JP5201313B2 - Electrode for electrochemical device and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for an electrochemical element for manufacturing an electrochemical element which is large in an electric capacity, and which is high in reliability in a charging/discharging cycle even in the case of a high voltage, for example, 3.8 V, a method for manufacturing the productivity, and an electrochmical element using such an electrode. <P>SOLUTION: In this electrode for electrochemical elements configured of a collector and an active material layer on the surface, the active material layer is formed by molding composite particles containing electrode active materials and conductive materials and binding agent by a dry process, and the electrode active materials contain graphite or graphite-shaped particles. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to electrochemical elements such as lithium ion secondary batteries and electric double layer capacitors (in the present invention, secondary batteries and capacitors that can be repeatedly charged and discharged are collectively referred to as electrochemical elements), and the like. Electrode.

  Electrochemical elements that are small and light, have high energy density, and can be repeatedly charged and discharged are rapidly expanding in demand by utilizing their characteristics. Lithium-ion secondary batteries are used in fields such as mobile phones and notebook personal computers because of their relatively high energy density, and electric double layer capacitors can be charged and discharged rapidly. It is used as. Furthermore, the electric double layer capacitor is expected to be applied as a large power source for electric vehicles. In addition, redox capacitors that utilize the oxidation-reduction reaction (pseudo electric double layer capacitance) on the surface of metal oxides or conductive polymers are also attracting attention due to their large capacity. With the expansion and development of applications, these electrochemical devices are required to be further improved, such as lowering resistance, increasing capacity, and improving mechanical properties. Under such circumstances, various improvements have been made on the material forming the current collector and the active material layer in order to improve the performance of the electrochemical element.

The electrode for an electrochemical element is formed by laminating an active material layer containing an electrode active material, a conductive material, and a binder on a current collector. As the electrode active material, various activated carbons (also referred to as carbon) are generally used (Patent Document 1). This is because activated carbon has a large surface area and can increase the electric capacity of the obtained electrochemical element. Also in Patent Document 1, it is considered preferable that the activated carbon has a surface area of 500 m ² / g or more.

  On the other hand, it has been proposed to use graphite or graphite-like particles instead of activated carbon as the electrode active material (Patent Documents 2 and 3) (in the present invention, the graphite-like particles are formed on the surface of particles made of graphite. And those having a coating layer of carbon allotrope having a crystal structure different from the crystal structure of the graphite). According to these documents, by using graphite or graphite-like particles, an electrode for an electrochemical element having a large electric capacity and high reliability in a charge / discharge cycle can be obtained even at a high voltage of 3.8 V, for example. ing. In these documents, graphite as an electrode active material, a conductive material, a binder and a solvent are made into a slurry, and this is applied onto a current collector and dried to form an active material layer, thereby obtaining an electrode for an electrochemical device. (In the present invention, the method of obtaining the active material layer by applying and drying the slurry in this way is referred to as a wet method). Further, it is described that a fluororesin such as PVDf or PTFE, rubber, or the like can be used as the binder.

JP 2002-260634 A JP 2006-332625 A WO2006 / 054747

  However, according to the study by the present inventors, when an active material layer is formed by a wet method using graphite as an electrode active material according to the methods disclosed in Patent Document 2 and Patent Document 3, streaks are formed on the electrode surface. There is an inconvenience that unevenness of the shape and bulge of the coating end are likely to occur. In order to prepare a uniform slurry, graphite is difficult to disperse in the slurry. Therefore, it is necessary to prepare the slurry by giving sufficient shear or lengthening the stirring time, which complicates the electrode manufacturing process. The production efficiency was inferior.

  An object of the present invention is, for example, an electrode for an electrochemical element that can produce an electrochemical element having a large electric capacity and high reliability in a charge / discharge cycle even at a high voltage of 3.8 V, and has excellent productivity. It is an object of the present invention to provide a manufacturing method and an electrochemical device using such an electrode.

  As a result of diligent efforts to achieve the above object, the inventors of the present invention have formed graphite, a conductive material, and a binder as an electrode active material when an active material layer is formed using graphite or graphite-like particles as an electrode active material. The present inventors have found that it is suitable to obtain composite particles containing, and form the active material layer on a current collector by a dry method. Furthermore, the present inventors have found that it is preferable to use a binder having a small degree of swelling with respect to the electrolytic solution. The present invention has been completed based on these findings.

Thus, according to the present invention,
An electrode for an electrochemical device having a current collector and an active material layer on the surface of the current collector, wherein the active material layer forms composite particles containing an electrode active material, a conductive material and a binder by a dry method There is provided an electrode for an electrochemical element, wherein the electrode active material contains graphite or graphite-like particles.
This binder preferably has a degree of swelling of 2 or less with respect to an electrolytic solution in which triethylene monomethyl ammonium tetrafluoroborate is dissolved in propylene carbonate at a concentration of 1.0 mol / L.
In one embodiment, the electrode active material is preferably graphite-like particles. Graphite-like particles have a coating layer of carbon allotrope having a crystal structure different from the crystal structure of the graphite on the surface of the graphite particles. The coating layer may be a crystalline carbon allotrope or an amorphous carbon allotrope, but is preferably an amorphous carbon allotrope.
In addition, according to the present invention, a step of obtaining composite particles containing graphite or graphite-like particles, a conductive material and a binder, and an active material layer is formed by heating and pressing the composite particles on a current collector. A method for producing an electrode for an electrochemical element characterized by having a step (in the present invention, a method of forming an active material layer by heating and pressing composite particles on a current collector in this way is called a dry method. ). The step of obtaining composite particles is preferably a spray drying granulation method.
The obtained electrode for an electrochemical element can be used as a positive electrode or a negative electrode to form an electrochemical element, and is preferably used as a positive electrode. Such an electrochemical element is preferably an electric double layer capacitor.

  ADVANTAGE OF THE INVENTION According to this invention, the electrochemical element using the electrode for electrochemical elements, the manufacturing method excellent in the production efficiency, and such an electrochemical rough use electrode is provided. The obtained electrochemical device has a large capacitance, a high capacity retention rate, and high reliability in the charge / discharge cycle.

<Composite particle>
In the present invention, each particle uses composite particles containing graphite or graphite-like particles, a conductive agent, and a binder.

In the present invention, it is essential to use graphite or graphite-like particles as the electrode active material. Graphite is an allotrope of carbon and is a substance having a portion having a crystal structure in which six carbon rings are linked by sp ² hybrid orbitals. Graphite is roughly classified into those produced naturally (natural graphite) and those produced artificially. Natural graphite is a hexagonal or hexagonal flat crystal, usually in the form of scales, granules, or earth. Artificially manufactured products are scale-like or massive. Here, graphite is a concept including a material generally recognized as “graphite”. Further, in the present invention, as the electrode active material, those known as electrode active materials such as carbon allotropes other than graphite (and graphite-like particles) such as activated carbon are used in combination as long as the object of the present invention is not impaired. You can also. In this case, the ratio of graphite and graphite-like particles in the electrode active material is usually 50% by weight or more and preferably 70% by weight or more.

Preferred graphite has a small distance between d (002) by X-ray diffraction, and is usually 0.3390 nm or less, and this microphone is 0.3370 nm or less, particularly preferably in the range of 0.3354 to 0.3362 nm. Preferable graphite has a specific surface area of 10 m ² / g or less, preferably 7 m ² / g or less, more preferably 5 m ² / g or less. The specific surface area can be determined by a BET method using N2 or CO2 as an adsorbent. Preferred graphite is highly crystalline. For example, the crystal lattice constant C0 (002) of the 002 plane may be 0.67 to 0.68 nm, preferably 0.671 to 0.674. Furthermore, the half width of the 002 peak in the X-ray crystal diffraction spectrum using CuKα rays is less than 0.5, preferably 0.1 to 0.4, more preferably 0.2 to 0.3. When the crystallinity of graphite is low, the irreversible capacity of the electric double layer capacitor tends to increase. Preferable graphite is one in which the graphite layer is moderately disturbed and the ratio between the basal plane and the edge plane falls within a certain range. The disorder of the graphite layer appears in the result of Raman spectroscopic analysis, for example. Preferable graphite has a ratio (hereinafter referred to as “I”) of a peak intensity of 1360 cm ⁻¹ (hereinafter referred to as “I (1360)”) and a peak intensity of 1580 cm ⁻¹ (hereinafter referred to as “I (1580)”) in a Raman spectrum. (1360) / I (1580) ") is 0.02 to 0.5, preferably 0.05 to 0.25, more preferably 0.1 to 0.2, and still more preferably 0.13 to 0. .17. In addition, when performing the CVD process mentioned later, this intensity ratio will not be materialized but will show the value of 2.5 or more. This is because the coated carbon has lower crystallinity than the base material. Moreover, preferable graphite can also be specified by the result of an X-ray crystal analysis. That is, the ratio (hereinafter referred to as “IB / IA”) of the rhombohedral peak intensity (hereinafter referred to as “IB”) and the hexagonal peak intensity (hereinafter referred to as “IA”) in the X-ray crystal diffraction spectrum. The graphite is 0.3 or more, preferably 0.35 to 1.3.

  The shape and dimensions of the graphite particles are not particularly limited as long as the obtained composite particles can be formed into an electrode for an electrochemical element. For example, flaky graphite particles, consolidated graphite particles, and spheroidized graphite particles can be used as graphite. The properties and production methods of these graphite particles are known. The flaky graphite particles generally have a thickness of 1 μm or less, preferably 0.1 μm or less, and the maximum particle length is 100 μm or less, preferably 50 μm or less. Flaky graphite particles can be obtained by pulverizing natural graphite or artificial graphite by a chemical or physical method. For example, artificial graphite materials such as natural graphite, quiche graphite, and highly crystalline pyrolytic graphite are treated with a mixed acid of sulfuric acid and nitric acid, heated to obtain expanded graphite, and exfoliated graphite is pulverized by an ultrasonic method or the like. A graphite-sulfuric acid intercalation compound obtained by electrochemically oxidizing graphite in sulfuric acid, or a graphite-organic intercalation compound such as graphite-tetrahydrofuran in an externally heated or internally heated furnace, It can be produced according to a known method such as rapid heating treatment by laser heating or the like to expand and pulverize. Alternatively, natural graphite or artificial graphite can be obtained by mechanically pulverizing with, for example, a jet mill. The flaky graphite particles can be obtained, for example, by flaking and granulating natural graphite or artificial graphite. As a method for thinning and granulating, for example, there is a method of mechanically or physically pulverizing these using ultrasonic waves or various pulverizers. For example, graphite particles obtained by pulverizing natural graphite and artificial graphite with a pulverizer that does not apply a share such as a jet mill are particularly referred to as scaly graphite particles. On the other hand, graphite particles obtained by pulverizing and flaking expanded graphite using ultrasonic waves or the like are particularly referred to as flake graphite. The flaky graphite particles may be annealed in an inert atmosphere at 2000 ° C. to 2800 ° C. for about 0.1 to 10 hours to further enhance crystallinity. The consolidated graphite particles are graphite particles having a high bulk density and generally have a tap density of 0.7 to 1.3 g / cm 3. Consolidated graphite particles are defined as containing at least 10% by volume of spindle-shaped graphite particles having an aspect ratio of 1 to 5 or containing at least 50% by volume of disk-shaped graphite particles having an aspect ratio of 1 to 10. . The consolidated graphite particles can be produced by consolidating the raw graphite particles. As the graphite particles used as a raw material, either natural graphite or artificial graphite may be used, but natural graphite is preferred because of its high crystallinity and availability.

  The above natural graphite and artificial graphite can be used as they are or pulverized into the graphite used in the present invention, but may be further subjected to consolidation treatment. The consolidation treatment is performed by applying an impact to the graphite particles as a raw material. Consolidation treatment using a vibration mill is particularly preferable because it can increase the consolidation. Examples of the vibration mill include a vibration ball mill, a vibration disk mill, and a vibration rod mill. When scaly raw graphite particles with a large aspect ratio are consolidated, the raw graphite particles are converted into secondary particles while being laminated mainly on the graphite basal plane (base surface), and the edges of the simultaneously laminated secondary particles are rounded. It is cut into a thick disk shape with an aspect ratio of 1 to 10 or a spindle shape with an aspect ratio of 1 to 5, and converted into graphite particles with a small aspect ratio. As a result of converting the graphite particles to those having a small aspect ratio in this manner, graphite particles having excellent isotropy and high tap density can be obtained even though the graphite particles are highly crystalline. Therefore, when the electrode for electrochemical devices is formed using the obtained composite particles, the density of graphite in such an electrode can be increased.

  The graphite may be spherical particles. Such spherical graphite particles are obtained by collecting the flakes and compressing them into a spherical shape while pulverizing the high crystalline graphite with an impact pulverizer having a relatively small crushing force. For example, a hammer mill or a pin mill can be used as the impact pulverizer. The outer peripheral linear velocity of the rotating hammer or pin is preferably about 50 to 200 m / sec. Moreover, it is preferable to perform supply and discharge | emission of graphite with respect to these grinders by making it accompany airflow, such as air. The degree of particle spheroidization can be expressed by the ratio of the major axis to the minor axis of the particle (major axis / minor axis). That is, in an arbitrary cross section of a particle, when an axis that is orthogonal to the center of gravity and having a long / short axis ratio that is the largest is selected, It will be close to. By the spheroidizing treatment, the ratio of major axis / minor axis can be easily set to 4 or less (1 to 4). Further, if the spheroidization treatment is sufficiently performed, the ratio of the major axis / minor axis can be set to 2 or less (1-2).

  The graphite may be highly crystalline graphite. Such highly crystalline graphite is obtained by increasing the thickness by growing a large number of AB planes in which carbon particles form a network structure and spread on a plane, and grow in a lump. The bonding force between the laminated AB surfaces (bonding force in the C-axis direction) is much smaller than the bonding force of the AB surface. Tends to be scaly. When a cross section perpendicular to the AB plane of the graphite crystal is observed with an electron microscope, a streak-like line indicating a laminated structure can be observed. The internal structure of scaly graphite is simple, and when a cross section perpendicular to the AB plane is observed, the streaky line indicating the laminated structure is always linear, and is a flat laminated structure.

  Compared to highly crystalline graphite, the internal structure of the above-mentioned spherical graphite particles is that the streaky lines indicating the laminated structure are often curved, and there are many voids, making the structure extremely complex. Yes. That is, it is spheroidized as if scaly (plate-like) particles were folded or rolled up. Thus, it is said that the layered structure that was originally linear changes into a curved shape due to compressive force or the like as a “folding”. What is more characteristic about the spheroidized graphite particles is that, even with a randomly selected cross section, the vicinity of the surface of the particle has a curved laminated structure along the roundness of the surface. That is, the surface of the spheroidized graphite particles is generally covered with a curved laminated structure, and the outer surface is an AB plane (ie, a basal plane) of graphite crystals.

  The surface of the graphite particles described above is preferably provided with a coating layer made of a carbon allotrope having a crystal structure different from the crystal structure of such graphite particles, which can be used as a substitute for the graphite of the present invention. . In the present invention, graphite having such a coating layer is referred to as carbon-coated graphite. When this carbon-coated graphite is used as an electrode active material and an electrode for an electrochemical element is formed in combination with a dry method, characteristics such as a remarkable improvement in charge / discharge rate of the electrochemical element obtained are particularly preferable.

  As a method for forming a coating layer on the surface of graphite particles, chemical vapor deposition using a fluidized bed reactor is excellent. Examples of the organic substance used as the carbon source for the chemical vapor deposition treatment include aromatic hydrocarbons such as benzene, toluene, xylene, and styrene, and aliphatic hydrocarbons such as methane, ethane, and propane. In the fluidized bed reactor, these organic substances are mixed and introduced with an inert gas such as nitrogen or a rare gas. As a density | concentration of the organic substance in mixed gas, 2-50 mol% is preferable and 5-33 mol% is more preferable. As chemical vapor deposition processing temperature, 850-1200 degreeC is preferable and 950-1150 degreeC is more preferable. By performing chemical vapor deposition under such conditions, the surface of the graphite particles as a raw material can be uniformly and completely covered with the AB surface (that is, the basal surface) of crystalline carbon. The amount of carbon necessary for forming the coating layer varies depending on the particle diameter and shape of the graphite particles used as a raw material, but is preferably 0.1 to 10% by mass as the carbon amount of the coating layer in the carbon-coated graphite. 5-7 mass% is more preferable, and 0.8-5 mass% is still more preferable. If the amount is too small, the effect of the coating layer cannot be obtained. On the other hand, if the amount is too large, the ratio of the graphite particles as the raw material in the carbon-coated graphite decreases, so that the charge / discharge amount of the obtained electrochemical element decreases. Produce.

  Depending on the type of carbon source and the conditions of chemical vapor deposition, the carbon allotrope in the coating layer may have a diamond-like crystal structure, a graphite-like crystal structure, or an intermediate amorphous state (both The crystal structure grows partially and can take an amorphous state as a whole. The carbon allotrope in the coating layer may be in these two crystalline states, in an amorphous state, and preferably in an amorphous state. Carbon-coated graphite having a preferred non-crystalline coating layer can also be obtained, for example, from Toyo Tanso under the product name PYROPRAPH.

  The conductive material is made of a particulate carbon material that has conductivity and does not have pores that can form an electric double layer, and improves the conductivity of the electrode for an electrochemical element. The conductive material has a weight average particle diameter of the above graphite particles having a small weight average particle diameter, and is usually in the range of 0.001 to 10 μm, preferably 0.05 to 5 μm, more preferably 0.01 to 1 μm. It is. When the particle size of the conductive material is within this range, high conductivity of the electrode for an electrochemical element can be obtained with a smaller amount of use. Specific examples of the conductive material include conductive carbon black such as furnace black, acetylene black, and ketjen black (registered trademark of Akzo Nobel Chemicals Bethloten Fennaut Shap); graphite such as natural graphite and artificial graphite. It is done. Among these, conductive carbon black is preferable, and acetylene black and furnace black are more preferable. These conductive materials can be used alone or in combination of two or more.

  The amount of the conductive material is usually 0.1 to 50 parts by weight, preferably 0.5 to 15 parts by weight, more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the electrode active material. By using an electrode in which the amount of the conductive material is within this range, the capacity of the electrochemical element can be increased and the internal resistance can be decreased.

  The binder is a compound having a binding force. As the binder, a dispersion type binder is preferable. The dispersion type binder is a binder having a property of being dispersed in a solvent, and examples thereof include polymer compounds such as a fluorine polymer, a diene polymer, an acrylate polymer, polyimide, polyamide, and polyurethane. More preferred are fluorine-based polymers, diene-based polymers, and acrylate-based polymers. These binders can be used alone or in combination of two or more.

  The fluorine-based polymer is a polymer containing a monomer unit containing a fluorine atom. The ratio of the monomer unit containing fluorine in the fluoropolymer is usually 50% by weight or more. Specific examples of the fluorine-based polymer include fluorine resins such as polytetrafluoroethylene and polyvinylidene fluoride, and polytetrafluoroethylene is preferable.

  The diene polymer is a polymer containing a conjugated diene-derived monomer unit such as butadiene or isoprene, and a hydrogenated product thereof. The proportion of conjugated diene-derived monomer units in the diene polymer is usually 40% by weight or more, preferably 50% by weight or more, more preferably 60% by weight or more. Specifically, conjugated diene homopolymers such as polybutadiene and polyisoprene; aromatic vinyl / conjugated diene copolymers such as styrene-butadiene copolymer (SBR) which may be carboxy-modified; acrylonitrile / butadiene copolymer Examples thereof include vinyl cyanide / conjugated diene copolymers such as a combination (NBR); hydrogenated SBR, hydrogenated NBR, and the like.

  The acrylate polymer is a polymer containing a monomer unit derived from an acrylate ester and / or a methacrylate ester. The proportion of monomer units derived from acrylic acid ester and / or methacrylic acid ester in the acrylate polymer is usually 40% by weight or more, preferably 50% by weight or more, more preferably 60% by weight or more. Specific examples of the acrylate polymer include 2-ethylhexyl acrylate / methacrylic acid / acrylonitrile / ethylene glycol dimethacrylate copolymer, 2-ethylhexyl acrylate / methacrylic acid / methacrylonitrile / diethylene glycol dimethacrylate copolymer, acrylic Crosslinking of 2-ethylhexyl acid / styrene / methacrylic acid / ethylene glycol dimethacrylate copolymer, butyl acrylate / acrylonitrile / diethylene glycol dimethacrylate copolymer, and butyl acrylate / acrylic acid / trimethylolpropane trimethacrylate copolymer Type acrylate polymer; ethylene / methyl acrylate copolymer, ethylene / methyl methacrylate copolymer, ethylene / ethyl acrylate copolymer, and Copolymer of ethylene and (meth) acrylic acid ester such as ethylene / ethyl methacrylate copolymer; Graft obtained by grafting a radical polymerizable monomer to the above copolymer of ethylene and (meth) acrylic acid ester Polymer; and the like. In addition, as a radically polymerizable monomer used for the said graft polymer, methyl methacrylate, acrylonitrile, methacrylic acid etc. are mentioned, for example. In addition, a copolymer of ethylene and (meth) acrylic acid such as an ethylene / acrylic acid copolymer or an ethylene / methacrylic acid copolymer can be used as a binder. In the present invention, “(meth) acryl” means acryl and / or methacryl.

  Among these, from the viewpoint that an active material layer excellent in binding property and surface smoothness with a current collector can be obtained, and an electrode for an electrochemical element having high capacitance and low internal resistance can be produced. Diene polymers and cross-linked acrylate polymers are preferred, and cross-linked acrylate polymers are particularly preferred.

The binder preferably has a small degree of swelling with respect to the electrolytic solution. Here, as an index of the degree of swelling, the degree of swelling with respect to a solution in which triethylene monomethyl ammonium tetrafluoroborate is dissolved at a concentration of 1.0 mol / L in propylene carbonate, which is a typical electrolyte, is employed. Preferably it is 2 or less. As a method for bringing the degree of swelling into such a range, for example, as a binder, a polymer or co-polymer having a solubility parameter (hereinafter referred to as SP value) of 16 to 20 MPa ^1/2 , preferably 17 to 20 MPa ^1/2 is used. A polymer can be used. If the SP value is too low, the affinity between the electrolytic solution and the binder becomes low, and the electrolytic solution hardly penetrates into the electrode inside the electrochemical device, making it difficult to manufacture the electrochemical device. On the other hand, if the SP value is too high, the binder easily swells and dissolves in the electrolytic solution, resulting in poor resistance to electrolytic properties.

Here, the SP value is J.P. Brandrup, E .; H. Immergut and E.M. A. It can be determined according to the method described in Grulk edition “Polymer Handbook” VII Solubility Parameter Values, p675-714 (John Wiley & Sons, 4th edition, 1999). Those not described in this publication can be determined according to the “molecular attraction constant method” proposed by Small. This method is a method for obtaining the SP value (δ) according to the following equation from the characteristic value of the functional group (atomic group) constituting the compound molecule, that is, the statistics of the molecular attractive constant (G) and the molecular volume.
δ = ΣG / V = dΣG / M
ΣG: Total of molecular attractive constant G V: Specific volume M: Molecular weight d: Specific gravity

  The binder having the SP value in the above preferred range is produced, for example, by copolymerizing the following compound (a), compound (b) and other monomer components added as necessary. can do.

The compound (a) is a compound represented by the general formula (1): CH ₂ ═CR ¹ —COOR ² . In the general formula (1), R ¹ represents a hydrogen atom or a methyl group, and R ² represents an alkyl group or a cycloalkyl group. R ² should be selected so that the SP value of the resulting copolymer falls within a predetermined range, but is preferably an alkyl group having 3 to 18 carbon atoms, more preferably 4 to 4 carbon atoms. 14 is particularly preferably an alkyl group having 5 to 12 carbon atoms. As the compound (a), specifically, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-amyl acrylate, isoamyl acrylate, Acrylic acid alkyl esters such as n-hexyl acrylate, 2-ethylhexyl acrylate, hexyl acrylate, nonyl acrylate, lauryl acrylate, stearyl acrylate; ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-methacrylate Butyl, isobutyl methacrylate, t-butyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, isodecyl methacrylate, Include; cycloalkyl methacrylate esters such as cyclohexyl methacrylate, acrylic acid cycloalkyl esters such as isobornyl acrylate; lauryl acrylic acid, tridecyl methacrylate, alkyl esters such as stearyl methacrylate. Among these, acrylic acid alkyl esters are preferable, and n-butyl acrylate and 2-ethylhexyl acrylate are particularly preferable. These compounds represented by the general formula (1) may be used alone or in combination of two or more. The amount of the monomer unit derived from the compound (a) in the copolymer should be appropriately determined so that the SP value of the copolymer falls within a predetermined range, but usually 90 to 99.9% by mass. , Preferably it is 92-99.5 mass%, More preferably, it is 94-99 mass%.

  A polyfunctional ethylenically unsaturated compound is used as the compound (b). By adding a polyfunctional ethylenically unsaturated compound, the resistance of the electrode of the chemical element to the electrolyte can be improved. The polyfunctional ethylenically unsaturated compound is a compound having two or more polymerizable ethylenic groups, such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, polyethylene glycol dimethacrylate. Dimethacrylic acid esters such as methacrylate; diethylene glycol diacrylate, 1,3-butylene glycol diacrylate, tripropylene glycol acrylate, 1,4-butanediol acrylate, neopentyl glycol diacrylate, 1,6-hexanediol acrylate, 1 , 9-nonanediol acrylate, diacrylic acid esters such as polyethylene glycol diacrylate; divinyl compounds such as divinylbenzene; And ethylenic unsaturated compounds, tri methacrylates such as trimethylolpropane trimethacrylate; triacrylate esters such as trimethylol propane triacrylate; trifunctional ethylenically unsaturated compounds, such as and the like. From the viewpoint of the binding properties of the resulting copolymer, the compound (b) is preferably a bifunctional ethylenically unsaturated compound.

  The amount of the monomer unit derived from the compound (b) in the copolymer is appropriately determined so that the SP value of the copolymer falls within a predetermined range. When the amount of the monomer unit derived from the compound (b) is too large, there is a problem that the binding property of the binder is lowered, so that it is usually 0.1 to 10% by mass, preferably 0.5 to 8%. It is 1 mass%, More preferably, it is 1-6 mass%.

  In addition to the compound (a) and the compound (b), other monomer components can also be used as other components for producing the copolymer. Typical examples of other monomer components include ethylenically unsaturated carboxylic acid (c).

  Examples of the ethylenically unsaturated carboxylic acid (c) include ethylenically unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid and isocrotonic acid; maleic acid, fumaric acid, citraconic acid, mesaconic acid, glutaconic acid, itaconic And ethylenically unsaturated dicarboxylic acids such as acids. Of these, ethylenically unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid are preferred. By adding these, the binding property can be further improved. The amount of the monomer unit derived from the ethylenically unsaturated carboxylic acid (c) in the copolymer is preferably 0.1 to 9.9% by mass, more preferably 1 to 9.9% by mass, and still more preferably 2 to 2%. 7% by mass.

  In addition to the above-mentioned ethylenically unsaturated carboxylic acid (c), other copolymerizable monomer units may be used as other monomer components as long as the effects of the present invention are not impaired. Examples of the copolymerizable monomer include 1-olefins such as ethylene, propylene, and 1-butene; for example, 1,3-butadiene, 1,3-pentadiene, 2,3-pentadiene, isoprene, 1, Conjugated dienes such as 3-hexadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-heptadiene; methyl crotonate, ethyl crotonate, propyl crotonate, crotonic acid Crotonic esters such as butyl, isobutyl crotonate, n-amyl crotonate, isoamyl crotonate, n-hexyl crotonate, 2-ethylhexyl crotonate, hydroxypropyl crotonate; dimethyl maleate, dibutyl maleate, di-maleate Maleic acid esters such as 2-ethylhexyl; dimethyl difumarate , Fumaric acid diesters, such as dibutyl fumarate; dimethyl itaconate, itaconic acid esters such as dibutyl itaconate; and the like. Two or more of these monomers may be used in combination, and the total amount of monomer units derived from these monomers is 8% by mass or less, preferably 5% by mass or less in the copolymer. .

  The method for producing such a copolymer is not particularly limited. For example, the copolymer is obtained by polymerizing each of the above monomers by a known polymerization method such as an emulsion polymerization method, a suspension polymerization method, a dispersion polymerization method, or a solution polymerization method. be able to. Among these, it is preferable to produce by an emulsion polymerization method because the particle diameter of the copolymer can be easily controlled. At that time, in order to reduce the contamination of the alkali metal ions that cause the corrosion of the current collector as much as possible, the alkali metal ion content in the deionized water for polymerization is reduced, or an alkali is used as a polymerization auxiliary material such as a polymerization initiator or an emulsifier. It is preferable to use one not containing metal. The glass transition temperature of the copolymer is preferably 10 ° C. or lower, more preferably 0 ° C. or lower, and particularly preferably −20 ° C. or lower. If the glass transition temperature is too high, the flexibility is lowered, and cracks are likely to occur during winding for producing an electrode for an electrochemical element.

  Such a copolymer preferably contains 30% by mass or more, preferably 30 to 98% by mass, more preferably 40 to 95% by mass, of an insoluble content in tetrahydrofuran (THF). When the THF-insoluble content is within this range, the electrolytic solution resistance can be improved, and the increase in internal resistance due to the binder covering the active material surface can be suppressed. Here, the insoluble matter in THF is the mass obtained by immersing 0.2 g of polymer in 20 ml of THF at a temperature of 25 ° C. for 72 hours, filtering through an 80 mesh sieve, and drying the components on the sieve. The value is expressed as a percentage with respect to 0.2 g of the original polymer mass. Such a copolymer is usually used after being dispersed or dissolved in water or an organic solvent, and is preferably used as an aqueous dispersion.

  The binding agent used in the present invention is not particularly limited depending on its shape as long as it is suitable for use in a dry method, but has good binding properties, and lowers or recharges the capacitance of the prepared electrode. Since deterioration due to repeated discharge can be suppressed, it is preferably in the form of particles. Examples of the particulate binder include, for example, latex in which the binder particles are dispersed in a solvent (dispersion), and powder obtained by drying such a dispersion. Is mentioned.

  Further, the binder used in the present invention may be particles having a core-shell structure obtained by stepwise polymerization of a mixture of two or more monomers. A binder having a core-shell structure is obtained by first polymerizing a monomer that gives the first-stage polymer to obtain seed particles, and in the presence of the seed particles, a single quantity that gives the second-stage polymer. It is preferable to manufacture by polymerizing the body. The ratio between the core and the shell of the binder having the core-shell structure is not particularly limited, but the core part: shell part is usually 50:50 to 99: 1, preferably 60:40 to 99: 1 by mass ratio. Preferably it is 70: 30-99: 1. The polymer compound constituting the core part and the shell part can be selected from the above polymer compounds. It is preferable that one of the core part and the shell part has a glass transition temperature of less than 0 ° C and the other has a glass transition temperature of 0 ° C or higher. Moreover, the difference of the glass transition temperature of a core part and a shell part is 20 degreeC or more normally, Preferably it is 50 degreeC or more.

  The binder used in the present invention is preferably in the form of particles. When the binder is in the form of particles, there is no particular limitation depending on the average particle diameter, but usually 0.0001 to 100 μm, preferably 0. It has an average particle diameter of 0.001 to 10 μm, more preferably 0.01 to 1 μm. When the average particle size of the binder is within this range, an excellent binding force can be imparted to the active material layer even when a small amount of the binder is used. Here, the average particle diameter is a number average particle diameter calculated as an arithmetic average value obtained by measuring the diameter of 100 binder particles randomly selected in a transmission electron micrograph. The shape of the particles can be either spherical or irregular. The amount of the binder used is usually in the range of 0.1 to 50 parts by weight, preferably 0.5 to 20 parts by weight, more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the electrode active material. .

  As the binder, in addition to the dispersible resin, a soluble resin can be used, and it is preferable to use this in combination. This soluble resin is a resin that dissolves in a solvent, and preferably further has an action of uniformly dispersing an electrode active material, a conductive material, and the like in the solvent. The dissolving resin may or may not have a binding force. Examples of the soluble resin include cellulosic polymers such as carboxymethylcellulose, methylcellulose, ethylcellulose and hydroxypropylcellulose, and ammonium salts or alkali metal salts thereof; poly (meth) acrylates such as sodium poly (meth) acrylate; polyvinyl Examples include alcohol, modified polyvinyl alcohol, polyethylene oxide; polyvinyl pyrrolidone, polycarboxylic acid, oxidized starch, phosphate starch, casein, various modified starches, chitin, and chitosan derivatives. These soluble resins can be used alone or in combination of two or more. Among these, a cellulose polymer is preferable, and carboxymethyl cellulose or an ammonium salt or an alkali metal salt thereof is particularly preferable. The use amount of the soluble resin is not particularly limited, but is usually 0.1 to 10 parts by weight, preferably 0.5 to 5 parts by weight, and more preferably 0.8 to 100 parts by weight of the electrode active material. It is in the range of 8 to 2 parts by weight. By using the soluble resin, it is possible to suppress sedimentation or aggregation of solids in the slurry when the composition for forming an active material layer is used as a slurry. Moreover, since the clogging of the atomizer at the time of spray-drying the composition for forming an active material layer can be prevented, the composite particles can be continuously performed with stable spray-drying.

  In producing the composite particles, in addition to the above components, other additives may be additionally used as necessary. Examples of other additives include a surfactant. Surfactants include anionic, cationic, and amphoteric surfactants such as nonionic and nonionic anions. Among them, anionic or nonionic surfactants that are easily thermally decomposed are used. preferable. The amount of the surfactant is not particularly limited, but is 0 to 50 parts by weight, preferably 0.1 to 10 parts by weight, more preferably 0.5 to 5 parts by weight with respect to 100 parts by weight of the electrode active material. It is a range.

  The composite particles can be produced, for example, by the following two production methods.

  The first production method is a production method called a fluidized bed granulation method, in which an electrode active material and other components are separately supplied and granulated. In this method, a process for forming a composition for forming an active material layer containing a conductive material, a binder, and other additives to be added as necessary, in a slurry A, fluidizing an electrode active material containing graphite as an essential component The slurry A is sprayed thereon and fluidized and granulated, and the particles obtained in the fluidized granulation step are tumbled and granulated. First, a slurry A containing a conductive material, a binder, and, if necessary, a soluble resin and other additives is obtained. As a solvent used for obtaining the slurry A, water is usually used, but an organic solvent can also be used. Examples of the organic solvent include alkyl alcohols such as methyl alcohol, ethyl alcohol and propyl alcohol; alkyl ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran, dioxane and diglyme; diethylformamide, dimethylacetamide and N-methyl- Examples include 2-pyrrolidone (hereinafter sometimes referred to as NMP) and amides such as dimethylimidazolidinone; sulfur solvents such as dimethyl sulfoxide and sulfolane; and alcohols are preferable. When an organic solvent having a lower boiling point than water is used in combination, the drying rate can be increased during fluid granulation. In addition, since the dispersibility of the binder or the solubility of the soluble resin changes, the viscosity and fluidity of the slurry A can be adjusted depending on the amount or type of the organic solvent, so that the production efficiency can be improved. The amount of the solvent used when preparing the slurry A is such that the solid content concentration of the slurry A is usually in the range of 1 to 50% by weight, preferably 5 to 50% by weight, more preferably 10 to 30% by weight. It is an amount like this. When the solid content concentration is in this range, the binder is preferably dispersed uniformly.

  A method or a procedure for dispersing or dissolving the conductive material and the binder in a solvent is not particularly limited. For example, a method of adding a conductive material and a binder to a solvent and mixing them; and a dispersion resin as a binder A method in which both a soluble resin and a soluble resin are dissolved in a solvent, then a dispersed resin (for example, latex) dispersed in the solvent is added and mixed, and finally a conductive material is added and mixed. And a method in which a conductive material is added to and mixed with a soluble resin dissolved in a solvent, and a dispersion resin dispersed in a solvent is added thereto and mixed. Examples of the mixing means include mixing equipment such as a ball mill, a sand mill, a bead mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, and a planetary mixer. Mixing is usually performed in the range of room temperature to 80 ° C. for 10 minutes to several hours.

  Next, the electrode active material is fluidized, and the slurry A is sprayed thereon for fluid granulation. Examples of fluidized granulation include a fluidized bed, a deformed fluidized bed, and a spouted bed. In the fluidized bed method, the electrode active material is fluidized with hot air, and the slurry A is sprayed onto the material by spraying or the like to perform agglomeration and granulation. The modified fluidized bed is the same as the fluidized bed, but is a method of giving a circulating flow to the powder in the bed and discharging the granulated material that has grown relatively large by using the classification effect. In addition, the method using the spouted bed is a method in which the slurry A from a spray or the like is attached to coarse particles using the characteristics of the spouted bed and granulated while drying simultaneously. As the production method of the present invention, a fluidized bed or a deformed fluidized bed is preferred among these three methods. The temperature of the slurry to be sprayed is usually room temperature, but may be heated to room temperature or higher. The temperature of the hot air used for fluidization is usually 80 to 300 ° C, preferably 100 to 200 ° C. The particles A obtained by fluid granulation may be completely dried with hot air, but in order to increase the granulation efficiency in the next rolling granulation step, the particles A may be in a wet state. preferable.

  Next, the particles A obtained in the fluidized granulation step are tumbled and granulated in the presence of the slurry A containing a conductive material and a binder. In addition, the slurry A used for rolling granulation should just contain a conductive material and a binder, and even if it is the same as the slurry A used in fluid granulation, it is different. Also good. There are various types of rolling granulation, such as a rotating coarse method, a rotating cylindrical method, and a rotating truncated cone method. In the rotary coarse method, the slurry A is sprayed on the particles A supplied into the inclined rotary finer to produce an agglomerated granulated product, and a granulated product that has grown relatively large by utilizing the classification effect of the rotary coarser. It is a method of discharging from the rim. The rotating cylinder system is a system in which wet particles A are supplied to an inclined rotating cylinder, and the particles A are rolled in the cylinder, and the slurry A is sprayed to obtain an agglomerated granulated product. The rotating truncated cone method is the same as the operating method of the rotating cylinder, but is a method in which the granulated material that has grown relatively large is discharged by utilizing the classification effect of the aggregated granulated material by the truncated cone shape. In this rolling granulation step, coating granulation is mainly performed, and agglomeration granulation is partially performed. Although the temperature at the time of rolling granulation is not specifically limited, in order to remove the solvent which comprises the slurry A, it is normally performed at 80-300 degreeC, Preferably it is 100-200 degreeC. Furthermore, in order to remove the residual solvent from the composite particles, it can be dried as necessary after rolling granulation.

  By the above method, composite particles containing an electrode active material, a conductive material, and a binder can be obtained. In this composite particle, an electrode active material and a conductive material are bound by a binder, and preferably, a composite particle outer layer portion is bound by an electrode active material and / or a conductive material having a relatively small average particle diameter. The composite particle inner layer is formed by binding an electrode active material and / or a conductive material having a relatively large average particle diameter.

  The second production method is a method called spray-drying granulation method, a step of obtaining slurry B (containing electrode active material, conductive material and binder) containing all necessary components for composite particles, and The slurry B is spray-dried with a pin-type atomizer and spray granulated.

  First, the electrode active material, the conductive material, the binder, and other additives used as necessary are dispersed or dissolved in a solvent to obtain a slurry B in which each component is dispersed or dissolved. . Examples of the solvent used for obtaining the slurry B include the same solvents as those mentioned in the first production method. The amount of the solvent used when preparing the slurry B is such that the solid content concentration of the slurry B is usually in the range of 1 to 50% by weight, preferably 5 to 50% by weight, more preferably 10 to 30% by weight. It is an amount like this.

  The method or procedure for dispersing or dissolving the electrode active material, conductive material, binder, soluble resin and other additives in water is not particularly limited, and for example, the electrode active material, conductive material, binder in water. A method of adding and mixing an adhesive; and, as a binder, using a dispersion resin and a dissolution resin, dissolving the dissolution resin in water and then dispersing the dispersion resin in water (for example, latex) Add and mix, and finally add and mix the electrode active material and conductive material, and add and mix the electrode active material and conductive material in a dispersed resin dispersed in water, then dissolve in water And a method of adding and mixing the dissolved resin. Examples of the mixing means include mixing equipment such as a ball mill, a sand mill, a bead mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, and a planetary mixer. Mixing is usually performed in the range of room temperature to 80 ° C. for 10 minutes to several hours.

  Next, the slurry B is spray-dried with a pin-type atomizer and spray-granulated. The spray drying method is a method of spraying and drying a slurry in hot air. The apparatus used for the spray drying method is a pin type atomizer. A pin-type atomizer is a type of centrifugal spraying device that uses a spraying plate, and the spraying plate has a plurality of spraying rollers removably mounted on a concentric circle along its periphery between upper and lower mounting disks. It consists of Slurry B is introduced from the center of the spray disc, adheres to the spraying roller by centrifugal force, moves outward on the roller surface, and finally sprays away from the roller surface. The temperature of the slurry B to be sprayed is usually room temperature, but may be heated to room temperature or higher. The hot air temperature at the time of spray drying is usually 80 to 250 ° C, preferably 100 to 200 ° C. In the spray drying method, the method of blowing hot air is not particularly limited. Examples include a contact method, and a method in which sprayed droplets first flow in parallel with hot air and then drop by gravity to make countercurrent contact.

  FIG. 1 shows a schematic diagram of a spray dryer used in such a method. In the figure, (51) is a hopper, (52) is a pump, (54) is a blower, (55) is a heat exchanger, (57) is a spray nozzle, (58) is a drying tower, (59) is a suction machine, And (62) represent cold air fans, respectively.

  The slurry B is spray-dried to remove the solvent in the slurry, whereby composite particles containing an electrode active material, a conductive material, and a binder are obtained. In this composite particle, an electrode active material and a conductive material are bound by a binder, and preferably, an electrode active material and / or a conductive material having a relatively small average particle diameter in the composite particle outer layer is bound. The composite particle inner layer is formed by binding an electrode active material and / or a conductive material having a relatively large average particle diameter.

  The composite particle is composed of an outer layer portion and an inner layer portion, and the outer layer portion and the inner layer portion are formed by binding the electrode active material and the conductive material with a binder, and the electrode active material forming the outer layer portion and The average particle diameter of the conductive material is preferably smaller than the average particle diameter of the electrode active material and the conductive material forming the inner layer portion. In this case, the composite particle outer layer portion is formed by binding an electrode active material and / or a conductive material having a relatively small average particle diameter. Therefore, it becomes a dense layer with few voids. On the other hand, the composite particle inner layer portion is formed by binding an electrode active material and / or a conductive material having a relatively large average particle diameter. Since it is formed of a material having a relatively large average particle diameter, the layer has many voids between the electrode active material and / or the conductive material.

  When a conductive material having a particle size smaller than that of the electrode active material is used, the conductive material is distributed more in the outer part of the composite particle, and the electrode active material is distributed more in the inner part of the composite particle. When the conductive material is distributed in a large amount in the outer layer portion, the surface of the composite particle becomes highly conductive. Since the composite particles are in contact with each other on the surface when the active material layer is formed, it is considered that electricity easily passes and resistance is lowered. In addition, since there are many voids leading to the electrode active material distributed in a large amount in the inner layer portion, it is considered that the ion mobility is improved, and it is assumed that the capacity is increased.

  The composite particles have a weight average particle diameter of usually 0.1 to 1000 μm, preferably 5 to 500 μm, more preferably 10 to 100 μm.

<Current collector>
The current collector used in the present invention can be used without particular limitation as long as it is known to be used for electrodes for electrochemical devices. As a material for the current collector, pure aluminum or an aluminum alloy that is an alloy of aluminum and other metals such as lead, silicon, iron, copper, manganese, magnesium, chromium, zinc, and titanium can be used. However, pure aluminum is preferred. In this case, the purity measured according to JIS H2111 is preferably 98% by mass or more, and particularly preferably 99.5% or more. The aluminum foil is manufactured by a known method using such a material. Although thickness is not specifically limited, Usually, it is 1-200 micrometers, Preferably it is 5-100 micrometers, More preferably, it is 10-50 micrometers.

  Carbon-coated aluminum can also be used as a current collector, which is preferable. Carbon-coated aluminum is a material in which a carbon-containing layer is provided on the surface of the aluminum foil as a substrate via an intervening layer. The intervening layer is a layer containing a carbide of aluminum in a portion where at least a part of the surface of the aluminum foil as a base material is carbonized to become a layer containing an aluminum element and carbon. The carbon-containing layer preferably extends in the form of a fiber or a filament from the surface of aluminum as a base material, and is a compound of aluminum and carbon. The carbon-containing layer may include aluminum particles, carbon particles, or both. Such carbon-coated aluminum is preferably obtained by a treatment (referred to as aluminum carbide treatment) in which carbon particles are fixed with an aluminum carbide whisker on a base aluminum foil without a binder. By performing such a treatment, the surface of the current collector can be electron-conducted without being affected by the natural oxide film formed on the aluminum foil.

Specifically, in the aluminum carbide treatment, if necessary, a carbon-containing substance, an aluminum powder, or both of them are attached to the surface of the aluminum foil as a base material and then heated in a space containing hydrocarbons. Is made by The thickness of the carbon-containing layer is 0.1 to 1000 times the thickness of the aluminum foil that is the base material. When a thin carbon-containing layer is formed, carbon-coated aluminum is obtained by heating in a space containing hydrocarbons without attaching anything to the surface of the aluminum foil that is the base material. Since the adhesion of the layer can be improved, it is preferable to use a carbon-containing substance attached to the surface of the aluminum foil. When forming a thick carbon-containing layer, it is preferable to obtain carbon-coated aluminum by heating in a space containing hydrocarbons after attaching a carbon-containing substance to the surface of an aluminum foil as a base material. In the case of forming a thicker carbon-containing layer, carbon-coated aluminum is obtained by heating in a space containing hydrocarbons after attaching a carbon-containing material and aluminum powder to the surface of the aluminum foil as a base material. Is preferred. Here, the surface of the aluminum foil as the base material may be used by roughening it in advance by etching, brass and treatment.

  The hydrocarbon is not particularly limited, but a straight or branched saturated hydrocarbon such as methane, ethane, propane, n-butane and i-butane, and a carbon-carbon double bond such as ethylene, propylene and 1-butene. Examples include unsaturated hydrocarbons having one, unsaturated hydrocarbons having two carbon-carbon double bonds such as butadiene and isoprene, unsaturated hydrocarbons having a carbon-carbon triple bond such as acetylene, and positional isomers thereof. be able to. Among these, straight-chain or branched-chain saturated hydrocarbons are preferable, and methane, ethane, and propane having a low boiling point are particularly preferable because they easily become gaseous in a space where the aluminum foil is heated. Particularly preferred is methane. Hydrocarbons may be used in a liquid or gas state, and can be used alone or filled with an inert gas in the space. The pressure in the space is not particularly limited, and may be normal pressure, reduced pressure, or increased pressure. The amount of hydrocarbon to be used is not particularly limited, but is usually 0.1 to 50 parts by weight, preferably 0.5 to 30 parts by weight with respect to 100 parts by weight of the aluminum foil to be treated.

  The carbon-containing substance may be appropriately selected from activated carbon fiber, activated carbon cloth, activated carbon felt, activated carbon powder, black ink, carbon black, or graphite. The attachment method may be made into a slurry or solution using a binder, a solvent, or water as necessary, and attached onto the aluminum foil by coating or thermocompression bonding. When a solvent, water, or the like is used, it may be dried in the range of 20 to 300 ° C. as necessary. When aluminum powder is used, it is usually used in the range of 0.01 to 10,000 parts by weight with respect to 100 parts by weight of the carbon-containing substance.

  The temperature at the time of the above heating is usually 300 ° C. or higher, preferably 450 to 660 ° C., more preferably 530 to 620 ° C. Although the heating time depends on the temperature, it is usually 1 to 100 hours. After heating and cooling an aluminum foil, you may heat again. The temperature of the heating again is 100 to 660 ° C.

  Such preferred carbon-coated aluminum is commercially available, for example from Toyo Aluminum under the product name Toyal Carbo.

<Electrodes for electrochemical devices>
An electrode for an electrochemical element is obtained by forming an active material layer on a current collector and cutting it into an appropriate size as necessary. In the present invention, the active material layer is formed by the dry method using the composite particles described above. The dry method is a method of forming an active material layer by heating and pressing composite particles on a current collector. Examples of the dry method include a pressure molding method and an extrusion molding method (also referred to as paste extrusion). The pressure forming method is a method of forming an active material layer by applying pressure to the composition for forming an active material layer and densifying the composite particles by rearrangement, deformation, and destruction. The extrusion molding method is a method in which an active material layer forming composition is formed into an extruded film, sheet, or the like with an extruder, and the active material layer can be continuously formed as a long product. Among these, it is preferable to use pressure molding because it can be performed with simple equipment. As pressure molding, for example, a method of supplying composite particles containing composite particles to a roll-type pressure molding device with a supply device such as a screw feeder and forming an active material layer (in this method, a current collector is The active material layer can be laminated directly on the current collector by feeding it into the roll at the same time as the supply of the composite particles.), Or the composite particles can be dispersed on the current collector and the composite particles can be leveled with a blade or the like. There are a method of adjusting the thickness and then forming with a pressurizing device, a method of filling composite particles into a mold and pressurizing the mold, and the like. The temperature during molding is preferably 0 to 200 ° C. Here, the composite particles are supplied between, for example, two rolls and heated and / or pressed to form in advance as another layered product, and then further heated and / or pressed over the current collector. The active material layer may be formed on the current collector by heating and / or pressurizing by supplying composite particles between, for example, the current collector and the roll. The active material layer may be formed and the active material layer and the current collector may be stacked at the same time.

  FIG. 2 shows a schematic diagram of a roll press machine suitable for manufacturing an electrode for an electrochemical element by such a dry method. In the figure, (1) is a current collector, (2) is an active material layer, (3) is a composite particle, (4) is a feeder, and (5) is a roll.

  In order to eliminate variations in the thickness of the molded electrode for an electrochemical element (or before cutting) and increase the density of the active material layer to increase the capacity, further post-pressurization may be performed as necessary. . The post-pressing method is generally a press process using a roll. In the roll press process, two cylindrical rolls are arranged in parallel at a narrow interval in the vertical direction, and each is rotated in the opposite direction. The temperature of the roll may be adjusted by heating or cooling.

<Electrochemical element>
The obtained electrochemical device electrode is used as a positive electrode and / or negative electrode, and a separator is interposed between the electrodes as necessary, and a predetermined electrolytic solution is sealed, whereby an electrochemical device is obtained. The electrode for an electrochemical element obtained by the present invention is particularly preferably used as a positive electrode of an electrochemical element. In this case, the negative electrode is conventionally known, for example, an electrochemical element using activated carbon as an electroactive material. An electrode for an electrochemical device manufactured by a wet electrode or a wet method may be used. As the separator and the electrolytic solution, those known for electrochemical devices can be appropriately selected and used.

  Hereinafter, the present invention will be described in more detail with reference to experimental examples. The present invention is not limited to these examples. The amount of each component used is based on weight unless otherwise specified.

First, the test method will be described.
(Active material layer density)
An electrode having a size of 40 mm × 60 mm (a part different from the case where the electrochemical elements of Examples and Comparative Examples were formed) was cut out from the electrode sheet for electrochemical elements, and the weight and volume of the electrodes were measured. The density of the active material layer excluding the electric part was calculated as the electrode density (g / cc).
(Calculation of capacitance and internal resistance)
A laminated capacitor was produced as an electrochemical element, charged at a voltage of 2.7 V in 1 hour, discharged to a voltage of 2.0 V over 15 minutes, and 1C discharge characteristics were obtained. The capacity was calculated from the obtained charge / discharge curve, and divided by the volume of the active material layer of the electrode of the electrochemical device, to determine the capacity per unit volume of the active material layer. The internal resistance was calculated according to the calculation method of standard RC-2377 established by the Japan Electronics and Information Technology Industries Association from the charge / discharge curve.
(Floating characteristic evaluation)
The evaluation of the floating characteristics of the above laminated capacitor was carried out at 45 ° C. for 72 hours at a voltage of 2.7 V, and then discharged at a voltage of 2.0 V for 15 minutes. Was calculated as the capacity retention rate from the change from the capacity before the evaluation of the floating characteristics.
(Measurement method of swelling degree of binder)
If the binder is solid, the solid can be formed into a film to form a test piece film. However, when the binder is a latex-like solution or dispersion, the sample is as follows: A piece film was made. The solution or dispersion was cast on a petri dish made of polytetrafluoroethylene and air-dried to produce a film having a thickness of about 0.5 mm, which was used as a test piece film. After cutting the test piece film into 1 cm square and measuring the weight, the test piece film was immersed in the electrolytic solution and taken out of the electrolytic solution after 72 hours at 60 ° C., and lightly pressed with a filter paper to wipe off the electrolytic solution. The weight was measured. The degree of swelling (unit: times) was defined as (weight after immersion test / weight before immersion test).

Reference Example 1 (Production of Binder A)
In a reaction vessel equipped with a stirrer, 494 parts of butyl acrylate and 5 parts of itaconic acid as monomers, 1 part of triethylene glycol dimethacrylate as a crosslinking agent, 5 parts of sodium dodecylbenzenesulfonate as a dispersing agent, 1000 parts of ion-exchanged water and a polymerization initiator After charging 5 parts of potassium persulfate and stirring sufficiently, it was heated to 80 ° C. and polymerized. When the monomer consumption reached 99.0%, the reaction was stopped by cooling to obtain an aqueous dispersion of binder A. The swelling degree of this binder A was 1.52 times.

Reference Example 2 (Production example of carbon-coated graphite)
After consolidating Brazilian natural graphite with a vibrating rod mill, it is sieved with a sieve having a pore size of 53 μm, and air oxidation treatment is performed on graphite particles having a bulk density of 0.800 g / cm ³ , which is the passage. For the air oxidation treatment, a rotary kiln is used, and a residence time of 5 minutes is set at a temperature of 650 ° C. while sending air of 25 liter / min per 1 kg of graphite. The combustion loss due to oxidation is 2.1% by mass. 60 kg of oxidized graphite was charged into a fluidized bed reactor, the temperature in the reactor was raised to 1000 ° C. while flowing nitrogen at 50 liters / min, and then nitrogen gas containing 40 mol% of toluene as a carbon source was added. Chemical vapor deposition is performed for 25 minutes while maintaining a fluid state by supplying at a liter / min. The obtained carbon-coated graphite is passed through a sieve having a pore size of 53 μm, and the passing portion is used as a sample of carbon-coated graphite.

Production Example 1 of Electrode Element Electrode Sheet (Electrode Sheet A)
100 parts of graphite (TIMREX KS6; manufactured by Timcal Co., Ltd.) as an electrode active material, 14 parts of an aqueous dispersion of binder A prepared in Reference Example 1 (solid content adjusted to 40%) as a dispersion-type binder, dissolved type 93.3 parts of resin (1.5% aqueous solution of carboxymethylcellulose “DN-800H”: manufactured by Daicel Chemical Industries, Ltd.) and 327.7 parts of ion-exchanged water were mixed with a mixer (made by Tokushu Kika Co., Ltd., product name TK). A slurry having a solid content of 20% (corresponding to the slurry B in the detailed description) was obtained by stirring and mixing with a homomixer. Next, this slurry is charged into a hopper 51 of a spray dryer (with a pin type atomizer manufactured by Okawara Chemical Co., Ltd.) as shown in FIG. 1, and sent to a nozzle 57 at the top of the tower by a pump 52. Spray on. At the same time, hot air of 150 ° C. was sent from the side of the nozzle 57 into the drying tower 58 through the heat exchanger 55 to obtain spherical composite particles А having a particle size of 10 to 100 μm (average particle size of 50 μm).
The obtained composite particles A are rolled (roll temperature 100 ° C., press linear pressure 3.9 kN / cm) in a roll press machine (pressed rough surface heat roll; manufactured by Hirano Giken Kogyo Co., Ltd.) as shown in FIG. Electrode sheet A having an active material layer of 350 μm thickness, 10 cm width, and electrode density 0.92 g / cm ³ , formed on a 40 μm thick aluminum current collector at a forming speed of 10.0 m / min. Got.

Production Example 2 of Electrochemical Element Sheet (Electrode Sheet B)
A composite particle B and an electrode sheet B are obtained in the same manner as in Production Example 1 except that the electrode active material graphite in Production Example 1 of the electrochemical device sheet is replaced with the carbon-coated graphite in Reference Example 2. The thickness of the electrode sheet B was 350 μm, and the electrode density was 0.84 g / cm ³ .

Production Example 3 of Electrode Element Sheet (Electrode Sheet C)
100 parts of activated carbon (active carbon having a specific surface area of 2000 m ² / g and an average particle diameter of 5 μm) as an electrode active material, 5 parts of conductive material (acetylene black “Denka Black Powder”: manufactured by Denki Kagaku Kogyo Co., Ltd.), dispersion-type binder 14 parts of an aqueous dispersion of a cross-linked acrylate polymer having an average particle size of 0.15 μm and a glass transition temperature of −40 ° C .: “AD211” manufactured by Nippon Zeon Co., Ltd., a soluble resin (1.5% aqueous solution of carboxymethyl cellulose) “DN-800H” (manufactured by Daicel Chemical Industries, Ltd.) 93.3 parts and ion-exchanged water 347.7 parts were stirred and mixed with a TK homomixer to obtain a slurry having a solid content of 20%. Next, this slurry was treated in the same manner as in Preparation Example 1 to obtain spherical composite particles C having a particle size of 10 to 100 μm (average particle size of 50 μm). The composite particle C includes an inner layer portion and an outer layer portion, and the average particle size of the outer layer portion is smaller than the average particle size of the inner layer portion. The obtained composite particles C were processed in the same manner as in Preparation Example 1 to obtain an electrode sheet C having an active material layer having a thickness of 350 μm, a width of 10 cm, and a density of 0.58 g / cm 3. This electrode sheet is preferable for use as a negative electrode for an electrochemical element.

Production Example 4 for Electrochemical Element Sheet (Electrode Sheet D)
The dispersion-type binder of Production Example 1 of the electrode sheet was dispersed from the aqueous dispersion of the binder A by the dispersion-type binder B (cross-linked acrylate weight having an average particle diameter of 0.15 μm and a glass transition temperature of −40 ° C. 40% aqueous dispersion of coalescence: “AD211” (manufactured by Nippon Zeon Co., Ltd.) An electrode D sheet was obtained in the same manner as in Production Example 1 except that 14 parts were used. The degree of swelling measured for AD211 was 2.33. The thickness of the electrode sheet E was 80 μm, and the electrode density was 0.89 g / cm ³ .

Production Example 5 of Electrochemical Element Sheet (Electrode Sheet E)
As an electroactive material, 100 parts of graphite (TIMREX KS6; manufactured by Timcal), 7.5 parts of a dispersion-type binder (“AD211”: manufactured by Nippon Zeon), a soluble resin (1.5% aqueous solution of carboxymethylcellulose “DN-”) 800H ": Daicel Chemical Industries, Ltd. 93.3 parts and ion-exchanged water 60.2 parts were stirred and mixed with a mixer (TK homomixer) to obtain a slurry having a solid content of 40%. Next, the slurry was applied onto a 40 μm thick aluminum current collector using a doctor blade and dried to obtain an electrode sheet E. Dispersion was insufficient and the electrode surface was rough. The thickness of the electrode sheet E was 80 μm, and the electrode density was 0.89 g / cm ³ .

Production Example 6 of Electrochemical Element Sheet (Electrode Sheet F)
An electrode sheet F was obtained in the same manner as in Production Example 5 except that 100 parts of carbon-coated graphite of Reference Example 2 was used as the electroactive material. Dispersion was insufficient and the electrode surface was rough. The electrode sheet E had a thickness of 80 μm and an electrode density of 0.81 g / cm ³ .

Capacitor Production Method Each of the electrode sheets obtained as described above is cut into 5 cm × 5 cm (excluding the uncoated part), and a tab material is attached to the uncoated part using an ultrasonic metal welder. Prepare a pair of electrodes with a tab material as a positive electrode and a negative electrode, face the electrode layers together, sandwich a separator (thickness 35 μm, TF40: manufactured by Nippon Kogyo Paper Industries), and vacuum this electrode pair at 160 ° C. for 10 hours After drying, the outside is fixed with a polyethylene plate and wrapped with an aluminum wrapping material, and then a liquid leakage preventing sealing material is sandwiched between the tabs taken out and sealed at 180 ° C. for 5 seconds. Finally, an electrolytic solution 1.5MTEMA · PF6 / PC is injected and vacuum sealed at 180 ° C. for 4 seconds to produce an electric double layer capacitor as an example of an electrochemical element.

Example 1 A capacitor is prepared using an electrode sheet A as a positive electrode and an electrode sheet C as a negative electrode.
Example 2: A capacitor is fabricated using the electrode sheet B as the positive electrode and the electrode sheet C as the negative electrode.
Comparative Example 1: A capacitor is fabricated using the electrode sheet C for both the positive and negative electrodes.
Example 3 A capacitor is fabricated using the electrode sheet D as the positive electrode and the electrode sheet C as the negative electrode.
Comparative Example 2: A capacitor is produced using the electrode sheet E as the positive electrode and the electrode sheet C as the negative electrode.
Comparative Example 3: A capacitor is fabricated using the electrode sheet F as the positive electrode and the electrode sheet C as the negative electrode.
The capacitor test results obtained above are shown in Table 1.

  Table 1 shows the following. Examples 1, 2, and 3 in which graphite or graphite-like particles were used as the positive electrode electroactive material and electrode sheets were produced by a dry method were excellent in the balance between the capacitance and capacity retention of the obtained capacitor. In particular, in Examples 1 and 2 in which the degree of swelling of the binder is smaller than 2, the capacitance and capacity retention are particularly excellent, and the internal resistance is also small and excellent. Even when the dry method is adopted, when activated carbon is used as the positive electrode active material, the electrostatic capacity is very poor as in Comparative Example 1. Even when graphite or graphite-like particles are used as the positive electrode active material, when an electrode sheet is produced by a dry method, as in Comparative Examples 2 and 3, the capacitance of the obtained capacitor and the capacity retention ratio are balanced. Inferior.

  ADVANTAGE OF THE INVENTION According to this invention, the electrochemical element using the electrode for electrochemical elements, the manufacturing method excellent in the production efficiency, and such an electrochemical rough use electrode is provided. The obtained electrochemical device has a large capacitance, a high capacity retention rate, and high reliability in the charge / discharge cycle. The obtained electrochemical element is a backup power source for memory of personal computers and portable terminals, power source for instantaneous power failure such as personal computers, application to electric vehicles or hybrid vehicles, solar power generation energy storage system combined with solar cells, combination with batteries It can be suitably used for various applications such as a load leveling power source.

The schematic diagram of the spray dryer which can be used by this invention is shown. The schematic diagram of the roll press suitable for manufacture of the electrode for electrochemical elements which can be used by this invention is shown.

Explanation of symbols

51: Hopper 52: Pump 54: Blower 55: Heat exchanger 57: Spray nozzle 58: Drying tower 59: Suction machine 62: Cold air fan 1: Current collector 2: Active material layer 3: Composite particles 4: Feeder 5: Roll

Claims (8)

An electrode for an electrochemical device comprising a current collector and an active material layer on the surface thereof,
The active material layer is obtained by molding composite particles containing an electrode active material, a conductive material and a binder by a dry method, and the electrode active material contains graphite or graphite-like particles,
It said binder is a crosslinked acrylate polymer, and the degree of swelling at a concentration of 1.0 mol / L in propylene carbonate to the electrolyte prepared by dissolving triethylene monomethyl ammonium tetrafluoroethane baud rate Ri der 2 or less,
The composite particle is composed of an outer layer portion and an inner layer portion, and the outer layer portion and the inner layer portion are formed by binding the electrode active material and a conductive material with a binder to form the outer layer portion. An electrode for an electrochemical element , wherein an average particle diameter of the electrode active material and the conductive material is smaller than an average particle diameter of the electrode active material and the conductive material forming the inner layer portion .   2. The electrochemical according to claim 1, wherein the electrode active material is a graphite-like particle having a coating layer of a carbon allotrope having a crystal structure different from the crystal structure of the graphite on the surface of the graphite particle. Element electrode.   The electrode for an electrochemical element according to claim 2, wherein the coating layer is a crystalline carbon allotrope.   The electrode for an electrochemical element according to claim 2, wherein the coating layer is an amorphous carbon allotrope. Having a step of obtaining composite particles containing graphite or graphite-like particles, a conductive material and a binder, and a step of forming an active material layer by heating and pressing the composite particles on a current collector;
It said binder is a crosslinked acrylate polymer, and the degree of swelling at a concentration of 1.0 mol / L in propylene carbonate to the electrolyte prepared by dissolving triethylene monomethyl ammonium tetrafluoroethane baud rate Ri der 2 or less,
The composite particle is composed of an outer layer portion and an inner layer portion, and the outer layer portion and the inner layer portion are formed by binding the electrode active material and a conductive material with a binder to form the outer layer portion. The method for producing an electrode for an electrochemical element , wherein an average particle diameter of the electrode active material and the conductive material is smaller than an average particle diameter of the electrode active material and the conductive material forming the inner layer portion . The method for producing an electrode for an electrochemical element according to claim 5 , wherein the step of obtaining composite particles is a spray drying granulation method. The electrochemical element which has the electrode for electrochemical elements in any one of Claims 1 thru | or 4 as a positive electrode or a negative electrode. The electrochemical device according to claim 7 , which is an electric double layer capacitor.

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