Composite particle for electrochemical element positive electrode, method for producing same, positive electrode for electrochemical element, method for producing same, and electrochemical element

Abstract

This composite particle for an electrochemical element positive electrode contains a positive electrode active material, a carbon-based conductive material, and a binder resin, wherein the total of a moisture content M (110°C) measured according to the Karl Fischer method at a heating temperature of 110°C, a moisture content M (170°C) measured according to the Karl Fischer method at a heating temperature of 170°C after the measurement of the moisture content M (110°C), and a moisture content M (300°C) measured according to the Karl Fischer method at a heating temperature of 300°C after the measurement of the moisture content M (170°C) (M (110°C) + M (170°C) + M (300°C)) is 20-400 ppm.

Description

Composite particles for electrochemical element positive electrodes and manufacturing method thereof, electrochemical element positive electrodes and manufacturing method thereof, and electrochemical element

[0001] The present invention relates to composite particles for a positive electrode of an electrochemical device and a method for producing the same, a positive electrode for an electrochemical device and a method for producing the same, 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 includes a current collector and a positive electrode composite layer provided on the current collector (see Patent Documents 1 and 2).

[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 pressurized to form a positive electrode mixture layer.

[0005] Japanese Patent Application Laid-Open No. 4-56064 (corresponding publication: European Patent Application Publication No. 0462575) Japanese Patent Application Laid-Open No. 10-40900

[0006] However, conventional composite particles have poor moldability when forming a positive electrode composite layer by a dry process, which can make it difficult to form a uniform positive electrode composite layer. Furthermore, electrochemical devices manufactured using conventional composite particles tend to have poor cycle characteristics and exhibit a significant decrease in capacity with repeated charge and discharge.

[0007] The present invention has been made in view of the above-mentioned problems, and aims to provide composite particles for electrochemical element positive electrodes and a method for producing the same, which have excellent moldability when forming a positive electrode composite layer by a dry process and enable the production of an electrochemical element with excellent cycle characteristics; a positive electrode for electrochemical elements including the composite particles for electrochemical element positive electrodes and a method for producing the same; and an electrochemical element including the positive electrode for electrochemical elements.

[0008] The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, the present inventors have found that composite particles having a moisture content within a specific range as measured by the Karl Fischer method can solve the above-mentioned problems, and have completed the present invention. That is, the present invention includes the following.

[0009] <1> Composite particles for electrochemical element positive electrodes, comprising a positive electrode active material, a carbon-based conductive material, and a binder resin, in which the sum (M(110°C) + M(170°C) + M(300°C)) of a water content M(110°C) measured according to the Karl Fischer method at a heating temperature of 110°C, a water content M(170°C) measured according to the Karl Fischer method at a heating temperature of 170°C after measurement at the water content M(110°C), and a water content M(300°C) measured according to the Karl Fischer method at a heating temperature of 300°C after measurement at the water content M(170°C) is 20 ppm or more and 400 ppm or less. <2> The composite particle for an electrochemical element positive electrode according to <1>, wherein the sum (M(110°C) + M(170°C)) of the moisture content M(110°C) and the moisture content M(170°C) of the composite particle for an electrochemical element positive electrode is 10 ppm or more and 250 ppm or less. <3> The composite particle for an electrochemical element positive electrode according to <1> or <2>, wherein the moisture content M(300°C) of the composite particle for an electrochemical element positive electrode is 10 ppm or more and 150 ppm or less. <4> The composite particle for an electrochemical element positive electrode according to any one of <1> to <3>, wherein the composite particle for an electrochemical element positive electrode has a D50 particle size of 30 μm to 150 μm. <5> The composite particle for an electrochemical element positive electrode according to any one of <1> to <4>, wherein the composite particle is for forming a dry positive electrode. <6> A method for producing composite particles for electrochemical element positive electrodes according to any one of <1> to <5>, the method comprising stirring and granulating a cathode active material, a carbon-based conductive material, a binder resin, and an organic solvent. <7> The method for producing composite particles for electrochemical element positive electrodes according to <6>, the method comprising: a step (i) of stirring the cathode active material to obtain a stirred state; and a step (ii) of supplying a liquid composition containing the carbon-based conductive material, the binder resin, and the organic solvent to the stirred cathode active material. <8> A positive electrode for electrochemical elements, comprising a current collector and a positive electrode mixture layer formed on the current collector, the positive electrode mixture layer containing the composite particles for electrochemical element positive electrodes according to any one of <1> to <5>. <9> A method for producing a positive electrode for electrochemical elements, the method comprising: a step of pressurizing the composite particles for electrochemical element positive electrodes according to any one of <1> to <5> on the current collector.<10> An electrochemical element comprising the positive electrode for an electrochemical element according to <8>.

[0010] According to the present invention, it is possible to provide composite particles for electrochemical element positive electrodes and a method for producing the same, which are excellent in formability when forming a positive electrode composite layer by a dry process and enable the production of electrochemical elements with excellent cycle characteristics; a positive electrode for electrochemical elements including the composite particles for electrochemical element positive electrodes and a method for producing the same; and an electrochemical element including the positive electrode for electrochemical elements.

[0011] 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.

[0012] The present invention will be described in detail below with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples described below, and can be implemented with any modifications within the scope of the claims and their equivalents.

[0013] In the following description, "ppm" is by weight unless otherwise specified.

[0014] 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.

[0015] 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.

[0016] 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°.

[0017] In the following description, unless otherwise specified, the term "(meth)acrylic acid" includes acrylic acid, methacrylic acid, and mixtures thereof.

[0018] In the following description, the term "long" for a certain member (e.g., a film or layer) means that the length is 5 times or more, preferably 10 times or more, the width, specifically a length that can be wound into a roll for storage or transportation. There is no particular upper limit to the length, and it can be, for example, 100,000 times or less the width.

[0019] <Moisture Content of Composite Particles> Composite particles for electrochemical element positive electrodes according to one embodiment of the present invention (hereinafter, may be abbreviated as "composite particles") are particles containing a positive electrode active material, a carbon-based conductive material, and a binder resin. Typically, one or more particles of a positive electrode active material and one or more particles of a carbon-based conductive material are bound by a binder resin to form a single composite particle. This composite particle can be used as a powder material for forming a positive electrode for an electrochemical element (hereinafter, may be abbreviated as "positive electrode").

[0020] For this composite particle, the sum "M(110°C) + M(170°C) + M(300°C)" of the moisture content M(110°C) measured according to the Karl Fischer method at a heating temperature of 110°C, the moisture content M(170°C) measured according to the Karl Fischer method at a heating temperature of 170°C after measurement at the moisture content M(110°C), and the moisture content M(300°C) measured according to the Karl Fischer method at a heating temperature of 300°C after measurement at the moisture content M(170°C) falls within a specific range.

[0021] Specifically, the range of the total water content "M(110°C) + M(170°C) + M(300°C)" is usually 20 ppm or more, preferably 50 ppm or more, more preferably 100 ppm or more, and usually 400 ppm or less, preferably 300 ppm or less, more preferably 270 ppm or less, even more preferably 259 ppm or less, even more preferably 250 ppm or less, and even more preferably 195 ppm or less. Therefore, the range of the total moisture content "M(110°C) + M(170°C) + M(300°C)" is, for example, 20 ppm or more and 400 ppm or less, 20 ppm or more and 300 ppm or less, 20 ppm or more and 270 ppm or less, 20 ppm or more and 259 ppm or less, 20 ppm or more and 250 ppm or less, 20 ppm or more and 195 ppm or less, 50 ppm or more and 400 ppm or less, 50 ppm or more and 300 ppm or less, 50 ppm or more and ... The moisture content may be in the range of 50 ppm to 270 ppm, 50 ppm to 259 ppm, 50 ppm to 250 ppm, 50 ppm to 195 ppm, 100 ppm to 400 ppm, 100 ppm to 300 ppm, 100 ppm to 270 ppm, 100 ppm to 259 ppm, 100 ppm to 250 ppm, or 100 ppm to 195 ppm. Composite particles having a moisture content within such a range have excellent moldability when forming a positive electrode mixture layer using a dry process. Therefore, a highly uniform positive electrode mixture layer can be formed. Furthermore, a positive electrode including a positive electrode mixture layer containing this composite particle can produce an electrochemical element with excellent cycle characteristics. Furthermore, the composite particles typically have low powder resistance, thereby suppressing the internal resistance of the electrochemical element.

[0022] The sum of the moisture content M(110°C) and the moisture content M(170°C) of the composite particles, "M(110°C) + M(170°C)", is preferably 10 ppm or more, more preferably 30 ppm or more, even more preferably 60 ppm or more, even more preferably 129 ppm or more, even more preferably 130 ppm or more, and is preferably 250 ppm or less, more preferably 170 ppm or less, even more preferably 160 ppm or less, even more preferably 140 ppm or less. Therefore, the range of the total moisture content "M(110°C) + M(170°C)" is, for example, 10 ppm to 250 ppm, 10 ppm to 170 ppm, 10 ppm to 160 ppm, 10 ppm to 140 ppm, 30 ppm to 250 ppm, 30 ppm to 170 ppm, 30 ppm to 160 ppm, 30 ppm to 140 ppm, 60 ppm to 250 ppm, 60 ppm to 17 ... The moisture content may be in the range of 0 ppm or less, 60 ppm to 160 ppm, 60 ppm to 140 ppm, 129 ppm to 250 ppm, 129 ppm to 170 ppm, 129 ppm to 160 ppm, 129 ppm to 140 ppm, 130 ppm to 250 ppm, 130 ppm to 170 ppm, 130 ppm to 160 ppm, or 130 ppm to 140 ppm. When the total moisture content "M(110°C) + M(170°C)" is within the above range, the moldability and cycle characteristics can be effectively improved, and further, usually, the powder resistance can be effectively reduced.

[0023] The moisture content M(300°C) of the composite particles is preferably 10 ppm or more, more preferably 20 ppm or more, even more preferably 40 ppm or more, and is preferably 150 ppm or less, more preferably 140 ppm or less, even more preferably 130 ppm or less, even more preferably 110 ppm or less, even more preferably 100 ppm or less, and even more preferably 65 ppm or less. Therefore, the range of the moisture content M(300°C) is, for example, 10 ppm or more to 150 ppm or less, 10 ppm or more to 140 ppm or less, 10 ppm or more to 130 ppm or less, 10 ppm or more to 110 ppm or less, 10 ppm or more to 100 ppm or less, 10 ppm or more to 65 ppm or less, 20 ppm or more to 150 ppm or less, 20 ppm or more to 140 ppm or less, 20 ppm or more to 130 ... The moisture content M(300°C) may be in the range of 20 ppm to 110 ppm, 20 ppm to 100 ppm, 20 ppm to 65 ppm, 40 ppm to 150 ppm, 40 ppm to 140 ppm, 40 ppm to 130 ppm, 40 ppm to 110 ppm, 40 ppm to 100 ppm, or 40 ppm to 65 ppm. When the moisture content M(300°C) is in the above range, the moldability and cycle characteristics can be effectively improved, and further, usually, the powder resistance can be effectively reduced.

[0024] The present inventors speculate that the mechanism by which the above-described excellent effects are obtained is as follows: However, the technical scope of the present invention is not limited to the mechanism below.

[0025] Of the moisture contents of the composite particles measured by the Karl Fischer method, the moisture content M(110°C) corresponds to the amount of moisture that can be vaporized in a temperature range from room temperature to 110°C. Furthermore, the moisture content M(170°C) corresponds to the amount of moisture that can be vaporized in a temperature range from 110°C to 170°C. The sum of the moisture content M(110°C) and the moisture content M(170°C), "M(110°C) + M(170°C)," corresponds to the amount of adsorbed water in the composite particles. This adsorbed water is water that exists in a free state without being bound to the positive electrode active material, the carbon-based conductive material, and the binder resin, and therefore can be vaporized at a relatively low temperature.

[0026] On the other hand, among the moisture contents of the composite particles measured by the Karl Fischer method, the moisture content M(300°C) corresponds to the amount of moisture that can be vaporized in a temperature range from 170°C to 300°C. This moisture content M(300°C) corresponds to the amount of bound water in the composite particles. This bound water is water that exists in a state bound to the positive electrode active material, the carbon-based conductive material, and the binder resin, and examples thereof include water of crystallization and water hydrogen-bonded to polymer molecules. This bound water can be vaporized at relatively high temperatures.

[0027] Therefore, the requirement regarding the moisture content of the composite particles described above indicates that the moisture content of the composite particles, including adsorbed water and bound water, is within a specific range that is extremely low. Such a low moisture content configuration can suppress the decrease in fluidity due to interparticle adhesive forces associated with water molecules, allowing for the formation of a uniform layer through dry layer formation. Furthermore, a layer containing such composite particles can be smoothly compressed by pressure due to the high fluidity of the composite particles. Therefore, when a positive electrode composite layer is formed using such composite particles through a dry process, the positive electrode composite layer can be formed uniformly, resulting in excellent moldability. Furthermore, such a low moisture content configuration typically allows for improved adhesion of the composite particles to the current collector.

[0028] When the composite particles have high fluidity as described above, the uneven distribution of the composite particles in the positive electrode mixture layer can be suppressed. For example, the flatness of the surface of the positive electrode mixture layer can be improved, and the formation of defects (regions where composite particles are locally absent) can be suppressed. Furthermore, for example, the interparticle adhesive force associated with water molecules between the composite particles can be suppressed to suppress aggregation, thereby making the shape of the composite particles uniform and aligning the particle size to a similar extent. Therefore, the occurrence of locally low mechanical strength areas in the electrode mixture layer can be suppressed.

[0029] Furthermore, when the composite particles have high fluidity as described above, residual stress in the positive electrode mixture layer can be suppressed. Typically, shear stress and compressive stress can be applied to the positive electrode mixture layer during pressure application to form the positive electrode mixture layer. Therefore, if the composite particles have low fluidity, localized areas of large residual stress can be formed in the positive electrode mixture layer. However, the composite particles according to this embodiment can have high fluidity, thereby suppressing such localized residual stress.

[0030] Generally, when the positive electrode active material repeatedly expands and contracts during charge and discharge, stress due to the expansion and contraction can occur in the positive electrode mixture layer. If there are areas in the positive electrode mixture layer where the mechanical strength is locally low or where large residual stress is locally present, the positive electrode mixture layer may peel off from the current collector from those areas as starting points, or the positive electrode mixture layer itself may be destroyed, resulting in disconnection of the conductive path. In contrast, the composite particles according to this embodiment can suppress the occurrence of such starting points, thereby reducing disconnection of the conductive path due to charge and discharge, thereby achieving high cycle characteristics.

[0031] Furthermore, moisture contained in composite particles usually causes electrical resistance. The composite particles according to this embodiment contain little moisture, which causes resistance, so the resistance in the positive electrode mixture layer can be suppressed, which also improves cycle characteristics. Furthermore, because the resistance due to moisture is thus small, the composite particles usually achieve low powder resistance.

[0032] The present inventors believe that the excellent effects of this embodiment are achieved by the extremely low moisture content of the composite particles. However, composite particles with a moisture content below the lower limit of the above-mentioned range may have poor moldability in terms of adhesion to the substrate, such as a current collector.

[0033] The moisture content M(110°C), moisture content M(170°C), and moisture content M(300°C) of the composite particles can be measured by the Karl Fischer method using a coulometric moisture meter in accordance with "JIS K-0068 (2001) Moisture Evaporation Method." Specifically, the moisture content M(110°C) can be measured under measurement conditions of a heating temperature of 110°C and an end condition of 0.01 μg / s, followed by measurement of the moisture content M(170°C) under measurement conditions of a heating temperature of 170°C and an end condition of 0.1 μg / s, and then measurement of the moisture content M(300°C) under measurement conditions of a heating temperature of 300°C and an end condition of 0.1 μg / s. Specific measurement methods may be performed as described in the Examples below (Method for measuring the moisture content of composite particles by the Karl Fischer method). By this method, the moisture content M(110°C), the moisture content M(170°C), and the moisture content M(300°C) can be measured using the weight of the composite particles before the moisture content M(110°C) is measured as the standard (1,000,000 ppm).

[0034] One method for obtaining a moisture content that satisfies the above-mentioned requirements is to dry the raw materials for the composite particles, which are the positive electrode active material, carbon-based conductive material, and binder resin. In particular, while the bound water contained in the positive electrode active material needs to be removed by drying at high temperatures, such high temperatures may oxidize the binder resin, so it is preferable to dry the raw materials separately. Furthermore, since the composite particles may absorb moisture from the atmosphere during the granulation process, it is preferable to further dry the composite particles after production, even if the raw materials are dried. Generally, it is difficult to remove moisture at a high level as described above during drying in conventional general composite particle production processes at temperatures below 50°C. Therefore, it is preferable to adopt harsh drying conditions within the range that allows the desired composite particles to be obtained. Furthermore, from the perspective of suppressing moisture absorption during the composite particle production process, as described above, it is preferable to dry the inside of the granulation tank and to thoroughly dry the seal gas supplied to the granulation tank.

[0035] <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 metal include Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Mo. In this case, the transition metal may be one type or two or more types.

[0036] Examples of transition metal oxides include MnO and MnO ２ , V ２ O ５ , V ６ O １３ , TiO ２ , Cu ２ V ２ O ３ , amorphous V ２ O-P ２ O ５ , MoO ３ Among them, MnO, V are preferred in terms of cycle stability and capacity. ２ O ５ , V ６ O １３ and TiO ２ is preferred.

[0037] Examples of transition metal sulfides include TiS ２ , TiS ３ , amorphous MoS ２ , FeS, etc.

[0038] 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 (Li(CoMnNi)O ２ ), lithium composite oxide of Ni—Mn—Al, lithium composite oxide of Ni—Co—Al, etc. Examples of lithium-containing composite metal oxides having a spinel structure include lithium manganate (LiMn ２ O ４ ), Li[Mn ３／２ M １ １／２ ]O ４ (Here, M １ represents a transition metal other than Mn, such as Cr, Fe, Co, Ni, or Cu. Examples of lithium-containing composite metal oxides having an olivine structure include Li Ｘ M ２ P.O. ４ (In the formula, M ２ represents at least one element selected from the group consisting of Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B, and Mo, and X represents a number satisfying 0≦X≦2. One type of positive electrode active material may be used alone, or two or more types may be used in combination.

[0039] The positive electrode active material usually has a particle shape. The D50 particle size of the positive electrode active material is preferably 0.03 μm or more, more preferably 0.1 μm or more, and even more preferably 1.0 μm or more, and is preferably 90 μm or less, more preferably 50 μm or less, and even more preferably 20 μm or less. When the D50 particle size of the positive electrode active material is within the above range, the moldability and cycle characteristics can be effectively improved, and further, the powder resistance can usually be effectively reduced.

[0040] The D50 particle size 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 becomes 50% can be determined as the D50 particle size of the positive electrode active material.

[0041] The range of the content of the positive electrode active material is preferably 90 wt % or more, more preferably 93 wt % or more, and even more preferably 95 wt % or more, and is preferably 99 wt % or less, more preferably 98 wt % or less, and even more preferably 97.5 wt % or less, relative to 100 wt % of the composite particles. When the content of the positive electrode active material is within this range, it is possible to effectively improve moldability and cycle characteristics, and furthermore, it is usually possible to effectively reduce powder resistance.

[0042] <Carbon-based conductive material> The carbon-based conductive material is a carbon material that forms a conductive path between the positive electrode active materials. Examples of the carbon-based conductive material include carbon black (e.g., acetylene black, Ketjen Black (registered trademark), furnace black, etc.); single-walled or multi-walled carbon nanotubes (multi-walled carbon nanotubes include cup-stacked types); carbon nanohorns; vapor-grown carbon fibers; milled carbon fibers obtained by calcining and then crushing polymer fibers; single-layered or multi-layered graphene; and carbon nonwoven fabric sheets obtained by calcining nonwoven fabrics made of polymer fibers. Among these, carbon black is preferred. One type of carbon-based conductive material may be used alone, or two or more types may be used in combination.

[0043] The shape of the carbonaceous conductive material is not particularly limited, and may be, for example, particulate, fibrous, or foil.

[0044] The range of the BET specific surface area of ​​the carbon-based conductive material is preferably 30 m ２ / g or more, more preferably 40m ２ / g or more, more preferably 50m ２ / g or more, preferably 600m ２ / g or less, more preferably 300m ２ / g or less, more preferably 200m ２ / g or less. The BET specific surface area can be measured by the BET method. When the BET specific surface area of ​​the carbon-based conductive material is in the above range, the moldability and cycle characteristics can be effectively improved, and further, the powder resistance can usually be effectively reduced.

[0045] The bulk density of the carbon-based conductive material is preferably in the range of 0.01 g / cm ３More preferably, 0.02 g / cm ３ More preferably, 0.03 g / cm ３ or more, preferably 0.40 g / cm ３ or less, more preferably 0.30 g / cm ３ More preferably, 0.20 g / cm ３ The bulk density of a carbonaceous conductive material is the value obtained by dividing the mass of the powder occupying a space as an aggregate of the carbonaceous conductive material by the volume of the space occupied by the powder, and can be measured based on the constant volume measurement method described in JIS R 1628-1997. When the bulk density of the carbonaceous conductive material is within the above range, it is possible to effectively improve the moldability and cycle characteristics, and furthermore, it is usually possible to effectively reduce the powder resistance.

[0046] The range of the content of the carbonaceous conductive material is preferably 0.5 wt % or more, more preferably 1.0 wt % or more, even more preferably 1.5 wt % or more, and is preferably 5 wt % or less, more preferably 4 wt % or less, even more preferably 3 wt % or less, relative to 100 wt % of the composite particles. When the content of the carbonaceous conductive material is within the above range, it is possible to effectively improve the moldability and cycle characteristics, and usually also to effectively reduce the powder resistance.

[0047] <Binder Resin> The binder resin is a resin that binds the positive electrode active material and the carbon-based conductive material. A polymer is usually used as the binder resin. Examples of polymers that can be used as the binder resin include conjugated diene polymers, acrylic polymers, aromatic vinyl block polymers, fluorine-based polymers, cellulose polymers, and cyclic olefin polymers.

[0048] The conjugated diene polymer refers to a polymer containing conjugated diene monomer units. Examples of conjugated diene monomers include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene, 2-chloro-1,3-butadiene (chloroprene), and piperylene. Specific examples of conjugated diene polymers include copolymers containing aromatic vinyl monomer units and aliphatic conjugated diene monomer units, such as styrene-butadiene copolymer (SBR); butadiene rubber (BR); acrylic rubber (NBR) (a copolymer containing acrylonitrile units and butadiene units); and hydrogenated products thereof.

[0049] Examples of acrylic polymers include polymers containing crosslinkable monomer units, (meth)acrylic acid ester monomer units, and acidic group-containing monomer units. The proportion of (meth)acrylic acid ester monomer units in the acrylic polymer is preferably 50% by weight or more, more preferably 55% by weight or more, and even more preferably 58% by weight or more, and is preferably 98% by weight or less, more preferably 97% by weight or less, and even more preferably 96% by weight or less.

[0050] 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.

[0051] 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).

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] Among the above-mentioned polymers, polymers with low polarity are preferred from the viewpoint of suppressing water adsorption to the polymer and reducing the water content, and for example, conjugated diene polymers, aromatic vinyl block polymers, and cyclic olefin polymers are preferred. Furthermore, copolymers containing aromatic vinyl monomer units and conjugated diene monomer units, and hydrogenated products thereof, are more preferred; block copolymers containing aromatic vinyl monomer blocks and conjugated diene monomer blocks, and hydrogenated products thereof are even 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.

[0059] The aromatic vinyl monomer unit represents a structural unit having a structure formed by polymerizing an aromatic vinyl monomer. The type of aromatic vinyl monomer unit may be one type or two or more types. The content of the aromatic vinyl monomer unit is preferably 5% by weight or more, more preferably 10% by weight or more, and even more preferably 20% by weight or more, relative to 100% by weight of the total of all structural units contained in the copolymer, and is preferably 50% by weight or less, more preferably 40% by weight or less, and even more preferably 30% by weight or less.

[0060] The conjugated diene monomer unit represents a structural unit having a structure formed by polymerizing a conjugated diene monomer. The type of conjugated diene monomer unit may be one type or two or more types. The content of the conjugated diene monomer unit is preferably 50% by weight or more, more preferably 60% by weight or more, and even more preferably 70% by weight or more, relative to 100% by weight of the total of all structural units contained in the copolymer, and is preferably 95% by weight or less, more preferably 90% by weight or less, and even more preferably 80% by weight or less.

[0061] The conjugated diene monomer unit may generally include a direct addition unit and a conjugated addition unit. The direct addition unit refers to a structural unit having a structure formed by a direct addition reaction occurring at the carbon-carbon double bond of a conjugated diene monomer, such as a structural unit derived from 1,2-addition polymerization of butadiene, a structural unit derived from 1,2-addition polymerization of isoprene, or a structural unit derived from 3,4-addition polymerization of isoprene. The conjugated addition unit refers to a structural unit having a structure formed by a carbon-carbon double bond of a conjugated diene monomer moving due to conjugation, resulting in an addition reaction occurring at carbon atoms at both ends of the conjugated system, such as a structural unit derived from 1,4-addition polymerization of butadiene or a structural unit derived from 1,4-addition polymerization of isoprene.

[0062] In the above-mentioned polymer, the proportion of directly added units relative to 100% by weight of conjugated diene monomer units is preferably 30% by weight or more, more preferably 40% by weight or more, even more preferably 50% by weight or more, and is preferably 80% by weight or less, more preferably 70% by weight or less, even more preferably 60% by weight or less. Furthermore, in the case of a hydrogenated polymer, when the polymer before hydrogenation contains conjugated diene monomer units, it is preferable that the proportion of directly added units in the polymer before hydrogenation is in the above-mentioned range.

[0063] 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.

[0064] The hydrogenation rate of the hydrogenated copolymer is not particularly limited, but is preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more. １ It can be measured by H-NMR.

[0065] The binder resin may be used alone or in combination of two or more.

[0066] The range of the binder resin content is preferably 0.01 wt % or more, more preferably 0.1 wt % or more, and even more preferably 0.5 wt % or more, and is preferably 5 wt % or less, more preferably 4 wt % or less, and even more preferably 3 wt % or less, relative to 100 wt % of the composite particles. When the binder resin content is within the above range, it is possible to effectively improve moldability and cycle characteristics, and usually also to effectively reduce powder resistance.

[0067] <Optional Components> The composite particles according to this embodiment may further contain optional components in combination with the above-described positive electrode active material, carbonaceous conductive material, and binder resin. Examples of the optional components include optional additives such as antioxidants, such as phenolic antioxidants; reinforcing materials; leveling agents; viscosity modifiers; and electrolyte additives. One type of optional additive may be used alone, or two or more types may be used in combination at any ratio.

[0068] Furthermore, the composite particles may contain an organic solvent in combination with the solid components, such as the above-mentioned positive electrode active material, carbon-based conductive material, binder, and optional additives. This organic solvent may be the organic solvent used in the composite particle manufacturing method that remains in the composite particles. The amount of organic solvent relative to 100% by weight of the composite particles is preferably 0% by weight to 5% by weight, more preferably 0% by weight to 2% by weight, even more preferably 0% by weight to 1% by weight, even more preferably 0% by weight to 0.3% by weight, even more preferably 0% by weight to 0.05% by weight, and may even be 0% by weight.

[0069] <D50 Particle Diameter of Composite Particles> The D50 particle diameter of the composite particles according to this embodiment is preferably 30 μm or more, more preferably 40 μm or more, even more preferably 60 μm or more, and preferably 150 μm or less, more preferably 120 μm or less, and even more preferably 100 μm or less. When the D50 particle diameter of the composite particles is equal to or greater than the lower limit of the above range, the flowability of the composite particles is particularly good. Furthermore, when the D50 particle diameter of the composite particles is equal to or less than the upper limit of the above range, the formation of streaks in the positive electrode mixture layer can be effectively suppressed, effectively improving the uniformity of the positive electrode mixture layer. Therefore, when the D50 particle diameter of the composite particles is within the above range, the moldability and cycle characteristics can be effectively improved, and further, the powder resistance can usually be effectively reduced.

[0070] The D50 particle size of the composite particles can be determined by measuring the particle size distribution of the composite particles using a laser diffraction particle size distribution analyzer, and determining the particle size at which the cumulative volume calculated from the smallest diameter side is 50% as the D50 particle size. The particle size distribution is preferably measured in a state where the composite particles are dispersed by an airflow using compressed air. Specific measurements may be performed using the method described in the Examples below (Method for measuring the D50 particle size of composite particles).

[0071] <Characteristics of Composite Particles> The composite particles according to this embodiment can have excellent moldability when forming a positive electrode composite layer by a dry process. Specifically, when forming a layer on a current collector by a dry process using the composite particles, the formation of unevenness and streaks can be suppressed, and the layer can be formed uniformly. Therefore, a highly uniform positive electrode composite layer can be formed.

[0072] Furthermore, since the composite particles according to this embodiment typically have high fluidity, when a layer of the composite particles is pressurized, the layer can be smoothly compressed. Therefore, when the layer of the composite particles is pressurized to form a positive electrode composite layer, uniform compression is possible, which also allows the formation of a highly uniform positive electrode composite layer.

[0073] Furthermore, since the composite particles according to this embodiment have high fluidity, the formation of a layer by powder coating or deposition of the composite particles can usually be performed at high speed. Furthermore, since smooth compression is possible as described above, the compression of the composite particle layer can be performed at high speed. Therefore, since both the formation and compression of the composite particle layer can be performed at high speed, the formation rate of the positive electrode mixture layer can be improved, and the positive electrode can be manufactured in a short time.

[0074] The composite particles according to the present embodiment can provide an electrochemical device with excellent cycle characteristics. Specifically, the decrease in capacity of the electrochemical device due to repeated charge and discharge cycles can be suppressed.

[0075] The composite particles according to this embodiment can generally have low powder resistance, and therefore a positive electrode with low resistance can be obtained, thereby suppressing the internal resistance of the electrochemical device.

[0076] Taking advantage of the above-described advantages, the composite particles according to this embodiment are preferably used as composite particles for forming a dry positive electrode. A dry positive electrode refers to a positive electrode manufactured by a dry manufacturing method. Specifically, a dry positive electrode refers to a positive electrode formed in a manner in which a liquid material is not mixed with the composite particles during the process of forming the positive electrode composite layer of the dry positive electrode. This dry positive electrode can be manufactured by the dry manufacturing method described below.

[0077] <Method for producing composite particles> The composite particles according to this embodiment can be produced by a production method including stirring and granulating a positive electrode active material, a carbon-based conductive material, a binder resin, and an organic solvent. In the stirring and granulation, the composition is stirred in a granulation tank to produce particles containing the solid content of the composition. In this case, the composition may be supplied to the granulation tank all at once, or may be continuously or intermittently added. Furthermore, if necessary, any additives may be added to the stirring and granulation in addition to the positive electrode active material, the carbon-based conductive material, the binder resin, and the organic solvent.

[0078] From the viewpoint of producing composite particles having moisture contents M(110°C), M(170°C), and M(300°C) within the above-mentioned ranges, it is preferable to dry the raw materials to be subjected to the agitation granulation, such as the positive electrode active material, carbon-based conductive material, and binder resin, before the agitation granulation. In particular, from the viewpoint of reducing the moisture content M(300°C), it is preferable to dry the positive electrode active material before the agitation granulation. It is preferable to appropriately set the drying conditions within a range that allows the moisture contents M(110°C), M(170°C), and M(300°C) to fall within the above-mentioned ranges.

[0079] Preferably, the method for producing composite particles includes: a step (i) of stirring a positive electrode active material in a granulation tank to obtain a stirred state; and a step (ii) of supplying a liquid composition containing a carbon-based conductive material, a binder resin, and an organic solvent to the stirred positive electrode active material. In this production method, a powder layer containing the positive electrode active material, the carbon-based conductive material, and the binder resin can be formed by supplying the liquid composition to the stirred positive electrode active material. The powder layer may further contain an organic solvent and any additives. Particle formation and sizing by stirring proceed within this powder layer, thereby producing the above-mentioned composite particles. Furthermore, if necessary, the method for producing composite particles may include a step (iii) of stirring the composite particles obtained in step (ii) after step (ii).

[0080] The granulation tank used for stirring granulation is usually equipped with a stirring blade for stirring. This stirring blade may be provided at the vertical lower part of the stirring tank so that it can rotate around a rotation axis parallel to the vertical direction. Hereinafter, this stirring blade may be referred to as the "main stirring blade." Furthermore, the granulation tank may, if necessary, be equipped with a secondary stirring blade provided so that it can rotate around a rotation axis different from that of the main stirring blade. This secondary stirring blade may be provided, for example, on the side of the granulation tank so as not to interfere with the main stirring blade. Below, examples of granulation tanks equipped with these stirring blades will be shown, and preferred examples of the method for producing composite particles will be specifically explained.

[0081] 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 Fig. 1, the granulation tank 10 may include a container 100 and one or both of a main stirring blade 200 and a sub-stirring blade 300.

[0082] The container 100 is configured to be able to store the positive electrode active material, the carbon-based conductive material, the binder resin, and the organic solvent, and these are stirred within the container 100. For example, the shape of the container 100 may be a cylindrical shape in which the bottom 110 and the ceiling 120 are circular, and the container 100 may be formed so that a portion of the height direction is tapered. For example, a portion 130 continuing from the ceiling 120 may be formed so that it is tapered. The container 100 is usually installed so that the bottom 110 is parallel to the horizontal direction. The container 100 may be provided with a supply port (not shown) for supplying raw materials such as the positive electrode active material into the container 100, and an outlet (not shown) for removing the composite particles from the container 100.

[0083] The main stirring blade 200 is usually attached to the bottom 110 of the container 100 with a rotation axis A ２００ From the viewpoint of uniform mixing, the rotation axis A of the main mixing 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 An example in which the main stirring impeller 200 is provided so that it can rotate around the center of gravity will be described. In addition, the main stirring impeller 200 usually has one or more main blades 210. The number and shape of the main blades 210 are not particularly limited, but in this embodiment, a main stirring impeller 200 equipped with three main blades 210 will be shown as an example.

[0084] Generally, the drive part 220 of the main stirring blade 200 is 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, carbon-based conductive material, composite particles, etc.) from penetrating into the drive part 220. The seal gas may be air or an inert gas such as nitrogen gas.

[0085] 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 is provided so as to be rotatable about the rotation axis A. ２００ and the rotation axis A of the auxiliary mixing blade 300 ３００ The angle θ between the rotation axis A of the main agitating blade 200 is usually 20° or more, preferably 30° or more, more preferably 45° or more, and is usually 90° or less. ２００ and the rotation axis A of the auxiliary mixing blade 300 ３００ The auxiliary stirring blade 300 is usually provided on the side 140 of the container 100. In this embodiment, the auxiliary stirring blade 300 is provided on the side 140 of the container 100 with a rotation axis A parallel to the horizontal direction. ３００ This description will be given by showing an example in which the auxiliary mixing blade 300 is provided so as to be able to 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. The seal gas may be air or an inert gas such as nitrogen gas.

[0086] Furthermore, as shown in FIG. 2 , the stirring tank 10 preferably includes a supply device 400 for supplying the liquid composition. For example, a drip nozzle capable of dripping the liquid composition or a spray nozzle capable of spraying the liquid composition in a mist form may be used as this supply device. When a spray nozzle is used, atomizing gas may be ejected from the periphery of the spray nozzle to pulverize and atomize the liquid composition and eject it in a mist form. From the viewpoint of suppressing the inflow of moisture into the granulation tank 10 through this atomizing gas, a drip nozzle is preferred as the supply device 400. Furthermore, when a spray nozzle is used, it is preferable to use atomizing gas that has been sufficiently dried to remove moisture. The atomizing gas may be air or an inert gas such as nitrogen gas. The number of supply devices 400 may be one or two or more. The supply device 400 may be provided at the ceiling portion 120 or the side portion 140 of the container 100.

[0087] 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.

[0088] The method for producing composite particles 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. Then, at least one of the main stirring blade 200 and the sub-stirring blade 300 is rotated to stir the positive electrode active material. Usually, the main stirring blade 200 is rotated, and if necessary, both the main stirring blade 200 and the sub-stirring blade 300 are rotated. Particles of the positive electrode active material as a raw material may be agglomerated, but the stirring in step (i) can break up the agglomerations.

[0089] The peripheral speed of the agitating blades, such as the main agitating blade 200 and the auxiliary agitating blade 300, in step (i) can be set within a range in which the composite particles described above can be produced. In one example, the peripheral speed range of the agitating blades is preferably 1 m / s or more, more preferably 3 m / s or more, and preferably 20 m / s or less, more preferably 12 m / s or less. The peripheral speed of the main agitating blade 200 and the peripheral speed of the auxiliary agitating blade 300 may be the same or different. If they are different, it is preferable that the peripheral speed of the auxiliary agitating blade 300 is faster than the peripheral speed of the main agitating blade 200.

[0090] During stirring in step (i), a seal gas is passed through the drive part 220 of the main stirring blade 200 and the drive part 320 of the sub-stirring blade 300 into the container 100. From the viewpoint of reducing the amount of moisture, it is preferable that the amount of moisture contained in the seal gas is small. In one example, the range of the absolute humidity of the seal gas is preferably 0.1 g / m ３ or less, more preferably 0.05 g / m ３ More preferably, 0.01 g / m or less ３ or less, and particularly preferably 0 g / m ３ is.

[0091] The flow rate (aeration rate) of the seal gas is preferably set so that the ratio (flow rate / volume) of 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 is within the range of 0.1 / min to 1000 / min. 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, particularly preferably 30°C or less, and is preferably 5°C or more, more preferably 10°C or more, and even more preferably 15°C or more.

[0092] The time for which stirring is carried out in step (i) (pre-stirring time) is not particularly limited and can be, for example, 5 minutes or more and 60 minutes or less.

[0093] Typically, in step (i), no liquid components are supplied into the granulation tank 10. However, the raw cathode active material may contain liquid components, such as moisture, that adhered to the raw material during production and storage. In contrast, the stirring in step (i) can reduce, and preferably remove, the amount of the liquid components. Therefore, the powder layer after the stirring in step (i) is able to have a high solid component concentration. In one example, the solid content of the powder layer after the stirring in step (i) is preferably 95% by weight or more, more preferably 97% by weight or more, even more preferably 98% by weight or more, and particularly preferably 100% by weight.

[0094] The solid content concentration of the powder layer can be measured by the following method. A sample Wo [g] is weighed out from the powder layer and placed on an aluminum dish with a weight Wa [g], and heated on a hot plate at 130°C for 1 hour. The weight W [g] after heating (total weight of the sample and the aluminum dish) can be measured, and the solid content concentration Cs [%] of the sample can be calculated using the following formula (M1): Cs = (W - Wa) / Wo × 100 [%] (M1)

[0095] The method for producing composite particles includes, after step (i), step (ii) of supplying a liquid composition containing a carbon-based conductive material, a binder resin, and an organic solvent to the stirred positive electrode active material. In step (ii), the liquid composition is supplied to the stirred positive electrode active material, so that the powder layer in the container 100 contains not only the positive electrode active material but also the carbon-based conductive material and the binder resin. Thus, the positive electrode active material, the carbon-based conductive material, and the binder resin aggregate to gradually form composite particles. Furthermore, in step (ii), at least one of the main stirring blade 200 and the auxiliary stirring blade 300 is rotated to stir the powder layer. Typically, the main stirring blade 200 is rotated, and if necessary, both the main stirring blade 200 and the auxiliary stirring blade 300 are rotated. Since the liquid composition is supplied while stirring is continued, collisions between particles and between particles and the organic 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 sizing of the particles proceed simultaneously in the presence of an organic solvent, thereby obtaining composite particles.

[0096] The liquid composition contains a carbon-based conductive material, a binder resin, and an organic solvent. The liquid composition may further contain any additives. In the liquid composition, the binder resin and any additives may be dissolved in the organic solvent, or may be dispersed without being dissolved. On the other hand, it is preferable that the carbon-based conductive material is dispersed without being dissolved in the organic solvent.

[0097] As the organic solvent, a liquid capable of dissolving or dispersing the carbon-based conductive material and the binder resin can be used. From the viewpoint of reducing the water content, organic solvents with low polarity are preferred. Furthermore, from the viewpoint of efficiently removing the organic solvent in the granulation tank, organic solvents with low boiling points are preferred. In one example, the boiling point of the organic solvent at 1 atm is preferably 95°C or lower, more preferably 90°C or lower, and even more preferably 85°C or lower. The lower limit of the boiling point of the organic solvent at 1 atm is preferably 50°C or higher. Specific examples of preferred organic solvents include alkanes such as cyclohexane, hexane, and heptane; esters such as ethyl acetate and propyl acetate; and ketones such as methyl ethyl ketone and acetone. Nonpolar solvents are preferred, and cyclohexane is particularly preferred. One type of organic solvent may be used alone, or two or more types may be used in combination. When two or more types of organic solvents are used, it is preferable that the proportion of the nonpolar solvent is higher. Furthermore, from the viewpoint of suppressing water adsorption and reducing the water content, it is preferable to dehydrate the organic solvent before use.

[0098] The amount of the organic 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 wt % or more, more preferably 2 wt % or more, even more preferably 3 wt % or more, and is preferably 40 wt % or less, more preferably 20 wt % or less, even more preferably 15 wt % or less.

[0099] 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 50 mPa·s or more, more preferably 100 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, even more preferably 400 mPa·s or less. The viscosity of the liquid composition can be measured using a Brookfield viscometer ("TVB-10M" manufactured by Toki Sangyo Co., Ltd.) under measurement conditions of 25°C and 60 rpm. When measuring, a rotor is appropriately selected according to the viscosity.

[0100] The liquid composition may be supplied continuously or intermittently with one or more supply stop periods. Among these, continuous supply is preferred. The supply rate of the liquid composition relative to 100 parts by weight of the positive electrode active material being stirred in the granulation tank 10 is, in terms of the amount of solids contained in the liquid composition, preferably 0.01 parts by weight / min or more, more preferably 0.1 parts by weight / min or more, even more preferably 0.2 parts by weight / min or more, and is preferably 4 parts by weight / min or less, more preferably 2 parts by weight / min or less, even more preferably 1 part by weight / min or less.

[0101] The peripheral speeds of the agitating blades, such as the main agitating blade 200 and the auxiliary agitating blade 300, in step (ii) can be set within a range in which the composite particles described above can be produced. In one example, the range of peripheral speeds of the agitating blades can be the same as the range of peripheral speeds of the agitating blades in step (i). The peripheral speeds of the main agitating blade 200 and the auxiliary agitating blade 300 may be the same or different. If they are different, it is preferable that the peripheral speed of the auxiliary agitating blade 300 is faster than the peripheral speed of the main agitating blade 200.

[0102] During stirring in step (ii), as in step (i), a seal gas is ventilated into the vessel 100 from the drive unit 220 of the main agitator 200 and the drive unit 320 of the sub-agitator 300. From the viewpoint of reducing the amount of moisture, it is preferable that the seal gas contains a small amount of moisture. In one example, the absolute humidity range of the seal gas in step (ii) may be the same as the absolute humidity range of the seal gas in step (i). Furthermore, the range of the ratio (flow rate / volume) obtained by dividing the flow rate of the seal gas flowing into the vessel 100 of the granulation tank 10 by the capacity of the vessel 100 in step (ii) may be the same as the range of the ratio (flow rate / volume) obtained by dividing the flow rate of the seal gas flowing into the vessel 100 of the granulation tank 10 by the capacity of the vessel 100 in step (i). Furthermore, the temperature range of the seal gas in step (ii) may be the same as the temperature range of the seal gas in step (i).

[0103] The time for supplying the liquid composition in step (ii) can be set within a range that allows the production of the above-described composite particles. In one example, the time for supplying the liquid composition can be 5 minutes or more and 60 minutes or less.

[0104] The method for producing composite particles may include, after the above-mentioned step (ii), a step (iii) of further stirring the composite particles produced in step (ii). In step (iii), at least one of the main stirring blade 200 and the sub-stirring blade 300 is rotated to stir the positive electrode active material. Usually, the main stirring blade 200 is rotated, and if necessary, both the main stirring blade 200 and the sub-stirring blade 300 are rotated. By further stirring after the completion of supply of the liquid composition, the composite particles can be sized to make the particle size uniform or to make the particle shape closer to a circle.

[0105] The peripheral speed of the agitating blades, such as the main agitating blade 200 and the auxiliary agitating blade 300, in step (iii) can be set within a range in which the composite particles described above can be produced. In one example, the peripheral speed of the agitating blades is preferably in the range of 0.1 m / s to 10 m / s. The peripheral speed of the main agitating blade 200 and the peripheral speed of the auxiliary agitating blade 300 may be the same or different. Furthermore, the peripheral speed of the agitating blade in step (iii) may be slower than the peripheral speed of the agitating blade in step (i) and / or step (ii).

[0106] During stirring in step (iii), as in steps (i) and (ii), a seal gas is ventilated into the vessel 100 from the drive unit 220 of the main agitator 200 and the drive unit 320 of the sub-agitator 300. From the viewpoint of reducing the amount of moisture, it is preferable that the seal gas contains a small amount of moisture. In one example, the absolute humidity range of the seal gas in step (iii) may be the same as the absolute humidity range of the seal gas in step (i). Furthermore, the range of the ratio (flow rate / volume) obtained by dividing the flow rate of the seal gas flowing into the vessel 100 of the granulation vessel 10 by the volume of the vessel 100 in step (iii) may be the same as the range of the ratio (flow rate / volume) obtained by dividing the flow rate of the seal gas flowing into the vessel 100 of the granulation vessel 10 by the volume of the vessel 100 in step (i). Furthermore, the temperature range of the seal gas in step (iii) may be the same as the temperature range of the seal gas in step (i).

[0107] The stirring time in step (iii) can be set within a range that allows the production of the above-described composite particles. In one example, the stirring time is preferably 10 seconds or more, and preferably 60 minutes or less, more preferably 20 minutes or less, even more preferably 10 minutes or less, and particularly preferably 3 minutes or less.

[0108] Throughout the above-described steps (i), (ii), and (iii), 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 less than 50°C, more preferably 45°C or less, and even more preferably 40°C or less, from the viewpoint of suppressing deterioration of the positive electrode active material. The lower limit may be, for example, 5°C or more, 10°C or more, or 15°C or more. Throughout the steps (i), (ii), and (iii), the temperature inside the granulation tank 10 may be constant or may vary. The temperature inside the granulation tank 10 can be measured as the temperature of the powder layer being stirred in the granulation tank 10.

[0109] The method for producing composite particles preferably includes a step of subjecting the composite particles to a drying treatment after producing the composite particles by agitation granulation as described above. Hereinafter, composite particles produced by agitation granulation before being subjected to a drying treatment may be referred to as "composite particles before drying." Even if measures are taken to prevent moisture from entering the agitation granulation system, moisture may inevitably enter the system, and the composite particles before drying may contain moisture. Therefore, from the viewpoint of removing the moisture and obtaining moisture contents M(110°C), M(170°C), and M(300°C) that satisfy the above-mentioned requirements, it is preferable to subject the composite particles before drying to a drying treatment.

[0110] The method for producing composite particles may further include any step in combination with the above-described steps. For example, the method for producing composite particles may include, before step (i), a step of stirring the positive electrode active material using a stirring device separate from granulation tank 10.

[0111] <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 usually includes a current collector and a positive electrode mixture layer formed on the current collector, and the positive electrode mixture layer contains the composite particles. The positive electrode mixture layer may contain only the composite particles.

[0112] 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.

[0113] The current collector generally has a film or sheet shape. The thickness of the current collector may be appropriately selected depending on the intended use, and is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more, and is preferably 200 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less.

[0114] 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 The following is the result.

[0115] The positive electrode can be manufactured, for example, by a method including a step of pressing composite particles on a current collector. By pressing, a large number of composite particles are bonded together to form a positive electrode composite layer. Furthermore, by pressing, the composite particles can be attached to the current collector, and therefore the positive electrode composite layer can be fixed on the current collector.

[0116] The positive electrode is manufactured as a dry positive electrode by a dry manufacturing method. The dry manufacturing method refers to a manufacturing method for manufacturing a positive electrode in a manner in which a liquid material such as water or an organic solvent is not added to the composite particles during the process of forming the positive electrode composite layer. In such a dry manufacturing method, the composite particles are used in the state of a dry powder containing the composite particles. This powder usually contains only the composite particles. In such a powder state, the composite particles according to this embodiment exhibit high fluidity, allowing the positive electrode composite layer to be formed uniformly.

[0117] This manufacturing method is preferably carried out using a long current collector. For example, the long current collector is conveyed in its longitudinal direction while the composite particles are pressed on the current collector. The method using a long current collector allows for continuous production of positive electrodes, thereby achieving high production efficiency in terms of time.

[0118] As a specific example, the method for producing a positive electrode may include feeding composite particles to a pressure device while feeding an aggregate to the pressure device, thereby pressing the composite particles on a current collector. As another specific example, the method for producing a positive electrode may include supplying and depositing composite particles on a current collector to form a composite particle layer, flattening the composite particle layer with a flattening device such as a blade and squeegee roll as necessary, and then pressing the composite particle layer with a pressure device. As the pressure device, for example, a roll-type pressure device equipped with a pair of rolls may be used. As a feeder for supplying the composite particles, for example, a vibration feeder, a screw feeder, or the like may be used.

[0119] For example, when the current collector and the composite particles are pressed between a pair of rolls, the linear pressure applied by the rolls is preferably 10 kN / m or more, more preferably 200 kN / m or more, and even more preferably 400 kN / m or more, and is preferably 2000 kN / m or less, more preferably 1500 kN / m or less, and even more preferably 1000 kN / m or less.

[0120] The pressure is usually applied using a pressure member heated to a specific temperature. For example, when applying pressure to the current collector and the composite particles between a pair of rolls, the pressure is applied with the rolls heated to a specific temperature. The temperature of the pressure member may be set depending on the glass transition temperature and softening point of the binder resin, and is, for example, preferably 70°C or higher, more preferably 80°C or higher, and even more preferably 90°C or higher, and is preferably 180°C or lower, more preferably 150°C or lower, and even more preferably 120°C or lower.

[0121] When applying pressure to the current collector and the composite particles between a pair of rolls, the current collector travels between the rolls. Then, pressure is applied to the composite particles as the current collector passes between the rolls. Therefore, the formation of the positive electrode composite layer usually proceeds at the traveling speed of the current collector. The composite particles according to this embodiment have excellent fluidity and therefore excellent formability, making it possible to form the positive electrode composite layer at high speed.

[0122] The method for producing a positive electrode may further include any optional steps in combination with the steps described above. For example, the method for producing a positive electrode may further include a post-pressing treatment from the viewpoint of reducing the variation in thickness of the positive electrode or increasing the density of the positive electrode composite layer to further increase the capacity. The method for the post-pressing treatment is preferably a roll pressing method. In the roll pressing method, the electrode is passed between two rolls placed in parallel to pressurize the electrode. At this time, the temperature of the rolls may be adjusted, for example, by heating or cooling, as necessary.

[0123] <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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" representing amounts are by weight unless otherwise specified. Furthermore, the operations described below were carried out at room temperature (23°C) unless otherwise specified.

[0131] <Measurement Method and Evaluation Method> (Method for Measuring Moisture Content of Composite Particles by Karl Fischer Method) Approximately 2 g of composite particles was weighed as a sample powder. Then, the moisture content of the sample powder was measured by the Karl Fischer method (JIS K-0068 (2001) moisture vaporization method) using a coulometric moisture meter (manufactured by Nitto Seiko Analytech: CA-200 model (coulometric titration method measuring device), VA-236S model (vaporizer)).

[0132] Specifically, the moisture content M (110°C) was measured under the following measurement conditions: heating temperature 110°C, termination condition 0.01 μg / s. The moisture content M (170°C) of the sample after measurement was then measured under the following measurement conditions: heating temperature 170°C, termination condition 0.1 μg / s. The moisture content M (300°C) of the sample after measurement was then measured under the following measurement conditions: heating temperature 300°C, termination condition 0.1 μg / s. The sum of the moisture content M (110°C) and the moisture content M (170°C) corresponds to the moisture content of adsorbed water. Furthermore, the moisture content M (300°C) corresponds to the moisture content of bound water.

[0133] (Method for measuring D50 particle size of composite particles) A ​​laser diffraction particle size distribution analyzer ("MT-3000II" manufactured by Microtrac) was prepared. This laser diffraction particle size distribution analyzer disperses sample particles using an airflow using compressed air, and measures the particle size distribution of the dispersed sample particles by laser diffraction. Using this laser diffraction particle size distribution analyzer, the particle size distribution of the composite particles was measured, and the particle size at which the cumulative volume calculated from the smallest diameter side became 50% was obtained as the D50 particle size. The measurement was carried out at a dispersion pressure (compressed air pressure) of 0.1 MPa.

[0134] (Method for measuring the solid content concentration of the positive electrode active material after preliminary stirring) Wo [g] of the positive electrode active material was weighed out and placed on an aluminum dish with a weight of Wa [g], and heated on a hot plate at 130°C for 1 hour. The weight after heating (total weight of the positive electrode active material and the aluminum dish) W [g] was measured, and the solid content concentration Cs [%] of the positive electrode active material was calculated using the following formula (M1): Cs = (W - Wa) / Wo × 100 [%] (M1)

[0135] (Method for evaluating moldability of composite particles) Approximately 5 g of composite particles was placed as a powder sample on a glass table (254 mm × 355 mm) with a clamp, and the powder sample was molded into a thin layer using an applicator (standard film thickness: 50 μm, coating width: 80 mm). The obtained thin film was observed, and the moldability was evaluated based on the following criteria.

[0136] Evaluation "A": A uniform thin layer was formed. Evaluation "B": There were some unevenness or streaks, but a thin layer was formed overall. Evaluation "C": The composite particles, which were powder samples, had poor fluidity, and a thin layer could not be formed.

[0137] (Method for Evaluating Powder Resistivity of Composite Particles) 4.0 g of composite particles were placed in the probe unit of a powder resistivity measurement system ("MCP-PD51" manufactured by Mitsubishi Chemical Analytech Co., Ltd.), and the powder resistivity was measured when a pressure of 20 kN was applied. The measured powder resistivity was evaluated according to the following criteria. Evaluation "A": Powder resistance is 18.0Ω or less Evaluation "B": Powder resistance is greater than 18.0Ω and less than or equal to 22.0Ω Evaluation "C": Powder resistance is greater than 22.0Ω and less than or equal to 24.5Ω Evaluation "D": Powder resistance is greater than 24.5Ω

[0138] (Method for Evaluating Cycle Characteristics of Lithium-Ion Secondary Battery) After injecting the electrolyte, the lithium-ion secondary battery was left standing at 25°C for 5 hours. Next, it was charged to a cell voltage of 3.65 V at 25°C using a constant current method at 0.2 C, and then aged for 12 hours at 60°C. Then, it was discharged to a cell voltage of 3.00 V using a constant current method at 0.2 C at 25°C. Thereafter, it was subjected to CC-CV charging (upper limit cell voltage 4.20 V) using a constant current method at 0.2 C, and CC discharging to 3.00 V using a constant current method at 0.2 C. This charge and discharge at 0.2 C was repeated three times to obtain an evaluation cell.

[0139] Next, the evaluation cell was subjected to 100 cycles of charge / discharge at a cell voltage of 4.20-3.00 V and a charge / discharge rate of 0.5 C in an environment at a temperature of 45°C. The discharge capacity at the first cycle was defined as X1, and the discharge capacity at the 100th cycle as X2. Using the discharge capacities X1 and X2, the capacity retention rate was calculated according to the following formula (M2): Capacity retention rate = (X2 / X1) x 100 (%) (M2)

[0140] A higher capacity retention rate indicates that the lithium ion secondary battery has better cycle characteristics. Therefore, the capacity retention rate was evaluated according to the following criteria: Rating "A": Capacity retention rate is 90% or more Rating "B": Capacity retention rate is 85% or more and less than 90% Rating "C": Capacity retention rate is 80% or more and less than 85% Rating "D": Capacity retention rate is less than 80%

[0141] 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 a period of 40 minutes. After the addition was completed, the entire contents were stirred for an additional 20 minutes at 60°C. The reaction solution was measured by gas chromatography, and 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 a period of 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 a period of 60 minutes, and after the addition was completed, the entire contents were stirred for an additional 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, yielding a polymer solution containing a block copolymer. Of all the isoprene-derived structural units 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 to the polymer solution while stirring, 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 polymer 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] (manufactured by Koyo Chemical Laboratory Co., Ltd., product name "Songnox 1010"), a phenolic antioxidant, was added to the filtrate and dissolved. Cyclohexane was further added to prepare a solution of binder resin A1.

[0142] (Measurement of the proportion of structural units derived from 1,2- and 3,4-addition polymerization among structural units derived from a chain conjugated diene compound contained in binder resin A1) The proportion of structural units derived from 1,2- and 3,4-addition polymerization among all structural units derived from isoprene contained in the block copolymer (block copolymer before hydrogenation) obtained in the production process of binder resin A1 is １ In the H-NMR spectrum (in deuterated chloroform), the carbon-carbon unsaturated bond in the polymer main chain was １ H bonded to the carbon of the carbon-carbon unsaturated bond in the polymer side chain １ The ratio calculated in this manner was obtained as the ratio of structural units derived from 1,2- and 3,4-addition polymerization to all structural units derived from isoprene in the binder resin A1 obtained by hydrogenating the block copolymer.

[0143] (Production of a liquid composition containing a carbon-based conductive material, a binder resin, and a solvent) Carbon black (BET specific surface area: 62 m) was used as the carbon-based conductive material. ２ / g, bulk density 0.16 g / cm ３ ) and 1.5 parts of the binder resin A1 solution in terms of solids (i.e., in terms of the amount of binder resin A1) were mixed, and cyclohexane was added as a solvent to obtain a mixture with a solids concentration of 10% and a total amount of 1 kg. Next, the obtained mixture was dispersed using a bead mill ("LMZ015" manufactured by Ashizawa Finetech Co., Ltd.) using zirconia beads with a diameter of 0.5 mm at a peripheral speed of 12 m / s for 1 hour to obtain a liquid composition. The obtained liquid composition had a solids concentration of 10 wt % and a viscosity of 300 mPa s.

[0144] (Production of Composite Particles) A ​​composite particle production apparatus was prepared as a granulation tank. This granulation tank included a cylindrical container (inner diameter 180 mm, internal volume 2 L) installed with its axis oriented vertically, and a main stirring blade and a sub-stirring blade installed within the cylindrical container. The main stirring blade was an inclined paddle equipped with three main blades with a diameter of 170 mm, and was rotatable around a vertical axis of rotation. The sub-stirring blade was equipped with a V-shaped anchor blade with a diameter of 30 mm, and was rotatable around a horizontal axis of rotation. To prevent raw materials from being mixed into the drive units of the main stirring blade and the sub-stirring blade, each drive unit was equipped with a sealing mechanism that ventilated air (hereinafter sometimes referred to as "sealing air"). Using the composite particle production apparatus, composite particles were produced by the following method, in this order: (i) a preliminary stirring operation, (ii) a composite particle formation operation, and (iii) a sizing operation.

[0145] (i) In the preliminary stirring operation, NMC532 (LiNi) as a positive electrode active material for a lithium ion battery ０．５ Mn ０．３ Co ０．２ O ２ 96.5 parts by weight (1344 g) of a powder containing the positive electrode active material (D50 particle size 6 μm) was prepared. This positive electrode active material was dried using a vacuum dryer at 150°C for 6 hours. The dried positive electrode active material was placed in a granulation tank to form a powder layer containing the positive electrode active material. In order to seal the drive parts of the main stirring blade and the sub-stirring blade, sealing air (absolute humidity 0 g / cm) at room temperature (25°C) was poured into the tank. ３ The positive electrode active material was stirred by rotating the main stirring blade and the auxiliary stirring blade at a peripheral speed of 5 m / s for the main stirring blade and 6 m / s for the auxiliary stirring blade for a 15-minute operation. The solids concentration of the positive electrode active material after stirring was measured and found to be 99 wt % or more.

[0146] Next, in the (ii) composite particle formation operation, 4 parts by weight (280 g) of the liquid composition (solid content concentration 10 wt %, viscosity 300 mPa s) containing binder resin A1, carbon black, and a solvent was continuously added over 15 minutes using a dropping funnel while rotating the main stirring blade and the auxiliary stirring blade, with sealing air at room temperature (25°C) flowing at 20 L / min (flow rate / volume ratio 10 / min). The peripheral speed of the main stirring blade was 5 m / s, and the peripheral speed of the auxiliary stirring blade was 6 m / s.

[0147] Next, in the (iii) particle size adjustment operation, room temperature (25°C) sealing air was circulated at 20 L / min (airflow rate 10 / min), and the main stirring blade was rotated at a peripheral speed of 2 m / s and the sub-stirring blade was rotated at a peripheral speed of 2 m / s for 10 minutes. The maximum temperature in the system throughout the above steps (i) to (iii) was 38°C. Composite particles were produced by carrying out the above operations (i) to (iii) in this order.

[0148] The composite particles thus produced were dried using a vacuum dryer for 24 hours at 30° C. For the dried composite particles, the moisture content was measured by the Karl Fischer method described above, the D50 particle size was measured, and the moldability and powder resistivity were evaluated.

[0149] (Production of a positive electrode for a lithium-ion secondary battery) The produced composite particles were supplied to a press roll (roll temperature 100°C, press linear pressure 500 kN / m) of a roll press machine ("Press-cut rough surface hot roll" manufactured by Hirano Giken Kogyo Co., Ltd.) using a quantitative feeder ("Nikka Spray K-V" manufactured by Nikka Corporation). An aluminum foil having a thickness of 20 μm was inserted between the press rolls, and the composite particles supplied from the quantitative feeder were adhered to the aluminum foil and press-molded at a molding speed of 1.5 m / min to a basis weight of 30 mg / cm. ２ A positive electrode raw sheet for a lithium ion secondary battery having a positive electrode mixture layer of 1.0 g / cm 3 was obtained. Here, "weight" represents the weight per unit area. This positive electrode raw sheet was rolled using a roll press to obtain a positive electrode mixture layer of 1.0 g / cm 3. ３ A sheet-shaped positive electrode was produced, which consisted of the positive electrode mixture layer and aluminum foil.

[0150] (Production of Negative Electrode) In a 5 MPa pressure vessel equipped with a stirrer, 33 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 3.5 parts of itaconic acid as an acidic group-containing monomer, 63.5 parts of styrene as an aromatic vinyl monomer, 0.4 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 parts of potassium persulfate as a polymerization initiator were placed, thoroughly stirred, and then heated to 50 ° C to initiate polymerization. When the polymerization conversion rate reached 96%, the mixture was cooled to stop the polymerization reaction, and a mixture containing a particulate binder (styrene-butadiene copolymer) was obtained. A 5% aqueous sodium hydroxide solution was added to this mixture to adjust the pH to 8, and unreacted monomer was removed by heated vacuum distillation. The mixture was then cooled to 30 ° C or below to obtain an aqueous dispersion containing the negative electrode binder.

[0151] Next, 48.75 parts of artificial graphite as a negative electrode active material, 48.75 parts of natural graphite, and 1 part of carboxymethyl cellulose as a thickener were added to a planetary mixer. The mixture was then diluted with ion-exchanged water to a solids concentration of 60%, and then kneaded for 60 minutes at a rotation speed of 45 rpm. Then, 1.5 parts of the aqueous dispersion containing the negative electrode binder obtained as described above was added in terms of solids content, and the mixture was kneaded for 40 minutes at a rotation speed of 40 rpm. Then, ion-exchanged water was added to the mixture to a viscosity of 3000±500 mPa s (measured with a Brookfield viscometer at 25°C and 60 rpm), thereby preparing a negative electrode composite layer slurry.

[0152] Next, a copper foil having a thickness of 15 μm was prepared as a current collector. The negative electrode composite layer slurry was applied to the copper foil in a coated amount of 15 mg / cm after drying. ２ The coating was dried at 60°C for 20 minutes and at 120°C for 20 minutes. Thereafter, the coating was heated at 150°C for 2 hours to obtain a negative electrode blank. This negative electrode blank was rolled using a roll press to a density of 1.6 g / cm. ３ A sheet-shaped negative electrode was produced, which consisted of negative electrode mixture layers (on both sides) of the above and copper foil.

[0153] (Production of Lithium-ion Secondary Battery) A single-layer laminate cell (discharge capacity equivalent to 250 mAh) was fabricated using the above-mentioned positive electrode, negative electrode, and separator (made of polyethylene, thickness 12 μm) and placed in an aluminum package. Then, a 1.0 M LiPF 6 electrolyte was placed in the aluminum package. ６ A solution (solvent: a mixed solvent of ethylene carbonate (EC) / diethyl carbonate (DEC) = 3 / 7 (volume ratio), additive: containing 2 volume % (solvent ratio) of vinylene carbonate) was filled in. Furthermore, in order to seal the opening of the aluminum packaging material, the aluminum packaging material was closed by heat sealing at a temperature of 150°C, and a lithium ion secondary battery was produced. Using this lithium ion secondary battery, the above-mentioned evaluations were carried out.

[0154] Example 2 Composite particles, positive electrodes, and lithium-ion secondary batteries were produced and evaluated in the same manner as in Example 1, except for the following: In the (i) preliminary stirring operation of the composite particle production process, the conditions for drying the positive electrode active material using a vacuum dryer before charging into a granulation tank were changed to 100°C and 3 hours. In the (iii) size regulation operation of the composite particle production process, the drying time of the composite particles performed after the size regulation operation was changed to 20 hours.

[0155] Example 3 Composite particles, positive electrodes, and lithium-ion secondary batteries were produced and evaluated in the same manner as in Example 1, except for the following: In the (i) preliminary stirring operation of the composite particle production process, the conditions for drying the positive electrode active material using a vacuum dryer before charging into a granulation tank were changed to 120°C and 3.5 hours. In the (iii) size regulation operation of the composite particle production process, the drying time of the composite particles after the size regulation operation was changed to 12 hours.

[0156] Comparative Example 1 Composite particles, a positive electrode, and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1, except for the following: - The positive electrode active material was not dried in the preliminary stirring operation (i) of the composite particle production process. - Drying was not performed after the sizing operation (iii) of the composite particle production process.

[0157] <Results> The results of the above-mentioned Examples and Comparative Examples are shown in the table below.

[0158]

[0159] 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 Supply device A ２００ Rotation axis A ３００ Rotation axis

Claims

1. Composite particles for electrochemical element positive electrodes, comprising a positive electrode active material, a carbon-based conductive material, and a binder resin, in which the sum (M(110°C) + M(170°C) + M(300°C)) of a moisture content M(110°C) measured according to the Karl Fischer method at a heating temperature of 110°C, a moisture content M(170°C) measured according to the Karl Fischer method at a heating temperature of 170°C after measurement at the moisture content M(110°C), and a moisture content M(300°C) measured according to the Karl Fischer method at a heating temperature of 300°C after measurement at the moisture content M(170°C) is 20 ppm or more and 400 ppm or less.

2. Composite particles for electrochemical element positive electrodes according to claim 1, wherein the sum of the moisture content M(110°C) and the moisture content M(170°C) (M(110°C) + M(170°C)) of the composite particles for electrochemical element positive electrodes is 10 ppm or more and 250 ppm or less.

3. Composite particles for electrochemical element positive electrodes according to claim 1, wherein the moisture content M (300°C) of the composite particles for electrochemical element positive electrodes is 10 ppm or more and 150 ppm or less.

4. Composite particles for a positive electrode of an electrochemical element according to claim 1, wherein the composite particles for a positive electrode of an electrochemical element have a D50 particle diameter of 30 μm to 150 μm.

5. The composite particles for a positive electrode of an electrochemical element according to claim 1, which are composite particles for forming a dry positive electrode.

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 carbon-based conductive material, a binder resin, and an organic 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 to obtain a stirred state; and a step (ii) of supplying a liquid composition containing the carbon-based conductive material, the binder resin, and the organic solvent to 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. A method for producing a positive electrode for an electrochemical element, comprising a step of pressing the composite particles for a positive electrode for an electrochemical element according to any one of claims 1 to 5 on a current collector.

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

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