Electrochemical element positive electrode composite particles, production method for same, electrochemical element positive electrode, and electrochemical element

Abstract

Electrochemical element positive electrode composite particles according to the present invention include a positive electrode active material and a binder resin and have a compressibility C of no more than 17.0% as found from expression (1). (1) C=(ρ180(1)-ρ0(1)) / ρ180(1)×100, in which ρ0(1) is the bulk density (g / cm3) of the composite particles at 0 taps and ρ180(1) is the tapped bulk density (g / cm3) of the composite particles at 180 taps.

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 use in positive electrodes of electrochemical devices, a method for producing the same, a positive electrode for electrochemical devices containing the composite particles, and an electrochemical device.

[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] In order to improve the productivity of the positive electrode mixture layer, it is conceivable to increase the conveying speed of the layer of composite particles deposited on the surface of the current collector. However, increasing the conveying speed may cause a portion of the produced positive electrode mixture layer to peel off from the current collector. In order to maintain the performance of the positive electrode, it is preferable that the positive electrode mixture layer has few locations where the compressed composite particles peel off. Therefore, there is a need for composite particles for electrochemical devices that can produce positive electrodes with little peeling of the positive electrode mixture layer; a method for producing such composite particles; a positive electrode for electrochemical devices containing such composite particles; and an electrochemical device containing such a positive electrode.

[0007] The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, they have found that the above-mentioned problems can be solved by setting the compression degree of the composite particles within a predetermined range, and have completed the present invention. That is, the present invention provides the following.

[0008] <1> Composite particles for a positive electrode of an electrochemical element, comprising a positive electrode active material and a binder resin, and having a compressibility C calculated by the following formula (1) of 17.0% or less: C=(ρ １８０ (1)-ρ ０ (1)) / ρ １８０ (1) × 100 (1) where, ρ ０ (1) is the bulk density (g / cm) of the composite particles when the tapping number is 0. ３ ) and ρ １８０ (1) is the packed bulk density (g / cm) of the composite particles after 180 tapping times. ３ <2> The bulk density ρ of the composite particles when the number of tapping times is 0 ０ (1) The bulk density ρ of the positive electrode active material when the tapping number is 0 ０ Ratio ρ to (0) ０ (1) / ρ ０<1> The composite particle for an electrochemical element positive electrode according to <1>, wherein (0) is 1.100 or more. <3> The composite particle for an electrochemical element positive electrode according to <1> or <2>, wherein the angle of repose is 32° or less. <4> The composite particle for an electrochemical element positive electrode according to any one of <1> to <3>, wherein particles having a particle diameter of 10 μm or less account for 2.5 vol% or less. <5> The composite particle for an electrochemical element positive electrode according to any one of <1> to <4>, wherein the ratio D90 / D10 of the particle diameter D90 to the particle diameter D10 is less than 4.4. <6> A method for producing the composite particle for an electrochemical element positive electrode according to any one of <1> to <5>, comprising stirring and granulating a positive electrode active material, a binder resin, and a solvent. <7> A method for producing composite particles for electrochemical element positive electrodes according to <6>, comprising: (i) agitating the positive electrode active material in a granulation tank to obtain a stirred state; and (ii) spraying a liquid composition containing the binder resin and the solvent onto the stirred positive electrode active material. <8> A positive electrode for electrochemical elements, comprising: a current collector; and a positive electrode mixture layer formed on the current collector, wherein the positive electrode mixture layer comprises the composite particles for electrochemical element positive electrodes according to any one of <1> to <5>. <9> An electrochemical element, comprising the positive electrode for electrochemical elements according to <8>.

[0009] According to the present invention, it is possible to provide composite particles for electrochemical devices that can produce positive electrodes with reduced peeling of the positive electrode mixture layer; a method for producing such composite particles; a positive electrode for electrochemical devices that includes such composite particles; and an electrochemical device that includes such a positive electrode.

[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.

[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 shown below, and can be modified as desired without departing from the scope of the claims of the present invention and their equivalents. The components of the embodiments shown below can be combined as appropriate. For example, any numerical value selected from a group of numerical values ​​listed as lower limits can be combined with any numerical value selected from a group of numerical values ​​listed as upper limits. Furthermore, in the drawings, identical components are denoted by the same reference numerals, and their description may be omitted.

[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] <1. Composite Particles for Electrochemical Element Positive Electrode> A composite particle for an electrochemical element positive electrode according to one embodiment of the present invention (hereinafter, sometimes referred to as a "composite particle") includes a positive electrode active material and a binder resin. Typically, particles of one or more positive electrode active materials and particles of optional materials 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] <Physical Properties of Composite Particles> The composite particles according to this embodiment usually have a compressibility C of 17.0% or less. Here, the compressibility C can be calculated by the following formula (1): C=(ρ １８０ (1)-ρ ０ (1)) / ρ １８０ (1) × 100 (1) In formula (1), ρ ０ (1) is the bulk density (g / cm) of the composite particles when the tapping number is 0. ３ ) and ρ １８０ (1) is the packed bulk density (g / cm) of the composite particles after 180 tapping times. ３ ) represents

[0018] The bulk density of the composite particles can be measured by the following method using a powder tester (for example, manufactured by Hosokawa Micron Corporation, product name "PT-S"). The composite particles whose mass has been weighed are placed in the device, and the bulk density ρ at the tapping number of 0 is measured. ０ (1) and the compacted bulk density ρ at 180 tapping times １８０ (1) is measured. The tapping conditions are a stroke of 18 mm, and one tap per second. The temperature and relative humidity during the measurement can be, for example, 20° C. or higher and 25° C. or lower, and, for example, 20% or higher and 80% or lower.

[0019] The smaller the compression degree C, the smaller the change in layer density before and after compression tends to be when the thickness of the composite particle layer is compressed to form a positive electrode mixture layer. When the change in layer density before and after compression is small, the force compressing the composite particle layer is easily transmitted to the composite particle layer, and it is thought that the composite particles are well compressed together. Because the composite particles are well compressed, it is possible to reduce peeling of the positive electrode mixture layer from the current collector and increase the production speed of the positive electrode mixture layer. Reducing peeling of the positive electrode mixture layer from the current collector and increasing the production speed of the positive electrode mixture layer means that the formability of the positive electrode mixture layer can be improved.

[0020] The compressibility C is usually 0.0% or more, for example, 2.5% or more, for example, 5.0% or more. Therefore, the compressibility C is, for example, 0.0% or more and 17.0% or less, for example, 2.5% or more and 17.0% or less, for example, 5.0% or more and 17.0% or less. In one embodiment, the compressibility C is, for example, 11.5% or more, for example, 11.5% or more and 17.0% or less, for example, 11.5% or more and 14.7% or less.

[0021] The degree of compression C can be reduced by reducing the proportion of particles with small particle diameters in the composite particles. For example, the proportion of particles with a particle diameter of 10 μm or less in the composite particles can be reduced to preferably 3.5 vol% or less, more preferably 3.0 vol% or less, and even more preferably 2.5 vol% or less. Reducing the proportion of particles with small particle diameters in the composite particles can be achieved, for example, by classifying the composite particles using a classifier such as a sieve. Alternatively, the degree of compression C can be reduced by adjusting the granulation conditions when producing the composite particles.

[0022] Bulk density ρ of composite particles at 0 tapping times ０ (1) The bulk density ρ of the positive electrode active material when the tapping number is 0 ０ Ratio ρ to (0) ０ (1) / ρ ０ (0) is preferably 1.100 or more, more preferably 1.200 or more, and even more preferably 1.260 or more, and the upper limit is not particularly limited, but can be, for example, 1.600 or less.０ (1) / ρ ０ (0) is preferably 1.100 or more and 1.600 or less, more preferably 1.200 or more and 1.600 or less, and even more preferably 1.260 or more and 1.600 or less. ０ (1) / ρ ０ The ratio ρ(0) is preferably 1.152 or more and 1.267 or less. ０ (1) / ρ ０ When (0) is 1.100 or more, the bulk density ρ of the composite particles ０ (1) is the bulk density ρ of the positive electrode active material for forming the composite particles ０ (0) is large. Therefore, the same bulk density ρ ０ From a layer of composite particles of the same thickness containing the positive electrode active material (0), the ratio ρ ０ (1) / ρ ０ The larger (0) is, the larger the mass per unit area of ​​the electrode mixture layer that can be formed.

[0023] The bulk density can be measured using a powder tester (for example, a product named "PT-S" manufactured by Hosokawa Micron Corporation). The temperature and relative humidity during the measurement can be, for example, from 20°C to 25°C, and from 20% to 80%, respectively.

[0024] Bulk density ρ of composite particles at 0 tapping times ０ (1) is not particularly limited. In one example, the bulk density ρ of the composite particles ０ The range of (1) is preferably 0.950 g / cm ３ More preferably, 1.000 g / cm ３ More preferably, 1.100 g / cm ３ or more, preferably 1.600 g / cm ３ or less, more preferably 1.500 g / cm ３ More preferably, 1.450 g / cm or less ３ More preferably, 1.400 g / cm or less ３ Therefore, the bulk density ρ ０ The range of (1) is preferably 0.950 g / cm ３ 1.600g / cm or more ３ or less, more preferably 1.000 g / cm３ More than 1.500g / cm ３ More preferably, 1.100 g / cm or less ３ 1.450g / cm or more ３ More preferably, 1.100 g / cm or less ３ 1.400g / cm or more ３ In one embodiment, the bulk density ρ ０ The range of (1) is preferably 1.184 g / cm ３ 1.302g / cm or more ３ The following is the result.

[0025] The angle of repose of the composite particles is preferably 32° or less, more preferably 31.5° or less, even more preferably 31.0° or less, and may be, for example, 25° or more. Therefore, the angle of repose of the composite particles is preferably 25° or more and 32° or less, more preferably 25° or more and 31.5° or less, even more preferably 25° or more and 31.0° or less. In one embodiment, the angle of repose of the composite particles is preferably 30.2° or more and 31.2° or less. The smaller the angle of repose of the composite particles, the greater the fluidity of the composite particles, and the more uniform the thickness of the composite particle layer can be. The angle of repose of the composite particles can be measured by the injection method using a powder tester (e.g., manufactured by Hosokawa Micron Corporation, product name "PT-S"). The temperature and relative humidity during measurement can be, for example, 20°C or more and 25°C or less, and, for example, 20% or more and 80% or less.

[0026] From the viewpoint of improving the formability of the positive electrode mixture layer, the composite particles preferably have a particle diameter of 10 μm or less of 3.5 vol% or less, more preferably 3.0 vol% or less, even more preferably 2.5 vol% or less, and usually 0.0 vol% or more. Therefore, the composite particles preferably have a volumetric ratio of particles having a particle diameter of 10 μm or less of 0.0 vol% or more and 3.5 vol% or less, more preferably 0.0 vol% or more and 3.0 vol% or less, even more preferably 0.0 vol% or more and 2.5 vol% or less. In one embodiment, the composite particles preferably have a volumetric ratio of particles having a particle diameter of 10 μm or less of 0.0 vol% or more and 1.3 vol% or less.

[0027] The proportion of particles having a particle diameter of 10 μm or less can be measured dry using a particle size distribution analyzer (e.g., Microtrac MT3300EX II; manufactured by Microtrac Bell Co., Ltd.). The integral particle size distribution (volume basis) of the composite particles is obtained, and the volume-based frequency of particles having a particle diameter of 10 μm or less in the particle size distribution is calculated to determine the proportion of particles having a particle diameter of 10 μm or less. Furthermore, the particle diameters D10, D50, and D90 described below can be the particle diameters at which the cumulative frequency, calculated from the smallest diameter side, is 10%, 50%, and 90%, respectively, in the volume-based particle size distribution.

[0028] From the viewpoint of improving the formability of the positive electrode mixture layer, the composite particles preferably have a narrow particle size distribution, and specifically, the ratio D90 / D10 of the volumetric particle diameter D90 to the volumetric particle diameter D10 is preferably small, preferably less than 4.4, and typically greater than or equal to 1. Therefore, the range of the ratio D90 / D10 is preferably greater than or equal to 1 and less than 4.4. In one embodiment, the ratio D90 / D10 is preferably greater than or equal to 2.1 and less than or equal to 4.3.

[0029] The particle diameter D10 of the composite particles is not particularly limited. In one example, the particle diameter D10 of the composite particles on a volume basis is preferably 15 μm or more, more preferably 20 μm or more, even more preferably 25 μm or more, and preferably 150 μm or less, more preferably 120 μm or less, and even more preferably 100 μm or less. Therefore, the particle diameter D10 of the composite particles on a volume basis is preferably 15 μm or more and 150 μm or less, more preferably 20 μm or more and 120 μm or less, and even more preferably 25 μm or more and 100 μm or less. In one embodiment, the particle diameter D10 of the composite particles on a volume basis is preferably 27 μm or more and 45 μm or less.

[0030] The particle diameter D50 of the composite particles is not particularly limited. In one example, the particle diameter D50 of the composite particles is preferably 20 μm or more, more preferably 30 μm or more, even more preferably 40 μm or more, and preferably 400 μm or less, more preferably 200 μm or less, and even more preferably 100 μm or less. Therefore, the particle diameter D50 of the composite particles on a volume basis is preferably 20 μm or more and 400 μm or less, more preferably 30 μm or more and 200 μm or less, and even more preferably 40 μm or more and 100 μm or less. In one embodiment, the particle diameter D50 of the composite particles on a volume basis is preferably 60 μm or more and 73 μm or less.

[0031] The particle diameter D90 of the composite particles is not particularly limited. In one example, the particle diameter D90 of the composite particles on a volume basis is preferably 50 μm or more, more preferably 60 μm or more, even more preferably 70 μm or more, and preferably 350 μm or less, more preferably 340 μm or less, and even more preferably 300 μm or less. Therefore, the particle diameter D90 of the composite particles on a volume basis is preferably 50 μm or more and 350 μm or less, more preferably 60 μm or more and 340 μm or less, and even more preferably 70 μm or more and 300 μm or less. In one embodiment, the particle diameter D90 of the composite particles on a volume basis is preferably 97 μm or more and 135 μm or less.

[0032] <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.

[0033] Examples of transition metal oxides include MnO and MnO ２ , V ２ O ５ , V ６ O １３ , TiO２ , 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.

[0034] Examples of transition metal sulfides include TiS ２ , TiS ３ , amorphous MoS ２ , FeS, etc.

[0035] 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 ２represents 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.

[0036] The positive electrode active material usually has a particle shape. The volume-based median diameter D50 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, and even more preferably 30 μm or less. Therefore, the volume-based median diameter D50 of the positive electrode active material is preferably 0.03 μm or more and 500 μm or less, more preferably 0.1 μm or more and 100 μm or less, and even more preferably 1.0 μm or more and 30 μm or less. When the median diameter D50 of the positive electrode active material is within the above range, the formability of the composite layer can be effectively improved.

[0037] The volume-based median diameter D50 of the positive electrode active material can be measured by the following method. 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 (median diameter D50) at which the cumulative volume calculated from the smallest diameter side is 50% can be determined as the volume-based median diameter D50 of the positive electrode active material.

[0038] Bulk density ρ of the positive electrode active material at 0 tapping times ０ (0) is not particularly limited. Bulk density ρ ０ (0) is, for example, 0.5 g / cm ３ or more, for example, 0.9 g / cm ３ or more, for example, 1.5 g / cm ３ Below, for example, 1.0 g / cm ３ Therefore, the bulk density ρ ０ (0) is, for example, 0.5 g / cm ３ 1.5g / cm or more ３ Below, for example, 0.9 g / cm ３ 1.5g / cm or more ３ Below, for example, 0.9 g / cm３ 1.0g / cm or more ３ The following is the result.

[0039] The content of the positive electrode active material is preferably 90% by mass or more, more preferably 93% by mass or more, and even more preferably 95% by mass or more, and is preferably 99.19% by mass or less, more preferably 99% by mass or less, and even more preferably 98% by mass or less, relative to 100% by mass of the composite particles. Therefore, the content of the positive electrode active material is preferably 90% by mass or more and 99.19% by mass or less, more preferably 93% by mass or more and 99% by mass or less, and even more preferably 95% by mass or more and 98% by mass or less, relative to 100% by mass of the composite particles.

[0040] <Binder Resin> The binder resin is a resin that binds the positive electrode active material and the 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.

[0041] The conjugated diene polymer refers to a polymer containing a conjugated diene monomer unit. 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 (a copolymer containing acrylonitrile units and butadiene units) (NBR); and hydrogenated products thereof. Examples of hydrogenated conjugated diene polymers include polymers obtainable by hydrogenating ethylenically unsaturated bonds that may be present in block copolymers containing aromatic vinyl monomer units and aliphatic conjugated diene monomer units (e.g., SEBS (styrene-ethylene-butylene-styrene block copolymer), SEPS (styrene-ethylene-propylene-styrene block copolymer)).

[0042] 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 mass or more, more preferably 55% by mass or more, even more preferably 58% by mass or more, and preferably 98% by mass or less, more preferably 97% by mass or less, and even more preferably 96% by mass or less. Therefore, the proportion of (meth)acrylic acid ester monomer units in the acrylic polymer is preferably 50% by mass or more and 98% by mass or less, more preferably 55% by mass or more and 97% by mass or less, and even more preferably 58% by mass or more and 96% by mass or less.

[0043] 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.

[0044] 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).

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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 mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, relative to 100% by mass of the total of all structural units contained in the copolymer, and is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. Therefore, the content of the aromatic vinyl monomer unit is preferably 5% by mass or more and 50% by mass or less, more preferably 10% by mass or more and 40% by mass or less, and even more preferably 20% by mass or more and 30% by mass or less, relative to 100% by mass of the total of all structural units contained in the copolymer.

[0053] 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 mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, relative to 100% by mass of the total of all structural units contained in the copolymer, and is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less. Therefore, the content of the conjugated diene monomer unit is preferably 50% by mass or more and 95% by mass or less, more preferably 60% by mass or more and 90% by mass or less, and even more preferably 70% by mass or more and 80% by mass or less, relative to 100% by mass of the total of all structural units contained in the copolymer.

[0054] 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.

[0055] 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, and is usually 100% or less. １ It can be measured by H-NMR.

[0056] The binder resin may be used alone or in combination of two or more.

[0057] The range of the binder resin content is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.3% by mass or more, and preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less, relative to 100% by mass of the composite particles. Therefore, the range of the binder resin content is preferably 0.01% by mass or more and 5% by mass or less, more preferably 0.1% by mass or more and 3% by mass or less, and even more preferably 0.3% by mass or more and 1% by mass or less, relative to 100% by mass of the composite particles. When the binder resin content is within the above range, the formability of the positive electrode mixture layer can be effectively improved.

[0058] <Optional Components> The composite particles according to this embodiment may further contain optional components in combination with the above-described positive electrode active material and binder resin. For example, the composite particles may contain a conductive material. Examples of conductive materials include carbon-based conductive materials, and carbon-based conductive materials are preferred. Carbon-based conductive materials are carbon materials that form conductive paths between the positive electrode active materials. Examples of carbon-based conductive materials include conductive carbon materials such as 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-walled or multi-walled graphene; and carbon nonwoven fabric sheets obtained by calcining nonwoven fabrics made of polymer fibers. Among these, carbon black is preferred.

[0059] The conductive material may be used alone or in combination of two or more.

[0060] The shape of the conductive material is not particularly limited, and may be, for example, particulate, fibrous, or foil.

[0061] The range of the volume-based median diameter D50 of the 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 range of the volume-based median diameter D50 of the conductive material in the composite particles is preferably 0.01 μm or more and 0.4 μm or less, more preferably 0.02 μm or more and 0.2 μm or less, and even more preferably 0.05 μm or more and 0.15 μm or less. When the median diameter D50 of the conductive material is within the above range, the formability of the positive electrode mixture layer can be effectively improved.

[0062] The volume-based median diameter D50 of the conductive material can be measured by the following method. The particle size distribution of the 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 (median diameter D50) at which the cumulative volume calculated from the smallest diameter side becomes 50% can be determined as the volume-based median diameter D50 of the conductive material.

[0063] The range of the content of the conductive material is preferably 0.8% by mass or more, preferably 1.0% by mass or more, more preferably 1.5% by mass or more, and preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less, relative to 100% by mass of the composite particle. Therefore, the range of the content of the conductive material is preferably 0.8% by mass or more and 5% by mass or less, preferably 1.0% by mass or more and 4% by mass or less, and even more preferably 1.5% by mass or more and 3% by mass or less, relative to 100% by mass of the composite particle.

[0064] Examples of optional components other than the conductive material include optional additives such as antioxidants such as phenolic antioxidants, reinforcing materials, leveling agents, viscosity modifiers, electrolyte additives, etc. One type of optional additive may be used alone, or two or more types may be used in combination at any ratio.

[0065] Furthermore, the composite particles may contain or may not contain a solvent in combination with the solid components such as the above-mentioned positive electrode active material, binder resin, and optional additives such as a conductive material. 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 mass of the composite particles is typically 0% by mass or more (i.e., 0% by mass or more), preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less, even more preferably 1% by mass or less, and even more preferably 0.5% by mass or less. Therefore, the amount is preferably 0% by mass to 10% by mass, more preferably 0% by mass to 5% by mass, even more preferably 0% by mass to 3% by mass, even more preferably 0% by mass to 1% by mass, even more preferably 0% by mass to 0.5% by mass, and may even be 0% by mass.

[0066] 2. Method for Producing Composite Particles The composite particles according to this embodiment can be produced by a production method including agitation granulation of a positive electrode active material, a binder resin, and a solvent. In agitation granulation, a composition is agitated 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, optional additives such as a conductive material may be supplied to the agitation granulation in addition to the positive electrode active material, the binder resin, and the solvent.

[0067] Preferably, the method for producing composite particles includes: 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 binder resin and the solvent onto the stirred positive electrode active material. In this production method, a powder layer containing the positive electrode active 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 optional additives such as a solvent and a conductive material. In this powder layer, particle formation and sizing by stirring proceed while optional additives such as the binder resin and the conductive material are supplied by spraying the liquid composition, thereby producing the above-mentioned composite particles.

[0068] The volumetric median diameter D50 of the positive electrode active material and the bulk density ρ at 0 tapping times ０(0) are the volume-based median diameter D50 and bulk density ρ of the positive electrode active material in the composite particles, respectively. ０ It can be in the same range as (0).

[0069] The liquid composition contains a binder resin and a solvent. The liquid composition may further contain any additives such as a conductive material. In the liquid composition, the binder resin and any additives may be dissolved in the solvent, or may be dispersed without being dissolved. When the liquid composition contains a conductive material, it is preferable that the conductive material is dispersed without being dissolved in the solvent.

[0070] When a conductive material is dispersed in a solvent in a liquid composition, the conductive material preferably has a volumetric median diameter D50 within a specific range. Specifically, the volumetric median diameter D50 range of the conductive material in the liquid composition may be the same as the volumetric median diameter D50 range of the conductive material in the composite particles.

[0071] The volume-based median diameter D50 of the 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 conductive material particles in the liquid composition is measured on a volume basis. In the obtained particle size distribution, the particle size (median diameter D50) at which the cumulative volume calculated from the smallest diameter side is 50% can be determined as the volume-based median diameter D50 of the conductive material in the liquid composition.

[0072] As the solvent, a liquid capable of dissolving or dispersing the binder resin can be used. 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.

[0073] The amount of 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 mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and preferably 40% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less. Therefore, the solid content of the liquid composition is preferably 1% by mass or more and 40% by mass or less, more preferably 2% by mass or more and 20% by mass or less, and even more preferably 3% by mass or more and 15% by mass or less.

[0074] 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. Therefore, the viscosity range of the liquid composition at 25°C is preferably 100 mPa·s or more and 800 mPa·s or less, more preferably 150 mPa·s or more and 600 mPa·s or less, even more preferably 200 mPa·s or more and 400 mPa·s or less. The viscosity of the liquid composition can be measured using a B-type viscometer ("TVB-10M" manufactured by Toki Sangyo Co., Ltd.) under measurement conditions of 25°C and 60 rpm. When measuring, a rotor is appropriately selected according to the viscosity.

[0075] 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 granulation 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 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, as necessary. 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.

[0076] 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 cross section indicated by the dashed dotted line II-II in Fig. 1. As shown in Figs. 1 and 2, 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.

[0077] The container 100 is configured to accommodate any additives, such as a positive electrode active material, a binder resin, a solvent, and a conductive material, and these are stirred within the container 100. For example, the container 100 may have a cylindrical shape in which the bottom 110 and the ceiling 120 are circular, and 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 typically 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 a positive electrode active material, into the container 100, and an outlet (not shown) for removing the composite particles from the container 100.

[0078] The main stirring blade 200 is usually provided on the bottom 110 of the container 100. From the viewpoint of uniform stirring, the rotation axis A of the main stirring 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 as to be able to 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, 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.

[0079] 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 300３００ The angle θ formed by the convexity is usually 20° or more, preferably 30° or more, more preferably 45° or more, and usually 90° or less. Therefore, the angle θ is usually 20° or more and 90° or less, preferably 30° or more and 90° or less, more preferably 45° or more and 90° or less. For example, when the rotation axis A of the main stirring blade 200 is ２００ and the rotation axis A of the auxiliary mixing blade 300 ３００ The auxiliary mixing blade 300 is usually provided on the side 140 of the container 100. In this embodiment, the auxiliary mixing 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.

[0080] Furthermore, the granulation 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 ) that can supply the liquid composition by spraying it in the form of a mist. The number of spray nozzles 400 may be one or two or more. The spray nozzle 400 may be provided at the ceiling 120 or the side 140 of the container 100.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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 or more and 1000 / min or less. 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.

[0085] The time for which stirring is carried out in step (i) (pre-stirring time) is not particularly limited, and can be, for example, from 5 minutes to 60 minutes.

[0086] The composite particle manufacturing method using the granulation tank 10 according to the example includes, after the step (i), step (ii) of spraying a liquid composition containing a binder resin, a solvent, and optional additives such as a carbon-based conductive material onto the stirred cathode active material. In step (ii), the liquid composition is sprayed onto the cathode active material, resulting in the powder layer in the container 100 containing not only the cathode active material but also optional additives such as the binder resin and the conductive material. Thus, the cathode active material, the 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.

[0087] The temperature inside the granulation tank 10 can be set within a range in which the above-described 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, and even more preferably 60°C or lower. Therefore, the temperature range inside the granulation tank 10 is preferably 0°C or higher and 100°C or lower, more preferably 10°C or higher and 80°C or lower, and even more preferably 20°C or higher and 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 in the granulation tank 10.

[0088] The peripheral speed range of the stirring blades, such as the main stirring blade 200 and the sub-stirring blade 300, can be set within a range in which the above-mentioned composite particles can be produced. In one example, the peripheral speed range of the stirring blades, such as the main stirring blade 200 and the sub-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.

[0089] 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 100 minutes or less.

[0090] The method for producing composite particles according to the example using the granulation tank 10 may further include any optional step in addition to the above-described steps (i) and (ii). The method for producing composite particles may, for example, include a step of stirring the composite particles after step (ii) to size the composite particles, or a step of classifying the composite particles after step (ii). When classifying the composite particles, classification may be performed to reduce the proportion of particles with a large particle size in the composite particles, to reduce the proportion of particles with a small particle size in the composite particles, or a combination of these. As the classification method, any method may be used, such as classification using a sieve or classification using an air flow classifier, and from the viewpoint of effectively reducing the proportion of particles with a particle size of 10 μm or less, classification using a sieve is preferred.

[0091] Furthermore, the method for producing composite particles may include, for example, a step of stirring the positive electrode active material with a stirring device separate from the granulation tank 10 before the step (i).

[0092] <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.

[0093] 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.

[0094] 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, even more preferably 10 μm or more, and is preferably 200 μm or less, more preferably 100 μm or less, even more preferably 50 μm or less. Therefore, the thickness of the current collector is preferably 1 μm or more and 200 μm or less, more preferably 5 μm or more and 100 μm or less, even more preferably 10 μm or more and 50 μm or less.

[0095] 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 positive 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 Therefore, the amount of the positive electrode mixture layer per unit area is preferably 1 mg / cm ２ 100mg / cm or more ２ More preferably, 2 mg / cm or less ２ 50mg / cm or more ２ More preferably, 5 mg / cm ２ 30mg / cm or more ２The following is the result.

[0096] 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.

[0097] <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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the examples shown below, and can be practiced with any modifications within the scope of the claims of the present invention and their equivalents.

[0105] In the following description, the units "%" and "parts" that represent amounts are by mass unless otherwise specified. Furthermore, the operations described below were carried out at room temperature (20°C ± 15°C) and atmospheric pressure (1 atm) unless otherwise specified.

[0106] <Measurement and Evaluation Methods> <Bulk density, compressibility C, and ratio ρ of positive electrode active material and composite particles> ０ (1) / ρ ０ (0)> Measurement was carried out using a powder tester (manufactured by Hosokawa Micron Corporation, product name "PT-S"). The mass of the positive electrode active material was placed in the device, and the loose bulk density (bulk density at tapping count 0) ρ ０ (0) (g / cm ３ The composite particles whose mass was weighed were placed in the apparatus, and the loose bulk density (bulk density at 0 tapping times) ρ ０ (1) (g / cm ３ ) and the compacted bulk density ρ at 180 taps １８０ (1) (g / cm ３ The tapping conditions were a stroke of 18 mm and one tap per second.

[0107] The obtained ρ １８０ (1) and ρ ０ From (1), the compressibility C was calculated according to the following formula (1): C = (ρ １８０ (1)-ρ０ (1)) / ρ １８０ (1) × 100 (1) Also, the ratio ρ ０ (1) / ρ ０ (0) was calculated.

[0108] <Angle of Repose> The angle of repose of the composite particles was measured by an injection method using a powder tester (for example, manufactured by Hosokawa Micron Corporation, product name "PT-S").

[0109] <Volume-based D10, D50, D90, and volume-based proportion of particles with a particle diameter of 10 μm or less of composite particles> Using a particle size distribution analyzer (Microtrac MT3300EX II; manufactured by Microtrac Bell Co., Ltd.) based on a laser scattering / diffraction method, the integral particle size distribution (volume-based) of the composite particles was obtained in a dry state with a dispersion air pressure of 0.1 MPa during measurement. The particle sizes at which the cumulative frequency, calculated from the smallest diameter side, was 10%, 50%, and 90% were adopted as the volume-based D10 particle size, D50 particle size, and D90 particle size, respectively. In addition, in the particle size distribution, the volume-based occupancy frequency of particles with a particle diameter of 10 μm or less was calculated and adopted as the proportion of particles with a particle diameter of 10 μm or less.

[0110] <Volume-Based Median Diameter D50 of Positive Electrode Active Material and Conductive Material> The integrated particle size distribution (volume-based) of the particles was measured using a particle size distribution analyzer (Microtrac MT3300EX II; manufactured by Microtrac Bell Co., Ltd.) based on a laser scattering / diffraction method, with the pressure of the dispersion air during measurement set to 0.1 MPa. The particle diameter at which the cumulative frequency, calculated from the smallest diameter side, reached 50% was adopted as the volume-based median diameter D50.

[0111] <Formation and evaluation of positive electrode composite layer> The composite particles produced in the examples and comparative examples were fed to the press rolls of a roll press machine (Hirano Giken Kogyo Co., Ltd.'s "Oshi-kuri Rough Surface Heat Roll") using a metering feeder (Nikka Spray K-V manufactured by Nikka Corporation). The roll temperature of the press rolls was set to 50°C, and the gap between the rolls was set to 230 μm. A sand-matt-processed polyester film (PTHA-25 manufactured by Unitika Ltd., thickness 25 μm, dynamic friction coefficient μ based on JIS K 7125) simulating a current collector was placed between the press rolls. ｋThe composite particles supplied from a metering feeder were attached to the sand-matt surface of the polyester film, and the polyester film was pressed with a press roll to form a positive electrode composite layer on the polyester film. The forming speed (film conveying speed) was as follows:

[0112] (1 cm of the positive electrode mixture layer ２ In forming the positive electrode mixture layer, the forming speed was 1 m / min. ２ The mass per unit was measured.

[0113] (Maximum Molding Speed) In molding the positive electrode composite layer, the molding speed was increased in increments of 1 m / min starting from 1 m / min (i.e., 1 m / min, 2 m / min, 3 m / min, 4 m / min), and the degree of peeling of the positive electrode composite layer on the polyester film obtained at each molding speed was visually evaluated according to the following criteria. Good: There were 0 or 1 locations where the positive electrode composite layer was missing in a roughly 3 cm square area of ​​the positive electrode composite layer. Poor: There were 2 or more locations where the positive electrode composite layer was missing in a roughly 3 cm square area of ​​the positive electrode composite layer. The highest molding speed at which the degree of peeling of the positive electrode composite layer was evaluated as good was defined as the maximum molding speed. When the degree of peeling was evaluated as poor at a molding speed of 1 m / min, the maximum molding speed was defined as 0 m / min. For example, if the peeling degree was evaluated as good at a forming speed of 2 m / min and poor at a forming speed of 3 m / min, the maximum forming speed was set to 2 m / min.

[0114] (Comprehensive evaluation of formability) When the mass of the positive electrode mixture layer on the polyester film is 15 mg / cm ２ When the mass of the positive electrode mixture layer on the polyester film was 15 mg / cm or more and the maximum forming speed was 2 m / min or more, the overall formability evaluation was judged to be good. ２ When the maximum forming speed was less than 2 m / min, or when the maximum forming speed was less than 2 m / min, the overall formability evaluation was judged to be poor.

[0115] <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.

[0116] <Production Example 2. Production of liquid composition> A liquid composition (solid content concentration 5 mass %, viscosity 300 mPa s) was produced by mixing 6.3 parts of binder resin A1 obtained by drying the solution produced in Production Example 1, 18.0 parts of carbon black as a carbon-based conductive material, and 461.7 parts of cyclohexane as a solvent. The median diameter D50 of the carbon black in the liquid composition on a volume basis was measured and found to be 0.1 μm.

[0117] 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) installed 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. The secondary stirring blade was equipped with a V-shaped anchor blade. 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.

[0118] (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 parts by mass (10,000 g) of a granulation tank containing 100% ammonium hydroxide (having a volumetric median diameter D50 of 4 μm) was added. While a seal gas at room temperature (25° C.) was passed through the tank at a rate of 170 L / min, the main and auxiliary stirring blades were rotated to stir the positive electrode active material. The peripheral speed of the main stirring blade was 4.0 m / s, and the peripheral speed of the auxiliary stirring blade was 15.7 m / s.

[0119] Next, as the composite particle formation operation (ii), 3 parts by mass (solids content equivalent) of the liquid composition produced in Production Example 2 (approximately 6,200 g of liquid composition) was sprayed onto the cathode active material over 90 minutes while stirring the cathode active material as described above. The liquid composition was sprayed from a spray nozzle (top nozzle) attached to the ceiling of the cylindrical container. By spraying the liquid composition, a powder layer consisting of a raw material composition containing the cathode active material and the solid content of the liquid composition (conductive material and binder resin A1) was formed in the stirring tank, and the formation of 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 40°C.

[0120] The composite particles produced by carrying out the above operations (i) to (ii) in this order were classified using sieves as follows. First, the composite particles were passed through a vibrating sieve with a mesh size of 150 μm to perform coarse particle classification to separate coarse particles. The composite particles remaining on the sieve were further passed through a vibrating sieve with a mesh size of 45 μm to perform fine particle classification to separate fine particles. The composite particles remaining on the sieve were evaluated by the method described above.

[0121] Example 2 Composite particles were obtained in the same manner as in Example 1, except for the following points, and evaluated by the above-mentioned method. The liquid composition was sprayed onto the positive electrode active material for 21 minutes. The temperature of the powder layer was set to 37.0°C. The temperature of the powder layer 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). Fine powder classification was not performed. Therefore, the composite particles that fell under the sieve obtained by performing coarse powder classification were used for evaluation.

[0122] Example 3 Composite particles were obtained in the same manner as in Example 1, except for the following points, and evaluated by the above-mentioned method. - The peripheral speed of the main stirring blade was 1.3 m / s. - The time for spraying the liquid composition onto the positive electrode active material was 17.5 minutes. - The temperature of the powder layer was 35.0°C. - Fine powder classification was not performed. Therefore, the composite particles that fell under the sieve obtained by performing coarse powder classification were used for evaluation.

[0123] Comparative Example 1 Composite particles were obtained in the same manner as in Example 1, except for the following: Instead of using a vibrating sieve with a mesh size of 45 μm, fine powder classification was performed using an air classifier.

[0124] Comparative Example 2 Composite particles were obtained in the same manner as in Example 1, except for the following points, and were evaluated by the above-mentioned method. The auxiliary stirring blade was not rotated. The liquid composition was sprayed onto the positive electrode active material for 42 minutes. The temperature of the powder layer was set to 65.0°C. Fine powder classification was not performed. Therefore, the composite particles that fell under the sieve obtained by performing coarse powder classification were used for evaluation.

[0125] Comparative Example 3 Composite particles were obtained in the same manner as in Example 1, except for the following points, and were evaluated by the above-mentioned method. The auxiliary stirring blade was not rotated. The liquid composition was sprayed onto the positive electrode active material for 42 minutes. The temperature of the powder layer was set to 72°C. Fine powder classification was not performed. Therefore, the composite particles that fell under the sieve obtained by performing coarse powder classification were used for evaluation.

[0126] Comparative Example 4 Composite particles were obtained in the same manner as in Example 1, except for the following points, and evaluated by the above-mentioned method. The liquid composition was sprayed onto the positive electrode active material for 42 minutes. The temperature of the powder layer was 72°C. Fine powder classification was not performed. Therefore, the composite particles that fell under the sieve obtained by performing coarse powder classification were used for evaluation.

[0127] Comparative Example 5 Composite particles were obtained in the same manner as in Example 1, except for the following points, and were evaluated by the above-mentioned method. The liquid composition was sprayed onto the positive electrode active material for 69 minutes. The temperature of the powder layer was 32.0°C. Fine powder classification was not performed. Therefore, the composite particles that fell under the sieve obtained by performing coarse powder classification were used for evaluation.

[0128] <Results> The results of the Examples and Comparative Examples are shown in the table below. In the table below, the abbreviations have the following meanings: ρ ０ (0): Bulk density ρ of the positive electrode active material at tapping count 0 ０(1): Bulk density of composite particles at 0 tapping times. Angle of repose: Angle of repose of composite particles. Fine powder ratio: Ratio of particles with a particle diameter of 10 μm or less. Mass of composite layer: 1 cm of the positive electrode composite layer. ２ Mass per unit (basis weight)

[0129]

[0130] From the above results, it is clear that composite particles having a compression degree C of 17.0% or less have good moldability.

[0131] 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. Composite particles for a positive electrode of an electrochemical element, comprising a positive electrode active material and a binder resin, and having a compressibility C calculated by the following formula (1) of 17.0% or less: C=(ρ １８０ (1)-ρ ０ (1)) / ρ １８０ (1) × 100 (1) where, ρ ０ (1) is the bulk density (g / cm) of the composite particles when the tapping number is 0. ３ ) and ρ １８０ (1) is the packed bulk density (g / cm) of the composite particles after 180 tapping times. ３ ) represents 2. Bulk density ρ of the composite particles when tapped 0 times ０ (1) The bulk density ρ of the positive electrode active material when the tapping number is 0 ０ Ratio ρ to (0) ０ (1) / ρ ０ 2. The composite particles for a positive electrode of an electrochemical element according to claim 1, wherein (0) is 1.100 or more.

3. Composite particles for a positive electrode of an electrochemical element according to claim 1, having an angle of repose of 32° or less.

4. Composite particles for electrochemical element positive electrodes according to claim 1, wherein particles having a particle diameter of 10 μm or less account for 2.5% by volume or less.

5. Composite particles for a positive electrode of an electrochemical element according to claim 1, wherein the ratio D90 / D10 of the particle diameter D90 to the particle diameter D10 is less than 4.

4.

6. A method for producing composite particles for electrochemical element positive electrodes according to any one of claims 1 to 5, comprising stirring and granulating a positive electrode active material, a binder resin, and a solvent.

7. The method for producing composite particles for an electrochemical element positive electrode according to claim 6, 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 binder resin and the solvent onto the positive electrode active material in the stirred state.

8. 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 5.

9. An electrochemical element comprising the positive electrode for an electrochemical element according to claim 8.

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