Composite particles for electrochemical element positive electrode, production method for same, positive electrode for electrochemical element, and electrochemical element

Abstract

Composite particles for an electrochemical element positive electrode, said composite particles including a positive electrode active material, a carbon-based conductive material, and a binder resin, wherein the degree of dispersion s2 of carbon atoms is in a specific range.

Description

Composite particles for positive electrodes of electrochemical elements and their manufacturing method, positive electrodes for electrochemical elements, and electrochemical elements

[0001] The present invention relates to composite particles for a positive electrode of an electrochemical device, a method for producing the same, and a positive electrode for an electrochemical device and an electrochemical device containing the composite particles.

[0002] Electrochemical devices such as lithium-ion secondary batteries are used in a wide range of applications, and there is a demand for further improvement in their performance. In many cases, the positive electrode of an electrochemical device comprises a current collector and a positive electrode mixture layer provided on the surface of the current collector.

[0003] A wet forming method has been widely used as a method for forming a positive electrode composite layer. The wet forming method here refers to a method in which a slurry composition containing a positive electrode active material, a binder resin, and a solvent is applied to the surface of a current collector and the slurry composition is dried to form a positive electrode composite layer.

[0004] However, in recent years, dry forming methods have been attracting attention for more efficient formation of positive electrodes. In the dry forming method, composite particles containing a positive electrode active material and a binder resin are prepared, the composite particles are deposited on the surface of a current collector to form a layer of the composite particles, and the layer is pressed to reduce its thickness, thereby forming a positive electrode mixture layer. As composite particles used in such a dry forming method, the technology disclosed in Patent Document 1 is known.

[0005] JP 2014-78497 A (corresponding publication: U.S. Patent Application Publication No. 2014 / 0079872)

[0006] From the viewpoint of reducing the internal resistance of an electrochemical device, it is desirable for the composite particles to have low powder resistance. The present invention has been made in view of such problems, and aims to provide composite particles for electrochemical device positive electrodes having low powder resistance and a method for producing the same, as well as a positive electrode for electrochemical devices and an electrochemical device containing the composite particles.

[0007] The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, the present inventors have found that composite particles for electrochemical element positive electrodes, which contain a positive electrode active material, a carbon-based conductive material, and a binder resin, and which have a characteristic value representing the dispersion of carbon atoms within a specific range, can have low powder resistance, and have completed the present invention. That is, the present invention includes the following.

[0008] <1> Composite particles for a positive electrode of an electrochemical element, comprising a positive electrode active material, a carbon-based conductive material, and a binder resin, wherein the degree of dispersion s of carbon atoms in the composite particles for a positive electrode of an electrochemical element is calculated by the following formula (1): ２ The composite particles for a positive electrode of an electrochemical element, wherein the content of ZnO is 0.5% or more and 1.0% or less. (In formula (1), n ​​represents the number of square images obtained by dividing a surface observation image of 1280 pixels x 1024 pixels obtained by photographing the composite particle for a positive electrode of an electrochemical element at a magnification of 2000 times using a scanning electron microscope, each image having a size of 100 pixels vertically x 100 pixels horizontally and not including a blank area where the composite particle for a positive electrode of an electrochemical element is not photographed, n is 80 or more and 120 or less, and x ｉ represents the area fraction of carbon atoms in each of the images, and x ａ represents the average area ratio of all carbon atoms in the image.) <2> The composite particles for electrochemical element positive electrodes according to <1>, having a particle strength of 0.6 or more, wherein the particle strength represents a ratio "D50(0.25MPa) / D50(0.1MPa)" of a D50 particle diameter "D50(0.1MPa)" measured under an applied pressure of 0.1 MPa to a D50 particle diameter "D50(0.25MPa)" measured under an applied pressure of 0.25 MPa. <3> A cross-sectional area of ​​3.1 cm ２The composite particles for electrochemical element positive electrodes according to <1> or <2>, wherein 4.0 g of the composite particles for electrochemical element positive electrodes are placed in a container and pressurized with 20 kN, and the powder resistance of the composite particles for electrochemical element positive electrodes is measured at 30 Ω or less. <4> The composite particles for electrochemical element positive electrodes according to any one of <1> to <3>, wherein the content of the positive electrode active material is 90% by weight or more and 99.19% by weight or less. <5> The composite particles for electrochemical element positive electrodes according to any one of <1> to <4>, wherein the content of the carbon-based conductive material is 0.8% by weight or more and 5% by weight or less. <6> The composite particles for electrochemical element positive electrodes according to any one of <1> to <5>, wherein the content of the binder resin is 0.01% by weight or more and 5% by weight or less. <7> The composite particle for an electrochemical element positive electrode according to any one of <1> to <6>, wherein the carbon-based conductive material has a D50 particle size of 0.01 μm to 0.4 μm. <8> A method for producing the composite particle for an electrochemical element positive electrode according to any one of <1> to <7>, comprising stirring and granulating a positive electrode active material, a carbon-based conductive material, a binder resin, and a solvent. <9> The method for producing the composite particle for an electrochemical element positive electrode according to <8>, comprising: a step (i) of stirring the positive electrode active material in a granulation tank to obtain a stirred state; and a step (ii) of spraying a liquid composition containing the carbon-based conductive material, the binder resin, and the solvent onto the stirred positive electrode active material. <10> The method for producing the composite particle for an electrochemical element positive electrode according to <9>, wherein the relative vapor pressure of the solvent in the granulation tank in the step (ii) is 0.1 or more and 0.9 or less. <11> The method for producing composite particles for electrochemical element positive electrodes according to <10>, wherein the step (ii) comprises spraying the liquid composition from a nozzle provided in a ceiling portion of the granulation tank, and the relative vapor pressure of the solvent in the granulation tank in the step (ii) is 0.5 or more. <12> The method for producing composite particles for electrochemical element positive electrodes according to <10>, wherein the step (ii) comprises spraying the liquid composition from a nozzle provided in a side portion of the granulation tank, and the relative vapor pressure of the solvent in the granulation tank in the step (ii) is less than 0.5.<13> A positive electrode for an electrochemical element, comprising: a current collector; and a positive electrode mixture layer formed on the current collector, wherein the positive electrode mixture layer contains the composite particles for an electrochemical element positive electrode according to any one of <1> to <7>. <14> An electrochemical element comprising the positive electrode for an electrochemical element according to <13>.

[0009] According to the present invention, it is possible to provide composite particles for electrochemical element positive electrodes having low powder resistance and a method for producing the same, as well as a positive electrode for electrochemical elements and an electrochemical element containing the composite particles.

[0010] Fig. 1 is a plan view schematically showing a granulation tank used in a method for producing composite particles according to one embodiment of the present invention. Fig. 2 is a cross-sectional view schematically showing a granulation tank used in a method for producing composite particles according to one embodiment of the present invention. Fig. 3 is a graph showing the relationship between dispersibility and powder resistivity for examples and comparative examples of the present invention.

[0011] The present invention will be described in detail below with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples described below, and can be implemented with any modifications within the scope of the claims and their equivalents.

[0012] In a polymer produced by copolymerizing multiple types of monomers, the ratio of structural units formed by polymerizing a certain monomer in the polymer usually coincides with the ratio (feed ratio) of the certain monomer to all the monomers used in the polymerization of the polymer, unless otherwise specified.

[0013] The structure of a molecule or a part thereof, such as a structural unit, is not limited by its production method. For example, an aromatic vinyl monomer unit is a structural unit having a structure formed by polymerization of an aromatic vinyl monomer, but the aromatic vinyl monomer unit also includes units formed by other formation methods that have the same structure as the structure formed by polymerization of an aromatic vinyl monomer. Furthermore, for example, a conjugated diene monomer unit is a structural unit having a structure formed by polymerization of a conjugated diene monomer, but the conjugated diene monomer unit also includes units formed by other formation methods that have the same structure as the structure formed by polymerization of a conjugated diene monomer.

[0014] In the following description, unless otherwise specified, the directions of elements as "parallel," "vertical," and "orthogonal" may include an error within a range that does not impair the effects of the present invention, for example, within a range of ±3°, ±2°, or ±1°.

[0015] In the following description, unless otherwise specified, the term "(meth)acrylic acid" includes acrylic acid, methacrylic acid, and mixtures thereof.

[0016] <Overview of Composite Particle> A composite particle for a positive electrode of an electrochemical element according to one embodiment of the present invention (hereinafter, sometimes referred to as a "composite particle") comprises a positive electrode active material, a carbon-based conductive material, and a binder resin. Typically, one or more particles of the positive electrode active material and one or more particles of the carbon-based conductive material are bound by the binder resin to form a single composite particle. This composite particle can be used as a powder material for forming a positive electrode of an electrochemical element.

[0017] The composite particles according to this embodiment have a specific range of "dispersity of carbon atoms s ２ " where the dispersion of carbon atoms s ２ is a characteristic value calculated by formula (1) and can represent the degree of dispersion of the positions of carbon atoms in the composite particle. The carbon atoms include both the carbon atoms contained in the carbon-based conductive material and the carbon atoms that can be contained in the binder resin.

[0018]

[0019] (In formula (1), n ​​represents the number of square images obtained by dividing a 1280 pixel x 1024 pixel surface observation image obtained by photographing a composite particle with a scanning electron microscope at a magnification of 2000, each image having a size of 100 pixels vertically x 100 pixels horizontally and not including a margin where no composite particle is photographed, n is 80 or more and 120 or less, and x ｉ represents the area ratio of the portion in each of the images in which carbon atoms are visible, and x ａ represents the average area ratio of all the carbon atoms in the image.)

[0020] The composite particles according to this embodiment can have low powder resistance. Therefore, the resistance of a positive electrode for an electrochemical device (hereinafter, sometimes abbreviated as "positive electrode") manufactured using this composite particle can be reduced, thereby reducing the internal resistance of the electrochemical device. Furthermore, the composite particles according to this embodiment can usually have high particle strength. Therefore, even when the particles of the positive electrode active material expand and contract due to charge and discharge, destruction of the composite particles can be suppressed, thereby reducing the disconnection of the conductive path due to destruction of the composite particles, and thus improving the cycle characteristics of the electrochemical device.

[0021] <Dispersion of Carbon Atoms> The dispersion of carbon atoms s in the composite particles according to this embodiment ２ The range of the dispersion degree s of carbon atoms is usually 0.5% or more, more preferably 0.6% or more, even more preferably 0.7% or more, even more preferably 0.8% or more, and even more preferably 0.81% or more. The upper limit is usually 1.0% or less, preferably 0.9% or less, more preferably 0.89% or less, and even more preferably 0.82% or less. Therefore, the dispersion degree s of carbon atoms ２ The ranges are, for example, 0.5% or more and 1.0% or less, 0.5% or more and 0.9% or less, 0.5% or more and 0.89% or less, 0.5% or more and 0.82% or less, 0.6% or more and 1.0% or less, 0.6% or more and 0.9% or less, 0.6% or more and 0.89% or less, 0.6% or more and 0.82% or less, 0.7% or more and 1.0% or less, 0.7% or more and 0.9% or less, 0. The dispersion degree s of carbon atoms can be in the range of 7% or more and 0.89% or less, 0.7% or more and 0.82% or less, 0.8% or more and 1.0% or less, 0.8% or more and 0.9% or less, 0.8% or more and 0.89% or less, 0.8% or more and 0.82% or less, 0.81% or more and 1.0% or less, 0.81% or more and 0.9% or less, 0.81% or more and 0.89% or less, or 0.81% or more and 0.82% or less. ２ When the particle diameter is within the above range, the powder resistance of the composite particles can be reduced, and furthermore, the particle strength of the composite particles can usually be increased.

[0022] Dispersion of carbon atoms s ２ is a characteristic value calculated by the above formula (1).２ can be calculated from the images based on formula (1) by photographing the composite particle at a magnification of 2000 times using a scanning electron microscope to obtain n square images. Specifically, the composite particle is photographed at a magnification of 2000 times to obtain a surface observation image with a size of 1280 pixels x 1024 pixels. This surface observation image is divided into square images with a size of 100 pixels vertically x 100 pixels horizontally. From the multiple square images thus obtained, n images that do not include blank areas are selected. The term "blank area" refers to the area where the composite particle is not photographed. In each of these n images, the area ratio x of carbon atoms to 100% of the image area is calculated. ｉ (where i represents an integer from 1 to n). In addition, the area ratio x of carbon atoms in all n images is calculated. ｉ Average x ａ Then, calculate the area ratio of carbon atoms x ｉ and average x ａ The squared value of the difference between ｉ -x ａ ) ２ The sum of all n images is then divided by the number of images n to obtain the dispersion of carbon atoms in the composite particle, s ２ The number n of images is an integer that is usually 80 or more, preferably 90 or more, and more preferably 95 or more. The upper limit of the number n is usually 120 or less, and may be 100 or less. In one example, the range of the number n of images may be 80 or more and 120 or less.

[0023] The area ratio x of carbon atoms in each of the n square images ｉcan be calculated by image analysis. Image analysis can be performed using the image processing software "OpenCv" (https: / / opencv.org / ). For example, if each image shows three parts: a positive electrode active material part, a carbon atom part, and a void part, the area ratio of the carbon atom part can be calculated by separating the positive electrode active material part, the carbon atom part, and the void part using a ternary thresholding process. Generally, each part has a different brightness value, so the ternary thresholding process can be performed based on the brightness value of the pixel. As a specific example, if the positive electrode active material is photographed as a high-brightness part, the voids as a low-brightness part, and the carbon atoms as an intermediate brightness part, the brightness value of the pixel with the highest brightness value in the image is set to "100," and the brightness value of the pixel with the lowest brightness value in the image is set to "0." A first threshold (e.g., 30) separating the voids from the carbon atoms and a second threshold (e.g., 70) separating the carbon atoms from the positive electrode active material are set. Then, a ternary value process is performed using the first threshold value and the second threshold value, and the area ratio of carbon atoms may be calculated from the area of ​​carbon atoms represented by the portion consisting of pixels having a brightness value between the first threshold value and the second threshold value. ２ The measurement may be carried out by the method described in the Examples below.

[0024] Dispersion of carbon atoms s ２ For example, in a method for producing composite particles by an agitation granulation method using a granulation tank, the dispersity s of carbon atoms in the specific range can be adjusted by the relative vapor pressure of the solvent in the granulation tank. This relative vapor pressure indicates how moist the environment in the granulation tank is due to the solvent. In general, the lower the relative vapor pressure, the higher the dispersity can be, and the higher the relative vapor pressure, the lower the dispersity can be. Therefore, by appropriately setting the relative vapor pressure in the granulation tank according to the composition of the raw materials of the composite particles, the dispersity s of carbon atoms in the specific range can be adjusted. ２ can be obtained.

[0025] <Positive Electrode Active Material> The positive electrode active material is a material that transfers electrons at the positive electrode of an electrochemical element. For example, as a positive electrode active material for a lithium ion secondary battery, a material capable of absorbing and releasing lithium can usually be used. This positive electrode active material is preferably an inorganic compound. Examples of inorganic compounds that can be used as the positive electrode active material include transition metal oxides, transition metal sulfides, and lithium-containing composite metal oxides containing lithium and transition metals. Examples of the transition metals include Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Mo.

[0026] Examples of transition metal oxides include MnO and MnO ２ , V ２ O ５ , V ６ O １３ , TiO ２ , Cu ２ V ２ O ３ , amorphous V ２ O-P ２ O ５ , MoO ３ Among them, MnO, V are preferred in terms of cycle stability and capacity. ２ O ５ , V ６ O １３ and TiO ２ is preferred.

[0027] Examples of transition metal sulfides include TiS ２ , TiS ３ , amorphous MoS ２ , FeS, etc.

[0028] Examples of the lithium-containing composite metal oxide include lithium-containing composite metal oxides having a layered structure, lithium-containing composite metal oxides having a spinel structure, and lithium-containing composite metal oxides having an olivine structure. Examples of the lithium-containing composite metal oxides having a layered structure include lithium-containing cobalt oxide (LiCoO ２ ), lithium-containing nickel oxide (LiNiO ２), Co—Ni—Mn lithium composite oxide, Ni—Mn—Al lithium composite oxide, Ni—Co—Al lithium composite oxide, etc. Examples of lithium-containing composite metal oxides having a spinel structure include lithium manganate (LiMn ２ O ４ ), Li[Mn ３／２ M １ １／２ ]O ４ (Here, M １ represents a transition metal other than Mn, such as Cr, Fe, Co, Ni, or Cu. Examples of lithium-containing composite metal oxides having an olivine structure include Li Ｘ M ２ P.O. ４ (In the formula, M ２ represents at least one element selected from the group consisting of Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B, and Mo, and X represents a number satisfying 0≦X≦2. One type of positive electrode active material may be used alone, or two or more types may be used in combination.

[0029] The positive electrode active material usually has a particle shape. The D50 particle size range of the positive electrode active material is preferably 0.03 μm or more, more preferably 0.1 μm or more, even more preferably 1.0 μm or more, and is preferably 500 μm or less, more preferably 100 μm or less, even more preferably 30 μm or less. When the D50 particle size of the positive electrode active material is within the above range, the powder resistance of the composite particles can be effectively reduced, and further, usually the particle strength of the composite particles can be effectively increased.

[0030] The D50 particle size of the positive electrode active material can be measured by the following method. The positive electrode active material is dispersed in an airflow at a dispersion pressure of 0.25 MPa, and the particle size distribution of the particles of the positive electrode active material is measured on a volume basis using a laser diffraction particle size distribution analyzer. In the obtained particle size distribution, the particle size at which the cumulative volume calculated from the smallest diameter side is 50% (median diameter D50) can be determined as the D50 particle size of the positive electrode active material.

[0031] The content of the positive electrode active material is preferably 90% by weight or more, more preferably 93% by weight or more, and even more preferably 95% by weight or more, and is preferably 99.19% by weight or less, more preferably 99% by weight or less, and even more preferably 98% by weight or less, relative to 100% by weight of the composite particles. Therefore, the content of the positive electrode active material relative to 100% by weight of the composite particles can be, for example, 90% by weight or more to 99.19% by weight or less, 90% by weight or more to 99% by weight or less, 90% by weight or more to 98% by weight or less, 93% by weight or more to 99.19% by weight or less, 93% by weight or more to 99% by weight or less, 93% by weight or more to 98% by weight or less, 95% by weight or more to 99.19% by weight or less, 95% by weight or more to 99% by weight or less, or 95% by weight or more to 98% by weight or less. When the content of the positive electrode active material is within the above range, the powder resistance of the composite particles can be effectively reduced, and furthermore, the particle strength of the composite particles can usually be effectively increased.

[0032] <Carbon-based conductive material> The carbon-based conductive material is a carbon material that forms a conductive path between the positive electrode active materials. Examples of the carbon-based conductive material include carbon black (e.g., acetylene black, Ketjen Black (registered trademark), furnace black, etc.); single-walled or multi-walled carbon nanotubes (multi-walled carbon nanotubes include cup-stacked types); carbon nanohorns; vapor-grown carbon fibers; milled carbon fibers obtained by calcining and then crushing polymer fibers; single-layered or multi-layered graphene; and carbon nonwoven fabric sheets obtained by calcining nonwoven fabrics made of polymer fibers. Among these, carbon black is preferred. One type of carbon-based conductive material may be used alone, or two or more types may be used in combination.

[0033] The shape of the carbonaceous conductive material is not particularly limited, and may be, for example, particulate, fibrous, or foil.

[0034] The D50 particle size range of the carbon-based conductive material in the composite particles is preferably 0.01 μm or more, more preferably 0.02 μm or more, even more preferably 0.05 μm or more, and preferably 0.4 μm or less, more preferably 0.2 μm or less, and even more preferably 0.15 μm or less. Therefore, the D50 particle size range of the carbon-based conductive material can be, for example, 0.01 μm or more to 0.4 μm or less, 0.01 μm or more to 0.2 μm or less, 0.01 μm or more to 0.15 μm or less, 0.02 μm or more to 0.4 μm or less, 0.02 μm or more to 0.2 μm or less, 0.02 μm or more to 0.15 μm or less, 0.05 μm or more to 0.4 μm or less, 0.05 μm or more to 0.2 μm or less, or 0.05 μm or more to 0.15 μm or less. When the D50 particle size of the carbon-based conductive material is within the above range, the powder resistance of the composite particles can be effectively reduced, and furthermore, the particle strength of the composite particles can usually be effectively increased.

[0035] The D50 particle size of the carbon-based conductive material can be measured by the following method. The carbon-based conductive material is dispersed in an airflow at a dispersion pressure of 0.25 MPa, and the particle size distribution of the carbon-based conductive material particles is measured on a volume basis using a laser diffraction particle size distribution analyzer. In the obtained particle size distribution, the particle size at which the cumulative volume calculated from the smallest diameter side is 50% (median diameter D50) can be determined as the D50 particle size of the carbon-based conductive material.

[0036] The content of the carbon-based conductive material is preferably 0.8 wt% or more, more preferably 1.0 wt% or more, and even more preferably 1.5 wt% or more, and preferably 5 wt% or less, more preferably 4 wt% or less, and even more preferably 3 wt% or less, relative to 100 wt% of the composite particles. Therefore, the content of the carbon-based conductive material relative to 100 wt% of the composite particles can be, for example, 0.8 wt% to 5 wt%, 0.8 wt% to 4 wt%, 0.8 wt% to 3 wt%, 1.0 wt% to 5 wt%, 1.0 wt% to 4 wt%, 1.0 wt% to 3 wt%, 1.5 wt% to 5 wt%, 1.5 wt% to 4 wt%, or 1.5 wt% to 3 wt%. When the content of the carbon-based conductive material is within the above range, the powder resistance of the composite particles can be effectively reduced, and typically, the particle strength of the composite particles can be effectively increased.

[0037] <Binder Resin> The binder resin is a resin that binds the positive electrode active material and the carbon-based conductive material. A polymer is usually used as the binder resin. Examples of polymers that can be used as the binder resin include conjugated diene polymers, acrylic polymers, aromatic vinyl block polymers, fluorine-based polymers, cellulose polymers, and cyclic olefin polymers.

[0038] The conjugated diene polymer refers to a polymer containing conjugated diene monomer units. Examples of conjugated diene monomers include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene, 2-chloro-1,3-butadiene (chloroprene), and piperylene. Specific examples of conjugated diene polymers include copolymers containing aromatic vinyl monomer units and aliphatic conjugated diene monomer units, such as styrene-butadiene copolymer (SBR); butadiene rubber (BR); acrylic rubber (NBR) (a copolymer containing acrylonitrile units and butadiene units); and hydrogenated products thereof.

[0039] Examples of acrylic polymers include polymers containing crosslinkable monomer units, (meth)acrylic acid ester monomer units, and acidic group-containing monomer units. The proportion of (meth)acrylic acid ester monomer units in the acrylic polymer is preferably 50% by weight or more, more preferably 55% by weight or more, and even more preferably 58% by weight or more, and is preferably 98% by weight or less, more preferably 97% by weight or less, and even more preferably 96% by weight or less.

[0040] Examples of aromatic vinyl block polymers include block polymers containing block regions composed of aromatic vinyl monomer units. Examples of aromatic vinyl monomers include styrene, styrene sulfonic acid and its salts, α-methylstyrene, p-t-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, and vinylnaphthalene, with styrene being preferred. Examples of aromatic vinyl block polymers include styrene-isoprene-styrene block copolymers, styrene-butadiene-styrene copolymers, and hydrogenated versions of these.

[0041] The term "fluorine-containing polymer" refers to a polymer that contains fluorine-containing monomer units and may further contain fluorine-free monomer units (fluorine-free monomers). Examples of fluorine-containing monomers include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, vinyl trifluoride, vinyl fluoride, trifluoroethylene, trifluorochloroethylene, 2,3,3,3-tetrafluoropropene, and perfluoroalkyl vinyl ether. Examples of fluorine-containing polymers include polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, perfluoroalkoxy fluororesin, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, and vinylidene fluoride-hexafluoropropylene copolymer (vinylidene fluoride-hexafluoropropylene copolymer).

[0042] Examples of the cellulose-based polymer include cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, and carboxylmethyl cellulose.

[0043] Examples of cyclic olefin polymers include polymers (addition polymers or ring-opening polymers) obtained by polymerizing cyclic olefin compounds and hydrogenated polymers thereof, as well as hydrogenated polymers obtained by polymerizing aromatic vinyl compounds. Among these, hydrogenated polymers obtained by ring-opening polymerization of cyclic olefin compounds and hydrogenated polymers obtained by polymerizing aromatic vinyl compounds are preferred because they allow for easy adjustment of the electrolyte swelling degree and glass transition temperature to appropriate levels.

[0044] Examples of the cyclic olefin compounds include norbornenes that are unsubstituted or have an alkyl group, such as norbornene, 5-methylnorbornene, 5-ethylnorbornene, 5-butylnorbornene, 5-hexylnorbornene, 5-decylnorbornene, 5-cyclohexylnorbornene, and 5-cyclopentylnorbornene; norbornenes that have an alkenyl group, such as 5-ethylidenenorbornene, 5-vinylnorbornene, 5-propenylnorbornene, 5-cyclohexenylnorbornene, and 5-cyclopentenylnorbornene; norbornenes that have an aromatic ring, such as 5-phenylnorbornene; 5-methoxycarbonylnorbornene, 5-ethoxycarbonylnorbornene, 5-methylnorbornene, and 5-methylnorbornene. norbornenes having a polar group containing an oxygen atom, such as norbornene-5-methoxycarbonylnorbornene, 5-methyl-5-ethoxycarbonylnorbornene, norbornenyl-2-methylpropionate, norbornenyl-2-methyloctanate, 5-hydroxymethylnorbornene, 5,6-di(hydroxymethyl)norbornene, 5,5-di(hydroxymethyl)norbornene, 5-hydroxy-i-propylnorbornene, 5,6-dicarboxynorbornene, and 5-methoxycarbonyl-6-carboxynorbornene; norbornenes having a polar group containing a nitrogen atom, such as 5-cyanonorbornene; dicyclopentadiene, methyldicyclopentadiene, tricyclo[5.2.1.0]di ... ２，６ ]dec-8-ene and other polycyclic norbornenes having three or more rings and not containing an aromatic ring structure; tetracyclo[9.2.1.0 ２，１０ .0 ３，８ ]tetradeca-3,5,7,12-tetraene (also known as 1,4-methano-1,4,4a,9a-tetrahydro-9H-fluorene), tetracyclo[10.2.1.0 ２，１１ .0 ４，９]pentadeca-4,6,8,13-tetraene (also called 1,4-methano-1,4,4a,9,9a,10-hexahydroanthracene), and other polycyclic norbornenes having three or more aromatic rings; tetracyclododecene, 8-methyltetracyclododecene, 8-ethyltetracyclododecene, 8-cyclohexyltetracyclododecene, 8-cyclopentyltetracyclododecene, 8-methoxycarbonyl-8-methyltetracyclo[4.4.0.1 ２，５ .1 ７，１０ tetracyclododecenes having an unsubstituted or alkyl group such as 8-methylidenetetracyclododecene, 8-ethylidenetetracyclododecene, 8-vinyltetracyclododecene, 8-propenyltetracyclododecene, 8-cyclohexenyltetracyclododecene, 8-cyclopentenyltetracyclododecene; tetracyclododecenes having an exocyclic double bond such as 8-phenyltetracyclododecene; tetracyclododecenes having an aromatic ring such as 8-methoxycarbonyltetracyclododecene, 8-methyl-8-methoxycarbonyltetracyclododecene, 8-hydroxymethyltetracyclododecene, 8-carboxytetracyclododecene, ... tetracyclododecenes having a substituent containing an oxygen atom, such as tetracyclododecene-8,9-dicarboxylic acid and tetracyclododecene-8,9-dicarboxylic anhydride; tetracyclododecenes having a substituent containing a nitrogen atom, such as 8-cyanotetracyclododecene and tetracyclododecene-8,9-dicarboxylic imide; tetracyclododecenes having a substituent containing a halogen atom, such as 8-chlorotetracyclododecene; tetracyclododecenes having a substituent containing a silicon atom, such as 8-trimethoxysilyltetracyclododecene; and hexacycloheptadecenes such as Diels-Alder adducts of the above-mentioned tetracyclododecenes and cyclopentadiene.

[0045] Among these, non-polar norbornene-based monomers are preferred as cyclic olefin compounds; for example, norbornenes having unsubstituted or alkyl groups (e.g., norbornene, 8-ethyltetracyclododecene), norbornenes having alkenyl groups (e.g., ethylidenetetracyclododecene (8-ethylidenetetracyclododecene)), dicyclopentadiene, norbornene derivatives having aromatic rings (e.g., tetracyclo[9.2.1.0], ２，１０ .0 ３，８ ]tetradeca-3,5,7,12-tetraene (also called 1,4-methano-1,4,4a,9a-tetrahydro-9H-fluorene)), unsubstituted or alkyl-substituted tetracyclododecenes (e.g., tetracyclododecene, 8-methoxycarbonyl-8-methyltetracyclo[4.4.0.1 ２，５ .1 ７，１０ ]-3-dodecene) is more preferred.

[0046] The polymer of a cyclic olefin compound that can be optionally hydrogenated may be a polymer using only a cyclic olefin compound as a monomer, or a polymer using a cyclic olefin compound and any copolymerizable compound other than a cyclic olefin compound as a monomer, among which a polymer using only a cyclic olefin compound as a monomer is preferred.

[0047] The polymer of a cyclic olefin compound that can be optionally hydrogenated is preferably a polymer using tetracyclododecene, dicyclopentadiene, and norbornene as monomers, and more preferably a ring-opening polymer using tetracyclododecene, dicyclopentadiene, and norbornene as monomers.

[0048] Among the above-mentioned polymers, copolymers containing aromatic vinyl monomer units and conjugated diene monomer units and hydrogenated products thereof are preferred; block copolymers containing aromatic vinyl monomer blocks and conjugated diene monomer blocks and hydrogenated products thereof are more preferred; and hydrogenated products of block copolymers containing aromatic vinyl monomer blocks and conjugated diene monomer blocks are particularly preferred. The aromatic vinyl monomer block is a block region containing aromatic vinyl monomer units and may contain only aromatic vinyl monomer units. Furthermore, the conjugated diene monomer block is a block region containing conjugated diene monomer units and may contain only conjugated diene monomer units.

[0049] The aromatic vinyl monomer unit represents a structural unit having a structure formed by polymerizing an aromatic vinyl monomer. The type of aromatic vinyl monomer unit may be one type or two or more types. The content of the aromatic vinyl monomer unit is preferably 5% by weight or more, more preferably 10% by weight or more, and even more preferably 20% by weight or more, relative to 100% by weight of the total of all structural units contained in the copolymer, and is preferably 50% by weight or less, more preferably 40% by weight or less, and even more preferably 30% by weight or less.

[0050] The conjugated diene monomer unit represents a structural unit having a structure formed by polymerizing a conjugated diene monomer. The type of conjugated diene monomer unit may be one type or two or more types. The content of the conjugated diene monomer unit is preferably 50% by weight or more, more preferably 60% by weight or more, and even more preferably 70% by weight or more, relative to 100% by weight of the total of all structural units contained in the copolymer, and is preferably 95% by weight or less, more preferably 90% by weight or less, and even more preferably 80% by weight or less.

[0051] When the copolymer is a block copolymer, the block structure may be, for example, a two-block structure having an aromatic vinyl monomer block-conjugated diene monomer block; a three-block structure having an aromatic vinyl monomer block-conjugated diene monomer block-aromatic vinyl monomer block; or a five-block structure having an aromatic vinyl monomer block-conjugated diene monomer block-aromatic vinyl monomer block-conjugated diene monomer block-aromatic vinyl monomer block.

[0052] The hydrogenation rate of the hydrogenated copolymer is not particularly limited, but is preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more. １ It can be measured by H-NMR.

[0053] The binder resin may be used alone or in combination of two or more.

[0054] The binder resin content range, relative to 100% by weight of the composite particles, is preferably 0.01% by weight or more, more preferably 0.1% by weight or more, even more preferably 0.3% by weight or more, and preferably 5% by weight or less, more preferably 3% by weight or less, and even more preferably 1% by weight or less. Therefore, the binder resin content range, relative to 100% by weight of the composite particles, can be, for example, 0.01% by weight to 5% by weight or less, 0.01% by weight to 3% by weight or less, 0.01% by weight to 1% by weight or less, 0.1% by weight to 5% by weight or less, 0.1% by weight to 3% by weight or less, 0.1% by weight to 1% by weight or less, 0.3% by weight to 5% by weight or less, 0.3% by weight to 3% by weight or less, or 0.3% by weight to 1% by weight or less. When the binder resin content is within the above range, the powder resistance of the composite particles can be effectively reduced, and typically, the particle strength of the composite particles can be effectively increased.

[0055] <Optional Components> The composite particles according to this embodiment may further contain optional components in combination with the above-described positive electrode active material, carbonaceous conductive material, and binder resin. Examples of the optional components include optional additives such as antioxidants, such as phenolic antioxidants; reinforcing materials; leveling agents; viscosity modifiers; and electrolyte additives. One type of optional additive may be used alone, or two or more types may be used in combination at any ratio.

[0056] Furthermore, the composite particles may contain a solvent in combination with the solid components, such as the above-mentioned positive electrode active material, carbon-based conductive material, binder, and optional additives. This solvent may be a solvent used in the composite particle manufacturing method that remains in the composite particles. The amount of solvent relative to 100% by weight of the composite particles is preferably 0% by weight to 10% by weight, more preferably 0% by weight to 5% by weight, even more preferably 0% by weight to 3% by weight, even more preferably 0% by weight to 1% by weight, even more preferably 0% by weight to 0.5% by weight, and may even be 0% by weight.

[0057] <Characteristics of Composite Particles> The composite particles according to this embodiment can have low powder resistance. Therefore, by using these composite particles, a positive electrode with low resistance can be produced, and therefore an electrochemical device such as a lithium ion secondary battery with low internal resistance can be obtained.

[0058] In one example, the cross-sectional area is 3.1 cm ２ 4.0 g of composite particles are placed in a container of this size and pressurized with 20 kN. As a result, a sample powder layer having the same area as the cross-sectional area of ​​the container is formed by the composite particles in the container. Therefore, the electrical resistance of this sample powder layer can be measured as the powder resistance of the composite particles. The powder resistance of the composite particles measured in this manner is preferably in the range of 30 Ω or less, more preferably 25 Ω or less, and even more preferably 20 Ω or less. The lower limit is preferably as low as possible, and may be, for example, 1 Ω or more, 5 Ω or more, 10 Ω or more, etc. The powder resistance can be measured, for example, by placing 4 g of composite particles in a probe unit having the cross-sectional area of ​​a powder resistivity measurement system ("MCP-PD51" manufactured by Mitsubishi Chemical Analytech Co., Ltd.) and applying a pressure of 20 kN. Specific measurements may be performed using the method described in the Examples below.

[0059] The composite particles according to this embodiment preferably have high particle strength. Composite particles with such high particle strength can suppress fracture of the composite particles when stress is applied. Normally, positive electrode active material particles expand and contract during charge and discharge, which can cause stress to be applied to the composite particles. In contrast, composite particles with high particle strength can suppress fracture even when such stress is applied, thereby reducing the disconnection of the conductive path during charge and discharge. Therefore, electrochemical devices such as lithium ion secondary batteries with minimal capacity loss during charge and discharge can be obtained. The specific particle strength range of the composite particles is preferably 0.60 or more, more preferably 0.65 or more, even more preferably 0.70 or more, and particularly preferably 0.75 or more, and is typically 1.0 or less.

[0060] The particle strength of a composite particle is represented by the ratio "D50 (0.25 MPa) / D50 (0.1 MPa)" of the D50 particle diameter of the composite particle measured under a relatively low pressure of 0.1 MPa, "D50 (0.1 MPa)," to the D50 particle diameter of the composite particle measured under a relatively high pressure of 0.25 MPa, "D50 (0.25 MPa)." Generally, when pressure is applied to a particle, the particle may be broken and the particle diameter may become smaller, and the higher the mechanical strength of the particle, the more this breakage is suppressed. Therefore, the higher the particle strength, the higher the resistance of the composite particle to breakage due to pressure, and therefore the higher the mechanical strength of the composite particle. The D50 particle size of the composite particles can be measured by measuring the volumetric particle size distribution of the composite particles by laser diffraction while the composite particles are dispersed in airflows at dispersion pressures of 0.1 MPa and 0.25 MPa, and determining the particle size at which the cumulative volume calculated from the smallest diameter side is 50%. This measurement can be performed, for example, using a laser diffraction particle size distribution analyzer ("MT-3000II" manufactured by Microtrac). Specific measurements may be performed by the method described in the Examples below.

[0061] The D50 particle size "D50 (0.1 MPa)" of the composite particles is not particularly limited. In one example, the D50 particle size "D50 (0.1 MPa)" of the composite particles is preferably 20 μm or more, more preferably 30 μm or more, even more preferably 40 μm or more, and is preferably 400 μm or less, more preferably 200 μm or less, even more preferably 100 μm or less.

[0062] <Method for producing composite particles> The composite particles according to this embodiment can be produced by a production method including stirring and granulating a positive electrode active material, a carbon-based conductive material, a binder resin, and a solvent. In the stirring and granulation, a composition is stirred in a granulation tank to produce particles containing the solid content of the composition. In this case, the composition may be supplied to the granulation tank all at once, or may be continuously or intermittently added. Furthermore, if necessary, any additives may be added to the stirring and granulation in addition to the positive electrode active material, the carbon-based conductive material, the binder resin, and the solvent.

[0063] Preferably, the method for producing composite particles includes: a step (i) of stirring a positive electrode active material in a granulation tank to obtain a stirred state; and a step (ii) of spraying a liquid composition containing a carbon-based conductive material, a binder resin, and a solvent onto the stirred positive electrode active material. In this production method, a powder layer containing the positive electrode active material, the carbon-based conductive material, and the binder resin can be formed by spraying the liquid composition onto the stirred positive electrode active material. The powder layer may further contain a solvent and any additives. In this powder layer, particle formation and sizing by stirring proceed while the carbon-based conductive material and the binder resin are supplied by the spraying of the liquid composition, thereby producing the above-mentioned composite particles.

[0064] The liquid composition contains a carbon-based conductive material, a binder resin, and a solvent. The liquid composition may further contain any additives. In the liquid composition, the binder resin and any additives may be dissolved in the solvent, or may be dispersed without being dissolved. On the other hand, it is preferable that the carbon-based conductive material is dispersed without being dissolved in the solvent.

[0065] When the carbon-based conductive material is dispersed in a solvent in the liquid composition, the carbon-based conductive material preferably has a D50 particle size within a specific range. Specifically, the D50 particle size range of the carbon-based conductive material in the liquid composition may be the same as the D50 particle size range of the carbon-based conductive material in the composite particles.

[0066] The D50 particle size of the carbon-based conductive material in the liquid composition can be measured by the following method. Using a laser diffraction particle size distribution analyzer, the particle size distribution of the carbon-based conductive material particles in the liquid composition is measured on a volume basis. In the obtained particle size distribution, the particle size at which the cumulative volume calculated from the smallest diameter side is 50% (median diameter D50) can be determined as the D50 particle size of the carbon-based conductive material in the liquid composition.

[0067] The solvent can be a liquid capable of dissolving or dispersing the carbon-based conductive material and binder resin. Examples of this solvent include water and organic solvents. Examples of organic solvents include N-methyl-2-pyrrolidone, cyclohexane, n-hexane, acetone, methyl ethyl ketone, ethyl acetate, tetrahydrofuran, methylene chloride, and chloroform. Among these, organic solvents are preferred, with organic solvents having a boiling point of 95°C or less at 1 atm being more preferred, organic solvents having a boiling point of 90°C or less at 1 atm being even more preferred, and organic solvents having a boiling point of 85°C or less at 1 atm being particularly preferred. The lower limit of the boiling point of the organic solvent at 1 atm is preferably 50°C or higher. Examples of preferred solvents having such a boiling point include cyclohexane, n-hexane, acetone, methyl ethyl ketone, ethyl acetate, tetrahydrofuran, methylene chloride, and chloroform, with cyclohexane being particularly preferred. One type of solvent may be used alone, or two or more types may be used in combination.

[0068] The amount of the solvent is preferably selected so that the solid content of the liquid composition falls within a specific range. Specifically, the solid content of the liquid composition is preferably 1% by weight or more, more preferably 2% by weight or more, and even more preferably 3% by weight or more, and is preferably 40% by weight or less, more preferably 20% by weight or less, and even more preferably 15% by weight or less.

[0069] The liquid composition preferably has a viscosity within a specific range at 25°C. Specifically, the viscosity range of the liquid composition at 25°C is preferably 100 mPa·s or more, more preferably 150 mPa·s or more, even more preferably 200 mPa·s or more, and preferably 800 mPa·s or less, more preferably 600 mPa·s or less, and even more preferably 400 mPa·s or less. The viscosity of the liquid composition can be measured using a Brookfield viscometer ("TVB-10M" manufactured by Toki Sangyo Co., Ltd.) under measurement conditions of 25°C and 60 rpm. During measurement, a rotor is appropriately selected according to the viscosity.

[0070] The granulation tank used for stirring granulation is usually equipped with a stirring blade for stirring. This stirring blade may be provided at the vertical lower part of the stirring tank so that it can rotate around a rotation axis parallel to the vertical direction. Hereinafter, this stirring blade may be referred to as the "main stirring blade." Furthermore, the granulation tank may, if necessary, be equipped with a secondary stirring blade provided so that it can rotate around a rotation axis different from that of the main stirring blade. This secondary stirring blade may be provided, for example, on the side of the granulation tank so as not to interfere with the main stirring blade. Below, examples of granulation tanks equipped with these stirring blades will be shown, and preferred examples of the method for producing composite particles will be specifically explained.

[0071] Fig. 1 is a plan view schematically showing a granulation tank 10 used in a method for producing composite particles according to one embodiment of the present invention. Fig. 2 is a cross-sectional view schematically showing the granulation tank 10 used in a method for producing composite particles according to one embodiment of the present invention. Fig. 2 corresponds to a cross-sectional view of the granulation tank 10 taken along the cut surface indicated by the dashed dotted line II-II in Fig. 1. As shown in Fig. 1, the granulation tank 10 comprises a container 100 and a rotation axis A ２００ The granulation tank 10 also includes a main agitating blade 200 that is rotatable around a rotation axis A. ２００ A rotation axis A is not parallel to ３００ The mixing chamber may be provided with a sub-mixing blade 300 that is rotatable around the center.

[0072] The container 100 is configured to be able to store the positive electrode active material, the carbon-based conductive material, the binder resin, and the solvent, and these are stirred within the container 100. For example, the shape of the container 100 may be a cylindrical shape in which the bottom 110 and the ceiling 120 are circular, and the container 100 may be formed so that a portion of the height direction is tapered. For example, a portion 130 continuing from the ceiling 120 may be formed so that it is tapered. The container 100 is usually installed so that the bottom 110 is parallel to the horizontal direction. The container 100 may be provided with a supply port (not shown) for supplying raw materials such as the positive electrode active material into the container 100, and an outlet (not shown) for removing the composite particles from the container 100.

[0073] The main agitating blade 200 is usually provided on the bottom 110 of the container 100. From the viewpoint of uniform agitation, the rotation axis A of the main agitating blade 200 is ２００ is preferably provided at the center of the bottom 110. When the container 100 has a cylindrical shape, the rotation axis A of the main stirring blade 200 ２００ may coincide with the central axis of the cylindrical shape of the container 100. In this embodiment, a rotation axis A parallel to the vertical direction is provided at the center of the bottom 110 of the container 100. ２００ This description will be given by showing an example in which the main agitator 200 is provided so that it can rotate around the center of gravity. Furthermore, the main agitator 200 typically has one or more main blades 210. The number and shape of the main blades 210 are not particularly limited, but this embodiment shows an example of a main agitator 200 equipped with three main blades 210. Furthermore, the drive unit 220 of the main agitator 200 is generally provided with a ventilation mechanism (not shown) for ventilating a seal gas into the container 100 to prevent powder (positive electrode active material, carbon-based conductive material, composite particles, etc.) from penetrating the drive unit 220. An inert gas is preferably used as the seal gas, and nitrogen gas, for example, can be used.

[0074] The auxiliary stirring blade 300 is connected to the rotation axis A of the main stirring blade 200. ２００ A rotation axis A is not parallel to ３００ The main agitating blade 200 can be provided rotatably around the rotation axis A. ２００ and the rotation axis A of the auxiliary mixing blade 300 ３００The angle θ between the rotation axis A of the main agitating blade 200 is usually 20° or more, preferably 30° or more, more preferably 45° or more, and is usually 90° or less. ２００ and the rotation axis A of the auxiliary mixing blade 300 ３００ The auxiliary stirring blade 300 is usually provided on the side 140 of the container 100. In this embodiment, the auxiliary stirring blade 300 is provided on the side 140 of the container 100 with a rotation axis A parallel to the horizontal direction. ３００ This section will explain an example in which the auxiliary mixing blade 300 is provided so that it can rotate around the center of gravity. Furthermore, the auxiliary mixing blade 300 typically has one or more auxiliary blades 310. The number and shape of these auxiliary blades 310 are not particularly limited, but this embodiment shows an example of an auxiliary mixing blade 300 equipped with anchor-type blades as the auxiliary blades 310. Furthermore, like the drive unit 220 of the main mixing blade 200, the drive unit 320 of the auxiliary mixing blade 300 is generally provided with a ventilation mechanism (not shown) for ventilating a seal gas into the container 100 to prevent powder from penetrating the drive unit 320. An inert gas is preferably used as the seal gas, and nitrogen gas, for example, can be used.

[0075] Furthermore, the stirring tank 10 preferably includes a supply device for supplying the liquid composition. This supply device is preferably a spray nozzle 400 (not shown in FIG. 1 ) capable of supplying the liquid composition in a mist-like spray. This spray nozzle 400 may be a two-fluid spray nozzle that ejects atomizing gas from around the spray nozzle 400, pulverizing and atomizing the liquid composition with the flow of atomizing gas, and then ejecting the liquid composition in a mist. An inert gas is preferably used as the atomizing gas, and nitrogen gas, for example, may be used. The number of spray nozzles 400 may be one or two or more. The spray nozzle 400 may be provided in the ceiling portion 120 or the side portion 140 of the container 100.

[0076] A commercially available product may be used as the granulation tank 10. Examples of commercially available granulation tanks 10 include the "High Speed ​​Mixer" manufactured by EarthTechnica Corporation, the "FM Mixer" manufactured by Nippon Coke Company, the "Vertical Granulator" manufactured by Powrex Corporation, the "CF Granulator" manufactured by Freund Corporation, the "High Speed ​​Stirring Mixer Granulator" manufactured by Nara Machinery Manufacturing Co., Ltd., the "SP Granulator" manufactured by Dalton Corporation, and the "Balance Gran" manufactured by Freund Corporation.

[0077] The composite particle manufacturing method according to the example using the granulation tank 10 includes step (i) of stirring the positive electrode active material in the granulation tank 10 to obtain a stirred state. Specifically, the positive electrode active material is supplied to the container 100 of the granulation tank 10, and a powder layer (not shown) containing the positive electrode active material is formed in the container 100. The main stirring blade 200 is then rotated to stir the positive electrode active material. If necessary, the stirring may be performed by rotating not only the main stirring blade 200 but also the auxiliary stirring blade 300. The particles of the raw positive electrode active material may be agglomerated, but the stirring in step (i) can break up the agglomeration. Furthermore, the raw positive electrode active material may contain liquid components, such as moisture, that adhered during production and storage. The stirring in step (i) can reduce, and preferably remove, the amount of the liquid components.

[0078] The peripheral speed of the main stirring blade 200 and the sub stirring blade 300 during stirring in step (i) is preferably 1 m / s or more and 20 m / s or less.

[0079] During stirring, a seal gas is passed through the drive unit 220 of the main stirring blade 200 and the drive unit 320 of the sub-stirring blade 300 into the vessel 100. The flow rate (aeration rate) of this seal gas is preferably set so that the value obtained by dividing the flow rate of the seal gas flowing into the vessel 100 of the granulation tank 10 by the volume of the vessel 100 (flow rate / volume) is 0.1 / min to 1000 / min. In addition, the temperature of the seal gas is, for example, preferably less than 50°C, more preferably 45°C or less, even more preferably 40°C or less, and particularly preferably 30°C or less, and is preferably 5°C or more, more preferably 10°C or more, and even more preferably 15°C or more.

[0080] The time for which stirring is carried out in step (i) (pre-stirring time) is not particularly limited and can be, for example, 5 minutes or more and 60 minutes or less.

[0081] The composite particle manufacturing method using the granulation tank 10 includes, after the step (i), step (ii) of spraying a liquid composition containing a carbon-based conductive material, a binder resin, and a solvent onto the stirred positive electrode active material. In step (ii), the liquid composition is sprayed onto the positive electrode active material, so that the powder layer in the container 100 contains not only the positive electrode active material but also the carbon-based conductive material and the binder resin. Thus, the positive electrode active material, the carbon-based conductive material, and the binder resin aggregate to gradually form composite particles. Furthermore, in step (ii), the powder layer is stirred by rotating the main stirring blade 200. If necessary, stirring may be performed by rotating not only the main stirring blade 200 but also the auxiliary stirring blade 300. Since the liquid composition is sprayed while stirring is continued, collisions between particles and between particles and the solvent occur in the powder layer simultaneously with the formation of the composite particles, resulting in the sizing of the composite particles. Therefore, in the step (ii), the formation of composite particles and the size regulation proceed simultaneously in the presence of a solvent, thereby obtaining the composite particles described above.

[0082] In step (ii), the relative vapor pressure P of the solvent in the granulation tank 10 (i.e., in the vessel 100) is Ｒ According to the investigations of the present inventors, it is preferable to carry out the process under conditions in which the dispersion degree s of carbon atoms of the composite particles to be produced falls within a specific range. ２ It has been found that the relative vapor pressure P of the solvent in the diffusion granulation atmosphere in step (ii) is greatly affected by the degree of wetting. Ｒ Specifically, the relative vapor pressure P Ｒ The larger the relative vapor pressure P of the solvent in the granulation tank 10, the more the solvent is in the liquid phase after being supplied to the granulation tank 10, and therefore the wetter the environment in the granulation tank 10. Ｒ By appropriately setting the dispersion degree s of carbon atoms, ２ Specifically, the relative vapor pressure P of the solvent in the granulation tank 10 in step (ii) can be smoothly produced. ＲThe range of the relative vapor pressure P is preferably 0.10 or more, more preferably 0.11 or more, and even more preferably 0.15 or more, and is preferably 0.9 or less, and more preferably 0.8 or less. Ｒ The range may be, for example, 0.10 to 0.9, 0.10 to 0.8, 0.11 to 0.9, 0.11 to 0.8, 0.15 to 0.9, or 0.15 to 0.8.

[0083] Relative vapor pressure P of the solvent in the granulation tank 10 Ｒ Is, P Ｒ =P ｍ / P ０ Here, "P ｍ " represents the pressure [kPa] of the solvent vapor in the granulation tank 10, assuming that all of the solvent supplied to the granulation tank 10 has evaporated into solvent vapor. ｍ Hereinafter, the "estimated pressure of solvent vapor" P ｍ It is sometimes called "P ０ " represents the saturated vapor pressure of the solvent at the temperature in the granulation tank 10.

[0084] Estimated pressure of solvent vapor P ｍ The pressure [kPa] can be measured by the following method: The flow rate [g / min] of the solvent in the liquid composition supplied into the granulation tank 10 is measured. Assuming that the solvent is completely vaporized in the granulation tank 10, the flow rate is expressed as the volume-based amount V ｍ This conversion can usually be performed using the pressure P and temperature T in the granulation vessel 10 and the equation of state for an ideal gas. Then, the concentration C of the solvent in the total flow rate of the gas supplied to the granulation vessel 10 is calculated. ｍ is calculated on a volume basis. For example, the flow rate V ｓ Seal gas and flow rate V ａ When the atomization gas is supplied, the concentration C ｍ is "C ｍ =V ｍ / (V ｍ +V ｓ +V ａ Then, the pressure P and concentration C in the granulation tank 10 can be calculated as follows: ｍ and multiplying it to obtain the estimated pressure P of the solvent vapor.ｍ can be obtained.

[0085] On the other hand, the saturated vapor pressure of the solvent at temperature T inside the granulation tank 10 can be calculated from the Antoine equation based on the temperature inside the granulation tank 10. In the above measurement, the pressure P inside the granulation tank 10 is usually atmospheric pressure, for example, 1 atm. Furthermore, the temperature T inside the granulation tank 10 can be the temperature of the powder layer being stirred inside the granulation tank 10 (the temperature of the powder layer usually coincides with the temperature of the positive electrode active material).

[0086] Relative vapor pressure P of the solvent in the granulation tank 10 Ｒ The measurement may be carried out by the method described in the Examples below.

[0087] When the spray nozzle 400 is provided on the ceiling 120 of the granulation tank 10, the liquid composition is usually sprayed vertically toward the positive electrode active material below. In this case, the relative vapor pressure P Ｒ Therefore, from the viewpoint of increasing the particle strength, the relative vapor pressure P Ｒ Specifically, when the spray nozzle 400 is provided on the ceiling portion 120, the relative vapor pressure P Ｒ The range is preferably 0.5 or more, more preferably 0.6 or more, and even more preferably 0.7 or more.

[0088] When the spray nozzle 400 is provided on the side 140 of the granulation tank 10, the liquid composition is usually sprayed toward the positive electrode active material on the side in the horizontal direction. In this case, the relative vapor pressure P Ｒ Therefore, from the viewpoint of increasing the particle strength, the relative vapor pressure P Ｒ Specifically, when the spray nozzle 400 is provided on the side portion 140, the relative vapor pressure P Ｒ The range is preferably less than 0.3, more preferably 0.2 or less.

[0089] Relative vapor pressure P ＲSpecifically, it can be adjusted by the spray rate [g / min] of the liquid composition from the spray nozzle 400, the flow rate [L / min] of the atomizing gas, the flow rate [L / min] of the seal gas, and the temperature inside the granulation tank 10. Unless otherwise specified, the spray rate of the liquid composition refers to the amount of the liquid composition sprayed from the spray nozzle 400 per unit time.

[0090] The ratio of the spray rate [g / min] of the liquid composition sprayed from the spray nozzle 400 to the flow rate [L / min] of the atomizing gas (spray rate of liquid composition / flow rate of atomizing gas) is preferably 0.2 g / L or more, more preferably 0.4 g / L or more, even more preferably 0.6 g / L or more, and is preferably 3.0 g / L or less, more preferably 2.0 g / L or less, even more preferably 1.5 g / L or less. The above ratio correlates with the particle size of the droplets of the liquid composition sprayed from the spray nozzle 400. When the ratio is within the above range, the particle strength of the composite particles can be increased. In addition, the above-mentioned dispersity s ２ Composite particles having the above structure can be easily produced.

[0091] The temperature inside the granulation tank 10 can be set within a range in which the above-mentioned composite particles can be produced. In one example, the temperature range inside the granulation tank 10 is preferably 0°C or higher, more preferably 10°C or higher, even more preferably 20°C or higher, and preferably 100°C or lower, more preferably 80°C or lower, even more preferably 60°C or lower. As described above, the temperature inside the granulation tank 10 can be measured as the temperature of the powder layer being stirred inside the granulation tank 10. The specific temperature is determined by the relative vapor pressure P in the above range depending on the composition of the components contained in the liquid composition such as the solvent, the injection speed, the flow rate of the atomizing gas, and the flow rate of the seal gas. Ｒ It is preferable to select it so that

[0092] As described above, gases such as a seal gas and an atomizing gas are passed through the granulation tank 10. The flow rate of these gases flowing into the granulation tank 10 divided by the volume of the granulation tank 10 (flow rate / volume) is preferably in the range of 0.1 / min to 1000 / min. The specific value (flow rate / volume) is determined by the relative vapor pressure PＲ It is preferable to select it so that

[0093] The range of the peripheral speed of the stirring blades, such as the main stirring blade 200 and the auxiliary stirring blade 300, can be set within a range in which the above-mentioned composite particles can be produced. In one example, the range of the peripheral speed of the stirring blades, such as the main stirring blade 200 and the auxiliary stirring blade 300, is preferably 1 m / s or more and 20 m / s or less, from the viewpoint of controlling the particle size of the composite particles within an appropriate range.

[0094] In step (ii), the liquid composition may be sprayed from the spray nozzle 400 intermittently, but is preferably sprayed continuously. The spray time of the liquid composition can be set within a range in which the composite particles described above can be produced. In one example, the spray time can be 5 minutes or more and 60 minutes or less.

[0095] The method for producing composite particles according to the example using the granulation tank 10 may further include any step in combination with the above-described steps (i) and (ii). The method for producing composite particles may include, for example, a step of stirring the composite particles after step (ii) to size the composite particles. Furthermore, the method for producing composite particles may include, for example, a step of stirring the positive electrode active material using a stirring device separate from the granulation tank 10 before step (i).

[0096] <Positive electrode for electrochemical device> The composite particles described above can be used to manufacture a positive electrode for an electrochemical device. Such a positive electrode typically includes a current collector and a positive electrode mixture layer formed on the current collector, the positive electrode mixture layer including the composite particles.

[0097] The current collector material is preferably a material that is electrically conductive and electrochemically durable. Specific examples of the current collector material include metals, carbon, and conductive polymers, with metals being preferred. Examples of metals include iron, copper, aluminum, gold, platinum, nickel, tantalum, titanium, stainless steel, and alloys thereof. Among these, aluminum and aluminum alloys are preferred in terms of conductivity and voltage resistance. When high voltage resistance is required, high-purity aluminum as disclosed in JP-A-2001-176757 can be preferably used. One type of current collector material may be used alone, or two or more types may be used in combination.

[0098] The current collector generally has a film or sheet shape. The thickness of the current collector may be appropriately selected depending on the intended use, and is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more, and is preferably 200 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less.

[0099] A positive electrode mixture layer containing composite particles is formed on the current collector. This positive electrode mixture layer may contain only composite particles. The amount of the electrode mixture layer per unit area is not particularly limited, but in one example, it is preferably 1 mg / cm ２ More preferably, 2 mg / cm ２ More preferably, 5 mg / cm ２ or more, preferably 100 mg / cm ２ or less, more preferably 50 mg / cm ２ More preferably, 30 mg / cm ２ The following is the result.

[0100] The positive electrode can be manufactured, for example, by a method including pressure molding of composite particles on a current collector. Preferably, the positive electrode can be manufactured by a manufacturing method including forming a composite particle layer by depositing composite particles on a current collector and applying pressure to the composite particle layer. For example, the composite particles may be subjected to a roll press and roll-pressed on the current collector to pressure mold the composite particles on the current collector to form a positive electrode mixture layer. The temperature and pressure conditions during pressing may be appropriately set according to the desired positive electrode density.

[0101] <Electrochemical element> An electrochemical element can be obtained by using the above-described positive electrode. Such an electrochemical element includes the above-described positive electrode. Examples of electrochemical elements include lithium ion secondary batteries, electric double layer capacitors, and lithium ion capacitors, and among these, lithium ion secondary batteries are preferred.

[0102] Hereinafter, a lithium ion secondary battery will be described as an example of an electrochemical element. The lithium ion secondary battery includes the above-described positive electrode, negative electrode, and electrolyte. The lithium ion secondary battery also typically includes a separator.

[0103] The negative electrode is not particularly limited and any known negative electrode can be used. Typically, the negative electrode includes a negative electrode current collector and a negative electrode mixture layer containing a negative electrode active material.

[0104] As the electrolyte, an organic electrolyte solution in which a supporting electrolyte is dissolved in an organic solvent is usually used. For example, in a lithium ion secondary battery, a lithium salt is used as the supporting electrolyte. For example, LiPF ６ , LiAsF ６ , LiBF ４ , LiSbF ６ , LiAlCl ４ , LiClO ４ , C.F. ３ SO ３ Li, C ４ F ９ SO ３ Li, CF ３ COOLi, (CF ３ CO) ２ NLi, (CF ３ SO ２ ) ２ NLi, (C ２ F ５ SO ２ Among them, LiPF is the most popular because it is easily soluble in solvents and shows a high degree of dissociation. ６ , LiClO ４ , C.F. ３ SO ３ Li is preferred. The electrolyte may be used alone or in combination of two or more.

[0105] As the organic solvent for the electrolyte, a solvent capable of dissolving the supporting electrolyte can be used. For example, preferred organic solvents for the electrolyte of a lithium ion secondary battery include carbonate solvents such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), ethyl methyl carbonate (EMC), and vinylene carbonate (VC); ester solvents such as γ-butyrolactone and methyl formate; ether solvents such as 1,2-dimethoxyethane and tetrahydrofuran; and sulfur-containing compound solvents such as sulfolane and dimethyl sulfoxide. These solvents may be used alone or in combination of two or more. The concentration of the electrolyte in the electrolyte may be appropriately adjusted. Furthermore, the electrolyte may contain any additive.

[0106] The separator is not particularly limited. For example, a separator substrate may be a microporous membrane formed of a polyolefin resin (e.g., polyethylene, polypropylene, polybutene, polyvinyl chloride). Furthermore, a separator with a functional layer, in which a functional layer (a porous membrane layer or an adhesive layer) is provided on one or both sides of the separator substrate, may be used.

[0107] A lithium ion secondary battery can be produced, for example, by stacking a positive electrode and a negative electrode with a separator interposed therebetween, rolling or folding the resulting battery as needed according to the battery shape, placing it in a battery container, injecting an electrolyte into the battery container, and sealing it. To prevent internal pressure rise, overcharging and overdischarging, and the like, a fuse, an overcurrent prevention element such as a PTC element, an expanded metal, a lead plate, or the like may be provided as needed. The shape of the secondary battery may be any of a coin type, a button type, a sheet type, a cylindrical type, a rectangular type, a flat type, and the like.

[0108] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" representing amounts are by weight unless otherwise specified. Furthermore, the operations described below were carried out under conditions of room temperature and normal pressure (23°C, 1 atm) unless otherwise specified.

[0109] <Measurement and Evaluation Methods> (Test 1. Dispersion of carbon atoms in composite particles s ２ Measurement method of composite particles) The composite particles were photographed at a magnification of 2000 times using an SEM (scanning electron microscope; "FE-SEM7800F" manufactured by JEOL Ltd.) to obtain a surface observation image (number of pixels: 1280 pixels x 1024 pixels). This surface observation image was divided into square small area images each having a size of 100 pixels vertically x 100 pixels horizontally. Of the obtained multiple small area images, small area images including blank areas where no composite particles were present were removed, and the remaining n small area images were obtained as measurement targets. In all of the examples and comparative examples described below, n was in the range of 80 or more and 120 or less.

[0110] In the surface observation images, the positive electrode active material was white, the carbon atoms (including the carbon atoms of the carbon black and the carbon atoms of the binder resin) were light gray, and the voids without these were dark gray or black. Therefore, the area ratio of the carbon atoms represented in light gray was measured in each small region image.

[0111] The area ratio of carbon atoms was measured using the image processing software "OpenCv" (https: / / opencv.org / ) as follows. Each small region image of the surface observation image was subjected to a ternary process to separate the image into a white positive electrode active material portion, a light gray carbon atom portion, and a dark gray or black void portion. In the surface observation image, the positive electrode active material portion, the carbon atom portion, and the void portion were clearly distinguishable visually based on differences in brightness. Therefore, in the ternary process, a brightness threshold value separating the positive electrode active material portion and the carbon atom portion was carefully determined by visual inspection. Similarly, a brightness threshold value separating the carbon atom portion and the void portion was carefully determined by visual inspection. These threshold values ​​were then used to perform a ternary process based on pixel brightness to separate the positive electrode active material portion, the carbon atom portion, and the void portion.

[0112] The area ratio of carbon atoms was calculated for each small-region image that had undergone this ternarization process. Specifically, binarization was performed to separate the carbon atom portion from the positive electrode active material portion and void portion in the small-region image. The ratio of the number of pixels included in the carbon atom portion to the total number of pixels included in the small-region image (100%) was calculated as the area ratio of carbon atoms. Hereinafter, the area ratio of carbon atoms in the i-th small-region image will be referred to as "x ｉ " " represents an integer from 1 to n.

[0113] Average area ratio of carbon atoms in n small area images x ａ Then, the area ratio of carbon atoms in the small area image x ｉ and average x ａ The squared value of the difference between ｉ -xa) ２ The sum of all n small region images is then divided by the number n of small region images to obtain the dispersion degree s of carbon atoms in the composite particle. ２ Specifically, the dispersity s was calculated based on the following formula (1): ２ was calculated.

[0114]

[0115] (Test 2. Method for measuring particle strength of composite particles) A ​​laser diffraction particle size distribution analyzer (Microtrac's "MT-3000II") was prepared. This laser diffraction particle size distribution analyzer was capable of dispersing sample particles using an airflow using compressed air and measuring the particle size distribution of the dispersed sample particles by laser diffraction. Using this laser diffraction particle size distribution analyzer, the particle size distribution of the composite particles was measured on a volume basis, and the particle size at which the cumulative volume calculated from the smallest diameter side reached 50% was obtained as the D50 particle size "D50". The measurement was performed at dispersion pressures (compressed air pressures) of 0.1 MPa and 0.25 MPa. The ratio of the D50 particle diameter "D50 (0.1 MPa)" measured at a dispersion pressure of 0.1 MPa to the D50 particle diameter "D50 (0.25 MPa)" measured at a dispersion pressure of 0.25 MPa, "D50 (0.25 MPa) / D50 (0.1 MPa)," was obtained as particle strength. The higher this particle strength, the higher the mechanical strength of the composite particle.

[0116] (Test 3. Method for Measuring Powder Resistivity of Composite Particles) A ​​probe unit (cross-sectional area 3.1 cm ) of a powder resistance measurement system ("MCP-PD51" manufactured by Mitsubishi Chemical Analytech Co., Ltd.) was used. ２ 4.0 g of the composite particles were placed in the container, and the powder resistance was measured when a pressure of 20 kN was applied.

[0117] (Relative vapor pressure P Ｒ In the examples and comparative examples described later, the relative vapor pressure in the granulation tank was measured by the following method. The flow rate [g / min] of the solvent (cyclohexane) in the liquid composition sprayed onto the positive electrode active material was measured, and the flow rate was converted to a volumetric basis [L / min] on the assumption that the solvent was completely vaporized in the granulation tank. Specifically, the solvent flow rate was converted to a substance amount basis [mol / min], and the pressure and temperature in the granulation tank were used to apply the equation of state for an ideal gas to determine the volumetric basis flow rate V of the solvent. ｍ [L / min] was calculated.

[0118] The solvent flow rate V thus obtained ｍThe concentration of the solvent relative to the total gas supplied to the granulation tank was calculated on a volume basis using the above formula. In the examples and comparative examples described below, atomizing gas (nitrogen gas) was injected into the granulation tank from around the nozzle to inject the liquid composition, and seal gas (nitrogen gas) was passed through each drive unit of the main and sub-stirring blades to prevent the raw materials from being mixed into the drive units. Therefore, the flow rate of the total gas supplied to the granulation tank is calculated by multiplying the flow rate V of the solvent by the above formula. ｍ [L / min] and the flow rate V of the atomizing gas ａ [L / min] and the flow rate of the seal gas V ｓ The solvent flow rate V is expressed as the sum of the solvent flow rate V and the solvent flow rate V. ｍ is the total gas flow rate (V ｍ [L / min] + V ａ [L / min] + V ｓ Divide by the solvent concentration C ｍ The concentration of this solvent, C ｍ Multiplying this by the pressure P inside the granulation tank gives the pressure of the solvent vapor inside the granulation tank (estimated pressure of the solvent vapor) P when it is assumed that all the supplied solvent has evaporated and become solvent vapor. ｍ [kPa] was calculated.

[0119] On the other hand, the temperature in the granulation tank is applied to the Antoine formula to calculate the saturated vapor pressure P of the solvent at the temperature in the granulation tank. ０ The coefficients of the Antoine formula were calculated using the values ​​listed in the Chemical Engineering Handbook (edited by the Society of Chemical Engineers, revised 5th edition, Maruzen, 2004, page II-182). ｍ [kPa] is the saturated vapor pressure P ０ The relative vapor pressure P of the solvent in the granulation tank is calculated by dividing by [kPa]. Ｒ =P ｍ / P ０ obtained.

[0120] <Production Example 1. Production of Binder Resin A1> 270 parts of dehydrated cyclohexane and 0.53 parts of ethylene glycol dibutyl ether were placed in a reactor equipped with a stirrer and the inside of which had been thoroughly purged with nitrogen, and 0.47 parts of n-butyllithium (15% cyclohexane solution) was further added. While stirring the entire contents at 60°C, 12.5 parts of dehydrated styrene were continuously added to the reactor over 40 minutes. After the addition was completed, the entire contents were stirred for an additional 20 minutes at 60°C. When the reaction solution was measured by gas chromatography, the polymerization conversion rate at this point was 99.5%. Next, 75.0 parts of dehydrated isoprene was continuously added to the reaction solution over 100 minutes, and stirring was continued for 20 minutes after the addition was completed. The polymerization conversion rate at this point was 99.5%. Thereafter, 12.5 parts of dehydrated styrene was continuously added over 60 minutes, and after the addition was completed, the entire contents were stirred for 30 minutes. The polymerization conversion rate at this point was nearly 100%. Here, 0.5 parts of isopropyl alcohol was added to the reaction solution to terminate the reaction. Of all the structural units derived from isoprene in the resulting block copolymer, the proportion of structural units derived from 1,2- and 3,4-addition polymerization was 58%. Next, the polymer solution was transferred to a pressure-resistant reactor equipped with a stirrer, and 7.0 parts of a diatomaceous earth-supported nickel catalyst (manufactured by JGC Catalysts and Chemicals, product name "E22U", nickel loading 60%) as a hydrogenation catalyst and 80 parts of dehydrated cyclohexane were added and mixed. The atmosphere inside the reactor was purged with hydrogen gas, and hydrogen was further supplied while stirring the solution, and the hydrogenation reaction was carried out at a temperature of 190°C and a pressure of 4.5 MPa for 6 hours. After completion of the hydrogenation reaction, the reaction solution was filtered to remove the hydrogenation catalyst. Thereafter, 1.0 part of a xylene solution containing 0.1 part of pentaerythrityl tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] ("Songnox 1010" manufactured by Koyo Chemical Research Institute), a phenolic antioxidant, was added to the filtrate and dissolved. Cyclohexane was further added to prepare a solution of binder resin A1.

[0121] <Production Example 2. Production of liquid composition> A liquid composition (solid content concentration 5 wt %, viscosity 300 mPa s) was produced by mixing 6.3 parts by weight of binder resin A1 obtained by drying the solution produced in Production Example 1, 18.0 parts of carbon black as a conductive additive, and 461.7 parts of cyclohexane as a solvent. The D50 particle diameter of the carbon black in the liquid composition was measured and found to be 0.1 μm.

[0122] Example 1 A composite particle production apparatus I (large-capacity type) was prepared as a granulation tank. This granulation tank included a cylindrical container (inner diameter 400 mm, internal volume 25 L) with its axial direction aligned vertically; a main stirring blade rotatably mounted around a vertical axis at the center of the bottom of the cylindrical container; and a secondary stirring blade rotatably mounted around a horizontal axis at the side of the cylindrical container. The main stirring blade was an inclined paddle equipped with three main blades with a diameter of 390 mm. The secondary stirring blade was equipped with a V-shaped anchor blade with a diameter of 100 mm. To prevent raw materials from being mixed into the drive units of the main stirring blade and secondary stirring blade, each drive unit was equipped with a sealing mechanism that allowed sealing gas (nitrogen gas) to pass through. Using the composite particle production apparatus I described above as a granulation tank, composite particles were produced by performing (i) a preliminary stirring operation and (ii) a composite particle formation operation in this order.

[0123] (i) As a preliminary stirring operation, NMC631 (LiNi) as a positive electrode active material for a lithium ion battery was added to a granulation tank. ０．６ Mn ０．３ Co ０．１ O ２ 97.0 parts by weight (11,215 g) of granulated cellulose (D50 particle size 4 μm) was added. The positive electrode active material was stirred by rotating the main stirring blade and the auxiliary stirring blade while passing a seal gas at room temperature (25° C.) through the granulation tank at a rate of 170 L / min. The peripheral speed of the main stirring blade was 4.0 m / s (196 rpm), and the peripheral speed of the auxiliary stirring blade was 15.7 m / s (3,000 rpm).

[0124] Next, as the composite particle formation operation (ii), 3.0 parts by weight (6937 g of liquid composition) of the liquid composition produced in Production Example 2 was sprayed onto the cathode active material at a rate of 300 g / min over approximately 20 minutes while stirring the cathode active material as described above. The liquid composition was sprayed from a two-fluid spray nozzle (top nozzle) attached to the ceiling of the cylindrical container. The flow rate of the atomizing gas (nitrogen gas) sprayed from around the nozzle to spray the liquid composition was 300 L / min. The spraying of the liquid composition formed a powder layer in the stirring tank, consisting of a raw material composition containing the cathode active material and the solid components of the liquid composition (the conductive material and the binder resin A1). The formation of the composite particles progressed as the powder layer was stirred. The temperature of the powder layer in step (ii) was measured with a thermocouple and found to be 35.0°C.

[0125] The composite particles produced by carrying out the above operations (i) to (ii) in this order were evaluated by the above-mentioned methods.

[0126] Example 2 A composite particle production apparatus II (small-capacity type) was prepared as a granulation vessel. This granulation vessel included a cylindrical vessel (inner diameter 180 mm, internal volume 1.5 L) with its axial direction aligned vertically; a main stirring blade rotatably mounted around a vertical axis at the center of the bottom of the cylindrical vessel; and a secondary stirring blade rotatably mounted around a horizontal axis at the side of the cylindrical vessel. The main stirring blade was an inclined paddle equipped with three main blades with a diameter of 170 mm. The secondary stirring blade was equipped with a V-shaped anchor blade with a diameter of 30 mm. To prevent raw materials from being mixed into the drive units of the main stirring blade and secondary stirring blade, each drive unit was equipped with a sealing mechanism that allowed sealing gas (nitrogen gas) to pass through. Using the composite particle production apparatus II, composite particles were produced by performing (i) a preliminary stirring operation and (ii) a composite particle formation operation in this order.

[0127] (i) As a preliminary stirring operation, 97.0 parts by weight (873.0 g) of the same positive electrode active material as in Example 1 was charged into the granulation tank. The positive electrode active material was stirred by rotating the main stirring blade while a seal gas at room temperature (25°C) was passed through the granulation tank at a rate of 200 L / min. The peripheral speed of the main stirring blade was 3.6 m / s (400 rpm). The secondary stirring blade was stopped.

[0128] Next, as the composite particle formation operation (ii), 3.0 parts by weight (540 g of liquid composition) in terms of solid content were sprayed onto the cathode active material over approximately 22 minutes at a spray rate of 25 g / min with the liquid composition prepared in Preparation Example 2 while stirring the cathode active material as described above. The liquid composition was sprayed from a two-fluid spray nozzle (side nozzle) attached to the side (horizontal end) of the cylindrical container. The flow rate of the atomizing gas (nitrogen gas) sprayed from around the nozzle to spray the liquid composition was 25 L / min. The spraying of the liquid composition formed a powder layer in the stirring tank, consisting of a raw material composition containing the cathode active material and the solid content of the liquid composition (the conductive material and the binder resin A1). The formation of the composite particles progressed as the powder layer was stirred. The temperature of the powder layer in step (ii) was measured with a thermocouple and found to be 21.0°C.

[0129] The composite particles produced by carrying out the above operations (i) to (ii) in this order were evaluated by the above-mentioned methods.

[0130] Example 3 Composite particles were produced and evaluated in the same manner as in Example 2, except that the temperature of the powder bed in step (ii) was changed to 32.0° C. The temperature of the powder bed was changed by changing the temperature of the water (jacket water) passed through the jacket covering the granulation tank (the same applies to the following Examples and Comparative Examples).

[0131] Example 4 Composite particles were produced and evaluated using the same method as in Example 1, except for the following: - The peripheral speed of the main stirring blade was changed to 1.3 m / s (66 rpm). - The auxiliary stirring blade was stopped. - The nozzle for spraying the liquid composition was changed from a top nozzle to a two-fluid spray nozzle (side nozzle) installed on the side (horizontal end) of the cylindrical container. - The temperature of the powder layer in step (ii) was changed to 72.0°C. - The spraying speed of the liquid composition was changed to 150 g / min. Therefore, the liquid composition was sprayed over approximately 42 minutes.

[0132] Comparative Example 1 Composite particles were produced and evaluated using the same method as in Example 2, except for the following: - The peripheral speed of the main stirring blade was changed to 4.1 m / s (460 rpm rotations). - The auxiliary stirring blade was rotated. The peripheral speed of the auxiliary stirring blade was 4.7 m / s (3000 rpm rotations). - The nozzle for spraying the liquid composition was changed from a side nozzle to a two-fluid spray nozzle (top nozzle) installed on the ceiling of the cylindrical container. - The temperature of the powder layer in step (ii) was changed to 24.9°C. - The flow rate of the seal gas was changed to 10 L / min.

[0133] Comparative Example 2 Composite particles were produced and evaluated using the same method as in Example 2, except for the following changes: The peripheral speed of the main stirring blade was changed to 2.7 m / s (300 rpm). The auxiliary stirring blade was rotated. The peripheral speed of the auxiliary stirring blade was 4.7 m / s (3000 rpm). The nozzle used to spray the liquid composition was changed from a side nozzle to a two-fluid spray nozzle (top nozzle) installed on the ceiling of the cylindrical container. The temperature of the powder layer in step (ii) was changed to 55.2°C. The spray rate of the liquid composition was changed to 4 g / min. Therefore, the liquid composition was sprayed over approximately 122 minutes. The flow rate of the seal gas was changed to 10 L / min.

[0134] Comparative Example 3 Composite particles were produced and evaluated using the same method as in Example 2, except for the following changes: The amount of positive electrode active material charged into the granulation tank was changed to 97.0 parts by weight (582 g). The amount of liquid composition sprayed onto the stirred positive electrode active material was changed to 3.0 parts by weight in terms of solid content (360 g of liquid composition). The temperature of the powder layer in step (ii) was changed to 41.0°C. The spraying speed of the liquid composition was changed to 4 g / min. Therefore, the liquid composition was sprayed over a period of approximately 81 minutes.

[0135] <Results> The results of the above-mentioned Examples and Comparative Examples are shown in the table below. The relationship between the degree of dispersion and the powder resistivity in the results of the Examples and Comparative Examples is shown in the graph of Figure 3. In the table below, the meanings of the abbreviations are as follows:

[0136] Amount of active material: Amount of positive electrode active material charged into the granulation tank. Amount of slurry: Amount of liquid composition sprayed into the granulation tank. Temperature inside the tank: Temperature inside the granulation tank in step (ii) where the composite particle formation operation is carried out. Spraying speed: Spraying speed of the liquid composition sprayed onto the positive electrode active material. Spraying position "top": Top nozzle provided on the ceiling of the cylindrical container. Spraying position "side": Side nozzle provided on the side of the cylindrical container. Saturated vapor pressure P ０ : saturated vapor pressure of the solvent at the temperature in the granulation tank. Estimated pressure P ｍ : Estimated pressure of solvent vapor in the granulation tank. Relative vapor pressure P Ｒ : Relative vapor pressure of the solvent in the granulation tank.

[0137]

[0138] REFERENCE SIGNS LIST 10 Granulation tank 100 Container 110 Bottom 120 Ceiling 130 Part 140 Side 200 Main stirring blade 210 Main blade 220 Drive unit 300 Sub-stirring blade 310 Sub-blade 320 Drive unit 400 Spray nozzle A ２００ Rotation axis A ３００ Rotation axis

Claims

1. A composite particle for an electrochemical element positive electrode, comprising a positive electrode active material, a carbon-based conductive material, and a binder resin, wherein the carbon atom dispersion s in the composite particle for an electrochemical element positive electrode is calculated by the following formula (1): ２ The composite particles for a positive electrode of an electrochemical element, wherein the content of ZnO is 0.5% or more and 1.0% or less. (In formula (1), n ​​represents the number of square images obtained by dividing a surface observation image of 1280 pixels x 1024 pixels obtained by photographing the composite particle for a positive electrode of an electrochemical element at a magnification of 2000 times using a scanning electron microscope, each image having a size of 100 pixels vertically x 100 pixels horizontally and not including a blank area where the composite particle for a positive electrode of an electrochemical element is not photographed, n is 80 or more and 120 or less, and x ｉ represents the area fraction of carbon atoms in each of the images, and x ａ represents the average area ratio of carbon atoms in all of the images.) 2. Composite particles for electrochemical element positive electrodes according to claim 1, having a particle strength of 0.6 or more, wherein the particle strength represents the ratio "D50 (0.25 MPa) / D50 (0.1 MPa)" of the D50 particle diameter "D50 (0.1 MPa)" measured under an applied pressure of 0.1 MPa to the D50 particle diameter "D50 (0.25 MPa)" measured under an applied pressure of 0.25 MPa.

3. Cross-sectional area 3.1cm ２ 2. The composite particles for electrochemical element positive electrodes according to claim 1, wherein 4.0 g of the composite particles for electrochemical element positive electrodes are placed in a container and pressurized with 20 kN, and the powder resistance of the composite particles for electrochemical element positive electrodes is measured in a state of being 30 Ω or less.

4. The composite particles for a positive electrode of an electrochemical element according to claim 1, wherein the content of the positive electrode active material is 90% by weight or more and 99.19% by weight or less.

5. Composite particles for electrochemical element positive electrodes according to claim 1, wherein the content of said carbonaceous conductive material is 0.8% by weight or more and 5% by weight or less.

6. The composite particles for a positive electrode of an electrochemical element according to claim 1, wherein the content of the binder resin is 0.01% by weight or more and 5% by weight or less.

7. The composite particles for electrochemical element positive electrodes according to claim 1, wherein the carbon-based conductive material has a D50 particle size of 0.01 μm to 0.4 μm.

8. A method for producing composite particles for electrochemical element positive electrodes according to any one of claims 1 to 7, comprising stirring and granulating a positive electrode active material, a carbon-based conductive material, a binder resin, and a solvent.

9. A method for producing composite particles for an electrochemical element positive electrode according to claim 8, comprising: a step (i) of stirring the positive electrode active material in a granulation tank to obtain a stirred state; and a step (ii) of spraying a liquid composition containing the carbon-based conductive material, the binder resin, and the solvent onto the stirred positive electrode active material.

10. The method for producing composite particles for a positive electrode of an electrochemical element according to claim 9, wherein the relative vapor pressure of the solvent in the granulation tank in step (ii) is 0.1 or more and 0.9 or less.

11. The method for producing composite particles for electrochemical element positive electrodes according to claim 10, wherein step (ii) comprises spraying the liquid composition from a nozzle provided in the ceiling of the granulation tank; and the relative vapor pressure of the solvent in the granulation tank in step (ii) is 0.5 or more.

12. The method for producing composite particles for electrochemical element positive electrodes according to claim 10, wherein step (ii) comprises spraying the liquid composition from a nozzle provided on the side of the granulation tank; and the relative vapor pressure of the solvent in the granulation tank in step (ii) is less than 0.

3.

13. A positive electrode for an electrochemical element, comprising a current collector and a positive electrode mixture layer formed on the current collector, wherein the positive electrode mixture layer contains the composite particles for electrochemical element positive electrodes according to any one of claims 1 to 7.

14. An electrochemical element comprising the positive electrode for an electrochemical element according to claim 13.

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