Binder powder for nonaqueous secondary battery electrode, mixed powder composition, electrode for nonaqueous secondary battery and manufacturing method therefor, and nonaqueous secondary battery

Abstract

This binder powder for a nonaqueous secondary battery electrode contains a particulate polymer, and has an electrolyte swelling degree of 1.0-1.5 and a glass transition temperature of 50-100°C. Preferably, the flexural modulus of a molded article having a thickness of 3 mm of the binder powder is 1000-2500 MPa. Preferably, the particulate polymer contains a (meth) acrylic acid ester monomer unit, and the proportion of the (meth) acrylic acid ester monomer unit in the binder powder is 95 mass% or more. Provided are a mixed powder composition containing the binder powder, an electrode for a nonaqueous secondary battery, a nonaqueous secondary battery, and a method for manufacturing an electrode.

Description

Binder powder for non-aqueous secondary battery electrodes, composite powder composition, electrode for non-aqueous secondary battery and method for manufacturing the same, and non-aqueous secondary battery

[0001] The present invention relates to a binder powder for a non-aqueous secondary battery electrode, a composite powder composition, an electrode for a non-aqueous secondary battery and a method for producing the same, and a non-aqueous secondary battery.

[0002] Electrodes for non-aqueous secondary batteries such as non-aqueous lithium-ion secondary batteries have generally been produced by a wet process using a liquid material containing a solvent. For example, an electrode mixture containing an electrode active material and a binder is mixed with a solvent to prepare a slurry composition, and the slurry composition is then applied to a current collector and dried to produce an electrode (Patent Document 1).

[0003] However, in recent years, attention has been drawn to the production of electrodes by dry processes using powdered materials. As such methods for producing electrodes by dry processes, for example, the methods disclosed in Patent Documents 2 and 3 are known.

[0004] International Publication No. 2018 / 034093 (corresponding publication: U.S. Patent Application Publication No. 2020 / 052270) Japanese Patent No. 6327249 U.S. Patent Application Publication No. 2020 / 0144591

[0005] From the viewpoint of improving battery performance, there is a need for the development of a technology for reducing the internal resistance of nonaqueous secondary batteries manufactured by a dry process. In particular, there is a need for nonaqueous secondary batteries with improved cycle characteristics, i.e., nonaqueous secondary batteries in which the increase in internal resistance due to repeated charge and discharge is suppressed.

[0006] In order to reduce internal resistance, it is particularly necessary to improve the adhesion between the current collector and the electrode active material layer that constitute the electrode. That is, an increase in internal resistance due to charge and discharge may occur due to a decrease in adhesion between the current collector and the electrode active material layer. Furthermore, such a decrease in adhesion not only increases the internal resistance during normal battery use, but also may reduce the durability of the battery in various usage situations (e.g., use that has undergone charge and discharge cycles exceeding normal use, use that involves external impact, etc.), so it is desirable to avoid this as much as possible. Therefore, there is a need for the development of a technology that increases the peel strength of the electrode, i.e., the magnitude of the force required to peel the current collector from the electrode active material layer.

[0007] In particular, a dry binder is required to perform a dry process. A dry binder is a powder binder that can impart properties suitable for forming an electrode active material layer by a dry process to the electrode active material layer material. Such a dry binder is required to achieve the above-mentioned improvement in peel strength and suppression of an increase in internal resistance.

[0008] Therefore, an object of the present invention is to provide a binder powder and composite powder composition for electrodes of non-aqueous secondary batteries that can provide highly durable non-aqueous secondary batteries in which an increase in internal resistance due to charging and discharging is suppressed; an electrode for a non-aqueous secondary battery and a method for manufacturing the same that can provide highly durable non-aqueous secondary batteries in which an increase in internal resistance due to charging and discharging is suppressed; and a highly durable non-aqueous secondary battery in which an increase in internal resistance due to charging and discharging is suppressed.

[0009] The present inventors conducted research to solve the above-mentioned problems. As a result, the present inventors found that when a binder powder comprising a particulate polymer having specific physical properties and a specific electrolyte swelling degree is used as a binder powder constituting an active material layer of an electrode, the peel strength of the electrode manufactured using the binder powder can be increased and an increase in internal resistance of a nonaqueous secondary battery can be suppressed. Specifically, when the binder powder has a low electrolyte swelling degree and a glass transition temperature within a specific high range, the elastic modulus of the binder powder can be maintained when immersed in an electrolyte, thereby increasing the peel strength of the electrode. In addition, when the binder powder has a low electrolyte swelling degree and a glass transition temperature within a specific high range, an increase in internal resistance due to charge and discharge can be suppressed. Based on these findings, the present inventors have completed the present invention. Specifically, the present invention includes the following.

[0010] <1> A binder powder for a non-aqueous secondary battery electrode, comprising a particulate polymer, having an electrolyte swelling index of 1.0 or more and 1.5 or less, and a glass transition temperature of 50° C. or more and 100° C. or less. <2> The binder powder for a non-aqueous secondary battery electrode according to <1>, wherein a 3 mm-thick molded product of the binder powder has a flexural modulus of 1000 MPa or more and 2500 MPa or less. <3> The binder powder for a non-aqueous secondary battery electrode according to <1> or <2>, wherein the particulate polymer contains (meth)acrylic acid ester monomer units, and a proportion of the (meth)acrylic acid ester monomer units in the particulate polymer is 95 mass% or more. <4> The binder powder for a non-aqueous secondary battery electrode according to any one of <1> to <3>, wherein the particulate polymer contains (meth)acrylic acid ester monomer units, and the proportion of the (meth)acrylic acid ester monomer units in the binder powder is 95 mass % or more. <5> The particulate polymer contains, as the (meth)acrylic acid ester monomer units, units (e1) represented by the following formula (e1), units (e2) represented by the following formula (e2), or both of them: -(CH ２ -C(-CH ３ ) (-COO-R １ )) - (e1) - (CH２ -CH(-COO-R ２ ))-(e2) R １ and R ２ and independently represent an alkyl group having a branched structure and having 4 or more carbon atoms. <6> The binder powder for non-aqueous secondary battery electrodes according to any one of <1> to <4>, <6> The binder powder for non-aqueous secondary battery electrodes according to <5>, comprising the unit (e1), and a proportion of the unit (e1) in the particulate polymer of 60% by mass or more and 100% by mass or less. <7> The binder powder for non-aqueous secondary battery electrodes according to <5> or <6>, comprising the unit (e2), and a proportion of the unit (e2) in the particulate polymer of 5% by mass or more and 40% by mass or less. <8> The binder powder for non-aqueous secondary battery electrodes according to any one of <5> to <7>, comprising both the unit (e1) and the unit (e2), and a mass ratio (e1) / (e2) of the unit (e1) to the unit (e2) in the particulate polymer of 60 / 40 or more and 95 / 5 or less. <9> The binder powder for a non-aqueous secondary battery electrode according to any one of <5> to <8>, which contains the unit (e1), and the unit (e1) has a glass transition temperature of 50° C. or higher. <10> The binder powder for a non-aqueous secondary battery electrode according to any one of <5> to <8>, which contains the unit (e1), and １ <11> The binder powder for a non-aqueous secondary battery electrode according to any one of <5> to <10>, which contains the unit (e2) and has a glass transition temperature of 50°C or lower. <12> The binder powder for a non-aqueous secondary battery electrode according to any one of <5> to <10>, which contains the unit (e2), and R ２ <13> The binder powder for a non-aqueous secondary battery electrode according to any one of <5> to <12>, wherein the unit (e1) has a glass transition temperature of 50°C or higher, and the unit (e2) has a glass transition temperature of 50°C or lower. <14> R １ is a tert-butyl group, and R ２<16> The binder powder for a non-aqueous secondary battery electrode according to any one of <1> to <15>, which is a binder powder for forming an electrode active material layer by a dry process. <17> The particulate polymer has an SP value of 9.1 (cal / cm －３ ) １／２ The binder powder for a non-aqueous secondary battery electrode according to any one of <1> to <16>, which is as follows: <18> A composite powder composition comprising the binder powder for a non-aqueous secondary battery electrode according to any one of <1> to <17> and an electrode active material. <19> A non-aqueous secondary battery electrode comprising a current collector and an electrode active material layer formed on the current collector from the composite powder composition according to <18>. <20> A non-aqueous secondary battery comprising a non-aqueous secondary battery electrode comprising a current collector and an electrode active material layer formed on the current collector from the composite powder composition according to <18>. <21> A method for producing an electrode for a non-aqueous secondary battery, comprising a step of dry-forming an electrode active material layer from the composite powder composition according to <18>.

[0011] According to the present invention, there are provided a binder powder and composite powder composition for electrodes of non-aqueous secondary batteries, which can provide non-aqueous secondary batteries in which the increase in internal resistance due to charging and discharging is suppressed and which have high durability; an electrode for a non-aqueous secondary battery and a method for manufacturing the same, which can provide non-aqueous secondary batteries in which the increase in internal resistance due to charging and discharging is suppressed and which have high durability; and a non-aqueous secondary battery in which the increase in internal resistance due to charging and discharging is suppressed and which has high durability.

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

[0013] In the following description, unless otherwise specified, an electrode active material layer refers to a layer containing an electrode active material, a positive electrode active material layer refers to an electrode active material layer for a positive electrode, and a negative electrode active material layer refers to an electrode active material layer for a negative electrode.

[0014] In the following description, the term "(meth)acrylic" encompasses "acrylic," "methacrylic," and combinations thereof. For example, the term "(meth)acrylic acid" encompasses acrylic acid, methacrylic acid, and combinations thereof.

[0015] In the following description, a polymerized unit having a structure formed by polymerization of a certain monomer may be expressed using the name of the monomer. For example, a unit having a structure formed by polymerization of a (meth)acrylic acid ester monomer may be referred to as a "(meth)acrylic acid ester monomer unit." However, in the present invention, the structures of the molecule and its constituent elements are not limited by the production method.

[0016] <Binder Powder: Physical Properties> The binder powder of the present invention contains a particulate polymer. The binder powder may consist solely of the particulate polymer. The binder powder may be a dry powder and may have a powdery form in a room temperature environment (generally, a 25°C environment).

[0017] The binder powder of the present invention has a degree of swelling in an electrolyte solution within a specific range: the degree of swelling in an electrolyte solution is 1.0 or more and 1.5 or less, preferably 1.4 or less, and more preferably 1.1 or less.

[0018] The electrolyte swelling degree of the binder powder is an index showing the degree to which a compact of the binder powder swells in the electrolyte solution to be measured. The compact of the binder powder is a film made by pressing the binder powder. The electrolyte solution to be measured is a 1.0 M LiPF6 solution, which is typically used as an electrolyte solution for non-aqueous secondary battery electrodes. ６A solution (solvent: a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3 / 7 (volume ratio), additive: containing 2 vol% vinylene carbonate (solvent ratio)) is used. After measuring the mass W0 of the film, the test piece is immersed in the electrolyte at 60°C for 72 hours, and the mass W1 of the test piece after the immersion test is measured. The electrolyte swelling degree is calculated from the values ​​of W0 and W1 according to the formula S = W1 / W0. More specifically, the electrolyte swelling degree can be measured using the measurement method described in the examples of this specification.

[0019] The binder powder of the present invention has a glass transition temperature within a specific range. The glass transition temperature is 50° C. or higher, preferably 52° C. or higher, and more preferably 60° C. or higher, and 100° C. or lower, preferably 95° C. or lower, and more preferably 90° C. or lower. Preferred ranges for the glass transition temperature of the binder powder of the present invention may be 50° C. or higher to 100° C. or lower, 50° C. or higher to 95° C. or lower, 50° C. or higher to 90° C. or lower, 52° C. or higher to 100° C. or lower, 52° C. or higher to 95° C. or lower, 52° C. or higher to 90° C. or lower, 60° C. or higher to 100° C. or lower, 60° C. or higher to 95° C. or lower, or 60° C. or higher to 90° C.

[0020] The glass transition temperature of the binder powder can be determined based on a DSC curve obtained by carrying out differential scanning calorimetry (DSC) measurement. DSC can be carried out at a temperature range of -100°C to 500°C and a heating rate of 10°C / min. More specifically, the glass transition temperature can be measured using the measurement method described in the Examples section of this specification. When all or most of the binder powder is made of a particulate polymer, the glass transition temperature of the particulate polymer can be the glass transition temperature of the binder powder.

[0021] The inventors have found that when the electrolyte swelling degree of the binder powder is within the above range and the glass transition temperature of the binder powder is within the above range, an increase in internal resistance due to charge and discharge can be suppressed. Without being bound by any particular theory, the inventors speculate that the mechanism by which such excellent effects are obtained is as follows. However, the technical scope of the present invention is not limited by the mechanism described below.

[0022] By setting the swelling degree to the above upper limit or less, expansion and contraction during charging and discharging of the secondary battery can be suppressed and ion diffusion in the electrolyte can be improved. When the electrolyte swelling degree of the binder powder is low, the elastic modulus of the binder powder can be maintained when immersed in the electrolyte, thereby increasing the peel strength of the electrode. In addition, when the electrolyte swelling degree of the binder powder is low, an increase in internal resistance during charging and discharging can be suppressed. Even when the swelling degree of the binder powder is low, a low glass transition temperature softens the active material layer in the electrode, reducing peel strength and resulting in a tendency for internal resistance to increase during charging and discharging. On the other hand, a high glass transition temperature reduces the deformability of the binder, resulting in a decrease in contact with the active material. Here, by using a binder powder with a low swelling degree and a glass transition temperature within the above-specified range, these problems can be suppressed, resulting in a suppression of an increase in internal resistance during charging and discharging, and improved peel strength and battery durability. On the other hand, if the binder powder contains a substance that can dissolve in the electrolyte, the swelling degree may fall below 1. However, if the binder powder does not contain such a substance, it will not have an adverse effect on the battery. Therefore, by keeping the swelling degree at or above the lower limit, such advantageous effects can be obtained.

[0023] In addition, when the electrolyte swelling degree of the binder powder is within the above range and the glass transition temperature of the binder powder is within the above range, good physical properties as a dry binder can be obtained.

[0024] The degree of swelling of the binder powder in an electrolyte and the glass transition temperature of the binder powder can be adjusted to fall within the above ranges by adjusting the type and ratio of the monomer units constituting the particulate polymer.

[0025] The binder powder of the present invention preferably has a flexural modulus within a specific range. Specifically, the flexural modulus of a 3 mm thick molded product of the binder powder preferably falls within a specific range. The flexural modulus of such a molded product is preferably 1000 MPa or more, more preferably 1500 MPa or more, and is preferably 2500 MPa or less, more preferably 2300 MPa or less. More specifically, the flexural modulus can be measured using the measurement method described in the Examples of this specification.

[0026] When the flexural modulus of the molded article is within the above range, an increase in internal resistance due to charging and discharging can be more effectively suppressed. In addition, when the flexural modulus of the molded article is within the above range, it becomes possible to mold the electrode active material layer containing the binder powder into a self-standing film, which results in the beneficial effect of increasing the degree of freedom in the structure and manufacturing process of the battery.

[0027] The flexural modulus of the binder powder molding can be adjusted to a desired value by appropriately adjusting factors such as the type and ratio of units constituting the particulate polymer and the molecular weight of the particulate polymer.

[0028] <Particulate polymer: particle shape> The particulate polymer contained in the binder powder may be a primary particle in which the particulate polymer particles are not aggregated, or a secondary particle formed by aggregation of a plurality of the particulate polymer particles, or a combination of the primary particles and secondary particles.

[0029] The primary particle diameter of the particulate polymer is preferably within a specific range. Specifically, the primary particle diameter D50 of the particulate polymer is preferably 0.1 μm or more, more preferably 0.5 μm or more, even more preferably 1.0 μm or more, and is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 15 μm or less. When the primary particle diameter D50 of the particulate polymer is within the above range, an increase in internal resistance due to charge and discharge of the nonaqueous secondary battery can be suppressed.

[0030] The primary particle size D50 of the particulate polymer can be measured by the following method. A 1% aqueous solution of linear alkylbenzenesulfonate sodium is mixed with the particulate polymer and dispersed by ultrasonic waves to obtain a dispersion in which primary particles of the particulate polymer are dispersed. The volume-based cumulative particle size distribution of this dispersion is measured using a Coulter counter. The particle size at which the integrated value, calculated from the small diameter side of this cumulative particle size distribution, reaches 50% can be obtained as the volume-based primary particle size D50 of the particulate polymer. A more specific measurement method can be the method described in the examples below.

[0031] The particulate polymer contained in the binder powder of the present invention preferably has an SP value within a specific range. Specifically, the SP value of the particulate polymer is preferably 9.1 (cal / cm －３ ) １／２ or less, more preferably 8.63 (cal / cm －３ ) １／２ or less, and even more preferably 8.5 (cal / cm －３ ) １／２ or less, and more preferably 8.0 (cal / cm －３ ) １／２ On the other hand, the lower limit of the SP value is 7.5 (cal / cm －３ ) １／２ or more, or 7.88 (cal / cm －３ ) １／２ The preferred range of the SP value of the particulate polymer is 7.5 (cal / cm －３ ) １／２ More than 9.1 (cal / cm －３ ) １／２ Below, 7.5 (cal / cm －３ ) １／２ More than 8.63 (cal / cm －３ ) １／２ Below, 7.5 (cal / cm －３ ) １／２ More than 8.5 (cal / cm －３ ) １／２ Below, 7.5 (cal / cm －３ ) １／２ More than 8.0 (cal / cm －３ ) １／２ Below, 7.88 (cal / cm －３ )１／２ More than 9.1 (cal / cm －３ ) １／２ Below, 7.88 (cal / cm －３ ) １／２ More than 8.63 (cal / cm －３ ) １／２ Below, 7.88 (cal / cm －３ ) １／２ More than 8.5 (cal / cm －３ ) １／２ or less, or 7.88 (cal / cm －３ ) １／２ More than 8.0 (cal / cm －３ ) １／２ The SP value of the particulate polymer can be set to the following. When the SP value of the particulate polymer is within the above range, the physical properties of the binder powder, such as the swelling degree, can be set to a desired range, and thus a binder powder that exhibits a desired effect can be obtained. The SP value of the particulate polymer can be adjusted to a desired value by appropriately adjusting the monomer units constituting the particulate polymer and their composition ratio. The SP value of the particulate polymer can be calculated from its molecular structure, and can also be measured by observing its affinity with various solvents. As a method for determining a specific SP value, the method described in the examples below can be adopted.

[0032] The particulate polymer contained in the binder powder of the present invention preferably has extremely low solubility in water. Specifically, the solubility of the particulate polymer in water at 20°C is preferably 0.1 g / 100 mL or less. The lower limit of the solubility is not particularly limited and can be 0 g / 100 mL. Such low solubility in water allows for the production of electrodes and batteries with favorable performance.

[0033] <Particulate polymer: constituent units> The particulate polymer may be any polymer that can achieve the above-mentioned electrolyte swelling degree and glass transition temperature, but in a preferred example, the particulate polymer contains a (meth)acrylic acid ester monomer unit, i.e., a unit having a structure obtained by polymerizing a (meth)acrylic acid ester.

[0034] In this example, the (meth)acrylic acid ester monomer unit is preferably the main component of the particulate polymer. Specifically, the proportion of the (meth)acrylic acid ester monomer unit in 100% by mass of the particulate polymer is preferably 95% by mass or more, more preferably 98% by mass or more, even more preferably 99% by mass or more, and may be 100% by mass. By using the (meth)acrylic acid ester monomer unit as the main component, it is possible to easily obtain a particulate polymer and a binder powder having the desired physical properties such as the above-mentioned electrolyte swelling degree and glass transition temperature.

[0035] Examples of the (meth)acrylic acid ester monomer unit include a unit (e1) represented by the following formula (e1) and a unit (e2) represented by the following formula (e2). The unit (e1) is a methacrylic acid ester monomer unit, and the unit (e2) is an acrylic acid ester monomer unit. The particulate polymer preferably contains the unit (e1), the unit (e2), or both.

[0036] - (CH ２ -C(-CH ３ ) (-COO-R １ )) - (e1) - (CH ２ -CH(-COO-R ２ ))-(e2) R １ and R ２ are independently alkyl groups having a branched structure and having 4 or more carbon atoms.

[0037] When the particulate polymer contains the unit (e1), the proportion of the unit (e1) in the particulate polymer is preferably 60% by mass or more, more preferably 65% ​​by mass or more, even more preferably 67% by mass or more, and even more preferably 68.4% by mass or more, and the upper limit thereof can be 100% by mass or less.

[0038] When the particulate polymer contains the unit (e2), the proportion of the unit (e2) in the particulate polymer is preferably 5% by mass or more, more preferably 12% by mass or more, even more preferably 14% by mass or more, and is preferably 40% by mass or less, more preferably 33% by mass or less, and even more preferably 31.6% by mass or less. The preferred range of the proportion of the unit (e2) in the particulate polymer may be 5% by mass or more to 40% by mass or less, 5% by mass or more to 33% by mass or less, 5% by mass or more to 31.6% by mass or less, 12% by mass or more to 40% by mass or less, 12% by mass or more to 33% by mass or less, 12% by mass or more to 31.6% by mass or less, 14% by mass or more to 40% by mass or less, 14% by mass or more to 33% by mass or less, or 14% by mass or more to 31.6% by mass or less.

[0039] When the particulate polymer contains the unit (e1) or the unit (e2) in a ratio within the above range, a particulate polymer and a binder powder having desired physical properties such as a degree of swelling in an electrolyte solution and a glass transition temperature can be more easily obtained.

[0040] In a more preferred example, the particulate polymer may contain both the unit (e1) and the unit (e2). In this case, the mass ratio (e1) / (e2) of the unit (e1) and the unit (e2) in the particulate polymer is preferably 60 / 40 or more, more preferably 67 / 33 or more, even more preferably 68.4 / 31.6 or more, while preferably 95 / 5 or less, more preferably 88 / 12 or less, even more preferably 86 / 14 or less. Preferred ranges for (e1) / (e2) may be 60 / 40 or more and 95 / 5 or less, 60 / 40 or more and 88 / 12 or less, 60 / 40 or more and 86 / 14 or less, 67 / 33 or more and 95 / 5 or less, 67 / 33 or more and 88 / 12 or less, 67 / 33 or more and 86 / 14 or less, 68.4 / 31.6 or more and 95 / 5 or less, 68.4 / 31.6 or more and 88 / 12 or less, or 68.4 / 31.6 or more and 86 / 14 or less.

[0041] When the particulate polymer contains the unit (e1) and / or the unit (e2), the total proportion of the unit (e1) and the unit (e2) in 100% by mass of the particulate polymer is preferably 95% by mass or more, more preferably 98% by mass or more, even more preferably 99% by mass or more, and may be 100% by mass.

[0042] When the particulate polymer contains both the unit (e1) and the unit (e2) in a ratio within the above range, it is possible to more easily obtain a particulate polymer and a binder powder having desired physical properties such as a desired degree of swelling in an electrolyte solution and a desired glass transition temperature.

[0043] Among the above examples, when the particulate polymer contains units (e1), the glass transition temperature of the units (e1) is preferably 50°C or higher. Furthermore, when the particulate polymer contains units (e2), the glass transition temperature of the units (e2) is preferably 50°C or lower. In particular, when the particulate polymer contains both units (e1) and units (e2), it is preferable that the glass transition temperature of the units (e1) is 50°C or higher and the glass transition temperature of the units (e2) is 50°C or lower. When the units (e1) and / or units (e2) have such glass transition temperatures, the glass transition temperature of the binder powder can be easily adjusted to a desired range. The upper limit of the glass transition temperature of the units (e1) can be, for example, 150°C or lower. The lower limit of the glass transition temperature of the units (e2) can be, for example, -100°C or higher.

[0044] The glass transition temperature of a unit constituting a polymer is the glass transition temperature measured by preparing a homopolymer consisting of only that unit. Such a homopolymer can have a weight average molecular weight of about 10,000 to 1,000,000. The glass transition temperature of the homopolymer can be measured by the same method as that for the particulate polymer described above. The glass transition temperature of the homopolymer of the main unit is also known.

[0045] In the above example, R １ and R ２ The number of carbon atoms in each of R is preferably 4 to 10, more preferably 4 to 8. １ and R ２ Each of these has a branched structure. The branched structure also includes a structure containing a saturated aliphatic ring. For example, when the number of carbon atoms is 4, R １ and R ２ Each of the groups is a —C group other than an n-butyl group. ４ H ９ (sec-butyl group, isobutyl group, and tert-butyl group) and a cyclobutyl group.

[0046] R １ and R ２ More specific examples of R include a tert-butyl group, a 2-ethylhexyl group, and a cyclohexyl group. In particular, in the above example where the particulate polymer contains both the unit (e1) and the unit (e2), R １ is a tert-butyl group, and R ２ is a 2-ethylhexyl group, in order to obtain a desired degree of swelling with an electrolyte and a desired glass transition temperature.

[0047] The particulate polymer may contain any unit other than the unit (e1) and the unit (e2). Examples of such any unit include a unit (e3) represented by the following formula (e3) and a unit (e4) represented by the following formula (e4): -(CH ２ -C(-CH ３ ) (-COO-R ３ )) - (e3) -(CH ２ -CH(-COO-R ４ ))-(e4) R ３ and R ４ are independently a methyl group, an ethyl group, an n-propyl group, an isopropyl group, or an alkyl group having a linear structure and 4 or more carbon atoms, and preferably an n-butyl group.

[0048] Further examples of the optional unit include a unit that can form a crosslinked structure in the particulate polymer.Specific examples thereof include a unit having a structure obtained by polymerizing a polyhydric ester, which is an ester of a dihydric or higher polyhydric alcohol and (meth)acrylic acid.An example of such a polyhydric ester is ethylene glycol dimethacrylate.By appropriately adjusting the type and amount of the unit that can form a crosslinked structure, the physical properties such as the elastic modulus of the particulate polymer can be adjusted to a desired value.

[0049] In order to obtain the effects of the present invention, such as the effects described above, it is particularly preferable that both the electrolyte swelling degree and glass transition temperature of the binder powder are within the preferred ranges. A particularly preferred example of a combination of the electrolyte swelling degree and glass transition temperature is that the electrolyte swelling degree is 1.0 to 1.4 and the glass transition temperature is 52 to 95°C. Furthermore, when the particulate polymer constituting the binder powder contains units (e1), it is particularly preferable that the electrolyte swelling degree and glass transition temperature of the binder powder, as well as the proportion of units (e1) in the particulate polymer, are all within the preferred ranges. A particularly preferred example of these combinations is that the electrolyte swelling degree of the binder powder is 1.0 to 1.4, the glass transition temperature of the binder powder is 52 to 95°C, and the proportion of units (e1) in the particulate polymer is 68.4% by mass to 86.0% by mass. Furthermore, when the particulate polymer constituting the binder powder contains the unit (e1) and the unit (e2), it is particularly preferable that the electrolyte swelling degree and glass transition temperature of the binder powder, and the proportion of the unit (e1) and the unit (e2) in the particulate polymer, are all within the preferred ranges. As a particularly preferred example of these combinations, it is preferable that the electrolyte swelling degree of the binder powder is 1.0 to 1.4, the glass transition temperature of the binder powder is 52 to 95°C, the proportion of the unit (e1) in the particulate polymer is 68.4% by mass to 86.0% by mass, and the proportion of the unit (e2) in the particulate polymer is 14.0% by mass to 31.6% by mass.

[0050] The particulate polymer may contain, as an optional unit, units other than those mentioned above.

[0051] The weight average molecular weight of the particulate polymer is preferably 20,000 or more, more preferably 30,000 or more, and is preferably 250,000 or less, more preferably 200,000 or less. When the molecular weight of the particulate polymer is within the above range, it is possible to obtain a particulate polymer having the desired electrolyte swelling degree, glass transition temperature, and other physical properties.

[0052] The binder powder may contain any component other than the particulate polymer as long as it does not significantly impair the effects of the present invention. Examples of the optional component include polymerization additives such as surfactants, emulsifiers, dispersion stabilizers, polymerization initiators, and chain transfer agents used in the polymerization of the particulate polymer. However, it is preferable that the amount of the optional component is small, and it is even more preferable that the binder powder does not contain any optional component.

[0053] In a preferred example, all or most of the binder powder is composed of the above-described particulate polymer. Specifically, the proportion of the particulate polymer in 100% by mass of the total binder powder is preferably 95% to 100% by mass, more preferably 97% to 100% by mass, even more preferably 99% to 100% by mass, and particularly preferably 100% by mass. When the binder powder contains such a high proportion of particulate polymer, the increase in internal resistance due to charging and discharging of a non-aqueous secondary battery can be effectively suppressed. In particular, it is preferable that all or most of the binder powder is composed of the above-described particulate polymer, and that all or most of the particulate polymer is composed of (meth)acrylic acid ester monomer units, in order to enable particularly good suppression of an increase in internal resistance. Specifically, the proportion of (meth)acrylic acid ester monomer units in 100% by mass of the total binder powder is preferably 95% by mass or more, more preferably 98% by mass or more, even more preferably 99% by mass or more, and may even be 100% by mass.

[0054] In particular, it is preferable for the binder powder to contain almost no or no fluorine atoms, either as a constituent element of the particulate polymer or as an optional component other than the particulate polymer, in order to exhibit good physical properties. Specifically, the proportion of fluorine atoms in the total amount of the binder powder is preferably 10,000 ppm or less, more preferably 100 ppm or less. Furthermore, it is even more preferable that the binder powder contain no fluorine atoms at all.

[0055] Furthermore, in order to achieve good battery performance, it is preferable that the binder powder contains little or no metals that impair battery performance, both as components of the particulate polymer and as optional components other than the particulate polymer. Examples of such metals include Fe, Ni, Cr, and Mn. The content of each of these metals relative to the total amount of the binder powder is preferably 10 ppm or less, more preferably 0.5 ppm or less. Furthermore, it is even more preferable that the binder powder contains no of these metals. The metal content can be measured using ICP-AES after appropriate pretreatment of the binder powder. More specifically, the measurement can be performed as follows: Approximately 1 g of binder powder is heated in an electric furnace at 550°C for approximately 3 hours and incinerated. Then, approximately 5 mL of concentrated sulfuric acid is added to the incinerated binder powder to dissolve it, and approximately 5 mL of concentrated nitric acid is gradually added to perform wet decomposition. After decomposition, the acid is concentrated and the volume is adjusted to 10 mL with ultrapure water, and the content of each metal in the binder powder (relative to the amount of binder powder) is measured using an ICP-AES device (manufactured by SII Nanotechnology, model number "SPS-5100").

[0056] The binder powder may or may not contain a solvent. Here, the solvent refers to a component that is liquid in a room temperature environment (generally, a 25°C environment). An example of a solvent is water. Preferably, the binder powder is a dry powder, and therefore preferably does not substantially contain a solvent. The amount of solvent contained in the binder powder is preferably 0% to 5% by mass, more preferably 0% to 1% by mass, even more preferably 0% to 0.5% by mass, and even more preferably 0% to 0.1% by mass, and particularly preferably less than 0.1% by mass.

[0057] There are no particular limitations on the method for producing the binder powder. For example, the binder powder can be produced by a method including a step of producing a particulate polymer.

[0058] The particulate polymer can be produced by a method including polymerizing a monomer. There is no particular limitation on the method for polymerizing the monomer. Examples of the polymerization method include solution polymerization, suspension polymerization, bulk polymerization, and emulsion polymerization. Among them, suspension polymerization and emulsion polymerization are preferred.

[0059] In the polymerization method, a particulate polymer can be produced by polymerizing a monomer composition containing a monomer in a reaction solvent. As such a monomer, a monomer corresponding to the monomer units listed above can be appropriately selected. For example, as the monomers corresponding to the units (e1) to (e4), the monomers (e'1) to (e'4) represented by the following formulas (e'1) to (e'4) can be used.

[0060] CH ２ =C(-CH ３ )-COO-R １ (e'1) CH ２ =CH-COO-R ２ (e'2) CH ２ =C(-CH ３ )-COO-R ３ (e'3) CH ２ =CH-COO-R ４ (e'4) where R １ ~R ４ indicates what has been described above.

[0061] The ratio of each monomer in the monomer composition is usually the same as the ratio of the corresponding structural units in the particulate polymer. The polymerization may also be carried out in a reaction system containing polymerization additives such as surfactants, emulsifiers, dispersants, polymerization initiators, and chain transfer agents. Specifically, in suspension polymerization (including microsuspension polymerization), a dispersant such as polyvinyl alcohol or magnesium hydroxide may be used to obtain an aqueous dispersion of the particulate polymer. Furthermore, in emulsion polymerization, a latex (aqueous dispersion) of the particulate polymer may be obtained using an emulsifier such as sodium dodecylbenzenesulfonate. The monomer composition may be a composition of multiple monomers or may consist of a single monomer. For convenience, in the present application, a particulate polymer material consisting of a single monomer is also included in the category of "monomer composition."

[0062] The method for producing a binder powder may include a step of drying the particulate polymer after its production. Preferably, the produced particulate polymer is washed and / or purified by an appropriate method, and then dried. In many cases, polymerization of the particulate polymer is carried out in water, so a drying method that can smoothly remove water is preferred. Furthermore, a drying method that can dry the particulate polymer in a redispersible state without excessive adhesion of the primary particles of the particulate polymer to each other is more preferred. Specific examples of drying methods include a method of spray-drying an aqueous dispersion of the particulate polymer; a method of drying in a rotary evaporator; and the like. Furthermore, after spray-drying or drying in a rotary evaporator as described above, it is more preferred to further dry the particulate polymer under vacuum conditions.

[0063] The method for producing the binder powder preferably includes a step of producing a particulate polymer, drying it as necessary, and then classifying the particulate polymer. There are no limitations on the classification method, but classification by a filtration method using a filter is preferred. Among these, from the viewpoint of smooth classification, filtration using a vibrating sieve such as an ultrasonic sieve is more preferred.

[0064] <Composite Powder Composition> The composite powder composition of the present invention includes the binder powder and the electrode active material described above. This composite powder composition can be a dry powder composition and can be in a powder form in a room temperature environment (generally, an environment of 25°C). This composite powder composition can provide a nonaqueous secondary battery that has excellent adhesive strength between the current collector and the electrode active material layer and a small increase in internal resistance.

[0065] In the composite powder composition, the particulate polymer and electrode active material contained in the binder powder are both in the form of particles. In the composite powder composition, the particulate polymer and the electrode active material may each exist as individual, independent particles. In addition, in the composite powder composition, one or more particulate polymers may adhere to the surface of a particle of the electrode active material to form a composite particle. Furthermore, in the composite powder composition, a plurality of particles of the particulate polymer and the electrode active material, and the composite particle may be bonded together while maintaining their particle shape to form a secondary particle. Usually, such secondary particles are smoothly crushed when subjected to an external force and can return to individual, independent particles (particulate polymer, electrode active material, or composite particle), so the composite powder composition can have high fluidity.

[0066] The binder powder contained in the composite powder composition is as described above. The amount of the binder powder relative to 100% by mass of the composite powder composition is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, even more preferably 1.5% by mass or more, and is preferably 10% by mass or less, more preferably 6% by mass or less, even more preferably 4% by mass or less. When the amount of the binder powder is within the above range, the increase in internal resistance of the nonaqueous secondary battery can be effectively reduced.

[0067] Also, as mentioned above, all or most of the binder powder is usually a particulate polymer, and therefore the range of the amount of particulate polymer per 100% by weight of the composite powder composition can be the same as the range of the amount of binder powder per 100% by weight of the composite powder composition.

[0068] The electrode active material can be selected depending on the type of nonaqueous secondary battery. For example, if the nonaqueous secondary battery is a lithium ion secondary battery, the electrode active material can be one that can reversibly insert or release lithium ions by applying a potential in an electrolyte. Such electrode active materials can be classified into positive electrode active materials as electrode active materials for the positive electrode and negative electrode active materials as electrode active materials for the negative electrode.

[0069] As the positive electrode active material for a lithium ion secondary battery, an active material that can be doped and dedoped with lithium ions is used, and examples thereof include positive electrode active materials made of inorganic compounds, positive electrode active materials made of organic compounds, and composite materials that combine these.

[0070] Examples of the inorganic positive electrode active material include transition metal oxides, transition metal sulfides, and lithium-containing composite metal oxides containing lithium and a transition metal, such as Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Mo.

[0071] Examples of transition metal oxides include MnO and MnO ２ , V ２ O ５ , V ６ O １３ , TiO ２ , Cu ２ V ２ O ３ , amorphous V ２ O-P ２ O ５ , MoO ３ Among them, MnO, V are preferred in terms of cycle stability and capacity. ２ O ５ , V ６ O １３ and TiO ２ is preferred.

[0072] Examples of transition metal sulfides include TiS ２ , TiS ３ , amorphous MoS ２ , FeS, etc.

[0073] Examples of the lithium-containing composite metal oxide include lithium-containing composite metal oxides having a layered structure, lithium-containing composite metal oxides having a spinel structure, and lithium-containing composite metal oxides having an olivine structure. Examples of the lithium-containing composite metal oxides having a layered structure include lithium-containing cobalt oxide (LiCoO ２ ), lithium-containing nickel oxide (LiNiO ２), Co—Ni—Mn lithium composite oxide, Ni—Mn—Al lithium composite oxide, Ni—Co—Al lithium composite oxide, etc. Examples of lithium-containing composite metal oxides having a spinel structure include lithium manganate (LiMn ２ O ４ ), Li[Mn ３／２ M １ １／２ ]O ４ (Here, M １ represents a transition metal other than Mn, such as Cr, Fe, Co, Ni, or Cu. Examples of lithium-containing composite metal oxides having an olivine structure include Li Ｘ M ２ P.O. ４ (In the formula, M ２ represents at least one element selected from the group consisting of Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B, and Mo, and X represents a number satisfying 0≦X≦2.

[0074] Examples of the positive electrode active material made of an organic compound include conductive polymer compounds such as polyacetylene and poly-p-phenylene.

[0075] Alternatively, for example, an iron-based oxide may be reduced and fired in the presence of a carbon source to produce a composite material covered with a carbon material, and this composite material may be used as a positive electrode active material. Although iron-based oxides tend to have poor electrical conductivity, such a composite material can be used as a high-performance positive electrode active material.

[0076] The positive electrode active material may be used alone or in combination of two or more. Also, a mixture of the inorganic compound and the organic compound described above may be used as the positive electrode active material.

[0077] Examples of negative electrode active materials for lithium ion secondary batteries include carbonaceous materials such as amorphous carbon, graphite, natural graphite, mesocarbon microbeads, and pitch-based carbon fibers; conductive polymer compounds such as polyacenes; metals or alloys thereof such as silicon, tin, zinc, manganese, iron, and nickel; oxides or sulfates of the above metals or alloys; metallic lithium; lithium alloys such as Li—Al, Li—Bi—Cd, and Li—Sn—Cd; lithium transition metal nitrides; and silicon. Furthermore, materials in which a conductive material is attached to the surface of particles of the negative electrode active material by, for example, mechanical modification, may also be used. The negative electrode active material may be used alone or in combination of two or more.

[0078] Typically, the electrode active material may be particles formed from the above-mentioned materials. The electrode active material preferably has a volume average particle size within a specific range. Specifically, the volume average particle size of the electrode active material is preferably 1 μm or more, more preferably 3 μm or more, even more preferably 5 μm or more, and preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 35 μm or less. When the volume average particle size of the electrode active material is within the above range, the adhesive strength between the current collector and the electrode active material layer of the electrode manufactured using the composite powder composition can be effectively increased, and the increase in internal resistance of the non-aqueous secondary battery can be effectively reduced.

[0079] In addition, the particle size ratio between the average primary particle size of the particulate polymer in the composite powder composition and the volume average particle size of the electrode active material ("average primary particle size of the particulate polymer" / "volume average particle size of the electrode active material") is preferably within a specific range. Specifically, the particle size ratio is preferably 0.01 or more, more preferably 0.03 or more, even more preferably 0.05 or more, and is preferably 1.0 or less, more preferably 0.8 or less, even more preferably 0.5 or less.

[0080] The volume average particle size of the electrode active material can be measured by the following method. The cumulative particle size distribution of the electrode active material is measured in a dry state using a laser diffraction / scattering particle size distribution analyzer. The particle size at which the integrated value of this cumulative particle size distribution, calculated from the small diameter side, is 50% can be obtained as the volume average particle size of the electrode active material. As a specific measurement method, the method described in "Volume average particle size of electrode active material" in the examples below can be adopted.

[0081] The amount of the electrode active material relative to 100% by mass of the composite powder composition is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, and is preferably 99% by mass or less, more preferably 98.5% by mass or less, even more preferably 98% by mass or less. When the amount of the electrode active material is within the above range, the adhesive strength between the current collector and the electrode active material layer of the electrode produced using the composite powder composition can be effectively increased, and an increase in the internal resistance of the non-aqueous secondary battery can be effectively reduced.

[0082] The composite powder composition may contain any component other than the binder powder and the electrode active material, as long as the effect of the present invention is not significantly impaired. Examples of the optional component include a conductive material. Examples of the conductive material include carbon black such as furnace black, acetylene black, and Ketjen Black (registered trademark); carbon nanotubes; carbon nanohorns; and conductive carbon such as graphene. Among these, carbon black is preferred, and acetylene black is more preferred. One type of conductive material may be used alone, or two or more types may be used in combination.

[0083] The conductive material is generally contained in the composite powder composition in the form of particles.

[0084] The amount of the conductive material is preferably 1 part by mass or more, and preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, per 100 parts by mass of the electrode active material.

[0085] The composite powder composition may contain a solvent or may not contain a solvent. Preferably, the composite powder composition is a dry powder and therefore preferably does not contain substantially a solvent. The amount of solvent contained in the composite powder composition is preferably 0% to 1% by mass, more preferably 0% to 0.5% by mass, even more preferably 0% to 0.1% by mass, and particularly preferably less than 0.1% by mass.

[0086] There are no particular limitations on the method for producing the composite powder composition. For example, the composite powder composition may be produced by a method including mixing a binder powder, an electrode active material, and, if necessary, optional components such as a conductive material. The mixing is preferably performed by dry mixing. "Dry mixing" refers to mixing in a state that is substantially free of liquid, specifically, mixing at a concentration of solids (components other than liquid) of 99% by mass or more during mixing.

[0087] Specific dry mixing methods include, for example, a container stirring method using a mixing device (e.g., a rocking mixer, a tumbler mixer, etc.) in which the container itself is shaken, rotated, or vibrated to mix; a mechanical stirring method using a mixing device (e.g., a horizontal cylindrical mixer, a V-type mixer, a ribbon mixer, a conical screw mixer, a high-speed fluid mixer, a rotating disk mixer, a high-speed rotating blade mixer, etc.) equipped with a rotating shaft installed horizontally or vertically in the container and an agitator such as a blade, a rotating disk, or a screw attached to the rotating shaft for stirring; and an airflow stirring method in which a swirling airflow caused by compressed gas is used to mix powders in a fluidized bed. These mixing methods may be performed alone or in combination of two or more. Furthermore, after dry mixing, disintegration may be performed using a disintegrator such as a mortar to break up agglomerates. Dry mixing maintains good dispersion of the composite powder composition, thereby improving various physical properties such as coating accuracy.

[0088] <Electrode for non-aqueous secondary battery> An electrode for a non-aqueous secondary battery according to one embodiment of the present invention includes a current collector and an electrode active material layer formed on the current collector using the composite powder composition described above. Therefore, the electrode active material layer typically contains the composite powder composition described above. Hereinafter, the electrode for a non-aqueous secondary battery may be simply referred to as "electrode."

[0089] The current collector material is preferably a material that is electrically conductive and electrochemically durable. Specific examples of the current collector material include metals, carbon, and conductive polymer compounds, with metals being preferred. Examples of metals include copper, aluminum, platinum, nickel, tantalum, titanium, stainless steel, and alloys thereof. Among these, copper, aluminum, and aluminum alloys are preferred in terms of conductivity and voltage resistance. When high voltage resistance is required, high-purity aluminum as disclosed in JP-A-2001-176757 can be preferably used. Among these, aluminum is preferred as the current collector material for the positive electrode, and copper is preferred as the current collector material for the negative electrode. These materials may be used alone or in combination of two or more.

[0090] The current collector generally has a film or sheet shape. The thickness of the current collector may be appropriately selected depending on the intended use, and is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more, and is preferably 200 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less.

[0091] The electrode active material layer is formed from the composite powder composition described above. Therefore, this electrode active material layer contains an electrode active material and a particulate polymer, and further contains optional components such as a conductive material, as necessary. In this electrode active material layer, particles of the electrode active material, particles of the conductive material, and particles of the electrode active material and conductive material are bound together by the particulate polymer. In the electrode active material layer, optional components such as the particulate polymer, the electrode active material, and the conductive material may maintain their particle shapes in the composite powder composition, or may be deformed by heat and pressure that may be applied in the process of forming the electrode active material layer. Typically, the electrode active material and the conductive material maintain their particle shapes in the composite powder composition. Furthermore, the particulate polymer may be deformed by heat and pressure.

[0092] The amount of the electrode active material layer per unit area is not particularly limited, but is preferably 10 mg / cm ２ More preferably, 15 mg / cm ２ More preferably, 20 mg / cm ２ or more, preferably 35 mg / cm ２ or less, more preferably 30 mg / cm ２ More preferably 25 mg / cm ２ The following is the result.

[0093] The density of the electrode active material layer is not particularly limited, but is preferably 2.5 g / cm ３ More preferably, 3.0 g / cm ３ More preferably, 3.3 g / cm ３ or more, preferably 4.0 g / cm ３ or less, more preferably 3.8 g / cm ３ More preferably, 3.6 g / cm or less ３ The following is the result.

[0094] The thickness of the electrode active material layer is not particularly limited, but is preferably 30 μm or more, more preferably 50 μm or more, and even more preferably 60 μm or more, and is preferably 100 μm or less, more preferably 90 μm or less, and even more preferably 80 μm or less.

[0095] The electrode according to this embodiment has excellent peel strength, i.e., adhesive strength indicated by the force required to peel the current collector from the electrode active material layer. In one example, the peel strength is preferably 15 N / m or more, more preferably 17 N / m or more, and even more preferably 20 N / m or more. The peel strength can be measured by pulling the current collector of an electrode having an electrode active material layer fixed to a flat surface at a pulling rate of 100 mm / min in a direction perpendicular to the flat surface to peel the current collector from the electrode active material layer. The specific method for measuring the peel strength may be the method described in "Peel Strength of Electrode Mixture Layer" in the Examples below.

[0096] The electrode according to this embodiment can be manufactured by a method including a step of forming an electrode active material layer from the composite powder composition described above. Typically, an electrode active material layer can be formed as a layer of the composite powder composition by forming a layer of the composite powder composition using an appropriate method. The electrode active material layer is preferably formed from the composite powder composition by a dry process. Here, the "dry process" of forming the electrode active material layer from the composite powder composition refers to the formation of the electrode active material layer using a powdered composite powder composition. The composite powder composition may contain a solvent to the extent that the composite powder composition remains in a powdered form. In one example, when forming the electrode active material layer by a dry process, it is preferable to form the electrode active material layer without mixing a liquid such as a solvent into the composite powder composition.

[0097] The electrode manufacturing method may include, for example, a step of forming an electrode active material layer by molding a composite powder composition into a layer, and a step of laminating the resulting electrode active material layer with a current collector. Specifically, the electrode may be manufactured by a method including a step of supplying the composite powder composition to a roll-type pressure molding device equipped with a pair of rolls, and pressure-molding the composite powder composition with the pair of rolls to form an electrode active material layer, and a step of laminating the electrode active material layer with a current collector. As another specific example, the electrode may be manufactured by a method including a step of filling a composite powder composition into a mold, pressure-molding the composite powder composition to form an electrode active material layer, and a step of laminating the electrode active material layer with a current collector. As yet another specific example, the electrode may be manufactured by a method including a step of applying the composite powder composition to a suitable support (e.g., a support sheet), and optionally performing a heat treatment and pressure treatment to form an electrode active material layer, a step of laminating the electrode active material layer with a current collector, and a step of peeling off the support.

[0098] From the viewpoint of efficiently manufacturing an electrode without laminating the electrode active material layer and the current collector, the manufacturing method of the electrode preferably includes a step of forming the electrode active material layer on the current collector. For example, the electrode active material layer can be formed on the current collector by forming the composite powder composition into a layer on the current collector, so that the step of laminating the electrode active material layer and the current collector can be omitted and the number of steps can be reduced.

[0099] As a specific example, the electrode manufacturing method may include using a roll-type pressure molding apparatus equipped with a pair of rolls, supplying a current collector and a composite powder composition so that the composite powder composition passes between the pair of rolls, and forming an electrode active material layer on the current collector. In this method, the current collector is fed by the pair of rolls while the composite powder composition is pressure-molded by the pair of rolls to form an electrode active material layer on the current collector. In this case, from the viewpoint of increasing the adhesive strength between the electrode active material layer and the current collector, the roll temperature is preferably (Tg + 10) ° C. or higher, more preferably (Tg + 30) ° C. or higher, even more preferably (Tg + 40) ° C. or higher, and preferably (Tg + 120) ° C. or lower, more preferably (Tg + 100) ° C. or lower, even more preferably (Tg + 80) ° C. or lower. Here, Tg represents the glass transition temperature of the binder powder. In one example, the roll temperature is preferably 25°C or higher, more preferably 50°C or higher, and even more preferably 80°C or higher, and preferably 200°C or lower, more preferably 150°C or lower, and even more preferably 120°C or lower. Furthermore, from the viewpoint of improving the uniformity of the thickness of the electrode active material layer, the press linear pressure between the rolls is preferably 10 kN / m or higher, more preferably 200 kN / m or higher, and even more preferably 500 kN / m or higher, and preferably 2000 kN / m or lower, more preferably 1500 kN / m or lower, and even more preferably 1200 kN / m or lower. Furthermore, the molding speed during pressure molding is preferably 0.1 m / min or higher, more preferably 4 m / min or higher, and preferably 20 m / min or lower, more preferably 10 m / min or lower.

[0100] As another specific example, the electrode manufacturing method may include coating a composite powder composition on a current collector to form an electrode active material layer. Coating of the composite powder composition can be performed, for example, by electrostatic coating. The electrostatic coating method is a method in which a composite powder composition charged by a charging device is coated on a current collector, and the composite powder composition can be efficiently fixed to the current collector by electrostatic attraction. In the electrostatic coating method, the current collector may be earthed or charged with a polarity opposite to that of the composite powder composition in order to increase the electrostatic attraction and efficiently fix the composite powder composition. Furthermore, coating of the composite powder composition is generally performed using a coating device separated from the current collector. For example, the composite powder composition may be applied to the current collector by dropping the composite powder composition from a nozzle installed above the current collector in the direction of gravity. Alternatively, the composite powder composition may be applied to the current collector using an injector (e.g., a spray gun) capable of spraying the composite powder composition by the pressure of a gas such as air. Typically, an electric charge is applied to the composite powder composition in an application device such as the nozzle and injector.

[0101] After the electrode active material layer is formed by coating the composite powder composition on the current collector, a thickness adjustment step may be performed to make the thickness of the electrode active material layer uniform. For example, the electrode active material layer may be smoothed with a blade to make the thickness uniform.

[0102] After the composite powder composition is applied to the current collector to form the electrode active material layer, the current collector and the electrode active material layer may be subjected to a heat treatment. The heat treatment can effectively bond the particulate polymer in the composite powder composition applied to the current collector to any component of the current collector, the electrode active material, and the conductive material, thereby increasing the adhesive strength between the current collector and the electrode active material layer and increasing the mechanical strength of the electrode active material layer.

[0103] After the electrode active material layer is formed by coating the composite powder composition on the current collector, the electrode active material layer may be subjected to a pressure treatment, which can increase the density of the electrode active material layer and thereby increase the capacity of the electrode.

[0104] Typically, heat treatment and pressure treatment are performed by passing the current collector and the electrode active material layer between a pair of heated rolls. In this case, the heat treatment temperature (roll temperature) is preferably (Tg + 10) ° C. or higher, more preferably (Tg + 30) ° C. or higher, even more preferably (Tg + 40) ° C. or higher, from the viewpoint of increasing the adhesive strength between the electrode active material layer and the current collector, and is preferably (Tg + 120) ° C. or lower, more preferably (Tg + 100) ° C. or lower, even more preferably (Tg + 80) ° C. or lower. Here, Tg represents the glass transition temperature of the binder powder. Furthermore, the pressure (linear pressure between the rolls) is preferably 10 kN / m or higher, more preferably 200 kN / m or higher, even more preferably 500 kN / m or higher, and preferably 2000 kN / m or lower, more preferably 1500 kN / m or lower, even more preferably 1200 kN / m or lower, from the viewpoint of improving the thickness uniformity of the electrode active material layer. Furthermore, the running speed of the current collector and the electrode active material layer passing between the rolls is preferably 0.1 m / min or more, more preferably 3 m / min or more, even more preferably 4 m / min or more, and is preferably 50 m / min or less, more preferably 20 m / min or less, even more preferably 10 m / min or less.

[0105] The above-described manufacturing method can produce an electrode including a current collector and an electrode active material layer, but the manufacturing method of the electrode may further include any other steps. For example, from the viewpoint of reducing the variation in the thickness of the electrode or increasing the density of the electrode active material layer to further increase the capacity, a post-pressing treatment may be performed as necessary. The method of the post-pressing treatment is preferably a roll pressing method. In the roll pressing method, the electrode is passed between two rolls placed in parallel to apply pressure to the electrode. In this case, the temperature of the rolls may be adjusted, for example, by heating or cooling, as necessary.

[0106] <Nonaqueous Secondary Battery> A nonaqueous secondary battery according to one embodiment of the present invention includes an electrode according to the above-described embodiment. Typically, such a nonaqueous secondary battery includes a positive electrode, a negative electrode, and a nonaqueous electrolyte solution, and includes an electrode according to the above-described embodiment as at least one of the positive electrode and the negative electrode. Therefore, in the nonaqueous secondary battery, the positive electrode may be the electrode according to the above-described embodiment, the negative electrode may be the electrode according to the above-described embodiment, or both the positive electrode and the negative electrode may be the electrodes according to the above-described embodiment.

[0107] The non-aqueous electrolyte solution may be, for example, an electrolyte solution in which a supporting electrolyte is dissolved in a non-aqueous solvent. The supporting electrolyte is preferably a lithium salt. For example, LiPF ６ , LiAsF ６ , LiBF ４ , LiSbF ６ , LiAlCl ４ , LiClO ４ , C.F. ３ SO ３ Li, C ４ F ９ SO ３ Li, CF ３ COOLi, (CF ３ CO) ２ NLi, (CF ３ SO ２ ) ２ NLi, (C ２ F ５ SO ２ Among them, LiPF6 is easily soluble in solvents and exhibits a high degree of dissociation. ６ , LiClO ４ , C.F. ３ SO ３ Li is preferred. The supporting electrolyte may be used alone or in combination of two or more. In general, the use of a supporting electrolyte with a higher degree of dissociation tends to result in higher ionic conductivity.

[0108] The concentration of the supporting electrolyte is preferably set in the range of 0.5 mol / L to 2.5 mol / L depending on the type of supporting electrolyte, since this range allows for high ionic conductivity and improves the charge and discharge characteristics of the nonaqueous secondary battery.

[0109] The nonaqueous solvent used in the nonaqueous electrolyte solution is not particularly limited as long as it can dissolve the supporting electrolyte. Examples of nonaqueous solvents include carbonate solvents such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and ethyl methyl carbonate (EMC); ester solvents such as γ-butyrolactone and methyl formate; ether solvents such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compound solvents such as sulfolane and dimethyl sulfoxide; and ionic liquids that are also used as supporting electrolytes. Among these, carbonate solvents are preferred because of their high dielectric constant and wide stable potential range. One type of nonaqueous solvent may be used alone, or two or more types may be used in combination. Generally, the lower the viscosity of the nonaqueous solvent, the higher the ionic conductivity, and the higher the dielectric constant, the higher the solubility of the supporting electrolyte. However, since there is a trade-off between the two, it is preferable to adjust the ionic conductivity by adjusting the type and mixing ratio of the solvent. The non-aqueous solvent may be used in combination with a solvent in which all or part of the hydrogen atoms are replaced with fluorine atoms, or the entire amount of the solvent may be used.

[0110] Among the above-mentioned solvents, a mixed solvent of EC and EMC is preferred from the viewpoints of acquisition cost, advantages in manifesting lithium ion secondary battery performance, etc. When a mixed solvent of EC and EMC is used, the volume ratio of EC / EMC is preferably 5 / 5 to 1 / 9.

[0111] The non-aqueous electrolyte may contain any additive in combination with the supporting electrolyte and the non-aqueous solvent. Examples of the optional additive include carbonate compounds such as vinylene carbonate (VC); sulfur-containing compounds such as ethylene sulfite (ES); and fluorine-containing compounds such as fluoroethylene carbonate (FEC). One type of additive may be used alone, or two or more types may be used in combination.

[0112] When the supporting electrolytes exemplified above are used, the desired effects due to the electrolyte swelling degree of the binder powder of the present invention can be obtained. In particular, when the supporting electrolyte is a mixed solvent of EC and EMC, the desired effects due to the electrolyte swelling degree of the binder powder of the present invention can be particularly well obtained.

[0113] The nonaqueous secondary battery may further include a separator. Examples of the separator include a microporous membrane or nonwoven fabric formed from a resin such as a polyolefin resin or an aromatic polyamide resin; a porous resin-coated membrane containing an inorganic ceramic powder; and the like. Specific examples of the separator include a microporous membrane formed from a resin such as a polyolefin polymer (e.g., polyethylene, polypropylene, polybutene, polyvinyl chloride) or a mixture or copolymer thereof; a microporous membrane formed from a resin such as polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimideamide, polyaramid, polycycloolefin, nylon, or polytetrafluoroethylene; a fabric material woven from polyolefin resin fibers or a nonwoven fabric of the fibers; and an aggregate of insulating material particles. Among these, a microporous membrane formed from a polyolefin resin is preferred from the viewpoint of reducing the overall separator thickness and increasing the active material ratio in the nonaqueous secondary battery to improve the capacity per volume.

[0114] The thickness of the separator is preferably 1.0 μm or more, more preferably 3 μm or more, and is preferably 40 μm or less, more preferably 30 μm or less, and even more preferably 25 μm or less, from the viewpoint of reducing an increase in internal resistance due to the separator in the nonaqueous secondary battery and from the viewpoint of excellent workability when producing the nonaqueous secondary battery.

[0115] The nonaqueous secondary battery according to this embodiment can be a battery in which an increase in internal resistance due to charging and discharging is suppressed. The internal resistance of a nonaqueous secondary battery can be evaluated by the DCR (direct current resistance) of the nonaqueous secondary battery at a temperature of 25°C. Specifically, the smaller the DCR (direct current resistance) of a nonaqueous secondary battery, the smaller the internal resistance of the nonaqueous secondary battery. The suppression of the increase in DCR due to charging and discharging of a nonaqueous secondary battery can be measured by the method described in "Internal resistance characteristics after charging and discharging" in the Examples below.

[0116] Examples of methods for producing nonaqueous secondary batteries include stacking a positive electrode and a negative electrode with a separator interposed therebetween, rolling or folding the resulting stack according to the battery shape, placing the stack in a battery container, injecting an electrolyte into the battery container, and sealing the container. Furthermore, if necessary, expandable metals; overcurrent protection elements such as fuses and PTC elements; lead plates, etc. may be inserted to prevent pressure buildup within the battery and overcharging and discharging. The shape of the nonaqueous secondary battery may be, for example, a coin type, button type, sheet type, cylindrical type, prismatic type, flat type, etc. The battery container is preferably made of a material that prevents moisture from penetrating into the battery, such as a metal or a laminate of aluminum.

[0117] The nonaqueous secondary battery does not require a large amount of solvent-containing slurry in the process of producing the composite powder composition and the electrode, which reduces the energy required for production. Furthermore, continuous operation is easy, and the yield can be increased.

[0118] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the examples shown below, and may be practiced with any modifications within the scope of the claims and their equivalents. In the following description, "%" and "parts" representing amounts are based on mass unless otherwise specified. Furthermore, the operations described below were carried out under atmospheric conditions at room temperature and normal pressure (25°C, 1 atm).

[0119] <Evaluation Method> <Electrolyte Swelling Degree> Approximately 0.2 g of the binder powder obtained in the Examples and Comparative Examples was pressed at 200°C and 5 MPa for 1 minute to obtain a film with a thickness ranging from 0.1 mm to 1 mm. The obtained film was then cut into 1 cm squares to obtain test pieces. The mass W0 of this test piece was measured. The test piece was immersed in an electrolyte at 60°C for 72 hours. Thereafter, the test piece was removed from the electrolyte, the electrolyte solution on the surface of the test piece was wiped off, and the mass W1 of the test piece after the immersion test was measured. From the values ​​of W0 and W1, the electrolyte swelling degree was calculated according to the formula S = W1 / W0. The electrolyte used for swelling degree measurement was 1.0 M LiPF ６ A solution (solvent: a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC)=3 / 7 (volume ratio), additive: containing 2% by volume of vinylene carbonate (solvent ratio)) was used.

[0120] <Glass Transition Temperature> The binder powders obtained in the examples and comparative examples were used as samples for measuring the glass transition temperature. 10 mg of the binder powder was weighed into an aluminum pan, and differential scanning calorimetry (DSC) measurements were performed using a differential thermal analyzer ("EXSTAR DSC6220" manufactured by SII NanoTechnology Inc.) at a temperature range of -100°C to 500°C at a heating rate of 10°C / min, using an empty aluminum pan as a reference, to obtain a DSC curve. During this heating process, the glass transition temperature (°C) was determined as the intersection of the baseline immediately before the endothermic peak of the DSC curve where the differential signal (DDSC) is 0.05 mW / min / mg or more appears and the tangent to the DSC curve at the first inflection point that appears after the endothermic peak.

[0121] <Weight-average molecular weight (Mw) of particulate polymer> The binder powder obtained in the examples and comparative examples was used as a sample for measuring the molecular weight of the particulate polymer. The binder powder was subjected to gel permeation chromatography (GPC) to measure the weight-average molecular weight (Mw). Specifically, the binder powder was dissolved in cyclohexane to a solids concentration of 0.2% to prepare a sample. After passing the sample through a 0.2 μm filter, a gel permeation chromatograph (Tosoh, HLC-8220) was used. One "TSK guard column α" and two "TSKgel Super HZM-M" columns, both manufactured by Tosoh, were connected in series, and cyclohexane was used as a solvent at a flow rate of 1.0 mL / min. The weight-average molecular weight (Mw) of the particulate polymer was determined as a standard polyisoprene equivalent value.

[0122] <Flexural Modulus> The binder powders obtained in the examples and comparative examples were molded by hot pressing to obtain sheets. The hot pressing was performed by sandwiching 0.1 g of the sample between Teflon (registered trademark) sheets (Nachias Naflon (registered trademark) PTFE tape TOMB (registered trademark) No. 9001 0.10 mm). The hot pressing was performed under the following conditions: a press temperature of 200°C, a press load of 4.5 kN, and a press time of 1 minute. The obtained sheets had a thickness of 3 mm. The sheets were further cut into test pieces measuring 127 mm x 13 mm x 3 mm. A bending test was performed in accordance with ASTM D790 (Method A) at a test speed of 1.3 mm / min, a support distance of 48 mm, and a test environment of 23°C and 50% RH, to measure the flexural modulus of the test pieces.

[0123] <Peel strength of electrode mixture layer> The positive electrodes for lithium ion secondary batteries obtained in the examples and comparative examples were cut into rectangular pieces with a length of 100 mm and a width of 10 mm to prepare test pieces. The test pieces were immersed in an electrolyte solution and left to stand in a thermostatic chamber at 40°C for 24 hours. The electrolyte solution was a 1.0 M LiPF ６A solution (solvent: a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3 / 7 (volume ratio), additive: containing 2 vol% vinylene carbonate (solvent ratio)) was used. After the immersion time, the test piece was removed from the electrolyte solution, and the electrolyte solution on the surface of the test piece was wiped off with a Kimtowel. Then, cellophane tape (compliant with JIS Z1522) was attached to the surface of the positive electrode composite layer, and the cellophane tape was fixed to a horizontal test stand. In this way, the test piece was fixed on the test stand with the positive electrode composite layer side facing downward and the current collector side facing upward. In this state, one of the longitudinal ends of the test piece was pulled and peeled in a direction perpendicular to the test stand at a pulling rate of 100 mm / min, and the stress at this time was measured. Measurements were performed three times, and the average value was calculated as the peel strength, which was evaluated according to the following criteria. A higher peel strength value after impregnation with the electrolyte solution indicates better adhesion between the positive electrode composite layer and the current collector. A: Peel strength is 20 N / m or more B: Peel strength is 17 N / m or more and less than 20 N / m C: Peel strength is 14 N / m or more and less than 17 N / m D: Peel strength is less than 14 N / m

[0124] <Internal Resistance Characteristics After Charge and Discharge> The following battery initialization, subsequent IV test, and IV test after cycle test were carried out to evaluate the internal resistance characteristics after charge and discharge.

[0125] (Battery Initialization) The lithium ion secondary batteries produced in the Examples and Comparative Examples immediately after production were left to stand for 5 hours in an environment at 25°C. Next, in an environment at 25°C, they were charged to a cell voltage of 3.65 V using a constant current method at 0.2 C, and then aged for 12 hours at a temperature of 60°C. Thereafter, in an environment at 25°C, they were discharged to a cell voltage of 3.00 V using a constant current method at 0.2 C. Thereafter, they were subjected to CC-CV charging at 0.2 C (upper limit cell voltage 4.20 V, end current 0.01 C), and CC discharging to 3.00 V using a constant current method at 0.2 C. This 0.2 C charge-discharge (CC-CV charging from 3.00 V to 4.20 V and CC discharging to 3.00 V) was repeated three times to initialize the batteries.

[0126] (IV test immediately after initialization) The following IV test was performed on the battery after initialization in an environment of 25°C to measure DCR (direct current resistance). First, the battery was discharged CC to 3.00 V using a constant current method of 0.2 C. Then, the battery was charged at 0.2 C to a state of charge (SOC) of 50% and left to stand for 600 seconds. The voltage at 600 seconds was V ０ Then, 0.5C (=I ０．５ ) constant current method for 10 seconds, and the voltage at the 10th second is V ０．５ After that, the battery was charged with the same amount of electricity as the previous discharge at a constant current of 0.2 C. Next, the battery was charged at 1.0 C (= I １．０ ) constant current method for 10 seconds, and the voltage at the 10th second is V １．０ Then, the battery was charged with the same amount of electricity as the previous discharge at a constant current of 0.2 C. Next, the battery was charged at 1.5 C (= I １．５ ) constant current method for 10 seconds, and the voltage at the 10th second is V １．５ The x and y coordinates (x, y) are ０．５ , V ０．５ ), (I １．０ , V １．０ ) and (I １．５ , V １．５ ) was plotted, and the slope b of the regression line was determined using the following formula (M1), and the slope b was obtained as the DCR (direct current resistance) before the cycle test.

[0127]

[0128] (IV Test After Cycle Test) A separate, initialized battery was subjected to the following cycle test and subsequent IV test at 25°C to measure the DCR. First, the battery temperature was adjusted to 25°C. The battery was then subjected to 100 charge-discharge cycles, consisting of charging to a cell voltage of 4.10 V at a constant current of 1.0 C and subsequently discharging to a cell voltage of 3.00 V at a constant current of 1.0 C. After 100 cycles, the same IV test as described above for the "IV Test Immediately After Initialization" was performed on the cell to determine the slope b, which was used as the DCR after the cycle test. The DCR relative to the DCR before the cycle test, defined as 100, was calculated and evaluated according to the following criteria. A smaller DCR relative value indicates a smaller increase in IV resistance due to charge-discharge loads, i.e., a smaller increase in internal resistance due to charge-discharge loads. A: DCR relative value is 105 or less B: DCR relative value is more than 105 and 110 or less C: DCR relative value is more than 110

[0129] <Primary particle size D50 of particulate polymer> A binder powder was added to a 1% aqueous solution of linear alkylbenzenesulfonate sodium, and the mixture was dispersed by ultrasonic waves to obtain a dispersion in which the particulate polymer contained in the binder powder was dispersed. The cumulative particle size distribution of this dispersion was measured using a Coulter counter (a particle size measuring instrument "Coulter Counter LS230" manufactured by Coulter). The particle size at which the integral value accumulated from the small diameter side of this cumulative particle size distribution reached 50% was obtained as the volume-based primary particle size D50 of the particulate polymer contained in the binder powder.

[0130] <Volume average particle size of electrode active material> The electrode active material was subjected to dry cumulative particle size distribution measurement using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3200II manufactured by Nikkiso Co., Ltd.) The particle size at which the integrated value, calculated from the small diameter side of this cumulative particle size distribution, reached 50% was obtained as the volume average particle size of the electrode active material.

[0131] <SP Value of Particulate Polymer> When the particulate polymer is a homopolymer, its SP value was determined by the Y-MB method of HSPiP ver. 5.3.04. When the particulate polymer is a copolymer, the SP value of each monomer unit constituting the copolymer was determined by the Y-MB method of HSPiP ver. 5.3.04, and the polar term δ for each ｐ , dispersion term δ ｄ and the hydrogen bond term δ ｈ The weighted average of the monomer unit molar ratios of each term (polarity term δ ｐ Weighted average, variance term δ ｄ Weighted average and hydrogen bond term δ ｈ For example, if the particulate polymer is a copolymer of monomer unit A and monomer unit B, and the content ratio of monomer unit A is 60 mol % and the content ratio of monomer unit B is 40 mol %, and the homopolymer of monomer unit A has a polar term δ ｐ A ｐ , dispersion term δ ｄ A ｄ , hydrogen bond term δ ｈ A ｈ In the homopolymer of the monomer unit B, the polar term δ ｐ is B ｐ , dispersion term δ ｄ is B ｄ , hydrogen bond term δ ｈ is B ｈ When the HSP of the particulate polymer is ｄ is the polar term δ ｐ２ = 0.4 × A ｐ +0.6 x B ｐ ”, “Dispersion term δ ｄ２ = 0.4 × A ｄ +0.6 x B ｄ ", "Hydrogen bond term δ ｈ２ = 0.4 × A ｈ +0.6 x B ｈ". In this example, the SP value of the particulate polymer was determined by the method described above. However, when the detailed structure of the particulate polymer is unknown, it can be determined, for example, by the following method. First, 0.5 g of particulate polymer that had been dried at 25°C for 7 days and then vacuum-dried at 60°C for 10 hours was added to 10 ml of each of 12 types of solvents (acetone, toluene, ethanol, tetrahydrofuran, dimethylformamide, methyl ethyl ketone, benzyl alcohol, γ-butyrolactone, nitrobenzene N-methyl-2-pyrrolidone, salicylaldehyde, and methyl acetate), and the mixture was allowed to stand at 25°C for 24 hours to obtain an evaluation liquid. This evaluation liquid was visually observed and scored as follows: - Insoluble (poor solvent): 0 - Turbid and / or unstable (poor solvent): 2 - Completely soluble (good solvent): 1 The SP value was determined using the above HSPiP according to the obtained score.

[0132] Example 1 (1-1. Production of binder powder) - Preparation of monomer composition (A) - 68.4 parts of tert-butyl methacrylate as a methacrylic acid alkyl ester monomer and 31.6 parts of 2-ethylhexyl acrylate as an acrylic acid alkyl ester monomer were mixed to prepare a monomer composition (A).

[0133] - Preparation of Metal Hydroxide - An aqueous magnesium chloride solution prepared by dissolving 10.0 parts of magnesium chloride in 200 parts of ion-exchanged water and an aqueous sodium hydroxide solution prepared by dissolving 7.0 parts of sodium hydroxide in 50 parts of ion-exchanged water were prepared. The aqueous sodium hydroxide solution was gradually added to the aqueous magnesium chloride solution with stirring to prepare a colloidal dispersion containing magnesium hydroxide as the metal hydroxide.

[0134] - Suspension Polymerization - A particulate polymer was prepared by suspension polymerization. Specifically, 100 parts of the monomer composition (A) obtained as described above was added to 267 parts of the colloidal dispersion containing the magnesium hydroxide, and the mixture was further stirred. Thereafter, 2.5 parts of t-butylperoxy-2-ethylhexanoate (manufactured by NOF Corporation, "Perbutyl O") as a polymerization initiator was further added to the colloidal dispersion to obtain a mixed solution. The obtained mixed solution was subjected to high-shear stirring at 12,000 rpm for 1 minute using an in-line emulsifying disperser (manufactured by Pacific Machinery Works, "Cavitron") to form droplets of the monomer composition in the colloidal dispersion containing magnesium hydroxide.

[0135] The colloidal dispersion in which droplets of the monomer composition were formed as described above was placed in a reactor, heated to 90°C, and subjected to a polymerization reaction for 5 hours to obtain a dispersion. This dispersion was purified by subjecting it to a reduced pressure treatment at 90°C for 2 hours using an evaporator to obtain an aqueous dispersion containing a particulate polymer.

[0136] Washing, Drying, and Classification While stirring the aqueous dispersion containing the particulate polymer, sulfuric acid was added dropwise at room temperature (25°C) and acid washing was performed until the pH reached 6.5 or less. Subsequently, a water washing treatment, which included, in this order, filtering out the solid content, dehydrating the obtained solid content, and adding 500 parts of ion-exchanged water to the solid content to form a reslurry, was repeated 10 times. After that, filtration was performed, and the obtained solid content was placed in a dryer and dried at 40°C for 48 hours. The dried solid content was classified using an ultrasonic sieve (mesh opening: 75 μm) to obtain a binder powder having a powdery form. The particulate polymer contained in the obtained binder powder was solid particles without internal voids. The obtained binder powder was evaluated by the method described above.

[0137] (1-2. Production of composite powder composition) NMC811 (LiNi) as a positive electrode active material was mixed in a high-speed mixer (FS2 type, manufactured by Earth Technica Co., Ltd.). ０．８ Mn ０．１ Co ０．１ O ２96.0 parts of carbon black (Super C65, manufactured by Imerys) as a conductive material, equivalent to the solid content, were added, and mixed for 30 minutes under the conditions of 10°C, an agitator rotation speed of 2000 rpm, and a chopper rotation speed of 3500 rpm. Thereafter, 2 parts of the binder powder obtained in (1-1) were added, and mixed for 30 minutes under the conditions of 10°C, an agitator rotation speed of 500 rpm, and a chopper rotation speed of 800 rpm, to obtain a powdered composite powder composition.

[0138] (1-3. Production of Positive Electrode: Dry Method (Electrostatic Coating)) Using an electrostatic screen printing device (manufactured by Berg Industries, "T-1"), the above composite powder composition was coated onto an aluminum foil (thickness 15 μm) as a current collector to obtain a positive electrode blank. The coating was carried out so that the amount of the coated composite powder composition per unit area of ​​the current collector (coating weight) was 18 mg / cm. ２ This positive electrode blank was subjected to a hot roll press (temperature 110°C, load 1000 kN / mmm) to obtain a positive electrode (density of the positive electrode active material layer: 3.3 g / cm ３ The resulting positive electrode was evaluated by the above-described method.

[0139] (1-4. Preparation of Negative Electrode) 63 parts of styrene, 34 parts of 1,3-butadiene, 2 parts of itaconic acid, 1 part of 2-hydroxyethyl acrylate, 0.3 parts of t-dodecyl mercaptan as a molecular weight modifier, 5 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 1 part of potassium persulfate as a polymerization initiator were added to a 5 MPa pressure vessel equipped with a stirrer, and after thorough stirring, the mixture was heated to a temperature of 55°C to initiate polymerization. When the monomer consumption reached 95.0%, the mixture was cooled to terminate the reaction. A 5% aqueous sodium hydroxide solution was added to the aqueous dispersion containing the polymer obtained in this way, and the pH was adjusted to 8. Thereafter, unreacted monomer was removed by heated distillation under reduced pressure. Thereafter, the mixture was cooled to a temperature of 30°C or below to obtain an aqueous dispersion containing a negative electrode binder (a negative electrode binder composition).

[0140] 48.75 parts of artificial graphite (theoretical capacity 360 mAh / g) as a negative electrode active material, 48.75 parts of natural graphite (theoretical capacity 360 mAh / g), and 1 part of carboxymethyl cellulose (solid content equivalent) were added to a planetary mixer. The mixture was then diluted with ion-exchanged water to a solid content of 60%, and then kneaded for 60 minutes at a rotation speed of 45 rpm. Then, 1.5 parts of the negative electrode binder composition obtained above (solid content equivalent) were added, and the mixture was kneaded for 40 minutes at a rotation speed of 40 rpm. Then, ion-exchanged water was added to the mixture to a viscosity of 3000 ± 500 mPa s (measured with a Brookfield viscometer at 25 ° C. and 60 rpm), thereby preparing a negative electrode slurry composition.

[0141] The negative electrode slurry composition was applied to the surface of a 10 μm thick copper foil current collector using a comma coater in an amount per unit area of ​​the current collector (coating weight) of 11±0.5 mg / cm ２ The copper foil coated with the negative electrode slurry composition was then transported at a speed of 400 mm / min through an oven at a temperature of 80°C for 2 minutes and then through an oven at a temperature of 110°C for 2 minutes, thereby drying the negative electrode slurry composition on the copper foil and obtaining a negative electrode blank. The negative electrode blank was then roll-pressed under a linear pressure of 1200 kN / m in an environment at a temperature of 25±3°C to obtain a negative electrode comprising a current collector and a negative electrode active material layer (the density of the negative electrode active material layer was 1.60 g / cm ３ ) was obtained.

[0142] (1-5. Manufacture of Secondary Battery) A laminated cell (equivalent to an initial design discharge capacity of 30 mAh) was manufactured using the above-mentioned negative electrode, positive electrode, and a single-layer polypropylene separator (manufactured by Celgard, "#2500"), placed in an aluminum package, and vacuum dried at 60°C for 10 hours. Then, a 1.0 M LiPF 6 electrolyte was added. ６A solution (solvent: a mixed solvent of ethylene carbonate (EC) / diethyl carbonate (DEC) = 3 / 7 (volume ratio), additive: containing 2 vol% vinylene carbonate (solvent ratio)) was filled into the aluminum packaging. Furthermore, in order to seal the opening of the aluminum packaging, the aluminum packaging was closed by heat sealing at a temperature of 150°C, and a lithium ion secondary battery was produced. The obtained lithium ion secondary battery was evaluated by the method described above.

[0143] Example 2 A binder powder, a positive electrode, and a lithium-ion secondary battery were obtained and evaluated by performing the same operations as in Example 1, except for the following changes: In step (1-1), the composition of the monomer composition (A) was changed to a mixture consisting of 77.8 parts of tert-butyl methacrylate and 22.2 parts of 2-ethylhexyl acrylate.

[0144] Example 3 A binder powder, a positive electrode, and a lithium ion secondary battery were obtained and evaluated by performing the same operations as in Example 1, except for the following changes: In step (1-1), the composition of the monomer composition (A) was changed to a mixture consisting of 86.0 parts of tert-butyl methacrylate and 14.0 parts of 2-ethylhexyl acrylate.

[0145] Example 4 A binder powder, a positive electrode, and a lithium-ion secondary battery were obtained and evaluated by performing the same operations as in Example 1, except for the following changes: In step (1-1), the composition of the monomer composition (A) was changed to a mixture consisting of 76.5 parts of tert-butyl methacrylate and 23.5 parts of butyl acrylate.

[0146] Example 5 A binder powder, a positive electrode, and a lithium-ion secondary battery were obtained and evaluated by performing the same operations as in Example 1, except for the following changes: In step (1-1), the composition of the monomer composition (A) was changed to a material consisting of 100 parts of cyclohexyl methacrylate.

[0147] Example 6 A binder powder, a positive electrode, and a lithium-ion secondary battery were obtained and evaluated by performing the same operations as in Example 1, except for the following changes: In step (1-1), the composition of the monomer composition (A) was changed to a mixture consisting of 76.8 parts of tert-butyl methacrylate, 22.2 parts of 2-ethylhexyl acrylate, and 1 part of ethylene glycol dimethacrylate as a crosslinkable monomer.

[0148] Example 7 A binder powder, a positive electrode, and a lithium-ion secondary battery were obtained and evaluated by performing the same operations as in Example 1, except for the following changes: In step (1-1), the composition of the monomer composition (A) was changed to a mixture consisting of 77.8 parts of tert-butyl methacrylate and 22.2 parts of 2-ethylhexyl acrylate. In step (1-1), the amount of polymerization initiator used in suspension polymerization was changed from 2.5 parts to 1 part.

[0149] Example 8 A binder powder, a positive electrode, and a lithium-ion secondary battery were obtained and evaluated by performing the same operations as in Example 1, except for the following changes: In step (1-1), the composition of the monomer composition (A) was changed to a mixture consisting of 77.8 parts of tert-butyl methacrylate and 22.2 parts of 2-ethylhexyl acrylate. In step (1-1), the amount of polymerization initiator used in suspension polymerization was changed from 2.5 parts to 5 parts.

[0150] Comparative Example 1 A binder powder, a positive electrode, and a lithium-ion secondary battery were obtained and evaluated by performing the same operations as in Example 1, except for the following changes: In step (1-1), the composition of the monomer composition (A) was changed to a mixture containing 82.0 parts of styrene as an aromatic monovinyl monomer and 18.0 parts of butyl acrylate as an acrylic acid alkyl ester monomer.

[0151] Comparative Example 2 A binder powder, a positive electrode, and a lithium ion secondary battery were obtained and evaluated by performing the same operations as in Example 1, except for the following changes: In step (1-1), the composition of the monomer composition (A) was changed to a mixture consisting of 65.5 parts of tert-butyl methacrylate and 34.5 parts of 2-ethylhexyl acrylate.

[0152] Comparative Example 3 A binder powder, a positive electrode, and a lithium ion secondary battery were obtained and evaluated by performing the same operations as in Example 1, except for the following changes: In step (1-1), the composition of the monomer composition (A) was changed to a mixture consisting of 90.0 parts of tert-butyl methacrylate and 10.0 parts of 2-ethylhexyl acrylate.

[0153] The outlines and evaluation results of the Examples and Comparative Examples are shown in Tables 1 and 2 below.

[0154]

[0155]

[0156] The glass transition temperatures of the homopolymers of each unit (measured using the same method as that used for the binder powder in the examples and comparative examples) are as follows: TBMA (tert-butyl methacrylate): 120°C 2EHA (2-ethylhexyl acrylate): -80°C BA (butyl acrylate): -70°C CHMA (cyclohexyl methacrylate): 110°C EDMA (ethylene glycol dimethacrylate): above 200°C (above the DSC measurement limit) ST (styrene): 110°C

[0157] The above results show that an electrode constructed using a binder powder whose electrolyte swelling degree and glass transition temperature satisfy the requirements of the present invention can exhibit high peel strength, and furthermore, a lithium ion secondary battery constructed using such an electrode exhibits good performance in which the increase in internal resistance after charge and discharge is suppressed.

Claims

1. A binder powder for non-aqueous secondary battery electrodes, comprising a particulate polymer, having an electrolyte swelling index of 1.0 or more and 1.5 or less, and a glass transition temperature of 50°C or more and 100°C or less.

2. The binder powder for a non-aqueous secondary battery electrode according to claim 1, wherein the flexural modulus of a molded product of the binder powder having a thickness of 3 mm is 1000 MPa or more and 2500 MPa or less.

3. The binder powder for a non-aqueous secondary battery electrode according to claim 1, wherein the particulate polymer contains (meth)acrylic acid ester monomer units, and the proportion of the (meth)acrylic acid ester monomer units in the particulate polymer is 95 mass % or more.

4. The binder powder for a non-aqueous secondary battery electrode according to claim 1, wherein the particulate polymer contains (meth)acrylic acid ester monomer units, and the proportion of the (meth)acrylic acid ester monomer units in the binder powder is 95 mass % or more.

5. The particulate polymer contains, as a (meth)acrylic acid ester monomer unit, a unit (e1) represented by the following formula (e1), a unit (e2) represented by the following formula (e2), or both of these: —(CH ２ -C(-CH ３ ) (-COO-R １ )) - (e1) - (CH ２ -CH(-COO-R ２ ))-(e2) R １ and R ２ The binder powder for a non-aqueous secondary battery electrode according to claim 1 , wherein each of the alkyl groups is independently an alkyl group having a branched structure and having 4 or more carbon atoms.

6. The binder powder for a non-aqueous secondary battery electrode according to claim 5, which contains the unit (e1), and the proportion of the unit (e1) in the particulate polymer is 60 mass % or more and 100 mass % or less.

7. The binder powder for a non-aqueous secondary battery electrode according to claim 5, which contains the unit (e2), and the proportion of the unit (e2) in the particulate polymer is 5% by mass or more and 40% by mass or less.

8. The binder powder for a non-aqueous secondary battery electrode according to claim 5, which contains both the unit (e1) and the unit (e2), and the mass ratio (e1) / (e2) of the unit (e1) to the unit (e2) in the particulate polymer is 60 / 40 or more and 95 / 5 or less.

9. The binder powder for a non-aqueous secondary battery electrode according to claim 5, which contains the unit (e1), and the glass transition temperature of the unit (e1) is 50° C. or higher.

10. A group containing the unit (e1) and R １ The binder powder for a non-aqueous secondary battery electrode according to claim 5, wherein is a tert-butyl group.

11. The binder powder for a non-aqueous secondary battery electrode according to claim 5, which contains the unit (e2), and the glass transition temperature of the unit (e2) is 50° C. or lower.

12. A group containing the unit (e2) and R ２ The binder powder for a non-aqueous secondary battery electrode according to claim 5, wherein is a 2-ethylhexyl group.

13. The binder powder for a non-aqueous secondary battery electrode according to claim 8, wherein the glass transition temperature of the unit (e1) is 50°C or higher, and the glass transition temperature of the unit (e2) is 50°C or lower.

14. R １ is a tert-butyl group, and R ２ The binder powder for a non-aqueous secondary battery electrode according to claim 8, wherein is a 2-ethylhexyl group.

15. The binder powder for a non-aqueous secondary battery electrode according to claim 1, wherein the content of each of Fe, Ni, Cr, and Mn is 10 ppm or less.

16. The binder powder for a non-aqueous secondary battery electrode according to claim 1, which is a binder powder for forming an electrode active material layer by a dry process.

17. The SP value of the particulate polymer is 9.1 (cal / cm －３ ) １／２ 2. The binder powder for a non-aqueous secondary battery electrode according to claim 1, wherein:

18. A composite powder composition comprising the binder powder for a non-aqueous secondary battery electrode according to any one of claims 1 to 17 and an electrode active material.

19. An electrode for a non-aqueous secondary battery, comprising a current collector and an electrode active material layer formed on the current collector using the composite powder composition according to claim 18.

20. A non-aqueous secondary battery comprising an electrode for a non-aqueous secondary battery, the electrode comprising a current collector and an electrode active material layer formed on the current collector using the composite powder composition according to claim 18.

21. A method for producing an electrode for a non-aqueous secondary battery, comprising the step of forming an electrode active material layer from the composite powder composition according to claim 18 by a dry process.

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