WO2025205057A1 - Electrochemical element positive electrode composite particles, production method for same, electrochemical element positive electrode, and electrochemical element - Google Patents

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

The present invention relates to composite particles for use in positive electrodes of electrochemical devices, a method for producing the same, positive electrodes for electrochemical devices containing the composite particles, and electrochemical devices.

Electrochemical elements such as lithium-ion secondary batteries are used in a wide range of applications, and there is a demand for ever-improved performance. The positive electrode of an electrochemical element often comprises a current collector and a positive electrode composite layer formed on its surface.

Conventionally, wet formation methods have been widely used to form positive electrode composite layers. The wet formation method referred to here is 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 then dried to form a positive electrode composite layer.

However, in recent years, dry forming methods have been attracting attention as a way to more efficiently form positive electrodes. In dry forming methods, composite particles containing a positive electrode active material and a binder resin are prepared, and the composite particles are deposited on the surface of a current collector to form a layer of composite particles. This layer is then pressed to reduce its thickness, thereby forming a positive electrode composite layer. Patent Document 1 discloses a technology for composite particles used in such dry forming methods.

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

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 portions where the compressed composite particles peel off.
Therefore, there is a demand for composite particles for electrochemical devices that can produce positive electrodes with less 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.

The present inventors have conducted extensive research to solve the above problems, and as a result have found that the above problems can be solved by setting the compression degree of the composite particles within a predetermined range, thereby completing the present invention.
That is, the present invention provides the following.

<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) represents the bulk density (g/cm ³ ) of the composite particles when tapped 0 times;
ρ ₁₈₀ (1) represents the packed bulk density (g/cm ³ ) of the composite particles after 180 tappings.
<2> The composite particle for electrochemical element positive electrode according to <1>, wherein a ratio _{ρ 0 (} 1)/ρ ₀ (0) of a bulk density ρ ₀ (1) of the composite particle at 0 tapping times to a bulk density ρ 0 (0) of the positive electrode active material at 0 tapping times is 1.100 or more.
<3> The composite particles for an electrochemical element positive electrode according to <1> or <2>, having an angle of repose of 32° or less.
<4> The composite particles 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% by volume or less.
<5> The composite particles 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 particles for an electrochemical element positive electrode according to any one of <1> to <5>,
A method for producing composite particles for a positive electrode of an electrochemical element, comprising stirring and granulating a positive electrode active material, a binder resin, and a solvent.
<7> Step (i) of stirring the positive electrode active material in a granulation tank to obtain a stirred state;
(ii) a step of spraying a liquid composition containing the binder resin and the solvent onto the positive electrode active material in a stirred state;
The method for producing composite particles for an electrochemical element positive electrode according to <6>, comprising:
<8> A battery comprising: a current collector; and a positive electrode mixture layer formed on the current collector,
A positive electrode for an electrochemical element, wherein the positive electrode mixture layer contains the composite particles for an electrochemical element positive electrode according to any one of <1> to <5>.
<9> An electrochemical element comprising the positive electrode for electrochemical elements according to <8>.

The present invention provides composite particles for electrochemical devices that can produce positive electrodes with minimal peeling of the positive electrode composite 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.

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.

The present invention will be described in detail below, showing embodiments and examples. However, the present invention is not limited to the embodiments and examples shown below, and can be modified and implemented 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 the group of numerical values listed as lower limit values can be combined as appropriate with any numerical value selected from the group of numerical values listed as upper limit values. Furthermore, in the figures, identical components are given the same reference numerals, and their description may be omitted.

In polymers produced by copolymerizing multiple types of monomers, the proportion of structural units formed by polymerizing a certain monomer in the polymer usually corresponds to the ratio (feed ratio) of that certain monomer to all the monomers used in the polymerization of the polymer, unless otherwise specified.

The structure of a molecule or a portion thereof, such as a structural unit, is not limited by its manufacturing method. For example, an aromatic vinyl monomer unit is a structural unit having a structure formed by polymerization of an aromatic vinyl monomer, but this 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. Also, for example, a conjugated diene monomer unit is a structural unit having a structure formed by polymerization of a conjugated diene monomer, but this 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.

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

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

<1. Composite particles for electrochemical element positive electrodes>
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") includes a positive electrode active material and a binder resin. Typically, particles of one or more positive electrode active materials and particles of other materials that may be optionally included 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.

<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 the formula (1), ρ ₀ (1) represents the bulk density (g/cm ³ ) of the composite particles when the number of tapping times is 0;
ρ ₁₈₀ (1) represents the packed bulk density (g/cm ³ ) of the composite particles after 180 tappings.

The bulk density of the composite particles can be measured by the following method using a powder tester (for example, product name "PT-S" manufactured by Hosokawa Micron Corporation).
The weighed composite particles are placed in the apparatus, and the bulk density ρ ₀ (1) at 0 taps and the packed bulk density ρ ₁₈₀ (1) at 180 taps are measured. The tapping conditions are a stroke of 18 mm and 1 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.

When a positive electrode mixture layer is formed by compressing the thickness of a layer of composite particles, the smaller the compression degree C, the smaller the change in density of the layer before and after compression tends to be.
When the change in density of the layer before and after compression is small, the force compressing the composite particle layer is easily transmitted to the composite particle layer, which is thought to result in good compression bonding between the composite particles. Because the composite particles are well compressed, peeling of the positive electrode mixture layer from the current collector can be reduced, and the production speed of the positive electrode mixture layer can be increased. Reducing peeling of the positive electrode mixture layer from the current collector and increasing the production speed of the positive electrode mixture layer mean that the formability of the positive electrode mixture layer can be improved.

The degree of compression C is usually 0.0% or more, for example, 2.5% or more, for example, 5.0% or more.
Therefore, the compression degree 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.

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 degree of compression C can be further reduced by setting the proportion of particles with a particle diameter of 10 μm or less in the composite particles to preferably 3.5 vol % or less, more preferably 3.0 vol % or less, and even more preferably 2.5 vol % or less.
In the composite particles, the proportion of particles having a small particle size can be reduced, for example, by classifying the composite particles using a classifier such as a sieve.
Alternatively, the compression degree C can be reduced by adjusting the granulation conditions when producing the composite particles.

The ratio ρ ₀ (1)/ρ ₀ (0) of the bulk density ρ ₀ (1) of the composite particles at 0 tapping times to the bulk density ρ ₀ (0) of the positive electrode active material at 0 tapping times 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. Therefore, the ratio ρ 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.
In one embodiment, the ratio ρ ₀ (1)/ρ ₀ (0) is preferably greater than or equal to 1.152 and less than or equal to 1.267.
When the ratio ρ ₀ (1)/ρ ₀ (0) is 1.100 or more, the bulk density ρ ₀ (1) of the composite particles is larger than the bulk density ρ ₀ (0) of the positive electrode active material for forming the composite particles. Therefore, when a layer of composite particles of the same thickness containing a positive electrode active material of the same bulk density ρ ₀ (0) is formed, the larger the ratio ρ ₀ (1)/ρ ₀ (0), the larger the mass per unit area of the electrode mixture layer that can be formed.

Bulk density can be measured using a powder tester (e.g., Hosokawa Micron Corporation, product name "PT-S"). The temperature and relative humidity during measurement can be, for example, between 20°C and 25°C, and between 20% and 80%, respectively.

The bulk density ρ ₀ (1) of the composite particles when the tapping count is 0 is not particularly limited. In one example, the range of the bulk density ρ ₀ (1) of the composite particles is preferably 0.950 g/cm ³ or more, more preferably 1.000 g/cm ³ or more, even more preferably 1.100 g/cm ³ or more, and preferably 1.600 g/cm ³ or less, more preferably 1.500 g/cm ³ or less, even more preferably 1.450 g/cm ³ or less, and even more preferably 1.400 g/cm ³ or less. Therefore, the range of the bulk density ρ ₀ (1) is preferably 0.950 g/cm ³ or more and 1.600 g/cm ³ or less, more preferably 1.000 g/cm ³ or more and 1.500 g/cm ³ or less, even more preferably 1.100 g/cm ³ or more and 1.450 g/cm ³ or less, and even more preferably 1.100 g/cm ³ or more and 1.400 g/cm ³ or less.
In one embodiment, the range of the bulk density ρ ₀ (1) is preferably 1.184 g/cm ³ or more and 1.302 g/cm ³ or less.

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 an injection method using a powder tester (for example, a powder tester manufactured by Hosokawa Micron Corporation, product name "PT-S"). The temperature and relative humidity during the measurement can be, for example, from 20°C to 25°C, and from 20% to 80%, respectively.

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% by volume or more and 1.3% by volume or less.

The proportion of particles with 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 diameter distribution (volume basis) of the composite particles is obtained, and the volume-based frequency of particles with a diameter of 10 μm or less in the particle diameter distribution is calculated to determine the proportion of particles with a 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.

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 usually 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 2.1 or more and 4.3 or less.

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 is 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 in the range of 27 μm or more and 45 μm or less.

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 in the range of 60 μm or more and 73 μm or less.

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 is 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 in the range of 97 μm or more and 135 μm or less.

<Cathode active material>
A positive electrode active material is a material that transfers electrons at the positive electrode of an electrochemical element. For example, a material capable of absorbing and releasing lithium can usually be used as a positive electrode active material for a lithium-ion secondary battery. 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.

Examples of transition metal oxides include MnO, 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 , and MoO ₃ , and among these, MnO, V ₂ O ₅ , V ₆ O ₁₃ , and TiO ₂ are preferred from the viewpoints of cycle stability and capacity.

Examples of transition metal sulfides include TiS ₂ , TiS ₃ , amorphous MoS ₂ , and FeS.

Examples of lithium-containing composite metal oxides 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 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, and Ni—Co—Al lithium composite oxide. Examples of lithium-containing composite metal oxides having a spinel structure include lithium manganate (LiMn ₂ O ₄ ) and Li[Mn _3/2 M ¹ _1/2 ]O ₄ in which part of the Mn is substituted with another transition metal (where M ¹ represents a transition metal other than Mn, such as Cr, Fe, Co, Ni, or Cu). An example of a lithium-containing composite metal oxide having an olivine structure is _an olivine _- type lithium phosphate compound represented by ^LiXM2PO4 (wherein ^M2 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.

The positive electrode active material typically has a particulate 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 this range, the formability of the composite layer can be effectively improved.

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 positive electrode active 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 volume-based median diameter D50 of the positive electrode active material.

The bulk density ρ ₀ (0) of the positive electrode active material when the tapping count is 0 is not particularly limited. The bulk density ρ ₀ (0) may be, for example, 0.5 g/cm ³ or more, for example, 0.9 g/cm ³ or more, and may be, for example, 1.5 g/cm ³ or less, for example, 1.0 g/cm ³ or less. Therefore, the bulk density ρ ₀ (0) is, for example, 0.5 g/cm ³ or more and 1.5 g/cm ³ or less, for example, 0.9 g/cm ³ or more and 1.5 g/cm ³ or less, for example, 0.9 g/cm ³ or more and 1.0 g/cm ³ or less.

The content of the positive electrode active material is preferably 90% by mass or more, more preferably 93% by mass or more, even more preferably 95% by mass or more, and 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.

<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.

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)).

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.

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. Preferred aromatic vinyl block polymers include styrene-isoprene-styrene block copolymers, styrene-butadiene-styrene copolymers, and hydrogenated versions of these.

A fluoropolymer refers to a polymer that contains fluorine-containing monomer units and may also 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).

Examples of cellulose-based polymers include cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, and carboxymethyl cellulose.

Examples of cyclic olefin polymers include polymers (addition polymers or ring-opening polymers) obtained by polymerizing cyclic olefin compounds and their hydrogenated derivatives, 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, as their electrolyte swelling degree and glass transition temperature can be easily adjusted to appropriate levels.

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; polycyclic norbornenes having three or more rings and not containing an aromatic ring structure, such as dicyclopentadiene, methyldicyclopentadiene, and tricyclo[5.2.1.0 ^{2,6 ]} dec-8-ene; Polycyclic norbornenes having three or more aromatic rings, such as tetracyclo[10.2.1.0 ^2,11 . 0 ^4,9 ]tetradeca-3,5,7,12-tetraene (also called 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); 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.

Among these, non-polar norbornene-based monomers are preferred as the cyclic olefin compound; unsubstituted or alkyl group-containing norbornenes (e.g., norbornene, 8-ethyltetracyclododecene), alkenyl group-containing norbornenes (e.g., ethylidenetetracyclododecene (8-ethylidenetetracyclododecene)), dicyclopentadiene, aromatic ring-containing norbornene derivatives (e.g., tetracyclo[9.2.1.0 ^2,10 .0 ^3,8 ]tetradeca-3,5,7,12-tetraene (also referred to as 1,4-methano-1,4,4a,9a-tetrahydro-9H-fluorene)), and unsubstituted or alkyl group-containing tetracyclododecenes (e.g., tetracyclododecene, 8-methoxycarbonyl-8-methyltetracyclo[4.4.0.1 ^2,5 .1 ^7,10 ]-3-dodecene) are more preferred.

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 monomers. Of these, a polymer using only a cyclic olefin compound as a monomer is preferred.

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.

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 an aromatic vinyl monomer block and a conjugated diene monomer block, and hydrogenated products thereof are more preferred; and hydrogenated products of block copolymers containing an aromatic vinyl monomer block and a conjugated diene monomer block 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. The conjugated diene monomer block is a block region containing conjugated diene monomer units and may contain only conjugated diene monomer units.

Aromatic vinyl monomer units refer to structural units having a structure formed by polymerizing aromatic vinyl monomers. There may be one type of aromatic vinyl monomer unit, or two or more types. The content of aromatic vinyl monomer units 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; it 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 aromatic vinyl monomer units 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.

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.

When the copolymer is a block copolymer, its 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.

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. The hydrogenation rate can be measured by ^1H -NMR.

The binder resin may be used alone or in combination of two or more types.

The binder resin content range 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 binder resin content range 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 this range, the formability of the positive electrode mixture layer can be effectively improved.

<Optional ingredients>
The composite particles according to this embodiment may further contain any optional components in addition to the above-described positive electrode active material and binder resin. For example, the composite particles may contain a conductive material. Examples of the conductive material include carbon-based conductive materials, and carbon-based conductive materials are preferred.
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.

The conductive material may be used alone or in combination of two or more types.

There are no particular restrictions on the shape of the conductive material, and it can be, for example, particulate, fibrous, foil, etc.

The median diameter D50 of the conductive material in the composite particles on a volume basis 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 median diameter D50 of the conductive material in the composite particles on a volume basis 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 this range, the formability of the positive electrode composite layer can be effectively improved.

The volumetric median diameter D50 of the conductive material can be measured using the following method. A laser diffraction particle size distribution analyzer is used to measure the volumetric particle size distribution of the conductive material particles. In the obtained particle size distribution, the particle diameter (median diameter D50) at which the cumulative volume calculated from the smallest diameter side is 50% can be determined as the volumetric median diameter D50 of the conductive material.

The range of the conductive material content 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 particles. Therefore, the range of the conductive material content 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 particles.

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; and electrolyte additives. One type of optional additive may be used alone, or two or more types may be used in combination in any ratio.

Furthermore, the composite particles may contain or may not contain a solvent in combination with the solid components, such as the aforementioned 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.

<2. 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 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. If necessary, optional additives such as a conductive material may be added to the stirring and granulation in addition to the positive electrode active material, the binder resin, and the solvent.

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;
(ii) a step of spraying a liquid composition containing the binder resin and the solvent onto the positive electrode active material in a stirred state;
In this manufacturing 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 the 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.

The volumetric median diameter D50 of the positive electrode active material and the bulk density ρ ₀ (0) at 0 tapping times may be in the same range as the volumetric median diameter D50 and bulk density ρ ₀ (0) of the positive electrode active material in the composite particles.

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

When a conductive material is dispersed in a solvent in a liquid composition, it is preferable that the conductive material have a volumetric median diameter D50 within a specific range. Specifically, the range of the volumetric median diameter D50 of the conductive material in the liquid composition can be the same as the range of the volumetric median diameter D50 of the conductive material in the composite particles.

The volumetric median diameter D50 of the conductive material in the liquid composition can be measured by the following method. A laser diffraction particle size distribution analyzer is used to measure the particle size distribution of the conductive material particles in the liquid composition on a volumetric basis. In the obtained particle size distribution, the particle diameter (median diameter D50) at which the cumulative volume calculated from the smallest diameter side is 50% can be determined as the volumetric median diameter D50 of the conductive material in the liquid composition.

The solvent can be a liquid capable of dissolving or dispersing the 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.

The amount of solvent is preferably selected so that the solids concentration of the liquid composition falls within a specific range. Specifically, the solids concentration 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 solids concentration 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.

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, and 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 Brookfield viscometer ("TVB-10M" manufactured by Toki Sangyo Co., Ltd.) at 25°C and 60 rpm. When measuring, the rotor used should be selected appropriately according to the viscosity.

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

FIG. 1 is a plan view schematically illustrating 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 illustrating 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 includes a container 100 and a main agitator 200 rotatable about a rotation axis A _200. The granulation tank 10 may also include a sub-agitator ₃₀₀ rotatable about a rotation axis A ₃₀₀ that is not parallel to the rotation axis A 200, as needed.

The container 100 is designed to store 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 with a circular bottom 110 and a circular ceiling 120, and may be tapered in part in the height direction. For example, a portion 130 continuing from the ceiling 120 may be tapered. The container 100 is typically installed so that its 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.

The main agitator 200 is typically provided on the bottom 110 of the vessel 100. From the perspective of uniform agitation, the rotation axis A ₂₀₀ of the main agitator 200 is preferably provided at the center of the bottom 110. If the vessel 100 has a cylindrical shape, the rotation axis A ₂₀₀ of the main agitator 200 may coincide with the central axis of the cylindrical shape of the vessel 100. In this embodiment, an example will be described in which the main agitator 200 is provided at the center of the bottom 110 of the vessel 100 so as to rotate around the rotation axis A ₂₀₀ parallel to the vertical direction. In addition, 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 will show an example of a main agitator 200 with three main blades 210. Furthermore, the drive part 220 of the main stirring blade 200 is generally provided with a ventilation mechanism (not shown) for ventilating a seal gas into the container 100 in order to prevent powder (positive electrode active material, conductive material, composite particles, etc.) from penetrating into the drive part 220. An inert gas is preferably used as the seal gas, and nitrogen gas, for example, can be used.

The auxiliary agitating blade 300 can be provided rotatably about a rotation axis _A300 that is not parallel to the rotation axis _A200 of the main agitating blade 200. The angle θ between the rotation axis A200 of the main agitating blade ₂₀₀ and the rotation axis A300 of the auxiliary agitating blade ₃₀₀ is typically 20° or more, preferably 30° or more, more preferably 45° or more, and typically 90° or less. Therefore, the angle θ is typically 20° to 90°, preferably 30° to 90°, and more preferably 45° to 90°. For example, the rotation axis _A200 of the main agitating blade 200 and the rotation axis A300 of the auxiliary agitating blade ₃₀₀ may be perpendicular. The auxiliary agitating blade 300 is typically provided on the side 140 of the container 100. In this embodiment, an example is shown and described in which the auxiliary agitating blade 300 is provided on the side 140 of the container 100 so as to be rotatable about a rotation axis _A300 that is parallel to the horizontal direction. Furthermore, the auxiliary mixing impeller 300 typically has one or more auxiliary blades 310. There are no particular restrictions on the number or shape of these auxiliary blades 310, but in this embodiment, an auxiliary mixing impeller 300 equipped with anchor-type blades as the auxiliary blades 310 is shown as an example. Furthermore, like the drive part 220 of the main mixing impeller 200, the drive part 320 of the auxiliary mixing impeller 300 is generally provided with a ventilation mechanism (not shown) for ventilating a seal gas into the container 100 in order to prevent powder from penetrating the drive part 320. An inert gas is preferably used as the seal gas, and nitrogen gas, for example, can be used.

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 Figure 1) that can supply the liquid composition by spraying it in a mist. The number of spray nozzles 400 may be one, or two or more. The spray nozzle 400 may be provided in the ceiling 120 or side 140 of the container 100.

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.

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 achieve 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 auxiliary stirring blade 300 may also be rotated in addition to the main stirring blade 200. The particles of the raw positive electrode active material may be agglomerated, but stirring in step (i) can break up the agglomerations. Furthermore, the raw positive electrode active material may contain liquid components, such as moisture, that adhered during production and storage. Stirring in step (i) can reduce, and preferably remove, the amount of the liquid components.

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.

During mixing, a seal gas is passed through the drive unit 220 of the main mixing blade 200 and the drive unit 320 of the sub-mixing blade 300 into the container 100. The flow rate (aeration rate) of this seal gas is preferably set so that the flow rate of the seal gas flowing into the container 100 of the granulation tank 10 divided by the volume of the container 100 (flow rate/volume) is 0.1/min or more and 1000/min. Furthermore, 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.

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

The composite particle manufacturing method according to the example using the granulation tank 10 includes, after the above-mentioned 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 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 optional additives such as the binder resin and the conductive material. As a result, the positive electrode active material, the conductive material, and the binder resin aggregate to gradually form composite particles. Also, 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 sub-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 step (ii), composite particle formation and particle size regulation proceed simultaneously in the presence of a solvent, allowing the composite particles described above to be obtained.

The temperature inside the granulation tank 10 can be set within a range that allows the production of the composite particles described above. 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 inside the granulation tank 10.

The range of peripheral speeds of the agitating blades, such as the main agitating blade 200 and the sub-agitating blade 300, can be set within a range that allows the composite particles described above to be produced. In one example, the range of peripheral speeds of the agitating blades, such as the main agitating blade 200 and the sub-agitating blade 300, is preferably 1 m/s or more and 20 m/s or less, from the perspective of controlling the particle diameter of the composite particles within an appropriate range.

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 that allows the composite particles described above to be produced. In one example, the spray time can be 5 minutes or more and 100 minutes or less.

The composite particle manufacturing method according to the example using the granulation tank 10 may further include any optional steps in addition to the above steps (i) and (ii). For example, the composite particle manufacturing method may 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, to reduce the proportion of particles with a small particle size, or a combination of these. Any classification method may be used, such as classification using a sieve or classification using an air classifier. From the perspective of effectively reducing the proportion of particles with a particle size of 10 μm or less, classification using a sieve is preferred.

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, prior to step (i).

<Positive electrode for electrochemical elements>
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.

The current collector material is preferably one that is electrically conductive and electrochemically durable. Specific examples of current collector materials 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. Of these, aluminum and aluminum alloys are preferred in terms of conductivity and voltage resistance. When high voltage resistance is required, the high-purity aluminum disclosed in JP 2001-176757 A can be preferably used. One type of current collector material may be used alone, or two or more types may be used in combination.

The current collector generally has a film or sheet shape. The thickness of the current collector may be selected appropriately 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 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.

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 or more, more preferably 2 mg/cm 2 or more, even more preferably 5 mg/cm ² or more, and preferably 100 mg/cm ² or less, more preferably 50 mg/cm ² or less, and even more preferably 30 mg/cm ² or less. Therefore, the amount of the positive electrode mixture layer per unit area is preferably 1 mg/cm ² or more and 100 mg/cm ² or less, more preferably 2 mg/cm ² or more and 50 mg/cm ² or less, and even more preferably 5 mg/cm ² or more and 30 mg/cm ² or ^less .

The positive electrode can be manufactured, for example, by a method including pressure-molding 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 can be subjected to a roll press and roll-pressed onto the current collector to pressure-molde the composite particles onto the current collector to form a positive electrode mixture layer. The temperature and pressure conditions during pressing can be set appropriately according to the desired positive electrode density.

<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 the electrochemical element include a lithium ion secondary battery, an electric double layer capacitor, and a lithium ion capacitor, and among these, a lithium ion secondary battery is preferred.

Below, we will explain a lithium-ion secondary battery as an example of an electrochemical element. A lithium-ion secondary battery comprises the above-mentioned positive electrode, negative electrode, and electrolyte. Furthermore, a lithium-ion secondary battery typically further comprises a separator.

The negative electrode is not particularly limited, and any known negative electrode can be used. Typically, the negative electrode comprises a negative electrode current collector and a negative electrode composite layer containing a negative electrode active material.

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. Examples of lithium salts include _LiPF6 , LiAsF6, _LiBF4 , _LiSbF6 , _{LiAlCl4 , LiClO4} , _CF3SO3Li , _C4F9SO3Li , CF3COOLi, _{( CF3CO ) 2NLi} , ( _CF3SO2 ) _2NLi , ( _{C2F5SO2 ) NLi} , etc. Among them _{, LiPF6} , _LiClO4 , and _CF3SO3Li are preferred because _they are easily _soluble in solvents and exhibit a _high degree of dissociation. The electrolyte may be used alone or in combination of two or more.

The organic solvent for the electrolyte can be a solvent capable of dissolving the supporting electrolyte. 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 gamma-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. The concentration of the electrolyte in the electrolyte may be adjusted as appropriate. The electrolyte may also contain optional additives.

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

A lithium-ion secondary battery can be manufactured, for example, by stacking a positive electrode and a negative electrode with a separator between them, rolling or folding the resulting assembly as needed according to the battery shape, placing it in a battery container, injecting electrolyte into the battery container, and sealing it. To prevent internal pressure increases and overcharging and overdischarging, etc., a fuse, an overcurrent prevention element such as a PTC element, expanded metal, lead plates, etc. may be provided as needed. The shape of the secondary battery may be any type, such as a coin type, button type, sheet type, cylindrical type, square type, or flat type.

The present invention will now be described in more detail with reference to the following examples. However, the present invention is not limited to the examples shown below, and can be modified and implemented as desired without departing from the scope of the claims of the present invention and their equivalents.

In the following explanation, "%" and "parts" used to represent quantities are based on 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.

<Measurement and evaluation methods>
<Bulk Density, Compressibility C, and Ratio ρ ₀ (1)/ρ ₀ (0) of Positive Electrode Active Material and Composite Particles>
Measurements were carried out using a powder tester (manufactured by Hosokawa Micron Corporation, product name "PT-S"). The weighed mass of the positive electrode active material was placed in the device, and the loose bulk density (bulk density at 0 tapping times) ρ ₀ (0) (g/cm ³ ) was measured. The weighed mass of the composite particles was placed in the device, and the loose bulk density (bulk density at 0 tapping times) ρ ₀ (1) (g/cm ³ ) and the packed bulk density at 180 tapping times ρ ₁₈₀ (1) (g/cm ³ ) were measured. The tapping conditions were a stroke of 18 mm, 1 tap/1 second.

From the obtained ρ ₁₈₀ (1) and ρ ₀ (1), the compressibility C was calculated according to the following formula (1).
C=(ρ ₁₈₀ (1)-ρ ₀ (1))/ρ ₁₈₀ (1)×100 (1)
In addition, the ratio ρ ₀ (1)/ρ ₀ (0) was calculated.

<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").

<D10, D50, D90, and volume ratio of particles with a particle size of 10 μm or less based on the volume of composite particles>
The integrated particle size distribution (volume basis) of the composite particles was obtained using a particle size distribution analyzer (Microtrac MT3300EX II; manufactured by Microtrac Bell Co., Ltd.) based on the laser scattering/diffraction method, with the dispersion air pressure during measurement set to 0.1 MPa. The particle sizes at which the cumulative frequency, calculated from the smallest diameter side, reached 10%, 50%, and 90% were used as the D10 particle size, D50 particle size, and D90 particle size, respectively, on a volume basis. Furthermore, in the particle size distribution, the volume-based occupancy frequency of particles 10 μm or less was calculated and used as the proportion of particles with a particle size of 10 μm or less.

<Volume-based median diameter D50 of positive electrode active material and conductive material>
Using a particle size distribution analyzer based on the laser scattering/diffraction method (Microtrac MT3300EX II; manufactured by Microtrac Bell Co., Ltd.), the integrated particle size distribution (volume basis) of the particles was obtained in a dry state with a dispersion air pressure of 0.1 MPa during measurement. The particle size at which the cumulative frequency, calculated from the smallest diameter side, reached 50% was adopted as the median diameter D50 on a volume basis.

<Formation and Evaluation of Positive Electrode Composite Layer>
The composite particles produced in the examples and comparative examples were supplied to the press rolls of a roll press machine (Hirano Giken Kogyo Co., Ltd.'s "Oshikuri Rough Surface Heat Roll") using a quantitative 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-matted polyester film (manufactured by Unitika Ltd., PTHA-25, thickness 25 μm, dynamic friction coefficient μ _k based on JIS K 7125: 0.28) simulating a current collector was inserted between the press rolls, and the composite particles supplied from the quantitative feeder were attached to the sand-matted surface of the polyester film. Pressurization was performed using the press rolls to form a positive electrode composite layer on the polyester film. The molding speed (film conveyance speed) was as follows:

(Mass per 1 ^cm2 of positive electrode mixture layer)
The positive electrode mixture layer was formed at a forming speed of 1 m/min. The mass per cm ² of the positive electrode mixture layer on the polyester film was measured.

(Maximum molding speed)
In the molding of 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: The number of chipped portions of the positive electrode mixture layer was 0 or 1 within a substantially square area measuring 3 cm on each side of the positive electrode mixture layer.
Poor: The positive electrode mixture layer had two or more chipped portions in a substantially square area measuring 3 cm on each side.
The maximum forming speed was the highest forming speed at which the degree of peeling of the positive electrode composite layer was evaluated as "good." When the degree of peeling was evaluated as "poor" at a forming speed of 1 m/min, the maximum forming speed was set to 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.

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

<Production Example 1. Production of Binder Resin A1>
A reactor equipped with a stirrer and thoroughly purged with nitrogen was charged with 270 parts of dehydrated cyclohexane and 0.53 parts of ethylene glycol dibutyl ether, and further added with 0.47 parts of n-butyllithium (15% cyclohexane solution). 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. Measurement of the reaction solution by gas chromatography revealed that the polymerization conversion 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 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 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.

<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.

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, capacity 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 be passed through. Using the composite particle production apparatus I 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.

(i) As a preliminary stirring operation, 97 parts by mass ( _{10,000 g} ) of NMC631 ( _{LiNi0.6Mn0.3Co0.1O2} , volume-based median diameter D50: 4 μm) serving as a positive electrode active material for lithium ion _batteries was added to the granulation tank. While passing a seal gas at room temperature (25°C) through the granulation tank at a rate of 170 L/min, the main stirring blade and the auxiliary stirring blade 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.

Next, (ii) as a composite particle formation operation, 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 positive electrode active material over 90 minutes while stirring the positive electrode 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 positive electrode 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 was found to be 40°C.

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

Example 2
The same procedure as in Example 1 was carried out except for the following points to obtain composite particles, which were then evaluated by the above-mentioned methods.
The time for spraying the liquid composition onto the positive electrode active material was 21 minutes.
The temperature of the powder bed was set to 37.0° 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).
Fine powder classification was not performed. Therefore, the composite particles below the sieve obtained by coarse powder classification were used for evaluation.

Example 3
The same procedure as in Example 1 was carried out except for the following points to obtain composite particles, which were then evaluated by the above-mentioned methods.
The peripheral speed of the main stirring blade was set to 1.3 m/s.
The time for spraying the liquid composition onto the positive electrode active material was set to 17.5 minutes.
The temperature of the powder layer was set to 35.0°C.
Fine powder classification was not performed. Therefore, the composite particles below the sieve obtained by coarse powder classification were used for evaluation.

<Comparative Example 1>
The same procedure as in Example 1 was carried out except for the following points to obtain composite particles, which were then evaluated by the above-mentioned methods.
Instead of using a vibrating sieve with 45 μm openings to classify the fine powder, an air classifier was used.

<Comparative Example 2>
The same procedure as in Example 1 was carried out except for the following points to obtain composite particles, which were then evaluated by the above-mentioned methods.
- The secondary mixing blade was not rotated.
The time for spraying the liquid composition onto the positive electrode active material was 42 minutes.
The temperature of the powder layer was set to 65.0°C.
Fine powder classification was not performed. Therefore, the composite particles below the sieve obtained by coarse powder classification were used for evaluation.

<Comparative Example 3>
The same procedure as in Example 1 was carried out except for the following points to obtain composite particles, which were then evaluated by the above-mentioned methods.
- The secondary mixing blade was not rotated.
The time for spraying the liquid composition onto the positive electrode active material was 42 minutes.
The temperature of the powder bed was set to 72°C.
Fine powder classification was not performed. Therefore, the composite particles below the sieve obtained by coarse powder classification were used for evaluation.

<Comparative Example 4>
The same procedure as in Example 1 was carried out except for the following points to obtain composite particles, which were then evaluated by the above-mentioned methods.
The time for spraying the liquid composition onto the positive electrode active material was 42 minutes.
The temperature of the powder bed was set to 72°C.
Fine powder classification was not performed. Therefore, the composite particles below the sieve obtained by coarse powder classification were used for evaluation.

Comparative Example 5
The same procedure as in Example 1 was carried out except for the following points to obtain composite particles, which were then evaluated by the above-mentioned methods.
The time for spraying the liquid composition onto the positive electrode active material was set to 69 minutes.
The temperature of the powder layer was set to 32.0°C.
Fine powder classification was not performed. Therefore, the composite particles below the sieve obtained by coarse powder classification were used for evaluation.

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

These results show that composite particles with a compression degree C of 17.0% or less have good moldability.

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 Rotating shaft A ₃₀₀ Rotating shaft

Claims (9)

A composite particle 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) represents the bulk density (g/cm ³ ) of the composite particles when tapped 0 times;
ρ ₁₈₀ (1) represents the packed bulk density (g/cm ³ ) of the composite particles after 180 tappings. 2. The composite particle for electrochemical element positive electrode according to claim 1, wherein a ratio ρ ₀ (1)/ρ ₀ (0) of a bulk density ρ ₀ (1) of the composite particle at 0 tapping times to a bulk density ρ ₀ (0) of the positive electrode active material at 0 tapping times is 1.100 or more. Composite particles for electrochemical element positive electrodes according to claim 1, having an angle of repose of 32° or less. Composite particles for electrochemical element positive electrodes according to claim 1, in which particles with a particle diameter of 10 μm or less account for 2.5% by volume or less. Composite particles for electrochemical element positive electrodes according to claim 1, wherein the ratio D90/D10 of particle diameter D90 to particle diameter D10 is less than 4.4. A method for producing the composite particles for an electrochemical element positive electrode according to any one of claims 1 to 5, comprising:
A method for producing composite particles for a positive electrode of an electrochemical element, comprising stirring and granulating a positive electrode active material, a binder resin, and a solvent. a step (i) of stirring the positive electrode active material in a granulation tank to obtain a stirred state;
(ii) a step of spraying a liquid composition containing the binder resin and the solvent onto the positive electrode active material in a stirred state;
The method for producing composite particles for a positive electrode of an electrochemical element according to claim 6, comprising: a current collector; and a positive electrode mixture layer formed on the current collector,
A positive electrode for an electrochemical element, wherein the positive electrode mixture layer comprises the composite particle for an electrochemical element positive electrode according to any one of claims 1 to 5. An electrochemical element comprising the positive electrode for an electrochemical element according to claim 8.