WO2024204433A1 - Method for manufacturing composite particles and electrode for electrochemical element - Google Patents

Abstract

In a granulation tank comprising two or more agitation blades having different agitation axes, the following steps are performed in this order: (i) a powder material containing an electrode active material is agitated and brought into an agitation state; and (ii) a composition containing a binder, an electrically conductive assistant, and a solvent is added to the powder material in the agitation state to form composite particles.

Description

Method for producing composite particles and electrodes for electrochemical devices

The present invention relates to a method for producing composite particles and electrodes for electrochemical devices.

Electrochemical elements such as lithium-ion secondary batteries are small, lightweight, have high energy density, and can be repeatedly charged and discharged, making them suitable for a wide range of applications.

In order to improve the performance of electrochemical elements, various improvements have been made to the materials that form the electrodes for electrochemical elements. Electrodes for electrochemical elements have a structure in which an electrode mixture layer is disposed on an electrode substrate, the electrode mixture layer containing an electrode active material as the main component and, as necessary, other components such as a conductive assistant and a binder in order to impart specific functions such as electrical conductivity, adhesion, and flexibility to the electrode. From the viewpoint of improving the performance of electrochemical elements, it is preferable that the electrode active material and other components are uniformly dispersed in the electrode mixture layer.

Methods that have been considered for forming an electrode mixture layer include a method in which a slurry composition containing an electrode active material, a conductive assistant, a binder, and a solvent is applied to an electrode substrate and then dried to form an electrode mixture layer, and a method in which a slurry composition containing an electrode active material, a conductive assistant, a binder, and a solvent is spray-dried to obtain composite particles, and the obtained composite particles are pressure-molded onto an electrode substrate to form an electrode mixture layer.

As methods for producing composite particles, the following have been considered: a method of spray-drying a slurry composition as described above (see, for example, Patent Document 1); a fluidized bed granulation method in which powder is granulated in a state suspended in a fluid such as an air current blown up from below (see, for example, Patent Document 2); and a granulation method that includes stirring the electrode active material and binder and then crushing them (see, for example, Patent Document 3).

International Publication No. WO 2005/124801 JP 2006-060193 A International Publication No. 2015/029829

However, conventional methods for producing granulated particles leave room for further improvement in the properties of electrodes formed using the resulting granulated particles and electrochemical elements equipped with such electrodes.

Therefore, an object of the present invention is to provide a method for producing composite particles that can increase the flexibility of an electrode, suppress cracking of the electrode active material in the electrode, and further improve the cycle characteristics of an electrochemical element equipped with such an electrode.
Another object of the present invention is to provide a method for producing an electrode for an electrochemical device by using the composite particles obtained according to the production method of the present invention.

The present inventors have conducted extensive research with the aim of solving the above problems. The present inventors have newly discovered that by forming composite particles by adding a composition containing a binder, a conductive assistant, and a solvent under stirring conditions, it is possible to manufacture composite particles that can improve the properties of the resulting electrodes and electrochemical elements, as described above, and have completed the present invention.

That is, an object of the present invention is to advantageously solve the above problems.
[1] A method for producing composite particles, comprising the steps of:
In a granulation tank equipped with two or more agitating blades having different agitation shafts,
(i) stirring a powder material containing an electrode active material to bring it into a stirred state;
(ii) adding a composition containing a binder, a conductive assistant, and a solvent to the powder material in a stirred state to form composite particles;
By carrying out the above operations (i) to (ii) in this order in a granulation tank equipped with two or more stirring blades having different stirring shafts, it is possible to provide composite particles which can increase the flexibility of the electrode, suppress cracking of the electrode active material in the electrode, and further improve the cycle characteristics of an electrochemical device equipped with such an electrode.

[2] Here, in the method for producing composite particles described in [1] above, it is preferable that the means for adding the composition in step (ii) is a spray nozzle. By spraying and supplying the composition using a spray nozzle when adding the composition in step (ii), the properties of the obtained composite particles can be further improved.

[3] In the method for producing composite particles described in [1] or [2] above, after the step (ii), a step (iii) of sizing the composite particles by stirring the particles after the addition of the composition is completed can be carried out.

[4] In the method for producing composite particles described in [3] above, it is preferable to add a conductive assistant in step (iii). By adding a conductive assistant in step (iii), the properties of the resulting composite particles can be further improved.

[5] In the method for producing composite particles according to any one of the above [1] to [4], the powder material in step (i) preferably contains a conductive assistant. By stirring the conductive assistant together with the electrode active material in step (i) and then carrying out step (ii), the properties of the resulting composite particles can be further improved.

[6] In the method for producing composite particles of the present invention described above in any one of [1] to [5], it is preferable that the solvent contained in the composition is a non-aqueous solvent having a boiling point of 95°C or less at 1 atm. By using a composition containing a solvent that satisfies such conditions in the above operation (ii), composite particles can be produced efficiently.

[7] The present invention also aims to advantageously solve the above problems, and the method for producing an electrode for an electrochemical element of the present invention is characterized by comprising the steps of producing composite particles according to any one of the methods for producing composite particles described in any one of [1] to [6] above, and pressure-molding the produced composite particles on an electrode substrate to form an electrode mixture layer. An electrode comprising an electrode mixture layer formed using composite particles obtained according to any one of the methods for producing composite particles described above has excellent flexibility, is less susceptible to cracking of the electrode active material contained therein, and can further improve the cycle characteristics of an electrochemical element comprising such an electrode.

According to the present invention, it is possible to provide a method for producing composite particles that can increase the flexibility of an electrode, suppress cracking of the electrode active material in the electrode, and further improve the cycle characteristics of an electrochemical element provided with such an electrode.
Furthermore, according to the present invention, there can be provided a method for producing an electrode for an electrochemical device by using the composite particles obtained according to the production method of the present invention.

FIG. 2 is a top view of an example of a granulation tank. 2 is a cross-sectional view taken along the line AA shown in FIG. 1.

Hereinafter, an embodiment of the present invention will be described in detail.
Here, according to the method for producing composite particles of the present invention, it is possible to efficiently provide composite particles that can be advantageously used as a compounding component of an electrode mixture layer provided in an electrode of an electrochemical device such as a secondary battery. Also, the method for producing an electrode for an electrochemical device of the present invention includes pressure molding the composite particles obtained according to the production method of the present invention.

(Method for producing composite particles)
The method for producing composite particles of the present invention includes the steps of:
(i) stirring a powder material containing an electrode active material to bring it into a stirred state;
(ii) adding a composition containing a binder, a conductive additive, and a solvent to the powder material in a stirred state to form composite particles;
The method is characterized in that the above steps (i) to (ii) are carried out in this order in a granulation tank equipped with two or more stirring blades having different stirring shafts. By carrying out the above steps (i) to (ii) in this order, it is possible to provide composite particles that can increase the flexibility of the electrode, suppress cracking of the electrode active material in the electrode, and improve the cycle characteristics of an electrochemical device equipped with such an electrode. Furthermore, optionally, following the above step (ii), a step (iii) of regulating the size of the composite particles by stirring them after the addition of the composition is completed may be carried out.

<Granulation tank>
The granulation tank needs to be provided with two or more stirring blades with different stirring shafts. By providing two or more stirring blades with different stirring shafts, the uniformity of the composition of the composite particles obtained is increased, and as a result, the cycle characteristics of an electrochemical element equipped with an electrode formed using such composite particles can be improved. An example of a granulation tank will be described with reference to Figs. 1 and 2. Fig. 1 is a top view of the granulation tank 1, and Fig. 2 is a cross-sectional view along the A-A section line shown in Fig. 1. The granulation tank 1 is provided with a main stirring blade 2 and a sub-stirring blade 3 having a stirring shaft different from that of the main stirring blade 2. The number of stirring blades is not particularly limited as long as it is two or more. By providing two or more stirring blades, the uniformity of the composition of the composite particles can be increased, and the cycle characteristics of an electrochemical element equipped with an electrode formed using such composite particles can be improved.

Furthermore, although not shown, the granulation tank 1 has at least one supply means capable of supplying a liquid composition. Examples of such supply means include a spray nozzle configured to be able to supply a mist of liquid, and a drip funnel. The number of supply means is not particularly limited, but multiple supply means may be arranged separately from each other depending on the size of the granulation tank. Furthermore, although not shown, the granulation tank 1 may have a supply port for the powder material and a discharge port configured to be able to discharge the formed composite particles.

In Figure 2, the stirring shaft of the main stirring blade 2 is shown by a dashed line as the first stirring shaft RA1, and the stirring shaft of the auxiliary stirring blade is shown by a dashed line as the second stirring shaft RA2. In Figure 2, the angle θ between the first stirring shaft RA1 and the second stirring shaft RA2 is approximately 90 degrees. The angle between the first stirring shaft RA1 and the second stirring shaft RA2 refers to the acute angle between the angles formed by these two axes. Here, in this specification, "different stirring shafts" means that the angle θ between the stirring shafts is 20° or more and 90° or less. The angle θ between the stirring shafts is preferably 30° or more, more preferably 45° or more, and even more preferably 85° or more. If the angle θ between the stirring shafts is within the above range, the powder material can be effectively stirred, and the particle size and coefficient of variation of the resulting composite particles can be well controlled. As a result, the flexibility of the electrode formed using such composite particles and cracking of the electrode active material in the electrode can be suppressed, and the cycle characteristics of the resulting electrochemical element can be improved. Note that the "coefficient of variation" refers to the coefficient of variation of the area-equivalent diameter of the composite particles, and is an index that represents the breadth of the particle size distribution. The coefficient of variation of the area-equivalent diameter can be calculated as a percentage by dividing the standard deviation of the area-equivalent diameter of the composite particles by the average value of the area-equivalent diameter, according to the method described in the examples of this specification.

The shape of the granulation tank is not particularly limited as long as it can accommodate the powder material containing the electrode active material for a predetermined period of time and can be stirred by at least two stirring blades. For example, the shape of the granulation tank may be cylindrical, with the bottom and top surfaces being circular and the upper part tapered in the height direction, as in the granulation tank 1 shown in Figures 1 and 2. When the shape of the granulation tank is a predetermined cylindrical shape as shown in Figures 1 and 2, one of the at least two stirring shafts may coincide with the central axis of the cylinder, and the other stirring shaft may coincide with a direction perpendicular to the central axis. Furthermore, when the shape of the granulation tank is a predetermined cylindrical shape as shown in Figures 1 and 2, the value obtained by dividing the diameter of the bottom by the height (diameter/height) is preferably 0.1 or more, more preferably 0.3 or more, even more preferably 0.5 or more, preferably 2.5 or less, more preferably 2.0 or less, and even more preferably 1.5 or less. This is because the powder material can be effectively stirred.

The main agitator 2 has three main blades 21. The shape and number of the main blades 21 are not particularly limited. The auxiliary agitator 3 has two auxiliary blades 31. The auxiliary blades 31 are illustrated as anchor blades in Figures 1 and 2, but are not limited to this. The number of auxiliary blades 31 is also not limited to the illustrated form, and may be one, or three or more. Furthermore, the granulation tank 1 may be equipped with a ventilation mechanism (not shown) configured to ventilate air and thereby suppress the mixing of powder material into each drive part of the main agitator 2 and the auxiliary agitator 3.

Examples of granulation tanks that satisfy the above conditions include the high-speed mixer manufactured by EarthTechnica, the Henschel mixer manufactured by Mitsui Mining (now the FM mixer manufactured by Nippon Coke Company), the vertical granulator manufactured by Powrex, the CF granulator manufactured by Freund Corporation, the high-speed stirring and mixing granulator manufactured by Nara Machinery Works, the SP granulator manufactured by Dalton, and the balance granulator manufactured by Freund Corporation.

The following describes the various operations carried out in the granulation tank.

<(i) Pre-stirring operation>
In the preliminary stirring operation, the powder material is stirred to a stirred state. Here, the powder material needs to contain an electrode active material, and may optionally contain a conductive assistant. By carrying out the preliminary stirring operation, it is possible to improve the cycle characteristics of an electrochemical device having an electrode formed using the obtained composite particles.

The positive electrode active material is not particularly limited, and examples thereof include lithium-containing cobalt oxide (lithium cobalt oxide, LiCoO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), lithium-containing nickel oxide (LiNiO ₂ ), Co—Ni—Mn lithium-containing composite oxide (Li(Co Mn Ni)O ₂ ), Ni—Mn—Al lithium-containing composite oxide, Ni—Co—Al lithium-containing composite oxide, olivine-type lithium iron phosphate (LiFePO ₄ ), olivine-type lithium manganese phosphate (LiMnPO ₄ ), Li ₂ MnO ₃ -LiNiO ₂ solid solution, lithium-excess spinel compound represented by Li _1+x Mn _2-x O ₄ (0<X<2), Li[Ni _0.17 Li _0.2 Co _0.07 Mn _0.56 ]O ₂ , LiNi _0.5 Mn _1.5 O ₄ , and other known positive electrode active materials. Examples of the negative electrode active material include carbon-based negative electrode active materials, metal-based negative electrode active materials, and negative electrode active materials that are a combination of these.

The particle diameter of the electrode active material is preferably 0.03 μm or more, more preferably 0.1 μm or more, even more preferably 0.5 μm or more, preferably 500 μm or less, more preferably 200 μm or less, and even more preferably 30 μm or less. The particle diameter of the electrode active material can be measured by a laser diffraction method. More specifically, in the particle diameter distribution (volume basis) measured using a laser diffraction type particle diameter distribution measuring device, the particle diameter D50 at which the cumulative volume calculated from the small diameter side is 50% is set as the volume average particle diameter, and this value preferably satisfies the above particle diameter range. If the particle diameter of the electrode active material is equal to or less than the above upper limit, the composition within the composite particle can be made more homogeneous. Furthermore, if the particle diameter of the electrode active material is equal to or less than the above upper limit, the electrode density of the obtained electrode can be increased, and the specific surface area of the electrode active material is sufficiently large, so that the electrochemical reaction when forming an electrochemical element can be optimized. If the particle size of the electrode active material is equal to or greater than the lower limit, the powder material can be easily handled when used to manufacture the composite particles, and the productivity of the composite particles can be improved. Furthermore, if the particle size of the electrode active material is equal to or greater than the lower limit, deterioration of the electrode active material during repeated charging and discharging of the electrochemical device can be effectively suppressed.

The conductive assistant material is not particularly limited, and examples thereof 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 crushing polymer fibers after firing, and single-walled or multi-walled graphene. These can be used alone or in combination.

When the electrode active material and the conductive assistant are used together, the mixing ratio of these is not particularly limited, and can be the general mixing ratio of these contained in electrodes for electrochemical elements.

It is preferable not to mix liquid components in the preliminary mixing operation. A small amount of liquid components may be unavoidably contained in the powder material due to the influence of moisture that may adhere during production and storage. In other words, the solid content concentration of the powder material at the start of the preliminary mixing operation is likely to be less than 100% by mass. From the viewpoint of improving the properties of the composite particles obtained and the production efficiency of the composite particles, it is preferable to increase the solid content concentration of the powder material by performing the preliminary mixing operation. Specifically, the solid content concentration of the powder material at the end of the preliminary mixing operation is preferably 95% by mass or more, more preferably 97% by mass or more, and even more preferably 98% by mass or more. The solid content concentration of the powder material can be measured by the method described in the Examples.

The peripheral speed of the main stirring blade and the auxiliary stirring blade in the preliminary stirring operation is preferably 1 m/s or more and 20 m/s or less. If the peripheral speed is within this range, the homogeneity of the composition of the obtained composite particles can be increased, thereby suppressing cracking of the electrode active material in the obtained electrode, and ultimately improving the cycle characteristics of an electrochemical element equipped with such an electrode. Here, the peripheral speeds of the main stirring blade and the auxiliary stirring blade in the preliminary stirring operation may be the same or different, and may be different, but if they are different, it is preferable that the peripheral speed of the auxiliary stirring blade is faster than the peripheral speed of the main stirring blade.

The aeration amount in the preliminary mixing operation is preferably 0.1/min to 100/min, calculated by dividing the flow rate of the air flowing into the granulation tank by the volume of the granulation tank (flow rate/volume). If the aeration amount is within this range, the solid content concentration of the powder material can be increased satisfactorily in the preliminary mixing operation. The aeration amount may be the amount of aeration provided by the ventilation mechanism for preventing the powder material from entering the drive parts of the main mixing blade and the auxiliary mixing blade, as described above. Furthermore, the temperature of the ventilated air is preferably less than 50°C, more preferably 45°C or less, even more preferably 40°C or less, and particularly preferably 30°C or less.

The time for which the pre-mixing operation is performed (pre-mixing time) is not particularly limited. For example, the pre-mixing time is preferably a time that allows the solids concentration to be equal to or greater than the preferred threshold value described above. For example, the pre-mixing time may be 5 minutes or more and 60 minutes or less.

The preliminary mixing operation may be carried out in multiple stages. In that case, it is preferable to carry out a preliminary mixing operation using a mixing device (hereinafter also referred to as "mixing device A") different from the granulation tank equipped with the above-mentioned mixing blades prior to the preliminary mixing operation in the granulation tank equipped with the above-mentioned mixing blades. The mixing device A is not particularly limited as long as it is a mixing device different from the granulation tank equipped with the above-mentioned mixing blades, and examples thereof include a dry mixing device and a wet mixing device. As a dry mixing device, for example, Miracle KCK manufactured by Asada Iron Works, and Hybridization System manufactured by Nara Machinery Co., Ltd. can be used. As a wet mixing device, for example, Planetary Despa manufactured by Asada Iron Works can be used. By carrying out such a preliminary mixing operation using the mixing device A before the preliminary mixing operation using the above-mentioned granulation tank equipped with the mixing blades, the rate characteristics of the obtained electrochemical element can be improved. This is thought to be because the volume resistivity of the obtained composite particles can be reduced by carrying out the preliminary mixing operation using the mixing device A.

<(ii) Composite particle formation operation>
In the composite particle forming operation, a composition containing a binder, a conductive assistant, and a solvent is added to the powder material in a stirring state to form composite particles. The binder is not particularly limited, and can be any suitable binder. Known binders that can be blended in electrodes for chemical elements can be used. In addition, in the composite particle forming operation, when a composition containing a binder, a conductive assistant, and a solvent is added to a powder material, The manner of addition is not particularly limited as long as it is a manner other than lump-sum addition. For example, the manner of addition may be a continuous addition throughout the composite particle formation operation, or a manner in which addition is stopped once or multiple times during the composite particle formation operation. Among them, a continuous addition mode is preferable. That is, while the composite particle forming operation is being performed, that is, while the powder material, the solvent, the conductive assistant, and the binder are all added, the continuous addition mode is preferable. In an atmosphere in which both are kept in a state of agitation, composite particles of the powder material and binder are gradually formed, and the particles and the particles collide with each other and with the solvent, resulting in a granulation effect. . In other words, during the composite particle formation operation, the composite particle formation action and the particle size regulation action can proceed simultaneously in the presence of a solvent. It can be formed while granulating.

As described above, the means for adding the composition containing the binder, the conductive assistant, and the solvent to the powder material include a spray nozzle and a dropping funnel. Among them, from the viewpoint of efficiency, it is preferable to use a spray nozzle. When using a two-fluid spray having a mechanism for pulverizing and atomizing the liquid by the flow of gas as the spray nozzle, the gas-liquid ratio (gas volume/liquid volume) is preferably 1.30 or more, more preferably 1.40 or more, even more preferably 1.45 or more, preferably 1.80 or less, more preferably 1.70 or less, and even more preferably 1.60 or less. If the gas-liquid ratio is equal to or more than the lower limit, the particle size of the composite particles can be suppressed from becoming too large. In addition, if the gas-liquid ratio is equal to or less than the upper limit, the particle size of the composite particles can be suppressed from becoming too small. In addition, the value of the spray surface density (g/ ^mm2 /min), which is a value corresponding to the amount of the composition sprayed per unit area on the stationary surface, is preferably 0.20 (g/ ^mm2 /min) or more, more preferably 0.25 (g/ ^mm2 /min) or more, even more preferably 0.38 (g/ ^mm2 /min) or more, preferably 0.60 (g/ ^mm2 /min) or less, more preferably 0.50 (g/ ^mm2 /min) or less, and even more preferably 0.41 (g/ ^mm2 /min) or less. If the value of the spray surface density (g/ ^mm2 /min) is equal to or more than the lower limit, the particle size of the composite particles can be prevented from becoming excessively small. That is, by controlling the gas-liquid ratio and/or the spray surface density to an appropriate range, the particle size of the obtained composite particles can be well controlled.

[binder]
Examples of the binder that can be used include conjugated diene polymers, acrylic polymers, aromatic vinyl block polymers, fluorine polymers, cellulose polymers, cyclic olefin polymers, etc. The binders may be used alone or in combination of two or more.

Conjugated diene polymers refer to polymers containing conjugated diene monomer units. Specific examples of conjugated diene polymers include, but are not limited to, copolymers containing aromatic vinyl monomer units and aliphatic conjugated diene monomer units, such as styrene-butadiene copolymer (SBR), butadiene rubber (BR), acrylic rubber (NBR) (copolymers containing acrylonitrile units and butadiene units), and hydrogenated versions of these.

The acrylic polymer is not particularly limited, and examples thereof include polymers containing crosslinkable monomer units, (meth)acrylic acid ester monomer units, and acidic group-containing monomer units. The proportion of (meth)acrylic acid ester monomer units in the acrylic polymer is preferably 50% by mass or more, more preferably 55% by mass or more, and even more preferably 58% by mass or more, and is preferably 98% by mass or less, more preferably 97% by mass or less, and even more preferably 96% by mass or less.

Aromatic vinyl block polymers include block polymers containing block regions consisting of aromatic vinyl monomer units. Examples of aromatic vinyl monomers include styrene, styrene sulfonic acid and its salts, α-methylstyrene, p-t-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, and vinylnaphthalene, with styrene being preferred. Preferred examples of aromatic vinyl block polymers include styrene-isoprene-styrene block copolymers, and styrene-butadiene-styrene copolymers, as well as hydrogenated versions of these.

The term "fluorine-based 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, but are not limited to, vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, vinyl trifluoride, vinyl fluoride, trifluoroethylene, trifluorochloroethylene, 2,3,3,3-tetrafluoropropene, and perfluoroalkyl vinyl ether. Examples of fluorine-based polymers include, but are not limited to, polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, perfluoroalkoxy fluororesin, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer (vinylidene fluoride-hexafluoropropylene copolymer), and the like.

Cellulosic polymers include, but are not limited to, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, and carboxymethyl cellulose.

Cyclic olefin polymers are not particularly limited, and examples include polymers (addition polymers or ring-opening polymers) synthesized using cyclic olefin compounds as monomers and their hydrogenated products, as well as hydrogenated polymers using aromatic vinyl compounds as monomers. Among these, hydrogenated ring-opening polymers using cyclic olefin compounds as monomers and hydrogenated polymers using aromatic vinyl compounds as monomers are preferred, since the electrolyte swelling degree and glass transition temperature can be easily adjusted to appropriate levels.

The cyclic olefin compound is not particularly limited and may be, for example,
norbornene, 5-methylnorbornene, 5-ethylnorbornene, 5-butylnorbornene, 5-hexylnorbornene, 5-decylnorbornene, 5-cyclohexylnorbornene, 5-cyclopentylnorbornene, and other unsubstituted or alkyl group-containing norbornenes;
Norbornenes having an alkenyl group, such as 5-ethylidenenorbornene, 5-vinylnorbornene, 5-propenylnorbornene, 5-cyclohexenylnorbornene, and 5-cyclopentenylnorbornene;
norbornenes having an aromatic ring, such as 5-phenylnorbornene;
norbornenes having a polar group containing an oxygen atom, such as 5-methoxycarbonylnorbornene, 5-ethoxycarbonylnorbornene, 5-methyl-5-methoxycarbonylnorbornene, 5-methyl-5-ethoxycarbonylnorbornene, norbornenyl-2-methylpropionate, norbornenyl-2-methyloctanonate, 5-hydroxymethylnorbornene, 5,6-di(hydroxymethyl)norbornene, 5,5-di(hydroxymethyl)norbornene, 5-hydroxy-i-propylnorbornene, 5,6-dicarboxynorbornene, and 5-methoxycarbonyl-6-carboxynorbornene;
Norbornenes having a polar group containing a nitrogen atom, such as 5-cyanonorbornene;
Polycyclic norbornenes having three or more rings and not containing an aromatic ring structure, such as dicyclopentadiene, methyldicyclopentadiene, and tricyclo[5.2.1.02,6]dec-8-ene;
Polycyclic norbornenes having three or more aromatic rings, such as tetracyclo[9.2.1.02,10.03,8]tetradeca-3,5,7,12-tetraene (also referred to as 1,4-methano-1,4,4a,9a-tetrahydro-9H-fluorene) and tetracyclo[10.2.1.02,11.04,9]pentadeca-4,6,8,13-tetraene (also referred to as 1,4-methano-1,4,4a,9,9a,10-hexahydroanthracene);
tetracyclododecenes having unsubstituted or alkyl groups, such as tetracyclododecene, 8-methyltetracyclododecene, 8-ethyltetracyclododecene, 8-cyclohexyltetracyclododecene, 8-cyclopentyltetracyclododecene, and 8-methoxycarbonyl-8-methyltetracyclo[4.4.0.12,5.17,10]-3-dodecene;
tetracyclododecenes having an exocyclic double bond, such as 8-methylidenetetracyclododecene, 8-ethylidenetetracyclododecene, 8-vinyltetracyclododecene, 8-propenyltetracyclododecene, 8-cyclohexenyltetracyclododecene, and 8-cyclopentenyltetracyclododecene;
tetracyclododecenes having an aromatic ring, such as 8-phenyltetracyclododecene;
tetracyclododecenes having a substituent containing an oxygen atom, such as 8-methoxycarbonyltetracyclododecene, 8-methyl-8-methoxycarbonyltetracyclododecene, 8-hydroxymethyltetracyclododecene, 8-carboxytetracyclododecene, tetracyclododecene-8,9-dicarboxylic acid, and tetracyclododecene-8,9-dicarboxylic anhydride;
tetracyclododecenes having a nitrogen atom-containing substituent, such as 8-cyanotetracyclododecene and tetracyclododecene-8,9-dicarboxylic acid 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;
hexacycloheptadecenes such as the Diels-Alder adducts of the above-mentioned tetracyclododecenes and cyclopentadiene;
etc.

Among them, non-polar norbornene monomers are preferred as cyclic olefin compounds, and 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[9.2.1.02,10.03,8]tetradeca-3,5,7,12-tetraene (also called 1,4-methano-1,4,4a,9a-tetrahydro-9H-fluorene)), and tetracyclododecenes having unsubstituted or alkyl groups (e.g., tetracyclododecene, 8-methoxycarbonyl-8-methyltetracyclo[4.4.0.12,5.17,10]-3-dodecene) are more preferred.

The polymer using a cyclic olefin compound as a monomer, which can be optionally hydrogenated, may be a polymer using only a cyclic olefin compound as a monomer, or may be a polymer using a cyclic olefin compound and a copolymerizable compound other than a cyclic olefin compound as monomers, but is preferably a polymer using only a cyclic olefin compound as a monomer.

The polymer using a cyclic olefin compound as a monomer, which 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.

[solvent]
The solvent is not particularly limited, and any solvent can be used as long as it can dissolve or disperse the binder. For example, organic solvents such as N-methyl-2-pyrrolidone, cyclohexane, n-hexane, acetone, methyl ethyl ketone, ethyl acetate, tetrahydrofuran, methylene chloride, and chloroform, and water can be used as the solvent. Among them, from the viewpoint of efficiently removing the solvent in the granulation tank to reduce the drying energy when forming the composite particles, it is preferable to use a non-aqueous solvent having a boiling point of 95° C. or less at 1 atm. Furthermore, from the viewpoint of achieving the above-mentioned effect more favorably, the boiling point of the non-aqueous solvent at 1 atm is more preferably 90° C. or less, and even more preferably 85° C. or less. The lower limit of the boiling point of the non-aqueous solvent at 1 atm is not particularly limited, but from the viewpoint of increasing the stability when forming the composite particles, it is preferably 50° C. or more. Examples of solvents that satisfy such conditions include cyclohexane, n-hexane, acetone, methyl ethyl ketone, ethyl acetate, tetrahydrofuran, methylene chloride, chloroform, and the like. These may be used alone or in combination of two or more kinds in any ratio.

[Composition Viscosity Index]
The viscosity index of the composition containing the binder, conductive assistant, and solvent, which is continuously added to the granulation tank in the composite particle formation operation, is preferably 100 mPa·s or more and 1000 mPa·s or less. By setting the viscosity index of the composition containing the binder, conductive assistant, and solvent within the above range, the particle size and variation coefficient of the obtained composite particles can be well controlled. The viscosity index of the composition is the value obtained by dividing the viscosity of the composition by the solid content concentration and multiplying it by 100, and can be measured and calculated by the method described in the examples.

[Mixing blade peripheral speed]
The peripheral speed of the main stirring blade and the auxiliary stirring blade in the composite particle forming operation is preferably 1 m/s or more and 20 m/s or less. If the peripheral speed of the main stirring blade is within the above range, the particle size of the obtained composite particles can be well controlled. In addition, if the peripheral speed of the auxiliary stirring blade is within the above range, the coefficient of variation of the obtained composite particles can be well controlled. Furthermore, in order to enhance the particle size regulation action occurring during the composite particle forming operation and to suppress gas generation during high-temperature storage of the electrode formed using the composite particles, the lower limit of the peripheral speed of the main stirring blade is preferably 6 m/s or more, and the upper limit is preferably 12 m/s or less.

[Ventilation volume]
The aeration amount in the composite particle formation operation is preferably 0.1/min to 100/min, calculated by dividing the flow rate of air flowing into the granulation tank by the volume of the granulation tank (flow rate/volume). If the aeration amount is within this range, the amount of solvent vapor in the granulation tank can be well controlled in the composite particle formation operation, and composite particles can be efficiently formed.

[time]
The duration of the composite particle formation operation (composite particle formation time) is not particularly limited. For example, the composite particle formation time may be 5 minutes or more and 60 minutes or less.

<(iii) Sizing operation>
In the sizing operation, the composite particles are sized by stirring after the addition of the composition is completed (i.e., after the composite particle formation operation (ii) is completed). From the viewpoint of enhancing the electrical conductivity, a conductive assistant may be further added.

The peripheral speed of the main stirring blade and the auxiliary stirring blade in the sizing operation is preferably 0.1 m/s or more and 10 m/s or less. If the peripheral speed of the main stirring blade is within the above range, the density coefficient and areal circularity of the obtained composite particles can be well controlled. Also, if the peripheral speed of the auxiliary stirring blade is within the above range, the variation coefficient and perimeter envelope of the obtained composite particles can be well controlled. The "perimeter envelope" of the composite particles is a value that serves as an index of the roughness of the outer periphery of the particle, and can be measured according to the method described in the examples of this specification.

It is preferable that the aeration rate during the sizing operation, calculated by dividing the flow rate of the air flowing into the granulation tank by the volume of the granulation tank (flow rate/volume), is 0.1/min or more and 100/min or less. If the aeration rate is within this range, the moist state of the composite particles can be well controlled during the sizing operation, and the composite particles can be efficiently formed.

When performing a sizing operation, the duration of the sizing operation (sizing time) is not particularly limited. The sizing time may be, for example, 10 seconds or more, or 60 minutes or less, preferably 20 minutes or less, preferably 10 minutes or less, and more preferably 3 minutes or less. By setting the sizing operation time to the above upper limit or less, it is possible to reduce the amount of gas generated when an electrode formed using the composite particles is stored under high temperature conditions.

<Temperature inside granulation tank>
Throughout the above operations (i) to (iii), the temperature in the granulation tank is preferably less than 50° C., more preferably not more than 45° C., and even more preferably not more than 40° C. By satisfying such temperature conditions, deterioration of the electrode active material contained in the obtained composite particles can be effectively suppressed, and cracking of the electrode active material in an electrode formed using the composite particles can be effectively suppressed.

(Composite particles)
The composite particles obtained through the above steps (i) to (iii) preferably satisfy the following attributes:

<Particle size of composite particles>
The composite particles preferably have a particle diameter of 20 μm or more, more preferably 30 μm or more, even more preferably 40 μm or more, preferably 250 μm or less, more preferably 200 μm or less, and even more preferably 150 μm or less. The particle diameter of the composite particles means the average particle diameter of the area equivalent diameter, and can be measured according to the method described in the examples of this specification. If the particle diameter of the composite particles is equal to or greater than the above lower limit, the flexibility of the electrode formed using the composite particles can be increased, and the rate characteristics of the electrochemical element equipped with such an electrode can be improved. In addition, if the particle diameter of the composite particles is equal to or less than the above upper limit, the cycle characteristics of the resulting electrochemical element can be improved.

<Coefficient of variation of composite particles>
The coefficient of variation of the composite particles is preferably 5% or more, more preferably 7% or more, even more preferably 10% or more, and preferably 50% or less, more preferably 45% or less, and even more preferably 40% or less. If the coefficient of variation is equal to or greater than the lower limit, the cracking of the electrode active material in the electrode formed using the composite particles can be suppressed well. Also, if the coefficient of variation is equal to or less than the upper limit, the flexibility of the obtained electrode can be improved.
In the present application, the coefficient of variation of a composite particle means the particle size distribution of the composite particle, and can be calculated as a percentage by dividing the standard deviation of the area-equivalent diameters of the composite particles by the average area-equivalent diameters, according to the method described in the examples of this specification.

<Bulk density>
The bulk density of the composite particles is preferably 1.0 to 4.0. If the bulk density is equal to or higher than the lower limit, cracking of the electrode active material in the electrode formed using the composite particles can be suppressed. If the bulk density is equal to or lower than the upper limit, the flexibility of the resulting electrode can be increased.

<Circularity of area>
The circularity of the composite particles is preferably 0.50 or more, more preferably 0.60 or more, even more preferably 0.70 or more, and preferably 0.93 or less, more preferably 0.92 or less, and even more preferably 0.91 or less. If the circularity of the composite particles is equal to or more than the lower limit, the cracking of the electrode active material in the electrode formed using the composite particles can be suppressed. In addition, if the circularity of the composite particles is equal to or less than the upper limit, the rate characteristics of the obtained electrochemical element can be improved.

<Circumference Envelope>
The circumferential envelopment degree of the composite particles is preferably 0.70 or more, more preferably 0.72 or more, even more preferably 0.75 or more, and preferably 0.97 or less, more preferably 0.94 or less, and even more preferably 0.92 or less. If the circumferential envelopment degree of the composite particles is the above lower limit or more, the flexibility of the electrode formed using the composite particles can be improved. If the circumferential envelopment degree of the composite particles is the above upper limit or less, the cycle characteristics of the obtained electrochemical element can be improved.

<Liquidity>
The flowability of the composite particles can be evaluated based on the angle of repose and the angle of collapse measured using a powder tester, and can also be evaluated based on the roughness of the surface smoothed with a doctor blade as described in the examples of the present application. The surface roughness is preferably 0.70 μm ³ or less, more preferably 0.50 μm ³ or less, even more preferably 0.30 μm ³ or less, and particularly preferably 0.20 μm ³ or less, in terms of spatial volume ^per 5.4 mm 2. The lower limit of the surface roughness is not particularly limited, but may be, for example, 0.01 μm ³ or more. If the composite particles have excellent flowability, the smoothness of the surface of the resulting electrode can be improved, thereby reducing the internal resistance of the electrochemical element and improving the rate characteristics.

(Method of manufacturing an electrode for an electrochemical device)
The method for producing an electrode for an electrochemical device of the present invention includes producing composite particles according to the above-mentioned production method of the present invention, and pressure-molding the produced composite particles on an electrode substrate to form an electrode mixture layer (pressure molding operation). The electrode for an electrochemical device obtained according to this production method has excellent flexibility and is less susceptible to cracking of the electrode active material contained therein, and furthermore, can improve the cycle characteristics of an electrochemical device equipped with this electrode.

<Pressure molding operation>
The pressure molding operation can be carried out according to a known method. For example, the composite particles produced according to the production method of the present invention can be subjected to a roll press machine and roll pressed on the electrode substrate to pressure mold the composite particles on the electrode substrate to form an electrode mixture layer. The pressure during pressing can be appropriately set according to the desired electrode density.

The electrode substrate is made of a material that is conductive and electrochemically durable. Specifically, the electrode substrate may be a collector made of, for example, iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, or the like. The above materials may be used alone or in combination of two or more types in any ratio.

(Electrochemical element)
The electrochemical element formed using the above-mentioned electrode for electrochemical elements of the present invention is not particularly limited, and may be, for example, a lithium ion secondary battery, an electric double layer capacitor, or a lithium ion capacitor, and is preferably a lithium ion secondary battery. The electrochemical element formed using the electrode for electrochemical elements of the present invention has excellent cycle characteristics.

Hereinafter, an example will be described in which the electrochemical element is a lithium ion secondary battery, but the present invention is not limited to the following example. A lithium ion secondary battery as the electrochemical element of the present invention typically comprises electrodes (positive and negative electrodes), an electrolyte, and a separator, and uses the electrochemical element electrode of the present invention for at least one of the positive and negative electrodes.

<Electrodes>
Here, the electrode other than the above-mentioned electrode for electrochemical elements of the present invention that can be used in a lithium ion secondary battery as an electrochemical element is not particularly limited, and a known electrode can be used. Specifically, the electrode other than the above-mentioned electrode for electrochemical elements can be an electrode formed by forming an electrode mixture layer on a current collector using a known manufacturing method.

<Electrolyte>
As the electrolyte, an organic electrolyte in which a supporting electrolyte is dissolved in an organic solvent is usually used. As the supporting electrolyte, for example, a lithium salt is used. As the lithium salt, for example, _LiPF6 , _LiAsF6 , _LiBF4 , LiSbF6, LiAlCl4, _LiClO4 , CF3SO3Li, _C4F9SO3Li , _CF3COOLi , ( _CF3CO ) _2NLi , ( _{CF3SO2 ) 2NLi} , ( _C2F5SO2 )NLi, _etc. are listed. _{Among them} , _LiPF6 , _LiClO4 , _{and CF3SO3Li are preferred} , and _{LiPF6 is} particularly preferred, because _they are easily dissolved in the solvent and show a high degree of _dissociation . The electrolyte may be used alone or in combination of two or more kinds in any ratio.

The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte, but for example, carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and methyl ethyl carbonate (EMC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; and sulfur-containing compounds such as sulfolane and dimethyl sulfoxide; are preferably used. A mixture of these solvents may also be used. The concentration of the electrolyte in the electrolyte can be adjusted as appropriate. Known additives, such as vinylene carbonate, fluoroethylene carbonate, and ethyl methyl sulfone, may also be added to the electrolyte.

<Separator>
The separator is not particularly limited and may be any known one. Among them, a microporous film made of a polyolefin resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferable. Furthermore, the separator may be a separator with a functional layer, in which a functional layer (porous membrane layer or adhesive layer) is provided on one or both sides of a separator substrate.

<Method of manufacturing lithium-ion secondary battery>
A lithium ion secondary battery can be manufactured, for example, by stacking a positive electrode and a negative electrode with a separator therebetween, wrapping or folding the stack according to the battery shape as necessary, placing the stack in a battery container, injecting an electrolyte into the battery container, and sealing the container. In order to prevent the occurrence of an internal pressure rise in the secondary battery, overcharging and overdischarging, etc., a fuse, an overcurrent prevention element such as a PTC element, an expanded metal, a lead plate, etc. may be provided as necessary. The shape of the secondary battery may be, for example, any of a coin type, a button type, a sheet type, a cylindrical type, a square type, a flat type, etc.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" expressing amounts are based on mass unless otherwise specified.
In addition, in a polymer produced by copolymerizing multiple types of monomers, the ratio of a repeating unit (monomer unit) formed by polymerizing a certain monomer in the polymer usually coincides with the ratio (feed ratio) of the certain monomer to all monomers used in the polymerization of the polymer, unless otherwise specified.
In the examples and comparative examples, the measurement and evaluation of various attributes were carried out according to the following methods.

<Solid content of powder material>
The measurement target was weighed out in an amount of Wo [g] on an aluminum dish with a mass of Wa [g] and heated for 1 hour on a hot plate at 130° C. The mass W [g] after heating was measured, and the solid content concentration Cs [%] of the powder material was calculated using the following formula.
Cs=(W-Wa)/Wo×100 [%]

<Viscosity index Cη of composition containing binder, conductive assistant, and solvent>
The viscosity index of the composition containing the binder, the conductive assistant, and the solvent was calculated using the following formula from the viscosity measured by the method shown below and the solid content measured by the method described above.
Viscosity measurement: The viscosity η was measured at 25° C. and 60 rpm using a Brookfield viscometer (TVB-10M, manufactured by Toki Sangyo Co., Ltd.) The rotor used was appropriately changed according to the viscosity.
Calculation of viscosity index: Cη = η / Cs × 100 [mPa s]

<Particle size, coefficient of variation of particle size distribution, circularity, and perimeter envelope of composite particles>
Based on the image analysis method in accordance with JIS Z 8827-1, image analysis processing was performed on the composite particles prepared in the examples and comparative examples, and the specified physical properties were calculated. Specifically, using Malvern's "Morphologi G3," images of 4,000 composite particles prepared in each example and comparative example were binarized and analyzed to determine the following physical properties. The definitions of terms are in accordance with JIS Z 8890, "Evaluation of particle characteristics of powders - Terminology."
Particle diameter: average particle diameter D _A (μm) of the area-equivalent diameter of 4,000 analyzed composite particles
Coefficient of variation of particle size distribution: A value calculated from the average value D _A of the area-equivalent diameters of 4,000 analyzed composite particles and its standard deviation σ CV
CV=σ/D _A ×100(%)
Average areal circularity: The average areal circularity _C of 4,000 analyzed particles calculated by 4πA/P ² (A: projected area, P: perimeter)
Average perimeter envelope: The average value of the perimeter of the convex circumscribing figure (minimum convex hull) of all particles in the observation field divided by the perimeter P

<Bulk density ρ _a >
The bulk density (g/cm ³ ) of the composite particles was measured based on the constant volume measurement method described in JIS R 1628-1997.

<Fluidity (evaluation based on surface roughness)>
25 g of the composite particles produced in the Examples and Comparative Examples were placed on a 20 cm square glass plate with a smooth surface so that the diameter was about 20 mm, and the particles were smoothed with a 280 μm doctor blade. The void volume ( ^μm3 ) per 5.4 ^mm2 of the smoothed surface was measured using a laser microscope.

<Electrode flexibility>
The positive electrodes prepared in the examples and comparative examples were wound around rods of different diameters to evaluate whether the positive electrode mixture layer cracked. The smaller the diameter of the rod on which the positive electrode mixture layer did not crack when wound around the rod, the more flexible the electrode was and the better the winding properties. The flexibility of the electrode was evaluated according to the following criteria, depending on the diameter of the thinnest rod on which the positive electrode mixture layer did not crack.
A: It does not break even when wrapped around a rod with a diameter of 1.50 mm.
B: It does not break even when wrapped around a rod with a diameter of 1.80 mm.
C: It does not break even when wrapped around a rod with a diameter of 2.10 mm.
D: It does not break even when wrapped around a rod with a diameter of 3.00 mm.

<Whether or not the active material is cracked>
Cross-sectional SEM images of the positive electrodes produced in the Examples and Comparative Examples were observed at 1000x magnification, and the number of cracks observed in the active material was evaluated as follows.
A: No cracked positive electrode active material was observed.
B: The number of broken positive electrode active materials was 1 or more and less than 3.
C: The number of cracked positive electrode active materials was 3 or more and less than 5.
D: The number of broken positive electrode active materials was 5 or more.

<Cycle characteristics>
The lithium ion secondary battery as the electrochemical element prepared in the examples and comparative examples was left at rest at a temperature of 25°C for 5 hours after injecting the electrolyte. Next, the battery was charged to a cell voltage of 3.65V at a constant current of 0.2C at a temperature of 25°C, and then aged at a temperature of 60°C for 12 hours. Then, the battery was discharged to a cell voltage of 3.00V at a constant current of 0.2C at a temperature of 25°C. Then, the battery was CC-CV charged (upper cell voltage 4.20V) at a constant current of 0.2C, and CC discharged to 3.00V at a constant current of 0.2C. This charge and discharge at 0.2C was repeated three times to obtain an evaluation cell.
Next, the above evaluation cell was subjected to 100 cycles of charge and discharge at a cell voltage of 4.20-3.00V and a charge and discharge rate of 0.5C in an environment at a temperature of 45°C. At this time, the discharge capacity of the first cycle was defined as X1, and the discharge capacity of the 100th cycle was defined as X2. Using the discharge capacity X1 and the discharge capacity X2, the capacity retention rate = (X2/X1) x 100 (%) was calculated and evaluated according to the following criteria. A larger value of the capacity retention rate indicates that the lithium ion secondary battery has better cycle characteristics.
A: Capacity retention rate is 90% or more. B: Capacity retention rate is 85% or more and less than 90%. C: Capacity retention rate is 80% or more and less than 85%. D: Capacity retention rate is less than 80%.

<Gas generation amount during high temperature storage>
The evaluation cell prepared in the above-mentioned <Cycle characteristics> section was CC-CV charged (upper cell voltage 4.20 V) by a constant current method of 0.2 C at a temperature of 25° C., and then stored for one week in a constant temperature environment of 60° C. The cell volume was measured before and after storage, and the increase was taken as the amount of gas generated, which was evaluated according to the following criteria.
A: The amount of gas generated is less than 5%. B: The amount of gas generated is 5% or more and less than 10%. C: The amount of gas generated is 10% or more and less than 20%. D: The amount of gas generated is 20% or more.

<Rate characteristics>
The lithium ion secondary battery as the electrochemical element prepared in the example was left to stand at a temperature of 25°C for 5 hours after injecting the electrolyte. Next, the battery was charged to a cell voltage of 3.65V at a constant current of 0.2C at a temperature of 25°C, and then aged at a temperature of 60°C for 12 hours. Then, the battery was discharged to a cell voltage of 3.00V at a constant current of 0.2C at a temperature of 25°C. Then, the battery was CC-CV charged (upper cell voltage 4.20V) at a constant current of 0.2C, and CC discharged to 3.00V at a constant current of 0.2C. This charge and discharge at 0.2C was repeated three times.
Next, in an environment of 25°C, the battery was charged to 4.2V by a constant current method of 0.1C, and then discharged to 3.0V at 0.1C to obtain the 0.1C discharge capacity. Furthermore, the battery was charged to 4.2V at 0.1C, and then discharged to 3.0V at 1C to obtain the 1C discharge capacity. These measurements were performed on 10 cells of each of the lithium ion secondary batteries as electrochemical elements prepared in the examples and comparative examples, and the average values of the respective measurements were taken as 0.1C discharge capacity a and 1C discharge capacity b. Then, the ratio of the electric capacity = b/a x 100 (%) was calculated and evaluated according to the following criteria. The larger the value of the ratio of the electric capacity, the more excellent the rate characteristics of the lithium ion secondary battery as an electrochemical element.
AA: Electric capacity ratio is 92 or more. A: Electric capacity ratio is 90% or more and less than 92. B: Electric capacity ratio is 80% or more and less than 90%. C: Electric capacity ratio is 70% or more and less than 80%. D: Electric capacity ratio is less than 70%.

Example 1
<Production of binder A1>
In a reactor equipped with a stirring device and the inside of which was sufficiently replaced with nitrogen, 270 parts of dehydrated cyclohexane and 0.53 parts of ethylene glycol dibutyl ether were placed, and 0.47 parts of n-butyllithium (15% cyclohexane solution) were further added. While stirring the entire volume at 60°C, 12.5 parts of dehydrated styrene were continuously added into the reactor over 40 minutes. After the addition was completed, the entire volume was further stirred at 60°C for 20 minutes. When the reaction liquid was measured by gas chromatography, the polymerization conversion rate at this point was 99.5%. Next, 75.0 parts of dehydrated isoprene was continuously added to the reaction liquid over 100 minutes, and after the addition was completed, stirring was continued for 20 minutes. The polymerization conversion rate at this point was 99.5%. Thereafter, 12.5 parts of dehydrated styrene was further continuously added over 60 minutes, and after the addition was completed, the entire volume was stirred for 30 minutes. The polymerization conversion rate at this point was almost 100%. Here, 0.5 parts of isopropyl alcohol was added to the reaction solution to terminate the reaction. The ratio of structural units derived from 1,2- and 3,4-addition polymerization to the total structural units derived from isoprene in the obtained block copolymer 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 inside of the reactor was replaced with hydrogen gas, and hydrogen was further supplied while stirring the solution, and the hydrogenation reaction was carried out at a temperature of 190°C and a pressure of 4.5 MPa for 6 hours. After the hydrogenation reaction was completed, the reaction solution was filtered to remove the hydrogenation catalyst, and then 1.0 part of a xylene solution in which 0.1 part of pentaerythrityl tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] (manufactured by Koyo Chemical Laboratory, product name "Songnox 1010"), a phenolic antioxidant, was dissolved, was added to the filtrate and dissolved. Cyclohexane was further added to prepare a binder A1 solution of a predetermined concentration.

<Evaluation of Binder A1>
- Proportion of structural units derived from 1,2- and 3,4-addition polymerization among structural units derived from linear conjugated diene compounds in polymer blocks -
The ratio of structural units derived from 1,2- and 3,4-addition polymerization among the structural units derived from the chain conjugated diene compound in the polymer block was calculated from the ratio of ^1H bonded to the carbon of the carbon-carbon unsaturated bond in the polymer main chain to ^1H bonded to the carbon of the carbon-carbon unsaturated bond in the polymer side chain from the ^1H -NMR spectrum (in deuterated chloroform) of the block copolymer. The value is shown above.

<Preparation of composition containing binder, conductive assistant, and solvent>
Two parts of carbon black (BET specific surface area: 62 m ² /g, bulk density 0.16 g/cm ³ ) as a conductive assistant were mixed with two parts of the binder A1 solution obtained above in terms of solid content, and cyclohexane was further added as a solvent to prepare a mixture of conductive assistant, binder, and solvent with a solid content concentration of 10% and a total amount of 1 kg. Next, the obtained mixture was dispersed for 1 hour at a peripheral speed of 12 m/s using a bead mill (LMZ015, manufactured by Ashizawa Finetech) using zirconia beads with a diameter of 0.5 mm, to prepare a composition containing conductive assistant, binder, and solvent. The obtained composition had a solid content concentration of 10 mass% and a viscosity index of 300 mPa·s.

<Preparation of Composite Particles>
A composite particle production device was prepared, which had a cylindrical container with an inner diameter of 180 mm and a capacity of 2 L as a granulation tank, and agitation blades on two axes, vertical and horizontal, with the axis of the cylindrical container being the vertical direction (the vertical direction is the main agitation blade, and the horizontal direction is the auxiliary agitation blade). The main agitation blade was an inclined paddle with three main blades with a diameter of 170 mm, and the auxiliary agitation blade had a V-shaped anchor blade with a diameter of 30 mm, and was configured with a mechanism that was sealed by ventilating air to prevent raw materials from being mixed into each drive part of the main agitation blade and the auxiliary agitation blade. Using the composite particle production device, (i) a preliminary mixing operation, (ii) a composite particle formation operation, and (iii) a sizing operation were performed in this order to produce composite particles.
First, in the (i) preliminary mixing operation, 96 parts by mass (1344 g) of NMC532 (average particle size 6 μm) was added as a positive electrode active material for lithium ion batteries into the granulation tank. Next, room temperature air (hereinafter also referred to as "sealing air") for sealing each driving part of the main mixing blade and the auxiliary mixing blade was circulated at 20 L/min (airflow rate 10/min), and the mixture was mixed for 15 minutes under the operating conditions of a peripheral speed of the main mixing blade of 5 m/s and a peripheral speed of the auxiliary mixing part of 6 m/s. The solid content concentration of the powder material after mixing was measured and found to be 99% by mass or more.
Next, (ii) as a composite particle formation operation, room temperature sealing air was circulated at 20 L/min (airflow rate 10/min), the main stirring blade was operated at a peripheral speed of 5 m/s, and the sub stirring blade was operated at a peripheral speed of 6 m/s. Under these operating conditions, 4 parts by mass (280 g) of a composition containing binder A1, carbon black as a conductive additive, and a solvent (solid content concentration: 10 mass%, viscosity index: 300 mPa·s, solvent: cyclohexane) was continuously added as a solid content using a dropping funnel over a period of 15 minutes.
Next, (iii) as a particle size adjustment operation, room temperature sealing air was circulated at 20 L/min (airflow rate 10/min), and the main stirring blade was operated at a peripheral speed of 2 m/s, and the auxiliary stirring blade was operated at a peripheral speed of 2 m/s for 10 minutes. The maximum temperature in the system throughout these steps (i) to (iii) was 38°C.
The composite particles prepared by carrying out the above steps (i) to (iii) in this order were subjected to various measurements. The results are shown in Table 1.

<Preparation of Positive Electrode for Lithium-Ion Secondary Battery>
The prepared composite particles were fed to a press roll (roll temperature 100 ° C., press line pressure 500 kN / m) of a roll press machine (Hirano Giken Kogyo Co., Ltd. "Press cut rough surface hot roll") using a quantitative feeder (Nikka Spray K-V) manufactured by Nikka Corporation. Between the press rolls, an aluminum foil having a thickness of 20 μm was inserted, and the composite particles supplied from the quantitative feeder were attached to the aluminum foil, and pressure-molded at a molding speed of 1.5 m / min to obtain a positive electrode raw sheet for lithium ion secondary batteries having a positive electrode active material layer with a basis weight of 30 mg / cm ^2. This positive electrode raw sheet was rolled with a roll press to produce a sheet-shaped positive electrode consisting of a positive electrode mixture layer with a density of 3.5 g / cm ³ and aluminum foil.
<Preparation 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 added, and the mixture was heated to 50 ° C. to start 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. After adding a 5% aqueous sodium hydroxide solution to this mixture to adjust the pH to 8, the unreacted monomer was removed by heating and vacuum distillation. The mixture was then cooled to 30 ° C. or less to obtain an aqueous dispersion containing a binder for the negative electrode.
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 the planetary mixer. The mixture was then diluted with ion-exchanged water to a solid content 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 solid content, and kneaded for 40 minutes at a rotation speed of 40 rpm. Then, ion-exchanged water was added so that the viscosity was 3000±500 mPa·s (measured with a B-type viscometer at 25°C and 60 rpm), to prepare a slurry for the negative electrode composite layer.
Next, a copper foil having a thickness of 15 μm was prepared as a current collector. The above-mentioned negative electrode composite layer slurry was applied to the copper foil so that the coating amount after drying was 15 mg/cm ² , and dried at 60 ° C for 20 minutes and at 120 ° C for 20 minutes. Then, the negative electrode raw material was heated at 150 ° C for 2 hours to obtain a negative electrode raw material. This negative electrode raw material was rolled with a roll press to produce a sheet-shaped negative electrode consisting of a negative electrode composite layer (both sides) having a density of 1.6 g/cm ³ and copper foil.
<Preparation of Lithium-Ion Secondary Battery>
Using the above positive electrode, negative electrode and separator (made of polyethylene, thickness 12 μm), a single-layer laminate cell (equivalent to a discharge capacity of 250 mAh) was prepared and placed in an aluminum packaging material. Then, a 1.0 M LiPF ₆ solution (solvent: mixed solvent of ethylene carbonate (EC) / diethyl carbonate (DEC) = 3 / 7 (volume ratio), additive: containing 2 volume% vinylene carbonate (solvent ratio)) was filled into the aluminum packaging material as an electrolyte. 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 prepared. Various evaluations were performed using this lithium ion secondary battery. The results are shown in Table 1.

Example 2
In the (ii) composite particle formation operation in <Preparation of composite particles>, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that a composition produced using binder A2 (solid content concentration: 10% by mass, binder liquid viscosity: 400 mPa·s, solvent: acetone) prepared as described below was used instead of binder A1. The results are shown in Table 1.
<Production of binder A2>
In a reactor having an internal volume of 10 liters, 100 parts of ion-exchanged water, 35 parts of acrylonitrile as a nitrile group-containing monomer, and 65 parts of 1,3-butadiene as an aliphatic conjugated diene monomer were charged, and 2 parts of potassium oleate as an emulsifier, 0.1 parts of potassium phosphate as a stabilizer, and 0.4 parts of tert-dodecyl mercaptan (TDM) as a molecular weight regulator were added, and emulsion polymerization was carried out at a temperature of 530 ° C. in the presence of 0.35 parts of potassium persulfate as a polymerization initiator, to copolymerize acrylonitrile and 1,3-butadiene. When the polymerization conversion rate reached 95%, 0.2 parts of hydroxylamine sulfate per 100 parts of monomer was added to terminate the polymerization. Subsequently, the mixture was heated and subjected to steam distillation at about 90 ° C. under reduced pressure to recover the residual monomer, and then 0.1 parts of dibutylhydroxytoluene (BHT) was added as a substituted phenol to obtain an aqueous dispersion of the polymer. A 25% by mass aqueous solution of calcium chloride (CaCl ₂ ) was added as a coagulant in an amount of 3 parts per 100 parts of polymer solids in the obtained aqueous dispersion while stirring, and the polymer in the aqueous dispersion was coagulated. After that, the polymer was filtered off, and 50 times the amount of ion-exchanged water was passed through the obtained polymer to wash it, and then the polymer was dried under reduced pressure at a temperature of 90° C. to obtain a polymer precursor. Next, an oil phase hydrogenation method was adopted as a hydrogenation method to hydrogenate the polymer precursor. The polymer precursor was dissolved in acetone so that the concentration of the polymer precursor was 12%, to obtain an acetone solution of the polymer precursor as the hydrogenation target, which was placed in an autoclave, and 500 ppm of palladium-silica (Pd/SiO ₂ ) was added as a catalyst to 100% of the polymer precursor as the hydrogenation target, and then a hydrogenation reaction was carried out at a temperature of 90° C. for 6 hours under a hydrogen pressure of 3.0 MPa to obtain a hydrogenation reaction product. After the hydrogenation reaction was completed, the palladium-silica was filtered off, and acetone was added so as to give a predetermined solid content concentration, thereby obtaining a binder A2 solution.

Example 3
Except for the following changes in the <Preparation of Composite Particles> step, the same operations, measurements, and evaluations were carried out as in Example 1. The results are shown in Table 1.
(i) Preliminary mixing operation in <Preparation of composite particles> was carried out in two stages. Specifically, the preliminary mixing operation in the granulation tank under the same conditions as in Example 1 was shortened to 1 minute. Furthermore, prior to this operation, a mixture of 96 parts by mass of NMC532 as a positive electrode active material for lithium ion batteries and 0.5 parts by mass of carbon black as a conductive assistant was mixed using Miracle KCK (registered trademark) (model: M.KCK-L) manufactured by Asada Iron Works, under conditions of a rotation speed of 40 rpm, a processing speed of 1 L/h, and a processing time of 10 minutes, and the obtained powder material was subjected to a preliminary mixing operation with a mixing time of 1 minute.
In addition, (ii) in the composite particle forming operation, the amount of conductive assistant added to the composition containing the binder, solvent, and conductive assistant added to the stirring tank was reduced so that the total amount in the composite particles was the same as in Example 1. Furthermore, in (ii) in the composite particle forming operation, the main stirring blade was operated at a peripheral speed of 8 m/s, room temperature sealing air was circulated at 10 L/min (airflow rate 5/min), and the addition means of the predetermined composition was changed to a two-fluid spray. The gas-liquid ratio (gas volume/liquid volume) and spray surface density at this time were as shown in Table 1. And, (iii) the operation time of the sizing operation was shortened to 1 minute. The maximum temperature in the system throughout these steps (i) to (iii) was 40°C.

Example 4
Except for the following changes in the <Preparation of Composite Particles> step, the same operations, measurements, and evaluations were carried out as in Example 1. The results are shown in Table 1.
In the (i) preliminary stirring operation in <Preparation of composite particles>, in addition to the electrode active material, a part of the conductive auxiliary material to be blended was also added. The preliminary stirring operation was performed in two stages. Specifically, the preliminary stirring operation in the granulation tank under the same conditions as in Example 1 was performed by shortening the time to 1 minute. Furthermore, prior to this operation, a mixture of NMC532 as a positive electrode active material for lithium ion batteries and carbon black as a conductive auxiliary material was mixed using Miracle KCK (registered trademark) (model: M-KCK-L) manufactured by Asada Iron Works, under conditions of a rotation speed of 40 rpm, a processing speed of 1 L/h, and a processing time of 10 minutes, and the obtained powder material was subjected to a preliminary stirring operation with a stirring time of 1 minute.

Example 5
<Preparation of Composite Particles> Various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that the steps were changed as follows. The results are shown in Table 1.
In the (ii) composite particle formation operation in <Preparation of composite particles>, the main stirring blade was operated at a peripheral speed of 8 m/s, and room temperature sealing air was circulated at 10 L/min (airflow rate 5/min). Then, the operation time of (iii) particle size adjustment operation was shortened to 1 minute. The maximum temperature in the system throughout these steps (i) to (iii) was 40°C.

Example 6
Except for the following changes in the <Preparation of Composite Particles> step, the same operations, measurements, and evaluations were carried out as in Example 1. The results are shown in Table 1.
In the (i) preliminary stirring operation in <Preparation of composite particles>, in addition to the electrode active material, a part of the conductive additive was also added. Specifically, a mixture of 96 parts by mass of NMC532 as a positive electrode active material for lithium ion batteries and 0.5 parts by mass of carbon black as a conductive additive was used as a powder material and subjected to the preliminary diffusion operation.
In addition, in (ii) the composite particle formation operation, the amount of conductive assistant blended in the composition containing the binder, solvent, and conductive assistant added to the stirring tank was reduced so that the total blended amount in the composite particles was the same as in Example 1. Furthermore, in (ii) the composite particle formation operation, the means of adding the predetermined composition was changed to a two-fluid spray. The gas-liquid ratio (gas volume/liquid volume) and spray surface density in this case were as shown in Table 1. The maximum temperature in the system throughout these steps (i) to (iii) was 40°C.

(Example 7)
The same operations, measurements and evaluations as in Example 6 were carried out, except for the following changes in the <Preparation of Composite Particles> step. The results are shown in Table 1.
(ii) In the composite particle forming operation, when a predetermined composition was added by two-fluid spray, the gas-liquid ratio (gas volume/liquid volume) and spray surface density were as shown in Table 1.
The maximum temperature in the system throughout steps (i) to (iii) was 36°C.

(Example 8)
The same operations, measurements and evaluations as in Example 6 were carried out, except for the following changes in the <Preparation of Composite Particles> step. The results are shown in Table 1.
(ii) In the composite particle forming operation, the main impeller was operated at a peripheral speed of 15 m/s, the auxiliary impeller was operated at a peripheral speed of 2 m/s, and the means of adding the predetermined composition was changed to a two-fluid spray. The gas-liquid ratio (gas volume/liquid volume) and spray surface density were as shown in Table 1.
(iii) In the sizing operation, the secondary stirring blade was operated at a peripheral speed of 10 m/s.
The maximum temperature in the system throughout steps (i) to (iii) was 42°C.

Example 9
The same operations, measurements and evaluations as in Example 6 were carried out, except for the following changes in the <Preparation of Composite Particles> step. The results are shown in Table 1.
(ii) In the composite particle forming operation, the main impeller was operated at a peripheral speed of 3 m/s, the auxiliary impeller was operated at a peripheral speed of 10 m/s, and the means of adding the predetermined composition was changed to a two-fluid spray. The gas-liquid ratio (gas volume/liquid volume) and spray surface density were as shown in Table 1.
The maximum temperature in the system throughout steps (i) to (iii) was 34°C.

Example 10
The same operations, measurements and evaluations as in Example 6 were carried out, except for the following changes in the <Preparation of Composite Particles> step. The results are shown in Table 1.
(ii) In the composite particle forming operation, the main impeller was operated at a peripheral speed of 8 m/s, the auxiliary impeller was operated at a peripheral speed of 6 m/s, and the means of adding the predetermined composition was changed to a two-fluid spray. The gas-liquid ratio (gas volume/liquid volume) and spray surface density were as shown in Table 1.
(iii) In the sizing operation, the main stirring blade was operated at a peripheral speed of 0.4 m/s.
The maximum temperature in the system throughout steps (i) to (iii) was 38°C.

(Example 11)
The same operations, measurements and evaluations as in Example 6 were carried out, except for the following changes in the <Preparation of Composite Particles> step. The results are shown in Table 1.
(ii) In the composite particle forming operation, the main impeller was operated at a peripheral speed of 5 m/s, the auxiliary impeller was operated at a peripheral speed of 10 m/s, and the means of adding the predetermined composition was changed to a two-fluid spray. The gas-liquid ratio (gas volume/liquid volume) and spray surface density were as shown in Table 1.
(iii) In the sizing operation, the main stirring blade was operated at a peripheral speed of 6 m/s.
The maximum temperature in the system throughout steps (i) to (iii) was 38°C.

(Comparative Example 1)
Except for using a granulation vessel not having a secondary stirring blade, the same operations, measurements, and evaluations (except for rate characteristics) as in Example 1 were carried out. The results are shown in Table 2.

(Comparative Example 2)
A granulation vessel was used in which the rotation axis of the auxiliary agitator was in the vertical direction, and the peripheral speeds of both the diffusion blades in (ii) the composite particle formation operation and (iii) the sizing operation were the same, except that various operations, measurements, and evaluations (except for the rate characteristics) were carried out in the same manner as in Example 1. The results are shown in Table 2.

(Comparative Example 3)
The same operations, measurements, and evaluations (except for rate characteristics) as in Example 1 were carried out, except that (i) no preliminary stirring operation was carried out, (ii) the electrode active material and the conductive assistant were charged into the granulation tank when the composite particle formation operation was started, and (ii) the conductive assistant was not mixed into the composition added in the composite particle formation operation. The results are shown in Table 2.

(Comparative Example 4)
(ii) No composite particle formation operation was performed, (i) in the preliminary stirring operation, the electrode active material, the conductive assistant, and the composition containing the binder and the solvent were added all at once to the granulation tank and stirred, and then (iii) a particle size adjustment operation was performed. Except for this, various operations, measurements, and evaluations (other than rate characteristics) were performed in the same manner as in Example 1. The results are shown in Table 2. The maximum temperature in the system throughout these steps was 52°C.

(Comparative Example 5)
(ii) In the composite particle forming operation, a composition not containing a conductive assistant and a binder, i.e., only a solvent, was added to the granulation tank. Specifically, (ii) in the composite particle forming operation, sealing air was circulated at 20 L/min (airflow rate 10/min), the main stirring blade was rotated at a peripheral speed of 5 m/s, and the auxiliary stirring blade was rotated at a peripheral speed of 6 m/s, and 280 g of cyclohexane as a solvent was continuously added to the granulation tank over 15 minutes. Other than this, various operations, measurements, and evaluations (other than rate characteristics) similar to those in Example 1 were performed. The results are shown in Table 2.

Tables 1 and 2 show that in Examples 1 to 11, which were carried out in this order in a granulation tank equipped with two or more agitating blades with different agitation shafts, (i) a powder material containing an electrode active material was agitated to create an agitated state; and (ii) a composition containing a binder, a conductive additive, and a solvent was added to the powder material in the agitated state to form composite particles, it was possible to produce composite particles that increase the flexibility of the electrode, suppress cracking of the electrode active material in the electrode, and further improve the cycle characteristics of an electrochemical element equipped with such an electrode.

According to the present invention, it is possible to provide a method for producing composite particles that can increase the flexibility of an electrode, suppress cracking of the electrode active material in the electrode, and further improve the cycle characteristics of an electrochemical element provided with such an electrode.
Furthermore, according to the present invention, there can be provided a method for producing an electrode for an electrochemical device by using the composite particles obtained according to the production method of the present invention.

1 Granulation tank 2 Main stirring blade 21 Main blade 3 Sub stirring blade 31 Sub blade RA1 First stirring shaft RA2 Second stirring shaft

Claims (7)

A method for producing composite particles, comprising the steps of:
In a granulation tank equipped with two or more agitating blades having different agitation shafts,
(i) stirring a powder material containing an electrode active material to bring it into a stirred state;
(ii) adding a composition containing a binder, a conductive assistant, and a solvent to the powder material in a stirred state to form composite particles;
A method for producing composite particles, comprising carrying out the above steps in this order. The method for producing composite particles according to claim 1, wherein the means for adding the composition in step (ii) is a spray nozzle. The method for producing composite particles according to claim 1, further comprising the step of (iii) sizing the composite particles by stirring the particles after the addition of the composition is completed, after the step (ii). The method for producing composite particles according to claim 3, wherein a conductive additive is added in step (iii). The method for producing composite particles according to claim 1, wherein the powder material in step (i) includes a conductive additive. The method for producing composite particles according to claim 1, wherein the solvent contained in the composition is a non-aqueous solvent having a boiling point of 95°C or less at 1 atm. Producing composite particles according to the method of any one of claims 1 to 6;
Pressing the produced composite particles onto an electrode substrate to form an electrode mixture layer;
A method for producing an electrode for an electrochemical element, comprising:

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