides such as NbSe ₃ , VSe ₂ , NbSe ₃ , Cr ₂ In addition to oxides such as O ₅ , Cr ₃ O ₈ , VO ₂ , V ₃ O ₈ , V ₂ O ₅ , V ₆ O ₁₃ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , LiVOPO ₄ , LiV ₃ O ₅ , LiV ₃ O ₈ , MoV ₂ O ₈ , Li ₂ FeSiO ₄ , Li ₂ MnSiO ₄ , LiFePO ₄ , LiFe _1/2 Mn _1/2 PO ₄ , LiMnPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ or the like.

Examples of the negative electrode active material of the secondary battery include Fe ₂ O ₃ , MnO, MnO ₂ , Mn ₂ O ₃ , Mn ₃ O ₄ , CoO, Co ₃ O ₄ , NiO, Ni ₂ O ₃ , TiO, and TiO _2. , SnO, SnO ₂ , SiO ₂ , RuO ₂ , oxides such as WO, WO ₂ , ZnO, metals such as Sn, Si, Al, Zn, LiVO ₂ , Li ₃ VO ₄ , Li ₄ Ti ₅ O ₁₂ Examples of the composite oxide include nitrides such as Li _2.6 Co _0.4 N, Ge ₃ N ₄ , Zn ₃ N ₂ , and Cu ₃ N.

Examples of the active material in the polarizable electrode of the electric double layer capacitor include carbon materials such as activated carbon, carbon nanofibers, carbon nanotubes, phenol resin carbide, polyvinylidene chloride carbide, and microcrystalline carbon having a large specific surface area. In the hybrid capacitor, the positive electrode active material exemplified for the secondary battery can be used for the positive electrode. In this case, the negative electrode is constituted by a polarizable electrode using activated carbon or the like. Moreover, the negative electrode active material illustrated for the secondary battery can be used for the negative electrode, and in this case, the positive electrode is constituted by a polarizable electrode using activated carbon or the like. Examples of the positive electrode active material of the redox capacitor include metal oxides such as RuO ₂ , MnO ₂ and NiO, and the negative electrode is composed of an active material such as RuO ₂ and a polarizable material such as activated carbon.

  The particle shape and particle size of the electrode active material are not limited, but the average particle size of the active material is preferably greater than 2 μm and not greater than 25 μm. This active material having a relatively large average particle size improves the electrode density by itself, and in the process of manufacturing the electrode material and the electrode, at least a part of the conductive carbon mixture is caused by the pressing force. Promotes pasting and densification of pasty oxidized carbon. Further, the active material is a fine particle having an average particle diameter of 0.01 to 2 μm, and a coarse particle having an average particle diameter of greater than 2 μm and 25 μm or less operable as an active material having the same polarity as the microparticle. It may be configured. Particles with a small particle size are said to be easily agglomerated, but at least a part of the conductive carbon mixture has a paste-like oxidized carbon attached to not only the surface of coarse particles but also the surface of fine particles. Therefore, aggregation of the active material can be suppressed, and the mixed state of the active material and the conductive carbon mixture can be made uniform.

  The mass ratio of the electrode active material to be mixed and the conductive carbon mixture is not particularly limited, but in order to obtain an electricity storage device having a high energy density, the mass ratio is 90:10 to 99.5: 0.5. It is preferable that it is the range of these. The conductive carbon mixture of the present invention having a DBP oil absorption amount of 70% or less, preferably 40 to 70%, particularly preferably 40 to 65% of the DBP oil absorption amount of the other conductive carbon is the electrode material and electrode. In the process of manufacturing the electrode active material, the surface of the electrode active material is densified while being particularly well coated, so that the amount of the electrode active material can be further increased. The ratio of the electrode active material and the conductive carbon mixture is 95 by mass ratio. : 5-99.5: 0.5 is preferable, and 97: 3-99.5: 0.5 is particularly preferable. When the proportion of the conductive carbon mixture is less than the above range, the conductivity of the active material layer is insufficient, and the coverage of the active material by the conductive carbon mixture tends to be reduced and the cycle life tends to be reduced.

  By mixing the conductive carbon mixture of the present invention and the electrode active material together with a binder and a solvent, an electrode material in the form of a slurry used for manufacturing an electrode can be obtained.

  As the binder, known binders such as polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, polyvinyl fluoride, and carboxymethyl cellulose are used. The binder content is preferably 1 to 30% by mass with respect to the total amount of the electrode material. If it is 1% by mass or less, the strength of the active material layer is not sufficient, and if it is 30% by mass or more, the discharge capacity of the electrode is reduced and the internal resistance becomes excessive. As the solvent, a solvent that does not adversely affect other components in the electrode material such as N-methylpyrrolidone, dimethylformamide, tetrahydrofuran, isopropyl alcohol, and water can be used without any particular limitation. The binder can be used in a form dissolved in a solvent. The amount of the solvent used is not particularly limited as long as it does not hinder the formation of the electrode active material layer described below.

  The electrode material in the form of a slurry can be manufactured by a method in which the conductive carbon mixture of the present invention and the electrode active material are dry-mixed and then the resulting mixture is mixed with a binder and a solvent. In the process of dry mixing of the conductive carbon mixture and the electrode active material, at least a part of the conductive carbon mixture spreads in the form of paste-like oxidized carbon to cover the surface of the electrode active material. For dry mixing, a lycaic device, a stone mill, a ball mill, a bead mill, a rod mill, a roller mill, a stirring mill, a planetary mill, a vibration mill, a hybridizer, a mechanochemical compounding apparatus, and a jet mill can be used. The dry mixing time varies depending on the total amount of the conductive carbon mixture and electrode active material subjected to mixing and the mixing apparatus used, but is generally between 10 minutes and 1 hour. The mixing method in the subsequent wet mixing with the binder and the solvent is not particularly limited, and may be performed by hand mixing using a mortar, or may be performed using a known mixing apparatus such as a stirrer or a homogenizer. The wet mixing time will also vary depending on the amount of material mixed and the mixing equipment used, but is generally between 10 minutes and 1 hour.

  Further, since the conductive carbon mixture of the present invention is familiar with the binder and the solvent, a method of wet-mixing all of the conductive carbon mixture, the electrode active material, the binder and the solvent may be adopted instead of the above method. Alternatively, a method in which the conductive carbon mixture, the binder, and the solvent are wet-mixed and the electrode active material is added and wet-mixed may be employed, or the conductive carbon mixture, the electrode active material, and the solvent are wet-mixed. You may employ | adopt the method of mixing, adding a binder, and wet-mixing. In these wet mixing methods, the mixing method is not particularly limited, and the mixing time is appropriately selected according to the mixing apparatus and the mixing amount. Although it is said that fine carbon particles are not easily compatible with the binder and the solvent, the use of the conductive carbon mixture makes it possible to easily obtain an electrode material in which each component is uniformly mixed regardless of the mixing method.

  Next, an active material layer is formed by applying an electrode material in the form of a slurry onto a current collector for constituting a positive electrode or a negative electrode of an electricity storage device, and if necessary, the active material layer is dried, and then the active material An electrode is obtained by applying pressure to the layer by rolling. The obtained electrode material may be formed into a predetermined shape and pressed on a current collector, and then rolled.

As the current collector for the electrode of the electricity storage device, a conductive material such as platinum, gold, nickel, aluminum, titanium, steel, or carbon can be used. As the shape of the current collector, any shape such as a film shape, a foil shape, a plate shape, a net shape, an expanded metal shape, and a cylindrical shape can be adopted. The active material layer may be dried by reducing the pressure and heating as necessary to remove the solvent. The pressure applied to the active material layer by the rolling treatment is generally in the range of 50,000 to 1,000,000 N / cm ² , preferably 100,000 to 500,000 N / cm ² . Moreover, there is no special restriction | limiting in the temperature of a rolling process, A process may be performed at normal temperature and may be performed on heating conditions.

  When pressure is applied to the active material layer on the current collector, at least part of the conductive carbon mixture is further pasted into a paste-like oxidized carbon, and the surface of the active material particles is densely covered. The active material particles are not only the gaps formed between the adjacent active material particles while the active material particles approach each other and the oxidized carbon that has changed into a paste-like shape covers the surface of the active material particles. The inside of the hole existing on the surface of the metal is also extruded together with the other conductive carbon and is densely filled. Therefore, the amount of active material per unit volume in the electrode increases, and the electrode density increases. In addition, the densely filled conductive carbon mixture has sufficient conductivity to function as a conductive agent and suppresses dissolution of the electrode active material in the electrolytic solution.

(3) Electric storage device The electrode of the present invention is used for an electrode of an electric storage device such as a secondary battery, an electric double layer capacitor, a redox capacitor, and a hybrid capacitor. The electricity storage device includes a pair of electrodes (a positive electrode and a negative electrode) and an electrolyte disposed therebetween as essential elements, and at least one of the positive electrode and the negative electrode is the electrode of the present invention.

In the electricity storage device, the electrolyte disposed between the positive electrode and the negative electrode may be an electrolyte solution held in a separator, a solid electrolyte, or a gel electrolyte. The electrolyte used in can be used without particular limitation. Examples of typical electrolytes are shown below. For a lithium ion secondary battery, a lithium salt such as LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , or LiN (CF ₃ SO ₂ ) _{2 is used in} a solvent such as ethylene carbonate, propylene carbonate, butylene carbonate, or dimethyl carbonate. The dissolved electrolyte is used in a state of being held in a separator such as a polyolefin fiber nonwoven fabric or a glass fiber nonwoven fabric. In addition, inorganic solid electrolytes such as Li ₅ La ₃ Nb ₂ O ₁₂ , Li _1.5 Al _0.5 Ti _1.5 (PO ₄ ) ₃ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₇ P ₃ S _11, etc. An organic solid electrolyte composed of a complex of a lithium salt and a polymer compound such as polyethylene oxide, polymethacrylate, or polyacrylate, or a gel electrolyte in which an electrolytic solution is absorbed in polyvinylidene fluoride, polyacrylonitrile, or the like is also used. For electric double layer capacitors and redox capacitors, an electrolytic solution in which a quaternary ammonium salt such as (C ₂ H ₅ ) ₄ NBF ₄ is dissolved in a solvent such as acrylonitrile or propylene carbonate is used. For the hybrid capacitor, an electrolytic solution in which a lithium salt is dissolved in propylene carbonate or the like, or an electrolytic solution in which a quaternary ammonium salt is dissolved in propylene carbonate or the like is used.

  However, when a solid electrolyte or a gel electrolyte is used as the electrolyte between the positive electrode and the negative electrode, in the electrode material preparation step, each of the above-described components is used for the purpose of securing an ion conduction path in the active material layer. Prepare by adding solid electrolyte to the element.

  The present invention will be described with reference to the following examples, but the present invention is not limited to the following examples.

Example 1
10 g of Ketjen Black (trade name EC300J, manufactured by Ketjen Black International, BET specific surface area 800 m ² / g) is added to 300 mL of 60% nitric acid, and the resulting solution is irradiated with ultrasonic waves for 10 minutes and then filtered. Ketjen black was recovered. The recovered ketjen black was washed with water three times and dried to obtain an acid-treated ketjen black. 0.5 g of this acid-treated ketjen black, 1.98 g of Fe (CH ₃ COO) ₂ , 0.77 g of Li (CH ₃ COO), 1.10 g of C ₆ H ₈ O ₇ .H ₂ O, and CH ₃ 1.32 g of COOH, 1.31 g of H ₃ PO ₄ and 120 mL of distilled water were mixed, and the resulting mixture was stirred with a stirrer for 1 hour and then evaporated to dryness at 100 ° C. in air to collect the mixture. . Next, the obtained mixture was introduced into a vibrating ball mill apparatus and pulverized at 20 hz for 10 minutes. The pulverized powder was heated in nitrogen at 700 ° C. for 3 minutes to obtain a composite in which LiFePO ₄ was supported on ketjen black.

1 g of the obtained complex is added to 100 mL of 30% hydrochloric acid aqueous solution, and the resulting liquid is dissolved in LiFePO ₄ while irradiating ultrasonic waves for 15 minutes, and the remaining solid is filtered and washed with water. And dried. A part of the solid after drying was heated to 900 ° C. in air by TG analysis, and the weight loss was measured. Until the weight loss is 100%, that is, it can be confirmed that no LiFePO ₄ remains, the steps of dissolving, filtering, washing and drying the LiFePO _{4 with} the hydrochloric acid aqueous solution are repeated to obtain LiFePO ₄ -free oxidized carbon. .

  Next, 0.1 g of the obtained oxidized carbon was added to 20 mL of an aqueous ammonia solution having a pH of 11, and subjected to ultrasonic irradiation for 1 minute. The resulting liquid was allowed to stand for 5 hours to precipitate the solid phase portion. After precipitation of the solid phase part, the remaining part from which the supernatant was removed was dried, and the weight of the solid after drying was measured. The weight ratio of the weight of the solid after drying is subtracted from the weight of 0.1 g of the first oxidized carbon to the weight of 0.1 g of the first oxidized carbon, and the content of the “hydrophilic portion” in the oxidized carbon is calculated as follows. did. The content of the hydrophilic portion was 15.2% by mass.

  The obtained oxidized carbon and acetylene black (DBP oil absorption: 207 mL / 100 g) are introduced into a vibrating ball mill device at a mass ratio of 1: 1, and dry mixed at 10 hz for 20 minutes to obtain a conductive carbon mixture. It was. About this mixture, the DBP oil absorption was measured.

2 parts by mass of the obtained conductive carbon mixture, 2 parts by mass of polyvinylidene fluoride, an appropriate amount of N-methylpyrrolidone, and 96 parts by mass of commercially available LiNi _1/3 Mn _1/3 Co _1/3 O ₂ Particles (average particle size 5 μm) are wet-mixed to form a slurry, and the resulting slurry is applied onto an aluminum foil and dried, followed by rolling to obtain a positive electrode for a lithium ion secondary battery. It was. Further, 93 parts by mass of graphite, 1 part by mass of acetylene black, 6 parts by mass of polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone were wet mixed to form a slurry, and the resulting slurry was placed on a copper foil. After being applied and dried, a rolling treatment was performed to obtain a negative electrode for a lithium ion secondary battery. The capacity of the positive electrode and the capacity of the negative electrode were adjusted so that the capacity ratio was 1: 1.2. Using the positive electrode and the negative electrode, a lithium ion secondary battery was prepared using a solution obtained by adding 1% by mass of vinylene carbonate to a 1M LiPF ₆ ethylene carbonate / dimethyl carbonate 1: 1 solution as an electrolyte. About the obtained battery, charge / discharge was repeated in the range of 4.2-3.0V on the conditions of 25 degreeC and the charge / discharge rate of 1C, and the capacity | capacitance maintenance factor after 200 cycles experience was calculated | required.

Example 2
Example 1 was repeated, except that the dry mixing conditions with the vibrating ball mill device to obtain the conductive carbon mixture in Example 1 were changed from 20 minutes at 10 hz to 10 minutes at 20 hz. .

Example 3
Example 1 was repeated, except that the dry mixing conditions with the vibrating ball mill device to obtain the conductive carbon mixture in Example 1 were changed from 20 minutes at 10 hz to 20 minutes at 20 hz. .

Example 4
Example 1 was repeated, except that the dry mixing conditions with the vibrating ball mill device to obtain the conductive carbon mixture in Example 1 were changed from 20 minutes at 10 hz to 30 minutes at 20 hz. .

Example 5
Example 1 was repeated, except that the dry mixing conditions with the vibrating ball mill device to obtain the conductive carbon mixture in Example 1 were changed from 20 minutes at 10 hz to 20 minutes at 30 hz. .

Example 6
Example 1 was repeated, except that the dry mixing conditions with a vibrating ball mill device to obtain the conductive carbon mixture in Example 1 were changed from 20 minutes at 10 hz to 30 minutes at 30 hz. .

Comparative Example Example 1 is the same as Example 1 except that the dry mixing condition by the vibrating ball mill apparatus for obtaining the conductive carbon mixture in Example 1 is changed from the condition of 20 minutes at 10 hz to the condition of 10 minutes at 10 hz. Repeated.

In Table 1, for the conductive carbon mixtures and lithium ion secondary batteries of Examples 1 to 6 and Comparative Example, the DBP oil absorption amount, the DBP oil absorption amount of the conductive carbon mixture, and the DBP oil absorption amount of acetylene black (207 mL / 100 g). The ratio and the capacity maintenance rate after 200 cycles of experience are shown together.

  As is apparent from Table 1, the use of the conductive carbon mixture of Examples 1 to 6 in which the DBP oil absorption is 70% or less of the DBP oil absorption of acetylene black provides a high capacity retention rate of the lithium ion secondary battery. Accordingly, the cycle life of the lithium ion secondary battery is extended.

  By using the conductive carbon mixture of the present invention, an electricity storage device having a good cycle life can be obtained.

Claims (7)

Conductive oxidized carbon, and
A conductive carbon different from the oxidized carbon;
A conductive carbon mixture for manufacturing an electrode of an electricity storage device, wherein the oxidized carbon coats the surface of the another conductive carbon,
The conductive carbon mixture, wherein the dibutyl phthalate oil absorption per 100 g of the conductive carbon mixture is 70% or less of the dibutyl phthalate oil absorption per 100 g of the other conductive carbon.   The conductive carbon mixture according to claim 1, wherein at least a part of the oxidized carbon is pasty.   The conductive carbon mixture according to claim 1 or 2, wherein the oxidized carbon includes a hydrophilic portion, and the content of the hydrophilic portion is 10% by mass or more of the entire oxidized carbon.   The dibutyl phthalate oil absorption per 100 g of the conductive carbon mixture is in the range of 40 to 70% of the dibutyl phthalate oil absorption per 100 g of the other conductive carbon. The conductive carbon mixture according to item. An electrode for an electricity storage device,
An electrode active material;
The conductive carbon mixture according to any one of claims 1 to 4,
An electrode comprising: an active material layer comprising: the oxidized carbon covering a surface of the electrode active material.   The electrode according to claim 5, wherein a ratio of the electrode active material and the conductive carbon mixture is in a range of 97: 3 to 99.5: 0.5 in terms of mass ratio.   The electrical storage device provided with the electrode of Claim 5 or 6.