JP2015181090A - Method for manufacturing electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an electrode which enables the achievement of a power storage device having a high energy density.SOLUTION: A method for manufacturing an electrode comprises the steps of: (A) obtaining a preliminary mixture by dry-blending conductive carbon resulting from oxidization of a carbon raw material with cavities, and particles of a first active material capable of working as a positive or negative electrode active material; (B) preparing an electrode material by dry-blending the preliminary mixture, and particles of a second active material capable of working as an active material of the same polarity as of that of the first active material particles and having an average particle diameter larger than that of the first active material particles; (C) preparing a slurry by blending the electrode material, a binder and a solvent; and (D) coating a collector with the slurry to form an active material layer, drying the solvent in the active material layer and then, applying a pressure to the material layer.

Description

  The present invention relates to a method for manufacturing an electrode that provides an electricity storage device such as a secondary battery, an electric double layer capacitor, a redox capacitor, and a hybrid capacitor having a high energy density.

  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 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 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.

  An electrode of an electricity storage device is usually formed by mixing an active material and conductive carbon with a binder such as polyvinylidene fluoride and a solvent such as N-methylpyrrolidone, and this slurry is placed on a current collector for the electrode. The active material layer is formed by coating, the solvent in the active material layer is dried, and then manufactured through a process of applying pressure to the active material layer. In this step, conductive carbon having a small particle diameter such as acetylene black is preferably used. 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. Although it is necessary, since the conductivity of the electrode decreases as the amount of the active material increases, the use of conductive carbon having a small particle size is used to cope with the problem of the decrease in conductivity.

  However, since conductive carbon with a small particle size has a large specific surface area and is not familiar with the binder and the solvent, when the conductive carbon is added to the mixed solution of the binder and the solvent, the conductive carbon aggregates in the mixed solution. There is a problem that a slurry and an electrode in which conductive carbon is uniformly dispersed cannot be obtained. Therefore, in Patent Document 1 (Japanese Patent Laid-Open No. 2004-31423), when forming a slurry containing a lithium transition metal oxide containing Ni and / or Co, a lithium manganese oxide, and conductive carbon, a lithium transition metal is used. A method is shown in which an oxide, a lithium manganese compound, and conductive carbon are dry-mixed in advance, and the resulting mixture is added to a solution containing a binder. Further, in this document, the above-described method causes a problem that lithium manganese oxide is pulverized in the process of dry mixing to increase the specific surface area and deteriorate high temperature storage characteristics. A method in which a transition metal oxide and conductive carbon are preliminarily dry mixed, and the resulting mixture and lithium manganese oxide are added to a solution containing a binder and mixed to prepare a slurry, and a lithium transition metal oxide And conductive carbon and lithium manganese oxide are dry-mixed under a condition that the increase rate of the BET specific surface area before and after mixing of lithium manganese oxide is 100% or less, and the mixture is added to a solution containing a binder and mixed. A method of preparing a slurry has been proposed.

JP 2004-31423 A

  As described above, in order to obtain an electricity storage device having a high energy density, it is necessary to reduce the amount of conductive carbon per unit volume and increase the amount of active material, but active material particles having a small particle size are used as electrodes. When used for, the number of active material particles per unit weight and the specific surface area increase, and accordingly, it is necessary to increase the amount of conductive carbon in order to establish electrical conduction to the surface of each active material particle. It is disadvantageous in terms of energy density. Further, the active material particles having a small particle size are likely to aggregate and are difficult to uniformly mix with the conductive carbon. Therefore, active material particles having a particle size on the order of μm are often used.

  However, the energy storage device is always required to further improve the energy density. Therefore, in addition to the active material particles having a large particle size, active material particles having a small particle size are used, and the active material particles having a small particle size are disposed in a space formed between the active material particles having a large particle size. If it is possible, it is expected that the above request can be answered. However, when the inventors studied using conductive carbon having a small particle diameter such as acetylene black and large and small active material particles, the method using dry mixing proposed in Patent Document 1, Aggregation of active material particles having a small particle size could not be sufficiently suppressed, and satisfactory results were not obtained.

  Therefore, an object of the present invention is to provide a method for manufacturing an electrode that leads to an electricity storage device having a high energy density.

  As a result of intensive studies, the inventors have found that the above object can be achieved by using dry mixing after using conductive carbon obtained by oxidizing a carbon material having voids.

Therefore, the present invention is a method of manufacturing an electrode of an electricity storage device,
(A) Conductive carbon obtained by oxidizing a carbon material having voids and the first active material particles operable as a positive electrode active material or a negative electrode active material are dry-mixed to obtain a premix Process,
(B) a second mixture that can operate as an active material having the same polarity as the first active material particles and has an average particle size that is larger than the average particle size of the first active material particles; A step of dry mixing active material particles to prepare an electrode material;
(C) mixing the electrode material, a binder, and a solvent to prepare a slurry; and
(D) applying the slurry onto a current collector to form an active material layer, drying the solvent in the active material layer, and then applying pressure to the active material layer. The present invention relates to a method for manufacturing an electrode.

  Hereinafter, the particles of the first active material having a relatively small average particle diameter are represented as “fine particles”, and the particles of the second active material having a relatively large average particle diameter are represented as “coarse particles”. Further, conductive carbon obtained by oxidizing a carbon raw material having voids is referred to as “oxidized carbon”. In addition to the pores of the porous carbon powder, the voids include ketchen black internal voids, carbon nanofibers and carbon nanotubes, and intertube voids.

  When the carbon raw material having voids is oxidized, it is oxidized from the surface of the particles, hydroxy groups, carboxy groups and ether bonds are introduced into the carbon, and conjugated double bonds of the carbon are oxidized to generate carbon single bonds. The carbon-carbon bond is partially broken, and a hydrophilic layer is formed on the particle surface. Oxidized carbon is more likely to adhere to the surface of active material particles compared to acetylene black or the like used as a conductive agent in electrodes of conventional power storage devices, and even if the average particle size of active material particles is small, It adheres to the surface of the material particles and effectively suppresses aggregation of the active material particles. As a result, when the oxidized carbon and fine particles, preferably fine particles having an average particle size in the range of 0.01 to 2 μm, are dry-mixed in the step (A), the aggregation of the fine particles is effective. Thus, a preliminary mixture in which fine particles coated with oxidized carbon are present in a highly dispersed state can be obtained. In addition, the oxidized carbon easily adheres to the surface of the coarse particles and effectively suppresses the aggregation of the coarse particles. As a result, in the step (B), when the dry mixture of the premix containing fine particles coated with oxidized carbon and coarse particles, preferably coarse particles having an average particle size of more than 2 μm and 25 μm or less, An electrode material in which coarse particles coated with oxidized carbon and fine particles are uniformly mixed is obtained. The average particle diameter of the active material particles means a 50% diameter (median diameter) in the measurement of particle size distribution using a light scattering particle size meter.

  In the step (C), a slurry is prepared using this electrode material. In the step (D), when pressure is applied to the active material layer formed on the current collector, coarse particles and Since the fine particles are uniformly mixed with good dispersibility, the fine particles are easily arranged in the space formed between the coarse particles. As a result, an electrode having a high electrode density is obtained, and the energy density of the electricity storage device is improved.

  The step (A) is preferably performed using an apparatus selected from a bead mill, a ball mill, a planetary ball mill, a vibrating ball mill, a pot mill, a mechano-fusion compounding apparatus, a jet mill and a planetary mixer. More preferably, the material particles and the oxidation-treated carbon are dry-mixed so that the mechanochemical treatment is performed. By using these apparatuses, the surface of the microparticles is more widely and uniformly coated with the oxidized carbon, and the aggregation of the microparticles is more effectively and uniformly suppressed, so that the electrode density is further improved. Further, the obtained electrode exhibits excellent rate characteristics.

  In the step (A) and / or the step (B), it is preferable to further dry-mix another conductive carbon having a higher conductivity than the oxidized carbon. The combined use of conductive carbon having high conductivity improves the conductivity of the entire electrode obtained by the method of the present invention, so that the energy density of the electricity storage device is further improved. In addition, the oxidized carbon easily adheres to the surface of another conductive carbon used in combination, and effectively suppresses aggregation of the other conductive carbon. Thus, an electrode material in which another conductive carbon is uniformly mixed with good dispersibility is obtained.

  In the method for producing an electrode of the present invention, it is preferable that the oxidized carbon contains a hydrophilic portion, and the content of the hydrophilic portion is 10% by mass or more of the entire oxidized carbon. The content of the hydrophilic portion is particularly preferably 12% by mass or more and 30% by mass or less of the entire oxidized carbon. In the present invention, the “hydrophilic portion” of the oxidized carbon has the following meaning. That is, 0.1 g of a carbon raw material 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 oxidation treatment 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 weight of 0.1 g of the first carbon raw material is the weight of the “hydrophilic portion” dispersed in the aqueous ammonia solution at pH 11. The weight ratio of the weight of the “hydrophilic portion” to the weight of 0.1 g of the first carbon raw material is the content of the “hydrophilic portion” in the oxidized carbon. The ratio of the hydrophilic portion in the conductive carbon such as acetylene black used as the conductive agent in the electrode of the conventional power storage device is 5% by mass or less.

  As described above, when the carbon raw material having voids is oxidized, it is oxidized from the surface of the particles, and a hydrophilic portion is generated on the particle surface. As the strength of the oxidation treatment is increased, the ratio of the hydrophilic portion in the carbon particles increases so that the hydrophilic portion occupies 10% by mass or more of the entire oxidation treatment carbon, and the particles are passed through the hydrophilic portion. Aggregates.

  FIG. 1 is a model diagram showing changes in aggregates when pressure is applied to such aggregates. When pressure is applied to the aggregate aggregated through the hydrophilic portion as shown in the upper diagram of FIG. 1, the fragile hydrophilic portion cannot withstand the pressure, as shown in the center diagram of FIG. Aggregates collapse. When the pressure is further increased, not only the hydrophilic portion on the surface of the carbon particles but also the non-oxidized portion at the center of the particle is deformed or partially broken, and the whole aggregate is compressed. However, even when compressed, the hydrophilic portion of the carbon particles becomes a binder, and the non-oxidized portion and the hydrophilic portion of the carbon particles are integrated into a paste as shown in the lower diagram of FIG. And the carbon which spreads in paste form is compressed very densely. The “glue-like” means a state where grain boundaries of primary carbon particles are not recognized and non-particulate amorphous carbon is connected in an SEM photograph taken at a magnification of 25000 times.

  Oxidized carbon containing 10% by mass or more of the hydrophilic portion as a whole is more likely to adhere to the surface of the active material, and when subjected to pressure, it is integrally compressed and spreads into a paste and is not easily separated. Have Therefore, when the oxidized carbon containing the hydrophilic portion of 10% by mass or more and the fine particles are dry-mixed in the step (A), the oxidized carbon is flexibly deformed in the process of mixing and is formed on the surface of the fine particles. Adhesion increases the adhesion and uniformity of the oxidized carbon, and more effectively suppresses the aggregation of fine particles. When the preliminary mixture and coarse particles are dry-mixed in the subsequent step (B), at least a portion of the oxidized carbon is brought to the surface of the coarse particles and fine particles by the pressure exerted on the oxidized carbon from the coarse particles during the mixing process. It spreads like a paste and covers the surface of coarse particles and fine particles. Then, when pressure is applied to the active material layer formed on the current collector through the steps (C) and (D) using this electrode material, an oxidation treatment is performed as shown in the lower diagram of FIG. Most or all of the carbon spreads further into a paste and becomes dense while covering the surface of the active material particles, the coarse particles approach each other, and along with this, the oxidized carbon covers the surface of the active material particles and the adjacent coarse particles The gaps formed between the particles are extruded together with the fine particles and are densely filled. Therefore, the amount of active material per unit volume in the electrode further increases, the electrode density further increases, and the energy density of the electricity storage device is greatly improved. In addition, in the electrode having an active material layer containing oxidized carbon containing 10% by mass or more of the hydrophilic portion as a whole, most or all of the surface of the active material particles in the active material layer spreads in a dense and paste-like manner. It is covered with oxidized carbon. This is considered to be because, when the electricity storage device is configured using this preferable electrode, the dissolution of the active material in the electrolytic solution in the electricity storage device is significantly suppressed.

  In the electrode manufacturing method of the present invention, the oxidized carbon easily adheres to the surfaces of the fine particles and the coarse particles. Therefore, in the dry mixing in the step (A), the aggregation of the fine particles is effectively suppressed, and the oxidized carbon is obtained. In the subsequent dry mixing in the step (B), coarse particles and fine particles coated with oxidized carbon have good dispersibility, and a premixture in which fine particles coated on the surface are present in a highly dispersed state is obtained. An electrode material that is uniformly mixed is obtained. When pressure is applied to the active material layer formed on the current collector through the steps (C) and (D) using this electrode material, coarse particles and fine particles covered with oxidized carbon in the electrode material are applied. Since the particles are mixed with good dispersibility, the fine particles are easily arranged in the space formed between the coarse particles. As a result, an electrode having a high electrode density is obtained, and the energy density of the electricity storage device is improved.

It is the figure which showed the change of the aggregate when a pressure is applied to the aggregate of the oxidation process carbon containing the hydrophilic part of 10 mass% or more of the whole. It is a SEM photograph of magnification 50000 times about the mixture obtained by dry mixing of microparticles and carbon, (1) is the SEM photograph of the mixture obtained by dry-mixing microparticles and acetylene black using a mortar. (2) is an SEM photograph of a mixture obtained by dry mixing fine particles and oxidized carbon using a mortar, and (3) is dry mixed using fine particles and oxidized carbon using a vibrating ball mill. The SEM photograph of the mixture obtained in this way is shown respectively. It is a SEM photograph of magnification 100000 times about the mixture obtained by dry mixing of coarse particles and carbon, (1) is a SEM photograph of a mixture of coarse particles and acetylene black, (2) is coarse particles and acetylene black. (3) shows an SEM photograph of a mixture of coarse particles and oxidized carbon, respectively. An electrode obtained by using an electrode material mixed with coarse particles after dry mixing of oxidized carbon and fine particles using a mortar, and dry mixing of oxidized carbon and fine particles using a vibrating ball mill It is the figure which showed the result of having compared the rate characteristic about each of the electrode obtained using the electrode material mixed with the coarse particle after performing.

  First, the production of oxidized carbon will be explained, and then the production method of the electrode of the present invention will be explained.

(1) Production of oxidation-treated carbon Oxidation-treated carbon is produced using carbon having voids such as porous carbon powder, ketjen black, carbon nanofibers, and carbon nanotubes as a carbon raw material. As such a carbon raw material, ketjen black is preferable. Even if the oxidation treatment is performed using solid carbon as a raw material, it is difficult to obtain carbon that easily adheres to the surface of the active material particles and effectively suppresses aggregation of the active material.

  For the oxidation treatment of carbon having voids, a known oxidation method can be used without any 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, oxidized carbon can be obtained by plasma treatment, ultraviolet irradiation, corona discharge treatment, and glow discharge treatment in an oxygen-containing atmosphere of the carbon raw material.

  When the carbon raw material having voids is oxidized, it is oxidized from the surface of the particles, hydroxy groups, carboxy groups and ether bonds are introduced into the carbon, and conjugated double bonds of the carbon are oxidized to generate carbon single bonds. The carbon-carbon bond is partially broken, and a hydrophilic layer is formed on the particle surface. Oxidized carbon having such a hydrophilic layer easily adheres to the surface of the active material particles, and effectively suppresses aggregation of the active material particles.

  It is preferable that the oxidation-treated carbon includes a hydrophilic portion, and the content of the hydrophilic portion is 10% by mass or more of the entire oxidation-treated carbon. 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. 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 entire oxidation-treated carbon. The oxidized carbon thus formed has a feature that it is more likely to adhere to the surface of the active material, and is compressed integrally when spread under pressure, spreads in a paste form, and does not easily fall apart. Moreover, in the electrode formed through the steps (A) to (D), an electrode having a particularly high electrode density is obtained, and the energy density of the electricity storage device including this electrode is greatly improved. In addition, it is considered that almost the entire surface of the active material particles in the active material is covered with the oxidized carbon containing a large amount of the hydrophilic portion, but the active material is greatly dissolved in the electrolytic solution of the electricity storage device. To be suppressed.

The oxidized carbon containing 10% by mass or more of the hydrophilic part of the whole
(A1) a step of treating the carbon material having voids with an acid,
(B1) a step of mixing the product after the acid treatment and the transition metal compound,
(C1) pulverizing the obtained mixture to cause a mechanochemical reaction;
(D1) a step of heating the product after the mechanochemical reaction in a non-oxidizing atmosphere, and
(E1) It can obtain suitably by the 1st 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 first production method, carbon having voids such as porous carbon powder, ketjen black, carbon nanofibers, and carbon nanotubes is used as a carbon raw material. As such a carbon raw material, ketjen black is preferable. Even if solid carbon is used as a raw material and the same treatment as that in the first production method is performed, it is difficult to obtain oxidized carbon containing 10% by mass or more of the hydrophilic portion of the whole.

  In the step (a1), the carbon raw material 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 the transition metal compound in the step (b1).

  The transition metal compound added to the carbon raw material in the step (b1) includes transition metal halides, nitrates, sulfates, carbonates and other inorganic metal salts, formate salts, acetate salts, oxalate salts, methoxides, ethoxides, isoforms. 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 used by being mixed with active material particles in the production of electrodes for power storage devices. Therefore, when a compound of elements constituting the active material is added to the carbon raw material, an element that can be an impurity with respect to the active material It is preferable because it can prevent contamination of the material.

  In step (c1), the mixture obtained in step (b1) is pulverized to cause a mechanochemical reaction. Examples of a pulverizer for this reaction include a lyker, ball mill, bead mill, rod mill, roller mill, stirring mill, planetary mill, vibration mill, hybridizer, mechanochemical compounding apparatus, and jet mill. 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. The step (d1) is performed in a non-oxidizing atmosphere such as a nitrogen atmosphere or an argon atmosphere. The heating temperature and the heating time are appropriately selected according to the transition metal compound used. In the subsequent step (e1), the transition metal compound and / or the reaction product thereof is removed from the heated product by means such as dissolution with an acid, and then washed thoroughly and dried to obtain a total of 10 masses. It is possible to obtain oxidized carbon containing at least% hydrophilic portion.

  In the first production method, in the step (c1), the transition metal compound acts so as to promote the oxidation of the carbon raw material by a mechanochemical reaction, and the oxidation of the carbon raw material proceeds rapidly. By this oxidation, oxidized carbon containing 10% by mass or more of the hydrophilic portion is obtained.

Oxidized carbon containing 10% by weight or more of the total hydrophilic portion is also
(A2) a step of mixing a carbon raw material having voids and a transition metal compound,
(B2) heating the resulting mixture in an oxidizing atmosphere; and
(C2) The second production method including the step of removing the transition metal compound and / or the reaction product thereof from the heated product can also be suitably obtained.

  Also in the second manufacturing method, carbon having voids such as porous carbon powder, ketjen black, carbon nanofiber, and carbon nanotube is used as the carbon raw material. As such a carbon raw material, ketjen black is preferable. Even if solid carbon is used as a raw material and the same treatment as in the second production method is performed, it is difficult to obtain an oxidized carbon containing a hydrophilic portion of 10% by mass or more of the whole.

  Examples of the transition metal compound added to the carbon raw material in the step (a2) include transition metal halides, nitrates, sulfates, carbonates, and other inorganic metal salts, formate salts, acetate salts, oxalate salts, methoxides, ethoxides, isoforms. 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 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 used by mixing with active material particles in the manufacture of electrodes for power storage devices. Therefore, when a compound of an element constituting the active material is added to the carbon raw material, an element that can be an impurity with respect to the active material. Since mixing can be prevented, it is preferable.

  The step (b2) is performed in an oxygen-containing atmosphere such as air, and is performed at a temperature at which carbon is partially lost but not completely lost, preferably at a temperature of 200 to 350 ° C. In the subsequent step (c2), 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 washed thoroughly and dried to obtain a total of 10 masses. It is possible to obtain oxidized carbon containing at least% hydrophilic portion.

  In the second production method, the transition metal compound acts as a catalyst for oxidizing the carbon raw material in the heating step in the oxidizing atmosphere, and the oxidation of the carbon raw material proceeds rapidly. By this oxidation, oxidized carbon containing 10% by mass or more of the hydrophilic portion is obtained.

  Oxidized carbon containing 10% by mass or more of the hydrophilic portion as a whole is obtained by subjecting a carbon raw material having voids to strong oxidation treatment, and voids are formed by a method other than the first manufacturing method and the second manufacturing method. It is also possible to promote the oxidation of the carbon material.

(2) Production of electrode The obtained oxidized carbon is used for the production of the electrode of the electricity storage device, the Faraday reaction with the exchange of electrons with the ions in the electrolyte of the electricity storage device or the non-Faraday reaction without the exchange of electrons. The first active material particles (microparticles) that express the capacity and can operate as the positive electrode active material or the negative electrode active material, can operate as the active material having the same polarity as the first active material, and the first active material It is used in a mixed form with second active material particles (coarse particles) having an average particle size larger than the average particle size of the active material particles.

The method for producing the electrode of the present invention comprises:
(A) a step of dry-mixing oxidized carbon and fine particles to obtain a premix,
(B) a step of dry-mixing the preliminary mixture and coarse particles to prepare an electrode material;
(C) mixing the electrode material, a binder, and a solvent to prepare a slurry; and
(D) applying the slurry to a current collector to form an active material layer, drying the solvent in the active material layer, and then applying pressure to the active material layer.

  In the step (A), the oxidized carbon and the fine particles are dry-mixed to obtain a preliminary mixture. As the active material constituting the fine particles used in the step (A), an active material used as a positive electrode active material or a negative electrode active material in a conventional power 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.

  In the step (A), the oxidation-treated carbon and the fine particles may be mixed by hand mixing using a mortar or a mixing apparatus as long as the mixing is dry mixing. As a mixing apparatus for the dry mixing, a lykai apparatus, 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. In particular, it is preferable to use a high-pressure dispersion treatment device selected from a bead mill, a ball mill, a planetary ball mill, a vibrating ball mill, a pot mill, a mechanofusion compounding device, a jet mill, and a planetary mixer. It is preferable to dry-mix so that the mechanochemical treatment may be performed on the treated carbon. By using these apparatuses, the surface of the fine particles is more uniformly and uniformly coated with the oxidized carbon, and the aggregation of the fine particles is more effectively and uniformly suppressed.

  Although the microparticles are likely to aggregate, the oxidized carbon adheres to the surface of the microparticles and covers the surface in the step (A) of dry mixing with the oxidized carbon. Aggregation of the substance particles can be suppressed, and the mixed state of the fine particles and the oxidized carbon can be made uniform. The average particle size of the fine particles is preferably 0.01 to 2 μm.

  The mass ratio of the fine particles and the oxidized carbon is preferably in the range of 70:30 to 90:10, and more preferably in the range of 75:25 to 85:15. The dry mixing time varies depending on the total amount of fine particles and oxidized carbon to be mixed and the mixing apparatus used, but is generally between 1 and 30 minutes.

  The oxidation-treated carbon is preferably carbon that contains a hydrophilic portion and the content of the hydrophilic portion is 10% by mass or more, preferably 12% by mass or more and 30% by mass or less. Such oxidation-treated carbon has a feature that it is more likely to adhere to the surface of the active material, and when it is subjected to pressure, it is integrally compressed and spreads into a paste shape and is not easily separated. For this reason, in the step (A), when the oxidation-treated carbon containing a large amount of the hydrophilic portion and the fine particles are dry-mixed, the oxidation-treated carbon adheres to the surface of the fine particles while being deformed flexibly during the mixing process. Carbon adhesion and adhesion uniformity are increased, and aggregation of fine particles is further effectively suppressed.

  In the process (A), carbon black such as ketjen black, acetylene black, channel black, fullerene, carbon nanotube, carbon nanofiber, amorphous carbon, carbon fiber, natural, which are used for electrodes of conventional power storage devices Another conductive carbon having a conductivity higher than that of oxidized carbon, such as graphite, artificial graphite, graphitized ketjen black, mesoporous carbon, and vapor grown carbon fiber, can be mixed. The combined use of this other conductive carbon improves the conductivity of the entire electrode obtained by the method of the present invention, and therefore the energy density of the electricity storage device is further improved. Further, it easily adheres to the surface of another conductive carbon used in combination with oxidized carbon, and effectively suppresses aggregation of the other conductive carbon.

(A) In the case where another conductive carbon is used in combination in the step, after all of the oxidized carbon, another conductive carbon, and fine particles are introduced into the dry mixing apparatus (including a mortar used in manual mixing). You can dry mix,
(A1) a step of dry-mixing oxidized carbon and another conductive carbon; and
(A2) The step (A) may be performed by dividing the mixture obtained in the step (A1) and the fine particles into a dry-mixing step.

  In the case where another conductive carbon is used only in the step (A), the ratio of the fine particles to the total amount of the oxidized carbon and the other conductive carbon is 70:30 to 90: mass ratio. A range of 10 is preferable, and a range of 75:25 to 85:15 is more preferable. The ratio of the oxidized carbon to another conductive carbon is preferably in the range of 3: 1 to 1: 3, more preferably in the range of 2.5: 1.5 to 1.5: 2.5, by mass ratio. .

  In the step (B), the preliminary mixture obtained in the step (A) and the coarse particles are dry-mixed to prepare an electrode material. The active material constituting the coarse particles used in the step (B) is used as a positive electrode active material or a negative electrode active material in a conventional power storage device as long as it can operate as the same active material as the microparticles. The active material can be used without any particular limitation. These active materials may be a single compound, a mixture of two or more compounds, the same compound as the compound constituting the fine particles, or a different compound. good. As an example of the active material constituting the coarse particles, the active material exemplified for the fine particles also applies here.

  The mixing in the step (B) may also be dry mixing. Dry mixing may be performed by hand mixing using a mortar or using a mixing device. As a mixing apparatus for the dry mixing, a lykai apparatus, 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.

  Coarse particles increase the electrode density and improve the energy density of the electricity storage device. The oxidized carbon easily adheres to the surface of the coarse particles and effectively suppresses the aggregation of the coarse particles. As a result, in the step (B), when the premix containing fine particles coated with oxidized carbon and the coarse particles are dry-mixed, the coarse particles coated with oxidized carbon and the fine particles have good dispersibility. A mixed electrode material is obtained. The average particle size of the coarse particles is preferably greater than 2 μm and not greater than 25 μm.

  When oxidized carbon containing a hydrophilic portion of 10% by mass or more, preferably 12% by mass or more and 30% by mass or less as a whole is used as the oxidized carbon, the oxidized carbon is converted into the oxidized carbon by coarse particles during the dry mixing process. Due to the applied pressure, at least a part of the oxidized carbon spreads on the surface of the coarse particles and fine particles in a paste-like manner, and the surfaces of the coarse particles and fine particles are widely covered. Therefore, the coarse particles and fine particles coated with the oxidized carbon are finely coated. The dispersibility with the particles and the uniformity of the dispersion are further improved.

  The ratio of the coarse particles to the premixed mixture obtained in the step (A) is preferably selected so that the coarse particles and the fine particles have a mass ratio of 80:20 to 95: 5, and 90: More preferably, it is selected to be in the range of 10 to 95: 5. In addition, the ratio of the total amount of coarse particles and fine particles to the oxidized carbon is preferably in the range of 90:10 to 99.5: 0.5, and 95: 5 to 99: A range of 1 is more preferable. When the ratio of the oxidized carbon is less than the above range, the conductivity of the active material layer is insufficient, and the coverage of the active material particles with the oxidized carbon tends to be reduced. Further, when the ratio of the oxidized carbon is larger than the above range, the electrode density tends to decrease, and the energy density of the electricity storage device tends to decrease. The dry mixing time varies depending on the total amount of coarse particles subjected to mixing and the premix, and the mixing apparatus used, but is generally between 1 and 30 minutes.

  In the process (B), carbon black such as ketjen black, acetylene black, channel black, fullerene, carbon nanotube, carbon nanofiber, amorphous carbon, carbon fiber, natural, which are used for electrodes of conventional power storage devices Another conductive carbon having a conductivity higher than that of oxidized carbon, such as graphite, artificial graphite, graphitized ketjen black, mesoporous carbon, and vapor grown carbon fiber, can be mixed. The combined use of this other conductive carbon improves the conductivity of the entire electrode obtained by the method of the present invention, and therefore the energy density of the electricity storage device is further improved. In addition, the oxidized carbon easily adheres to the surface of another conductive carbon, and effectively suppresses aggregation of the other conductive carbon.

(B) When another conductive carbon is used together in the step, the dry mixture is introduced after all the premix, coarse particles, and another conductive carbon have been introduced into the dry mixing apparatus (including the mortar used for manual mixing). May be mixed,
(B1) a step of dry mixing the premix and another conductive carbon, and
(B2) The step (B) may be performed by dividing the mixture obtained in the step (B1) and coarse particles into a dry-mixing step.

  In the case where another conductive carbon is used only in the step (B), the ratio between the fine particles and the total amount of the oxidized carbon and the other conductive carbon is 70:30 to 90: The amount of other conductive carbon used is selected so as to be in the range of 10, preferably in the range of 75:25 to 85:15. The ratio of the oxidized carbon to another conductive carbon is preferably in the range of 3: 1 to 1: 3, more preferably in the range of 2.5: 1.5 to 1.5: 2.5, by mass ratio. . When using another conductive carbon in both the (A) process and the (B) process, the above range is determined by the total amount of the different conductive carbons added in the (A) process and the (B) process. A different amount of conductive carbon used in each step is selected to satisfy.

  In step (C), the electrode material obtained in step (B), a binder, and a solvent are mixed to prepare a slurry. In the step (C), known binders such as polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, polyvinyl fluoride, and carboxymethylcellulose are used as the binder mixed with the electrode material. The content of the binder is preferably 1 to 30% by mass with respect to the total amount of the mixed 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 mixed with the electrode material, a solvent that does not adversely affect the electrode material such as N-methylpyrrolidone can be used without any particular limitation. The amount of the solvent is not particularly limited as long as the electrode material, the binder, and the solvent are uniformly mixed.

  The wet mixing for preparing the slurry is not particularly limited, and may be performed by hand mixing using a mortar, or may be performed using a known mixing device such as a stirrer or a homogenizer. If the electrode material, the binder, and the solvent are mixed uniformly, there is no problem even if the mixing time is short. In the step (B), an electrode material in which coarse particles coated with oxidized carbon and fine particles are mixed with good dispersibility is obtained, and this electrode material is familiar with the binder and the solvent. A uniform slurry can be easily obtained in the process.

In the step (D), the slurry obtained in the step (C) is coated on a current collector to form an active material layer, and after the solvent in the active material layer is dried, pressure is applied to the active material layer. To obtain an electrode. In the step (D), a conductive material such as platinum, gold, nickel, aluminum, titanium, steel, or carbon can be used as the current collector for the electrode of the electricity storage device. 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 is generally in the range of 50,000 to 1,000,000 N / cm ² , preferably 100,000 to 500,000 N / cm ² .

  Since the coarse particles and the fine particles are uniformly mixed in the electrode material with good dispersibility, the fine particles are easily arranged in the space formed between the coarse particles in the step (D). As a result, an electrode having a high electrode density is obtained, and the energy density of the electricity storage device is improved.

  In particular, when the oxidation-treated carbon is an oxidation-treated carbon containing 10% by mass or more of the hydrophilic portion, the oxidation-treated carbon further spreads in a paste shape and covers the surface of the active material by applying pressure in the step (D). As the coarse particles approach each other, the oxidized carbon is pushed together with the fine particles into the gap formed between the adjacent coarse particles while covering the surface of the active material, and is densely packed. . Oxidized carbon that has changed into a paste is not only a gap formed between adjacent active material particles, but also pores existing on the surface of the active material particles (including gaps between primary particles observed in secondary particles). It is also extruded into the inside of the slab and filled with precision. Therefore, the amount of active material per unit volume in the active material layer further increases, and the electrode density further increases. In addition, in an electrode having an active material layer containing oxidized carbon containing 10% by mass or more of the hydrophilic portion as a whole, most or all of the surface of the active material particles in the active material layer is on the surface of the active material particles. The inside of the existing pores is covered with oxidized carbon that is dense and spreads in a paste-like manner, and is 80% or more, preferably 90% or more, particularly preferably 95% of the surface (outer surface) of the active material particles. The above is in contact with the densified, oxidized oxide-treated carbon. This is considered to be because, when an electricity storage device is configured using this electrode, dissolution of the active material in the electrolytic solution in the electricity storage device is significantly suppressed.

  The electrode obtained by the production method of the present invention is used for an electrode of an electricity 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 manufactured by the manufacturing method 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 step (C), in the step (B) for the purpose of securing an ion conduction path in the active material layer. A solid electrolyte is added to the obtained electrode material, and a binder and a solvent are further added to prepare a slurry.

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

(1) Production of oxidized carbon 1 Oxidized carbon 1
10 g of Ketjen black (trade name EC300J, manufactured by Ketjen Black International) was added to 300 mL of 60% nitric acid, and the resulting solution was irradiated with ultrasonic waves for 10 minutes, and then filtered to collect Ketjen black. 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. Content of the hydrophilic part was 15 mass% of the whole.

Oxidized carbon 2
10 g of Ketjen black (trade name EC300J, manufactured by Ketjen Black International) was added to 300 mL of 60% nitric acid, and the resulting solution was irradiated with ultrasonic waves for 1 hour and then filtered to recover Ketjen black. The recovered ketjen black was washed with water three times and dried to obtain an acid-treated ketjen black. This acid-treated ketjen black was heated in nitrogen at 700 ° C. for 3 minutes. About the obtained oxidation treatment carbon, content of the hydrophilic part was measured in the same procedure as the procedure in the oxidation treatment carbon 1. The content of the hydrophilic portion was 9.1% by mass.

(2) Mixing of carbon and active material In order to confirm the change in mixing of the active material and carbon, the following experiment was conducted.
(I) Mixing of fine particles and carbon Experiment 1
1.6 g of LiNi _0.5 Mn _0.3 Co _0.2 O ₂ fine particles having an average particle diameter of 0.32 μm and 0.4 g of oxidized carbon 1 were introduced into a vibrating ball mill apparatus (fine particles: carbon = 80: 20), 30 minutes of dry mixing at 20 hz. The obtained mixture was observed by SEM photographs.

Experiment 2
1.6 g of LiNi _0.5 Mn _0.3 Co _0.2 O ₂ microparticles having an average particle diameter of 0.32 μm and 0.4 g of oxidized carbon 1 were introduced into a mortar (microparticle: carbon = 80 20) Hand mixing was performed for 10 minutes. The obtained mixture was observed by SEM photographs.

Experiment 3
1.6 g of LiNi _0.5 Mn _0.3 Co _0.2 O ₂ fine particles having an average particle diameter of 0.32 μm and 0.4 g of acetylene black (primary particle diameter of about 40 nm) were introduced into a mortar (fine Particle: Carbon = 80: 20) Manual mixing was performed for 10 minutes. The obtained mixture was observed by SEM photographs.

  FIG. 2 shows SEM photographs (magnification: 50000 times) obtained in Experiments 1 to 3. When acetylene black is used as carbon (Experiment 3), fine particles are agglomerated in spite of the same mixing conditions as compared with the case of using oxidized carbon 1 (Experiment 2). I understand. Further, even when the oxidized carbon 1 is used, in the case of mixing by a vibration ball mill (Experiment 1), the aggregation of fine particles is further suppressed as compared with the case of manual mixing by a mortar (Experiment 2). I understand that. Therefore, it has been found that the use of oxidized carbon 1 is preferable and the use of a vibration ball mill is more preferable in order to suppress aggregation of fine particles.

(Ii) Inhibition of dissolution of active material Each of the oxidized carbon 1 and acetylene black was mixed with LiFePO ₄ particles having an average particle size of 0.22 μm, LiCoO ₂ particles having an average particle size of 0.26 μm, and LiNi having an average particle size of 0.32 μm. _0.5 Mn _0.3 Co _0.2 O ₂ particles are mixed at a mass ratio of 5:95, and 5% by mass of polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone are added and kneaded thoroughly. A slurry was formed, applied onto an aluminum foil, dried, and subjected to a rolling process to obtain an electrode. Using this electrode and an electrolyte obtained by adding 1000 ppm of water to an ethylene carbonate / diethyl carbonate 1: 1 solution of 1M LiPF ₆ , a coin-type battery was produced. In this test, fine particles having a large specific surface area were used for the purpose of increasing the area of the active material in contact with the electrolytic solution. Further, 1000 ppm of water was added for the purpose of an accelerated test because the active material is more easily dissolved as the amount of water increases. The battery was allowed to stand at 60 ° C. for 1 week and then decomposed, the electrolyte was collected, and the amount of metal dissolved in the electrolyte was analyzed by an ICP emission analyzer. Table 1 shows the results obtained.

  As is apparent from Table 1, the oxidized carbon 1 significantly suppresses dissolution of the active material in the electrolyte as compared with acetylene black. This is because even if the oxidized carbon 1 is a microparticle having an average particle diameter of 0.22 to 0.32 μm, the aggregation of the microparticles is effectively suppressed, and the surface of the active material particles This is probably because the entire surface is covered.

(Iii) Mixed state of coarse particles and carbon Experiment 4
0.96 g of LiNi _0.5 Mn _0.3 Co _0.2 O ₂ coarse particles having an average particle diameter of 5 μm and 0.04 g of oxidized carbon 1 were introduced into a mortar (coarse particles: carbon = 96: 4 ) Hand mixing was performed for 5 minutes. The obtained mixture was observed by SEM photographs.

Experiment 5
0.96 g of LiNi _0.5 Mn _0.3 Co _0.2 O ₂ coarse particles having an average particle diameter of 5 μm, 0.02 g of oxidized carbon 1 and 0.02 g of acetylene black were introduced into a mortar. (Coarse particles: carbon = 96: 4) Manual mixing was performed for 5 minutes. The obtained mixture was observed by SEM photographs.

Experiment 6
0.96 g of LiNi _0.5 Mn _0.3 Co _0.2 O ₂ coarse particles having an average particle diameter of 5 μm and 0.04 g of acetylene black were introduced into a mortar (coarse particles: carbon = 96: 4), Hand mixing was performed for 5 minutes. The obtained mixture was observed by SEM photographs.

  FIG. 3 shows SEM photographs (magnification: 100,000 times) obtained in Experiments 4-6. When only acetylene black is used as carbon (experiment 6), coarse particles and acetylene black exist separately, but when oxidized carbon 1 is used as carbon (experiment 4 and experiment 5). It can be seen that the coarse particles are covered with the paste and the outline of the coarse particles is not clearly grasped. This paste-like material is obtained by spreading the oxidized carbon 1 while covering the surface of the coarse particles by the mixing pressure. In the SEM photograph of Experiment 4, the outline of the coarse particles is more unclear than in the SEM photograph of Experiment 5, because the amount of oxidized carbon 1 is large.

(3) Production of electrode Example 1
Li ₂ CO ₃ , Ni (CH ₃ COO) ₂ , Mn (CH ₃ COO) ₂ , and Co (CH ₃ COO) ₂ were introduced into distilled water, and the resulting mixture was stirred with a stirrer for 1 hour. Then, after evaporating to dryness at 100 ° C. in air, mixing with a ball mill and heating in air at 800 ° C. for 10 minutes, LiNi _0.5 Mn _0.3 Co _{0. 2} O ₂ microparticles were obtained. 1.6 g of the particles and 0.4 g of oxidized carbon 1 were introduced into a vibration ball mill and dry mixed for 30 minutes. Next, 0.1 g of the obtained preliminary mixture, 0.02 g of acetylene black (primary particle diameter 40 nm), and commercially available LiNi _0.5 Mn _0.3 Co _0.2 O ₂ coarse particles having an average particle diameter of 5 μm 0.88 g of the mixture is dry-mixed for 10 minutes using a mortar, and further 5% by mass of polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone are added and kneaded sufficiently to form a slurry. The electrode was obtained by applying, drying, and rolling a plurality of times at a pressure of 30 kN / cm. The electrode density was calculated from the measured values of the volume and weight of the electrode material on the aluminum foil. The electrode density was 4.00 g / cc.

Example 2
Using a mortar, 1.6 g of LiNi _0.5 Mn _0.3 Co _0.2 O ₂ microparticles having an average particle diameter of 0.5 μm obtained in Example 1 and 0.4 g of oxidized carbon 1 were used. Dry mixed for minutes. Next, 0.1 g of the obtained preliminary mixture, 0.02 g of acetylene black (primary particle diameter 40 nm), and commercially available LiNi _0.5 Mn _0.3 Co _0.2 O ₂ coarse particles having an average particle diameter of 5 μm Was mixed by dry mixing for 10 minutes using a mortar, and 5% by mass of polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone were added and kneaded thoroughly to form a slurry. Using the obtained slurry, an electrode was obtained in the same procedure as in Example 1, and the electrode density was calculated. The electrode density was 3.83 g / cc.

Example 3
The procedure of Example 2 was repeated using 0.4 g of oxidized carbon 2 instead of 0.4 g of oxidized carbon 1. The electrode density was 3.55 g / cc.

Comparative Example 1
Using a mortar, 0.08 g of LiNi _0.5 Mn _0.3 Co _0.2 O ₂ microparticles having an average particle diameter of 0.5 μm obtained in Example 1 and 0.02 g of acetylene black were used. Dry mixed for minutes. To this, 0.88 g of commercially available LiNi _0.5 Mn _0.3 Co _0.2 O ₂ coarse particles having an average particle diameter of 5 μm was added and dry-mixed for 10 minutes using a mortar. Vinylidene chloride and an appropriate amount of N-methylpyrrolidone were added and sufficiently kneaded to form a slurry. Using the obtained slurry, an electrode was obtained in the same procedure as in Example 1, and the electrode density was calculated. The electrode density was 3.50 g / cc.

Comparative Example 2
0.96 g of commercially available LiNi _0.5 Mn _0.3 Co _0.2 O ₂ particles having an average particle diameter of 5 μm and 0.04 g of acetylene black were dry-mixed for 10 minutes using a mortar. 5% by mass of polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone were added and sufficiently kneaded to form a slurry. Using the obtained slurry, an electrode was obtained in the same procedure as in Example 1, and the electrode density was calculated. The electrode density was 3.40 g / cc.

  As can be understood from the comparison between Comparative Example 1, Comparative Example 2 and Example 3, the electrode density can be obtained only by using oxidized carbon 2 and acetylene black at a mass ratio of 1: 1 instead of acetylene black. It turns out that it improves. This is because, in the electrode material containing the oxidized carbon 2, coarse particles and fine particles are mixed with good dispersibility and uniformly, so that a space formed between the coarse particles is formed by rolling treatment at the time of electrode preparation. This is probably because the fine particles are easily arranged.

  Further, it is grasped from a comparison between Example 1 and Example 2 in which the oxidation-treated carbon 1 and acetylene black were used at 1: 1, and Example 3 in which the oxidation-treated carbon 2 and acetylene black were used at 1: 1. Thus, it can be seen that the electrode density is greatly improved by using the oxidized carbon 1 containing 10% by mass or more of the hydrophilic component as a whole. As shown in FIG. 3, since the oxidized carbon 1 spreads in a paste shape and covers the active material particles, an electrode material in which the active material particles are mixed with good dispersibility is obtained. Due to the rolling process at the time of preparation, the oxidized carbon further spreads in a paste-like manner and becomes dense while covering the surface of the active material particles, the coarse particles approach each other, and the oxidized carbon covers the surface of the active material particles accordingly. However, it is considered that the gap formed between the adjacent coarse particles was extruded together with the fine particles and densely filled.

  Furthermore, as can be understood from the comparison between Example 1 and Example 2, even when the oxidized carbon 1 is used, when the dry mixing of the fine particles and the oxidized carbon 1 is performed with a vibration ball mill (implemented) In Example 1), it can be seen that the electrode density is further improved as compared with the case (Example 2) in which dry mixing of fine particles and oxidized carbon 1 was performed using a mortar. This is because, as shown in FIG. 2, fine particles are dispersed more finely and more uniformly by dry mixing using a vibrating ball mill, and therefore, a gap formed between adjacent coarse particles by the rolling process at the time of electrode preparation. This is considered to reflect that the fine particles are more easily filled in the portion.

Using the electrode obtained in Example 1 or Example 2 as a positive electrode, a lithium ion secondary battery having a 1M LiPF ₆ ethylene carbonate / diethyl carbonate 1: 1 solution as an electrolyte and a counter electrode as lithium was prepared. . The obtained battery was evaluated for charge / discharge characteristics under a wide range of current density conditions. FIG. 4 is a diagram showing the relationship between the rate and the discharge capacity. The battery using the electrode of Example 1 exhibited excellent rate characteristics as compared with the battery using the electrode of Example 2. This is because, as shown in FIG. 2, the fine particles are dispersed more finely and more uniformly by dry mixing using a vibrating ball mill, and the gap formed between adjacent coarse particles by the rolling process during electrode formation. It is thought that this is because the finely dispersed fine particles are filled in.

  By using the electrode of the present invention, an electricity storage device having a high energy density can be obtained.

Claims (5)

A method for producing an electrode of an electricity storage device, comprising:
(A) Conductive carbon obtained by oxidizing a carbon material having voids and the first active material particles operable as a positive electrode active material or a negative electrode active material are dry-mixed to obtain a premix Process,
(B) a second mixture that can operate as an active material of the same polarity as the particles of the first active material and has an average particle size that is larger than the average particle size of the particles of the first active material. A step of dry mixing active material particles to prepare an electrode material;
(C) a step of preparing a slurry by mixing the electrode material, a binder, and a solvent; and
(D) applying the slurry onto a current collector to form an active material layer, drying the solvent in the active material layer, and then applying pressure to the active material layer. A method for manufacturing an electrode.   The dry mixing in the step (A) is performed using an apparatus selected from a bead mill, a ball mill, a planetary ball mill, a vibrating ball mill, a pot mill, a mechanofusion compounding device, a jet mill, and a planetary mixer. Electrode manufacturing method.   The method for producing an electrode according to claim 1, wherein in the step (A) and / or the step (B), another conductive carbon having a higher conductivity than the conductive carbon is further mixed.   The average particle diameter of the particles of the first active material is in the range of 0.01 to 2 μm, and the average particle diameter of the particles of the second active material is greater than 2 μm and 25 μm or less. The manufacturing method of the electrode of any one.   The method for producing an electrode according to claim 1, wherein the conductive carbon includes a hydrophilic portion, and the content of the hydrophilic portion is 10% by mass or more of the entire conductive carbon.