Binder solution for producing composite particles and conductive material dispersion liquid for electrochemical element

Abstract

This binder solution for producing composite particles is formed by dissolving a binder in a solvent A having a boiling point of 95.0°C or lower at normal pressure. In the binder solution, the absolute value of the difference between the surface free energy (E1) of the binder and the surface free energy (E2) of the solvent A is 10.0 mN / m or less. The solvent A includes one or more types of solvents.

Description

Binder solution for manufacturing composite particles and conductive material dispersion liquid for electrochemical devices

[0001] The present invention relates to a binder solution for producing composite particles and a conductive material dispersion liquid for an electrochemical device.

[0002] Electrochemical devices such as nonaqueous secondary batteries (e.g., lithium ion secondary batteries) are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and are therefore used in a wide range of applications. Therefore, in recent years, improvements to battery components such as electrodes have been investigated with the aim of further improving the performance of electrochemical devices.

[0003] In order to improve the performance of electrochemical devices, various improvements have been made to the materials that form the electrodes for electrochemical devices. Electrodes for electrochemical devices have a structure in which an electrode mixture layer, which is mainly composed of an electrode active material and, as necessary, contains other components such as a conductive additive and a binder to impart specific functions such as conductivity, adhesion, and flexibility to the electrode, is disposed on an electrode substrate.

[0004] As methods for forming an electrode mixture layer, various methods have been investigated to date, including a method in which a slurry composition containing an electrode active material, a conductive carbon material, a binder, and a solvent is applied to an electrode substrate and dried to form an electrode mixture layer, and a method in which a slurry composition containing an electrode active material, a conductive carbon material, 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.

[0005] Various attempts have been made to improve the binders that can be used in the various ways described above in order to impart excellent performance to electrochemical elements.

[0006] For example, Patent Document 1 discloses a water-soluble non-aqueous secondary battery electrode binder containing a resin component, which has a surface free energy γ Ｂ is 70 mJ / m ２ and the dipole component of the surface free energy γ ｐ Ｂ is 26 mJ / m ２The following non-aqueous secondary battery electrode binders have been disclosed. Furthermore, for example, Patent Document 2 discloses a coated positive electrode active material for lithium ion batteries, in which at least a portion of the surface of the positive electrode active material for lithium ion batteries is coated with a coating layer containing a coating polymer compound and a conductive agent. Patent Document 2 also discloses that the solvent used in producing the positive electrode active material for lithium ion batteries is a solvent having an absolute value of the difference in surface free energy (ΔE) from the positive electrode active material of 10 to 30 mN / m.

[0007] JP 2021-166199 JP 2021-097036

[0008] In recent years, among the methods for forming an electrode mixture layer, a method has been attracting attention in which composite particles are obtained from a slurry composition containing an electrode active material, a binder, a solvent, etc., and the obtained composite particles are pressure-molded onto an electrode substrate to form an electrode mixture layer. The composite particles obtained by this method are required to have a certain level of strength. However, the binders proposed in the above-mentioned prior art, if used to produce composite particles, may not be able to sufficiently increase the strength of the obtained composite particles.

[0009] Therefore, an object of the present invention is to provide a binder solution for producing composite particles that can sufficiently increase the strength of the resulting composite particles, and a conductive material dispersion liquid for electrochemical elements that can form composite particles with excellent strength.

[0010] The present inventors have conducted extensive research with the aim of solving the above-mentioned problems, and have newly discovered that the strength of the resulting composite particles can be increased when a binder solution for producing composite particles is prepared by dissolving a binder in a solvent A having a boiling point of 95.0°C or less at normal pressure, and the absolute value of the difference between the surface free energy (E1) of the binder and the surface free energy (E2) of the solvent A is 10.0 mN / m or less, and have completed the present invention.

[0011] That is, the present invention aims to advantageously solve the above-mentioned problems. The present invention provides [1] a binder solution for producing composite particles, comprising a binder dissolved in a solvent, the solvent being a solvent A containing one or more solvents and having a boiling point of 95.0°C or less at atmospheric pressure, wherein the surface free energy (E1) of the binder and the surface free energy (E2) of the solvent A satisfy the following formula (1): |E1-E2|≦10.0 mN / m (1). When the absolute value of the difference between the surface free energy (E1) of the binder and the surface free energy (E2) of the solvent A is 10.0 mN / m or less, the strength of the resulting composite particles can be increased. In the present invention, the "surface free energy" can be measured by the method described in the Examples. In the present invention, "atmospheric pressure" refers to 1 atm (1013 hPa).

[0012] [2] In the binder solution for producing composite particles according to the above [1], it is preferable that the solvent A is a mixed solvent of a plurality of solvents. By using a mixed solvent as the solvent A, composite particles having high strength can be produced efficiently.

[0013] [3] In the binder solution for producing composite particles according to the above [1] or [2], the surface free energy of the solvent A is preferably 20.0 mN / m or more and 30.0 mN / m or less. If the surface free energy of the solvent A is within the above range, high-strength composite particles can be produced efficiently.

[0014] [4] In the binder solution for producing composite particles according to any one of [1] to [3] above, it is preferable that the binder is a block copolymer, and the proportion of block regions consisting of aromatic vinyl monomer units in the block copolymer is 10% by mass or more and 80% by mass or less. If the binder is a block copolymer with such a specific composition, the strength of the obtained composite particles can be further increased. Note that the proportion of block regions consisting of aromatic vinyl monomer units in the block copolymer is determined by the mass ratio of the block copolymer. １ It can be determined from the H-NMR spectrum.

[0015] [5] The binder solution for producing composite particles according to any one of [1] to [4] above preferably has a viscosity of 50 mPa·s or less. If the viscosity of the binder solution is 50 mPa·s or less, the strength of the resulting composite particles can be further increased. The viscosity of the binder solution can be measured according to the method described in the Examples section of this specification.

[0016] [6] In the binder solution for producing composite particles according to any one of [1] to [5] above, it is preferable that the binder is a block copolymer, and the block copolymer contains a block region having at least one of an aliphatic conjugated diene monomer unit and an alkylene structural unit. If the binder is a block copolymer having such a specific composition, the strength of the obtained composite particles can be further increased. The "alkylene structural unit" refers to a unit represented by the general formula: -C ｎ H ２ｎ - [where n is an integer of 2 or more].

[0017] [7] In the binder solution for producing composite particles according to any one of [1] to [6] above, it is preferable that the binder is a block copolymer, and the block copolymer contains at least one of a diblock copolymer and a triblock copolymer. If the binder is a block copolymer with such a specific structure, the strength of the obtained composite particles can be further increased.

[0018] Another object of the present invention is to advantageously solve the above-mentioned problems, and the present invention provides a conductive material dispersion for electrochemical elements, comprising [8] a conductive carbon material and any one of the binder solutions for producing composite particles according to [1] to [7] above. In this way, by using a conductive material dispersion for electrochemical elements containing the binder solution for producing composite particles, composite particles for electrochemical elements having excellent strength can be produced.

[0019] According to the present invention, it is possible to provide a binder solution for producing composite particles, which can sufficiently increase the strength of the obtained composite particles. Also, according to the present invention, it is possible to provide a conductive material dispersion for electrochemical elements, which can form composite particles having excellent strength.

[0020] Hereinafter, embodiments of the present invention will be described in detail. Here, the binder solution for producing composite particles of the present invention (hereinafter also simply referred to as "binder solution") can be used when preparing a conductive material dispersion for an electrochemical element of the present invention (hereinafter also simply referred to as "conductive material dispersion").

[0021] (Binder Solution for Producing Composite Particles) The binder solution for producing composite particles of the present invention is a binder solution for producing composite particles, in which a binder is dissolved in a solvent A. Here, the solvent A is a solvent containing one or more solvents and having a boiling point of 95.0°C or less at normal pressure. Furthermore, in the binder solution of the present invention, the surface free energy (E1) of the binder and the surface free energy (E2) of the solvent A must satisfy the following formula (1): |E1-E2|≦10.0 mN / m (1)

[0022] The reason why the use of the binder composition of the present invention satisfying the above-mentioned characteristics can sufficiently increase the strength of the resulting composite particles is unclear, but is presumed to be as follows. When the absolute value of the difference between the surface free energy (E1) of the binder and the surface free energy (E2) of solvent A is 10.0 mN / m or less, the binder dissolves well in solvent A, thereby enabling the binder to be uniformly distributed in the binder solution and reducing the viscosity of the binder solution. Here, during the production of composite particles, the binder solution comes into contact with the electrode active material and conductive carbon material, etc., to be composited, and the binder solution penetrates into the voids between the powders. This dries, binding the powders together. Therefore, a low viscosity binder solution can be advantageous in the process of the binder liquid penetrating into the voids between the powders, which is thought to promote composite formation and increase particle strength.

[0023] <Value of |E1-E2|> From the viewpoint of further increasing the strength of the obtained composite particles, the value of |E1-E2|, which is the absolute value of the difference between the surface free energy (E1) of the binder and the surface free energy (E2) of the solvent A, is preferably 6.0 mN / m or less, and more preferably 4.5 mN / m or less. The lower limit of the value of |E1-E2| is not particularly limited, and may be zero, that is, the surface free energy (E1) of the binder and the surface free energy (E2) of the solvent A may be the same. The value of |E1-E2| can be adjusted by changing the composition of the binder and the type / composition of the solvent A.

[0024] <Viscosity of the binder solution> The viscosity of the binder solution is preferably 50 mPa·s or less, more preferably 40 mPa·s or less, and more preferably 33 mPa·s or less. The lower limit of the viscosity is not particularly limited, but may be, for example, 1 mPa·s or more. If the viscosity of the binder solution is equal to or less than the upper limit, the strength of the obtained composite particles can be further increased. The viscosity of the binder solution can be adjusted, for example, depending on the value of |E1-E2| described above, the concentration of the binder solution, etc. For example, the smaller the value of |E1-E2| described above, the more the viscosity increase can be reduced.

[0025] <Concentration of Binder Solution> The binder solution preferably has a solids concentration of 30% by mass or less, more preferably 20% by mass or less, and preferably 1% by mass or more, more preferably 5% by mass or more. If the solids concentration of the binder solution is within the above range, the strength of the obtained composite particles can be further increased.

[0026] Here, the proportion of the binder in the total solid content of the binder solution is preferably 90% by mass or more, more preferably 95% by mass or more, and may be 100% by mass. If the proportion of the binder is equal to or greater than the above lower limit, the strength of the obtained composite particles can be further increased.

[0027] <Solvent A> Solvent A is a compound capable of dissolving the binder. Here, the state in which the binder is dissolved in solvent A means that no particle size peak is detected when measured with a laser diffraction / scattering particle size distribution analyzer that is capable of detecting measurement targets down to the nm order (for example, a measurable range of 0.01 μm to 3000 μm).

[0028] <<Boiling Point of Solvent A>> Solvent A is not particularly limited, and any solvent can be used as long as its boiling point at atmospheric pressure is 95.0°C or less. The boiling point of solvent A at atmospheric pressure is preferably 90.0°C or less, and more preferably 85.0°C or less. If the boiling point of solvent A at atmospheric pressure is equal to or less than the above upper limit, the solvent can be quickly dried during the production of composite particles, thereby further increasing the strength of the obtained composite particles. Note that the lower limit of the boiling point of solvent A at atmospheric pressure is not particularly limited, but is preferably 10.0°C or more. If the boiling point of solvent A at atmospheric pressure is equal to or greater than the above lower limit, the uniformity of the composite particles can be further increased.

[0029] As solvent A, one solvent alone or a mixture of multiple solvents can be used. When using a single solvent, it is sufficient that the boiling point of the solvent at atmospheric pressure satisfies the above-mentioned temperature threshold. On the other hand, when using a mixture of multiple solvents, it is not necessary for all of the solvents to have a boiling point of 95.0°C or less. In this case, the boiling point of the mixed solvent can be a value obtained by weighting the boiling points of the various solvents by mass fraction. Solvents that can be used in the mixed solvent are not particularly limited, and examples include propyl acetate (boiling point at atmospheric pressure: 102°C). From the standpoints of operability and ease of processing, it is preferable that the solvent be a single solvent. On the other hand, by using solvent A as a mixed solvent, it is possible to combine the advantageous properties of various solvents, and as a result, composite particles with excellent properties such as strength can be formed. For example, when a mixed solvent of cyclohexane and another solvent is used as solvent A, static electricity may accumulate in the system during the granulation step due to the low electrical conductivity of cyclohexane, but by using a solvent with a relatively high electrical conductivity in addition to cyclohexane, it is possible to suppress the accumulation of static electricity in the system. In this way, when a mixed solvent is used as solvent A, it is possible to obtain the advantages of each solvent while reducing the disadvantages that may be caused by each solvent, compared to when a single solvent is used.

[0030] <<Surface Free Energy of Solvent A>> In particular, the surface free energy (E2) of solvent A is preferably 20.0 mN / m or more, more preferably 22.0 mN / m or more, and is preferably 30.0 mN / m or less, and more preferably 29.0 mN / m or less. If the surface free energy of solvent A is within the above range, the strength of the obtained composite particles can be further improved.

[0031] <<Type of Solvent>> Examples of solvents that can constitute solvent A include cyclohexane (boiling point at atmospheric pressure: 81°C; surface free energy: 24.7 mN / m), acetone (boiling point at atmospheric pressure: 56°C; surface free energy: 23.3 mN / m), methyl ethyl ketone (boiling point at atmospheric pressure: 79.6°C; surface free energy: 24.6 mN / m), ethyl acetate (boiling point at atmospheric pressure: 77.1°C; surface free energy: 24 mN / m), and benzene (boiling point at atmospheric pressure: 80.1°C; surface free energy: 28.8 N / m). Among these, cyclohexane is preferred from the viewpoint of the solubility of block regions formed from aromatic vinyl monomer units when such block regions are used as the binder. The inventors' studies have also revealed that the difference in surface free energy between the binder and solvent A and the surface free energy of solvent A itself within the above range have a greater impact on improving the strength of the resulting composite particles than the properties and structure of the solvent itself.

[0032] As described above, one or more solvents can be used in combination as solvent A. If a mixed solvent containing multiple solvents is used as solvent A, the surface free energy of the entire solvent A can be calculated by weighting and averaging the surface free energies of the various solvents used in combination by the volume fraction of the entire solvent. Here, when multiple solvents are used in combination, a solvent not listed above can be used in combination with the solvents listed above.

[0033] For example, when a mixed solvent containing cyclohexane as the main component (50% by mass or more) is used as solvent A, the content of cyclohexane in solvent A is preferably 50% by mass or more, and more preferably 60% by mass or more. When the content of cyclohexane in solvent A as a mixed solvent is equal to or greater than the above lower limit, high-strength composite particles can be efficiently obtained.

[0034] <Binder> The binder contained in the binder solution is a component that can bind, for example, powders of an electrode active material and a conductive carbon material to each other in composite particles produced using the binder solution. Furthermore, when such composite particles are used to form an electrode mixture layer, the binder is a component that can hold the powder and the composite particles themselves so that they do not detach from the electrode mixture layer.

[0035] <<Surface Free Energy of Binder>> The surface free energy (E1) of the binder is not particularly limited as long as the value of |E1-E2| described above is 10.0 mN / m or less. Preferably, the surface free energy (E1) of the binder is 10.0 mN / m or more, more preferably 15.0 mN / m or more, even more preferably 19.0 mN / m or more, preferably 40.0 mN / m or less, more preferably 32.0 mN / m or less, and even more preferably 25.0 mN / m or less. If the surface free energy of the binder is within the above range, the strength of the resulting composite particles can be further increased. Furthermore, if the surface free energy of the binder is within the above range, the binder can be uniformly dispersed in the binder solution, and as a result, it is believed that variation in particle size of the resulting composite particles can be suppressed. The surface free energy of the binder can be controlled based on the binder composition.

[0036] <<Binder Structure>> The binder may be a random copolymer, but is preferably a block copolymer. The block copolymer preferably contains at least a block region (A) composed of aromatic vinyl monomer units. Furthermore, the block copolymer preferably contains a block region (B) having at least one of an aliphatic conjugated diene monomer unit and an alkylene structural unit. The block copolymer may optionally contain other polymer chain portions other than the above-described block regions (A) and (B). However, from the viewpoint of effectively increasing the strength of the resulting composite particles, it is preferable that the block copolymer does not contain other polymer chain portions.

[0037] The block copolymer may be, for example, a diblock copolymer having one of each of two types of block regions (e.g., a copolymer having a structure in which the above-mentioned block region (A) and the above-mentioned block region (B) are connected) or a triblock copolymer having three block regions (e.g., a copolymer having a structure in which the above-mentioned block region (A), the above-mentioned block region (B), and the above-mentioned block region (A) are connected). Furthermore, in a triblock copolymer, the block regions (A) at both ends may differ from each other, for example, in composition and / or weight-average molecular weight. Such a triblock copolymer may also be referred to as an asymmetric triblock copolymer. The block copolymer that can constitute the binder of the present invention may contain one or more of a diblock copolymer, a triblock copolymer, and an asymmetric triblock copolymer. In particular, from the viewpoint of easily controlling the strength of the obtained composite particles, it is preferable that the block copolymer contain at least one of a diblock copolymer and a triblock copolymer. Regardless of which structure the block copolymer contains, as long as the block copolymer as a whole has a certain surface free energy (E1) depending on the composition of the block copolymer, and this value, in relation to the surface free energy (E2) of solvent A, satisfies the relationship of formula (1): |E1-E2|≦10.0 mN / m, it is believed that the effect of the present invention, that is, increasing the strength of the obtained composite particles, can be achieved regardless of the structure of the block copolymer.

[0038] [Block Region (A) Composed of Aromatic Vinyl Monomer Units] The block region (A) composed of aromatic vinyl monomer units (hereinafter also referred to as "aromatic vinyl block region (A)") is a region containing a portion in which only aromatic vinyl monomer units are linked together. The aromatic vinyl block region (A) is a region containing mainly aromatic vinyl monomer units as repeating units. In this specification, the term "mainly containing" an aromatic vinyl monomer unit means that, assuming that the total monomer units contained in a certain block region is 100% by mass, 80% by mass or more of the block region is occupied by aromatic vinyl monomer units. Here, one aromatic vinyl block region (A) may be composed of only one type of aromatic vinyl monomer unit or multiple types of aromatic vinyl monomer units, but is preferably composed of only one type of aromatic vinyl monomer unit.

[0039] The aromatic vinyl monomer that can be used to form the aromatic vinyl monomer units that constitute the aromatic vinyl block region (A) is not particularly limited as long as it is an aromatic vinyl compound, but examples include styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene, 2,4-diisopropylstyrene, 2,4-dimethylstyrene, 4-t-butylstyrene, 5-t-butyl-2-methylstyrene, 2-chlorostyrene, 3-chlorostyrene, 4-chlorostyrene, 4-bromostyrene, 2-methyl-4,6-dichlorostyrene, 2,4-dibromostyrene, vinylnaphthalene, and the like. Among these, styrene is preferred. These can be used alone or in combination of two or more, but it is preferable to use one type alone.

[0040] The proportion of the aromatic vinyl block region (A) in the block copolymer is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, and preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less, when the amount of all repeating units (monomer units and structural units) in the copolymer is taken as 100% by mass. When the proportion of the aromatic vinyl block region (A) in the block copolymer is equal to or greater than the above-mentioned lower limit, the influence of the surface free energy derived from the aromatic vinyl block region on the surface free energy of the entire block copolymer can be sufficiently enhanced. In other words, the microphase-separated structure of the block copolymer can promote the formation of domains derived from the aromatic vinyl monomer, thereby contributing to the surface free energy of the entire block copolymer. Furthermore, when the proportion of the aromatic vinyl block region (A) in the block copolymer is equal to or greater than the above-mentioned lower limit, the strength of the block copolymer as a binder can be increased, thereby promoting the formation of composite particles. Furthermore, when the proportion of the aromatic vinyl block domain (A) in the block copolymer is equal to or less than the above upper limit, the influence of the surface free energy derived from the aromatic vinyl block domain on the surface free energy (E1) of the entire block copolymer can be prevented from becoming excessively high. In other words, by setting the proportion of the aromatic vinyl block domain (A) in the block copolymer within the above range, the surface free energy (E1) of the block copolymer can be efficiently controlled within an appropriate range.

[0041] The weight-average molecular weight of the aromatic vinyl block region (A) is preferably 5,000 or more, more preferably 6,500 or more, even more preferably 10,000 or more, particularly preferably 20,000 or more, and preferably 120,000 or less, more preferably 50,000 or less, even more preferably 30,000 or less, and particularly preferably 25,000 or less. When the weight-average molecular weight of the aromatic vinyl block region (A) is equal to or greater than the above-mentioned lower limit, the influence of the surface free energy derived from the aromatic vinyl block region on the surface free energy (E1) of the entire block copolymer can be sufficiently enhanced. Furthermore, when the weight-average molecular weight of the aromatic vinyl block region (A) is equal to or less than the above-mentioned upper limit, the influence of the surface free energy derived from the aromatic vinyl block region on the surface free energy (E1) of the entire block copolymer can be prevented from becoming excessively high. In short, by setting the weight-average molecular weight of the aromatic vinyl block region (A) within the above-mentioned range, the surface free energy (E1) of the block copolymer can be efficiently controlled within an appropriate range.

[0042] [Block Region (B) Having At Least Either an Aliphatic Conjugated Diene Monomer Unit or an Alkylene Structural Unit] The block region (B) having at least either an aliphatic conjugated diene monomer unit or an alkylene structural unit (hereinafter also referred to as "aliphatic conjugated diene and / or alkylene block (B)") is (1) a region containing a portion in which only aliphatic conjugated diene monomer units are linked and bonded, (2) a region containing a portion in which only alkylene structural units are linked and bonded, or (3) a region containing a portion in which aliphatic conjugated diene monomer units and alkylene structural units are mixed and linked and bonded. The aliphatic conjugated diene and / or alkylene block (B) is a region mainly containing both or either an aliphatic conjugated diene monomer unit and an alkylene structural unit. In this specification, the expression "mainly comprising" the block region (B) both or either of aliphatic conjugated diene monomer units and alkylene structural units means that, assuming that the total monomer units contained in a certain block region is 100% by mass, 80% by mass or more is occupied by both or either of aliphatic conjugated diene monomer units and alkylene structural units. In particular, the proportion of alkylene structural units in the block region (B) is preferably 95% by mass or more, more preferably 99% by mass or more, and even more preferably 100% by mass. That is, the block region (B) is preferably a block region composed of alkylene structural units. Here, the aliphatic conjugated diene and / or alkylene block (B) may be composed of one type of repeating unit or multiple types of repeating units.

[0043] - Aliphatic conjugated diene monomer unit - Examples of aliphatic conjugated diene monomers that can form aliphatic conjugated diene monomer units include conjugated diene compounds having 4 or more carbon atoms, such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. These may be used alone or in combination of two or more in any ratio. Among these, isoprene and 1,3-butadiene are preferred from the viewpoint of further increasing the strength of the resulting composite particles.

[0044] When 1,3-butadiene is used as the aliphatic conjugated diene, the total content of units derived from 1,2-addition polymerization and units derived from 1,4-addition polymerization is preferably 95% by mass or more, more preferably 99% by mass or more, and may even be 100% by mass, based on 100% by mass of all repeating units derived from 1,3-butadiene. When isoprene is used as the aliphatic conjugated diene, the total content of units derived from 1,2-addition polymerization and units derived from 3,4-addition polymerization is preferably 95% by mass or more, more preferably 99% by mass or more, and may even be 100% by mass, based on 100% by mass of all repeating units derived from isoprene.

[0045] —Alkylene structural unit— The alkylene structural unit is represented by the general formula: —C ｎ H ２ｎ - [where n is an integer of 2 or more]. The alkylene structural unit may be linear or branched, but the alkylene structural unit is preferably linear, i.e., a linear alkylene structural unit. The alkylene structural unit preferably has 4 or more carbon atoms (i.e., n in the above general formula is an integer of 4 or more).

[0046] Here, the method for introducing alkylene structural units into a block copolymer is not particularly limited, and examples thereof include the following methods (1) and (2): (1) a method in which a copolymer is prepared from a monomer composition containing an aliphatic conjugated diene monomer and the copolymer is hydrogenated to convert the aliphatic conjugated diene monomer units into alkylene structural units; (2) a method in which a copolymer is prepared from a monomer composition containing a 1-olefin monomer (e.g., ethylene, propylene, 1-butene, 1-hexene, etc.). Among these, method (1) is preferred because it allows for easy production of the copolymer.

[0047] As the aliphatic conjugated diene monomer used in the above method (1), for example, those described above as aliphatic conjugated diene monomers capable of forming an aliphatic conjugated diene monomer unit can be used. Among these, 1,3-butadiene and isoprene are preferred. That is, the alkylene structural unit is preferably a structural unit (aliphatic conjugated diene hydrogenated unit) obtained by hydrogenating an aliphatic conjugated diene monomer unit, and more preferably a structural unit (1,3-butadiene hydrogenated unit) obtained by hydrogenating a 1,3-butadiene unit or a structural unit (isoprene hydrogenated unit) obtained by hydrogenating an isoprene unit. When all of the carbon-carbon double bonds derived from the aliphatic conjugated diene contained in the main chain of the copolymer are hydrogenated, the aliphatic conjugated diene and / or alkylene block (B) of the block copolymer obtained by the above method (1) forms a region including a portion where only alkylene structural units are linked together. Alternatively, when the hydrogenation is carried out according to the above method (1), if carbon-carbon double bonds derived from the aliphatic conjugated diene contained in the main chain of the copolymer remain, the aliphatic conjugated diene and / or alkylene block (B) of the obtained block copolymer has a region including a portion in which aliphatic conjugated diene monomer units and alkylene structural units are linked together in a mixed state.

[0048] The above-mentioned aliphatic conjugated diene monomers and 1-olefin monomers can be used alone or in combination of two or more kinds.

[0049] When 1,3-butadiene is used as the aliphatic conjugated diene, the structural units derived from hydrogenated 1,2-addition polymerization can form polyethylene chains in the main chain of the block copolymer, and the structural units derived from hydrogenated 1,4-addition polymerization can form polybutylene chains. The total content of these structural units is preferably 95% by mass or more, more preferably 99% by mass or more, and even more preferably 100% by mass, with all repeating units derived from 1,3-butadiene being 100% by mass. When isoprene is used as the aliphatic conjugated diene, the structural units derived from hydrogenated 1,4-addition polymerization can form a structure in which ethylene and propylene are alternately copolymerized in the main chain of the block copolymer. The structural units derived from hydrogenated 3,4-addition polymerization and 1,2-addition polymerization can be linked to form polypentene. The total content of these structural units is preferably 95% by mass or more, more preferably 99% by mass or more, and even more preferably 100% by mass, with all repeating units derived from isoprene being 100% by mass.

[0050] The total proportion of the aliphatic conjugated diene and / or alkylene block (B) in the block copolymer is preferably 20% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, and preferably 95% by mass or less, and more preferably 80% by mass or less, when the amount of all repeating units (structural units and monomer units) in the block copolymer is taken as 100% by mass. When the proportion of the aliphatic conjugated diene and / or alkylene block (B) in the block copolymer is equal to or greater than the above-mentioned lower limit, the influence of the surface free energy derived from the aliphatic conjugated diene and / or alkylene block (B) on the surface free energy (E1) of the entire block copolymer can be sufficiently increased. Furthermore, when the proportion of the aliphatic conjugated diene and / or alkylene block (B) in the block copolymer is equal to or less than the above-mentioned upper limit, the influence of the surface free energy derived from the aliphatic conjugated diene and / or alkylene block (B) on the surface free energy (E1) of the entire block copolymer can be prevented from becoming excessively high. In short, by setting the proportion of the aliphatic conjugated diene and / or alkylene block (B) in the block copolymer within the above range, the surface free energy (E1) of the block copolymer can be efficiently controlled within an appropriate range.

[0051] The weight-average molecular weight of the aliphatic conjugated diene and / or alkylene block (B) is preferably 50,000 or more, more preferably 60,000 or more, even more preferably 90,000 or more, and preferably 200,000 or less, more preferably 180,000 or less. When the weight-average molecular weight of block (B) is equal to or greater than the above-mentioned lower limit, the effect of the surface free energy derived from block (B) on the surface free energy (E1) of the entire block copolymer can be sufficiently enhanced. Furthermore, when the weight-average molecular weight of block (B) is equal to or less than the above-mentioned upper limit, the effect of the surface free energy derived from block (B) on the surface free energy (E1) of the entire block copolymer can be prevented from becoming excessively enhanced. In short, by setting the weight-average molecular weight of block (B) within the above-mentioned range, the surface free energy (E1) of the block copolymer can be efficiently controlled within an appropriate range.

[0052] -Other repeating units- Monomers capable of forming other repeating units (hereinafter also referred to as "other monomers") are not particularly limited, and examples thereof include (meth)acrylic acid ester monomers and polymerizable monomers having a hydrophilic group. These monomers may be used alone or in combination of two or more. In the present invention, "(meth)acrylic" means acrylic and / or methacrylic.

[0053] Here, examples of the (meth)acrylic acid ester monomer include alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, isopentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, and stearyl acrylate; and alkyl methacrylates such as ethyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, and stearyl methacrylate. Among these, preferred (meth)acrylic acid ester monomers are ethyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate, with n-butyl acrylate being more preferred.

[0054] Furthermore, examples of the polymerizable monomer having a hydrophilic group include a monomer having a carboxylic acid group, a monomer having a sulfonic acid group, a monomer having a phosphoric acid group, and a monomer having a hydroxyl group.

[0055] Examples of monomers having a carboxylic acid group include monocarboxylic acids and their derivatives, dicarboxylic acids and their acid anhydrides, and their derivatives. Examples of monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Examples of monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, and β-diaminoacrylic acid. Examples of dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, and maleic acid esters such as methylallyl maleate, diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleates. Examples of dicarboxylic acid anhydrides include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride. Furthermore, examples of monomers having a carboxylic acid group include acid anhydrides that generate a carboxyl group upon hydrolysis. Other examples include monoesters and diesters of α,β-ethylenically unsaturated polycarboxylic acids, such as monoethyl maleate, diethyl maleate, monobutyl maleate, dibutyl maleate, monoethyl fumarate, diethyl fumarate, monobutyl fumarate, dibutyl fumarate, monocyclohexyl fumarate, dicyclohexyl fumarate, monoethyl itaconate, diethyl itaconate, monobutyl itaconate, and dibutyl itaconate.

[0056] Examples of the monomer having a sulfonic acid group include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, styrene sulfonic acid, (meth)acrylic acid-2-ethyl sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, etc. In the present invention, "(meth)allyl" means allyl and / or methallyl.

[0057] Examples of the monomer having a phosphate group include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, ethyl-(meth)acryloyloxyethyl phosphate, etc. In the present invention, "(meth)acryloyl" means acryloyl and / or methacryloyl.

[0058] Examples of the monomer having a hydroxyl group include ethylenically unsaturated alcohols such as (meth)allyl alcohol, 3-butene-1-ol, and 5-hexene-1-ol; alkanol esters of ethylenically unsaturated carboxylic acids such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, di-2-hydroxyethyl maleate, di-4-hydroxybutyl maleate, and di-2-hydroxypropyl itaconate; and compounds of the general formula: CH ２ =CR １ -COO-(C ｎ H ２ｎ O) ｍ -H (wherein m is an integer from 2 to 9, n is an integer from 2 to 4, R １represents hydrogen or a methyl group) and (meth)acrylic acid esters; mono(meth)acrylic acid esters of dihydroxy esters of dicarboxylic acids such as 2-hydroxyethyl-2'-(meth)acryloyloxyphthalate and 2-hydroxyethyl-2'-(meth)acryloyloxysuccinate; vinyl ethers such as 2-hydroxyethyl vinyl ether and 2-hydroxypropyl vinyl ether; alkyl ethers such as (meth)allyl-2-hydroxyethyl ether, (meth)allyl-2-hydroxypropyl ether, (meth)allyl-3-hydroxypropyl ether, (meth)allyl-2-hydroxybutyl ether, (meth)allyl-3-hydroxybutyl ether, (meth)allyl-4-hydroxybutyl ether, and (meth)allyl-6-hydroxyhexyl ether; mono(meth)allyl ethers of ethylene glycol; polyoxyalkylene glycol mono(meth)allyl ethers such as diethylene glycol mono(meth)allyl ether and dipropylene glycol mono(meth)allyl ether; mono(meth)allyl ethers of halogen- and hydroxy-substituted (poly)alkylene glycols such as glycerin mono(meth)allyl ether, (meth)allyl-2-chloro-3-hydroxypropyl ether and (meth)allyl-2-hydroxy-3-chloropropyl ether; mono(meth)allyl ethers of polyhydric phenols such as eugenol and isoeugenol and halogen-substituted products thereof; (meth)allyl thioethers of alkylene glycols such as (meth)allyl-2-hydroxyethyl thioether and (meth)allyl-2-hydroxypropyl thioether; and the like.

[0059] The proportion of other repeating units in the block copolymer is preferably 15% by mass or less, more preferably 5% by mass or less, when the amount of all repeating units (structural units and monomer units) in the block copolymer is taken as 100% by mass. It is also preferable that the block copolymer does not contain other repeating units, i.e., 0% by mass. If the proportion of other repeating units is not more than the above upper limit, the strength of the resulting composite particles can be further increased.

[0060] -Method of Preparing Binder- The method of preparing the binder described above is not particularly limited, and any method such as solution polymerization, suspension polymerization, bulk polymerization, or emulsion polymerization can be used. Furthermore, addition polymerization such as ionic polymerization, radical polymerization, or living radical polymerization can be used as the polymerization method. Furthermore, known polymerization initiators such as redox polymerization initiators containing iron-based compounds can be used as the polymerization initiator.

[0061] When the binder used in the present invention is a block copolymer, the block copolymer can be produced by a conventionally known method. Specifically, for example, a block copolymer can be prepared by adding a second monomer component different from the first monomer component to a solution obtained by polymerizing a first monomer component, polymerizing the second monomer component, and optionally further repeating the addition and polymerization of the monomer component.

[0062] Furthermore, when the above-described block copolymer is produced by the above-described method (1), the hydrogenation of the block copolymer can be carried out using a known hydrogenation method such as an oil phase hydrogenation method or an aqueous phase hydrogenation method. Furthermore, the catalyst used for hydrogenation can be any known selective hydrogenation catalyst, and examples thereof include palladium-based catalysts, rhodium-based catalysts, and nickel(II) acetylacetonate. Two or more of these hydrogenation catalysts may be used in combination. In this case, a co-catalyst such as triisobutyl may be optionally used.

[0063] Then, if necessary, an aqueous solution containing a compound selected from the group consisting of an aminocarboxylic acid chelate compound, a phosphonic acid chelate compound, gluconic acid, citric acid, malic acid, and tartaric acid as a metal capture agent, and a surfactant, can be added to the reaction liquid after the hydrogenation reaction to remove metal components.

[0064] <Other Components> In addition to the above components, the binder solution may contain components such as antioxidants such as phenolic antioxidants, reinforcing materials, leveling agents, viscosity modifiers, and electrolyte additives. These components are not particularly limited as long as they do not affect the electrochemical reaction, and known components, such as those described in WO 2012 / 115096, can be used. Furthermore, these components may be used alone or in combination of two or more at any ratio.

[0065] <Method for preparing binder solution> The binder solution is not particularly limited, and can be obtained, for example, by preparing a binder according to the above-mentioned binder preparation method, then adding additives as necessary, and mixing by a known method. At this time, a necessary amount of the above-mentioned solvent may be added to adjust the binder solution to a desired solid content concentration.

[0066] (Conductive material dispersion for electrochemical elements) The conductive material dispersion for electrochemical elements of the present invention contains the binder solution of the present invention described above and a conductive carbon material, and may optionally further contain other components used in the field of electrochemical elements and conductive materials other than the conductive carbon material. Furthermore, since the conductive material dispersion of the present invention contains the binder solution of the present invention, the strength of the resulting composite particles can be increased.

[0067] <Binder Solution> The binder solution may be any of those described above. The amount of the binder solution, calculated as solid content, is preferably 20 parts by mass or more, more preferably 40 parts by mass or more, and preferably 80 parts by mass or less, and even more preferably 60 parts by mass or less, per 100 parts by mass of the conductive carbon material. When the amount of the binder solution is equal to or greater than the lower limit, the strength of the resulting composite particles can be further increased. When the amount of the binder solution is equal to or less than the upper limit, the internal resistance of the electrode formed using the binder solution can be effectively reduced.

[0068] <Conductive Carbon Material> The conductive carbon material is a component that functions as a conductive material that ensures electrical contact between electrode active materials in an electrode mixture layer formed using composite particles. Examples of conductive carbon materials include carbon black (e.g., acetylene black, Ketjen Black (registered trademark), furnace black, etc.), graphite (graphene), carbon fiber (carbon nanofiber), carbon flakes, and ultrashort carbon fibers (e.g., carbon nanotubes (CNTs) and vapor-grown carbon fibers). Among these, from the viewpoint of conductivity, carbon black, carbon fiber (carbon nanofiber), graphite (graphene), and carbon nanotubes (CNTs) are preferred, and carbon black is preferred. These can be used alone or in combination of two or more.

[0069] <Solvent> As the solvent, for example, the same solvent A contained in the binder solution described above can be used. In other words, the solvent A carried over from the binder solution can be used as it is as the solvent for the conductive material dispersion liquid.

[0070] <Other Components> Other components that can be blended into the conductive material dispersion liquid are not particularly limited, and include the same components as the other components that can be blended into the binder composition of the present invention. These components may be used alone or in combination of two or more types in any ratio.

[0071] <Other Conductive Materials> Conductive materials other than conductive carbon materials (other conductive materials) are not particularly limited, and fibers, foils, etc. of various metals can be used.

[0072] <Method for preparing conductive material dispersion> The conductive material dispersion can be prepared by mixing the above-mentioned components by a known mixing method. Among them, from the viewpoint of dispersing the conductive carbon material well, it is preferable to prepare the conductive material dispersion by adding the conductive carbon material and, optionally, an additional solvent to a binder solution and mixing them. The mixing can be performed using a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, or a Filmix.

[0073] (Composite particles for electrochemical device electrodes) Composite particles for electrochemical device electrodes can be formed using the binder composition of the present invention. Such composite particles contain an electrode active material, a binder derived from the binder solution of the present invention described above, and a conductive carbon material, and may optionally further contain other components used in the field of electrochemical devices, conductive materials other than conductive carbon materials, etc. Furthermore, since such composite particles are formed using the binder solution of the present invention, they have excellent strength. Note that, below, as an example, a case where the composite particles are composite particles for lithium ion secondary battery positive electrodes will be described, but the present invention is not limited to the following example.

[0074] <Electrode active material> The electrode active material is a material that transfers electrons at the electrode of an electrochemical element. For example, as a positive electrode active material for a lithium ion secondary battery, a material that can absorb and release lithium is usually used. Hereinafter, a positive electrode active material for a lithium ion secondary battery will be described as an example, but the present invention is not limited to the following example.

[0075] The positive electrode active material for lithium ion secondary batteries can be a compound containing a transition metal, such as a transition metal oxide, a transition metal sulfide, or a composite metal oxide of lithium and a transition metal, including Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Mo.

[0076] <Binder> Examples of the binder include the binders contained in the binder solution of the present invention described above.

[0077] <Conductive carbon material> The conductive carbon material that can be blended into the composite particles is not particularly limited, and examples thereof include the same conductive carbon materials that can be blended into the conductive material dispersion of the present invention. The blending amount of the conductive carbon material relative to the electrode active material can be within a general range.

[0078] <Other Components> Other components that can be added to the composite particles are not particularly limited, and include the same components as those that can be added to the conductive material dispersion of the present invention.

[0079] <Other Conductive Materials> Other conductive materials that can be blended into the composite particles are not particularly limited, and examples thereof include the same conductive materials as those that can be blended into the conductive material dispersion of the present invention.

[0080] <Method for producing composite particles> The method for producing composite particles is not particularly limited, but the composite particles can be formed by spray drying granulation, tumbling bed granulation, compression granulation, stirring granulation, extrusion granulation, crushing granulation, and fluidized bed granulation. Among these, stirring granulation is preferred from the viewpoint of further increasing the strength of the composite particles.

[0081] In the production of composite particles by the stirring granulation method, it is preferable to carry out the following steps in this order in a granulation tank equipped with two or more stirring blades having different stirring shafts: (i) a step of stirring a powder material containing an electrode active material to create a stirred state; (ii) a step of adding a composition containing a binder, a conductive additive, and a solvent to the powder material in the stirred state to form composite particles. Optionally, following the operation (ii) above, a step of sizing the composite particles by stirring them after the addition of the composition is complete may be carried out.

[0082] (Electrode for electrochemical device) An electrode for electrochemical device formed using the composite particles of the present invention comprises, for example, a current collector and an electrode mixture layer formed on the current collector. Here, the electrode mixture layer is formed using composite particles formed using the binder solution of the present invention. That is, the electrode mixture layer contains at least an electrode active material, a conductive carbon material, and a binder. Note that the components contained in the electrode mixture layer are those contained in the composite particles. Examples of materials that can be used for the current collector include metals, carbon, conductive polymers, etc., and metals are preferably used. Metals that are typically used include copper, aluminum, platinum, nickel, tantalum, titanium, stainless steel, and other alloys. Among these, copper, aluminum, or aluminum alloys are preferred in terms of conductivity and voltage resistance.

[0083] In the following, an electrode for a lithium ion secondary battery will be described as an example, but the present invention is not limited to the following example.

[0084] <Method for manufacturing an electrode for a lithium ion secondary battery> The electrode for a lithium ion secondary battery is not particularly limited, and may be manufactured by forming the composite particles into a sheet and then laminating it on a current collector. However, it is preferable to manufacture the electrode by directly pressure-molding the composite particles on the current collector. Examples of the pressure-molding method include a roll pressure molding method using a roll pressure molding device equipped with a pair of rolls, and feeding the composite particles to the roll pressure molding device with a feeder such as a vibration feeder or a screw feeder while feeding the current collector with the rolls to form an electrode active material layer on the current collector; a method in which the composite particles are sprayed on the current collector, smoothed with a blade or the like to adjust the thickness, and then molded with a pressure device; and a method in which the composite particles are filled into a mold and pressurized to mold the mold. Among these, the roll pressure molding method is preferred.

[0085] Furthermore, to eliminate variations in thickness of the formed lithium-ion secondary battery electrode and increase the density of the electrode active material layer to achieve high capacity, post-pressing may be performed as needed. A preferred method of post-pressing is a roll pressing process. In the roll pressing process, two cylindrical rolls are arranged parallel to each other with a small gap between them, rotated in opposite directions, and pressed by clamping the electrode between them. In this process, the temperature of the rolls may be adjusted, for example, by heating or cooling.

[0086] In order to increase the adhesive strength and electrical conductivity of the electrode active material layer, an intermediate layer may be formed on the surface of the current collector, and among these, it is preferable to form a conductive adhesive layer.

[0087] (Electrochemical device) An electrochemical device can be provided using an electrode for an electrochemical device formed using the composite particles of the present invention. The electrochemical device includes, for example, a positive electrode, a negative electrode, an electrolyte, and a separator, and uses an electrode made of composite particles formed using the binder solution of the present invention as at least one of the positive electrode and the negative electrode, preferably the positive electrode. Note that, as an example, the electrochemical device will be described below as a lithium ion secondary battery, but the present invention is not limited to the following example.

[0088] <Electrode> Known electrodes can be used as electrodes other than the electrode of the present invention. Specifically, the electrode can be, for example, a negative electrode made of a thin plate of metallic lithium, or an electrode formed by forming an electrode mixture layer on a current collector. The current collector can be made of a metal material such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, or platinum. The electrode mixture layer can be a layer containing an electrode active material and a binder. Furthermore, the binder is not particularly limited, and any known material can be used.

[0089] <Electrolyte> As the electrolyte, an organic electrolyte solution 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, LiPF ６ , LiAsF６ , 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 particularly preferred 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, and LiPF ６ is particularly preferred. Note that one type of electrolyte may be used alone, or two or more types may be used in combination in any ratio. Generally, the lithium ion conductivity tends to increase as the supporting electrolyte with a higher degree of dissociation is used, so the lithium ion conductivity can be adjusted by the type of supporting electrolyte.

[0090] The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte. 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) are preferred. Other suitable solvents include 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. Mixtures of these solvents may also be used. Among these, carbonates are preferred because of their high dielectric constant and wide stable potential range, and a mixture of ethylene carbonate and ethyl methyl carbonate is even more preferred. The concentration of the electrolyte in the electrolyte can be adjusted as appropriate. For example, it is preferably 0.5 to 15% by mass, more preferably 2 to 13% by mass, and even more preferably 5 to 10% by mass.

[0091] <Separator> The separator is not particularly limited, and for example, those described in JP 2012-204303 A can be used. Among these, a microporous film made of a polyolefin resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred because it allows the thickness of the entire separator to be thin, thereby increasing the proportion of electrode active material in the electrochemical device and increasing the capacity per volume.

[0092] The electrochemical element is assembled by, for example, stacking a positive electrode and a negative electrode with a separator interposed therebetween, rolling or folding the stack as necessary according to the shape of the electrochemical element, placing the stack in a container, injecting an electrolyte into the container, and sealing the container. To prevent internal pressure buildup, overcharging and overdischarging, and the like, a fuse, an overcurrent protection element such as a PTC element, expanded metal, lead plates, and the like may be provided as necessary. The shape of the assembled electrochemical element may be any of, for example, a coin type, a button type, a sheet type, a cylindrical type, a rectangular type, a flat type, and the like.

[0093] 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 based on mass unless otherwise specified. In the examples and comparative examples, various measurements and evaluations were carried out as follows.

[0094] <Binder Composition> The binders obtained in the examples and comparative examples were as follows: １ H-NMR was used to measure this. In all examples and comparative examples, it was confirmed that the block regions thought to be derived from the aliphatic conjugated diene present in the main chain of the copolymer were block regions (B) consisting of alkylene structural units. The proportions of the aromatic vinyl block regions (A) and the block regions (B) were then obtained.

[0095] <Method for confirming that the binder is dissolved in the solvent in the binder solution> Apparatus used: Laser diffraction / scattering particle size distribution analyzer HORIBA LA-950 The binder solution was diluted with cyclohexane and adjusted to a total solids concentration of 0.1% by mass to obtain a test solution. 10 mL of the obtained test solution was placed in a plastic bottle container, and ultrasonic dispersion was performed for 10 minutes using an ultrasonic cleaner (manufactured by SND Corporation, "US-105N"). 1 mL was dropped into the sample inlet of the analyzer, and measurement was performed to confirm whether a peak in the particle size distribution was detected. As a result, no peak was detected in all examples and comparative examples, confirming that the binder was dissolved in the solvent in the binder solution.

[0096] <Weight-Average Molecular Weight of Block Region of Binder> First, the weight-average molecular weight of the binder was measured by gel permeation chromatography (GPC) under the following measurement conditions: Separation column: Shodex KD-806M (Showa Denko K.K.) Detector: Differential refractometer detector RID-10A (Shimadzu Corporation) Eluent flow rate: 0.3 mL / min Column temperature: 40°C Standard polymer: TSK standard polystyrene (Tosoh Corporation) In addition, to calculate the weight-average molecular weights of the block regions (A) and (B) of the binder, samples were taken at the stage when the weights of each block were determined, and the above-mentioned GPC measurement was carried out. Although not shown in the table, the weight average molecular weight (M) of the entire binder was measured, and based on the binder composition measured as described above, the weight average molecular weight of the block region (A) was calculated using the mass (W1) of the conjugated diene block region (A) and the mass (W2) of the entire binder according to the following formula: The weight average molecular weight of the block region (B) can also be calculated in a similar manner: Weight average molecular weight of block region (A) = M × (W1 / W2)

[0097] <Surface Free Energy> The binder solutions prepared in the Examples and Comparative Examples were molded by hot pressing to prepare sheet samples as specimens. Hot pressing was performed by sandwiching 0.1 g of the sample between Teflon sheets (Nachias Naflon (registered trademark) PTFE tape TOMB (registered trademark) No. 9001 0.10 mm). The hot pressing was performed under conditions of a press temperature of 200°C, a press load of 4.5 kN, and a press time of 1 minute. The thickness of the obtained sheet samples was 0.1 mm to 0.3 mm. Droplets of water, formamide, and ethylene glycol were dropped onto the surfaces of the specimens prepared as described above, and the contact angles of each were measured. The contact angles were measured using the θ / 2 method. A portable contact angle meter (Kyowa Interface Science Co., Ltd., "PCA-11") was used as the measuring device. Measurements were performed under conditions of a drop volume of 2.0 μL and a measurement waiting time of 100 mS. Using the measured contact angles of water, formamide, and ethylene glycol, the dispersion component γSd and polar component γSp (unit: mJ / m) of the surface free energy γS of the sheet sample were calculated by the OWRK method.２ ) was calculated. Here, the dispersion component γ of the surface free energy of water, formamide, and ethylene glycol used in the calculation Ｌ ｄ and polar component γ Ｌ ｐ The values ​​of were as follows: Water: Dispersion component γ Ｌ ｄ is 21.8 (mJ / m ２ ), polar component γ Ｌ ｐ is 51 (mJ / m ２ ) Formamide: Dispersion component γ Ｌ ｄ is 32.4 (mJ / m ２ ), polar component γ Ｌ ｐ is 25.8 (mJ / m ２ ) Ethylene glycol: Dispersion component γ Ｌ ｄ is 29.4 (mJ / m ２ ), polar component γ Ｌ ｐ is 18.3 (mJ / m ２ The surface free energy of solvent A was measured at 25° C. using an automatic surface tensiometer (manufactured by Kyowa Interface Science Co., Ltd., "DY-300"). In Examples 7 to 9, in which a mixed solvent was used as solvent A, the surface free energy value for each solvent was calculated, and then these values ​​were weighted and averaged by the blending mass ratio to obtain the surface free energy value for solvent A as a whole.

[0098] <Boiling Point of Solvent A at Normal Pressure> In Examples 7 to 9, in which a mixed solvent was used as solvent A, the boiling point values ​​of each solvent at normal pressure were weighted by the blending mass ratio and averaged to obtain the boiling point value of solvent A as a whole.

[0099] <Viscosity index Cη of binder solution or conductive material dispersion> Except for Example 6, the viscosity index of the binder solution was calculated using the viscosity value measured by the method described below and the formula below. In Example 6, the viscosity value of the conductive material dispersion containing acetylene black was measured as follows. The total solids concentration (Cs) of the binder solution / conductive material dispersion was adjusted to 5 mass %. 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 changed appropriately according to the viscosity. Calculation of viscosity index: Cη = η / Cs × 100 [mPa s]

[0100] <Granulated particle strength> Granulated particle strength was calculated using the volume average particle diameter D50 (i.e., D50 particle diameter, which is the volume average median diameter) measured by the method described below and the following formula. [Measurement of volume average particle diameter D50] Measurement was performed according to the dry measurement method using a particle size distribution measuring device (manufactured by Microtrac, "MT3000"). Specifically, the volume average particle diameter D50 was automatically calculated from the particle size distribution when the air dispersion pressure was set to 0.10 MPa, and the volume average particle diameter value (D50) at the air dispersion pressure of 0.10 MPa was used. Ａ Similarly, the volume average particle diameter D50 was automatically calculated from the particle diameter distribution when the air dispersion pressure was set to 0.25 MPa, and the volume average particle diameter value (D50 Ｂ ) was obtained. From the obtained values, the composite particle strength (Sp) value was calculated according to the following formula. The "volume average particle diameter D50" of the particles represents the particle diameter at which the cumulative volume calculated from the small diameter side in the particle size distribution (volume basis) measured by the laser diffraction method becomes 50%. Sp = D50 Ｂ / D50 Ａ A: Particle strength Sp is 0.6 or more B: Particle strength Sp is 0.4 or more and less than 0.6 C: Particle strength Sp is 0.2 or more and less than 0.4 D: Particle strength Sp is less than 0.2

[0101] Example 1 Polymerization Step A reactor equipped with a stirrer and thoroughly purged with nitrogen was charged with 135 parts of dehydrated cyclohexane, 0.07 parts of dibutyl ether, and 6.8 parts of dehydrated styrene, and 0.02 parts of n-butyllithium (15% cyclohexane solution) was further added. The entire volume was then stirred at 60°C for 20 minutes. Measurement of the reaction solution by gas chromatography revealed that the polymerization conversion at this point was 99.5%. Next, 31.5 parts of dehydrated butadiene was continuously added to the reaction solution over 30 minutes, and after completion of the addition, the entire volume was stirred for 30 minutes. The polymerization conversion at this point was 99.5%. Subsequently, 6.8 parts of dehydrated styrene was added and stirred for 20 minutes. The polymerization conversion at this point was 99.7%. The reaction was terminated by adding 0.1 parts of ethanol to the reaction solution, yielding a polymer solution. The proportion of 1,2-addition polymerization units and 1,4-addition polymerization units in all butadiene monomer units in the obtained block copolymer was 99.8%.

[0102] <Hydrogenation Step> Next, the polymer solution was transferred to a pressure-resistant reactor equipped with a stirrer, and 0.3 parts of nickel (II) acetylacetonate as a hydrogenation catalyst and 1.2 parts of triisobutylaluminum as a co-catalyst were added, followed by adding 28 parts of dehydrated cyclohexane and mixing. The atmosphere inside the reactor was replaced with hydrogen gas, and hydrogen was further supplied while stirring the solution, and a hydrogenation reaction was carried out at a temperature of 80°C and a pressure of 0.9 MPa for 6 hours.

[0103] <Decalcification Step> Next, to remove metal components derived from the catalyst used during hydrogenation, 1.1 parts of malic acid and 0.2 parts of a nonionic surfactant ethylene oxide and propylene oxide block copolymer (manufactured by ADEKA Corporation, product name "L-64") were dissolved in 500 parts of ion-exchanged water in the polymer solution, and the solution was then added to the reactor and stirred for 5 hours. The mixture was then allowed to stand for 1 hour to allow separation of the ion-exchanged water in which the malic acid and ethylene oxide and propylene oxide block copolymer had been dissolved from Solvent A, and the ion-exchanged water in which the malic acid and ethylene oxide and propylene oxide block copolymer had been dissolved was discharged in the amount of the solution charged. Then, 1 part of a xylene solution in which 0.1 parts of the phenolic antioxidant pentaerythrityl tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate (manufactured by Koyo Chemical Laboratory, product name "Songnox 1010") had been dissolved was added and dissolved. Further, cyclohexane was added to prepare a binder solution of a predetermined concentration (solid content concentration 5%). The viscosity of the obtained binder solution was measured as described above. The results are shown in Table 1.

[0104] <Preparation of Composite Particles> A composite particle preparation device was prepared, consisting of a cylindrical vessel with an inner diameter of 180 mm and a capacity of 2 L as a granulation vessel, with the axis of the cylindrical vessel being the vertical direction, and two agitating blades on the vertical and horizontal axes (the main agitating blade is the vertical axis, and the auxiliary agitating blade is the horizontal axis). The main agitating blade was an inclined paddle with three main blades each 170 mm in diameter, and the auxiliary agitating blade had a V-shaped anchor blade with a diameter of 30 mm. To prevent raw materials from being mixed into the drive parts of the main agitating blade and auxiliary agitating blade, the device had a mechanism for sealing by ventilating air. Using the composite particle preparation device, composite particles were prepared by carrying out (i) a preliminary agitation operation, (ii) a composite particle formation operation, and (iii) a sizing operation, in this order. First, in the (i) preliminary stirring operation, 97 parts by mass (1,358 g) of NMC532 (average particle diameter: 6 μm) as a positive electrode active material for a lithium ion battery and acetylene black (BET specific surface area: 62 m) as a conductive carbon material were placed in a granulation tank. ２ / g, bulk density 0.16 g / cm ３) was added. Next, room temperature air for sealing the drive parts of the main and auxiliary stirring blades (hereinafter also referred to as "sealing air") was circulated at 20 L / min (airflow rate 10 / min), and stirring was carried out for 15 minutes under operating conditions of a main stirring blade peripheral speed of 5 m / s and a auxiliary stirring blade peripheral speed of 6 m / s. The solids concentration of the powder material after stirring 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), and the main stirring blade peripheral speed was 5 m / s and the auxiliary stirring blade peripheral speed was 6 m / s. 1 part by mass of the binder solution obtained above was continuously added as solids over 15 minutes using a dropping funnel. Next, (iii) as a particle size adjustment operation, room temperature sealing air was circulated at 20 L / min (airflow rate 10 / min), and the system was operated for 10 minutes under the operating conditions of a main stirring impeller peripheral speed of 2 m / s and a sub-stirring impeller peripheral speed of 2 m / s. The maximum temperature in the system throughout these steps (i) to (iii) was 38°C. The strength of the composite particles produced by carrying out the above operations (i) to (iii) in this order was measured as described above. The results are shown in Table 1.

[0105] Example 2 Various operations, measurements, and evaluations were performed in the same manner as in Example 1, except that the polymerization step in preparing the binder solution was changed as follows. The results are shown in Table 1. <Polymerization Step> 135 parts of dehydrated cyclohexane, 0.04 parts of dibutyl ether, and 4.2 parts of dehydrated styrene were placed in a reactor equipped with a stirrer and the inside of which had been thoroughly purged with nitrogen, and 0.01 parts of n-butyllithium (15% cyclohexane solution) was further added. The entire contents were then stirred at 60°C for 20 minutes. When the reaction solution was measured by gas chromatography, the polymerization conversion rate at this point was 99.5%. Next, 13.4 parts of dehydrated butadiene were continuously added to the reaction solution over 30 minutes, and after the addition was completed, the entire contents were stirred for 30 minutes. The polymerization conversion rate at this point was 99.5%. Subsequently, 4.2 parts of dehydrated styrene was added and stirred for 20 minutes. The polymerization conversion rate at this point was 99.7%. The reaction was stopped by adding 0.05 parts of ethanol to the reaction solution, and a polymer solution was obtained. The proportion of 1,2-addition polymerization units and 1,4-addition polymerization units in the total butadiene monomer units of the obtained block copolymer was 99.8%.

[0106] Example 3 Various operations, measurements, and evaluations were performed in the same manner as in Example 1, except that the polymerization step in preparing the binder solution was changed as follows. The results are shown in Table 1. <Polymerization Step> 135 parts of dehydrated cyclohexane, 0.04 parts of dibutyl ether, and 1.9 parts of dehydrated styrene were placed in a reactor equipped with a stirrer and the inside of which had been thoroughly purged with nitrogen, and 0.01 parts of n-butyllithium (15% cyclohexane solution) was further added. The entire volume was then stirred at 60°C for 20 minutes. When the reaction solution was measured by gas chromatography, the polymerization conversion rate at this point was 99.5%. Next, 16.8 parts of dehydrated butadiene was continuously added to the reaction solution over 30 minutes, and after the addition was completed, the entire volume was stirred for 30 minutes. The polymerization conversion rate at this point was 99.5%. Subsequently, 1.9 parts of dehydrated styrene was added and stirred for 20 minutes. The polymerization conversion rate at this point was 99.7%. The reaction was stopped by adding 0.05 parts of ethanol to the reaction solution, and a polymer solution was obtained. The proportion of 1,2-addition polymerization units and 1,4-addition polymerization units in the total butadiene monomer units of the obtained block copolymer was 99.8%.

[0107] Example 4 Various operations, measurements, and evaluations were performed in the same manner as in Example 1, except that the polymerization step in preparing the binder solution was changed as follows. The results are shown in Table 1. <Polymerization Step> 120 parts of dehydrated cyclohexane, 0.1 parts of dibutyl ether, and 12 parts of dehydrated styrene were placed in a reactor equipped with a stirrer and the inside of which had been thoroughly purged with nitrogen, and 0.03 parts of n-butyllithium (15% cyclohexane solution) was further added. The entire contents were then stirred at 50°C for 30 minutes. When the reaction solution was measured by gas chromatography, the polymerization conversion rate at this point was 99.5%. Next, 28 parts of dehydrated isoprene was continuously added to the reaction solution over 30 minutes, and after the addition was completed, the entire contents were stirred for 30 minutes. The polymerization conversion rate at this point was nearly 100%. Here, 0.3 parts of ethanol was added to the reaction solution to stop the reaction, and a polymer solution was obtained. The proportion of 1,2-addition polymerization units and 3,4-addition polymerization units in all isoprene monomer units of the obtained block copolymer was 99.8%.

[0108] Example 5 Various operations, measurements, and evaluations were performed in the same manner as in Example 1, except that the polymerization step in preparing the binder solution was changed as follows. The results are shown in Table 1. <Polymerization Step> A reactor equipped with a stirrer and whose interior had been thoroughly purged with nitrogen was charged with 120 parts of dehydrated cyclohexane, 0.07 parts of dibutyl ether, and 28 parts of dehydrated styrene, and 0.02 parts of n-butyllithium (15% cyclohexane solution). The entire contents were then stirred at 50°C for 30 minutes. The reaction solution was measured by gas chromatography, and the polymerization conversion rate at this point was found to be 99.5%. Next, 12 parts of dehydrated isoprene was continuously added to the reaction solution over 30 minutes, and after the addition was completed, the entire contents were stirred for 30 minutes. The polymerization conversion rate at this point was nearly 100%. At this point, 0.3 parts of ethanol was added to the reaction solution to terminate the reaction, yielding a polymer solution. The proportion of 1,2-addition polymerization units and 3,4-addition polymerization units in all isoprene monomer units of the obtained block copolymer was 99.8%.

[0109] (Example 6) A conductive carbon material was added to a binder solution prepared in the same manner as in Example 1, as described below, to prepare a conductive material dispersion. Using this conductive material dispersion, the same operation as in Example 1 was carried out to produce composite particles, and the strength was evaluated. The results are shown in Table 1. <Preparation of conductive material dispersion> Acetylene black (BET specific surface area: 62 m) was used as the conductive carbon material. ２ / g, bulk density 0.16 g / cm ３ 2 parts of acetylene black, binder, and solvent were mixed with 1 part of binder solution (solids equivalent), and cyclohexane was added as a solvent to prepare a 1 kg mixture of acetylene black, binder, and solvent with a solids concentration of 5%. The resulting mixture was then dispersed for 1 hour using a bead mill (LMZ015, manufactured by Ashizawa Fine Tech) using zirconia beads with a diameter of 0.5 mm at a peripheral speed of 12 m / s to prepare a conductive material dispersion containing carbon, binder, and solvent. The resulting conductive material dispersion had a solids concentration of 5% by mass.

[0110] (Example 7) In the deashing step during binder preparation, methyl ethyl ketone (boiling point at normal pressure: 79.6°C) was added so that the mass ratio to cyclohexane was as shown in Table 1. Except for this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0111] (Example 8) In the deashing step during binder preparation, ethyl acetate (boiling point at normal pressure: 77.1°C) was added so that the mass ratio to cyclohexane was as shown in Table 1. Except for this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0112] (Example 9) In the deashing step during binder preparation, propyl acetate (boiling point at normal pressure: 102°C) was added so that the mass ratio to cyclohexane was as shown in Table 1. Except for this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0113] Comparative Example 1 Various operations, measurements, and evaluations were performed in the same manner as in Example 1, except that the polymerization step for preparing the binder solution was changed as follows. The results are shown in Table 1. <Polymerization Step> 120 parts of dehydrated cyclohexane, 0.07 parts of dibutyl ether, and 44 parts of dehydrated styrene were placed in a reactor equipped with a stirrer and the inside of which had been thoroughly purged with nitrogen, and 0.02 parts of n-butyllithium (15% cyclohexane solution) was further added. The entire contents were then stirred at 50°C for 30 minutes. Measurement of the reaction solution by gas chromatography revealed that the polymerization conversion rate at this point was 99.5%. Next, 2 parts of dehydrated isoprene was continuously added to the reaction solution over 30 minutes, and after the addition was completed, the entire contents were stirred for 30 minutes. The polymerization conversion rate at this point was nearly 100%. At this point, 0.3 parts of ethanol was added to the reaction solution to terminate the reaction, yielding a polymer solution. The proportion of 1,2-addition polymerization units and 3,4-addition polymerization units in all the monomer units of the obtained block copolymer was 99.8%.

[0114] The results shown in Table 1 show that in Examples 1 to 6, which used a binder solution / conductive material dispersion for producing composite particles, in which a binder was dissolved in solvent A containing one or more solvents and having a boiling point at normal pressure of 95.0°C or less, and in which the absolute value of the difference between the surface free energy (E1) of the binder and the surface free energy (E2) of solvent A was 10.0 mN / m or less, composite particles with high strength were obtained. On the other hand, in Comparative Example 1, which used a binder solution in which the absolute value of the difference between the surface free energy (E1) of the binder and the surface free energy (E2) of solvent A exceeded 10.0 mN / m, the composite particles obtained were inferior in strength.

[0115] According to the present invention, it is possible to provide a binder solution for producing composite particles, which can sufficiently increase the strength of the obtained composite particles. Also, according to the present invention, it is possible to provide a conductive material dispersion for electrochemical elements, which can form composite particles having excellent strength.

Claims

1. A binder solution for producing composite particles, comprising a binder dissolved in a solvent, the solvent being a solvent A containing one or more solvents and having a boiling point of 95.0° C. or less at normal pressure, the surface free energy (E1) of the binder and the surface free energy (E2) of the solvent A satisfy the following formula (1): |E1-E2|≦10.0 mN / m (1) 2. The binder solution for producing composite particles according to claim 1, wherein the solvent A is a mixed solvent of a plurality of solvents.

3. The binder solution for producing composite particles according to claim 1, wherein the surface free energy of the solvent A is 20.0 mN / m or more and 30.0 mN / m or less.

4. A binder solution for producing composite particles as described in claim 1, wherein the binder is a block copolymer, and the proportion of block regions consisting of aromatic vinyl monomer units in the block copolymer is 10% by mass or more and 80% by mass or less.

5. The binder solution for producing composite particles according to claim 1, having a viscosity of 50 mPa·s or less.

6. The binder solution for producing composite particles according to claim 1, wherein the binder is a block copolymer, and the block copolymer includes block regions having at least one of an aliphatic conjugated diene monomer unit and an alkylene structural unit.

7. The binder solution for producing composite particles according to claim 1, wherein the binder is a block copolymer, and the block copolymer includes at least one of a diblock copolymer and a triblock copolymer.

8. A conductive material dispersion for electrochemical devices, comprising a conductive carbon material and the binder solution for producing composite particles according to any one of claims 1 to 7.

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